Probing Formability Improvement of Ultra-thin Ferritic Stainless Steel Bipolar Plate of PEMFC in Non-conventional Formin
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CENTLY, the proton exchange membrane fuel cell (PEMFC) has gained increasing attention as a substitute for internal combustion engines in transportation applications due to its superior performance at low temperatures, prolonged operation time, rapid initiation, and compact structure.[1] In this application, the bipolar plate (BP) is the primary component of fuel cell, which comprises 60 to 80 pct of the whole cell weight and 30 to 45 pct of the cost of the PEMFC stack.[2] As a material candidate for BP, stainless steels have gained extensive attention because of their low stack cost, superior mechanical, electrical, and thermal properties, and satisfactory workability.[2] To reduce the weight of a fuel cell and to establish stainless steel sheets as competitive with other materials, the gage of the BPs should be as thin as possible. However, the forming of this thin sheet for a BP presents certain engineering challenges[3] and major issues that need to be overcome prior to full commercialization. One of the current concerns for the production of BPs using ultra-thin
metal sheets is the lack of a manufacturing process that provides low cost, high productivity, superior precision, and robust fabrication. Many researchers have integrated servo-press technology into metal forming processes by imposing various forming histories to the workpiece. Matsumoto et al.[4] utilized a servo-press with controlled slide speed for the indentation plastic joining process of aluminum alloy bar and plate. This method reduced the indentation pressure during the process and improved the bonding strength of the indented bar plate during accelerated slide motion. To reduce the friction, which is the most serious problem in the compression process, a pulsation slide motion was proposed and examined for an aluminum alloy[5] and stainless steel.[6] Nakano[7] conducted a deep drawing test for an austenitic stainless steel sheet sample, SUS304, with an optimized slide motion. In this work, the punch contacted the sheet at a slow velocity and the slide motion was reversed once between the preforming stages. Near the end of the stroke at the bottom dead point (BDP),* the sheet was *The term ‘‘BDP’’ refers to the position of the slide at the end of the stroke.
HYUK JONG BONG, Postdoctoral Researcher, is with the Department of Materials Science and Engineering, Ohio State University, 2041 College Road, Columbus, OH 43210. FRE´DE´RIC BARLAT, Professor, is with the Graduate Institute of Ferrous Technology, Pohang University of Science and Technology, Pohang 790-784, South Korea. MYOUNG-GYU LEE, Associate Professor, is with the Department of Materials Science and Engineering, Korea University, Seoul 136-701, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted March 2, 2016. Article published online May 23, 2016 4160—VOLUME 47A, AUGUST 2016
gradually formed by stepwise motion. Fracture was not observed during this optimized process. Although many of the research works optimized the forming process in connection with complex
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