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Plastic functions as electric car enabler

The BMW i3 electric vehicle employs several innovative components enabled by plastics. These include the backrests of the front seats, key reinforcement parts in the carbon fiber composite body, and the rear seat shell.

The BMW i3 electric vehicle employs several innovative components enabled by plastics. These include the backrests of the front seats, key reinforcement parts in the carbon fiber composite body, and the rear seat shell.

The seat backrest in the driver's and passenger seats is the first injection molded and uncoated structural component made from polyamide (PA) to have a visible surface and to be used in the vehicle interior. This lightweight hybrid component, weighing only 2 kg, while integrating multiple functions. It is molded from a highly UV-stable PA 6 compound developed by BASF (Ludwigshafen, Germany) especially for such applications (Ultramid B3ZG8 UV). As well as providing sufficient rigidity, this material also ensures adequate elongation and toughness to meet the mechanical requirements of the BMW Group, and this within a temperature range of -30°C to +80°C.

bmw
BMW electric car is kitted out with various BASF materials.
BASF's Ultrasim simulation tool was employed in the early stages of component development for optimization, resulting in the very slim shape of the final complex part. Ultrasim also delivered accurate crash simulation data for behavior of the backrest, release lever and belt guide. This optimization helped to avoid modifications later on in component development. 

Furthermore, the particular Ultramid grade is especially low-emission. Its high scratch resistance and "remarkable" surface quality allow cosmetic use of the seat structure. In addition, the seat release lever material must not fail in a crash. Therefore, a special long glass fiber reinforced Ultramid grade is employed in this application: Ultramid Structure B3WG8 LF.

 The BMW i3's carbon body also incorporates PBT (polybutylene terephthalate) structural parts between the inner and outer shell. The largest component and the first of its kind is a so-called integral component located in the rear side area between the carbon fiber body shells. Apart from its load-bearing function in the event of a crash, it also serves to keep the two body shells apart and forms the rear opening for the side window. The PBT Ultradur B4040 G6 from BASF is ideal for this since it is dimensionally stable irrespective of surrounding climate conditions and offers the necessary buckling resistance. Simulation provided by BASF engineers also reportedly made a major contribution to low-warpage production and the glass fiber orientation suitable for the occurring loads. The injection-molded component integrates several smaller components planned in the past thus reducing complexity and costs. More than two dozen smaller PBT components with a combined weight of around nine kilograms are integrated in other areas of the vehicle's body where they provide reinforcement and achieve the desired acoustics.

Carbon fiber/PU composite seat shell

The self-supporting rear seat shell is made from BASF's Elastolit polyurethane system. For the first time in a serial production vehicle, carbon fibers are combined with a polyurethane matrix. The component integrates a variety of functions such as the cup holder attachment and storage tray, saving on both assembly work and weight. A key feature of BASF's Elastolitis reportedly its wide processing window together with its high fatigue strength and damage tolerance. Because of the material's special properties, the crash-compliant part meets the stringent safety requirements by the BMW Group despite its wall thickness of just 1.4 mm.

The PU structural foam Elastolit D is used as a reinforcing material in the entire roof frame, including the A-pillar. The highly pressure-resistant foam is processed in the form of a carbon sandwich composite, thus supporting the structural rigidity of the vehicle.

More components

The BMW i3 incorporates many other parts made of BASF plastics which have already been established in a number of vehicles. These include various electrical and electronic applications made of Ultramid, Ultradur and polyurethane. Examples include  the fuse box made of Ultramid B3ZG3, which meets the stringent demands for rigidity and tensile strength, as well as a high-voltage connector made of Ultramid A3EG6. Furthermore, cable sheathings and cable glands are made of the Elastollan and Elastoflex polyurethanes.

In the vehicle interior, the semi-rigid foam PU Elastoflex E is utilized for back foaming the instrument panel, while the C-pillar cover is made of Ultramid B3ZG3 PA resin.

Two different Elastoflex E polyurethane foams are employed in the roof construction for improved interior acoustics: in the roof liner, forming the core material of a sandwich composite which has excellent thermoformability and high rigidity; an extremely low-density, open-cell Elastoflex E foam is used as the basis for acoustically effective parts.

In the module production of the optional sliding roof, the UV- and weather-resistant glass encapsulation system Elastolit R 8919 PU is applied. The frame of the sliding roof is made of Ultradur B 4040 G6, a low-warpage PBT/PET-blend.

Lightweight spring aids made of Cellasto, a micro-cellular special elastomer, can be found in the front and back axle suspension of the BMW i3 as well.

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