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.