中文摘要：

变极性等离子弧（Variable polarity plasma arc，VPPA）焊接在厚板铝合金焊接中具有独特的优势。维弧及其维弧电源对变极性等离子电弧形态、力学特性和电弧静特性等有重要影响。通过高速摄像、压力传感器和基于工控机的信号检测系统，分析了维弧对变极性等离子电弧形态、电弧力和焊接工艺的影响规律。发现在变极性等离子弧反极性期间由于维弧电源的分流作用，电弧力下降，并易造成双弧和降低电弧电压等现象。试验结果对变极性等离子弧焊接工艺稳定性及其焊接过程控制有重要的理论指导意义。

英文摘要：

Variable polarity plasma arc （VPPA） welding has shown its unique advantages in the welding of thick aluminum alloy plate. Pilot arc and its power source have great influences on arc shape, mechanical properties and static characteristic of arc in variable polarity plasma arc. By means of high-speed photograph, pressure sensor and signal detection system based on industrial computer, the rule of influences of pilot arc on arc shape, arc force and welding process are systematically analyzed. It is found that during the reversed polarity period of VPPA, the arc force is decreasing due to the shunting action of power source of pilot arc, which can easily cause such phenomena as double arc and decrease of arc voltage. The experimental results have important theoretical guiding significance to the stability of plasma welding process and to the welding process control.