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G. Hirt,D. Schafer 한국소성가공학회 2010 기타자료 Vol.2010 No.6
For the process design of incremental forming processes like ring rolling or stretch forging there is need for fast and accurate simulation techniques. For many applications it would be necessary to predict the microstructural evolution during the process. For this reason the FEM-software Larstran/Shape which is used for the plastomechanical simulation can be coupled with the microstructure simulation module Strucsim. This software uses phenomenological equations for the calculation of recrystallization (dynamic and static) and grain size evolution [7]. To accelerate the simulation a multi mesh method has been developed. This method uses an adapted simulation mesh with fine elements only in the locally limited contact and forming zone to achieve a reduction of the number of elements. Due to the relative movement of the tool and workpiece the adapted FE-mesh has to be remeshed regularly according to the position of the tool. To avoid loss of information caused by the use of coarse elements the multi mesh method uses a second storage mesh which represents the entire workpiece and which is discretized using only fine elements. For the update of the storage mesh the displacement vectors and changes of scalar values like temperature can be interpolated. For the application of the multi mesh method to the microstructure simulation the update algorithm for the microstructure values has to be modified. The microstructure and plastomechanical simulation have to be uncoupled and the static recrystallization and grain growth outside the forming zone have to be calculated separately. Using the multi mesh method the simulation of incremental bulk metal forming processes including a microstructural simulation can be accelerated. The acceleration factor of the simulation compared to a simulation without adaptive meshing is dependent on the reduction of elements and nodes.
Prediction of Microstructure in High-Strength Ductile Forging Parts
M. Urban,C. Keul,A. Back,W. Bleck,G. Hirt 한국소성가공학회 2010 기타자료 Vol.2010 No.6
Governmental, environmental and economic demands call for lighter, stiffer and at the same time cheaper products in the vehicle industry. Especially safety relevant parts have to be stiff and at the same time ductile. The strategy of this project was to improve the mechanical properties of forging steel alloys by employing a high-strength and ductile bainitic microstructure in the parts while maintaining cost effective process chains to reach these goals for high stressed forged parts. Therefore, a new steel alloy combined with an optimized process chain has been developed. To optimize the process chain with a minimum of expensive experiments, a numerical approach was developed to predict the microstructure of the steel alloy after the process chain based on FEM simulations of the forging and cooling combined with deformation-time-temperature-transformation-diagrams.