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hapter 1. Introduction
F
iller metal in the form of wire is commonly added to welds in the GTA weld-
ing process, particularly when heavy wall thicknesses are being welded. A
wire feeder is used to deliver the wire to the weld pool and a power supply (or
controller) controls the rate of wire entry. The wire may be either cold (ambi-
ent temperature) or hot. Hot wire is normally fed into the trailing edge of the
pool while cold wire is fed into the leading edge. The hot wire GTAW (TIG)
welding process differs from the cold wire process in that the filler wire is
electrically pre-heated to near melting temperature before entering the weld
pool. This prevents the wire from chilling the weld pool and allows the filler
metal to flow out across the weld puddle resulting in a smooth, attractive
weld bead. Since nearly all of the full energy of the welding arc is available for
penetration, more wire can be deposited and fill rates are significantly higher
than with cold wire. (See graph on page 2.)
The Arc Machines, Inc. Hot Wire Power Supply Model 501 has controls for
(heating wire) voltage. The standard mode of operation for
Hot-wire set-up with GTAW torch and Model 2
