TI 809-26
5.
a. Process Principles. Gas Tungsten Arc Welding (GTAW), also frequently called TIG (Tungsten
Inert Gas) welding, is done using the heat of an arc between a non-consumable tungsten electrode and
external shielding gas or gas mixture. Direct current electrode negative (DCEN) (straight) polarity is used
to produce a deep, narrow penetration when welding thicker materials. Direct current electrode positive
metals. Alternating current (AC) is generally used for welding aluminum and magnesium alloys. A high
frequency oscillator is usually incorporated into GTAW power supplies to initiate the arc. This reduces
tungsten to the base metal. The process may be performed manually, but may also be used as
automatic. The tungsten electrode in the welding "torch" gets very hot under high duty cycles, therefore
deposition rate through the use a continuous filler metal, supplied with current from a separate power
source, to preheat the wire using resistance heating.
welding torch are classified in AWS A5.12, Specification for Tungsten and Tungsten Alloy Electrodes for
. The filler metal used, if any, is rod classified for GMAW in AWS A5.18 or
A5.28, with a designation ER at the beginning. Tungsten electrodes are summarized in Table C-17.
spatter, with excellent arc control that is very beneficial for root passes. It can be used on material
thicknesses that range from thin sheet metals up to maximum of about 10 mm (3/8 in.). However,
welding processes. Gas shielding is also critical, and wind speeds over 8 km per hour (5 mph) cause
quality and mechanical property degradation. GTAW, as an unfluxed welding process, also requires very
C-31
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