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UBC Theses and Dissertations

Thermo-mechanical modelling of hot flat-rolling of components with curved profiles Xiao, Ming


A complete mathematical model for implementing the VGR process (a flat rolling process for producing components with variable thickness) under hot working conditions has been established. The work is based on an idea that a combination of separate submodels, such as, deformation, flow stress, roll force, temperature, etc., should be used, so that new development in each of these areas can be easily incorporated. A deformation submodel, based on the upper bound theorem, is given for the analysis of three-dimensional deformation of the work piece. A simple velocity field is proposed. To preserve the theoretical consistency, an equivalent coefficient of friction is adopted for the roll force calculation. Furthermore, the basic assumption, i.e., the rigid perfectly-plastic material assumption, is modified by introducing a concept of an isotropic rate-dependent material. Satisfactory results were obtained in spread, torque and force prediction. To obtain the mean temperature of the work piece, a temperature submodel is formulated based on one-dimensional transient flow in the roll-bite and two-dimensional flow outside the roll-bite. The model is capable of predicting the through-thickness temperature distribution in the roll-bite, estimating the mean temperature of the deforming body, and roughly calculating the mean temperature distribution along the work piece. To characterize the high temperature behaviour of steels, the well-known unified creep relationship is chosen as the flow stress submodel. Reasonably accurate prediction of the flow stress is achieved by using some experimental data reported in the literature.

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