Experimental study on longitudinal-torsional ultrasonic vibration drilling of carbon fiber reinforced plastics/titanium alloy stacks

Abstract Carbon fiber reinforced plastics (CFRP)/Titanium alloy (Ti) stacks are being extensively applied in the aerospace industry for excellent mechanical properties. However, their poor machinability poses great challenges to the aircraft manufacturing industry. In this study, longitudinal-torsional ultrasonic vibration drilling (LT-UVD) is innovatively introduced to improve the quality of CFRP/Ti drilling. First, the separation mode of LT-UVD was analyzed by kinematic equation. Then, an experimental platform was built based on LT-UVD vibration actuator to carry out CFRP/Ti drilling experiments. The thrust force, interface temperature, hole wall quality, hole defects, Ti chip morphologies and tool wear in conventional drilling (CD), Longitudinal ultrasonic vibration drilling (L-UVD), and LT-UVD were compared in the experiment. The experimental results show that compared with CD and L-UVD, the thrust force of CFRP in LT-UVD decreases by 20.36%-40.55% and 2.04%-14.61%, and the thrust force of Ti decreases by 19.08%-24.83% and 1.95%-9.34%. At the same time, a relatively low maximum interface temperature is achieved in LT-UVD. In addition, the hole size accuracy, surface roughness for hole inner surface, and delamination factor are improved in LT-UVD. Due to the existence of torsional vibration in LT-UVD, the cavity and fiber pull-out defects, chip breaking performance, and tool wear of CFRP are improved. Finally, it is observed by high-speed camera that the damage forms of the interface area are different when drilling CFRP/Ti stacks with different drilling sequence.