null  null
I. The GTAW (TIG) Process
Advantages of the GTAW Process
The necessary heat for Gas Tungsten Arc Welding (TIG)
is produced by an electric arc maintained between a
nonconsumable tungsten electrode and the part to be welded.
The heat-affected zone, the molten metal, and the tungsten
electrode are all shielded from the atmosphere by a blanket of
inert gas fed through the GTAW torch. Inert gas is that which
is inactive, or deficient in active chemical properties. The
shielding gas serves to blanket the weld and exclude the
active properties in the surrounding air. It does not burn, and
adds nothing to or takes anything from the metal. Inert gases
such as argon and helium do not chemically react or combine
with other gases. They possess no odor and are transparent,
permitting the welder maximum visibility of the arc. In some
instances a small amount of reactive gas such as hydrogen
can be added to enhance travel speeds.
The greatest advantage of the GTAW process is that it will
weld more kinds of metals and metal alloys than any other arc
welding process. TIG can be used to weld most steels including
stainless steel, nickel alloys such as Monel® and Inconel®,
titanium, aluminum, magnesium, copper, brass, bronze, and
even gold. GTAW can also weld dissimilar metals to one
another such as copper to brass and stainless to mild steel.
The GTAW process can produce temperatures of up to
35,000˚ F/ 19,426˚ C. The torch contributes only heat to the
workpiece. If filler metal is required to make the weld, it may
be added manually in the same manner as it is added in the
oxyacetylene welding process. There are also a number of
filler metal feeding systems available to accomplish the task
automatically. Figure 1.1 shows the essentials of the manual
GTAW process.
Concentrated Arc
The concentrated nature of the GTAW arc permits pin point
control of heat input to the workpiece resulting in a narrow
heat-affected zone. A high concentration of heat is an advantage
when welding metals with high heat conductivity such as
aluminum and copper. A narrow heat-affected zone is an
advantage because this is where the base metal has undergone
a change due to the superheating of the arc and fast cooling
rate. The heat-affected zone is where the welded joint is
weakest and is the area along the edge of a properly made
weld that would be expected to break under a destructive test.
Gas
Valve
Regulator/
Flowmeter
Shielding
Gas
Power Source
Coolant System
Power Cord
Gas
In
Remote Control
Gas
Out
Work Cable
Work
Clamp
Coolant In
Adapter
Block Coolant Out
Torch
Work
Figure 1.1 Essentials of the GTAW process (water cooled).
4
Coolant System
The main disadvantage of the GTAW process is the low filler
metal deposition rate. Another disadvantage is that the
hand-eye coordination necessary to accomplish the weld is
difficult to learn, and requires a great deal of practice to
become proficient. The arc rays produced by the process
tend to be brighter than those produced by SMAW and
GMAW. This is primarily due to the absence of visible fumes
and smoke. The increased amounts of ultraviolet rays from
the arc also cause the formation of ozone and nitrous oxides.
Care should be taken to protect skin with the proper clothing
and protect eyes with the correct shade lens in the welding
hood. When welding in confined areas, concentrations of
shielding gas may build up and displace oxygen. Make sure
that these areas are ventilated properly.
No Sparks or Spatter
In the GTAW process there is no transfer of metal across the
arc. There are no molten globules of spatter to contend with
and no sparks produced if the material being welded is free
of contaminants. Also under normal conditions the GTAW arc
is quiet without the usual cracks, pops, and buzzing of
Shielded Metal Arc Welding (SMAW or Stick) and Gas Metal
Arc Welding (GMAW or MIG). Generally, the only time noise
will be a factor is when a pulsed arc, or AC welding mode is
being used.
No Smoke or Fumes
The process itself does not produce smoke or injurious
fumes. If the base metal contains coatings or elements such as
lead, zinc, nickel or copper that produce fumes, these must
be contended with as in any fusion welding process on these
materials. If the base metal contains oil, grease, paint or other
contaminants, smoke and fumes will definitely be produced
as the heat of the arc burns them away. The base material
should be cleaned to make the conditions most desirable.
Process Summary
GTAW is a clean process. It is desirable from an operator
point of view because of the reasons outlined. The welder
must maintain good welding conditions by properly cleaning
material, using clean filler metal and clean welding gloves,
and by keeping oil, dirt and other contaminants away from
the weld area. Cleanliness cannot be overemphasized,
particularly on aluminum and magnesium. These metals are
more susceptible to contaminants than are ferrous metals.
Porosity in aluminum welds has been shown to be caused by
hydrogen. Consequently, it is most important to eliminate all
sources of hydrogen contamination such as moisture and
hydrocarbons in the form of oils and paint.
TIG
There is no requirement for flux with this process; therefore,
there is no slag to obscure the welder’s vision of the molten
weld pool. The finished weld will not have slag to remove
between passes. Entrapment of slag in multiple pass welds is
seldom seen. On occasion with materials like Inconel® this
may present a concern.
for GTAW • Gas Tungsten Arc Welding
GTAW Disadvantages
HANDBOOK
No Slag
II. GTAW Fundamentals
If you’ve ever had the experience of hooking up a car battery
backwards, you were no doubt surprised at the amount of
sparks and heat that can be generated by a 12 volt battery. In
actual fact, a GTAW torch could be hooked directly to a battery
and be used for welding.
When welding was first discovered in the early 1880s it was
done with batteries. (Some batteries used in early welding
experiments reached room size proportions.) The first
welding machine, seen in Figure 2.1, was developed by
N. Benardos and S. Olszewski of Great Britain and was issued
a British patent in 1885. It used a carbon electrode and was
powered by batteries, which were in turn charged with a
dynamo, a machine that produces electric current by
mechanical means.
Figure 2.1 Original carbon electrode welding apparatus — 1885.
5
The main disadvantage of the GTAW process is the low filler
metal deposition rate. Another disadvantage is that the
hand-eye coordination necessary to accomplish the weld is
difficult to learn, and requires a great deal of practice to
become proficient. The arc rays produced by the process
tend to be brighter than those produced by SMAW and
GMAW. This is primarily due to the absence of visible fumes
and smoke. The increased amounts of ultraviolet rays from
the arc also cause the formation of ozone and nitrous oxides.
Care should be taken to protect skin with the proper clothing
and protect eyes with the correct shade lens in the welding
hood. When welding in confined areas, concentrations of
shielding gas may build up and displace oxygen. Make sure
that these areas are ventilated properly.
No Sparks or Spatter
In the GTAW process there is no transfer of metal across the
arc. There are no molten globules of spatter to contend with
and no sparks produced if the material being welded is free
of contaminants. Also under normal conditions the GTAW arc
is quiet without the usual cracks, pops, and buzzing of
Shielded Metal Arc Welding (SMAW or Stick) and Gas Metal
Arc Welding (GMAW or MIG). Generally, the only time noise
will be a factor is when a pulsed arc, or AC welding mode is
being used.
No Smoke or Fumes
The process itself does not produce smoke or injurious
fumes. If the base metal contains coatings or elements such as
lead, zinc, nickel or copper that produce fumes, these must
be contended with as in any fusion welding process on these
materials. If the base metal contains oil, grease, paint or other
contaminants, smoke and fumes will definitely be produced
as the heat of the arc burns them away. The base material
should be cleaned to make the conditions most desirable.
Process Summary
GTAW is a clean process. It is desirable from an operator
point of view because of the reasons outlined. The welder
must maintain good welding conditions by properly cleaning
material, using clean filler metal and clean welding gloves,
and by keeping oil, dirt and other contaminants away from
the weld area. Cleanliness cannot be overemphasized,
particularly on aluminum and magnesium. These metals are
more susceptible to contaminants than are ferrous metals.
Porosity in aluminum welds has been shown to be caused by
hydrogen. Consequently, it is most important to eliminate all
sources of hydrogen contamination such as moisture and
hydrocarbons in the form of oils and paint.
TIG
There is no requirement for flux with this process; therefore,
there is no slag to obscure the welder’s vision of the molten
weld pool. The finished weld will not have slag to remove
between passes. Entrapment of slag in multiple pass welds is
seldom seen. On occasion with materials like Inconel® this
may present a concern.
for GTAW • Gas Tungsten Arc Welding
GTAW Disadvantages
HANDBOOK
No Slag
II. GTAW Fundamentals
If you’ve ever had the experience of hooking up a car battery
backwards, you were no doubt surprised at the amount of
sparks and heat that can be generated by a 12 volt battery. In
actual fact, a GTAW torch could be hooked directly to a battery
and be used for welding.
When welding was first discovered in the early 1880s it was
done with batteries. (Some batteries used in early welding
experiments reached room size proportions.) The first
welding machine, seen in Figure 2.1, was developed by
N. Benardos and S. Olszewski of Great Britain and was issued
a British patent in 1885. It used a carbon electrode and was
powered by batteries, which were in turn charged with a
dynamo, a machine that produces electric current by
mechanical means.
Figure 2.1 Original carbon electrode welding apparatus — 1885.
5
A SIMPLE WELDING CIRCUIT
CURRENT FLOW (AMPS)
_
BATTERY
(VOLTAGE)
+
Figure 2.2 A simple welding circuit showing voltage source and current flow.
Figure 2.2 shows what a welding circuit using a battery as a
power source would look like.
The two most basic parameters we deal with in welding are
the amount of current in the circuit, and the amount of voltage
pushing it. Current and voltage are further defined as follows:
Current — The number of electrons flowing past a given
point in one second. Measured in amperes (amps).
Voltage — The amount of pressure induced in the circuit to
produce current flow. Measured in voltage (volts).
Resistance in the welding circuit is represented mostly by the
welding arc and to a lesser extent by the natural resistance of
the cables, connections, and other internal components.
Chapters could be written on the theory of current flow in an
electrical circuit, but for the sake of simplicity just remember
that current flow is from negative to positive. Early
researchers were surprised at the results obtained when the
battery leads were switched. We’ll examine these differences
in more detail later in the section when we discuss welding
with alternating current.
Even after alternating current (AC) became available for welding
with the use of transformer power sources, welds produced
were more difficult to accomplish and of lesser quality than
those produced with direct current (DC). Although these AC
transformer power sources greatly expanded the use of commercial power for SMAW (Stick), they could not be used for
GTAW because as the current approached the zero value, the
arc would go out. (see Figure 2.4). Motor generators followed
quickly. These were machines that consisted of an AC motor, that
turned a generator, that produced DC for welding. The output
of these machines could be used for both SMAW and GTAW.
It was with a motor generator power source that GTAW was
first accomplished in 1942 by V.H. Pavlecka and Russ
Meredith while working for the Northrup Aviation Company.
Pavlecka and Meredith were searching for a means to join
magnesium, aluminum and nickel, which were coming into
use in the military aircraft of that era.
6
Figure 2.3 The original torch and some of the tips used by Pavlecka and
Meredith to produce the first GTAW welds in 1942. Note the torch still
holds one of the original tungstens used in those experiments.
Although the selenium rectifier had been around for some
time, it was the early 1950s when rectifiers capable of handling
current levels found in the welding circuit came about. The
selenium rectifier had a profound effect on the welding industry.
It allowed AC transformer power sources to produce DC. And
it meant that an AC power source could now be used for
GTAW welding as well as Stick welding.
The realization is that high frequency added to the weld circuit
would make AC power usable for TIG welding. The addition
of this voltage to the circuit keeps the arc established as
the weld power passes through zero. Thus stabilizing the
GTAW arc, it also aids in arc starting without the risk of
contamination. The later addition of remote current control,
remote contactor control, and gas solenoid control devices
evolved into the modern GTAW power source. Further
advances such as Squarewave, and Advanced Squarewave
power sources have further refined the capabilities of this
already versatile process.
Alternating Current
Alternating current (AC) is an electrical current that has both
positive and negative half-cycles. These components do not
occur simultaneously, but alternately, thus the term alternating
current. Current flows in one direction during one half of the
cycle and reverses direction for the other half cycle. The half
cycles are called the positive half and the negative half of the
complete AC cycle.
Frequency
The rate at which alternating current makes a complete cycle
of reversals is termed frequency. Electrical power in the
United States is delivered as 60 cycles per second frequency,
or to use its proper term 60 hertz (Hz). This means there are
120 reversals of current flow directions per second. The
power input to an AC welding machine and other electrical
equipment in the United States today is 60 Hz power. Outside
of North America and the United States, 50 Hz power is more
commonly used. As this frequency goes up, the magnetic
effects accelerate and become more efficient for use in transformers, motors and other electrical devices. This is the
WORK
3/32" ELECTRODE
ELECTRODE
GAS
IONS
+ –
+ –
+
–
ELECTRONS
WORK
Figure 2.6 AC welding machine connection.
Squarewave AC
The AC Sine Wave
In some of the following sections we will be seeing alternating
current waveforms which represent the current flow in a
circuit. The drawing in the first part of Figure 2.5 is what
would be seen on an oscilloscope connected to a wall receptacle and shows the AC waveform known as a sine wave. The
other two types of waveforms that will be discussed are
Squarewave and Advanced Squarewave. Figure 2.5 shows a
comparison of these three waveforms. These waveforms
represent the current flow as it builds in amount and time in
the positive direction and then decreases in value and finally
reaches zero. Then current changes direction and polarity
reaching a maximum negative value before rising to the zero
value. This “hill” (positive half) and “valley” (negative half)
together represent one cycle of alternating current. This is
true no matter what the waveform is. Note however, the
amount of time at each half cycle is not adjustable on the sine
wave power sources. Also notice the reduced current high
points with either of Squarewave type power sources.
Current
200
+
0
_
200
Sine
Wave
Square
Wave
Advanced
Square
Wave
Figure 2.5 Comparison of the three different AC waveforms all
representing a time balanced condition and operating at 200 amperes.
Some GTAW power sources, due to refinements of electronics,
have the ability to rapidly make the transition between the
positive and negative half cycles of alternating current. It is
obvious that when welding with AC, the faster you could
transition between the two polarities (EN and EP), and the
more time you spent at their maximum values, the more
effective the machine could be. Electronic circuitry makes it
possible to make this transition almost instantaneously. Plus
the effective use of the energy stored in magnetic fields
results in waveforms that are relatively square. They are not
truly square due to electrical inefficiencies in the Squarewave
power source. However, the Advanced Squarewave GTAW
power source has improved efficiencies and can produce a
nearly square wave as compared in Figure 2.5.
Advanced Squarewave
for GTAW • Gas Tungsten Arc Welding
Figure 2.4 An oscilloscope representation of normal 50 and 60 Hz in
relation to increased frequency rate.
TIG
AC
WELDING
POWER
SUPPLY
HANDBOOK
fundamental principal on how an “inverter power source
works”. Frequency has major effect on welding arc performance. As frequencies go up, the arc gets more stable,
narrows, and becomes stiffer and more directional. Figure 2.4
represents some various frequencies.
+
0
–
Figure 2.7 Advanced Squarewave superimposed over a sine wave.
Advanced Squarewave allows additional control over the
alternating current waveforms. Figure 2.7 shows an AC sine
wave and an Advanced Squarewave superimposed over it.
Squarewave machines allow us to change the amount of time
within each cycle that the machine is outputting electrode
positive or electrode negative current flow. This is known
as balance control. They also reduce arc rectification and
resultant tungsten spitting. With Advanced Squarewave
technology, AC power sources incorporate fast switching
electronics capable of switching current up to 50,000 times
per second, thus allowing the inverter type power source to
be much more responsive to the needs of the welding arc.
These electronic switches allow for the switching of the
direction the output welding current will be traveling. The
output frequency of Squarewave or sine wave power sources
is limited to 60 cycles per second, the same as the input
power from the power company. With this technology and
7
advancements in design, the positive and negative amplitude
of the waveform can be controlled independently as well as
the ability to change the number of cycles per second.
Alternating current is made up of direct current electrode
negative (DCEN) and direct current electrode positive
(DCEP). To better understand all the implications this has on
AC TIG welding, let’s take a closer look at DCEN and DCEP.
Direct Current Electrode Negative
(Nonstandard Term is Straight Polarity)
DC
WELDING
POWER
SUPPLY
1/16" ELECTRODE
Direct Current
Direct current (DC) is an electrical current that flows in one
direction only. Direct current can be compared to water flowing
through a pipe in one direction. Most welding power sources
are capable of welding with direct current output. They
accomplish this with internal circuitry that changes or rectifies
the AC into DC.
Figure 2.8 shows what one cycle of AC sine wave power
would look like and what it would look like after it has been
rectified into DC power.
0˚
Alternating Current
180˚
360˚
Single Phase Direct Current
(Rectified AC)
Figure 2.8 Single-phase AC — single-phase direct current (rectified AC).
Polarity
Earlier in this section it was stated how the earliest welders
used batteries for their welding power sources. These early
welders found there were profound differences in the welding
arc and the resulting weld beads when they changed the battery
connections. This polarity is best described by what electrical
charge the electrode is connected for, such as direct current
electrode negative (DCEN) or direct current electrode positive
(DCEP). The workpiece would obviously be connected to the
opposite electrical charge in order to complete the circuit.
Review Figure 2.2.
When GTAW welding, the welder has three choices of welding
current type and polarity. They are: direct current electrode
negative, direct current electrode positive and alternating
current. Alternating current, as we are beginning to understand, is actually a combination of both electrode negative
and electrode positive polarity. Each of these current types
has its applications, its advantages, and its disadvantages.
A look at each type and its uses will help the welder select the
best current type for the job. Figures 2.9 and 2.11 illustrate
power supply connections for each current type in a typical
100 amp circuit.
8
+
–
–
+
WORK
Figure 2.9 Direct current electrode negative.
Direct current electrode negative is used for TIG welding of
practically all metals. The torch is connected to the negative
terminal of the power source and the work lead is connected
to the positive terminal. Power sources with polarity switches
will have the output terminals marked electrode and work.
Internally, when the polarity switch is set for DCEN, this will
be the connection. When the arc is established, electron flow
is from the negative electrode to the positive workpiece. In a
DCEN arc, approximately 70% of the heat will be concentrated
at the positive side of the arc and the greatest amount of heat
is distributed into the workpiece. This accounts for the deep
penetration obtained when using DCEN for GTAW. The electrode receives a smaller portion of the heat energy and will
operate at a lower temperature than when using alternating
current or direct current electrode positive polarity. This
accounts for the higher current carrying capacity of a given
size tungsten electrode with DCEN than with DCEP or AC. At the
same time the electrons are striking the work, the positively
charged gas ions are attracted toward the negative electrode.
+
Figure 2.10 GTAW with DCEN produces deep penetration because it
concentrates the heat in the joint area. No cleaning action occurs with this polarity.
The heat generated by the arc using this polarity occurs in the workpiece,
thus a smaller electrode can be used as well as a smaller gas cup and reduced
gas flow. The more concentrated arc allows for faster travel speeds.
(Nonstandard Term is Reverse Polarity)
–
1/4" ELECTRODE
+
GAS
IONS
+ –
+ –
+
–
ELECTRONS
WORK
Figure 2.11 Direct current electrode positive.
At this point, one might wonder how this polarity could be of
any use in GTAW. The answer lies in the fact that some nonferrous metals, such as aluminum and magnesium, quickly
form an oxide coating when exposed to the atmosphere. This
material is formed in the same way rust accumulates on iron.
It’s a result of the interaction of the material with oxygen. The
oxide that forms on aluminum, however, is one of the hardest
materials known to man. Before aluminum can be welded,
this oxide, because it has a much higher melting point than
the base metal, must be removed. The oxide can be removed
by mechanical means like wire brushing or with a chemical
cleaner, but as soon as the cleaning is stopped the oxides
begin forming again. It is advantageous to have cleaning
done continuously while the welding is being done.
The oxide can be removed by the welding arc during the
welding process when direct current electrode positive is
The good penetration of electrode negative plus the cleaning
action of electrode positive would seem to be the best
combination for welding aluminum. To obtain the advantages
of both polarities, alternating current can be used.
+
for GTAW • Gas Tungsten Arc Welding
When welding with direct current electrode positive (DCEP),
the torch is connected to the positive terminal on the welding
power source and the ground or work lead is connected to
the negative terminal. Power sources with polarity switches
will have the output terminals marked electrode and work.
Internally, when the polarity switch is set for DCEP, this will
be the connection. When using this polarity, the electron flow
is still from negative to positive, however the electrode is now
the positive side of the arc and the work is the negative side.
The electrons are now leaving the work. Approximately 70%
of the heat will be concentrated at the positive side of the arc;
therefore, the greatest amount of heat is distributed into the
electrode. Since the electrode receives the greatest amount of
heat and becomes very hot, the electrode must be very large
even when low amperages are used, to prevent overheating
and possible melting. The workpiece receives a smaller
amount of the total heat resulting in shallow penetration.
Another disadvantage of this polarity is that due to magnetic
forces the arc will sometimes wander from side to side when
making a fillet weld when two pieces of metal are at a close
angle to one another. This phenomena is similar to what is
known as arc blow and can occur in DCEN, but DCEP polarity
is more susceptible.
For example, to weld at 100 amperes it would take a tungsten
1/4" in diameter. This large electrode would naturally produce
a wide pool resulting in the heat being widely spread over the
joint area. Because most of the heat is now being generated
at the electrode rather than the workpiece, the resulting
penetration would probably prove to be insufficient. If DCEN
were being used at 100 amperes, a tungsten electrode of
1/16" would be sufficient. This smaller electrode would
also concentrate the heat into a smaller area resulting in
satisfactory penetration.
HANDBOOK
DC
WELDING
POWER
SUPPLY
used. The positively charged gas ions which were flowing
from the workpiece to the tungsten when welding with DCEN
are now flowing from the tungsten to the negative workpiece
with DCEP. They strike the workpiece with sufficient force to
break up and chip away the brittle aluminum oxide, and
provide what is called a cleaning action. Because of this
beneficial oxide removal, this polarity would seem to be
excellent for welding aluminum and magnesium. There are,
however, some disadvantages.
TIG
Direct Current Electrode Positive
Figure 2.12 GTAW with DCEP produces good cleaning action as the argon
gas ions flowing toward the work strike with sufficient force to break up
oxides on the surface. Since the electrons flowing toward the electrode
cause a heating effect at the electrode, weld penetration is shallow.
Because of the lack of penetration and the required use of very large
tungsten, continuous use of this polarity is rarely used for GTAW.
+
Figure 2.13 GTAW with AC combines the good weld penetration of DCEN
with the desired cleaning action of DCEP. With certain types of AC waveforms
high frequency helps re-establish the arc, which breaks each half cycle.
Medium size tungstens are generally used with this process.
9
Welding with Alternating Current
When using alternating current sine waves for welding, the
terms electrode positive (reverse polarity) and electrode
negative (straight polarity) which were applied to the workpiece and electrode lose their significance. There is no control
over the half cycles and you have to use what the power
source provides. The current is now alternating or changing
its direction of flow at a predetermined set frequency and with
no control over time or independent amplitude. During a
complete cycle of alternating current, there is theoretically one
half cycle of electrode negative and one half cycle of electrode
positive. Therefore, during a cycle there is a time when the
work is positive and the electrode is negative. And there’s a
time when the work is negative and the electrode is positive.
In theory, the half cycles of alternating current sine wave arc
are of equal time and magnitude as seen in Figure 2.14.
0˚
Figure 2.15 A reproduction of an actual unbalanced AC sine wave. Note
the positive half cycle is "clipped off". The missing portion was lost due to
rectification of the arc. What can also be seen is a high current spike which
can lead to tungsten breakdown and tungsten spitting.
Arc Rectification
Indicators for
the Welder
Results
Cures*
90˚
Arc noise
Tungsten
inclusions
Don’t dwell in
the weld pool
+
Weld pool oscillation
Erratic arc
Add filler metal
Tungsten electrode
breakdown
Lack of
cleaning action
Keep arc moving
along weld joint
180˚
360˚
0˚
–
270˚
AC CYCLE
Figure 2.14 One complete cycle of AC sine wave showing reversal of
current flow that occurs between the positive and negative half cycles.
The degree symbol represents the electrical degrees. The arc goes out
at 0˚, 180˚ and 360˚ and maximum amplitude is at 90˚ and 270˚.
Arc Rectification
When GTAW welding with alternating current, we find that the
equal half cycle theory is not exactly true. An oscilloscope
Figure 2.15 will show that the electrode positive half cycle is
of much less magnitude than the electrode negative half
cycle. There are two theories accounting for this. One is the
oxide coating on nonferrous metals such as aluminum. The
surface oxide acts as a rectifier, making it much more difficult
for the electrons to flow from the work to the electrode, than
from the electrode to the work. The other theory is that
molten, hot, clean aluminum does not emit electrons as easily
as hot tungsten. This results in more current being allowed to
flow from the hot tungsten to the clean molten weld pool,
with less current being allowed to flow from the clean molten
weld pool to the electrode. This is referred to as “arc rectification” and must be understood and limited by the welder as
indicated in Figure 2.16.
*Power source of proper Advanced Squarewave design will eliminate this
phenomenon.
Figure 2.16 Arc rectification.
Balanced and Unbalanced
Waveforms
Squarewave AC power sources have front panel controls
which allow the welder to alter the length of time the machine
spends in either the electrode positive (cleaning) portion of
the half cycle or electrode negative (penetration) portion of
the half cycle. Machines of this type are very common for TIG
welding in industry today. Very few industrial GTAW AC sine
wave power sources are being produced today.
Waveform Balance Control
% Time Electrode
Negative*
% Time Electrode
Positive
Not applicable,
control not
available
Not applicable,
control not
available
Squarewave
45 – 68
32 – 55
Advanced
Squarewave
10 – 90**
10 – 90
AC sine wave
power source
*This time controls the penetration and is most advantageous. Set to as
high a percentage as possible without losing the cleaning. Very rare to
set below 50%.
**Note the expanded electrode negative time available on the Advanced
Squarewave machine.
Figure 2.17 Balance control time available from different types of machines.
10
■
■
■
■
Can use higher currents with smaller electrodes
Increased penetration at a given amperage and
travel speed
Use of smaller gas cup and reduced shielding gas
flow rate
Reduced heat input with resultant smaller heat affected
zone and less distortion
MORE HEAT INTO WORK
GREATEST CLEANING ACTION
NOTE BALANCE CONTROL
BY ADJUSTABLE DWELL
ELECTRODE
POSITIVE
ELECTRODE
NEGATIVE
LINE VOLTAGE COMPENSATION
HOLDS AVERAGE CURRENT TO
_1%
+
WITH _10%
+
LINE VARIATION
4
5
6
3
7
1
9
2
8
0
10
MAX.
CLEANING
ELECTRODE
POSITIVE
ELECTRODE
NEGATIVE
4
5
NOTE BALANCE CONTROL
BY ADJUSTABLE DWELL
6
3
7
2
8
9
1
0
The benefits of the balance control should be well understood
and applied in an appropriate manner. Figure 2.21 shows
actual welds made at a given current and given travel speed
with only the balance control being changed.
10
MAX.
PENETRATION
Figure 2.18 Maximum penetration balance control setting. The waveform
has been set to an unbalanced condition, this allows more time in the negative
half cycle where current flow is from the electrode to the work. (This produces
more heat into the work and consequently deeper penetration.)
Balanced is when the balance control is set to produce equal
amounts of time electrode negative and electrode positive.
Thus on 60 Hz power, 1/120th of a second is spent electrode
negative (penetration) heating the plate and 1/120th of a second
is spent electrode positive (cleaning) removing oxides.
■
for GTAW • Gas Tungsten Arc Welding
Figure 2.20 Maximum cleaning control setting. The waveform has been
set to an unbalanced condition; this allows more time in the positive
half-cycle where positive gas ions can bombard the work. Only a certain
amount of total cleaning action is available, and increasing the time in the
electrode positive half cycle will not provide more cleaning and may melt
the tungsten, and damage the torch.
HANDBOOK
Max Penetration is when the balance control is set to
produce the maximum time at electrode negative and
minimum time at electrode positive.
TIG
Balance Wave Control Advantages
Arc cleaning action is increased
BALANCED WAVE
50%
ELECTRODE
POSITIVE
50%
ELECTRODE
NEGATIVE
AC BALANCE
BALANCED
4
5
6
3
7
1
9
2
8
0
10
BALANCE LOCATION VARIES
BETWEEN MODELS
Figure 2.19 Balanced control setting. The waveform has been set to
balanced. This allows equal time on each of the half cycles. Note on this
example balance occurs at a setting of 3 rather than at 5 as you might
expect. Other machines have digital read out that displays the exact % of
time set. Whatever the method of setting, a plateau is reached where
additional time in the positive half cycle is unproductive and will result in
damage to the tungsten or torch. Therefore, most Squarewave machines
will not permit settings that might cause damage to be made on the AC
balance control.
Max Cleaning is when the balance control is set to produce
the maximum time at electrode positive and minimum time at
electrode negative.
■
The most aggressive arc cleaning action is produced
Figure 2.21 Note the variation in the cleaning band, and the weld profiles
penetration pattern.
Adjustable Frequency (Hz)
As stated earlier in this section, alternating current makes
constant reversals in direction of current flow. One complete
reversal is termed a cycle and is referred to as its frequency.
As stated, in the United States the frequency of its delivery
is 60 cycles per second, or to use the preferred term 60 Hz.
This means there are 120 reversals of current flow
direction through the arc per second. The faster the current
going through the arc changes direction, increases the arc
pressure making the arc more stable and directional.
11
Figure 2.22 shows an illustration of the frequency effects on
a welding arc and the resultant weld profile.
This can be beneficial in automated welding by reducing the
amount of deflection and wandering that occurs in the direction
of travel when fillet welding.
Figure 2.24 Advanced Squarewave arc at 180 Hz fillet weld on aluminum.
Figure 2.22 Normal 60 Hz arc compared to a 180 Hz arc. The current is
changing direction 3 times faster than normal with a narrower arc cone and
a stiffer more directional arc. The arc does not deflect but goes directly to
where the electrode is pointed. This concentrates the arc in a smaller area
and results in deeper penetration.
Frequency Adjustability
Figure 2.25 An Advanced Squarewave power source with arc frequency
and enhanced balance control benefits.
Adjustable Frequency Advantages
■
Hz Range
■
AC sine wave
power source
Not adjustable, must use what the
power company supplies
■
Squarewave
Not adjustable, must use what the
power company supplies
Advanced
Squarewave
20 – 400
Figure 2.23 Frequency adjustment only available on the Advanced
Squarewave designed power sources.
A lower than normal frequency (60 Hz) can be selected on the
Advanced Squarewave power source, all the way down to 20 Hz,
as indicated in Figure 2.23. This would have applications
where a softer, less forceful arc may be required — build up,
outside corner joints, or sections where a less penetrating,
wider weld is required. As the frequency is increased, the arc
cone narrows and becomes more directional. This can be
beneficial for manual and automatic welding by reducing the
amount of deflection and wandering that occurs in the direction of travel when making groove or fillet welds. Figure 2.24
is an example of a high cycle arc on an aluminum fillet weld.
Figure 2.25 is an example of an Advanced Squarewave power
source capable of frequency adjustment and enhanced
balance control.
12
■
Higher frequency yields narrower arc
Higher frequency increases penetration
Lower frequency widens arc
Lower frequency produces a softer less forceful arc
Independent Current Control
The ability to control the amount of current in the negative
and positive half cycle independently is the last item in the AC
cycle that is controllable. Certain Advanced Squarewave power
sources allow this control. These power sources provide separate and independent amperage control of the electrode negative
(penetration) and electrode positive (cleaning) half cycles.
