Evaluation of Wire Electrochemical Machining With Rotating Electrode for the Manufacture of Fir Tree Slots

Abstract

Components with best surface integrities — without any white layer or mechanically damaged rim zones — and regardless of mechanical properties of the material can be produced with electrochemical machining (ECM). Wire ECM combines the outstanding advantages of the ECM working principle with the kinematic of wire electrical discharge machining (wire EDM). A task-specific tool design — such as for classical sinking ECM — is not required for cutting 2.5-dimensional geometries like fir tree slots in turbine discs. Established manufacturing technologies for fir trees are broaching and recently wire EDM. However, high requirements on surface integrity of these turbine parts afford cost intensive finishing processes. Thus, wire ECM could be an attractive cost efficient alternative manufacturing process. Due to an insufficient flushing concept, a process development of wire ECM for fir tree slots with relevant disc heights failed in the past. A combination of an axial flushing with rotating structured electrode provides a promising approach to meet these challenges. Therefore, this paper presents investigations of cutting Inconel 718 direct-aged using the new flushing principle. Workpieces with heights up to 40 mm are machined, which is comparable to a low pressure turbine disc height. Reachable feed rates respectively cutting rates are presented. Due to the process specific edge rounding, the formation of the leading edges is examined. Finally, the evolving surface integrities with the help of surface roughness, cross sections and residual stresses are investigated and discussed.