Gas Tungsten Arc Welding (GTAW)

7/21/2019 Gas Tungsten Arc Welding (GTAW)

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Gas Tungsten Arc Welding





Objectives

• Describe the gas tungsten arc welding process

– List other terms used to describe it

• What makes tungsten a good electrode

• liminate tungsten erosion

• !hape and clean a tungsten electrode

• Grind a point on a tungsten electrode



Objectives "continued#

• $emove a contaminated tungsten end

• %elt the end o& the tungsten electrode into thedesired shape

• 'ompare water(cooled GTA welding torches toair(cooled torches

• The purpose o& the three hoses connecting a

water(cooled torch to the welding machine




• 'hoose an appropriate no))le

• *ow to get an accurate reading on a &lowmeter

• 'ompare the three t+pes o& welding current used&or GTA welding

• !hielding gases used in the GTA welding process




• De&ine pre&low and post&low

• ,roblems resulting &rom an incorrect gas &low rate

• ,roperl+ set up a GTA welder

• stablish a GTA welding arc





,ower !ource /asics





Tungsten lectrodes



Tungsten

• Tungsten has the &ollowing properties0

– *igh tensile strength

– *ardness

– High melting temperature

– *igh boiling temperature

– Good electrical conductivity



Tungsten "continued#

• Tungsten is the best choice &or a non consumableelectrode

– High melting temperature

– Good electrical conductivity• As the tungsten electrode becomes hot the arc

between the electrode and the work stabili)es

– /ut a clean and correctl+ ground tungsten isneeded

• /ecause o& the intense heat some erosion o& theelectrode will occur



1igure 23(2 !ome tungsten will erode and be trans&erred across the arc4




• Wa+s to limit erosion0

– Good mechanical and electrical contact

– 5se as low a current as possible

– 5se a water(cooled torch

– 5se as large a tungsten electrode as possible

– 5se D'6 current

– 5se as short an electrode e7tension as possible – 5se the proper shape electrode

– 5se an allo+ed tungsten electrode



Torch /uild Out



Torch /uild Out




• The collet is the cone(shaped sleeve that holdsthe electrode in the torch

• Large(diameter electrodes conduct more current

• The current(carr+ing capacit+ at D'6 is aboutten times greater than at D',

• The pre&erred electrode shape impacts thetemperature and erosion o& the tungsten

• With alternating current. the tip is subjected tomore heat than with D'6



1igure 23(8 The smooth sur&ace o& a centerless ground tungsten electrode4 'ourtes+ o&Larr+ 9e&&us4



T+pes o& Tungsten lectrodes

• ,ure tungsten is an e7cellent nonconsumableelectrode

• ,ure tungsten can be improved b+ adding0

– 'erium

– Lanthanum

– Thorium

– :irconium





Table 23(2 Tungsten lectrode T+pes and -denti&ication4



!haping the Tungsten

• To obtain the desired end shape0

– Grinding "&or %! and !!#

– /reaking "not recommended due to cost#

– $e melting the end "Aluminium welding#

– 5sing chemical compound "doesn;t work that well#



Grinding

• O&ten used to clean a contaminated tungsten orto point the end

• !hould have a &ine. hard stone

– A coarse grinding stone with result in moretungsten breakage

• !hould be used &or grinding tungsten onl+

– %etal particles will <uickl+ break &ree when the arcis started. causing contamination



1igure 23(= 'orrect wa+ o& holding a tungsten when grinding4 'ourtes+ o& Larr+ 9e&&us4



/reaking and $emelting

• Tungsten is hard but brittle

– -& struck sharpl+. it will break without bending

– Try not to do this because of $$$$$$$$

• *olding against a sharp corner and hitting resultsin a s<uare break

• A&ter breaking s<uarel+. melt back the end



'hemical 'leaning and ,ointing

• Tungsten can be cleaned and pointed using oneo& several compounds

• *eated b+ shorting it against the work

• Dipped in the compound

• When the tungsten is removed. cooled. andcleaned. the end will be tapered to a &ine point

• The chemical compound will dissolve thetungsten. allowing the contamination to &all &ree



,ointing and $emelting

• Tapered tungsten with a balled end is made b+&irst grinding or chemicall+ pointing

• The ball should be made large enough so that the

color o& the end sta+s dull red and bright red• -ncrease ball si)e b+ appl+ing more current

• !ur&ace tension pulls the molten tungsten up ontothe tapered end



1igure 23(2> %elting the tungsten end shape4



GTAW <uipment



GTA Welding <uipment“Cadillac Stick Welder

• GTA welding torches are water( or air(cooled

• Water(cooled GTA welding torch is more e&&icient

• Water(cooled torch has three hoses connecting it

to the welding machine

• 6o))le directs the shielding gas directl+ on thewelding )one

• 1lowmeter regulates the rate o& gas &low



1igure 23(?2 !chematic o& a GTA welding setup with a water(cooled torch4



T+pes o& Welding 'urrent

• D'6 concentrates about ?@8 o& its welding heaton the work

– %a7 penetration

– *igh 1re<4 – start onl+• D', concentrates about 2@8 o& its welding heat

on the work

– %a7 cleaning action

– ?@8 o& heat at tungsten – primaril+ used &or ballingtungsten &or aluminium welding

