Visualization of cathode spot control using laser irradiation and oxide addition in wire arc additive manufacturing of titanium alloys

Arc instability is one of the most critical problems in gas-metal-arc (GMA) based wire arc additive manufacturing of titanium (Ti) alloys. It can result in a poor bead surface, surface oxidation, and spattering. In particular, the relocation of the cathode spot area is the main cause of big spatters because of the high thermal energy of the molten droplet at the molten pool surface. In this study, two cathode spot control techniques were applied using auxiliary laser heating and prelaid oxides, and the behaviors of the cathode spots and arc were visualized using high-speed photography. When the laser beam was irradiated in front of the GMA, a cathode spot was formed at the laser irradiation position, and the cathode jet did not interfere with the arc plasma and droplet transfer from the GMA. However, when the distance between the GMA and the laser irradiation position increased by more than 8 mm, multiple cathode spots were established, and spattering increased. The prelaid Ti oxide particles increased the metal deposition efficiency by establishing multiple and dispersed cathode spots rather than a concentrated cathode spot by droplet impingement. It was found that the volumetric transfer efficiencies (excluding spattering) for the laser-assisted control and Ti oxide powder were up to 99.87% and 91.2%, respectively.