Gas tungsten arc welding

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TIG welding of a bronze sculpture





Russel Meredith of Northrop Aircraft perfected the process in 1941.[7] Meredith named the process Heliarc because it used a tungsten electrode arc and helium as a shielding gas, but it is often referred to as tungsten inert gas welding (TIG); in parts of the world where tungsten is called wolfram, it is known as WIG. The official American Welding Society term is gas tungsten arc welding (GTAW). Linde Air Products, a Division of Union Carbide Corporation, purchased US patent 2,274,631 and name from Northrup and developed the process. Linde, along with others, developed a wide range of air-cooled and water-cooled torches, gas lenses to improve shielding and other accessories that increased the use of the process. Initially, the electrode overheated quickly and, despite tungsten's high melting temperature, particles of tungsten were transferred to the weld.[6] To address this problem, the polarity of the electrode was changed from positive to negative, but the change made it unsuitable for welding many non-ferrous materials. Finally, the development of alternating current units made it possible to stabilize the arc and produce high quality aluminum and magnesium welds.[6][8]

Developments continued during the following decades. Linde Air Products developed water-cooled torches that helped to prevent overheating when welding with high currents.[9] Additionally, during the 1950s, as the process continued to gain popularity, some users turned to carbon dioxide as an alternative to the more expensive welding atmospheres consisting of argon and helium. However, this proved unacceptable for welding aluminum and magnesium because it reduced weld quality, so it is rarely used with GTAW today.[10] The use of any shielding gas containing an oxygen compound, such as carbon dioxide, quickly contaminates the tungsten electrode and should not be used with the TIG process.



GTAW weld area

Manual gas tungsten arc welding is often considered the most difficult of all the welding processes commonly used in industry. Because the welder must maintain a short arc length, great care and skill are required to prevent contact between the electrode and the workpiece. Similar to torch welding, GTAW normally requires two hands, since most applications require that the welder manually feed a filler metal into the weld area with one hand while manipulating the welding torch in the other. However, some welds combining thin materials (known as autogenous or fusion welds) can be accomplished without filler metal; most notably edge, corner, and butt joints.

To strike the welding arc, a high frequency generator (similar to a Tesla coil) provides an electric spark. This spark is a conductive path for the welding current through the shielding gas and allows the arc to be initiated while the electrode and the workpiece are separated, typically about 1.5–3 mm (0.06–0.12 in) apart. The electric arc produced can reach temperatures of at least 5000 °C. This high voltage, high frequency burst can be damaging to some vehicle electrical systems and electronics, because induced voltages on vehicle wiring can also cause small conductive sparks in the vehicle wiring or within semiconductor packaging. Vehicle 12V power may conduct across these ionized paths, driven by the high-current 12V vehicle battery. These currents can be sufficiently destructive as to disable the vehicle; thus the warning to disconnect the vehicle battery power from both +12 and ground before using welding equipment on vehicles.

An alternate way to initiate the arc is the "scratch start". Scratching the electrode against the work with the power on also serves to strike an arc, in the same way as SMAW ("stick") arc welding. However, scratch starting can cause contamination of the weld and electrode. Some GTAW equipment is capable of a mode called "touch start" or "lift arc"; here the equipment reduces the voltage on the electrode to only a few volts, with a current limit of one or two amps (well below the limit that causes metal to transfer and contamination of the weld or electrode). When the GTAW equipment detects that the electrode has left the surface and a spark is present, it immediately (within microseconds) increases power, converting the spark to a full arc.


Welders often develop a technique of rapidly alternating between moving the torch forward (to advance the weld pool) and adding filler metal. The filler rod is withdrawn from the weld pool each time the electrode advances, but it is never removed from the gas shield to prevent oxidation of its surface and contamination of the weld. Filler rods composed of metals with low melting temperature, such as aluminum, require that the operator maintain some distance from the arc while staying inside the gas shield. If held too close to the arc, the filler rod can melt before it makes contact with the weld puddle. As the weld nears completion, the arc current is often gradually reduced to allow the weld crater to solidify and prevent the formation of crater cracks at the end of the weld.[13][14]


