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

为了在双极板的应用中利用聚合物相对于金属材料迫切需要的成本和寿命优势，需要高的填料含量来实现足够高的导电性。然而，以这种方式改性的热塑性熔体由于显著增加的粘度和增加的熔体导热性的负面影响，表现出恶化的复制和模具填充行为。这就限制了当前双极板几何形状在注射成型过程中可能的厚度尺寸和精细通道结构的成型。由于每个电池的输出电压最大只有1.23 V。在美国，为了获得更高的电压，需要将多个电池串联起来，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和成本相当大。在注射成型过程中，通过提高注射速度和模具温度，只能在有限的程度上实现所需的板厚减少，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填充过程中的压力要求过高，以及沿流动路径的压力和温度场不均匀。在组件级别，这反映在流道相关的尺寸精度和通道结构的成型精度的恶化。除了复制问题外，高度填充的聚合物组件还表现出明显的方向依赖性机械和电气组件行为，这在很大程度上取决于过程中的温度-压力-剪切条件。因此，该项目的目的是将所需的时间-温度-压力-剪切注射压缩成型条件的分析和实验设计知识与动态模具温度控制相结合，以制造薄壁和高度填充的双极板，具有最高的尺寸稳定性和通道结构的成型精度，同时优化电气和机械性能。在这种情况下，聚合物熔体的流动性是保持在成型过程中，通过动态模具温度控制的手段。这种现代工艺策略与压纹工艺的结合允许二维保压效果和高板宽高比的实现，同时实现流道上通道结构的最高尺寸精度和复制质量。通过控制温度和压力并间接影响过程中的剪切，现有的如何影响电气和机械部件性能的知识也可以转化为动态控制模具温度的注射压缩成型制造过程，以最大限度地发挥材料的潜力。

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.