This paper introduces a new kind of variable polarity plasma arc welding (VPPAW) process in which plasma arc current of positive
and
negative half waves flows in separate paths. It can be used adequately for welding aluminum, magnesium and their alloys. Compared to the VPPAW in which plasma arc is supplied by one power source and current of positive and negative half waves shares the same path, the significant difference of this method is that the current of positive and negative half waves is supplied by two independent power sources. This method makes the current of plasma arc and pilot arc in negative half wave to flow in separate paths. This practice not only avoids the current instability caused by interference between plasma arc and pilot arc, but also makes the negative half wave current of the new method on weld
formation. It is found that positive half wave is the main factor influencing the weld formation, while negative half wave has less effect on the weld formation, and its main function is cleaning the oxide film on the work surface.