GAS METAL ARC WELDING-PRINCIPLE OF OPERATIONGas Metal Arc Welding (GMAW) is one of the arc welding processes in which an electric arc is formed and maintained between a continuously fed filler metal electrode wire and the weld pool. In the arc heat, the electrode wire is melted and the molten metal (droplets) is transferred across the arc into the weld pool. The arc and the weld pool is shielded from the atmospheric contamination by an externally supplied shielding gas. The shielding gas can be Argon, CO2 or Argon + CO2 gas mixture depending on the type of base metal being welded. Generally for welding of non ferrous metals argon is used as the shield gas and then the process is called as Metal Inert Gas (MIG) welding.
For welding of ferrous metals, CO2 or Argon + CO2 gas mixture is used and then the process is called as Metal Active Gas (MAG) welding. The process is found to provide a stable arc and good process control when a direct current (DC) power source is employed with electrode positive (DCEP) polarity. The DCEP provides stable arc, greater heat input to the cathodic base metal for good penetration and a fluid weld pool. Equipment required for GMAW is shown. The system comprises of a DC power source with flat characteristics, wire feed unit, welding gun, cable assembly and gas cylinder. The wire electrode is fed continuously into the arc by the wire feed unit at a speed preset by the operator. The wire feed rate can be varied generally from 1 m / min. to 20 m / min. For a given wire material and diameter, the arc current is determined by the wire feed rate. The required voltage is selected by adjusting the voltage control knobs provided at the power source.