The four major independently controllable functions of the
Advanced Squarewave AC power source are:
1. Balance (% of time electrode is negative)
2. Frequency in hertz (cycles per second)
3. Electrode negative current level in amps*
4. Electrode positive current level in amps*
*Specially designed Advanced Squarewave power sources only.
Figure 2.26 shows you what an Advanced Squarewave output
might look like on an oscilloscope.
TIG
ADVANCED SQUAREWAVE AC WAVE
CLEAN
50 A
0
–
HANDBOOK
AMPS
+
WELD
100 A
TIME
Figure 2.26 An Advanced Squarewave AC wave with independent
current control.
The benefits of Advanced Squarewave forms go beyond
increased travel speeds. This type of welding allows a
narrower and deeper penetrating weld bead compared to that
of Squarewave or sine wave machines. The Advanced
Squarewave AC is capable of welding thicker material than
Squarewave or sine wave power sources at a given amperage.
Figure 2.27 shows an example of welds made with
Squarewave and Advanced Squarewave power sources. Note
with an extended balance control the etched cleaning zone
can be narrowed or eliminated.
Figure 2.28 An Advanced Squarewave AC power source.
The transition through zero on Advanced Squarewave power
sources is much quicker than Squarewave machines;
therefore, no high frequency is required even at low amperages. High frequency is only used to start the arc and is not
needed at all in touch start mode.
Advanced Squarewave Advantages
■
■
■
■
■
■
More efficient control results in higher travel speeds
Narrower more deeply penetrating arc
Able to narrow or eliminate etched zone
Improved arc stability
Reduced use of high frequency arc starts
Improved arc starting (always starts EP independent
of current type or polarity set)
for GTAW • Gas Tungsten Arc Welding
The ability to control these separate functions with the
Advanced Squarewave power source provides some unique
advantages. A more efficient method of balancing heat input
and cleaning action is available, which in turn, results in
increased travel speeds.
Figure 2.27 At 250 amps, note the weld profile comparison between the
Squarewave and Advanced Squarewave on this 1/2" aluminum plate.
13
Controlling the Advanced Squarewave Power Source
Feature
Waveform
AC Balance Control
51 – 99% EN
Amperage
Controls arc cleaning action. Adjusting the
% EN of the AC wave controls the width of
the etching zone surrounding the weld.
Effect on Bead
% EP
Reduces balling
action and helps
maintain point
Bead
% EN
Deep, narrow
penetration
Amperage
30 – 50% EN
% EP
Increases balling
action of the electrode
No Visible Cleaning
Wider bead and
cleaning action
0
Bead
% EN
Time (1 AC Cycle)
60 Cycles per Second
AC Frequency Control
Amperage
Narrow bead, with no
visible cleaning
0
Time (1 AC Cycle)
Controls the width of the arc cone. Increasing
the AC Frequency provides a more focused arc
with increased directional control.
Effect on Appearance
% EP
Shallow
penetration
Wider bead,
good penetration —
ideal for buildup work
Cleaning
Wider bead and
cleaning action
0
Bead
% EN
Time (1 AC Cycle)
Amperage
120 Cycles per Second
%
EP
0
%
EP
Cleaning
Narrower bead for
fillet welds and
automated applications
Narrower bead and
cleaning action
Bead
% EN
% EN
Time (1 AC Cycle)
Allows the EN and EP amperage values to be
set independently. Adjusts the ratio of EN to
EP to precisely control heat input to the work
and the electrode.
Current
Independent AC Amperage Control
0
EP+
EN –
Cleaning
More current in
EN than EP:
Deeper penetration
and faster travel
speeds
Narrow bead, with no
visible cleaning
Bead
Time
Current
No Visible Cleaning
EP+
0
EN –
More current
in EP than EN:
Shallower
penetration
Wider bead and
cleaning action
Bead
Time
Cleaning
Figure 2.29 The Advanced Squarewave power source allows the operator to shape the arc and control the weld bead. Separately or in any combination, the
user can adjust the balance control, frequency (Hz) and independent current control, to achieve the desired depth of penetration and bead characteristics for
each application.
Note: All forms of AC create audible arc noise. Many Advanced Squarewave AC combinations, while greatly improving desired weld performance,
create noise that may be objectionable to some persons. Hearing protection is always recommended.
14
Arc Starting Methods
Gas Tungsten Arc Welding uses a non-consumable electrode.
Since this tungsten electrode is not compatible with the metals
being welded (unless you happen to be welding tungsten), it
requires some unique arc starting and arc stabilizing methods.
Gas Ionization
Gas ionization is a fundamental requirement for starting and
having a stable arc. An ionized gas, a gas that has been electrically charged, is a good conductor of electricity. There are
two ways of charging this gas. Heat the gas to a high enough
temperature and electrons will be dislodged from the gas
atoms and the gas atoms will become positively charged gas
ions. The heat of a welding arc is a good source for this thermal
ionization. Unfortunately, when AC welding with conventional
sine waves, as the current approaches zero there is not sufficient heat in the arc to keep the gas ionized and the arc goes
out. The other ionization method is to apply enough voltage
to the gas atom. The electrons will be dislodged from the gas
atom and it is left as a positive gas ion.
High Frequency
This is a high voltage/low amperage generated at a very high
cycle or frequency rate. Frequency rates of over 16,000 Hz
and up to approximately 1 million Hz are typical. This high
voltage allows for good arc starting and stability, while the
high frequency it is generated at allows it to be relatively safe
in the welding operation. Due to this high safe frequency, the
high voltage ionizes the shielding gas, thus providing a good
DCEP +
DCEN –
Primary
Current
(60 Hz)
for GTAW • Gas Tungsten Arc Welding
Figure 2.30 With and without use of FASTIG™ flux for enhanced penetration.
When alternating current first became available for SMAW,
researchers immediately began looking for a means to assist
the re-ignition of the arc during the positive half of the AC
cycle. Shielded Metal Arc Welding electrodes at this time did
not have arc stabilizers in the coating for AC welding. It was
found that the introduction of a high frequency/high voltage
into the secondary welding circuit of the power source
assured arc re-ignition. This high-frequency source is actually
superimposed on the existing voltage of the power source.
The high frequency is used to eliminate the effects of the arc
outage. While the primary 60 cycle current is going through
its zero point, the HF may go through many cycles, thus preventing the arc from stopping. A common misconception is
that the high frequency itself is responsible for the cleaning
action of the arc. But the high frequency only serves to
re-ignite the arc which does the cleaning. Figure 2.31 shows
the relationship of superimposed high frequency to the
60 cycle frequency of the primary current.
HANDBOOK
As has been seen, the type of
welding current and polarity
has a big effect on welding
penetration. Developments
have been made in producing
chemical fluxes that effect the
surface tension of the weld
pool molecules and allow
improved penetration on
certain metals. The flux is
applied prior to welding and at a given amperage penetration
will be increased. Figure 2.30 is an example of weld profiles
with and without the use of this “Fast TIG Flux”.
path for the current to follow. So the path between the
electrode and the work becomes much more conducive to the
flow of electrons, and the arc will literally jump the gap
between the electrode and the workpiece. On materials
sensitive to impurities, touching the tungsten to the work will
contaminate it as well as the tungsten. This benefit of high
frequency is used to start the arc without making contact with
the work, eliminating this possible chance of contamination.
TIG
Welding Fluxes for GTAW
High Frequency
(over 16,000 Hz)
Figure 2.31 AC high frequency (not to scale).
With GTAW, high frequency is used to stabilize the arc. During
the negative half of the AC cycle, electron flow is from the
relatively small tungsten electrode to the much wider area of
the pool on the workpiece. During the positive half cycle the
flow is from the pool to the electrode. Aluminum and magnesium are poorer emitters of electrons when they are hot and
molten than the hot tungsten. Plus the area of current flow on
the molten weld pool is so much larger than the area on the
end of the tungsten. The arc has a tendency to wander and
become unstable. Because the high frequency provides an
ionized path for the current to follow, arc re-ignition is much
easier and the arc becomes more stable. Some power
sources use high frequency for starting the arc only and
some allow continuous high frequency to take advantage of
its stabilizing characteristics.
15
High frequency has a tendency to get into places where it’s
not wanted and falls under control of the Federal
Communication Commission (FCC). It can be a major interference problem with all types of electrical and electronic
devices. See Figure 2.33 for installation information.
The additional circuitry and parts required for the spark gap
oscillator and its added expense is an additional drawback.
High-Frequency Usage
Control Setting
Effect
Application
OFF
Removes HF from the weld leads
For SMAW welding or where HF interference is a concern
Continuous
Imposes HF on the weld leads, all the time,
when welding power is energized
For GTAW welding of the refractory oxide metals like
aluminum and magnesium
Start only
Limit the time HF is imposed on the welding
leads to when starting the arc
For GTAW DCEN welding of all metals that do not have refractory
oxides (titanium, stainless steel, nickel, carbon steel, etc.)*
*Can also be used on aluminum and magnesium when welding with Advanced Squarewave power sources.
Figure 2.32 Explains proper use and applications.
1. Sources of Direct High Frequency Radiation
High frequency source (welding power source
with built-in HF or separate HF unit), weld cables,
torch, work clamp, workpiece, and work table.
2. Sources of Conduction of High Frequency
Input power cable, line disconnect switch, and
input supply wiring.
Weld Zone
3. Sources of Reradiation of High Frequency
Ungrounded metal objects, lighting, wiring, water
pipe and fixtures, external phone and power lines.
3
50 ft
(15 m)
3
3
3
2
1
1
2
1
Figure 2.33 Illustrates sources of high-frequency radiation caused by an improper installation. The Federal Communications Commission has established
guidelines for the maximum high-frequency radiation permissible.
16
Lift-Arc™ allows the tungsten to be placed in direct contact
with the metal to be welded. As the tungsten is lifted off the
part, the arc is established. This is sometimes referred to as
touch start. Little if any chance of contamination is possible
due to special power source circuitry. When the Lift-Arc switch
is activated, lower power level is supplied to the tungsten
electrode. This low power allows some preheating of the
tungsten when it is in initial contact with the part. Remember
hot tungsten is a good emitter of electrons. This power level
is low enough not to overheat the tungsten or melt the work
thus eliminating the possibility of contamination. Once the
arc is established the power source circuitry switches from
the Lift-Arc mode to the weld power mode and welding can
commence. Figure 2.34 illustrates the proper techniques to
use with the Lift-Arc starting method.
These machines produce a high voltage discharge from a
bank of capacitors to establish the arc. The momentary spark
created by these machines is not unlike a static discharge.
Although capacitive discharge machines have good arc starting
capability, they do not have the arc stabilization properties of
high-frequency machines. They are typically used only for DC
welding and not usable on AC welding.
Arc Starting
Methods
Alternating Current
Direct Current
Electrode Neg.
High frequency
In continuous mode*
In start only mode
Pulse HF
In continuous mode*
In start only mode
Lift-Arc
Only with Advanced
Squarewave power
source**
Usable on any
DC welding with
appropriately equipped
power source
Scratch start
Not recommended
Capacitor
discharge
Not recommended
Not recommended
for x-ray quality
welding due to
tungsten inclusions
possibility
for GTAW • Gas Tungsten Arc Welding
Lift-Arc™
Capacitive Discharge
HANDBOOK
These machines utilize special circuitry to impose a high
intensity pulse on the output circuit when the voltage is at a
specific value. Lets assume we have a machine that provides
this pulse when voltage is 30 volts or more. When not welding,
voltage (or pressure) is at maximum because no current is
being allowed to flow and the pulsing circuitry is enabled. As
the electrode is brought near the work, the pulses help jump
start the arc and welding begins. Once the arc is started, weld
circuit voltage typically drops to a value somewhere in the
low teens to low twenties and the pulsing circuit senses this
change and drops out. The pulse mode circuitry can also help
stabilize the AC arc because it is enabled during times the
voltage sine wave is transitioning through zero. The high
intensity pulses do affect other electronic circuitry in the
immediate vicinity, but the effect is not as pronounced as that
of a high-frequency power source. You may find it necessary
to move the electrode slightly closer to the workpiece to initiate
the arc with pulse assist than you would with traditional highfrequency arc starting methods.
welding on a power source designed for SMAW only. These
machines are not equipped with an arc starter so the only way
to start the arc is with direct contact of the tungsten electrode
with the metal. This is done at full weld power level and generally results in contamination of the electrode and or weld
pool. This method as the name implies is accomplished
much like scratching or striking the arc as would be done for
Shielded Metal Arc Welding.
TIG
Pulse Mode HF
Usable on any
DC welding with
appropriately equipped
power source
*With specially designed Squarewave power sources and Advanced
Squarewave power sources it can be done in start mode as well.
**With specially designed Squarewave power sources appropriately
equipped with Lift-Arc circuitry.
Figure 2.35 The various arc starting methods and applications of each.
“Touch”
1 – 2 Seconds
Do NOT Strike
Like A Match!
Figure 2.34 Proper arc starting procedure when using the Lift-Arc method.
Scratch Start
Scratch start is not generally considered an appropriate arc
starting method as it can easily lead to contamination in the
weld area. It is usually preformed when doing GTAW DC
Figure 2.36 A Squarewave GTAW welding power source.
17
Pulsed GTAW
Some of the advantages of Pulsed GTAW are:
■
■
■
■
■
Good penetration with less heat input
Less distortion
Good control of the pool when welding out of position
Ease of welding thin materials
Ease of welding materials of dissimilar thickness
The main advantage of the Pulsed GTAW welding arc is that the
process produces the same weld as a standard arc, but with
considerably less heat input. As peak amperage is reached,
penetration is quickly achieved. Before the workpiece can
become heat saturated, the amperage is reduced to the point
where the pool is allowed to cool but current is sufficient to keep
the arc established. The pulsed arc greatly reduces the need to
adjust heat input as the weld progresses. This gives the welder
much greater pool control when welding out of position and in
situations where joints are of differing thicknesses.
The basic controls for setting pulse parameters are:
Peak Amperage — This value is usually set somewhat higher
than it would be set for a non-pulsed GTAW weld.
Background Amperage — This of course would be set lower
than peak amperage.
Pulses Per Second — Is the number of times per second that
the weld current achieves peak amperage.
% On Time — Is the pulse peak duration as a percentage of
total time. It controls how long the peak amperage level is
maintained before it drops to the background value.
direct current, and the signal does not switch between plus
and minus values as it does in the AC sine wave. This is not
to say that AC cannot be pulsed between two different output
levels, as there are applications and power sources capable of
doing just this.
High-Frequency Pulsed Welding
Although the majority of Pulsed GTAW welding is done in a
frequency range of .5 to 20 pulses per second, there are
applications where much higher frequencies are utilized. The
advantage of high-frequency pulsing (200 to 500 pulses per
second) is that the high-frequency pulse provides a much
“stiffer” arc. Arc stiffness is a measure of arc pressure. As
pressure increases, the arc is less subject to wandering
caused by magnetic fields (arc blow). Welding with higher
frequencies has also proven beneficial by producing better
agitation of the weld pool which helps to float impurities to
the surface resulting in a weld with better metallurgical properties.
High-frequency pulsing is used in precision mechanized and
automated applications where an arc with exceptional directional
properties and stability is required. It is also used where a stable
arc is required at very low amperages.
Since the electronic SCR and inverter type power sources
have inherently very fast response time they can easily be
pulsed. The SCR machines are somewhat limited in speed as
compared to the inverters. However pulse controls are available
for both types. They can be add-on controls like seen in
Figure 2.38 or built directly into the power source.
Refer to Figure 2.37 to see what effect each of these settings
has on the pulsed waveform.
DC PULSED WAVE TERMS
Peak Bkgrnd.
Amp. Amp.
Pulses Per
Second Adj.
% On Time
Adj.
AMPS
Figure 2.38 An add-on pulse control for the SCR and inverter power sources.
0
TIME
1 PPS
4 PPS
1 PPS
50 ON 50 OFF
50 ON 50 OFF
80 ON 20 OFF
Figure 2.37 DC pulsed wave terms.
The pulsed waveform is often confused with the AC sine, or
Squarewave. The AC sine wave represents direction of current
flow in the welding circuit, while the pulsed waveform represents
the amount and duration of two different output levels of the
power source. The pulse waveform is not a sine wave at all.
Note in Figure 2.37 that the actual output being displayed is
18
Safety First
Figures 3.2 through 3.7 show some different types of
welding machines and controllers.
Figure 3.1 GTAW power source plugged into wall connection. Primary
connection to the commercial power.
Notice the fuse box on the wall, where primary power to the
machine must be shut off if work needs to be done on any
part of the welding equipment. Also, the primary power at the
fuse box should be shut off when the machine is idle for long
periods of time.
Caution should always be taken when installing any welding
equipment. Should a welding machine be improperly connected,
a dangerous situation could exist. Improper connections
could lead to an electrically “hot” welding machine case,
which could result in a severe shock to anyone touching it.
Primary wiring should only be done by an electrically qualified
person who is absolutely sure of the electrical codes in a
given area. Before any primary power is connected to welding
equipment, the equipment’s operation manual should be
read, and the instructions strictly followed.
Selecting a Power Source
Figure 3.2 An inverter-based welding machine which has the capability of
modifying the frequency of the AC arc. This machine has multiprocess
capability including GTAW, SMAW, and pulsing capability.
for GTAW • Gas Tungsten Arc Welding
Larger DC TIG welding machines used for heavy plate, structural
fabrication and high production welding generally need threephase AC input power. Most industrial locations are supplied
with three-phase power since it provides the most efficient
use of the electrical distribution system and it is required by
many electric motors and other industrial electrical equipment.
These welding machines often have capacities of over 200 amps,
and often have 100% duty cycles.
HANDBOOK
Even though the majority of welding done is in the direct current
mode, welding power is most often obtained from the local
power company out of an AC wall socket.
Light welding, (low output requirements of about 200 amps
or less) can often be done with single-phase welding
machines. Duty cycles are often in the 60% or less range.
These types of welding machines are especially suited for
shops and garages where only single-phase power is available.
Some of these smaller single-phase machines may be capable
of using 115 volt AC primary power. Other machines may use
230 volt or higher primary power.
TIG
III. GTAW Equipment
Figure 3.3 An electronically controlled AC/DC power source. Features
include wave balance control to selectively unbalance the wave to optimize
welding characteristics.
With the many types of welding machines available, certain
considerations must be made in order to fit the right machine
to the job.
Rated output of the welding machine is an important consideration. The ranges of voltage and amperage needed for a
particular process must be determined. Then, a welding machine
can be selected to meet these output needs. Remember, the
output must be within a proper duty cycle range.
Figure 3.4 An AC/DC machine which was specifically designed for GTAW.
It includes many built-in components that make it adaptable to a wide
variety of applications.
19
The Constant Current Power Source
Arc welding power sources are classified in terms of their output characteristics with regard to voltage and amperage. They
can be constant current (CC), constant voltage (CV) or both.
Figure 3.5 An AC/DC machine of the type commonly used for Stick
electrode (SMAW) welding. With the addition of other components, it will
meet the requirements of many GTAW applications.
A constant current machine, the kind used in GTAW welding,
maintains close to a constant current flow in the weld circuit
no matter how much the voltage (arc length) varies.
Processes like GTAW and Shielded Metal Arc Welding (SMAW)
require the welder to maintain the arc length not the equipment.
A constant voltage power source maintains voltage at close to
a preset value no matter how much current is being used in the
process. This is the type of power source that is used in Gas
Metal Arc Welding (GMAW) or Metal Inert Gas (MIG) welding.
Processes like GMAW and Flux Cored Arc Welding (FCAW)
require the equipment to maintain a specific arc length.
You’ll notice that in both cases we say these machines maintain
current and voltage values close to preset values respectively.
They will vary slightly due to the fact that no power source is
perfectly efficient.
The relationship between voltage and current output is best
represented by plotting these values on a graph.
40
5
4
6
3
7
1
9
2
Figure 3.6 A multiprocess engine-driven welding generator capable of
AC and DC GTAW welding when fitted with an optional high-frequency
arc starter.
VOLTS
30
8
0
10
ADJUSTING VOLTS
20
10
0
10
20
30
AMPS
40
50
Figure 3.8 Volt-amp curve of a perfect battery.
In order to best understand the arc welding power source and
its requirements, it is best to start at the arc and work back to
the wall receptacle. The GTAW process requires the welder to
maintain the arc length. Any variation in arc length will affect
the voltage. The longer the arc the higher the voltage, and the
shorter the arc the lower the voltage. The welder will have difficulty maintaining the arc length, the voltage will change, as
the arc is moved across the part being welded. This change
in voltage (arc length) causes the output current (amperage)
to fluctuate. This output current should be kept as constant
as possible with the TIG process. The amperage creates the
heat that melts the metal and allows for consistent welding.
20
80
4
5
6
3
7
1
9
2
60
VOLTS
Figure 3.7 An advanced power source with a built-in programmer that
enables the operator to program the entire welding sequence. This is
recommended for automatic welding or whenever repeatability is required.
Figure 3.8 shows the volt-amp curve of a perfectly efficient
battery. This would be considered a CV power source
because no matter how much current is produced, the
voltage remains constant at twelve volts.
8
0
10
ADJUSTING AMPS
40
20
0
50
100 150
AMPS
200
250
Figure 3.9 Volt-amp curve of a perfect CC power source.
VOLTS
CC
40
50
100
AMPS
150
25
CV
VOLTS
20
15
10
5
0
100
AMPS
200
Figures 3.11 CV volt-amp curve.
The volt-amp curve shown in Figure 3.10 is indicative of
those seen in GTAW power sources, and the volt-amp curve
seen in Figure 3.11 represents the output of a constant voltage
or GMAW power source. The sloping line on the constant current
graph represents the output of a magnetic amplifier power
source. Because of this sloping characteristic, these power
sources are often referred to as droopers.
Figure 3.12 is an example of a basic DC power source for TIG
welding. The single-phase high voltage, low amperage is
applied to the main transformer. The transformer transforms
this high voltage to low voltage and at the same time transforms
the low amperage to high amperage for welding. It does not
affect the frequency, 60Hz in and 60Hz out. This low voltage
high amperage is now rectified from AC to DC in the rectifier.
This produces a fairly rough DC unlike the power provided by
a battery. The filter is used to smooth and stabilize the output
for a more consistent arc. The filtered DC is now supplied to
the TIG torch. These line frequency type power sources tend
to be large and very heavy. Their arc performance is slow and
sluggish and won’t allow them to be used for advanced wave
shaping or pulsing.
for GTAW • Gas Tungsten Arc Welding
Figures 3.10 CC volt-amp curve.
HANDBOOK
80
The true constant current power sources are an advantage in
that what current is set is what is delivered to the welding arc.
These electronically controlled power sources are desired
over the older-style power sources and find applications in
manual through automatic welding. The current settings are
very accurate and welds are very repeatable. The electronically
controlled and inverter-type power sources have special
circuits that maintain their output very consistently. This is
accomplished with a closed loop feedback circuit. This circuit
compares the output current going to the arc against what
has been set on the machine. It acts much like a car with the
cruise control activated — if going up and down a hill the
speed is maintained. If the welder raises and lowers the arc,
the amperage is maintained. Figure 3.13 shows a block diagram of this closed loop feedback sense circuit. This feature
is also helpful for line voltage compensation. By law the power
company must supply a consistent voltage. However they are
allowed a range, which can be as much as plus or minus 10%
of the nominal voltage. If the primary voltage to a non-compensated GTAW power source changed up to 10%, the power
going into the arc can fluctuate from 10 – 20%. With the line
voltage compensated machine, a plus or minus fluctuation of
up to 10% on the primary will only have a plus or minus
2% change in the arc, thus a very consistent weld. Most
electronically-controlled power sources can also be used to
provide pulsed welding current. Due to their fast response
time and great control over the current level setting, two different
heat levels pose no difficulty for these type power sources.
These machines can also be remotely controlled and these
controls can be very small and compact. They are small
enough to be mounted directly on the torch or built into the
torch handle. Limitations of this design can make them more
complex to operate, and are relatively expensive in comparison
to simpler control designs.
TIG
A perfectly efficient power source of the CC variety as seen in
Figure 3.9 would exhibit a volt-amp curve where a constant
current of 100 amps is output no matter what the voltage.
Squarewave Silicon-Controlled
Rectifier (SCR) Power Sources
These type power sources were introduced to the welding
industry in the mid 70s. They have now virtually replaced all
the AC sine wave power sources for the GTAW process. The
block diagram shown in Figure 3.14 is a representative of this
type of control. These type power sources use the large bulky
50 or 60 Hz transformer. They are typically very similar in size
and weight to the older style mechanically or magnetically
controlled power sources. They do have simple wave shaping
technology and possess closed loop feedback for consistent
weld output.
21
VOLTAGE
TRANSFORMATION
AND ISOLATION
CONTROL
CIRCUIT
FILTER
RECTIFIER
WELDING
OUTPUT
POWER
AC PRIMARY
POWER
(50/60 Hz)
AC
AC
DC
Figure 3.12 A conventional line frequency power source block diagram.
VOLTAGE
TRANSFORMATION
AND ISOLATION
CONTROL/
CONDITIONING
FILTER
ELEMENTS
WELDING
OUTPUT
POWER
AC PRIMARY
POWER
(50/60 Hz)
AC
DC
CONTROL
CIRCUIT
SENSE
CIRCUIT
Figure 3.13 The closed loop feedback keeps the output consistent when the arc voltage is varied and to compensate for primary line voltage fluctuations.
VOLTAGE
TRANSFORMATION
AND ISOLATION
CONTROL/
CONDITIONING
FILTER
ELEMENTS
AC PRIMARY
POWER
(50/60 Hz)
WELDING
OUTPUT
POWER
AC
DC
Figure 3.14 Block diagram of an SCR controlled power source, utilizes a line frequency weld transformer.
INVERTER SECTION
INPUT
RECTIFIER
FILTER
POWER
SWITCHES
TRANSFORMER
ISOLATION
OUTPUT
RECTIFIER
FILTER
WELDING
OUTPUT
POWER
AC PRIMARY
POWER
(50/60 Hz)
50/60 Hz AC
DC
25 kHz AC
CONTROL
CIRCUIT
Figure 3.15 An inverter power source block diagram.
22
DC
SENSE
CIRCUIT
Inverter power sources were first conceived in the 1940s, but
weren’t successfully marketed until the 1970s.
The Engine-Driven Power Source
Some of the first electric arc welding power sources invented
were the motor generator type that produced welding current
by means of a rotor moving inside a stator. This is the same
principle of current generation by means of moving a conductor
through a magnetic field. The movement in these machines
was provided by an electric motor.
The concept is still being put to good use by modern power
sources that replace the electric motor with gasoline or diesel
engines. The most important feature of these electro-mechanical
devices is that they free the welder from dependence on commercial power, and allow them the mobility to accomplish
Figure 3.16 Maintenance welding on agricultural equipment with an
engine driven power source.
Duty Cycle
for GTAW • Gas Tungsten Arc Welding
Figure 3.15 is a block diagram of an inverter type power
source. Machines of this type can run on single or threephase power, which will be covered later in this section. The
first thing the inverter does is rectify the high voltage low
amperage AC into DC. It is then filtered and fed to the inverter’s
high-speed switching devices. Just like a light switch they
turn the power on and off. They can switch at a very fast rate,
up to 50,000 times per second. This high voltage, low amperage
fast DC switching looks like AC to the transformer, which is
many times smaller than a 60 Hz transformer. The transformer
steps the voltage down and increases the amperage for welding.
This low voltage high amperage is filtered for improved DC
arc welding performance or converted to AC through the
electronic polarity control. This AC or DC power is then
provided to the TIG torch. This AC is fully adjustable as
described in the section on Advanced Squarewave AC.
The DC is extremely smooth and very capable of being pulsed
or sequenced.
Engine driven welding power sources are usually referred to
as rotating power sources of which there are two basic types.
The ALTERNATOR, which produces alternating current,
and the GENERATOR, which produces direct current. Most
manufacturers produce machines that provide both AC and
DC from the same unit.
HANDBOOK
Instead of operating at a common input power frequency of
50 or 60 Hz, inverters boost the frequency as much as 1000
times that of input frequency. This allows for a drastic reduction
in the number of transformer coil turns and reduced core area
resulting in a machine much smaller and lighter in weight
than a conventional transformer rectifier power source.
Another major advantage of this type of machine is its primary
power requirements. Some inverters can be used on either
three-phase or single-phase input power, and either 50 or 60 Hz.
This is due to the fact that incoming primary power is rectified and converted to the extent that it is not a critical factor.
Some inverters due to their unique circuitry, are multiprocess
machines capable of GTAW, GMAW, SMAW, FCAW (Flux
Cored) and Carbon Arc Gouging. Although these inverters are
capable of accomplishing these multi-processes, some are
specifically designed for and specialized for the TIG process.
tasks nearly anywhere in the world. Most of these machines
are welder generators that along with welding output produce
AC/DC current for the operation of lights and power tools.
TIG
The Inverter Power Source
As mentioned earlier in this section, duty cycle is of prime
importance in the selection of a welding machine. The duty
cycle of a welding power source is the actual operating time
it may be used at its rated load without exceeding the
temperature limits of the insulation in the component parts.
The duty cycle is based on a ten minute time period in the
United States. However, in some parts of the world, Europe
for example, the duty cycle is based on a five minute time
period. Simply stated, if a power source is rated at a 50%
duty cycle and it is operated at its rated output for five minutes,
it must be allowed to cool for five minutes before operating
again. The duty cycle is not accumulative. For example, a
power source with a 50% duty cycle cannot be operated for
thirty minutes then allowed to cool for 30 minutes. This violates
the ten minute rule. Also a machine rated at 50% should not
be operated at maximum for five minutes and then shut off.
The cooling fan must be allowed to operate and cool the internal
components, otherwise the machine might incur damage.
A power source with a 100% duty cycle may be operated at
or below its rated output continuously. However if the machine
is operated above its rated output for a period of time, it no
longer has a 100% duty cycle.
23
Single-Phase — Three-Phase
DC welding machines normally require either single-phase or
three-phase power. Three-phase power sources are quite popular
in the welding industry because, generally speaking, a threephase machine will deliver a smoother arc than a singlephase machine.
0
Most AC/DC TIG machines operate from single-phase power.
Some power sources can be powered by either single-phase or
three-phase power. These are usually inverter-type power sources.
A typical example of a three-phase rectified sine wave is
shown in Figure 3.17.
+
–
Two Cycles
Three-Phase Rectified Sine Wave
Figure 3.17 Three-phase DC current.
1
Have only qualified persons
make this installation.
1. Line Disconnect Device of
Proper Rating
2. Input Conductors
8
3
3. Grounding Conductor
Conductor rating must comply
with national, state, and local
electrical codes. Use lugs of
proper amperage capacity and
correct hole size.
4. Strain Relief Connector
Insert conductors through strain
relief.
5. Input Terminal Board
6. Line Terminals
2
7. Ground Terminal
Connect grounding conductor
and input conductors to line
terminals and to ground terminal.
Install and connect grounding
conductor and input conductors
in conduit or equivalent to
de-energized line disconnect
device.
Be sure grounding conductor
goes to an earth ground.
Reinstall side panel.
4
5
6
8. Line Fuses
Install into de-energized line
disconnect switch.
7
3
Figure 3.18 Typical input conductor connections and component locations — single-phase.
24
Figure 3.18 shows connections for a single-phase connection
to primary power. With single-phase power there are two current
carrying conductors and a ground wire, as you can see in the
electrical box, and the three connections on the terminal
board of the power source.
If a three-phase inverter power source is connected to a
single-phase line the output rating will be reduced. Check the
specific power source’s specification for details.
