Study of the surface integrity of the machined workpiece in the EDM of tungsten carbide

A comprehensive study of the surface integrity of the machined workpiece in the electrical discharge machining (EDM) of tungsten carbide is presented in this paper. EDM tests on a tungsten carbide workpiece were conducted on a Charmilles Technologies Roboform 40 EDM Die-Sinking Machine, with the peak current and pulse duration varied. The EDMed surface morphology was examined with a scanning electron microscope (SEM) (JEOL JSM-5600LV) with energy dispersive spectrometers. Surface hardness was determined with a macro-hardness tester. It is found that there is no difference between the hardness of the EDMed surface and the original hardness of the workpiece for all EDM conditions. It is observed from the SEM micrographs that there is a clear EDM damaged layer on the workpiece, distinguished by the amount of WC grains and micro-cracks. The amount or concentration of WC grains decreases from the internal structure of the workpiece to the top surface layer. Another feature on EDMed surfaces is the abundance of cracks, especially at high peak current and pulse duration. It is also observed that the EDM conditions have no effect on the microstructures of the bulk workpiece material. This means that damage caused by EDM on the EDMed surface is limited to a certain depth only. However, it is observed that the depth of the damaged layer and the average length, width and number of micro-cracks increase with the peak current and pulse duration. The damaged layer and micro-cracks seem to disappear when the peak current and pulse duration were set at very low values.