Experimental study of micro-EDM machining performances on silicon wafer

The micro-EDM silicon machining performances have been studied on a highly doped P-type {100} silicon wafer. To demonstrate and to emphasis the special performances of silicon micro-EDM, one kind of stainless steel is machined as a reference material. Both materials are sparked with specific sparking energy in micro-Joule energy range and machining characteristics such as material removal mechanism, cutting rate, relative electrode Hear ratio and surface quality are examined and analyzed. The thermally induced microcracks are also examined and analyzed using an optical and a Scanning Electron Microscope (SEM). It is found that for silicon, the micro-EDM material removal mechanism is not completely similar to conventional metal micro-EDM; besides melting and evaporation there is a significant contribution from thermal spallation, which is a kind of direct mechanical material damage without melting. This paper also presents that microcrack generation is not only related to the sparking energy but also has a close relationship with the silicon crystal lattice. In order to get microcrack free silicon surfaces, the sparking energy should be controlled to low levels, which are much lower than the voltage levels used in metal micro-EDM. All in all, thermal spalling should be reduced as much as possible, to obtain smooth and crack free machined surfaces.