High-performance processing of film cooling holes with a picosecond fiber laser in DD6 single-crystal superalloy

The configuration accuracy and inner surface quality of film cooling holes (FCHs) critically influence the cooling efficiency and fatigue resistance of aero-engine turbine blades. A highly stable and high-power picosecond fiber laser was input into a helical scanning machining head, and integrated into a five-axis cradle machine, so as to establish a high-efficiency and high-stability system for precision drilling FCHs. In order to overcome the high thermal effects of picosecond laser, a three-step processing strategy was proposed and systematically optimized. In step 1, a through-hole was rapidly pierced by fully spiral scanning, where high-pressure gas effectively removes ablated ejecta, thereby improving processing efficiency and depressing thermal effects. Step 2 produces taper-free holes with designed sizes by half spiral scanning. Step 3 eliminates the thin surface layer on the inner wall by helical scanning, effectively reducing the oxygen content and surface roughness. High-quality taper-free FCHs were efficiently fabricated on a 1.5 mm thick DD6 single-crystal superalloy in 39 s, featured with a diameter of 500 ± 3.5 μm, roundness of 98%, and heat affected zone width below 7 μm on average. Furthermore, the inner wall surface quality was excellent, characterized by extremely low roughness and oxygen content, with average values of 0.145 μm and 2.95 wt.%, respectively. This technique has been successfully applied to turbine blade specimens, where the processed FCHs demonstrate stable water flow performance compliant with design requirements, indicating broad prospects for industrial applications. • A ps fiber laser with a helical scanning head enables stable FCH drilling in DD6. • A three-step processing strategy reduces thermal effects and improves efficiency. • Taper-free FCHs (500 ± 3.5 μm, 98% roundness, 2.9 μm HAZ) achieved within 39 s. • Inner walls show Ra 0.145 μm and 2.95 wt.% Oxygen with uniform LIPSS distribution. • Turbine blade with FCHs demonstrates stable water flow and industrial applicability.