Identification of parameters for complex friction models in hot bulk metal forming by an extension of the conical tube upsetting test
Final Report Abstract
Friction occurs in all metal forming production processes and has a significant influence on the material flow and the required forming force. Friction must therefore be taken into account when designing tools and forming processes. This applies in particular to the design tool commonly used today, the finite element method (FEM). The friction models used for this differ in terms of complexity, in the form of the number of parameters to be determined, and their area of application. The necessary parameter determination for the forming process to be described is often carried out in laboratory tests under process conditions that are as close as possible to the actual conditions. The conical tube-upsetting test is one of these tests, where the forming-induced change in outer shape can be used to determine the occurring friction conditions. However, the methods used to date for evaluating such laboratory tests are only suitable for simple friction models where there is only one parameter to be determined. These simple friction models (e.g. the Coulomb model) provide sufficiently accurate results for many applications. However, simple models sometimes reach their limits in forming processes with a large variation range for process variables that influence friction (e.g. normal stresses, relative speeds). Here, more complex friction models with two or more parameters to be determined can potentially provide more accurate solutions. Until now there has been a lack of evaluation methods to determine the parameters of such models using laboratory experiments. A methodology for determining parameters for friction models with more than one parameter was therefore developed as part of this project. The conical tube-upsetting test serves as a laboratory test, with which forming conditions of (hot) bulk metal forming can be modelled. In the evaluation method developed, the measured data from two laboratory test series are compared with corresponding simulation models. An optimization algorithm then automatically adjusts the required friction parameters of the selected friction model until the simulation and experiment agree as accurately as possible. This evaluation method is known as inverse modelling. The change in the outer specimen contour of the conical tube-upsetting test is used as the data basis; this is recorded using a line laser during the experiments. Under typical hot forging conditions, this methodology was tested for two different friction models with more than one parameter. The results show that each friction model requires its own modelling strategy, depending on which process parameters are considered by the model parameters to be determined. First, process parameters are checked in order to determine model parameters. Then the two test series for the inverse modelling are selected. The developed methodology was finally validated using the example of cup-back extrusion tests.
Publications
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Parametrisierung moderner Reibmodelle, Umformtechnik 04/2019, 2019, 22–23
M. Henze, G. Hirt & M. Teller
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Parametrization of bi-parametric friction models through inverse modelling of conical tube-upsetting tests. AIP Conference Proceedings, 2113(2019), 120002. AIP Publishing.
Henze, Michel; Teller, Marco & Hirt, Gerhard
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Sensitivity Analysis regarding the Inverse Modelling of Conical Tube-Upsetting Tests, 39th SENAFOR, 2019, Porto Alegre, Brasilien
M. Henze, M. Teller & G. Hirt
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Conical Tube-Upsetting Test and T-Shape Test as Performance Tests for Lubricants, 33. Aachener Stahlkolloquium, 2022
G. Kleefisch, M. Henze, J. Ostrowski, G. Streefland & L. Thompson
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Increasing the Occurring Normal Stresses in Conical Tube-Upsetting Test Using Adapted Specimen Geometries. Lecture Notes in Mechanical Engineering, 711-718. Springer Nature Switzerland.
Henze, Michel; Bailly, David & Hirt, Gerhard
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Robust parametrization of combined Coulomb- Tresca model for hot bulk metal forming through inverse modelling of conical-tube upsetting tests, MSE Congress, 2024
L. Koch, M. Henze, D. Bailly & G. Hirt
