Correction method of servo feed trajectory in block divided EDM for diffusion shaped film cooling holes

Diffusion shaped film cooling holes can improve cooling performance on turbine blades of aeroengines. The diffusion structures are difficult to machine due to the complicated shape, especially for the special materials such as single crystal superalloys. In our previous work, a novel process of block divided electrical discharge machining (EDM) based on a slender rod electrode was proposed to efficiently machine the diffuser structure of diffusion shaped film cooling holes. Although the rod electrode wear can be quickly repaired in the block divided EDM process, the shape accuracy of diffuser structures still needs to improvement. In this research, the novel process is firstly analyzed to find that the error of servo feed trajectory in 3D space is a key to the shape accuracy. Furthermore, a correction method of servo-feed tool trajectory is proposed by applying a correction velocity perpendicular to a target trajectory for correcting tool position. The specific implementation algorithm of the correction method is described in detail. The repeated experiments of diffusion structures verify the feasibility of the block divided EDM with trajectory correction method. The experimental results show that the proposed method and algorithm can effectively reduce the trajectory error by ~20 μm and the shape error of diffusion structure by ~10 μm. The typical film cooling holes with diffusion structures were machined successfully on Inconel 718 and nickel-based single crystal superalloys, based on the self-developed experimental setup by integrating the high speed EDM drilling on cylindrical-hole part and the block divided EDM with the trajectory correction method on diffusion-structure part.