Study of monopolar plate springback applying zoned multistage forming process

Two monopolar plates (MPPs) can be assembled into a bipolar plate (BPP) through welding, and the BPP is one of the main components of a proton exchange membrane fuel cell (PEMFC). The uniformity of the thickness of an MPP can affect the thickness uniformity of the BPP, thereby influencing the performance of the fuel cell. The length and width of an MPP both exceed 150 mm, but the thickness of its raw material plate is less than 0.1 mm, posing a significant challenge to the uniformity of its thickness after forming. The characteristic patterns on an MPP are relatively complex, with varying characteristic sizes and positions. Consequently, during the forming process, the different internal stress states within patterns lead to inconsistent springback, which further results in uneven thicknesses. In this study, two specially designed molds were manufactured to perform zoned multistage stamping. On the basis of the experimental results, a set of numerical models was constructed to analyze the mechanism of springback behavior in different zones from the perspective of residual stresses. Compared with traditional single-stage forming, this newly formed process successfully reduced the absolute springback in the main channel area of the MPP from 0.05 mm to less than 0.02 mm, and the springback difference among various zones decreased from 0.035 mm to less than 0.015 mm. This forming process can enhance the uniformity of the MPP thickness by reducing the springback difference, thereby minimizing the potential for performance loss in fuel cells during assembly and operation. The zoned multi-stage forming process can effectively suppress springback.The novel process makes the thickness of the monopolar plate more uniform.The mechanism of suppressing springback is the preservation and release of residual stresses inside the material.The interfacial contact resistance of the monopolar plates formed by this novel process is relatively low. The zoned multi-stage forming process can effectively suppress springback. The novel process makes the thickness of the monopolar plate more uniform. The mechanism of suppressing springback is the preservation and release of residual stresses inside the material. The interfacial contact resistance of the monopolar plates formed by this novel process is relatively low.