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。这在现代模拟技术中尤其适用，如有限元法（FEM）。除了经典的库仑模型和摩擦因数模型外，还存在大量具有多个摩擦参数的金属热体成形复杂摩擦模型。这些现代摩擦模型考虑了对摩擦条件的不同影响因素。经典摩擦模型的参数化可以在不同的有代表性的实验中进行（如环压缩试验）。对于现代摩擦模型，通常是通过实际成形过程与模拟过程的比较来拟合多个摩擦参数。在项目的第一阶段，使用类比试验（锥形管镦粗试验）的逆建模来开发一种允许多参数摩擦模型参数化的方法。使用库仑模型，可以表明所开发的方法在原则上是有效的，并且对其他输入参数的波动具有高度的鲁棒性。然后，该方法可以成功地转移到多参数摩擦模型中。结果表明，对于复杂的摩擦模型，没有普遍有效的策略。相反，根据模型和其中考虑的参数，不同的过程条件或建模策略会导致成功。因此，这一延续提案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，以这样一种方式，可以通过具有鲁棒方法的逆建模来实现热体金属成形过程中工艺参数的现代摩擦模型参数的一致确定。到目前为止所取得的结果清楚地表明，对于多参数模型没有普遍有效的解，需要一个相应的过程窗口，以便为所使用的摩擦模型的明确参数化提供足够的数据基础。因此，下一步是使用热体金属成形工艺的典型工艺窗口。相对速度和正应力的发生过程窗口应通过受强烈摩擦影响的示例过程来确定，并转移到锥形管镦粗试验中。随后，为每个考虑的模型制定了最佳建模策略，以便最终将其应用于实验结果，并通过示例性过程对确定的参数进行验证。随着项目的完成，为热成型复杂摩擦模型的参数化提供了可靠的测试和安全的方法。

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.