Ultrafast laser processing of shaped film cooling holes for aero-turbine blades: Surface integrity, parameter influence and forming mechanism

Shaped film cooling holes (FCHs) can effectively improve the film cooling efficiency of turbine blades, but due to their complex structure and precision requirements, there is currently no reliable and high-quality machining method. In this paper, a segmented processing method of fan-shaped FCHs is proposed, which realizes high-quality processing of fan-shaped FCHs. The effects of processing parameters on the machining efficiency, geometric accuracy and surface morphology of fan-shaped FCHs were analyzed. And the microstructure, composition, surface roughness and residual stress of the hole wall under specific processing parameters were characterized. The influence mechanism of processing parameters on the processed results is clarified by laser overlap rate and laser energy density of the processing area. The important role of focus compensation in the segmented machining method is discussed. The formation mechanism of microstructures was explained by the plasma exciton theory and the energy shielding effect. Furthermore, the process method is promoted through expansion section model segmentation and processing attitude adjustment to realize the processing of cat-ear-shaped and bat-face-shaped FCHs.