Effects of stepped cylindrical electrode in electrical discharge machining of blind holes

Electrical discharge machining (EDM) is a non-conventional machining process which has been widely used to machine difficult-to-cut materials. However, the efficiency of EDM hole making processes is low, and the quality of drilled holes is a concern especially when machining deep blind holes due to the poor removal of debris in the discharging gap. In this study, a new strategy based on shape modification of the electrode was developed to address this issue by indirectly changing the flow of dielectric. The electrodes of five different shapes with identical machining area were applied to improve the debris removal during the machining process. The effects of various electrode profiles on the machining performance were investigated. Machine time, material removal rate (MRR) and electrode wear rate (EWR) were used to evaluate the machining performance. The computational fluid dynamic (CFD) software Fluent was used to simulate the flow of dielectric caused by different electrode profiles. The results show that, compared with the straight electrode, the maximum effective cutting depth of curved electrodes and long-curved electrodes increased 13.793% and 132.184%, respectively, and the MRR of stepped electrodes was significantly higher after the machining depth reached 2 mm and 4 mm for electrodes with the working length of 2 mm and 4 mm, respectively. The surface roughness was identical for holes machined by all types of electrode. However, obvious carbon adhesion can be observed at lower cutting depth for straight electrode, followed by curved and long-curved electrodes.