A comparative investigation on surface quality of CFRP laminates between rotary drilling and rotary ultrasonic-assisted drilling

Abstract

Carbon fiber reinforced polymers (CFRP) laminates are susceptible to defects such as delamination, burrs, and tearing during drilling, which can seriously reduce component stiffness and strength. This paper aims to investigate the difference between rotary drilling (RD) and rotary ultrasonic drilling (RUD) in the surface quality of CFRP laminates. Firstly, based on the principle of energy conservation in crack propagation, the analytic models of critical drilling thrust force for RD and RUD are established. Then, the drilling thrust force and critical drilling thrust force for both processes are calculated and analyzed using full-factor experiments, and the entrance, inner wall, and exit qualities of the machined holes are evaluated. The results show that the analytic model can better predict the critical drilling thrust force, and the RUD can increase the critical drilling thrust force by up to 44.29 % when Ψ = 7000 r/min and S = 30 mm/min. Meanwhile, the RUD produces fewer defects at the entrance of the hole and more even fiber cutting on the inner wall, and RUD also significantly reduces the delamination damage at the exit, with a maximum reduction of 12.5 % when Ψ = 5000 r/min and S = 30 mm/min, and effectively suppressing the delamination and burr defects at the exit.