Focus increment-based laser-mechanical drilling process: A case study on film-cooling hole fabrication in SiCf/SiC composites

Laser drilling is attractive for fabricating deep microholes with large aspect ratios because of its non-contact and highly precise. Nevertheless, simultaneously increasing throughput and preserving hole wall integrity remains challenging. This study introduces a Focus increment-based Laser-Mechanical Drilling (F-LMD) process that integrates the dynamic response capability of galvanometer-based drilling with the superior penetration of laser rotary drilling, while enabling precise taper control by adjusting the laser’s incident angle during processing. To elucidate the governing mechanisms, a kinematic model was established and validated experimentally. In parallel, a high-fidelity, transient, three-dimensional finite element model was developed by coupling the solid heat conduction equation with a level-set interface-tracking algorithm to reveal material removal process. Compared with conventional laser drilling, the F-LMD technique improves laser beam-energy continuity and stabilizes ablation behavior, while significantly enlarging the effective focus increment. Using F-LMD, holes with diameters 4.2 mm thick silicon carbide fibre-reinforced silicon carbide (SiC f /SiC) plates in as little as 18.61 s. Furthermore, this approach can optimize hole taper and suppress recast-layer. The versatility of this method is evidenced by the fabrication of straight, positively and negatively tapered, and inclined holes. Notably, it fabricated a 0.35 mm diameter hole with an aspect ratio of 17 within 60 s. The F-LMD process would provide a high-performance and broadly applicable route for laser processing film-cooling hole.