The typical MIG welding gun has a number of
key parts—a control switch, a contact tip, a power cable, a gas nozzle, an
electrode conduit and liner,
and a gas hose. The
control switch, or trigger, when pressed by the operator, initiates the wire feed,
electric power, and the shielding gas flow, causing
an electric arc to be struck. The contact tip is connected to the welding power
source through the power cable and transmits the electrical energy to the
electrode while directing it to the weld area. It must be firmly secured and
properly sized, since it must allow the passage of the electrode while
maintaining an electrical contact. Before arriving at the contact tip, the wire is
protected and guided by the electrode conduit and liner, which help prevent
buckling and maintain an uninterrupted wire feed. The gas nozzle is used to evenly
direct the shielding gas into the welding zone—if the flow is inconsistent,
it may not provide adequate protection of the weld area. Larger nozzles provide
greater shielding gas flow, which is useful for high current welding
operations,
in which the size of the molten weld pool is increased. The gas is supplied to the
nozzle through a gas hose, which is connected to the tanks of shielding
gas. Sometimes, a water hose is also built into the welding gun, cooling the gun in
high heat operations.
The wire feed unit supplies the wire to the
work, driving it through the conduit and on to the contact tip. Most models provide
the wire at a constant feed rate,
but more advanced machines can vary the feed rate in response to the arc length and
voltage. Shielding gases are necessary for gas metal arc welding
to protect the welding area from atmospheric gases, such as nitrogen and oxygen,
which can cause fusion defects.
