Lightweight construction and electromobility

Electric vehicles are attracting much attention lately due in part to the growing focus on sustainability. Electromobility holds out the promise of greater environmental compatibility due to lower fuel consumption and fewer exhaust emissions. However, these advantages can only be attained with the alternative drive unit of the much heavier electric battery that has to be compensated through the lightweight construction of the vehicle.

Electric cars, such as the breakthrough BMW i3, are taking full advantage of the expertise of leading companies in the plastics industry. The BMW i3 design defines the automobile of tomorrow. Its innovative BMW eDrive power train was designed in the scope of the BMW EfficientDynamics technology and is not only locally emission-free, but also offers an incomparable and nearly silent driving experience. BMW is the first company to undertake commercial production of vehicles that feature carbon-fibre reinforced plastics (CRP) aimed at reducing fuel consumption.

BMW has tapped several leading companies in the plastics industry to undertake production of the BMW i3 parts. Exterior parts made of thermoplastics and structural components made of fibre-reinforced plastic are produced in injection moulding and reaction process machines of KraussMaffei (www.kraussmaffei.com) .

As supplier of production equipment and with the aid of refined processes, KraussMaffei is helping to process carbon fibre-reinforced plastics for the first time in series production through its injection moulding machines in swivel plate technology and the mature high-pressure resin transfer moulding process (HP-RTM). “That is our contribution towards a new generation of vehicles in order to facilitate the breakthrough for lightweight construction and electromobility,” says Nicolas Beyl, President of the Reaction Process Machinery Segment of KraussMaffei.

KraussMaffei has supplied BMW with premium quality injection moulding and reaction process machines, for example two double swivel plate machines which are fully automated with two industrial robots. Weighing 400 tonnes, each MX 4000-17200/12000/750 WL is 24 metres long, 9 metres wide and 7 meters high. The thermoplastic outer shells of the BMW i3 are produced on these machines, which have a clamping force of 4,000 tonnes, at the BMW plant in Leipzig. Using the “joining in injection moulding” process, the outer door shell and its substructure are injected in a single pass, are joined as the two swivel plates turn and are bonded with a third plastic component. “The combined work processes ensure very high dimensional accuracy of the parts,” says Frank Peters, Vice President Sales of the KraussMaffei brand.

The “face” of the BMW i3

In addition to the sidewall panels and the rear bumper, the hood of the BMW i3 comes from a KraussMaffei injection moulding machine. “They are produced on the most complex machines we have ever developed”, stressed Mr. Peters. ”We showed a great deal of commitment in accepting the challenge to contribute the most innovative machine technology which places maximum demands on availability. I am proud of what our team has achieved.”

High filling pressures for optimum fibre wetting

In addition to injection moulding technologies and automation solutions, the Reaction Process Machinery Segment is involved in the BMW i3. Twenty machines for high-pressure resin transfer moulding (HP-RTM) supply reactive resin components for the supporting structures, for example the side frame, at the BMW plants in Leipzig and Landshut. HP-RTM allows fast reacting resin systems to be processed in order to attain short cycle times. High-pressure injection produces a high degree of fibre wetting. A 10-man team from the KraussMaffei Reaction Process Machinery Segment set out to improve metering technology and provide mixing heads with the possibility of adding an internal separating agent. The experts worked under high pressure to meet the specific requirements relating to chemistry and the process.

In order to produce fibre-reinforced parts with an epoxy matrix in larger series, KraussMaffei enhanced HP-RTM for series use. In this process a self-cleaning, high-pressure mixing head injects the resin into the closed cavity and saturates the fibres inside under high pressure and with precise stipulations of the duration and temperature so that the resin and hardener are fully networked. After it has hardened, the component becomes stiff and very light. Compared with the previous autoclave process or vacuum infusion, the advantage of automated production is that the cycle times are reduced from up to 24 hours to minutes depending on the complexity and size of the component.

This type of HP-RTM process is also suitable for the use of polyurethane instead of epoxy resin as a matrix material. In addition to easier handling of the generally lower raw material price, another advantage of polyurethane is the reduced processing temperature.

Megatrend of electromobility

Agreeing on the basics was one of the many continually recurring individual questions, specifications and deadlines. “This complexity could only be mastered by our experienced team and through close cooperation with the technology experts from BMW and other partners in the areas of compression moulding, mouldmaking, handling and automation,” emphasizes Erich Fries, Head of the Composites Business Unit at KraussMaffei. Many years of experience in this field were also required: For example, the Reaction Process Machinery Segment of KraussMaffei has been refining its range of fibre composite technologies since the 1990s, initially for utility vehicles in particular and lately to an increasing extent for car manufacturers. “With the BMW i3, we implemented our improved HP-RTM technology for the first time under series conditions within the context of a completely new production concept. This provides us with a broader view of the process chain in efficient fiber composite production and is our competitive edge for other projects”, according to Josef Renkl, Head of Research, Development and Application Technology. BMW i3 lightweight car is therefore the vehicle for the megatrend of electromobility that has paved the way for large number of drivers to glide smoothly, quietly and with less emissions along roads in future.