Integration of a complex control system into a numerical process model for the simulation of ring rolling processes

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In conventional Finite Element Simulation of the ring rolling process the motions of all tools have to be defined for the entire process prior to simulation. Since in the real process all motions are adaptively controlled by sophisticated closed-loop control systems according to actual process variables and preselected control strategies, it is not possible to prescribe all motions beforehand. Therefore, in the first part of the investigation the complex control algorithms of an industrial controller have been integrated into a numerical process model of ring rolling. For this purpose, a precompiled version of an industrial controller, which was provided by the manufacturer of ring rolling mills, has been coupled to the FE simulation of ring rolling. Within the model all translational and rotational velocities of the tools are adapted as actuators according to current sensor values (positions, forces and torques), which are calculated within the FE simulation. Furthermore, the control considers the force and torque restrictions of the machine while taking into account initial user requirements (rolling strategy, desired ring growth rate and geometry). The new approach enables for the first time the simulation of a complete ring rolling process with realistic machine specific kinematic history without using kinematic variables from the experiment. Since industrial control systems are designed to perform the process at the power limit of the machine, a correct estimation of forces and torques is of utmost importance in feedback controlled simulation. As these values were not always accurately predicted, the main goal of the second phase of the proposal is to investigate and improve the force and torque calculation in FE model. On the one hand this involves evaluation and if necessary improvement of the thermal field calculation. On the other hand it must be evaluated under which conditions static softening mechanisms, which might occur between the roll gaps, influence the flow behavior significantly. Two materials with highly different softening behaviors will be analyzed by experiments with large and small runtimes between the roll gaps. Using the simulations of these experiments the recrystallization can be calculated by extracting the local thermal and mechanical history of distinct elements. Since in some cases, the simulated torque differs from the experimental results though forces are computed correctly, the accuracy of the rolling torques measurement should be verified. As the provided industrial controller contains only one relevant industrial rolling strategy as a black-box, it is not always possible to identify the reasons for the minor differences between simulations and experiments. Furthermore, another drawback of this approach is that the control algorithms cannot be enhanced and modified. Therefore, a model with technologically reasonable control algorithms similar to the industrial controller will be implemented.