GTAW (Gas Tungsten Arc Welding) Fundamentals
This domain tests GTAW fundamentals: polarity, tungsten selection, shielding gas, arc starting, filler addition and contamination control. Questions often compare DCEN, DCEP and AC for different metals.
Core rules
- DCEN puts the tungsten negative and concentrates heat at the work; it is used for carbon steel, stainless steel and many other metals.
- AC is used for aluminium and magnesium because the positive half-cycle gives oxide cleaning; it also needs a suitable tungsten and balance setting.
- Argon is the common shielding gas; helium mixes can increase heat for thick sections.
- Use high-frequency or lift-arc starting where available; touching the tungsten to the work contaminates it.
- Set preflow and postflow so the hot tungsten is shielded after the arc stops.
Worked example
A 3 mm aluminium sheet is to be TIG welded. Reasoning: use AC, argon shielding, a clean tungsten suitable for AC, and remove the oxide with a stainless-steel brush dedicated to aluminium. Set balance so there is enough cleaning without melting the tungsten. Add 4043 filler where the joint needs it, and maintain a short arc. If the same job were stainless steel, DCEN would be the normal choice.
Traps
Do not use DCEN for aluminium and expect oxide cleaning. Do not touch the tungsten and keep welding; grind or replace it. Do not omit postflow on stainless steel. Do not use a dirty brush or glove that contaminates the weld.