Influence of draw restraining force on the springback in advanced high strength steels

Advanced high strength steels (AHSS) are engineered to have both high strength and enhanced formability characteristics. Yet, the formed components undergo springback due to elastic recovery after removal of the forming tools. This severely affects the dimensional accuracy of the part. Many techniques have been evolved to deal with springback. A simple approach is to design forming tools that compensate for springback [1]. As the springback increase, its variability will also increase that result in the die correction estimation difficulties, especially when the part has complex geometry [2]. An effective approach to reduce springback is by attaining adequate strain levels in the part. This can be achieved by utilizing draw beads to induce large strain and reduce elastic recovery process in the part [3]. Dual phase steels have excellent ductility and work-hardening rate resulting in a superior strength-ductility balance. Higher strength levels and improved formability are achieved in the parts due to increased values of work-hardening exponent of the dual-phase steels. This in turn increases problems such as springback, higher loads on the forming tools, etc. This study focuses on the influence of drawing restraining force on the springback characteristics of the dual-phase steel using draw-bend test. Draw-bend tests imitate typical forming procedure involving tensile loading, bending, and unbending as the specimen is drawn over the roller [4]. As the sheet tension is increased, through a hydraulic actuator in the draw-bend tester, springback reduces at different rates for different materials [5].