Chapter 10 Gas Metal Arc Welding

Chapter 10 Gas Metal Arc Welding
Chapter 10
Gas Metal Arc Welding
Topics
1.0.0
Introduction to the Process
2.0.0
Principles of Operation
3.0.0
Equipment for Welding
4.0.0
Installation, Setup, and Maintenance of Equipment
5.0.0
Shielding Gas and Electrodes
6.0.0
Welding Applications
7.0.0
Welding Metallurgy
8.0.0
Weld and Joint Design
9.0.0
Welding Procedure Variables
10.0.0
Welding Procedure Schedules
11.0.0
Preweld Preparations
12.0.0
Welding Discontinuities and Problems
13.0.0
Postweld Procedures
14.0.0
Welder Training and Qualification
15.0.0
Welding Safety
To hear audio, click on the box.
Overview
Gas metal arc welding (GMAW), sometimes referred to by its subtypes as metal inert
gas (MIG) welding or metal active gas (MAG) welding, is an electric arc welding process
where the heat for welding is produced by an arc between a continuously fed,
consumable filler metal electrode and the work. The shielding of the molten weld pool
and the arc is obtained from an externally supplied gas or gas mixture.
This chapter is designed to give you a basic understanding of the GMAW process and
equipment, along with the key variables that affect the quality of welds, such as
electrode extension, travel speed, welding position, amperage, arc length, and electrode
angles. We will also cover core competencies such as setting up welding equipment,
preparing weld materials, fitting up weld materials, starting an arc, welding pipes and
plates, and repairing welds. And lastly, you will get an understanding of the safety
precautions for GMAW and an awareness of the importance of safety in welding.
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Although this chapter is very comprehensive, always refer to the manufacturer’s
manuals for specific operating and maintenance instructions.
Objectives
When you have completed this chapter, you will be able to do the following:
1. Describe the process of gas metal arc welding.
2. Describe the principles of operation used for gas metal arc welding.
3. Describe the equipment associated with gas metal arc welding.
4. Describe the processes for installation, setup, and maintenance of equipment for
gas metal arc welding.
5. State the shielding gas and electrodes for gas metal arc welding.
6. Identify the welding applications for gas metal arc welding.
7. Describe the welding metallurgy of gas metal arc welding.
8. Identify weld and joint designs used for gas metal arc welding.
9. Describe the welding procedure variables associated with gas metal arc welding.
10. Identify welding procedure schedules used for gas metal arc welding.
11. Describe preweld preparations for gas metal arc welding.
12. Identify defects and problems associated with gas metal arc welding.
13. Describe postweld procedures for gas metal arc welding.
14. State t he w elder t raining and q ualifications associated w ith g as metal ar c
welding.
15. Describe the welding safety associated with gas metal arc welding.
Prerequisites
None
This course map shows all of the chapters in Steelworker Basic. The suggested training
order begins at the bottom and proceeds up. Skill levels increase as you advance on
the course map.
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Introduction to Reinforcing Steel
Introduction to Structural Steel
Pre-Engineered Structures:
Buildings, K-Spans, Towers and Antennas
Rigging
Wire rope
S
T
E
E
L
Fiber Line
W
Layout and Fabrication of Sheet-Metal and Fiberglass Duct
O
Welding Quality Control
R
K
Flux Core Arc Welding-FCAW
E
Gas-Metal Arc Welding-GMAW
R
Gas-Tungsten Arc Welding-GTAW
Shielded Metal Arc Welding-SMAW
B
A
Plasma Arc Cutting Operations
S
Soldering, Brazing, Braze Welding, Wearfacing
I
Gas Welding
C
Gas Cutting
Introduction to Welding
Basic Heat Treatment
Introduction to Types and Identification of Metal
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1.0.0 INTRODUCTION to the PROCESS
Versatile and widely used, the gas metal arc welding process can be used to weld both
ferrous and non-ferrous metals and all thicknesses above thin gage sheet metal. It is
the major process used for welding relatively thick sections in the nonferrous metals.
The arc and weld pool are clearly visible to the welder. This process sometimes leaves
a thin, partial slag covering on the surface of the weld bead, which must be removed.
The equipment is generally easy to use because the welder only needs to connect a
work lead and the welding gun to the point of welding. The filler metal does transfer
across the arc, so there is some weld spatter created (Figure 10-1).
Efforts were made in the 1920s
to shield the atmosphere from
the electric arc to improve the
properties of welds. The advent
of the coated electrode
eliminated interest in gas
shielded processes at that time.
As a matter of fact, coated
electrodes utilized the gas
produced by the disintegration of
the coatings and were thus
actually gas shielded welds. The
gas tungsten arc welding
process, or TIG as it is
commonly called, was introduced
in the late 1930s and was the
forerunner of the current gas
shielded processes. It was slow,
however, and this led to the
development of the gas metal arc
welding (GMAW) process in the
late 1940s. In this process, the
Figure 10-1 — Gas metal arc welding.
tungsten electrode was replaced
by an electrode filler wire which was continuously fed through the center of a torch and
surrounded by an inert gas blanket to prohibit atmospheric contamination. The secret of
this process was the small diameter electrode wire and the system for automatically
maintaining the correct arc length. This process immediately became popular and was
used to weld most non-ferrous metals. Research found also that the process could be
utilized for welding mild and low alloy steels, but the cost of the inert shielding gas did
not allow the MIG process to compete with manual coated electrodes for most
applications.
Further welding technology development discovered that the predominant gas evolved
from a covered electrode coating was carbon dioxide. This quickly led to the use of
carbon dioxide as a shielding gas for use with the gas metal arc welding process when
welding on mild and low alloy steel. Early efforts were not too successful, but continuing
research did develop the CO2 welding process. A major problem encountered with CO2
was porosity caused by low quality gas that contained too much moisture. Because of
this, only high purity, welding grade CO2 could be used.
The CO2 process became very popular during the 1950s, especially fully automatic
installations in the automotive industry. High deposition rates and fast travel speeds
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were characteristic of the process. It was limited, however, in that it could be used only
in the flat position and for making horizontal fillet welds. In addition, the process was so
fast that manual travel was difficult, and spatter was sometimes a problem. The
shortcomings of the CO2 process led to further developments.
One development was the improvement of the electrical characteristics of the power
sources used for CO2 welding. This involved the addition of reactance in motor
generators to the secondary welding circuit. In this way the short-circuiting currents
were limited and the spatter was considerably reduced.
Another area of investigation was the utilization of smaller electrode wires. In utilizing
smaller electrode wires, the total heat input into the arc was reduced. However, the
current density carried by the electrode wire was greatly increased. The reduced heat
input provided a small concentrated arc and a small weld pool. The high current density
of the arc provided a very forceful and directional arc which could be controlled and
directed. This quickly led to the all position welding process variation known as Microwire which had a short-circuiting type of metal transfer. Originally the gas used to shield
micro-wire was 100% CO2 gas, and this is still the shielding gas predominantly used.
However, to soften the arc, argon gas was introduced into the CO2 and a popular
mixture of 75% argon and 25% CO2 gas is employed for certain applications.
A third development was with different shielding gases which led to "spray arc" welding.
This mode employed larger diameter electrode wires and mixtures of argon and small
percentages of oxygen for welding steels. This mode produced a smooth weld bead and
a directional arc that was easy for the welder to control.
1.1.0 Methods of Application
Gas metal arc welding is widely used in the semiautomatic, mechanized, and automatic
modes. Manual welding cannot be done by this process. The most popular method of
applying this process is semi-automatically where the welder guides the gun along the
joint and adjusts the welding parameters. The wire feeder continuously feeds the filler
wire electrode, and the power source maintains the arc length.
The second most popular method of applying this process is automatically where the
machinery controls the welding parameters, arc length, joint guidance, and wire feed.
The process is only under the observation of the operator.
The mechanized method of welding has only limited popularity. Mechanized welding is
where the machine controls the arc length, wire feed, and joint guidance. The operator
adjusts the welding parameters.
1.2.0 Advantages and Limitations
The gas metal-arc welding process (GMAW) has revolutionized arc welding. In this
process, a consumable electrode (in the form of wire) is fed from a spool through the
torch (welding gun) at a preset controlled speed. As the wire passes through the contact
tube of the gun, it picks up the welding current. The consumable wire electrode serves
two functions: it maintains the arc and provides filler metal to the joint. The method of
delivery of the filler metal allows GMAW welding to be basically a one-handed operation
which does not require the same degree of skill as Gas Tungsten Arc Welding (GTAW).
The gas metal arc welding process has many advantages over most of the other arc
welding processes. These advantages make the process particularly well suited to high
production and automated welding applications. Gas metal arc welding has been the
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process choice for robotic applications. Some of the advantages to gas metal arc
welding are the following:
1. It is the only consumable electrode process that can be used to weld most all
commercial metals and alloys, ferrous and non-ferrous.
2. A relatively small amount of spatter is produced.
3. The filler metal is fed continuously, so very little time is spent on changing
electrodes.
4. It can be used easily in all positions.
5. The arc and weld pool are clearly visible.
6. Little or no slag is produced, resulting in minimal postweld cleaning.
7. A relatively small diameter electrode is used, which gives high current densities.
8. A high percentage of the filler metal is deposited in the weld.
9. Travel speeds and deposition rates are significantly higher than those obtained
with shielded metal arc welding and gas tungsten arc welding.
10. Lightweight power sources can be hand carried to the job site.
11. When spray transfer is used, deeper penetration is possible than with shielded
metal arc welding, which may permit the use of smaller size fillet welds for
equivalent strengths.
Some limitations of the process are the following:
1. The equipment is more complex, more costly, and less portable than that for
shielded metal arc welding.
2. The arc requires protection from wind drafts, which can blow the stream of
shielding gas away from the arc.
3. The larger welding gun must be close to the work to ensure proper shielding, and
it s less adaptable to welding in difficult to reach areas than shielded metal arc
welding.
4. Relatively high levels of radiated heat and arc intensity can result in operator
resistance to the process.
2.0.0 PRINCIPLES of OPERATION
The gas metal arc welding process uses the heat of an electric arc produced between a
bare electrode and the part to be welded. The electric arc is produced by electric current
passing through an ionized gas. The gas atoms and molecules are broken up and
ionized by losing electrons and leaving a positive charge. The positive gas ions then
flow from the positive pole to the negative pole, and the electrons flow from the negative
pole to the positive pole. About 95% of the heat is carried by the electrons, and the rest
is carried by the positive ions. The heat of the arc melts the surface of the base metal
and the electrode. The molten weld metal, heated weld zone, and the electrode are
shielded from the atmosphere by a shielding gas supplied through the welding gun. The
molten electrode filler metal transfers across the arc and into the weld puddle. This
process produces an arc with more intense heat than most of the arc welding
processes.
The arc is struck by starting the wire feed, which causes the electrode wire to touch the
workpiece and initiate the arc. Normally, arc travel along the work is not started until a
weld puddle is formed. The gun then moves along the weld joint manually or
mechanically so that the adjoining edges are joined. The weld metal solidifies behind
the arc in the joint and completes the welding process.
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2.1.0 Arc Systems
The gas metal arc welding process may be
operated on both constant voltage and
constant current power sources. Any welding
power source can be classified by its voltampere characteristics as either a constant
voltage (also called constant potential) or
constant current (also called variable voltage)
type although there are some machines that
can produce both characteristics. Constant
voltage power sources are preferred for a
majority of gas metal arc welding
applications.
In the constant voltage arc system, the
voltage delivered to the arc is maintained at a
relatively constant level, which gives a flat or
nearly flat volt-ampere curve (Figure 10-2).
This type of power source is widely used for
the processes that require a continuously fed
Figure 10-2 — Volt-amp curve.
bare wire electrode. In this system, the arc
length is controlled by setting the voltage level on the power source, and the welding
current is controlled by setting the wire feed speed.
Most machines have a fixed slope that is built in for a certain type of gas metal arc
welding. Some constant voltage welding machines are equipped with a slope control
that is used to change the slope of the volt-ampere curve. Figure 10-3 shows different
slopes obtained from one power source. The slope has the effect of limiting the amount
of short-circuiting current that the power supply can deliver. This is the current available
from the power source on the short circuit between the electrode wire and the work.
A slope control is not required but is best
when welding with small diameter wire and
low current levels. The short-circuit current
determines the amount of pinch force
available on the electrode. The pinch forces
cause the molten electrode tip to neck down
so that the droplet will separate from the
solid electrode. The flatter the slope of the
volt-ampere curve, the higher the shortcircuit current and the pinch force. The
steeper the slope the lower the short circuit
current and pinch force. The pinch force is
important because it affects the way the
droplet detaches from the tip of the electrode
wire, which also affects the arc stability in
short-circuiting transfer. When a high shortcircuit and pinch force are caused by a flat
Figure 10-3 — Volt-amp slopes.
slope, excessive spatter is created. When a
very low short circuit current and pinch force
are caused by a steep slope, the electrode wire tends to freeze in the weld puddle or
pile upon the work piece. When the proper amount of short-circuit current is used, very
little spatter with a smooth electrode tip is created.
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The inductance of the power supply also has an effect on the arc stability. When loads
on the power supply change, the output current will fluctuate, taking time to find its new
level. The rate of current change is determined by the inductance of the power supply.
The rate of the welding current buildup and pinch force buildup increases with the
current, which is also affected by the inductance in the circuit. Increasing the inductance
will reduce the rate of current rise and the pinch force. (In short-circuiting welding,
increasing the inductance will increase the arc time between short-circuit and decrease
the frequency of short-circuiting, thereby reducing the amount of spatter). Increased arc
time or inductance produces a flatter and smoother weld bead as well as a more fluid
weld puddle. Too much inductance will cause more difficult arc starting.
The constant current (CC) arc system
provides a nearly constant welding current to
the arc, which gives a drooping volt-ampere
characteristic (Figure 10-4). This arc system
is used with the shielded metal arc welding
and gas tungsten arc welding processes.
The welding current is set by a dial on the
machine, and the welding voltage is
controlled by the arc length held by the
welder. This system is necessary for manual
welding because the welder cannot hold a
constant arc length, which causes only small
variations in the welding current. When gas
metal arc welding is done with a constant
current system, a special voltage sensing
wire feeder is used to maintain a constant
arc length.
Figure 10-4 — CC volt-amp curve.
For any power source, the voltage drop
across the welding arc is directly dependent
on the arc length. An increase in the arc length results in a corresponding increase in
the arc voltage, and a decrease in the arc length results in a corresponding decrease in
the arc voltage. Another important relationship exists between the welding current and
the melt off rate of the electrode. With low current, the electrode melts off slower and
the metal is deposited slower. This relationship between welding current and wire feed
speed is definite, based on the wire size, shielding gas, and type of filler metal; a faster
wire feed speed will give a higher welding current.
In the constant voltage system, instead of regulating the wire to maintain a constant arc
length, the wire is fed into the arc at a fixed speed, and the power source is designed to
melt off the wire at the same speed. The self-regulating characteristic of a constant
voltage power source comes about by the ability of this type of power source to adjust
its welding current to maintain a fixed voltage across the arc.
With the constant current arc system with a voltage sensing wire feeder, the welder
would change the wire feed speed as the gun is moved toward or away from the weld
puddle. Since the welding current remains the same, the burn-off rate of the wire is
unable to compensate for the variations in the wire feed speed, which allows stubbing or
burning back of the wire into the contact tip to occur. To lessen this problem, a special
voltage sensing wire feeder is used which regulates the wire feed speed to maintain a
constant voltage across the arc.
The constant voltage system is preferred for most applications, particularly for small
diameter wire. With smaller diameter electrodes, the voltage sensing system is often not
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able to react fast enough to feed at the required burn--off rate, resulting in a higher
instance of burnback into the contact tip of the gun.
Figure 10-5 shows a comparison of the volt-ampere curves for the two arc systems.
This shows that for these particular curves, when a normal arc length is used, the
current and voltage level is the same for both the constant current and constant voltage
systems. For a long arc length, there is a slight drop in the welding current for the
constant current machine and a large drop in the current for a constant voltage
machine. For constant voltage power
sources, the volt-ampere curve shows that
when the arc length shortens slightly, a
large increase in welding current occurs.
This results in an increased burn-off rate
which brings the arc length back to the
desired level. Under this system, changes in
the wire feed speed caused by the welder
are compensated for electrically by the
power source. The constant current system
is sometimes used, especially for welding
aluminum and magnesium because the
welder can vary the current slightly by
changing the arc length. This varies the
depth of penetration and the amount of heat
input. With aluminum and magnesium,
preheating the wire is not desirable.
2.2.0 Metal Transfer
Figure 10-5 — Volt-amp curves.
The types of arcs obtainable and the
different modes of gas metal arc welding are determined by the type of metal transfer.
The four modes of welding are the short circuiting, globular, spray, and pulsed arc metal
transfer. Each mode has its own advantages and applications. The type of metal
transfer is determined by the welding current, shielding gas, and welding voltage.
2.2.1 Short Circuiting Transfer
At the beginning of the short-circuiting arc cycle, the end of the electrode wire melts into
a small globule which moves toward the weld puddle. When the tip of this globule
comes in contact with the workpiece, the arc is momentarily extinguished. When the
wire touches the workpiece, the current increases because a short circuit is created.
The current increases to the point that the molten globule is pinched off and the arc is
re-ignited (Figure 10-6). This cycle then repeats itself, occurring approximately 20 to
200 times a second depending on the current level and the power supply. The filler
metal is transferred to the weld puddle only during the period when the electrode is in
contact with the work. No filler metal is transferred across the arc.
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Figure 10-6 — Short-circuiting transfer.
Short-circuiting transfer applies the lowest welding currents and voltages used with gas
metal arc welding, which produces low heat input. The type of shielding gas used has
very little effect on this type of transfer but most gas metal arc welding done in this
mode employs a CO2 shielding gas. This type of metal transfer produces a small, fastfreezing weld pool, usually with some small, fine spatter. Because of this, this mode is
well suited for joining thin sections of metal by welding in the vertical, horizontal, and
overhead positions, and for filling large root openings.
2.2.2 Globular Transfer
The globular transfer cycle starts when a droplet forms on the end of the electrode wire.
The molten droplet grows in size until it is larger than the diameter of the electrode. The
droplet then detaches from the end of the electrode and transfers across the arc due to
the force of gravity. Globular transfer is shown in Figure 10-7.
Globular transfer occurs at relatively low
operating currents and voltages but higher
than those used to obtain short-circuiting
transfer. It can occur with all types of
shielding gases, but with gases other than
CO2 it generally occurs at current and
voltage levels toward the bottom of the
operating range. With CO2 shielding gas,
globular transfer will take place at most
operating current and voltage levels.
Because of the large droplet size and the
dependence on gravity to transfer the filler
metal, this mode of gas metal arc welding is
not suitable for many out-of-position welding
applications, especially overhead welding
where the droplets tend to fall into the nozzle
of the welding gun. Globular transfer is also
characterized by a less stable arc and higher
Figure 10-7 — Globular transfer.
amounts of spatter. The arc is less stable
because it will shift around and move to the part of the droplet that is closest to the weld
puddle, (electric current will always try to take the shortest path). The arc will wave
around on the end of the droplet, creating more spatter.
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2.2.3 Spray Transfer
The spray transfer cycle begins when the end of the electrode tapers down to a point.
Small droplets are formed and electromagnetically pinched off at the tapered point of
the electrode tip. The droplets are smaller than the diameter of the electrode and detach
much more rapidly than in globular transfer. The rate of transfer can vary from less than
one hundred times a second up to several
hundred times a second. The arc is also
more directional than in the globular mode.
Spray transfer is shown in Figure 10-8.
Spray transfer is generally associated with
the higher amperage and voltage levels and
occurs with argon or argon-rich shielding
gases. The spray transfer mode is best
adapted for welding thick sections because
of the higher welding currents. Spray
transfer produces a very stable arc that is
well adapted for out-of-position as well as
flat position welding. When welding out-ofposition, operators need to consider how the
high voltage and current levels used may
produce a weld puddle that is difficult to
control. This mode also produces the least
amount of spatter.
Figure 10-8 — Spray transfer.
2.2.4 Pulsed Current Transfer
To overcome the work thickness and welding position limitations of spray transfer,
specially designed power supplies have been developed. These machines produce
controlled wave forms and frequencies that "pulse" the welding current at regularly
spaced intervals. They provide two levels of current: one a constant, low background
current which sustains the arc without providing enough energy to cause drops to form
on the wire tip; the other is a superimposed pulsing current with amplitude greater than
the transition current necessary for spray transfer. During this pulse, one or more drops
are formed and transferred. The frequency and amplitude of the pulses control the
energy level of the arc, and therefore the rate at which the wire melts. By reducing the
average arc energy and the wire-melting rate, pulsing makes the desirable features of
spray transfer available for joining sheet metals and welding thick metals in all positions.
Test your Knowledge (Select the Correct Response)
1.
What shielding gas is predominantly used for GMAW?
A.
B.
C.
D.
2.
O2
NO2
CO2
He
Which is NOT a mode of GMAW metal transfer?
A.
B.
C.
D.
Pulsed
Spherical
Globular
Spray
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3.0.0 EQUIPMENT for WELDING
The basic design of a GMAW system is shown in Figure 10-9 and includes four principal
components:
1. Power source.
2. Wire drive and accessories (drive rolls, guide tubes, reel stand, etc.).
3. GMAW gun and cable assembly designed to deliver the shielding gas and the
electrode to the arc.
4. Shielding gas apparatus and accessories.
Figure 10-9 — Equipment for gas metal arc welding.
3.1.0 Power Sources
The purpose of the power source or welding machine is to provide the electric power of
the proper current and voltage to maintain a welding arc. Many power sources operate
on 200, 230, 460, or 575 volt input electric power. The power sources operate on singlephase or three-phase input power with a frequency of 50 or 60 Hz.
3.1.1 Power Source Duty Cycle
The duty cycle of a power source is defined as the ratio of arc time to total time. Most
power sources used for gas metal arc welding have a duty cycle of 100%, which
indicates that they can be used to weld continuously. Some machines used for this
process have duty cycles of 60%, which means that they can be used to weld six of
every ten minutes. In general, these lower duty cycle machines are the constant current
type that are used in plants where the same machines are also used for shielded metal
arc welding and gas tungsten arc welding. Some of the smaller constant voltage
welding machines have a 60% duty cycle.
3.1.2 Types of Current
Most gas metal arc welding is done using steady direct current. Steady direct current
can be connected in one of two ways: electrode positive (reverse polarity DCEP) and
electrode negative (straight polarity DCEN). The electrically charged particles flow
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between the tip of the electrode and the work (Figure 10-10). The electrode positive
connection is used for almost all welding applications of this process. It gives better
penetration than electrode negative and can be used to weld all metals. Electrode
negative is sometimes used when a minimum amount of penetration is desired.
Pulsed direct current is used for applications where good penetration and reduced heat
input are required. Pulsed current occurs when the welding current is operated at one
level for a set period of time, switches to another level for a time, and then repeats the
cycle (Figure 10-11). The pulsing action can be provided from one power source or
combining the outputs of two power sources working at two current levels. The welding
current varies from as low as 20 amps at 18 volts up to as high as 750 amps at 50 volts,
and the frequency of pulsing can be varied. When using pulsed current, welding thinner
sections is more practical than when using steady direct current in the spray transfer
mode, because there is less heat input, which reduces the amount of distortion.
Figure 10-10 — Particle flow for
DCEP and DCEN.
Figure 10-11 — Pulsed current
terminology.
3.1.3 Types of Power Sources
Many types of direct current power sources
may be used for gas metal arc welding,
including engine-driven generators (rotating)
and transformer-rectifiers (static). Inverters
are included in the static category.
3.1.3.1 Generator Welding Machines
A generator welding machine can be
powered by an electric motor for shop use or
by an internal combustion engine (gas or
diesel) for field use. Engine-driven welders
can have either water- or air-cooled engines,
and many of them provide auxiliary power
as well (Figure 10-12).
Many of the engine-driven generators used
for gas metal arc welding in the field are
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Figure 10-12 — Engine-driven
power source.
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combination constant current-constant voltage types. These are popular for applications
such as pipe welding so that both shielded metal arc welding and gas metal arc welding
can be done using the same power source. The motor-driven generator welding
machines are becoming less popular and are being replaced by transformer-rectifier
welding machines. Motor-driven generators produce a very stable arc, but they are
noisier and more expensive, consume more power, and require more maintenance than
transformer-rectifier machines.
3.1.3.2 Transformer-Rectifier Welding
Machines
The more popular welding machines used
for gas metal arc welding are the
transformer-rectifiers. A method of supplying
direct current to the arc other than the use of
a rotating generator is by adding a rectifier
to a basic transformer circuit. A rectifier is an
electrical device which changes alternating
current into direct current. These machines
are more efficient electrically than motorgenerator welding machines, they respond
faster when arc conditions change, and they
provide quieter operation. There are two
basic types of transformer-rectifier welding
machines: those that operate on singlephase input power and those that operate
on three-phase input power (Figure 10-13).
Figure 10-13 — Three-phase
constant voltage.
The single-phase transformer-rectifier
machines provide DC current to the arc and a constant current volt-ampere
characteristic. These machines are not as popular as three-phase transformer-rectifier
welding machines for gas metal arc welding. When using a constant current power
source, a special variable speed or voltage sensing wire feeder must be used to keep
the current level uniform.
Machines used for shielded metal arc welding and gas tungsten arc welding can be
adapted for use with gas metal arc welding. A limitation of the single-phase system is
that the power required by the single-phase input power may create an unbalance of the
power supply lines, which is objectionable to most power companies. Another limitation
is that short-circuiting metal transfer cannot be used with this type of power source.
These machines normally have a duty cycle of 60%.
One of the most widely used types of power sources for this process is the three-phase
transformer rectifier. These machines produce DC current for the arc and most have a
constant voltage volt-ampere characteristic. When using these machines, a constant
speed wire feeder is normally employed. This type of wire feeder maintains a constant
wire feed speed with slight changes in welding current. The three-phase input power
gives these machines a more stable arc than single-phase input power, and avoids the
line unbalance that occurs with the single-phase machines. Many of these machines
also use solid-state controls for the welding. A solid-state machine will produce the
flattest volt-ampere curve of the different constant voltage power sources.
NAVEDTRA 14250A
10-15
3.1.3.3 Inverter Power Sources
The inverter machine is different from a
transformer-rectifier. The inverter will rectify
60 Hz alternating line current, utilize a
chopper circuit to produce a high frequency
alternating current, reduce that voltage with
an AC transformer, and finally rectify that to
obtain the required direct current output.
Changing that alternating current frequency
to a much higher frequency allows a greatly
reduced size of transformer and reduced
transformer losses as well (Figure 10-14).
Inverter circuits control the output power
using the principle of time ratio control
(TRC). The solid-state devices
(semiconductors) in an inverter act as
switches; they are either switched "on" and
conducting, or they are switched "off" and
blocking. This operation of switching "on"
Figure 10-14 — Inverter power
and "off" is sometimes referred to as switch
source.
mode operation. TRC is the regulation of the
"on" and "off" time of the switches to control the output. Faster response times are
generally associated with the higher switching and control frequencies, resulting in more
stable arcs and superior arc performance. However, other variables, such as length of
weld cables, must be considered since they may affect the power supply performances.
3.2.0 Controls
The controls for this process are located on the front of the welding machine, on the
welding gun, and on the wire feeder or a control box.
The welding machine controls for a constant voltage machine are an on-off switch, a
voltage control, and sometimes a switch to select the polarity of direct current. The
voltage control can be a single knob, or it can have a top switch for setting the voltage
range and a fine voltage control knob. Other controls are sometimes present such as a
switch for selecting CC (constant current) or CV (constant voltage) output on
combination machines or a switch for a remote control. On the constant current welding
machines there is an on-off switch, a current level control knob, and sometimes a knob
or switch for selecting the polarity of direct current.
The trigger or switch on the welding gun is a remote control that is used by the welder in
semiautomatic welding to stop and start the welding current, wire feed, and shielding
gas flow.
For semiautomatic welding, a wire feed speed control is normally part of the wire feeder
assembly or close by. The wire feed speed sets the welding current level on a constant
voltage machine. For machine or automatic welding, a separate control box is often
used to control the wire feed speed. On the wire feeder control box, there may also be
switches to turn the control on and off and gradually feed the wire up and down.
Other controls for this process are used for special applications, especially when using
a programmable power source. A couple of examples are items such as timers for spot
welding and pulsation.
NAVEDTRA 14250A
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3.3.0 Wire Feeders
The electrode feed unit (wire feeder) provides the power for driving the electrode
through the cable and gun and to the work (Figure 10-15). There are several different
electrode feed units available, but the best type of system depends on the application.
Most of the electrode feed units used for gas metal arc welding are the constant speed
type which are used with constant voltage power sources. This means that the wire feed
speed is set before welding. The wire feed speed controls the amount of welding
current.
Figure 10-15 — Wire feed assembly.
Variable speed or voltage sensing wire feeders are used with constant current power
sources. With a variable speed wire feeder, a voltage sensing circuit is used to maintain
the desired arc length by varying the wire feed speed. Variations in the arc length
increase or decrease the wire feed speed. The wire-feed speed is measured in inches
per minute (ipm). For a specific amperage setting, a high wire-feed speed results in a
short arc, whereas a low speed produces a long arc. Therefore, you would use higher
speeds for overhead welding than for flat-position welding.
An electrode feed unit consists of an electric motor connected to a gearbox with drive
rolls in it. Systems may have two or four feed rolls in the gearbox. In a four roll system,
the lower two rolls drive the wire and have a circumferential "V" groove in them,
depending on the type and size of wire being fed. Figure 10-16 shows several of the
most common drive rolls and their uses.
NAVEDTRA 14250A
10-17
Figure 10-16 — Common types of drive rolls and their uses.
Wire feed systems may be of the push, pull,
or push-pull types depending on the type
and size of the electrode wire and the
distance between the welding gun and the
coil or spool of electrode wire. The push
type is the wire feeding system most
commonly used for steels. It consists of the
wire being pulled from the wire feeder by
the drive rolls and then being pushed into
the flexible conduit and through the gun.
The length of the conduit can be up to
about 12 ft. (3.7m) for steel wire and 6 ft.
(1.8m) for aluminum wire.
A typical push wire feeder is shown in
Figure 10-17. This solid-state wire feeder
has the wire feeder control box and the wire
reel support mounted with the wire feed
motor and gear box.
NAVEDTRA 14250A
Figure 10-17 — Solid-state control
wire feeder and wire support.
10-18
Pull type wire feeders have the drive rolls
attached to the welding gun. This type of
system works best for feeding wires up to
about .045 in. (1.1mm) in diameter with a
hand-held welding gun. Most machine and
automatic welding stations also use this type
of system.
The push-pull system is particularly well
suited for use with low strength wires such
as aluminum and when driving wires long
distances. This system can use synchronous
drive motors to feed the electrode wire,
which makes it good for soft wires and long
distances. The wire feeding system shown in
Figure 10-18 uses the standard feeder as
the drive motor (push) and the gun as a
slave motor (pull).
3.4.0 Welding Guns
Figure 10-18 — Standard push-pull
wire feeding system.
A typical GMAW gun is shown in Figure 10-19. The welding gun transmits the welding
current to the electrode. Because the wire is fed continuously, a sliding electrical contact
is used. The welding current is passed to the electrode through a copper base alloy
contact tube. The contact tubes have various hole sizes, depending on the diameter of
the electrode wire. The gun also has a gas supply connection and a nozzle to direct the
shielding gas around the arc and weld puddle. To prevent overheating of the welding
gun, cooling is required to remove the heat generated. Shielding gas or water circulating
in the gun, or both are used for cooling. An electrical switch is used to start and stop the
electrode feeding, welding current, and shielding gas flow. This is located on the gun in
semiautomatic welding and separately on machine welding heads.
Figure 10-19 — Cross-sectional view of a welding gun.
3.4.1 Semiautomatic Guns
The hand-held semiautomatic guns usually have a curved neck, which makes them
flexible, and a curved handle that adds comfort and balance. The gun is attached to the
service lines which include the power cable, water hose, gas hose, and wire conduit or
NAVEDTRA 14250A
10-19
liner. The guns have metal nozzles, which have orifice diameters from 3/8 to 7/8 in. (1022 mm), depending on the welding requirements, to direct the shielding gas to the arc
and weld puddle.
Welding guns are either air-cooled or water-cooled. The choice between the guns is
based on the type of shielding gas, amount of welding current, voltage, joint design, and
the shop practice. A water-cooled gun is similar to an air-cooled gun except that ducts
have been added that permit the cooling water to circulate around the contact tube and
nozzle. Water-cooled guns provide more
efficient cooling of the gun.
Air-cooled guns are employed for applications
where water is not readily available. These
are actually cooled by the shielding gas. The
guns are available for service up to 600
amperes used intermittently with a CO2
shielding gas. These guns are usually limited
to 50% of the CO2 rating with argon or helium.
CO2 cools the welding gun, where argon or
helium do not. Water-cooling permits the gun
to operate continuously at the rated capacity
with lower heat buildup. Water-cooled guns
are generally used for applications requiring
between 200 and 750 amperes. Air-cooled
guns of the same capacity as water-cooled
guns are heavier but they are easier to
manipulate in confined spaces or for out-ofposition applications because there are fewer
cables.
There are three general types of guns
available. The one shown in Figure 10-20 has
the electrode wire fed through a flexible
conduit from a remote wire feeder. The
conduit is generally 10 to 15 feet due to the
wire feeding limitations of a push type wire
feeding system. Figure 10-21 shows the
second type of welding gun, which has a selfcontained wire feeding mechanism and
electrode wire supply. This wire supply is in
the form of a 1 lb. (.45 kg) spool. This gun
employs a pull type wire feed system and is
particularly good for feeding aluminum and
other softer electrode wires which tend to jam
in long conduits. The third type of gun has a
wire feed motor on the gun, and the wire is
fed through a conduit from a remote wire feed
supply. This system has a pull type wire
feeder and can use longer length conduits.
Figure 10-20 — Semi-automatic.
Figure 10-21 — Spool gun.
3.4.2 Machine Welding Guns
The machine welding guns use the same basic design principles and features as the
semiautomatic welding guns. These guns have capacities up to 1200 amperes and are
NAVEDTRA 14250A
10-20
generally water-cooled because of the higher
amperages and duty cycles required. The
gun is mounted directly below the wire
feeder. Large diameter wires up to 1/4 in.
(6.4 mm) are often used. Figure 10-22 shows
a GMAW control panel for a machine
welding gun system.
3.5.0 Shielding Gas Equipment
The shielding gas system used in gas metal
arc welding consists of a gas supply source,
a gas regulator, a flowmeter, control valves,
and supply hoses to the welding gun.
The shielding gases are supplied in liquid
form when they are in storage tanks with
vaporizers or in a gas form in high-pressure
Figure 10-22 — Control panel.
cylinders. An exception to this is carbon
dioxide. When put in high-pressure cylinders,
it exists in both the liquid and gas forms. The bulk storage tank system is used when
there are large numbers of welding stations using the same type of shielding gas in
large quantities. For applications where there are large numbers of welding stations but
relatively low gas usage, a manifold system is often used. This consists of several highpressure cylinders connected to a manifold which then feeds a single line to the welding
stations. Individual high-pressure cylinders are used when the amount of gas usage is
low, when there are few welding stations, or when portability is required.
You should use the same type of regulator and flowmeter for gas metal-arc welding that
you use for gas tungsten-arc welding. The gas flow rates vary, depending on the types
and thicknesses of the material and the joint design. At times it is necessary to connect
two or more gas cylinders (manifold)
together to maintain higher gas flow.
For most welding conditions, the gas flow
rate is approximately 35 cubic feet per hour
(cfh). This flow rate may be increased or
decreased, depending upon the particular
welding application. Final adjustments
usually are made on a trial-and-error basis.
The proper amount of gas shielding results
in a rapid crackling or sizzling arc sound.
Inadequate gas shielding produces a
popping arc sound and results in weld
discoloration, porosity, and spatter.
Regulators and flowmeters are designated
for use with specific shielding gases and
should be used only with the gas for which
they were designed (Figure 10-23).
Figure 10-23 — Regulator and
flowmeter.
The hoses are normally connected to
solenoid valves on the wire feeder to turn
the gas flow on and off with the welding current. A hose is used to connect the
flowmeter to the welding gun. The hose is often part of the welding gun assembly.
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3.6.0 Welding Cables
Welding cables, normally made of copper or aluminum, and connectors connect the
power source to the electrode holder and to the work. They consist of hundreds of wires
enclosed in an insulated casing of natural or synthetic rubber. The cable that connects
the power source to the welding gun is called the electrode lead. In semiautomatic
welding, this cable is often part of the cable assembly, which also includes the shielding
gas hose and the conduit through which the electrode wire is fed. For machine or
automatic welding, the electrode lead is normally separate. The cable that connects the
work to the power source is called the work lead; it is usually connected to the work by a
pincer clamp or a bolt.
Table 10-1 — Recommended cable sizes for different currents and cable lengths.
Weld
Length of Cable Circuit in Feet – Cable Size AWG.
Weld
Current
60’
100’
150’
200’
300’
400’
Manual
100
4
4
4
2
1
1/0
(Low Duty
Cycle)
150
2
2
2
1
2/0
3/0
200
2
2
1
1/0
3/0
4/0
250
2
2
1/0
2/0
300
1
1
2/0
3/0
350
1/0
1/0
3/0
4/0
400
1/0
1/0
3/0
450
2/0
2/0
4/0
500
2/0
2/0
4/0
Automatic
400
4/0
4/0
(High
Duty
Cycle)
800
4/0 (2)
4/0 (2)
1200
4/0 (3)
4/0 (3)
Type
Three factors determine the size of welding cable to use: the duty cycle of the machine,
its amperage rating, and the distance between the work and the machine. If either
amperage or distance increases, the cable size also must increase. Cable sizes range
from the smallest at AWG No.8 to AWG No. 4/0 with amperage ratings of 75 amperes
and upward. Table 10-1 shows recommended cable sizes for use with different welding
currents and cable lengths. A cable too small, or too long, for the current load will
become too hot to handle during welding.
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3.7.0 Other Equipment
A good ground clamp is essential to
producing quality welds. Without proper
grounding, the circuit voltage fails to
produce enough heat for proper welding,
and there is the possibility of damage to the
welding machine and cables. Three basic
methods are used to ground a work lead.
You can fasten the ground cable to the
workbench with a C-clamp, attach a springloaded clamp directly onto the workpiece, or
bolt or tack-weld the end of the ground cable
to the welding bench or workpiece. For a
workbench, the third way creates a
permanent common ground.
3.7.1 Water Circulators
Figure 10-24 — Water circulator.
When a water-cooled gun is used, a water
supply must be included in the system. This
can be supplied by a water circulator or directly from a hose connection to a water tap.
The water is carried to the welding torch through hoses that may or may not go through
a valve in the welding machine. A water circulator is shown in Figure 10-24.
3.7.2 Motion Devices
Motion devices are used for machine and automatic welding. These motion devices can
be used to move the welding head, workpiece, or gun depending on the type and size of
the work and the preference of the user.
Motor driven carriages that run on tracks or directly on the workpiece are commonly
used. Carriages can be used for straight line contour, vertical, or horizontal welding.
Side beam carriages, supported on the vertical face of a flat track, can be used for
straight line welding.
