TUNGSTEN
INERT GAS
WELDING
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Tungsten
lnertCgsffi
lntroductron
For Ouiz Purcqlg!
Read llnit 30 - l9 to 20 and demonstrationnotet\
Originsand Terminologv;
Tunsstentnert Gas 6m) weldinq: The original rerm for rhe TIG weldingprocess
was "Heli-Arc" becauseof the inert gas - helium which was used with this 0?e of
wclding. Heli-arc began in the latc 1940'sand by the carly 50's (the Korean
Conflict),heliarc wasintroducedinto industry. As thc proccsswasimprovedupon,
argon was used as the shielding gas becauseof its heavier atomic weight and
thereforeits ability to stayin the weld zone more effoctively.
The mostproper currentnamefor this weldingprocessis GasTungstenArc Welding
(GTAW); however,it has also been known as "high freq." welding in the trades
becauseof using high frequencyclectricity.
Metallic Inert Gas (MIG) Welding:This is an entirelydifferent processand will be
dealt with in a subsequentunit. Do not confuseMIG with TIG.
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TIG Welding; This processusesa non-consumable
electrodoto help establisha high
tiequencycurrent arc in an inert gasenvironment.Fiiler rod is then addedinto the
weld zoneby a separatewire feeder machineor by hand feeding.
Non-ConsumableElectrodes: The electrodeis not usedup in the woldingprocess.
(Thc melting point of tungsten is 6,125 degrees.) There are different alloy
compositionsin the color codedelectrodes.
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Grecn - Pure tungsten- usedfor weldingaluminum. This electrodetendsto
qush rhe hear outward to the edgesof the liquid pool as the weld is in
progress. ThJs is beneficial when welding a conductive metal such as
aluminum.
Ycllow - 17oThoriated- Thorium raisesmeltingtcmperatureof the tungsten.
This clcctrodc is a gencralpurposeelectrode,but we don't useit in this lab.
Red/Purpfc- 2 % Thaiatcd - To bc used on stainless,chrome-moly.,and
copper alloys. It is lqt to be used on aluminum as it will tend to give off
sparkjcsand wilJ leavc smallpits on the aluminumsurfacc. The sparklestell
of thorium burnout.
Brown - Zirconium To be used on titanium and has still a higher mclting
point. It is alsousedin weldingoperations
whcrchighpurity is a necessity.
This is an cxocnsiveclectrodecomoaredto the others.
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TIG Welding Introduction (Con't.)
BASIC TIG WELDING
SYSTEM
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Inert Gas: A gas on th€ chgmical glgmentschart that does not easily mix or
chemicallycombinewith anyother gasesor elements.This gasis colorless,odorless,
and tasteless.This gasprotectsthe weld in a gasbubble or envelope.The envelope
preventsthe atmospherewe live in from g€ttingto the weld and contaminatingit.
Inert Gases: Argon, Helium, Krypton, Xenon, Radon,and Neon.
Helium was the first gasto be usedwith the process;however,it didn't stay in the
weld zonebecauseof its light atomicweight. Therefore,it took more gasto prev€nt
contaminationof the weld. In our laboratorywe use Argon as the shieldinggas.
High Frequenc-yElectricirv: TIG welding requires the use of high frequency
(acceleratedalternatingculrent) to do the work, The electricalcurrentusedin this
processis upwardsof 200,000cyclesper second- the normalAC wall currentin the
United Statcsis 60 cyclesper second.The acceleratedcurent helpsin two waysfor
this weldingproccss:
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Hclps establishthe arc by jumping the arc gap to the metal surface. The
operator doesn'tneed to touch the work surfacewith the electrode.
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I:or rlllnrinunrand ils a llo y s .t h c h ig h lf c q u c n c \ c u rf c f l c s t rb lis h c sa v c r v h ( ) t
unii(Jlnr. n()n dircctionalarc ncccssar!ii)f \\cldin!.
Mctals Wcldablc rvith Prmcss:
*Aluninum, Castlron, Copperand its alloys '-Staink:sr
Stcel StcolAlloys
and Magncsium(whi(hwc donI iry in this lab.)
includingChrornc-Moly,
' Thcsearc the mostcommonmctalswcldcdin thislab.with the'l lC welder.
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Con(rol Panel of ]'IG Welder in l-ab.
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Parts& dcscriolionof PurDosc:
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Fifst Row ol (lonrrols
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Contactor Sct t() "remoie" hccausc thc loot pcdal i\ rcnr()tc(jr lrvav front thc
nlachinccontrol pancl. This switchprovidcsthc full anrountot curfcnl dialcd on thc
C\rrrcnt (ontrol Knob whilc thc arc is being cslablir,hcd.
thcn cur: L)utand you fltust
dcprcsslhc ii)()t control to providc thc anloLrnlol cltrrcnt rccdai to do thc \rcld
('urrenl Switch Sct lo "remote"also bccauscol thc l()o1c()nlrirlbcing awa] fronl
th c p.rnrl. I'uncl i. frrI indu s t rie sl c t lin g s\ \ h r-rct h c $ r' lijin go p . : . rl(lI is ru n n i n ul h c
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cquip n rc n l1 r()n rlh c l)rn c l.