Most power sources are equipped with an input terminal
board. This board is for the proper connection of the power
source to the line voltage it is being supplied. This must be
properly connected or severe damage can occur to the welding
equipment. If the power source is moved from location to
location with different input voltages, relinking this board will
be required. Certain power sources are equipped with devices
that will detect the input voltage and automatically set the
equipment for proper operation. Two common types are
Have only qualified persons
make this installation.
1. Line Disconnect Device of
Proper Rating
5
7
3
2. Input Conductors
6
2
3. Grounding Conductor
Conductor rating must comply
with national, state, and local
electrical codes. Use lugs of
proper amperage capacity and
correct hole size.
for GTAW • Gas Tungsten Arc Welding
Three-Phase Input Connections
Many industrial DC welding power sources for GTAW utilize
three-phase primary power. Three-phase DC power exhibits
very smooth arc characteristics. This is because there are
three separate sine wave traces within the same time span
(1/60th of a second) as the single-phase sine wave trace.
Input Voltage
TIG
Figure 3.19 shows how primary power is connected to the input
of a three-phase power source. There are three current carrying
conductors and a ground wire, as seen in the electrical box. The
power source also shows three current carrying terminals
and a ground terminal connection.
HANDBOOK
Single-Phase Input Connections
AC and AC/DC transformer power sources operate from singlephase primary power. DC power sources may be either single
or three-phase. Check the nameplate, literature, or owners
manual to obtain this information.
4. Strain Relief Connector
Insert conductors through strain
relief.
5. Input Terminal Board
6. Line Terminals
1
8
4
3
7. Ground Terminal
Connect grounding conductor
and input conductors to line
terminals and to ground terminal.
Install and connect grounding
conductor and input conductors
in conduit or equivalent to
de-energized line disconnect
device.
Be sure grounding conductor
goes to an earth ground.
Reinstall side panel and top.
8. Line Fuses
Install into de-energized line
disconnect switch.
Figure 3.19 Typical input conductor connections and component connections — three-phase.
25
referred to as Auto-Link® and Auto-Line™. Auto-Link uses a
sensing circuit to mechanically relink the primary to the transformer as needed while Auto-Line electronically, on a sliding
scale, constantly monitors and maintains the appropriate
voltage to the transformer. Figure 3.20 represents how these
two systems function.
“DC Component” generates additional heat in the power
source. Some older GTAW power source designs used
Ni-Chrome resistor bands to help balance and dissipate this
heat, others used large capacitor banks built into the power
source, while still others used battery banks connected in
series with the arc. All were used to reduce this unbalance
phenomenon. Since this phenomenon affects the AC sine
wave power sources, it becomes an issue only on these type
power sources. Since AC Squarewave power sources are
designed to control the waveform, balance is not a concern
with these type power sources.
Heating in the main transformer due to DC component causes
at least two major problems:
1. Breakdown of insulation on the coils and core material.
2. A decrease in efficiency of the transformer due to the
higher resistance of the heated coils and core.
When power sources not specifically designed for GTAW
welding are used for welding aluminum or magnesium, DC
component must be taken into account by derating the
machines’ duty cycle. The lowering of the current available will
prevent overheating and damaging the main power transformer.
Derating Procedure
Figure 3.20 Note these automatic systems work on various voltages,
frequencies, single- and three-phase power.
Accessory Items
Some of these items are required for the GTAW process while
others are considered options.
Arc Starters/Stabilizers
High-frequency arc starters and stabilizers are for use with
AC or DC GTAW welding power sources. (See the chapters on
GTAW fundamentals, and GTAW techniques for more information
on the use of high frequency for welding). These units are
particularly useful when welding aluminum, magnesium,
stainless steel, titanium, brass, copper and other hard to weld
materials. Some DC GTAW power sources are not equipped
with HF. They use Lift-Arc™ or touch start technology which
allow them to function on specific metals. Some units will
feature gas valves, time delay relays, and control circuits to
regulate the flow of gas along with the high-frequency current.
Adding these type accessories to a power source not
designed for TIG (especially the AC type sine wave machines)
will require special precautions. An unbalanced condition
occurs when the AC sine wave power sources are used
for AC TIG welding. This unbalanced condition produces a
circulating current that the power source must deal with. This
26
This derating procedure is necessary only with AC GTAW, and
not with DC GTAW. It generally only applies to SMAW power
sources that have had an HF arc starter added to them so they
can be used for TIG welding.
Derate the AC sine wave power source by 30% from its rated
amperage.
For example, a power source for SMAW is rated at 200 amps,
60% duty cycle. For GTAW, we lower the 200 amps by 30%
to 140 amps at 60% duty cycle. It’s important to remember
with this method that the duty cycle for GTAW stays the same
as it was for SMAW. If the GTAW welding will be done continuously, find the 100% duty cycle amperage rating for
SMAW, then reduce this amperage by 30% for GTAW.
Remember, power sources specifically designed for GTAW do
not have to be derated. This fact can usually be found on the
machine’s nameplate, or in its accompanying literature.
Figure 3.21 A high-frequency arc starter and stabilizer.
Torches used for GTAW welding may be either water- or aircooled. High production or high amperage torches are usually
water-cooled while lighter duty torches for low amperage
applications may be air-cooled.
The water-cooled torch is designed so that water is circulated
through the torch cooling it and the power cable. Figure 3.23
shows an exploded view of a water-cooled torch.
Figure 3.24 A GTAW welding set-up with a water-cooled torch and
radiator cooling system.
GTAW Torch Components
Figure 3.22 An air-cooled GTAW torch.
COLLET BODY
CUP
TUNGSTEN
ELECTRODE
COLLET
BACKCAP
for GTAW • Gas Tungsten Arc Welding
Air-cooled torches are popular for lower amperage applications.
They require no additional cooling other than the surrounding
air. The higher amperage versions are less flexible and harder
to manipulate than water-cooled torches. The power cable must
be heavier than the cable in water-cooled torches, and may be
wound around the gas carrying hose or located inside the gas
hose to provide additional cooling. Figure 3.22 illustrates the
typical air-cooled torch, showing the basic components.
HANDBOOK
When welding with the TIG process it is true that the majority
of heat goes into the arc, however a significant amount is
retained in the torch. Consequently, some means must be
provided to remove the wasted heat.
contains a fuse link, which is also cooled by the water. If there
is no cooling water circulating, the fuse link will melt in two
and prevent damage to other more expensive components.
The fuse link is easily replaced. When the fuse link is replaced
and water flow is maintained, welding can continue. Figure
3.24 shows a GTAW welding setup using a water-cooled
torch and a radiator recirculating system.
TIG
GTAW Torch
Collet Body
The collet body screws into the torch body. It is replaceable
and is changed to accommodate various size tungstens and
their respective collets.
TORCH BODY
Collets
The welding electrode is held in the torch by the collet. The
collet is usually made of copper or a copper alloy. The collet’s
grip on the electrode is secured when the torch cap is tightened
in place. Good electrical contact between the collet and tungsten
electrode is essential for good current transfer.
Figure 3.23 A water-cooled GTAW torch.
The power cable is contained inside a hose, and the water
returning from the torch flows around the power cable
providing the necessary cooling. In this way, the power cable
can be relatively small making the entire cable assembly light
and easily maneuverable by the welder. When using a watercooled torch a lack of cooling water or no cooling water at all
will cause the polyethylene or braided rubber sheath to melt
or possibly burn the power cable in two. A torch manufacturer’s
specifications will designate the required amount of cooling
water for a specific torch. A safety device known as a “fuse
assembly” can be installed in the power cable. This assembly
Gas Lenses
A gas lens is a device that replaces the normal collet body. It
attaches to the torch body and is used to reduce turbulence
and produce a longer undisturbed flow of shielding gas. A
gas lens will allow the welder to move the nozzle further away
from the joint allowing increased visibility of the arc. A much
larger diameter nozzle can be used, which will produce a large
blanket of shielding gas. This can be very useful in welding
material like titanium. The gas lens will also enable the welder
to reach joints with limited access such as inside corners.
Figure 3.25 is an example of a gas lens and its set up on a
torch with a large nozzle and exaggerated tungsten extension.
27
Figure 3.25 Gas lens and set up for welding on a TIG torch.
Nozzles
Gas nozzles or cups as they are better known, are made of
various types of heat resistant materials in different shapes,
diameters and lengths. The nozzles are either screwed into the
torch head or pushed in place. Nozzles can be made of ceramic,
metal, metal-jacketed ceramic, glass, or other materials.
Ceramic is the most popular, but are easily broken and must be
replaced often. Nozzles used for automatic applications and high
amperage situations often use a water-cooled metal design.
Gas nozzles or cups must be large enough to provide adequate
shielding gas coverage to the weld pool and surrounding
area. A nozzle of a given size will allow only a given amount
of gas to flow before the flow becomes turbulent. When this
occurs the effectiveness of the shielding is reduced, and nozzle
size must then be increased to restore an effective nonturbulent flow of gas.
Coolers and Coolants
Water free-flowing directly out of the tap from well or city water
sources is not recommended to continuously cool the torch
head. Since cold tap water can be below the dew point and cause
moisture build-up inside the torch body, this may lead to weld
zone contamination until the torch temperature exceeds the dew
point. Continuous flow of tap water is not recommended as a
coolant because of its inherent mineral content, which can build
up over a period of time and clog the small cooling orifices in
the torch head. Conservation also dictates use of less wasteful
methods, such as coolant radiator re-circulating systems.
The re-circulating coolant must be of the proper type. Since
high frequency is being used it should be de-ionized to prevent the coolant from bleeding off the HF prior to it getting to
the arc. If the ambient temperature can drop below freezing it
must also be protected, but DO NOT use antifreeze. Antifreeze
contains leak preventers or other additives and is electrically
conductive. Some method of reducing algae growth is advisable. Consult with the coolant system manufacturer for their
recommendation on proper coolant solution. De-ionized water
can be used if the prior concerns are addressed. All coolants
must be clean. Otherwise, blocked passages may cause overheating and damage the equipment. It is advisable to use a
water strainer or filter on the coolant supply source. This prevents scale, rust, and dirt from entering the hose assembly.
28
The rate of coolant flow through the torch is important. Rates
that are too low may decrease cooling efficiency. Rates that
are too high damage the torch and service line. The direction
the coolant flows through the torch is critical. It should flow
from the coolant source directly through the water hose to
the torch head. The torch head is the hottest spot in the
coolant system and should be cooled first with the coolant at
its most efficient thermal transfer temperature. This coolant
upon leaving the torch head should cool the electrode power
cable on its return to the re-circulating system.
Remote Control
Sometimes a welding application requires the welder to place
a weld in a location where access to controls on the power
source is not readily available. The welder may need to control
the amount of current being used. Extra amperage may be
required at the start to establish a weld pool more quickly on
cold metal, or when making long welds on materials such as
aluminum, where weld current must be gradually reduced
because of the arc pre-heating the work.
Most welding machines designed primarily for TIG welding
provide remote control capability. The remote control capabilities
usually include output and current control. Generally, output
and current control are located as separate switches on the
machine’s front panel and can be operated independently if
desired. By using a remote control device, the welder can
safely get to a location away from the power source, activate
the power source and its systems, (gas flow, arc starter, etc.)
and vary the amperage levels as desired.
Remote output gives the welder control of open circuit voltage
(OCV) which is present at the output studs of the power
source with no load attached. Once a torch is connected to
the output, the electrode would be continuously energized if
it were not for the output control. The remote outputs primary
job then is to interrupt the weld circuit until the welder is
prepared to start the arc.
The current control switch on the power source when in the
remote position works in conjunction with the main current
control. If the main current control is set at 50%, the maximum
output current available through the remote device is 50%. To
obtain full machine output current through the remote device,
the main current control must be set at 100%. Understanding
this relationship allows the welder to fine tune the remote
control device for the work being done.
The most popular of the remote output and current controls
is the foot pedal type seen in Figure 3.26. This type operates
much the same as the gas pedal in an automobile: the
more it is depressed, the more current flows. Another type
which affords greater mobility is the finger-tip control seen in
Figure 3.27. The finger-tip control mounts on the torch.
Figure 3.26 TIG foot control. A foot-operated remote output and
current control.
Running Gear and Cylinder Racks
In order for the GTAW process to work most effectively, it
is necessary to keep the TIG torch to a fairly short length,
generally never over about 50 feet. To allow the power source to
be moved within easy reach of the work, having it mounted on a
running gear is very advantageous. It not only allows for ease
in mobility but aides in keeping the workshop clean. Having the
power source mounted a few additional inches off the floor
also keeps the internal components in the machine cleaner.
Figure 3.29 Examples of “Hard” Automation. Note the stationary
workpiece in one case while the arc is stationary in the other.
One of the most common forms of automation with the GTAW
process is its use in orbital welding. The orbital welding equipment
clamps onto the workpiece and is used to make tube to tube and
tube to sheet type welds. Continued refinement in the computer
controls and the inverter power sources systems have made
them extremely reliable for precise repeatability. Figure 3.30
shows an orbital welding head and related equipment.
for GTAW • Gas Tungsten Arc Welding
Figure 3.27 Finger-tip control. A finger-tip torch mounted output and
current control.
HANDBOOK
With increasing needs for high productivity and quality,
automated welding is becoming more popular. This can be as
simple as a fixed torch head (arc) with the workpiece (joint)
being moved by it. Or a fixed workpiece (joint) with the torch
(arc) being moved along it. Figure 3.29 shows an example
of this type of automation.
TIG
Automated TIG Welding
Cylinders are considered high-pressure vessels and must be
protected from damage. If the cylinder cap is not in place and
the cylinder is not secured, a serious accident can occur.
Never leave one of these high-pressure cylinders in an
unsecured manner. Figure 3.28 shows a combination running
gear and cylinder rack.
Figure 3.30 An orbital welding head and related equipment.
Whichever method is used, additional control is required over
the welding sequence for automation.
A weld sequence is what happens when a signal is given to
start the welding operation and also what happens when the
welding operation is shutdown. Figure 3.31 is an example of
a weld sequence.
Initial
Slope
Initial
Current
Preflow
Figure 3.28 Cylinder is securely chained in a safe operating condition with a
running gear to allow ease of moving the power source and related equipment.
Weld/Peak
Current
Final
Slope
Final
Current
Postflow
Figure 3.31 The various functions controlled by the weld sequence controller.
29
These sequence controllers can be built directly into the
power source (see Figure 3.32) or be housed in a separate
control box (see Figure 3.33).
Microprocessors
The ability to control the weld sequence is brought about by
the use of microprocessors. These powerful controllers are
almost always used in automated welding systems where
repeatability is of great importance.
Microprocessor controllers usually have the ability to store
numerous weld programs in memory assuring repeatability
as well as reducing set-up time.
Those functions controlled by microprocessors might include:
■
■
■
■
■
Figure 3.32 An inverter type power source with built-in weld sequencer
primarily used for automated welding.
■
■
■
Arc starting
Initial current, initial time and initial slope
Weld current, and weld time
Final slope, final current and final time
Pulse peak and background current
Pulse frequency
Percent of on time (pulse)
Post-flow
Connection for Automation
Applications
Figure 3.33 A precision TIG controller with built-in weld sequencer, HF,
timers for gas flow, metering and relay control for fixturing.
In order to interface the automatic welding power source
with the peripheral equipment some means of connection
must be provided. This peripheral equipment can be the fixture holding the part, to initiate part clamping or positioning
for welding. It can also be for starting the arc movement
along the seam or the part moving under the fixed arc. This
is a timing function and can best be handled by the weld
controller. Figure 3.34 is a 10-pin connection port for connecting this power source to peripheral equipment. It provides indications of the output at specific points in time.
Arc Length Control System
Figure 3.34 The 10-pin connector on an inverter power source capable of
being connected for automation operation.
Figure 3.35 An arc length control
and head mechanism.
30
Figure 3.36 Control and magnetic
head for arc manipulation.
Since arc length is critical on some applications, devices like
Figure 3.35 are available to maintain it consistently to plus or
minus 0.1 volts. Arc length and arc voltage mean the same
thing. Monitoring the voltage and using this data to control
the arc length will provide for consistent weld appearance,
profile and penetration.
Figure 3.37 A cold wire TIG set up.
Figure 3.38 A seam tracker for
maintaining the arc and joint
alignment.
Cold Wire Feed System
IV. Electrodes and
Consumables
Tungsten Electrodes for GTAW
Electrodes made of tungsten and tungsten alloys are secured
within a GTAW torch to carry current to the welding arc.
Tungsten is preferred for this process because it has the
highest melting point of all metals.
The tungsten electrode establishes and maintains the arc. It
is said to be a “nonconsumable” in that the electrode is not
melted and included in the weld pool. In fact, great care must
be taken so that the tungsten does not contact the weld pool
in any way, thereby causing a contaminated, faulty weld. This
is generally referred to as a “tungsten inclusion”.
Tungsten electrodes for GTAW come in a variety of sizes and
lengths. They may be composed of pure tungsten, or a combination of tungsten and other elements and oxides.
Electrodes are manufactured to specifications and standards
developed by the American Welding Society and the
American Society For Testing And Materials. Electrodes come
in standard diameters from .010" through 1/4", as seen in
Figure 4.1. The diameter of tungsten electrode needed is
often determined by the thickness of base metal being welded
and the required amperage to make the weld.
Lengths of tungstens needed are often determined by the
type of torch used for a particular application. Standard
lengths are shown in Figure 4.2. Of these, the 7" length is the
In order to keep the welding arc on track when following a
constantly varying weld seam, systems like Figure 3.38 have
been developed. This type control allows the equipment to
constantly monitor the weld joint location both horizontally
and vertically over the joint. In order to have consistency at high
travel speeds, devices like this can control the position of the
welding arc within plus and minus 0.005 inch or 0.13 mm.
Standard Tungsten Sizes
SI Units
U.S. Customary
Diameter
in
0.300
0.50
1.00
1.60
2.00
2.40
2.50
3.00
3.20
4.00
4.80
5.00
6.40
8.00
Diameter
Tolerance
in
± in. b, c
a
0.010
0.001
0.020
0.002
0.040
0.002
0.060
0.002
0.093
0.003
0.125 (1/8)
0.003
0.156 (5/32)
0.003
0.187 (3/16)
0.003
0.250 (1/4)
0.003
Tolerance
± mm b, c
0.025
0.05
0.05
0.05
0.05
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
for GTAW • Gas Tungsten Arc Welding
GTAW is generally considered a low-deposition process.
However, by automating it and adding the filler wire in an
automatic fashion its deposition rate can be increased.
Increased weld deposition means higher travel speeds and
more parts out the door at the end of the day. Figure 3.37
Seam Tracking
HANDBOOK
This control uses magnetic fields to deflect the arc in advantageous directions. It is useful for high speed automatic welding
to even out the weld pool, prevent undercut, and promote
uniform penetration. The oscillation and positioning effects of
these magnetic fields on the arc improve weld appearance
and weld bead profiles. See Figure 3.36.
represents a Cold Wire Feed System. Improved penetration
and weld profiles can be had by feeding the filler wire into the
back edge of the weld pool versus the front half of the weld
pool, which is typically done with manual welding. Some systems can be set up where the filler wire is preheated electrically. These systems are referred to as Hot Wire TIG.
TIG
Magnetic Arc Control
Notes:
a. 0.010 in. (0.30 mm) electrodes are also available in coils.
b. Tolerances, other than those listed, may be supplied as agreed upon
between supplier and user.
c. Tolerances shall apply to electrodes in both the clean finish and
ground finish conditions.
Figure 4.1 Diameters of standard tungsten electrodes (Courtesy AWS).
3" (76 mm)
6" (152 mm)
7" 178 mm)
12" (305 mm)
18" (457 mm)
24" (610 mm)
Figure 4.2 Standard tungsten lengths.
most commonly used. For special applications some suppliers
provide them in cut lengths to your specifications. For example,
.200" – .500", .501" – 3.000" and 3.001" – 7.000".
31
Cold Wire Feed System
IV. Electrodes and
Consumables
Tungsten Electrodes for GTAW
Electrodes made of tungsten and tungsten alloys are secured
within a GTAW torch to carry current to the welding arc.
Tungsten is preferred for this process because it has the
highest melting point of all metals.
The tungsten electrode establishes and maintains the arc. It
is said to be a “nonconsumable” in that the electrode is not
melted and included in the weld pool. In fact, great care must
be taken so that the tungsten does not contact the weld pool
in any way, thereby causing a contaminated, faulty weld. This
is generally referred to as a “tungsten inclusion”.
Tungsten electrodes for GTAW come in a variety of sizes and
lengths. They may be composed of pure tungsten, or a combination of tungsten and other elements and oxides.
Electrodes are manufactured to specifications and standards
developed by the American Welding Society and the
American Society For Testing And Materials. Electrodes come
in standard diameters from .010" through 1/4", as seen in
Figure 4.1. The diameter of tungsten electrode needed is
often determined by the thickness of base metal being welded
and the required amperage to make the weld.
Lengths of tungstens needed are often determined by the
type of torch used for a particular application. Standard
lengths are shown in Figure 4.2. Of these, the 7" length is the
In order to keep the welding arc on track when following a
constantly varying weld seam, systems like Figure 3.38 have
been developed. This type control allows the equipment to
constantly monitor the weld joint location both horizontally
and vertically over the joint. In order to have consistency at high
travel speeds, devices like this can control the position of the
welding arc within plus and minus 0.005 inch or 0.13 mm.
Standard Tungsten Sizes
SI Units
U.S. Customary
Diameter
in
0.300
0.50
1.00
1.60
2.00
2.40
2.50
3.00
3.20
4.00
4.80
5.00
6.40
8.00
Diameter
Tolerance
in
± in. b, c
a
0.010
0.001
0.020
0.002
0.040
0.002
0.060
0.002
0.093
0.003
0.125 (1/8)
0.003
0.156 (5/32)
0.003
0.187 (3/16)
0.003
0.250 (1/4)
0.003
Tolerance
± mm b, c
0.025
0.05
0.05
0.05
0.05
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
0.08
for GTAW • Gas Tungsten Arc Welding
GTAW is generally considered a low-deposition process.
However, by automating it and adding the filler wire in an
automatic fashion its deposition rate can be increased.
Increased weld deposition means higher travel speeds and
more parts out the door at the end of the day. Figure 3.37
Seam Tracking
HANDBOOK
This control uses magnetic fields to deflect the arc in advantageous directions. It is useful for high speed automatic welding
to even out the weld pool, prevent undercut, and promote
uniform penetration. The oscillation and positioning effects of
these magnetic fields on the arc improve weld appearance
and weld bead profiles. See Figure 3.36.
represents a Cold Wire Feed System. Improved penetration
and weld profiles can be had by feeding the filler wire into the
back edge of the weld pool versus the front half of the weld
pool, which is typically done with manual welding. Some systems can be set up where the filler wire is preheated electrically. These systems are referred to as Hot Wire TIG.
TIG
Magnetic Arc Control
Notes:
a. 0.010 in. (0.30 mm) electrodes are also available in coils.
b. Tolerances, other than those listed, may be supplied as agreed upon
between supplier and user.
c. Tolerances shall apply to electrodes in both the clean finish and
ground finish conditions.
Figure 4.1 Diameters of standard tungsten electrodes (Courtesy AWS).
3" (76 mm)
6" (152 mm)
7" 178 mm)
12" (305 mm)
18" (457 mm)
24" (610 mm)
Figure 4.2 Standard tungsten lengths.
most commonly used. For special applications some suppliers
provide them in cut lengths to your specifications. For example,
.200" – .500", .501" – 3.000" and 3.001" – 7.000".
31
Chemical Composition Requirements for Electrodes a
Weight Percent
AWS
Classification
UNS
Number b
W Min.
(difference)c
EWP
EWCe-2
EWLa-1
EWLa-1.5
EWLa-2
EWTh-1
EWTh-2
EWZr-1
EWG d
R07900
R07932
R07941
R97942
R07943
R07911
R07912
R07920
—
99.5
97.3
98.3
97.8
97.3
98.3
97.3
99.1
94.5
CeO2
—
1.8 – 2.2
—
—
—
—
—
—
La2O3
ThO2
ZrO2
—
—
—
—
—
—
0.8 – 1.2
—
—
1.3 – 1.7
—
—
1.8 – 2.2
—
—
—
0.8 – 1.2
—
—
1.7 – 2.2
—
—
—
0.15 – 0.40
NOT SPECIFIED
Other Oxides or
Elements Total
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
Notes:
a. The electrode shall be analyzed for the specific oxides for which values are shown in this table. If the presence of other elements or
oxides is indicated, in the course of the work, the amount of those elements or oxides shall be determined to ensure that their total
does not exceed the limit specified for “Other Oxides or Elements, Total” in the last column of the table.
b. SAE/ASTM Unified Numbering System for Metals and Alloys.
c. Tungsten content shall be determined by subtracting the total of all specified oxides and other oxides and elements from 100%.
d. Classification EWG must contain some compound or element additive and the manufacturer must identify the type and minimal
content of the additive on the packaging.
Figure 4.3 Tungsten electrode requirements (Courtesy AWS).
Types of tungsten and tungsten alloy electrodes for GTAW are
classified according to the chemical makeup of the particular
electrode types. Figure 4.3 shows the nine types of electrodes
classified by the American Welding Society.
In the first column of Figure 4.3, the AWS identifies the nine
classifications as they would for filler metal specifications.
The letter “E” is the designation for electrode. The “W” is the
designation for the chemical element tungsten.
The next one or two letters designates the alloying element
used in the particular electrode. The “P” designates a pure
tungsten electrode with no intentionally added alloying
elements. The “Ce”, “La”, “Th”, and “Zr” designate tungsten
electrodes alloyed with cerium, lanthanum, thorium, or
zirconium, respectively.
The number “1”, “1.5” or “2” behind this alloy element
indicates the approximate percentage of the alloy addition.
The last electrode designation, “EWG”, indicates a “general”
classification for those tungsten electrodes that do not fit
within the other categories. Obviously, two electrodes bearing
the same “G” classification could be quite different, so the
AWS requires that a manufacturer identify on the label the
type and content of any alloy additions.
Electrodes are color coded for ease of identification. Care
should be exercised when working with these electrodes so
that the color-coding can be kept intact.
32
Types of Electrodes
EWP (100% Tungsten, Green)
These electrodes are unalloyed, “pure” tungsten with a 99.5%
tungsten minimum. They provide good arc stability when using
AC current, with either balanced wave or unbalanced wave and
continuous high-frequency stabilization. Pure tungsten electrodes
are preferred for AC sine wave welding of aluminum and
magnesium because they provide good arc stability with both
argon and helium shielding gas. Because of their inability to
carry much heat, the pure tungsten electrode forms a balled end.
EWCe-2 (2% Cerium, Orange)
Alloyed with about 2% ceria, a non-radioactive material and
the most abundant of the rare earth elements, the addition of
this small percentage of cerium oxide increases the electron
emission qualities of the electrode which gives them a better
starting characteristic and a higher current carrying capacity
than pure tungsten. These are all-purpose electrodes that will
operate successfully with AC or DC electrode negative.
Compared with pure tungsten, the ceriated tungsten electrodes
provide for greater arc stability. They have excellent arc starting
properties at low current for use on orbital tube, pipe, thin sheet
and small delicate part applications. If used on higher current
applications the cerium oxide may be concentrated to the
excessively hot tip of the electrode. This condition and oxide
change will remove the benefits of the cerium. The
nonradioactive cerium oxide has slightly different electrical
properties as compared to the thoriated tungsten electrodes.
For automated (orbital tube, etc.) welding these slight changes
may require welding parameters and procedures to be adjusted.
The cerium electrodes work well with the Advanced Squarewave
power sources and should be ground to a modified point.
EWG (unspecified alloy, Gray)
This classification covers tungsten electrodes containing
unspecified additions of rare earth oxides or combinations of
oxides. As specified by the manufacturer, the purpose of the
additions is to affect the nature or characteristics of the arc.
The manufacturer must identify the specific addition or
additions and the quantity or quantities added.
Some “rare earth” electrodes are in this category and they
contain various percentages of the 17 rare earth metals. One
mixture is 98% tungsten, 1.5% lanthanum oxide, and a .5%
special mixture of other rare earth oxides. Some of these
electrodes work on AC and DC, last longer than thoriated
tungsten, can use a smaller size diameter tungsten for the
same job, can use a higher current than similar sized thoriated
tungstens, reduce tungsten spitting, and are not radioactive.
TIG
The thoriated electrode does not ball as does the pure tungsten,
cerium or lanthana electrodes. Instead, it forms several small
projections across the face of the electrode when used on
alternating current. When used on AC sine wave machines,
the arc wanders between the multiple projections and is often
undesirable for proper welding. Should it be absolutely necessary
to weld with these type machines, the higher content lanthana
or thoria electrodes should be used. The thoriated electrodes
work well with the Advanced Squarewave power sources and
should be ground to a modified point. These electrodes are
usually preferred for direct current applications. In many DC
EWZr-1 (1% Zirconium, Brown)
A zirconium oxide (zirconia) alloyed tungsten electrode is
preferred for AC welding when the highest quality work is
necessary and where even the smallest amounts of weld pool
contamination cannot be tolerated. This is accomplished
because the zirconium alloyed tungsten produces an
extremely stable arc which resists tungsten spitting in the arc.
The current carrying capability is equal to or slightly greater
than an equal sized cerium, lanthana or thorium alloyed
electrode. Zirconium electrodes are typically used only for
AC welding with a balled end.
for GTAW • Gas Tungsten Arc Welding
EWTh-2 (2% Thorium, Red) and EWTh-1
(1% Thorium, Yellow)
Commonly referred to as 1 or 2% thoriated tungstens, these
are very commonly used electrodes since they were the first
to show better arc performance over pure tungsten for DC
welding. However, thoria is a low-level radioactive material,
thus vapors, grinding dust and disposal of thorium raises
health, safety and environmental concerns. The relatively
small amount present has not been found to represent a
health hazard. But if welding will be done in confined spaces
for prolonged periods of time, or if electrode grinding dust
might be ingested, special precautions should be taken
concerning proper ventilation. The welder should consult
informed safety personnel and take the appropriate steps to
avoid the thoria.
applications, the electrode is ground to a taper or pointed.
The thorium electrode will retain the desired shape in those
applications where the pure tungsten would melt back and
form the ball end. The thoria content in the electrode is
responsible for increasing the life of this type over the pure
tungsten, EWP.
HANDBOOK
EWLa-1 (1% Lanthanum, Black), EWLa-1.5 (1.5%
Lanthanum, Gold) and EWLa-2 (2% Lanthanum, Blue)
Alloyed with nonradioactive lanthanum oxide, often referred
to as lanthana, another of the rare earth elements. These
electrodes have excellent arc starting, low-burn-off rate, arc
stability, and excellent re-ignition characteristics. The addition
of 1 – 2% lanthana increases the maximum current carrying
capacity by approximately 50% for a given size electrode
using alternating current compared to pure tungsten. The
higher the percentage of lanthana, the more expensive the
electrode. Since lanthana electrodes can operate at slightly
different arc voltages than thoriated or ceriated tungsten
electrodes these slight changes may require welding parameters
and procedures to be adjusted. The 1.5% content appears to
most closely match the conductivity properties of 2% thoriated tungsten. Compared to cerium and thorium the
lanthana electrodes had less tip wear at given current levels.
Lanthanum electrodes generally have longer life and provide
greater resistance to tungsten contamination of the weld.
