Influence of longitudinal-torsional ultrasonic vibration on drilling carbon fiber-reinforced polymer composite

Carbon fiber-reinforced polymer (CFRP) parts are prone to forming defects during machining, so their applications are limited in many fields. In recent years, longitudinal-torsional ultrasonic vibration assisted drilling (LTUVD) has been attracting increasing attention due to its broad application prospect in CFRP machining. In this paper, both theoretical analysis and experimental research was conducted to reveal the influence mechanism of longitudinal-torsional vibration on CFRP drilling process. The movement characteristics, and the forces acting on the tool of longitudinal-torsional vibration in LTUVD process were studied theoretically. The analysis shows that the unique movement mode and force state of the tool in LTUVD process can effectively reduce the mean thrust force and machining defects. LTUVD experiments were carried out to verify the theoretical analysis. The experimental results showed that the existence of longitudinal torsional vibration changes the movement mode and force state of conventional drilling (CD) and reduces the mean thrust of LTUVD by 34.7%. Under different fiber orientation angles, the unique movement and force of LTUVD change the stress state and material removal mode of CFRP during CD processing. The hole wall morphology of LTUVD was better than that of CD. The comprehensive damage factor of LTUVD was decreased by 18.83%.