Abstract
A number of special blanking processes are available for producing fine cut edges and blanking with a negative clearance is one of them. The aim of this study is to elucidate the mechanism of precision blanking with a negative clearance by using finite element method. Experiments were performed for two kinds of aluminum sheets over a wide range of clearances between -30 and 20 percent of the sheet thickness. Fine blanked products with no fractured zone were obtained in the case with negatively large clearances, while fractured zone appeared on the cut edge by conventional blanking. Corresponding simulations were carried out by using the Ayada's and the Jeong's criterion to predict ductile fracture initiation. Numerical results with both criteria agreed well with the experimental results except a few cases accompanied by secondary shear. The difference in blanking mechanism between the positive and the negative clearance blanking was explained by the variation of the damage value; it reached the threshold value for positive clearances, while it was kept low and never exceeded the threshold for negatively large clearances.
