Multi-scale simulation of thermoplastic foam injection molding using a geometrically and physically motivated microscale model.

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Physically foamed thermoplastic injection molded parts have many advantages over compact parts. Due to the foam structure, a significant weight reduction can be achieved while maintaining the same volume. Furthermore, shrinkage and warpage are reduced by the pressure of the blowing agents in the bubbles. In the course of resource efficiency and increasing technical requirements, the demand for foamed plastic components is continuously increasing for these reasons.Today, the precise technical design of plastic components is carried out using injection molding and structural simulation software. While a simulation-based design of technical components is state of the art for compact injection molding, this is not reliably possible for foamed injection molded parts. This is due to numerous simplifications such as a symmetrical bubble geometry or constant diffusion rates assumed in commercial simulation software. Effects such as cell deformation due to shear effects as well as coalescence and bubble collapse are not considered, which reduces the prediction accuracy of the injection molding simulation. Therefore, the simulated cell structures cannot be used for an accurate simulation of the effective part properties such as the Young's modulus or the thermal conductivity. The aim of this project is to accurately describe the cell structure of foamed components, considering the dynamic boundary conditions that occur during injection molding, using a multi-scale simulation approach. On the macroscale, classical process parameters of the injection molding process such as temperature, pressure and velocity vector field are provided. On the microscale, a complete model description of nucleation, cell growth as well as cell stabilization for predefined will be provided for predefined points. For this purpose, existing physical models will be adapted and calibrated for the injection molding process. A coupling of micro and macro scale is achieved by the overset-mesh-approach in the multiphysics simulation software OpenFOAM. Practical foam injection molding trials are performed to validate and calibrate the micro- and macroscale models. The produced test specimens are then examined by CT scans with respect to cell size distribution and orientation. The precise calculation of the foam structure will lay the foundation for an efficient simulation-based design of technical foamed thermoplastic parts.