Laser stabilisation of arc cathode spots in titanium welding

Abstract

Cathode spot formation is very pronounced during arc welding of titanium and titanium alloys. The dynamic behaviour of these spots was observed to interfere with metal transfer during welding, this interference being a fundamental cause of poor weld quality in these alloys. In the present work, stabilisation of the arc cathode spot with a focused Nd–YAG laser beam during pulsed gas metal arc welding of titanium was investigated. The laser beam was focused near the leading edge of the weld pool and the laser power and focus spot size were varied to determine the values required to confine the cathode spot to the laser focus position. The results showed that, for fixed welding conditions, the laser power required to prevent cathode spot motion varied as a function of focus spot size. The required laser power was minimised at 200 W for a spot size of 0.6 mm. The laser stabilised arcs had lower voltage but approximately the same current density as stabilised arcs. Increased welding speeds required marginally higher laser powers to stabilise the spot, but the minimum power was still attained with a 0.6 mm focus spot diameter. The laser power density required for stabilisation decreased as spot size was increased, varying from almost 10⁶ W cm^?2 at the smallest spot size to approximately 10⁴ W cm^?2 at the largest. Cathode spot stabilisation improved weld quality by reducing spatter generation and weld bead irregularity.