Like other arc welding processes, GTAW can be dangerous if proper precautions are not taken. Welders wear protective clothing, including light and thin leather gloves and protective long sleeve shirts with high neck collars, to avoid exposure to strong ultraviolet light. Due to the absence of smoke in GTAW, the electric arc light is not covered by fumes and particulate matter as in stick welding or shielded metal arc welding, and thus is a great deal brighter. making operators especially susceptible to the effects of strong ultraviolet light exposure. The welding arc has a different range and strength of UV light wavelengths to sunlight - however the welder is very close to the source and the light intensity is very strong. The arc light damage include accidental flashes to the eye or arc eye and skin damage similar to strong sunburn. Opaque full face and neck Helmets with dark eye lenses are worn to prevent this exposure to ultraviolet light, and in recent years, new helmets often feature a liquid crystal-type face plate that self-darkens upon exposure to the bright light of the struck arc. Transparent welding curtains, made of a polyvinyl chloride plastic film, are often used to shield nearby workers and bystanders from exposure to the UV light from the electric arc.[15]





GTAW fillet weld



If the amount of current used exceeds the capability of the electrode, tungsten inclusions in the weld may result. Known as tungsten spitting, it can be identified with radiography and prevented by changing the type of electrode or increasing the electrode diameter. In addition, if the electrode is not well protected by the gas shield or the operator accidentally allows it to contact the molten metal, it can become dirty or contaminated. This often causes the welding arc to become unstable, requiring that electrode be ground with a diamond abrasive to remove the impurity.[19]


GTAW torch with various electrodes, cups, collets and gas diffusers
GTAW torch, disassembled


Welding torch[edit]




Power supply[edit]


GTAW power supply




WP Green EWP Green None
WC20 Gray EWCe-2 Orange ~2% CeO2
WL10 Black EWLa-1 Black ~1% La2O3
WL15 Gold EWLa-1.5 Gold ~1.5% La2O3
WL20 Sky-blue EWLa-2 Blue ~2% La2O3
WT10 Yellow EWTh-1 Yellow ~1% ThO2
WT20 Red EWTh-2 Red ~2% ThO2
WT30 Violet ~3% ThO2
WT40 Orange ~4% ThO2
WY20 Blue ~2% Y2O3
WZ3 Brown EWZr-1 Brown ~0.3% ZrO2
WZ8 White ~0.8% ZrO2



  • Cerium oxide (or ceria) as an alloying element improves arc stability and ease of starting while decreasing burn-off. Cerium addition is not as effective as thorium but works well,[25] and cerium is not radioactive.
  • Using an alloy of lanthanum oxide (or lanthana) has a similar effect. Addition of 1% lanthanum has the same effect as 2% of cerium.
  • Electrodes containing zirconium oxide (or zirconia) increase the current capacity while improving arc stability and starting and increasing electrode life. Zirconium-tungsten electrodes melt easier than thorium-tungsten.
  • In addition, electrode manufacturers may create alternative tungsten alloys with specified metal additions, and these are designated with the classification EWG under the AWS system.


Shielding gas[edit]

GTAW system setup






Aluminum and magnesium[edit]

A TIG weld showing an accentuated AC etched zone
Closeup view of an aluminium TIG weld AC etch zone

Aluminum and magnesium are most often welded using alternating current, but the use of direct current is also possible, depending on the properties desired. Before welding, the work area should be cleaned and may be preheated to 175 to 200 °C (347 to 392 °F) for aluminum or to a maximum of 150 °C (302 °F) for thick magnesium workpieces to improve penetration and increase travel speed.[30] AC current can provide a self-cleaning effect, removing the thin, refractory aluminium oxide (sapphire) layer that forms on aluminium metal within minutes of exposure to air. This oxide layer must be removed for welding to occur.[30] When alternating current is used, pure tungsten electrodes or zirconiated tungsten electrodes are preferred over thoriated electrodes, as the latter are more likely to "spit" electrode particles across the welding arc into the weld. Blunt electrode tips are preferred, and pure argon shielding gas should be employed for thin workpieces. Introducing helium allows for greater penetration in thicker workpieces, but can make arc starting difficult.[30]




Dissimilar metals[edit]



Welding Parameters[edit]

Regardless of the technology, efficiency or variability, these are the list of parameters that affect the quality and outcome of the weld. When these parameters are improperly configured or out of range for the equipment or materials, this can lead to a variety of problems.


Too much current can lead to splatter and workpiece damage. In thin materials, it can lead to a widening of the material gap. Too little current can lead to sticking of the filler wire. This can also lead to heat damage and a much larger weld affected area, as high temperatures must be applied for much longer periods of time to deposit the same amount of filling materials. Current limiting helps prevent splatter when the tungsten tip accidentally comes too close or in contact with the workpiece. Fixed current mode varies the voltage to maintain a constant arc current.

