Experimental, modeling, and numerical simulation of ultrasonic assisted drilling of CFRP/Ti stacks

Carbon fiber reinforced polymer (CFRP) and Ti-6Al-4V alloy (Ti) stacks structures are increasingly utilized in aircraft load-bearing applications, where the quality of hole processing significantly impacts their connection performance. Conventional drilling (CD) methods for CFRP/Ti stacks often encounter challenges such as severe interface damage, high cutting forces, and excessive heat generation. This study investigates the application of ultrasonic-assisted drilling (UAD) on CFRP/Ti stacks by integrating finite element method (FEM) modeling with experimental approaches to analyze the machinability of these materials under different machining methods and parameters. A self-developed high-frequency vibration spindle was employed to process CFRP/Ti stacks using both CD and UAD techniques. The newly developed numerical model effectively elucidates the mechanical and thermal coupling involved in the machining process and the transfer behavior of temperature and stress at the laminate interface. The experimental results of cutting force, hole inlet and outlet surface morphology, inner wall condition, chips, tool wear, etc. under different machining parameters were studied and analyzed. To ensure the reliability of our findings, experimental data were validated against simulation results. The findings reveal that UAD, when optimal separation conditions are achieved, significantly reduces cutting forces and enhances the surface morphology of both the inner and outer hole surfaces. Specifically, UAD lowers cutting forces by 27.2 % and the damage coefficient (Fd) by 15.7 % compared to CD. Furthermore, the high-frequency vibration generated by UAD markedly extends tool life. The specially designed high-frequency vibration spindle successfully meets drilling requirements, thereby significantly improving the machining performance of CFRP/Ti stacks materials, and it provides a certain reference for practical industrial applications.