Dual-Rotary Trepanning of High-Quality Film Cooling Holes in DD6 Superalloy Using a Nanosecond Fiber Laser

High-quality and high-efficiency machining of film cooling holes (FCHs) is critical for enhancing the performance of gas turbines and aero-engines. Nanosecond fiber lasers offer advantages such as high stability, good beam quality, and ease of integration. However, when machining FCHs, issues including low drilling efficiency and significant thermal effects severely limit their industrial applications. In this study, a dual-rotary trepanning system was developed based on a nanosecond fiber laser, a galvanometer, and a five-axis cradle machine. High-quality FCHs with a diameter of 0.6 mm were efficiently machined in a 3-mm-thick DD6 superalloy plate within only 6.5 s. Compared with the method using machine tool rotation alone, the average recast layer thickness on the inner wall was reduced by 62.1% to 6.7 μm, and the average surface roughness was reduced by 61.1% to 0.35 μm. These improvements are primarily attributed to the galvanometer speed being two orders of magnitude higher than that of the machine tool, which significantly reduces the laser pulse overlap rate and the thermal accumulation effect. Moreover, the kerf widened by the galvanometer rotation allows the ablation products to expand more fully and be expelled efficiently, thereby reducing impact, scratching, and debris adhesion on the inner wall and improving the drilling efficiency. Furthermore, 10 × 10 FCH arrays were machined on both vertical and inclined plates, demonstrating high consistency and stability, indicating the potential for industrial applications in the field of FCH machining.