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TIG welding lntroduction (Con't.)
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Current Control - Set this before enteringthe booth The white band is the high
range,the black band is the low rangedetermined-bythe levertnob in the third row
dorin of controls. Set the current control knob for aboul zOVomole current than
what is believed to be needed. Don't set this control higher than 20Vabecauseit
affgcts the "Contactor" and the burst of current crossingthe arc gap to start th€
welding process. Also, the higher the amperagesettingmade,the more difficult to
foot pedal' (With a high
weldingheatftom
get a p-r;ise control of the necessary
-the
ietting, a slightmovementof the foot pedalis a major differencein the heatprovided
for the weldingProce:s.
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voltmeter - While welding,an observershouldseethis meter runningabout 18 - 21
volts. The voltagevariesby the sizeof the arc gap being used A largearc gapwill
require more voltagefor the arc to be rnaintained'a smallergap will take less) A
proper arc gaPwill bc 18 - 2l volts.
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Ammeter - Again an observer can see the amperageactually used !s the amperage
dialed on the-"Current Control" knob. lf the indicator fluctuates,the operator is
varyingthe foot control.
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instructor
Power Light Do not use the welder if this light fails to come on
'-all
immedia6ly. The "power light" is electricallyconnected.toall circuit boads in the
machineand is a way of cheiking that the systemis functioningcorrectlybeforeit is
used.
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SecondRow of Controls .
High FrequencySwitch - A three position switch. Start position is for all metals
aluminum. Offposition is for usingthe machine-instandardarc welding and
exC-ept
Continuousis for continuoushigh frequencyas used for aluminum and aluminum
alloys. If the switch is to "Stad" there will be a burst of high fr€quencycurent to
heli establishthe arc, then the high frequencywill cut out leavinga quiet DC arc'
"dntinuous" means the high frequenry will continuouslybe on for aluminum
welding.
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Crater Fill - At thc end of all weldsthere is a dishedout crater' This occursin TIG
from the force of the arc "Crater Fill" can bo usedto eliminatethis problemat the
end of a weld. Run all the weldsfirst without "CraterFill'" Put "CraterFill" to "ln"
and repair all the craten at the end of the welds.
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Start Current Switch and Knob - The "Contactor"and this switchwork together'
This switchcontrolsrhe sizeof arc gapthe currentwill jump to start thc arc' Setthis
jump a gap so
switchand knob for 1 ll2 to 2. To set it highermay causethe arc to
larsc the operator is not expcctingthis to happen- it becomesdangerous'
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TIG WeldingIntroduction(C.on't.)
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AC BalanceSwitch and Knob - This machineproducesa "square"high frequency
wave pattern. Below you seea normal pattern,a settingof "1" on the knob, and a
settingof # l0 on the knob. If the seftingis "1" the arc will havea maximumcleaning
affoct on the basemetal surface. A "10"settingwould give a maximumpenetration
affect to the depth of thc weld on the base metal.
No'e/YteL Sat
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.. Post Flow Timer - Use a ratio of 10 - 1 on this control. For every10 amperesseron
',', the "Currcnt Control" knob, give the "Post Flow Timer" 1 secondincreasein time.
This controlsthe lengthof time the inert gaswill flow afterbreakingoff the arc. The
advantagesof a post flow of gasare:
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Cool down the torch
Cool the tungsten electrode in an inert environment- prevents surface
oxidationwhich will contaminatethe upcomingwelds,
Keepingthe torch over the endcrater ofthe weld dudngpostflow time allows
the end of the weld to solidiryin an inert environment.
PowerSwitch- Turns power on/off.
Third Row of Controls
AC, DC I-ever' Allow selectionof AC or DC current. AC is usedfor aluminumand
aluminumalloys. DC is used for all olher metals. If set at A
Frgglency"switchmustbe sel ar "Continuous.if setatlDc' ihe "Hi
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Polarity l*ver - This relatesto "DC" current only. It allows for the selectionof
DCSP(Direct Current StraightPolarity)or DCRP (Direct CurrentReversePola ty).
electrod€to probablythen be used
rye-tungsten
for aluminumwelilFng. DCSP is usedfor welding on all metalsexceptaluminum.
NEI'ER LEAVETHIS LE!'ERON'Rf,VERSE," EXCEPTWHENPUTTINGA BALL
ON THE ELECTRODE! This is usuallyfor a matter of two - three secondsactual
"on" timc. Failure to siide the lever off the DCRP Dositionwill result in serious
mcltdowndamageinsidethe torch. This will happenin a matterof seconds!As
soon as finishcdballins the clcctrode.set this control off DCRP!
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TIG welding Introduction (Con't.)
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Rrng€ L€ver - This relates to the "Current Control" tnob, "High" position Fovides
for use of the White band, "Low" position usesthe Black band.
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DEMONSTRATION NOTESAND THOUGHTS
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