Influence of Downstream Process Combinations on Surface Integrity in Wire EDM of Fir-Tree Slots for Turbine Discs

The manufacture of fir-tree slots in nickel-based superalloy turbine discs places stringent demands on surface integrity, as the resulting surface roughness, white layer thickness, and residual stress state directly influence the fatigue life of safety-critical rotating components. Wire electrical discharge machining (WEDM) offers a geometrically flexible, almost force-free alternative to conventional broaching for this application, but its thermal material removal mechanism introduces tensile residual stresses and a white layer into the workpiece. This study investigates the surface integrity achievable with current WEDM cutting strategies and evaluates the potential of post-processing treatments to further improve surface conditions. To this end, the influences of chemical etching, wet blasting, clean blasting, and shot peening at two intensity levels, as well as selected process combinations, were systematically examined. Surface integrity was characterised by surface roughness, white layer thickness using three complementary evaluation methods and residual stress depth profiles measured by X-ray diffraction. Wet blasting shows considerable potential for improving surface integrity after WEDM.