– *igh 1re<4 – start onl+



T+pes o& Welding 'urrent

• A' concentrates its heat at 3@3

– !ign wave provides &or D'$, "cleaning action#and D'!, "penetration action#

– !<uare wave technolog+ allows &or adjusting thecleaning or penetration c+cle4

– *igh 1re<4 is on 'ontinuous so there is e<ual&iring o& both sides o& sign wave4

– D' 'omponent will take place i& there is no *igh1re<4



1igure 23(?B lectrons collect under the o7ide la+er during the D', portion o& the c+cle4



1igure 23(8 !ine wave o& alternating current at C c+cle4



!hielding Gas



!hielding Gases

• !hielding gases used &or GTA welding process0

– Argon "Ar#

– *elium "*e#

– Or a mi7ture o& two or more gases



!hielding Gases "continued#

• Argon e&&ectivel+ shields welds in deep grooves in&lat positions

• *elium o&&ers the advantage o& deeperpenetration




• *ot start allows a surge o& welding current

• ,re&low is the time gas &lows to clear out air in theno))le

– !ome machines do not have pre&low• ,ost&low is the time the gas continues &lowing

a&ter the welding current has stopped




• -oni)ation ,otential

– Amount o& voltage needed to kick startE the arc• The ioni)ation potential. or ioni)ation energ+. o& a gas atom is the energ+ re<uired to strip it o& an electron4 That is

wh+ a shielding gas such as helium. with onl+ ? electrons in its outer shell. re<uires more energ+ "higher voltageparameters# &or welding4 The ioni)ation potential o& a shielding gas also establishes how easil+ an arc will initiate and

stabili)e4 A low ioni)ation potential means the arc will start relativel+ eas+ and stabili)e <uite well4 A high ioni)ationpotential has di&&icult+ initiating and ma+ have di&&icult+ keeping the arc stable4

• Argon

– 234F electron volts

• *elium – ?>4> electron volts

– %ore penetration



1igure 23(83 Too steep an angle between the torch and work ma+ draw in air4



$emote 'ontrols1oot or 1inger



$emote 'ontrols

• 'an be used to0

– !tart the weld

– -ncrease the current

– Decrease the current – !top the weld

• $emote can be &oot(operated or hand(operateddevice



Welding Techni<ues



Objectives

• Applications using the gas tungsten arc weldingprocess

• &&ects on the weld o& var+ing torch angles

• Wh+ and how the &iller rod is kept inside theprotective )one o& the shielding gas• *ow tungsten contamination occurs and what to

do

• 'auses o& change in welding amperage• 'orrect settings &or the minimum and ma7imum

welding current




• T+pes and si)es o& tungsten and metal• 1actors a&&ecting gas pre&low and post&low times• %inimum and ma7imum gas &low settings0

– 6o))le si)e – Tungsten si)e – Amperage setting

• 'haracteristics o& low carbon and mild steels.

stainless steel. and aluminum• %etal preparation &or GTA welding• %ake GTA welds in all positions



-ntroduction

• Gas tungsten arc is also called GTA welding• GTA welding can be used to &or nearl+ all t+pes

and thicknesses o& metal

• GTA welding is &lu7less. slagless. and smokeless• Welders have &ine control o& the welding process• GTA welding is ideal &or close(tolerance welds• !ome GTA welds make the critical root pass

• GTA used when appearance is important



-ntroduction "continued#

• !etup o& GTA e<uipment a&&ects weld <ualit+ – 'harts give correct settings

• 1ield conditions a&&ect the variables in the charts

• 7periments designed to evaluate theappearance o& a weld

• A&ter welding in the lab. troubleshooting &ieldwelding problems is easier

• To make a weld is good0 to solve a weldingproblem is better



Torch Angle

• As close to perpendicular as possible• %a+ be angled (23 degrees &rom perpendicular

&or better visibilit+

• As the gas &lows out it &orms a protective )one around the weld• Too much tilt distorts protective shielding gas

)one



1igure 2C(3 1iller being remelted as the weld is continued4 'ourtes+ o& Larr+ 9e&&us4



Torch Angle "continued#

• elocit+ o& shielding gas a&&ects protective )one• Low(pressure area develops behind the cup

when velocit+ increases

• !harper angle and higher &low rate increasescontamination



1iller $od %anipulation

• 1iller rod must be kept inside the protective )one• -& &iller rod is removed &rom the gas protection. it

o7idi)es rapidl+

– O7ide is added to the molten weld pool• When a weld is temporaril+ stopped. the

shielding gas must be kept &lowing



1iller $od %anipulation "continued#

• -& the rod tip becomes o7idi)ed. i& should be cuto&& be&ore restarting

• The rod should enter the shielding gas as close

to the base metal as possible• An angle less than 23 degrees prevents air &rombeing pulled in the welding )one



