Optimizing die parameters of microstamping process for PEMFC 316L bipolar plate using NCL fracture criterion and response surface methodology

We investigated the impact of die fillet shape, fillet size, die clearance, and die height on the microstamping of ultrathin 316L bipolar plates (BPPs) with stepped flow channels. Using the normalized Cockcroft–Latham damage fracture criterion combined with the response surface method, we developed an effective predictive model for the fracture behavior of ultrathin 316L BPPs. This model was employed to optimize the mold parameters. Numerical simulation results reveal that different fillet shapes—90° sector, irregular sector, ellipse, and parabola—significantly affect the formation of ultrathin 316L BPPs. Among these, the elliptical fillet shape yielded the best results. Further analysis indicated that increasing the radius of the die fillet while reducing the die height led to decreases in the stress, strain, thinning rate, and damage value of the BPPs. Conversely, the draft angle increased linearly. However, with varying die clearance, the stress, strain, thinning rate, and damage value of the BPPs initially decreased and then increased, while the draft angle continued to rise linearly. The optimized die parameters were identified using the damage prediction model: a fillet radius of 0.2 mm, clearance of 0.26 mm, height of 0.49 mm, and stepped height of 0.24 mm. The validity of these optimized parameters was confirmed experimentally.