The Prestrain Effect on the Sheared Edge Flangeability of Dual Phase 780 Steels

Edge flanging represents one of the forming modes employed in multistage forming, and advanced high strength steels (AHSS) are more prone to edge cracking during sheared edge flanging than the conventional high strength steels (HSS) and mild steels. The performance of the sheared edge in flanging operation depends on the remaining ductility of the material in the sheared edge after the work hardening (WH) and damage produced by blanking and subsequent forming operations. Therefore, it is important to analyze the effect of work hardening produced by blanking and subsequent forming operations prior to edge flanging on the edge flanging performance. In this study, the effect of different forming operation sequences prior to edge flanging on the edge flanging performance was analyzed for a dual phase 780 steel. Sheared edge flanging performance was evaluated by hole expansion testing of specimens produced by the following forming operation sequences:

• Punching and flanging
• Uniaxial stretching, punching and flanging
• Biaxial stretching, punching and flanging
• Punching, biaxial stretching and flanging

The results show that the hole expansion limit is not affected by uniaxial or biaxial prestraining prior to hole punching. Therefore, work hardening in multistage forming prior to edge trimming should have little or no effect on edge flangeability