Dielectric flushing optimization of fast hole EDM drilling based on debris status analysis

Fast hole electrical discharge machining (EDM) drilling can machine holes of Φ0.1–3 mm with a rotating tube electrode passed through by high-pressure dielectric. It is widely believed that the machined debris can be washed away quickly under the high pressure of dielectric flushing to achieve the high processing efficiency. However, in our experiments, it was found that the machining efficiency in the final stage of drilling the holes decreases obviously. In this paper, by analyzing the machining process and simulating the debris status, a problem is discovered that there is debris accumulation into the machining gap without dielectric flow. To solve this problem, we propose the combined flushing with tube-inner dielectric under high pressure and tube-outer dielectric with high velocity. In the final stage (breakthrough-hole stage), the external flushing can update the dielectric in the machining gap. The multi-factors’ effect including the inner-flushing pressure, the external flushing velocity and angle, and the combined flushing on the EDM drilling process is researched by flow field simulations and machining experiments while considering different hole depths. The processing efficiency in the breakthrough-hole stage is significantly improved by ~ 89% because the debris concentration can be reduced by ~ 94% owing to the external flushing.