Tool Wear and Surface Roughness Evaluation During Drilling and Helical Milling in Ti6Al4V Titanium Alloy

Conventional drilling operation is extensively employed for hole-making in structural assemblies made of titanium alloys. However, low thermal conductivity and work hardening behavior make it a difficult material to machine. Moreover, these properties can lead to temperature build-up and material adhesion, accelerating tool wear and failure. Also, high temperatures during drilling can alter microstructure and decrease fatigue and stress corrosion resistance. The study, therefore, investigates the utility of helical milling as an alternative for processing holes in Ti6Al4V titanium alloy. The two processes were evaluated by studying tool wear and its effect on surface roughness. Holes were processed using cutting speed and feed conditions considering parity in machining time. The twist drill and helical mill showed signs of tool wear in form of coating loss. In addition, work material adhesion at cutting edges of the two tools was observed. Moreover, helical milling displayed more serious built-up edge formation as compared to drilling process. However, severity of tool damage was significantly lower during the helical milling operation. Tool wear influenced surface roughness. Surface roughness increased as the tool wear progressed. But, magnitude of surface roughness was lower in helically milled holes than in drilled holes. Overall, initial assessment indicates helical milling as an adept process for making bores in titanium alloys.