Stainless Steel Deep Hole Drilling with EDM

The electro discharge machining is a promising production technique allowing to overcome the limits of standard drilling process especially in case of small and deep holes production in tough materials. A drawback of the EDM technique is the necessity to find optimal machining conditions depending on materials and dimensions of the workpiece and the electrode. Even in case of an optimal set of machining parameters, the machining process still shows instability mainly related to the flushing and debris removal mechanism. The aim of this study is to find how the machining flushing level, the machining feed rate, and the machining process stability relate to the machined hole's depth for a combination of the sinking process with a hollow electrode with inner flushing. We machined out series of holes that show that inner flushing increases the machining depth compared to machining with no electrode inner flushing. Experiments also showed the machining feed rate increases with a decreasing dielectric oil flushing pressure. There was not found any limit in the hole depth up to the depth of 48 mm in stainless steel, even for a low-level flushing corresponding to dropping of individual drops at the electrode tip. It was found that decreasing of the flushing pressure increases the standard deviation of the feed rate measured along the hole machining depth. There was also found an effect of strong drop of the feed rate in a small hole depth related to the increases of the machining area caused by workpiece inner peak formation inside the hollow electrode.