Improvement of EDM performance in high-aspect ratio slot machining using multi-holed electrodes

Machining of high-aspect ratio slots is a common operation in industry, particularly in the mold and die and aerospace sectors. Electrical Discharge Machining (EDM) is a competitive technology for this operation, since it does not depend on material hardness and can fulfill strict geometrical requirements. However, due to debris accumulation in the narrow gap, the machining depth for stable machining is limited. The present work includes original findings about the influence of machined holes on flushing efficiency. Different configurations for this basic approach have been proposed and their performance discussed in terms of machining time and electrode wear. A remarkable and original finding is that continuous pockets or open holes are much better than the separated or closed holes. Furthermore, the paper shows that a sudden change in material removal rate occurs when the vacant spaces of the holes are sunk in the slot. A deeper insight into the EDM phenomena has been achieved through a study of discharge parameters, by analyzing discharge frequency, duty factor, discharge delay time and discharge off-time. In this study, using the proposed electrode reduced the process time by as much as 65% in the machining of 10 mm depth slots. Moreover, machining stability can be guaranteed if the flushing pockets machined on the electrode go through the whole depth of the machine.