A comparative study of auxiliary gases’ effects on film cooling hole machining quality in femtosecond laser helical drilling

Femtosecond laser is commonly used in the processing of turbine blade film cooling holes (FCHs), and the quality of this processing significantly influences the strength of the blades. In this study, FCHs were processed on nickel-based single crystal materials using femtosecond laser, and the effects of the type of auxiliary blowing gas and gas blowing pressure on the processing quality of the FCHs were investigated. The quality of FCHs prepared through femtosecond helical drilling under varying pressures of air and argon auxiliary blowing was analyzed from the perspectives of geometric characteristics, surface morphology, and oxidation ablation. The results indicate that the blowing pressure of both gases has minimal impact on the geometric characteristics and surface morphology of the FCHs; however, the quality of FCHs processed under high-pressure blowing is superior. When comparing argon to air as the blowing gas, the FCHs processed with argon exhibited smaller diameters, reduced taper, and lower surface roughness, with almost no oxygen present on the hole wall. Combined with debris splashing and plasma shielding effect, the formation mechanism of debris deposition at the entrance of the FCHs produced by argon blowing is revealed. There is a debris deposition at the entrance side of the FCH due to the plasma shielding effect, which is caused by the debris being blown out by the auxiliary blowing, and the secondary processing of the hole avoids this defect. Overall, the surface quality of the FCH walls processed with argon blowing is the best, characterized by a nano-strip structure on the hole walls.