Gas Tungsten Arc Welding (GTAW)

 

Gas Tungsten Arc Welding (GTAW), also known as TIG (Tungsten Inert Gas) welding, the filler metal is supplied from a filler wire as shown in the figure below. The tungsten electrode is not used during this welding operation; a constant and stable arc gap is maintained at a consistent current level. The filler metals are similar to the metals to be welded and flux is not used. The shielding gas used in this welding process is usually argon or helium (or a mixture of these both gases). Welding with gas tungsten-arc welding may be done without using filler metals, for example, welding close-fit joints.

Depending on the metal type to weld, the power supply is either DC at 200A or AC at 500A (see below image). In general, AC is preferred for welding metals aluminium and magnesium because the cleaning action of AC removes oxides and improves weld quality. Thorium or zirconium can be used in the tungsten electrodes to improve their electron emission characteristics. The power supply ranges from 8 to 20 kW. Contamination of the tungsten electrode by the molten metal can be a significant problem, particularly in critical applications, because it can cause discontinuities in the weld. Contact of the electrode with the molten-metal pool should be avoided.

The gas tungsten arc welding process is used for various applications and metals, particularly aluminium, magnesium, titanium and refractory metals. It is highly suitable for thin metals. The cost of the inert gas makes this process more expensive than Shielded Metal-arc Welding but provides welds of very high quality and surface finish. The equipment used for the gas tungsten arc welding process is portable.

Applications of Gas Tungsten Arc Welding:

• Initially developed for welding Aluminium and Magnesium.
• The other metals are Stainless steel, High carbon steel, Copper, Monel(Ni + Cu+ Fe + Mg)), Inconel (Cu + Cr + Fe), Brass, Bronze, Silver, Molybdenum etc.
• This process is used for joining various combinations of dissimilar metals like brazing and braze welding.
• Pipework is required for high-pressure steam lines, chemical and petroleum industries.
• Welding of aircraft frame, jet engine casing, rocket motor casing.
• Accuracy welding of parts in atomic energy.
• Expansions bellows, transistors cases, instrument diagrams etc.

Advantages of Gas Tungsten Arc Welding:

• Gas Tungsten-arc welds are stronger and more ductile.
• No danger of corrosion due to no flux is used.
• No post weld cleaning because of no slag.
• A wide variety of joints can be made because no flux is used.
• There is very little or no smoke, fumes or sparks at all. This helps in making a neat and sounder weld.
• The operator can clearly observe the weld as the shielding gas is transparent.
• Fusion welds can be made in merely all commercial metals.

Limitations of Gas Tungsten Arc Welding:

• Because of inert gas, coolant and coolant pump etc., the cost of Tungsten Inert Gas welding is very high.
• The maximum thickness of the plate joined by this welding process is up to 5mm.
• An additional filler rod must be used to weld above a 5 mm thickness plate.
• Even though the tungsten electrode is not melting at a high temperature, the atoms of tungsten may get diffused from the tip of electrodes and enter the weld pool, increasing the brittleness of the weld bead.

The following welding process developed is Gas Metal Arc Welding to overcome this limitation.