Double rotation picosecond laser drilling of CFRP: ablation mechanism and quality prediction

Carbon fiber reinforced polymer (CFRP) is prone to thermal damage propagation and deterioration in hole quality during ultrashort pulsed laser drilling, owing to its anisotropic thermal conductivity and the disparity in thermal responses between fiber and resin phases. This study employs a picosecond laser double rotation drilling method and, for the first time, takes the rotation angle of the ablation unit as a spatial energy regulation variable, systematically investigating the effects of energy density, scanning speed, and rotation angle on the heat affected zone (HAZ) and hole taper. The results indicate that increasing the energy density enhances local heat accumulation and promotes the formation of laser-induced ablation plasma. The induced plasma shielding effect restricts laser propagation toward the hole depth direction, thereby reducing the energy coupling efficiency in the deep region. Scanning speed primarily governs pulse dwell time and thermal diffusion behavior. The rotation angle influences heat accumulation and the uniformity of material removal by altering the overlap of ablation trajectories and the layer-by-layer energy coupling along the hole depth. Machine learning models based on LightGBM are developed to achieve high-precision prediction of HAZ and hole taper, yielding the coefficient of determination (R 2 ) values of 99.5% and 99.3%, and mean absolute error (MAE) values of 13.64 μm and 0.23°, respectively. Shapley Additive Explanations (SHAP) analysis reveals that energy density dominates HAZ evolution, whereas rotation angle contributes most significantly to hole taper. These findings provide valuable guidance for process optimization and intelligent quality control in picosecond laser drilling of CFRP.