<P> To perform gas metal arc welding, the basic necessary equipment is a welding gun, a wire feed unit, a welding power supply, a welding electrode wire, and a shielding gas supply . </P> <P> The typical GMAW 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, normally made of copper and sometimes chemically treated to reduce spatter, 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 electrode to pass while maintaining electrical contact . On the way to 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 directs the shielding gas evenly into the welding zone . Inconsistent flow may not adequately protect the weld area . Larger nozzles provide greater shielding gas flow, which is useful for high current welding operations that develop a larger molten weld pool . A gas hose from the tanks of shielding gas supplies the gas to the nozzle . Sometimes, a water hose is also built into the welding gun, cooling the gun in high heat operations . </P> <P> The wire feed unit supplies the electrode 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 . Some wire feeders can reach feed rates as high as 30.5 m / min (1200 in / min), but feed rates for semiautomatic GMAW typically range from 2 to 10 m / min (75--400 in / min). </P> <P> The most common electrode holder is a semiautomatic air - cooled holder . Compressed air circulates through it to maintain moderate temperatures . It is used with lower current levels for welding lap or butt joints . The second most common type of electrode holder is semiautomatic water - cooled, where the only difference is that water takes the place of air . It uses higher current levels for welding T or corner joints . The third typical holder type is a water cooled automatic electrode holder--which is typically used with automated equipment . </P>

What is the function of wire feeder in mig mag welding