8 th International Conference on Management of Innovative Technologies MIT 2005 MIT 2005 217 Selection of optimal EDM machining parameters for the given machining surface J. Valentinčič, D. Kušer, S. Smrkolj, M. Junkar University of Ljubljana, Faculty of Mechanical Engineering, Slovenia Abstract To achieve high removal rate and low electrode wear when roughing by the sinking electrical discharge machining process (EDM), appropriate average surface power density is required in the gap between the workpiece and the electrode, i.e. rough machining parameters have to be tuned to the machining surface. Since machining surface varies with the depth of machining, the rough machining parameters have to be selected on-line to obtain appropriate average surface power density in the gap. The systems for on-line selection of the rough machining parameters of EDM process presented in the literature either have hardly acceptable disadvantages or they are very complex. Thus, a simple solution could be a significant step towards better automation of the EDM rough machining and micro electrical discharge machining (MEDM). In this paper, a system for on-line selection of the machining parameters according to the given machining surface is presented. The selection of the machining parameters is based on the acquisition of only one process attribute, i.e. the percentage of short-circuit discharges, which is significant improvement comparing to known systems. Keywords: electrical discharge machining, monitoring, machining parameters, process attributes, rough machining. 1 Introduction Sinking electrical discharge machining (EDM) and wire electrical discharge machining (WEDM) are most commonly used technologies in tool production. EDM is a relatively slow machining process and it usually requires an electrode that is made specially for machining of a given product. The shape of the electrode is mapped into the shape of the cavity in the tool. The advantage of EDM is the ability to produce small, even micro features. The EDM process is used mostly for making moulds whereas WEDM is used for precise contour cutting. The electrode in WEDM is a wire and its trajectory defines the contour of the cut. Nowadays, research on the EDM process is mainly focused on micro machining [1] and improving surface roughness [2]. However, there are still attempts of improving the EDM process by tuning a vast variety of machining parameters for optimal machining [3,4]. Most of the EDM machine producers present on the world market have solved the problem of the gap contamination by employing various monitoring systems, different flushing methods and anti-arc systems, but only few of them have solved the problem of controlling the rough machining parameters when the machining surface varies during the machining. In the case of roughing, when the quality of the surface can be neglected, it is necessary to obtain optimal average electric power (further referred as optimal power) in the gap between the electrode and the workpiece to achieve the highest material removal rate. The average electric power (further referred as power) in the gap is determined by the machining parameters that are set on the EDM machine. Optimal power depends on the eroding surface size (Figure 1), which is a projection of the machining surface, i.e. the surface between the workpiece and the electrode, to the plane perpendicular to the machining direction [5]. Many approaches have been described in the literature and patented on the EDM and WEDM processes for on-line selection of the rough machining parameters. The systems based on the capacitance or the conductivity of the gap [6-8] are very sensitive to the contamination of the gap between the workpiece and the electrode. But the main drawback is that both, capacitance and conductivity reflect the size of the machining surface and not the size of the eroding surface.