Gas Tungsten Arc Welding

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1 FUSION WELDING

Fusion welding is a joining process in which the coalescence of metals is accomplished by fusion.
The major fusion welding processes are listed below:
• Gas welding
 Oxyacetylene gas welding (OAW)
• Arc welding
 Shielded metal arc welding (SMAW)
 Gas tungsten arc welding (GTAW)
 Plasma arc welding (PAW)
 Gas metal arc welding (GMAW)
 Submerged arc welding (SAW)
 Electroslag welding (ESW)
• High-energy beam welding
 Electro beam welding (EBW)
 Laser beam welding (LBW)
1.1 Gas Tungsten Arc Welding (GTAW)
1.1.1 Description of the Process
GTAW consists of an AC/DC arc burning between a non-consumable electrode and the work piece to melt the joint area. The area of the arc is enveloped in a protective gas shield which protects the weld pool and electrode from contamination while allowing a stable arc to be maintained. The filler wire is added either by hand, or in the mechanized process, by feed rollers attached to the torch.


1.1.2 Application
Common applications consists of high quality welding on stainless steels; aluminium and its alloys; copper; nickel alloys and rare materials such as titanium and zirconium. Mild steels are welded when full penetration welds are required within certain tolerances, both in size and x-ray quality. Used widely in the aerospace, chemical and nuclear industries.
1.1.3 Electrical Conditions
DC (direct current) - most normally used for GTAW welding of stainless steels and heat resisting steels, mild and low alloy steels, copper, nickel alloys, lead, silver, titanium and other metals that do not contain aluminium, magnesium or their alloys. The electrode must be connected to the negative terminal, where one third of the heat is generated. Two thirds of the heat of the arc is generated at the positive pole. A tungsten electrode connected to the positive pole would overheat and melt causing...