Numerical modelling, simulation and fabrication of 3-D hemi-spherical convex micro features using Reverse Micro EDM

Reverse Micro Electrical Discharge Machining (RMEDM), a variant of Micro Electrical Discharge Machining (MEDM) is a non-contact thermal micro machining process extensively used for fabrication of high aspect ratio single or multiple 2.5-D features with different cross-sections like square, circular, triangular etc. The process capability is limited by difficulty in debris ejection through the small inter-electrode gap (few μm) which causes debris sticking to electrodes and thereby creating unwanted secondary and higher order erosion that affects the features generated. In this paper, an attempt has been made to numerically model, simulate and experimentally investigate the fabrication of 3-D convex hemi-spherical micro feature by taking advantage of the effect of secondary and higher order erosion of debris. Array of 3-D hemispherical shaped micro features finds application in the field of micro lens let arrays, solar cells etc. Results indicate that use of taper ended blind hole leads to debris accumulation towards the corners and edges of cathode which enhances the possibility of secondary and higher order erosion at those areas leading to generation of 3-D convex hemi-spherical micro feature on the anode. Also, the relation between material removal by secondary and higher order erosion to that of primary erosion during machining was derived. Different values of k0 (averaged for entire machining depth) were found affecting the shape of generated micro feature. In this study, material removal by secondary and higher order erosion was found to be five times that of primary erosion.