TIG Welding
TIG Welding
FOR
DUl\1MI£tY
lviILLER ELECTRIC 6PECIAL EDITION
by John Swartz and Brad Hemmert
with special contributions by Mark Kadlec and Kirk Webb
.
. 1c:.rtTI:"'''' IAL
.
i 1807 :
= @WILEY~
~ 2007 ~
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Wiley Publishing, Inc.
TlG Welding For Dummies' , Miller Electric Special Edition
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Table of Contents
••••••••••••••••• ••••••••••••••••••••••
Introduction . ..................................... 1
About This Book ......... .................................. ......... ..................... 1
Foolish Assumptions ....... ........................ .... .... ......... ....... ........... 1
How This Book Is Organized ...................................................... 1
The Icons Used in This Book .....................................................2
Where to Get Started .................................... ................. .... .........2
Chapter 1: Getting to Know TIG Welding . ............ 3
Discovering TIG Welding ............................................................ 3
Advantages of the TIG Welding Process ...... .................... .... ... .4
Disadvantages of the TIG Welding Process .............. ....... ........ 6
Getting the Gist of TIG Welding ................................................. 6
Alternating Current ................... ............................. ............ ......... 7
Direct Current ........................... ..... ..................... .... ............ .... ..... 9
Aligning the Poles: Discovering Polarity ............ ...................... 9
Getting to Know Arc Starting Methods .................................. 12
Chapter 2: Gearing Up: TIG Welding Equipment . ..... 15
Choosing the Right Welding Machine ..................................... 15
Keeping Current: Constant Current Power Sources ............ .16
Becoming Familiar with the Inverter Power Source .............19
Understanding Duty Cycles .......................... .... ....................... 20
Knowing It's Just a Phase: Single- or Three-Phase ............ .... 21
Getting Your Input: Input Voltage .......... ........ .............. ........... 23
Keeping Your Cool: Torch Cooling Methods ......................... 24
Carrying a Torch: Components, That Is .. .... .......................... .24
Not Just for Couch Potatoes: Remote Control ...................... 25
Chapter 3: Choosing Electrodes and Consumable
Materials . ................................... . 27
All about Tungsten Electrodes ................... ..... ................. ....... 27
Choosing a Tungsten Electrode .................. ...... ...................... 28
The Three Main Types of Electrodes .............. ....................... 29
Preparing Electrodes for AC Sine Wave and
Conventional Squarewave ..................................... ............... 30
i (/
TIG Welding For Dummies, Miller Electric Special Edition _ _
Preparing Electrodes for DC Electrode Negative Use
(pointed) ......... .................................................... .... ........ ....... 31
Shields Up, Captain: Shielding Gas ........ .. .... ........................... 34
Going with the Flow: Flow Rate ................ .... ..... ......... ........... .. 36
Selecting a Filler Metal ...... ............................ ..... ...................... 37
Chapter 4: Putting Safety First . .................... 41
Watching Out for Electrical Shock ....................................... .. .41
Avoiding Fumes .............. ................ ... ........... ............................. 43
Being Wary of Arc Rays ............................................. ...... ........ .43
Securing the Welding Environment .... ................ ....................45
Safely Handling Cylinders .. .................................. .... ...... .. .... ... .45
Chapter 5: Preparing to Weld . ...... . .............. 47
Getting the Power Source Ready .... .................... .... ...... .... ...... 47
Preparing the Weld Joint .............. .................. .... ..... ........ ........ .50
Preparing Mild Steel for Welding ...... .... .... .... .... ...... ...... ........ .. 51
Preparing Stainless Steel for Welding ........ ........ .......... ........... 52
Preparing Aluminum for Welding .......... .................. ...... .......... 53
Chapter 6: Selecting Joints and Welds ............. 55
Getting to Know the Types of Joints .......... .... ........................ 55
Working with Fillet Welds ............... ... ..... ...... .............. ........ .... .. 61
Using Groove Welds ... ....... .................. ....... .... ................. .......... 63
Creating a Basic Weld Joint .. ............ ...... .... ........ ...... ............... 66
Introduction
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II ~lcome to TIC Welding For Dummies, Miller Electric
W
Special Edition! In this book, we tell you all about the
innovative process of TIG (Tungsten Inert Gas) welding, also
known as GTAW (Gas Tungsten Arc Welding). Along the way,
we cover the get-in, get-out information you need to know:
basics of the process, info about equipment and peripherals,
safety tips, and the different types of joints and welds you
may run across.
About This Book
So that we can draw your attention to new terms and define
them for you, we put these terms in italic typeface.
Foolish Assumptions
We assume that you are either new to welding or, at the very
least, new to TIG welding. For that reason, we cover the basic
concepts of TIG welding and how it differs from other welding
processes that you may (or may not) be familiar with.
How This Book Is OrfJanized
This book is divided into six chapters that hit the highlights of
the TIG welding process.
V'
Chapter 1: Getting to Know TIG Welding. In this chapter, we cover the basics and background of TIG welding:
current, polarity, and arc starting methods. We also cover
the pros and cons of the TIG process compared to other
arc-welding processes.
V'
Chapter 2: Gearing Up: TIG Welding Equipment. This
chapter covers the major equipment you need: welding
machines, torch, coolants, and remote controls.
2
TIG Welding For Dummies, Miller Electric Special Edition - - " Chapter 3: Choosing Electrodes and Consumable
Materials. This chapter goes into detail on electrodes
and consumables used in the TIG welding process, such
as shielding gas and filler metal.
" Chapter 4: Putting Safety First. Chapter 4 shows you
how to avoid the hazards that go with the territory, like
electrical shock, flash burn, and fumes .
" Chapter 5: Preparing to Weld. This chapter covers
preparation: getting the power source, joint, and base
metals ready for welding.
" Chapter 6: Selecting Joints and Welds. At last, you're
ready to weld, and this chapter delves into the topic. We
cover the different types of joints and welds and their
uses.
The Icons Used in This Book
Like all books in the For Dummies series, this one uses icons
to draw your attention to important points.
Keep an eye out for this icon: It indicates a clever or useful bit
of info you'll need.
This icon indicates a hazardous situation, which if not
avoided, could result in death or serious injury.
When you see this icon, you find a fact that you want to file
away in your brain for future reference.
This icon denotes interesting, but not necessarily crucial,
technical information that you may want to skip over if you're
so inclined.
Where to Get Started
Get started anywhere you like! Begin at Chapter 1 and read
the book straight through if you feel like you need a real
overview of the TIG welding process. Otherwise, flip to the
chapter that interests you most and jump in!
Chapter 1
Getting to Know
11G Welding
••••••••••••••••••••••••••••••••••••••
In This Chapter
Discovering the uses of TIG welding
Understanding alternating and direct current
Starting the arc
••
•
• ••••••••••••••••••••••••••••
A
re you a complete beginner to welding? Or do you
wonder how TIG welding differs from the other types
of welding you're familiar with? If so, look no further : In this
chapter, we give you the lowdown on TIG welding: its advantages and disadvantages , how it works , and how it compares
to other types of welding.
DiscotlerinfJ
TIe WeldinfJ
Arc welding uses an electrical power supply to create an arc
between an electrode and the base material. TIC welding (TIC
stands for Tungsten Inert Gas) is the more commonly used
name for the Gas Tungsten Arc Welding (GTAW) process and
is one of many types of arc welding. The necessary heat for
TIG welding is produced by an electric arc that is maintained
between a non-consumable tungsten electrode and the part to
be welded. Non-consumable means that the tungsten will not
melt to become part of the weld pool.
The molten metal and the tungsten electrode are both
shielded from the atmosphere by a blanket of inert gas fed
through the TIG torch. Inert gas is inactive, or deficient in
active chemical properties. The shielding gas blankets the
II
TIG Welding For Dummies, Miller Electric Special Edition - - weld and excludes the active properties in the surrounding
air, which keeps impurities out of the final weld. The shielding
gas doesn't burn, add, or take anything from the metal. Inert
gases such as argon and helium are the most commonly used
for TIG welding. These gases possess no odor and are transparent, giving the welder maximum visibility of the arc. The
TIG welding process, shown in Figure 1-1 , can produce temperatures of up to 35,000° F/19,426° C. The torch contributes
heat only to the work piece. If filler metal is required to make
the weld, you can add it manually in the same manner as you
would in the oxyacetylene welding process.
Regulator/
Flowmeter
Gas
Valve
Work _ _--".~~
Clamp
Coolant System
Adapter
Block
Figure 1-1: The TIG welding process.
Ad(/antages of the TIG
Weldin9 Process
The biggest advantage of the TIG welding process is that it
will weld more kinds of metals and metal alloys than other
arc-welding processes. You can use TIG to weld most metals,
including stainless steel, nickel alloys, titanium, aluminum, magnesium, copper, brass, bronze, and even gold. You can also use
TIG welding to weld dissimilar metals to one another, such as
copper to brass and stainless to mild steel. In the next sections,
we look at a few more advantages of the TIG welding process.
- - - - - - - - Chapter 1: Getting to Know TIG Welding
5
Concentrated arc
TIG welding has a concentrated arc, which permits pin-point
control of heat applied to the work piece, resulting in a
narrow heat-affected zone. The heat-affected zone is where the
base metal has undergone a change due to the superheating
of the arc, followed by fast cooling. The heat-affected zone is
where the welded joint is weakest and is the area along the
edge of a weld that would be expected to break under a
destructive test. A narrow heat-affected zone is the result that
is typically desired. TlG welding is great for producing a
narrow heat-affected zone. A high concentration of heat is an
advantage when you're working with metals with high heat
conductivity such as aluminum and copper.
