Abstract
Laser welding is the most effective joining method for thin metallic bipolar plates (BPPs) to achieve reliable seal and fulfill the requirements for fuel cell stacks. However, distortion caused by the welding heat will produce shape error in BPPs. The shape error will cause uneven assembly stress distribution and unacceptable contact resistance between BPPs and the gas diffusion layer (GDL), eventually affect the fuel cell performance.In this study, transverse deformation and angular distortion are considered to be the main sources of BPPs shape error and studied by modeling and experimental methods. An analytical model based on inherent strain theory is established to predict the transverse deformation of BPPs. Meanwhile, a model based on the weld pool geometry is proposed to evaluate the angular distortion. Experiments are performed to validate the models by welding 316L stainless steel sheets of 0.1 mm and 0.2 mm thick with a multi-mode fiber laser system. A good correlation is found between experimental results and the prediction models. Finally, a formula based on the former prediction models is proposed to calculate the welding induced shape error of BPPs with two pass welds. The formula is validated by experiments. The methodology in this study can be applied to guide the laser welding process design and manufacturing of the metallic BPPs.
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