Next-generation electrical discharge machining

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Electrical discharge machining (EDM) is a precision material removal process that utilizes the heat generated from controlled, rapid electrical spark discharges struck between the tool and workpiece electrodes. Until recently, the thermal nature of material removal in EDM has limited its application in the manufacture of safety-critical components like those in an aircraft engine. Recent advances in EDM machine tools to do with advanced solid-state generator technologies have however paved the way for EDM to emerge as a staple in the aerospace industry, to the extent that it is even displacing processes like broaching, in the machining of fir-tree blade retention slots in turbine disks. EDM is poised for an even more widespread application in the coming years with the advent of aerospace materials of declining thermal conductivity, which renders them extremely difficult to cut, due to the higher energy partition to the cutting tool that accelerates tool wear. Significant progress notwithstanding, EDM continues to be largely limited by a low material removal rate relative to cutting processes, and surface integrity issues referring to recast material and micro-cracks. Interestingly, these issues are interrelated in EDM, in the context of the mechanism of material removal at the scale of a single discharge. The removal of molten material is presently understood to be due to the implosion of the gas bubble that is manifest from the evaporation of the dielectric fluid following a discharge, and it is estimated that less than 20% of the molten material is removed, due to insufficient ejection forces. The rest of the material is recast back on the work surface; not only does this render the process highly inefficient in terms of material removal, it also severely affects the integrity of the machined surface, because of the micro-cracks that result from rapid solidification and shrinkage of the molten material. An improvement in the ejection efficiency would therefore bring about an increase in the removal rate and concurrently yield a better surface quality. Currently, aspects of process and generator technology are at such a sophisticated stage of development that it is imperative to gain additional fundamental physical insights into the process, and peruse outside-the-box radical ideas, to further enhance EDM performance. In this context, the long-term objective of the proposed work is to investigate the mechanism of material removal in EDM at increasingly higher spatial and temporal resolutions and in fundamental terms, with the objective of increasing the material ejection efficiency. In the short-term, the research seeks to develop novel process concepts, and pursue science-based innovative approaches to bring about a simultaneous and substantial enhancement in both the removal rate and the quality of the machined surface.