New EDM polishing and texturing process with conductive polymer electrodes

Abstract

This paper presents a new hybrid electrical discharge machining (EDM) process, that innovates by the use of a polymer–carbon electrode material which can be molded repeatedly into complex geometries and used to perform precision EDM machining in deionised water. This hybrid EDM process is a novel manufacturing method tailored to perform automated finishing and polishing operations of electrically conductive metal parts with minimum environmental impact. Two distinct hybrid EDM finishing procedures are described in details, namely the “replica” and the “successive imprints” EDM methods. Their main objective is to reduce or completely replace rather tedious and costly hand polishing procedures, which are common practice in the mold making industry. To carry out these new EDM processes, an electrically conductive polymer electrode made of styrene-carbonaceous composite was investigated by design of experiments to minimize its electrical resistivity (0.08 Ω cm) and to maximize its thermal conductivity and formability. A compression molding module was also designed to perform efficiently multiple compression molding cycles of a same electrode. Since water is used as dielectric in the projected EDM processes, a preliminary evaluation of water as a dielectric medium, in conjunction with graphite EDM electrode, was performed. Finally, an experimental simulation of the “replica” method is presented, whereas a P20 tool steel workpiece with a macro-level 0.35 mm Peek-Valley milled surface roughness is smoothed down to a 0.25 mm PV in a single EDM iteration step in deionised water.