The lanthana is dispersed evenly throughout the entire length
of the electrode and it maintains a sharpened point well,
which is an advantage for welding steel and stainless steel on
DC or the AC from Advanced Squarewave power sources.
Thus the lanthana electrodes work well on AC or DC electrode
negative with a pointed end or they can be balled for use with
AC sine wave power sources.
Tungsten electrodes for GTAW can easily be recognized by
their color code. See Figure 4.4.
Electrode Identification Requirementsa,b
AWS Classification
Color
EWP
EWCe-2
EWLa-1
EWLa-1.5
EWLa-2
EWTh-1
EWTh-2
EWZr-1
EWG
Green
Orange
Black
Gold
Blue
Yellow
Red
Brown
Gray
Notes:
a. The actual color may be applied in the form of bands, dots,
etc., at any point on the surface of the electrode.
b. The method of color coding used shall not change the
diameter of the electrode beyond the tolerances permitted.
Figure 4.4 Color codes for tungsten electrodes (Courtesy AWS).
33
Use of Tungsten Electrodes
Electrodes used for GTAW welding differ greatly in many
respects from electrodes used in consumable metal arc welding.
The tungsten electrode is not melted or used as filler metal as
is the case with SMAW or GMAW electrodes. At least it is not
intended to be melted and become part of the weld deposit.
However, in cases where the wrong electrode type, the wrong
size of electrode, the wrong current, the wrong polarity or
technique is used, tungsten particles can be transferred
across the arc. The power source used may affect the amount
of tungsten which may be transferred across the arc. A
machine designed specifically for GTAW welding will usually
have characteristics advantageous for the process. Excessive
current surges or “spikes” will cause “spitting” of tungsten.
Excessive arc rectification on aluminum or magnesium will
cause a half-wave effect, and cause particles of tungsten to be
transferred across the arc. An understanding of the electrode
materials and types of electrodes and their recommended
uses will enable the user to make the proper electrode selection.
Tungsten is a very hard steel gray metal. It is a highly refractory
metal and does not melt or vaporize in the heat of the arc. It
has a melting point of 6170˚ F (3410˚ C), and a boiling point
of 10,220˚ F (5600˚ C). Tungsten retains its hardness even
when red hot.
With the choice of several alloy types and a variety of sizes,
many factors must be considered when selecting the electrode.
One of the main considerations is welding current. The welding
current will be determined by several factors including base
metal type and thickness, joint design, fit-up, position, shielding
gas, type of torch, and other job quality specifications.
An electrode of a given diameter will have its greatest current
carrying capacity with direct current electrode negative
(DCEN), less with alternating current and the least with direct
current electrode positive (DCEP). Figure 4.5 lists some typical
current values for electrodes with argon shielding.
Tungsten has a high resistance to current flow and therefore,
heats up during welding. In some applications the extreme tip
forms a molten hemisphere. The "ball" tip is characteristic of
pure tungsten and is most desirable for AC welding with sine
wave power sources. The extreme tip is the only part of
the electrode which should be this hot. The remainder of the
electrode should be kept cool. Excessive electrode stickout
beyond the collet will cause heat build-up in the electrode. In
a water-cooled torch, the heat is more rapidly dissipated from
the collet assembly and helps cool the electrode. Excessive
current on a given size electrode will cause the tip to become
excessively hot.
Typical Current Range (Amps)
Direct Current,
DC
Alternating Current,
AC
DCEN
Tungsten
Diameter
Gas Cup
Inside
Diameter
Ceriated
Thoriated
Lanthanated
.040
#5 (3/8 in)
.060 (1/16 in)
70% Penetration
(50/50) Balanced
Wave A
Pure
Ceriated
Thoriated
Lanthanated
Pure
Ceriated
Thoriated
Lanthanated
15 – 80
20 – 60
15 – 80
10 – 30
20 – 60
#5 (3/8 in)
70 – 150
50 – 100
70 – 150
30 – 80
60 – 120
.093 (3/32 in)
#8 (1/2 in)
150 – 250
100 – 160
140 – 235
0 – 130
100 – 180
.125 (1/8 in)
#8 (1/2 in)
250 – 400
150 – 200
225 – 325
100 – 180
160 – 250
All values are based on the use of Argon as a shielding gas. Other current values may be employed depending on the
shielding gas, type of equipment, and application.
DCEN = Direct Current Electrode Negative (Straight Polarity)
Figure 4.5 Typical current ranges for electrodes with argon shielding.
34
1
2
2-1/2 Times
Electrode Diameter
1. Tungsten Electrode
2. Tapered End
Grind end of tungsten on fine grit, hard abrasive wheel before welding.
Do not use wheel for other jobs or tungsten can become
contaminated causing lower weld quality.
For improved arc focus set the balance control to maximum
penetration and try a ceriated, lanthanated or thoriated tungsten with a modified point.
1
2
3
For Advanced Squarewave Use (Pointed)
With the expanded balance control of up to 90% electrode
negative, the electrode shape is very nearly the same as for
DC electrode negative welding. This improves the ability to
focus the arc along with an even greater localization of the
heat into the work. Do not use with pure tungsten.
For DC Electrode Negative Use (Pointed)
Since all of the weld energy is provided by electrode negative,
there is very little heating affect on the tungsten and a sharp
pointed tungsten is generally preferred. Figure 4.6 shows the
preferred shapes for balled and the various types of points
used with the DC and AC wave shaped power sources.
4
for GTAW • Gas Tungsten Arc Welding
For AC Sine Wave and Conventional Squarewave
These electrodes should have a hemispheric or balled end
formed. The diameter of the end should not exceed the diameter
of the electrode by more than 1.5 times. As an example, a
1/8" electrode should only form a 3/16" diameter end. If it
becomes larger than this because of excessive current, there
is the possibility of it dropping off to contaminate the weld. If the
end is excessively large, and the current is decreased before
the molten tip drops off, the arc tends to wander around on the
large surface of the electrode tip. The arc becomes very hard to
control as it wanders from side to side. If welding conditions
are correct, a visual observation of the electrode should
reveal a ball end of uniform shape and proper size.
A common practice in pointing electrodes is to grind the taper
for a distance of 2 to 2-1/2 electrode diameters in length for
use on DC and usually to a sharp needle point (see top of
Figure 4.7). Using this rule for a 1/8" electrode, the ground
surface would be 1/4 to 5/16" long.
TIG
Electrode Preparation
Pointing of electrodes is a subject which has received much
discussion. There are many theories and opinions on the
degree of the point. Again, the application has a bearing on
the configuration of the point. Along with application experience,
the following should serve as a guide to pointing of electrodes.
HANDBOOK
After the proper size and type of electrode has been selected,
how the electrode is used and maintained will determine its
performance and life. There are many misconceptions about
tungsten electrodes and their correct use. The following
information is intended to serve as a guideline to common
sense decisions about tungsten electrodes.
Ideal Tungsten Preparation – Stable Arc
1. Stable Arc
2. Flat
3. Grinding Wheel
4. Straight Ground
1
2
3
4
Wrong Tungsten Preparation – Wandering Arc
1. Arc Wander
2. Point
3. Grinding Wheel
4. Radial Ground
Figure 4.6 The ball diameter should never exceed 1.5 times the electrode
diameter. Pointed tungstens are as noted.
Figure 4.7 Preparing tungsten for DC electrode negative welding and AC
with wave shaping power sources.
35
Figure 4.8 Arc shape and
weld profile as a function
of electrode tip angle.
Image courtesy of
American Welding Society
(AWS) Welding Handbook,
8th ed., Volume 2,
“Welding Processes.”
Miami: American Welding
Society.
Needle-pointed electrodes are usually preferred on very thin
metals in the range of .005" to .040". In other applications, a
slightly blunted end is preferred because the extreme point
may be melted off and end up in the deposit. In many applications, pointing is done where actually a smaller electrode
should be used. Figure 4.8 shows examples of various arcs
and weld profiles produced by changing the electrode tip angle.
Tungsten is harder than most grinding wheels, therefore it is
chipped away rather than cut away. The grinding surface
should be made of some extremely hard material like diamond
or borazon. The grinding marks should run lengthwise with the
point (see middle and bottom of Figure 4.7). If the grinding is
done on a coarse stone and the grinding marks are
concentric with the electrode, there are a series of ridges on
the surface of the ground area. There is a possibility of the
small ridges melting off and floating across the arc. If the
stone used for grinding is not clean, contaminating particles
can be lodged in the grinding crevices and dislodge during
welding, ending up in the deposit. The grinding wheel used
on tungsten electrodes should be used for no other material.
The surface of the tungsten after use should be shiny and
bright. If it appears dull, an excess of current is indicated. If
it appears blue to purple or blackened, there is insufficient
postflow of the shielding gas. This means the surrounding
atmosphere oxidized the electrode while still hot, and it is
now contaminated. Continuing to weld with this condition
can only result in the oxide flaking off and ending up in the
weld deposit. A general rule for postflow is one second
for each ten amperes of welding current. This is normally
adequate to protect the tungsten and weld pool until they
both cool below their oxidizing temperature.
36
Contamination of the electrode can occur in several ways in
addition to the lack of postflow shielding gas. The most common
form of contamination is contact between electrode and weld
pool or electrode and filler rod. Loss of shielding gas or
contamination of the shielding gas due to leaking connections
or damaged hoses causes electrode contamination.
Excessive gas flow rates and nozzles that are dirty, chipped or
broken cause turbulence of the shielding gas. This aspirates
atmospheric air into the arc area causing contamination.
The electrode that has been contaminated by contact with the
pool or filler rod will have a deposit of the metal on the electrode.
If this is not too serious, maintaining an arc on a scrap piece
of material for a period of time may vaporize the deposit off
the electrode. If the contamination cannot be removed in this
manner, the preferred method is to grind the electrode to
remove the contamination. Use good grinding techniques, as
improper techniques can cause problems or injury. Breaking
the contaminated tungsten off is generally not recommended
as it may cause a jagged end, split or bend the electrode. This
may result in excessive electrode heating and a poorly shaped
arc. Proper tungsten shaping and removal of contamination
is a key to maintaining consistent welds. A properly prepared
tungsten will reduce or eliminate arc wandering, splitting,
spitting and weld quality inconsistencies. Figure 4.9 shows a
specially designed grinder for tungsten preparation.
TIG
HANDBOOK
Shielding Gas
All arc welding processes utilize some method of protecting
the molten weld pool from the atmosphere. Without this
protection, the molten metal reacts with gases in the atmosphere
and produces porosity (bubbles) in the weld bead greatly
reducing weld strength.
Figure 4.10 Tungsten electrode preparation.
Use good techniques when grinding the electrode to remove
contamination. Grinding should be done on a fine grit
hard abrasive wheel. Figure 4.11 shows several 1/8" tungsten
electrodes. Notice the different tip configurations.
A
B
C
D
The importance of atmospheric shielding is reflected in the
fact that all arc welding processes take their names from the
method used to provide the shielding; Gas Tungsten Arc, Gas
Metal Arc, Submerged Arc, Shielded Metal Arc, Flux Cored, etc.
E
F
for GTAW • Gas Tungsten Arc Welding
Figure 4.12 A typical air separation facility operated by the Canadian
Liquid Air company at Varennes, Quebec, Canada.
Figure 4.9 Bench model tungsten grinder.
G
Figure 4.11 1/8" Tungstens.
ELECTRODE “A” has the “ball” end. This pure tungsten was used with
alternating current with a sine wave power source on aluminum. Notice the
end is uniform in shape and possesses a “shiny bright” appearance.
ELECTRODE “B” is a 2% thoriated tungsten ground to a taper and was
used with direct current electrode negative, or a similar shape for Advanced
Squarewave applications.
ELECTRODE “C” is a 2% thoriated tungsten used with an alternating
current sine wave power source on aluminum. Note that this electrode has
several small ball shaped projections rather than a round complete “ball
end” like the pure tungsten.
ELECTRODE “D” is a pure tungsten used with alternating current sine
wave power source or balance control set to excessive cleaning action on
an AC wave controlled power source on aluminum. This electrode was
subjected to a current above the rated capacity. Notice the “ball” started to
droop to one side. It became very molten during operation and continuing
to operate would have caused the molten end to drop into the weld pool.
ELECTRODE “E” is a pure tungsten that was tapered to a point and used
on direct current electrode negative. Notice the “ball” tip characteristic of
the pure tungsten. Pointing of pure tungsten is not recommended as the
extreme point will always melt when the arc is established, and often times
the molten tip will drop into the molten weld pool.
ELECTRODE “F” was severely contaminated by touching the filler rod to
the tungsten. In this case, the contaminated area must be broken off and
the electrode reshaped as desired.
ELECTRODE “G” did not have sufficient gas postflow. Notice the black
surface which is oxidized because the atmosphere contacted the electrode
before it cooled sufficiently. If this electrode were used, the oxidized
surface will flake off and drop into the weld pool. Postflow time should be
increased so the appearance is like electrode “A” after welding.
37
Primarily two inert gases are used for shielding purposes for
TIG. They are argon and helium. Shielding gases must be of
high purity for welding applications. The purity required is at
a level of 99.995%.
Although the primary function of the gas is to protect the
weld pool from the atmosphere, the type of gas used has an
influence on the characteristics and behavior of the arc and the
resultant weld bead. The chief factor influencing the effectiveness
of a shielding gas is the gas density. Argon, with an atomic
weight of 40, is about one and a half times heavier than air
and ten times heavier than helium which has an atomic
weight of 4. Argon after leaving the torch nozzle tends to form
a blanket over the weld, whereas helium tends to rise rapidly
from the arc area. In order to obtain equivalent shielding, flow
rates for helium are usually two to three times that of argon.
An examination of the characteristics and a comparison of
these gases will serve as a guide to shielding gas selection.
Argon
Argon is obtained as a byproduct in the manufacturing of
oxygen. Breaking down the contents of the atmosphere
would approximately yield the following:
.9% Argon
78.0% Nitrogen
21.0% Oxygen
.1% Other rare gases
Looking at these percentages, it’s evident that many cubic
feet of air must be processed in order to obtain a cylinder of
argon. The price of argon may vary widely depending on
locality and volume purchased.
Argon may be obtained in the gaseous state in cylinders or as
a liquid in specially constructed cylinders or in bulk tanks.
As a liquid, argon will be at a temperature of slightly below
-300˚ F (-184˚ C). The most commonly used size of cylinder
contains 330 cubic feet (935 Liters) at 2640 p.s.i.
(18,203 kPa) at 70˚ F (21˚ C). When large volumes are
required a bulk liquid supply is most desirable and economical.
Each gallon (3.785 liters) of liquid will produce approximately
112 cubic feet (317 L) of gaseous argon. Liquid argon may
be obtained in cylinders containing up to 4,000 cubic feet
(11.328 kL) of gaseous argon. If larger quantities are desired,
a bulk liquid tank may be installed.
When choosing a shielding gas, a fact that must be considered
is the ionization potential of the gas. Ionization potential is
measured in volts and is the point where the welding arc will
be established between the electrode and the workpiece
through the shielding gas. In other words, it is the voltage
necessary to electrically charge the gas so that it will conduct
electricity. The ionization potential of argon is 15.7 volts.
So this is the minimum voltage that must be maintained in the
welding circuit to establish the arc or to weld with argon. The
38
ionization potential is different for every gas and has a major
effect on the arc and weld bead. The ionization potential for
helium is 24.5 volts. Comparing two welding circuits, each
being equal except for shielding gas, the arc voltage produced
with argon would be lower than that produced by helium.
Argon has low thermal conductivity which means it is not a
good conductor of heat. This results in a more compact, higher
density arc. Arc density refers to the concentration of energy
in the arc. With argon this energy is confined to a narrow or
more “pinpointed” area.
Argon provides excellent arc stability and cleaning action
even at low amperages.
Helium
Unlike argon, helium has high thermal conductivity. Due to
this higher thermal conductivity, the arc column expands,
reducing current density in the arc. The arc column will
become wider and more flared out than the arc column with
argon shielding gas. Figure 4.13 illustrates the two arc
columns. The more flared out the arc column, the more work
surface area is being heated. The heat at the center of the arc
can move more readily downward toward the colder metal
at the bottom of the workpiece. This results in a deeper
penetrating arc. Figure 4.13 also illustrates the resultant weld
beads and the difference in penetration produced by argon
and helium.
It was mentioned previously that with an equivalent arc
length, helium will produce a higher arc voltage than will
argon. Since the total power is a product of voltage and
amperage, it is apparent that more heat energy is available
with helium. Helium or argon-helium mixtures are desirable
on thick material and where high travel speeds are desired.
The use of a 2:1 helium to argon gas mixture has also been
shown to yield lower porosity welds in production situations
by allowing wider variation in welding parameters. With helium
shielding any slight variation of arc length can have quite an
affect on arc voltage and consequently total arc power. For
this reason, helium is not as desirable as argon for manual
welding applications.
Because of its higher ionization potential, it is more difficult
to start an arc with helium shielding gas, especially at lower
amperages. Argon is used almost exclusively when welding
at 150 amps and lower.
Because helium is a light gas, flow rates are usually two or
three times higher than argon for equivalent shielding. The
cost of helium is considerably more than argon, and with the
increased flow rate, total cost of shielding goes up sharply.
The cost must be weighed against increased penetration on
thick material and the increased travel speed attainable.
ARGON
Figure 4.13 A representation of the affects on the arc and bead produced
by argon and helium shielding gases. Note the wider arc and deeper
penetration produced by the helium shielding gas.
Nitrogen
Nitrogen when mixed with argon provides the capability of
producing more energy to the work than with argon alone.
This can be particularly beneficial when welding materials of
high conductivity such as copper. However, a nitrogen mix
cannot be used on ferrous metals such as steel and stainless
steel because nitrogen pick up in the weld pool causes a significant reduction in strength and a weaker, more porous bead.
Figure 4.15 The regulator/flowmeter regulates the flow of shielding gas
from the cylinder to the welding torch. This meter displays the amount of
pressure in the cylinder as well as the rate of flow.
1
for GTAW • Gas Tungsten Arc Welding
Hydrogen
Just as helium is mixed with argon to take advantage of the best
features of both gases, hydrogen is mixed with argon to further
constrict the arc and produce a cleaner weld with a greater depth
to width ratio (penetration). This mix is used primarily for welding
austenitic stainless steel and some nickel alloys. The addition of
hydrogen to argon also increases travel speed. It should be noted
that an argon hydrogen mix will introduce the risk of hydrogen
cracking and metal porosity particularly in multipass welds.
HANDBOOK
HELIUM
The correct flow rate is an adequate amount to shield the molten
weld pool and protect the tungsten electrode. Any greater
amount than this is wasted. The correct flow rate in cubic feet per
hour is influenced by many variables that must be considered on
each application. Generally speaking, when the welding current,
nozzle diameter, or electrode stickout is increased, the flow rate
should be increased. When welding in the AC mode the current
reversals have a disturbing affect on the shielding gas and
flow should be increased by 25%. And of course when welding
in a drafty situation, flow rate should be doubled. When welding
corner or edge joints, excessive flow rates can cause air
entrapment. In this situation, the effectiveness of the shielding
gas can be improved by reducing the gas flow by about 25%.
TIG
Flow Rate
Obtain gas cylinder and chain
to running gear, wall, or other
stationary support so the
cylinder cannot fall and break
off valve.
1. Cap
2. Cylinder Valve
Remove cap, stand to side of
valve, and open valve slightly.
Gas flow blows dust and dirt
from valve. Close valve.
2
3. Cylinder
4. Regulator/Flowmeter
Install so face is vertical.
5. Gas Hose Connection
Fitting has 5/8 – 18 right-hand
threads. Obtain and install gas
hose.
6
3
5
4
Figure 4.14 A typical regulator/flowmeter installation.
6. Flow Adjust
Typical flow rate is 15 cfh
(cubic feet per hour)
Make sure flow adjust is closed
when opening cylinder to avoid
damage to the flowmeter.
Argon Gas
39
Preflow and Postflow
GTAW and Use of Filler Metal
The purpose of both preflow and postflow is to prevent
contamination of both the weld pool and the tungsten
electrode by the surrounding atmosphere.
The GTAW tungsten electrode is a nonconsumable (does not
melt) and thus does not become part of the weld, as do
SMAW or GMAW electrodes that melt and become filler metal
which adds to the weld volume. This is advantageous on thin
materials (usually under 1/16") where the GTAW weld fuses
the edges of the base materials together. This is referred to as
an “autogenous” weld (no filler), and is common on thin
metal butt, lap and flange joints.
When the torch is not in use, air will enter the system through
the nozzle. Moisture in the air can condense inside the nozzle
and gas hose and then cause hydrogen contamination during
initial stages of the weld. The shielding gas preflow will clear the
air and moisture from the torch and prevent this contamination.
Postflow works a little differently. Immediately after the welding
arc is extinguished, the weld bead, filler rod and the tungsten
electrode remain hot enough to cause a chemical reaction with
oxygen in the atmosphere. The result of this oxidization is
quite obvious when it occurs because it causes the weld bead,
filler rod and tungsten to turn black. Proper postflow will
prevent oxidization from occurring by shielding the hot electrode
and weld area, and by speeding up the cooling process. It
should be remembered that a tungsten that has discolored
because of oxidization must be properly removed.
Backing Dams and Trailing Shields
Just as the surface of the weld bead must be protected from
atmospheric contamination, the backside must be protected
as well. In the case of pipe welding or other full penetration
butt joints, this can be accomplished with a backing dam, as
seen in Figure 4.16. Often a backing dam can be something
as simple as heavy paper used to close off the ends of the
pipe through which a gas hose is passed to fill the pipe with
shielding gas to elaborate diaphragms, hoses and valves. A
length of angle iron can be clamped to the backside of straight
line weldments to hold the gas in place for that type of weld.
In some cases where the weld occurs too fast for the torch
supplied shielding gas to protect the pool and tungsten, a
trailing shield may be used. Trailing shields are available as
separate devices that attach to the torch or torch nozzle. Back
or trail shielding is required on reactive metals like titanium,
duplex steels, stainless steels, etc. This type shielding keeps
the welds bright and shiny without discoloration and oxidation,
thus reducing rework due to contamination.
Welds on thicker metals (about 1/16" and up), beveled joints
and poor fitup joints may need filler wire added to the weld
pool for proper fusion and weld strength. This is usually done
by hand feeding the filler wire into the pool. The filler rod
diameter should be approximately the same as the electrode
diameter. The hot end of the filler rod should be kept in the
blanket of shielding gas and/or postflow until it has cooled
below its oxidation temperature.
Automated GTAW uses a wire feeder to automatically feed a
continuous wire into the weld pool as the weld proceeds
along the joint. Figure 3.37 on page 30 shows this type
of equipment.
Types of GTAW Filler Metals
Perhaps the most common filler material for GTAW takes the
form of 36" straight rods that are fed by one hand while the
other hand manipulates the torch. Figure 4.17 shows
standard sizes for filler rods, according to the American
Welding Society. These rods usually come in 10 or 50 pound
boxes or tubes and often have the wire type on a tag or
stamped into the side of each piece of filler rod. TIG is
preferred for critical work that is generally done to a code and
approved welding procedures. To maintain control the filler
metal must be identifiable.
Standard Sizesa
Standard
Package Form
Straight lengthsb,c
and Coils
without support
1/16
3/32
1/8
5/32
3/16
1/4
Diameter
in.
(0.0625)
(0.094)
(0.125)
(0.156)
(0.187)
(0.250)
mm
1.6
2.4
3.2
4.0
4.8
6.4
Toleranceb
in.
mm
±0.0015 ±0.04
Notes:
a. Dimensions, tolerances, and package forms (for round
filler metal) other than those shown shall be agreed by
purchaser and supplier.
b. There is no specified tolerance for cast rod in straight lengths.
c. Length of wrought rods shall be 36 in.,+0. — – 1/2 in.
(approximately 900 ± 20 mm). Length of cast rods shall be
18 in. ± 1/2 in. (approximately 450 ± 12 mm)
Figure 4.17 Sizes of GTAW filler rod.
Figure 4.16 A welder prepares to install a backing dam over the end of a
pipe to be welded.
40
Typical Sizes of Flattened Rods*
Equivalent Round
Diameter
in.
mm
1.6
2.4
3.2
4.0
4.8
6.4
in.
0.047
0.070
0.095
0.115
0.140
0.187
mm
1.2
1.8
2.4
2.9
3.6
4.8
Width
in.
0.072
0.105
0.142
0.175
0.210
0.280
mm
1.8
2.7
3.6
4.4
5.3
7.1
*Standard length shall be 36 in. +0, –1/2 in. (approximately 900 ±20 mm).
Figure 4.18 Flattened rod sizes for GTAW.
Filler Metal Specifications
The American Welding Society (AWS) publishes several
booklets of specifications for GTAW filler materials. Often
these booklets are used as specifications for GMAW electrode
wires as well. Figure 4.19 is a list of AWS filler material,
shielding gas and tungsten electrode specification booklets.
A5.7
A5.9
A5.10
A5.12
A5.13
A5.14
Copper and Copper Alloy
Bare Welding Rods and
Electrodes
Corrosion Resisting
Chromium and
Chromium-Nickel Steel
Bare and Composite
Metal Cored and Stranded
Welding Electrodes and
Welding Rods
Bare Aluminum and
Aluminum Alloy Welding
Electrodes and Rods
Tungsten and Tungsten
Alloy Electrodes for Arc
Welding and Cutting
Solid Surfacing Welding
Rods and Electrodes
Nickel and Nickel Alloy
Bare Welding Rods and
Electrodes
A5.16 Titanium and Titanium
Alloy Welding Electrodes
and Rods
A5.18 Carbon Steel Filler Metals
for Gas Shielded Arc
Welding
A5.19 Magnesium Alloy
Welding Rods and Bare
Electrodes
A5.21 Composite Surfacing
Welding Rods and
Electrodes
A5.24 Zirconium and Zirconium
Alloy Bare Welding Rods
and Electrodes
A5.28 Low Alloy Steel Filler
Metals for Gas Shielded
Arc Welding
A5.30 Consumable Inserts
A5.32 Welding Shielding Gases
Figure 4.19 AWS specifications for GTAW filler materials, shielding gases
and tungsten electrodes.
Types and Designations of
Filler Metals
Steel
There are seven designations for carbon steel filler rods. A
typical designation would be ER70S-6 for TIG. The “ER”
Stainless Steels
There are many more stainless steel designations than there
are steel designations. A typical classification of a stainless
rod would be ER308. The “ER”, as it is in steel, stands for either
continuous electrode, or electrode rod. The “308” designates
a specific stainless steel chemical composition. These numbers
are often used to match the filler rod to specific compositions
of base metals being welded.
Certain types of stainless steel rods may have letters or numbers
after the three digits, such as “L” meaning low carbon
content, or “Si” meaning high silicon content. Sometimes a
manufacturer’s brand name may use “ELC” instead of “L” to
mean Extra Low Carbon, or “HiSil” instead of “Si” meaning
High Silicon Content.
It’s important to remember the “ER” designations because
the AWS has separate specification books for “ER” filler metals
and for “E” filler metals. “E” filler metals, such as E308-16,
would refer to covered welding electrodes, such as those
used for SMAW (Stick).
for GTAW • Gas Tungsten Arc Welding
1/16
3/32
1/8
5/32
3/16
1/4
Thickness
HANDBOOK
Another type of filler material is coiled wire for automated
GTAW. This would be the same wire used on a given material
for the GMAW process.
means the filler can be used for either GTAW or GMAW. If the
designation lacked the “R” it would signify a continuous electrode
for use with GMAW only. There is no designation for rod
using just the “R”, it will always be “ER”. The “70” stands for
the welded tensile strength, measured in thousands of
pounds per square inch. “S” stands for “Solid” electrode as
opposed to a tubular or hollow wire such as that used in the
flux cored welding process. And the “6” refers to the particular
degree of manufactured chemical percentages within the rods
composition. In other words, the number at the end of the
description refers to which classification of wire is being used.
TIG
Also used to a lesser degree are flattened rods. These are preferred by some welders who feel it is easier to feed the rods
because of their shapes. Figure 4.18 shows sizes of flattened rods.
Titanium
There are approximately 13 different designations for titanium
filler rods. A typical designation would be ERTi-5ELI. The
“ER” means the filler can be used for either GTAW or GMAW.
The “Ti” indicates titanium, the “5” is specific characteristics
such as alloy content, and the “ELI” means extra-low interstitial
impurities. If the base metal has extra-low interstitial impurities
the filler metal selected should also carry the same classification. The interstitial nature of elements such as carbon,
hydrogen, oxygen and nitrogen are kept very low with the
ELI classification.
When welding titanium and its alloy, the filler metal should
closely match the alloy content of the base metal being welded.
The ERTi-1, -2, -3 and -4 are designations for commercially
pure titanium (CP) welding. These unalloyed filler metals can
tolerate some contamination from the welding atmosphere
without significant loss in ductility. Unalloyed filler metals
may be used to weld titanium alloys when ductility is more
important than joint strength. Less than 100% joint efficiencies
can be expected.
41
Filler metal contamination is very serious when welding
titanium. The filler wire should be wiped clean with acetone
and a lint-free cloth. Cleaning should continue until the cloth
is free from any indications of contamination. The filler wire
should also be inspected for any physical defects such as
cracks, seams or laps. These defects may trap contaminations
making them difficult or impossible to remove. To prevent
recontamination of the filler rod, it should be handled after
cleaning in a so-called “white glove” procedure (clean lint
free gloves).
Aluminum
There are approximately 12 designations for aluminum
filler rods. A common all purpose rod is ER4043. The “ER”
designates electrode or rod, and the “4043” designates a
specific chemical composition. ER4043 is used with many
aluminum base metals, but always consult electrode wire
manufacturers for the proper filler to use in critical welds.
Figure 4.20 contains some typical examples.
Base Metal, (T)Temper
Filler Metal
1100
ER1100
2014-T6
ER4043
2219-T81
ER2319
3003
ER1100
5005
ER5356
5456
ER5556
6061-T4
ER4043
6061T-6
ER5356
7005T-53
ER5356
Figure 4.20 Typical aluminum base metal filler metal recommendations.
Figure 4.21 represents some GTAW filler metals cross referenced between the AWS classification number and a typical
manufacturers specification number.
Figure 4.21 Cross reference chart on GTAW filler metals. Courtesy of the Aluminum Association.
42
As in any welding process, GTAW safety precautions are very
important. All information relating to the safe operation of the
welding equipment and the welding process must be fully
understood before attempting to begin work. A careless
welder who does not observe simple rules can cause a dangerous
situation for everyone in the area. The process of arc welding
creates several hazards which must be guarded against.
Useful safety information can be found in the owner’s manual that comes with each piece of welding equipment.
Several possible hazards exist due to the electric arc which
include infrared and ultraviolet rays. The light and rays can
produce a burn similar to sunburn. The arc rays, however, are
more severe than sunburn since the welder is so close to the
source. Any exposed skin can be quickly burned by these rays.
Electrical Shock
Welders must be concerned about the possibility of electrical
shock. It should be remembered that electricity will always
take the path of least resistance. If there is a proper secondary
circuit, the current will follow that path. However, if there are
poor connections, bare spots on cables, or wet conditions,
the possibility of electrical shock does exist.
Clothing made from a dark-colored, tightly woven material is
best suited for welding. Flammability of clothing material
must also be considered since sparks could ignite the fabric.
Oxygen, for instance, supports combustion and should never
be used for blowing off equipment or used on any person or
personal clothing.
Shirt collars and shirt cuffs should be buttoned, and open
front pockets are not advisable as they may catch sparks.
