Van Loozen says the Ultramid grade selected for the battery pack “is not exceedingly exotic,” noting that the material has been used in radiator end tank and other auto applications for some time. Based on results obtained with Dassault Systèmes’ (Vélizy-Villacoublay, France) Abaqus FEA simulation tools, BASF recommended that end and repeating frames be injection molded from its Ultramid 1503-2F, a hydrolysis-resistant, 33 percent glass-filled polyamide 6/6. Toward those ends, a team headed by GM account manager Steven Van Loozen evaluated the structural performance of several molding materials, based on GM’s battery pack CAD model. Another challenge was the design of an integrated cooling and heating system that would keep the battery operating safely and at peak efficiency. Each frame’s dimensional precision would have to approach that of a machined part, yet it needed to be achieved in an injection molding process. The key engineering challenge was to design and produce composite frames that, when stacked in the pack assembly, would form a finished structure within acceptable dimensional tolerances. “We put a team together committed to best practices and system solutions.” “This was a design that pushed the edge, and we needed buy-in from everyone to get there,” Kollar recalls. This dual demand tested the skill sets of GM’s partners in the project, material supplier BASF (Ludwigshafen, Germany), molder MANN+HUMMEL (Portage, Mich.) and Canadian toolmaker Omega Corp. Section 3 features one six-cell group module plus three 12-cell group modules, for a total of 126 cells.Ĭraig Kollar, General Motors’ engineering group manager for cell release, says the complex battery pack - essentially an underbody part - had to meet exacting requirements for dimensional stability and robust durability. Section 2 contains two 12-cell group modules, totaling 72 cells. Section 1 is made up of one six-cell group module plus two 12-cell group modules, for a total of 90 cells. Each is built up from a fundamental unit called a cell group, which comprises three lithium-ion cells connected in parallel. The assembled battery pack is T-shaped: 1,600 mm long by 900 mm wide at the top of the T (63 inches by 35.4 inches) it narrows to 400 mm/15.75 inches wide to fit within the Volt’s underbody tunnel, with a height throughout of about 300 mm/11.81 inches. The end frames each hold one cell, and a metal plate is inserted into the center of the frame to fill and seal its open area. Each repeating frame holds two lithium-ion cells, one on each side, separated by a layer of insulating foam. Enclosing the cells are 135 repeating frames, each approximately 250 mm wide and tall by 15 mm thick (9.8 inches square by 0.60 inch thick), and 18 similarly sized end frames (see diagram). The battery features 288 individual battery cells housed in a lightweight glass fiber-reinforced thermoplastic battery pack that incorporates an integral thermal management system. CW Trending: A New Video Series From CompositesWorld
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