Investigation and evaluation of formability of thin metallic bipolar plates by stamping process

Metallic materials have been considered as a material for bipolar plates in proton exchange membrane fuel cells due to the higher electrical and thermal conductivity, mechanical strength, and lower cost. But there are some difficulties to be addressed especially in case a forming process is applied, such as cracking, wrinkling, excessive thinning, and an uneven distribution of channel depths along the flow field. The stamping process of SS-316L and CP-Ti thin sheets, which are widely used as metallic based bipolar plates, is extensively studied in this paper, both experimentally and numerically. Experiments demonstrate that using blank holder force can significantly reduce the wrinkled areas on the plate. The channel depths of sheets increase as the applied press force rises. However, ruptures in CP-Ti sheets occur when the ratio of press force to the formed channel base area exceeds 0.164 kN/mm2. Lower press velocities result in larger channel depth values in CP-Ti sheet and more homogenous channel depth distributions in SS-316L sheet. Severe thinning zones are formed between the contact regions of metal sheets and punch/die. In the view of the evaluation of strain values according to the forming limit diagrams in the simulations, the CP-Ti bipolar plate has a risk of crack areas, whereas the SS-316L bipolar plate is completely in safe. The springback analysis revealed a maximum deviation of 25.12% when compared to the base SS-316L bipolar plate.