Micro-EDM drilling of tapered holes for industrial applications

This papers details the development of a novel technique to produce reverse tapered micro-holes (EDM electrode exit diameter is larger than EDM electrode entry diameter) using EDM (electro-discharge machining), to a production standard that could be applied to real products in industry. Existing EDM systems are generally used to produce straight, parallel-walled holes. However there are certain application areas where tapered holes, especially reverse taper, can give an advantage. One such application area is where fluid is flowing through an orifice (entering at the large diameter and exiting at the small diameter). A reverse tapered hole increases the coefficient of discharge of the hole. Existing EDM systems generally produce poor quality reverse tapered holes and in most cases it is not possible. This paper reports the development of a new technique which enables reverse tapered holes to be produced. Tapered holes with 100 μm diameter at electrode entry and 160 μm diameter at electrode exit can be produced with this technique. The quality of the holes produced is examined using a novel 3D impression technique, as well as SEM, surface roughness, and 3D optical measurements.