1igure 2C(? The hot &iller rod end is well within the protective gas envelope4 'ourtes+ o&

Larr+ 9e&&us4



1igure 2C(F Too much &iller rod angle has caused o7ides to be &ormed on the &iller rod

end4 'ourtes+ o& Larr+ 9e&&us4



Tungsten 'ontamination

• %ost &re<uent problem is tungstencontamination

• Tungsten becomes contaminated i& it touches0

– Molten weld pool – Filler metal

• !ur&ace tension pulls the contamination up ontothe hot tungsten

• 7treme heat causes some o& the metal tovapori)e and &orm a large o7ide la+er



Tungsten 'ontamination "continued#

• 'ontamination caused b+ the tungsten touchingthe molten pool or &iller metal &orms a weak weld

• The weld and tungsten must be cleaned be&ore

an+ more welding can be done• Tin+ tungsten particles will show up i& the weld is7(ra+ed

• 'ontamination can be knocked o&& <uickl+ b+&lipping the torch head

• This procedure should never be used with heav+contamination or in the &ield



1igure 2C(= 'ontaminated tungsten4 'ourtes+ o& Larr+ 9e&&us4



'urrent !etting

• Amperage on the machineHs control is the sameat the arc when0 – ,ower to the machine is e7actl+ correct

– Lead length is ver+ short – All cable connections are per&ect – Arc length is e7actl+ right – $emote current control is in the &ull on position



1igure 2C(2 %elting &irst occurring4 'ourtes+ o& Larr+ 9e&&us4



1igure 2C(2? O7ides &orming due to inade<uate gas shielding4 'ourtes+ o& Larr+ 9e&&us4



Gas 1low

• Gas pre&low and post&low times depend upon0

– Wind or dra&t speed

– Tungsten si)e used

– Amperage – 9oint design

– Welding position

–T+pe o& metal welded• %a7imum &low rates must never be e7ceeded

– Air can be sucked into the weld )one



,ractice Welds

• ,ractice welds are grouped according to theweld position and t+pe o& joint

• %ild steel is ine7pensive and re<uires the least

amount o& cleaning• With aluminum. cleanliness is a critical &actor

• Tr+ each weld with each metal to determinewhich metal will be easier to master



Low 'arbon and %ild !teels

• Low carbon and mild steel are two basic steelclassi&ications

• !mall pockets o& primar+ carbon dio7ide gas

become trapped• ,orosit+ most likel+ when not using a &iller metal

• %ost &iller metals have some allo+s. calleddeo7idi)ers



!tainless !teel

• !etup and manipulation are nearl+ the same as&or low carbon and mild steels

• %ost welds on stainless steels show e&&ects o&

contamination• %ost common problem is the bead color a&ter

the weld

• 5sing a low arc current with &aster travel speedsis important



Aluminum

• %olten aluminum weld pool has high sur&acetension

• ,reheat the base metal in thick sections

• ,reheat temperature is around 8I 1ahrenheit• 'leaning and keeping the metal clean is time

consuming

• Aluminum rapidl+ o7idi)es at weldingtemperatures



%etal ,reparation

• /ase and &iller metals must be thoroughl+cleaned

• 'ontamination will be deposited into the weld

• O7ides. oil. and dirt are the most common• 'ontaminants can be removed mechanicall+ or

chemicall+



1igure 2C(23 Aluminum &iller being correctl+ added to the molten weld pool4 'ourtes+ o&

Larr+ 9e&&us4



1igure 2C(2C 1iller rod being melted be&ore it is added to the molten pool4 'ourtes+ o&

Larr+ 9e&&us4



1igure 2C(2= !ur&acing weld4 'ourtes+ o& Larr+ 9e&&us4



1igure 2C(? stablish a molten weld pool and dip the &iller rod into it4 'ourtes+ o& Larr+

9e&&us4



1igure 2C(?2 6ote the di&&erence in the weld produced when di&&erent si)e &iller rods are

used4 'ourtes+ o& Larr+ 9e&&us4



1igure 2C(?? %ove the electrode back as the &iller rod is added4 'ourtes+ o& Larr+ 9e&&us4



1igure 2C(8> /e sure both the top and bottom pieces are melted4 'ourtes+ o& Larr+

9e&&us4



1igure 2C(83 O7ides &orm during tack welding4 'ourtes+ o& Larr+ 9e&&us4



1igure 2C(8C A notch indicates the root was not properl+ melted and &used4 'ourtes+ o&

Larr+ 9e&&us4



1igure 2C(8F Watch the leading edge o& the molten weld pool4 'ourtes+ o& Larr+ 9e&&us4



!ummar+

• ,ositioning +oursel& to control the electrode &illermetal and to see the joint is critical

• 7perienced welders reali)e the+ need to seeonl+ the leading edge o& the weld pool

• Good idea to graduall+ reduce +our need &orseeing 2J o& the weld pool

– -ncreasing this skill is signi&icant advantage in the&ield

• Welding in the &ield ma+ have to be done out o&

Documents

Gas Tungsten Arc Welding (GTAW)