Welding head manipulators may be used for longitudinal welds and, in conjunction with
a rotary weld positioner, for circumferential welds. These welding head manipulators
come in many boom sizes and can also be used for semiautomatic welding with
mounted welding heads.
Oscillators are optional equipment used to oscillate the gun for surfacing, vertical-up
welding, and other welding operations that require a wide bead. Oscillator devices can
be either mechanical or electromagnetic.
3.7.3 Accessories
Accessory equipment used for gas metal arc welding consists of items used for cleaning
the weld bead and cutting the electrode wire. In many cases cleaning is not required,
but when slag is created by the welding, a chipping hammer or grinder is used to
remove it. Wire brushes and grinders are sometimes used for cleaning the weld bead,
and wire cutters and pliers are used to cut the end of the electrode wire between stops
and starts.
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Test your Knowledge (Select the Correct Response)
3.
What type of current is predominantly used for GMAW?
A.
B.
C.
D.
4.
Alternating
Direct
Negative
Positive
Of what material are welding cables most commonly made?
A.
B.
C.
D.
Stainless steel
Copper
Bronze
Silver alloy
4.0.0 INSTALLATION, SETUP, and MAINTENANCE of
EQUIPMENT
Learning to arc weld requires you to possess many skills. Among these skills are the
abilities to set up, operate, and maintain your welding equipment.
In most factory environments, the work is brought to the welder. In the Seabees, the
majority of the time the opposite is true. You will be called to the field for welding on
buildings, earthmoving equipment, well drilling pipe, ship to shore fuel lines, pontoon
causeways, and the list goes on. To accomplish these tasks, you have to become
familiar with your equipment and be able to maintain it in the field. It would be
impossible to give detailed maintenance information here because of the many different
types of equipment found in the field; therefore, only the highlights will be covered.
You should become familiar with the welding machine that you will be using. Study the
manufacturer’s literature and check with your senior petty officer or chief on the items
that you do not understand. Machine setup involves selecting current type, polarity, and
current settings. The current selection depends on the size and type of electrode used,
position of the weld, and the properties of the base metal.
Cable size and connections are determined by the distance required to reach the work,
the size of the machine, and the amperage needed for the weld.
Operator maintenance depends on the type of welding machine used. Transformers
and rectifiers require little maintenance compared to engine-driven welding machines.
Transformer welders require only to be kept dry and to be given a minimal amount of
cleaning. Internal maintenance should be done only by electricians due to the
possibilities of electrical shock. Engine-driven machines require daily maintenance. In
most places you will be required to fill out and turn in a daily inspection form called a
“hard card” before starting the engine. This form is a list of items, such as oil level, water
level, visible leaks, and other things, that affect the operation of the machine.
After all of these items have been checked, you are now ready to start welding.
Listed below are some additional welding rules that should be followed.
•
•
•
Clear the welding area of all debris and clutter.
Do not use gloves or clothing that contains oil or grease.
Check that all wiring and cables are installed properly.
NAVEDTRA 14250A
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•
•
•
•
•
Ensure that the machine is grounded and dry.
Follow all manufacturers’ directions on operating the welding machine.
Have on hand a protective screen to protect others in the welding area from flash
burns.
Always keep fire-fighting equipment on hand.
Clean rust, scale, paint, and dirt from the joints that are to be welded.
4.1.0 Power Source Connections
As a safety precaution, turn the power switches on the wire feeder and the power
source to the off position before checking electrical connections. Also, always wear your
safety glasses when you are in the welding area.
Check all electrical connections to make sure they are tight, and check cables for cracks
and exposed wire.
On power sources that are set up for
electrode positive (reverse polarity), the
positive terminal that supplies welding
voltage and amperage is connected to the
wire feeder.
The gun trigger takes its power from a
connection on the wire feeder.
The work lead is connected to the negative
terminal; it should be attached to the work or
to the welding table.
4.2.0 Gun Cable Assembly
To remove the gun cable assembly:
disconnect the gun trigger lead, loosen the
retaining knob on the wire feeder, and pull
the gun cable out of the wire feeder with a
twisting motion.
Check the O-rings for damage (Figure 1025).
Figure 10-25 — O-ring inspection.
Check the gun to make sure it is in good
condition.
Clean the nozzle.
Use a nozzle cleaner or a pair of needle
nose pliers to remove spatter from the
nozzle. A dirty or damaged nozzle may
interrupt the flow of shielding gas, causing
porosity.
Inspect the contact tube and gas diffuser
(Figure 10-26).
Clean spatter from the contact tube with a
pair of needle nose pliers.
NAVEDTRA 14250A
Figure 10-26 — Contact tube and
gas diffuser inspection. 10-25
NOTE: Replace the contact tube if the opening is worn into an oval shape.
Check the gas diffuser for blockage, and clean it if necessary.
Clean the liner.
•
•
•
Remove the contact tube and outlet guide.
Stretch the cable straight.
Blow shop air through the liner.
NOTE:
You should clean the liner each time you change wire to prevent dirt buildup.
You should replace the liner if it is kinked or shows signs of excessive wear, such as an
enlarged or oval opening. Install a new liner according to manufacturer’s specification.
Insert the liner into the gun cable slowly to avoid kinking it.
4.3.0 Wire Installation
Remove the contact tube.
Open the feed roll assembly (Figure 10-27).
Remove the spool retaining ring.
Slide the spool onto the spool hub so the
wire feeds from bottom.
Replace the spool retaining ring.
Keep hand pressure on the wire to prevent
the spool from uncoiling as you feed the wire
through the inlet guide, across the bottom
wire feed roller, and into the outlet guide.
Close the feed roll assembly.
Test tension by pressing the “jog” button
until the wire feeds through the gas diffuser.
Replace the contact tube and nozzle.
Clip the wire to a 1/4 to 3/8 in. stick-out.
Figure 10-27 — Wire installation.
The correct amount of electrode extension
or wire stick-out is important because it influences the welding current of the power
source. Since the power source is self-regulating, the current output is automatically
decreased when the wire stick-out increases. Conversely, when the stick-out
decreases, the power source is forced to furnish more current. Too little stick-out
causes the wire to fuse to the nozzle tip, which decreases the tip life.
For most GMAW, the wire stick-out should measure from 3/8 to 3/4 inch. For smaller
(micro) wires, the stick-out should be between 1/4 and 3/8 inch.
NOTE: Make sure the drive rolls and contact tube are matched to the diameter of the
wire.
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4.4.0 Gas Cylinder Installation
Transport a cylinder on the proper cart, chain
it in place, and remove the cap.
To clear dirt from the valve opening, open
and quickly close the cylinder valve.
Install the pressure regulator and flow meter
assembly.
When installing 100% CO2, insert a nonmetallic washer inside the regulator
connection so the regulator does not frost
(Figure 10-28). To prevent freezing for flow
rates greater than 25 cubic feet per hour
(cfh), use a line heater or manifold system.
Attach the gas hose to the flowmeter and
wire feeder.
Open the valve slowly until pressure
registers on the regulator, then open the
valve completely to seat it in the fully open
position.
Figure 10-28 — Installation of
pressure regulator.
Press the purge button and adjust the flow meter to the correct flow rate.
4.5.0 Amperage and Voltage Settings
Set amperage and voltage to the middle of the range specified in the welding
procedure.
Fine tune the settings by performing a series of test welds.
4.6.0 Equipment Shutdown and Clean Up
Completely close the valve on the gas cylinder or gas manifold.
Press the purge button to bleed gas from the line.
Close the flowmeter finger tight.
Power down the wire feeder and power source.
Clean up the work area.
4.7.0 Burn Back
Burn back occurs when the molten tip of the electrode fuses to the end of the contact
tube.
If burn back occurs, check the following:
Voltage. If the voltage is too high in relation to the amperage, the electrode melts faster
than the wire feeder can deliver wire to the puddle.
Drive roll tension. The drive rolls could be too loose, causing the wire to slip.
NAVEDTRA 14250A
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Liner and contact tube. A damaged liner or restricted contact tube may also cause burn
back.
4.8.0 Bird Nests
Bird nests occur when the wire is impeded
somewhere between the wire feeder and
the work, causing the wire to pile up
between the drive rolls and the outlet guide
(Figure 10-29).
The most common cause of bird nests is
having too much drive roll tension
combined with a dirty or damaged liner, a
restricted contact tube, or burnback.
To clear a bird nest:
Clip the wire behind the inlet and outlet
guides, and remove the tangle of wire.
Remove the gun cable assembly, nozzle,
and contact tube.
Figure 10-29 — Bird nest.
Extract the wire from the back of the gun
cable.
Rethread the wire.
Replace the contact tube and nozzle.
5.0.0 SHIELDING GAS and ELECTRODES
The shielding gas is an important consumable of gas metal arc welding; its main
purpose is to shield the arc and the molten weld puddle from the atmosphere. The
electrodes used for this process are also consumable and provide the filler metal to the
weld. The chemical composition of the electrode wire in combination with the shielding
gas will determine the weld metal composition and mechanical properties of the weld.
5.1.0 Shielding Gases
Air in the weld zone is displaced by a shielding gas in order to prevent contamination of
the molten weld puddle. This contamination is caused mainly by nitrogen, oxygen, and
water vapor present in the atmosphere.
As an example, nitrogen in solidified steel reduces the ductility and impact strength of
the weld and can cause cracking. In large amounts, nitrogen can also cause weld
porosity.
Excess oxygen in steel combines with carbon to form carbon monoxide (CO). This gas
can be trapped in the metal, causing porosity. In addition, excess oxygen can combine
with other elements in steel and form compounds that produce inclusions in the weld
metal.
When hydrogen, present in water vapor and oil, combines with either iron or aluminum,
porosity will result, and ”underbead” weld metal cracking may occur.
To avoid these problems associated with contamination of the weld puddle, three main
gases are used for shielding: argon, helium, and carbon dioxide. In addition, small
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amounts of oxygen, nitrogen, and hydrogen have proven beneficial for some
applications. Of these gases, only argon and helium are inert gases.
Both inert and active gases may be used for gas metal arc welding. When welding the
non-ferrous metals, inert shielding gases are used because they do not react with the
metals. The inert gases used in gas metal arc welding are argon, helium, and argonhelium mixtures.
Active or inert gases may be employed when welding the ferrous metals. Active gases
such as carbon dioxide, mixtures of carbon dioxide, or oxygen-bearing shielding gases
are not chemically inert and can form compounds with the metals.
Compensation for the oxidizing tendencies of other gases is made by special wire
electrode formulations. Argon, helium, and carbon dioxide can be used alone, in
combinations, or mixed with others to provide defect-free welds in a variety of weld
applications and weld processes.
The basic properties of shielding gases that affect the performance of the welding
process include the following:
1. Thermal properties at elevated temperatures
2. Chemical reaction of the gas with the various elements in the base plate and
welding wire
3. Effect of each gas on the mode of metal transfer
The thermal conductivity of the gas at arc temperatures influences the arc voltage as
well as the thermal energy delivered to the weld. As thermal conductivity increases,
greater welding voltage is necessary to sustain the arc. For example, the thermal
conductivity of helium and CO2 is much higher than that of argon; because of this, they
deliver more heat to the weld. Therefore, helium and CO2 require more welding voltage
and power to maintain a stable arc. The compatibility of each gas with the wire and
base metal determines the suitability of the various gas combinations.
Carbon dioxide and most oxygen-bearing shielding gases should not be used for
welding aluminum, as aluminum oxide will form. However, CO2 and O2 are useful at
times and even essential when MIG welding steels. They promote arc stability and good
fusion between the weld puddle and base material. Oxygen is a great deal more
oxidizing than CO2. Consequently, oxygen additions to argon are generally less than 12
percent by volume, whereas 100 percent CO2 can be used for GMAW mild steels. Steel
wires must contain strong deoxidizing elements to suppress porosity when used with
oxidizing gases, particularly mixtures with high percentages of CO2 or O2 and especially
100 percent CO2.
Shielding gases also determine the mode of metal transfer and the depth to which the
workpiece is melted (depth of penetration). Table 10-2 summarizes recommended
shielding gases for various materials and metal transfer types. Spray transfer is not
obtained when the gas is rich in CO2. For example, mixtures containing more than
about 20 percent CO2 do not exhibit true spray transfer. Rather, mixtures up to 30
percent CO2 can have a ”spray-like” shape to the arc at high current level but are
unable to maintain the arc stability of lower CO2 mixtures. Spatter levels will also tend to
increase when mixtures are rich in CO2.
NAVEDTRA 14250A
10-29
Table 10-2 — Use of different shielding gases for gas metal arc welding.
Type of Gas
Typical Mixtures
Primary Uses
Argon
Non-ferrous metals
Helium
Aluminum, magnesium, and
copper alloys
Carbon dioxide
Mild and low alloy steel
Argon-helium
20-80%
Aluminum, magnesium,
copper and nickel alloys
Argon-oxygen
1-2% O2
Stainless steel
3-5% O2
Mild and low alloy steels
Argon-carbon dioxide
20-50% CO2
Mild and low alloy steels
Helium-argon-carbon dioxide
90%He-7 1/2%Ar-2 1/2%CO2
Stainless steel
60-70%He-25-35%Ar-5%CO2
Low alloy steels
Nitrogen
Copper alloys
Several factors are usually considered in determining the type of shielding gas to be
used, including the following:
1.
2.
3.
4.
5.
6.
7.
8.
Type of metal to be welded
Arc characteristics and type of metal transfer
Speed of welding
Tendency to cause undercutting
Penetration, width, and shape of the weld bead
Availability
Cost of the gas
Mechanical property requirements
5.1.1 Argon
Argon shielding gas is chemically inert and used primarily on the non-ferrous metals.
This gas is obtained from the atmosphere by the liquification of air. Argon may be
supplied as a compressed gas or a liquid, depending on the volume of use.
Argon shielding gas promotes spray type metal transfer at most current levels. Because
argon is a heavier gas than helium, lower flow rates are used because the gas does not
leave the welding area as fast as it does with helium. Another advantage of argon is that
it gives better resistance to drafts. For any given arc length and welding current, the arc
voltage is less when using argon than when using helium or carbon dioxide. This means
that there is less arc energy, which makes argon preferable for welding thin metal and
for metals with poor thermal conductivity.
Argon is less expensive than helium and has greater availability. It also gives easier arc
starting, quieter and smoother arc action, and good cleaning action.
5.1.2 Helium
Helium shielding gas is chemically inert and is used primarily on aluminum, magnesium,
and copper alloys. Helium is a light gas obtained by separation from natural gas. It may
be distributed as a liquid but it is more often used as compressed gas in cylinders.
NAVEDTRA 14250A
10-30
Helium shielding gas is lighter than air and because of this, high gas flow rates must be
used to maintain adequate shielding. Typically, the gas flow rate is 2 to 3 times of that
used for argon when welding in the flat position. Helium is often preferred in the
overhead position because the gas floats up and maintains good shielding, while argon
tends to float down. Globular metal transfer is usually obtained with helium, but spray
transfer may be obtained at the highest current levels. Because of this, more spatter
and a poorer weld bead appearance will be produced, as compared to argon. For any
given arc length and current level, helium will produce a hotter arc, which makes helium
good for welding thick metal and metals like copper, aluminum, and magnesium, which
have a high thermal conductivity. Helium generally gives wider weld beads and better
penetration than argon.
5.1.3 Carbon Dioxide
Carbon dioxide is manufactured from fuel gases given off by the burning of natural gas,
fuel oil, or coke. It is also obtained as a by-product of calcination operation in lime kilns,
from the manufacturing of ammonia, and from the fermentation of alcohol. The carbon
dioxide given off by manufacturing ammonia and the fermenting alcohol is almost 100%
pure. Carbon dioxide is made available to the user in either cylinder or bulk containers
with the cylinder being more common. With the bulk system, carbon dioxide is usually
drawn off as a liquid and heated to the gas state before going to the welding torch. The
bulk system is normally used only when supplying a large number of welding stations.
In the cylinder, the carbon dioxide is in both a liquid and a vapor form, with the liquid
carbon dioxide occupying approximately two thirds of the space in the cylinder. By
weight, this is approximately 90% of the content of the cylinder. Above the liquid it exists
as a vapor gas. As carbon dioxide vapor is drawn from the cylinder, it is replaced with
carbon dioxide that vaporizes from the liquid in the cylinder, and therefore the overall
pressure will be indicated by the pressure gage.
When the pressure in the cylinder has dropped to 200 psi (1.4 MPa), the cylinder should
be replaced with a new cylinder. A positive pressure should always be left in the
cylinder in order to prevent moisture and other contaminants from backing up into the
cylinder. The normal discharge rate of the CO2 cylinder is from about 4 to 35 cubic feet
per hour (1.9 to 17 liters per minute). However, a maximum discharge rate of 25 cfh (12
l/min) is recommended when using a single
cylinder for welding.
As the vapor pressure drops from the
cylinder pressure to discharge pressure
through the CO2 regulator, it absorbs a
great deal of heat. If flow rates are set too
high, this absorption of heat can lead to
freezing of the regulator and flow meter,
which interrupts the gas shielding. When
flow rates higher than 25 cfh (12 l/min) are
required, normal practice is to manifold two
CO2 cylinders in parallel or to place a heater
between the bottle and gas regulator,
pressure regulator, and flowmeter. Figure
10-30 shows a manifold system used for
connecting several cylinders together.
Excessive flow rates can also result in
drawing liquid from the cylinder.
NAVEDTRA 14250A
Figure 10-30 — Manifold system for
carbon dioxide.
10-31
Carbon dioxide has become widely used for welding mild and low alloy steels. Most
active gases cannot be used as shielding, but carbon dioxide offers several advantages
for use in welding steel:
1. Better joint penetration
2. Higher welding speeds
3. Lower welding costs (the major advantage)
Carbon dioxide produces short-circuiting transfer at low current levels and globular
transfer at the higher current levels. Because carbon dioxide is an oxidizing gas, most
electrode wires available for welding steel contain deoxidizers to prevent porosity in the
weld. The surface of the weld bead is usually slightly oxidized even when there is no
porosity.
The major disadvantage of carbon dioxide is that it produces a harsh arc and higher
amounts of spatter. A short arc length is usually desirable to keep the amount of spatter
to a minimum. Another problem with carbon dioxide is that it adds some carbon to the
weld deposit. This does not affect mild steels, but it tends to reduce the corrosion
resistance of stainless steel and reduce the ductility and toughness of the weld deposit
in some of the low alloy steels.
5.1.4 Argon-Helium Mixtures
Regardless of the percentage, argon-helium mixtures are used for non-ferrous materials
such as aluminum, copper, nickel alloys, and reactive metals. These gases used in
various combinations increase the voltage and heat of GTAW and GMAW arcs while
maintaining the favorable characteristics of argon. Generally, the heavier the material
the higher the percentage of helium you would use. Small percentages of helium, as low
as 10%, will affect the arc and the mechanical properties of the weld. As helium
percentages increase, the arc voltage, spatter, and penetration will increase while
minimizing porosity. A pure helium gas will broaden the penetration and bead, but depth
of penetration could suffer. However, arc stability also increases. The argon percentage
must be at least 20% when mixed with helium to produce and maintain a stable spray
arc.
Argon-25% He (HE-25) – This little used mixture is sometimes recommended for
welding aluminum where an increase in penetration is sought and bead appearance is
of primary importance.
Argon-75% He (HE-75) – This commonly used mixture is widely employed for
mechanized welding of aluminum greater than one inch thick in the flat position. HE-75
also increases the heat input and reduces porosity of welds in ¼-and 1/½-in. thick
conductivity copper.
Argon-90% He (HE-90) – This mixture is used for welding copper over ½ in. thick and
aluminum over 3 in. thick. It has an increased heat input, which improves weld
coalescence and provides good X-ray quality. It is also used for short circuiting transfer
with high nickel filler metals.
5.1.5 Argon-Oxygen Mixtures
Argon-oxygen gas mixtures usually contain 1%, 2% or 5% oxygen. The small amount of
oxygen in the gas causes the gas to become slightly oxidizing, so the filler metal used
must contain deoxidizers to help remove oxygen from the weld puddle and prevent
porosity. Pure argon does not always provide the best arc characteristics when welding
NAVEDTRA 14250A
10-32
ferrous metals. In pure argon shielding, the filler metal has a tendency not to flow out to
the fusion line.
The addition of small amounts of O2 to argon greatly stabilizes the weld arc, increases
the filler metal droplet rate, lowers the spray arc transition current, and improves wetting
and bead shape. The weld puddle is more fluid and stays molten longer, allowing the
metal to flow out towards the toe of the weld. This reduces undercutting and helps
flatten the weld bead. Occasionally, small oxygen additions are used on non-ferrous
applications. For example, it has been reported by NASA that .1% oxygen has been
useful for arc stabilization when welding very clean aluminum plate.
Argon-1% O2 – This mixture is primarily used for spray transfer on stainless steels. One
percent oxygen is usually sufficient to stabilize the arc, improve the droplet rate, provide
coalescence, and improve appearance.
Argon-2% O2 – This mixture is used for spray arc welding on carbon steels, low alloy
steels and stainless steels. It provides additional wetting action over the 1% O2 mixture.
Mechanical properties and corrosion resistance of welds made in the 1 and 2% O2
additions are equivalent.
Argon-5% O2 – This mixture provides a more fluid but controllable weld pool. It is the
most commonly used argon-oxygen mixture for general carbon steel welding. The
additional oxygen also permits higher travel speeds.
Argon-8-12% O2 – Originally popularized in Germany, this mixture has recently
surfaced in the U.S. in both the 8% and 12% types. The main application is single pass
welds, but some multi-pass applications have been reported. The higher oxidizing
potential of these gases must be taken into consideration with respect to the wire alloy
chemistry. In some instances a higher alloyed wire will be necessary to compensate for
the reactive nature of the shielding gas. The higher puddle fluidity and lower spray arc
transition current of these mixtures could have some advantage on some weld
applications.
Argon-12-25% O2 – Mixtures with very high O2 levels have been used on a limited
basis, but the benefits of 25% O2 versus 12% O2 are debatable. Extreme puddle fluidity
is characteristic of this gas. A heavy slag/scale layer over the bead surface can be
expected, which is difficult to remove. With care and a deoxidizing filler metal, sound
welds can be made at the 25% O2 level with little or no porosity. Removal of the
slag/scale before subsequent weld passes is recommended to ensure the best weld
integrity.
5.1.6 Argon-Carbon Dioxide Mixtures
The argon-carbon dioxide mixtures are mainly used on carbon and low alloy steels with
limited application on stainless steels. The argon additions to CO2 decrease the spatter
levels usually experienced with pure CO2 mixtures. Small CO2 additions to argon
produce the same spray arc characteristics as small O2 additions. The difference lies
mostly in the higher spray arc transition currents of argon-CO2 mixtures. In GMAW
welding with CO2 additions, a slightly higher current level must be reached in order to
establish and maintain stable spray transfer of metal across the arc. Oxygen additions
reduce the spray transfer transition current. Above approximately 20% CO2, spray
transfer becomes unstable, and random short circuiting and globular transfer occur.
Argon-3-10% CO2 – These mixtures are used for spray arc and short circuiting transfer
on a variety of carbon steel thicknesses. Because the mixtures can successfully utilize
both arc modes, this gas has gained much popularity as a versatile mixture. A 5%
NAVEDTRA 14250A
10-33
mixture is very commonly used for pulsed GMAW of heavy section low alloy steels
being welding out-of-position. The welds are generally less oxidizing than those with 98
Ar-2% O2. Improved penetration is achieved with less porosity when using CO2
additions as opposed to O2 additions. In the case of bead wetting, it requires about
twice as much CO2 to achieve the same wetting action as identical amounts of O2. From
5 to 10% CO2 the arc column becomes very stiff and defined. The strong arc forces that
develop give these mixtures more tolerance to mill scale and a very controllable puddle.
Argon-11-20% CO2 – This mixture range has been used for various narrow gap, out-ofposition sheet metal and high speed GMAW applications. Most applications are on
carbon and low alloy steels. By mixing the CO2 within this range, maximum productivity
on thin gauge materials can be achieved. This is done by minimizing burn through
potential while at the same time maximizing deposition rates and travel speeds. The
lower CO2 percentages also improve deposition efficiency by lowering spatter loss.
Argon-21-25% CO2– Used almost exclusively with short circuiting transfer on mild steel,
it was originally formulated to maximize the short circuit frequency on .030- and .035- in.
diameter solid wires, but through the years it has become the de facto standard for most
diameter solid wire welding and has been commonly used with flux cored wires. This
mixture also operates well in high current applications on heavy materials and can
achieve good arc stability, puddle control, and bead appearance as well as high
productivity.
Argon-50% CO2 – This mixture is used where high heat input and deep penetration are
needed. Recommended material thicknesses are above 11/8 in., and welds can be
made out-of-position. This mixture is very popular for pipe welding using the short
circuiting transfer. Good wetting and bead shape without excessive puddle fluidity are
the main advantages for the pipe welding application. Welding on thin gauge materials
has more of a tendency to burn through, which can limit the overall versatility of this
gas. In welding at high current levels, the metal transfer is more like welding in pure
CO2 than previous mixtures, but some reduction in spatter loss can be realized due to
the argon addition.
Argon-75% CO2 – A 75% CO2 mixture is sometimes used on heavy wall pipe and is the
optimum in good side-wall fusion and deep penetration. The argon constituent aids in
arc stabilization and reduced spatter.
5.1.7 Helium-Argon-Carbon Dioxide Mixtures
Three-part shielding gas blends continue to be popular for carbon steel, stainless steel,
and, in restricted cases, nickel alloys. For short-circuiting transfer on carbon steel, the
addition of 40% helium to argon and CO2 as a third component to the shielding gas
blend provides a broader penetration profile.
Helium provides greater thermal conductivity for short-circuiting transfer applications on
carbon steel and stainless steel base materials. The broader penetration profile and
increased sidewall fusion reduces the tendency for incomplete fusion.
For stainless steel applications, three-part mixes are quite common. Helium additions of
55% to 90% are added to argon and 2.5% CO2 for short-circuiting transfer. They are
favored for reducing spatter, improving puddle fluidity, and providing a flatter weld bead
shape.
Common Ternary (tur-nuh-ree) Gas Shielding Blends
90% Helium + 7.5% Argon + 2.5% CO2 — This is the most popular of the shortcircuiting blends for stainless steel applications. The high thermal conductivity of helium
NAVEDTRA 14250A
10-34
provides a flat bead shape and excellent fusion. This blend has also been adapted for
use in pulsed spray transfer applications, but it is limited to stainless or nickel base
materials greater than .062–in. (1.6 mm) thick. It is associated with high travel speeds
on stainless steel applications.
55% Helium + 42.5% Argon + 2.5% CO2 — Although less popular than the 90% helium
mix discussed above, this blend features a cooler arc for pulsed spray transfer. It also
lends itself very well to the short-circuiting mode of metal transfer for stainless and
nickel alloy applications. The lower helium concentration permits its use with axial spray
transfer.
38% Helium + 65% Argon + 7% CO2 — This tertiary blend is for use with shortcircuiting transfer on mild and low alloy steel applications. It can also be used on pipe
for open root welding. The high thermal conductivity broadens the penetration profile
and reduces the tendency to cold lap.
5.1.8 Nitrogen
Nitrogen is occasionally used as a shielding gas when welding copper and copper
alloys. Nitrogen has characteristics similar to helium because it gives better penetration
than argon and tends to promote globular metal transfer. Nitrogen is used where the
availability of helium is limited, such as in Europe. It can be mixed with argon for
welding aluminum alloys.
5.2.0 Shielding Gas Flow Rate
The shielding gas flow rate should be high enough to maintain adequate shielding for
the arc and weld puddle but should not be so high that it causes turbulence in the weld
puddle. The gas flow rate is primarily dependent on the type of shielding gas, position of
welding, and amount of electrode extension or stick-out. Higher flow rates are required
for helium than for carbon dioxide and argon. These are often twice those used for
carbon dioxide and argon because helium is a very light gas that floats away from the
weld puddle quicker than the heavier carbon dioxide and argon gases.
In welding in the overhead position, slightly higher flow rates are often used with the
heavier shielding gases because they tend to fall away from the weld puddle. The last
item that affects the gas flow rate is the amount of electrode extension used. For a long
electrode extension, higher gas flow rates are required to provide adequate shielding
because of the greater distance between the tip of the nozzle and the weld puddle.
5.3.0 Electrodes
One of the most important factors to consider in GMAW welding is the correct filler wire
selection. The electrode used in gas metal arc welding is bare, solid, consumable wire.
In many cases, the electrode wires are chosen to match the chemical composition of
the base metal as closely as possible. In some cases, electrodes with a somewhat
different chemical composition will be used to obtain maximum mechanical properties or
better weldability. Almost all electrodes used for gas metal arc welding of steels have
deoxidizing or other scavenging elements added to minimize the amount of porosity and
improve the mechanical properties. The use of electrode wires with the right amount of
deoxidizers is most important when using oxygen- or carbon dioxide-bearing shielding
gases.
The filler wire, in combination with the shielding gas, will produce the deposit chemistry
that determines the resulting physical and mechanical properties of the weld. Five major
factors influence the choice of filler wire for GMAW welding:
NAVEDTRA 14250A
10-35
1.
2.
3.
4.
5.
Base plate chemical composition
Base plate mechanical properties
Shielding gas employed
Type of service or applicable specification requirements
Type of weld joint design
However, long experience in the welding industry has generated American Welding
Society Standards to greatly simplify the selection. Wires have been developed and
manufactured that consistently produce the best results with specific plate materials.
Although there is no industry-wide specification, most wires conform to an AWS
standard (Table 10-3).
Table 10-3 — AWS filler metal specifications for gas metal arc welding.
AWS Specification
Metal
A5.7
Copper and copper alloys
A5.9
Stainless steel
A5.10
Aluminum and aluminum alloys
A5.14
Nickel and nickel alloys
A5.16
Titanium and titanium alloys
A5.18
Carbon steel
A5.19
Magnesium alloys
A5.24
Zirconium and zirconium alloys
A5.28
Low alloy steel
5.3.1 Classification
The classification system for bare, solid wire electrodes used throughout industry in the
United States was devised by the American Welding Society. Because of the wide
variety of metals that can be welded by this process, there are numerous classifications
and many are the same as those used to classify filler rods for gas tungsten arc
welding.
Most classifications of GMAW electrodes are based on the chemical composition of the
weld deposit. A major exception to this is the classification of electrodes used for
welding steel, which are classified by both the chemical composition of the wire and
mechanical properties produced in the weld.
A typical steel classification is ER70S-6.
1. The E indicates the filler wire is an electrode that may be used for gas metal arc
welding. The R indicates it may also be used as a filler rod for gas tungsten arc
or plasma arc welding.
2. The next two (or three) digits indicate the nominal tensile strength of the filler
wire.
3. The letter to the right of the digits indicates the type of filler metal. An S stands
for a solid wire and a C stands for a metal-cored wire which consists of a metal
powder core in a metal sheath.
NAVEDTRA 14250A
10-36
4. The digit or letters and digit in the suffix indicate the special chemical
composition of the filler metal and the other mechanical properties required.
For example, an ER90S-B3 classification indicates that the filler metal may be used as
an electrode or a filler rod, produces a weld metal tensile strength of 90,000 psi (620
MPa), is a solid electrode wire, and produces a weld deposit with specific chemical
compositions and mechanical properties. These are shown in Tables 10-4 and 10-5,
taken from the AWS Filler Metal Specifications A5.18 and A5.28 respectively.
NAVEDTRA 14250A
10-37
Table 10-4 — Chemical composition of bare solid electrodes and deposited
weld metal for composite cored electrodes for carbon and low alloy steels
(AWS A5.18, A5.28.
C
Mn
Si
P
S
CARBON STEELS
ER70S-2
.07
.90-1.40
.40-.70
.025
ER70S-3
.06-15
.90-1.40
.45-.70
ER70S-4
.07-.15
1.00-1.50
ER70S-5
.07-.19
ER70S-6
Cu
Other
.035
.50
Ti Zr AI
.025
.035
.50
.65-.85
.025
.035
.50
.90-1.40
.30-.60
.025
.035
.50
.07-15
1.40-1.85
.80-1.15
.025
.035
.50
ER70S-7
ER70S-G
.07-.15
1.50-2.00
.50-.80
.025
.035
No Chemical Requirements
CHROMIUM-MOLYBDENUM STEELS
ER80S-B2
.07-.12
.40-.70
.40-.70
.025
.025
.20
1.2-1.5
.40-.65
.35
ER80S-B2L
.05
.40-.70
.40-.70
.025
.025
.20
1.2-1.5
.40-.65
.35
ER90S-B3
.07-.12
.40-.70
.40-.70
.025
.025
.20
2.3-2.7
.90-1.20
.35
ER90S-B3L
.05
.40-.70
.40-.70
.025
.025
.20
2.3-2.7
.90-1.20
.35
E80C-B2L
.05
.40-1.00
.25-.60
.025
.030
.20
1.00.. 1.5
.40-.65
.35
E80C-B2
.07-.12
.40-1.00
.25-.60
.025
.030
.20
1.0-1.50
.40-.65
.35
E90C-B3L
.05
.40-1.00
.25-.60
.025
.030
.20
2.0-2.5
.90-1.20
.35
E90C-B3
.07-.12
.40-1.00
.25-.60
.025
2.0-2.5
.90-1.20
.35
ER80S-Ni1
ER80S-Ni2
.12
.12
1.25
1.25
.40-.80
.40-.80
.030
.20
NICKEL STEELS
.025
.025
.80-l.10
025
.025
2.00-2.75
.15
.15
.35
.35
ER80S-Ni3
E80C-Ni1
.12
.12
1.25
1.25
.40-.80
.60
.025
.025
.025
.030
3.00-3.75
.80-1.10
E80C-Ni2
.12
1.25
.60
.025
.030
2.00-2.75
.35
E80C-Ni3
.12
1.25
.60
.025
.030
3.00-3.75
MANGANESE-MOLYBDENUM STEELS
.35
ER80S-D2
.07-.12
1.60-2.10
.50-.80
.025
.025
.15
OTHER LOW ALLOY STEEL ELECTRODES
ER100S-1
.08
1.25-1.80
.20-.50
.010
.010
1.40-2.10
ER100S-2
.12
1.25-1.80
.20-.60
.010
.010
.80-l.25
ERll0S-1
ER120S-1
ERXXS-G
EXXC-G
.09
.10
1.40-1.80
.20-.55
.010
1.40-1.80
.25-.60
.010
No Chemical Requirements
No Chemical Requirements
NAVEDTRA 14250A
1.90-2.60
2.00-2.80
Ni
Cr
Mo
AI
.50
.65
.35
.35
V
V
.40-.60
.50
.30
.25-.55
V Ti Zr AI
.30
.20-.55
.25
.35.65
.50
.60
.25-.55
.30-.65
.25
.25
V Ti Zr AI
V Ti Zr AI
V Ti Zr AI
10-38
Table 10-5 — Tension and impact test of weld metal deposits of carbon steel electrodes.
AWS
Classification
ER70S-2
ER70S-3
ER70S-4
ER70S-5
ER70S-6
ER70S-7
ER70S-G
E70C-3X
E70C-6X
E70C-G(X)
E70C-GS(X)
Tension Test Requirements (As Welded)
Tensile
Yield
Strength
Strength
(minimum)
(minimum)
Shielding
Gas
psi
Mpa
psi
Mpa
Elongation
Percent
(minimum)
CO2
70,000
480
58,000
400
22
d
75-80% Ar/balance
CO2
d
d
70,000
480
58,000
400
22
70,000
480
58,000
400
22
70,000
70,000
480
480
58,000 400
Not Specified
22
Not Specified
a. The final X shown in the classification represents. "C” or "M" which corresponds to the
shielding gas with which the electrode is classified. The use of "C” designates 100% CO2,
shielding; "M" designates 75·80% Ar/balance CO2. For E70C-GQ and E70C-GS. The final
"C" or "M" may be omitted.
b. Yield strength at 0.2% offset and elongation in 2 in. (51 mm) gage length.
c. CO2 = carbon dioxide shielding gas. The use of CO2 for classification purposes shall not be
construed to preclude the use of Ar/CO2 or Ar/O2 shielding gas mixtures. A filler metal
tested with gas blends such as Ar/O2 or Ar/CO2 may result in weld metal having higher
strength and lower elongation.
d. Shielding gas shall be as agreed to between purchaser and supplier.
NAVEDTRA 14250A
10-39
Impact test requirements (as welded)
AWS
Average Impact Strength
Classification
(minimum)
ER70-2
20 ft lbf at -20°F([email protected]°C)
ER70-3
20 ft lbf at 0°F([email protected]°C)
ER70-4
Not Required
ER70-5
Not Required
ER70-6
20 ft lbf at -20°F([email protected]°C)
ER70-7
20 ft lbf at -20°F([email protected]°C)
ER70S-G
As agreed between supplier and purchaser
ER70S-G(X)
As agreed between supplier and purchaser
E70C-3X
20 ft lbf at 0°F([email protected]°C)
E70C-6X
20 ft lbf at -20°F([email protected]°C)
E70C-GS(X)
Not Required
a. Both the highest and lowest of the five test values obtained shall be disregarded in computing the impact strength. Two of the
remaining three values shall equal or exceed 20 ft-lbf; one of the three remaining values may be lower than 20 ft-Ibl but not
lower than 15 ft-lbf. The average of the three shall not be less than the 20 ft-Ibf specified.
b. For classifications with the "N" (nuclear) designation, three additional specimens shall be tested at room temperature. Two of
the three shall equal or exceed. 75 ft-lbf (102J), and the third shall not be lower than 70 ft-lbf (95J). Average of the three values
shall equal or exceed 75 ft Ibf (102J).
Filler metals for other base metals are classified according to the chemical compositions
of the weld metal produced. Some examples are the stainless steel classifications
shown in Table 10-6, the aluminum classifications shown in Table 10-7, the copper
classifications shown in Table 10-8, the magnesium classifications shown in Table 10-9,
and the nickel classifications shown in Table 10-10.
NAVEDTRA 14250A
10-40
Table 10-6 — Chemical composition of bare stainless steel welding electrodes
and rods (AWS A5.9).
