Abstract
In order to find out whether 100% clean-cut surface can be prepared after crack formation in the shear zone, contact stress was measured by PVDF film stress sensors on the cold-rolled medium-carbon steel sheet surface in the fineblanking processes. Characteristics of contact stress was revealed by comparing the outputs of the FB processes with the maximum and minimum blank-holder force, which prepared 100% clean-cut surface respectively. Penetration depth of the punch in the sheet increased with the number of times of the FB proesses. And the microstructure evolution in the shear zone was observed by scanning electron microscopy (SEM). Local fluctuations in the sensor output indicated the crack ever propagated in the shear zone during the sheet punching process. The crack tip hardened zone and pre-existing microcracks in front of the crack tip caused the crack deflection. The crack path formed a protuberance which was then extruded by the die corner to continue forming clean-cut surface until the end. Microhardness of the cut surface first increased and then decreaed because of the crack propagation, whereas the exponential increase in microhardness occurred in the case that no crack initiated.
Published Version
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