No slat}
Unlike some other types of welding, flux is not needed;
therefore, no slag is produced to obscure the welder's vision
of the molten weld pool. The finished weld has no slag to be
removed between passes. Entrapment of slag in multiple pass
welds is seldom seen.
No sparks or spatter
In the TIG welding process, no metal is transferred across the
arc. You have no molten globules of spatter to contend with
and no sparks are produced, as long as the material being
welded is free of contaminants. When welding in DC (direct
current) polarity, the TIG welding 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 is a factor is while welding on
alternating current (AC) with the TIG process. AC does produce a buzzing sound.
No smoke or fumes
The TIG process itself does not produce smoke or fumes . If
the base metal being welded contains coatings or elements
(such as lead, zinc, nickel, or copper) that produce fumes ,
these must be contended with as in any fUSion-welding
6
TIG Welding For Dummies, Miller Electric Special Edition - - process done on these materials. If the base metal contains
oil, grease, paint, or other contaminants, smoke and fumes are
produced as the heat of the arc burns them away. To avoid
this, be sure to clean the base metal before you begin welding.
DisadflantafJes of the
TIG WeldinfJ Process
Here's a list of the disadvantages you can encounter with TIG
welding.
" The main disadvantage of the TIG welding process is the
low filler metal deposition rate, which refers to how much
filler you can place in a period of time.
" 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.
" Also, arc rays produced by the process tend to be brighter
than those produced by stick and MIG welding. This situation is primarily due to the absence of visible fumes and
smoke created by these other welding processes.
To avoid the hazards of the bright UV rays, be sure to follow
the safety procedures we outline in Chapter 4: Take care to
protect your skin with the proper clothing and protect your
eyes with the correct lens. Also, concentrations of shielding
gas may build up and displace oxygen in confined spaces, so
make sure that the areas you're welding in are ventilated
properly.
GettinfJ the Gist of TIG WeldinfJ
The two most basic parameters of 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) .
_ _ _ _ _ _ _ _ _ Chapter 1: Getting to Know TIG Welding
TIG welding is typically done with Direct Current Electrode
Negative (DC EN) polarity, and in alternating current (AC).
Welding with DCEN polarity is typically used for welding
steel, stainless steel, copper, and most other materials that
are weldable. AC is typically used for welding aluminum and
magnesium.
AlternatinfJ Current
Alternating current (AC) , as shown in Figure 1-2, is an electrical current that has both positive and negative half-cycles.
These current cycles don't 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. The half cycles are called the positive half
and the negative half of the complete AC cycle. Together, this
"hill" (positive half) and "valley" (negative half) represent one
cycle of alternating current.
90·
o·
-+_ _ _ _,--_ 360·
_ - - L -_ _ _
270·
AC CYCLE
Figure 1-2: Alternating current.
Alternating current is used while welding aluminum and magnesium. An AC sine wave (refer to Figure 1-2) is a graphical
representation of alternating current.
7
8
TIG Welding For Dummies, Miller Electric Special Edition - - -
Squareulafle AC
Some TIG welding 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. When you're welding with AC, the faster you can
transition between the two polarities (EN and EP) and the
more time you spend at their maximum values, the more
effective the machine is. The miracle of modern electronic
circuitry now makes it possible to make this transition almost
instantaneously. The effective use of the energy stored in
magnetic fields results in waveforms that are relatively
square. Note: Waveforms aren't truly square due to electrical
inefficiencies in the Squarewave power source. However,
the Advanced Squarewave TIG welding power source has
improved efficiencies and can produce a nearly perfect
squarewave.
FrequenClJ
The rate at which alternating current makes a complete cycle
is termed frequency. Figure 1-3 illustrates a couple of different
frequencies. Electrical power in the United States is delivered
as 60 cycles per second frequency, or to use the proper terminology, 60 hertz (Hz). This means that 120 times per second
the current changes to positive, then negative. 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 . The operating frequency that we refer to
here isn't the same as high frequency that's used to start,
and stabilize, the welding arc.
Frequency has a big effect on the performance of the
welding arc. Increasing the frequency of an AC wave will
narrow your arc cone and make the arc more focused.
This more focused arc translates into more control of the
welding puddle.
- - - - - - - - Chapter 1: Getting to Know TIG Welding
9
1/6Oth of a
second
-
+
c
Go)
~
=
0
r---T-------r------r------~----~r_
(.)
1/50th of a
second
-
+
c
Go)
~
=
0
r----r--------r-------+--------1------~.__
(.)
Figure 1-3: Various freguencies.
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.
10
TIG Welding For Dummies, Miller Electric Special Edition - - -
Ali9nin9 the Poles: Discoflerin9
PolaritlJ
With DC, welding can be done on electrode negative or electrode positive (which is rarely used for TIG). These two
options cause a change in the electrical charge that the electrode has and changes the direction that the electrons are
flowing in the welding circuit. This positive or negative charge
is referred to as polarity. If you use a negative electrode while
welding, you get a negative polarity.
When T1G welding, the welder has three choices of weldingcurrent type and polarity. These choices are
V Direct current electrode negative (DCEN, or straight
polarity)
v Direct current electrode positive (DCEP, or reverse
polarity)
v Alternating current (AC), which 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, which we cover in the next few
sections. Taking a look at each type and its uses helps you to
select the best current type for your job.
Direct current electrode net}ttti(le
Direct Current Electrode Negative (DCEN) is also sometimes
called straight polarity. DCEN is used while welding steel, stainless steel, copper, titanium , gold, and pretty much any other
material that can be welded with the exceptions of aluminum
and magnesium, which are welded using AC.
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 have the output
terminals marked electrode and work.
When the arc is established while welding in DCEN, electrons
flow from the negative electrode to the positive work piece. In
_ _ _ _ _ _ _ _ Chapter 1: Getting to Know 11G Welding
11
a DCEN arc, approximately 70 percent of the heat generated
by the arc occurs in the work piece - thus you can use a
smaller electrode, as well as a smaller gas cup and reduced
gas flow. The more concentrated arc allows for faster travel
speeds. This concentrated arc also accounts for the deep penetration when using DCEN for TIG welding.
Direct current electrode posititJe
Direct Current Electrode Positive (DCEP) is also known as
reverse polarity. Welding is not typically done with DCEP.
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. About 70 percent of the heat of the arc is focused on the positive side of
the welding arc. On DCEP, 70 percent of the heat is focused
directly on the tungsten, which creates a large ball on the
tungsten. For welding with DCEP, a very large tungsten is typically needed. Between the large tungsten and the nature of a
DCEP arc , the arc can be very erratic and quick to wander which is the main reason that this polarity is typically undesirable for TIG welding.
The arc, though erratic, does create a cleaning effect for welding on aluminum and magnesium.
Alternatin9 current
To weld aluminum, the best combination is the good penetration of electrode negative plus the cleaning action of electrode
positive. To obtain the advantages of both polarities, use
alternating current to weld aluminum.
During a complete cycle of alternating current, there is theoretically one half-cycle of electrode negative and one halfcycle of electrode positive. Therefore, during every cycle,
there is a time when the work is positive and the electrode is
negative, and 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.
12
TIG Welding For Dummies, Miller Electric Special Edition - -AC is used while welding aluminum and magnesium. The main
reason why AC works so well for aluminum and magnesium
is that both materials have a thin layer of protection called
an oxide layer. This oxide layer has a melting temperature
of about 3700 oF. Aluminum and magnesium melt at about
1200 of . In order to break through this oxide layer, the electrode positive side of an AC waveform has a cleaning effect
that lifts this oxide off the surface. This is why when welding
aluminum on DCEN, the weld looks so dirty. DCEN does not
have the cleaning portion of DCEP to help lift this oxide layer
off the surface.
Gettint) to Knoul Arc
Startint) Methods
TIG welding uses a non-consumable electrode, which means
that the electrode doesn't melt to become part of the weld
pool. Because this tungsten electrode isn't compatible with the
metals being welded (unless you happen to be welding tungsten), it requires some unique arc-starting and arc-stabilizing
methods. We cover these methods in the next few sections.
Hi9" fret{uenCIJ
High frequency, shown in Figure 1-4, is a high voltage/ low
amperage charge generated at a very high cycle or frequency
rate. Frequency rates of up to approximately 1 million cycles,
or Hz, are typical. High frequency is used for two main purposes. The first purpose is starting the welding arc. This arcstarting method makes it possible to start welding without
your tungsten making contact with the material being welded.
High frequency ionizes the shielding gas used in this process
and provides a good path for the current to follow. The path
between the electrode and the work becomes much more conducive to the flow of elect rons, and the arc literally jumps the
gap between the electrode and the work peice. Touching the
tungsten to the work can contaminate the work as well as the
tungsten. High frequency can be used to start the arc without
making contact with the work, eliminating this possible
chance of contamination.
_ _ _ _ _ _ _ _ Chapter 1: Getting to Know TIG Welding
13
High Frequency
(over 16,000 Hz)
Figure 1-4: High freguency is used to stabilize and start the arc.
High frequency is also used to stabilize the welding arc. When
welding on AC, your amperage is positive and negative alternately. At the point that the amperage switches negative to
positive, the arc becomes very unstable. If high frequency is
used continuously, the arc is much more stable. Without high
frequency, it is very common for the arc to experience an
outage (the arc will extinguish).
High frequency falls under the control of the Federal
Communication Commission (FCC) and can cause interference problems with all types of electrical and electronic
devices if the welding machine is not properly installed.
Lift..Arc
The Lift-Arc arc-starting method is often mistaken with
scratch start (see the following section). Scratch start and
Lift-Arc are not the same thing. The Lift-Arc arc-starting
method 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 contamination is possible due to special power-source circuitry. After the arc is established, the
power-source circuitry switches from the Lift-Arc mode to the
weld power mode, and welding can begin.