Composition, Wt%a,b
AWS
Other Elements
UNS
cd
Classification
Number
e
ER209
ER218
ER219
ER240
S20980
S21880
S21980
S24080
ER307
ER308
S30780
S30880
ER308H
ER308L
ER308Mo
ER308LMo
ER308Si
ER308LSi
ER309
ER309L
ER309Mo
ER309LMo
ER309Si
ER309LSi
S30880
S30883
S30882
S30886
S30881
S30888
S30980
S30983
S30982
S30986
S30981
S30988
ER310
ER312
ERJ16
S31080
S31380
S31680
ER316H
ER316L
ER316Si
ER316LSi
ERJ17
ER317L
ER318
ERJ20
ER320LR
ER321
S31680
S31683
S31681
S31688
S31780
S31783
S31980
N08021
N08022
S32180
ER330
ER347
ER347Si
N0S331
S34780
S34788
ER383
ER385
ER409
ER409Cb
ER410
ER410NiM0
N08028
N08904
S40900
S40940
S41080
S41086
ER420
ER430
ER446LM0
ER502h
ER505h
S42080
S43080
S44687
S50280
S50480
ER630
S17480
ER19-10H
S30480
ER16-8-2
ER2209
ER2553
S16880
S39209
S39553
ERJ556
RJ0556
C
0.05
0.10
0.05
0.05
0.040.14
0.08
0.040.08
0.03
0.08
0.04
0.08
0.03
0.12
0.03
0.12
0.03
0.12
0.03
0.080.15
0.15
0.08
0.040.08
0.03
0.08
0.03
0.08
0.03
0.08
0.07
0.025
0.08
0.180.25
0.08
0.08
Cr
20.5-24.0
16.0-18.0
19.0-21.5
17.0-19.0
Ni
9.5-12.0
8.0-9.0
5.5-7.0
4.0-6.0
Mo
1.5-3.0
0.75
0.75
0.75
Mn
4.0-7.0
7.0-9.0
8.0-10.0
10.5-13.5
Si
0.90
3.5-4.5
1.00
1.00
P
0.03
0.03
0.03
0.03
S
0.03
0.03
0.03
0.03
N
0.10-0.30
0.08-0.18
0.10-0.30
0.10-0.30
19.5-22.0
19.5-22.0
8.0-10.7
9.0-11.0
0.5-1.5
0.75
3.3-4.75
1.0-2.5
0.30-0.65
0.30-0.65
0.03
0.03
0.03
0.03
0.75
0.75
19.5-22.0
19.5-22.0
18.0-21.0
18.0-21.0
19.5-22.0
19.5-22.0
23.0-25.0
23.0-25.0
23.0-25.0
23.0-25.0
23.0-25.0
23.0-25.0
9.0-11.0
9.0-11.0
9.0-12.0
9.0-12.0
9.0-11.0
9.0-11.0
12.0-14.0
12.0-14.0
12.0-14.0
12.0-14.0
12.0-14.0
12.0-14.0
0.50
0.75
2.0-3.0
2.0-3.0
0.75
0.75
0.75
0.75
2.0-3.0
2.0-3.0
0.75
0.75
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
0.30-0.65
0.30-0.65
0.30-0.65
0.30-0.65
0.65-1.00
0.65-1.00
0.30-0.65
0.30-0.65
0.30-0.65
0.30-0.65
0.65-1.00
0.65-1.00
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
25.0-28.0
28.0-32.0
18.0-20.0
20.0-22.5
8.0-10.5
11.0-14.0
0.75
0.75
2.0-3.0
1.0-2.5
1.0-2.5
1.0-2.5
0.30-0.65
0.30-0.65
0.30-().65
0.03
0.03
0.03
0.03
0.03
0.03
0.75
0.75
0.75
18.0-20.0
18.0-20.0
18.0-20.0
18.0-20.0
18.5-20.5
18.5-20.5
18.0-20.0
19.0-21.0
19.0-21.0
18.5-20.5
11.0-14.0
11.0-14.0
11.0-14.0
11.0-14.0
13.0-15.0
13.0-15.0
11.0-14.0
32.0-36.0
32.0-36.0
9.0-10.5
2.0-3.0
2.0-3.0
2.0-3.0
2.0-3.0
3.0-4.0
3.0-4.0
2.0-3.0
2.0-3.0
2.0-3.0
0.75
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
1.0-2.5
2.5
1.5-2.0
1.0-2.5
0.30-().65
0.30-0.65
0.65-1.00
0.65-1.00
0.30-0.65
0.30-0.65
0.30-0.65
0.60
0.15
0.30-0.65
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.015
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.02
0.03
0.75
0.75
0.75
0.75
0.75
0.75
0.75
3.0-4.0
3.0-4.0
0.75
15.0-17.0
19.0-21.5
19.0-21.5
34.0-37.0
9.0-11.0
9.0-11.0
0.75
0.75
0.75
1.0-2.5
1.0-2.5
1.0-2.5
0.30-0.65
0.30-0.65
0.65-1.00
0.03
0.03
0.03
0.03
0.03
0.03
0.025
0.025
0.08
0.08
0.12
0.06
0.250.40
0.10
0.015
0.10
0.10
26.5-28.5
19.5-21.5
10.5-13.5
10.5-13.5
11.5-13.5
11.0-12.5
30.0-33.0
24.0-26.0
0.6
0.6
0.6
4.0-5.0
3.2-4.2
4.2-5.2
0.50
0.50
0.75
0.4-0.7
1.0-2.5
1.0-2.5
0.8
0.8
0.6
0.6
0.50
0.50
0.8
1.0
0.5
0.5
0.02
0.02
0.03
0.04
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.03
0.75
0.75
0.75
0.701.5
1.2-2.0
0.75
0.75
0.75
0.75
12.0-14.0
15.5-17.0
25.0-27.5
4.6-6.0
8.0-10.5
0.6
0.6
f
0.6
0.5
0.75
0.75
0.75-1.50
0.45-0.65
0.8-1.2
0.6
0.6
0.4
0.6
0.6
0.5
0.5
0.4
0.5
0.5
0.03
0.03
0.02
0.03
0.03
0.03
0.03
0.02
0.03
0.03
0.05
0.040.08
16.0-16.75
4.5-5.0
0.75
0.25-0.75
0.75
0.03
0.03
0.75
0.75
f
0.75
0.75
3.254.00
18.5-20.0
9.0-11.0
0.25
1.0-2.0
0.30-0.65
0.03
0.03
0.75
0.10
0.03
0.04
0.050.15
14.5-16.5
21.5-23.5
24.0-27.0
7.5-9.5
7.5-9.5
4.5-6.5
1.0-2.0
2.5-3.5
2.9-3.9
1.0-2.0
0.50-2.0
1.5
0.30-0.65
0.90
1.0
0.03
0.03
0.04
0.03
0.03
0.03
0.08-0.20
0.10-0.25
21.0-23.0
19.0-22.5
2.5-4.0
0.50-2.00
0.20-0.80
0.04
0.015
0.10-0.30
0.015
Cu
0.75
0.75
0.75
0.75
Element
V
Amount
0.10-0.30
Cbg
Cbg
Cbg
Ti
8xC min/1.0 max
8xC min/1.0 max
8xC min/0.40 max
9xC min/1.0 max
Cbg
Cbg
10xC min/1.0 max
10xC min/1.0 max
Ti
Cbg
10xC min/1.0 max
10xC min/1.0 max
Cbg
0.15-0.30
Cbg
Ti
0.05
0.05
0.75
0.75
1.5-2.5
Co
16.0-21.0
W
2.0-3.5
Cb
0.30
Ta
0.30-1.25
AI
0.10-0.50
Zr
0.001-0.10
La
0.005-0.10
B
0.02
a. Analysis shall be made for the elements for which specific values are shown in this table. If the presence of other elements is indicated in the course of this work, the amount of those elements
shall be determined to ensure that their total, excluding iron, does not exceed 0.50 percent.
b. Single values shown are maximum percentages.
c. In the designator for composite. stranded, and strip electrodes, the "R" shall be deleted. A designator "C" shall be used for composite and stranded electrodes and a designator "0" shall be
used for strip electrodes. For example, ERXXX designates a solid wire and EQXXX designates a strip electrode of the same general analysis, and the same UNS number. However, ECXXX
designates a composite metal cored or stranded electrode and may not have the same UNS number. Consult ASTM/SAE Uniform Numbering System for the proper UNS Number.
d. For special applications, electrodes and rods may be purchased with Iess than the specified silicon content.
e. ASTM/SAE Unified Numbering System for Metals and Alloys.
f. Nickel + copper equals 0.5 percent maximum.
g. Cb(Nb) may be reported as Cb(Nb) + Ta.
h. These classifications also will be included in the next revision of ANSI/AWS AS.2B, Specification for Low Alloy Steel Filler Metals for Gas Shielded Metal Arc Welding. They will be deleted from
ANSl/ AWS AS.9 in the final revision following publication of the revised ANSl/AWS AS.2B document.
NAVEDTRA 14250A
10-41
Table 10-7 — Chemical composition of bare aluminum and aluminum alloy
welding electrodes and rods (AWS A5.10).
Weight Percenta,b
AWS
Classification
UNS
Numberc
Si
Fe
ER1100
R1100
ER1188g
R1188g
A91100
A91100
A91188
A91188
d
d
0.06
0.06
d
d
0.06
0.06
Cu
0.050.20
05-0.20
0.005
0.005
ER2319h
A92319
0.20
0.30
5.8-6.8
R2319h
ER4009
R4009
ER4010
R4010
R4011k
ER4043
R4043
A92319
A94009
A94009
A94010
A94010
A94011
A94043
A94043
0.30
0.20
0.20
0.20
0.20
0.20
0.8
0.8
ER4047
A94047
0.8
0.8
0.8
0.8
0.8
0.8
0.30
3.3-4.7
3.3-4.7
0.10
0.10
0.15
0.15
0.15
0.05
0.05
0.10
0.15
0.15
0.10-0.30
0.10-0.30
0.40
0.10
0.50-1.0
4.3-5.2
R4047
ER4145
R4145
ER4643
R4643
A94047
A94145
A94145
A94643
A94643
0.20
4.5-5.5
4.5-5.5
6.5-7.5
6.5-7.5
6.5-7.5
4.5-6.0
4.5-6.0
11.013.0
11.013.0
9.3-10.7
9.3-10.7
3.6-4.6
3.6-4.6
ER5183
A95183
0.40
Mn
5.8-6.8
1.0-1.5
1.0-1.5
0.20
0.20
0.20
0.30
0.30
0.05
0.05
0.01
0.01
0.200.40
0.200.40
0.10
0.10
0.10
0.10
0.10
0.05
0.05
0.30
0.15
R5183
A95183
0.40
0.40
0.10
ER5356
A95356
0.25
0.40
0.10
R5356
A95356
0.25
0.4
0.1
0.50-1.0
0.050.20
0.050.20
ER5554
A95554
0.25
0.40
0.10
0.50-1.0
Mg
Ti
Each
0.01
0.01
0.05e
0.05e
0.01e
0.01e
0.15
0.15
0.01
0.01
0.10
0.10
0.03
0.03
99.0 minf
99.0 minf
99.88 minf
99.88 minf
0.02
0.10
0.10-0.20
0.05e
0.15
Remainder
0.02
0.45-0.6
0.45-0.6
0.30-0.45
0.30-0.45
0.45-0.7
0.05
0.05
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10-0.20
0.20
0.20
0.20
0.20
0.04-0.20
0.20
0.20
0.05e
0.05e
0.05e
0.05e
0.05e
0.05
0.05e
0.05e
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
0.10
0.20
0.05e
0.15
Remainder
0.20
0.20
0.20
0.10
0.10
e
0.15
0.15
0.05
0.05e
0.05e
0.05e
0.05e
0.15
0.15
0.15
0.15
0.15
Remainder
Remainder
Remainder
Remainder
Remainder
0.25
0.15
0.05e
0.15
Remainder
0.25
0.15
0.05
e
0.15
Remainder
0.10
0.06-0.20
0.05e
0.15
Remainder
0.1
0.06-0.20
0.05
e
0.15
Remainder
0.25
0.05-0.20
0.05e
0.15
Remainder
0.25
0.05-0.20
0.05
e
0.15
Remainder
0.25
0.05-0.20
0.05e
0.15
Remainder
0.25
0.05-0.20
0.05
e
0.15
Remainder
0.20
0.05-0.15
0.05e
0.15
Remainder
0.20
0.05-0.15
0.05e
0.15
Remainder
0.10
0.1
0.10
0.05
0.10
0.15-0.30
0.2
0.20
0.20
0.04-0.20
0.05
0.05
0.05
0.05
0.05
0.15
0.15
0.15
0.15
0.15
Remainder
Remainder
Remainder
Remainder
Remainder
4.3-5.2
2.4-3.0
4.5-5.5
4.5-5.5
R5554
A95554
0.25
0.40
0.10
0.50-1.0
2.4-3.0
ER5556
A95556
0.25
0.40
0.10
0.50-1.0
4.7-5.5
R5556
A95556
0.25
0.40
0.10
0.50-1.0
4.7-5.5
ER5654
A95654
i
i
0.05
0.01
3.1-3.9
R5654
A95654
i
i
0.05
3.1-3.9
A02060
A33550
A13560
A03570
A13570
0.10
4.5-5.5
6.5-7.5
6.5-7.5
6.5-7.5
0.15
0.2
0.20
0.15
0.20
4.2-5.0
1.0-1.5
0.20
0.05
0.20
0.01
0.200.50
0.1
0.10
0.03
0.10
j
R-206.0
R-C355.0
R-A356.0
R-357.0
R-A357.0k
0.15-0.35
0.40-0.6
0.25-0.45
0.45-0.6
0.40-0.7
Cr
Ni
0.15
0.15
0.050.25
0.050.25
0.050.20
0.050.20
0.050.20
0.050.20
0.050.20
0.050.20
0.150.35
0.150.35
0.05
Zn
Other
Elements
Total
AI
a. The filler metal shall be analyzed for the specific elements for which values are shown in this table. If the presence of other elements is indicated in the course of this
work, the amount of those elements shall be determined to ensure that they do not exceed the limits specified for "Other Elements".
b. Single values are maximum. except where otherwise specified.
c. SAE/ASTM Unified Numbering System for Metals and Alloys.
d. Silicon plus iron shall not exceed 0.95 percent.
e. Beryllium shall not exceed 0.0008 percent.
f. The aluminum content for unalloyed aluminum is the difference between 100.00 percent and the sum of all other metallic elements present in amounts of
0.010 percent or more each, expressed to the second decimal before determining the sum.
g. Vanadium content shall be 0.05 percent maximum. Gallium content shall be 0.03 percent maximum.
h. Vanadium content shall be 0.05-0.15 percent. Zirconium content shall be 0.10-0.25 percent.
i. Silicon plus iron shall not exceed 0.45 percent.
j. Tin content shall not exceed 0.05 percent.
k. Beryllium content shall be 0.04-0.07 percent.
NAVEDTRA 14250A
10-42
Table 10-8 — Chemical composition of copper and copper alloy bare
welding electrodes and rods (AWS A 5.7).
abc
Composition weight percent
Cu
Ni
Total
Including
Including
other
AWS
UNS
Classification
Numberd
Common
name
Ag
ERCu
CI8980
Copper
98.0 min
ERCuSi-A
C6S600
Silicon bronze
(coppersilicon)
Remainder
ERCuSn-A
C51800
Phosphor
bronze
Zn
1.0
C71S80
Copper-nickel
Mn
1.0
0.50
1.0
1.5
Fe
Si
Co
0.50
0.50
P
Al
Pb
0.15
0.01
0.02
0.50
0.01
0.02
0.50
0.01
0.02
0.5
2.8-
Ti
elements
4.0
Remainder
(copper-tin)
ERCuNie
Sn
4.0-
0.10-
6.0
0.35
1.00
Remainder
0.40-
0.25
0.75
29.0-
0.02
0.02
32.0
0.20
0.50
to
0.50
ERCuAl-Al
C61000
Remainder
0.20
0.50
0.10
6.0-
0.02
0.50
0.02
0.50
0.02
0.50
0.02
0.50
0.02
0.50
8.5
ERCuAl-A2
C61800
Aluminum
bronze
Remainder
0.02
1.5
0.10
8.511.0
ERCuAl-A3
C62400
Remainder
0.10
2.0-
0.10
10.0-
4.5
ERCuNiAl
C63280
Nickelaluminum
C63380
Manganesenickel
Remainder
0.10
bronze
ERCuMnNiAl
Remainder
aluminum
bronze
0.15
0.60-
3.0-
3.50
5.0
11.0-
2.0-
14.0
4.0
11.5
0.10
0.10
4.0-
8.50
5.50
9.50
1.5-
7.0-
3.0
8.5
a. Analysis shall be made for the elements for which specific values are shown in this table. However. the presence of other elements is indicated in the course of routine analysis, further analysis shall be made to
determine that the total of these other elements is not present in excess of the: limits specified for 'Total other elements' in the last column in this table.
b. Single values shown are maximum, unless otherwise noted.
c. Classifications RBCuZn-A, RCuZn-B, RCuZn-C, and RBCuZn-D now are included in A5.27-78, Specification/or Copper and Copper Alloy Gas Welding Rods.
d. ASTM-SAE Unified Numbering System for Metals and Alloys.
e. Sulfur shall be 0.01 percent maximum for the ERCuNi classification.
NAVEDTRA 14250A
10-43
Table 10-9 — Chemical compositions of magnesium alloy bare welding
electrodes and rods (AWS A5.19).
Weight Percentab
AWS
Other
Classi-
UNS
Rare
fication
Number'
Mg
Al
Be
Mn
Zn
ERAZ61A
M11611
Remainder
5.8
0.0002
0.15
0.40
to
to
to
to
RAZ61A
ERAZ92A
M11922
Remainder
RAZ92A
ERAZ101A
M11101
Remainder
RAZ101A
EREZ33A
M12331
REZ33A
Remainder
7.2
0.0008
0.5
1.5
8.3
0.0002
0.15
1.7
to
to
to
to
9.7
0.0008
0.5
2.3
9.5
0.0002
0.15
0.75
to
to
to
to
10.5
0.0008
0.5
1.25
0.0008
Zr
Earth
2.0
0.45
2.5
to
to
to
3.1
1.0
4.0
Elements
Cu
Fe
Ni
Si
Total
0.05
0.005
0.005
0.05
0.30
0.05
0.005
0.005
0.05
0.30
0.05
0.005
0.005
0.05
0.30
0.30
a. The filler metal shall be analyzed for the specific elements for which values are shown in this table. If the presence of other elements is
indicated in the course of this work, the amount of those elements shall be determined to ensure that their total does not exceed the limits
specified for I<Other Elements, Total".
b. Single values are maximum.
c. SAE/ASTM Unified Numbering System for Metals and Alloys.
NAVEDTRA 14250A
10-44
Table 10-10 — Chemical compositions of nickel and nickel alloy bare welding
electrodes and rods (AWS A5.14).
Weight percentab
AWS
Classification
ERNi-1
UNS
Numberc
N02061
C
0.15
Mn
1.0
Fe
1.0
P
0.01
S
0.015
Si
0.75
Cu
0.25
Nid
93.0
min
ERNiCu-7
N04060
0.15
4.0
2.5
0.02
0.015
1.25
Rem
ERNiCr-3
N06082
0.10
3.0
0.03
0.015
0.50
0.50
ERNiCrFe-5
N06062
0.08
2.5
to
3.5
1.0
62.0
to
69.0
67.0
min
0.03
0.015
0.35
0.50
70.0
min
ERNiCrFe-6
N07092
0.08
0.03
0.015
0.35
0.50
67.0
min
ERNiFeCr-1
N08065
0.05
2.0
to
2.7
1.0
6.0
to
10.0
8.0
22.0
min.
0.03
0.03
0.50
ERNiFeCr-2g
N07718
0.08
0.35
Rem
0.015
0.015
0.35
1.50
to
3.0
0.30
ERNiMo-1
N10001
0.08
1.0
0.025
0.03
1.0
0.50
2.5
ERNiMo-2
N10003
1.0
0.015
0.02
1.0
0.50
Rem
0.20
ERNiMo-3
N10004
0.04
to
0.08
0.12
4.0
to
7.0
5.0
38.0
to
46.0
50.0
to
55.0
Rem
0.04
0.03
1.0
0.50
Rem
2.5
ERNiMo-7
N10665
0.02
1.0
4.0
to
7.0
2.0
0.04
0.03
0.10
0.50
Rem
1.0
ERNiCrMo-1
N06007
0.05
0.03
1.0
2.5
0.04
0.03
1.0
Rem
0.50
to
2.5
ERNiCrMo-3
N06625
0.05
to
0.15
0.10
1.5
to
2.5
0.50
Rem
N06002
18.0
to
21.0
17.0
to
20.0
5.0
0.04
ERNiCrMo-2
1.0
to
2.0
1.0
0.02
0.015
0.50
0.50
58.0
min
ERNiCrMo-4
N10276
0.02
1.0
0.04
0.03
0.08
0.50
Rem
2.5
ERNiCrMo-7
N06455
0.015
1.0
4.0
to
7.0
3.0
0.04
0.03
0.08
0.50
Rem
2.0
ERNiCrMo-8
N06975
0.03
1.0
Rem
0.03
0.03
1.0
ERNiCrMo-9
N06985
0.015
1.0
18.0
to
21.0
0
0.04
0.03
1.0
0.7
to
1.20
1.5
to
2.5
47.0
to
52.0
Rem
1.0
0.50
Co
Al
1.5
1.25
e
Ti
2.0
to
3.5
1.5
to
3.0
0.75
e
0.20
0.20
to
0.80
2.5
to
3.5
0.60
to
1.2
0.65
to
1.15
Other
Elements
Total
0.50
0.40
0.70
0.70
to
1.50
Mo
V
W
0.50
18.0
to
22.0
14.0
to
17.0
14.0
to
17.0
19.5
to
23.5
17.0
to
21.0
1.0
2.0
to
3.0f
1.5
to
3.0f
21.0
to
23.5
20.5
to
23.0
20.0
to
23.0
14.5
to
16.5
14.0
to
18.0
23.0
to
26.0
21.0
to
23.5
0.50
0.50
0.50
4.75
to
5.50
6.0
to
8.0
4.0
to
6.0
1.0
0.40
5.0
Cr
Cb
plus
Ta
1.75
to
2.50
3.15
to
4.15
0.50
2.5
to
3.5
2.80
to
3.30
26.0
to
30.0
15.0
to
18.0
23.0
to
26.0
26.0
to
30.0
5.5
to
7.5
8.0
to
10.0
8.0
to
10.0
15.0
to
17.0
14.0
to
18.0
5.0
to
7.0
6.0
to
8.0
0.50
0.50
0.20
to
0.40
0.50
1.0
0.50
0.50
0.50
0.60
1.0
0_50
1.0
0.50
1.0
0.50
0.20
to
1.0
0.50
0.50
0.35
3.0
to
4.5
0.50
0.50
0.50
0.50
1.5
0.50
a.) The filler metal shall be analyzed for the specific elements for which values are shown in this table.
In the course of this work, if the presence of other elements is indicated, the amount of those elements shall be determined to ensure that their total does not exceed
the limit specified for "Other Elements, Total" in the last column of the table.
b) Single values are maximum, except where otherwise specified.
c) SAE/ASTM Unified Numbering System for Metals and Alloys.
d) Includes incidental cobalt.
e) Cobalt—0.12 maximum. when specified.
f) Tantalum--0.30 maximum. when specified.
g) Boron is 0.006 percent maximum.
NAVEDTRA 14250A
10-45
5.3.2 Sizing
The electrodes used for gas metal arc welding are generally small in diameter when
compared to the other arc welding processes. Wire diameters ranging from .030 to 1/16
in. (.8-1.6mm) are the used most widely. Wire diameters as small as .020 in. (.5mm)
and up to 1/8 in. (3.2mm) are sometimes used. The electrodes are provided in a long,
continuous strand of wire which is normally packaged in a coil or spool. Spools of wire
normally range in weight from 2 to 60 Ibs. (.9-27 kg) and coils normally weigh 60 Ibs.
(27 kg).
The electrodes’ melting rates normally range from about 100 to 600 in./min. (40-255
mm/s) due to the small electrode wire sizes and the relatively high welding current
levels used. Because of the small size of the electrode wire, which gives it a high
surface to volume ratio, cleanliness of the wire is very important. Drawing compounds,
rust, oil, or other foreign matter on the surface of the electrode wire tends to be in high
proportion relative to the amount of metal present, and these items can cause weld
metal defects such as porosity and cracking.
5.4.0 Electrode Selection
The type of metal being welded and the specific chemical and mechanical properties
desired are the major factors in determining the choice of a filler metal. Identification of
the base metal is absolutely required to select the proper filler metal. If the type of base
metal is not known, tests can be made based on appearance, weight, magnetic check,
chisel tests, flame tests, fracture tests, spark tests, and chemistry tests.
The selection of the proper filler metal for a specific job application is quite involved but
can be based on the following factors:
1. Base Metal Strength Properties - This is done by choosing a filler metal to match
the tensile or yield strength of the base metal. This is usually the most important
factor with low carbon and low alloy steels, as well as with some aluminum and
magnesium welding applications.
2. Base Metal Chemical Compositions - The chemical composition of the base
metal should be known. Closely matching the filler metal composition to the base
metal composition is needed when corrosion resistance, color match, creep
resistance, and electrical or thermal conductivity are important considerations.
The filler metal for non-ferrous metals, stainless steels, and many alloy steels are
chosen by matching the chemical compositions.
3. Thickness and Shape of Base Metal Weldments - The workpiece may include
thick sections or complex shapes, which may require maximum ductility to
prevent weld cracking. Filler metal that gives the best ductility should be used.
4. Service Conditions and/or Specifications - When weldments are subjected to
severe service conditions such as low temperatures, high temperatures, or
shock, a filler metal that closely matches the base metal composition, ductility,
and impact resistance properties should be used.
5.5.0 Conformances and Approvals
The electrodes used for gas metal arc welding must conform to the specifications or be
approved by code-making organizations for many applications of the process. Some of
the code-making organizations that issue specifications or approvals are the American
Welding Society (AWS), American Society of Mechanical Engineers (ASME), American
Bureau of Shipping (ABS), Federal Bureau of Roads, U.S. Coast Guard, and the
NAVEDTRA 14250A
10-46
Military. The American Welding Society (AWS) provides specifications for bare solid
wire electrodes. The electrodes manufactured must meet specific requirements in order
to conform to a specific electrode classification. Many code-making organizations such
as the American Society of Mechanical Engineers (ASME) and the American Petroleum
Institute (API) recognize and use the AWS specifications. Some of the code-making
organizations such as the American Bureau of Shipping (ABS) and the Military must
directly approve the electrodes before they can be used for welding on a project that is
covered by that code. These organizations send inspectors to witness the welding and
testing and to approve the classification of the solid wire electrodes.
To conform to the AWS specifications for low carbon and low alloy filler metals, the
electrodes must produce a weld deposit that meets specific mechanical and chemical
requirements. For the non-ferrous and stainless steel filler metal, the electrodes must
produce a weld deposit with a specific chemical composition. The requirements will vary
depending on the class of the electrode.
Test your Knowledge (Select the Correct Response)
5.
Which inert gas is primarily used on non-ferrous metals?
A.
B.
C.
D.
6.
Argon
Nitrogen
Oxygen
Carbon dioxide
(True or False) One of the most important factors to consider in GMAW welding
is the correct filler wire selection.
A.
B.
True
False
6.0.0 WELDING APPLICATIONS
Gas metal arc welding is very adaptable to many different applications. It provides the
ability to weld thick metals and allows you to take your welding machine to remote
locations. As you will see GMAW has become a very accepted method of welding in all
industries.
6.1.0 Industries
Gas metal arc welding is becoming more popular for many different welding
applications. When this process is used semi-automatically, higher deposition and
production rates can be obtained than with the manual arc welding processes. This
process is also versatile because it can be used to weld ferrous and most non-ferrous
metals in all positions. It is often the only welding process practical for welding thick sections in non-ferrous metals. Gas metal arc welding lends itself easily to machine and
automatic welding which are often used for producing consistent, high quality welds at
the fastest travel speeds possible. This process is used extensively in the automotive
industry where high production rates are required, but it is also used in the field because
the equipment is relatively light and portable compared to the other continuous
electrode wire processes. For this reason, gas metal arc welding is widely used in field
welding of cross-country transmission pipelines and for many construction and
maintenance applications.
NAVEDTRA 14250A
10-47
6.1.1 Pressure Vessels
Gas metal arc welding is one of the more commonly used processes for welding on
pressure vessels. It is used in the manufacture of plain carbon, low alloy, and stainless
steel vessels as well as non-ferrous vessels. Low heat input is important on pressure
vessels. Multi-layer welds are generally built up in relatively thin layers which produce
better ductility and impact resistance than larger welds. Gas metal arc welding has
several advantages because it produces small weld beads at much faster travel speeds
than shielded metal arc welding. It also has some advantages over submerged arc
welding because it can be used in all positions and the arc is not hidden beneath a flux
layer. The short-circuiting and pulsed arc modes are used for out-of-position welding to
reduce the heat input. Figure 10-31 shows gas metal arc welding being used to weld a
large mild steel vessel for an industrial refrigeration system. This process is often used
for welding all passes, but sometimes it is used for welding the root passes only (Figure
10-32). Submerged arc welding is then employed for making the fill and cover passes.
Figure 10-31 —GMAW pressure
vessel welding.
Figure 10-32 —GMAW root pass
weld.
6.1.2 Industrial Piping
Gas metal arc welding also has application in the industrial piping industry. This process
is widely used for welding of carbon steel, stainless steel, aluminum, copper, and nickel
piping. The main advantage over shielded metal arc welding is the higher deposition
rates obtained. Small diameter electrode wires are the most popular, and the shortcircuiting mode of metal transfer is widely employed. Tack welds must be carefully
prepared because inadequate penetration can occur if proper variables and techniques
are not used. For critical applications, skilled welders and close attention to details are
required to produce complete fusion, especially on heavy parts. Thin weld layers should
be avoided for this type of welding. Carbon dioxide and argon-carbon dioxide gas
mixtures are used as shielding on carbon steel pipe. Open root joints in the pipe are
welded in the vertical-down position when the pipe is horizontal. The rest of the weld
passes may be welded either vertical up or vertical down. Gas metal arc welding is
widely used for welding the fill and cover passes over a gas tungsten arc welded root
pass because higher deposition rates are obtained as compared to gas tungsten arc
welding.
NAVEDTRA 14250A
10-48
6.1.3 Transmission Pipelines
Gas metal arc welding is widely used in the cross-country transmission pipeline welding
industry. Most gas metal arc pipe welding is done in the field using gasoline or diesel
engine driven generator-welding machines. Small diameter electrode wires are
commonly employed because there is much
out-of-position welding. Almost all pipes for
transmission pipelines are made of carbon
steel, so carbon dioxide and argon-carbon
dioxide mixtures are the most popular.
Gas metal arc welding is employed using
various procedures. When the process is
used, most joints are welded completely with
gas metal arc welding. However, some root
passes are welded with shielded metal arc
welding and then the joint is filled out with
gas metal arc welding. A less common
procedure is to use gas metal arc welding
for the root pass and shielded metal arc
welding for the fill and cover passes. Figure
10-33 shows a root pass being welded in a
48 in. (1.2 mm) diameter natural gas
pipeline.
Figure 10-33 — GMAW root pass
of small diameter pipe.
Because the welding is being done in the
field, the wind can often deflect the flow of
shielding gas away from the arc. This can be prevented by setting up wind shields. An
automatic welding system is sometimes employed to improve the consistency and
deposition rate of the process. This equipment is normally used with special tracks that
clamp on the pipe, but the equipment must be portable enough to handle in the field.
When an automatic welding system is used, pipe fitup must be more precise.
6.1.4 Nuclear Power Facilities
Gas metal arc welding is employed but has
a limited applicability in the nuclear power
plants and components area. It is primarily
used for welding components that are not
directly part of the reactor. In the nuclear
power industry, the quality of the weld
deposit is the most important factor for
selecting the process. Figure 10-34 shows
gas metal arc welding being used to weld a
portion of a nuclear plenum, which is part of
a nuclear filtration system. The plenum is
fabricated from low carbon steel ranging in
thickness from 1/16-1½ in. (1.6 -12.7 mm)
and is being welded using .035 in. (.9 mm)
diameter low carbon steel electrodes.
Nuclear filtration systems are made of
carbon or stainless steel. Other items such
NAVEDTRA 14250A
Figure 10-34 — GMAW of a
nuclear plenum.
10-49
as piping fittings, vessels, and liquid metal pumps are also common applications.
6.1.5 Structures
The construction industry includes buildings,
bridges, and other related structures. Gas
metal arc welding is popular for many
applications because it can be used in the
field and it produces higher deposition rates
than shielded metal arc welding. The
development of wire feeding systems that
can feed the electrode wire greater
distances have helped increase the
versatility of the process. The field welding
applications employ gasoline or diesel
engine driven generator-welding machines.
The full range of electrode wire diameters is
used because of the wide variety of joint
designs and metal thicknesses welded.
GMAW is the most popular process for
welding aluminum and other non-ferrous
Figure 10-35 — GMAW of a
structures. Wind shields are often employed
structural beam.
for field welding to prevent the loss of
shielding gas. Figure 10-35 shows a shop
welding application where brackets are being welded on a steel structural beam. GMAW
is also widely used for many multiple pass joints because of the higher deposition rates
obtained.
6.1.6 Ships
Most of the arc welding processes are used in the shipyards, and GMAW has become
widespread because of its versatility. Most ships are made of carbon steel, but nonferrous ships are welded also. Gas metal arc welding is popular because it yields higher
deposition rates than shielded metal arc
welding and lends itself better to welding in
all positions than the other continuous wire
processes.
In shipbuilding, deposition rate is the most
important consideration, and because of the
vast amount of welding done on a ship,
GMAW is the best process for welding nonferrous metal ships and components.
Other items commonly welded are piping in
the ship, non-structural components, and
components that require out-of-position
welding. Wire feeding systems that allow the
welder to move greater distances from the
source of the electrode wire are widely
used. Figure 10-36 shows an example of
GMAW flat position welding. Portable wire
feeders are often used so welders can move
from one location to another more easily.
NAVEDTRA 14250A
Figure 10-36 — GMAW vertical
weld.
10-50
Using .045-in. (1.1 mm) diameter electrode wire, these welds can be produced at three
times the rate of shielded metal arc welding. This is a great advantage because a large
percentage of the welds made in a ship are vertical fillet welds. In ship members where
distortion is a problem, this process is used to get the best deposition rates with the
lowest heat input.
6.1.7 Railroads
Gas metal arc welding is used for welding engines and cars in the railroad industry. Rail
cars are fabricated from carbon steel, stainless steel, and aluminum. Machine,
semiautomatic, and automatic welding are all commonly employed. GMAW and
resistance welding are almost exclusively used in the manufacture of aluminum railroad
cars. This process is often employed for welding in positions other than flat and for all
parts of the engines and cars. Sheet metal covers for cabs, hoods, sides, and roofs are
extensively welded. Because rimmed steel is widely used, filler metals of the ER70S-3
and ER70S-6 are employed; they have high amounts of deoxidizers in them to
compensate for the rimmed condition of the steel sheet metal. It is used for many sheet
metal welding applications because of the fast travel speeds, which help minimize
distortion problems. This process can be used for almost all components of the engines
and cars, but the primary applications of the process are on thin materials and nonferrous metals, or in locations where the higher deposition rate processes, such as flux
cored and submerged arc welding, cannot be used.
6.1.8 Automotive
In the automobile and truck manufacturing industries, both semi-automatic and
automatic gas metal arc welding are widely used. It is the major process used in this
industry because of the fast travel speeds obtained. Many of these applications are on
items such as frames, axle housings, wheels, and body components. This process is
used to weld low carbon, low alloy, and stainless steels, as well as many aluminum
parts. This process is popular for welding thin sheet metal in the short-circuiting mode
because it lessens the heat input and prevents burn through. The high speeds produced
by this process make it very good because of the high production rates required. All
thicknesses of metal are welded.
Fully automatic welding operations are used
for many applications that had formerly
been done using shielded metal arc welding
and submerged arc welding. Gas metal arc
welding has become very popular for
automatic welding because it is one of the
least difficult processes to fully automate.
Figure 10-37 shows a subframe being
welded. In this application, the part is being
rotated automatically, but the welder is
providing joint guidance. Carbon dioxide
shielding gas and a .035 in. (.9 mm)
diameter electrode are being used. Gas
metal arc welding is the only arc welding
process being used to weld aluminum
automobile body components, truck cabs,
and van bodies. Figure 10-38 shows the
NAVEDTRA 14250A
Figure 10-37 — Automotive
welding.
10-51
welding of an aluminum truck transmission cross-member.
Gas metal arc spot welding has many
applications in the automotive and truck
industries for welding the thinner metal
gages of carbon steels, stainless steels, and
aluminum. This process has several
advantages in this industry because
accessibility to the weld joint only has to be
from one side, whereas resistance spot
welding must have accessibility to both sides
of the joint. This process is preferred
because the spot welds produced have a
consistent high quality and the process
requires a minimum of operator skill.
Typically, semi-automatic equipment is
adapted for this process.
6.1.9 Aerospace
GMAW is also used in the aerospace
industry for many applications. It is generally
employed for welding heavier sections of
steel and aluminum, but it is not as widely
used as gas tungsten arc welding in this
industry. Gas metal arc welding allows faster
travel speeds to be used, which helps
minimize weld distortion and the size of the
heat affected zone. Machine or automatic
welding has many applications in the
manufacture of in-flight refueling tanks for jet
aircraft and aluminum fuel tanks for rocket
motor fuel. The use of semi-automatic
welding has generally been limited to less
critical aircraft components. An exception to
this is shown in Figure 10-39 where the
ribbing for an aileron is being welded with a
small diameter electrode wire. Gas metal arc
welding is used because it can weld thin
metal in all positions at high production rates.
6.1.10 Heavy Equipment
Figure 10-38 — Aluminum
welding.
Figure 10-39 — Welding an
aileron.
Farm equipment manufacturers are major
users of gas metal arc welding. It is used in the manufacture of tractors, combines,
plows, tobacco harvesters, grain silos, and many other items. Other heavy equipment
manufactured includes mining equipment, earthmoving equipment, and many other
products. These types of equipment are generally made of mild and low carbon steels.
High deposition rates are desired, so large diameter electrode wires are employed when
possible. Because of this, spray and globular transfer welding are used for much of the
flat position welding, but GMAW is also widely employed for producing welds in out-of
position joints.
NAVEDTRA 14250A
10-52
6.2.0 Variations of the Process
Of the numerous variations of the GMAW process, two of the most notable are arc spot
welding and narrow gap welding.
6.2.1 Arc Spot Welding
The gas metal arc spot welding process is used for making small localized fusion welds
by penetrating through one sheet and into the other. The differences between this
process and normal gas metal arc welding are that there is no movement of the welding
gun and the welding takes place for only a few seconds or less. The equipment for arc
spot welding usually consists of a special gun nozzle and arc timer added to a standard
semi-automatic welding setup. Gas metal arc spot welding is commonly applied to mild
steel, stainless steel, and aluminum, but can be used on all the metals welded by gas
metal arc welding. On steel, CO2 shielding is used to get the best penetration.
The advantages of this process over resistance spot welding are the following:
1.
2.
3.
4.
5.
The gun is light and portable and can be taken to the weldment.
Spot welding can be done in all positions more easily.
Spot welds can be made when there is accessibility only to one side of the joint.
Spot-weld production is faster for many applications.
Joint fitup is not as critical.
The major disadvantage of this process is that the consistency of weld strength or size
is not as good as with resistance spot welding.
The weld is made by placing the welding gun on the joint. Pulling the trigger initiates the
shielding gas and after a pre-flow interval, starts the arc and the wire feed. When the
pre-set weld time is finished, the arc and wire feed are stopped, followed by the gas
flow. The longer the weld time, the greater the penetration obtained and the higher the
weld reinforcement becomes. The rest of the welding variables affect the spot weld size
and shape the same way they affect a normal weld. Vertical and overhead arc spot
welds can be made in metal up to .05-in. (1 .3 mm) thick. For other than flat position
welding, the short-circuiting mode of transfer must be used.
Many different weld joint types are made including lap, corner, and plug. The best
results are obtained when the arc side member is equal to or thinner than the other.
