Trajectory servo scanning 3D electro discharge machining for diffusion shaped film cooling holes

Diffusion shaped film cooling holes with compound-angle diffuser structures exhibit superior cooling performance, which have gradually been applied in turbine blades of the advanced aeroengines. In our previous research, the method of servo scanning three-dimensional electrical discharge machining (SS-3D EDM) has been proven effective for high-precision machining of complex 3D cavities, offering notable advantages such as low tool cost, automatic compensation of electrode wear, and high machining flexibility. However, using tubular electrodes in SS-3D EDM, challenges persist under the conditions of the large layer depth. The lateral discharge phenomenon of tubular electrodes causes significant deformation at the electrode tip, increases the risk of lateral collisions, and complicates the accurate calculation of electrode wear length. To address these limitations, this research proposes a trajectory servo scanning three-dimensional electrical discharge machining (TSS-3D EDM) process. Axial servo motion of tubular electrode is used to maintain the discharge gap of electrode bottom, and an innovative trajectory servo motion along the tangential orientation is introduced to stabilize the lateral discharge gap, enabling automatic compensation for tool wear at the rotating electrode tip. The effect of servo control parameters on machining depth accuracy is analyzed. Furthermore, a method for electrode wear length calculation is proposed based on the voltage signals of discharge gaps. An estimation method for the electrode wear coefficient is presented. Machining experiments on superalloys validate the effectiveness and capabilities of the TSS-3D EDM method by fabricating fan-shaped and conical diffusion shaped film cooling holes. The results show that the calculation error of tubular electrode wear length <5%, the dimensional error of hole profile dimensions as 4%-6%, the repeatability error <±4 μm, and the material removal rate up to 0.664 mm 3 /min using tubular electrodes with an outer diameter of 0.4 mm.