Development and Validation of a Heat Generation Model for Friction Press Joining

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Friction Press Joining (FPJ) is an innovative technology used to join thermoplastic polymers with metal sheets in overlap configuration. It was first developed in a collaboration between Airbus Innovation Works in Ottobrunn (Germany) and the Institute for Machine Tools and Industrial Management (iwb) of the Technical University of Munich (TUM) and it is an especially promising technique for the development of lightweight design concepts. The process is very similar to Friction Stir Welding (FSW), only the tool consists of only a shoulder and the materials are not mixed. Heat generated at the tool-shoulder interface is conducted to the metal-polymer interface, causing the polymer to melt. Upon cooling, the polymer solidifies and the joint is complete. Because of the narrow temperature range, in which thermoplastic polymers are able to melt without undergoing degradation, the ability to control the temperature at the metal-polymer interface is critical to assure a reliable joining process. Currently, there is no literature available pertaining to the thermal modeling of FPJ. Although a vast amount of literature has been published regarding the modeling of heat generation in FSW, the temperature ranges pertinent to these processes are vastly different, and research suggests that the mechanisms for heat generation in FSW process may be different than those for FPJ. The goal of the proposed project is to be able to supply an FPJ user with the methods necessary to determine the suitable process parameters (focus on feed rate, rotational speed, and axial force) in order to produce a desired temperature at the metal-polymer interface. The first step in achieving this is to assess the contact conditions and create a semi-analytical model to predict, for example, the friction coefficient based on the process parameters. This model will then be adapted and implemented in order to determine the heat generation at any given point on the FPJ tool and to describe the shape of the heat source distribution over the tool surface. The generated models will be supported and validated by experimental trials employing simplified and full FPJ setups. Additionally, a means of determining the heat transport at the metal-polymer interface will be derived. Numerical solutions concerning the heat source distributions will be used to assess the model validity. Additionally, a simulation-based parameter study will be used to construct a metamodel of the heat transport from the tool-workpiece interface to the metal-polymer interface. After these steps have been taken, the user will be able to predict the time-temperature profile at the metal-polymer interface based on the process parameters. In the final step, the models will be coupled and assessed in an inverse manner in order to give the user the suitable process parameters to generate a desired time-temperature profile at the metal-polymer interface.