When the top plate is thicker than the bottom one, a plug weld should be made.
Incomplete fusion is a common defect with this type of weld. A copper backing bar is
used to prevent excessive penetration through the bottom of the weld. Another
advantage of gas metal arc spot welding over resistance spot welding is that the
strength can be determined from a visual examination of the weld nugget size, whereas
a resistance spot weld would have to be tested to determine the strength.
NAVEDTRA 14250A
10-53
6.2.2 Narrow Gap Welding
Narrow gap welding is another
variation of the GMAW process in
which square-groove or V-groove
joints with small groove angles
are used in thick metal sections.
Root openings normally range
from ¼ to 3/8 in. (6.4-9.5 mm).
Narrow gap welding is generally
done on ferrous metals, with the
use of specially designed welding
guns (Figure 10-40), but some
narrow gap welding has been
done on aluminum. Two small
electrode wires are normally
used in tandem with the wire
being fed through 1 or 2 contact
tubes. Each of the electrodes is
fed so that the weld bead is
directed toward each groove
face. The special welding guns
have water-cooled contact tubes
and nozzles that provide
Figure 10-40 — Narrow gap weld.
shielding gas from the surface of
the plate. Spray transfer is the
most commonly used mode of
the process, but pulsed current transfer is sometimes employed. High travel speeds are
used, resulting in a low heat input and small weld puddles with narrow heat affected
zones. This low heat input produces weld puddles which are easy to control in out-of
position welding. Welds are normally made from one side of the plate.
The major problem encountered in narrow gap welding is incomplete fusion because of
the low heat input in thick metal, but careful placement of the electrode wires and
removing slag islands between passes to prevent slag inclusions can avoid any
problems.
When used for welding metal thicknesses over 2 in. (51 mm), narrow gap welding is
competitive with the other automatic arc welding processes. This type of welding has
several advantages:
1.
2.
3.
4.
5.
6.
7.
8.
Welding costs are lower because less filler metal is required.
Lower residual stresses and less distortion are produced.
Better welded joint properties are obtained.
The main disadvantages are the following:
It is more prone to defects.
Defects are more difficult to remove.
Fitup of the joint must be more precise.
Placement of the welding gun must be more precise.
NAVEDTRA 14250A
10-54
Test your Knowledge (Select the Correct Response)
7.
What development has improved the field versatility of GMAW by increasing the
distance between the gun and the welding machine?
A.
B.
C.
D.
8
Stiffer welding electrodes
Portability
Lighter welding guns
Water cooling systems
What is the major disadvantage of gas metal arc spot welding compared to
resistance spot welding?
A.
B.
C.
D.
Weld size
Weld strength
Amount of spatter
Directionality of the weld
7.0.0 WELDING METALLURGY
Knowing the basics of welding metallurgy will provide a firm foundation for
understanding the chemical and physical changes that occur on metal when using the
GMAW process.
7.1.0 Properties of the Weld
A weld has the following properties:
•
•
•
Chemical composition
Mechanical strength and ductility
Microstructure
These items will determine the quality of the weld. The chemical properties are affected
by the types of materials used. The mechanical properties and microstructure of the
weld are determined by the heat input of welding as well as by the chemical
composition of the materials.
7.1.1 Chemical and Physical Properties
The chemical and physical properties such as the chemical composition, melting point,
and thermal conductivity have a great influence on the weldability of a metal. These
three items influence the amount of preheating and postheating used, as well as the
welding parameters. Preheating and postheating are used to prevent the weld and
adjacent area from becoming brittle and weak.
In welding a metal, the chemical composition of the base metal and filler metal will affect
corrosion and oxidation resistance, creep resistance, high and low temperature
strength, and the mechanical properties and the microstructure. For welding stainless
steels and non-ferrous metals, the chemical composition of the weld is often the most
important property. When corrosion resistance, thermal and electrical conductivity, and
appearance are major considerations, the chemical composition of the weld must match
the composition of the base metal.
Preheating reduces the cooling rate of the weld to prevent cracking. The amount of
preheat needed depends on the type of metal being welded, the metal thickness, and
the amount of joint restraint. In steels, those with higher carbon contents need more
NAVEDTRA 14250A
10-55
preheating than those with lower carbon equivalents. For the non-ferrous metals, the
amount of preheat will often depend on the melting points and thermal conductivity of
the metal. Table 10-11 shows typical preheat values for different metals welded by
GMAW.
Another major factor that determines the amount of preheat needed is the thickness of
the base metal. Thicker base metals usually need higher preheat temperatures than
thinner base metals because of the larger heat sinks that thicker metals provide. Thick
metal draws the heat away from the welding zone quicker because there is a large
mass of metal to absorb the heat. This would increase the cooling rate of the weld if the
same preheat temperature was used as is used on thinner base metals.
The third major factor for determining the amount of preheating needed is the amount of
joint restraint. Joint restraint is the resistance of a joint configuration to moving or
relieving the stresses due to welding during the heating and cooling of the weld zone.
Where there is high resistance to moving or high joint restraint, large amounts of
internal stresses build up and higher preheat temperatures are needed as the amount of
joint restraint increases. Slower cooling rates reduce the amount of internal stresses
that build up as the weld cools.
NAVEDTRA 14250A
10-56
Table 10-11 — Typical Recommended Preheats for Various Metals.
Type of Metal
Preheat
Low-Carbon Steel
Room Temperature or up to 200°F (93°C)
Medium-Carbon Steel
400-500°F (205-260°C)
High-Carbon Steel
500-600°F (260-315°C)
Low Alloy Nickel Steel
-Less than ¼-inch (6.4 mm) thick
Room Temperature
-More than ¼-inch (6.4 mm) thick
500°F (260°C)
Low Alloy Nickel-Chrome Steel
-Carbon content below .20%
200-300°F (93-150°C)
-Carbon content .20% to .35%
600-800°F (315-425°C)
-Carbon content above .35%
900-1100°F (480-595°C)
Low Alloy Manganese Steel
400-600°F (205-315°C)
Low Alloy Chrome Steel
Up to 750°F (400°C)
Low Alloy Molybdenum Steel
-Carbon content below .15%
Room Temperature
-Carbon content above .15%
400-650°F (205-345°C)
Low Alloy High Tensile Steel
150-300°F (66-150°C)
Austenitic Stainless Steel
Room Temperature
Ferritic Stainless Steel
300-500°F (66-260°C)
Martensitic Stainless Steel
400-600°F (66-150°C)
Cast Irons
700-900°F (370-480°C)
Copper
500-800°F (260-425°C)
Nickel
200-300°F (93-150°C)
Aluminum
Room Temperature or up to 300°F (150°C)
Note: The actual preheat needed may depend on several other factors such as the thickness of the base
metal, the amount of joint restraint, and whether or not low-hydrogen types of electrodes are used. This
chart is intended as general information; the specifications of the job should be checked for the specific
preheat temperature used.
NAVEDTRA 14250A
10-57
The melting point of the base metal is a major consideration in determining the
weldability of a metal. Metals with very low melting points are difficult to weld because
the intense heat of the welding arc will melt them too quickly to join them easily. These
metals must be brazed because welding is not practical.
Another property that affects the weldability is the thermal conductivity. The thermal
conductivity is the rate at which heat is conducted by the metal, and it determines the
rate at which heat will leave the welding area. Metals that have a high thermal
conductivity often require higher preheats and welding currents to avoid cracking.
Metals that have very low thermal conductivity may require no preheat and lower
welding currents to prevent overheating an area, which can cause distortion, warpage,
and changes in mechanical properties.
7.1.2 Mechanical Properties
The most important mechanical properties in the weld are the following:
•
•
•
•
•
tensile strength
yield strength
elongation
reduction of area
impact strength
The first two are measures of the strength of the material, the next two are a measure of
the ductility, and the last is a measure of the impact toughness. These properties are
often important in GMAW, especially for welding steel and the non-ferrous alloys that
have been developed to give maximum strength, ductility, and toughness.
The toughness and ductility of the heat
affected zone produced by this process are
sometimes slightly less than those produced
by many of the other welding processes.
This is caused because of the relatively
quick cooling rates commonly associated
with gas metal arc welding, which produce a
more brittle heat affected zone. Quicker
cooling rates occur because of the fast
travel speeds used and the use of shielding
gas, which does not slow the cooling rate as
well as a slag layer. One advantage of the
quicker cooling rate is that distortion is less
of a problem.
The yield strength, ultimate tensile strength,
elongation, and reduction of area are all
measured from a .505-in. (12.B mm)
Figure 10-41 — Tensile strength
diameter machined testing bar. The metal is
testing bars.
tested by pulling it in a tensile testing
machine. Figure 10-41 shows a tensile bar
before and after testing. The yield strength
of the metal is the stress at which the material is pulled beyond the point where it will
return to its original length.
The tensile strength is the maximum load that can be carried by the metal. This is also
measured in psi (MPa). Elongation is a measure of ductility that is also measured on the
NAVEDTRA 14250A
10-58
tensile bar. Two points are marked on the bar 2 in. (51 mm) apart before testing. After
testing, the distance between the two points is measured again and the percent of
change in the distance between them, or
percent elongation, is measured.
Reduction of area is another method of
measuring ductility. The original area of the
cross section of the testing bar is .505 sq. in
(104 sq. mm). During the testing the
diameter of the bar reduces as it elongates.
When the bar finally breaks, the diameter of
the bar at the breaking point is measured,
which is then used to determine the area.
The percent reduction of this cross-sectional
area is called the reduction of area.
Impact tests are used to measure the
toughness of a metal. The toughness of a
metal is the ability of a metal to absorb
mechanical energy by deforming before
breaking. The Charpy V-notch test is the
most commonly used method of making
Figure 10-42 — Charpy V-notch
impact toughness tests. Figure 10-42 shows
bars.
some typical Charpy V-notch test bars.
These bars are usually 10 mm square and
have V-notches ground or machined in them. They are put in a machine where they are
struck by a hammer attached to the end of a pendulum. The energy that it takes to
break these bars is known as the impact strength and it is measured in foot-pounds
(Joules).
7.1.3 Microstructure
There are three basic microstructural areas within a weldment: the weld metal, the heat
affected zone, and the base metal. The weld
metal is the area that was molten during
welding. This is bounded by the fusion line,
which is the maximum limit of melting. The
heat affected zone is the area where the
heat from welding had an effect on the
microstructure of the base metal. The limit of
visible heat affect is the outer limit of this
area. The base metal zone is the area that
was not affected by the welding. Figure 1043 shows a cross section of a weld
indicating the different areas.
The extent of change of the microstructure
is dependent on four factors:
1. Maximum temperature that the weld
metal reached
2. Time that the weld spent at that
temperature
3. Chemical composition of the base
metal
NAVEDTRA 14250A
Figure 10-43 — Cross section of
a weld.
10-59
4. Cooling rate of the weld
The weld metal zone, which is the area that is melted, usually has the coarsest grain
structure of the three areas. Generally, a fairly fine grain size is produced in most metals
on cooling, but in some metals, especially refractory metals, rapid grain growth in the
weld metal can become a problem.
Large grain size is undesirable because it gives the weld poor toughness and poor
cracking resistance. The solidification of the
weld metal starts at the edge of the weld
puddle next to the base metal. The grains
that form at the edge, called dendrites, grow
toward the molten center of the weld. Figure
10-44 shows the solidification pattern of a
weld. These dendrites give the weld metal its
characteristic columnar grain structure. The
grains that form in the weld zone are similar
to the grains that form in castings.
Deoxidizers and scavengers are often added
to filler metal to help refine the grain size in
the weld. The greater the heat input to the
weld and the longer that it is held at high
temperatures, the larger the grain size. A fast
cooling rate will produce a smaller grain size
than a slower cooling rate. Preheating will
give larger grain sizes, but is often necessary
to prevent the formation of a hard, brittle
microstructure.
Figure 10-44 — Solidification
pattern of a weld.
The heat affected zone is the area where
changes occur in the microstructure of the base metal; the area closest to the weld
metal usually undergoes grain growth. Other parts of the heat affected zone will go
through grain refinement, while still other areas may be annealed and considerably
softened. Because of the changes due to the heat input, areas of the heat affected zone
can become embrittled and become the source of cracking. A large heat input during
welding will cause a larger heat affected zone, which is often not desirable, so the
welding parameters used can help influence the size of the heat affected zone.
7.2.0 Metals Weldable
The GMAW process can be used to weld most metals and their alloys, the most
common of which are aluminum, copper, magnesium, nickel, mild steel, low alloy steel,
stainless steel, and titanium.
7.2.1 Aluminum and Aluminum Alloys
GMAW is one of the most widely used processes for welding aluminum and its alloys.
The major alloying elements used in aluminum are copper, manganese, silicon,
magnesium, and zinc. Table 10-12 shows how the aluminum alloys are classified
according to their alloy content. Aluminum alloys are also classified into heat treatable
and non-heat treatable categories; alloys of the 2XXX, 6XXX, and 7XXX series are heat
treatable.
NAVEDTRA 14250A
10-60
Table 10-12 — Aluminum Alloy Classifications.
Aluminum Classification
Major Alloying Element
1XXX
Commercially pure
2XXX
Copper
3XXX
Manganese
4XXX
Silicon
5XXX
Magnesium
6XXX
Silicon + Magnesium
7XXX
Zinc
8XXX
Other
Gas metal arc welding is used to weld all metal thicknesses, but welding is most
commonly done on thicknesses greater than 1/8-in. (3.2 mm). This process is the best
method for the thicker metals because it produces higher deposition rates and travel
speeds than gas tungsten arc welding. Aluminum as thin as .030-in. (.8 mm) can be
welded using pulsed current. High welding speeds may be obtained with this process
and when welding aluminum, high welding speeds are desirable to prevent overheating.
Argon shielding gas is preferred for welding the thinner metal. Argon-helium mixtures
are preferred for welding thicker metal because of the better penetration obtained.
Argon-oxygen and argon-helium-oxygen mixtures are sometimes used to improve the
arc stability and make out-of-position welding easier.
Most GMAW applications are done with the spray transfer method, but pulsed current is
used for aluminum to reduce the heat input and use larger diameter electrode wires.
Larger electrode wires are less expensive and are easier to feed. Globular and shortcircuiting transfer are rarely used when welding aluminum.
The filler metal used for welding aluminum is generally of the non-heat treatable type.
Consequently, when welding some of the higher strength heat treatable alloys, the weld
deposit will be weaker than the base metal. Using heat treatable filler metal often
causes weld cracking, so non-heat treatable filler is preferred. Choosing the type of filler
metal to use for welding a specific aluminum alloy is based on ease of welding,
corrosion resistance, strength, ductility, elevated temperature service, and color match
with the base metal after welding. Table 10-13 shows a filler metal selection chart based
on the specific properties desired. Table 10-14 shows a filler metal selection chart for
welding different grades of aluminums together.
The typical oxide layer on the surface of aluminum makes it more difficult to weld than
many other types of metals. This oxide layer has a very high melting point compared to
the melting temperature of the aluminum itself. Direct current electrode positive gives
the welding arc an oxide-cleaning action which breaks the oxide layer so that welding
can take place. Before welding, the surface of the base metal should be cleaned to
prevent oxide inclusions and hydrogen entrapment.
NAVEDTRA 14250A
10-61
Table 10-13 — Aluminum Filler Metal Selection.
Property Desired
Type of
base metal
Strength Ductility
Color match after
anodizing
Corrosion
resistance
Least cracking
tendency
1100
4043
1100
1100
1100
4043
2219
2319
2319
2319
2319
2319
3003
4043
1100
1100
1100
4043
5052
5356
5654
5356
5554
5356
5083
5183
5356
5183
5193
5356
5086
5356
5356
5356
5356
5356
5454
5356
5554
5554
5554
5356
5456
5556
5356
5556
5556
5356
6061
5356
5356
5654
4043
4043
6063
5356
5356
5356
4043
4043
7005
5039
5356
5036
5039
5356
7039
5039
5356
5039
5039
5356
A preheat is used on aluminum only when the temperature of the parts is below 15°F (10°C), or when a large mass of metal is being welded, which will draw the heat away
very quickly. Aluminum has a high thermal conductivity, so heat is drawn away from the
welding area. Because aluminum has a relatively low melting point and a high thermal
conductivity, overheating can be a problem, especially on thin metal; therefore,
preheating is seldom used. The maximum preheat normally used on aluminum is 300° F
(150° C). Rather than use preheating, it is usually preferable to increase the voltage and
current levels to obtain adequate heat input. Alloys such as 5083, 5086, and 5456
should not be preheated to between 200 and 400° F (95-205°C) because their
resistance to stress corrosion cracking will be reduced due to high magnesium contents.
NAVEDTRA 14250A
10-62
Table 10-14 — Aluminum Filler Metal Selection Chart.
513.0
206.0
224.0
319.0,
333.0
354.0,
355.0
C355.0
413.0, 443.0
A444.0
ER4145
ER4145
ER4145
ER4145e
ER2319a
ER4145
ER4145e
ER4145e
ER4043b
ER4043b
ER4043b
201.0
Base Metal
1060, 1070, 1080,
1350
1100, 3003, Alc
3003
2014, 2036
2219
3004, Alc3004
5005 5050
5052 5652
5083
5086
5154, 5254
5454
5456
6005, 6061, 6063
6101, 6151, 6201
6351, 6951
6009, 6010, 6070
7004, 7005, 7039
710.0, 712.0
511.0, 512.0, 513.0
514.0, 535.0
356.0, A356.0, 357.0
A357.0, 413.0
443.0, A444.0
319.0, 333.0
354.0, 355.0
C355.0
201.0, 206.0, 224.0
Base Metal
1060, 1070,1080,
1350
1100, 3003, Alc3003
2014, 2036
2219
3004, Alc3004
5005
5052, 5652i
5083
5086
5154 5254i
511.0
356.0,
A356.0
357.0,
A357.0
ER4043b
512.0
6005, 6061
6009
6063, 6101
514.0
535.0
7004,
7005
7039,
710.0
712.0
6010
6070
6151, 6201
6351, 6951
5456
5454
ER4043ab
ER5356cd
ER5356cd
ER4043ab
ER4043ab
ER5356d
ER4043bd
ER4043ab
ER4145
ER4145bc
ER4043b
ER4043b
ER4043f
ER5356cd
ER5356cd
ER4043f
ER4043f
ER5356cd
ER5356cd
ER5356cd
ER4043bd
ER4043
ER5356f
ER5356f
ER5356f
ER5183d
ER5356d
ER5356f
ER5356f
ER5556d
ER4043ab
ER4145
ER4043ab
ER4043bf
ER4043bf
ER5356cf
ER5356d
ER5356d
ER5356f
ER5356ef
ER5356d
ER5356d
ER4043
ER5356f
ER5356f
ER5356f
ER5356d
ER5356d
ER5356f
ER5356f
ER5356d
ER4043ab
ER4145
ER4043ab
ER4043b
ER4043b
ER4043b
ER4043b
ER4145
ER4145bc
ER4043bfg
ER5356f
ER5356cf
ER4043abg
ER4145
ER4145bc
ER4043b
ER4043abg
ER4043bf
ER4043
ER5356f
ER4043
ER5356d
ER4043abg
ER4043f
ER5356f
ER4145
ER4145bc
ER4145e
ER4145bch
ER5356d
ER5356d
ER5356f
ER5183d
ER5356d
ER5356f
ER5356f
ER5556d
ER4043b
ER5356f
ER5356f
ER5356f
ER5356d
ER5356d
ER5356f
ER5554cf
ER4043bfg
ER4043bh
ER2319ah
5154
5254
5086
5083
5052
5652
5005
5050
3004
Alc.3004
ER5356cd
ER5356cd
ER5356d
ER5356d
ER5356d
ER5356d
ER4043bd
ER4043bd
ER4043
ER5356f
ER5356f
ER5356f
ER5356d
ER5356d
ER5356fi
ER5356d
ER5356d
ER5356d
ER5356d
ER5356d
ER5356d
ER5356d
ER5356d
ER5183d
ER1100bc
ER1100bc
ER4145
ER4043ab
ER5356cf
ER5356cf
ER4043bd
ER4043bd
ER4145
ER4043ab
ER5356cf
ER4043b
ER5356cf
ER5356cd
ER5354cfi
2219
ER4145bc
ER4145bc
ER4145e
ER2319a
1100
3003
Alc.3003
2014
2036
ER4145
ER4145
ER4145e
ER1001bc
ER1001bc
1060
1070
1080
1350
ER1188bchj
1. Service conditions such as immersion in fresh or salt water, exposure to specific chemicals or a sustained high temperature (over 150°F (66 °C)) may limit the choice of filler
metals. Filler metals ER5IS3, ER5356, ER5556, and ER5654 are not recommended for sustained elevated temperature service.
2. Recommendations in this table apply to gas shielded arc welding processes. For oxyfuel gas welding, only ER118S, ER1100, ER4043, ER4047, and ER4145 filler metals
are ordinarily used.
3. Where no filler metal is listed, the base metal combination is not recommended for welding.
a. ER4145 may be used for some applications.
b. ER4047 may be used for some applications.
c. ER4043 may be used for some applications.
d. ER5183, ER5356, or ER5556 may be used.
e. ER2319 may be used for some applications. It can supply high strength when the weldment is postweld solution heat treated and aged.
f. ER5183, ER5356, ER5554, ER5556, and ER5654 may be used. In some cases, they provide: (I) improved color match after anodizing treatment, (2) highest weld ductility,
and (3) higher weld strength. ER5554 is suitable for sustained elevated temperature service.
g. ER4643 will provide high strength in 1/2 in. (12 mm) and thicker groove welds in 6XXX hase alloys when postweld solution heat treated and aged.
h. Filler metal with the same analysis as the base metal is sometimes used. The following wrought filler metals possess the same chemical composition limits as cast filler
alloys: ER4009 and R4009 as R-C355.0: ER4010 and R4010 as R-A356.0: and R4011 as R-A357.0.
i. Base metal alloys 5254 and 5652 are used for hydrogen peroxide service. ER5654 filler metal is used for welding both alloys for service temperatures below 150°F (66°C).
j. ER 1100 may he used for some applications.
NAVEDTRA 14250A
10-63
7.2.2 Copper and Copper Alloys
Gas metal arc welding is well suited for welding copper and copper alloys because of
the intense arc generated by this process. This is advantageous because copper has a
very high thermal conductivity and the heat is conducted away from the weld zone very
rapidly. An intense arc is important in completing the fusion with minimum heating of the
surrounding base metal.
The main alloying elements used in copper are zinc (brasses), phosphorous (phosphor
bronzes), aluminum (aluminum bronzes), beryllium (beryllium coppers), nickel (nickel
silvers), silicon (silicon bronzes), tin and zinc (tin brasses), and nickel and zinc (nickel
silvers). All of these are weldable with this process but some are easier than others. The
best are the deoxidized coppers, aluminum bronzes, silicon bronzes, and copper
nickels. The alloys having the poorest weldability are those with the highest zinc
contents, which have a high cracking tendency, and electrolytic tough pitch copper,
which gives problems with porosity. Care must be taken when welding beryllium
coppers because the fumes given off are dangerous to the welder’s health. For this
reason, extra special precautions should be taken. Table 10-15 shows the relative ease
of welding copper and copper alloys.
Table 10-15 — Weldability Ratings of Coppers and Copper Alloys.
(1=excellent, 2=good, 3=fair)
Type
Weldability Rating
Oxygen-free copper
2
Electrolytic tough pitch copper
3
Deoxidized copper
1
Beryllium copper
2
Low-zinc brass
2
High-zinc brass
3
Tin brasses
3
Nickel silvers
3
Phosphor bronzes
2
Aluminum bronzes
2
Silicon bronzes
1
Copper nickels
1
Most applications of this process are for welding metal thicknesses greater than 1/8 in.
(3.2 mm). For thicknesses less than this, the gas tungsten arc welding process is more
popular. GMAW is the most practical process to use on thicknesses greater than 1/2 in.
(12.7) because of the higher deposition rates obtained. Generally, preheating is not
used on the thinner sections, but it is often used on sections thicker than 1/8 in. (3.2
mm) so that the heat does not leave the weld area as quickly. A temperature of 500800° F (260-425° C) is typical when preheat is used. Welding currents used for copper
are often 50-75% higher than those used for aluminum.
Most welding of copper and copper alloys is done in the flat position, but when welding
has to be done in other positions, the gas metal arc welding process is preferred over
NAVEDTRA 14250A
10-64
gas tungsten arc welding and shielded metal arc welding. Out-of-position welding uses
small diameter electrodes, lower currents, and short-circuiting transfer, and is generally
done on the less fluid alloys such as the aluminum bronzes, silicon bronzes, and copper
nickels.
The shielding gases most commonly used for welding copper are argon and helium.
Argon has the lowest energy output but produces spray transfer and the least amount of
spatter. Helium produces globular transfer with heavy spatter. This gas produces more
heat, so the penetration patterns are broader and more uniform in depth than those
produced by argon. Nitrogen is occasionally used, but spatter is particularly heavy.
Mixtures of argon and helium are often used to get the stable arc characteristics of
argon and the deep penetration of helium.
The filler metal is usually selected so the chemical composition of the filler rod closely
matches the base metal. When welding copper and copper alloys, a deoxidized
electrode is required; this is often necessary to obtain a strong weld joint in some of the
copper alloys. For example, a silicon bronze filler metal is used with silicon bronze base
metal. A filler metal with a different chemical composition than the base metal may be
selected when welding some of the weaker alloys to give the weld joint added strength.
The best choice of filler metal depends primarily on the type of copper alloy being
welded with the application also being considered.
7.2.3 Magnesium and Magnesium Alloys
Gas metal arc welding is widely used for welding magnesium alloys. The major alloying
elements used in magnesium are aluminum, zinc, and thorium (thawr-ee-uh m). Most
magnesium alloys are weldable with this process but the weldability will vary with the
alloy. Table 10-16 shows the main alloying elements used and the relative weldability of
the alloys. The rating is based mainly on the susceptibility to cracking. Aluminum
contents up to about 10% help the weldability because it promotes grain size
refinement. Zinc contents above about 1% will increase the tendency towards hot
cracking. Alloys that have high zinc content are very susceptible to cracking and have
poorer weldability. Thorium alloys generally have excellent weldability. Magnesium
forms an oxide similar to aluminum oxide, which gives these two metals similar welding
characteristics.
GMAW can be used to weld all thicknesses of magnesium; it is the most popular
process for welding thicknesses greater than 3/8 in. (9.5 mm). The higher deposition
rates and the faster travel speeds used, which reduce distortion, are primary reasons for
the popularity of this process. Welding is generally done in the flat, horizontal, and
vertical-up positions if possible, because of the higher deposition rates and the more
fluid weld puddle produced compared to gas tungsten arc welding.
Inert gases must be used for welding magnesium alloys because the base metal will
react chemically with an active gas. Argon is generally used as the shielding, but
occasionally, mixtures of argon and helium are used to give better filler metal flow and
heat input. Helium is not recommended because it produces globular transfer and more
spatter.
The three types of metal transfer useful for welding magnesium alloys are the shortcircuiting, spray, and pulsed arc methods. The pulsed arc mode is used in current
ranges between the short-circuiting mode and the spray mode to avoid the highly
unstable globular transfer mode.
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Preheating is often used on thin sections and highly restrained joints to prevent weld
cracking. Thicker sections generally do not require preheating unless there is a high
degree of joint restraint.
If the filler metal has been selected properly, the GMAW-produced welds are often
stronger than the base metal. Electrodes with lower melting points and a wider freezing
range than the base metal are often used to avoid cracking. Electrodes for gas metal
arc welding magnesium alloys consist of four different types (refer again to Figure 1059). The type of electrode used is governed by the chemical composition of the base
metal.
Table 10-16 — Magnesium Alloy Classification, Weldability and Filler Selection.
(1=excellent, 2=good, 3=fair, 4 =poor)
Magnesum
Alloy
Wrought
AZ10A
AZ31B
AZ31C
AZ61A
AZ80A
HK31A
HM21A
HM31A
LA141A
M1A
ZE10A
ZK21A
ZK60A
CastAlloys
AM100A
AZ63A
AZ81A
AZ91C
AZ92A
EK41A
EZ33A
HK31A
HZ32A
K1A
QE22A
ZE41A
ZH62A
ZK51A
ZK61A
Major Alloying
Elements
Alloys
Aluminum,Zinc
Aluminum,Zinc
Aluminum,Zinc
Aluminum,Zinc
Aluminum,Zinc
Thorium,Zirconium
Thorium,Manganese
Thorium,Manganese
Lithium,Aluminum
Manganese
Zinc,Rare Earths
Zinc,Zirconium
Zinc,Zirconium
Aluminum,Manganese
Aluminum,Zinc
Aluminum,Zinc
Aluminum,Zinc
Aluminum,Zinc
Rare
Earths,Zirconium
Rare Earths,Zinc
Thorium,Zirconium
Thorium,Zinc
Zirconium
Silver,Rare Earths
Zinc,Rare Earths
Zinc,Thorium
Zinc,Zirconium
Zinc,Zirconium
Weldability
Rating
Filler
Metal
1
1
1
2
2
1
1
1
2
1
1
2
4
AZ61A,AZ92A
AZ61AAZ92A
AZ61AAZ92A
AZ61A,AZ92A
AZ61AAZ92A
EZ33A
EZ33A
EZ33A
LA141A,EZ33A
AZ61A,AZ92A
AZ61A,AZ92A
AZ61A,AZ92A
EZ33A
2
3
2
2
2
AZ101A,AZ92A
AZ101A,AZ92A
AZ101A,AZ92A
AZ101A,AZ92A
AZ101A
2
1
2
2
1
2
2
3
4
4
EZ33A
EZ33A
EZ33A
EZ33A
EZ33A
EZ33A
EZ33A
EZ33A
EZ33A
EZ33A
7.2.4 Nickel and Nickel Alloys
Gas metal arc welding is one of the major processes used for welding nickel and nickel
alloys. The major alloying elements used in nickel are iron, chromium, copper,
molybdenum, and silicon. Trade names are widely used, but a classification system is
shown in Table 10-17. This process is used for welding the solid-solution strengthened
alloys; the precipitation-hardening alloys are more readily welded by gas tungsten arc
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welding because it is difficult to transfer hardening elements across the arc. Many of the
cast alloys, especially ones with high silicon contents, are more difficult to weld.
Table 10-17 — Classifications of nickel and nickel alloys.
Series
Alloy Group
200
Nickel, solid solution
300
Nickel, precipitation-hardenable
400
Nickel-copper, solid solution (Monel)
500
Nickel-copper, precipitation-hardenable (Monel)
600
Nickel-chromium, solid solution (Inconel)
700
Nickel chromium, precipitation-hardenable (Inconel)
800
Nickel-iron-chromium solid solution (Incoloy)
900
Nickel-iron-chromium, precipitation-hardenable (Incoloy)
One of the most important factors in welding nickel and nickel alloys is the cleanliness
of the base metal. These metals are susceptible to embrittlement caused by sulfur,
phosphorous, and lead. Therefore, the surface of the metal to be welded should be
cleaned of any grease, oil, paint, dirt, and processing chemicals. Another welding
characteristic of nickel is that the weld puddle is not very fluid; therefore, it is more
difficult to get complete fusion.
Short-circuiting, globular, or spray transfer may be used depending on the welding heat
input and the thickness of the metal being welded. The pulsed arc method is also used.
Argon shielding gas is widely used and normally recommended for welding in the spray
and pulsed arc modes. Argon-helium mixtures are used to produce wider and flatter
beads and are generally used with the short-circuiting mode. This process is employed
for welding most thicknesses of nickel and nickel alloys.
The filler metals used for welding of these metals are generally similar in composition to
the base metal being welded. The filler metals are alloyed to resist hot cracking and
porosity in the weld metal.
7.2.5 Steels
GMAW is widely used for welding steels. In general, steels are classified according to
the carbon content, such as low carbon, medium carbon, or high carbon steels. In
addition, steels are also classified according to the types of alloy used, such as chromemoly, nickel-manganese, etc. For discussion purposes in this chapter, steels will be
classified according to their welding characteristics.
In welding steel, the hardness and hardenability of the weld metal are influenced by the
carbon and any other alloy content, which in turn influences the amount of preheat
needed. The two terms, hardness and hardenability, are not the same. The maximum
hardness of steel is primarily a function of the amount of carbon in the steel.
Hardenability is a measure of how easily a martensite structure is formed when the steel
is quenched. Martensite is the phase or metallurgical structure in steel where the
maximum hardness of the steel can be obtained. Steels with low hardenability must
have very high cooling rates after welding to form martensite, where steels with high
hardenability will form martensite even when they are slow cooled in air. Hardenability
will determine to what extent a steel will harden during welding. The carbon equivalent
formula is one of the best methods of determining the weldability of steels. This value is
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determined by the amounts of the alloying elements. There are several different
formulas used; one of the most popular is as follows:
Steels with lower carbon equivalents generally are more readily weldable and require
fewer precautions such as the use of preheat and postheat. Steels with higher carbon
equivalents are generally more difficult to weld. In welding some of the steels, it is more
important to match the mechanical properties than the chemical compositions of the
filler metal to the base metal. Often, filler metal with a lower carbon content than the
base metal is used because the weld metal absorbs carbon from the base metal. This is
done to minimize the tendency for weld cracking.
7.2.5.1 Low Carbon and Mild Steels
Low carbon and mild steels generally have low carbon contents and are the most
readily weldable. They are the most widely used type of steel for industrial fabrication
and include the high strength structural steels.
Low carbon steels have carbon contents up to .14%; mild steels have carbon contents
ranging from .15 to .29%. For many applications, preheating is not required except on
thick sections and highly restrained joints, or where codes require preheating, but other
precautions such as interpass temperature control and postheating are sometimes
used. With thicker sections and highly restrained joints, preheating, interpass
temperature control, and postheating are usually required to prevent cracking.
Electrodes of the ER70S class are employed with carbon dioxide, inert gas, or carbon
dioxide-inert gas mixtures, and all types of metal transfer are used. Carbon dioxide is
the most widely used gas because it is the least expensive and provides good
penetration. The filler metal should be chosen to match the tensile strength of the base
metal. A filler metal with sufficient amounts of deoxidizers must be chosen to prevent
porosity when welding rimmed steels, which have a silicon content of less than .05%.
This precaution is not necessary for welding steels containing more than .05% silicon.
The high strength structural steels are steels whose yield strength falls between 45,000
psi (310M Pa) and 70,000 psi (483 MPa) and their carbon content is generally below
.25%. These steels have relatively small amounts of alloying elements. Some common
examples of these steels are the ASTM designations of A242, A441, A572, A588, A553,
and A537.
7.2.5.2 Low Alloy Steels
The low alloy steels discussed here will be those steels that are low carbon and have
alloy additions less than 5%. This includes the quenched and tempered steels, heat
treated low alloy steels, and the low nickel alloy steels. Elements such as nickel,
chromium, manganese, and molybdenum are the main alloying elements used.
These steels have a higher hardenability than mild steels, and this factor is the principal
complication in welding. Low alloy steels have good weldability but are not as easily
weldable as the mild steels. This higher hardenability permits martensite to form at
lower cooling rates. As the alloy content and the carbon content increase, the
hardenability also increases.
In general, as the hardenability of the material increases, the ability to weld it
decreases. One of the best methods for determining the weldability of a low alloy steel
is the use of the carbon equivalent formula. Steels that have carbon equivalents below
about .40% usually do not require the use of preheating and postheating in the welding
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procedure and generally have the best weldability. Steels with carbon equivalents
higher than .40% require more precautions for welding.
Typically, the higher the carbon equivalent, the more difficult the steel is to weld. Except
in the case of the low nickel alloys, the selection of electrodes for welding steel is
usually based on the desired strength and mechanical properties of the weld rather than
on matching chemical compositions. Short-circuiting, globular, and spray metal transfers
may be used. The most commonly used shielding gases are carbon dioxide or argoncarbon dioxide mixtures.
The quenched and tempered heat treated steels have yield strengths ranging from
50,000 psi (345 MPa) to very high yield strengths, and have carbon contents ranging to
.25%. Some common examples of these types of steel are the ASTM designations
A533 Grade B, A537 Grade B, A514, A517, A543, and A553. The .25% carbon limit is
used to provide fairly good weldability. These steels provide high tensile and yield
strength along with good ductility, notch toughness, corrosion resistance, fatigue
strength, and weldability. The presence of hydrogen is always bad in steel, but it is even
more critical in these types of steels compared to mild steels. Low hydrogen electrodes
should be used when welding these steels. Preheat is generally not used on thinner
sections, but it is used on thicker or highly restrained sections. Postweld heat treatment
is generally not used because the shielded metal arc welds have good toughness. The
steels are generally used in the welded or stress relieved conditions.
The nickel alloy steels included in these low alloy steel groups are those with less than
5% nickel contents. The 2 1/4% and 3 1/2% nickel steels are usually welded with
covered electrodes that have the same general chemical composition as the base
metal. Preheating is required with highly restrained joints.
7.2.5.3 Heat Treatable Steels
The heat treatable steels are the medium and high carbon steels and medium carbon
steels that have been alloyed. This group includes the steels quenched and tempered
after welding, normalized or annealed steels, and medium and high carbon steels.
These steels are more difficult to weld than the other types of steels already mentioned
in this chapter. The most important factor for selecting the type of covered electrode to
be used is matching the chemical compositions of the base metal and the filler metal.
Medium carbon steels are those that have carbon contents ranging from .30% to .59%,
and high carbon steels have carbon contents ranging from .60% to about 1.0%. When
medium and high carbon steels are welded, precautions should be included in the
welding procedure because of the hardness that can occur in the weld joint. As the
carbon content increases up to .60%, the hardness of the fully hardened structure (or
martensite) increases to a maximum value. When the carbon content is above .60%,
the hardness of the fully hardened structure does not increase, so these steels can be
welded using about the same welding procedures as the medium carbon steels.
Martensite, which is the phase that steel is in at its fullest hardness, is harder and more
brittle in high carbon steel than it is in low carbon steel. A high carbon martensitic
structure can have a tendency to crack in the weld metal and heat affected zone during
cooling. Welding procedures that lower the hardness of the heat affected zone and the
weld metal will reduce the tendency to crack. This can be done by using a procedure
that requires lower carbon content in the filler metal and by slowing the cooling rate. The
procedure would include preheating, interpass temperature control, and postheating.
The procedures used for welding medium carbon steels can be simpler than the one
just mentioned, but that depends on the specific applications. Medium carbon steels can
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be welded with the ER70S-ER90S classifications. High carbon steels should be welded
with the ER80S-ER120S using the electrode of the proper tensile strength to match the
tensile strength of the base metal. Generally, high carbon steels are not used in welded
production work. These steels are usually welded only in repair work. Mild steel
electrodes may also be used, but the deposited weld metal absorbs carbon from the
base metal and thus loses a considerable amount of ductility. Stainless steel electrodes
of the austenitic type are sometimes used, but the fusion zone may still be hard and
brittle. A preheat and/or postheat will help eliminate the brittle structure.
Steels quenched and tempered after welding have carbon contents ranging from about
.25% to .45%, which distinguishes them from the steels that are quenched and
tempered before welding. These steels also have small additions of alloying elements.
