Evaluating Surface Roughness of Ductile Cast Iron Machined by EDM Using Solid and Hollow Cylindrical Copper Electrodes

This study reports a comparative analysis to evaluate the performance of solid cylindrical and hollow cylindrical copper electrodes in terms of average surface roughness 'Ra' for machining ductile cast iron (DCI) using the electrical discharge machining (EDM) process. Experiments were conducted by varying the peak current, spark-on duration, spark-off duration, and flushing pressure according to Taguchi's L9 (43) orthogonal array experimental design matrix. Nine experiments were conducted using each tool electrode. Thus, a total of eighteen experiments were performed in this study. It was found that surface roughness increased with an increase in peak current and spark-on duration and decreased with an increase in spark-off duration and flushing pressure. Peak current and spark-on duration have a significant influence on surface roughness. Analysis of variance (ANOVA) was employed to identify substantial EDM variables and to develop a model for predicting the average surface roughness. The interaction graphs show the relationships between the considered EDM variables. Microstructural analysis of the best-finished machined surfaces was conducted using a scanning electron microscope (SEM). The SEM micrographs reveal that irregular, deeper, and non-uniform craters are formed on the DCI surface machined with the hollow cylindrical copper electrode. This comparative study concluded that the solid cylindrical copper electrode produced lower surface roughness than the hollow cylindrical copper electrode. Thus, a better surface finish of DCI can be achieved by EDM using the solid cylindrical copper electrode.