Design and dimensioning of manufacturing processes based on filling molds with polyurethane foams still require the use of highly empirical approaches. This includes numerous experimental runs with expensive prototypes. Therefore, a method has to be found to analyze the molding process at an early stage of product development to shorten time-to-market cycles and cut costs by using fewer prototypes. With the computational power available today and growing computational power in the future, the tool of choice is the numerical simulation of mold filling processes with computational fluid dynamics software.

Polyurethane foam is used for manufacturing different kinds of products, such as refrigerators, car dashboards or steering wheels. First, we developed a macro-scale simulation tool that is able to predict foam flow in such complex molds. Depending on the location within a product, final properties of polyurethane foams may vary significantly. These properties (e.g. thermal conductivity or impact strength) are strongly dependent on local foam structure. Modeling complex geometries like refrigerators completely on bubble scale is neither possible nor would it be efficient. The computational effort would be enormous. Therefore, we developed a micro-scale model describing bubble growth and the evolution of the foam microstructure in polyurethane foams considering a limited number of bubbles in a representative volume. Finally, we coupled our macro and micro-scale simulation approaches. For that purpose, we introduced tracer particles into our mold filling simulations. We are able to record information about density and temperature changes or varying flow conditions along particle trajectories. This information is then used to set up corresponding simulations on bubble scale. Through this coupling, a basis for studying the evolution of the local foam microstructure in complex geometries is provided.

Polyurethane foam is used for manufacturing different kinds of products, such as refrigerators, car dashboards or steering wheels. First, we developed a macro-scale simulation tool that is able to predict foam flow in such complex molds. Depending on the location within a product, final properties of polyurethane foams may vary significantly. These properties (e.g. thermal conductivity or impact strength) are strongly dependent on local foam structure. Modeling complex geometries like refrigerators completely on bubble scale is neither possible nor would it be efficient. The computational effort would be enormous. Therefore, we developed a micro-scale model describing bubble growth and the evolution of the foam microstructure in polyurethane foams considering a limited number of bubbles in a representative volume. Finally, we coupled our macro and micro-scale simulation approaches. For that purpose, we introduced tracer particles into our mold filling simulations. We are able to record information about density and temperature changes or varying flow conditions along particle trajectories. This information is then used to set up corresponding simulations on bubble scale. Through this coupling, a basis for studying the evolution of the local foam microstructure in complex geometries is provided. MACROSCOPIC SCALE: MOLD FILLING SIMULATIONSIn this section the mold filling simulation approach is briefly outlined. A detailed description of this approach and some validation examples can be found in [7]. In order to reduce the computational effort, the mold filling problem is reduced to a two-phase flow problem considering an air phase and a pseudo-homogeneous foam phase. The real system consists of an air phase and a foam phase containing small gas bubbles in a polymer phase, see left hand side of Fig.