A Hybrid Hydroforming and Mechanical Bonding Process for Fuel Cell Biopolar Plates.

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.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58504/1/sasawat_1.pd

Microstructural and Diffusion Analysis of Au-Sn Diffusion Couple Layer Undergoing Heat Treatment at Near Eutectic Temperatures

Diffusion couples of pure gold and pure tin were created by mechanical cold rolling method. The couples were isothermally treated at temperatures slightly above and below the eutectic temperature near tin-rich region of the equilibrium phase diagram. Differences in the diffusion behaviors were observed as a function of treatment temperatures below (473 K) and above (498 K) the eutectic temperature. At the boundary, it was found that first solid state inter-diffusion was initiated which resulted in local compositional change and solid-state formation of intermetallic compounds. As the composition shifts away towards mixing, the growth of the intermetallic phases was monitored as a function of temperature and time. At temperature above the eutectic, there may be a liquid fraction as the interface isothermally melted. The kinetic involves dissolution of Au atoms into locallized tin-rich liquid. At below eutectic temperature, the formation and growth kinetic of phases follows a solid state diffusion mechanism. By investigation the exponent n values in the growth equation l = k(t/t0)n, the values were found to be in between 0.62 - 0.77 which implies that the kinetics of IMC formations experiment are controlled by both diffusion and intermetallic reaction. The bonding temperature was found to be faster and more reliable at bonding temperature slightly above the eutectic

Closed-loop control of product properties in metal forming

Metal forming processes operate in conditions of uncertainty due to parameter variation and imperfect understanding. This uncertainty leads to a degradation of product properties from customer specifications, which can be reduced by the use of closed-loop control. A framework of analysis is presented for understanding closed-loop control in metal forming, allowing an assessment of current and future developments in actuators, sensors and models. This leads to a survey of current and emerging applications across a broad spectrum of metal forming processes, and a discussion of likely developments.Engineering and Physical Sciences Research Council (Grant ID: EP/K018108/1)This is the final version of the article. It first appeared from Elsevier via https://doi.org/10.1016/j.cirp.2016.06.00

Formability Effects of Variable Blank Holder Force on Deep Drawing of Stainless Steel

This paper investigates the formability effects of variable blank holder force on deep drawing of AISI 304 rectangular cup. Various sets of blank holder forces were set to observe the formability, which was indicated by the percentage of sheet thinning in this study. The results showed that the blank holder forces at the locations of the sheet edges surrounding the cavity areas were considered dominant to reduce sheet thinning and enhance the formability

Formability Effects of Variable Blank Holder Force on Deep Drawing of Stainless Steel

This paper investigates the formability effects of variable blank holder force on deep drawing of AISI 304 rectangular cup. Various sets of blank holder forces were set to observe the formability, which was indicated by the percentage of sheet thinning in this study. The results showed that the blank holder forces at the locations of the sheet edges surrounding the cavity areas were considered dominant to reduce sheet thinning and enhance the formability