Influence of energy input process on the white layer and residual stress in electrical discharge machining

The influences of electrical and non-electrical parameters on surface integrity during the EDM process have been widely researched in past years. However, the effect of the energy input process at the same discharge energy is seldom reported. To select more suitable processing parameters according to the processing requirements, we have studied the influence of the energy input process on processing characteristics and surface properties. Two different energy input modes (high discharge current with short pule-on time (HIST) and low discharge current with long pule-on time (LILT)) are used. When the discharge energy is the same, the HIST mode has a higher material removal amount, while the sample produced by the LILT mode presents a lower surface roughness and residual stress. More surface cracks are detected on the samples processed by the LILT mode, and their dimensions in terms of length and width are greater than that of the HIST mode. The microstructure of the EDM surface is composed of α-Fe, γ-Fe, and cementite. When the discharge energy is higher than 0.24 mJ, the intensities of diffraction peaks γ-Fe and cementite on the EDM workpiece surface produced by the HIST mode are higher. The white layer thickness is related to the discharge energy and its input process. When the discharge energy is lower than 0.51 mJ, the white layer is thinner under the LILT mode. However, the white layer of the EDM sample fabricated by the HIST mode is thinner when the discharge energy is higher than 0.51 mJ.