What is the difference in AC welding machine and DC welding machine?

Alternating current flows from the welder through the torch into your welder, through the grounding cable, and back into your machine. It then flows in the exact opposite direction. The result is deep penetration, and removal of impurities in the weld. It is used mainly on aluminum and alloys. Direct current has both a positive and negative setting: the difference is the direction of the current. One flows from the welder, through the torch, through the material and back into the ground; the other flows in the opposite direction.