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

物理发泡热塑性注塑成型零件比紧凑型零件有许多优势。由于泡沫结构，可以在保持相同体积的情况下实现显著的重量减轻。此外，气泡中发泡剂的压力减少了收缩和翘曲。在资源效率和技术要求不断提高的过程中，对泡沫塑料部件的需求也在不断增加。如今，塑料部件的精确工艺设计是利用注塑成型和结构模拟软件进行的。虽然基于模拟的技术部件设计对于紧凑型注塑成型来说是最先进的，但对于发泡注塑成型零件来说，这并不可靠。这是由于大量的简化，例如对称的气泡几何形状或商业模拟软件中假设的恒定扩散速率。由于没有考虑剪切效应引起的泡孔变形、聚结和气泡坍塌等影响，降低了注塑成型模拟的预测精度。因此，模拟的电池结构不能用于精确模拟有效部件的性质，如杨氏模数或导热系数。本项目的目的是利用多尺度模拟方法，考虑注塑成型过程中发生的动态边界条件，准确地描述发泡组件的泡孔结构。在宏观尺度上，给出了注塑成型过程的经典工艺参数，如温度、压力和速度矢量场。在微观尺度上，将为预定义的点提供成核、细胞生长以及细胞稳定的完整模型描述。为此，将对现有物理模型进行调整和校准，以适应注塑工艺。利用多物理模拟软件OpenFOAM中的覆盖网格法实现了微观尺度与宏观尺度的耦合。为了验证和校准微观和宏观模型，进行了实际的泡沫注射成型试验。然后，通过CT扫描检查产生的测试样本的细胞大小、分布和方向。对泡沫塑料结构的精确计算将为技术发泡热塑性塑料部件的高效模拟设计奠定基础。

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.