Compensate for longitudinally discrepant springback and bow in chain-die forming processes by multiple sections optimization

As a gradual deformation process like roll forming, chain-die forming is attractive to manufacturing advanced high-strength steel (AHSS) channels. The gradual forming mode induces complex and longitudinally discrepant springback and brings additional difficulty to the die design of AHSS forming. In this work, a new chain-die design method by adopting a multi-cross-section compensation strategy is proposed to compensate for the longitudinally discrepant springback and bow. A hat geometry with six design variables is adopted to ensure an undercut-free and smooth optimized die surface. The sectional springback compensation is taken as a multi-objective optimization problem, and the non-dominated sorting genetic algorithm-II is used to minimize the deviation between calculated sectional springback profiles and desired geometry. In addition, the longitudinal bow is also taken into account with an optimal counterpart arc on the web. The optimal results indicate that the non-uniform springback in chain-die forming exhibits a linear variation along the longitudinal direction for the constant hat channel. Chain-die forming experiments of constant and variable AHSS channels are carried out for verification, and both the springback and longitudinal bow are reduced by using the proposed die design method.