Creating Productive Conditions for Electric Discharge Machining of Non-conductive Ceramics

Fabricating structures from non-conductive ceramic materials like silicon nitride (Si3N4) is difficult through traditional machining, but their applications are increasing in engineering field due to their high hardness, low thermal conductivity and resistance to oxidation. High electrical resistivity of such ceramics restricts the use of electric discharge machining (EDM) on them. An assistive electrode together with graphite powder-mixed dielectric mixture of hydrocarbon fluids was used to create favourable conditions for deposition of conductive layer on the non-conductive SiAlON having 105 Ω cm resistivity. The experiments were conducted according to Taguchi design. Analysis of variance using signal-to-noise ratios showcased significant parameters and their optimal values for material removal, electrode wear and size overcut. The elemental composition of the sample confirmed the deposition of carbon particles on ceramic surface which has helped in propagation of sparking beyond exhaustion of assistive layer. The SEM images confirmed the presence of deposited carbon layer and material removal by spalling and evaporation.