Investigation on formability of bipolar plates during flexible micro forming of Cu/Ni clad foils

The formability of metal micro-parts is difficult to predict by the traditional theories because of the size effects induced by the interactive effects of specimen intrinsic and extrinsic characteristics with miniaturization. In this study, the interactive effects of different parameters on the forming quality of micro channel by flexible forming were conducted. The forming characteristic of Cu/Ni clad foils was studied from the microstructure and stress-strain state. Experimental results show that the forming depth, the irregular deformation and surface roughness increased when the annealing temperature was elevated. Due to the reduction of the micro channel feature size (cavity width), the relative forming depth and surface roughness value decreased, the located thickness thinning became serious. The surface roughness of formed part was related to plastic deformation degree, grain size and the surface quality of micro-die. And the effect of stacking sequence on forming results related to the grain sizes and the feature sizes for Cu/Ni clad foils. The formability was generally better when the Cu layer located outside. However, when the feature size reduced and grain size of Ni layer was fine and uniform, the forming quality when the Ni layer located outside was improved, even exceeded the other resulted. The difference of stress-strain states between during forming bipolar plate and forming micro channel was analyzed. Several parameters such as forming load, lubrication mode and holding time were optimized, and the bipolar plates were fabricated and evaluated by the optimized parameters.