1 Improving the fatigue life of electro- discharge-machined SDK11 tool steel via the suppression of surface cracks Assistant : Wan-Ching Weng Department of Mechanical Engineering & Institute of Nanotechnology, Southern Taiwan University of Science and Technology, Tainan, TAIWAN Date 2015/06/07 Introduction Experimental procedure Results and discussion Morphology of EDMd surface Influence of surface cracks on fatigue strength Influence of recast layer thickness on fatigue strength Fatigue section observations Conclusion Outline Introduction 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 s or 16 s. The various specimens are then fatigue tested at loads ranging from 1470 to 2401 N in order to determine their respective fatigue lives. Experimental procedure Results and discussion Fig. 9. SEM images showing increasing white layer thickness with increasing pulseon duration: (a) thin white layer with no cracks (pulse current 16 A, pulse-on duration 4 s) and (b) thick white layer with no cracks (pulse current 32 A, pulse-on duration 16 s). Fatigue section observations Conclusion Increasing the pulse current or reducing the pulse-on duration suppresses the formation of surface cracks in the SKD11 machined surface, and hence improves the fatigue life. The average thickness of the white layer increases as the pulse current and pulse-on duration increase. As the thickness of the white layer increases, it becomes more brittle and therefore fractures more readily. As a result, the fatigue life reduces as the thickness of the white layer increases. The specimens considered in the present study can be ranked in terms 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. 11 Thanks for your attention !! STUST