Enhancing process capabilities of electric discharge machining for nonconductive ceramics

Abstract

The application of nonconductive ceramic materials is growing in engineering and manufacturing field due to their properties such as high hardness, low thermal conductivity, and resistance to oxidation. But fabricating structures from such materials are difficult and most of the traditional machining techniques are not appropriate. The electrical discharge machining has become a popular machining process for machining nonconducting oxide and nonoxide ceramics such as alumina, silicon nitrides, SiAlON, and zirconium. In the present study, a technique to machine the nonconductive SiAlON ceramic, having resistivity of the order of 100000 Ω-cm is developed. An assistive electrode technique along with graphite powder mixed specially made dielectric mixture of hydrocarbon fluids was used for the electrical discharge machining process. The experiments were conducted according to the Taguchi design and analysis of variance using signal-to-noise ratios showcasing significant parameters and their optimal values for material removal, electrode wear, and size overcut achieved after electrical discharge machining. For multiparameter optimization, the grey relational analysis was carried out for response parameters with suitable weights. Analysis of variance on the grey relational grade showed discharge current, duty factor, and additive percentage as most significant parameters. As the central aim of this research is material removal, the significant parameters found for material removal rate were further used for response surface methodology and their optimum values as central design values for experimentation. A second-order response model was formulated to estimate the machining performance. To validate the study, confirmation experiments were carried out and predicted results have been found to be in good agreement with experimental findings. Based on the experimental investigations, it can be said that a novel and efficient technique has been developed to machine the high resistivity ceramics. The scanning electron microscopic images confirmed that material is removed mostly by spalling and no significant cracks are visible.