Tool wear analysis in high-frequency vibration-assisted drilling of additive manufactured Ti6Al4V alloy

Drilling of Additive Manufactured (AM) Ti6Al4V alloy parts represents a necessary operation in the prosthetics manufacturing to guarantee tight tolerances and acceptable surface finishing. However, due to the AM process, the parts are characterized by a different microstructure if compare to the wrought material of the same chemical compositions and thus a different machinability. In this research, an innovative system of high-frequency Vibration-Assisted Drilling (VAD) was implemented to investigate the tool wear and holes quality in drilling of Ti6Al4V parts fabricated through Laser Powder Bed Fusion (LPBF). AM cylindrical samples were manufactured and holes with a diameter of 1.6 mm were produced using both Conventional Drilling (CD) and VAD for which the values of frequency and amplitude were determined by analytical modelling. Tool wear was evaluated during subsequent drilling cycles and related to the hole quality. The results showed that VAD not only preserved tool life, but it also improved the overall holes quality. The reasons for these improvements were ascribed to the VAD kinematics, characterized by an interrupted cut mechanism favoring the chip removal and evacuation. In summary, the impulsive separation between the drill bit and hole surface in VAD was proved to favour the machinability of AM alloys.