Study of polarity effect on die-sinking EDM with graphite electrodes

Electrical discharge machining (EDM) is widely utilized for processing molds and aerospace components due to its high precision and non-contact characteristics. However, EDM exhibits significant polarity effects, which notably influence machining efficiency, electrode wear, and surface quality. This study investigated the polarity effects of graphite electrodes in die-sinking EDM through process experiments, considering the influence of graphite material properties, workpiece materials, electrical parameters, and flushing conditions. The results reveal that the polarity effects of graphite electrodes stem from the intrinsic properties of graphite, exert a more pronounced influence on positive polarity, and remain unaffected by the workpiece material. Additionally, EDM with positive polarity leads to less carbon deposition on the workpiece surface and reduced electrode wear compared to negative polarity. Under various pulse durations and peak current conditions, the material removal rate (MRR) with graphite electrodes at negative polarity is 3 to 5 times higher than that at positive polarity. The high efficiency of negative polarity machining relies on good flushing conditions, requiring an inter-electrode gap flow velocity of at least 0.15 m/s to maintain stable discharge. In contrast, positive polarity machining is less sensitive to variations in flushing conditions.