Investigation of water-assisted nanosecond Laser machining of CFRP composites for improved quality hole fabrication

Carbon fiber-reinforced plastic (CFRP) composites are widely used in the aerospace and automotive industries, where high-quality micro-holes are essential for mechanical fastening and assembly. This study investigates static-water-assisted nanosecond infrared laser trepan micro-drilling of 1 mm-thick CFRP laminates and compares its performance with conventional open-air drilling. The effects of pulse width (9, 13, and 17 ns) and scan speed (40, 50, and 60 mm/s) on hole diameter, ovality, apparent taper angle, and heat-affected zone (HAZ) are evaluated. Compared with open-air drilling, static-water assistance reduces the entry- and exit-side HAZ by approximately 92–93% and 70–78%, respectively, and decreases the mean entry and exit ovality from 8.63% to 4.68% and from 40.48% to 27.45%, respectively. Confocal and scanning electron microscopy (SEM) further reveal reduced fiber pull-out, fiber breakage, and fiber-matrix debonding under static-water conditions. However, static-water drilling also produces greater entry overcut relative to the 500 µm target diameter (mean entry diameter of 747 µm versus 602 µm in open air), a higher mean apparent taper angle (10.34° versus 8.40°), localized redeposited and thermally degraded epoxy around the hole periphery. The increased taper is attributed to the larger entry-side material removal combined with progressive attenuation and scattering of the laser beam by cavitation bubbles and ablation debris in the stagnant water as drilling proceeds through the laminate. Overall, static-water assistance substantially suppresses thermal damage and improves hole circularity, although these benefits are accompanied by reduced entry-side dimensional accuracy and increased apparent taper.