Microstructure improvement during closed die forming operations by the help of Finite Element simulation combined with processing maps

 

This project aims at the adaption of a closed die forming operation to produce a gear wheel by the help of Finite Element (FE) simulations combined with processing maps to ensure a homogenous fine grain size after forging.

  Multi-stage forging operation Copyright: © ICMEaix Multi-stage forging operation to ensure a homogenous fine grain size in the complete part

During the design of closed die forming operations one goal is to ensure a fine homogenous grain size in the stressed parts of the component. Within the investigated process chain to produce a gear wheel it was shown that a single-stage deformation is incapable to realize these fine grain size in all parts of the component. Therefore, multi-stage deformation has to be used. Due to the high number of variable boundary conditions for such a process design, usually costly trial-and error tests are necessary. To reduce the number of necessary tests, in this case a FE simulation study based on the process model developed at Institute of Metal Forming IBF in combination with processing maps was used to examine the effect of different forging temperatures and steps in a multi-stage process. The processing maps determined at the Steel Institute IEHK were implemented as a user-subroutine in the simulation model. This allows for a description of the microstructure evolution during deformation and thus a verification whether the investigated process conditions result in a homogenous fine grain microstructure. Based on this simulation study four forging designs were develop and validated using a 6.3 MN forging press at IBF.

As a result an optimized multi-stage forging process was developed resulting in dynamic recrystallization in the complete component and thus a homogeneous fine grain size that can be seen in Figure 1. This process consist of a two-stage pre-forging at 1100 °C and a final stage at 900 °C. During two stage pre-forging the billet is rotated by 180° to introduce a homogeneous deformation. The final stage is conducted using a decreasing die speed to trigger the niobium precipitations. From the micrographs of the validation experiments it can be seen, that this process results in a recrystallized microstructure in the whole component, while the single step deformation shows no recrystallization in measuring points 1 and 3.

 

Project Partners

Organization Address
Steel Institute IEHK,
RWTH Aachen University
Intzestr. 1,
52072 Aachen,
Germany
Institute of Metal Forming IBF,
RWTH Aachen University
Intzestr. 10,
52072 Aachen,
Germany

 

Publications

  1. Bleck, W.; Brecher, C; Herty, M.; Hirt, G.; Hopmann, C.; Klocke, F.; Borchmann, N.; Dierdorf, J.; Farivar, H.; Fayek, P.; Häck, A.; Kripak, V.; Schmitz, G. J.; Spekowius, M.; Springer, P.; Teixeira, A. M., 2016. Integrated Computational Materials and Production Engineering (ICMPE). In Integrative Production Technology - Theory and Applications. ISBN: 978-3-319-47451-9
  2. Springer, P., Prahl, U., 2016. Characterisation of mechanical behavior of 18CrNiMo7-6 steel with and without Nb under warm forging conditions through processing maps analysis. J. Mater. Process. Technol. 237, 216-234.
  3. Henke, T.; Bambach, M.; Hirt, G. 2013 Die and Process Design for Hot Forging of a Gear Wheel – A Case Study. Key Engineering Materials, Vols. 554-557, 307-316.