Effect of two-stage press blanking on edge stretchability with third-generation advanced high-strength steels

Abstract

Two-stage punching has been recently developed to reduce the sheared edge sensitivity of advanced high-strength steels by dramatically improving the hole expansion ratio via reduction of internal confinement. However, there is still no way to effectively apply this concept for the large-scale press blanking process. In this paper, a novel two-stage press blanking process is proposed to selectively improve the edge stretchability of third-generation advanced high-strength steels for regions with concentrated edge tensioning. Pre-hole design concepts were newly adopted for selective improvement. In the two-stage blanking with pre-holes, inducing the uniform shearing angle is critical for reducing work hardening and ensuring high sheared edge quality. The process is governed by the design and composition of the pre-hole for the first blanking and specifying the lengths of the blanking gap for the second blanking. The proposed two-stage blanking has been experimentally validated by sheared edge tensioning, sheared edge quality, and microhardness tests. A comparison with waterjet cutting showed that it was possible to achieve remarkable edge stretchability that was similar to that obtained for waterjet cutting.