Modelling and experimental investigation on the effect of nanopowder-mixed dielectric in micro-electrodischarge machining of tungsten carbide

Abstract

Micro-electrodischarge machining (micro-EDM) is one of the most effective methods used in die and mould industries for machining difficult-to-cut tool and die materials such as tungsten carbide (WC). The quality and integrity of the surface finish resulting from the micro-EDM process in die and mould making can have a significant impact on the product performance. The present study intends to investigate the feasibility of improving the surface finish in micro-EDM of WC in a dielectric mixed with graphite (Gr), aluminium (Al), and alumina (Al2O3) nanopowders. The mechanism of powder-mixed micro-EDM is presented theoretically in terms of the effect of additive powder characteristics on the dielectric breakdown and gap width. In addition, the effect of the nanopowders’ mixed dielectric on surface topography, average surface roughness ( Ra), peak-to-valley roughness ( Rmax), material removal rate (MRR), and electrode wear ratio (EWR) was studied experimentally. It has been shown theoretically that the presence of a conductive or semi-conductive powder lowers the breakdown strength and increases the spark gap during powder-mixed micro-EDM. The surface finish and topography was improved significantly owing to the increased spark gap and uniform discharging in powder-mixed micro-EDM. In addition, the lower breakdown strength of dielectric and increased spark gap contribute to higher MRR and lower EWR in addition to improved surface finish. Among the three types, semi-conductive graphite nanopowder was found to provide a smooth and shiny surface with lower Ra and Rmax, whereas the spark gap and MRR was found to be higher when aluminium powder was used. The non-conductive alumina powder was found to have very little effect on the performance of powder-mixed micro-EDM of WC. Finally, from analytical and experimental study, it has been concluded that the particle size, concentration, density, and thermal and electrical conductivity of powder materials are the most influencing factors in powder-mixed micro-EDM of WC.