Development of a model to describe springback and residual stresses resulting from bending at elevated temperatures

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For the steady weight reduction of bent parts by the application of lightweight metals with increasing strength, new challenges arise to keep dimensional accuracy and to deal with the decreased formability in conventional forming processes as the fast clocked progressive dies. Bending at elevated temperatures through inductive heating in progressive dies represents an innovative solution to produce high accuracy and complex bent parts in a large scale despite of the limited formability due to the higher strength. Hence, the aim of the project is the prediction of springback and residual stresses for bending at elevated temperatures, during which numerous temperature and time dependent influences can occur. In this context, temperature and time dependent, physical mechanisms with a relevant effect on the springback and the stress state will be characterized in hot tensile tests and further bending tests. The experimental results serve further to model the produced geometry as well as the residual stresses through an analytical or a semi-analytical approach. The focus will be on creep strains during forming and loaded holding, the plastic flow during quenching with an active load, and the variable Youngs modulus in a cold and a hot state. The mechanism will be investigated through warm tensile tests and a parameter analysis. Subsequently, the modeling will be supported by bending tests with cooled and also tempered tools. The approach will be verified further with numerical simulations. Finally, the deduced correlation gives an analytical comprehension of the product properties as the bending angle and the residual stresses in relation to process temperatures, times, and the strain rate.