Some common examples of these steels are the AISI designations 4130, 4140, and
4340. Because of the higher carbon contents, the steels in this group can be heat
treated to extremely high levels of strength and hardness. Some of these steels have
enough alloy content to give them high hardenability. Because of this combination of
carbon and alloy content, the steels must be preheated before welding. Their weldability
is also influenced by the purity of the steels. High amounts of sulfur and phosphorous in
the steel increase the sensitivity to cracking and reduce the ductility. Gas metal arc
welding is often used for welding these steels, and a filler metal of the same chemical
composition as the base metal is required to obtain the maximum strength.
7.2.5.4 Chromium-Molybdenum Steels
The low chromium molybdenum steels in this section are those with alloy contents of
about 6% or less. These steels are in the low carbon range, generally up to .15%, and
are readily weldable. The chromium and molybdenum alloying elements provide these
steels with good oxidation resistance and high temperature strength. The chromium is
mainly responsible for the resistance, and the molybdenum is mainly responsible for the
high temperature strength.
The higher chrome-moly steels contain about 6-10% chromium and .5-1% molybdenum.
These steels are limited to a maximum carbon content of about .10% to limit the
hardness because these steels are very sensitive to air hardening. For the welding of
these steels, preheating, interpass temperature control, slow cooling, and postweld heat
treatment are required to make a weld with good mechanical properties. These steels
generally do not require preheating except when welding thick sections or highly
restrained joints. Postheating is usually not required on chromium molybdenum steels
that contain less than 2 1/4% Cr and 1% Mo.
Gas metal arc welding is one of the most common methods of welding the chromium
molybdenum steels. Short-circuiting or spray transfer is generally used. The steels with
less than 6% chromium are welded with a carbon dioxide or argon-carbon dioxide
mixture, depending on the type of metal transfer desired. For the steels with 6%
chromium or more, argon, argon-helium mixtures, and argon with small additions of
oxygen or carbon dioxide are used. Pulsed arc transfer is often employed to fill the gap
between short-circuiting and spray transfer to avoid globular transfer. The filler metal is
chosen to match the chemical composition of the base metal as closely as possible to
give good corrosion resistance.
7.2.5.5 Free Machining Steels
Free machining steels are steels that have additions of sulfur, phosphorous, selenium,
or lead in them to make these steels easier to machine. Except for the high sulfur, lead,
or phosphorous, these steels have chemical compositions similar to mild, low alloy, and
NAVEDTRA 14250A
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stainless steels. The addition of these elements makes these steels nearly unweldable
because lead, phosphorous, and sulfur have melting points much lower than the melting
point of the steel. As the weld solidifies, these elements remain liquid much longer than
the steel, so they coat the grain boundaries, causing hot cracking in the weld. Hot
cracking is cracking that occurs before the weld has had a chance to cool. Because of
this hot cracking problem, free machining steels cannot be welded easily. High
manganese filler metal and low base metal dilution will help give the best results
possible.
7.2.5.6 Stainless Steels
Most types of stainless steels can be welded by GMAW. The types that are very difficult
to weld are types such as 303, 416, 416 Se, 430 F, and 430 FSe, which have high
sulfur and selenium contents, and Type 440, which has a high carbon content. The
major alloying element which distinguishes stainless steels from the other types of steel
is the chromium. Steels that have chromium contents greater than 11% are considered
stainless steels. The high chromium content gives these steels very good corrosion and
oxidation resistance. The three major groups of stainless steels that are welded are the
austenitic, martensitic, and ferritic types.
The austenitic types of stainless steels are generally the easiest to weld. In addition to
the high chromium content of about 16-26%, these types have high nickel contents
ranging from 6-22%. These steels are designated by the AISI as the 300 series. The
200 series, which have high manganese contents to replace some of the nickel, are
also austenitic. Nickel and manganese are strong austenite formers and maintain an
austenitic structure at all temperatures. This structure gives these steels good
toughness and ductility but also makes them non-hardenable. A major problem when
welding these types of steels is carbide precipitation or sensitization, which occurs only
in the austenitic structure. This occurs when the temperature of the steel is between
approximately 1000-1600° F (540-870° C) and can greatly reduce the corrosion
resistance. There are several methods for preventing this problem:
1. Fast cooling rate after welding through this temperature range. This is a major
reason why preheating is usually not used and why these steels require a
relatively low maximum interpass temperature on multiple pass welds.
2. Use of extra low carbon base and filler metal (.03% carbon max). Examples are
304L and 316L.
3. Use of a stabilized alloy containing columbium, tantalum (tan-tl-uh m), or
titanium. Examples are 347 and 321.
4. Use of a solution heat treatment to redissolve the carbides after welding.
Martensitic stainless steels are not as easy to weld as the austenitic stainless steels.
These stainless steels have approximately 11-18% chromium, which is the major
alloying element, and are designated by the AISI as the 400 series. Some examples are
403, 410, 420, and 440. These types of stainless steel are heat treatable because they
generally contain higher carbon contents and a martensitic structure. Stainless steels
with higher carbon contents are more susceptible to cracking and some, such as Type
440, have carbon contents so high that they are often considered unweldable. A
stainless steel with a carbon content greater than .10% will often need preheating,
usually in the range of 400-600° F (205-315°C) to avoid cracking. For steels containing
carbon contents greater than .20%, a postweld heat treatment such as annealing is
often required to improve the toughness of the weld produced.
Ferritic stainless steels are also more difficult to weld than austenitic stainless steels
because they produce welds having lower toughness than the base metal. These
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stainless steels form a ferritic grain structure and are also designated by the AISI as the
400 series. Some examples are types 405, 430, 442, and 446. These types are
generally less corrosion resistant than austenitic stainless steel. To avoid a brittle
structure in the weld, preheating and postheating are often required. Typical preheat
temperatures range from 300-500° F (150-260° C). Annealing is often used after heat
treatment welding to increase the toughness of the weld.
GMAW is well suited for welding stainless steel. Lower current levels may be desirable
for welding stainless steel compared to welding mild steel because of the higher thermal
expansion, lower thermal conductivity, and lower melting point of stainless steel. The
lower thermal conductivity and higher thermal expansion cause more distortion and
warpage for a given heat input. All of the different modes of metal transfer are used
when welding stainless steel. Pulsed arc welding is popular because it helps reduce
distortion and warpage. An argon-oxygen mixture of 99% Ar-1 % O2, or 98% Ar-2% O2,
or pure argon is used to obtain spray transfer. The argon-oxygen mixtures are used to
improve arc stability and weld puddle wetting. Helium-argon-carbon dioxide mixtures
are used to obtain short-circuiting transfer. Argon-carbon dioxide mixtures are
sometimes used. Carbon dioxide causes a loss of silicon and manganese, and an
increase in carbon in the low carbon stainless steels. Carbon dioxide is restricted for
welding many of the stainless steels, especially austenitic grades, because corrosion
resistance may be reduced due to the carbon the gas adds to the weld. GMAW may be
used on most thicknesses of stainless steel
The filler metal for welding stainless steel is generally chosen to match the chemical
composition of the base metal. For the 200 series austenitic stainless steels, a 300
series austenitic filler metal is usually used due to lack of an available 200 series filler
metal. This weId joint will generally be weaker than the surrounding base metal. 300
series filler metal is used on 300 series base metal.
Type 410 and 420 electrodes are the only martensitic stainless steel types recognized
by the AWS. This limitation is often the reason why austenitic stainless steel filler metal
is often used when welding martensitic stainless steel. Austenitic filler metal provides a
weld with lower strength but higher toughness and eliminates the need for preheating
and postheating. For welding ferritic stainless steels, both ferritic and austenitic filler
metal may be used. Ferritic filler metal is used when higher strength and an annealing
postheat are required. Austenitic filler metal is used when higher ductility is required.
Table 10-18 shows filler metal selection for stainless steels.
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Table 10-18 — Filler metal selection for welding stainless steel.
Filler
C%
Mn%
Si%
Cr%
Ni%
No.
Other
Metal
Elements
Selection
201
0.15 max
5.5-7.5
1.00
16.00-18.00
3.50-5.50
N 0.25 max
308
202
0.15 max
7.5-10.0
1.00
17.00-19.00
4.00-6.00
N 0.25 max
308
301
0.15 max
2.00
1.00
16.00-18.00
6.00-8.00
-
308
302
0.15 max
2.00
1.00
17.00-19.00
8.00-10.00
-
308
3028
0.15 max
2.00
2.00-3.00
17.00-19.00
8.00-10.00
-
308
304
0.08 max
2.00
1.00
18.00-20.00
8.00-12.00
-
308
304L
0.03 max
2.00
1.00
18.00-20.00
8.00-12.00
-
308L
305
0.12 max
2.00
1.00
17.00-19.00
10.00-13.00
-
308 310
308
0.08 max
2.00
1.00
19.00-21.00
10.00-12.00
-
308
309
0.20 max
2.00
1.00
22.00-24.00
12.00-15.00
-
309
309S
0.08 max
2.00
1.00
22.00-24.00
12.00-15.00
-
309
310
0.25 max
2.00
1.50
24.00-26.00
19.00-22.00
-
310
310S
0.08 max
2.00
1.50
24.00-26.00
19.00-22.0
-
310
314
0.25 max
2.00
1.50-3.00
23.00-26.00
19.00-22.00
-
310 312
316
0.08 max
2.00
1.00
16.00-18.00
10.00-14.00
Mo 2.00-3.00
316
316L
0.03 max
2.00
1.00
16.00-18.00
10.00-14.00
Mo 2.00-3.00
316L
317
0.08 max
2.00
1.00
18.00-20.00
11.00-15.00
Mo 2.00-3.00
317
321
0.08 max
2.00
1.00
17.00-19.00
9.00-12.00
Ti 5xCmin
347
330
0.35 max
2.00
2.50
13.00-17.00
33.00-37.00
-
330
347
0.08 max
2.00
1.00
17.00-19.00
9.00-13.00
Cb+Ta
347
348
0.08 max
2.00
1.00
18.00-19.00
9.00-13.00
Cb+Ta 10 C
10xC min
347 348
min.Ta 0.10
403
0.15 max
1.00
0.50
11.50-13.00
-
-
410 309 310
410
0.15 max
1.00
1.00
11.50-13.50
-
-
410 309 310
414
0.15 max
1.00
1.00
11.50-13.50
1.25-2.50
-
410 309 310
420
Over 0.15
1.00
1.00
12.00-14.00
-
-
410 420
431
0.20 max
1.00
1.00
15.00-17.00
1.25-2.50
-
430 309 310
501
Over 0.10
1.00
1.00
4.00-6.00
-
Mo 0.40-
502
0.65
502
0.10 max
1.00
1.00
4.00-6.00
-
Mo 0.40-0.65
502
405
0.08 max
1.00
1.00
11.50-14.50
-
Al0.10-0.30
410 309 310
430
0.12 max
1.00
1.00
14.00-18.00
-
-
430 309 310
442
0.20 max
1.00
1.00
18.00-23.00
-
-
309 310
446
0.20 max
1.50
1.00
23.00-27.00
-
N20.25max
309 310
NAVEDTRA 14250A
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7.2.6 Titanium and Titanium Alloys
Titanium and many of the titanium alloys are welded by GMAW. The major alloying
elements contained in titanium alloys are aluminum, tin, zirconium, vanadium and
molybdenum. There are four basic groups of this metal:
1.
2.
3.
4.
Unalloyed titanium
Alpha alloys
Alpha-beta alloys
Beta alloys
The unalloyed titanium and alpha alloys are all weldable. The weakly beta-stabilized
alpha-beta alloys are weldable but strongly beta-stabilized alpha-beta alloys are
embrittled by welding. Most beta alloys can be welded, but proper heat treatment must
be used to prevent the welds from becoming brittle.
In general, titanium requires the same welding techniques used for welding stainless
steel with two exceptions: titanium requires greater cleanliness and an auxiliary
shielding gas. The molten weld puddle reacts with most materials, and contamination
from the atmosphere or from material on the surface of the metal can cause
embrittlement in the weld zone and a loss of corrosion resistance. The surface of the
metal to be welded must be cleaned thoroughly to avoid these problems. Argon or
helium shielding gases are almost exclusively used for welding titanium. The only other
shielding gas used is an argon-helium mixture. Welding titanium requires a shielding
gas on the backside of the root pass also. In many cases, welding is done in an inert
gas filler chamber. For out of chamber welding, a trailing shielding gas is used behind
the torch to protect the hot metal until it cools below about 600°F (315°C). A leading
shield is also used to prevent oxidation of any spatter that may be remelted into the
weld puddle. GMAW is used for welding metal thicknesses greater than 1/8 in. (3.2mm),
but gas tungsten arc welding is often preferred instead, even when welding thicker
metal, because of the weld spatter and arc instability, which can occur in GMAW, thus
reducing the weld quality. Preheating is rarely used except when removing moisture
from the surface of the metal.
Electrodes of the same chemical composition as the base metal are usually used.
Sometimes electrodes with a yield point lower than the base metal are used to improve
the joint ductility when welding higher strength titanium alloys. The electrode wire must
also be very clean because it can also cause contamination of the weld metal.
Test your Knowledge (Select the Correct Response)
9.
What are the grains called that form on the edge of a weld?
A.
B.
C.
D.
Deoxidizers
Dendrites
Slag
Dross
NAVEDTRA 14250A
10-74
10.
Why is preheating used when welding titanium?
A.
B.
C.
D.
To increase base metal temperature.
To remove moisture from the base metal.
To soften the base metal.
To increase the hardenability of the base metal.
8.0.0 WELD and JOINT DESIGN
The weld joint design used for gas metal arc welding is determined by the design of the
workpiece, metallurgical considerations, and codes or specifications.
Joints are designed for accessibility and economy during construction. The purpose of a
joint design is to obtain the required strength and highest quality at the lowest possible
cost. A weld joint consists of a specific weld made in a specific joint. A joint is defined as
being the junction of members who are to be, or have been, joined. Figure 10-45 shows
the five basic joint types. Each of the different joints may be joined by many different
types of welds. Figure 10-45 shows the most common types of welds. The type of weld
made is governed by the joint configuration, and each of the different welds has its own
specific advantages. Figure 10-45 lists the nomenclature used for groove and fillet
welds.
Several factors influence the joint design to be used:
1.
2.
3.
4.
5.
Strength required
Welding position
Metal thickness
Joint accessibility
Type of metal being welded
The edge and joint preparation are important because they will affect both the quality
and cost of welding. The cost items to be considered are the amount of filler metal
required, the method of preparing the joint, the amount of labor required, and the level
of quality required. Difficult to weld joints will often have more repair work necessary
than those that are the easier to weld.
GMAW is applicable to all five basic joint types, with butt and tee joints the most
commonly welded. Lap joints have the advantage of not requiring much preparation
other than squaring off the edges and making sure the metal is in close contact. Edge
joints are widely used on thin metal. Corner joints generally use similar edge
preparations to those used on tee joints.
In some cases, the joint designs used for gas metal arc welding are similar to shielded
metal arc welding, but there are often differences due to the different characteristics of
the process. Gas metal arc welding has some characteristics that are different from
many other processes, which will sometimes affect the joint design. One of the main
items is that the joint must be designed so the welder can obtain good access to the
joint to be able to manipulate the electrode properly. In addition, a joint must not be
located so it creates an excessive distance between the root of the joint and the nozzle
of the welding gun. A large nozzle-to-work distance may prevent adequate root
penetration and adequate gas shielding.
NAVEDTRA 14250A
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Figure 10-45 — Weld nomenclature.
NAVEDTRA 14250A
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Figure 10-46 — Welding test positions.
NAVEDTRA 14250A
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8.1.0 Strength
The strength required of a weld joint is a major factor governing weld joint design. Weld
joints may be either full or partial penetration depending on the strength required of the
joint. Full or complete penetrating welds are those that have weld metal through the full
cross section of the joint; partial penetrating welds are those that have an unfused area
in the joint. Welds subject to cyclic, impact, or dynamic loading require complete
penetration welds. This is even more important for applications that require low
temperature service.
Partial penetration welds may be adequate for joints where loading is static only, and
they are easier to prepare and require less filler metal than full penetration joints.
The amount of penetration obtained will be affected by the root opening and root face
used. A root opening is used to allow good access to the root of the joint and is usually
used in full penetrating weld joints. A root opening is usually not used in partial
penetration weld joints because access to the root is not necessary and parts are easier
to fit together without a root opening. The size of the root face is also affected. A larger
root face is used for partial penetration welds than for complete penetration welds
because less penetration is required.
Because GMAW uses relatively small diameter electrode wire, the arc produced is more
intense than the arcs produced by shielded metal arc welding and gas tungsten arc
welding. Slightly larger root faces are needed because of the greater penetrating
characteristics of the gas metal arc welding process, especially when using carbon
dioxide shielding gas. Smaller root openings may also be used to keep the weld metal
from falling through the root of the joint. These differences apply to the globular, spray,
and pulsed arc modes only. Because lower welding current values are used with the
short-circuiting mode of metal transfer, joint designs used are similar to those used for
shielded metal arc welding. The short-circuiting mode requires larger root openings and
smaller root faces. This metal transfer mode is widely used for welding thin metal and
for depositing the root pass in thick metal, while the rest of the groove may be filled
using the spray or globular transfer modes. Smaller groove angles are required with
GMAW because of the relatively small electrode diameter used, which allows better
access to the root of the joint.
8.2.0 Position
GMAW may be used in all welding positions. The position in which welding is done
often affects the joint configuration. A diagram of the welding position capabilities (also
the welding test positions) is shown in Figure 10-46. Good quality welding in the flat,
horizontal, vertical, and overhead positions depends on the skill of the welder and the
mode of metal transfer. Welding positions are classified by a set of numbers and letters.
The four basic welding positions are designated by the numbers 1 for flat, 2 for
horizontal, 3 for vertical, and 4 for overhead. F designations are used for fillet welds and
G designations are used for groove welds. The 5G and 6G positions are used in pipe
welding.
NAVEDTRA 14250A
10-78
The major effects that the position of a proposed weld will have are on the the types of
metal transfer used and the groove angles.
The short-circuiting, spray, and pulsed arc
modes may be used in all positions.
Globular and spray transfer using high
current levels are used for welding in the flat
position.
Wider groove angles are often used when
welding in the vertical position. Joints that
are welded in the horizontal position often
have an asymmetrical joint configuration.
This usually consists of a groove angle that
has horizontal lower groove face as shown
in Figure 10-47. The upper groove face is
raised accordingly to allow adequate access
to the root of the joint. The horizontal lower
groove face is used as a shelf to support the
molten weld metal. This joint configuration is
Figure 10-47 — Single bevel joint
less expensive to prepare than symmetrical
in horizontal position.
groove joints for welding in other positions
because only one groove face has to be
beveled. Other joint design differences will occur on many out of position joints when
using the shortcircuiting mode of metal transfer where larger root openings and smaller
root faces are required.
8.3.0 Thickness
The thickness of the base metal has a large influence on the joint preparation required
to produce the best weld joint possible. Gas metal arc welding can be used to weld
metal thicknesses down to .020 in. (.5 mm). This process is suitable for welding fairly
thick metal so there are a wide variety of applicable joint preparations. The most
common groove preparations used on butt joints are the square-, V-, J-, U-, bevel-, and
combination grooves. The square-, J-, bevel-, and combination-groove preparations are
also used on tee joints. The different preparations are employed on different
thicknesses to make it possible to get complete or adequate penetration.
Square-groove welds are used on the thinnest metal thicknesses. The square-groove
joint design is the easiest to prepare and requires the least filler metal. Thicknesses up
to 3/8 in. (9.5 mm) can be welded with full penetration from both sides. This is thicker
than the square-groove joints that can be welded with full penetration by shielded metal
arc welding or gas tungsten arc welding because of the hotter arc produced by this
process. Root openings are used to allow complete penetration through the joint. Many
square-groove welds are made in one pass. A backing strip may be used so the root
can be opened enough to provide better accessibility and ensure adequate penetration.
V-grooves for butt joints and bevel-grooves for tee joints are commonly used for thicker
metal up to about ¾-in. (19.1 mm). These joints are more difficult to prepare and require
more filler metal than square groove welds. The included angle for a V-groove is usually
up to 75°. The wider groove angles are used to provide better accessibility to the root of
the joint. Because of the deeper penetrating characteristics of this process, single-Vgroove or single-bevel-groove welds are often welded with little or no root opening.
Larger root faces and smaller groove angles are often used compared to those
employed for shielded metal arc welding and gas tungsten arc welding. This helps to
NAVEDTRA 14250A
10-79
minimize the amount of distortion and reduce the amount of filler metal required. For
complete penetration welds, root faces usually are close to 1/8-in. (3.2 mm).
U- and J-grooves are generally used on thicknesses greater than 5/8-in. (14.3 mm).
These joint preparations are the most difficult and expensive to prepare, but the radius
at the root of the joint allows better access to the root of the joint. Another advantage is
that smaller groove angles may be used compared to those used in V-grooves. On
thicker metal, this reduces the amount of filler metal required and on very thick metals,
this savings becomes very substantial.
8.4.0 Accessibility
The accessibility of the weld joint is another important factor in determining the weld
joint design. Welds can be made from either one side or both sides of the joint. SingleV-, J-, U-, bevel-, and combination grooves are used when accessibility is from one side
only and on thinner metal. Double-V -, J-, U-, bevel-, and combination grooves are used
on thicker metal where the joint can be welded from both sides. Double-groove welds
have three major advantages over single-groove welds where accessibility is only from
one side. The first is that distortion is more easily controlled through alternate weld bead
sequencing. Weld beads are alternated from one side to the other to keep the distortion
from building up in the one direction. The roots are nearer the center of the plate. A
second advantage is that less filler metal is required to fill a double-groove joint than a
single-groove joint. The third advantage is that complete penetration can be more easily
ensured. The root of the first pass on the plate can be gouged or chipped out before the
root pass on the second side is welded to make sure there is complete fusion at the
root. The disadvantages of joints welded from both sides are that more joint preparation
is required and gouging or chipping is usually required to remove the root of the first
pass. Both of these add to the labor time required. Welding on both sides of a squaregroove weld joint provides fuller penetration in thicker metal than metal welded from one
side only. This would also save joint preparation time.
8.4.1 Backing Strips
When backing strips are used, joints are accessible from one side only. Backing strips
allow better access to the root of the joint and support the molten weld metal. These
strips are available in two forms, fusible or non-fusible. Fusible backing strips are made
of the metal being welded and remain part of the weldment after welding. These may be
cut or machined off. Non-fusible backing strips are made of copper, carbon, flux, or
ceramic backing in tape or composite form. These forms of backing do not become part
of the weld. Backing strips on square-groove joints make a full penetration weld from
one side easier. For this application, using a backing is more expensive because of the
cost of a backing strip and the larger amount of filler metal required. This is not always
the case. On V-groove joints, the backing strip allows wider root openings and removes
the need for a root face, which reduces the groove preparation costs. Another
advantage is that because the root may be opened up, the groove angle may be
reduced, which will reduce the amount of filler metal required in thicker metal. These
effects are shown in Figure 10-48 where single V-groove joints are shown with and
without a backing strip.
NAVEDTRA 14250A
10-80
Figure 10-48 — Single V-groove joints with and without backing strips.
8.5.0 Types of Metal
The type of metal being welded is another factor that affects the joint design for gas
metal arc welding. For example, aluminum has a high thermal conductivity and low
melting point. Stainless steel has a lower thermal conductivity and a higher melting
point. The maximum thickness that a square groove joint design may be used in
aluminum is slightly less than that for stainless steel because the heat leaves the
welding area quicker, which does not allow the weld puddle to melt as deeply. Another
example is in nickel, where a larger root opening is used because the weld puddle is not
very fluid. The larger root opening is required to allow proper manipulation of the
electrode to get adequate fusion.
8.6.0 Weld Joint Designs
The weld joint designs in the rest of the chapter are those typically used for GMAW. The
exact dimensions of the joint design used will vary depending on the mode of metal
transfer being used. Some of the joint designs may not be acceptable when using the
short circuiting mode of metal transfer. For many of the root opening dimensions and
some of the root face dimensions, ranges are given to account for varying fitup or for
different modes of metal transfer.
Several joint designs using backing strips are included. The thicknesses given are those
typically used with the joint design. For different thickness of base metals, Table 10-19
shows the minimum effective throat thicknesses for partial penetration groove welds.
Figure 10-49 through 10-59 shows the American Welding Society "Standard Welding
Symbols," some of which have been used in the weld joint designs.
NAVEDTRA 14250A
10-81
Table 10-19 — Effective Throat Thickness for Partial Joint Penetration Groove
Welds.
Base Metal Thickness of Thicker Part Joined
Inch
(mm)
Minimum Effective Throat
Inch
(mm)
To
1/4
6.5
inclusive
1/8
3
Over
1/4 to 1/2
6.4 to 12.7
inclusive
3/16
5
Over
1/2 to 3/4
12.7 to 19.0
inclusive
1/4
6
Over
3/4 to 1 1/2
19.0 to 38.1
inclusive
5/16
8
Over
1 1/2 to 2 1/4
38.1 to 57.1
inclusive
3/8
10
Over
2 1/4 to 6
57.1 to 152
inclusive
1/2
13
Over
6
152
5/8
16
8.6.1 Welding Symbols
AWS welding symbols are the shorthand of welding. They enable the engineer and
draftsman to convey complete welding instructions to the welder on blueprints and
drawings.
Using welding symbols promotes standardization and a common understanding of
design intent. It also eliminates unnecessary details on drawings and mistakes caused
by lack of information or misunderstanding.
NAVEDTRA 14250A
10-82
NAVEDTRA 14250A
Figure 10-49 — Welding symbols.
10-83
NAVEDTRA 14250A
Figure 10-50 — Welding symbols (cont.).
10-84
NAVEDTRA 14250A
Figure 10-51 — Welding symbols (cont.).
10-85
NAVEDTRA 14250A
Figure 10-52 — Welding symbols (cont.).
10-86
NAVEDTRA 14250A
Figure 10-53 — Welding symbols (cont.).
10-87
NAVEDTRA 14250A
Figure 10-54 — Welding symbols (cont.).
10-88
Figure 10-55 — Welding symbols (cont.).
NAVEDTRA 14250A
10-89
Figure 8-57 — Specification of location and extent of fillet welds.
NAVEDTRA 14250A
Figure 10-56 — Welding symbols (cont.).
10-90
NAVEDTRA 14250A
Figure 10-57 — Welding symbols (cont.).
10-91
NAVEDTRA 14250A
Figure 10-58 — Welding symbols (cont.).
10-92
NAVEDTRA 14250A
Figure 10-59 — Welding symbols (cont.).
10-93
8.7.0 Welding Positions
In GMAW, the proper position of the welding torch and weldment are important. The
position of the torch in relation to the plate is called the work and travel angle. Work and
travel angles are shown in Figure 10-60. If the parts are equal in thickness, the work
angle should normally be on the center line of the joint; however, if the pieces are
unequal in thickness, the torch should angle toward the thicker piece.
Figure 10-60 — Travel angle and work angle for GMAW.
The travel angle refers to the angle in which welding takes place. This angle should be
between 5 and 25 degrees. The travel angle may be either a push angle or a drag
angle, depending on the position of the torch.
When the torch is angled ahead of the
weld, it is known as pulling (dragging) the
weld or backhand welding. When the torch
is angled behind (over) the weld, it is
referred to as pushing the metal or
forehand welding (Figure 10-61).
The pulling or drag technique is for heavygauge metals. Usually the drag technique
produces greater penetration than the
pushing technique. Also, since the welder
can see the weld crater more easily, better
quality welds can consistently be made.
The pushing technique is normally used for
light-gauge metals. Welds made with this
technique are less penetrating and wider
because the welding speed is faster.
For the best results, you should position the
Figure 10-61 — Pulling and
weldment in the flat position. This position
pushing travel angle techniques.
improves the molten metal flow and bead
contour, and gives better shielding gas protection.
NAVEDTRA 14250A
10-94
Figure 10-62 — Multi-pass welding.
After you have learned to weld in the flat position, you should be able to use your
acquired skill and knowledge to weld out-of-position. These positions include horizontal,
vertical-up, vertical-down, and overhead welds. The only difference in welding out-ofposition from the flat position is a 10% reduction in amperage.
When welding heavier thicknesses of metal with GMAW, you should use the multi-pass
technique (buildup sequence discussed in Chapter 3, Introduction to Welding). This is
accomplished by overlapping single, small beads or making larger beads, using the
weaving technique. Various multi-pass welding sequences are shown in Figure 10-62.
The numbers refer to the sequences in which you make the passes
8.7.1 Flat-Position Welding
Welding can be done in any position, but it is much simpler when done in the flat
position. In this position, the work is less tiring, welding speed is faster, the molten
puddle is not as likely to run, and better penetration can be achieved. Whenever
possible, try to position the work so you can weld in the flat position. In the flat position,
the face of the weld is approximately horizontal.
Butt joints are the primary type of joints used in the flat position of welding; however,
flat-position welding can be made on just about any type of joint providing you can
rotate the section you are welding to the appropriate position. Techniques that are
useful in making butt joints in the flat position, with and without the use of backing strips,
are described below.
Butt joints without backing strips — A butt joint is used to join two plates having surfaces
in about the same plane. Several forms of butt joints are shown in Figure 10-63.
NAVEDTRA 14250A
10-95
Plates up to 1/8 in. thick can be welded in one pass with no special edge preparation.
Plates from 1/8 to 3/16 in. thick also can be welded with no special edge preparation by
welding on both sides of the joint. Tack welds should be used to keep the plates aligned
for welding. The gun motion is the same as that used in making a bead weld.
Figure 10-63 — Butt joints in the flat position.
In welding 1/4-in.plate or heavier, you should prepare the edges of the plates by
beveling or by J-, U-, or V-grooving, whichever is the most applicable. You should use
single or double bevels or grooves when the specifications and/or the plate thickness
require it. The first bead is deposited to seal the space between the two plates and to
Figure 10-64 — Butt welds with multi-pass beads.
NAVEDTRA 14250A
10-96
weld the root of the joint. This
bead or layer of weld metal must
be thoroughly cleaned to remove
all slag and dirt before the second
layer of metal is deposited.
In making multi-pass welds,the
second, third, and fourth layers of
weld metal are made with a
weaving motion of the gun, as
shown in Figure 10-64. Clean
each layer of metal before laying
additional beads. You may use
one of the weaving motions
shown in Figure 10-65, depending
upon the type of joint.
Figure 10-65 — Weave motions.
In the weaving motion, oscillate or
move the gun uniformly from side
to side, with a slight hesitation at
the end of each oscillation. Incline
the gun 5 to 15 degrees in the
direction of welding as in bead
welding. When the weaving
motion is not done properly, undercutting can
occur at the joint, as shown in Figure 10-66.
Excessive welding speed also can cause
undercutting and poor fusion at the edges of the
weld bead.
Figure 10-66 — Undercutting in
butt joint welds.
Figure 10-67 — Use of back strips in welding
butt joints.
NAVEDTRA 14250A
Butt joints with backing strips —
Welding 3/16-in. plate or thicker
requires backing strips to ensure
complete fusion in the weld root
pass and to provide better control
of the arc and the weld metal.
Prepare the edges of the plates in
the same manner as required for
welding without backing strips.
10-97
For plates up to 3/8 in. thick, the backing strips should be approximately 1 in. wide and
3/16 in. thick. For plates more than ½ in. thick, the backing strips should be 1 1/2 in.
wide and ¼ in. thick Tack weld the backing strip to the base of the joint, as shown in
Figure 10-67. The backing strip acts as a cushion for the root pass. Complete the joint
by welding additional layers of metal. After you complete the joint, the backing strip may
be “washed” off or cut away with a cutting torch. When specified, place a seal bead
along the root of the joint.
Bear in mind that many times it will not always be possible to use a backing strip;
therefore, the welder must be able to run the root pass and get good penetration without
the formation of icicles.
8.7.2 Horizontal-Position Welding
You will discover that it is impossible to weld all pieces in the flat position. Often the
work must be done in the horizontal position. The horizontal position has two basic
forms, depending upon whether it is used with a groove weld or a fillet weld. In a groove
weld, the axis of the weld lies in a relative horizontal plane and the face of the weld is in
a vertical plane (Figure 10-68). In a fillet weld, the welding is performed on the upper
side of a relatively horizontal surface and against an approximately vertical plane
(Figure 10-69).
Figure 10-68 — Horizontal groove
weld.
Figure 10-69 — Horizontal fillet
weld.
Inexperienced welders usually find the horizontal position of arc welding difficult, at least
until they develop a fair degree of skill in applying the proper technique. The primary
difficulty is that in this position you have no “shoulder” of previously deposited weld
metal to hold the molten metal.
NAVEDTRA 14250A
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Gun Movement
In horizontal welding, position the gun so
points upward at a 5- to 10-degree angle in
conjunction with a 20-degree travel angle
(Figure 10-70). Use a narrow weaving
motion in laying the bead. This weaving
motion distributes the heat evenly, reducing
the tendency of the molten puddle to sag.
You should use the shortest arc length
possible, and when the force of the arc
undercuts the plate at the top of the bead,
lower the gun a little to increase the upward
angle.
As you move in and out of the crater, pause
slightly each time you return. This keeps the
crater small and the bead has fewer
tendencies to sag.
Joint Type
Figure 10-70 — Horizontal
welding angles.
Horizontal-position welding can be used on
most types of joints; the most common are tee, lap j, and butt joints.
Tee joints — When you make tee joints in the horizontal position, the two plates are at
right angles to each other in the form of an inverted T. The edge of the vertical plate
may be tack welded to the surface of the horizontal plate, as shown in Figure 10-71.
A fillet weld is used in making the tee joint, and a short arc is necessary to provide good
fusion at the root and along the legs of the weld (Figure 10-72, View A). Hold the gun at
an angle of 45 degrees to the two plate surfaces (Figure 10-72, View B) with an incline
of approximately 15 degrees in the direction of welding.
Figure 10-71 — Tack weld to hold
the tee joint elements in place.
Figure 10-72 — Position of
electrode on a fillet weld.
When practical, weld light plates with a fillet weld in one pass with little or no weaving of
the gun. Welding of heavier plates may require two or more passes in which the second
NAVEDTRA 14250A
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pass or layer is made with a semicircular weaving motion, as shown in Figure 10-73. To
ensure good fusion and to prevent undercutting, you should make a slight pause at the
end of each weave or oscillation.
For fillet-welded tee joints on 1/2-in. plate or heavier, deposit stringer beads in the
sequence shown in Figure 10-74.
Figure 10-73 — Weave motion for
multipass fillet weld.
Figure 10-74 — Order of string
beads for tee joint on heavy.
Chain-intermittent or staggeredintermittent fillet welds are used on long tee joints (Figure 10-75). Fillet welds of these
types are for joints where high weld strength is not required; however, the short welds
are arranged so the finished joint is equal in strength to that of a joint that has a fillet
weld along the entire length of one side. Intermittent welds also have the advantage of
reduced warpage and distortion.
Lap joints — When you make a lap joint, two overlapping plates are tack welded in
place (Figure 10-76), and a fillet weld is deposited along the joint.
Figure 10-75 — Intermittent fillet
welds.
NAVEDTRA 14250A
Figure 10-76 — Tack welding a
lap joint.
10-100
The procedure for making this fillet weld is
similar to that used for making fillet welds in
tee joints. You should hold the gun so it
forms an angle of about 30 degrees from
the vertical and is inclined 15 degrees in the
direction of welding. The position of the gun
in relation to the plates is shown in Figure
10-77. The weaving motion is the same as
that used for tee joints, except that the
pause at the edge of the top plate is long
enough to ensure good fusion without
undercutting. Lap joints on 1/2-in. plate or
heavier are made by depositing a sequence
of stringer beads, as shown in Figure 10-77
Figure 10-77 — Position of
electrode on a lap joint.
In making lap joints on plates of different
thickness, you should hold the gun so that it
forms an angle of between 20 and 30
degrees from the vertical (Figure 10-78). Be
careful not to overheat or undercut the
thinner plate edge.
Figure 10-78 — Lap joints on
plates of different thickness.
Butt joints— Most butt joints designed for
horizontal welding have the beveled plate
positioned on the top. The plate that is not
beveled is on the bottom, and the flat edge of
this plate provides a shelf for the molten
metal so it does not run out of the joint
(Figure 10-79). On other joint designs, both
edges are beveled to form a 60-degree
included angle. When this type of joint is
used, more skill is required because you
do not have the retaining shelf to hold
the molten puddle.
The number of passes required for a
joint depends on the diameter of the gun
and the thickness of the metal. When
multiple passes are required (Figure 1080), place the first bead deep in the root
of the joint. The gun should be inclined
about 5 degrees downward. Clean and
remove all slag before applying each
following bead. The second bead should
be placed with the gun held about 10
degrees upward. For the third pass, hold
the gun 10 to 15 degrees downward from
the horizontal. Use a slight weaving
NAVEDTRA 14250A
Figure 10-79 — Horizontal butt
joint.
10-101
motion and ensure that each bead penetrates the base metal.
Figure 10-80 — Multiple passes.
8.7.3 Vertical-Position Welding
A vertical weld is a weld that is applied to a vertical surface or one that is inclined 45
degrees or less (Figure 10-81). Erecting structures, such as buildings, pontoons, tanks,
and pipelines, require welding in this
position. Welding on a vertical surface is
much more difficult than welding in the flat or
horizontal position due to the force of
gravity; gravity pulls the molten metal down.
Vertical welding is done in either an upward
or downward position. The terms used for
the direction of welding are vertical up or
vertical down. Vertical down welding is
suited for welding light gauge metal because
the penetration is shallow and diminishes
the possibility of burning through the metal.
Furthermore, vertical down welding is faster,
which is very important in production work.
Current Settings and Gun Movement
In vertical arc welding, the current settings
Figure 10-81 — Vertical weld
should be less than those used for the same
plate positions.
gun in the flat position. Another difference is
that the current used for welding upward on
a vertical plate is slightly higher than the current used for welding downward on the
same plate.
To produce good welds, you must maintain the proper angle between the gun and the
base metal. In welding upward, you should hold the gun at 90 degrees to the vertical
(Figure 10-82, View A). When weaving is necessary, oscillate the gun as shown in
Figure 10-82, View B.
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10-102
In vertical down welding, incline the outer end of the gun downward about 15 degrees
from the horizontal while keeping the arc pointing upward toward the deposited molten
metal (Figure 10-82, View C). When vertical down welding requires a weave bead, you
should oscillate the gun as shown in Figure 10-82, View D.
Vertical welding is used on most types of joints. The types of joints you will most often
use it on are tee joints, lap joints, and butt joints.
Figure 10-82 — Bead welds in the vertical position.
Hold the gun at 90 degrees to the plates or not more than 15 degrees off the horizontal
for proper molten metal control when making fillet welds in either tee or lap joints in the
vertical position. Keep the arc short to obtain good fusion and penetration.
Tee joints — To weld tee joints in the vertical position, start the joint at the bottom and
weld upward. Move the gun in a triangular weaving motion as shown in Figure 10-83,
View A. A slight pause in the weave at the points indicated improves the sidewall
penetration and provides good fusion at the root of the joint.
When the weld metal overheats, you should quickly shift the gun away from the crater
without breaking the arc, as shown in Figure 10-83, View B. This permits the molten
metal to solidify without running downward. Return the gun immediately to the crater of
the weld in order to maintain the desired size of the weld.
When more than one pass is necessary to make a tee weld, you may use either of the
weaving motions shown in Figure 10-83, Views C and D. A slight pause at the end of
the weave will ensure fusion without undercutting the edges of the plates.