Pant cuffs are not recommended, as they will also catch
sparks. Matches or lighters should never be stored in pockets.
Since welding sparks can burn through clothing, for many
applications leather capes, sleeves and aprons are recommended. To protect the feet, high-top leather shoes or boots are
necessary. Canvas shoes are definitely not suitable. Clothing
and shoes must be kept free of oil and grease or other flammable materials. Gauntlet type leather gloves should be worn
to protect the hands and wrists. See Figure 5.1 and 5.2.
A welder should never weld while standing in water. If wet
working conditions exist, certain measures should be taken.
Such measures include standing on a dry board or a dry rubber
mat when welding. Likewise, the welding equipment should
not be placed in water. In addition, gloves and shoes must be
kept dry. Even a person’s perspiration can lower the body’s
resistance to electrical shock.
for GTAW • Gas Tungsten Arc Welding
Gas Tungsten Arc Welding (TIG) is an electrical welding
process. Therefore, electrical energy is required from a welding
machine. If the welding machine has the characteristics of a
transformer or a motor-generator design, electrical energy is
required as primary power to operate it. The welding machine
must be installed according to the manufacturer’s recommendation and in accordance with the National Electrical
Code and local code requirements.
Clothing
TIG
Arc Rays
HANDBOOK
V. Safety
Fumes
As with most welding processes, the heat or the arc and
molten pool generate fume. Since TIG does not typically use
flux or produce slag, it is highly recommended that the material
being welded is clean. Few fumes are produced compared to
other arc welding processes like SMAW or FCAW. However,
the base metals may contain coatings or elements such as
lead, zinc, copper, nickel, etc. that may produce hazardous
fumes. Ozone can also be produced as the ultraviolet light
emitted by the arc hits the oxygen in the surrounding area,
producing a very distinctive, pungent odor.
The welder should keep their head and helmet out of the
fumes rising off the workpiece. Proper ventilation should be
supplied, especially in a confined space. Since this is a gas
shielded process, care must be taken not to extract too much
air from the arc area, which would disturb the process.
Figure 5.1 Properly dressed welder.
Figure 5.2 Boots, leathers, gloves.
43
It is essential to know that some Gas Tungsten Arc Welding
results in relatively high levels of visible light and infrared
radiant energy. This can add to the disintegration of cotton
clothing due to ultraviolet radiation. Thus, recommended
clothing should be worn at all times.
Eye Protection
The welding arc should never be observed with unprotected
eyes. A short exposure to the arc, which sometimes occurs
accidentally, may cause an eye condition known as “flash
burn”. Usually this is not a permanent injury, but may be
painful for a short time after exposure. The feeling can be
described as having sand in one’s eyes. Sometimes it is
possible for a period of 4 to 8 hours to pass before a painful
sensation in the eyes develops. Mild cases of flash burn can
possibly be treated by a doctor. Continued exposure to flash
burn could cause permanent eye damage.
Persons passing by an area where welding is being done
could possibly get a mild flash burn from a stray arc glare. It
is recommended that not only welders, but all people in the
welding area, wear approved tinted safety glasses. Most
industrial locations require the use of safety glasses, but they
are absolutely necessary in the welding area. See Figure 5.3.
Figure 5.3 Safety glasses.
The welder should wear a welding helmet equipped with the
proper shade lens for the work being done. Welding lenses
are not simply colored glass, but are special lenses which
screen out almost 100% of the infrared and ultraviolet rays.
Lenses are manufactured in various shades designated by a
shade number, and the higher the shade number, the darker
the lens. The choice of a shade may vary depending upon a
person’s sensitivity of eyesight and the welding variables.
Generally speaking, the current used determines the shade
lens needed. The higher the current, the darker the shade
lens. The welding helmet can be equipped with an electronic
lens which automatically lightens and darkens as required, as
shown in Figure 5.4. Some electronic lens have adjustment
for the darkness level. Safety rules can be found in the AWS
approved ANSI Z49.1 booklet, Safety In Welding And Cutting.
Another source of information is the booklet, Recommended
Practices For Gas Tungsten Arc Welding (AWS C5.5). Refer to
table 8 in Section XI for proper lens selection.
44
Figure 5.4 Welding helmet.
The Welding Environment
The area surrounding the welder can be called the welding
environment. The Gas Tungsten Arc Welding process can
create light, heat, smoke, sparks and fumes which influence
that environment. In addition to the protective clothing the
welder wears, other precautions must be taken.
The light given off from welding may bother other workers in
the area. Permanent booths or portable partitions can be used to
contain the light rays in one area. The heat and sparks given off
are capable of setting flammable materials on fire. Welding
should not be done in areas containing flammable gases, vapors,
liquids or dusty locations where explosions are a possibility.
Many injuries have resulted from welding on containers that
have held materials easily capable of catching fire or exploding.
These are often referred to as combustibles. This problem not
only refers to containers such as petroleum tanks, but also to
tanks which have a volatile (explosive) nature when heated by
a welding arc. Acceptable methods of cleaning such containers
before welding are outlined in AWS A6.0, Safe Practices
For Welding And Cutting Containers That Have Held
Combustibles. Unless these procedures are read and carried
out, no attempt should be made to weld on these containers.
Metals that have plating, coatings, paint or other materials
near the arc area may give off smoke and fumes during welding. Health hazards, especially to the lungs, may exist from
these fumes. Exhaust hoods or booths can remove fumes
from a particular area. When welding in confined spaces such
as inside tanks, in compartments of a ship or inside other
containers, toxic (poisonous) fumes may gather. Also, the
oxygen we breathe can be replaced by shielding gases used
for welding or purging in an enclosed room. This condition
can cause death due to the lack of oxygen. Care must be
taken to provide enough clean air for breathing. Some type of
system should be present to bring clean air to an area where
fumes are being exhausted. In some instances, it may even
be necessary to provide welders with air masks or self-contained breathing equipment.
Handwheel
Outlet
Nozzle
Figure 5.6 Shielding gas cylinder.
Valve
Safety
Nut
for GTAW • Gas Tungsten Arc Welding
Cylinders should be securely fastened at all times (Figure 5.5).
Chains are usually used to secure a cylinder to a wall or cylinder cart. When moving or storing a cylinder, a threaded protector cap must be fastened to the top of the cylinder. This
protects the valve system should it be bumped or the cylinder
dropped (Figure 5.6). It is accepted procedure to roll a cylinder
in the upright position when moving the cylinder. Figure 5.7
shows this. In some shops cylinder carts are used to move
cylinders about. Whatever the method, common sense must
be used to ensure a safe working area.
Protector
Cap
HANDBOOK
Regardless of the content, pressurized cylinders must at all
times be handled with great care. Shielding gases such as
carbon dioxide, argon and helium are nonflammable and
nonexplosive. A broken off valve, however, will release
extremely high pressures, which could cause the cylinder to
be hurled about at dangerously high speeds. Another way of
thinking about this pressure is to compare a cylinder to a
balloon. If a balloon is blown up and then released, the jet
force of air escaping causes the balloon to fly about quite rapidly
and erratic. The same would be true if a cylinder valve would
break off. The weight of the cylinder and the extremely high
pressure could easily cause a very damaging and possibly
fatal accident.
TIG
Safe Handling of Cylinders
Figure 5.5 Securing cylinder to cart.
It is also very important to keep excess heat of any kind away
from cylinders. Never weld on any cylinder. When a cylinder
is exposed to too much heat, the pressure inside the cylinder
will increase. To prevent the excess pressure from causing
the cylinder to explode, the cylinder valve is equipped with a
safety nut and bursting disc as shown in Figure 5.8.
Figure 5.7 Rolling a cylinder.
45
Cylinders should not be stored or used in a horizontal position.
This is because some cylinders contain a liquid which would
leak out or be forced out if the cylinder was laid in a flat position.
Handwheel
Double
Seating
Valve
It is very important to be absolutely sure of yourself before
attempting to use any welding equipment. Always think about
what you are doing, and if you are not sure of the next step
to take in any procedure, be sure to talk it over first with
your welding supervisor. Remember, safety is an important factor not only for you, but for everyone around you!
Safety Cap
And Disc
Outlet
Connection
Figure 5.8 Cross section of cylinder valve.
VI. Preparation for Welding
Certain basic preparations should be made prior to establishing
an arc. Preparations include base metal preparation, set up of
the machine and its controls. (Basic preparation of commonly
welded base metals will be covered later in this section.)
Figure 6.1 illustrates the front panel of a typical AC/DC
machine designed for GTAW welding. Keep in mind that not
all power sources will have all the features or controls of this
machine. And the controls and switches mentioned in the
following paragraphs may be found in locations on the power
source other than the front panel. The various controls each
have a specific function and the operator changes or varies
them as the application changes. Power sources have
symbols that represent these various controls; table 10 in
Section XI covers these symbols.
Preparing the Power Source
Power Switch
This switch controls the primary line power to the transformer.
When the switch is in the "on" position, voltage is applied to
the control circuit. Operation of the fan with the power switch
is dependent upon if the power source is equipped with FanOn-Demand™ or not. In some cases, a pilot light will indicate
the power source is in the “on” mode. In other cases the LED
meters will indicate that the power is on. Before activating the
“On” switch make certain the electrode is not in contact
with the work lead or any portion of the work circuit!
46
Welding torches and other cables should not be hung on or
near cylinders. A torch near a cylinder could cause an arc
against the cylinder wall or valve assembly, possibly resulting
in a weakened cylinder or even a rupture.
It can be said that common sense is the most important tool a
welder can bring to the welding area. Common sense tells us
we must respect the basic safety steps which must be taken
to avoid both personal injury and injury to a fellow worker.
Horseplay or practical jokes have no place in the working area!
SMAW/GTAW Mode Switch
This switch should be set for the particular process being
used. It will disable various functions that are not required
when running one process or the other. For example, the gas
solenoid valves will not be active in the SMAW mode as they
are not required for this process.
Amperage Control Panel/Remote Switch
When a remote control device is being used, the switch must
be in the “remote” position. When amperage control is to be
at the front panel of the machine, the switch must be in the
“panel” position.
Output Control Panel/Remote Switch
When a remote output control device is being used, the
switch must be in the “remote” position. When using SMAW
and not using a remote output control device, the switch
must be in the “on” position. The “on” position means the
output terminal of the machine will have voltage applied as
soon as the power switch is turned on.
Arc Force/Balance Control
On this particular power source, when the high-frequency
switch is enabled for GTAW welding, the arc force (Dig)
circuitry drops out, and this control becomes the balance arc
control. This will set the amount of time spent in the electrode
negative (maximum penetration equals more DCEN) and
electrode positive (maximum cleaning equals more DCEP)
portions of the AC cycle. For additional information, refer to
section II on GTAW fundamentals on the balance control. In
Cylinders should not be stored or used in a horizontal position.
This is because some cylinders contain a liquid which would
leak out or be forced out if the cylinder was laid in a flat position.
Handwheel
Double
Seating
Valve
It is very important to be absolutely sure of yourself before
attempting to use any welding equipment. Always think about
what you are doing, and if you are not sure of the next step
to take in any procedure, be sure to talk it over first with
your welding supervisor. Remember, safety is an important factor not only for you, but for everyone around you!
Safety Cap
And Disc
Outlet
Connection
Figure 5.8 Cross section of cylinder valve.
VI. Preparation for Welding
Certain basic preparations should be made prior to establishing
an arc. Preparations include base metal preparation, set up of
the machine and its controls. (Basic preparation of commonly
welded base metals will be covered later in this section.)
Figure 6.1 illustrates the front panel of a typical AC/DC
machine designed for GTAW welding. Keep in mind that not
all power sources will have all the features or controls of this
machine. And the controls and switches mentioned in the
following paragraphs may be found in locations on the power
source other than the front panel. The various controls each
have a specific function and the operator changes or varies
them as the application changes. Power sources have
symbols that represent these various controls; table 10 in
Section XI covers these symbols.
Preparing the Power Source
Power Switch
This switch controls the primary line power to the transformer.
When the switch is in the "on" position, voltage is applied to
the control circuit. Operation of the fan with the power switch
is dependent upon if the power source is equipped with FanOn-Demand™ or not. In some cases, a pilot light will indicate
the power source is in the “on” mode. In other cases the LED
meters will indicate that the power is on. Before activating the
“On” switch make certain the electrode is not in contact
with the work lead or any portion of the work circuit!
46
Welding torches and other cables should not be hung on or
near cylinders. A torch near a cylinder could cause an arc
against the cylinder wall or valve assembly, possibly resulting
in a weakened cylinder or even a rupture.
It can be said that common sense is the most important tool a
welder can bring to the welding area. Common sense tells us
we must respect the basic safety steps which must be taken
to avoid both personal injury and injury to a fellow worker.
Horseplay or practical jokes have no place in the working area!
SMAW/GTAW Mode Switch
This switch should be set for the particular process being
used. It will disable various functions that are not required
when running one process or the other. For example, the gas
solenoid valves will not be active in the SMAW mode as they
are not required for this process.
Amperage Control Panel/Remote Switch
When a remote control device is being used, the switch must
be in the “remote” position. When amperage control is to be
at the front panel of the machine, the switch must be in the
“panel” position.
Output Control Panel/Remote Switch
When a remote output control device is being used, the
switch must be in the “remote” position. When using SMAW
and not using a remote output control device, the switch
must be in the “on” position. The “on” position means the
output terminal of the machine will have voltage applied as
soon as the power switch is turned on.
Arc Force/Balance Control
On this particular power source, when the high-frequency
switch is enabled for GTAW welding, the arc force (Dig)
circuitry drops out, and this control becomes the balance arc
control. This will set the amount of time spent in the electrode
negative (maximum penetration equals more DCEN) and
electrode positive (maximum cleaning equals more DCEP)
portions of the AC cycle. For additional information, refer to
section II on GTAW fundamentals on the balance control. In
When it is desired to use high frequency only to start the arc,
the “start” position is selected. The high frequency remains
on only until an arc is established and then it is automatically
removed from the circuit. This allows for starting the arc
without touching the electrode to the work. This setting
should be used when welding materials that might contaminate
the electrode.
The “off” position is used when high frequency is not desired,
such as when scratch starts are suitable, or when the
machine is used for Stick electrode welding.
“Lift” arc is selected when high frequency is undesirable and
yet tungsten inclusions must be eliminated.
The “continuous” position is selected when welding with
alternating current on aluminum or magnesium. This provides
continuous high frequency for arc stabilization and starting.
Primary Overload Circuit Breaker
The circuit breaker provides protection against overloading
the main components of the welding machine. The circuit
breaker must be “on” before the primary contactor of the
machine can be energized.
Weld Current Control or Amperage Control
This control sets the output current of the machine when no
remote current device is being used. With a remote device
attached, the control provides a percentage of total output.
For example, if the control is set at 50%, the remote device at
full output will deliver 50% of the machines available current.
Remote Amperage Control Receptacle
This receptacle is provided for connecting a remote hand
control or a remote foot control. This allows the operator to
have amperage control while welding at a work station which
may be a considerable distance from the power source. With
the foot control, the operator can vary the amperage as he
progresses along a joint. This is particularly helpful when
starting on a cold workpiece. Amperage may be increased to
establish a weld pool quickly, and as the material heats up,
the operator can decrease the amperage. When coming to the
end of a joint, the amperage can be further decreased to taper
off and "crater out".
for GTAW • Gas Tungsten Arc Welding
Start Mode
The high-frequency switch has four (4) selections: start, off,
lift, and continuous.
Figure 6.1 Front panel of a typical AC/DC machine designed for
GTAW welding.
HANDBOOK
Preflow and Postflow
Preflow control is not always a standard feature on all GTAW
power sources. It is made up of a timer control and an on/off
function switch. When “on”, the arc will not start until the preflow timer has timed out assuring the arc will start in an inert
atmosphere. This reduces the possibility of air contaminating
the start of the weld. When “off” the preflow timer is out of
the circuit and the arc is able to start as soon as the remote
output control is activated. Postflow is a standard feature on
all GTAW power sources and consists of only a timer control.
It is used to allow the electrode, weld pool and filler rod to be
protected from the air while they cool down from welding
temperatures. Once they have cooled, they will no longer
oxidize. The postflow timer should time out and conserve
shielding gas. It is usually set to allow one second of postflow
time for each 10 amperes of welding current being used.
The tungsten should cool bright and shiny. Any bluing or
blackening indicates a lack of postflow.
TIG
the SMAW or Stick electrode welding mode, the arc force
control will affect the arc action from a soft mushy type arc
(minimum arc control) to a driving-digging, forceful type arc
(maximum arc control). The arc force control is also referred
to as “dig”, and when used with the SMAW process it
increases the short circuit amperage. When set at 0, short
circuit amperage is the same as normal weld amperage.
AC/DC Selector and Polarity Switch
This three-position switch permits the operator to select
direct current electrode positive, direct current electrode
negative, or alternating current.
High-Frequency Intensity Control
This control allows the operator to choose the proper intensity
for the high-frequency output. As this control is increased,
the current in the high-frequency circuit is increased. It
should be set for the required intensity to start the arc. It is
recommended that this control be kept at a minimum setting
that will provide satisfactory weld starts. The higher the
setting the greater the amount of radiation which will cause
interference with communication equipment.
Spark Gap Assembly
The spark gap points are normally set at the factory for
optimum performance. A feeler gauge can be used to check
the spacing or make adjustments on some machines.
47
Preparing the Weld Joint
Many GTAW problems, or supposed problems, are a direct
result of using improper methods to prepare the joint. Chief
among these is the improper use of grinding wheels to
prepare joints. Soft materials such as aluminum become
impregnated with microsized abrasive particles which, unless
subsequently removed, will result in excessive porosity.
Grinding wheels should be cleaned and dedicated exclusively
to the material being welded. The ideal joint preparation is
obtained with cutting tools such as a lathe for round or cylindrical joints, or a milling machine for longitudinal preparations.
Cleaning
Cleanliness of both the weld joint area and the filler metal is an
important consideration when welding with the Gas Tungsten
Arc Welding process. Oil, grease, shop dirt, paint, marking
crayon, and rust or corrosion deposits all must be removed
from the joint edges and metal surfaces to a distance beyond
the heat affected zone. Their presence during welding may
lead to arc instability and contaminated welds. If a weld is
made with any of these contaminants present, the result
could be a weld bead with pores, cracks, or inclusions.
Cleaning may be accomplished by mechanical means, by the
use of vapor or liquid cleaners, or by a combination of these.
Fixturing
Fixturing may be required if the parts to be welded cannot be
self supported during welding or if any distortion cannot be
tolerated or corrected by straightening. Fixturing should be
massive enough to support the weight of the weldment and
to withstand stresses caused by thermal expansion and
contraction. The decision to use fixturing for the fabrication of a
weldment is governed by economics and quality requirements.
Preheating
Preheating is sometimes required, the necessity being dictated
for the most part by the thickness of the material to be welded.
Preheating is most often achieved with the use of an oxyacetylene torch. However care must be taken when using this
method that localized overheating doesn’t occur, and the base
metal is not contaminated with combustion by-products of
the oxy-fuel process. Other methods of preheating include
induction coils, heating blankets and heating furnaces.
Preparing Aluminum for Welding
The preparation of aluminum deserves more consideration
than it is often times given. Aluminum is very susceptible to
contaminants which can cause considerable problems when
welding. First of all, aluminum has a surface oxide which
must be removed. This oxide removal is mentioned in detail
in the text devoted to Squarewave current. There have been
various theories as to how the arc action actually provides the
cleaning action. High speed photographs and films of the arc
let us observe the oxide removal.
48
When the electrode is positive and the work is negative
(reverse polarity or during one half of the AC cycle), the
positively charged gas ions are attracted to the negative
workpiece. These ions strike the surface with sufficient force
to chip away at the brittle oxide much like a miniature sandblasting operation. The electron flow from the work to the
electrode lifts the loosened oxide leaving clean base metal to
be welded.
Figure 6.2 Aluminum TIG Weld. Note bright area where oxides have been
removed through cleaning action of the arc.
This cleaning action should not be relied upon to do all the
cleaning. Mechanical or chemical cleaning methods should
be employed to remove heavy oxide, paint, grease, and oil, or
any other materials that will hinder proper fusion. Mechanical
cleaning may be done with abrasive wheels, wire brushes, or
other methods. Special abrasive wheels are available for
aluminum, and stainless steel wire brushes are recommended.
The important point is that the abrasive wheels and wire
brushes should be used only on the material being cleaned.
If a wire brush for example were used on rusty steel, and then
on aluminum, the brush could carry contaminants from one
piece to another. The vigorous brushing can impregnate the
contaminants carried in the brush into the aluminum. The
same is true of the abrasive wheel and equipment used to cut
and form aluminum.
There’s another problem that sometimes occurs when only
the side of the joint being welded is cleaned. Contamination
from the backside or between butting edges can be drawn
into the arc area. It is recommended that both sides of the
joint be cleaned if it contains foreign material.
Another frequent source of contamination is the filler metal.
Aluminum filler wire and rod oxidizes just like the base metal.
If it is severe enough the rod must be cleaned prior to use.
The operator sometimes transfers contaminants from dirty
welding gloves onto the filler rod and consequently into the
weld area. Stainless steel wool is a good material to use for
cleaning filler wire and rod.
Welding Aluminum
The information contained in Figures 6.3a and 6.3b will serve
as a guide to aluminum welding parameters.
Aluminum is a very good conductor of heat. The heat is rapidly
conducted away from the arc area and spread over the workpiece. On small weldments, the entire part may heat up to a
TIG
Aluminum…Manual Welding – Alternating Current – High Frequency Stabilized
Tungsten Electrode Filler Rod Diameter
Diameter
(If Required)
Joint Type
1/16"
Butt
Lap
Corner
Fillet
1/16"
1/16"
1/16"
1/16"
1/8"
Butt
Lap
Corner
Fillet
Gas
Flow-CFH
Type
1/16"
1/16"
1/16"
1/16"
60 – 85
70 – 90
60 – 85
75 – 100
Argon
Argon
Argon
Argon
15
15
15
15
3/32" – 1/8"
3/32" – 1/8"
3/32" – 1/8"
3/32" – 1/8"
3/32"
3/32"
3/32"
3/32"
125 – 150
130 – 160
120 – 140
130 – 160
Argon
Argon
Argon
Argon
20
20
20
20
3/16"
Butt
Lap
Corner
Fillet
1/8" – 5/32"
1/8" – 5/32"
1/8" – 5/32"
1/8" – 5/32"
1/8"
1/8"
1/8"
1/8"
180 – 225
190 – 240
180 – 225
190 – 240
Argon
Argon
Argon
Argon
20
20
20
20
1/4"
Butt
Lap
Corner
Fillet
5/32" – 3/16"
5/32" – 3/16"
5/32" – 3/16"
5/32" – 3/16"
3/16"
3/16"
3/16"
3/16"
240 – 280
250 – 320
240 – 280
250 – 320
Argon
Argon
Argon
Argon
25
25
25
25
Figure 6.3a Aluminum weld parameters.
Aluminum with Advanced Squarewave…Manual Welding – Alternating Current – High Frequency Stabilized
Metal
Thickness
Joint
Type
Tungsten
Size
Filler
Material
Diameter
Electrode
Positive
Amperage
Electrode
Negative
Amperage
AC
Frequency
Setting (Hz)
Balance
Setting
Shielding
Gas
1/16"
Butt
Lap
Corner
Fillet
1/16"
1/16"
1/16"
1/16"
1/16"
1/16"
1/16"
1/16"
20
20
20
20
50
50
50
50
110
110
110
110
75% EN
70% EN
70% EN
70% EN
100% Argon
100% Argon
100% Argon
100% Argon
1/8"
Butt
Lap
Corner
Fillet
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
60
60
60
60
120
120
120
125
140
140
140
175
70% EN
73% EN
68% EN
78% EN
100% Argon
100% Argon
100% Argon
100% Argon
1/4"
Lap
Corner
Fillet
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
110
110
110
230
220
240
250
140
250
73% EN
70% EN
75% EN
100% Argon
100% Argon
100% Argon
for GTAW • Gas Tungsten Arc Welding
Amperage
HANDBOOK
Metal Thickness
Figure 6.3b Aluminum with Advanced Squarewave weld parameters.
point that requires reduction of amperage from the original
setting. Remote foot amperage controls are advantageous in
these situations. When welding out-of-position, the amperages
shown in Figures 6.3a and 6.3b may be decreased by about
15%. A water-cooled torch is recommended for amperages
over 150. The electrode stickout beyond the cup may vary
from approximately 1/16" on butt joints to possibly 1/2" in
joints where it is difficult to position the torch. The normal
recommended arc length is approximately the same as the
electrode diameter.
Preparing Stainless Steel
for Welding
magnetic and non-magnetic types of stainless steel. There are
a large number of alloy types and each type possesses some
specific properties as to corrosion resistance and strength. A
check with the manufacturer is recommended when in doubt
about the specific properties of an alloy.
When welding stainless steel, it should be thoroughly
cleaned. Protective paper or plastic coatings are applied to
many stainless sheets. Foreign material may cause porosity
in welds and carburetion of the surface which will lessen the
corrosion resisting properties. Any wire brushing should be
done with stainless steel wire brushes to prevent iron pick up
on the stainless surfaces. As with other welding procedures,
clean and dry filler metal should be used and proper
precautions taken to prevent contamination during welding.
“Stainless steel” is a common term used when referring to
chromium alloyed and chromium-nickel alloyed steel. There are
49
Welding Stainless Steel
Figure 6.4 contains parameters which will serve as a guide for
welding stainless steel.
Chromium-nickel stainless steels are considered readily
weldable. Normally the welding does not adversely affect the
strength or ductility of the deposit, parent metal, or fusion
zone. The filler metal used should be compatible, of similar
composition, to the base metal. The heat conductivity of
chrome-nickel stainless steels are about 50% less than mild
steel with a high rate of thermal expansion. This increases the
tendency for distortion on thin sections.
Values shown in Figure 6.4 are for single pass welds on the
thinner sections, multiple pass welds on heavier material, and
for welding out-of-position. Job conditions will affect the
actual amperage, flow rate, filler rod, and tungsten used.
Some examples are:
■
■
■
■
■
Joint design and fit-up
Job specifications
Use of backing (gas, rings, bars)
Specific alloy
Operator
Heat input can be critical. In many applications, it is desirable
to keep the heat input as low as possible. In the weld and heat
affected zone, a metallurgical change takes place known as
carbide precipitation. If corrosion resistance is a big factor in the
completed weld, it should be noted that some of the corrosion
resistance properties are lost in the weld and adjacent areas
that are heated above the temperature where carbide precipitation occurs (800 – 1400˚ F). Keeping heat input to a
minimum is necessary in this situation. The longer the work is
at the 800 –1400˚ F temperature, the greater the precipitation.
Rapid cooling through this range will help keep precipitation
to a minimum. On some alloys of stainless steel, columbium
or titanium are added to prevent carbide precipitation. It is
important that the filler metal used is of the same general
analysis as the material being welded.
Preparing Titanium for Welding
Titanium’s light weight, excellent corrosion resistance, and high
strength-to-weight ratio make this a desirable metal for applications in the chemical, aerospace, marine and medical fields. Its
use in the petrochemical industry and in the manufacture of
sports equipment is some more recent application areas. Many
consider titanium as very hard to weld. Titanium alloys can be
embrittled by not following proper welding techniques, but
titanium is much more readily welded than typically believed.
Before welding titanium, it is essential that the weld area and
the filler metal be cleaned. All mill scale, oil, grease, dirt,
grinding dust and any other contamination must be removed.
If the titanium is scale free, degreasing is all that is required.
If oxide scale is present, it should be degreased prior to
descaling. An area at least 1 inch (25mm) from where the
weld is to be made should be cleaned. The joint edges should
be brushed with a stainless steel wire brush and degreased
with acetone just prior to welding. Any titanium part handled
after cleaning should be done so in a so-called “white glove”
procedure to eliminate recontamination of the weld area. The
cleaned parts should be welded within a few hours or properly
stored by wrapping in lint-free and oil-free materials.
If grinding or sanding is used to clean titanium or prepare a
joint, be very cautious of the fine titanium dust particles.
Titanium is flammable and the smaller the dust particles are,
the more flammable it becomes.
Stainless Steel…Manual Welding…Direct Current – Electrode Negative
Joint Type
1/16"
Butt
Lap
Corner
Fillet
1/16"
1/16"
1/16"
1/16"
1/8"
Butt
Lap
Corner
Fillet
Gas
Flow-CFH
Amperage
Type
1/16"
1/16"
1/16"
1/16"
40 – 60
50 – 70
40 – 60
50 – 70
Argon
Argon
Argon
Argon
15
15
15
15
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
65 – 85
90 – 110
65 – 85
90 – 110
Argon
Argon
Argon
Argon
15
15
15
15
3/16"
Butt
Lap
Corner
Fillet
3/32"
3/32"
3/32"
3/32"
1/8"
1/8"
1/8"
1/8"
100 – 125
125 – 150
100 – 125
125 – 150
Argon
Argon
Argon
Argon
20
20
20
20
1/4"
Butt
Lap
Corner
Fillet
1/8"
1/8"
1/8"
1/8"
5/32"
5/32"
5/32"
5/32"
135 – 160
160 – 180
135 – 160
160 – 180
Argon
Argon
Argon
Argon
20
20
20
20
Figure 6.4 Stainless steel weld parameters.
50
Tungsten Electrode Filler Rod Diameter
Diameter
(If Required)
Metal Thickness
Figure 6.5 contains parameters which will serve as a guide for
welding titanium.
1. Titanium (CP). Commercially pure (98 to 99.5% Ti), can
be strengthened by small additions of oxygen, nitrogen,
carbon and iron.
3. Alpha-Beta Alloys. They have a characteristic two-phase
microstructure brought about by the addition of up to
6% aluminum and varying amounts of beta formers. Beta
forming alloys are vanadium, chromium, and molybdenum.
Figure 6.6 shows some of the relative weldability of these various
alloy groups. Also displayed are recommended filler metals.
When welding titanium and its alloy, the filler metal should
closely match the alloy content of the base metal being welded.
Gas
Flow-CFH*
Metal Thickness
Joint Type
Tungsten Electrode
Diameter
Filler Rod Diameter
(If Required)
Amperage
Type
1/16"
Butt
Lap
Corner
Fillet
1/16" – 3/32"
1/16" – 3/32"
1/16" – 3/32"
1/16" – 3/32"
1/16"
1/16"
1/16"
1/16"
65 – 105
100 – 165
65 – 105
100 – 165
Argon
Argon
Argon
Argon
15
15
15
15
1/8"
Butt
Lap
Corner
Fillet
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
3/32"
95 – 135
150 – 200
95 – 135
150 – 200
Argon
Argon
Argon
Argon
15
15
15
15
3/16"
Butt
Lap
Corner
Fillet
3/32" – 1/8"
3/32" – 1/8"
3/32" – 1/8"
3/32" – 1/8"
3/32"
3/32"
3/32"
3/32"
150 – 225
150 – 250
150 – 225
150 – 250
Argon
Argon
Argon
Argon
20
20
20
20
1/4"
Butt
Lap
Corner
Fillet
1/8"
1/8"
1/8"
1/8"
3/32" – 1/8"
3/32" – 1/8"
3/32" – 1/8"
3/32" – 1/8"
175 – 275
200 – 300
175 – 275
200 – 300
Argon
Argon
Argon
Argon
20
20
20
20
for GTAW • Gas Tungsten Arc Welding
Titanium…Manual Welding – Direct Current Electrode Negative
HANDBOOK
These welding parameters are useable on the three various
types of titanium alloys. The three types of titanium alloys are:
2. Alpha Alloy. Generally single-phase alloys which contain
up to 7% aluminum and a small amount <0.3% of oxygen,
nitrogen and carbon.
