In this welding process, a non-consumable electrode of tungsten is used as shown in Figure 20.37. Filler material is supplied externally if it is required. The tungsten electrode is connected at negative pole of power supply and work at positive pole of power supply. Inert gas like argon or helium is supplied through a gas nozzle to protect the molten metal pool. The current used in TIG welding is both AC and DC. Gases used as shielding gases are nitrogen for stainless steel and argon for aluminium and magnesium. Reactivity of nitrogen is very high with aluminium and magnesium at an elevated temperature. When an explosion problem does not exist, hydrogen gas may be used.
Figure 20.37 Tungsten Inert Gas Arc Welding
The TIG welding may be used as fusion welding of aluminium, magnesium, stainless steel, alloy steel, monel, inconel, brass, bronze, tungsten, silver, molybdenum, etc. To avoid the melting of the electrodes, for larger current and better thermionic emission thorium or zirconium is added to the tungsten electrode.
Advantages
- Since no flux is used, no special cleaning or slag removal is required. Most of the fluxes are corrosive in nature which prevents their use in food, drink, and some chemical industries.
- It produces smooth and sound welds with fewer spatters.
- It can be easily automated.
- Welding can be done in all positions.
Limitations
- Cost of inert gases is high.
- Due to slow speed it cannot be used for thick metal plates.
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