| In this study, a novel manufacturing process is proposed as an alternative method for fabrication of double metallic bipolar plates from initially flat thin sheets. The proposed process combined hydroforming of thin sheet metal blanks to create micro-channel arrays with in-die mechanical bonding to create double bipolar plates in a single-step and single-die operation to result in thin, lightweight, and flexible bipolar plates where flow fields are formed on both sides and internal cooling channels are formed in the middle, eliminating further welding, assembly and sealing operations otherwise required with the existing methods.; For a successful development of the proposed process, different scientific and research issues are investigated and discussed in this study. First, to characterize the material behavior of thin sheet metals at micro-scale, hydraulic bulge tests are performed to investigate the so-called "size effects" (i.e., grain, specimen, and feature size) on the material behavior. Based on the bulge test results, new material models are developed to include the size effect parameters. Second, to understand the deformation mechanics of thin sheet metals in micro-feature fabrication under complex loading conditions, hydroforming of different micro-channel sizes using thin sheets is performed. Effects of channel design and process condition on the overall channel formability are discussed. With the use of FEA and appropriate material models, a parametric study is conducted to establish design guidelines for process and tooling design. Third, a mechanical bonding process, specifically, pressure welding of thin sheet metals, is investigated to gain a full understanding of the process limitation and characterization. The understanding from the welding tests suggests different process windows for successful bonding of thin sheets. Finally, predictive process models of the hybrid process are developed using a finite element (FE) tool for rapid evaluation the process producibility. Based on the simulation results, a set of experimental tooling is developed and tested to demonstrate the feasibility of the hybrid process for fabrication of fuel cell bipolar plates in a single-step and single-die operation. |
