Department of Mechanical engineering

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    Effect of various factors influencing the generation of hemispherical micro features using non-conformal RMEDM
    (Sage, 2019-04) Roy, Tribeni
    Non-conformal reverse micro electrical discharge machining (NC-RMEDM) is a variant of conventional RMEDM developed by the present authors wherein modification in the tool is carried out to generate different shapes of micro features. In this study, the effect of various factors like flat bottom and taper bottom hole, inversing the position of tool and workpiece and changing the hole depth have been experimentally investigated to determine the optimal combination required for generating hemispherical shaped micro features. It was found that hemispherical shaped micro feature can be generated by employing tapered bottom blind hole as tool. Buoyancy assisted machining (BAM) with traverse of workpiece (anode) downwards into the tool (cathode) and vice versa, i.e., buoyancy opposed machining (BOM) with traverse of tool downwards into the workpiece were carried out to study the generation of hemispherical micro feature based on inversion of electrode positions. Although both BAM and BOM generated hemispherical shaped feature, BAM is preferred due to reduced machining time as opposed to BOM. Also, increasing the hole depths led to altering the shape of micro feature from hemispherical to cylindrical with hemispherical end and coni-spherical end. An array of hemispherical micro features was fabricated based on the finding from this study, and surface roughness analysis was carried out which showed that irrespective of the position of micro feature on the array, surface roughness at the tip and base of the micro feature is lower as compared to side portion.
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    Numerical modelling and simulation of surface roughness of 3-D hemispherical convex micro-feature generated by reverse micro-EDM
    (Springer, 2018-04) Roy, Tribeni
    Reverse micro-electrical discharge machining (RMEDM) is a non-contact electro-thermal micro-machining process that is primarily used for generating high aspect ratio extruded 2.5-D features with different cross-sections like square, circular and triangular. The authors have already evolved a method to generate 3-D hemispherical convex micro-feature by using pre-drilled tapered blind hole as a tool in RMEDM. Debris suspension in dielectric as well as debris adhesion to walls of either electrodes in the confined space in this method leads to reduction in inter-electrode gap creating secondary and higher order discharges. These secondary and higher order discharges occurring mostly on the sides of 3-D hemispherical convex micro-feature leads to higher crater size which increases surface roughness on the sides of the micro-feature as compared to other regions on the surface. In this paper, an attempt has been made to numerically model, simulate and experimentally investigate this variation in surface roughness on the 3-D hemispherical convex micro-feature by incorporating a multiphysics simulation approach including different physical processes viz. electrostatics, heat transfer and fluid flow occurring during RMEDM as well as the effect of secondary and higher order discharges which play a key role in determining the variation in surface roughness on the micro-feature. Simulated result matches well with the experimentally determined surface roughness (maximum error of 13%), thereby confirming that the nature of discharges (viz. secondary and higher order) occurring during RMEDM is responsible for variation of surface roughness on the generated 3-D hemispherical convex micro-feature.