To Investigate the Phenomenon of Surface Modification in Die Steels Using EDM Process

Abstract

Electrical Discharge Machining (EDM) has established itself as one of the most versatile machining process in the manufacture of press tools, dies and punches. In this process, a tool (electrode) cuts the work material by a series of electrical sparks generated in a dielectric medium and produces a mirror image of itself by advancing into the workpiece. Some of the reasons for the tremendous popularity of this process are its ability to machine complex internal shapes in hardened materials, negligible cutting forces because of absence of any physical contact between the tool and work material, distortion-free accurate machining, easy fabrication of the tool and simple operation of the machine. newline Though EDM is essentially a material removal process, a number of phenomena observed during machining make it a suitable technology for application in the field of surface improvement. Each spark generates a temperature in the range of 8,000 to 12,000 0C and creates a plasma channel; causing fusion or partial vapourization of the workpiece material, tool electrode and the dielectric fluid at the point of discharge. As the plasma channel collapses towards the end of the machining cycle, some of these constituents may get deposited on the machined surface under appropriate process conditions. Suitable alloying elements may be introduced in the tool electrode bodies or added to the dielectric medium in the form of fine powders for specific surface modifications. These elements may migrate to the machined surface either in free form or as carbides by combining with carbon generated from the breakdown of the hydrocarbon dielectric. The changes in chemical composition of the surface and its quenching by the flowing dielectric bring about desirable improvements in properties. Additive powders in the dielectric medium also change the sparking pattern and hence, significantly affect the properties of the machined surface.