FRANKFURT, GERMANY (Dec. 7, 10:55 a.m. ET) Battery housings for electric vehicles (EV), previously made of metal, are now being developed in thermoplastics and thermosets, and thermoplastic battery module frames are already going into production.
Plastic processor Rehau AG + Co. is one of 80 partners in the Street-Scooter short distance vehicle (SDV), a lightweight electric drive concept car. Rehau presented its new Ultralitec production process for the car's battery housing when the StreetScooter was unveiled at the IAA 2011 automotive industry fair in Frankfurt, Germany in September.
Easily formed metal housings have previously been used for EV battery boxes. But StreetScooter project managers said they decided to use a thermoplastic housing to save weight and avoid corrosion.
In addition, the low thermal conductivity of plastics eliminates the foam sheet thermal insulation needed for metal housings. Connectors integrated in the housing provide a thermal barrier, protecting batteries from overheating while charging and against cold temperatures in the winter.
The plastic housing has to retain a 250 kg. battery under crash conditions and it also contributes to overall vehicle stiffness. Rehau says: “Plastic makes the ideal structural battery casing, metal having almost no future at all in this regard.”
In the Ultralitec process, fiber-reinforced thermoplastic is used in a structure of up to 27 layers. The process uses 3D simulation to optimize stretched fiber placement in the direction of maximum load, creating rigidity where most needed.
The assembled fiber plies are heated and compression molded, and other components are added by injection molding. The resulting battery housing has 50 percent less volume than a metal equivalent and is 30 percent lighter.
A thermosetting plastic battery housing has been developed by Fraunhofer Institute for Chemical Technology (ICT) and other Fraunhofer mechanical and materials institutes for an electric drive prototype of the polyurethane bodied Artega GT sports car. The housing holds a 340 kg. battery and weighs 35 kg., around 35 percent less than a metal equivalent.
Manfred Reif, project manager for Fraunhofer System Research for Electromobility, says the thermosetting battery housing withstands a crash with ten-fold gravitational acceleration and protects the battery from collisions with sharp objects up to 60 km. per hour. A semi-permeable membrane equalizes pressure.
Production cycle time has been optimized for higher output volumes than those typical in the aviation composites sector. Reif says this is achieved “with a process chain designed with many steps running simultaneously. The plastic is heated up parallel with the production stage. Preparation of directionally oriented fibreglass structures or custom-made metal inserts are assembled and pressed together in a one-shot process to ensure load and tensile strength, or by attachment to the Artega's rear storage area.”
Mann+Hummel announced at the IAA 2011 fair in September that it has received the largest contract in the company's history - a “two digit million dollar order” for daily production of 160,000 lithium ion battery module frames for General Motors. The frames are for the Chevrolet Volt and Opel Ampera hybrid extended range electric drive cars, in a project which started in October 2010, with full-scale deliveries starting in 2014.
The battery plastic parts are designed as a “market ready solution” in BASF's Ultramid 1503-2F grade of PA66, which is 33 percent glass fiber reinforced and hydrolysis stabilized. These parts will be produced at M+H's plant in Portage, Mich. Before full production starts, 40,000 parts/day will be supplied in 2012 from GM's plant in Brownstown, Mich.
The frames support and align the battery cells, contain sensors for overheating protection, provide electrical insulation and have molded-in channels for cooling fluid.
There are 288 parts in a battery, 160 of which are made by M+H. Among these are 18 end frames and 135 stack frames, plus a fluid distributor, all made in the same PA66 material. With 8 million to 9 million precision moldings/year to be produced, M+H says fast cycle time is essential and it has accordingly developed “a new production process” for the parts.
The battery application won the powertrain category in the SPE US automotive awards in November. Autodesk's Moldflow simulation software had been used in the design of the parts and a Synventive hot runner system was used in tooling.