An efficient high-quality cutting method for thick SiCf/SiC ceramic matrix composites using UV laser multiline layered scanning with focus increment optimization

Laser-layered scanning techniques have achieved considerable success in cutting and drilling applications. However, their effectiveness in processing SiC_f/SiC ceramic matrix composites—critical materials for next-generation aerospace thermal components—remains less than optimal. This study addresses the challenge of enhancing the quality and efficiency of cutting thick samples by being the first to highlight the crucial influence of focus increment adjustments in the laser-layered scanning process. Specifically, it examines the relationship between the predetermined laser focus drop per layer and the actual ablation depth achieved. Systematic analysis explores the impact of focus increment adjustments on both the macroscopic structural alterations during cutting and the microstructural characteristics of the cut surfaces. The findings demonstrate that the UV nanosecond laser multi-line layered scanning technique is particularly effective for processing thick SiC_f/SiC samples, achieving a surface area of 5 × 5 mm² (Sa 366.92 nm) in just 117.58 s. By optimising the focus increment, a high and stable material removal rate is maintained throughout the process, reducing surface oxidation, minimising the formation of a recast layer, and reducing fibre interface debonding. Additionally, the study reveals the mechanism behind the formation of surface taper and presents a method to achieve a taper-free surface by adjusting the laser incidence angle. These findings provide valuable insights for the rapid and high-quality machining of matrix composites, offering significant improvements over existing methods.