Achieving precision in high density batch mode micro-electro-discharge machining

This paper reports a parametric study of batch mode micro-electro-discharge machining (μEDM) of high density features in stainless steel. Lithographically fabricated copper tools with single cross, parallel line and 8 × 8 circle/square array features of 5–100 μm width and 5–75 μm spacing were used to quantify trends in machining tolerance and the impact of debris accumulation. As the tool feature density is increased, debris accumulation effects begin to dominate, eventually degrading both tool and workpiece. Two independent techniques for mitigating this debris buildup are separately investigated. The first is a passivation coating which suppresses spurious discharges triggered from the sidewalls of the machining tool. By this method, the mean tool wear rate decreases from a typical of about 34% to 1.7% and machining non-uniformity reduces from 4.9 μm to 1.1 μm across the workpiece. The second technique involves a two-step machining process that enhances the hydrodynamic removal of machining debris compared to standard methods. This improves surface and edge finish, machining time and tool wear. (Some figures in this article are in colour only in the electronic version)