Prediction of springback in air-bending of Advanced High Strength steel (DP780) considering Young׳s modulus variation and with a piecewise hardening function

• Young׳s modulus variation and variable K and n are included in bending theory.
• Advanced High Strength Steel is considered due to its modulus reduction.
• A numerical method by assigning discrete modulus values is used.
• Using variable K and n values to describe material׳s property gives a good prediction.
• Both analytical model and finite element model show the improved accuracy.

Advanced High-Strength steels (AHSS) are increasingly used in industry. Thus, the springback prediction in bending of AHSS is important to maintain close geometric tolerances in deformed parts. The unique properties of AHSS: a non-constant Young׳s modulus and a stress–strain relation which does not follow a simple flow stress equation make the prediction of springback very difficult. In this study, an analytical model was developed to predict the springback in air-bending of AHSS, considering the special properties of these materials. A computer code which is developed based on classical bending theory was updated based on the new model. The finite element simulation which includes the properties of the AHSS is also presented in the paper. The comparison between the experimental results and predictions indicates that the detailed consideration of the properties of AHSS affects the accuracy of the springback prediction with the analytical method. It is hoped that this new analysis can be incorporated into the controller of a press brake to adjust the machine for compensating springback during bending.