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GAS TUNGSTEN - ARC WELDING (TIG) , ITS PROCESS AND ADVANTAGES

This process, often called TIG (Tungsten inert gas) welding, is similar to MIG in that it uses the gases for shielding. This arc-welding process uses the intense heat of an electric arc between a non consumable tungsten electrode and the material to be wielded.

The shielding is obtained form an inert gas such as helium or argon or a mixture of the two. Argon is more widely used than helium because it is a heavier gas, producing better shielding at lower flow rate. the shielding gas displaces the air surrounding the arc and weld pool. This prevents the contamination of the weld by the oxygen and nitrogen in the air.

Filler metal may or may not be used. However, it is usually employed, except the material. When a filler metal rod is used, it is usually employed, except thin material. When a filler metal rod is used, it is usually fed manually into the weld pool. Automatic feeding of the filler wire into the TIG arc to speed up the process has now been developing.

Electrodes used in this process are made of tungsten and tungsten alloys. The tungsten electrode is used only to generate an arc. The arc does not melt the tungsten, which has a melting point of over 3300*C. The end of the welding gun where the arc is created either is made of  high-impact ceramic or is water-cooled.

The TIG process lends itself ably to the fusion welding of  aluminum and its alloys, stainless steel, magnesium alloy, nickel-base alloys, copper-base alloys, carbon steel and low alloy steel. TIG welding can also be used for the combining of dissimilar metals, hard facing and the surfacing of metals. But this process is not used as often on plate over 64 mm thick, but it is easier than MIG welding for thin plates and small parts.

The torch used in this welding method holds the electrode and directs shielding gas and welding power to the arc. Arc spot welds can also be made with a TIG torch fitted with special adapters. In this case a 3 mm electrode is often used for a total cycle time of 1/2 to 3 s depending on the alloy and its thickness.

In general, an arc power source is best for TIG welding non ferrous alloys except deoxidized copper. For ferrous alloys the dc power source with straight polarities (electrode negative) is better for gas tungsten-arc welding because it greatly reduces the volumetric loss from the tungsten electrode. For example, a TIG torch which has a rating of 250A when used with straight polarity (dcsp) must be derated to 15 to 25A when used with reversed polarity ( dcrp - electrode positive) . As little as 3 A may be used for work on very thin metals and intricate parts.


Gas Tungsten - Arc Welding (TIG)


Advantages of  TIG Welding :

1.) It produces high- quality welds in non-ferrous metals, 

2.) Practically no weld cleaning is necessary 

3.) The arc and the weld pool are clearly visible to the welder. 



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