GMAW POWER SOURCE
A power source wit h a flat characteristics is almost universally used for GMAW process as it provides self adjustment and stabilisation of the arc. Also it meets the special requirements of the dip transfer welding. GMAW wire feeding units are designed to maintain the feed speed constant at a preset value irrespective of any variations in the arc behaviour. Thus, the GMAW system consists of a power source with constant voltage characteristics and wire feeder with constant feed speed. In these systems if arc length tends to change, the current varies significantly and the burn off behaviour acts in such a way as to counteract the change in arc length.
Increase in the arc length results an increase in arc voltage & the power source output current must decrease in order to meet the higher voltage demand. Since wire melting rate is dependent, the reduced current will result in reduced melting rate and since less wire is consumed and the arc length is shortened. Shortening the arc length will produce an increase in current, increased melting rate and again the arc length will return to its original value. In this way the Constant Voltage power source provides a self adjusted arc.