Fabrication of taper-free holes by laser based on multi-physics field coupling

Film cooling holes are vital for thermal management in high-bypass-ratio aero-engines, and this study introduces an advanced Underwater Ultrasonic-assisted Laser Drilling (UW-UALD) technique to fabricate these holes in nickel-based alloys. By integrating a femtosecond laser (PHAROS Yb:YAG, 1032 nm) with acoustic field modulation, the study optimizes the multi-physics interactions governing drilling precision. The effects of acoustic field amplitude (0–40 μm), incline angle (0–45°), and processing time (120–360 s) are systematically evaluated to minimize taper, enhance surface quality (Ra), and improve efficiency for vertical and inclined holes. A robust Response Surface Methodology (RSM) model (R² > 0.99) is developed to correlate process parameters with geometric outcomes, revealing that the sensitivity of every parameter to taper and hole wall roughness. Experimental results demonstrate superiority of UW-UALD: vertical holes exhibit zero taper with Ra = 0.5 μm and a depth-to-diameter ratio of 5.8:1, while 30°inclined holes achieve Ra = 1.0 μm and a 6.6:1 aspect ratio. Compared to conventional methods, UW-UALD reduces oxygen content by 68.4 % (from 26.6 at.% to 8.4 at.%), lowers surface roughness by 84 % (from 3.2 μm to 0.5 μm), and enhances efficiency by 17 %. A coupled debris transport model elucidates the synergistic mechanism. The study investigates the mechanisms and debris removal channel evolution, summarizing the mechanisms of UW-UALD at various stages based on acoustic streaming and cavitation effects. These advancements position UW-UALD as a breakthrough for manufacturing high-precision, oxidation-resistant film cooling holes, directly addressing the demands of next-generation turbine blades and advancing high-bypass-ratio engine technology.