Effect of plasma main arc on droplet transfer in skew-coupling arc welding

摘要

A method of controlling droplet transfer by plasma arc was proposed to solve the problem that cathode spot force hindered the transition of cathode droplet under high current of twin-wire indirect arc (TWIA) in skew-coupling arc (SCA) welding. The effects of the plasma arc on droplet transfer were analyzed from the perspectives of plasma arc current (PAC) and plasma gas flow rate (PGFR). The current-voltage waveform, arc shape and the transition process of droplet were studied by using an electric signal and high-speed camera acquisition system. The results show that controlling droplet transfer by the plasma arc is feasible and effective in the SCA welding. With the increase of the PAC, the degree of the plasma arc deflection increased, and increasing the PGFR has a shrinkage effect on the top of the SCA. Increasing the PAC or the PGFR made the TWIA current vary in a small range, and the plasma arc voltage increase. Increasing the PGFR is more effective to promote the transition of cathode droplet than increasing the PAC, because the plasma fluid force of the TWIA on cathode droplet is enhanced by the double axial thrust of the plasma arc and the TWIA. The cooling effect of the plasma gas on anode droplet weakens the promoting effect of the plasma gas on the transition of anode droplet. The existence of the fluid beam hanging at the cathode wire is important to improve the transition of cathode droplet. The PGFR and the PAC could be cooperatively adjusted to promote the transition process of anode and cathode droplet.