Mechanisms of Hole Quality Improvement in Ultrasonic‐Assisted Drilling of Carbon Fiber Reinforced Polyetherketoneketone Composites

ABSTRACT Carbon fiber‐reinforced polyetherketoneketone (CF/PEKK) thermoplastic composites are prone to hole‐wall roughening, diameter fluctuation, and exit damage during precision drilling. This study evaluates the effectiveness of ultrasonic vibration‐assisted drilling (UVAD) in improving drilled‐hole quality and establishes an integrated characterization framework for hole‐wall surface integrity, diameter stability, and CT‐detectable damage around the hole. Three‐dimensional areal roughness measurement, slice‐by‐slice equivalent diameter (EqDiameter) reconstruction using industrial computed tomography (CT), a CT‐apparent volumetric damage factor, and correlation analysis were combined to compare the hole quality obtained by conventional drilling (CD) and UVAD. The results show that, compared with CD, UVAD reduced the average hole‐wall Sa and Sq values by approximately 25.2% and 21.4%, respectively, across all drilling conditions. The average absolute diameter deviation, |Δ D |, decreased from 0.036 to 0.028 mm, while the mean standard deviation and range of the slice‐by‐slice EqDiameter were reduced by approximately 55.4% and 60.6%, respectively. In addition, CT‐detectable damage around the hole in the exit region was reduced under UVAD. Hole‐wall roughness, diameter deviation, and the CT‐apparent volumetric damage factor showed strong associations with the average thrust force. These findings provide experimental support for low‐damage precision drilling, diameter stability control, and damage evaluation around drilled holes in CF/PEKK thermoplastic composites.