Improving the fatigue life of electro-discharge-machined SDK11 tool steel via the suppression of surface cracks

The present study performs an experimental investigation to identify the EDM processing parameters which suppress the formation of surface cracks in the machined surface of SKD11 tool steel specimens. In the EDM trials, the specimens are machined using pulse currents of 4 A, 16 A or 32 A with pulse-on durations of either 4 μs or 16 μs. The various specimens are then fatigue tested at loads ranging from 1470 to 2401 N in order to determine their respective fatigue lives. A polished SKD11 specimen is also fatigue tested for comparison purposes. Finally, the fracture surfaces are examined using scanning electron microscopy to examine the crack propagation characteristics.The results show that increasing the pulse current and reducing the pulse-on duration provides an effective means of suppressing the surface cracking phenomenon. Higher values of the pulse current and pulse-on duration are found to increase the average thickness of the recast layer. Overall, the present results show that the four specimens considered in the fatigue test can be ranked in order of reducing fatigue life as follows: (1) the polished specimen, (2) the specimen with a thin recast layer and no surface cracks, (3) the specimen with a thick recast layer and no surface cracks and (4) the specimen with surface cracks.