EDM drilling of high aspect ratio micro holes

The increasing demand for mechanical micro components has enhanced the development of numerous production technologies, like micro-EDM. Micro-EDM is able to guarantee the latest market requirements both in terms of miniaturization capabilities and quality of the features obtained. With this production technique it is possible to fabricate several types of features such as, small 3D milled features and HAR (High Aspect Ratio) micro holes. One of the main concerns in micro machining, and most of all in HAR micro holes machining, is the geometrical and dimensional qualification of the drilled features. Since inner HAR micro holes can be considered an almost inaccessible environment, in some cases it is important to carry out a non-destructive investigation procedure, in order to preserve the quality and the integrity of the micro holes obtained. The present paper describes a study on micro-EDM machining of HAR micro holes (both through and blind holes) with different aspect ratios. Moreover, a preliminary non-destructive geometrical characterization of the holes was carried out. The experimental campaign was executed using a micro-EDM machine Sarix SX200 with a specific ceramic guide system for the deep hole drilling process. The emphasis of the study was on the evaluation of both the process performances and the dimensional properties of the holes depending on both the hole aspect ratio and the process parameters. This study confirmed the micro-EDM capabilities in deep drilling; in particular, holes having AR equal to 100 were obtained. The drilling time under the worst working conditions was longer than two hours with relevant tool wear. Certain deviations from the ideal hole profile, like tapered and barrelled holes, were observed.