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

物理发泡的热塑性注塑成型部件与紧凑部件相比具有许多优点。由于泡沫结构，可以在保持相同体积的同时实现显著的重量减轻。此外，通过气泡中发泡剂的压力减少收缩和翘曲。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因此不断增加。如今，塑料部件的精确技术设计使用注塑成型和结构模拟软件进行。虽然基于模拟的技术部件设计是紧凑型注塑成型的最新技术，但对于发泡注塑成型部件来说，这并不可靠。这是由于商业模拟软件中假设的许多简化，例如对称的气泡几何形状或恒定的扩散速率。由于剪切效应，以及聚结和气泡崩溃，如细胞变形的影响没有被考虑，这降低了预测精度的注射成型模拟。因此，模拟的单元结构不能用于精确模拟有效部分特性，例如杨氏模量或热导率。该项目的目的是准确地描述泡沫部件的泡孔结构，考虑到注塑成型过程中发生的动态边界条件，使用多尺度模拟方法。在宏观上，给出了注塑成型过程的温度场、压力场和速度矢量场等经典工艺参数。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，现有的物理模型将进行调整和校准的注塑工艺。利用多物理场模拟软件OpenFOAM中的重叠网格方法实现了微观尺度和宏观尺度的耦合。实际的泡沫注射成型试验进行验证和校准的微观和宏观模型。然后通过CT扫描检查所产生的试样的泡孔尺寸分布和取向。泡沫结构的精确计算将为基于仿真的高效率热塑性发泡制品设计奠定基础。

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.