AG2 battery.General Motors develops composite anti-collision shield to protect car power batteries in severe collisions

　　As conventionally powered passenger vehicles become more electronic and require larger batteries to run onboard systems, protecting batteries during severe crashes becomes more difficult. Although the structure around the battery is already high-strength and provides adequate protection from normal impacts, in the event of a severe impact, the protective structure itself can deform and puncture the battery, rendering it inoperable. In this case, additional battery protection is needed, but preferably without sacrificing design or other safety features, without adding too much weight or cost, and without hampering battery repair or replacement during the vehicle's lifetime. As a result, a new component called a battery impact shield was developed to protect the larger 12-volt battery in a severe crash, one of a growing number of applications for composites. Tough vehicle safety standards prompted GM to develop battery crash shields The already stringent U.S. Federal Motor Vehicle Safety Standard (FMVSS) 208 currently requires automakers to test at a 30-degree offset in frontal barrier testing. The test impactor was designed to miss the frame rail completely, allowing one corner of the bumper to hit completely before being pushed into the engine bay. The severe crash loads simulated by this test prompted General Motors Co. of Detroit, Michigan, USA, to strengthen the battery tray and develop a battery crash shield, which is designed to spread the crash load over a larger area so that the battery can be protected. Will not be punctured or shorted out by surrounding components when the car's front end is crushed. This gives the onboard diagnostic system enough time to detect an incident and send an "offboarding" safety call to first responders before the battery ceases to function - a feature that can be used if a passenger is unconscious or unable to call. Save lives on the phone. The shields are designed to be placed on the metal battery tray and wrapped around the parts of the battery closest to the engine compartment components, which crash simulations have identified are most likely to damage the battery in a severe crash. In use, the control module and other components connected to the battery hang from the crash guard and hold it in place, so there are no NVH issues. During maintenance or battery replacement, simply remove the impact guard and put it back on. A team working on the 2018 Buick Enclave sport utility vehicle (SUV) discovered late in the development cycle that a steel shield used to protect the truck's 12-volt battery wouldn't pass required crash tests. To avoid costly start-of-production (SOP) delays, General Motors' Advanced Materials and Development teams were brought in to quickly find alternative technologies. The new replacement technology for next-generation GMT composites needs to meet or exceed all federal safety regulations, including flammability requirements (FMVSS302), and also meet GM’s overall system cost goals. The researchers turned to a different technology - glass mat thermoplastic (GMT) composites. The research team evaluated three commercial-grade polypropylene-matrix GMTex fiberglass fabric-reinforced composites from Quadrant Plastic Composites AG (QPC, a group company of Mitsubishi Chemical, Lenzburg, Switzerland). The material ultimately selected for the battery shield was the highest performing grade, 4.3 mm thick, with multi-layer woven directional glassmats (4/1 weave, 0/90 degrees) with a randomly oriented 50 mm core Chopped glass fiber. The integration of woven fibers and chopped glass fibers provides a high-impact, consistent and uniform laminate with a FWF of 61%. Integrating woven and chopped fibers While fabric-reinforced GMT is not a new invention and has been commercially available in the automotive industry for decades, it is a product of General Motors and Continental Structural Plastics (CSP, a Teijin Group company, Auburn Hills, Mich., USA) For the first time, a new generation of hybrid mat GMT composites combining fabric and chopped glass fibers has been used. The person in charge of the battery anti-collision shield design project. "The higher-performing, thicker material gave us an important safety factor, which is what we wanted," explained General Materials Engineer Kestutus "Stu" Sonta. Next, small-scale testing was verified using full-scale parts. result. A non-optimized C-shaped design has been developed to evaluate GMT materials through simulation. The model was used to quickly cut GM's prototype aluminum tooling to mold preliminary test parts in the 4.3mm thick grade (GMTexX103F61-4/1-0/90). Multiple rounds of testing were completed and the team recorded loads that were very similar to previous full vehicle crash test results that validated the concept and material/process combination. The Hot Pressing and Cutting GM and CSP teams worked together to further optimize the design of the c-shield, which was subsequently used to produce the production tooling, waterjet fixtures and inspection fixtures used to inspect finished parts. The materials provided by QPC are pre-cut blanks of approximately 930×500 mm. A single blank is used per molding cycle to form a C-shaped section from which production parts are cut. The material first passes through a four-stage infrared furnace at CSP's Conneaut, Ohio, facility before being transferred to an adjacent low-tonnage compressor. When heated, the shredded glass fibers in the consolidated blank are approximately twice their previous thickness due to a phenomenon called glass rebound, in this case the blank entering the tool was almost 9 mm thick and in the mold Re-solidified during the forming process. Button-to-button cycle time is approximately one minute. No modifications to the part (by means of flame retardants or foils, etc.) are required to meet FMVSS302 flammability requirements. An interesting feature of this GMT material is that it has limited mobility due to the high glass loading and fabric layers. Therefore, it is not technically compression molded, but rather thermoformed (or hot pressed) at low molding pressure. Since the forming pressure is low and there is little material flow, no shear edges are required on the tool. By simplifying part and tool design, a set of tools is quickly produced that enables projects such as design technology execution and reduces costs. Prototypes and early pre-production parts were formed on aluminum tooling, but given the volume of the vehicle, GM selected P20 steel for the production tooling to extend service life. Laval International (Canada) produces this tool. Final Part Design The final designed part has a flat back and two 90 degree angled flanges and measures approximately 187 x 142 x 161 mm with nominal walls of 4.0 mm. Best estimates are that the composite design would weigh 75% less and cost 60% less than a comparable metal shield. Despite the rapid pace at which the project progressed, the panel agreed that the process and design worked as expected, with the new shield passing crash tests and providing additional protection for critical safety systems.

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