During the early years of the tungsten inert-gas and metallic inert-gas processes the main effort was aimed at gaining basic knowledge of the arc and its uses. Emphasis was placed on the development of apparatus, shielding gases, filler wires and welding conditions. As these processes grew from their basic forms the troubles which arose were associated with these same factors. Due to a lack of knowledge of the effect of power supply response on the arc, power supplies designed for welding with covered electrodes were originally used for the TIG and MIG processes.

As knowledge was gained in these new fields of welding, it became obvious that the power supply could also have a marked effect on the results. In the last decade interest in, and knowledge of, power supply characteristics has grown rapidly. The problems were not as complex in the case of TIG welding and as a result satisfactory power supplies have now been developed. In the case of MIG welding, however, the problem is more complex. Power supplies for this process are still under development. This report is aimed at the MIG power supply although some reference is made to the TIG power supply in the earlier parts of the report.