Influence of jet flushing on corner shape accuracy in wire EDM

摘要

In wire electrical discharge machining (EDM), wire electrode easily breaks and the shape accuracy tends to decrease when cutting corner shapes. The wire electrode during the process is subjected to discharge explosive forces, electrostatics force with open voltage application and hydrodynamics force by jet flushing. Then, the wire always deflects in the opposite side of cutting direction. On the other hands, wire breakage is caused mainly by discharge concentrations at the same location due to much debris stagnation in the narrow machined kerf. Therefore, jet flushing of dielectric fluid with nozzles has been conventionally applied for smooth debris exclusion. However, excessive flow rate may promote large wire vibration and deflection. In addition, the influence of jet flushing conditions on the debris exclusion and wire deflection in the corner shape cutting has not yet been investigated so far. In this study, the flow fields and debris movements in the machined kerf during the corner shape cutting in 1st-cut wire EDM were simulated by CFD analysis. Also, wire deflection was discussed by a structural analysis of wire with stress distribution due to hydrodynamics force obtained by the CFD analysis. The results showed that the flow field and pressure field around the wire by jet flushing changed significantly just after changing the cutting direction at the corner. Furthermore, steady circulation area behind the wire disappeared temporarily just after the corner, and debris stagnation in the machined kerf decreased at that time. Additionally, the corner shape error with wire deflection was experimentally measured and compared to analytical result of wire deflection by hydrodynamics force. It was found that the influence of hydrodynamics force on wire deflection was as large as discharge explosive force under general 1st-cut conditions, which suggests that the influence of jet flushing on the corner shape accuracy is large under relatively high flow rate conditions.