The basic features of the equipment used in TIG welding are shown in figure 10-33. The major components required for TIG welding are:

(2) the welding electrode holder and the tungsten electrode

(3) the shielding gas supply and controls

(4) Several optional accessories are available, which include a foot rheostat to control the current while welding, water circulating systems to cool the electrode holders, and arc timers.

NOTE

There are ac and dc power units with built-in high frequency generators designed specifically for TIG welding.

These automatically control gas and water flow when welding begins and ends.

If the electrode holder (torch) is water-cooled, a supply of cooling water is necessary.

Electrode holders are made so that electrodes and gas nozzles can readily be changed.

Mechanized TIG welding equipment may include devices for checking and adjusting the welding torch level, equipment for work handling, provisions for initiating the arc and controlling gas and water flow, and filler metal feed mechanisms.

Advantages

Gas tungsten arc welding is the most popular method for welding aluminum stainless steels, and nickel-base alloys.

It produces top quality welds in almost all metals and alloys used by industry.

The process provides more precise control of the weld than any other arc welding process, because the arc heat and filler metal are independently controlled.

Visibility is excellent because no smoke or fumes are produced during welding, and there is no slag or spatter that must be cleaned between passes or on a completed weld.

TIG welding also has reduced distortion in the weld joint because of the concentrated heat source.

The gas tungsten arc welding process is very good for joining thin base metals because of excellent control of heat input.

As in oxyacetylene welding, the heat source and the addition of filler metal can be separately controlled.

Because the electrode is nonconsumable, the process can be used to weld by fusion alone without the addition of filler metal.

It can be used on almost all metals, but it is generally not used for the very low melting metals such as solders, or lead, tin, or zinc alloys.

It is especially useful for joining aluminum and magnesium which form refractory oxides, and also for the reactive metals like titanium and zirconium, which dissolve oxygen and nitrogen and become embrittled if exposed to air while melting.

In very critical service applications or for very expensive metals or parts, the materials should be carefully cleaned of surface dirt, grease, and oxides before welding.

Disadvantages

TIG welding is expensive because the arc travel speed and weld metal deposition rates are lower than with some other methods.

Some limitations of the gas tungsten arc process are:

(1) The process is slower than consumable electrode arc welding processes.

(2) Transfer of molten tungsten from the electrode to the weld causes contamination. The resulting tungsten inclusion is hard and brittle.

(3) Exposure of the hot filler rod to air using improper welding techniques causes weld metal contamination.

(4) Inert gases for shielding and tungsten electrode costs add to the total cost of welding compared to other processes. Argon and helium used for shielding the arc are relatively expensive.

(5) Equipment costs are greater than that for other processes, such as shielded metal arc welding, which require less precise controls.

For these reasons, the gas tungsten arc welding process is generally not commercially competitive with other processes for welding the heavier gauges of metal if they can be readily welded by the shielded metal arc, submerged arc, or gas metal arc welding processes with adequate quality.