FE-Simulation of Thin Strip and Temper Rolling Processes

Within the production chain of cold-rolled flat products skin-pass and temper rolling represent the final forming stage, in which material and surface properties as well as flatness are tailored to satisfy even the most demanding customer requirements. Almost all skin-pass and temper-mill setups are based on offline calculations, supplemented by trial and error procedures during operation. To minimize strip segments that do not match the prescribed tolerances, which occurs especially after changes in sheet sizes, it is of vital importance to incorporate appropriate offline and online models to the automation structure of such rolling mills. Key objectives of adequate models are the precise determination of the rolling force, of the roughness transfer and of the roll-flattening behaviour. As is well known for thin sheet, foil and temper rolling processes, the simplified assumption of a circular arc of contact breaks down. Therefore, the correct non-circular surface contour of the work roll has to be determined simultaneously with the resulting contact pressure distribution between strip and work roll. To attain a comprehensive understanding of these underlying process details, and to check and tune semi-analytical model approaches, highly sophisticated numerical approaches based on the method of finite elements have been performed by utilizing the non-linear capabilities of Abaqus Standard and Explicit. Due to extremely short contact lengths in temper rolling processes, a very fine spatial discretization is essential, often leading to several hundred thousand degrees of freedom even for plane strain calculations. Special emphasis has to be put on work roll flattening and on the formation of contained plastic flow regions.