III
TIG Welding For Dummies, Miller Electric Special Edition _ __
Scratch start
The scratch-start method of starting an arc is not generally
considered appropriate as it can easily lead to contamination
in the weld area. Scratch start is typically used when doing
TIG DC welding on a power source designed for stick welding
only. These machines are not equipped with an arc starter, so
the only way to start the arc is by 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. The scratch-start method, as the name
implies, is accomplished much like scratching or striking the
arc, as would be done with stick welding.
Chapter 2
Gearing Up: 11G Welding
Equipment
••••••••••••••••••••••••••••••••••••••
In This Chapter
.... Deciding on the right machine
.... Choosing the sources of power
.... Discovering duty cycles
.... Working through different phases
.... Cooling the torch
.... Taking in the joy of remote controls
•••••••••••••••••••••••••••••••••••••••
n
efore you can start welding, you have to gear up with the
CJ right equipment. You have decisions to make about everything from the welding machine itself to peripherals like torches
and coolers. In this chapter, we tell you everything you have to
know about selecting the right equipment to get you started.
Choosin9 the Ri9ht
Weldint) Machine
With the many types of welding machines available, you have
to take a lot of factors into consideration in order to make
sure that you're using the right machine for the job. You have
to determine the range of amperage (amps) needed for a particular process and select a welding machine to meet those
needs. Rated output of the welding machine is also an important consideration. Remember, the output must be within a
proper duty-cycle range. A duty cycle is the time for which
you can use a specific machine.
16
TIG Welding For Dummies. Miller Electric Special Edition _ __
You often can do light welding (with low output requirements
of about 200 amps or less) with single-phase welding
machines. Duty cycles are often in the 60 percent or less range.
(For more on how duty cycles are measured, flip ahead to the
"Understanding Duty Cycles" section later in this chapter.)
These single-phase 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.
Larger DC TIG welding machines used for heavy-plate,
structural-fabrication, and high-production welding generally
need three-phase AC input power. Most industrial locations
are supplied with three-phase power because it provides the
most efficient use of the electrical distribution system - and
it's required by many electric motors and other industrial
electrical equipment.
These large DC TIG welding machines often have capacities of
more than 200 amps, and often have 100 percent duty cycles.
So that you can best understand the arc welding power
source and its requirements, we start at the arc and work
back to the wall receptacle.
The TIG welding process requires the welder to maintain a consistent arc length. Any variation in arc length affects the voltage.
The longer the arc, the higher the voltage - and the shorter the
arc, the lower the voltage. As the arc is moved across the part
being welded, the welder will have difficulty maintaining the arc
length and the voltage will change. This change in arc length/
voltage causes inconsistencies in the final weld bead.
Keepin9 Current: Constant
Current Power Sources
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 (Cy),
or both. A constant-current machine, the kind used in T1G
_ _ _ _ _ _ Chapter 2: Gearing Up: TIG Welding Equipment
17
welding, maintains close to a constant-current flow in the
weld circuit no matter how much the voltage (arc length)
varies.
Processes like TIG and Shielded Metal Arc Welding (SMAW),
also known as stick welding, require the welder, not the equipment, to maintain the arc length. A constant-voltage power
source maintains voltage close to a preset value no matter
how much current is used in the process. This type of power
source is used in Gas Metal Arc Welding (GMAW), also known
as Metal Inert Gas (MIG) welding. Processes like MIG and Flux
Cored Arc Welding (FCAW) utilize the equipment to help maintain a specific arc length.
You'll notice that in both cases we say that these machines
maintain current and voltage values close to preset values
respectively. Be aware, however, that the values will vary
slightly because no power source is perfectly efficient.
The volt-amp curve shown in Figure 2-1 is indicative of those
curves seen in TIG-welding power sources. 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 .
50
100
150
AMPS
Figure 2-1: Volt amp curve of a CC power source.
Figure 2-2 is an example of a basic DC power source for T[G
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. [t does
18
TIG Welding For Dummies, Miller Electric Special Edition _ __
not affect the frequency, which is 60 Hz in and 60 Hz out. This
low voltage, high amperage is now rectified from AC to DC in
the rectifier.
VOLTAGE
TRANSFORMATION
AND ISOLATION
CONTROL
CIRCUIT
RECTIFIER
FILTER
[I :1B J"-~I-::~l.;
A:~~1~~1]1 :f~1
Figure 2-2: A conventional line freguency power source block diagram .
Rectification produces a fairly rough DC current unlike the
power provided by a battery. A filter is used to smooth and
stabilize the output for a more consistent arc. The filtered DC
is now supplied to the T1G torch. Line frequ ency (the frequency at which electricity is sent over power lines, which is
60 Hz) power sources tend to be large and very heavy. Their
arc performance is slow and sluggish, which eliminates them
from being used for advanced wave shaping or pulsing.
True constant-current power sources are an advantage in that
the current that is set is what's delivered to the welding arc.
These electronically controlled power sources are more desirable than the older-style power sources and have applications
in both manual and 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. Think of a car with the
cruise control on: If the car goes up and down a hill, the speed
is maintained without input from the driver. In that same fashion, if the welder raises and lowers the arc, the amperage is
maintained.
This ability to maintain a consistent output is also helpful for
line-voltage compensation. By law, power companies must
supply a consistent voltage. However, power companies
are allowed a range, which can be as much as plus or minus
10 percent of the nominal voltage. If the primary voltage to
a non-compensated TIG-welding power source changed up
_ _ _ _ _ _ Chapter 2: Gearing Up: TIG Welding Equipment
19
to 10 percent, the power going into the arc can fluctuate from
10 to 20 percent. With a line-voltage-compensated machine, a
plus or minus fluctuation of up to 10 percent on the primary
will only have a plus or minus 2 percent change in the arc ,
thus creating a very consistent weld. Most electronically
controlled power sources can also be used to provide pulsed
welding current. Due to the fast response time and great
control over the current level setting that electronically controlled power sources offer, two different heat levels pose no
difficulty for these types of power sources.
Electronically controlled power sources can also be remotely
controlled, and these controls can be very small and compact.
The remote controls are small enough to be mounted directly
on the torch or built into the torch handle. However, design
limitations can make them more difficult to operate, and may
take more time to learn and get used to than simpler control
designs .
8ecominfJ Familiar with the
In(lerter Power Source
Inverter power sources were first conceived of in the 1940s,
but weren't successfully marketed until the 1970s. Instead
of operating at a line frequency input power of 50 or 60 Hz,
inverters boost the frequency to as much as 1,000 times that
of the input frequency. This allows for a drastic reduction in
the number of transformer coil turns and a reduced coil 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 because the incoming primary power is
rectified and converted to the extent that it's not a critical
factor. This is an advantage because you can use this type of
machine in both an industrial setting (three-phase) and in the
home (single-phase). This type of machine can also be used
internationally because many other countries use 50 Hz line
frequ ency. (Welders in the U.S. use 60 Hz.)
20
TIG Welding For Dummies, Miller Electric Special Edition _ __
Inverter machines can run on single- or three-phase power,
which we cover in the next section. As Figure 2-3 illustrates,
the first thing the inverter does is rectify the high-voltage,
low-amperage AC into DC. The DC current is then filtered and
fed to the inverter's high-speed switching devices. Just like a
light switch, the switching devices turn the power on and of(.
These devices 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. The AC or DC power is then provided
to the TIG torch. This AC is fully adjustable.
INVERTER SECTION
______
r -______
A~
~,
INPUT
RECTIFIER
FILTER
POWER TRANSFORMER OUTPUT
SWITCHES ISOLATIO N RECTIFIER
50/60 Hz AC
DC
25 kHz AC
FILTER
C PRIMARY
POWER
(50/60 Hz)
DC
Figure 2-3: An inverter power source block diagram.
Understandin9 Dutl) Cl)cles
As mentioned earlier in this chapter, 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
you can use it at its rated load, without exceeding the temperature limits of the insulation in the component parts.
The duty cycle in the United States is based on a lO-minute
time period. Simply stated, if a power source is rated at a 50
percent duty cycle and it is operated at its rated output for
_ _ _ _ _ _ Chapter 2: Gearing Up: TIG Welding Equipment
21
5 minutes, the power source must be allowed to cool for 5
minutes before operating again. The duty cycle is not cumulative. For example, a power source with a 50 percent duty cycle
cannot be operated for 30 minutes then allowed to cool for 30
minutes. This violates the lO-minute rule. Read on.
The JO-minute rule states that no matter what the duty-cycle
rating is, it's measured over a lO-minute time period. The preceding example uses 50 percent for a given output (say, 150
amps). The amount of welding time required for the overall
project you're working on doesn't matter; the machine can
only weld continuously for 5 minutes at 150 amps. The
machine must remain idle then to cool for 5 minutes or it will
overheat. So, if a given project takes 30 minutes of welding
time and the machine can only weld for 5 minutes at a time,
the overall job will take 60 minutes using 150 amps. However,
that same machine may have a 100 percent duty cycle, but
at a lower amperage (say 80 amps). Then, by using only
80 amps, the welder can weld continuously for 30 minutes
without overheating the machine.
A machine rated at 50 percent should not be operated at the
maximum for 5 minutes and then shut off. The cooling fan
must be allowed to operate and cool the internal components,
otherwise the machine may incur damage.
A power source with a 100 percent 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 percent duty cycle.
Knoulin9 It's Just a Phase:
Sin9le-- or 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 three-phase machine will deliver a smoother arc than a
single-phase machine.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
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.
SintJle . .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 owner's
manual to find out for sure what power your machine will
require.
With single-phase power, you have two current-carrying
conductors and a ground wire that are connected to the
terminal board of the power source.
