Dynamic debris particles evacuation mechanism and combined femtosecond laser drilling strategy for high-aspect-ratio film cooling holes

With the continuous increase in performance requirements for aero-engines, film cooling holes (FCHs) play a critical role in enhancing engine efficiency. To address the challenge of machining large-aspect-ratio FCHs in turbine blades, this study establishes a theoretical model of the femtosecond laser–DD6 alloy interaction based on the material point method (MPM). The evolution of hole-depth saturation under femtosecond laser irradiation is systematically analyzed, revealing that hindered material removal in deep holes results from a periodic accumulation–ejection–accumulation cycle of particles. Real-time observation of particle dynamics during hole penetration was conducted using a CCD camera. When the hole depth reaches saturation, plasma within the holes exhibits four characteristic behaviors: energy transfer and reflection coupling, a piston effect with shock waves, in-hole zoning, and stabilization. During the chip removal stage, the ejected particles pass through four states: initial penetration, internal ejection, stable emission, and re-ignition with splashing. Based on these insights, a dynamic, monitored machining strategy was developed. Using this method, large-aspect-ratio FCHs with an inlet diameter of 360 μm and an aspect ratio of 22:1, free of recast layers, were successfully fabricated on 8 mm-thick nickel-based alloy substrates.