Feasibility study on ultrasonic-assisted drilling of CFRP/Ti stacks by single-shot under dry condition

Carbon fiber reinforced plastic (CFRP) and titanium alloy (Ti) in a stacked structure have been widely applied in aerospace industry. Due to disparate mechanical and physical properties of CFRP and Ti, it is difficult to achieve high-quality holes and low tool wear, by drilling CFRP/Ti stacks by single-shot, even though this process exhibits high productivity in the industrial practice. In this study, for the first time, ultrasonic vibration was applied in drilling CFRP/Ti stacks by single-shot under dry condition, and its feasibility was evaluated. First, the separated cutting mode of ultrasonic-assisted drilling (UAD) was analyzed based on kinematics. Second, an experimental platform was set up, where several output parameters, during UAD of CFRP/Ti stacks, were monitored, including thrust force and torque, the interface temperature, hole accuracy, hole surface integrity, Ti chip morphologies, and tool wear conditions. Experimental results indicated that, compared to conventional drilling (CD), average thrust force and torque in UAD of CFRP decreased by 41.2 to 46.8% and 36.2 to 48.9%, respectively, and thrust force and torque in UAD of Ti decreased by 15.2 to 26.1% and 21.4 to 29.0%, respectively. Lower maximum CFRP/Ti interface temperature (353.4 °C vs. 468.1 °C) was achieved in UAD. Besides, both hole diameter accuracy and hole surface quality were significantly improved in UAD. Also, both narrow sectional ribbon Ti chips and separated Ti chips were observed in UAD, while serrated continuous ribbon Ti chips were obtained in CD. In addition, tool wear conditions in UAD were also significantly alleviated.