Three . .phase input connections
Many industrial DC welding power sources for TlG welding
utilize three-phase primary power. Three-phase DC power
exhibits very smooth arc characteristics because there are
three separate sine wave traces within the same time span
(l/60th of a second) as the single-phase sine wave trace. A
typical example of a three-phase rectified output is shown in
Figure 2-4.
Primary power is connected to the input of a three-phase
power source using three current-carrying conductors and
a ground wire. The power source also has three currentcarrying terminals and a ground terminal connection.
If a three-phase inverter power source is connected to a
single-phase line, the output rating will be reduced. Check
the power source's specification for details.
_______ Chapter 2: Gearing Up: TIG Welding Equipment
0
+
I
\ I
\/
I,
./
'
\ I
\I
-/
' ,\' '
- \. >, \
\ I
\I
""
_/
23
\ I
\ I
/
\I
_/
\ I
\I
I
_/
Two Cycles
Three-Phase Rectified Sine Wave
Figure 2-4: Three-phase DC current.
GettinfJ Your Input:
Input floltafJe
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 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 , you'll have to relink this
board. Certain power sources are equipped with devices that
detect the input voltage and automatically set the equipment
for proper operation.
Two common types of input boards are Auto-Link and
Auto-Line. Auto-Link uses a sensing circuit to mechanically
relink the primary to the transformer as needed, whereas
Auto-Line electronically - on a sliding scale - constantly
monitors and maintains the appropriate voltage to the
transformer.
24
TIG Welding For Dummies, Miller Electric Special Edition _ __
KeepinfJ. Your Cool: Torch
CoolinfJ. Methods
When welding with the TIG process, the majority of heat goes
into the arc; however, a significant amount of heat is retained
in the torch. Consequently, some means must be provided to
cool the torch. Torches used for TIG welding may be either
water- or air-cooled.
High production or high amperage torches are usually watercooled, whereas lighter duty torches for low amperage applications may be air-cooled.
These low-amperage torches 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 gascarrying hose or located inside the gas hose to provide
additional cooling. The water-cooled torch is designed so
that water is circulated through the torch that's cooling it
and the power cable.
CarrljinfJ. a Torch: Components,
That Is
You need to think about several torch components, which are
-, Y'
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 .
, Y'
Collet: The collet holds the welding electrode in the
torch and 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.
_ _ _ _ _ _ Chapter 2: Gearing Up: TIG Welding Equipment
25
yI
Gas lenses: A gas lens is a device that replaces the
normal collet body. The lens attaches to the torch body
and is used to reduce turbulence and produce a longer
undisturbed flow of shielding gas. A gas lens allows 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 produces a large
blanket of shielding gas. This can be very useful in welding material such as titanium. The gas lens also enables
the welder to reach joints with limited access, such as
inside corners.
yI
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 into place.
Nozzles can be made of ceramic, metal, metal-jacketed
ceramic, glass, or other materials.
Ceramic nozzles are 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 allows 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 non-turbulent flow of gas.
Not Just for Couch Potatoes:
Remote Control
Sometimes a welding task requires the welder to place a weld
in a location where he cannot access the controls on the
power source. The welder may need to control the amount of
current being used. Extra amperage may be required at the
beginning of the weld 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.
26
TIG Welding For Dummies. Miller Electric Special Edition _ __
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 (such as the gas flow,
arc starter, and so on) , 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 output's primary
job then is to interrupt the weld circuit until the welder is prepared to start the arc.
When remote control is activated, the current-control switch
on the power source works in conjunction with the main current control. If the main current control is set at 50 percent,
the maximum output current available through the remote
device is 50 percent. To obtain full machine output current
through the remote device, the main current control must be
set at 100 percent. 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. This type operates much the same as
the gas pedal in an automobile: The more the pedal is
depressed, the more the current flows . Another type that
affords greater mobility is the finger-tip control. The finger-tip
control mounts on the torch.
Chapter 3
Choosing Electrodes and
Consumable Materials
In This Chapter
... Selecting an electrode
.. Understanding the types of electrodes
~
Prepping electrodes for use
.... Working with shielding gas
~
Using a filler metal
~om
electrodes to shielding gas to filler metal, TIG weldr:ng requires a number of consumable materials. In this
chapter, we cover what you need to know to get started.
All about Tun9sten Electrodes
Electrodes made of tungsten and tungsten alloys are secured
within the TIG welding torch to carry current to the welding
arc. Tungsten is preferred for this process because it has one
of the highest melting points of all metals.
The tungsten electrode establishes and maintains the arc.
This electrode is said to be non-consumable because it isn't
melted and included in the weld pool. In fact, you must take
great care so that the tungsten doesn't contact the weld pool
in any way, thereby causing a contaminated, faulty weld - a
defect known as a tungsten inclusion.
28
TIG Welding For Dummies. Miller Electric Special Edition _ __
Tungsten electrodes for TIG welding 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.
The American Welding Society CAWS) identifies many electrode classifications as they do for filler metal specifications.
The classification code is pretty easy to decipher once you
know what the different letters and numbers mean. For example, the classification for a ceriated tungsten electrode is
EWCe-2. The letter E in the classification is the designation for
electrode. The W is the designation for the chemical element
tungsten.
Additional letters in a code designate the alloying element
used in the particular electrode. The letter P designates a
pure tungsten electrode with no intentionally added alloying
elements. The letters Ce, La, Th, or Zr designate tungsten electrodes alloyed with cerium, lanthanum, thorium, or zirconium,
respectively.
The numbers I, l.5, or 2 behind the alloy element indicate the
approximate percentage of the alloy addition. So, using our
EWCe-2 example, this code indicates a tungsten electrode
alloyed with 2 percent cerium.
Note: There is one other electrode designation: EWG. The
letter G 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. Exercise
care when working with these electrodes so that the colorcoding is kept intact.
ChoosinfJ a TunfJsten Electrode
You can use several different types of tungsten electrodes in
TIG welding, and each has its strengths and weaknesses. In
the next few sections, we give you a run-down on the most
commonly used tungsten electrodes.
___ Chapter 3: Choosing Electrodes and Consumable Materials
29
One of the main considerations of the tungsten diameter is
the welding current. The welding current is 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 has its greatest current-
carrying capacity with Direct Current Electrode Negative
(DCEN), less with alternating current, and the least with
Direct Current Electrode Positive (DCEP).
The Three Main TlJpes
of Electrodes
Tungsten electrodes come in several different types, however
the three main types are
V Pure (EWP)
v Ceriated (EWCe-2)
v Thoriated (EWTh-2)
We take a look at each of these main three types of tungsten
electrodes in the following sections.
EWP (100 percent
TuntJsten, Green)
EWP electrodes are unalloyed, "pure" tungsten with a minimum of 99.5 percent tungsten. These electrodes are designated with a green band of paint around one end of the
electrode. Pure tungsten is typically used with a conventional
(non-inverter) type power source. Pure tungsten provides
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 very much heat, the
pure tungsten electrode forms a balled end.
30
TIG Welding For Dummies, Miller Electric Special Edition _ __
EWCe .. 2 (2 percent
Cerium, Orant)e)
EWCe-2 electrodes are alloyed with about 2 percent cerium,
which is a non-radioactive material and the most abundant of
the rare earth elements. These electrodes are designated with
an orange paint band. Ceriated tungsten has better starting
characteristic and a higher current-carrying capacity than
pure tungsten. These electrodes are all-purpose and operate
successfully with AC or DC electrode negative. Ceriated tungsten is typically recommended with all inverter type power
sources in both AC and DCEN.
EWTh .. 2 (2 percent Thoria, Red)
EWTh-2 electrodes are alloyed with 2 percent thoria and
are designated with a red band of paint. These are very commonly used electrodes and were the first to show better arc
performance over pure tungsten for DC welding. However,
thoria is a low-level radioactive material, so its vapors, grinding dust, and disposal raise health, safety, and environmental
concerns. Note: Be sure to properly dispose of any grinding
dust in an environmentally safe way.
The thoriated electrodes are usually preferred for direct current applications. In many DC applications, the electrode is
ground to a taper or pointed.
The thoriated electrode retains the desired shape in those
applications in which 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.
Preparin9 Electrodes for AC Sine
Wa"e and Con"en tiona I
St{uareUla"e
After you've selected the proper size and type of electrode,
how you prepare and maintain the electrode determines its
___ Chapter 3: Choosing Electrodes and Consumable Materials
31
performance and life. Many misconceptions exist about tungsten electrodes and their correct use. In this section, we tell
you what you need to know to make common-sense decisions
about tungsten electrodes.
Always wear proper face, hand, and body protection when
preparing tungsten electrodes.
Electrodes that will be used with AC sine wave or conventional squarewave current will form a balled end. The diameter of the end should not exceed the diameter of the electrode
by more than 1.5 times. As an example, a )Is" electrode should
only form a ~t diameter end. If the end becomes larger than
this because of excessive current, it may drop off and contaminate the weld. For improved arc focus, set the balance control to maximum penetration and try a ceriated or thoriated
tungsten with a modified point.
PreparinlJ Electrodes for DC
Electrode NelJatifle Use
(Pointed)
With DCEN, most of the weld energy is provided by electrode
negative, so very little heating effect occurs on the tungsten,
and a sharp, pointed tungsten is generally preferred. Figure 3-1
shows the preferred shapes for balled ends and the various
types of points used with the DC and AC wave-shaped power
sources.
Pointing of electrodes is a hotly discussed topic: Many theories and opinions exist on the degree of the pOint. Your application will determine how you should prepare your tungsten.
A common practice in pointing electrodes is to grind the taper
length for a distance of 2 to 2 Y, times the electrode diameter
for use on DC and usually to a sharp needle pOint, then
slightly blunted (see top of Figure 3-2). Using this rule for a )ls"
electrode, the ground surface would be );,1" to ~s" long.
