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

金属成形过程中的摩擦影响材料流动和必要的成形力。对于工具和工艺的设计，应考虑摩擦。这尤其适用于现代仿真技术，如有限元法（FEM）。除了经典的库仑模型和摩擦因子模型外，还存在大量的多摩擦参数的复杂摩擦模型。这些现代摩擦模型允许考虑摩擦条件的不同影响因素。经典摩擦模型的参数化可以在实验室规模的不同代表性实验中完成（例如环压缩试验）。通常，对于现代摩擦模型，多个摩擦参数是通过比较真实的成形过程和模拟结果来拟合的。在项目的第一阶段，采用了模拟试验（锥形管镦粗试验）的逆模型来开发多参数摩擦模型的参数化方法。使用库仑模型，它可以表明，开发的方法的工作原理，并具有高度的鲁棒性对其他输入参数的波动。之后，该方法可以成功地转移到多参数摩擦模型。结果表明，对于复杂的摩擦模型，目前还没有普遍有效的策略。相反，根据模型和模型中考虑的参数，不同的工艺条件或建模策略会导致成功。因此，本延续建议的目的是进一步发展迄今为止在项目过程中开发的建模策略，以便能够一致地确定用于大块金属热成形工艺中出现的工艺参数的现代摩擦模型的参数通过鲁棒方法的逆建模。到目前为止所取得的结果清楚地表明，没有普遍有效的解决方案，多参数模型和相应的过程窗口是必要的，以便有一个足够的数据基础，明确的参数化所使用的摩擦模型。因此，下一步是使用热块体金属成形工艺的典型工艺窗口。相对速度和法向应力的出现工艺窗口应通过受强烈摩擦影响的示例工艺确定，并转移到锥形管镦粗试验中。随后，为每个所考虑的模型开发最佳建模策略，以便最终将其应用于实验结果，并通过示例性过程对所确定的参数进行验证。随着该项目的完成，一个强大的测试和安全的方法参数化复杂的摩擦模型，热大块金属成形。

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.