Refinement of a material model for springback after press forming

Abstract

.The best tool for characterizing the behaviour of sheet metal during press forming is numerical modelling based on the finite element method (FEM). Using this technique, the response of the press-formed part can already be predicted during the process design stage. The main input data for the process simulation include the tool geometry and materials properties and process conditions, such as temperature, pressing velocity, lubrication and others. The resultant shape of the press-formed part is governed predominantly by the shape of the tools and the workpiece material. The input information on the workpiece material has the form of a material model whose accuracy dictates the accuracy of results. Where high-strength steels are used in the automotive industry, one should focus on springback which alters the shape of press-formed parts. Springback is an undesirable change to the part’s shape caused by residual stresses being released after its removal from the tool. Tooling designers need to take springback into account by choosing an appropriate material model. Conventional hardening models, such as kinematic and isotropic hardening rules, are not adequate for modelling springback. Instead, more sophisticated models, such as the one introduced by Lemaitre and Chaboche are a better choice. In this paper, the options for measuring and FE modelling of the Bauschinger effect are discussed. The proposed idea was tested on a 1.5 mm sheet of DC01 deep-drawing steel.