32
TIG Welding For Dummies, Miller Electric Special Edition _ __
Figure 3-1: Three main tip preparations (L to R): Tapered w/point, Tapered
w/ land, and Balled.
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 3-2). 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 that may melt off and float 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 weld. Note: The grinding
wheel used on tungsten electrodes should not be used for any
other material.
___ Chapter 3: Choosing Electrodes and Consumable Materials
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.
.
Ideal Tungsten Preparation - Stable Arc
1. Stable Arc
2. Flat
3. Grinding Wheel
4. Straight Ground
~r:d,'
2~;qy'
4
Wrong Tungsten Preparation - Wandering Arc
1. Arc Wander
2. Point
3. Grinding Wheel
4. Radial Ground
Figure 3-2: Proper tungsten grind pattern and technique .
33
3lJ,
TIG Welding For Dummies, Miller Electric Special Edition _ __
The surface of the tungsten after it has been used should be
shiny and bright. If the surface appears dull, an excess of current is indicated. If it appears blue to purple or blackened, the
shielding gas is insufficient, which may be caused from insufficient gas flow, gas contamination, or insufficient post-flow. This
condition means that the surrounding atmosphere oxidized the
electrode while it was still hot, and it is now contaminated.
Continuing to weld with this condition will result in the oxide
flaking off and ending up in the weld deposit. A general rule for
post-flow 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.
Contamination of the electrode can occur for several reasons
besides a lack of post-flow 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 also
causes electrode contamination.
~
Excessive gas-flow rates and nozzles that are dirty,
chipped, or broken cause turbulence of the shielding gas.
This draws air into the arc area, which also causes contamination.
An electrode that has been contaminated by contact with
the pool or filler rod will have a deposit of the metal on it.
Grind the electrode to remove the contamination. Use good
grinding techniques, as improper techniques can cause problems or injury. Breaking off the contaminated tungsten is generally not recommended as it may cause a jagged end or split
or bend the electrode. A properly prepared tungsten reduces
or eliminates arc wandering, splitting, and weld-quality inconsistencies.
Shields Up} Captain:
Shieldint) Gas
All arc welding processes utilize some method to protect the
molten weld pool from the atmosphere. Without this protection,
___ Chapter 3: Choosing Electrodes and Consumable Materials
35
the molten metal reacts with gases in the atmosphere and produces porosity (bubbles) in the weld bead, which greatly
reduces weld strength.
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, and so on.
Two inert gases are primarily used for shielding purposes for
TIG: argon and helium. Shielding gases must be of high purity
for welding applications: at a level of 99.995 percent.
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. 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
those of argon.
Argon is obtained as a byproduct in the manufacturing of
oxygen. The earth's atmosphere is composed of .9 percent
argon, 78.0 percent nitrogen, 21.0 percent oxygen, and .1 percent other rare gases. Looking at these percentages, you can
see 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 provides excellent arc stability and cleaning action
even at low amperages. Argon is the most commonly used
inert gas for all TIG welding applications.
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 becomes
wider and more flared out than the arc column with argon
shielding gas. Figure 3-3 illustrates the two arc columns. The
more flared out the arc column, the more the work surface
36
TIG Welding For Dummies, Miller Electric Special Edition _ __
area is heated. The heat at the center of the are, while using
helium, is very hot - which results in a deeper penetrating
arc. In Figure 3-3, note the wider arc and deeper penetration
produced by the helium shielding gas.
Helium produces a higher arc voltage than argon does.
Because the total power is a product of voltage and amperage,
it's 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. Typical
argon/helium mixtures are 75/25 and 50/50, argon, helium.
HELIUM
ARGON
Figure 3-3: A representation of the effects on the arc and bead
produced by argon and helium shielding gases.
Goin9 with the Flow: Flow Rate
The correct flow rate for shielding gas 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 (CFH) is influenced by many variables. 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 effect on the shielding gas, and flow
should be increased by 25 percent. And, of course, when welding in a drafty situation, you want to double the flow rate. When
welding corner or edge joints, excessive flow rates can cause
air entrapment. In this situation, you can improve the effectiveness of the shielding gas by reducing the gas flow by about 25
percent. A good starting point is approximately 15 to 20 CFH.
- - - Chapter 3: Choosing Electrodes and Consumable Materials
37
The purpose of both pre-flow and post-flow is to prevent contamination of both the weld pool and the tungsten electrode
by the surrounding atmosphere.
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, causing hydrogen contamination during initial
stages of the weld. The shielding gas pre-flow clears the air
and moisture from the torch and prevents this contamination.
Post-flow works a little differently. Immediately after the welding arc is extinguished, the weld bead, filler rod , and 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 the oxidation causes
the weld bead, filler rod, and tungsten to turn black. Proper
post-flow prevents oxidization from occurring by shielding the
hot electrode and weld area while the puddle solidifies.
A tungsten that has discolored because of oxidization must be
properly removed from the torch and replaced. Refer to the
owner's manual for instructions on how to do so.
SelectiniJ a Filler Metal
The TIG welding tungsten electrode is a non-consumable
electrode and therefore does not become part of the weld as do stick welding or MIG welding electrodes, which melt and
become filler metal that adds to the weld volume. This nonconsumable electrode is advantageous on thin materials (usually narrower than X6') where the TIG weld fuses the edges of
the base materials together. This fusion is referred to as an
"autogenous" weld (no filler) and is common on thin metal
butt, lap, and flange joints.
Welds on thicker metals (about XG" and up) , beveled jOints,
and poor fit-up joints may need filler wire added to the weld
pool for proper fusion and weld strength. You usually do this
by hand-feeding the filler wire into the pool. The filler rod
diameter should be apprOximately the same as the electrode
diameter. You want to keep the hot end of the filler rod in the
blanket of shielding gas and/ or post-flow until it has cooled
below its oxidation temperature.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
Automated TIG welding uses a wire feeder to automatically
feed a continuous wire into the weld pool as the weld proceeds along the joint.
Shapes of fitler metals
The most common filler material for TIG welding takes the
form of 36" straight rods that are fed by one hand while the
other hand manipulates the torch. 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 welding 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.
Also used to a lesser degree are flatten ed rods. These rods are
preferred by some welders who feel it is easier to feed the
rods because of their shapes.
Another type of filler material is coiled wire for automated TIG
welding. This would be the same wire used on a given material for the MIG welding process.
Steel
Carbon steel filler rods come in seven designations. A typical
designation is ER70S-6 for TIG. In this example, the ER means
that you can use the filler for either TIG or MIG welding. If the
designation lacked the R, it would signify a continuous electrode to be used with MIG welding only. No designation exists
for a filler rod using just the R: the designation 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. The 6 refers to the
chemical percentages within the rod's composition. In other
words , the number at the end of the description refers to the
classification of wire being used.
Stainless steel
Many more stainless steel designations exist than steel designations. A typical classification of a stainless rod would be
ER308. The ER, as it is in steel, stands for either continuous
- - - Chapter 3: Choosing Electrodes and Consumable Materials
39
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 HiSii instead of Si meaning High Silicon
Content.
Aluminum
Aluminum filler rods have approximately 12 designations. 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 be sure to always consult electrode wire manufacturers
for the proper filler to use in critical welds.
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TIG Welding For Dummies. Miller Electric Special Edition - - -
Chapter 4
Putting Safety First
In This Chapter
Preventing electrical shock
~
Protecting yourself with safety gear
!II>- Handling cylinders safely
A
s in any welding process, in TIG welding, safety precautions are very important. Be sure that you understand
all the information relating to the safe operation of the welding equipment and the welding process before you begin
work. A careless welder who doesn't observe simple rules
can cause a hazardous situation for everyone in the area. The
process of arc welding creates several hazards that must be
guarded against: everything from electrical shock to fumes
to eye injuries. In this chapter, we take a look at the most
common hazards and how to guard against them.
Be sure to review the instruction manuals that come
with each piece of welding equipment for important
safety information. This chapter contains general safety
information, but does not take the place of reviewing the
instruction manual for the specific equipment that you're
working with.
Common sense is the most important tool a welder can
bring to the welding area. Horseplay or practical jokes
have no place in the working area. (Save practical jokes
for the appropriate time and place, like your Aunt Susie's
wedding reception or your cousin Dave's graduation
speech.)
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WatchiniJ Out for
Electrical Shock
TIG welding is an electrical welding process, which means
that a TIG welding machine puts out electrical energy. Always
install a welding machine according to the manufacturer's recommendation and in accordance with the National Electrical
Code and local code requirements.
As a welder, you must always be concerned about the possibility of electrical shock. Electricity will always take the path
of least resistance. If a proper secondary circuit exists , the
current will follow that path. However, if poor connections,
bare spots on cables, or wet conditions exist, the possibility
of electrical shock is a real hazard.
Never weld while standing in water. If you're working in wet
conditions, take the following precautions:
" Stand on a dry board or a dry rubber mat when welding.
" Do not place the welding equipment in water.
" Keep gloves and shoes dry. Even perspiration can lower
your body's resistance to electrical shock.
Although the majority of welding is done in the direct current
(DC) mode, welding power is most often obtained from the
local power company out of an AC wall socket.
If the welding machine is "hard wired" directly to the wall
rather than using a plug and wall socket, you must shut off the
primary power to the machine at the fuse box if work needs to
be done on any part of the welding equipment. Also, remember to shut off the primary power at the fuse box when the
machine is idle for long periods of time.
Note: Always use caution when installing any welding equipment. Improper connections can lead to an electrically "hot"
welding machine case, which could result in a severe shock to
anyone who touches it.
_ _ _ _ _ _ _ _ _ _ _ _ Chapter 4: Putting Safety First
113
Primary wiring should only be done by a qualified electrician
who is absolutely sure of the electrical codes in a given area.
