Experimental investigation on micro-EDM hybrid drilling process

Micro-EDM drilling is highly appreciated to produce micro-holes on any type of conductive material. Several industrial fields use this technology thanks to its capability to realize very accurate machining. A greater use of micro-EDM drilling process is limited by its poor performance in terms of machining time. To overcome this limit, hybrid solutions are being tested. The idea consists of benefitting from the advantages of at least two technologies trying to overcome the limitation of each one of them. Typically, EDM is used as secondary operation and the process consists of executing the micro-hole on a pre-hole realized by another process like laser. In this way, both the process performance and the quality aspects are guaranteed. Aim of this work is the investigation of the behaviour of the micro-EDM drilling on a pre-hole. In fact, the presence of a pre-hole changes deeply the machining conditions especially in terms of the dielectric flushing. In order to understand how the pre-hole changes the performance of the EDM drilling process, several aspects were investigated: the effects of the diameter of the pre-hole, the behaviour of the type of electrode, the influence of the accuracy of centring operation on the pre-hole and the hole depth. Titanium alloy sheets were used to execute final hole using electrode diameter of 0.3 mm. The process was evaluated considering both the process performance and the accuracy of the machining. The study of the law of electrode motion along its Z axis was also used to gather process information. In general, working with pre-holes yields much better performances than traditional EDM drilling thanks to different level of debris contamination in the machining zone. It was found that increasing the dimension of the pre-hole, the Material Removal Rate undergoes little changes. The electrode type (cylinder or tubular) on the pre-hole does not have evident effects on the process performance but only on the geometrical characteristics. The misalignment of the final hole on the pre-hole can improve the debris flow making the process more efficient but only when a part of the pre-hole lays outside the final hole. Within the limit of this experiments, the hole depth does not affect the presented results.