Sheared Edge Characterization of Steel Products used for Closure Panel Applications

Application of Advanced High Strength Steels (AHSS) to closure and structural parts in the automotive industry is increasing in future models. In addition to weight reduction, the other primary motivation to consider these products is the improvement of structural performance that is needed to meet future stringent safety standards. AHSS products have a combination of unique microstructures and mechanical behavior. It is important to develop basic knowledge and understanding of all the manufacturing aspects of forming these products, so that robust forming processes can be engineered to successfully form parts in a production environment. The edge condition obtained after post-draw operations such as trimming has a significant influence on processes such as stretch flanging. A study to investigate the influence of punching clearance on the edge characteristics of various AHSS products has been initiated at Mittal Steel R&D. Hole expansion test conducted using a conical punch was used as a measure of stretch flangeability of products with different edge conditions. Results for DP500 product and the commonly used BH210 and DQSK used for closure applications are presented in this paper. In addition, guidelines to obtain optimum edge conditions to facilitate successful stretch flanging will be discussed.