Through hole making by electro-discharge machining on Inconel 625 super alloy using hollow copper tool electrode

Abstract

A case experimental research on through hole making process on Inconel 625 super alloy by using hollow (tubular) copper tool electrode in electro-discharge machining has been delineated herein. Based on three controllable process variables namely peak discharge current, pulse-on duration, and gap voltage, experiments on through hole making have been carried out following the electro-discharge machining route (die-sinking electro-discharge machining without flushing). In addition to surface morphology, topographical features of the electro-discharge machined work surface have been examined for both internal cylindrical surface of the hole produced and also the external peripheral surface of the removed cylindrical part. The influence of the process parameters have been analyzed on various process performance features like material removal rate, surface roughness, surface crack density, white layer thickness, circularity, radial overcut, and hole taper. An optimal parameter setting has been identified for sound hole making and thereby to improve electro-discharge machining performance. Additionally, energy-dispersive X-ray spectroscopic analysis has been carried out to investigate the extent of carbon enrichment onto the electro-discharge machined work surface of Inconel 625 as affected by the pyrolysis of the dielectric fluid whilst executing electro-discharge machining operation. X-ray diffraction tests have been carried out to compare metallurgy of the electro-discharge machined work surface (various phases/precipitates present in bulk of the matrix material, extent of grain refinement, crystallite size, strain, and dislocation density) with respect to that of “as received” Inconel 625. Results, thus obtained, have also been compared to that of the micro-hardness test data.