Non-destructive surface characterization of reverse micro-EDM-induced arrayed μ-features with varying aspect ratio

Abstract

Reverse micro-EDM (RMEDM), a contactless electro-thermal micro-machining process, is extensively used for generating array of similar aspect ratio of protruded micro-features. The drawback of this process is the formation of recast layer on the fabricated surface that has different mechanical and chemical properties as compared with the base material. Usually, destructive characterization techniques are employed to assess the extent of recast layer formation which eventually renders the surface unusable for any further application. This study, therefore, initially aims to extend the capabilities of the existing RMEDM process in generating simultaneously varying aspect ratio of arrayed micro-features. Furthermore, the measurement of recast layer thickness on each micro-feature was carried out using 3-D X-ray micro-computed tomography (XMCT). This is the first instance of using XMCT for recast layer measurement, to the best of our knowledge. Finally, surface roughness analysis was carried out on the micro-features. Results from this study showed that arrayed micro-features of varying aspect ratios can be fabricated using RMEDM with tapered blind holes as tool (hole depths of 0.1 mm, 0.3 mm, and 0.5 mm). The height of fabricated micro-features on the array is limited by the corresponding hole depths on the tool. Also, increase in the height of micro-feature results in an increase in the thickness of recast layer (~ 20 μm, ~ 30 μm, and ~ 35 μm, respectively). Debris agglomeration and adhesion lead to occurrences of abnormal discharges resulting in higher surface roughness at the sides (maximum of ~ 9 μm). However, surface roughness was comparatively less at other locations on the micro-feature (maximum of ~ 2 μm).