Observation of Arc and Metal Transfer Behavior according to Shielding Gas in the WAAM of Ti–6Al–4V Alloy Using the Pulsed Gas Metal Arc Process

In arc welding and wire arc additive manufacturing (WAAM) of Ti alloys, pulsed gas metal arc (GMA) processes have a higher deposition than shortcircuiting GMA mode processes, such as cold metal transfer, surface tension transfer, and controlled short-circuit processes. In this study, pulsed GMA WAAM of Ti–6Al–4V alloy was conducted under Ar, Ar50%/He50% mixed, and He shielding gases. Owing to the thermionic emission of electrons from the Ti substrate, cathode jets were emitted from the high-temperature region of the weld pool, which interfered with droplet transfer into the weld pool. The arc shape surrounding the droplet varied according to the shielding gas, and the arc was established at the bottom of the hanging droplet under the He shielding gas, which disturbed droplet detachment. Two spatter generation modes of droplet ejection from the weld pool surface and inflight droplet repelling were observed, and droplet ejection was the most frequent spatter generation mechanism. The mixed shielding gas showed the best performance in terms of arc stability, wire melting, droplet transfer, and spatter suppression. The arc, cathode, and metal transfer characteristics were elucidated in this study, and a suitable gas composition for pulsed GMA WAAM of Ti alloys was proposed.