Sidewall Curl Reduction Using Active Drawbead

As environmental consciousness rises and greenhouse effect becomes worse, design for lightweight automobiles becomes a major goal for vehicle manufacturers in order to reduce ⻒2;⻓4;2 emissions. Because advanced high strength steels (AHSS) are lightweight and high strength, AHSS have been widely used in automobile structural parts. However, as the strength of steels increases, stamping defects such as sidewall curl and distortion become worse. In order to reduce stamping defects of AHSS, such as springback, wrinkling and distortion, drawbeads are often used in stamping process. In order to design drawbeads quickly and properly in stamping processes, this study investigates the feasibility of active drawbeads in sheet metal forming. This study focuses on the establishment of active drawbeads design process. Because Baushinger effect is much stronger in AHSS than in low strength steels, this study investigates the difference between physical drawbeads and equivalent drawbeads in CAE simulation. According to the simulation results, physical drawbeads can correctly take Baushinger effect into account in stamping. This study also investigates the effect of geometric parameters of drawbeads on sidewall curl. In addition, this study investigates the effect of parameters of round bead on sidewall curl and thinning. By studying the contact forces among punch, mold and drawbeads during stamping process, this study establishes a design process of active drawbeads. It shows that sidewall curl can be significantly diminished. Radiuses of sidewall curl of NUMISHEET 2011 benchmark 4 are higher than 1000mm in 780Y, 980Y, 1180Y by using active drawbeads without cracking.