Elasto-Plastic Simulation Concepts For Profile Transfer And Flatness Prediction In Flat Hot Rolling

For the prediction of the material flow behavior of wide strips in hot and cold rolling, highly sophisticated procedures are essential, which are able to couple the deformation of the strip and the elastic response of the rolls. Especially for thin, wide strips, where the aspect ratio width over thickness is extremely unfavorable for standard FEM-calculations, the determination of profile transfer and flatness obviously leads to extremely high calculation times with commercial FEM-programs. Therefore, a tailor-made FEM-code for the efficient simulation of the elasto-plastic material flow inside the roll gap has been developed. The underlying formalism for the strip-routines is based on pseudo-steady-state streamline-update techniques for the stress-field, coupled iteratively with the principle of virtual power for the determination of the velocity field and the contact stress distribution between strip and work roll. Coupling of the strip models with the routines for elastic roll stack deflection is a precondition to get reliable results concerning profile transfer and residual stresses inside the strip, which allows the prediction of flatness defects, such as buckling. Of particular interest is the dependence of the longitudinal stress distributions and of the corresponding specific rolling force-distribution across the strip width on the underlying constitutive elasto-viscoplastic laws including rate-dependence, work hardening, softening and creep effects.