Advancing the micro-EDM technique with powder-mixed dielectric and process modelling

Abstract

The electrical discharge machining (EDM) process possesses inherent characteristics that make it a promising micro-machining technique. However, micro electrical discharge machining (micro-EDM) is only used in niche applications due to the lack of an established knowledge base to facilitate process planning. The stochastic nature of material removal, sensitivity of process performance to process parameters and conditions and numerous process parameter permutations available for machining contribute to the difficulties in building a knowledge base for micro-EDM. Compounding to this complication, the process parameters and conditions in EDM and micro-EDM are distinctly different, thereby rendering limited transferability of knowledge base. Thus, focused studies on micro-EDM are needed to improve process reliability and controllability as well as to enhance process capabilities. This research has endeavoured to achieve advancement of the micro-EDM technique through a two-pronged approach of process performance enhancement and process modelling.

The proposed use of powder-mixed dielectric in micro-EDM (PMD micro-EDM) is a novel initiative to adopt this established technological development in EDM (PMD-EDM) for micro-EDM. By reproducing the effects of improved machined surface quality and enhanced machined surface functional properties of PMD-EDM in PMD micro-EDM, advancements to the micro-EDM process has been achieved. The realisation of PMD micro-EDM has been achieved through employing discharge energies less than 25 µJ with sub-microsecond pulse on time durations and complemented by the use of nano-powder additives of semi-conductive and non-conductive materials in concentrations below 1 g/l. Initial investigations on the unit removal characteristics of PMD micro-EDM have shown a distinct difference in the morphology of craters produced in a powder-free and powder-mixed dielectric, thereby proving the feasibility of PMD micro-EDM. Furthermore, the observation of craters having smaller peak-to-valley heights when generated under single electrical discharge conditions has been exhibited as reductions in arithmetical mean surface roughness of 14 % to 24 % when processing with PMD micro-EDM. Improvements in machined surface quality have also been displayed through reductions in recast layer thickness of between 15% and 35%.