Simulation And Experimental Study On Multistage Forming Of Micro Channel For Fuel Cell Titanium Bipolar Plate

Metallic bipolar plates are key component of the high specific power fuel cell,which undertake the important functions of transmitting reactive gases,conducting electrical current,isolating the media,etc.Titanium bipolar plates with fine and high-aspect-ratio sub-millimeter channels manufactured by stamping process featuring light weight and good corrosion resistance are important direction for the development of highperformance fuel cell bipolar plates in the future.However,titanium sheet shows low elongation and obvious anisotropy.The forming limit of micro channels is low and can not meet the requirement of high aspect ratio by using the traditional stamping process.The multistage stamping process can avoid the fracture caused by local deformation in the traditional stamping forming process,which can effectively increase the forming depth of the channel.Investigating how anisotropy of titanium sheet influences the formation of micro channels is of great significance for the design and fabrication of fuel cell metallic bipolar plates.In this paper,the TA2 ultra-thin titanium sheet with a thickness of0.1 mm was employed and uniaxial tensile experiments with different orientations were carried out to establish an anisotropic yield model.Based on the sheet forming simulation,the influence of anisotropy of TA2 sheet on the forming quality of micro channels was studied.A simulation model of multistage forming process with variable tool fillets was built to study the law of material deformation influenced by the anisotropic yield behavior and process parameters.Micro channel forming experiments were carried out to verify the accuracy of the simulation model.The feasibility and effectiveness of the multistage forming process to manufacture titanium bipolar plates was verified by the contact resistance testing results.The main work in this study includes:(1)Study on anisotropic yield behavior of ultra-thin titanium sheet.The tensile tests of the TA2 titanium sheet along 0 °,45 ° and 90 °to the rolling direction were carried out to measure the mechanical properties in 3 directions.Based on the Mises and Hill 48 yield criteria,a model considering anisotropic behavior for TA2 sheet was established.Finite element simulation analysis was carried out and compared with experiments.And the anisotropy of the material was analyzed by XRD pole figure.The research indicated that TA2 sheet featured significant anisotropy and the Hill 48 yield model obtained by r value and least squares calibration method can better describe the anisotropy.(2)Simulation analysis of micro channel forming considering material anisotropy.A micro channel forming finite element simulation model was established and it was verified by experiments.The influence of titanium's anisotropic yield behavior on the stamping process is studied via simulation.The research indicated that the anisotropic yield behavior of the sheet greatly affected the forming force and material thinning.When the channel direction is parallel to the rolling direction,the forming depth is the highest and perpendicular to the rolling direction with the lowest.The depth of the micro channel is greater when the fillet radius of the tool is larger.The results showed that multistage forming process can effectively increase the forming depth.(3)Experimental study on the forming of micro channel with high aspect ratio of ultra-thin titanium sheet.The multistage(two and three)forming experiment parameters were designed and forming experiments were carried out based on the simulation analysis and single stage forming experiment results.The influence of process parameters on the forming depth of the channel and thinning law of the sheet was studied.Moreover,the contact resistance between the micro channels obtained by different forming process with carbon paper was measured.The research indicated that the final forming depth of the channels increased when the loading displacements was greater in the previous stamping stages.The fillet radius of the channel formed by multistage is smaller,which leads to a lower contact resistance with the carbon paper.