Identification of parameters for complex friction models in hot bulk metal forming by an extension of the conical tube upsetting test

• Applicant: Professor Dr.-Ing. Gerhard Hirt
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 381365387

Friction in metal forming processes influences material flow and necessary forming forces. For the design of tools and processes friction should be considered. This holds especially within modern simulation techniques like the Finite Element Method (FEM). Beside of the classical Coulomb and friction factor model a significant number of complex friction models with multiple friction parameters exists for hot bulk metal forming. These modern friction models allow for consideration of different influencing factors on the friction conditions. A parametrization of classical friction models can be done in different representative experiments in laboratory scale (e.g. ring compression test). Usually, for modern friction models the multiple friction parameters are fitted by comparison between the real forming process and a simulation.In the first phase of the project, an inverse modelling of an analogy test (conical tube-upsetting test) was used to develop a methodology that allows for the parameterisation of multi-parametric friction models. Using the Coulomb model, it could be shown that the developed methodology works in principle and has a high degree of robustness against fluctuations of other input parameters. Afterwards, the methodology could be successfully transferred to multi-parametric friction models. The results showed that there is no generally valid strategy for complex friction models. Rather, depending on the model and the parameters considered in it, different process conditions or modelling strategies lead to success.The aim of this continuation proposal is therefore to further develop the modelling strategy developed in the course of the project to date in such a way that a consistent determination of the parameters of modern friction models for the process parameters occurring in hot bulk metal forming processes can be achieved by inverse modelling with robust methods. The results achieved so far clearly show that there is no generally valid solution for multi-parametric models and that a corresponding process window is needed in order to have a sufficient data basis for the definite parameterization of the friction models used. The next step is therefore to use typical process windows of a hot bulk metal forming process. The occurring process windows for relative velocities and normal stresses shall be determined by means of a strongly friction influenced example process and transferred to the conical tube-upsetting test. Subsequently, an optimal modelling strategy is developed for each of the considered models in order to finally apply it to experimental results and to perform a validation of the determined parameters by means of an exemplary process. With the completion of the project a robust test and a secured methodology for the parameterization of complex friction models for hot bulk metal forming is available.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Marco Teller