Analysis of Characteristic Process Parameters to Identify Unstable Process Conditions during Wire EDM

Abstract

The demand for higher efficiency in aircraft propulsion engines leads to materials with increasing thermo-mechanical strengths. The high mechanical process forces in conventional cutting processes cause inacceptable geometrical deviations. Due to the electro-thermal material removal mechanism, wire electrical discharge machining (EDM) is a promising alternative manufacturing process. The manufacturing process is not restricted to thermo-mechanical properties (e.g. hardness or high-temperature strength). However, it is necessary to increase productivity to get a better competitive position. Unstable process conditions limit the productivity of the wire EDM process and the quality of the workpieces. These process conditions are characterized by misdischarges and short discharges, which lead to undesirable changes of material properties and thus to wire breakages. Moreover, a wire breakage interrupts the wire EDM process and extends the machining time. Therefore, this paper deals with the analysis of characteristic parameters to identify unstable process conditions during wire EDM. For that purpose, the differences between characteristic parameters of a stable and unstable wire EDM process are investigated. Furthermore, the distribution of the different types of discharges are analyzed. Results of the investigations are supposed to provide a basis for early detection of possible wire breakages and thus an adaption of control algorithm. Therefore, a stable and an automatable manufacturing process can be achieved and increase the productivity especially when machining relevant turbomachinery parts like fir tree slots in disks.