Gas tungsten arc welding

Gas Tungsten Arc Welding (GTAW) is a process that produces an electric arc maintained between a non-consumable tungsten electrode and the part to be welded. The heat-affected zone, the molten metal, and the tungsten electrode are all shielded from atmospheric contamination by a blanket of inert gas fed through the GTAW torch. GTAW can also weld dissimilar metals to one another such as copper to brass and stainless steel to mild steel. Heat input in GTAW does not depend on the filler material rate.

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Gas tungsten arc welding process:   

This process is also known as tungsten inert gas (TIG), although small amounts of non-inert gases may be used in the shielding mixture, such as hydrogen or nitrogen.

  • Autogenous GTAW welding (without filler metal) is used in thin square edged sections (2mm), while V and X type edge preparations are needed in thicker sections.
  • In this case, the addition of filler metal is necessary. This process is extensively used for welding thin components of stainless steel, aluminum, magnesium or titanium alloys as well pieces of carbon and low alloy steels.
  • Heat input in GTAW does not depend on the filler material rate.

Power Sources:

  • Power sources for GTAW are generally of the constant current type with drooping volt-ampere static curves.
  • Light weight transistorized direct current power sources are currently used, being more stable and versatile than the old thyristor-controlled units.
  • In rectifier-inverter power sources the incoming AC current is rectified and then converted into AC current at a higher frequency than that of the mains supply, in the inverter.
  • Afterwards high voltage AC current is transformed into low voltage AC current suitable for welding.
  • The aim to increase the current frequency is to reduce the weight of the transformer and other components of the source such as inductors and capacitors.

Fig: Plot of the arc voltage vs. current voltage for GTAW power sources                                   Fig: Sketch of the inverter principle of the power sources

Effects of High Current:

EFFECT OF ARC PRESSURE ON THE WELD POOL FOR STATIONARY AND TRAVELING WELDS (A) = 0. (B) > 0, WITH WEAK RADIAL PRESSURE GRADIENT, P1. (C) > 0, WITH STRONG RADIAL PRESSURE GRADIENT, PB.