Relation Between Flow in the Kerf and Excessive Adhesion of Sludge in the Wire Electrical Discharge Machining

Abstract

In wire electrical discharge machining, sludge adhesion deteriorates surface integrity. This study investigates the effects of coolant volume flow rate and nozzle geometry on sludge adhesion in the actual machining process. Excessive adhesion was observed for the smaller volume flow rate and the larger nozzle-to-workpiece distance. A series of numerical simulations using OpenFOAM were performed to understand the unsteady coolant flow near the wire and the kerf tip. The geometrical and operational conditions of the simulation were set as close as possible to those of the experiment. Although the actual flow is multi-physical, including phase and temperature changes, the present simulation considers single-phase iso-thermal flow to focus on the fundamental flow features. It is clear that the asymmetric nozzle configuration, where the top nozzle-to-workpiece distance is set to be larger than the bottom one, causes the flow from bottom to top. The analysis suggests that the stagnation region is formed near the wire, which can trigger the sludge adhesion. The sludge-clearing effect is limited because of the inactive flow, namely weak turbulence in this region. These observations are consistent with the results of the actual machining, suggesting the present simulation is helpful to improve the machining quality.