Deposition quality and efficiency improvement method for additive manufacturing of Ti–6Al–4V using gas metal arc with CMT

In this study, the method to improve the bead quality and increase the wire-feed deposition efficiency propose in the CMT-GMA (cold metal transfer-gas metal arc) process of Ti-6Al-4 V alloy deposition. The proposed method uses He shielding gas to improve the Ti deposition quality by increasing the wettability through the effective arc energy transfer realized by suppressing the adverse effect of cathode spot on the molten pool. The cathode spot is dispersed by the high ionization energy of He shielding gas, which improves the Ti deposition quality owing to the stability, narrow tip, and broad tail of the arc, which enables a bead shape that improves the sound deposition quality. Increasing the detachment current increased the deposition rate, attributed to the electromagnetic force-induced separation in the molten bridge and increase in droplet repetition. Under a detachment current of 290 A and when using the He shielding gas, the deposition rate was 2.69 kg/h, which was 20.5 % higher than that under a detachment current of 50 A and when using Ar shielding gas. Through multilayer deposition, the deposition efficiency in single-bead multilayer deposition (1 ×5) was reduced to 30.1 % under Ar shielding gas and to 12.5 % under He shielding gas. In the case of multi-bead multilayer deposition (5 ×5), the Ar shielding gas induced cavities in the deposition structure. This result confirmed that the application of He shielding gas can help fabricate a high-density multilayer structure without interlayer defects.