Before any primary power is connected to welding equipment,
be sure to read the equipment's operation manual and follow
its instructions to the letter.
Afloidin9 Fumes
As with most welding processes, the heat of the arc and the
molten pool in TlG welding generate fumes . Because TIG does
not typically use flux or produce slag, we highly recommend
that the material being welded is clean.
The flux on a stick electrode or in a flux-cored wire has several functions, one of which is to clean the base material. If
the base material isn't clean, the weld can become defective.
Compared to other arc-welding processes like stick- or fluxcored welding, few fumes are produced. However, the base
metals being welded may contain coatings or elements such
as lead, zinc, copper, nickel, and so on, that may produce hazardous fumes. These fumes may create health hazards, especially for the lungs. Exhaust hoods or booths can remove
fumes from a particular area. 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.
When welding, keep your head and helmet out of the fumes
rising off the workpiece.
Be sure that proper ventilation is supplied, especially in a confined space. Because TlG welding is a gas-shielded process ,
you must take care not to extract too much air from the arc
area, which would disturb the process. Be careful that the
device used to pull the welding fumes from the area isn't so
close or so strong that it pulls the shielding gas away from the
weld. This leaves the molten puddle exposed to the air, which
results in a defective weld.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
BeinfJ WarlJ of Arc RalJs
The electric arc used in TIG welding creates several hazards,
including infrared and ultraviolet rays . The light and rays can
produce a burn similar to sunburn. The arc rays, however, are
more severe than sunburn because the welder is so close to
the source. These rays can quickly burn any exposed skin.
To protect yourself from the rays , you must wear proper
safety gear while welding. A welding arc produces ultraviolet
rays as well as very high temperatures in the area near the
arc. If you weld without protection, you risk a chance of flash
burn, which causes redness of the skin and can produce a
painful burning and itching in your eyes.
Proper clothiniJ
The clothing recommended for TIG welding is a tightly woven
long sleeve shirt, leather gloves, pants that cover the legs
completely, and a pair of closed-toe shoes that will protect
your feet.
To prevent fires, be sure that all the protective equipment you
use is free of oil, grease, or anything else that is flammable .
E'le protection
Always use eye protection for welding. As standard practice,
wear safety glasses - even under the welding hood - at all
times during welding. Never look at the welding arc with
unprotected eyes. A short exposure to the arc, which sometimes occurs accidentally, may cause flash burn to your eyes.
Usually, this injury isn't permanent but may be painful for a
short time after exposure. The feeling is similar to having
sand in your eyes , without all the fun of a trip to the beach
first. Sometimes four to eight hours may pass before a painful
sensation in the eyes develops. Mild cases of flash burn can
sometimes be treated , but continued exposure to flash burn
can cause permanent eye damage.
Because the TIG welding process produces so little smoke, the
arc can appear very bright even if you're wearing a welding
hood. For this reason, you should wear a welding hood while
_ _ _ _ _ _ _ _ _ _ _ _ Chapter 4: Putting Safety First
45
welding. Welding lenses are not simply colored glass, but are
special lenses that screen out almost 100 percent 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 on a
person's sensitivity of eyesight and the welding variables.
Generally speaking, the current that you use determines the
shade of the lens needed. The higher the current, the darker
the shade lens should be. You can get the welding helmet
equipped with an electronic lens that automatically lightens
and darkens as required. You can find safety rules related to
eye protection in the AWS-approved ANSI Z49.1 booklet, Safety
in Welding and Cutting.
Securin9 the Wetdin9
Enflironment
The TIG welding process can create light, heat, and fumes. In
addition to wearing protective clothing, you (the welder)
must take other precautions as well.
Be aware that the light given off from welding may bother
other workers in the area. You can use permanent booths or
portable partitions to contain the light rays in one area.
Be aware also that the heat given off during welding is capable
of setting flammable materials on fire. Therefore, welding
should not be done in areas containing flammable gases,
vapors, liquids, or in dusty locations where explosions are a
possibility.
Many injuries have resulted from welding done on containers
that have previously held combustible materials. Acceptable
methods of cleaning such containers before welding are outlined in the American Welding Society's booklet, AWS A6.0,
Safe Practices for Welding and Cutting Containers That Have
Held Combustibles. Never attempt to weld such containers
without first reviewing and implementing the safety procedures outlined in this booklet.
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SafellJ HandlinfJ ClJlinders
Regardless of a cylinder's content, you must handle any pressurized cylinder at all times with great care. Shielding gases
such as carbon dioxide, argon, and helium are nonflammable
and non-explosive. A broken valve, however, releases extremely
high pressures, which could cause the cylinder to be hurled
about at hazardously high speeds. Think of a child's balloon:
If a balloon is blown up and then released, the jet force of air
escaping causes the balloon to fly about rapidly and erratically.
The same is true if a cylinder valve breaks off. The weight of the
cylinder and the extremely high pressure could easily cause a
very damaging and possibly fatal accident.
Keep cylinders securely fastened at all times. Chains are usually used to secure a cylinder to a wall or cylinder cart. When
moving or storing a cylinder, fasten a threaded protector cap
to the top of the cylinder. This cap protects the valve system
should it be bumped or the cylinder dropped. Use a cylinder
cart whenever you have to move a cylinder.
Be sure 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 increases. To
prevent the excess pressure that can cause the cylinder to
explode, the cylinder valve is equipped with a safety nut and
bursting disc.
Do not hang welding torches and other cables 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.
Chapter 5
Preparing to Weld
In This Chapter
_ Readying the power source
Preparing the weld joint
... Welding different types of base metals
on
efore you start the arc, you need to make certain basic
preparations, like making sure to read and follow all
equipment labels and owner's manuals carefully. These preparations also include getting the base metal ready and setting
up the machine and its controls. In this chapter, we show you
how to get ready to weld, including how to prepare each of
the commonly welded base materials.
Gettin9 the Power Source ReadlJ
Figure 5-1 illustrates the front panel of a typical AC/DC
machine designed for TIG welding. Keep in mind that not all
power sources will have all the features or controls of this
machine. Depending on the make and model of your machine,
the controls and switches mentioned in the following information may be found in locations other than the front panel. The
various controls each have a specific function and the operator changes them as the application changes.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
Figure 5-1: The front panel of a typical AC/DC TIG welding machine.
Power switch
When the switch is in the "on" position, voltage is applied to
the control circuit. A light or an LED meter 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! If this happens , the machine could
begin welding prematurely and cause a potential danger.
SMA WIGTA W mode switch
The SMAWjGTAW switch should be set for the particular
process that you're using: either SMAW or GTAW. The machine
will disable the functions that aren't required by the process
being used . For example, the gas solenoid valves will not be
active in the SMAW mode because they're only required for
TIG welding.
- - - - - - - - - - - - Chapter 5: Preparing to Weld
49
Amperage control panel/
remote switch
When you're using a remote control device (foot pedal/fingertip
control), the panel/remote switch on the front panel needs to
be in the Remote position. When you're controlling amperage
from the front panel of the machine, you must have the switch
in the Panel position.
Weld current control
or amperage control
The weld current or amperage 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 machine is set at 50 percent of the capable
amperage, the remote device at full output delivers 50 percent
of the machine's available current.
Remote amperage
control receptacle
The remote amperage control receptacle is provided for connecting a remote hand control or a remote foot control. This
feature allows you to have amperage control while welding at
a work station that is a long distance from the power source.
With the foot or fingertip control, you can vary the amperage
as you progress along a joint. This is particularly helpful when
you're starting on a cold workpiece. You can increase amperage to establish a weld pool quickly, and as the material heats
up, you can decrease the amperage. When coming to the end
of a joint, you can further decrease the amperage to taper off
and "crater out."
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TIG Welding For Dummies, Miller Electric Special Edition _ __
ACIDC polaritlJ (material
selector) switch
The AC/DC polarity switch allows you to select Direct Current
Electrode Negative (DCEN) for welding material such as mild
steel, stainless steel, chromoly, and so on, or alternating current CAC) for materials like aluminum and magnesium.
Preparint) the Weld Joint
Many TIG welding problems, or supposed problems, are a
direct result of a welder using improper methods to prepare
the joint. Chief among these methods is the improper use of
grinding wheels to prepare joints.
Grinding wheels should be clean and dedicated exclusively to
the material being welded. If grinding is the method that you
choose, using a sanding disc on your grinder is generally a
good choice for preparing a joint to be welded.
CleaninfJ
The cleaning process is as critical if not more critical than
welding itself as far as the TIG process is considered.
When getting ready to weld, you must remove oil, grease, dirt,
paint, marking crayon, and corrosion from the joint edges and
metal surfaces to a distance of about Y2" on both sides of the
joint. Their presence during welding may lead to arc instability and contaminated welds. If you make a weld with any of
these contaminants present, the result could be a weld bead
with pores, cracks, or inclusions.
Any of these results could lead to a possible weld failure in
the future .
You can clean by using a mechanical method such as sanding
discs, wire brushes, and files. Chemical cleaning, which
includes degreasers or deoxidizers , is also an option. You also
can use a combination of mechanical and chemical cleaning
methods. When cleaning aluminum or stainless steel, use a
stainless steel wire brush.
_ _ _ _ _ _ _ _ _ _ _ _ Chapter 5: Preparing to Weld
51
Use the abrasive wheels and wire brushes only on one specific type of material. For example, if you use a wire brush
on rusty steel and then on aluminum, the brush you use can
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 abrasive wheels.
Sometimes, a welding operator can transfer contaminants
from dirty welding gloves onto the filler rod and consequently
into the weld area. This is why it is critical to have gloves that
are fairly clean while TIG welding.
Preheatinfl.
Preheating, if needed, is typically dictated by the thickness of
the material to be welded. When welding on thicker material,
preheating may be needed to establish a puddle to make welding possible.
