Femtosecond Laser Drilling of Cylindrical Holes for Carbon Fiber-Reinforced Polymer (CFRP) Composites

TLDR

Ultrafast laser drilling reduces the heat‑affected zone in CFRP, yet most work has focused on picosecond lasers and the large cross‑sectional taper remains a challenge, so the effects of femtosecond parameters are largely unexplored. This study applies femtosecond laser technology to produce cylindrical holes in carbon‑fiber‑reinforced polymer composites. By varying laser power, rotational speed, and spiral passes, the authors compared circular and spiral drilling modes, analyzing how laser energy and feed depth influence ablation depth, hole diameter, and taper. The optimized femtosecond spiral drilling produced cylindrical holes with a depth‑to‑diameter ratio of about 3:1, taper less than 0.32°, and a heat‑affected zone below 10 mm.

Abstract

Ultrafast laser drilling has been proven to effectively reduce the heat-affected zone (HAZ) of carbon fiber-reinforced polymer (CFRP) composites. However, previous research mainly focused on the effects of picosecond laser parameters on CFRP drilling. Compared with a picosecond laser, a femtosecond laser can achieve higher quality CFRP drilling due to its smaller pulse width, but there are few studies on the effects of femtosecond laser parameters on CFRP drilling. Moreover, the cross-sectional taper of CFRP produced by laser drilling is very large. This paper introduces the use of the femtosecond laser to drill cylindrical holes in CFRP. The effect of laser power, rotational speed of the laser, and number of spiral passes on HAZ and ablation depth in circular laser drilling and spiral laser drilling mode was studied, respectively. It also analyzed the forming process of the drilling depth in the spiral drilling mode and studied the influence of laser energy and drilling feed depth on the holes’ diameters and the taper. The experimental results show that the cylindrical hole of CFRP with a depth-to-diameter ratio of about 3:1 (taper < 0.32∘, HAZ < 10 m) was obtained by using femtosecond laser and a spiral drilling apparatus.