NAVEDTRA 14250A
10-103
Lap joints — To make welds on lap joints in the vertical position, you should move the
gun in a triangular weaving motion, as shown in Figure 10-83, View E). Use the same
procedure, as outlined above for the tee joint, except direct the gun more toward the
vertical plate marked G. Hold the arc short, and pause slightly at the surface of plate G.
Try not to undercut either of the plates or to allow the molten metal to overlap at the
edges of the weave.
Figure 10-83 — Fillet welds in the vertical position.
Lap joints on heavier plate may require more
than one bead. If it does, clean the initial bead
thoroughly and place all subsequent beads as
shown in Figure 10-83, View F. The
precautions to ensure good fusion and uniform
weld deposits that were previously outlined for
tee joints also apply to lap joints.
Butt joints — Prepare the plates used in
vertical welding identically to those prepared
for welding in the flat position. To obtain good
fusion and penetration with no undercutting,
you should hold a short arc and carefully
control its motion.
Butt joints on beveled plates ¼ in. thick can be
welded in one pass by using a triangular
NAVEDTRA 14250A
Figure 10-84 — Butt joint welding
in the vertical position. 10-104
weave motion, as shown in Figure 10-84, View A.
Welds made on 1/2-in. plate or heavier should be done in several passes, as shown in
Figure 10-84, View B. Deposit the last pass with a semicircular weaving motion with a
slight “whip-up” and pause of the gun at the edge of the bead. This produces a good
cover pass with no undercutting. Welds made on plates with a backup strip should be
done in the same manner.
8.7.4 Overhead-Position Welding
Overhead welding is the most difficult position in welding. Not only do you have to
contend with the force of gravity, but the majority of the time you also have to assume
an awkward stance. Nevertheless, with practice it is possible to make welds equal to
those made in the other positions.
Current Settings and Gun Movement
To retain complete control of the molten puddle, use a very short arc and reduce the
amperage as recommended. As in the vertical position of welding, gravity causes the
molten metal to drop or sag from the plate. When too long an arc is held, the transfer of
metal from the gun to the base metal becomes increasingly difficult, increasing the
chances of large globules of molten metal dropping from the gun. When you routinely
shorten and lengthen the arc, dropping molten metal can be prevented; however, you
will defeat your purpose should you carry too large a pool of molten metal in the weld.
One of the problems encountered in overhead welding is the weight of the cable. To
reduce arm and wrist fatigue, drape the cable over your shoulder when welding in the
standing position. When sitting, place the cable over your knee. With experience, cable
placement will become second nature.
WARNING
Because of the possibility of falling molten metal, use a protective garment that
has a tight fitting collar that
buttons or zips up to the neck.
Roll down your sleeves and
wear a cap and appropriate
shoes.
Type of Welds
Techniques used in making bead
welds, butt joints, and fillet welds
in the overhead position are
discussed in the following
paragraphs.
Bead welds — For bead welds,
the work angle of the gun is 90
degrees to the base metal
(Figure 10-85, View A). The
travel angle should be 10 to 15
degrees in the direction of
welding (Figure 10-85, View B).
Weave beads can be made by
using the motion shown in Figure
10-85, View C. A rather rapid
NAVEDTRA 14250A
Figure 10-85 — Position of electrode and
weave motion in the overhead position.
10-105
motion is necessary at the end of each semicircular weave to control the molten metal
deposit. Avoid excessive weaving because this can cause overheating of the weld
deposit and the formation of a large, uncontrollable pool.
Butt Joint — Prepare the plates
for overhead butt welding in the
same manner as required for the
flat position. The best results are
obtained when backing strips are
used; however, you must
remember that you will not
always be able to use a backing
strip. When you bevel the plates
with a featheredge and do not
use a backing strip, the weld will
repeatedly burn through unless
you take extreme care.
For overhead butt welding, bead
welds are preferred over weave
welds. Clean each bead and chip
out the rough areas before
placing the next pass. The gun
position and the order of
deposition of the weld beads
when welding on 1/4- or 1/2-in.
Figure 10-86 — Multi-pass butt joint in the
plate are shown in Figure 10-86,
overhead position.
Views B and C. Make the first
pass with the gun held at 90 degrees to the plate, as shown in Figure 10-86, View A.
When you use a gun that is too large, you cannot hold a short arc in the root area. This
results in insufficient root penetration and inferior joints.
Fillet welds — In making fillet welds in either tee or lap joints in the overhead position,
maintain a short arc and refrain from weaving the gun. Hold the gun at approximately 30
degrees to the vertical plate and move it uniformly in the direction of welding, as shown
in Figure 10-87, View B. Control the arc motion to secure good penetration in the root of
the weld and good fusion with the sidewalls of the vertical and horizontal plates. When
the molten metal becomes too fluid and tends to sag, whip the gun quickly away from
the crater and ahead of the weld to lengthen the arc and allow the metal to solidify.
Immediately return the gun to the crater and continue welding.
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10-106
Overhead fillet welds for either tee or lap joints on heavy plate require several passes or
beads to complete the joint. One example of an order of bead deposition is shown in
Figure 10-87, View A. The root pass is a string bead made with no weaving motion of
the gun. Tilt the gun about 15 degrees in the direction of welding, as shown in Figure
10-87, View C, and with a slight circular motion make the second, third, and fourth pass.
Figure 10-87 — Fillet welds in the overhead position.
This motion of the gun permits greater control and better distribution of the weld metal.
Remove all slag and oxides from the surface of each pass by chipping or wire brushing
before applying additional beads to the joint.
Welding is the simplest and easiest way to join sections of pipe. The need for
complicated joint designs and special threading equipment is eliminated. Welded pipe
has less flow restriction when compared to mechanical connections and the overall
installation costs are less. The most popular method for welding pipe is the shielded
metal arc process; however, gas shielded arc methods (GMAW, GTAW) have made big
inroads as a result of new advances in welding technology.
NAVEDTRA 14250A
10-107
Pipe welding has become recognized as a profession in itself. Even though many of the
skills are comparable to other types of welding, pipe welders develop skills that are
unique only to pipe welding. Because of the hazardous materials that most pipelines
carry, pipe welders are required to pass specific tests before they can be certified
In the following paragraphs, pipe
welding positions, pipe welding
procedures, definitions, and
related information are discussed.
You may recall from Figure 10-46,
there are four positions used in
pipe welding. The American
Welding Society’s (AWS) welding
positions for pipe are the
horizontal rolled position (1G), the
horizontal fixed position (5G), the
pipe inclined fixed (6G), and the
vertical position (2G). Remember,
these terms refer to the position of
the pipe and not to the weld
Pipe Welding Procedures
Welds you cannot make in a
single pass should be made in
interlocked multiple layers, not
less than one layer for each 1/8
Figure 10-88 — Butt joints and socket fitting
inch of pipe thickness. Deposit
joints.
each layer with a weaving or
oscillating motion. To prevent
entrapping slag in the weld metal, you should clean each layer thoroughly before
depositing the next layer.
Butt joints are commonly used
between pipes and between pipes
and welded fittings. They are also
used for butt welding flanges and
welding stubs. In making a butt
joint, place two pieces of pipe end
to end, align them, and then weld
them. (Figure 10-88)
When the wall thickness of the
pipe is ¾ in. or less, you can use
either the single V or single U
type of butt joint; however, when
the wall thickness is more than ¾
in., only the single U type should
be used.
Fillet welds are used for welding
slip-on and threaded flanges to
pipe. Depending on the flange
and type of service, fillet welds
may be required on both sides of
NAVEDTRA 14250A
Figure 10-89 — Flange connections.10-108
the flange or in combination with a bevel weld (Figure 10-89). Fillet welds are also used
in welding screw or socket couplings to pipe, using a single fillet weld (Figure 10-87).
Sometimes flanges require alignment. Figure 10-90 shows one type of flange square
and its use in vertical and horizontal
alignment.
Another form of fillet weld used in pipe fitting
is a seal weld. A seal weld is used primarily
to obtain tightness and prevent leakage.
Seal welds should not be considered as
adding strength to the joint.
Joint Preparation and Fitup
You must carefully prepare pipe joints for
welding if you want good results. Clean the
weld edges or surfaces of all loose scale,
slag, rust, paint, oil, and other foreign matter.
Ensure that the joint surfaces are smooth
and uniform. Remove the slag from flamecut edges; however, it is not necessary to
remove the temper color.
When you prepare joints for welding,
Figure 10-90 — Flange alignment.
remember that bevels must be cut
accurately. Bevels can be made by
machining, grinding, or using a gas cutting
torch. In fieldwork, the welding operator usually must make the bevel cuts with a gas
torch. When you are beveling, cut away as little metal as possible to allow for complete
fusion and penetration. Proper beveling reduces the amount of filler metal required,
which in turn reduces time and expense. In addition, it also means less strain in the
weld and a better job of design and welding.
Align the piping before welding and maintain it in alignment during the welding
operation. The maximum alignment
tolerance is 20% of the pipe thickness. To
ensure proper initial alignment, you should
use clamps or jigs as holding devices. A
piece of angle iron makes a good jig for a
small-diameter pipe (Figure 10-91), while a
section of channel or I-beam is more suitable
for larger diameter pipe.
Tack Welding
When welding material solidly, you may use
tack welds to hold it in place temporarily.
Tack welding is one of the most important
steps in pipe welding or any other type of
welding. The number of tack welds required
depends upon the diameter of the pipe. For
1/2-in. pipe, you need two tacks; place them
directly opposite each other. As a rule, four
Figure 10-91 — Angle iron jig.
tacks are adequate for standard size of pipe.
The size of a tack weld is determined by the wall thickness of the pipe. Be sure that a
tack weld is not more than twice the pipe thickness in length or two thirds of the pipe
NAVEDTRA 14250A
10-109
thickness in depth. Tack welds should be the same quality as the final weld. Ensure that
the tack welds have good fusion and are thoroughly cleaned before proceeding with the
weld.
Spacers
In addition to tack welds, spacers sometimes are required to maintain proper joint
alignment. Spacers are accurately machined pieces of metal that conform to the
dimensions of the joint design used. Spacers are sometimes referred to as chill rings or
backing rings, and they serve a number of purposes. For example, they provide a
means for maintaining the specified root opening, provide a convenient location for tack
welds, and aid in the pipe alignment. In addition, spacers can prevent weld spatter and
the formation of slag or icicles inside the pipe.
Weather Conditions
Do not assign a welder to a job under any of the following conditions listed below unless
the welder and the work area are properly protected:
•
•
•
•
When the atmospheric temperature is less than 0°F
When the surfaces are wet
When rain or snow is falling, or moisture is condensing on the weld surfaces
During periods of high wind
Before beginning to weld at temperatures between 0°F and 32°F, heat the weld area
within 3 inches of the joint with a torch to a temperature warm to the hand.
Test your Knowledge (Select the Correct Response)
11.
How many basic types of weld joints are there?
A.
B.
C.
D.
12.
4
5
6
8
Which type of weld is used for welding slip-on and threaded flanges to pipe?
A.
B.
C.
D.
Fillet
Bead
Butt
Tee
9.0.0 WELDING PROCEDURE VARIABLES
Welding procedure variables control the welding process and the quality of the welds
produced. The selection of the welding variables is done after the base metal, filler
metal, and joint design are selected. A proper selection of welding variables will make
the welding easier for the welder, increasing the chances of producing the weld
properties required. The three major types of welding variables are fixed or preselected,
primary adjustable, and secondary adjustable.
The fixed or preselected variables are those that are set before the welding takes place.
These are items such as the electrode size, type of shielding gas, and shielding gas
flow rate. Preselected variables are set according to the type of metal being welded,
NAVEDTRA 14250A
10-110
metal thickness, welding position, deposition rate required, and mechanical properties
required. These are variables that cannot be easily changed once the welding starts.
The primary adjustable variables are the major variables used to control the welding
process after the fixed variables have been selected. They control the formation of the
weld bead by affecting items such as bead width, bead height, depth of penetration, arc
stability, and weld soundness. The primary adjustable variables for gas metal arc
welding are the welding current, welding voltage, and travel speed. These are the best
controls over welding because they are
easily measured and can be continually
adjusted over a wide range.
The secondary adjustable variables are
the minor variables that can be continually
changed and used to control the welding
process. These variables are often more
difficult to measure or the effects of them
may not be as obvious. In many cases,
they do not directly affect the bead
formation, but they may cause a change in
a primary variable, which in turn causes a
change in bead formation. The secondary
variables are items such as the electrode
extension and the travel angles.
The different variables affect the
characteristics of the weld, such as the
Figure 10-92 — Bead height,
penetration of the weld, bead height and
width, and penetration.
bead width, and the deposition rate. The
definitions of bead height, bead width, and
penetration are shown in Figure 10-92. The penetration of the weld is defined as the
greatest depth below the surface of the base metal or previous weld bead that the weld
metal reaches. The bead height is the height of the weld metal above the surface of the
base metal. The bead width is the width of the weld bead. The deposition rate is the
weight of metal that is deposited per unit of time.
The welding variables are discussed with particular attention to the three major
characteristics of penetration, deposition rate, and bead shape. Table 10-20 shows the
effects of welding variables on the three major characteristics.
NAVEDTRA 14250A
10-111
Table 10-20 — Recommended welding variable adjustments for GMAW.
Welding
Variable
Change
Required
Arc Voltage
1
Travel Speed
Stick-out or
Tip to Work
Distance
Trailing
Max. 25°
Wire Size
2
5
Gas Type
Increase
Decrease
4
Smaller
CO2
3
Shallower
Penetration
Bead Width
Nozzle
Angle
3
Deeper
Penetration
Bead Height
Welding
Current (See
footnote)
1
1
Larger Bead
Decrease
Increase
2
Leading
Decrease
2
3
5
Increase
Increase
Larger
4
Ar+CO2 c
2
Smaller Bead
Higher
Narrower Bead
Flatter Wider
Bead
1
1
1
Decrease
Decrease
Slower
Disposition Rate
Increase
Trailing
Max. 25°
2
90° or
Leading
3
3
3
Increase
Faster
Deposition Rate
2
1
1
Increase
Decrease
2
2
Decrease
Increase
Decrease
Increase
Decrease
3
3
Smaller b
Larger b
FOOTNOTE SAME ADJUSTMENT IS REQUIRED FOR WIRE FEED SPEED. KEY 1 FIRST CHOICE, 2 SECOND CHOICE, 3 THIRD CHOICE. 4
FOURTH CHOICE, 5 FIFTH CHOICE.
a WHEN THESE VARIABLES ARE CHANGED, THE WIRE FEED SPEED MUST BE ADJUSTED SO THAT THE WELDING CURRENT REMAINS
CONSTANT.
b SEE DEPOSITION RATE SECTION OF WELDING VARIABLES SECTION.
c THIS CHANGE IS ESPECIALLY HELPFUL ON MATERIALS 20 GAGE AND SMALLER IN THICKNESS.
9.1.0 Fixed Variables
The size of the electrode and the type of shielding gas used are fixed variables.
9.1.1 Electrode Size
Each electrode wire diameter of a given chemical composition has a usable welding
current range. Larger diameter electrodes use higher current levels and produce higher
deposition rates and deeper penetration. The rate at which the electrode melts is a
function of the current density. If two electrode wires of different diameters are operated
at the same current level, the smaller one will give a higher deposition rate because the
heat is more concentrated. Figure 10-93 shows deposition rates produced by different
diameters of electrode wires. The penetration is also a function of the current density. A
smaller electrode wire will produce deeper penetration than a larger diameter wire at the
same current setting. The weld bead will be wider when using the larger electrode wire.
The choice of the size of the electrode wire to be used is dependent on the thickness of
the metal being welded, the amount of penetration required, the deposition rate desired,
the bead profile desired, the position of welding, and the cost of the different electrode
wires. A smaller electrode wire is more costly on a weight basis, but for each application
there is a wire size that will produce minimum welding costs.
NAVEDTRA 14250A
10-112
Figure 10-93 — Deposition rates of different sizes of electrode wires using CO2.
9.1.2 Type of Shielding Gas
The different shielding gases used in gas metal arc welding each have their own
penetration, bead shape, and deposition rate characteristics. The choice of shielding
gas will also have an effect on the amount of smoke, gases, and spatter produced, the
welding speed used, the mechanical properties obtained, and the type of metal transfer.
For welding ferrous metals, carbon dioxide, argon-carbon dioxide, and argon-oxygen
mixtures are used most widely. Carbon dioxide shielding gas produces the highest
electrode burn-off rates, greatest depth of penetration, widest weld bead, and most
convex weld bead for a given current level. Carbon dioxide is the least expensive but
produces the most spatter and smoke. Because of the high heat input, faster travel
speeds may be used. Argon or argon-oxygen mixtures are the opposite of carbon
dioxide. These gases will give the lowest electrode burn-off rates, the least penetration,
and the narrowest, flattest weld bead for a given current level. Argon or argon-oxygen
mixtures produce the least amount of smoke and spatter. Argon-carbon dioxide
mixtures have characteristics in between carbon dioxide and argon-oxygen mixtures.
Figure 10-94 shows the bead profile and penetration characteristics of carbon dioxide,
argon-carbon dioxide mixtures, and argon-oxygen mixtures.
NAVEDTRA 14250A
10-113
For welding the non-ferrous
metals, the most commonly
used shielding gases are argon,
argon helium mixtures, and
helium. Argon produces the
least amount of penetration and
lowest electrode burn-off rates.
It also produces the narrowest
and flattest weld bead. Argon is
the least expensive of the three
types and produces the least
spatter. Helium produces the
most penetration, higher
electrode burn-off rates, and the
widest and most convex weld
bead. Helium causes higher
voltages for a given arc length,
is more expensive, and requires
higher flow rates than argon.
Argon-helium mixtures have
characteristics between argon
and helium. Figure 10-94 also
shows the weld bead profile
characteristics of argon, argonhelium mixtures, and helium.
Figure 10-94 — Weld bead profile and
penetration characteristics of different
shielding gases.
9.2.0 Primary Variables
As with any other type of welding, the GMAW procedure consists of certain variables
that you must understand and follow. Many of the variables have already been
discussed. This section applies some of these variables to the actual welding
procedure.
9.2.1 Starting the Arc
For a good arc start, the electrode must
make good electrical contact with the
work. For the best results, you should
clean the metal of all impurities. The wire
stick-out must be set correctly because as
the wire stick-out increases, the arc
initiation becomes increasingly difficult
(Figure 10-95).
Figure 10-95 — Electrode stickout.
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10-114
When preparing to start the arc, hold the torch at an angle between 5 and 20 degrees.
Support the weight of the welding cable and gas hose across your shoulder to ensure
free movement of the welding torch. Hold the torch close to, but not touching, the
workpiece. Lower your helmet and squeeze the torch trigger. Squeezing the trigger
starts the flow of shielding gas and energizes the welding circuit. The wire-feed motor
does not energize until the wire electrode comes in contact with the work-piece. Move
the torch toward the work, touching the wire electrode to the work with a sideways
scratching motion (Figure 10-96). To prevent sticking, you should pull the torch back
quickly, about 1/2 inch, the instant contact is
made between the wire electrode and the
workpiece. The arc strikes as soon as
contact is made, and the wire-feed motor
feeds the wire automatically as long as you
hold the trigger.
A properly established arc has a soft,
sizzling sound. Adjustment of the wire-feed
control dial or the welding machine itself is
necessary when the arc does not sound
right. For example, a loud crackling sound
indicates that the arc is too short and that
the wire-feed speed is too fast. You may
correct this problem by moving the wire-feed
dial slightly counterclockwise. This
decreases the wire-feed speed and
Figure 10-96 — Arc strike.
increases the arc length. A clockwise
movement of the dial has the opposite
effect. With experience, you can recognize
the sound of the proper length of arc to use
(Figure 10-97).
To break the arc, you simply release the
trigger. This breaks the welding circuit and
de-energizes the wire-feed motor. Should
the wire electrode stick to the work when
striking the arc or during welding, release
the trigger and clip the wire with a pair of
side cutters.
Figure 10-97 — Following the arc.
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9.2.2 Welding Current
The amount of welding current used has the greatest effect on the deposition rate, the
weld bead size and shape, and the penetration of the weld. In a constant voltage
system, the welding current is controlled by the knob on the wire feeder control, which
controls the wire feed speed. As the wire feed speed is increased, the welding current
increases. In a constant current system, the welding current is set by a knob on the front
of the welding machine. As shown earlier in Figure 10-93, the deposition rate of the
process increases as the welding current increases. The lower part of the curve is flatter
than the upper part because at higher current levels, the melting rate of the electrode
increases at a faster rate as the current increases. This can be attributed to resistance
heating of the electrode extension beyond the contact tube. When all of the other
welding variables are held constant, increasing the welding current will increase the
depth and width of the weld penetration and the size of the weld bead. Figure 10-98
shows the effects of varying the welding current. An excessive current level will create a
large, deep penetrating weld bead, which wastes filler metal and can burn through the
bottom of the joint. An excessively low welding current produces insufficient penetration
and buildup of weld metal on the surface.
Figure 10-98 — Effect of welding current on bead.
9.2.3 Welding Voltage (Arc Length)
The welding voltage or arc voltage is determined by the distance between the tip of the
electrode and the work. In a constant voltage system, the welding voltage is adjusted by
a knob on the front of the power source because the machine maintains a given
voltage, which maintains a certain arc length. In a constant current system, the welding
voltage is controlled by the arc length held by the welder and the voltage sensing wire
feeder. The arc voltage required for an application is dependent on the electrode size,
type of shielding gas, position of welding, type of joint, and base metal thickness. There
is no set arc length that will consistently give the same weld bead characteristics. For
example, normal arc voltages in carbon dioxide and helium are much higher than those
obtained in argon. When the other variables are held constant and the arc voltage is
increased, the weld bead becomes flatter and wider. The penetration will increase up to
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an optimum voltage level and then begin to decrease, as shown in Figure 10-99. A
higher voltage is often used to bridge a gap because of the decreased penetration
obtained. An excessively high arc voltage causes excessive spatter, porosity, and
undercutting. A decrease in the arc length produces a narrower weld bead with a
greater convexity and, down to the optimum voltage level, deeper penetration. An
excessively low arc voltage may cause porosity and overlapping at the edges of the
weld bead. Figures 10-100 and 10-101 show the effects of welding voltage on the bead
height and bead width respectively. Figure 10-102 shows the effects of varying the arc
length on the weld profile.
Figure 10-99 — Effect of travel
speed, arc volts, and welding
current on penetration.
Figure 10-100 — Effect of travel
speed, arc volts, and welding
current on bead height.
Figure 10-101 — Effect of travel
speed, arc volts, and welding
current on bead width.
NAVEDTRA 14250A
10-117
Figure 10-102 — Effect of arc voltage on bead and bead formation.
9.2.4 Travel Speed
The travel speed is the rate at which the arc travels along the workpiece.The travel
speed is controlled by the welder in semiautomatic welding. In machine and automatic
welding it is controlled by the machine. As shown in Figure 10-99, the penetration is
Figure 10-103 — Effect of travel speed on bead.
maximum at a certain travel speed. Increasing or decreasing the travel speed from this
point will reduce the amount of penetration. When the travel speed is decreased, the
amount of filler metal deposited per unit length increases, which creates a large, shallow
weld puddle. Weld metal tends to get slightly ahead of the arc, which reduces the
amount of penetration and produces a wide weld bead. Reducing the travel speed will
increase the bead height, as shown in Figure 10-100. An excessively slow travel speed
NAVEDTRA 14250A
10-118
can cause excessive piling up of the weld puddle overlapping at the edges, and
excessive heat input to the plate, which creates a larger heat affected zone. As the
travel speed is increased, the heat transmitted to the base metal is reduced, which
reduces the melting of the base metal and limits the amount of penetration. The bead
width and bead height are also decreased, as shown in Figures 10-100 and 10-101. An
excessive travel speed will tend to cause undercutting along the edges of the weld bead
because there is not enough filler metal to fill the groove melted by the arc. Figure 10103 shows the effects on the size and shape of the weld bead of different travel speeds.
9.3.0 Secondary Variables
Secondary variables include electrode
extension and angle.
9.3.1 Electrode Extension
The electrode extension, sometimes
referred to as stick-out, is the distance
between the tip of the contact tube and the
tip of the electrode (Figure 10-104). As this
distance is increased, the electrical
resistance of the electrode increases, which
increases the preheating on the electrode.
Because of this, less welding current is
required to melt the electrode at a given
wire feed rate. This is shown in Figure 10105. The measurements are made from the
tip of the contact tube to the surface of the
work using a constant welding voltage or
Figure 10-104 — Electrode.
arc length. This distance is usually used
extension.
because it is easier to measure than the
actual electrode extension. Increasing the
electrode extension will reduce the amount
of penetration (Figure 10-106). An excessively long electrode extension results in an
excess of weld metal being deposited at low heat. This produces a poor weld bead
Figure 10-105 — Effect of
electrode extension current.
NAVEDTRA 14250A
Figure 10-106 — Effect of
electrode extension on
penetration.
10-119
shape and shallow penetration. As the
contact tube-to-work distance increases, the
arc has a tendency to become less stable. A
longer electrode extension will also produce
a higher deposition rate, as shown in Figure
10-107. Typical electrode extensions range
from 1/4-1/2 in. (12.7-25.4 mm) for the other
types of metal transfer. The electrode
extension is often used to make adjustments
of the characteristics of the weld bead to
compensate for changes over a short length
of the weld, such as an area where the root
opening of the joint is excessively large or
small. If the penetration needed is to be
reduced to compensate for a large root
opening, the welder could increase the stickout, which reduces the welding current and
penetration in this area.
9.3.2 Electrode Angles
Figure 10-107 — Effect of
electrode extension on
deposition rate.
The position of the welding electrode with
respect to the weld joint affects the shape of the weld bead and the amount of
penetration. The electrode angles are called the travel and work angles. The travel
angle of the electrode is the angle between the joint and electrode in the longitudinal
plane. A push angle exists when the electrode points in the direction of travel (forehand
welding) and a drag angle exists when the electrode points in the direction opposite to
travel (backhand welding). The work angle is the angle between the electrode and the
plane perpendicular to the direction of travel. The travel and work angles are shown in
Figure 10-108.
The effects on the weld bead with respect to travel angle are shown in Figure 10-109.
When the electrode angle is changed from 90° to a push angle, the amount of
penetration is decreased and the weld bead becomes wider and flatter. When changing
the electrode angle from 90° to a drag angle, the penetration will increase up to a travel
angle of 25° from the vertical where the maximum penetration is obtained. A travel
angle above this will start reducing the penetration and is not recommended because it
greatly increases the chances of overlapping. The drag angle produces a narrower,
more convex weld bead as well as a more stable arc with less spatter. A drag angle is
commonly used on steel; a push angle is used on aluminum to avoid contamination and
give good penetration but minimize the heat input to the base metal. Electrode travel
angles of approximately 5-15° are normally used in all positions for good control of the
molten weld puddle. When making fillet welds, the work angle should be approximately
45° from the plate.
NAVEDTRA 14250A
10-120
Figure 10-108 — Travel angle and work angle.
Figure 10-109 — Effects of travel angle on penetration and bead shape.
NAVEDTRA 14250A
10-121
10.0.0 WELDING PROCEDURE SCHEDULES
The welding procedure schedules in this chapter give typical welding conditions which
can be used to obtain high quality welds under normal welding conditions. Gas metal
arc welding uses a wide variety of operating conditions for welding a wide variety of
base metal types. The procedure schedules presented in this chapter are in no way a
complete guide to the procedures that can be used for GMAW, and are not the only
conditions that may be used to obtain a specific weld. These are not the only conditions
that could be used because factors such as weld appearances, welder skill, method of
application, and the specific application often require variations from the schedules. For
example, automatic GMAW usually employs higher welding currents and faster travel
speeds than semiautomatic welding.
The mode of metal transfer in GMAW has a large effect on the welding conditions. This
is because the different modes of metal transfer are dependent on the welding current
and voltage levels used, as well as the type of shielding gas. For example, the spray
transfer mode requires a higher welding current and often a different shielding gas than
the globular transfer mode. As the particular requirements of the application become
known, the settings may be adjusted to obtain the optimum welding conditions.
Qualifying tests or trials should be made under the actual conditions before using this
process for production welding.
When changing or adjusting the variables for welding, you must consider the effect of
the variables on each other. One variable cannot usually be drastically changed without
adjusting or changing the other variables to obtain a stable arc and good overall welding
conditions.
The following schedules are based on welding specific metals and using a specific
mode of metal transfer and method of application. The welding schedules for steel
include the semiautomatic and automatic methods of application and short-circuiting,
globular, and spray transfer modes of welding. Other base metals such as stainless
steel, aluminum, copper, magnesium, and nickel are also included. The tables use the
base metal thickness or fillet size, number of weld passes, electrode diameter, welding
current (wire feed speed), gas flow rate, and welding travel speed as variables. Each
table contains the type of shielding gas, type of joint, and the position of welding being
used. All of the schedules are based on using direct current electrode positive. Both the
welding current and wire feed speed values are given because even though the welding
current is set by the wire feed speed, it is sometimes more convenient to directly
establish the welding current without exactly knowing the wire feed speed. Figure 10110 shows wire feed speeds and their corresponding welding currents for several sizes
of steel electrode wire. Figure 10-111 shows wire feed speeds and their corresponding
welding currents for several sizes of non-ferrous metal electrode wire. Welding
procedure schedules for gas metal arc spot welding are given at the end of this section.
Many of the tables include welding conditions for both groove and fillet welds given on
the same chart. In general, fillet welds will use the higher current levels for the ranges
given and groove welds will generally use the lower end of the current range. See
Tables 10-21 through 10-33 for specific welding schedules.
NAVEDTRA 14250A
10-122
Figure 10-110 — Wire-feed speed vs. welding current for steel electrodes.
Figure 10-111 — Wire feed speed vs. welding current for several non-ferrous
electrodes.
NAVEDTRA 14250A
10-123
Table 10-21 — Welding procedure schedules for GMAW of plain carbon and
low alloy steels using short circuiting metal transfer.
Thickness
of Base
Metal or
Electrode
Wire Feed
Gas
Flow
Travel
Speed
Rate
Speed
Fillet Size
No. of
Diameter
Welding
Welding
in./min
ft/hr
in./min
in. (mm)
Passes
in. (mm)
Voltage
Current
(mm/s)
(I/min)
(mm/s)
90-130
20 ga (.9)
1
.035 (.9)
15-17
65-85
18 ga ( 1.2)
1
.035 (.9)
17-19
80-100
(38-55)
35-40
20 (9)
(15-17)
20 (9)
(15-17)
120-170
(51-72)
35-40
150-190
1/16" (1.6)
1
.035 (.9)
17-19
90-110
(63-80)
30-35
25 (12)
190-240
3/32" (2.4)
1
.035 (.9)
18-20
110-130
(80-102)
1/8" (3.2)
1
.035 (.9)
19-21
140-160
(118-135)
25-30
25 (12)
250-320
1
045 (1.1)
20-23
180-200
(89-102)
1
.035 (.9)
19-21
140-160
(118-135)
25 (12)
1
.045 (1.1)
20-23
180-200
(89-102)
25 (12)
1
.035 (.9)
19-21
140-160
( 118-135)
25 (12)
NAVEDTRA 14250A
1
.045 (1.1)
20-23
180-200
(118-135)
(7.5-10)
10-15
25 (12)
210-240
1/4" (6.4)
(6-8)
18-23
280-320
1/4" (6.4)
(11-14)
14-19
210-240
3/16" (4.8)
(6-8)
27-32
280-320
3/16" (4.8)
(11-13)
20-25
25 (12)
210-240
1/8" (3.2)
(13-15)
(4-6.5)
12-17
25(12)
(5-7)
10-124
Table 10-22 — Welding procedure schedules for GMAW of plain carbon and
low alloy steels using short circuiting metal transfer.
Fillet
size
in.
(mm)
Passes
in. (mm)
Voltage
Current
3/8
(9.5)
1-2
.035 (.9)
19-21
150-160
1/2
(12.7)
2-3
.035 (.9)
20-22
160-170
3/4
(19.1)
3-4
.035 (.9)
20-22
170-180
No. of
NAVEDTRA 14250A
Electrode
Diameter Welding Welding
Wire
Feed
Speed
in./min.
Gas
Flow
Rate
Ft3/hr.
(mm/s)
290-320
(123135)
320-350
(135148)
350-380
(148161)
(l/min)
(mm/s)
6-7
25 (12)
(2.5-3)
5-6
25 (12)
(2-2.5
4-5
25 (12)
(1.5-2)
Travel
Speed
in./min
10-125
Table 10-23 — Welding procedure schedules for GMAW of plain carbon and
low alloy steels using short circuiting metal transfer.
Fillet
size
in.
(mm)
Passes
in. (mm)
Voltage
Current
3/8 (9.5)
3
.035 (.9)
19-21
150-160
1/2
(12.7)
3
.035 (.9)
20-22
160-170
3/4
(19.1)
6
.035 (.9)
20-22
170-180
No. of
NAVEDTRA 14250A
Electrode
Diameter Welding Welding
Wire
Feed
Speed
in./min.
Gas
Flow
Rate
FT3/hr.
(mm/s)
290-320
(123135)
320-350
(135148)
350-380
(148161)
(l/min)
(mm/s)
11-12
25 (12)
(5-5.5)
7-8
25 (12)
(3-3.5)
6-7
25 (12)
(2.5-3)
Travel
Speed
in./min
10-126
Table 10-24 — Welding procedure schedules for GMAW of plain carbon and
low alloy steels using globular metal transfer.
Thickness
of Base
Metal or
Electrode
Wire Feed
Gas
Flow
Travel
Speed
Rate
Speed
Fillet Size
No. of
Diameter
Welding
Welding
in./min
ft/hr
in./min
in. (mm)
Passes
in. (mm)
Voltage
Current
(mm/s)
(I/min)
(mm/s)
325-375
18 ga ( 1.2)
1
.045 (1.1)
24-26
260-290
(137-159)
16 ga (1.5)
1
.045 (1.1)
26-28
300-340
(169-203)
180-190
25 (12)
400-480
140-150
35 (17)
410-500
14 ga (1.9)
1
.045 (1.1)
27-29
310-350
(173-212)
1
1/16 (1.6)
27-29
360-400
(114-131)
35 (17)
1
045 (1.1)
28-30
330-370
(190-233)
35 (17)
1
1/16 (1.6)
30-32
375-425
(118-135)
1/4" (6.4)
1
1/16 (1.6)
31-33
450-500
(152-178)
35 (17)
35 (17)
(30-34)
35 (17)
(19-23)
45-55
125-150
1
3/32 (2.4)
33-35
550-600
( 53-63)
30-40
35 (17)
150-175
1/2 (12.7)
NAVEDTRA 14250A
1
3/32 (2.4)
35-37
600-650
(63-74)
(38-47)
70-80
360-420
3/8 (9.5)
(32-40)
90-110
280-320
3/16" (4.8)
(42-55)
75-95
450-550
1/8" (3.2)
(59-63)
100-130
270-310
1/8" (3.2)
(76-80)
(13-17)
25-35
35 (17)
(11-15)
10-127
Table 10-25 — Welding procedure schedules for GMAW of plain carbon and
low alloy steels using globular metal transfer.
Thickness
of Base
Electrode
Wire
Feed
Gas
Flow
Travel
Speed
Rate
Speed
Metal
No. of
Diameter
Welding
Welding
in./min
ft/hr
in./min
in. (mm)
Passes
in. (mm)
Voltage
Current
(mm/s)
(I/min)
(mm/s)
35 (17)
200-30
(8.513)
130-145
1/2 (12.7)
1
3/32 (2.4)
35-37
525-575
(55-61)
150-175
5/8 (15.9)
1
3/32 (2.4)
36-38
600-650
(63-74)
17-25
35 (17)
(7-11)
35 (17)
15-23
(6.510)
90-100
3/4 (19.1)
1
1/8 (3.2)
36-38
650-700
(38-42)
90-100
1 (25.4)
NAVEDTRA 14250A
2
1/8 (3.2)
36-38
650-700
(38-42)
12-20
35 (17)
(5-8.5)
10-128
Table 10-26 — Welding procedure schedules for GMAW of plain carbon and
low alloy steels using spray transfer.
Thickness
of Base
Metal
in. (mm)
1/8 (3.2)
No. of
Passes
Electrode
Diameter
in. (mm)
Welding
Voltage
Welding
Current
1
1/16 (1.6)
23-25
275-325
Wire Feed
Speed
in./min
(mm/s)
Gas
Flow
Rate
ft/hr
(I/min)
Travel
Speed
in./min
(mm/s)
45 (21)
(14-15)
155-175
(66-74)
34-36
210-260
3/16 (4.8)
1
1/16 (1.6)
24-26
325-375
(89-110)
31-33
45 (21)
210-260
1/4 (6.4)
1-2
1/16 (1.6)
24-26
325-375
1/4 (6.4)
1-2
3/32 (2.4)
26-29
400-450
(89-110)
30-32
45 (21)
(13-14)
45 (21)
(14-15)
100-120
(42-51)
32-35
100-120
3/8 (9.5)
2
1/16 (1.6)
24-26
325-375
(42-51)
20-24
45 (21)
100-120
3/8 (9.5)
1-2
3/32 (2.4)
26-29
400-450
(42-51)
3
1/16 (1.6)
24-26
325-375
(89-110)
45 (21)
3
3/32 (2.4)
26-29
400-450
3/4 (19.1)
4-5
1/16 (1.6)
24-26
325-375
(42-51)
45 (21)
45 (21)
4
3/32 (2.4)
26-29
400-450
(42-51)
NAVEDTRA 14250A
7
1/16 (1.6)
24-26
325-375
(89-110)
(9-11)
24-28
45 (21)
210-260
1 (25.4)
(11-13)
22-26
45 (21)
100-120
3/4 (19.1)
(9-11)
26-30
210-260
(89-110)
(8-12)
22-26
100-120
1/2 (12.7)
(8-10)
20-28
210-260
1/2 (12.7)
(13-14)
(10-12)
22-26
45 (21)
(9-11)
10-129
1 (25.4)
7
1/16 (1.6)
24-26
325-375
3/32 (2.4)
26-29
400-450
6
1 (25.4)
2
(89-110)
45 (21)
(9-11)
45 (21)
(10-12)
100-120
(42-51)
24-28
Table 10-27 — Welding procedure schedules for GMAW of stainless steel.
Thickness
of Base
Metal
No. of
Electrode
Diameter
Welding
Welding
in. (mm)
Passes
in. (mm)
Voltage
Current
1/16 (1.6)
1
.035 (.9)
15-18
60-100
Wire Feed
Speed
in./min
(mm/s)
125-200
(53-85)
Gas
Flow
Rate
ft/hr
(I/min)
15 (7)
250-320
3/32 (2.4)
1
.035 (.9)
18-21
125-150
(106-135)
1
.045 (1.1)
18-21
125-150
(55-68)
15 (7)
1
.035 (.9)
19-24
130-160
(110-140)
15 (7)
1
.045 (1.1)
19-24
150-225
(68-106)
5/32 (4.0)
1
.045 (1.1)
22-26
190-250
(85-123)
15 (7)
15 (7)
(8-13)
20 (9)
(11-13)
25-30
250-370
NAVEDTRA 14250A
2
.045 (1.1)
24-30
225-300
(106-157)
(8-11)
20-30
200-290
1/4 (6.4)
(11-13)
20-25
160-250
1/8 (3.2)
(11-13)
25-30
260-330
1/8 (3.2)
(mm/s)
25-30
(11-13)
25-30
130-160
3/32 (2.4)
Travel
Speed
in./min
25-30
25 (12)
(11-13)
10-130
Table 10-28 — Welding procedure schedules for GMAW of aluminum and
alloys.
