With the press hardening technology it is possible to produce components with tailor- made material properties. The present work is based on a comprehensive thermo-mechanical material model for simulation of press hardening and similar processes. The model accounts for and predicts time dependent and time-independent phase transformations, mechanical and thermal properties as well as transformation plasticity during the complete cooling and deformation process from 900 °C to room temperature. The model predicts the microstructure evolution during the complete process as well as the final fractions. The thermal contact properties and the thermal properties in the tools have influence on the final material state. Solutions for tool heating and cooling for manufacturing of components with soft zones are studied. Based on the results from the press hardening simulations, thermal properties of special tool materials are taken into account in order to optimise the manufacturing thermal cycle.
In metal forming operations the stress and strain levels can locally reach much higher magnitudes than those measurable in a standardised uniaxial tension test. Additionally, the stress and strain states are in many cases multi-axial. In this paper an inverse method to obtain material data is proposed. The aim is to yield more accurate data for a wider range of strain compared to a standard uniaxial tensile test. The outline of the work is that a forming experiment is designed to reproduce tensile strains present in a full-scale cold forming process. The blanks used are made of relatively thick high strength hot-rolled steel. Process data from experiments, i.e. punch force and punch displacement, are used as input to an in-house optimisation software package. The direct problem solved in the inverse modelling and optimisation scheme is a finite element analysis (FEA) of the experiment. The goal is to find parameters in a constitutive model of the material that minimises the difference between experimental and FE-calculated data. The experiments are modelled in a commercial FE software. Four different isotropic hardening laws are used in the FE-model. One of the optimised models is applied in a forming simulation and geometric optimisation of a demonstrator part.
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