Influence of tool electrode material on material removal and surface integrity in electrical discharge machining

Abstract

In electrical discharge machining (EDM), it is known that the kind of tool electrode material would influence the machining results obviously. To better understand the reason, in this study, the material removal with three kinds of tool electrode material (copper, tungsten and graphite) were observed using a high-speed camera in single pulse discharge. It was found that more molten workpiece material was ejected from the molten pool during the discharge when graphite was used as tool electrode material, followed by copper and tungsten. Simulation results of temperature distribution show that under the same discharge conditions, larger volume of tool electrode material was vaporized when graphite was used compared with copper and tungsten, which means stronger vapor jets was generated from the graphite tool electrode and thus more workpiece material was removed. It can also be concluded that in EDM the easiness of generating vapor jets is not only decided by the boiling point of the tool electrode material, but also influenced by the other thermo-physical properties, such as density, thermal conductivity, electrical conductivity and specific heat. Then continuous discharge experiments were conducted to compare the material removal rate and surface integrity (including surface roughness, white layer thickness and micro-cracks defect) with different tool electrode materials. It was found that under the same discharge conditions, the material removal rate was higher and the surface was rougher with a thinner recast layer and less serious micro-cracks when using tool electrode material which can generate stronger vapor jets.