Hot stamping of ultra-thin stainless steel sheets for bipolar plates

Dimensional deviations of channel features affect the assembly accuracy of bipolar plates, thereby influencing the efficiency and performance of a proton exchange membrane fuel cell. A challenge faced by the stamping process is how to further improve the dimensional accuracy of bipolar plates. This work proposes the hot stamping process for stainless steel bipolar plates, where a lab-scale hot stamping platform with an on-site resistance heating device is built. Influences of forming temperature, lubrication condition, grain size on the formability, and dimensional accuracy of ultra-thin stainless steel bipolar plate are investigated by employing this established hot stamping platform. It is found that within the investigated forming temperature range, the dimensional accuracy of hot-stamped ultra-thin SS316L bipolar plates increases as forming temperature increases, and a forming temperature of 1000 degrees C results in the highest dimensional accuracy and lowest dimensional variations of channel depth and rib width. BN lubricant increases the formability of ultra-thin SS316L bipolar plates, in particular when the forming temperature is higher than 600 degrees C. In addition, grain size exhibits the greatest influence on the formability of ultra-thin SS316L during hot stamping, and larger grain size (>24.8 mu m) increases the thinning rate and consequently the cracking risk of hot-stamped ultra-thin SS316L bipolar plates.