Damage-free processing of carbon-carbon composites based on ultrafast laser and rotational optics

High-precision processing of fiber reinforced composites is one of the important methods to expand its application range. This study focuses on solving the problems of interlayer cracking and fiber tear in the traditional processing of carbon fiber composites. The combination of ultrafast laser and rotating optical system enables flexible control of scanning turns and radius, and achieves high-precision and damage-free processing of materials through ring cutting drilling technology. Based on the response surface methodology, the micro-hole processing parameters are optimized using the measurement results of the ablation threshold, finally the variation law of the geometric dimensions of the micro-hole inlet and outlet is obtained. The laser defocus amount has the greatest effect on the dimensions of the micro-hole inlet, while the single-layer feed amount will have a greater effect on the micro-hole outlet. In addition, the ring cutting drilling method can effectively eliminate defects such as fiber pullout, severe ablation at the end of the fiber and ablation product accumulation. For the vertical surface of the micro-hole sidewall, the roughness can be reduced to Rq 0.6 μm, the fiber and the matrix are removed synchronously. The roughness of the parallel surface after ultrafast laser polishing is about Rq 5 μm, which is about 36 % of the initial roughness. In addition, the parallel surface and vertical surface of the composite material exhibit different states of laser-induced periodic surface structures (LIPSS).