Surface Roughness Model for CNC Wire Electro Discharge Machining

In Wire electrical discharge machining (WEDM) process the removal of metal takes place due to successive sparks generated between the wire electrode and the gap of the work-piece. WEDM machines are widely applied to produce complex and intricate shapes of components in hard and conductive materials. In order to predict the performance of the WEDM process many researchers have attempted using various experimental parameters such as applied voltage, pulse on time, delay time, ignition current, dielectric pressure, wire tension, servo reference mean voltage, wire feed speed. However the results of these studies are limited to certain process parameters and materials. In WEDM process there is no direct contact between the toot electrode and work-piece. Therefore there is no shear stress exerted during machining. In this present work, the study and development of a surface roughness prediction model for machining of Oil Hardened Non Shrinkage (OHNS) steel, using response surface methodology (RSM) was developed. A five axis Robofil 290 CNC WEDM manufactured by Charmilles Technologies is applied to carry out experiments. Experiments have been planned according to Taguchi's L16 fractional factorial orthogonal array. A 0.25 mm diameter zinc coated brass wire was selected as toot electrode. A first order mathematical model for surface roughness has been developed, in terms of pulse on time, wire tension, delay time and ignition current intensity. The effect of these cutting parameters on the surface roughness has been carried out using design of experiments and RSM. In addition, the analysis of variance (ANOVA) is applied to identify the significance of the developed model. The test results confirm the validity and adequacy of the developed RSM model.