Investigation of system induced causes of defects on metallic bipolar plates in progressive die forming

As the demand of the fuel cell electric vehicle (FCEV) keeps increasing, the cost-efficient production of its components become more important. For cost-efficient production of a crucial component, the bipolar plate (BPP), the progressive die forming has been receiving highlights in the industry. The progressive die forming has numerous advantages for high volume production of BPPs, such as short cycle time and automation potential. However, most of current system setting is oriented for typical sheet metal applications such as automotive and electronic parts. The dimensional tolerances of system technologies for these applications may not be precise enough to form desired channel geometries on BPP mainly due to its extremely thin sheet thickness (typically under 100 μm) and small channel geometries (typically height under 0.5 mm and cell pitch under 1.5 mm). In this study, the influence of misalignment between the stamp and die is investigated based on a numerical simulation model as one of potential system induced sources of defects on the BPP. A finite element simulation model for a stamping process is developed, which contains a pair of the stamp and die with a single serpentine flow field design. Based on the model, four different cases with translational misalignments were defined and compared to the ideally aligned case. The influence of the tool misalignment on BPP quality was then analyzed by comparing four outputs for each case: the channel height, von Mises stress, equivalent plastic strain, and thickness. The analysis shows that the translational misalignment on tools causes reduction of the formed channel height, stress concentration on curved corners of the serpentine, asymmetric strain and thinning on the channel geometry, and thickening of outer area of the serpentine.