Wire EDM for the Manufacture of Fir Tree Slots Using Different Wire Electrodes

Abstract The use of materials with increasing high-temperature strengths for turbine disks brings conventional manufacturing processes to their technical and economical limits. As an alternative manufacturing approach, the wire EDM process was therefore tested in several investigations. Despite the many advantages of this manufacturing process, EDM has significantly lower productivity compared to conventional processes. This can be increased by using enlarged wire diameter of the electrodes (bigger wires). The increased wire diameter improves wear resistance so that higher energies can be used. However, the higher energy input has a negative effect on surface integrity. Especially for safety-critical components, these changes in surface properties must be considered critically. This paper therefore examines the use of bigger wire electrodes for the electrical discharge machining of fir-tree slots on turbine disks. For this purpose, the process performance and surface integrity of Inconel 718 machined by using brass and coated wire electrodes with standard diameters and a new generation of 0.4 mm diameter wire electrodes are compared. Depending on the wire electrode, individual processing technologies are developed and tested with a focus on high productivity and low wire consumption. Finally, a technological and economical assessment is carried out, and the best-performing wire electrode with appropriate technology variant for rough machining a fir tree slot is selected.