Effect of cold metal transfer mode on the microstructure and machinability of Ti–6Al–4V alloy fabricated by wire and arc additive manufacturing in ultra-precision machining

The effect of cold metal transfer (CMT) mode on ultra-precision machining (UPM) was investigated to explore phase transformation and potential improvements of surface integrity for a wire and arc additive manufactured (WAAMed)Ti–6Al–4V alloy part. Both CMT and CMT + Pulse (CMT + P) modes are taken into account, which is proved to be the stable methods to fabricate Ti–6Al–4V components. The calculation result shows that the heat input of the CMT + P mode is higher than that of the CMT mode. In the reheated conditions of the CMT + P mode, the α′ → α+β phase transformation occurs, which leads to a decrease in the number of acicular α′ martensite phases decreased and an increase in the size of the lamellar α+β phases. The UPM results showed that the cutting force increase with the cutting speed increases. In addition, the cutting force of the specimens fabricated in CMT mode is a little larger than that in CMT + P mode due to the higher strength and more α′ martensite phases. UPM can create a better surface finish with a reduction of surface roughness up to ∼90%. Moreover, the machine surface quality of the specimens in CMT mode is much better with the surface roughness of ∼0.1  μm at a low cutting speed.