Examination of the Internal Profiles of Micro-Electrodischarge Machined Holes and the Detection of Material Defects

Micro-electrodischarge machining (micro-EDM) is used to machine micro-features such as holes, slots and cavities in electrically conductive materials. This paper looks at the fabrication of micro-holes for ink jet printing nozzles where hole diameters are smaller than SOJ.lm. It is important that the printing medium be able to flow through unimpeded, so the bore must be as smooth as possible. However, it is difficult to inspect the internal profiles of such small features non-destructively. In this study, micro-holes were machined along the join between two adjacent foils to provide a natural means of separation without using a secondary process to cut the holes in half. It was then possible to investigate the holes and unmachined control samples using scanning electron microscopy (SEM). It was found that defects such as micro-cavities, cracks and inclusions were already present prior to machining by micro-EDM, seemingly as a result of the material rolling process.