High-precision bipolar plates by injection compression molding with dynamic mold temperature control

在双极板的应用中，为了利用聚合物相对于金属材料迫切需要的成本和寿命优势，需要高填充量以获得足够高的导电性。然而，由于粘度的显著增加和熔体导热系数增加的负面影响，以这种方式改性的热塑性熔体表现出恶化的复制和充模行为。这导致在注塑过程中当前双极板几何形状的可能厚度尺寸和精细通道结构的成型方面的限制。由于每个电池的最大输出电压只有1.23V，因此需要多个电池串联才能获得更高的电压，这也导致由聚合物化合物制成的更厚的双极板的安装空间体积和成本相当大。只有在注塑成型过程中通过提高注射速度和模具温度才能在一定程度上实现所需的板厚减薄，因为无论模具温度控制的类型如何，减少的流动截面都会导致充填过程中的过高压力要求和流动路径上的不均匀压力和温度场。在部件级别，这反映在通道结构的取决于流动路径的尺寸精度和成型精度的劣化。除了复制问题，高填充聚合物组分还表现出明显的方向相关的机械和电气组件行为，这在很大程度上由工艺中的温度-压力-剪切条件决定。因此，该项目的目的是通过动态模具温度控制来传递注塑压缩成型所需时间-温度-压力-剪切条件的分析和实验设计知识，以制造具有最高尺寸稳定性和通道结构成型精度的薄壁和高度填充的双极板，同时优化电气和机械性能。在这种情况下，在成型过程中通过动态模温控制来保持聚合物熔体的流动性。这种现代工艺策略与压花工艺相结合，可实现二维保压效果和实现高板宽比，同时在流道上实现最高的尺寸精度和通道结构的复制质量。通过控制温度和压力并间接影响过程中的剪切，现有关于如何影响电气和机械部件性能的知识也可以转化为具有动态模具温度控制的注塑压缩成型制造过程，以最大限度地发挥材料潜力。

In order to utilize the urgently needed cost and lifetime advantages of polymers compared to metallic- materials for the application of bipolar plates, high filler contents are necessary to achieve sufficiently high electrical conductivity. However, thermoplastic melts modified in this way show deteriorated replication and mold filling behavior due to significantly increased viscosity and the negative effect of an increased melt thermal conductivity. This results in limitations in the possible thickness dimensions and the molding of fine channel structures of current bipolar plate geometries in the injection molding process. Since the output voltage per cell is only 1.23 V max., several cells connected in series are required for higher voltages, which also results in considerably larger installation space volumes and costs for thicker bipolar plates made of polymer compound. The desired reduction in plate thickness can only be achieved to a limited extent by higher injection speeds and mold temperatures in the injection molding process, since the reduced flow cross-section results in excessive pressure requirements during filling and inhomogeneous pressure and temperature fields along the flow path, irrespective of the type of mold temperature control. At component level, this is reflected in a deterioration of the flow path-dependent dimensional accuracy and molding precision of the channel structures. In addition to replication problems, highly filled polymer components also exhibit a pronounced direction-dependent mechanical and electrical component behavior, which is largely determined by the temperature-pressure-shear conditions in the process. The aim of the project is therefore to transfer the knowledge of the analytical and experimental design of the required time-temperature-pressure-shear conditions in injection compression molding with dynamic mold temperature control to manufacture thin-walled and highly filled bipolar plates with the highest possible dimensional stability and molding accuracy of the channel structures with simultaneously optimized electrical and mechanical properties. In this context, the flowability of the polymer melt is to be maintained during the molding process by means of dynamic mold temperature control. The combination of this modern process strategy with an embossing process allows a two-dimensional holding pressure effect and the realization of high plate aspect ratios while at the same time achieving the highest possible dimensional accuracy and replication quality of the channel structures over the flow path. By controlling temperature and pressure and indirectly influencing shear in the process, the existing knowledge of how to influence electrical and mechanical component properties can also be translated into the manufacturing process of injection compression molding with dynamic mold temperature control to maximize the material potential.