Characterization of circumferential surface roughness of micro-EDMed holes using replica technology

Circumferential surface roughness of micro-EDMed holes is an important parameter determining their performance in applications involving fluid flow (cooling micro-holes of turbines, micro-holes in fuel injectors), metal/polymer flow (wire drawing dies, micro extrusion dies) and micro-assemblies. In case of macro-holes, surface roughness measurements can be directly performed e.g. by wire EDM cutting the sample into two halves. However, characterization of circumferential surface roughness of micro-holes is not so straight-forward. In this paper, silicone replica technology is investigated to characterize circumferential surface roughness of micro-EDMed holes by performing indirect measurements on the replicated surface. This paper evaluates this concept for micro-holes of nominal diameter 0.35 and 0.5 mm. Commercial silicone replica (Microset (R)) is used for micro-hole replication. Micro-hole drilling experiments are carried out using SARIX (R) micro-EDM technology on STAVAX mold steel using three different micro-EDM energy conditions and three replications of each micro-hole are analyzed. The measurements are performed using a Sensofar (R) 3D optical microscope using confocal technology. A comparison of surface roughness measurements on actual and replicated surfaces is also presented. This paper demonstrates that replica technology is a viable concept in assessing circumferential surface roughness of micro-holes made by micro-EDM without destroying the actual workpiece. Results indicate that there is a limitation on maximum aspect ratios which can be replicated. The accuracy of roughness prediction using replica technology was +/- 60 nm and +/- 50 nm respectively for 0.35 and 0.5 mm nominal diameter micro-holes. (C) 2018 The Authors. Published by Elsevier B.V.