Wire Feed
Fillet
Electrode
Gas Flow
Travel
Speed
Rate
Speed
in./min.
ft3/hr.
in./min
Current
(mm/s)
(l/min)
(mm/s)
15 (7)
12-24
(6-10)
size
No. of
Diameter
Welding
Welding
in. (mm)
Passes
in. (mm)
Voltage
1/16 (1.6)
1
.035 (.9)
13-14
55-60
250-300
(106-127)
3/32 (2.4)
1
.035 (.9)
16-18
90-100
300-350
(127-148)
30 (14)
24-36
(10-15)
1/8 (3.2)
1
3/64 (1.2)
19-21
110-130
160-200
(68-85)
35 (17)
22-26
(9-11)
3/16 (4.8)
1
3/64 (1.2)
19-21
150-190
225-275
(95-116)
35 (17)
20-25
(8-11 )
1/4 (6.4)
1
1/16 (1.6)
20-22
175-225
150-190
(63-80)
35 (17)
20-25
(8-11 )
3/8 (7.9)
2
1/16 (1.6)
21-26
200-250
170-210
(72-89)
40 (19)
24-30
(10-13)
112 (12.7)
3-5
1/16 (1.6)
24-29
200-250
170-210
(72-89)
50 (24)
12-18
(5-7.5)
1/2 (12.7)*
2-3
3/32 (2.4)
26-28
240-280
140-150
(59-63)
45 (21)
15-20
(6.5-8.5)
3/4 (19.1)
4-8
1/16 (1.6)
22-27
250-300
230-260
(97-110)
50 (24)
10-16
(4-7)
3/4 (19.1)*
3-4
3/32 (2.4)
27-29
280-320
150-160
(63-68)
50 (24)
16-22
(7-9.5)
1 (25.4)
6-10
1/16 (1.6)
22-27
250-300
230-260
(97-110)
50 (24)
8-14
(3.5-6)
1 (25.4)*
5-6
3/32 (2.4)
27-29
280-320
150-160
(63-68)
50 (24)
14-26
(6-8.5)
NAVEDTRA 14250A
10-131
Table 10-29 — Welding procedure schedules for GMAW of copper and copper
alloys.
Thickness
of Base
Metal
in. (mm)
Welding
Current
Wire Feed
Speed
in./min
(mm/s)
Gas Flow
Rate
ft/hr
(I/min)
Travel
Speed
in./min
(mm/s)
22-24
150-170
210-220
(89-93)
35 (17)
20-23
(8-10)
3/64 (1.2)
22-25
180-200
240-270
(102-114)
40(19)
20-25
(8.5-11 )
1
3/64 (1.2)
23-27
200-230
270-290
(114-123)
40 (19)
20-25
(8.5-11 )
1/8 (3.2)
1
3/64 (1.2)
23-27
210-240
280-300
(118-127)
40 (19)
20-25
(8.5-11 )
1/4 (6.4)
1
1/16 (1.6)
23-27
340-360
190-210
(80-89)
40 (19)
12-15
(5-6.5)
3/8 (7.9)
2
1/16 (1.6)
24-28
380-410
220-240
(93-102)
40 (19)
12-15
(5-6.5)
1/2 (12.7)
2
1/16 (1.6)
24-28
400-440
270-290
(114-123)
50 (19)
8-10
(3.5-4)
3/4 (19.1)
2-3
1/16 (1.6)
24-30
420-460
280-300
(118-127)
50 (24)
7-9
(3.5-4)
1 (25.4)
4
1/16 (1.6)
24-30
420-460
280-300
(118-127)
50 (24)
7-9
(3.5-4)
No. of
Passes
Electrode
Diameter
in. (mm)
Welding
Voltage
1/16 (1.6)
1
3/64 (1.2)
5/64 (2.0)
1
7/64 (2.8)
NAVEDTRA 14250A
10-132
Silicon Bronze
Thickness
of Base
Metal
in. (mm)
No. of
Electrode
Diameter
Welding
Welding
Passes
in. (mm)
Voltage
Current
1/8 (3.2)
1
3/64 (1.2)
25-28
220-230
1/4 (6.4)
1-3
1/16 (1.6)
27-30
170-190
1/4 (6.4)
1
1/16 (1.6)
25-28
220-250
1/2 (12.7)
3-5
1/16 (1.6)
27-30
180-200
Wire Feed
Speed
in./min
Gas Flow
Rate
ft/hr
(mm/s)
(I/min)
220-230
(93-97)
170-190
(72-80)
220-250
(93-106)
180-200
(76-85)
Aluminum Bronze
Thickness
of Base
Electrode
35 (17)
40 (19)
50 (24)
50(24)
Travel
Speed
in./min
(mm/s)
25-32
(11-14)
25-32
(11-14)
30-34
(13-14)
15-20
(6.5-8.5)
Wire Feed
Speed
Gas
Flow
Rate
Travel
Speed
Metal
No. of
Diameter
Welding
Welding
in./min
ft/hr
in./min
in. (mm)
Passes
in. (mm)
Voltage
Current
(mm/s)
(I/min)
(mm/s)
1/8 (3.2)
1
3/64 (1.2)
22-25
190-225
1/4(6.4)
2
1/16 (1.6)
23-29
275-300
3/8(7.9)
3-6
1/16 (1.6)
23-29
300-340
1/2 (12.7)
6-8
1/16 (1.6)
23-29
320-350
5/8 (15.9)
6-8
1/16(1.6)
23-29
320-350
3/4 (19.1)
6-8
1/16 (1.6)
23-29
340-370
NAVEDTRA 14250A
280-300
(118-127)
170-190
(72-80)
190-210
(80-89)
200-220
(85-93)
200-220
(85-93)
210-230
(89-97)
40 (19)
50 (24)
50 (24)
50 (24)
50 (24)
50 (24)
18-24
(7.5-10)
16-22
(7-9.5)
16-22
(7-9.5)
11-15
(4.5-6.5)
9-13
(4-5.5)
8-12
(3.5-5)
10-133
Table 10-30 — Welding procedure schedules for GMAW of nickel and nickel
alloys.
Thickness
of Base
Electrode
Wire Feed
Speed
Gas
Flow
Rate
Travel
Speed
ft/hr
in./min
(I/min)
(mm/s)
55-65
(23-27)
30-35
(13-15)
20-25
(8.5-11 )
Metal
No. of
Diameter
Welding
Welding
in./min
in. (mm)
Passes
in. (mm)
Voltage
Current
1/16 (1.6)
1
3/64 (1.2)
21-23
200-230
1/8 (3.2
)1
1/16 (1.6)
25-27
310-350
1/4 (6.4)
2
1/16 (1.6)
26-28
300-350
(mm/s)
290-310
(123-131 )
190-215
(80-91 )
180-215
(76-91 )
NAVEDTRA 14250A
50 (24)
50 (24)
50 (24)
10-134
Table 10-31 — Welding procedure schedules for GMAW of magnesium alloys.
Thickness
of Base
Metal
in. (mm)
Welding
Current
Wire Feed
Speed
in./min
(mm/s)
Gas Flow
Rate
ft/hr
(I/min)
Travel
Speed
in./min
(mm/s)
14-17
40-70
225-325
(95-137)
50 (24)
30-36
(13-15)
.040 (1.0)
14-17
50-90
275-425
(116-180)
50 (24)
30-36
(13-15)
1
1/16 (1.6)
15-19
100-140
275-350
(116-148)
50 (24)
30-36
(13-15)
1/8 (3.2)
1
1/16 (1.6)
15-19
120-160
310-380
(131-161)
50 (24)
24-32
(10-14)
3/16 (4.8)
1
1/16 (1.6)
24-29
220-270
515-615
(218-260)
65 (31)
24-32
(10-14)
1/4 (6.4)
1
1/16 (1.6)
24-29
250-300
575-675
(243-286)
65 (31)
24-32
(10-14)
3/8 (9.5)
2
1/16 (1.6)
24-29
275-375
625-725
(264-307)
65 (31)
24-32
(10-14)
3/8 (9.5)
1
3/32 (2.4)
24-29
300-350
330-380
(140-161 )
65 (31)
24-32
(10-14)
1/2 (12.7)
3
1/16 (1.6)
23-26
320-370
725-825
(307-349)
65 (31)
24-32
(10-14)
1/2 (12.7)
2-3
3/32 (2.4)
24-29
330-380
365-410
(154-173)
65 (31)
24-32
(10-14)
5/8 (15.9)
3
3/32 (2.4)
25-30
350-400
380-430
(161-182)
65 (31)
20-30
(8.5-13)
1 (25.4)
5
3/32 (2.4)
25-30
350-400
380-430
(161-182)
65 (31)
20-30
(9.5-13)
No. of
Passes
Electrode
Diameter
in. (mm)
Welding
Voltage
.044 (1.0)
1
.040 (1.0)
1/16 (16)
1
3/32 (2.4)
NAVEDTRA 14250A
10-135
Table 10-32 — Welding procedure schedules for GMAW of plain carbon steel.
Wire
Consumed
Per Spot
Gas Flow
Rate
ft/hr
(I/min)
Shear
Strength
Per Spot
lbs. (kN)
Metal
Thickness
in. (mm)
Electrode
Diameter
in. (mm)
Arc Spot
Time
sec.
Welding
Voltage
Welding
Current
24 ga. (.6)
.030 (.8)
1.0
24
90
4.6(117)
25 (12)
625 (2.78)
22 ga. (.8)
.030 (.8)
1.2
27
120
5.0 (127)
25 (12)
730 (3.25)
in./min
22 ga (.8)
.035 (.9)
1.0
26
140
6.0 (152)
25 (12)
800(3.561
20 ga. (.9)
.030 (.8)
1.2
27
120
10.1 (257)
25 (12)
1337 (5.95)
20 ga. (.9)
.035 (.9)
1.0
26
140
6.0 (152)
25 (12)
1147 (5.10)
18 ga. (1.2)
.035 (.9)
1.0
27
190
8.5 (216)
25 (12)
1507 (6.70)
18 ga. (1.2)
.045 (1.1)
0.7
27
200
4.0 (102)
25 (12)
1414 (6.29)
1434 (6.38)
16 ga.(1.5)
.035 (.9)
2.0
28
190
17.3 (438)
25 (12)
16 ga. (1.5)
.045 (1.1)
1.0
29
260
6.0 (152)
25 (12)
2070 (9.21)
16 ga (1.5)
1/16 (1.6)
1.0
29
250
2.8 (70)
35 (17)
1654 (7.36)
14 ga. (1.9)
.035 (.9)
5.0
28
190
40.5 (1029)
25 (12)
2600 (11.57)
14 ga. (1.9)
.045 (1.1)
1.5
30
300
12.8 (324)
25 (12)
3224 (14.34)
14 ga (1.9)
1/16 (1.6)
1.0
31
360
5.5 (140)
35 (17)
3340 (14.86)
12 ga. (2.7)
.045 (1.1)
3.5
30
300
28.5 (724)
25 (12)
4300 (19.13)
12 ga. (2.7)
1/16~1.6)
1.0
32
440
7.3 (184)
35 (17)
5000 (22.24)
4114 (18.30)
11 ga (3.0)
.045(1.1)
4.2
30
300
4 (864)
25 (12)
11 ga. (3.0)
1/16 (1.6)
1.0
32
490
8.5 (216)
35 (17)
634 (25.06)
5/32 (4.0)
1/16 (1.61
1.5
32
490
9 (229)
35 (17)
5447 (24.25)
3/16 (4.8)
1/16 (1.6)
2.0
32
490
16.8 (425)
35(17)
6834 (30.40)
1/4 (6.4)
1/16 (1.6)
3.5
32
490
28.1 (714)
35 (17)
8667 (38.55)
NAVEDTRA 14250A
10-136
Table 10-33 — Welding procedure schedules for GMAW of aluminum and
aluminum alloys.
Metal
Electrode
Arc
Spot
Thickness
in. (mm)
.020 (.5)
.030 (.8)
.040 (1.0)
.040 (1.0)
.050 (1.3)
.050 (1.3)
.064 (1.6)
.064 (1.6)
.080 (2.0)
.092 (2.3)
.125 (3.2)
Diameter
in. (mm)
3/64 (1.2)
3/64 (1.2)
3/64 (1.2)
1/16 (1.6)
3/64 (1.2)
1/16(1.6)
3/64 (1.2)
1/16 (1.6)
1/16 (1.6)
1/16 (1.6)
1/16 (1.6)
Time
sec.
0.3
0.3
0.3
0.8
0.4
1.0
0.5
1.2
1.4
2.0
2.2
NAVEDTRA 14250A
Welding
Voltage
23
23
24
24
25
24
26
24
24
23
23
Welding
Current
105
135
175
320
225
335
270
340
375
300
300
Wire
Gas
Flow
Consumed
Rate
Per Spot
in./min
0.8 (21)
1.0 (25)
1.3 (33)
4.4 (113)
2.2 (56)
6.0 (152)
3.1 (79)
7.5 (191)
9.5 (241)
10.9 (277)
12 (305)
ft/hr
(I/min)
35 (17)
35 (17)
35 (17)
50 (24)
35 (17)
50 (24)
35 (17)
50 (24)
50 (24)
50 (24)
50 (24)
10-137
11.0.0 PREWELD PREPARATIONS
Preparation is the key to producing quality weldments with the gas metal arc welding
process. Several operations may be required before making a weld. These include
preparing the weld joint, cleaning the nozzle of the weld gun, setting up or fixturing the
weldment, setting the variables, and in some cases preheating. The amount of preweld
preparation depends upon the size of the weld, the material to be welded, the ease of
fitup, the quality requirements, the governing code or specification, and the welder.
11.1.0 Preparing the Weld Joint
For the most part, the same joint designs recommended for other arc welding processes
can be used for GMAW (refer to Chapter 3). However, some minor modifications should
be considered due to the welding characteristics of the GMAW process. Since the arc in
GMAW is more penetrating and narrower than the arc for shielded metal arc welding,
groove joints can have smaller root faces and root openings. Also, since the nozzle
does not have to be placed within the groove, less beveling of the plates is required.
GMAW welding can actually lower material costs since you use less weld metal in the
joint.
There are different ways of preparing the edges of the joint for welding. The methods
most often used for edge preparation are oxygen fuel cutting, plasma arc cutting,
shearing, machining, air carbon arc gouging, grinding, and chipping. When they can be
used, the thermal cutting methods, oxy fuel, plasma arc cutting, and air carbon arc
cutting are generally faster than the mechanical cutting methods, with the exception of
shearing. Oxygen fuel cutting is used on carbon and low alloy steels; plasma arc cutting
is used on ferrous and non-ferrous metals, and is best for applications where high
production rates are required. Air carbon arc cutting is used for preparing joints in most
steels including stainless steels, but this process should not be used on stainless steels
for critical corrosion applications because of the carbon deposited, unless the cut
surfaces are cleaned by grinding and brushing. The surfaces cut by these thermal
methods often have to be ground lightly to remove scale or contamination. Common
types of prepared joints are the V-, U-, J-, bevel-, and combination grooves, The more
complex types of bevels require longer joint preparation times, which makes the joint
preparation more expensive.
Since GMAW is used on all metal thicknesses, all of the different joint preparations are
widely employed. Joints for fillet or square-groove welds are prepared simply by
squaring the edges of the members to be welded if the as-received edge is not suitable.
Next to the square-edge preparation, the V-groove and single-bevel grooves are the
types most easily prepared by oxygen fuel cutting, plasma arc cutting, chipping, or
machining. These methods leave a smooth surface if properly done. The edges of Uand J-grooves can be done by using special tips and techniques with oxy fuel cutting or
machining, which will produce a uniform groove. Carbon arc cutting is used extensively
for preparing U-grooves in steels, and for removing part of root passes, so the joint can
be welded from both sides. Chipping is done on the backside of the weld when full
penetration is required on non-ferrous metals.
Weld backings are commonly used in GMAW to provide support for the weld metal and
to control the heat input. Copper, steel, stainless steel, and backing tape, which are
used as weld backing, are the three most common methods. Copper is a widely used
method of weld backing because it does not fuse to thin metals. It also provides a fast
cooling rate because of the high heat conductivity of copper, which makes this the best
NAVEDTRA 14250A
10-138
method of controlling the heat input. Steel backing is used when welding steels. These
are fusible and remain part of the weldment unless they are cut off, usually by oxy fuel,
air carbon arc cutting, or grinding. Stainless steels are good backing materials for
GMAW of aluminum, magnesium, and the other non-ferrous metals. Backing tape is
popular because it can be molded to any joint configuration, such as the inside of a
pipe.
11.2.0 Cleaning the Work Metal
Welds made by gas metal arc welding are very susceptible to contamination during the
welding process. The surface of the base metal must be free of grease, oil, paint,
plating, dirt, oxides, or any other foreign material. This is especially critical when welding
aluminum and the non-ferrous metals. Except for titanium, very dirty workpieces are
usually cleaned by using solvent cleaners, followed by vapor degreasing. Simple
degreasing is often used for cleaning metals that have oxide-free surfaces. Acid pickling
is generally used for cleaning metals that have a light oxide coating; heavier oxide
coatings are generally removed mechanically by grinding and abrasive blasting.
The type of cleaning operation will vary, depending on the type of metal. Aluminum
forms a thick, refractory oxide coating, which has a high electrical resistance. This oxide
coating is removed by deoxidation with a hot alkaline cleaning solution, followed by
rinsing in distilled water. Carbon and low alloy steels may be cleaned chemically in a
hydrochloric acid solution. Nickel alloys and stainless steels may be cleaned by pickling,
which removes iron, sand blast residue, and other contaminants. Titanium and titanium
alloys may be cleaned in molten salt baths or by abrasive blasting. Chlorinated solvents,
which are used for degreasing operations, should not be used on titanium because they
will cause corrosion cracking. Welding should never be done near chlorinated solvents
because the arc can create phosgene gas, which is toxic. Chemical cleaning can be
done by pickling.
Just before welding, you should perform several other tasks. One is to file the edges of
the joint smooth so there are no burrs. Burrs can cause physical pain as well as create
a place to trap contaminants in a weld joint. You can use grinding on plain carbon and
low alloy steels to remove burrs and rust or mill scale from the area in and around the
joint. You should wire brush the surfaces of the joint and surrounding area. Use mild
steel brushes for cleaning plain carbon and low alloy steel, and stainless steel wire
brushes for cleaning stainless steel, aluminum, and the other non-ferrous metals.
You should also brush off the joint surfaces and surface of the previous weld bead
between passes of a multiple pass weld. Use stainless steel brushes on these metals to
avoid contamination due to rust or carbon from the mild steel wire brushes. Begin
welding soon after cleaning, especially on metals that form moderate or thick surface
oxides, such as stainless steel, aluminum, and magnesium. Wire brushing does not
completely remove the oxide, but it reduces their thickness and makes the metals
easier to weld. Wear gloves while cleaning stainless steels and non-ferrous metals to
prevent oil or dirt from your fingers from getting on the joint surfaces, which can also
cause contamination.
11.3.0 Fixturing and Positioning
Fixturing can affect the shape, size, and uniformity of a weld bead. Fixtures are devices
that are used to hold the parts to be welded in proper relation to each other. When
fixturing is not used, it usually indicates that the resulting weld distortion can be
NAVEDTRA 14250A
10-139
tolerated or be corrected by straightening operations. The three major functions of
fixtures are the following:
1. Locate and maintain parts in their positions relative to the assembly.
2. Increase the welding efficiency of the welder.
3. Control distortion in the weldment.
When a welding fixture is used, the components of a weldment can be assembled and
securely held in place while the weldment is positioned and welded. Using these
devices is dependent on the specific application. They are used more often when large
numbers of the same parts are produced. When fixtures can be used, the production
time for the weldments can be greatly reduced. They are also good for applications
where close tolerances must be held.
Positioners are used to move the workpiece into a position so welding can be done
more conveniently, which affects the appearance and quality of the weld bead.
Positioning is sometimes needed simply to make the weld joint more accessible. The
main objective of positioning is to put the joint in the flat or other more favorable
position, which increases the efficiency of the welder because higher welding speeds
can be used. This also allows the use of larger diameter wires with globular and high
current spray transfer. These modes of metal transfer will produce the highest
deposition rates, and flat position welding usually increases the quality of the weld
because it makes the welding easier.
11.4.0 Preheating
Preheating is sometimes required, but this depends on the type of metal being welded,
the base metal thickness, and the amount of joint restraint. The specific amount of
preheat needed for a given application is often obtained from the welding procedure.
The preheat temperature of the metal is often carefully controlled. There are several
good methods of performing this such as furnace heating, electric induction coils, and
electric resistance heating blankets. On thin materials, hot air blasts or radiant lamps
may be used. With these methods, temperature indicators are attached to the parts
being preheated. Oxy fuel torches are another method of preheating. This method gives
a more localized heating than the previously mentioned methods. When using oxy fuel
torches, it is important to avoid localized overheating and deposits of incomplete
combustion products from collecting on the surface of the parts to be welded. There are
several methods of measuring the temperature of preheat, such as temperature color
crayons, pellets, and hand-held temperature indicators. The crayons and pellets melt at
a specific predetermined temperature. The hand-held temperature indicators can give
meter readings, digital readings, or recorder readings, depending on the type of
temperature indicators.
Test your Knowledge (Select the Correct Response)
13.
Which is NOT a major type of welding variable?
A.
B.
C.
D.
Fixed
Primary adjustable
Secondary adjustable
Secondary fixed
NAVEDTRA 14250A
10-140
14.
What is the main objective of a positioning fixture?
A.
B.
C.
D.
Stop warping
Proper alignment
Increase access
Portability
12.0.0 WELDING DISCONTINUITIES and PROBLEMS
Once you get the feel of welding with GMAW equipment, you will probably find the
techniques are less difficult to master than many of the other welding processes;
however, as with any other welding process, GMAW does have some pitfalls. To
produce good quality welds, you must learn to recognize and correct possible welding
defects. The following are a few of the more common defects you may encounter, along
with corrective actions that you can take.
12.1.0 Discontinuities Caused by Welding Technique
Like all welding processes, GMAW can develop discontinuities or defects that include
one or a combination of multiple defects, including inclusions, porosity, wormhole
porosity, undercutting, incomplete fusion, overlapping, melt-through, whiskers,
excessive spatter, arc strikes, and craters.
These problems with the welding technique or procedure weaken the weld and can
cause cracking. A poor welding technique and improper choice of welding parameters
are major causes of weld defects. Some defects are caused by the use of improper
base metal, filler metal, or shielding gas.
The base metal and filler metal should also be clean to avoid creating a discontinuity.
These defects will appear in many of your early attempts, but will usually disappear as
you put forth more practice effort and gain experience.
12.1.1 Inclusions
There are two basic types of inclusions that
can occur in gas metal arc welding: slag
inclusions and oxide inclusions (Figure 10112). Inclusions cause a weakening of the
weld and often serve as crack initiation
points. GMAW does not have as many
problems with slag inclusions as shielded
metal arc welding because the weld puddle
is protected by a shielding gas instead of by
Figure 10-112 — Inclusions.
a slag layer. Some electrodes, particularly
those used for welding steel, will sometimes
leave small, glassy slag islands on the surface of the weld. Slag inclusions can be
caused by welding over these in multiple pass welds. The best method of preventing
this problem is to clean the surface of the weld bead, especially the toes of the weld
where any slag can be easily trapped.
An oxide inclusion is a film type inclusion. These inclusions often occur when
excessively high travel speeds are used when welding metals such as aluminum,
magnesium, or stainless steel, which have heavy oxide coatings; the oxide coatings on
the surface of these metals become mixed in the weld puddle. Methods of preventing or
NAVEDTRA 14250A
10-141
correcting this problem are to reduce the travel speed, increase the welding voltage,
and use a more highly deoxidized type of electrode.
Another major cause of oxide inclusions is by welding the metal without cleaning.
Because of the thick oxide coatings on the surface of aluminum, magnesium, and
stainless steel, you should reduce the thickness of the oxide layer by chemical cleaning,
grinding, or wire brushing before welding. This will decrease the chance of an oxide
inclusion being formed.
12.1.2 Porosity
Porosity is the presence of gas pockets in the weld metal that may be scattered in small
clusters or along the entire length of the weld (Figure 10-113). These voids left in the
weld cause it to be weakened. Porosity may be internal, on the surface of the weld
bead, or both. This discontinuity is caused by one or more of the following:
1. Inadequate shielding gas flow rate
2. Wind drafts that deflect the shielding
gas coverage
3. Blockage of the shielding gas flow
when spatter builds up on the nozzle
4. Contaminated or wet shielding gas
5. Excessive welding current.
6. Excessive welding voltage
7. Excessive electrode extension
Figure 10-113 — Porosity.
8. Excessive travel speed which
causes freezing of the weld puddle
before gases can escape
9. Rust, grease, oil, moisture, or dirt on the surface of the base metal or filler wire
including moisture trapped in aluminum oxide
10. Impurities in the base metal, such as sulfur and phosphorous in steel
Porosity can be prevented or corrected by the following:
1. Increasing the shielding gas flow rate.
2. Setting up wind shields.
3. Cleaning the nozzle of the welding gun.
4. Replacing the cylinder of shielding gas.
5. Lowering the welding current (reducing the wire feed speed).
6. Decreasing the voltage.
7. Decreasing the electrode extension.
8. Reducing the travel speed.
9. Cleaning the surface of the base metal or filler metal.
10. Changing to a different base metal with a different composition.
12.1.3 Wormhole Porosity (Piping Porosity)
Wormhole porosity is the name given to
elongated gas pockets, and is usually caused
by sulfur in the steel or moisture on the
surface of the base metal which becomes
trapped in the weld joint (Figure 10-114).
Wormhole porosity can seriously reduce the
strength of the weld. The best methods of
preventing this are to clean the surfaces of
NAVEDTRA 14250A
Figure 10-114 — Wormhole.
10-142
the joint and preheat to remove moisture. If sulfur in the steel is the problem, a more
weldable grade of steel should be selected.
12.1.4 Undercutting
Undercutting is a groove melted in the base metal next to the toe or root of a weld that
is not filled by the weld metal (Figure 10-115). This is particularly a problem with fillet
welds. Undercutting causes a weaker joint at the toe of the weld, which may result in
cracking.
It is caused by one or more of the following:
1. Excessive welding current
2. Arc voltage too high
3. Excessive travel speed which does
not allow enough filler metal to be
added
4. Erratic feeding of the electrode wire.
5. Excessive weaving speed
6. Incorrect electrode angles, especially
on vertical and horizontal welds
It can be prevented by the following:
Figure 10-115 — Undercutting.
1. Reducing the welding current.
2. Reducing the welding voltage.
3. Using a travel speed slow enough so the weld metal can completely fill all of the
melted-out areas of the base metal.
4. Cleaning the nozzle inside of the contact tube, or removing the jammed electrode
wire.
5. Pausing at each side of the weld bead when a weaving technique is used.
6. Correcting the electrode angles being used.
12.1.5 Incomplete Fusion
Incomplete fusion occurs when the weld
metal is not completely fused to the base
metal (Figure 10-116). This can occur
between the weld metal and the base
metal, or between passes in a multiple pass
weld. Incomplete fusion between the weld
metal and the base metal is usually due to
inadequate penetration. This is often a
major problem with the short-circuiting
Figure 10-116 — Incomplete
mode of metal transfer. When shortfusion.
circuiting welding is done, wider root
openings are often used to allow better
penetration. You should take more care when using a weaving technique to prevent
creating an area of incomplete penetration because short-circuiting welding has the
poorest penetration characteristics of the different modes of gas metal arc welding.
Incomplete fusion between passes in a multiple pass weld is often caused by welding
over a previous weld bead that has an excessive convexity. If an excessively convex
weld bead is created, grind the surface off enough so complete fusion can be made by
the next pass. Causes of incomplete fusion can be the following:
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1. Excessive travel speed which causes an excessively convex weld bead or does
not allow adequate penetration
2. Welding current too low
3. Poor joint preparation
4. Letting the weld metal get ahead of the arc or letting the weld layer get too thick,
which keeps the arc away from the base metal
Incomplete fusion can be prevented by the
following:
1.
2.
3.
4.
Reducing the travel speed.
Increasing the welding current.
Preparing the joint better.
Using proper electrode angles or
increasing the travel speed.
A special type of incomplete fusion is
wagon tracks, shown in Figure 10-117.
Figure 10-117 — Wagon tracks.
Wagon tracks are linear voids along both
sides of a weld deposit and are usually caused by a highly convex weld bead. The area
where the bead fuses to the side of the joint is depressed, and the following weld bead
may not completely fill the void. The excessive convexity of the bead can be reduced by
using a slightly higher arc voltage, or increasing the travel speed. If you must weld over
a bead with an excessively convex profile, grinding is often required to make the voids
more accessible.
12.1.6 Overlapping
Overlapping is the protrusion of the weld
metal over the edge or toe of the weld bead
(Figure 10-118). This defect can cause an
area of incomplete fusion which creates a
notch and can lead to crack initiation. If this
is allowed to occur, you can grind off the
excess weld metal after welding.
Overlapping is produced by one or more of
the following:
Figure 10-118 — Overlapping.
1. Too slow a travel speed, which
permits the weld puddle to get ahead of the electrode
2. Arc welding current that is too low.
3. Incorrect electrode angle that allows the force of the arc to push the molten weld
metal over unfused sections of the base metal
Overlapping can be prevented or corrected by the following:
1. Using a higher travel speed.
2. Using a higher welding current.
3. Using the correct electrode angles.
12.1.7 Melt-through
Melt-through occurs when the arc melts
through the bottom of the weld and creates
holes (Figure 10-119). This can be caused
by one or more of the following:
NAVEDTRA 14250A
Figure 10-119 — Melt through.10-144
1. Excessive welding current
2. Travel speed that is too slow
3. Root opening that is too wide or a root face that is too small.
This can be prevented by the following:
1. Reducing the welding current.
2. Increasing the travel speed.
3. Reducing the width of the root opening, using a slight weaving motion, or
increasing the electrode extension.
12.1.8 Whiskers
Whiskers are short lengths of weld
electrode wire, visible on the top or bottom
surface of the weld or contained within the
weld (Figure 10-120). They are caused by
pushing the electrode wire past the leading
edge of the weld puddle. The small sections
of wire will protrude inside the joint and are
welded to the deposited metal.
They can be prevented by the following:
1.
2.
3.
4.
Reducing the travel speed.
Using a weaving motion.
Increasing electrode extension.
Reducing electrode current.
12.1.9 Excessive Weld Spatter
Figure 10-120 — Whiskers.
Spatter consists of the metal particles
expelled during welding. Excessive weld spatter creates a poor weld appearance,
wastes electrodes, causes difficult slag removal, and can lead to incomplete fusion in
multi-pass welds. In addition, excessive spatter can block the flow of shielding gas from
the nozzle, which causes porosity. The amount of welding spatter produced in GMAW
varies depending on the type of metal transfer and the type of shielding gas. For
example, globular transfer with carbon dioxide shielding creates high levels of spatter
compared to spray transfer with argon shielding.
Excessive spatter is caused by an excessive welding current, arc voltage, or electrode
extension. Methods of reducing the amount of spatter would then be to reduce the
welding current, the arc voltage, or the amount of stick-out. Another method of reducing
weld spatter when using carbon dioxide shielding gas would be to change to an argoncarbon dioxide mixture, which in many cases produces spray transfer and less
spattering. You can also remove spatter by grinding or chipping.
12.1.10 Arc Strikes
Many codes prohibit striking the arc on the surface of the workpiece. Striking the arc on
the base metal outside of the weld joint can produce a hard spot on the base metal
surface. Failures can then occur due to the notch effect. The arc strikes might create a
small notch on the surface of the metal which can act as an initiating point for cracks.
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12.1.11 Craters
Weld craters are depressions on the weld
surface at the point where the arc was
broken (Figure 10-121). These are caused
by the solidification of the metal after the arc
has been broken. The weld crater often
cracks and can serve as an origin for linear
cracking back into the weld metal or into the
base metal. These craters can usually be
removed by chipping or grinding and the
Figure 10-121 — Craters.
depression filled in with a small deposit of
filler metal. There are three common
methods of preventing craters. The first is to reverse the travel of the electrode a little
way back into the weld bead from the end before breaking the arc. For automatic
welding, a downslope control is sometimes used. This is done by gradually reducing the
welding current at the end of the weld, which gradually reduces the size of the molten
weld puddle. The third method is by stopping the travel long enough to fill the crater
before breaking the arc.
12.2.0 Cracking
Weldment cracking can be caused by an improper welding procedure, welder
technique, or materials. All types of cracking can be classified as either hot or cold
cracking. These cracks are transverse or longitudinal to the weld. Transverse cracks are
perpendicular to the axis of the weld where longitudinal shrinkage strains are acting on
excessively hard and brittle weld metal. Longitudinal cracks are often caused by high
joint restraint and high cooling rates. Preheating will often help to reduce these
problems.
Hot cracking occurs at elevated temperatures and generally happens just after the weld
metal starts to solidify. This type of cracking is often caused by excessive sulfur,
phosphorous, and lead contents in the steel base metal. In non-ferrous metals, it is
often caused by sulfur or zinc. It can also be caused by an improper method of breaking
the arc, or in a root pass when the cross-sectional area of the weld bead is small
compared to the mass of the base metal.
Hot cracking often occurs in deep penetrating welds and can continue through
successive layers if not repaired. Hot cracking may be prevented or minimized by the
following:
1.
2.
3.
4.
5.
Preheating to reduce shrinkage stresses in the weld.
Using clean or uncontaminated shielding gas.
Increasing the cross-sectional area of the weld bead.
Changing the contour of the weld bead.
Using base metal with very low
contents of those elements that tend
to cause hot cracking.
6. In steel, using filler metals that are
high in manganese.
Crater cracks are shallow hot cracks caused
by improperly breaking the arc; Figure 10122 shows two types. Crater cracks may be
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Figure 10-122 — Cracking.
10-146
prevented the same way craters are, by reversing the travel of the electrode back into
the weld bead a little way, gradually reducing the welding current at the end of the weld,
or by stopping the travel before breaking the arc.
Cold cracking occurs after the weld metal solidification is complete. Cold cracking may
occur several days after welding and is generally caused by hydrogen embrittlement,
excessive joint restraint, and rapid cooling. Preheating and using a dry high purity
shielding gas help reduce this problem.
Centerline cracks are cold cracks that often
occur in single pass concave fillet welds. A
centerline crack is a longitudinal crack that
runs down the center of the weld (Figure
10-123).
This problem may be caused by one or
more of the following:
1. Weld bead too small for the
thickness of the base metal
2. Poor fitup
3. High joint restraint
4. Extension of a crater crack
Figure 10-123 — Crater cracks.
The best methods of preventing centerline
cracks are the following:
1.
2.
3.
4.
Increasing the bead size.
Decreasing the gap width.
Preheating.
Preventing weld craters.
Base metal and underbead cracks are cold
cracks that form in the heat affected zone of
Figure 10-124 — Underbead
the base metal. Underbead cracks occur
cracks.
underneath the weld bead, as shown in
Figure 10-124. Base metal cracks are those
cracks that originate in the heat affected zone of the weld. These types of cracking are
caused by excessive joint restraint, entrapped hydrogen, and a brittle microstructure. A
brittle microstructure is caused by rapid cooling or excessive heat input. Underbead and
base metal cracking can be reduced or eliminated by using preheat.
12.3.0 Other Problems
Other problems that can occur and reduce the quality of the weld are arc blow, loss of
shielding gas coverage, defective electrical contact between the contact tube and the
electrode, and wire feed stoppages.
12.3.1 Arc Blow
The electric current that flows through the electrode, workpiece, and work cable sets up
magnetic fields in a circular path perpendicular to the direction of the current. When the
magnetic fields around the arc are unbalanced, it tends to bend away from the greatest
concentration of the magnetic field. This deflection of the arc is called arc blow.
Deflection is usually in the direction of travel or opposite to it, but it sometimes occurs to
the side. Arc blow can result in an irregular weld bead and incomplete fusion.
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Direct current is highly susceptible to arc blow, especially when welding is being done in
corners and near the end of joints. Arc blow occurs with direct current because the
induced magnetic field is in one direction. Arc blow is shown in Figure 10-125.
It is often encountered when welding magnetized metal or near a magnetized fixture.
This problem also occurs when welding complex structures and on massive structures
with high currents and poor fitup. Forward arc blow is encountered when welding away
from the ground connection or at the beginning of a weld joint. Backward arc blow
occurs toward the grounding connection, into a corner, or toward the end of a weld joint.
You can use several corrective methods to correct the arc blow problem:
1. Weld toward an existing weld or tack weld.
2. Reduce the welding current and reduce the arc voltage.
3. Place the work connection as far as possible from the weld, at the end of the
weld, or at the start of the weld, and weld toward the heavy tack weld.
4. Change the position of the fixture or demagnetize the base metal or fixture.
Figure 10-125 — Arc blow.
12.3.2 Inadequate Shielding
Many defects that occur in gas metal arc welding are caused by an inadequate flow or
blockage of shielding gas to the welding area.
An inadequate gas supply can cause oxidation of the weld puddle, which causes
porosity in the weld bead, usually appearing as surface porosity. This can be easily
detected because the arc will change color, the weld bead will be discolored, and the
arc will become unstable and difficult to control. The most common causes of this
problem are the following:
1. Blockage of gas flow in the torch or hoses, or freezing of the regulator with
carbon dioxide
2. Leak in the gas system
3. Weld spatter blocking the nozzle of the welding gun
4. Very high travel speed
5. Improper flow rate
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6. Wind or drafts
7. Distance between the nozzle and the work too long
There are several ways you can correct or prevent this problem. Check the torch and
hoses before welding to make sure the shielding gas can flow freely and is not leaking.
Clean spatter from the nozzle and contact tube regularly. A very high travel speed may
leave the weld puddle or part of it exposed to the atmosphere. This may be corrected in
some cases by inclining the gun in the direction of travel, using a nozzle that directs
shielding gas back over the heated area, or by increasing the gas flow rate. The best
method is to slow the travel speed.
Increasing the gas flow rate will increase the expense of the welding. An improper flow
rate may occasionally be a problem. For example, when using argon and welding in the
overhead position, you may have to use higher gas flow rates to provide adequate
shielding. This is because argon is heavier than air and it will fall away from the weld
area. Too high of a flow rate can cause excessive turbulence in the weld puddle.
When winds or air drafts are present, you may take several corrective steps. Setting up
screens around the operation is the best method of solving this problem. Increasing the
gas flow rate is another method, but again, this will increase the cost of welding. An
excessive distance between the end of the nozzle and the molten weld puddle will also
create a problem in providing adequate shielding, which can be corrected by shortening
this distance.
