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TIG (tungsten inert gas) welding is a high-quality welding technique
with a low fusion rate. The arc burns between a tungsten electrode
and the workpiece; the electrode does not melt, so it acts only
as a current conductor and arc carrier.
For thin sheet metal work, TIG welding can be used without a filler
metal.For thicker items or when joining different materials, a
filler metal is used in the form of a handheld rod or a wire supplied
by a separate feed device, generally currentless.In standard TIG
welding the arc is free, but a variant known as plasma welding
uses a secondary nozzle to constrict the arc.
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The melt, the hot tungsten electrode and the molten end of the
filler metal are protected from the atmosphere by an envelope
of inert gas. Argon is generally used, although there are quality
and productivity advantages in using a mixture of either argon
and helium or argon and reduced hydrogen
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