Influence of Nozzle Jet Flushing in Wire EDM of Workpiece with Stepped Thickness

Abstract

The demands for precise machining of complicated shapes have been increased with the miniaturization of industrial products. Thus, wire electrical discharge machining (EDM) for plate parts with stepped thickness have been sometimes required. In this case, it is well known that wire breakage frequently occurs around the step without taking any appropriate measures. In order to clarify the reason for frequent wire breakage, the wire breakage occurrence distributions were firstly investigated when a steel plate with stepped thickness was rough-cut. Next, the flow fields and debris movements in the machined kerf, and wire deflection due to jet flushing were simulated by using computational fluid dynamics (CFD) and structural analysis.The experimental results showed that the wire EDM characteristics deteriorate including frequent wire breakage before the step. It was also found by the simulations that the flow fields around the wire change drastically near the step, and debris more stagnates there in the machined kerf during wire EDM. Furthermore, the wire deflection also becomes unsteady before the step, where the wire breakage often occurs. Therefore, it can be concluded that the deterioration in debris exclusion and the instability in wire deflection would be the cause of frequent wire breakage before the step. In addition, the optimum flow rates of nozzle jet flushing during machining a workpiece with stepped thickness were discussed. It was found that wire EDM characteristics could be improved by increasing the total flow rate from both upper and lower nozzles and the flow rate from the nozzle with wide stand-off distance.