Welding Voltage[edit]

This can be fixed or adjustable depending on the equipment. Some metals require a specific voltage range to be able to work

A high initial voltage allows for easy arc initiation and allows for a greater range of working tip distance. Too large a voltage, however, can lead to greater variability in workpiece quality (depending on the workpiece distance and a greater variation in power and heat delivered to the workarea).

Pulsed-current, frequency & waveform[edit]

In the pulsed-current mode, the welding current rapidly alternates between two levels. The higher current state is known as the pulse current, while the lower current level is called the background current. During the period of pulse current, the weld area is heated and fusion occurs. Upon dropping to the background current, the weld area is allowed to cool and solidify. Pulsed-current has a number of advantages, including lower heat input and consequently a reduction in distortion and warpage in thin workpieces. In addition, it allows for greater control of the weld pool, and can increase weld penetration, welding speed, and quality. A similar method, 'manual programmed' allows the operator to program a specific rate and magnitude of current variations, making it useful for specialized applications.[33]

Gas Flow and Composition[edit]

Various welding or shielding gasses are available including mixtures of argon, carbon dioxide, oxygen, nitrogen, helium, hydrogen, nitric oxide, sulfur hexafluoride and dichlorodifluoromethane. The choice of gas is specific to the working metals and affects the production costs, electrode life, weld temperature, arc stability, welder control complexity, molten weld fluidity, weld speed, splatter. Most importantly it also affects the finished weld penetration depth and subsurface profile, surface profile, composition, porosity, corrosion resistance, strength, ductility, hardness and brittleness.

Welding techniques[edit]



Lay Wire[edit]

Another method of adding filler rod is instead of dabbing, to rest the filler rod next to the puddle, and melt it down with the TIG torch. This method is typically high deposition and in some cases, can have an advantage over dabbing. One case where it is superior over dabbing is on thin metal (16 gauge / 1.6 mm). You can move faster by working the puddle therefore it helps with burn through.

Vacuum welding[edit]

For industrial applications, superior results can be achieved by eliminating the effects of absorbed gasses at the weld. This can lead to reduced oxidation, reduced workpiece heat carried by convection and stronger materials due to dissolved or reacted gases such as oxygen, nitrogen and hydrogen.


  3. ^ a b Anders, A. (2003). "Tracking down the origin of arc plasma science-II. early continuous discharges". IEEE Transactions on Plasma Science 31 (5): 1060–9. doi:10.1109/TPS.2003.815477. 
  7. ^ Russel Meredith US Patent Number 2,274,631
  8. ^ Advanced Automotive Welding by Jerry Uttrachi Published by CarTech 2012, p. 32.
  9. ^ Cary & Helzer 2005, p. 8
  10. ^ a b Lincoln Electric 1994, pp. 1.1–8
  11. ^ Cary & Helzer 2005, p. 75
  12. ^ Lincoln Electric 1994, pp. 5.4-7–5.4-8
  13. ^ Jeffus 2002, p. 378
  14. ^ Lincoln Electric 1994, pp. 9.4–7
  15. ^ a b Cary & Helzer 2005, pp. 42, 75
  16. ^ Cary & Helzer 2005, p. 77
  17. ^ Watkins and Mizia, 424–426
  18. ^ Minnick 1996, pp. 120–21
  19. ^ a b c Cary & Helzer 2005, pp. 74–75
  20. ^ a b c Cary & Helzer 2005, pp. 71–72
  21. ^ Cary & Helzer 2005, p. 71
  23. ^ ISO 6848; AWS A5.12. The information in AWS A5.12 can be found at
  24. ^ Jeffus 1997, p. 332
  26. ^ Cary & Helzer 2005, pp. 72–73
  27. ^ Minnick 1996, pp. 71–73
  28. ^ Jeffus 2002, p. 361
  29. ^ Weman 2003, p. 31
  30. ^ a b c d e Minnick 1996, pp. 135–149
  31. ^ a b Minnick 1996, pp. 156–169
  32. ^ a b c Minnick 1996, pp. 197–206
  33. ^ Cary & Helzer 2005, pp. 75–76
  34. ^ Cary & Helzer 2005, pp. 76–77


External links[edit]