Mechanisms of machining and damage suppression in thermoset carbon fiber composites via robotic ultrasonic-assisted drilling

This study investigates machining mechanisms and damage suppression in robotic ultrasonic-assisted drilling (RUAM) of thermoset CFRP. A novel non-contact integrated ultrasonic spindle (IUS) was developed to overcome robotic structural instability and abrasive tool wear. A 100-hole drilling campaign was conducted to evaluate the temporal evolution of machining quality. Experimental results reveal a significant shift in parameter dominance as tool wear progresses. Initially, with a fresh tool, ultrasonic amplitude is the statistically most significant factor (60.94% contribution to data variance), supporting the hypothesis that it promotes localized fiber shearing. However, as cutting-edge rounding (CER) increases, the removal mechanism transitions from a shearing-dominated to a ploughing-dominated regime, where feed rate becomes the most critical factor (36.65% contribution) in late-stage machining. Comparative analysis demonstrates that the optimized RUAM system achieves an 11.3% reduction in the delamination factor ( F d ) and a 21% decrease in CER progression compared to conventional drilling. This research establishes a wear-adaptive framework for high-precision robotic manufacturing of aerospace-grade composite components, effectively overcoming the limitations of conventional robotic machining through hardware innovation and mechanistic optimization.