12.3.3 Clogged or Dirty Contact Tube
The power delivered to the arc in GMAW depends on a transfer of current from the tip of
the contact tube to the electrode by means of a sliding contact tube. A clogged, dirty, or
worn contact tube can cause changes in the amount of power transferred to the
electrode, which can have an effect on the arc characteristics. It can also cause an
irregular weld bead and possibly incomplete fusion because of the power fluctuations. A
clogged contact tube can stop the feed of the electrode wire, which stops the welding
arc. A contact tube can become dirty or clogged by spatter from the arc, by rust, scale,
copper wire coating, drawing compounds left from the manufacture of the wire on the
surface of the electrode, or by metal chips created by tight wire feed rolls. These
problems can best be prevented by making sure that the electrode wire is clean and the
wire feed rolls are tight enough to feed the wire without creating chips. A wire wipe
made of cloth is often attached to the wire feeder to clean the electrode wire as it is fed.
12.3.4 Wire Feed Stoppages
GMAW has the greatest problem with wire feed stoppages compared to the other
continuous wire feed welding processes because of the relatively small diameter of the
electrode wires used. Wire feed stoppages cause the arc to be extinguished and can
create an irregular weld bead because of the stops and starts. Wire stoppages can also
cause a loss of welding time because many of the problems take a long time to correct
when wire becomes wrapped around the wire feed rolls, wadded up in bird nests in the
wire feeder, or broken. Wire feed stoppages can be caused by the following:
1.
2.
3.
4.
5.
6.
Clogged contact tube
Clogged conduit in the welding gun assembly
Sharp bends or kinks in the wire feed conduit
Excessive pressure on the wire feed rolls which can cause breakage of the wire
Inadequate pressure on the wire feed rolls
Attempting to feed the wire over excessively long distances
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7. Spool of wire clamped too tightly to the wire reel support
Problems such as sharp bends or kinks in the wire feed conduit, excessive pressure on
the wire feed rolls, or attempting to feed the wire over excessively long distance are
particularly troublesome when using soft electrode wires such as aluminum,
magnesium, and copper. In many cases, wire feed stoppages must be corrected by
taking the gun assembly apart and cutting and removing the wire or by cutting and
removing the wire from the wire feeder. These both result in time lost to locate the
problem and feed the new length of wire through the assembly to the gun. Wire
stoppages can be prevented by the following:
1.
2.
3.
4.
5.
6.
Cleaning the contact tube.
Cleaning the conduit, which is usually done with compressed air.
Straightening or replacing the wire feed conduit.
Reducing the pressure on the wire feed rolls to prevent breakage.
Increasing the pressure on the wire feed rolls to provide adequate driving force.
Using a shorter distance from the wire feeder to the gun or from the wire feeder
to the electrode wire source.
7. Reducing clamping pressure on the spool of wire.
13.0.0 POSTWELD PROCEDURE
Several operations may be required after welding, such as cleaning, inspecting the
welds, and postheating. These are items which may or may not be part of the
procedure. The operations performed will depend on the governing code or
specification, type of metal, and the quality of the weld deposit.
13.1.0 Cleaning
Gas metal arc welding generally produces a very smooth weld bead with very little slag,
so in some cases cleaning the weld bead may be omitted. When welding steel, you can
remove the slag islands left by the process with a chipping hammer, an air chisel, or a
grinder. Removal of these slag islands is particularly important between passes of a
multiple pass weld because if they are not removed from the weld surface and then
welded over, slag inclusions can be formed. A certain amount of spatter is normally
produced, which you can remove by wire brushing, chipping, or grinding. Wire brushing
or buffing may be required to remove the discoloration around the weld bead. Mild steel
brushes can be used on most steels. Stainless steel brushes should be used on
stainless steels and non-ferrous metals to prevent contamination by rust from a mild
steel brush.
13.2.0 Inspection and Testing
Inspection and testing the weld to determine the quality of the weld joint are done after
cleaning. The many different methods of inspection and testing were covered in
previous chapters. The uses of these methods wiII often depend on the code or
specification that covered the welding. Testing of a weldment may be done
nondestructively or destructively.
Nondestructive testing is used to locate defects in the weld and base metal. Of the
many different nondestructive testing methods, some of the most widely used methods
are visual, magnetic particle, liquid penetrant, ultrasonic, and radiographic. Visual,
magnetic particle and liquid penetrant inspection are used to locate surface defects
where ultrasonic and radiographic inspections are used to locate internal defects.
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Destructive testing is used to determine the mechanical properties of the weld such as
the strength, ductility, and toughness. Destructive testing is also done by several
methods, depending on the mechanical properties being tested for. Some of the most
common types of destructive testing are tensile bar tests, impact tests, and bend tests.
13.3.0 Repairing of Welds
Repairing the weld is sometimes necessary when defects are found during inspection.
When a defect is found, it can be gouged, ground, chipped, or machined out depending
on the type of material being welded. For steels, grinding and air carbon arc gouging
are commonly used. Air carbon arc gouging is used on stainless steels when maximum
corrosion resistance is required, after grinding or wire brushing the groove face to
remove carbon deposits is done. It is not used on the non-ferrous metals because it
causes contamination in the form of carbon deposits.
For the stainless steels and the non-ferrous metals, chipping is a common method of
removing defects. Air carbon arc gouging is preferred for many applications because it
is usually the quickest method. Grinding is popular for removing surface defects and
shallow lying defects. Once the defects have been removed, the low areas created by
the grinding and gouging can be rewelded using GMAW or some other welding process.
The welds are then reinspected to make sure the defects have been properly repaired.
13.4.0 Postheating
Postheating is the heat treatment applied to the weld or weldment after welding.
Postheating is often required after the weld has been completed, but this depends upon
the type of metal being welded, the specific application, and the governing code or
specifications. Many of the low carbon steels and non-ferrous metals are rarely
postheated.
Various types of postheating are used to obtain specific properties. Some of the most
commonly used postheats are annealing stress relieving, normalizing, and quenching
and tempering. Stress relieving is the most widely used heat treatment after welding.
Postheating is accomplished by most of the same methods used for preheating such as
furnaces, induction coils, and electric resistance heating blankets. One method used for
stress relieving that does not involve the reheating of the weldments is called vibratory
stress relief. This method vibrates the weldment during or after welding to relieve the
residual stresses during or after solidification.
Annealing is a process involving heating and cooling that is usually applied to induce
softening. This process is widely used on metals that become very hard and brittle
because of welding. There are several different kinds, and when used on ferrous metals
it is called full annealing. Annealing is the heating up of a material to cause
recrystallization of the grain structure, which causes softening. Full annealing is a
softening process in which a ferrous alloy is heated to a temperature above the
transformation range and is slowly cooled to a temperature below this range. This
process is usually done in a furnace to provide a controlled cooling rate.
Normalizing is a heat treatment that is applied only to ferrous metals. Normalizing
occurs when the metal is heated to a temperature above the transformation range and
is cooled in still air to a temperature below this range. The main difference between
normalizing and annealing is that a normalized weldment is cooled in still air which
produces a quicker cooling rate than an annealed weldment which is slowly cooled in a
furnace. A normalizing heat treatment will refine the metal grain size and yield a tougher
weld, where an annealing heat treatment will result in a softer weld.
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Stress relieving is the uniform heating of a weldment to a high enough temperature
below the critical range to relieve most of the residual stresses due to welding. This is
followed by uniform cooling. This operation is performed on the ferrous metals and
some of the non-ferrous metals. This process also reduces warpage during machining
that may occur with a high residual stress buildup. Stress relieving is performed on nonferrous metal when stress buildup is a problem, but, for example in the case of
aluminum alloys, this heat treatment also will reduce the mechanical properties of the
base metal. In the case of magnesium alloyed with aluminum, stress relieving is
performed to avoid problems with stress corrosion. On parts and metals that are likely to
crack due to the internal stress created by welding, the parts should be put into stress
relief immediately after welding without being allowed to cool to room temperature. The
terms normalizing and annealing are misnomers for this heat treatment.
Quenching and tempering is another postweld heat treatment that is commonly used;
the metal is heated up and then quenched to form a hard and brittle metallurgical
structure. The weldment is then tempered by reheating to a particular temperature
dependent on the degree of ductility, strength, toughness, and hardness desired.
Tempering reduces the hardness of the part as it increases the strength, toughnes, and
ductility of the weld.
Test your Knowledge (Select the Correct Response)
16.
What causes inclusions?
A.
B.
C.
D.
17.
Steady travel speed
Too narrow a weaving motion
Slag left on the previous weld pass
Too small an electrode being used
Why i s a c ommon n on-stainless steel w ire br ush N OT used o n no n-ferrous
metals?
A.
B.
C.
D.
It causes etching.
The metal is too soft.
It will cause a static charge to build up.
It causes contamination in the form of carbon deposits.
14.0.0 WELDER TRAINING and QUALIFICATION
14.1.0 Welder Training
Gas metal arc welding requires a certain degree of welder skill to produce good quality
welds. Semi-automatic GMAW requires that the welder must still control the
manipulation of the welding gun and the speed of travel. This process will generally take
less skill to operate when compared to the manual welding processes because the
machine controls the arc length and feeds the filler wire. A welder who is skilled in the
manual welding processes (SMAW, GTAW) will generally have less difficulty learning to
weld with this process, but since the settings on the welding machine are more
important, a higher knowledge of how the equipment works is needed.
The exact content of a training program will vary depending on the specific applications
of the process. A training program should have enough flexibility so it can be adapted to
changing needs and applications. Because of this, emphasis may be placed on certain
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areas of training based on the complexity of the parts to be welded, and the type of
metal and governing code or specification. A pipe welding course would take more
training than a plate welding course.
Because of the wide variety of ferrous and non-ferrous metals welded and the wide
variety of equipment used, the exact content of a training course will vary. For example,
welding aluminum takes different equipment and has different welding characteristics
compared to welding steel. The major purpose of a training program is to give the
welder the skill and knowledge to be able to do the best job possible. A training program
may be broken up into several areas depending on the training requirements of the
student. The training discussed in the rest of the chapter has been divided into several
different areas.
14.1.1 Basic Gas Metal Arc Welding
The basic gas metal arc welding training program is used to teach the students the
basic skills necessary to weld plate. This course provides training on how to make tack
welds, strike the arc, make weld beads, and produce good quality fillet and groove
welds. This course also gives the student the knowledge of the process of setting up the
equipment and cleaning the metal, the basic operating principles, and the difficulties
that are commonly encountered. The training obtained by the student should give the
skill to perform a job welding plate material. This course should also provide the
background skill and knowledge required to take an advanced course for welding pipe.
The following is an outline for a course approximately 70 hours long.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Gas Metal Arc Welding Introduction
Safety and Health of Welders
Preparation for Welding
Surface Weld-Flat Position
Adjustment of Equipment
Square-Groove and Fillet Weld-Butt, Lap, Tee Joints-Flat Position (1 G, 1F)
Square-Groove and Fillet Weld-Butt, Lap, Tee Joints-Horizontal Position (2G, 2F)
Quality Butt and Fillet Welds
Square-Groove and Fillet Welds-Butt, Lap, Tee-Joints-Vertical Position, Down
(3G, 3F)
10. Square-Groove and Fillet Weld-Butt, Lap, Tee-Joints-Vertical Position, Up (3G,
3F)
11. Metal Transfer and Shielding Gas
12. Square-Groove and Fillet Weld-Butt, Lap, Tee Joints-Overhead Position (4G, 4F)
13. Single-V-Groove Weld-Butt Joint-Horizontal Position (2G)
14. Single-V-Groove Weld-Butt Joint-Guided Bend Tests
15. Single-V-Groove Weld-Butt Joint-Vertical Position, Down (3G)
16. Single-V-Groove Weld-Butt Joint-Guided Bend Test
17. Variations of Gas Metal Arc Welding (Spray Transfer, Globular Transfer, ShortCircuiting Transfer, Spot Welding)
18. Single-V-Groove Weld-Butt Joint-Flat Position
19. Single-V-Groove Weld-Butt Joint-Overhead Position (4G)
20. Fillet Weld-Lap and Tee-Joints-Horizontal Position (2F)
21. Fillet Weld-Lap and Tee-Joints-Vertical Position, Down (3F)
A specific program could then be taken for welding the different non-ferrous metals. A
program should explain the specific properties and welding characteristics of the metal.
Other parts of the program should explain the types and compositions of the different
alloys, the selection of filler metal and shielding gas, the equipment variations, and the
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special precautions such as cleaning and postweld operations. This training program
should provide the student the basic skills necessary for the welding of these metals.
The following course outline is for training of gas metal arc welding of aluminum and
aluminum alloys. It is approximately 35 hours in length.
1. Introduction to "Gas Metal Arc Welding of Aluminum"
2. Safety and Health of Welders
3. Stringer Bead-Flat Position (Machine Adjustment)
4. Fillet Weld-Lap and Tee-Joint-Horizontal Position (2F)
5. Fillet Weld-Lap and Tee-Joints-Vertical Position, Up (3F)
6. Weldability of Aluminum Alloys
7. Fillet Weld-Tee-Joint-Overhead Position (4F)
8. Fillet Weld-Outside Corner and Tee-Joint Flat Position (1 F)
9. Shielding Gases for Gas Metal Arc Welding of Aluminum
10. Single-Vee-Groove Weld-Butt Joint-Flat Position (with backing) (1 G)
11. Fillet Weld-Outside Corner and Tee-Joint Vertical Position ,Up (3F)
12. Fillet Weld-Tee-Joint-Vertical Position Up (Visual and Etch Tests) (3F)
13. Fillet Weld-Tee-Joint-Overhead Position (4F)
14. Gas Metal Arc Welding of Non-ferrous Metals Other than Aluminum
14.1.2 Gas Metal Arc Welding Steel Pipe
Since pipe welding is more difficult than plate welding, the student should be skilled in
welding groove joints in all positions on plate before welding pipe. Pipe welding usually
involves fixed position welding. Vertical position, downhill welding is used on crosscountry transmission pipelines. Vertical position, uphill welding is used on power plants,
refinery, and chemical installation applications. The following outline is for a general
course on pipe welding and is approximately 70 hours in length.
1.
2.
3.
4.
5.
6.
7.
8.
Introduction to Gas Metal Arc Pipe Welding
Safety and Health of Welders
Preparation of Equipment for Gas Metal Arc Pipe Welding
Preparation and Assembly of a Pipe Workpiece
Single-V-Groove Weld Butt Joint, Horizontal
Fixed Position Downhill Travel (5G)
Single-V-Groove Weld, Horizontal Fixed Position Travel, Guided Bend-Test (5G)
Single-V-Groove Weld, Butt Joint, Horizontal Fixed Position (5G), Downhill
Travel-Root Pass, Uphill Travel-Fill and Cover Passes
9. Welding Discontinuities in Gas Metal Arc Pipe Welding
10. Single-V-Groove Weld, Butt Joint, Vertical Fixed Position (2G)
11. Single-V-Groove Weld, Vertical Fixed Position (2G), Guided Bend Test
12. Single-V-Groove Weld, Butt Joint, 45° Fixed Position (6G)
14.2.0 Welder Qualification
Before the welder can begin work on any job covered by a welding code or
specification, the welder must become certified under the code that applies. Many
different codes are in use today, and it is very important that the specific code is
referred to when taking qualification tests. In general, the following types of work are
covered by codes: pressure vessels and piping, highway and railway bridges, public
buildings, tanks and containers, cross-country pipelines, ordnance material, ships and
boats, and nuclear power plants. Several of the specifications include consideration of
the GMAW process:
1. ANSI/API 1104 Standard for Welding Pipelines and Related Facilities
NAVEDTRA 14250A
10-154
2. ASME Boiler and Pressure Vessel Code, Section IX, Welding and Brazing
Qualifications
3. ANSI/AWS 01.1 Structural Welding Code Steel
4. AWS 05.2 Standard for Welded Steel Elevated Tanks, Standpipes, and
Reservoirs for Water Storage
5. AWS 010.9 Specification for Qualification of Welding Procedures and Welders for
Piping and Tubing
6. ANSI/AWS 014.1 Specification for Welding Industrial and Mill Crane and Other
Material Handling Equipment
7. ANSI/AWS 014.2 Specification for Metal Cutting Machine Tool Weldments
8. ANSI/AWS 014.3 Specification for Welding Earthmoving and Construction
Equipment
9. ANSI/ASME B96.1 Specification for Welded Aluminum Alloy Storage Tanks
10. Marine Engineering Regulations and Material Specifications (CG 115)
These specifications do not provide qualifications of the GMAW process for all
applications and service requirements. For applications where AWS or other
specifications are not available and generalized criteria for qualification are desired,
AWS B3.0, Welding Procedure and Performance Qualification is often used.
Certification is obtained differently under the various codes. Certification under one
code will not necessarily qualify a welder to weld under a different code. In most cases,
certification for one employer will not allow the welder to work for another employer. If
the welder uses a different process or the welding procedure is altered drastically,
recertification is required. In most codes, if the welder is continually employed, welding
recertification is not required providing the work performed meets the quality
requirements.
Qualification tests may be given by responsible manufacturers or contractors. On
pressure vessel work, the welding procedure must also be qualified and this must be
done before the welders are qualified; under other codes, this is not necessary. To
become qualified, the welder must make specified welds using the required process,
base metal, thickness, electrode type, position, and joint design.
Because of the versatility of the GMAW process, the type of metal transfer and shielding
gas must also be considered. For example, in the AWS Structural Welding Code (01.1),
certain joint designs are considered prequalified for gas metal arc welding in the spray
and globular metal transfer modes. The short-circuiting mode is not considered
prequalified for these joint designs because of the lower welding voltage and welding
current values used, which can more easily cause an incomplete penetration
discontinuity if the process is not used properly.
Test specimens must be made according to standardized sizes and under the
observation of a qualified person. For most government specifications, a government
inspector must witness making the weld specimens. Specimens must be properly
identified and prepared for testing.
The most common test is a guided bend test. In some cases, radiographic
examinations, fracture tests, or other tests are employed. Satisfactory completion of test
specimens, providing they meet acceptability standards, will qualify the welder for
specific types of welding. Again, the welding that will be allowed depends on the
particular code. In general, the code indicates the range of thicknesses which may be
welded, the positions which may be employed, and the alloys which may be welded.
Qualification of welders is a highly technical subject and cannot be covered fully here.
You should obtain and study the actual code prior to taking any tests.
NAVEDTRA 14250A
10-155
15.0.0 WELDING SAFETY
Safety is an important consideration when welding. Every welding shop should have a
safety program and take adequate safety precautions to protect welders. Every welder
should be made aware of safety precautions and procedures. Employees who fail to
follow adequate safety precautions can cause physical injury to themselves and others
as well as damage to property. Failure to take safety precautions can result in physical
discomfort and loss of property, time, and money. Welding is a safe occupation when
safety rules and common sense are followed. A set of safety rules which should be
followed is presented in the American National Standard Z49.1, "Safety in Welding and
Cutting," published by the American Welding Society.
There are a number of hazards associated with gas metal arc welding. These do not
necessarily result in serious injuries. They can also be of a minor nature which can
cause discomforts that irritate and reduce the efficiency of the welders. These hazards
are the following:
1.
2.
3.
4.
5.
6.
Electrical shock
Arc radiation
Air contamination
Compressed gases
Fire and explosion
Weld cleaning and other hazards
15.1.0 Electrical Shock
You can take several precautions to prevent an electrical shock hazard. First, make
sure that the arc welding equipment is properly installed, grounded, and in good working
condition. The electrical equipment should be maintained and installed in accordance
with the National Electrical Code and any state and local codes that apply. Equipment
should be operated within NEMA Standards usual operating conditions for proper safety
and equipment life. The case or frame of the power supply should be connected to an
adequate electrical ground such as an approved building ground, cold water pipe, or
ground rod. Welding cables with frayed or cracked insulation and faulty or badly worn
connections can cause electrical short circuits and shocks. An improperly insulated
welding cable is both an electrical shock hazard and a fire hazard.
The welding area should be dry and free of any standing water. When it is necessary to
weld in a damp or wet area, wear rubber boots and stand on a dry, insulated platform.
15.2.0 Arc Radiation
Gas metal arc welding produces an intense welding arc that emits ultraviolet and
infrared rays. Skin exposed to the arc for a short time can suffer serious ultraviolet and
infrared burns, which are essentially the same as sunburn, but the burn caused by
welding can take place in a much shorter time and can be very painful. Because of this,
you should always wear protective clothing suitable for the welding to be done. These
clothes should be fairly heavy and not easily burned. Leather is often used to make
jackets, capes, and bibs, or other similar arrangements to shield the arms, shoulders,
chest, and stomach from the arc radiation and arc spatter. Leather is also used to make
gloves for the welder.
You should also protect your eyes from the radiation emitted by the welding arc;
otherwise, arc-burn can result. Arc-burn of the eye is similar to sunburn of the skin, and
it is extremely painful for about 24 to 48 hours. Usually arc-burn does not permanently
NAVEDTRA 14250A
10-156
injure the eyes, but it can cause intense pain. There are several commercial solutions
available to soothe the skin and eyes during the period of suffering. Infrared arc rays
can cause fatigue of the retina of the eye.
The effects of infrared rays are not nearly as noticeable or immediate as the effects of
ultraviolet rays. Infrared rays are probably more dangerous in that their effects can be
longer lasting and result in impaired vision. Gas metal arc welding produces a brighter
arc than shielded metal arc welding because there is no smoke and it is often used on
bright shiny metals such as aluminum and stainless steel.
Protect your eyes and face by a head shield that has a window set in it with a filter lens
in the window. Head shields are generally made of fiberglass or a pressed fiber material
so they will be lightweight. The filter lens is made of a dark glass capable of absorbing
infrared rays, ultraviolet rays, and most visible light coming from the arc. The type of
lens used varies for different welders, but it should be dark enough so that you can view
the arc without discomfort but not so dark that the you cannot see the puddle clearly
while welding. Table 10-34 shows the different lenses commonly recommended for use
in shielded metal arc welding (SMAW). The higher the lens numbers the darker the
lens. A clear glass should be put on the outside of the welding lens to protect it from
spatter and breakage. Never weld with a broken filter lens or cracks in your head shield.
Table 10-34 — Recommended Filter Lens Shades Used in Shielded Metal Arc
Welding (ANSI/AWS Z49.1).
Electrode Diameter-In. (mm)
Lens Shade Number
1/16 (1.6), 3/32 (2.4), 1/8 (3.2), 5/32 (4.0)
10
3/16 (4.8), 7/32 (5.6), 1/4 (6.4)
12
5/16 (7.9), 3/8 (9.5)
14
15.3.0 Air Contamination
Provide enough ventilation wherever welding and cutting are performed. Proper
ventilation will protect you from the evolving noxious fumes and gases. The degree and
type of ventilation will depend on the specific welding and cutting operation. It varies
with the size of work area, the number of operators, and types of materials to be welded
or cut. Potentially hazardous materials may exist in certain fluxes, coatings, and filler
metals, and they can be released into the atmosphere during welding and cutting.
In some cases, general natural-draft ventilation may be adequate. Other operations may
require forced-draft ventilation, local exhaust hoods or booths, or personal filter
respirators or air supplied masks. Welding inside tanks, boilers, or other confined
spaces requires special procedures, such as the use of an air-supplied hood or hose
mask. Check the welding atmosphere and ventilation system if workers develop unusual
symptoms or complaints. Measurements may be needed to determine whether
adequate ventilation is being provided. A qualified person, such as an industrial
hygienist, should survey the welding operations and environment. Follow their
recommendations for improving the ventilation of the work area. Do not weld on dirty
plate or plate contaminated with unknown material; the fumes and gases formed could
be hazardous to your health. Remove all paint and galvanized coatings before welding.
Consider all fumes and gases as potentially hazardous. More complete information on
health protection and ventilation recommendations for general welding and cutting can
be found in the American National Standard Z49.1,”Safety in Welding and Cutting.”
NAVEDTRA 14250A
10-157
15.4.0 Compressed Gasses
Use compressed gases only for their intended purpose. Store cylinders containing
oxygen separately from cylinders containing fuel gases. Securely fasten cylinders in
use, or in stores or cargo, to prevent their shifting or falling under any weather
conditions. Open the valve of the cylinder slowly and stand away from the face of the
regulator when doing this. Never strike the welding arc on a compressed gas cylinder.
When not in use, store gas cylinders with their caps on; caps should also be on when
they are moved. If the valve should get knocked off, the cylinder acts like a missile
because of the escaping gas and can cause injury and damage. When compressed gas
cylinders are empty, the valve should be closed and they should be marked empty. This
is done by marking the letters "MT" or "EMPTY" on the cylinder.
Move cylinders by tilting and rolling them on their bottom edges; avoid dragging and
sliding cylinders. When cylinders are transported by vehicle, secure them in position.
Cylinders should not be dropped, struck, or permitted to strike each other violently.
Discontinue the use of any cylinder before the pressure falls to zero. In particular,
oxygen cylinders should not be used in welding or cutting operations after the pressure
falls below approximately 25 lb/in2.
15.5.0 Fires and Explosions
Fires and explosions are hazards that can exist in a welding area if the proper
precautions are not taken. The GMAW process produces sparks and spatters which can
start a fire or explosion in the welding area if it is not kept free of flammable, volatile, or
explosive materials. Welding should never be done near degreasing and other similar
operations. Welders need to wear leather clothing to protect from burns because the
leather is fireproof.
Fires can also be started by an electrical short or by overheated worn cables. In case of
a fire that is started by a flammable liquid or an electrical fire, a CO2 or dry chemical
type of fire extinguisher is used. Fire extinguishers should be kept at handy spots
around the shop and the welders should make a mental note of where they are located.
Welders should not have disposable butane or propane lighters when welding. Sparks
or weld spatter hitting them can cause an explosion which may cause injury.
Other precautions that have to do with explosions are also important. A welder should
not weld on containers that have held combustibles unless it is certain that there are no
fumes or residue left. Welding should not be done on sealed containers without
providing vents and taking special precautions. When the welding gun is set down or
not in use, it should never be allowed to touch a compressed gas cylinder.
15.6.0 Weld Cleaning and Other Hazards
You can also encounter hazards during the weld cleaning process. Take precautions to
protect your skin and eyes from hot slag particles. The welding helmet, gloves, and
heavy clothing protect your skin from slag chipping and grinding of the weld metal. Wear
safety glasses with side shields underneath the welding helmet to protect your eyes
from particles that could get inside the welding helmet. Set up screens if there are other
people in the area to protect them from arc burn.
15.7.0 Summary of Safety Precautions
1. Make sure your arc welding equipment is installed properly, grounded, and in
good working condition.
NAVEDTRA 14250A
10-158
2. Always wear protective clothing suitable for the welding to be done.
3. Always wear proper eye protection when welding, grinding, or cutting.
4. Keep your work area clean and free of hazards. Make sure no flammable,
volatile, or explosive materials are in or near the work area.
5. Handle all compressed gas cylinders with extreme care. Keep caps on them
when they are not in use.
6. Make sure compressed gas cylinders are secured to the wall or other structural
supports.
7. When compressed gas cylinders are empty, close the valve and mark the
cylinder “Empty” or “MT.”
8. Do not weld in a confined space without extra special precautions.
9. Do not weld on containers that have held combustibles without taking extra
special precaution.
10. Do not weld on sealed containers or compartments without providing vents and
taking special precautions.
11. Use mechanical exhaust at the point of welding when welding lead, cadmium,
chromium, manganese, brass, bronze, zinc, or galvanized steel.
12. When it is necessary to weld in a damp or wet area, wear rubber boots and stand
on a dry, insulated platform.
13. Shield others from the light rays produced by your welding arc.
14. Do not weld near degreasing operations.
15. When the welding gun is not in use, do not hang it on a compressed gas cylinder.
Summary
This chapter has introduced you to the GMAW process from the types of power
sources, controls, and welding guns to the types of training and qualifications needed. It
described the industries that use the GMAW process and its applications. Welding
metallurgy, weld and joint design, and welding procedure variables were also
discussed. The chapter concluded with a description of possible weld defects and how
to identify them, and safety precautions used for the GMAW process. As always, refer
to the manufacturer’s operator manuals for the specific setup and safety procedures of
the welding machine you will be using.
NAVEDTRA 14250A
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Review Questions (Select the Correct Response)
1.
What type of current is used in gas metal arc welding?
A.
B.
C.
D.
2.
How can the gas metal arc welding process be applied?
A.
B.
C.
D.
3.
C.
D.
Circuit voltage that fails to produce enough heat
Damaged welding machine
Damaged cables
All of the above
Which safety device should you use to protect other personnel in a welding work
area from eye flash burns?
A.
B.
C.
D.
6.
Size of the electrode and number of lock connections
Amperage rating of the machine and distance from the work to the
machine
Size of the ground cable and capacity of the electrode holder
Distance from the ground clamp and type of electrode
The use of a good ground clamp that provides proper grounding is essential to
the production of quality welds. Which condition could develop without this proper
grounding?
A.
B.
C.
D.
5.
Semi-automatically and manually
Semi-automatically only
Semi-automatically and mechanized
Semi-automatically, mechanized, and automatically
What factors determine the size of a welding cable needed for a job?
A.
B.
4.
Constant
Indirect
Unmodulated low frequency
Modulated high frequency
Welding helmets
Flash goggles
Face masks
Welding screens
Electrodes manufactured in the U.S. must conform to what standards?
A.
B.
C.
D.
AISC/CRSI
AWS /ASTM
NAVOP 1061 (welding)
Engineering Standards, U.S. (1996 Ed.)
NAVEDTRA 14250A
10-160
7.
When the gun is positive and the workpiece is negative, the electrons flow from
the workpiece to the gun. What polarity is being used?
A.
B.
C.
D.
8.
What kind of sound does improper polarity emit?
A.
B.
C.
D.
9.
B.
C.
D.
True
False
What condition occurs when the welding current is too high?
A.
B.
C.
D.
13.
Hold the electrode at right angles to the work and strike it sharply against
the base metal.
Bring the electrode into contact with the work by using lateral motion.
Slowly lower the electrode onto the work until the arc strikes.
Place the electrode on the work until the base metal melts.
(True or False) Upon striking an arc, you immediately start the weld to ensure
good fusion and penetration.
A.
B.
12.
Changing the position of the ground clamp
Welding away from the ground clamp
Changing to alternating current
All of the above
What is the first thing you should do to start an arc by the striking method?
A.
11.
Cracking
Humming
Whistling
Hissing
Which step do you take to correct arc blow?
A.
B.
C.
D.
10.
Straight
Negative
Positive
Reverse
Overlap
Poor fusion
Undercutting
Porosity
What condition(s) can develop when the welding current is too low?
A.
B.
C.
D.
Overlap only
Poor fusion only
Undercutting and poor fusion
Overlap and poor fusion
NAVEDTRA 14250A
10-161
14.
What kind of sound does a good arc produce when the electrode, current, and
polarity are correct?
A.
B.
C.
D.
15.
What is the maximum thickness, in inches, a plate can be welded in one pass,
without edge preparation?
A.
B.
C.
D.
16.
(a.) 1 1/2
(a.) 1 1/4
(a.) 1 1/4
(a.) 1 1/2
(b.) 1/4
(b.) 3/8
(b.) 1/8
(b.) 1/4
What angle from the vertical should you hold the electrode when welding a lap
joint on plates of varying thicknesses?
A.
B.
C.
D.
19.
To reinforce the weld.
To hold plates in position while tack welding in place.
To obtain complete fusion at the root pass of the weld.
To reflect the heat from the electrode.
What (a) width and (b) thickness, in inches, of backing strip should be used on
plate over ½ inch thick?
A.
B.
C.
D.
18.
1/16
1/8
3/16
1/4
For what purpose do you use a backing strip when making a butt weld on 3/16inch plate or heavier in the flat position?
A.
B.
C.
D.
17.
Sharp cracking
Humming
Whistling
Hissing
15° to 20°
20° to 30°
30° to 40°
40° to 50°
When vertical welding upwards, how many degrees do you hold the electrode to
the vertical?
A.
B.
C.
D.
30°
45°
60°
90°
NAVEDTRA 14250A
10-162
20.
Which mistake can cause excessive spatter in welds?
A.
B.
C.
D.
21.
Which mistake can cause cracked welds?
A.
B.
C.
D.
22.
¼-inch or less
½-inch or less
½-inch or more
¾-inch or more
A tack weld should not exceed what size when applied to a pipe with a wall
thickness of ½ inch?
A.
B.
C.
D.
26.
Current too low
Current too high
Rigid joints
Faulty preheating
Only the single U-type of butt joint should be used to weld joints between pipes
when pipe has what wall thickness?
A.
B.
C.
D.
25.
Current too low
Current too high
Welding speed too slow
Rigid joints
Which mistake can cause brittle welds?
A.
B.
C.
D.
24.
Improper welding procedures
Improper welder techniques
Improper welding materials
All of the above
Which mistake can cause poor penetration?
A.
B.
C.
D.
23.
Arc too short
Arc too long
Current too low
Rigid joints
1 inch long and two thirds of the thickness of the pipe in depth
¾ inch long and two thirds of the thickness of the pipe in depth
½ inch long and 2/3 inch deep
1 ¼ inches long and 1/8 inch deep
The root of a fillet weld is where the _______.
A.
B.
C.
D.
edge of the weld intersects the base metal
back of the weld intersects the base metal surfaces.
face of the weld and the base metal meet
face and the toe meet
NAVEDTRA 14250A
10-163
27.
Which description refers to the face of a fillet weld?
A.
B.
C.
D.
28.
Which description refers to the toe of a fillet weld?
A.
B.
C.
D.
29.
Wear the proper lens shade in the helmet
Use eye drops
Close your eyes
Turn your head away from the arc
Ultra-violet rays from the arc _______.
A.
B.
C.
D.
33.
face to the toe
root of the weld to the face
root to the toe
toe to the leg
The welding arc gives off ultra-violet rays which can cause eye injury. How can
you prevent this injury?
A.
B.
C.
D.
32.
length of the weld
distance from the root of the joint to the toe
groove face adjacent to the root joint
exposed surface of the weld
The throat of a fillet is the shortest distance from the _______.
A.
B.
C.
D.
31.
Junction between the face of the weld and the base metal
Rippled surface of the weld
Root of the weld to the face
Edge of the weld that intersects the base metal
The leg of the weld is the _______.
A.
B.
C.
D.
30.
Exposed surface of the weld
Edge of the weld that intersects the base metal
Groove face adjacent to the root joint
Separation between the members to be joined
do not damage skin
can cause skin damage similar to sunburn
are a good source of vitamin C
are harmful if inhaled
Welding on contaminated metal surfaces can create gases that are________.
A.
B.
C.
D.
hazardous
inert
used as shielding gases
benign
NAVEDTRA 14250A
10-164
34.
Compressed gas cylinders_______.
A.
B.
C.
D.
35.
Compressed gases_______.
A.
B.
C.
D.
36.
an imaginary line drawn through the weld along its length
an imaginary line drawn through the weld across its width
the rippled surface of the weld
parallel to the leg of the weld
In the flat position welding, the face of the weld is approximately_____.
A.
B.
C.
D.
40.
hold a long arc to melt the slag on the previous bead
use a weaving motion for deep penetration
tap the weld bead and electrode several times
clean the previous bead thoroughly before depositing the next weld
In a groove weld, the axis of a weld is ______.
A.
B.
C.
D.
39.
are not needed in welding areas
should be worn during welding and cleaning operations
are not authorized at any time during welding operations
provide adequate protection for welding operations
When welding over a previously deposited bead, ______.
A.
B.
C.
D.
38.
are extremely expensive and should be used sparingly
are not temperature sensitive
may be used to blow dirt off clothes and work area
are to be used only for the purpose intended
Safety glasses with side shields______.
A.
B.
C.
D.
37.
should be kept at below freezing
should be handled and stored with care
need no special care
should be painted fluorescent green
perpendicular
at a right angle
horizontal
vertical
Horizontal position fillet welding is performed_____.
A.
B.
C.
D.
with the electrode in the horizontal position
with the electrode in the vertical position
on the upper side of an approximately horizontal surface and against an
approximately vertical surface
on the lower side of an approximately vertical surface against an
approximately horizontal surface
NAVEDTRA 14250A
10-165
41.
When making a horizontal fillet weld in a lap joint, the electrode should be positioned with a______ work angle and a _______ travel angle.
A.
B.
C.
D.
42.
Tack welds should be______.
A.
B.
C.
D.
43.
excessive penetration
dross
overlap
fingernailing
The distance that the fusion zone extends below the surface of the base metal is
called______.
A.
B.
C.
D.
45.
cleaned before the weld is made
half the length of the weld joint
welded over without cleaning
only on opposite corners
Excess weld metal beyond the toe line of the weld is called______.
A.
B.
C.
D.
44.
30°; 15°
10°; 45°
45°; 30°
30°; 45°
intrusion
penetration
undercutting
a crater
The metal particles expelled during welding which do not form a part of the weld
are called______.
A.
B.
C.
D.
porosity
spatter
dross
inclusions
NAVEDTRA 14250A
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Trade Terms Introduced in this Chapter
Alloy
An alloy is a compound of one or more metals or other
elements. For example, brass is the alloy of copper and
zinc.
American Wire Gauge
(AWG)
Standard numbering system for the diameters of round,
solid, nonferrous, electrically conducting wire.
Austenitic
Consisting mainly of austenite, which is a nonmagnetic
solid solution of ferric carbide, or carbon in iron used in
making corrosion-resistant steel.
Ferritic
Consisting of the pure iron constituent of ferrous metals,
as distinguished from the iron carbides.
Ferrous
An adjective used to indicate the presence of iron. The
word is derived from the Latin word ferrum ("iron").
Ferrous metals include steel and pig iron (with a carbon
content of a few percent) and alloys of iron with other
metals (such as stainless steel).
Inverter
An electrical converter that converts direct current into
alternating current.
Martensitic
Consisting of a solid solution of iron and up to one
percent of carbon, the chief constituent of hardened
carbon tool steels.
Nonferrous
The term used to indicate metals other than iron and
alloys that do not contain an appreciable amount of iron.
Tantalum
A gray, hard, rare, metallic element occurring in
columbite and tantalite and usually associated with
niobium; used because of its resistance to corrosion by
most acids, for chemical, dental, and surgical
instruments and apparatus.
Ternary
Consisting of three different elements or groups.
Thorium
A grayish-white, lustrous, somewhat ductile and
malleable, radioactive metallic element present in
monazite; used as a source of nuclear energy, as a
coating on sun-lamp and vacuum-tube filament
coatings, and in alloys.
NAVEDTRA 14250A
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Additional Resources and References
This chapter is intended to present thorough resources for task training. The following
reference works are suggested for further study. This is optional material for continued
education rather than for task training.
Principles of Shielded Metal Arc Welding, Miller Electric Manufacturing Company,
Appleton, WI.
Safety in Welding, Cutting, and Allied Processes, ANSI/ASC Z49.1:2005 An American
National Standard, American Welding Society, Miami FL, 2005.
Shielded Metal Arc Welding, Hobart Institute of Welding Technology , Troy Ohio,1998.
Welding and Allied Processes, S9086-CH-STM-010/CH-074R4, Commander, Naval
Sea Systems Command, Washington Navy Yard, Washington D.C.,1999.
Welding Theory and Application, TC 9-237, Department of the Army Technical Manual,
Headquarters, Department of the Army, Washington D.C., 1993.
Welding Theory and Application, TM 9-237, Department of the Army Technical Manual,
Headquarters, Department of the Army, Washington D.C., 1976.
NAVEDTRA 14250A
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