Research on material removal and damage suppression of CFRP/Ti stacks by longitudinal torsional ultrasonic vibration-assisted drilling

The heterogeneous nature of CFRP/Ti stacks poses a significant challenge for drilling, particularly considering their critical importance in the aerospace sector. While longitudinal torsional ultrasonic vibration-assisted drilling (LTUVD) has demonstrated significant potential to address this issue, its underlying material removal mechanism remains unclear. Moreover, systematic studies on the influence of amplitude on machining damage remain insufficient. This study adopts simulation and experiments to explore the material removal of CFRP/Ti stacks. The damage suppression mechanisms of longitudinal and torsional vibrations are elucidated from the perspectives of crack propagation and material deformation. Simulations show that LTUVD at 6 μm amplitude reduces the interface gap and Ti chip size in the CFRP-Ti stack by 63.1% and 12.6%, respectively. The CFRP entrance edge failure length of the Ti-CFRP stack decreases by 0.81 mm, and exit interlayer cracking is alleviated. The influence of amplitude on machining damage is examined experimentally. Results show that increasing amplitude from 3 μm to 6 μm reduces entrance and CFRP interface damage in the CFRP-Ti stack by 22.33% and 10.4%, respectively. CFRP interface damage in the Ti-CFRP stack decreases by 11.61%, and Ti burr height by 23.71%. CFRP hole wall roughness decreases by 22.6% and 14.52% in CFRP-Ti and Ti-CFRP stacks, respectively.