| To predict the final shape of the deformed part after springback, the calculation of the internal stress distribution in the sheet metal must be accurate. The Bauschinger effect exists when the element of sheet metal undergoes both loading and reverse loading processes, i.e. cyclical loading. Therefore, the influence of the Bauschinger effect becomes more important when the deformation history of the sheet metal is more complicated. For an accurate prediction of springback, the Bauschinger effect must be considered to obtain an accurate internal stress distribution within the sheet metal after deformation.; Based on the foundation of the isotropic kinematic hardening model, the Mroz multiple surface model, and plane strain assumptions, and experimental observation, a new incremental method and hardening model is proposed in this study. In comparison with methods based purely on isotropic hardening, kinematic hardening, and Mroz multiple surfaces models, this new methodology compares well with the experimental results for aluminum sheet metals undergoing multiple bending processes. This new hardening model is not only a generic method for springback prediction but also a hardening model for sheet metal forming process simulation.; An efficient and low cost multiple bending experiment has been designed and performed to investigate the influence of the Bauschinger effect on springback in sheet metal forming. Three different steel sheet metals (high strength, back hard, and AKDQ) and two types of aluminum (AA6111-T4 and AA6022-T4) were used as experimental materials in this study. Based on the experimental results from this research, it can be seen that the influence of the Bauschinger effect on springback is more significant for aluminum than for steels. Therefore, both the deformation history and the Bauschinger effect must be considered to predict springback of aluminum stamping parts. Through this multiple bending experiment, the material parameters (called CM values here) after reverse yield can be obtained. Then, these parameters can be applied to the new hardening model to get more accurate simulation results than can be obtained using the isotropic hardening model, kinematic hardening model, or Mroz multiple yield surfaces regardless of the tooling geometry and the clearance between die and punch. |
