Introduction In
Gas Metal Arc Welding (GMAW), also known as Metal Inert Gas (MIG) welding, an
electric arc is established
between the workpiece and a consumable bare wire electrode. The arc continuously
melts the wire
as it is fed to the weld puddle. The weld metal is shielded from the atmosphere
by a flow of an inert gas,
or gas mixture. Figure 1-1 shows
this process and a portion of the welding torch. The
mig welding process operates on D.C. (direct current) usually with the wire electrode
positive. This is known
as ”reverse” polarity. ”Straight” polarity, is seldom used
because of poor transfer of molten metal from the
wire electrode to the workpiece. Welding currents of from 50 amperes up to more
than 600 amperes are commonly
used at welding voltages of 15V to 32V. A stable, self correcting arc is obtained
by using the constant
potential (voltage) power system and a constant wire feed speed.
Continuing developments have made the
mig process applicable to the welding of all commercially
important metals such as steel, aluminum,
stainless steel, copper and several others. Materials above .030
in. (.76 mm) thick can be welded in
all positions, including flat, vertical and overhead. It
is simple to choose the equipment, wire electrode, shielding gas, and welding
conditions capable of producing
high-quality welds at a low cost. Basic
Mig Welding Process
1
