A study of the machining characteristics of micro EDM milling and its improvement by electrode coating

Micro electrical discharge machining (micro EDM) is one of the most powerful technologies for the fabrication of microstructures. This paper uses a Grey-Taguchi method to examine the optimization of process parameters for the micro EDM of high-speed steel alloy (SKH59), using tungsten carbide (WC) electrodes. The effect of the micro EDM milling parameters (discharge current, pulse duration, pulse off, and jump distance) on electrode wear rate, material removal rate, and overcut are studied. A Taguchi method with an L-9 (3(4)) orthogonal array and a signal-to-noise ratio (S/N) and analysis of variance (ANOVA) are used to investigate the performance characteristics of the micro EDM. The grey relational analysis shows that the electrode wear rate is reduced from 8.0 x 10(-6) to 4.0 x 10(-6) mm(3)/min, material removal rate increases from 1.94 x 10(-4) to 1.96 x 10(-4) mm(3)/min, and overcut decreases from 7.5 x 10(-3) to 7.3 x 10(-3) mm. A comparative study of the performance of WC, WC-coated Ag, and WC-coated Cu electrodes for the micro EDM milling is also presented. The confirmation runs show that the WC-coated Ag electrodes yield the lowest surface roughness of the three electrode materials. The WC-coated Cu electrodes achieve the highest material removal rate, followed by the WC-coated Ag and WC electrodes. The WC electrodes exhibit the lowest wear rate. The experimental results illustrate the effectiveness of this electrode coating method, which gives better electrical and thermal properties.