Arc interference and a unique push-pull arc solution in alternating current plasma arc welding of aluminium alloys

This paper analyses the are interference in an a.c. combined (both the pilo t are and the plasma are exist in the welding process) plasma are welding o f aluminium alloys. This phenomenon results in an unstable welding process and weld formation. To maintain the pilot are during the period when the el ectrode is positive, a cathode region must be formed in front of the tungst en electrode tip. However, to guarantee plasma are initiation during the sa me period, this region must be the anode region. Consequently, neutralizati on of the positive and negative charge in the region in front of the tungst en electrode tip will occur. This will result in the instantaneous disappea rance of the conducting region in front of the tungsten electrode tip, whic h will cause the plasma are or pilot are or both to be instantaneously exti nguished. Are interference appears because the potential of the nozzle is u nable to adapt to that of the conducting plasma are column in the d.c. posi tive electrode mode. A unique push-pull are solution for solving the trade- off between the are interference and the reliable initiation of the a.c. pl asma are is proposed and implemented. In addition, high-quality weld format ion in the keyhole mode, which is energy efficient and avoids a double are, is achieved.