TIG
Welding Titanium
*This is the torch (primary) shielding gas flow rate, a trailing (secondary) shield gas flow rate should be 2 to 4 times this rate. A trailing shielding gas is
generally required for welding titanium.
Figure 6.5 Titanium weld parameters.
Weldability Rating
Alloy
Commercially Pure (CP)
Alpha Alloys
Alpha-Beta Alloys
Rating
Filler Metal
ERTi-1
Ti-0.15 O2
A
Ti-0.20 O2
A
ErTi-2
Ti-0.35 O2
A
ERTi-4
Ti-0.2 Pd
A
ERTi-7
Ti-5 Al-2.5 Sn
B
ERTi-6
Ti-5 Al-2.5 Sn ELI*
A
ERTi-6ELI
Ti-6 Al-4V ELI
A
ERTi-5ELI
Ti-7 Al-4Mo
C
ERTi-12
Ti-8 Mn
D
Welding Not Recommended
Figure 6.6 Titanium welding ability.
*ELI = Extra-low interstitial impurities are specified. These interstitial
impurities are carbon, hydrogen, oxygen and nitrogen and both the filler
metal and base metal are low in these impurities.
Key
A = Excellent; useful as-welded, near 100% joint efficiency if base metal
annealed condition.
B = Fair to good; useful as-welded, near 100% joint efficiency if base metal
annealed condition.
C = Limited to special applications; cracking can occur under high restraint.
D = Welding not recommended; cracking under moderate restraint; use
preheat (300 – 350˚ F) followed by post weld heat treatment.
51
Shielding of the titanium weld and surrounding metal (this
includes the hot end of the filler rod) that reach temperatures
of 1200˚ F (650˚ C) is required. When doing manual “open
air” (not in a bubble or totally enclosed chamber) care must
be taken to prevent atmospheric contamination of the titanium.
Since titanium has a very low thermal conductivity, it will stay
hot for a long time after the welding arc has moved along the
joint. Thus a trailing gas is essential. This can be accomplished with a large gas lens on the torch or a trailing gas
shoe that attaches to the TIG torch. This metal shoe (chamber)
has a porous metal diffuser to allow the gas to blanket the
titanium until it has cooled below its oxidation temperature.
Figure 6.7 is an example of a trailing gas shield. The primary
gas shielding is what is flowing through the torch and the
secondary gas shielding is what is flowing through the trailing
shield. If the back side of the joint is going to be exposed to
oxidation temperatures >500˚ F, it must also be protected
from the atmosphere by a backing gas shielding or in the
case of pipe or tubing purging the inside of the pipe or tube.
Preparing Mild Steel for Welding
Mild steel should always be mechanically cleaned prior to
welding. Rust, paint, oil and grease, or any surface contaminants should be removed. Hot-rolled products such as angle
iron, plate, and pipe may contain a heavy mill scale. For best
results, remove scale prior to welding. Black pipe usually
contains a varnish type coating, which should be removed
before welding.
Welding Mild Steel
Low carbon steels, commonly referred to as mild steels, are
readily welded by the GTAW process. These groups of steels
are available in many different alloys and types. The familiar
structural shapes, plates, and hot rolled sheet metal are
usually comprised of what is termed “semi-killed steel”. This
term means the steel has been partially deoxidized during
manufacture. The steel, however, still contains some oxygen,
and this oxygen can cause problems when welding. These
problems will appear in the form of bubbles in the weld pool,
and possibly in the finished weld bead. “Killed steel” has had
more oxygen removed in its manufacture, and presents less
of a problem when welding.
A filler wire containing sufficient silicon and manganese,
added as deoxidizers, is necessary. Lower grade filler rods
used for oxyacetylene welding of many hot rolled products
are not suitable for making high-quality GTAW welds.
Direct current electrode negative is recommended with
high-frequency start. A 2% thoriated tungsten with point or
taper on the electrode should be used.
Figure 6.7 Torch trailing shield for TIG welding of titanium and other
reactive metals.
Figure 6.8 contains parameters which will serve as a guide for
welding mild steel.
Mild Steel…Manual Welding…Direct Current – Electrode Negative
Joint Type
1/16"
Butt
Lap
Corner
Fillet
1/16"
1/16"
1/16"
1/16"
1/8"
Butt
Lap
Corner
Fillet
3/16"
1/4"
Gas
Flow-CFH
Amperage
Type
1/16"
1/16"
1/16"
1/16"
60 – 70
70 – 90
60 – 70
70 – 90
Argon
Argon
Argon
Argon
15
15
15
15
1/16" – 3/32"
1/16" – 3/32"
1/16" – 3/32"
1/16" – 3/32"
3/32"
3/32"
3/32"
3/32"
80 – 100
90 – 115
80 – 100
90 – 115
Argon
Argon
Argon
Argon
15
15
15
15
Butt
Lap
Corner
Fillet
3/32"
3/32"
3/32"
3/32"
1/8"
1/8"
1/8"
1/8"
115 – 135
140 – 165
115 – 135
140 – 170
Argon
Argon
Argon
Argon
20
20
20
20
Butt
Lap
Corner
Fillet
1/8"
1/8"
1/8"
1/8"
5/32"
5/32"
5/32"
5/32"
160 – 175
170 – 200
160 – 175
175 – 21 0
Argon
Argon
Argon
Argon
20
20
20
20
Figure 6.8 Mild steel weld parameters.
52
Tungsten Electrode Filler Rod Diameter
Diameter
(If Required)
Metal Thickness
To obtain a quality weld and cost-effective use of filler metal,
joint design must be considered in any type of weldment.
This will depend upon several factors including material type,
thickness, joint configuration and strength required.
A proper joint design will provide the required strength and
the highest quality weld at the most economical cost. The
joint design selected will dictate what type of weld is required.
Edge joints are often used when the members to be welded
will not be subjected to great stresses. Edge joints are not
recommended where impact or great stress may occur to one
or both of the welded members. An edge joint occurs when
the edges of parallel or nearly parallel members meet and are
joined by a weld. Figure 7.2 shows different types of edge
joints. Figure 7.2 demonstrates the various types of edges
that can be applied to the joints. If required, the joints can be
altered by grinding, cutting or machining the edges into a
groove. The groove can be a square, beveled, V, J, or U. The
main purpose of the groove is to allow proper penetration or
depth of fusion. See Figure 7.3.
Corner
Butt
Square Groove
Bevel
V-Groove
U-Groove
for GTAW • Gas Tungsten Arc Welding
It is quite possible that a welder would have little to do with how
a particular joint is designed. However, a good welder should be
familiar enough with joint design to carry out a welding job.
Edge Joints
HANDBOOK
A weld joint is the term used for the location where two or
more pieces of metal will be or have been welded together.
Figure 7.1 shows the five basic weld joint designs.
A few considerations for joint design are specific to GTAW.
Naturally the weld joint must be accessible to the GTAW torch,
making it possible for proper torch movements. Weld joints
should not be too narrow, so as to restrict access of the gas cup.
In some cases, using a narrower gas cup, or a gas lens with the
electrode extending up to an inch beyond the gas cup will help.
TIG
VII. Joint Design and
Types of Welds
Lap
T
Edge
Figure 7.1 Five basic joint designs.
The five basic joint designs are typically welded with the TIG
process using either a groove or a fillet weld. Groove welds
are those made into a prepared joint to get deeper penetration.
To prepare the joint, material must be removed and replaced
with weld metal. Groove welded joints are very efficient but
are more expensive than a fillet welded joint. Groove welds
generally require some form of joint preparation while fillet
welds are made on joints requiring no joint preparation.
When the edge or surface of joint members come together at
a right angle to each other, the resulting weld, which is triangular in shape, is called a fillet weld. Fillet welds on lap or
T-joints are commonly used in the welding industry.
J-Groove
Figure 7.2 Edge Joints
Depth Of Fusion
Joint
Penetration
Root Penetration
Figure 7.3 Depth of fusion and types of penetration. Complete joint penetration refers to weld metal that extends completely through the groove and
has complete fusion into the base metal. What is shown is a partial joint
penetration, which if not intended is referred to as incomplete joint penetration.
53
Butt Joints
Groove Angle
(Included Angle)
A butt joint occurs when the surfaces of the members to
be welded are in the same plane with their edges meeting.
Figure 7.4 shows butt joints with various types of grooves.
Butt joints are often used to join pressure vessels, boilers,
tanks, plate, pipe, tubing or other applications where a
smooth weld face is required. They generally require more
welding skill than other joints. Butt joints have very good
mechanical strength if properly made. They can be expensive
joints since a prepared groove is generally required to get the
proper penetration and weld size. This involves the extra
operation of joint preparation, removal of material to open up
the joint and then welding to penetrate and fill the groove.
Square Groove
Square Groove
With Root Opening
Beveled Butt
V-Groove
J-Groove
U-Groove
Figure 7.4 Butt joints.
Distortion and residual stresses can be problems with
butt joints.
Butt joints can be designed in various ways. They may be
welded with or without a piece of metal or ceramic backing
the joint, usually referred to as a “backing bar” or “backing
strip”. The edges can be prepared into a groove that is square,
beveled, V, J, or U grooved. Edges may be held tight together or a small gap known as a root opening may be left
between the edges.
Figure 7.5 shows the various parts of a V-groove butt joint.
Note the groove angle, groove face, root face and root
opening. The groove angle is the total included angle of the
joint. If two 37.5˚ bevels are brought together, they form a
75˚ V-groove. The groove face is the surface of the metal in
the groove, including the root face. The root face is sometimes called the “land”. In this example, the root face is 1/8"
and the root opening 3/32". The main purpose of the various
grooves and root openings is to allow proper penetration and
depth of fusion.
Bevel Angle
Groove
Face
Root Face
Root Opening
Figure 7.5 V-groove butt joint.
If material thickness is less than approximately 1/8" thick,
square edges butted tight together (no root opening) can be
used. (Aluminum would probably require a small root opening.)
Plate thicknesses 1/8" and greater generally require single or
double V-groove and root openings for proper penetration
and depth of fusion. Joint preparation before welding will
depend upon the joint design and the equipment available to
do the edge preparation. The oxy-fuel torch, carbon arc gouging
or plasma arc cutting/gouging is often used to cut a bevel-,
J-, U-, or square-groove edge on steel plates. Aluminum is
best prepared with mechanical cutting tools or the plasma arc
cutting/gouging process.
Lap Joints
Another joint design used a great deal in the welding industry is
the lap joint. Various types of lap joints are shown in Figure 7.6.
As can be seen in the figure, lap joints occur when the surfaces
of joined members overlap one another. A lap joint has good
mechanical properties, especially when welded on both sides.
The type of weld used on a lap joint is generally a fillet weld.
If a groove weld is called for, it can be applied as shown in the
figure with a single or double bevel. The groove weld may or
may not be followed with a fillet weld. This would be indicated
by the appropriate welding symbol. The degree of overlap of the
members is generally determined by the thickness of plate. In
other words, the thicker the plate, the more overlap is required.
Double Bevel Groove
Single Or Double Fillet
Single Bevel Groove
Figure 7.6 Lap joints.
54
Open Corner
Figure 7.8 T-Joints
Fillet Welds
Fillet welds are approximately triangular in cross sectional
shape and are made on members whose surfaces or edges
are approximately 90˚ to each other. Fillet welds can be as
strong, or stronger than the base metal if the weld is the correct
size and the proper welding techniques are used. When
discussing the size of fillet welds, weld contour must first be
determined. Contour is the shape of the face of the weld.
Figure 7.9 shows a cross section profile of the three types of
fillet weld contours: flat, convex, and concave.
for GTAW • Gas Tungsten Arc Welding
There are two main types of corner joints, open corner and
closed corner. On lighter gauge material, it may be necessary
to increase travel speed somewhat, especially on open corner
joints where excessive melt through is a possibility.
J-Groove
Fillet T-Joint
HANDBOOK
When members to be welded come together at about 90˚ and
take the shape of an “L”, they are said to form a corner joint.
Several types of corner joints and grooves are shown in
Figure 7.7. Welds made on the inside of the “L” are considered
fillets and welds made on the outside of the “L” are considered
groove welds. Corner joints are quite easily assembled and
require little if any joint preparation. After welding, the welds
are generally finished, that is, ground smooth to present a
smooth attractive appearance. When this is the case, all effort
by the welder should be made to prevent overlap (weld material
rolling onto one of the members and not fusing), high spots,
low spots and undercut. These problems can all mean more
work since additional grinding time, rewelding and regrinding
may be required.
T-joints possess good mechanical strength, especially when
welded from both sides. They generally require little or no
joint preparation and are easily welded when the correct
parameters are used. The edges of the T-joint may be left
square if only a fillet weld is required. For groove welding they
may be altered by thermal cutting/gouging, machining
or grinding.
TIG
Corner Joints
Flat
Closed Corner
Convex
V-Groove Corner
Figure 7.7 Corner joints.
T-Joints
A T-joint occurs when the surfaces of two members come
together at approximately right angles, or 90˚, and take the
shape of a “T”. See Figure 7.8. On this particular type of joint,
a fillet weld is used.
Concave
Figure 7.9 Fillet face contours.
55
Fillet Weld Size
It is important when discussing weld size and joint design
to be familiar with the various parts of a weld. Figure 7.10
indicates the parts of a fillet weld.
Toe
Leg
Face
Throat
Convexity
Toe
Leg
Root
Fillet Weld Terms
Figure 7.10 Convex fillet weld.
The size of a convex fillet weld is generally the length of the
leg referenced. Figure 7.11 shows a convex fillet weld and the
associated terms.
Figure 7.11 Convex fillet weld.
For concave fillet welding, the size and leg are two different
dimensions. The leg is the dimension from the weld toe to the
start of the joint root, however, the actual size of a convex fillet
weld as shown in Figure 7.12, is measured as the largest
triangle that can be inscribed within the weld profile. A special
fillet weld gauge is used to measure concave fillet welds. If the
weld is flat, the concave or convex fillet weld gauge can be used.
Fillet welds can also be measured in a slightly more complex
way — by determining throat size. Three different throat sizes
may be referred to when discussing the size of fillet welds, as
seen in Figure 7.11 and 7.12.
Design engineers sometimes refer to the theoretical throat of
a weld. As Figure 7.11 and 7.12 show, the theoretical throat
extends from the point where the two base metal members
join (beginning of the joint root), to the top of the weld minus
any convexity on the convex fillet weld and on the concave fillet
weld, to the top of the largest triangle that can be inscribed in
the weld. The theoretical measurement looks at the weld as if
it were an actual triangle and the penetration is not figured
into the theoretical throat size.
The effective throat of a fillet weld is measured from the depth
of the joint root penetration. This is an important consideration
as the penetration is now considered part of this dimension.
However, no credit is given for the convexity. (The convexity
by many is considered reinforcement, which would indicate more strength. The exception is a fillet weld where too
much convexity is detrimental to the overall joint strength.
Excess convexity increases stresses at the weld toes and
can lead to cracking.) On convex and concave fillet welds,
effective throat is measured to the top of the largest triangle
that can be drawn in the weld. This measurement can be used
to indicate the size of the weld. The outward appearance of
the weld may look too small but if the penetration can be
assured, the weld will be of sufficient strength.
The actual throat of a fillet weld is the same as the effective
throat on a concave fillet weld. But as can be seen on Figure 7.11,
there is a difference. This throat dimension can also be used to
indicate size and strength. If anything other than the theoretical
throat is used to size a fillet weld, the welding procedure would
have to be carefully written and in-process inspection would
be required to assure that the joint is being properly penetrated. The overall reduction in fillet weld size, increased
speed of welding, reduced heat input and reduction of internal
stresses and distortion may make the effort worthwhile.
The general rule for fillet weld size is the leg should be the
same size as the thickness of the metals. If 1/4" thick plate
is being welded, a 1/4" leg fillet is needed to properly join the
members. The old saying, “If a little is good, a lot is
better,” may be true in some cases but not with fillet welds.
Consider again the 1/4" thick plate. If a lot of weld would be
better, think of 1/2" legs on the fillet. This would result in what
is termed over-welding. This weld is not just twice as large as
required, but its volume is three times that required. This
wastes weld metal, the welder’s time, causes more distortion
and may even weaken the structure because of residual
stress. Figure 7.13 shows correct and incorrect fillet welds.
Figure 7.12 Concave fillet weld.
56
TIG
1/4"
A
1/4"
1/4"
1/4"
1/2"
Correctly Made Fillet Weld.
Leg Equals Thickness Of Plate
1/2"
Unequal Leg Fillet (Best
Procedure, Least Possible
Chance Of Joint Failure)
B
1/2"
1/2"
B
1/2"
Over Welded (Base Metal Will
Break At Toes Of Weld) Legs
Of Weld Too Large For
Thickness Of Plate
1/2"
C
1/2"
Equal Leg 1/2" Fillet (Wasted Weld
Metal, Time And Extra Heat Input)
Weakest Point Will Be At The Toe
Of The Weld On The 1/4" Plate
1/8"
1/4"
1/4"
1/8"
Under Welded (Weld May
Break Through Legs Of Weld)
Need Larger Legs On Fillet
C
1/4"
Figure 7.13 Correct/incorrect fillets.
A weld or weld joint is no stronger than its weakest point.
Even though B of Figure 7.13 would appear to be much
stronger, it will not support more stress than A. It may even
support less stress due to the additional residual stresses
built up in the joint that is over-welded.
When metals of different thicknesses are to be joined, such
as welding a 1/4" thick plate onto a 1/2" thick plate in the form
of a T-joint, the rule for fillet weld size is size of fillet weld leg
should equal the thickness of the metal being welded.
Since there are two different thicknesses, the best weld
results will be obtained by making an unequal leg fillet weld.
Figure 7.14 shows correct and incorrect examples.
for GTAW • Gas Tungsten Arc Welding
1/4"
1/4"
HANDBOOK
A
1/4"
1/2"
1/4"
Equal Leg 1/4" Fillet (Less Time,
Less Weld Metal Less Heat Input
Equals Better Weld) Just As
Strong As Figure B
Figure 7.14 Unequal leg fillet.
The correct, unequal leg fillet weld has a 1/4" weld leg on the
1/4" plate and a 1/2" weld leg on the 1/2" plate. This would be
the best way to handle this weldment. However, consider the
results of making the weld with an equal leg fillet. There
would then be two choices: a 1/2" fillet or a 1/4" fillet. In this
instance, the 1/4" fillet would be the more practical, since a
weldment is no stronger than its weakest point. The extra
welds in the 1/2" fillet will also require more time, electrode
wire, and induce more heat into the metal, causing more
residual stress.
57
Groove Welds
The groove name is taken from the profile of the groove. A
groove weld is made in square, V, bevel, U, J, flare-V or flarebevel type grooves between workpieces. These are the most
common type grooves to be encountered with the TIG process.
Review Figure 7.4 for typical grooves found on butt type joints.
Square-Groove
A square-groove weld can be made with either a closed or an
open groove. Usually if the base metal is thin (such as thin
sheet metal gauge thicknesses), a square groove weld can be
used. Remember the higher a gauge number, the thinner the
material. In the base metal thickness range of 1/8" to 1/4",
it is good to weld both sides of an open-square-groove-weld
to provide proper penetration into the groove. Usually,
open-square-groove-welds will not be made with groove
openings of more than about 5/32". In some cases where
welding is done from only one side of the joint, a temporary
or permanent backup bar or strip can be used. On critical
welds, a consumable insert can be used. These backings or
inserts can ensure proper joint penetration, help avoid excessive
melt-through, or provide a flush backing to the weld.
V-Groove
V-groove weld designs require careful preparation, yet they
are quite popular. V-groove welds are usually made on medium
to thicker metals, and are used quite often for pipe welding.
They can provide excellent weld quality if properly completed.
V-groove weld designs may or may not use permanent or
temporary backups or consumable inserts, depending upon
the joint design and type of joint penetration needed. Usually
if backups are used, root openings can be somewhat wider.
The groove angle for a groove weld must be large enough for
the torch to fit into the groove. The groove angle depends
upon metal thickness, desired electrode extension and torch
nozzle size. Usually V-groove welds are made on material
over 1/8" to 1/4" in thickness. Adjusting the root face thickness
can help control penetration.
Usually, the root pass of a weld without backing is done with
some melt-through. Proper penetration and fusion of the root
pass is necessary to avoid weld defects.
V-groove welds are often made on material up to about 3/8"
thickness, while double V-groove welds are normally made
on thicker materials up to roughly 3/4" in thickness. Double
V-groove welds on thicker materials can use less deposited
weld metal and limit distortion in the weld, especially if a
small root face of about 1/8" is used on each member. Usually
the weld passes on such a joint would be made alternating
from one side of the joint to the other, helping avoid distortion.
Bevel-Groove
The bevel-groove weld also requires preparation, but in this case
only one member need be beveled. The single bevel-groove
can be used on material up to about 3/8", while double
bevel-grooves are used on thicker material up to about 3/4".
In most cases, up to 1/8" root openings are used on single
and double bevels. Backing may or may not be used on single
bevel-grooves, depending upon joint penetration requirements.
A bevel-groove is sometimes used when welding in the horizontal position. Root faces up to about 1/8" are normally used
for either single or double bevel-grooves.
U- and J-Grooves
On thicker materials, U- or J-grooves can provide good
penetration. They do not use as much deposited weld metal
as a V-groove or bevel-groove joint design. With thicker
materials, the U- and J-grooves can be used with a smaller
groove angle and still maintain proper fusion. A normal
groove angle for either a U- or J-groove is about 20˚ to 25˚.
This would also apply to the double U- and double J-grooves.
One disadvantage of U- and J-groove design is the preparation
of the base material. Air carbon arc, plasma gouging or special
mechanical cutting tools are required for preparation of the
J- or U-type design. V- or bevel-grooves are easier to prepare.
Flare-V and Flare-Bevel
Flared-groove welds are named after the shape of the base
members to be welded. One or both of the members have a type
of rounded edge, which already forms a groove for welding.
They take their shape from the curved, bent or circular material
the joint is being constructed from. Usually no preparation is
needed for flare type groove welds.
Groove Weld Size
When a weld is called for on a joint, the size of the weld is
important for the joint to carry the load applied to it. In order to
understand groove weld size, it is important to understand some
of the terms applied to typical groove—such as a V-groove joint.
One must have an understanding of groove angle, bevel angle,
root face and root opening. These are shown in Figure 7.15.
Groove Angle
(Included Angle)
Bevel Angle
Groove
Face
Root Face
Root Opening
Figure 7.15 V-Groove butt joint with terms.
58
Joint design for various types of groove welds can be expensive,
since some groove weld joints require more preparation than
others. Therefore, it is helpful to know when preparation is
necessary and when it can be avoided.
Weld Length
The groove weld size relates to how deep the weld fuses into
the joint. The groove should be completely filled, excess fill
called weld reinforcement should be minimal. Any extra reinforcement decreases the strength of the joint by creating
extra stresses at the weld toes. In most cases, the weld size
does not take any weld reinforcement into its measurement.
Figure 7.17 shows a complete joint penetration groove weld.
Fillet and groove welds are usually made the full length of the
joint. In some cases, fillet welded joints can achieve their full
strength by only welding a portion of the joint. The effective
length of a fillet weld is measured as the overall length of the
full-size fillet weld. The start and stop of the weld must be
allowed for in the length measurement. The TIG process is
very capable of making excellent starts and with crater filling
to the welds full cross section. However, the weld starts and
stops are not square so allowance is made when measuring
the length to account for the start and stop radius.
If a specific weld length is specified, it will be shown on the
print. In some cases, the fillet weld will be made at intermittent
intervals. The spaces between the welds are determined by
the center-to-center distance of the welds, which is called the
pitch. If intermittent fillet welds are called for, the print will
indicate their length and pitch.
Figure 7.17 V-Groove butt joint multi-pass weld with complete joint
penetration with face and root reinforcement shown.
By reducing the bevel angle and thus the groove angle, the
amount of weld metal required to fill the groove is reduced.
Figure 7.18 shows the great reduction in weld volume by
decreasing the groove angle from 60˚ to 45˚.
60˚
for GTAW • Gas Tungsten Arc Welding
Figure 7.16 V-Groove butt joint with partial joint penetration and terms.
TIG
A smaller groove angle can reduce the cost of filler metal
needed to fill the joint and thus help to reduce time and labor
costs. The amount of heat input to the joint is reduced, which
will reduce distortion and residual stresses that could cause
the weld to crack. Less scrap is produced, as less metal is
removed to produce the smaller beveled angle. When changing
the groove angle, the weld size must be maintained.
HANDBOOK
If a groove weld is indicated and no weld size is specified, a
full size weld completely penetrating the joint should be used.
If the weld size can be made smaller, indications of this
should be shown on the drawing and welding symbol.
Smaller weld size is referred to as a partial penetration joint
and is acceptable if it will carry the applied load.
Multiplying the weld length with the weld size equals the weld
area. Area = weld size X weld length. It is important to understand that this will determine how much stress the joint
can take. The design engineer is aware of the base material
properties and the loads it will see in service and applies the
formula. Stress = Load/Weld Area. Safety margins are built in
and the designer applies the weld size and length to the print.
Much weld efficiencies are lost due to over welding; follow
the specifications on the print and do not over weld.
45˚
Figure 7.18 Compare joint designs.
59
Weld Positions
When discussing groove welds a “G” is used to signify a
groove weld, and a number is assigned to signify welding
position. Plate weld designations are as:
1G — flat position, groove weld
2G — horizontal position, groove weld
3G — vertical position, groove weld
4G — overhead position, groove weld
Pipe welds as:
1G — flat position groove weld, pipe rotated
2G — horizontal groove weld, pipe axis is vertical
5G — multiple positions (overhead, vertical and flat)
groove weld, pipe axis is horizontal and is not rotated
6G and 6GR — multiple positions groove weld, pipe axis is
45˚ from horizontal and is not rotated
Figure 7.19 represents a graphic view of these groove weld
positions on plate and pipe.
When discussing fillet welds an “F” is used to signify a fillet
weld, and a number is assigned to signify the welding position. Plate positions are designated as:
1F — flat position, fillet weld
2F — horizontal position, fillet weld
3F — vertical position, fillet weld
4F — overhead position, fillet weld
Figure 7.19 Groove weld positions.
Figure 7.20 Fillet weld positions.
60
Pipe positions as:
1F — flat position, fillet weld pipe axis is 45˚ from the
horizontal and the pipe is rotated
2F — horizontal position, fillet weld pipe axis is vertical
2FR — horizontal position, fillet weld pipe axis is horizontal
and the pipe is rotated
4F — overhead position, fillet weld pipe axis is vertical
5F — multiple positions (overhead, vertical and horizontal),
fillet weld pipe axis is horizontal and is not rotated
6F — multiple positions, fillet weld pipe axis is 45˚ from
horizontal and is not rotated
Figure 7.20 represents a graphic view of these fillet weld positions on plate and pipe.
If possible, it is best to make both fillet and groove welds in
the flat (1) position. This allows for proper penetration, proper
wetting action and avoidance of undercut. Positioners are
often used to keep welds in the flat position for the highest
weld productivity. However, there are times when this is not
possible and the weld must be made in the position encountered.
The TIG process is very applicable to welding in all positions,
as the filler metal is deposited directly in the weld pool and
does not transfer across the arc as it does in other arc welding
processes. Proper welding techniques must still be observed
to weld in the various positions.
3
2
4
90°
1
10-15 °
4
5
6
ELECTRODE
1/16 in
WORK
3/16 in
The inside diameter of the gas cup should be at least three
times the tungsten diameter to provide adequate shielding
gas coverage. For example, if the tungsten is 1/16" in diameter,
the gas cup should be a minimum of 3/16" diameter.
Figure 8.2 is an example of gas cup size and torch position.
Tungsten extension is the distance the tungsten extends out
beyond the gas cup of the torch. Electrode extension may
vary from flush with the gas cup to no more than the inside
diameter of the gas cup. The longer the extension the more
likely it will accidentally contact the weld pool, filler rod being
fed in by the welder, or touch the side of a tight joint. A general
rule would be to start with an extension of one electrode
diameter. Joints that make the root of the weld hard to reach
will require additional extension.
Torch Position for Arc Starting
with High Frequency
The torch position shown in Figure 8.3 illustrates the recommended method of starting the arc with high frequency when
the torch is held manually. In this way the operator can position the torch in the joint area and after lowering the welding
hood, close the contactor switch and initiate the arc. By resting
the gas cup on the base metal there is little danger of touching
the electrode to the work. After the arc is initiated, the torch
can be raised to the proper angle for welding.
Bottom View Of Gas Cup
Figure 8.2 Gas cup size and torch positions. 1-Workpiece, 2-Work Clamp,
3-Torch, 4-Filler Rod (If Applicable), 5-Gas Cup, 6-Tungsten Electrode.
for GTAW • Gas Tungsten Arc Welding
5
6
10-25 °
Figure 8.1 Illustration shows the relationship between electrode diameter
and arc length.
HANDBOOK
Arc Length, Gas Cup Size, and
Electrode Extension
As a rule of thumb, the arc length is normally one electrode
diameter as seen in Figure 8.1. This would hold true when AC
welding with a balled end on the electrode. When welding
with direct current using a pointed electrode, the arc length
may be considerably less than the electrode diameter. Torches
held in a fixed position allow for holding a closer arc than for
manually held torches.
TIG
VIII. Techniques for Basic
Weld Joints
GAS CUP
ELECTRODE
WORK
Figure 8.3 Resting the gas cup against the work in preparation for a highfrequency start.
Manual Welding Techniques
Making the Stringer Bead
The torch movement used during manual welding is
illustrated in Figure 8.4. Once the arc is started, the electrode
is held in place until the desired weld pool is established. The
torch is then held at a 75˚ angle from the horizontal as shown
in the illustration and is progressively moved along the joint.
When filler metal is used, it is added to the leading edge of
the pool.
61
Tungsten Without Filler Rod
75°
Welding direction
Form pool
Tilt torch
Move torch to front
of pool. Repeat process.
Tungsten With Filler Rod
75°
Welding direction
Form pool
Tilt torch
15°
Add filler metal
Remove rod
Move torch to front
of pool. Repeat process.
Figure 8.4 Torch movement during welding.
The torch and filler rod must be moved progressively and
smoothly so the weld pool, the hot filler rod end, and the
solidifying weld are not exposed to air that will contaminate
the weld metal area or heat affected zone. Generally a large
shielding gas envelope will prevent exposure to air.
The filler rod is usually held at about a 15˚ angle to the surface
of the work and slowly fed into the molten pool. Or it can be
dipped in and withdrawn from the weld pool in a repetitive
manner to control the amount of filler rod added. During
welding, the hot end of the filler rod must not be removed
from the protection of the inert gas shield. When the arc is
turned off, the postflow of shielding gas should not only
shield the solidifying weld pool but the electrode and the hot
end of the filler rod.
Butt Weld and Stringer Bead
Torch and Rod Position
When welding a butt joint, be sure to center the weld pool on
the adjoining edges. When finishing a butt weld, the torch
angle may be decreased to aid in filling the crater. Add
enough filler metal to avoid an unfilled crater.
Cracks often begin in a crater and continue through the bead.
A foot operated amperage control will aid in the finishing of a
bead as amperage can be lowered to decrease pool size as
filler metal is added.
