Innovative Approach for Machining Twin Holes on Superalloy-Nimonic 263 Using <bold>μ</bold>-EDM

Nimonic 263 superalloy is a hard-to-machine engineering material. These materials are predominantly used in engine parts like disks, casings, turbine blades, etc. Closely spaced multiple holes are having the importance in turbine blades for effusion cooling. The current paper investigates the machining of twin holes on a 1.2 mm Nimonic 263 plate with hollow copper tools of each & Oslash;0.5 mm using an in-house developed micro-electro discharge machine (mu -EDM). Two holes are machined at a stretch to improve the production rate with a tailor-made twin tool setup. Masking of Nimonic with copper foil is adopted to avoid EDM effects around the holes and also to avoid post-processing operations. Scanning electron microscope (SEM) micrographs, including high-resolution back-scatted electron (BSE) images, are used to reveal the EDM effects around the holes, which are machined with and without masking. A full factorial design was utilized to perform 27 experiments. Process parameters such as current, pulse-on time (Ton), and pulse-off time (Toff) are varied to analyze material removal rate (MRR), tool wear rate (TWR), circularity error (CE), and taper angle (TA). Gray relational analysis (GRA) determines the optimum parameters to achieve maximum MRR, minimum TA, TWR, and CE. The optimum solution is obtained at current: 8 A, Ton: 80 mu s, and Toff: 20 mu s, and the most significant parameter is identified as current for most of the individual responses from ANOVA. In addition, twin holes are machined on plates of different thicknesses, varying from 3 to 5 mm, with the obtained optimum parameters and the obtained aspect ratio (AR) of the twin holes being 3.30,4.13,5.14. The surface crack density (SCD) of different AR hole surfaces is studied along with the four responses mentioned above, and the investigations are detailed in the paper.