Influence of Nozzle Jet Flushing on Working Fluid Flow and Wire Electrode in Trim-cut WEDM

摘要

In wire electrical discharge machining (WEDM) process, smooth exclusion of debris and bubble generated in the narrow gap is important to keep stable machining performance. Conventionally, the debris exclusion has been carried out by jet flushing of working fluid from upper and lower nozzles. This study aims to clarify the effects of jet flushing on WEDM characteristics by utilizing computational fluid dynamics (CFD) analysis. Then, the fluid flow fields and debris exclusion in the machined kerf during lst-cut WEDM have been clarified so far. On the other hand, a trim cut is carried out after lst-cut WEDM. The effects of jet flushing with smaller flow rate have not been investigated, since the geometrical workpiece shape around the wire is quite different from that in lst-cut. In this study, the flow field of working fluid around the discharging site by jet flushing using nozzles and the influence on wire behavior were analytically investigated by CFD analysis in trim-cut situation. Also, the accuracy of CFD analysis results was verified by comparison with high-speed observation of actual fluid flow in WEDM. Furthermore, the wire deflection in trim-cut situation was simulated by using a structural analysis with considering pressure distribution acting on the wire surface obtained by the CFD analysis. The analytical results showed that the flow field around the wire periodically fluctuated regardless of flow rates with jet flushing when the workpiece thickness is relatively small. The wire deflection shape also changed due to the periodic fluctuation of fluid flow field around the wire. Furthermore, in order to investigate the influence on the trim-cut WEDM performance, the surface roughness of trimmed surface was measured for various workpiece thicknesses. It was found that the surface roughness become larger by the periodic fluctuation when the workpiece thickness is relatively thin.