Abstract: The discharge proportion of the bottom gap in EDM of deep and narrow slot directly affects the machining efficiency and precision. However, there is currently a lack of intuitive understanding of the discharge point distribution mechanism and law within the gap, which limits the further improvement of its machining technology level. For this problem, the discharge point distribution mechanism is explained through observation experiments and simulation analysis. Further combined with discharge images and waveforms, the influence law of electrical parameter on the discharge proportion of the bottom gap are studied. The results show that affected by the dynamic evolution of bubbles and the distribution of machining debris within the inter-electrode gap, the discharge point is generated from the local position of the bottom gap and spreads to the side gap. The discharge proportion of the bottom gap under each electrical parameter shows a decreasing trend with the increase of machining depth. The influence of peak current on the discharge ratio of bottom gap is related to the processing depth. When the depth is shallow, the discharge ratio is close under various peak currents. When the depth exceeds 4 mm, the maximum bottom gap discharge ratio is under the peak current of 13.5 A. With the increase of pulse width, the discharge proportion of the bottom gap shows a characteristic of first increasing and then decreasing. For open-circuit voltage, the introduction of the high-voltage auxiliary breakdown mode reduces the discharge proportion of the bottom gap, thereby reducing the machining efficiency. The results of the study reveal the distribution mechanism and law of the discharge point in the machining gap of deep and narrow slot EDM, which provides new ideas for adjusting the process parameters and improving the level of deep and narrow slot by EDM process.

Key words: electrical discharge machining (EDM), deep and narrow slot, discharge point distribution, high-speed observation, simulation