Preheating is most often done with an oxyacetylene torch.
However, when you use this method, you must take care that
localized overheating doesn't occur, and that the base metal
(especially aluminum) is not contaminated with combustible
by-products of the oxy-fuel process. Other methods of preheating include induction coils and heating ovens.
PreparinfJ Mild Steel for WeldinfJ
Low carbon steels, commonly referred to as mild steels, are
readily welded by the TIC-welding process. 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
any scale or coatings prior to welding.
Mild 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 that 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 occur in the form of bubbles in the weld
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TIG Welding For Dummies. Miller Electric Special Edition _ __
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 for TIG-welding mild steel.
Lower-grade filler rods used for the oxyacetylene welding of
many hot-rolled products are not suitable for making highquality TIG welds.
When working with mild steel, direct current electrode negative is recommended, with a high-frequency, or Lift-Arc start.
You should use a 2-percent ceriated or 2-percent thoriated
tungsten with point or taper on the electrode.
PreparinfJ Stainless Steel
for WeldinfJ
Stainless steel is the common term for chromium-nickel
alloyed steel. You can find both magnetic and non-magnetic
types of stainless steel. You also can find many types of alloys,
and each type possesses its own properties of corrosion
resistance and strength. Check with the manufacturer when
you're in doubt about the specific properties of an alloy.
When welding stainless steel, you need to first thoroughly clean
it. Protective paper or plastic coatings are applied to many
stainless steels to keep the material clean. Foreign material may
cause porosity in welds and carburization (uniting with carbon)
of the surface, which lessens the corrosion-resisting properties.
If you clean the surface with a wire brush, be sure to use a
stainless steel wire brush, dedicated to this material, to prevent iron pickup on the stainless surfaces. As with other welding procedures, use clean and dry filler metal and take proper
precautions to prevent contamination during welding.
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. Tungsten type and
preparation should be the same as previously noted for mild
steel. When welding stainless steel, be sure that the filler material is compatible. The heat conductivity of stainless steels is
_ _ _ _ _ _ _ _ _ _ _ _ Chapter 5: Preparing to Weld
53
about 50 percent less than mild steel with a high rate of thermal expansion. This increases the tendency for distortion on
thin sections.
When welding stainless, try to keep the heat input as low as
possible. If the heat input is too much, a metallurgical change
known as carbide precipitation can take place. If corrosion
resistance is a big factor in the completed weld, be aware that
some of the corrosion-resistance properties are lost in the weld
and adjacent areas that are heated above 800 F to 1400 F on
stainless steels. Keeping heat input to a minimum is necessary
in this situation. The longer the work is within this critical temperature range, the greater the precipitation will be. Rapid cooling through the 800 F to 1400 F range helps keep this
precipitation to a minimum.
0
0
0
0
The most common tungstens used for welding stainless steel
are 2-percent thoriated and 2-percent ceriated. You'll want to
prepare the tungsten as we discuss in Chapter 3. The filler
metal that you choose must be of the same general analysis as
the material being welded. A good example is stainless steel,
which isn't welded with mild steel filler because mild steel
filler won't have the same corrosion-resistant properties as
the stainless does. If your filler metal selection isn't compatible with your base material, failure can eventually occur.
PreparinfJ Aluminum
for WeldinfJ
The preparation of aluminum deserves more consideration
than it is usually given. Aluminum is very susceptible to contaminants , which can cause considerable problems when
welding. Aluminum has a surface oxide that must be removed
during the welding process.
When the electrode is positive and the work is negative
(reverse polarity or during one half of the AC cycle; refer to
Chapter 1), 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.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
Do not rely on this cleaning action to do all the cleaning. You
should also use the mechanical or chemical cleaning methods
mentioned in the "Cleaning" section earlier in this chapter to
remove anything from the material that will hinder proper
fusion .
A problem 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 weld pool.
Both sides of the joint should 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 the oxidation is severe enough, the rod must be cleaned
prior to use. Stainless steel wool is good for cleaning filler
wire and rod that is heavily oxidized.
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 the extent that you need to reduce amperage from its original setting while you are welding. Remote foot and fingertip
amperage controls are useful in these situations.
A 2-percent ceriated tungsten electrode is recommended for
aluminum. Grind the electrode to a point as you would if welding mild steel. However, after you've created a point, remove
the tip by grinding a small land, or flat, on the end. The taper
on the tungsten allows for a more focused arc, which is espeCially beneficial on thin base material. The flat on the end
keeps the sharp point of your tungsten from breaking off and
falling into the molten puddle. Note: This will cause contamination in your weld. The electrode stick-out beyond the cup
may vary from approximately Xs" on butt joints to possibly Y2"
in joints where it is difficult to position the torch. The normal
recommended arc length (distance from your tungsten to the
material) is approximately the same as the electrode diameter. (For proper tungsten preparation, refer to Chapter 3.)
Chapter 6
Selecting Joints and Welds
••••••••
c~~~_
•••
¥~
In This Chapter
.... Getting familiar with types of joints
.... Discovering fillet and groove welds
.... Creating basic weld joints
A
weld joint is the term used for the location where two or
more pieces of metal are welded together. If your goal is
a quality weld and cost-effective use of filler metal (and why
wouldn't it be?), joint design should be a prime consideration.
The proper joint design depends on several factors, including
material type, thickness, joint configuration, and strength
required.
Often, a welder has 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. In this chapter,
we cover the ins and outs of the different types of jOints and
welds and their uses .
GettinfJ to Know the
TlJpes of Joints
A proper joint design offers the required strength and the
highest quality weld at the lowest cost. The joint design dictates what type of weld is required. Figure 6-1 shows the five
basic weld joint designs , which are edge, butt, lap, corner, and
T-joints.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
Corner
Edge
Figure 6-1: 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 welds made into a prepared joint to get deeper penetration. 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.
ONe go into more detail on fillet and groove welds later in this
chapter in the "Working with Fillet Welds" and "Using Groove
Welds" sections.)
To prepare the joint, you must remove the base material (typically by grinding) and replace it with weld metal. Groovewelded jOints are very efficient but take more time to make
than a fillet-welded jOint, primarily because they require some
form of joint preparation. Fillet welds are made on jOints that
require no prep.
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57
A few considerations of joint design are specific to TIG welding specifically. Naturally, the weld joint must be accessible to
the TlG welding torch, allowing proper torch movements.
Weld joints should not be narrow enough 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 improve access.
EdiJe joints
An edge joint occurs when the edges of parallel or nearly parallel members meet and are joined by a weld.
Edge joints are often used when the edges of the parts 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 edges. If necessary, 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, as shown in Figure 6-2.
Depth Of Fusion
Joint
Penetration
t
~II
C/f l'
~ ' =~=t
Root Penetration
Figure 6-2: 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. Partial joint penetration, which if not
intended, is referred to as incomplete joint penetration.
Butt joints
A butt joint occurs when the surfaces of the members to be
welded are in the same plane with their edges meeting.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
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 they're properly done. They can be
expensive joints because a prepared groove is generally
required to get the proper penetration and weld size. Getting
the groove ready involves preparing the jOint, removing material to open up the joint, and then welding to penetrate and fill
the groove.
Distortion and residual stresses can be problems with butt
joints.
Butt joints can be designed in various ways. They can 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 shaped, as shown in Figure 6-3.
Square Groove
Square Groove
With Root Opening
Beveled Butt
V-Groove
J-Groove
U-Groove
Figure 6-3: Types of grooves. (A butt joint is used as an example.)
Edges may be held tight together, or a small gap known as a
root opening may be left between the edges. When speaking
about groove jOints, a few key features of the joint are referred
to: the groove angle, groove face, root face, and root opening,
shown in Figure 6-4. 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
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59
metal in the groove, including the root face. The root face is
sometimes called the land or flat spot at the bottom of the
joint. The main purpose of the various grooves and root openings is to allow proper penetration and depth of fusion.
\\~/~ Groove Angle
\
/
\
(Included Angle)
/
Bevel Angle
Groove _ _
Face
I
I --- Root Opening
I
Figure 6-4: Parts of a groove weld . (A V-groove is shown as reference .)
If material thickness is less than approximately )Is" thick,
square edges butted tight together, with no root opening can
be used. (Aluminum usually requires a small root opening.)
Plate thicknesses of )Is" and greater generally require single or
double V-groove and root openings for proper penetration
and depth of fusion. The way the joint needs to be prepared
before welding depends on the joint design and the equipment available to do the edge preparation. An oxy-fuel torch
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.
Lap joints occur when the surfaces of joined members overlap
one another. A lap joint has good mechanical properties,
especially when it's welded on both sides. The type of weld
used on a lap joint is generally a fillet weld. The degree that
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TIG Welding For Dummies, Miller Electric Special Edition _ __
the members overlap is generally determined by the thickness
of the plate. In other words, the thicker the plate, the more
overlap that's required.
Corner joints
0
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.
Welds made on the inside of the "L" are called fillets, and
welds made on the outside of the "L" are called groove welds.
Corner joints are easy to assemble and require little if any
joint preparation. After welding, the welds are generally finished, meaning that they're ground smooth to improve their
appearance. When finishing a weld, you as the welder should
make every effort to prevent overlap, high spots, low spots,
and undercut. These problems can all mean more work
because they result in additional grinding, rewelding, and
regrinding.
Corner joints come in two main types: open corner (there's
a gap) and closed corner (edges are tight together). When
you're working on lighter gauge material, you may need to
increase travel speed somewhat, especially on open corner
joints where excessive melt-through (the weld puddle droops
through the joint to the other side) is a possibility.
f.-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". On this particular type of joint, a fillet weld
is used .
