The Prediction of Surface Finish and Cutting Speed for Wire Electro-discharge Machining of Polycrystalline Diamond

This paper presents an experimental investigation of Wire Electro Discharge Machining of Polycrystalline Diamond. The objective was to understand how the PCD reacts to the process parameters and to determine if there was a relationship between the parameters and surface finish and processing speed. Taguchi design of experiments was used to obtain the optimum conditions through the study of signal- noise (S/N) ratio for surface finish (Ra) and cutting speed (mm/s). ANOVA analysis was used to predict the significant machining parameters and develop a regression equation to model the machining process. Two L9 orthogonal arrays were developed in order to study the pulse generator parameters, (on-time, off-time, and servo voltage) and the physical parameters (wire tension, wire unspooling speed and injection pressure). A parallel experiment was performed using different coated wires. A total of six wires were tested (hard brass wire included), core materials such as Cu, CuZn36 and CuZn 63/37 and coating materials such as zinc diffused and zinc rich brass double layer were used. The results showed that coated wires will increase cutting speed to a value of 4.7 mm/min without affecting surface roughness drastically (0.8 μm Ra). Following the experimental analysis, successful results were achieved with an actual surface finish value of 0.68 μm Ra, which had an error of 12% compared with the predicted value. The highest cutting speed achieved was 4.8 mm/min, which was 8% less than the predicted value.