In recent years the finite-element-method (FEM) simulation has become applicable for the development, design and optimisation of metal forming processes. To obtain accurate results within the simulation the exact description of the flow stress kr during the process is essential. The implementation of the flow curve into FE-packages can be realised through different methods. Using the measured data in tabular form seems to be the easiest way, but special interpolation methods are necessary and extrapolation is strictly forbidden. Hence the exact flow stress measurement up to highest strain rates (between 0.0001 and 300/s) to simulate industrial processes like rolling or extrusion is essential. This paper presents actual studies in the field of high-speed testing by use of a servohydraulic testing system in a temperature range between room temperature and 1300 DC. Furthermore the use of material models to describe the material behaviour is getting more and more popular. Therefore hot compression tests must be carried out to determine the necessary parameters for reliable prediction. Specifically for aluminium alloys, where homogeneous deformation in the temperature range above 300 DC is not possible at present, new strategies for the determination of the material models have been developed. The compression tests are deliberately performed under sticking conditions to obtain strong gradients of the forming and microstructure parameters within a sample. The model equations are then adapted by consideration of the local parameters. Finally an optimisation coupled with an FEM program is applied to the models. FlieBkurvenaufnahme im Zylinderstauchversuch und spezielle Anwendungen in der Umformtechnik. In den letzten Jahren bekam die Simulation mit Hilfe der Finiten-Elemente-Methode eine immer greBere Bedeutung in der Anwendung fur die Entwicklung, Auslegung und Optimierung von Umformprozessen. Urn hinreichend genaue Ergebnisse in der Simulation zu erhalten, ist die exakte Beschreibung der FlieBspannung kr wah rend des Umformprozesses notwendig. Die Implementierung der FlieBspannungsbeschreibung in ein FEM-Programmpaket kann auf verschiedene Weise erfolgen. Einerseits konnen die Daten direkt wahrend der Rechnung aus einer Tabelle eingelesen werden, andererseits konnen uber Regressionsverfahren verschiedenste Gleichungen mittels Interpolation angepaBt werden, die die FlieBspannung in Abhangigkeit von den Umformparametern beschreiben. Extrapolation so lite keinesfalls angewendet werden. Foiglich ist die genaue FlieBspannungsmessung im Stauchversuch bis zu hohen Umformgeschwindigkeiten (0.0001 bis 300/s) notwendig, urn Prozesse -wie z.B. das Warmwalzen oder Strangpressen -simulieren zu konnen, In dieser Veroftentlichunq werden unter anderem aktuelle Arbeiten im Bereich der Hochgeschwindigkeitsversuche auf einer servohydraulischen Prutmaschine in einem Temperaturbereich von RT bis 1300 DC erlautert, Weiterhin kommt der Ermittlung von Werkstoffmodellen zur Beschreibung des Werkstoffverhaltens in der Simulation immer greBere B...
Knowledge of correct flow stress curves of Ni-based alloys at high temperatures is of essential importance for reliable plastomechanical simulations in materials processing and for an effective planning and designing of industrial hot forming schedules like hot rolling or forging. The experiments are performed on a computer controlled servohydraulic testing machine at IBF. To avoid an inhomogeneous deformation due to the influence of friction and initial microstructure, a suitable specimen geometry and lubricant is used and a thermal treatment before testing has to provide a microstructure, similar to the structure of the material in the real process. The compression tests are performed within a furnace, which keeps sample, tools, and surrounding atmosphere on the defined forming temperature. The uniaxial compressions were carried out in the range of strain rates between 0.001 and 50s−1 and temperatures between 950 and 1280°C. Furthermore, two-stage step tests are carried out to derive the work hardening and softening behavior as well as the recrystallization kinetics of the selected Ni-based alloys. At the end of this work a material model is adapted by the previously determined material data. This model is integrated into the Finite Element program LARSTRAN/SHAPE to calculate a forging process of the material Alloy 617.
Knowledge of correct flow stress curves of Ni-based alloys at high temperatures is of essential importance for reliable plasto-mechanical simulations in materials processing and for an effective planning and designing of industrial hot forming schedules like hot rolling or forging. The experiments are performed on a computer controlled servo-hydraulic testing machine at IBF (Institute of Metal Forming). To avoid an inhomogeneous deformation due to the influence of friction and initial microstructure, a suitable specimen geometry and lubricant is used and a thermal treatment before testing has to provide a microstructure, similar to the structure of the material in the real process. The compression tests are performed within a furnace, which keeps sample, tools and surrounding atmosphere at the defined forming temperature. The uniaxial compressions were carried out in the range of strain rates between 0.001 and 50 s−1 and temperatures between 950 and 1280°C. Furthermore two-stage step tests are carried out to derive the work hardening and softening behaviour as well as the recrystallisation kinetics of the selected Ni-based alloys. At the end of this work a material model is adapted by the previously determined material data. This model is integrated into the Finite Element program LARSTRAN/SHAPE to calculate a forging process of the material Alloy 617.
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