Experimental and Numerical Study on Blanking Process with Negative Clearance

Abstract

This study summarizes the characteristics of blanking behavior with a negative clearance. Several experiments were performed for two aluminum sheets over a wide range of clearances including negative values. Blanking with negatively large clearances was found to produce fine cut edges with less roll-over and no fracture zone even for a brittle material. Corresponding simulations were performed using the Ayada's criterion for predicting ductile fracture initiation. Each zone of blanked part edges such as roll-over and fractured zone agreed well with that obtained in the experiments except a few cases accompanied by secondary shear. The reason for prevention of fracture by using negative clearances was explained with the change of the damage value during the process; the damage value was kept low throughout the blanking operation since the mean stress dominating the damage value became compressive around the die edge. Influences of blanking parameters on load-stroke curves were also investigated. The curves for negative clearances showed gradual increase in load toward the end of stroke. The earlier fracture initiated, the earlier the load reached a peak. Simulated curves showed the same tendency and in good agreement with the experimental ones quantitatively.