High-Precision Thin Wall Bipolar Plates for Fuel Cell Applications via Injection Compression Molding with Dynamic Mold Temperature Control

Abstract

In recent years, the demand for polymer compound solutions for the application of bipolar plates in polymer electrolyte membrane fuel cells (PEMFC) has increased continuously due to significant cost and lifetime advantages compared to metallic solutions. The main challenge of the compounds is the high filler content required to ensure sufficient electrical conductivity of the bipolar plates. The associated increase in viscosity and simultaneously increased thermal conductivity limit the conventional injection molding process in terms of achievable flow path length to wall thickness ratios (plate aspect ratio). In order to evaluate the extent to which highly modified electrically conductive polymer material systems can be processed into thin-walled and highly dimensionally stable bipolar plates, an injection compression molding process with dynamic mold temperature control (ICM-DT) has been developed. For this purpose, a compound was prepared from polypropylene (PP) and graphite-flakes. The compound was characterized with respect to the achieved filler content, the electrical conductivity, as well as the pressure- and temperature-dependent solidification range. The ICM-DT experiments were carried out by varying the maximum mold temperature and the compression force. In addition, the process was designed with multiple compression and decompression steps to account for a possible pressure-dependent solidification of the compound. The plates were characterized with respect to the achieved plate aspect ratio and the flow-path-dependent dimensional thickness stability. It was shown that the plate aspect ratio could be increased by up to 125% with the maximum filler content compared to conventional injection molding processes provided in the literature. With the multi-stage ICM-DT process, it was also possible to optimize the thickness dimensional stability with a maximum deviation of 3% over the flow path.

Investigating the Integration of Nonwoven Carbon Fibers for Mechanical Enhancement in Compression Molded Fiber-Reinforced Polymer Bipolar Plates

“…Etching the surface of the samples, on the other hand, has little effect on the specific conductivity, regardless of the configuration, as shown in Figure 6. In agreement with the observations described in Section 3.2, this suggests that, in contrast to the injection compression molded samples investigated [17], there is hardly any protective polymer surface layer present. Eliminating the necessity of a post-processing step would offer significant advantages for an industrial process.…”

“…Additionally, due to lower shear rates compared to injection molding and therefore the absence of particle segregation in CM, a polymer-rich skin layer is less pronounced. Hence, the necessity for post-processing methods like surface etching, commonly employed to uncover particles and minimize surface resistance, is diminished [17]. Further advantages over injection molding include low tooling costs due to the simplicity of the process [18], reduced wastage, and reduced post-processing requirements resulting from the absence of a gating system [19].…”

Characterization of Epoxy-Based Rapid Mold with Profiled Conformal Cooling Channel

“…In this study, the developed empirical material formulation was used to manufacture a wax injection mold. It is important to note that the developed empirical material formulation can be further applied to plastic extrusion [ 28 ], gravity die casting, hot stamping, blow molding, metal injection molding, powder metallurgy, die casting, injection compression molding [ 29 ], or rotational molding [ 30 ]. These issues are currently being investigated and the results will be presented in a later work.…”

Compounding, Rheology and Numerical Simulation of Highly Filled Graphite Compounds for Potential Fuel Cell Applications

“…However, the processing of such highly filled composite materials still poses an enormous challenge. Processing by injection compression molding [ 5 ] or, more recently, by film and sheet extrusion, requires an extensive rheological characterization in the first step. Without the knowledge of the flow behavior of the highly filled polymer, molding tools, extrusion dies, and entire processing steps can only be insufficiently designed.…”