0
,
T-joints possess good mechanical strength, especially when
welded from both sides. They generally require little or no
joint preparation and are easy to weld when the correct
parameters are used. The edges of the T-joint may be left
square only if a fillet weld is required. For groove welding, the
edges may be altered by thermal cutting/gouging, machining,
or grinding.
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61
Workint) with 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
as or stronger than the base metal if the weld is the correct
size and the proper welding techniques are used.
0
Figure 6-5 shows a cross section profile of the three types of
fillet weld contours: flat, convex, and concave. (Contour is the
shape of the face of the weld.)
The size of a convex fillet weld is generally the length of the
leg referenced. Figure 6-6 shows a convex fillet weld and the
terms associated with it.
Flat
!
Convex
Concave
Figure 6-5: Fillet face contours.
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TIG Welding For Dummies, Miller Electric Special Edition _ __
CONVEXITY
ACTUAL THROAT
EFFECTIVE THROAT
THEORETICAL THROAT
(AI CONVEX FILLET WELD
Figure 6-6: The parts of a fillet weld. (A convex fillet is used as the example.)
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 6-6, 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.
The general rule for fillet weld size is that the leg should be
the same size as the thickness of the metals. If X" thick plate
is being welded, a X" 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 a X" thick plate. If a lot of weld would be better,
think of 12 legs on the fillet. This would result in what is known
as over-welding. This weld isn't just twice as large as required,
but its volume is three times what's required. This wastes weld
metal and the welder's time, causes more distortion, and may
even weaken the structure because of residual stress.
A weld or weld joint is no stronger than its weakest point.
Even though you may think that a joint welded with a larger
weld (one with longer legs) would be stronger, it won't
_ _ _ _ _ _ _ _ _ Chapter 6: Selecting Joints and Welds
63
support more stress than if the correct sized weld was used. 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 X" thick plate onto a )1;;" thick plate in the form
of a T-joint, the rule for fillet weld size is that the size of the
fillet weld leg should equal the thickness of the metal being
welded. So, one would think that because there are two different thicknesses, the best weld results would be obtained by
making an unequal leg fillet weld (that is, the fillet weld has a
X" weld leg on the X" plate and a Y2" weld leg on the Y2" plate).
However, consider the results of making the weld with an
equal leg fillet. There would then be two choices: a Y2" fillet
or a X" fillet. In this instance, the X" fillet would be the more
practical because a weldment is no stronger than its weakest
point. The extra welds in the Y2" fillet will also require more
time, filler wire, and induce more heat into the metal, causing
more residual stress.
UsinfJ Groo(/e Welds
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 of grooves used in the TIG process. Each type
of groove weld takes its name from the profile of the groove
it uses . Review Figure 6-3 for typical grooves found on butt
joints.
Groofle weld size
When a weld is called for on a joint, the size of the weld is
important to enable the joint to carry the load applied to it.
In order to understand groove weld size, you have to first
understand some of the terms applied to a typical groove,
such as a V-groove jOint - which we talk about in mere
seconds. The groove angle, bevel angle, root face, and root
opening are all illustrated back in Figure 6-4.
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 kept to a minimum. Any
extra reinforcement decreases the strength of the joint by creating extra stresses at the weld toes .
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TIG Welding For Dummies, Miller Electric Special Edition _ __
Joint design for various types of groove welds can be expensive because some groove weld joints require more preparation than others. Therefore, be mindful of what types of
preparation are necessary and what you can avoid.
St{uare"'lJrOOfle
You can make a square-groove weld 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 that the higher a gauge number, the thinner
the material. If your base metal has a thickness of between )Ia"
and X", you want to weld both sides of an open-square-grooveweld to provide proper penetration into the groove. Usually,
open-square-groove-welds are not made with groove openings
of more than about %2". In cases where welding is done from
only one side of the joint, you can use a temporary or permanent backup bar or strip. On critical welds, you can use a consumable insert.
These backings or inserts can ensure proper joint penetration, help avoid excessive melt-through, or provide a flush
backing to the weld.
V-groove weld designs require careful preparation, but for all
the extra work involved, they are still quite popular. V-groove
welds are usually made on medium to thicker metals, and are
used quite often for pipe welding. These welds can be of
excellent quality if they're properly completed.
The groove angle for a groove weld must be large enough for
the torch to fit into the groove. The groove angle depends on
metal thickness, desired electrode extension, and torch nozzle
size. Usually V-groove welds are made on material thicker
than Ys" to X" . Adjusting the root face thickness can help control penetration.
Usually, the root pass (the first weld pass of a groove weld
done at the bottom or root of the joint) 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.
_ _ _ _ _ _ _ _ _ Chapter 6: Selecting Joints and Welds
65
V-groove welds are often made on material up to about %"
thickness , whereas double V-groove welds are normally made
on thicker materials up to roughly 7:\" in thickness. Double
V-groove welds (V-grooves on both the top and bottom of the
joint) on thicker materials can use less deposited weld metal
and limit distortion in the weld , especially if a small root face
of about Va" is used on each member. Usually the weld passes
on such a joint are made alternating from one side of the joint
to the other, which helps to prevent distortion.
The bevel-groove weld requires preparation, but only one
member must be beveled. The single bevel-groove can be
used on material up to about %" in thickness, whereas double
bevel-grooves are used on thicker material up to about 7:1".
In most cases, up to Va" root openings are used on single and
double bevels.
A bevel-groove is sometimes used when welding in the horizontal position. Root faces up to about Va" are normally used
for either single or double bevel-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 also applies to
the double U- and double J-grooves.
One disadvantage of U- and J-groove design is the difficulty
of preparing the base material. 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.
CreatinfJ a Basic Weld Joint
As a general rule, the arc length is normally one electrode
diameter. However, when welding with direct current using a
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TIG Welding For Dummies, Miller Electric Special Edition _ __
pointed electrode, the arc length may be considerably less
than the electrode diameter. 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 Yt6" in diameter, the gas cup should be a minimum
of Yt6" diameter.
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 come into contact with the weld pool
or the filler rod being fed in by the welder, or touch the side of
a tight joint. A general rule is to start with an extension of one
electrode diameter. Joints that make the root of the weld hard
to reach require additional extension.
0
To start the arc, hold the torch vertical (90 from horizontal).
After you start the arc, hold the electrode in place until the
desired weld pool is established. Then tip the torch at a 75
angle from the horizontal so that the tungsten points in the
direction of travel, and progressively move it along the joint,
as shown in Figure 6-7.
0
Tungsten without Filler Rod
Welding
d~
W
f;!~
d::;b
r/i/UJTJTft27t7//d
"'r/'7J"'7?
//
""/?'~677'
y~
Form pool
Move torch to front
of pool. Repeat proce ss.
Tungsten with Filler Rod
Welding
d~
W
d::;b
-~iV'2l
15°
V J'"J"'JTJT..0777/?'21
Form pool
Add filler metal
~f;!
?VI.0W'~
IZd/VA0'7ii7!&d
Remove rod
Remove torch to front
of pool. Repeat process.
Figure 6-7: Proper torch and filler metal positioning.
_ _ _ _ _ _ _ _ _ Chapter 6: Selecting Joints and Welds
67
Filler metal
If you're using filler metal, dip it into the leading edge of the
pool using the heat from the molten puddle to melt the filler.
Be sure to move the torch and filler rod progressively and
smoothly so that 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. Use a large shielding gas envelope to prevent exposure to air.
0
The filler rod is usually held at about a 15 angle to the
surface of the work and slowly fed into the molten pool (refer
to Figure 6-7). Alternatively, you can dip it in and withdraw it
from the weld pool repeatedly to control the amount of filler
rod added. During welding, do not remove the hot end of the
filler rod from the protection of the inert gas shield. When you
turn the arc off, make sure that the postflow of shielding gas
not only shields the solidifying weld pool but also the electrode and the hot end of the filler rod.
Butt weld
When welding a butt joint, be sure to center the weld pool on
the adjoining edges. When finishing a butt weld, you can
decrease the torch angle to aid in filling the crater in the bead
at the end of the joint. Add enough filler metal to avoid an
unfilled crater: Cracks often begin in a crater and continue
through the bead.
Utilizing an amperage control device (either a foot pedal or
torch-mounted hand control; refer to Chapter 5) is useful
during the finishing of a bead. You can use it to lower amperage to decrease pool size as you add filler metal.
Lap joint
In a lap joint, the pool is formed so that the edge of the overlapping piece and the flat surface of the second piece flow
together. Because the edge becomes molten before the flat
surface, it is important not to angle your torch toward the
edge too much. If too much heat is directed toward the edge, it
will also tend to burn back or undercut. You can control this by
dipping the filler rod next to the edge as it tries to melt away.
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TIG Welding For Dummies. Miller Electric Special Edition _ __
T..joint
A T-joint involves a similar situation as a lap joint: An edge
and a flat surface are to be joined together. The edge will heat
up and melt sooner than the flat surface. Angling the torch
more toward the flat surface directs more heat onto it. The
electrode may need to be extended further beyond the cup
than in the previously mentioned 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 prevent undercutting. Again, the
crater should be filled to avoid excessive concavity.
Corner joint
When welding a corner joint, melt both edges of the adjoining
pieces and keep the pool on the joint centerline. When adding
filler metal, be sure to use sufficient deposit to create a convex
bead. A flat bead or concave deposit results in a throat thickness less than the metal thickness. On thin materials, the
corner joint design lends itself to autogenous welding, which is
fusion welding without the addition of filler rod. Good fit-up is
required for autogenous welding.
EdiJe joint
As mentioned earlier in the chapter, edge joints are often used
on thin material and when the members to be welded won't
be subjected to great stresses. Because of this, an autogenous
weld can be used on this joint as well. Or, if additional reinforcement is desired, filler metal can be added with the same
procedure mentioned in the "Butt weld" section.
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