Nanofinishing of hard materials using micro-electrodischarge machining

Micro-electrodischarge machining (micro-EDM) has been found to be an effective method of machining all types of conductive material, regardless of hardness. The process is being widely used in the production of tools and dies using hard and difficult-to-cut materials, where the surface quality of the product is of prime importance. The purpose of the present study is to investigate the feasibility of achieving fine surface finish in the micro-EDM of hard tungsten carbide (WC) and tool steel (SKH-51). Three different approaches: sinking, milling, and powder mixed dielectric (PMD) micro-EDM were applied in order to obtain a fine surface finish. The surface characteristics of machined WC and SKH-51 were studied and compared based on the surface topography achieved, the average surface roughness (R-a), and the peak-to-valley toughness (R-max) of the machined surface. It has been found that the topography and finish of the machined surface greatly depend on the discharge energy during machining. The surface generated using micro-EDM milling is found to be smoother and defect-free compared with those generated by die-sinking. At the same discharge energy, SKH-51 tool steel provides lower R-a and R-max when compared with WC. Finally, graphite PMD has been applied in the micro-EDM of SKH-51, as it provides comparatively lower R-a and R-max. It has been found that both the R-a and R-max were significantly reduced and crater distribution became more uniform when graphite nanopowder mixed dielectric was applied. Among the approaches, PMD milling micro-EDM has been found to provide a relatively improved surface finish during machining SKH-51.