Influence of longitudinal-torsional ultrasonic-assisted vibration on micro-hole drilling Ti-6Al-4V

As Ti-6Al-4V is a typical hard to machine material, especially in micro drilling aviation parts, chip breaking difficulty is of increasing interest to explore its further development. In this study, Longitudinal-Torsional Ultrasonic Assisted Drilling (LTUAD) was employed to machine Ti-6Al-4V, and its feasibility was evaluated by comparing with Conventional Drilling (CD). By combining periodical characteristics and vibration models (the separated or the unseparated ultrasonic elliptical vibration), the influence of ultrasonic frequency on the intersection characteristics of trajectories were analyzed. And the intersection characteristics were divided into four categories: even periodicity, odd periodicity, non-odd and even periodicity and composite periodicity, indicating different capability for chip breaking. By applying the longitudinal-torsional compound vibration horn, the micro-hole drilling experiment was carried out on machining center. The chip morphology, the thrust force, and the burr height were discussed. Experimental results showed that the morphology of chips presented as smaller and more fragmentary ones in LTUAD compared with continuous helical conical ones and fold-shaped ones in CD. Compared with CD, the average values of the thrust force in LTUAD reduced by 1.98% to 24.9%. According to the burr around the hole exit in both LTUAD and CD, the height of the latter was greatly affected by the drilling parameters. And the burr around the exit of the hole were distributed rather evenly with smaller extension in LTUAD. Consequently, the LTUAD employed in micro-hole drilling was effective.