Surface quality and process optimization in rotary ultrasonic-assisted drilling of carbon-fiber-reinforced plastics

To address the issue of exit delamination and burr defects during the drilling of carbon-fiber-reinforced plastics (CFRPs), this study employs rotary ultrasonic-assisted drilling (RUD) technology. A three-factor, three-level drilling experiment was designed using the Box–Behnken method to analyze the morphology of drilling-induced defects. Based on response surface methodology (RSM), the influence of process parameters on exit defects was quantitatively evaluated, the interactions among process parameters were investigated, and the RUD parameters were optimized. The results indicate that delamination damage and burr defects are prone to occur at the drill exit. Increasing the spindle speed (7000 r min−1) effectively suppresses delamination, while reducing the feed rate (30 mm min−1) and using a coarse-grit tool (60 grits) significantly minimize fiber tearing and burr formation. The optimal parameter combination (7000 r min−1, 30 mm min−1, 60-grit tool), obtained through multi-objective optimization, was experimentally validated. The delamination factor and burr height coefficient were reduced to 1.047 and 0.016, respectively, consistent with the model predictions. This study provides a process strategy for high-precision drilling of CFRP that enables synergistic control of multiple defects.