Study on the influence of tool point angle on ultrasonic vibration-assisted drilling of titanium alloy

The paper presents simulation and experiment to analyze the thrust force and cutting heat of conventional drilling (CD) and ultrasonic vibration-assisted drilling (UAD) with different tool point angles. The HAAS vertical machining center combined with ultrasonic vibrating shank has been used to study the hole quality in drilling of Ti-6Al-4V material without cooling, including surface roughness, residual stress, exit burrs, and tool wear. Stimulation results show that the thrust force and cutting heat can be greatly reduced by applying ultrasonic assistance. An increase in tool point angle will cause the thrust force and cutting heat to increase in varying degrees. On the other hand, the experimental results show that the thrust force and cutting heat are consistent with those obtained in the simulation, and the surface roughness has been reduced accompanied by change in surface topography after UAD. Moreover, the optimal parameters for the minimum surface roughness have been found by orthogonal test. It is observed that the residual compressive stress has been improved effectively in UAD and become a maximum at the tool point angle of 130 degrees in CD and UAD. According to a lot of experiments, the height of the exit burr can be also significantly reduced by UAD and reaches the minimum at the tool point angle of 130 degrees. Results show that UAD is capable of reducing tool wear greatly, and the minimum tool wear rate has been obtained when the tool point angle is 130 degrees. Besides, the rate of such tool wear generally increases if the number of the processed holes exceeds 30.