A novel recast layer in situ thinning method for film cooling holes in fast EDM drilling

As the main machining method of film cooling holes, fast EDM (electrical discharge machining) drilling has the defect that the thickness of a recast layer is difficult to control, which can severely affect the service life of a turbine blade on the aero engine parts. In order to reduce the thickness of a recast layer in fast EDM drilling while ensuring machining precision and efficiency, a novel recast layer in situ thinning method, which uses the precision-controlled discharge erosion and tiny energy layer-by-layer thinning strategy, is proposed. Moreover, the recast layer removal mechanism, as well as the influence of this method on fast EDM drilling are systemically investigated, thereby, the optimal combination of machining parameters with different electrode diameters of the in situ thinning method is obtained. Machining results show that with the proposed method, the maximum and average thickness of the recast layer can be well controlled within 2.5 μm and 2 μm, with the highest reduction rate of the recast layer reaching 85.39%, which greatly improves the machining quality of film cooling holes of a turbine blade.