Analytical model for prediction of springback parameters in the case of U stretch–bending process as a function of stresses distribution in the sheet thickness

One of the main undesired phenomena that affects the dimensional accuracy and shape of the cold formed parts made from metallic sheets is the springback. An important cause that determines and influences the intensity of this phenomenon is the distribution of stresses generated by the cold forming process in the deformed material. The determination of a relationship between springback and generated stresses distribution needs the knowledge of the law of stresses and springback parameters variation and of their causes and factors of influence. A model for prediction of springback parameters in the case of U stretch–bending process as a function of stresses distribution in the sheet thickness was established and analyzed in the paper. The results obtained from the performed analysis show that the normal anisotropy influences the level of stresses on the inner and outer faces and finally the springback intensity. The blankholder force and friction coefficient have not a major influence on the stresses level but the increase of their values determines the increase of the distance between the neutral and middle axes of sheet and hence the decreases of springback intensity. Based on the established model the prediction of springback was done in the phase of tools design and hence the drawn part accuracy was increased.

► The model for prediction of springback parameters was constructed using the Hill’48 yield criterion.
► The springback was predicted as a function of stresses distribution in sheet thickness.
► The stress in sheet thickness was determined based on strains due to bending and tensile loadings.
► The neutral axis position was determined based on strains due to bending and tensile loadings.
► The unloading moment was expressed using the equality: strain energy=external loadings energy.