Tungsten inert gas welding

Tungsten inert gas welding or TIG is also known as gas tungsten arc welding (GTAW) or HELIARC, a trade name of Linde.

A fixed tungsten electrode protected by a shielding gas is used to create an arc that melts the metal of the parts to be joined. As there is no continuous feed wire electrode as with MIG welding, a filler rod is dipped in the puddle of molten metal to join the two parts in a manner similar to gas welding. This allows thin strips cut from the same stock of the material to be welded to be used as filler, guaranteeing a match between the filler rod and the workpiece.

Because of its high melting point (3422 °C), the tungsten electrode is not used up by TIG welding, though to prolong its life, tungsten is usually combined with thorium, lanthanum, cerium, or zirconium oxides (1-2%). A 2% thorium dioxide alloy is the most common, but is being phased out because of its radioactivity.

Welding Aluminium

Welding aluminium is done with AC current rather than DC and pure tungsten or zirconiated tungsten tips are preferred. The electrode is generally larger than that used with steel, and is often slightly blunted as the arc tends to wander around a sharp tip when using AC. Only inert gases can be used as shielding gas with aluminum, as other gases oxidize the tungsten electrode and the base metal. The most common shielding gas is argon, which is sometimes mixed with helium to get better penetration and/or higher welding speed. A high helium content makes it harder to ignite and maintain the arc.