Abstract: It’s considered that the electric potential gradient would raise, and it is apt to generate double-arc if inappropriate welding parameters are selected, all these two results are affected by three compressive effects：mechanical compression, heat compression, magnetic compression. Compared with positive polarity time, reverse polarity time in aluminum alloy variable polarity plasma arc welding (VPPAW) is easier to generate double-arc. The reasonable matching of welding current with plasma gas flow rate, orifice diameter with electrode neck-in, and the power source structure of VPPAW are the main factors that influence the double-arc of VPPA. By improving welding force configurations and controls, joining-up MOSFET tubes in main circuit of dimensional arc power supply which can be controlled with the switch of MOSFET tubes, the formation of double-arc is avoided. Furthermore, by reasonably selecting the welding parameters, the double-arc phenomenon in aluminum alloy VPPAW is solved, thus obtaining desirable welding quality.

Key words: Arc force, Arc morphology, Double-arc, Plasma arc welding