2016 Volume 57 Issue 670 Pages 1062-1069
In stretch flange forming, the sheet-edge quality is important since it affects the appearance of fractures at the edge. In this study, the effect of the edge trimming conditions of the blank sheet on both the sheet-edge quality and flange-up formability is investigated. It is found that in the case of edge trimming of a sheet with high tensile strength and poor ultimate ductility, a large burr generates at the edge, which easily causes fractures, when the shearing clearance between the upper and lower dies is large. This tendency in trimming for flange-up forming is not observed in hole piercing for hole expansion. It is clarified that the burr is caused by excessive bending behavior under large shearing clearance conditions, and that the forming limit in flange-up forming is independent of the clearance unless a large burr generates. Then, a new shearing die structure, which suppresses excessive bending, is developed in order to avoid the creation of large burrs, and consequently, high formability is attained.
