Fluid Dynamics in Electrode Flushing Channel and Electrode-Workpiece Gap During EDM Drilling

摘要

Evacuation of removed material is a key limitation factor in EDM drilling, as debris particles remaining in the gap between electrode and workpiece could reattach to the workpiece or cause ineffective discharges. In order to increase particle evacuation rate, electrodes with internal flushing channels are used. In this work, the influence of drilling conditions to the pressure drop and dielectric flow during EDM drilling is investigated analytically and through computational fluid dynamics (CFD) simulations. The electrode diameter, gap, configuration of the flushing channel, electrode length and drill depth are analysed to estimate and describe the influence on the flow. The change of flow with wearing out of the electrode needs to be taken into account. Also the configuration of the channel cross section has a great influence to the flow. Turbulences, pressure and velocity distribution are analysed through the numerical simulation. The gap between electrode and workpiece matters when the electrode is short and/or the drilling hole is deep. The flushing efficiency has a significant effect on the recast layer thickness (RLT), which can influence the workpiece quality. With the shortening of the electrode during the process the RLT is reduced by more than 15% with the faster dielectric flow, which has to be considered for achieving constant process conditions. The results of the simulations are compared and verified with drilling experiments by investigating the flow conditions as well as the process performance for various electrodes and the influence on the RLT.