62
90˚
70˚
20˚
Figure 8.5 Welding the butt weld and stringer bead.
Torch and Rod Position
Having established an arc, the pool is formed so that the edge
of the overlapping piece and the flat surface of the second
piece flow together. Since the edge will become molten
before the flat surface, the torch angle is important. The edge
will also tend to burn back or undercut. This can be controlled
by dipping the filler rod next to the edge as it tries to melt
away. Enough filler metal must be added to fill the joint as
shown in the lap joint illustration. Finish the end of the weld
the same as before by filling the crater.
TIG
Lap Joint
20˚
HANDBOOK
70˚
10˚
Torch and Rod Position
A similar situation exists with the T-joint as with the lap joint.
An edge and a flat surface are to be joined together. The edge
again will heat up and melt sooner. The torch angle illustrated
will direct more heat onto the flat surface. The electrode may
need to be extended further beyond the cup than in the previous
butt and lap welds in order to hold a short arc. The filler rod
should be dipped so it is deposited where the edge is melting
away. Correct torch angle and placement of filler rod should
avoid undercutting. Again, the crater should be filled to avoid
excessive concavity.
20˚
Figure 8.6 Welding the lap joint.
40˚
Corner Joint
Torch and Rod Position
The correct torch and filler rod positions are illustrated for the
corner joint. Both edges of the adjoining pieces should be
melted and the pool kept on the joint centerline. When adding
filler metal, sufficient deposit is necessary to create a convex
bead. A flat bead or concave deposit will result in a throat
thickness less than the metal thickness. On thin materials,
this joint design lends itself to autogenous welding or fusions
welding without the addition of filler rod. Good fit-up is
required for autogenous welding.
70˚
for GTAW • Gas Tungsten Arc Welding
T-Joint
20˚
30˚
Figure 8.7 Welding the T-joint.
90˚
70˚
20˚
Figure 8.8 Welding the corner joint.
63
Techniques for Out-of-Position
Weld Joints
During the welding process, all action is centered in the weld
pool. The weld pool is the point at which fusion and penetration
occur. With practice controlling the pool becomes quite easy
while welding in the flat position. Eventually as additional
experience is acquired, welding out-of-position will be much
easier for the welder. Controlling the weld pool and penetration
is the prime concern for all positions of welding.
There are many variables to take into consideration in out-ofposition welding, such as amperage, travel speed, tungsten type
and torch position. Volumes could be devoted to this subject
alone. Therefore, we will try to provide a few tips and make a
few general statements regarding out-of-position weld joints.
Vertical down welding makes use of both surface tension and
arc force to hold the molten weld pool in the joint. Mastery of
the vertical down technique is useful when welding on thin
material. Practicing the vertical up and down techniques on a
flat sheet or plate will greatly assist the welder who desires to
move on to pipe welding because nearly all pipe beads are
accomplished with the same techniques. However, vertical
down is rarely used when TIG welding thicker sections of
plate or pipe.
Welding in the Overhead Position
Welding in the Vertical Position
Figure 8.10 Welding in the overhead position.
Welding in the overhead position is thought by most welders
to be the most difficult of all positions. The welder who can
consistently produce high quality overhead welds is much
sought after by industry.
Figure 8.9 Welding in the vertical position.
Gravity is the enemy of all out-of-position welding. In the vertical
position, both up and down, gravity will try to pull the molten
weld pool downward and out of the joint. A good welder
however, will learn to use gravity to his or her advantage.
In vertical up welding, the weld is begun at the bottom of the
joint with the filler metal being added from above. Attempt to
establish a “shelf” with each dab of filler metal for the next
filler metal addition to rest on. If the joint is wide, work back
and forth across the joint to establish this shelf.
If the joint to be welded is a V-groove, the tungsten electrode
extension can be increased, and the gas cup can be rested
against the edges of the joint and maneuvered back and forth.
This will greatly assist in providing a steady hand, although
this technique makes it difficult to actually see the weld pool.
64
As with vertical welding techniques, gravity is the enemy of
overhead welding. Unlike the vertical position, overhead
welding cannot rely on the building of shelves on which to
place consecutive beads. Instead, it relies on surface tension
of the pool, arc force, and a combination of lower amperage
and higher travel speeds.
One of the techniques used in vertical welds that can be utilized
in the overhead position is extending the tungsten electrode
and resting the gas cup against one or both sides of the joint
to be welded. This procedure is usually used only in groove
welds and some fillet welds. When the welder is putting in fill
passes he can extend a few fingers on either the torch hand
or the filler rod hand and actually rest them on the plate to be
welded. This will help steady the hand.
GTAW produces the highest quality pipe weld of all the arc
processes and with a minimum of distortion.
As with our previous segments on out-of-position welding,
the different combinations of metals, positions, tungstens,
gases and so on make this a subject to which an entire book,
or even library, could be devoted. Therefore this segment will
be limited to a few helpful hints and tips.
Because most pipe joints require a gapped joint, protection of
the weld bead in the form of gas coverage inside the pipe is
necessary. This coverage can be accomplished by covering
the ends of the pipe with pipe caps made for that purpose, or
by simply covering the ends with paper and tape, and then
inserting a shielding gas hose.
GTAW pipe welding also requires a special treatment of the
tungsten electrode tip. A common electrode would be a 1.5%
lanthanated or 2% thoriated tungsten. Once the tip is ground
to a point, the very tip is flattened to a width of about .020.
This small flat spot helps to distribute the arc evenly at the
joint edges.
Figures 8.11 and 8.12 Demonstrations of two common methods of
grasping the torch for pipe welding. There is no single “correct” method
of doing this and each welder is encouraged to experiment with several
different methods until one is found that is most comfortable, and results
in satisfactory welds.
for GTAW • Gas Tungsten Arc Welding
Consumable inserts are items often used in pipe welding.
Consumable inserts are composed of the same type of material
that is being welded and are used to keep root passes uniform.
The consumable insert is melted into the root pass and
becomes an integral part of the weld bead.
HANDBOOK
Pipe welding with the GTAW process requires a great deal
of skill, and should only be attempted when the welder has
mastered the principles of GTAW welding on plate.
TIG
Techniques for Pipe Welding
One of the most popular techniques for GTAW welding of pipe
joints is the walking-the-cup technique. This technique utilizes
a specific manner of manipulating the torch, along with a
series of increasingly larger gas cups to produce consistently
good welds with a minimum of fatigue.
Heat input to the overhead weld pool is extremely important.
Generally speaking, the heat input of an overhead joint would
be less than the amount used for a comparable weld in the
horizontal or flat position. This keeps the pool size small and
thereby prevents sagging or the weld pool from falling out of
the joint.
The possibility of falling molten metal makes the need of
proper protective clothing and equipment absolutely essential.
Never attempt to make this type of weld without all safety
gear in place.
No doubt the overhead position is difficult. It is extremely
fatiguing for the welder to accomplish, making it a slow
process and increasing the time needed to accomplish the
job. This is one of the major reasons industrial use of
overhead welding is kept to a minimum.
Figure 8.13 Demonstration of how the torch and filler rod are held to
accomplish the “walking-the-cup” method of pipe welding.
The two sections of pipe to be welded should be gapped
slightly less than the diameter of the filler rod to be used. The
65
filler rod should rest in the groove without slipping through.
For the root pass, rest the gas cup in the groove contacting
both sides and aimed slightly to either the right or left of the
joint. The cup is then rocked slowly back and forth and slight
pressure is applied to the torch so that it travels forward
along the groove at the same time.
The filler rod is not dipped in and out of the pool, but remains
in contact with the leading edge at all times. When the root
pass is completed, a larger cup is then placed on the torch so
that it now contacts both sides of the groove as well as the
surface of the root pass. The torch is now rocked back and
forth in the joint pivoting on the surface of the root pass while
being guided by the sides of the groove. The filler rod is kept
at the leading edge of the pool without dipping in and out. The
third and all remaining passes are accomplished in the same
manner except that increasingly larger gas cups are used.
Make sure the tungsten extension is adjusted so that it does
not dip into the weld pool, but remains close enough for
proper control.
Arc Starting Procedures
The arc starting requirements of the material to be welded will
have a great impact on the choice of welding power sources.
Scratch Start — This method of arc initiation is utilized by
GTAW power sources with no added arc starting capability.
The arc is started by briefly placing the tungsten electrode in
contact with the work and then quickly withdrawing it as the
arc is established. The advantage of this method is simplicity
of operation. This starting method is not acceptable for critical
applications since small tungsten particles may become
embedded in the workpiece and contaminate the weld. It is
not advisable to use this method with inverter-type power
sources equipped with touch start.
Lift-Arc™ — This type of arc starting method was developed to
eliminate tungsten contamination associated with the scratch
start method. With touch start the tungsten is brought into
contact with the workpiece. When this occurs, the power
source senses a short circuit and establishes a low voltage
current in the weld circuit. This voltage and current are not
great enough to establish an arc, but do contribute to heating
the electrode. When the electrode is lifted from the workpiece, the power source senses the absence of the short
circuit condition and automatically switches to the current
set on the machine. The fact that the electrode has been
pre-heated assists in arc initiation.
Carbon Start — In this method, the tungsten is placed close
to the work, then the resulting gap is momentarily bridged
with a carbon rod or block. Once the arc has begun, the
carbon rod or block is removed or the arc is moved to the
beginning point of the weld. This method is also unacceptable
in critical weld applications because carbon particles may
easily become entrapped in the work. The application of the
carbon rod may be frequently impractical.
Pilot Arc—A small current is maintained between the electrode
and the gas nozzle to provide a conductive path for the main
weld current. This is a method used often with the GTAW spot
welding process and when the process is used for machine
or automatic welding applications.
Hot Tungsten Arc — The tungsten is resistively heated to a
cherry red. At this temperature, the shielding gas in the area
of the tungsten becomes ionized and therefore will conduct
electricity. The presence of the power sources open circuit
voltage under these circumstances is enough for the arc to
establish itself between the electrode and the work. The
necessity of heating the electrode and the resulting preheating
of the work are considered disadvantages of this method.
Capacitor Discharge (CD) — In this method, the arc is
initiated with a momentary burst of high voltage (normally
provided by a bank of capacitors) between the electrode and
the work. This high-energy spark creates an ionized path
through which the weld current starts flowing. This method
is generally used with DC power supplies in machine or automatic welding applications.
Figure 8.14 This welder (who happens to be left handed) demonstrates
still another style of torch and filler rod manipulation used to accomplish a
pipe weld.
66
High-Frequency Start—Perhaps the most common of all arc
starting methods, high frequency can be used with DC or AC
power sources for manual through automatic applications.
This method uses the ionizing capability of a high-frequency
voltage superimposed over the welding current to provide a
path for the arc to become established. Some power sources
discontinue the high frequency once the arc is established
and some feature continuous high frequency to take advantage
of the stabilizing control it has on the arc. Special precautions
■
■
■
■
■
GTAW Arc Starting Tips
The following list is developed from the experiences of welding
engineers, welding technicians, welding instructors, and others
employed in the welding field. They were asked to provide
tips and techniques they have used for the sometimes difficult
task of starting the gas tungsten arc. The list of arc starting
“hints and tips” are in no particular order of importance, and
are submitted in the interest of taking advantage of the many
years of experience of welding professionals.
■
■
■
■
■
■
■
■
Tips for Automatic Applications
■
■
■
for GTAW • Gas Tungsten Arc Welding
■
Arc Assist — Utilizes a high voltage DC spike that is induced
into the weld circuit to assist starts and provide stabilization
during AC welding. These high voltage spikes are present
only when the output voltage is greater than 30 volts. In DC
welding, as the welder brings the electrode close enough to
the work, the pulses jump start the arc, the weld circuit voltage drops to its normal 14 or so volts, and the arc assist circuitry drops out. In AC welding, the voltage passes through
the zero point twice each cycle and the arc will tend to go out.
Because the voltage increases during these arc outages, the
Arc Assist circuitry is automatically engaged for that part of
the cycle only, thereby providing a stabilizing effect.
Use the shortest length torch possible.
Use premium quality cable for torch and work leads.
Keep torch and work leads as short as possible. Move
the power source as close as possible to the work. If
the power source cannot be moved closer and a highfrequency arc starter is being used, move it closer to
the weld.
Attach work lead as close as possible to the weld.
Avoid long cable runs over bare concrete floors, or
insulate cables from floor by laying them on boards.
If the welding machine is being used for both GTAW
welding and for Stick electrode welding, make sure the
Stick electrode holder is detached from the machine
when GTAW welding.
Check and tighten all connections.
Keep the torch cable from contacting any grounded
metal such as work benches, steel floor plates, and
the machine case.
Use 100% argon shielding gas if possible.
Check the secondary current path and tighten
all connections.
If the machine has adjustable high-frequency spark gaps,
increase gap to manufacturer’s recommended maximum.
Check for mineral deposit build up in water-cooled
torches to avoid high-frequency shunting back to
ground through deposit material.
Increase intensity adjustment if available.
HANDBOOK
Impulse Arc Start — Used when a noncontact, TIG arc starting
method is required. A single pulse of high-frequency (HF)
voltage is superimposed from the electrode to the workpiece
to initiate the arc. Impulse arc starting can be used for DC TIG
or AC TIG using the Advanced Squarewave power source.
The main advantage to impulse arc starting is the electromagnetic interference (EMI) generated by the welding power
source is significantly reduced. Thus, the chance of causing
other electronic equipment in the immediate vicinity to malfunction or be damaged is diminished.
■
TIG
must be taken to prevent the high frequencies electromagnetic interference (EMI) from radiating too much energy and
causing interference with communication systems and
computerized equipment.
Check all of the above, they still apply.
Mount the torch in a non-metallic holder or clamp.
Use a metallic gas cup on the torch. Attach a 6000 volt
lead with a .001 mfd mica-capacitor between gas cup
and ground.
Use the smallest diameter tungsten possible.
Buy the highest quality tungsten available
(of the proper alloy).
67
IX. Cost Considerations of
the GTAW Process
It is important to take into consideration all the facts that
relate to a welding situation when attempting to attach a cost
to a foot of weld. Not only do direct costs such as filler wire,
shielding gas, equipment, and labor have a bearing, but indirect
costs such as overhead and training of personnel have an
affect as well.
Training should be considered in the cost since GTAW is
generally considered a more advanced process and will
require time by the welder to familiarize with the technical and
manipulative aspects of the process.
A cost evaluation of a welding process should include:
1. Labor and overhead cost per foot of weld.
2. Filler wire cost per foot of weld.
3. Gas cost per foot of weld.
4. Power cost per foot of weld.
Computing these figures on a chart or proposal will show the
economics of a particular process.
Standard formulas for cost estimating as presented in this
book (Figure 9.1) are a reasonable measure for computing
data for cost comparison.
The formulas as presented have no “plug-in” numerical values.
The values will vary with each application and each company.
The cost of proper equipment to efficiently accomplish the
job at hand is of great importance. Manual GTAW equipment
in a production setup can run into thousands of dollars. If
there are many repetitive welds, automatic equipment should
be considered, and those costs can run into the tens of
thousands of dollars.
Formulas to Figure Total Welding Cost
Welder Rate in $ Per Hour
1. Labor = __________________________________________
= Cost per ft.
Weld Travel Speed (IPM) x Duty Cycle x 60 min./hr.
12"/ft.
Overhead Rate
2. Overhead = __________________________________________
= Cost per ft.
Weld Travel Speed (IPM) x Duty Cycle x 60 min./hr.
12"/ft.
3. Filler Metal Cost
Foot of Weld
Weight of Deposit x Filler Metal Cost
Deposition Efficiency
Cost of Gas/cu. ft. x Flow Rate (cfh) = Cost per ft.
4. Gas = ________________________________
Weld Travel Speed (IPM) x 60 min./hr.
12"/ft.
Volts x amps x power cost/kw. hr.
5. Power = ______________________________________________________
= Cost per ft.
Weld Travel Speed (IPM) x Machine Efficiency x 60 min./hr. x 1000
12"/ft.
6. Total = Total of Above Applying Formulas x Total Length of Weld = Total Cost
*The factor 5 will appear in some of the formula examples: This was derived from the ratio of:
60 min./hr.
12"/ft.
Figure 9.1 Formulas for cost considerations.
68
The data collected here discusses some of the common
problems of the TIG welding processes.
The assumption of this data is that a proper welding condition
has been achieved and has been used until trouble developed.
In all cases of equipment malfunction, the manufacturer’s
recommendations should be strictly adhered to and followed.
HANDBOOK
PROBABLE CAUSES
SUGGESTED REMEDY
1. Inadequate gas flow.
Check to be sure hose, gas valve, and torch are not restricted
or the tank is not out of gas. Gas flow should typically be set
at 15 to 20 cfh.
2. Operation on electrode positive (DCEP).
Switch to electrode negative (DCEN).
3. Improper size tungsten for current used.
General purpose tungsten size is 3/32" diameter at a
maximum of 220 amps.
4. Excessive heating in torch body.
Air-cooled torches do get very warm. If using a water-cooled
torch, coolant flow may be restricted or coolant may be low.
5. Tungsten oxidation during cooling.
Keep shielding gas flowing 10–15 seconds after arc stoppage.
1 second for each 10 amps of weld current.
6. Use of gas containing oxygen or CO2.
Use argon gas.
7. Tungsten melting back into cup (AC).
If using pure tungsten, change to ceriated or lanthanated.
If machine has Balance Control, adjust setting towards
maximum penetration (70-90). Tungsten diameter may be
too small for the amount of current being used. Increase
tungsten size.
for GTAW • Gas Tungsten Arc Welding
When troubleshooting Gas Tungsten Arc Welding process
and equipment problems, it is ideal to isolate and classify
them as soon as possible into one of the following categories:
TIG
X. GTAW Troubleshooting
1. Electrical
2. Mechanical
3. Process
PROBLEM 1: Burning Through Tungsten Fast
PROBLEM 2: Tungsten Contamination
PROBABLE CAUSES
SUGGESTED REMEDY
1. Tungsten melting into weld puddle.
Use less current or larger tungsten. Use ceriated (AC),
thoriated (DC), or lanthanated tungsten.
2. Touching tungsten to weld puddle.
Keep tungsten from contacting weld puddle. Raise the torch
so that the tungsten is off of the work piece 1/8" to 1/4".
PROBLEM 3: High-Frequency Present — No Arc Power
PROBABLE CAUSES
SUGGESTED REMEDY
1. Incomplete weld circuit.
Check work connection. Check all cable connections.
2. No shielding gas.
Check for gas flow at end of torch. Check for empty cylinder
or closed shut-off valve. Gas flow should typically be set at
15 to 20 cfh.
69
PROBLEM 4: Porosity and Poor Weld Bead Color
PROBABLE CAUSES
SUGGESTED REMEDY
1. Condensation on base metal.
Blow out all air and moisture condensation from lines.
Remove all condensation from base metal before welding.
Metals stored in cold temperatures will condensate when
exposed to warm temperatures.
2. Loose fittings in torch or hoses.
Tighten fittings on torch and all hoses.
3. Inadequate gas flow.
Adjust flow rate as necessary. Gas flow should typically be
set at 15 to 20 cfh.
4. Defective gas hose or loose connection.
Replace gas hose and check connections for leaks, cuts, or
pin holes.
5. Contaminated or improper filler metal.
Check filler metal type. Remove all grease, oil, or moisture
from filler metal.
6. Base metal is contaminated.
Remove paint, grease, oil, and dirt, including mill scale from
base metal.
PROBLEM 5: Yellow Powder or Smoke on Cup—Tungsten Discolor
PROBABLE CAUSES
SUGGESTED REMEDY
1. Shielding gas flow rate too low.
Increaseflow rate. Gas flow should typically be set at 15 to 20 cfh.
2. Incorrect shielding gas or mixture.
Use argon gas.
3. Inadequate post flow.
Increase post flow time. Set at 10 to 15 seconds.
4. Improper tungsten size or cup size.
Match tungsten size and cup size to joint being welded.
General purpose tungsten size is 3/32" diameter and #8 cup.
PROBLEM 6: Unstable Arc
PROBABLE CAUSES
SUGGESTED REMEDY
While AC Welding
70
1. Excessive rectification in base metal.
Increase travel speed. Increase balance control toward more
penetration. Add filler metal.
2. Improper shielding gas.
In some cases, when welding on 3/8" to 1/2" thick aluminum,
argon/helium is used.
3. Incorrect arc length.
Use correct arc length. Adjust the torch so that the tungsten
is off of the work piece 1/8" to 1/4".
4. Tungsten is contaminated.
Remove 1/2" of contaminated tungsten and repoint tungsten.
5. Base metal is contaminated.
Remove paint, grease, oil, and dirt, including mill scale from
base metal.
6. Frequency set too low.
On welders with adjustable AC frequency, increase frequency
to give proper arc stability and direction. 100 to 180 Hertz is
acceptable.
7. Improperly prepared tungsten.
With Squarewave and inverter machines, use pointed
tungsten. Point will eventually round off after welding.
TIG
PROBLEM 6: Unstable Arc
PROBABLE CAUSES
SUGGESTED REMEDY
While DC Welding
Check polarity switch on welder. Select DCEN (Direct Current
Electrode Negative).
2. Tungsten is contaminated.
Remove 1/2" of contaminated tungsten and repoint tungsten.
3. Arc too long.
Shorten arc length. Lower torch so that the tungsten is off of
the work piece no more than 1/8" to 1/4".
4. Base metal is contaminated.
Remove paint, grease, oil, and dirt, including mill scale from
base metal.
PROBABLE CAUSES
SUGGESTED REMEDY
While DC Welding
1. Improper arc length/tungsten in poor condition.
Lower the torch so that the tungsten is off of the work piece
1/8" to 1/4". Clean and sharpen tungsten.
2. Improperly prepared tungsten.
Grind marks should run lengthwise with tungsten, not circular.
Use proper grinding method and wheel.
3. Light gray frosted appearance on end of tungsten.
Remove 1/2" of tungsten and repoint tungsten.
4. Improper gas flow.
Gas flow should typically be set at 15 to 20 cfh.
While AC Welding
1. Improper tungsten preparation.
With Squarewave and inverter machines, use pointed
tungsten. Point will eventually round off after welding.
2. Tungsten is contaminated.
Remove 1/2" of contaminated tungsten and repoint tungsten.
3. Base metal is contaminated.
Remove paint, grease, oil, and dirt, including mill scale from
base metal.
4. Incorrect balance control setting.
Increase balance toward more penetration. Normal Balance
Control setting is 70 - 90.
5. Improper tungsten size and type.
Select proper size and type. General purpose tungsten size is
3/32" diameter and ceriated or thoriated.
6. Excessive rectification in base metal.
Increase travel speed. Increase balance setting toward more
penetration. Add filler metal.
7. Improper shielding gas flow.
Gas flow should typically be set at 15 to 20 cfh.
8. Frequency set too low.
Increase AC frequency on machines so equipped to stabilize
and direct the arc. The higher the frequency, the narrower
and deeper the penetration.
for GTAW • Gas Tungsten Arc Welding
PROBLEM 7: Arc Wanders
HANDBOOK
1. Weld circuit polarity is incorrect.
71
PROBLEM 8: Arc Will Not Start or is Difficult to Start
PROBABLE CAUSES
SUGGESTED REMEDY
While DC Welding
1. No shielding gas.
Gas flow should typically be set at 15 to 20 cfh.
2. Incorrect power supply switch positions.
Place switches in proper positions, either HF impulse or start HF.
3. Improper tungsten electrode.
Use ceriated or thoriated tungsten.
4. Loose connections.
Tighten all cable and torch connections.
5. Incomplete weld circuit.
Make sure work clamp is connected.
6. Improper tungsten size.
Use smallest tungsten possible. Most common tungsten size
is 3/32" diameter.
While AC Welding
72
1. Incomplete weld circuit.
Check work clamp to assure it is securely fastened to work.
2. Incorrect cable installation.
Check circuit breakers and fuses. Check and tighten all cable
connections.
3. No shielding gas.
Check for gas flow at end of torch. Check for empty cylinder
or closed shut-off valve. Gas flow should typically be set at
15 to 20 cfh.
4. Loss of high frequency.
Check torch and cables for cracked insulation or bad
connections. Check spark gaps and adjust if necessary.
5. Improper tungsten size.
Use smallest tungsten possible. Most common tungsten size
is 3/32" diameter.
6. Incorrect tungsten type.
Use ceriated, thoriated, or lanthanated tungsten.
TIG
XI. Tables
Table 1
Type of
Tungsten (Alloy)
Color
Code
Available
Finish*
EWP
Pure
Green
Cleaned
and ground
Provides good arc stability for AC welding.
Reasonably good resistance to contamination.
Lowest current carrying capacity. Least
expensive. Maintains a clean balled end.
EWCe-2
Ceria
CeO2
1.8% to 2.2%
Orange
Cleaned
and ground
Similar performance to thoriated tungsten.
Easy arc starting, good arc stability,
long life. Possible nonradioactive
replacement for thoria.
EWLa-1
Lanthana
La2O3
0.9% to 1.2%
Black
Cleaned
and ground
Similar performance to thoriated tungsten.
Easy arc starting, good arc stability,
long life, high current capacity. Possible
nonradioactive replacement for thoria.
EWLa-1.5
Lanthana
La2O3
1.3% to 1.7%
Gold
Cleaned
and ground
Similar performance to thoriated tungsten.
Easy arc starting, good arc stability,
long life, high current capacity. Possible
nonradioactive replacement for thoria.
EWLa-2
Lanthana
La2O3
1.8% to 2.2%
Blue
Cleaned
and ground
Similar performance to thoriated tungsten.
Easy arc starting, good arc stability,
long life, high current capacity. Possible
nonradioactive replacement for thoria.
EWTh-1
Thoria
ThO2
0.8% to 1.2%
Yellow
Cleaned
and ground
Easier arc starting. Higher current capacity.
Greater arc stability. High resistance to
weld pool contamination. Difficult to maintain
balled end on AC.
EWTh-2
Thoria
ThO2
1.7% to 2.2%
Red
Cleaned
and ground
Easier arc starting. Higher current capacity.
Greater arc stability. High resistance to
weld pool contamination. Difficult to maintain
balled end on AC.
EWZr-1
Zirconia
ZrO2
0.15% to 0.40%
Brown
Cleaned
and ground
Excellent for AC welding due to favorable
retention of balled end, high resistance to
contamination, and good arc starting.
Preferred when tungsten contamination
of weld is intolerable.
EWG
Specify
Gray
Remarks
for GTAW • Gas Tungsten Arc Welding
AWS
Classification
HANDBOOK
Types of Tungsten Electrodes
Contains other rare earths or a combination
of oxides.
*Clean finish designates electrodes that are chemically cleaned and etched. Ground finish designates electrodes
with a centerless ground finish to provide maximum smoothness and consistency.
Centerless ground tungsten electrodes are used where minimum resistance loss at the collet-electrode contact
point is desired.
73
Table 2
Typical Current Ranges for Tungsten Electrodes*
Direct Current,
DC
Alternating Current,
AC
DCEN
Tungsten
Diameter
Gas Cup
Inside
Diameter
Ceriated
Thoriated
Lanthanated
.040
#5 (3/8 in)
.060 (1/16 in)
70% Penetration
(50/50) Balanced
Wave A
Pure
Ceriated
Thoriated
Lanthanated
Pure
Ceriated
Thoriated
Lanthanated
15 – 80
20 – 60
15 – 80
10 – 30
20 – 60
#5 (3/8 in)
70 – 150
50 – 100
70 – 150
30 – 80
60 – 120
.093 (3/32 in)
#8 (1/2 in)
150 – 250
100 – 160
140 – 235
0 – 130
100 – 180
.125 (1/8 in)
#8 (1/2 in)
250 – 400
150 – 200
225 – 325
100 – 180
160 – 250
*All values are based on the use of Argon as a shielding gas. Other current values may be employed depending on the
shielding gas, type of equipment, and application.
DCEN = Direct Current Electrode Negative (Straight Polarity)
74
TIG
Table 3
Recommended Types of Current, Tungsten Electrodes and
Shielding Gases for Welding Different Metals1
Aluminum
Copper,
copper alloys
Magnesium alloys
Electrode2
Shielding Gas
All
All
All
DCEN
All
All
Pure or zirconium
Lanthanated, cerium
thoriated
Lanthanated, cerium
thoriated
Lanthanated, cerium
thoriated
Pure or zirconium
Lanthanated, cerium
thoriated
Lanthanated, cerium
thoriated
Argon or argon-helium
Argon or argon-helium
over 1/4"
AC
AC Advanced
Squarewave
DCEN
Nickel, nickel alloys
All
Plain carbon,
low-alloy steels
Stainless steel
All
DCEN
All
DCEN
All
DCEN
All
DCEN
Lanthanated, cerium
thoriated
Lanthanated, cerium
thoriated
Lanthanated, cerium
thoriated
Lanthanated, cerium
thoriated
100% Helium
Helium
Argon
Argon
Argon, argon-helium,
argon-hydrogen
(5% max)
Argon or argon-helium
Argon or argon-helium
Argon
Argon
These recommendations are general guidelines based on methods commonly used in industry.
Where thoriated electrodes are recommended, lanthanated, ceriated or rare earth containing electrodes should
be used.
3
A glove box is often required to prevent atmospheric contamination.
2
for GTAW • Gas Tungsten Arc Welding
Type of Current
AC
AC Advanced
Squarewave
DCEN
Titanium, zirconium,
hafnium3
Refractory Metals3
1
Thickness
HANDBOOK
Types of Metal
75
Table 4
AWS Specifications for Filler Metals, Shielding Gases and Electrodes
Suitable for Gas Tungsten Arc Welding
Specification Number
Title
A 5.7
Copper and Copper Alloy Bare Welding Rods and Electrodes
A 5.9
Stainless Steel Bare Welding Rods and Electrodes
A 5.10
Aluminum and Aluminum Alloy Welding Rods and Bare Electrodes
A 5.12
Tungsten and Tungsten Alloy Electrodes
A 5.13
Surfacing Welding Rods and Electrodes
A 5.14
Nickel and Nickel Alloy Bare Welding Rods and Electrodes
A 5.16
Titanium and Titanium Alloy Bare Welding Rods and Electrodes
A 5.18
Carbon Steel Filler Metals for Gas Shielded Arc Welding
A 5.19
Magnesium-Alloy Welding Rods and Bare Electrodes
A 5.21
Composite Surfacing Welding Rods and Electrodes
A 5.24
Zirconium and Zirconium Alloy Bare Welding Rods and Electrodes
A 5.28
Low Alloy Steel Filler Metal for Gas Shielded Arc Welding
A 5.30
Consumable Inserts
A 5.32
Welding Shielding Gases
Table 5
Welding Position Designations
Plate Welds
Groove Welds
1G Flat position
2G Horizontal position
3G Vertical position
4G Overhead position
Fillet Welds
1F Flat position
2F Horizontal position
3F Vertical position
4F Overhead position
Pipe Welds
Groove Welds
1G Flat position, pipe axis horizontal and rotated
2G Horizontal position, pipe axis vertical
5G Multiple positions, (overhead, vertical and flat) pipe axis horizontal and is not rotated (fixed)
6G Multiple positions, (overhead, vertical and horizontal) pipe axis in inclined 45˚ from horizontal
and is not rotated (fixed)
6GR Multiple positions, (overhead, vertical and horizontal) pipe axis in inclined 45˚ from horizontal
and is not rotated (fixed), with restriction ring
Fillet Welds
1F Flat position, pipe axis is 45˚ from the horizontal and the pipe is rotated
2F Horizontal position, pipe axis is vertical
2FR Horizontal position, weld pipe axis is horizontal and the pipe is rotated
4F Overhead position, pipe axis is vertical
5F Multiple positions, (overhead, vertical and horizontal) pipe axis is horizontal and is not rotated
6F Multiple positions, (overhead, vertical and flat) pipe axis is 45˚ from horizontal and is not rotated
76
TIG
Table 6
Welding Process Comparison Based on Quality and Economics
All Positions
GMAW
SMAW
Carbon steel plate (over 3/16")
G
E
E
Carbon steel sheet (to 3/16")
E
E
G
Carbon steel structural
F
F
E
E
F
F
Carbon steel pipe — over 4" IPS
G
G
G
Stainless steel plate (over 3/16")
G
E
G
Stainless steel sheet (to 3/16")
E
G
F
Stainless steel pipe — 3" IPS and under
E
F
F
Stainless steel pipe — over 4" IPS
G
G
F
Aluminum plate (over 3/16")
G
E
NR
Aluminum sheet (to 3/16")
E
G
NR
Aluminum structural
E
G
NR
Aluminum pipe — 3" IPS and under
E
NR
NR
Aluminum pipe ” over 4" IPS
E
F
NR
Nickel and nickel alloy sheet
E
F
F
Nickel and nickel alloy tubing
E
NR
NR
Nickel and nickel alloy pipe — 3" IPS and under
E
F
NR
Nickel and nickel alloy pipe — over 4" IPS
E
F
NR
Reflective metals, titanium — sheet, tubing, and pipe
E
NR
NR
Refractory metals, TA and Cb — sheet, tubing
E
NR
NR
GTAW — Gas Tungsten Arc (TIG)
GMAW — Gas Metal Arc (MIG)
SMAW — Shielded Metal Arc (Stick)
for GTAW • Gas Tungsten Arc Welding
Carbon steel pipe — 3" IPS and under
HANDBOOK
GTAW
Applications
E — Excellent
G — Good
F — Fair
NR — Not recommended on basis of cost, usability, or quality.
