Predictive modelling of longitudinal bow in Chain-die formed AHSS profiles and its experimental verification

Abstract Chain-die forming, as a newly developed technology, is considered as an alternative method to fabricate AHSS automotive structural parts. The longitudinal bow is one of the most general geometric deviations of cold-formed materials. This paper utilizes analytical modelling, finite element analysis and experimental verification to disclose the mechanism of the formation of the longitudinal bow of Chain-die forming of AHSS profiles. To improve accuracy, the Chaboche hardening model is adopted in the simulation work to characterize the Bauschinger effect of the AHSS products. A detailed comparison of the mechanisms of the formation of the longitudinal bow of Chain-die-formed and roll-formed AHSS profiles is carried out to emphasize their differences. The analytical model indicates that, in contrast to roll-formed profiles, longitudinal bow in Chain-die-formed profiles is primarily caused by the elastic recovery of the accumulated incremental plastic deformation in the bend corner. It can be understood as a follow-up phenomenon accompanied by springback. With a certain material, its severity is related to the thickness, the bend corner radius and the second moment of area of a product. This is consistent with the simulation and experimental results. Finally, a comprehensive numerical investigation is used to quantify the effect of critical parameters on the longitudinal bow.