Effect of Carbon in the Dielectric Fluid and Workpieces on the Characteristics of Recast Layers Machined by Electrical Discharge Machining

Electrical discharge machining (EDM) is a popular non-traditional machining technique that is usually performed in kerosene. Carbon from the kerosene is mixed into the recast layer during EDM, increasing its hardness. EDM can be performed in deionized water, which causes decarburization. We studied the effects of carbon in the dielectric fluid and workpiece on the characteristics of recast layers. Experiments were conducted using gray cast iron and mild steel workpieces in deionized water or kerosene under identical operating conditions. Scanning electron microscopy revealed that the recast layer formed on gray iron was rougher than that produced on mild steel. Moreover, the dispersion of graphite flakes in the gray iron seemed to cause subsurface cracks, even when EDM was performed in deionized water. Dendritic structures and iron carbides were found in the recast layer of gray iron treated in deionized water. Kerosene caused more microcracks to form and increased surface roughness compared with deionized water. The microcrack length per unit area of mild steel treated in deionized water was greater than that treated in kerosene, but the cracks formed in kerosene were wider. The effect of the diffusion of carbon during cooling on the characteristics of the recast layer was discussed.