Table 7
Cost Information
Weld Process
Approximate
Equipment Cost
Average Gas and
Power Cost Per Hour
Relative
Labor Cost
GTAW
$1,500 –10,000
7.00
Medium
GMAW
$2,000 –10,000
8.00
Low
SMAW
$500 – 2,000
1.50
Low/Medium
77
Table 8
Guide for Shade Numbers
Operation
Shielded Metal Arc Welding
Electrode Size
1/32 in. (mm)
Less than 3 (2.5)
3 – 5 (2.5 – 4)
5 – 8 (4 – 6.4)
More than 8 (6.4)
Gas Metal Arc Welding
and Flux Cored Arc Welding
Gas Tungsten Arc Welding
Air Carbon
Arc Cutting
Plasma Arc Welding
(Light)
(Heavy)
Plasma Arc Cutting
(Light)**
(Medium)**
(Heavy)**
Torch Brazing
Torch Soldering
Carbon Arc Welding
Plate thickness
Gas Welding
Light
Medium
Heavy
Oxygen Cutting
Light
Medium
Heavy
Arc
Current (A)
Less than 60
60 – 160
160 – 250
250 – 550
Less than 60
60 – 160
160 – 250
250 – 550
Less than 50
50 – 150
150 – 500
Less than 500
500 – 1000
Less than 20
20 – 100
100 – 400
400 – 800
Less than 300
300 – 400
400 – 800
—
—
—
Minimum
Protective
Shade
7
8
10
11
7
10
10
10
8
8
10
10
11
6
8
10
11
8
9
10
—
—
—
Suggested*
Shade No.
(Comfort)
—
10
12
14
—
11
12
14
10
12
14
12
14
6 to 8
10
12
14
9
12
14
3 or 4
2
14
Under 1/8"
1/8 to 1/2"
Over 1/2"
Under 3.2 mm
3.2 to 12.7 mm
Over 12.7 mm
4 or 5
5 or 6
6 or 8
Under 1"
1 to 6"
Over 6"
Under 25 mm
25 to 150 mm
Over 150 mm
3 or 4
4 or 5
5 or 6
*As a rule of thumb, start with a shade that is too dark to see the weld zone. Then go to a lighter shade which
gives sufficient view of the weld zone without going below the minimum. In oxyfuel gas welding or cutting where
the torch produces a high yellow light, it is desirable to use a filter lens that absorbs the yellow or sodium line in
the visible light of the (spectrum) operation.
**These values apply where the actual arc is clearly seen. Experience has shown that lighter filters may be used
when the arc is hidden by the workpiece.
78
TIG
Table 9
Conversion Table
U.S. Customary Units to International System of Units (SI) — Metric System
Area
Impact Strength
To
Millimeters (mm)
Meters (m)
Millimeters (mm)
Meters (m)
mm2
m2
m2
Amperes/mm2
Kilograms (kg)/hour (h)
Litre/minute
Pascals (Pa)
Multiply By
25.4
0.0254
304.8
0.3048
645.16
0.000645
0.0929
0.00155
0.0454
0.472
6895.0
mm/s
cm/m
Kg
Celsius (C˚)
(centigrade)
Fahrenheit
(F˚)
Joules
0.423
2.54
0.454
tF – 32
1.8
tc x 1.8 + 32
1.356
for GTAW • Gas Tungsten Arc Welding
Current Density
Deposition Rate
Flow Rate
Pressure,
Tensile Strength
Travel Speed,
Wire Feed Speed
Weight, Mass
Temperature
Convert From
Inches (in)
Inches (in)
Feet (ft)
Feet (ft)
in2
in2
ft2
Amperes/in2
Pounds (lb)/hour (h)
ft3/h
Pounds /sq in
(psi)
in/min
in/min
lb
Fahrenheit
(F˚), tF
Celsius (C˚)
(centigrade), tc
ft lbs
HANDBOOK
Property
Measurement
79
Table 10
Control Symbols Found on GTAW Machines
Functional Area
Control
Wordage/Abbrev.
Power
ON
OFF
Electrode Positive
Electrode Negative
Alternating Current
SMAW
GTAW
Off
Lift Arc
HF Start Only
HF Continuous
Impulse
On
Remote
Two Step Maintained
Two Step Momentary
Four Step Momentary
Panel
Remote
Preflow Time
Postflow Time
Gas Inlet
Gas Outlet
Balance Phase Control
AC Frequency
Maximum Cleaning
Maximum Penetration
Electrode Positive Amperage
Electrode Negative Amperage
Percentage Arc Force
Initial Amperage
Initial Time
Initial Slope Time
Spot Time
Weld Time
Final Slope
Final Amperage
Final Time
Pulse Frequency
Percent Peak Time
Percent Background Amperage
Pulser
Coolant Inlet
Coolant Outlet
ON
OFF
Electrode Positive/DCEP
Electrode Negative/DCEN
Alternating Current/AC
Stick
TIG
Off
Lift Arc
HF Start
HF Cont.
Impulse
On
Remote
Standard/STD
2T Trigger Hold/2T
4T Trigger Hold/4T
Current Panel/A PNL
Current Remote/ARMT
Preflow
Postflow
Gas In
Gas Out
Balance/BAL
Frequency/AC f
Maximum Cleaning/MAX CLEAN
Maximum Penetration/MAX PEN
Electrode Positive Amperage/EP AMPS
Electrode Negative Amperage/EN AMPS
DIG
Initial Amperage/INITIAL A
Initial Time/INITIAL t
Initial Slope
Spot Time/SPOT t
Weld Time/WELD t
Final Slope
Final Amperage/FINAL A
Final Time/FINAL t
Pulses Per Seconds/PPS
Peak Time/PK t
Background Amperage/BKGND A
Pulser
Coolant In
Coolant Out
Polarity
Process
Start Mode
Output
Trigger
Amperage
Gas
AC Waveshaping
Arc Force
Sequencing
Pulsing
Coolant
80
Symbol
V
V
HF
HF
t1
t2
A
t
t
None
Advanced Squarewave: The advanced AC output available
from certain types of power sources. The wave is much more
square than the conventional Squarewave power source. It also
has expanded balance control to 90% electrode negative
(max penetration) and the ability to control arc frequency
(arc direction). Some have the additional ability to adjust the
amount of current in the electrode negative and electrode
positive cycles independently.
Bevel Angle: An angle formed between a plane, perpendicular
to the surface of the base metal and the prepared edge of the
base metal. This angle refers to the metal that has been removed.
Air Carbon Arc Cutting: A cutting process by which metals are
melted by the heat of an arc using a carbon electrode. Molten
metal is forced away from the cut by a blast of forced air.
Amperage: The measurement of the amount of electricity
flowing past a given point in a conductor per second. Current
is another name for amperage.
Annealing: The opposite of hardening. A heat treating
process used to soften a metal and relieve internal stresses.
Anodize: To anodize aluminum is to coat the metal by either
chemical or electrical means. The coating provides improved
corrosion and wear resistance. The thickness of this coating
depends upon the length of the treatment. This coating is
often removed from the area to be welded. This coating can
be reapplied after welding.
Arc: The physical gap between the end of the electrode and
the base metal. The physical gap causes heat due to resistance
of current flow and arc rays.
Arc Length: Distance or air space between the tip of the
electrode and the work.
Arc Voltage: Measured across the welding arc between the
electrode tip and the surface of the weld pool.
Asymmetric Waveform: The output waveform of a welding
power source that has the ability to modify both the amplitude
and duration of the positive and negative half cycles of
alternating current.
Carbide Precipitation: Occurs when austenitic stainless steel is
heated within a temperature range of 800˚–1600˚ F, 427˚– 870˚ C
for a critical period of time. Carbon moves from a solid
solution to grain boundaries and combines with chromium.
The metal adjacent to the grain boundaries is left with less
chromium and is said to be sensitized. Corrosion resistance is
therefore reduced in the grain boundary region. See Figure 12.1.
Carbon Arc Gouging: A cutting process by which metals are
melted by the heat of an arc using a carbon electrode. Molten
metal is forced away from the cut by a blast of forced air.
Cerium Tungsten: GTAW tungsten electrode with small amount
of the rare earth and nonradioactive ceria added. Improves
arc starting and provides for use of wider current range.
Characteristics: Special qualities or properties. For instance,
some welding machines have certain internal characteristics
which allow a welder to perform more welding applications
than with other welding machines.
Circuit: The complete path or route traveled by the electrical
current. A circuit for GTAW can include the welding machine,
weld cables, torch assembly, arc, base metal and work clamp
with cable.
Cold Lap: See preferred term Incomplete Fusion.
Conductor: An electrical path where current will flow with
the least amount of resistance. Most metals are good
electrical conductors.
Constant Current (CC) Welding Machine: These welding
machines have limited maximum short circuit current. They
have a negative volt-amp curve and are often referred to as
“droopers”. The voltage will change with different arc lengths
while only slightly varying the amperage, thus the name constant
current or variable voltage.
Autogenous Weld: When a TIG weld is made without the
addition of filler metal.
Chromium-Depleted Zone
Automatic Welding (AU): Uses equipment which welds without
the constant adjusting of controls by the welder or operator.
Equipment controls joint alignment by using an automatic
sensing device.
Grain
Boundaries
Axis of Weld: Can be thought of as an imaginary line through
the center of a weld, lengthwise.
Back Gouging: The removal of weld metal and base metal
from the other side (root side) of a weld joint. When this
gouged area is welded, complete penetration of the weld
joint is assured.
for GTAW • Gas Tungsten Arc Welding
Alternating Current (AC): An electrical current that reverses
its direction at regular intervals, such as 60 cycles alternating
current (AC), or 60 hertz (Hz).
Butt Joint: A weldment where the material surfaces and
joining edges are in or near the same plane.
TIG
Balanced Wave: An alternating current waveform that has
equal negative and positive polarity current values.
HANDBOOK
XII. Glossary
Chromium
Carbides
Figure 12.1 Carbide precipitation.
81
Constant Voltage (CV), Constant Potential (CP) Welding
Machine: “Potential” and “voltage” are basically the same in
meaning. This type of welding machine output maintains a
relatively stable, consistent voltage regardless of the amperage
output. It results in a relatively flat volt-amp curve as opposed
to the drooping volt-amp curve of a typical GTAW (TIG)
welding machine.
Consumable Insert: Preplaced filler metal that is completely
fused into the joint root and becomes part of the weld.
Contactor: An electrical switch that is used to energize or
de-energize output terminals of a welding machine. In some
types of welding machines they can be of solid state design,
with no moving parts and thus no arcing of contact points.
Corner Joint: Produced when the weld members meet at
approximately 90˚ to each other in the shape of an “L”.
Crater: A depression at the end of a weld bead.
Current: Another name for amperage. The amount of electricity
flowing past a point in a conductor every second.
Current Density: The amount of current per square inch of
cross-sectional area in an electrode. For any electrode diameter,
find the current density by dividing the current value by the
electrode cross-sectional area in square inches.
Cycle: One cycle equals 360 electrical degrees. For alternating
current, current flow is in one direction through a circuit for
180˚ and in the opposite direction for the other 180˚. For 60
cycle power, a cycle is repeated 60 times per second. Some
welding machines, especially outside the United States, require
50 cycle (hertz) power. Hertz stands for cycles per second.
Defect: One or more discontinuities that exceed the acceptance
criteria as specified for a weld.
Depth of Fusion: The depth or distance that deposited weld
metal extends into the base metal or the previous pass.
Direct Current: Flows in one direction and does not reverse
its direction of flow as does alternating current.
Direct Current Electrode Negative (DCEN): The specific direction
of current flow through a welding circuit when the electrode
lead is connected to the negative terminal and the work lead
is connected to the positive terminal of a DC welding machine.
Direct Current Electrode Positive (DCEP): The specific direction
of current flow through a welding circuit when the electrode
lead is connected to a positive terminal and the work lead is
connected to a negative terminal to a DC welding machine.
Discontinuity: Any change in a metal’s typical structure. It is
the lack of consistence in mechanical, metallurgical or physical
characteristics. Discontinuities are found in all metals and
welds because they have some degree of inconsistency in
them. However, this is acceptable as long as the discontinuities
do not exceed the acceptance criteria of the weld or metal in
question. If a discontinuity exceeds the acceptance criteria,
they are defects and must be repaired.
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Distortion: The warpage of a metal due to the internal residual
stresses remaining after welding from metal expansion (during
heating), and contraction (during cooling).
Duty Cycle: The number of minutes out of a 10-minute time
period an arc welding machine can be operated at maximum
rated output. An example would be 60% duty cycle at 300
amps. This would mean that at 300 amps the welding machine
can be used for 6 minutes and then must be allowed to cool
with the fan motor running for 4 minutes. (Some imported
welding machines are based on a 5-minute cycle).
Edge Joint: A joint that occurs when the surfaces of the two
pieces of metal to be joined are parallel or nearly parallel, and
the weld is made along their edges.
Electrode Extension: While welding, the length of electrode
extending beyond the end of the gas cup. Also referred to as
electrical stickout.
Electron: A very small atomic particle which carries a negative
electrical charge. Electrons can move from one place to
another in atomic structures. It is electrons that move when
electrical current flows in an electrical conductor.
Etching: When a weld specimen is cut through a weld, an
acid or similar solution can be applied to the weld area to
bring out the features of the weld. These include the deposited
weld metal, heat affected zone, penetration and weld profile.
Many different etching solutions and techniques exist for the
various kinds of metals.
Excessive Melt-Through: A weld defect occurring in a weld
joint when weld metal no longer fuses the base metals being
joined. Rather, the weld metal falls through the weld joint or
“burns through”. Also referred to as excess penetration.
Face: The surface of the weld as seen from the side of the
joint on which the weld was made.
Face Rotation: Can be thought of as an imaginary line from
the axis of the weld through the center of the welds face.
This face rotation angle along with the axis angle determine
the actual welding position. Face rotation is measured in a
clockwise direction starting from the 6 o’clock position.
A weld with the face rotation at 12 o’clock would have the
face rotation at 1800.
Ferrous: Refers to a metal that contains primarily iron, such
as steel, stainless steel and cast iron.
Filler Metal: The metal added when making a welded,
brazed, or soldered joint.
Fillet Weld: A weld that is used to join base metal surfaces
that are approximately 90˚ to each other, as used on T-joint,
corner joint or lap joint. The cross sectional shape of a fillet
weld is approximately triangular.
Freeze Lines: The lines formed across a weld bead. They are the
result of the weld pool freezing. In appearance they sometimes
look as if one tiny weld was continuously laid upon another.
Frequency: The number of double directional changes made
by an alternating current in one second. Usually referred to
as “hertz per second” or “cycles per second”. In the United
States, the frequency or directional change of alternating
current is usually 60 hertz. Some Advanced Squarewave
power sources allow the arc frequency to be adjusted. As arc
frequency is increased the arc becomes more directional.
Gas Metal Arc Welding (GMAW): An arc welding process
which joins metals by heating them with an arc. The arc is
between a continuously fed solid filler wire (consumable)
electrode and the workpiece. Externally supplied gas or gas
mixtures provide shielding for GMAW. Sometimes called MIG
welding (Metal Inert Gas) or MAG welding (Metal Active Gas).
Gas Nozzle: That part of the GTAW torch that directs the
shielding gas flow over the weld area. Made of ceramic,
glass, or metal in various styles.
Gas Tungsten Arc Welding (GTAW): Sometimes called TIG
welding (Tungsten Inert Gas), it is a welding process which
joins metals by heating them with a tungsten electrode which
should not become part of the completed weld. Filler metal is
sometimes used and argon inert gas or inert gas mixtures are
used for shielding.
Groove Angle: When a groove is made between two materials
to be joined together, the groove angle represents the total
size of the angle between the two beveled edges and denotes
the amount of material that is to be removed.
Heat Affected Zone (HAZ): The portion of a weldment that
has not melted, but has changed due to the heat of welding.
The HAZ is between the weld deposit and the unaffected base
metal. The physical makeup or mechanical properties of this
zone are different after welding.
Heat Sink: A good weld needs a certain amount of base
metal to absorb the high heat input from the welding arc area.
The more base metal, or the thicker the base metal, the better
heat sink effect. If this heat sink is not present, too much heat
will stay in the weld area, and defects can occur.
High Frequency: Covers the entire frequency spectrum
above 50,000 Hz. Used in GTAW welding for arc ignition
and stabilization.
Horizontal Position: Occurs when the axis of the weld is
from 0˚ –15˚ from the horizontal, and the face rotation is
from either 80˚ –150˚ or 210˚ – 280˚ for groove welds, or
from either 125˚ –150˚ or 210˚ – 235˚ for fillet welds.
Impedance: In electricity, impedance will slow down, but not
stop, amperage flowing in a circuit. It is the resistance in an
alternating current circuit. Impedance is the combination of
the natural resistance to current flow in any conductor and
the inductive or capacitive reactance in an electric circuit. It is
brought about by the building and collapsing field of alternating
current. This building and collapsing induces a counter electro
motive force (CEMF) (voltage) that holds back, but does not
stop, current flow.
TIG
Flux Cored Arc Welding (FCAW): An arc welding process
which melts and joins metals by heating them with an arc
between a continuous, consumable tubular electrode wire
(consumable) and the workpiece. Shielding is obtained from
a flux contained within the electrode’s tubular core. Depending
upon the type of flux-cored wire, added shielding may or may
not be provided from externally supplied gas or gas mixture.
Ground Lead: When referring to the connection from the
welding machine to the work, see preferred term Work Lead.
for GTAW • Gas Tungsten Arc Welding
Flat Position: When welding is done from the top side of a
joint, it is in the flat position if the face of the weld is approximately horizontal. Sometimes referred to as downhand welding.
The axis angle can be from 0˚ – 15˚ in either direction from a
horizontal surface. Face rotation can be from 150˚ – 210˚.
Ground Connection: A safety connection from a welding
machine frame to the earth. Often used for grounding an
engine driven welding machine where a cable is connected
from a ground stud on the welding machine to a metal stake
placed in the ground. See Work Connection for the difference
between work connection and ground connection.
HANDBOOK
Fit-Up: Often used to refer to the manner in which two members are brought together to be welded, such as the actual
space or any clearance or alignment between two members
to be welded. Proper fit-up is important if a good weld is to
be made. Tacking, clamping or fixturing is often done to
ensure proper fit-up. Where it applies, base metal must be
beveled correctly and consistently. Also, any root openings or
joint angles must be consistent for the entire length of a joint.
An example of poor fit-up can be too large of a root opening
in a V-groove butt weld.
Included Groove Angle: See preferred term Groove Angle.
Incomplete Fusion: Molten filler metal rolling over a weld edge
but failing to fuse to the base metal. Also referred to as cold lap.
Inductance: Inductance (an inductor) will slow down the
changes in current, as if the electrons were sluggish.
Inert Gas: A gas that will not combine with any known element.
At present 6 are known; argon, helium, xenon, radon, neon,
and krypton. Only argon and helium are used as shielding
gases for welding.
Inverter: Power source which increases the frequency of the
incoming primary power, thus providing for a smaller size
machine and improved electrical characteristics for welding,
such as faster response time and more control for waveshaping
and pulse welding.
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Joint Design: A cross-sectional design and the given measurements for a particular weld. Generally includes included
angles, root opening, root face, etc.
Joint Root: That part of a joint that comes closes together
where the weld is to be made. This maybe an area of the joint
or just a line or point of that joint.
Lanthanum Tungsten: GTAW tungsten electrode with
small amount of the rare earth and nonradioactive lanthana
added. Improves arc starting and provides for use of wider
current range.
Lap Joint: A joint that is produced when two or more members
of a weldment overlap one another.
Lift Arc: An arc starting method built into the GTAW power
source to allow contact type starts. Tungsten contamination is
virtually eliminated.
Load Voltage: Measured at the output terminals of a welding
machine while a welder is welding. It includes the arc voltage
(measured while welding), and the voltage drop through
connections and weld cables.
Machine Welding (ME): Uses equipment which welds with
the constant adjusting and setting of controls by a welder
or operator.
Microprocessor: One or more integrated circuits that can be
programmed with stored instructions to perform a variety
of functions.
Nonferrous: Refers to a metal that contains no iron, such as
aluminum, copper, bronze, brass, tin, lead, gold, silver, etc.
Plasma: The electrically charged, heated ionized gas which
conducts welding current in a welding arc.
Plug Welding: A weld made by filling (or partially filling) a hole
in one member of a joint, fusing that member to another member.
Pool: The weld pool is the liquid state of a weld prior to its
becoming solid weld metal. It indicates no limit to depth as
the nonstandard term puddle tends to note a shallower depth.
Open Circuit Voltage (OCV): As the name implies, no current
is flowing in the circuit because the circuit is open. The voltage
is impressed upon the circuit, however, so that when the circuit
is completed, the current will flow immediately. For example,
a welding machine that is turned on but not being used for
welding at the moment will have an open circuit voltage
applied to the cables attached to the output terminals of the
welding machine.
Porosity: A cavity type discontinuity formed by gas entrapment
during solidification.
Output Control: An electrical switch that is used to energize
or de-energize output terminals of a welding machine. In some
types of welding machines they can be of solid state design,
with no moving parts and thus no arcing of contact points.
Primary Power: Often referred to as the input line voltage and
amperage available to the welding machine from the shop’s
main power line. Often expressed in watts or kilowatts (kw),
primary input power is AC and may be single- or three-phase.
Welding machines with the capability of accepting more than
one primary input voltage and amperage must be properly
connected for the incoming primary power being used.
Overhead Position: When the axis angle is from 0˚ – 80˚ and
the face rotation is from 0˚ – 80˚ or 280˚ – 360˚ for groove
welds or from 0˚ – 125˚ or 235˚ – 360˚ for fillet welds, the
weld position is considered to be in the overhead position.
Parameters: The welding settings on a welding machine such
as voltage and amperage, normally read on a volt meter and
an amp meter. It may also include things as travel speed,
electrode size, torch angle, electrode extension and weld joint
position and preparation.
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Penetration: The nonstandard term used to describe
the following:
Depth of Fusion: The distance from the surface melted
during welding to the extent of the fusion into the base
metal or previous weld bead.
Joint Penetration: The depth that a weld extends from the
weld face into the joint, minus reinforcement. Joint penetration may include root penetration.
Root Penetration: The depth that a weld extends into the
root of a joint.
Complete Joint Penetration: Occurs when the “filler”
metal completely fills the groove, and good fusion to the
base metal is present.
Incomplete Joint Penetration: A condition in the root of a
groove weld when the weld metal does not extend through
the joint thickness. This is generally considered a defect when
the joint by design was to have complete joint penetration.
Partial Joint Penetration: A condition in the root of a groove
weld when the weld metal does not extend through the
joint thickness. By design this is acceptable and not a defect,
because it will carry the load for which it was intended.
Positioner: A device which moves the weldment when a
stationary arc is used. Positioners include turning rolls,
head and tail stocks and turntables.
Pounds Per Square Inch (psi): A measurement equal to a
mass or weight applied to one square inch of surface area.
Puddle: More properly referred to as molten weld pool, the
weld puddle is the liquid state of a weld prior to its becoming
solid weld metal.
Pulsing: Varying the current from a high peak amperage level
to a lower background amperage level at regular intervals.
Pulse controls also adjust for the number of pulses per second
and the percent of time spent at the peak amperage level.
Pulsing is used to control heat input and allow for improved
weld profile.
Rectifier: An electrical device that allows the flow of electricity
in basically only one direction. Its purpose is to change
alternating current (AC) to direct current (DC).
Residual Stress: The stress remaining in a metal resulting
from thermal or mechanical treatment or both. When welding,
stress results when the melted material expands and then
cools and contracts. Residual stresses can cause distortion
as well as premature weld failures.
Resistance Spot Welding (RSW): A process in which two
pieces of metal are joined by passing current between electrodes positioned on opposite sides of the pieces to be welded.
There is no arc with this process, and it is the resistance of
the metal to the current flow that causes the fusion.
Reverse Polarity: An old nonstandard term denoting electron
flow from the workpiece to the electrode.
Root: A nonstandard term to denote joint root or weld root.
Root Opening: The separation of the members to be welded
together at the root of the joint.
SCR: Silicon Controlled Rectifier. Used to change AC current
to DC. Functions as an output control device for regulating
the current/voltage and arc off-on ability.
Secondary Power: Refers to the actual power output of
a welding machine. This includes the load voltage while
welding, measured at the output terminals and the current
(amperage) flowing in the circuit outside the welding machine.
Secondary amperage can be measured at any point along the
secondary circuit.
Sensitization: The changing of a stainless steel’s physical
properties when being exposed to a temperature range of
800˚ – 1600˚ F, 427˚ – 870˚ C for a critical period of time.
See also Carbide Precipitation.
Sequencing: The control over all aspects of the weld. This
would include the weld start, initial current, initial current
time, upslope time, weld current level, weld current time,
final slope, final current level and final current time.
Shielded Metal Arc Welding (SMAW): An arc welding
process which melts and joins metals by heating them with
an arc, between a covered metal electrode and the workpiece.
Shielding gas is obtained from the electrodes outer coating,
often called flux. Filler metal is primarily obtained from the
electrodes core.
Slot Welding: A weld made by filling (or partially filling) an
external hole (slot) in one member of a joint, fusing that
member to another member. The hole (slot) may be completely enclosed, or it may be open at one end of the metal.
Solenoid: An electrical device which either stops or permits
the flow of gas used to shield the weld pool and arc or the
flow of water used to cool a welding torch.
Spatter: Metal particles blown away from the welding arc.
These particles do not become part of the completed weld.
Squarewave: The AC output of a power source that has the
ability to rapidly switch between the positive and negative
half cycles of alternating current. Advanced Squarewave is
an enhanced version of this output waveform.
Stabilizer: A device used in AC welding to assist re-ignition of
the arc as current passes through the sine wave zero point.
Straight Polarity: An old nonstandard term denoting electron
flow from the electrode to the workpiece.
Submerged Arc Welding (SAW): A process by which metals
are joined by an arc or arcs between a bare solid metal
electrode or electrodes and the work. Shielding is supplied
by a granular, fusible material usually brought to the work
from a flux hopper. Filler metal comes from the electrode and
sometimes from a second filler wire or strip.
for GTAW • Gas Tungsten Arc Welding
Resistance: The opposition to the flow of electrical current in
a conductor. This opposition to current flow changes electric
energy into heat energy. Resistance is measured in ohms
with an ohm meter.
Single-Phase: When an electrical circuit produces only
one alternating cycle within a 360˚ time span, it is a
single-phase circuit.
HANDBOOK
Quenching: The dipping of a heated metal into water, oil or
other liquid to obtain necessary hardness.
Shielding Gas: Protective gas used to prevent atmospheric
contamination of the weld pool.
TIG
Purging: Cleaning, purifying or removing something from a
container. Such as applying shielding gas to the inside of a
piping structure prior to welding it with the GTAW process.
T-Joint: A joint produced when two members are located
approximately 90˚ to each other in the shape of a “T”.
Thoriated Tungsten: GTAW tungsten electrode with small
amount of thorium added. Improves arc starting and provides
for use of wider current range.
Three-Phase: When an electrical circuit delivers three cycles
within a 360˚ time span, and the cycles are 120 electrical
degrees apart, it is a three-phase circuit.
TIG: The abbreviation for Tungsten Inert Gas. A shop term for
the Gas Tungsten Arc Welding process.
Torch: A device used in the GTAW process to control the
position of the electrode, to transfer current to the arc, and
to direct the flow of shielding gas.
Transverse: A measurement made across an object, or basically at or near a right angle to a longitudinal measurement.
Travel Angle: The angle at which the torch is positioned from
the perpendicular as the weld progresses. Travel angles are
usually 5˚ to 15˚.
Tungsten: Rare metallic element with extremely high melting
point (3410˚ C). Used in manufacturing GTAW electrodes.
85
Undercut: A groove melted into the base metal usually along
the toes of a weld. Undercut can also occur on either side of
the first pass of a full penetration weld, such as an open
groove butt weld. Undercutting produces a weak spot in the
weld, if it exceeds the acceptance criteria for undercut it is
considered a defect, and must be repaired. GTAW is an
excellent process used for dressing this type of defect.
Vertical Position: When the axis of the weld is between
15˚– 80˚ and the face rotation is between 80˚– 280˚ for
groove welds or 125˚– 235˚ for fillet welds, the weld position
is considered to be in the vertical position. When the axis
angle is increased to between 80˚– 90˚, the face rotation can
be any angle from 0˚– 360˚ for both groove and fillet welds.
Voltage: The pressure or force that pushes the electrons
through a conductor. Voltage does not flow, but causes
amperage or current to flow. Voltage is sometimes termed
electro-motive force (EMF) or difference in potential.
Weld Metal: The filler wire and base metal that was melted
while welding was taking place. This forms the welding bead.
Weld Root: When looking at the weld profile or cross section, it
is the deepest point or points the weld fused into the joint root.
Welder: A person who performs manual or semiautomatic
welding. Sometimes incorrectly used to describe a
welding machine.
Welding Operator: A person who operates a machine or
automatic welding equipment.
Workpiece Connection: A means to fasten the work lead
(work cable) to the work (metal to be welded on). Also, the
point at which this connection is made. One type of work
connection is made with an adjustable clamp.
Workpiece Lead: The conductor cable or electrical conductor
between the arc welding machine and the work.
Zirconiated Tungsten: GTAW tungsten electrode which
combines desirable effects of pure tungsten and starting
characteristics of thoriated tungsten.
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TIG
HANDBOOK
for GTAW • Gas Tungsten Arc Welding
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