Study on arc behavior and droplet transfer in twin-electrode TIG-MIG indirect arc welding

A twin-electrode TIG-MIG (T-TIG-MIG) indirect arc welding method was proposed in this paper. The arc behavior and droplet transfer process were preliminarily investigated; moreover, the process stability was assessed, and bead-on-plate welding was conducted. Results showed T-TIG-MIG indirect arc burnt between a wire and two tungsten electrodes and was essentially formed by the coupling of two single-electrode TIG-MIG indirect arcs. The wire feeding speed (WFS) determined the equilibrium position of the wire end, and the vicinity of the tungsten tips was an ideal position for arc shape and droplet detachment, where the arc was more concentrated with a higher coupling degree. With the increase of the welding current, the arc length and stiffness increased gradually; so did the process stability and the spreadability of the weld bead. When the current exceeded the critical current, the droplet transfer mode changed into streaming spray transfer, since the electromagnetic force and the arc pressure increased considerably. Compared to conventional cold-wire T-TIG welding under the same current, the wire deposition rate of T-TIG-MIG indirect arc welding increased by about 186%, while the range of the heat-affected zone reduced by about 41%.