Femtosecond laser helical drilling on nickel-based single crystal superalloy: Parameter influence laws, surface integrity and formation mechanisms

Aiming at the problem of poor quality in the current femtosecond laser drilling process, this paper analyzed and compared the influence of different femtosecond laser drilling process parameters on the surface quality of film cooling hole (FCH) wall from the perspectives of geometric characteristics, processing efficiency and FCH wall ablation. The single factor test and orthogonal test were used to reveal the influence mechanism of process parameters from the aspects of removal efficiency, pulse overlap rate and plasma absorption. The results show that with the increase of laser output power (P), the material removal efficiency increases, and the FCH wall ablation increases. The amount of focus drop per scan layer (H) and single-layer scan dwell time (T) jointly determine the feed rate during helical drilling, which affects the quality of the FCH wall. The number of helical scanning path cycle (R) has the greatest influence on the surface ablation of the FCH wall. When the R is small, the scanning of the outermost circle of the helical drilling processing path increases, the material is removed more fully, and the quality of the FCH wall is improved. The change of pulse overlap rate caused by rotation speed of helical scan module (V) has no significant effect on the quality of FCH wall. Based on the influence of parameters, a better combination of process parameters has obtained. Under this parameter combination, the processing time is 25 s, the taper reaches 0.027°, the hole wall exhibits a nano stripe structure with no ablation, and the roughness Ra is only 0.405 μm.