BASF with materials and construction know-how in the BMW i3

“By bringing together all our plastics expertise in the division Performance Materials, we can offer customised solutions to innovative customers such as the BMW Group and their suppliers worldwide as well as support them during component construction”, said Raimar Jahn, Head of BASF’s Performance Materials division. “With the BMW i3, the BMW Group has taken a ground-breaking step into the future of the automotive industry, and BASF’s intelligent solutions are making a key contribution here.”

Seat backrest made of polyamide

According to BASF, the seat backrest in the driver’s and passenger seats is the first injection moulded and uncoated structural component made from polyamide to have a visible surface and to be used in the vehicle interior. This lightweight hybrid component, weighing only 2 kg, embodies all the know-how of the company’s Global Seat Competence Team. The backrest, which integrates multiple functions, is made from a highly UV-stable polyamide 6 compound developed by BASF 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.

The seat backrest owes its final, complex and above all very slim shape to the early use of BASF’s universal simulation tool Ultrasim. Thanks to the precise numerical simulation of the materials used for the backrest, release lever and belt guide, the calculated behaviour in the crash simulation matched the subsequent tests very accurately. Optimisation could thus take place on the computer in the early stages, avoiding modifications later on in component development. The BASF simulation method Ultrasim effectively accompanied all the certificates required by law at different seat positions, temperatures and loads.

Furthermore, the particular Ultramid grade is especially low-emission. Its very high scratch resistance and surface quality allow a visible use of the seat structure, which thus becomes an important element. Regarding the seat release lever, its material must not fail in a crash. Therefore, a special long glass fibre-reinforced Ultramid grade is employed in this application: Ultramid Structure B3WG8 LF.

Multifunctional structural body parts made of PBT

The BMW i3’s carbon body contains 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 fibre 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. The simulation provided by BASF’s engineers has made a major contribution here to low-warpage production and the glass fibre orientation suitable for the occurring loads. The injection-moulded component comprises several smaller components planned in the past thus reducing complexity and costs. More than two dozen smaller Ultradur components with a combined weight of around 9 kg are integrated in other areas of the vehicle’s body where they provide reinforcement and achieve the desired acoustics

Rear seat shell made of carbon fibres and a PU matrix

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

Structural foam for reinforcing the roof frame

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

Other components made of BASF plastics in the vehicle interior and exterior

The BMW i3 incorporates many other parts made of BASF plastics which have already been established in a number of vehicles:

• These include different electrical and electronic applications made of Ultramid, Ultradur or polyurethane; e. g. the fuse box made of Ultramid B3ZG3, which meets the stringent demands on rigidity and tensile strength, as well as a high-voltage connector made of Ultramid A3EG6; apart from that also cable sheathings and cable glands made of the polyurethanes Elastollan and Elastoflex.
• In the vehicle interior, the PU semi-rigid foam Elastoflex E is utilised for back foaming the instrument panel, while the C-pillar cover is made of Ultramid B3ZG3.
• 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 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, the micro-cellular special polyurethane elastomer, can be found in the front and back axle suspension of the BMW i3 as well.

Finally, BASF’s Coatings operating division contributes to the extraordinary design of the BMW i3. It supplies the new production line for the BMW i3 at the Leipzig factory with basecoats in four colours which meet the requirements of the coating of add-on components and of the painting processes involved.