Mechanical drilling force model for longitudinal ultrasonic vibration-assisted drilling of unidirectional CFRP

Carbon fiber reinforced polymer (CFRP) drilling operation is a very important machining process in the aerospace industries. Ultrasonic vibration-assisted drilling (UVAD) has achieved some positive effects in CFRP drilling. Because of the strong correlation between the drilling force and the hole quality, it is important to predict drilling force to optimize drilling parameters for improving the machining quality and efficiency. However, the prediction of drilling force for CFRP in UVAD is still a problem. In this paper, a mechanical drilling force model for unidirectional CFRP (UD-CFRP) in longitudinal ultrasonic vibration-assisted drilling (LUVAD) is established. In particular, the cutting lip of drill is divided into several discrete elements with different dynamic cutting characteristics. The cutting forces of different discrete elements, including the indentation force, the cutting force and the ploughing force of the cutting edge, were calculated by considering the dynamic change of fiber orientation during drilling. Then they are transformed into the thrust force and torque of the drilling process. Finally, the validity of the maximum, minimum and mean of the drilling force predicted by the model is verified through LUVAD experiments of UD-CFRP. The prediction errors of maximum thrust, minimum thrust and mean thrust can reach 14.09%, 15.72% and 8.81% respectively, and the prediction errors of maximum torque, minimum torque and mean torque are 16.20%, 18.61% and 14.96% respectively, demonstrating the validity of the model for LUVAD of UD-CFRP. In addition, the hole surface morphology of UD-CFRP under different processing conditions was compared.