Tungsten inert gas (T.I.G.) welding
|Fig. 22-8 Tungsten inert gas welding.|
28. The most common form of tungsten inert gas welding, fig, 22-7, in use is the direct current straight polarity i.e., electrode negative pole. This is widely used and the most economical method of producing high quality welds for the range of high strength/high temperature materials used in gas turbine engines. For this class of work, high purity argon shielding gas is fed to both sides of the weld and the welding torch nozzle is fitted with a gas lens to ensure maximum efficiency for shielding gas coverage. A consumable four per cent thoriated tungsten electrode, together with a suitable non-contact method o! arc starting is used and the weld current is reduced in a controlled manner at the end of each weld to prevent the formation of finishing cracks. All welds are visually and penetrant inspected and in addition, weld associated with rotating parts i.e., compressor and/or turbine are radiologically examined to Quality Acceptance Standards. During welding operations and to aid in the control of distortion and shrinkage the use of an expanding fixture is recommended and, whenever possible, mechanised welding employed together with the pulsed arc technique is preferred. A typical T.I.G. welding operation is illustrated in fig. 22-8.