Tungsten arc inert gas shielded welding, EN process number 144 abbreviated to TIG, TAGS or GTAW (USA), is an arc welding process that uses a non-consumable tungsten electrode and an inert gas shield to protect the electrode, arc column and weld pool, as illustrated in Fig. 6.1. The welding arc acts as a heat source only and the welding engineer has the choice of whether or not to add a filler wire. The weld pool is easily controlled such that unbacked root passes can be made, the arc is stable at very low welding currents enabling thin components to be welded and the process produces very good quality weld metal, although highly skilled welders are required for the best results. It has a lower travel speed and lower filler metal deposition rate than MIG welding, making it less cost effective in some situations.
TIG tends to be limited to the thinner gauges of aluminium, up to perhaps 6 mm in thickness. It has a shallower penetration into the parent metal than MIG and difficulty is sometimes encountered penetrating into corners and into the root of fillet welds. Recommended weld preparations taken from BS 3019 ‘TIG Welding of Aluminium’ are given in Table 6.1.