Application of fast models to realize a closed-loop control of microstructure in open-die forging

• Applicant: Professor Dr.-Ing. Gerhard Hirt
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452539735

Open-die forging is an incremental bulk metal forming process, which is mainly used for the production of highly loaded large-scale parts with very high requirements regarding the mechanical properties. Since these mechanical properties are mainly determined by the workpieces’ microstructure, one main challenge in open-die forging is to alter the inhomogeneous and coarse microstructure resulting from the casting process towards a fine-grained and homogeneous microstructure. Although the microstructural properties, especially the grain size, are mainly depending on the process parameters as well as the chosen pass-schedule, nowadays open-die forging processes are mainly designed and realized based on practical knowledge, so that during forging neither an observation nor a control of the microstructure can be realized. Instead, geometry-based pass-schedule algorithms or FE-simulations are used to calculate an ideal process sequence, which is subsequently realized as good as possible in the actual forging process. Due to the main characteristics of open-die forging, such as the large forming temperature and enormous size of the workpieces, in reality deviations from the pass-schedule can occur easily and can accumulate during the large number of single forming steps and therefore negatively affect the resulting microstructure in the ingot.The aim of this research proposal is the realization of a closed-loop control of microstructure in open-die forging. Here, the control shall be realized following the “Operator-in-the-loop” concept, where the actual process operator is included as final decision-making body in the process control.For this purpose, at first fast models for strain, temperature and microstructure, which were developed at IBF, are implemented as observer for the microstructure during forging. Based on measurement data of surface temperature as well as geometry, the models are used to calculate the current microstructure during the process. Based on this, control algorithms are used to develop suggestions for the continuation of the process, which are presented to the operator. Hence, the proposed control concept features the properties of an assistant system. To realize the process control, in a first step the controllability of the microstructure has to be evaluated in detail. Based on this, appropriate algorithms need to be identified and implemented which based on the process parameters allow a closed-loop control of the microstructure towards an optimum final state. Preliminary work proved that the microstructure mainly depends on the process parameters and therefore in general the concept appears to be realistic.Therefore the first funding period is used to realize a whole system, in which the operator evaluates the suggestions of the assistance system and decides how the process is continued. A second funding period aims to improve the system to realize a fully automatic control of the microstructure in open-die forging.

• DFG Programme: Research Grants