Lightweight plastics make for a sustainable drive

Krauss Maffei is supplying the injection moulding and reaction process machines used to produce the exterior parts made of thermoplastics and structural components made of fibre-reinforced plastic on BMW’s electric car, the i3.

The company is helping BMW to process carbon fibre-reinforced plastics (CRP) for the first time in series production, with its injection moulding machines, swivel plate technology and the high-pressure resin transfer moulding process (HP-RTM) all being utilised.

"That is our contribution towards a new generation of vehicles in order to facilitate the breakthrough for lightweight construction and electromobility," said Nicolas Beyl, President of the Reaction Process Machinery Segment of KraussMaffei.

KraussMaffei has supplied BMW with injection moulding and reaction process machines, including two double swivel plate machines that are fully automated with two industrial robots.

Weighing 400 tonnes, each MX 4000-17200/12000/750 WL is 24 metres long, nine metres wide and seven metres 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," commented Frank Peters, Vice President of Sales at  KraussMaffei.

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,” continued Peters.

In addition to injection moulding technologies and automation solutions, KraussMaffei’s Reaction Process Machinery Segment is also involved in the manufacture of parts for the BMW i3. Some 20 machines for high-pressure resin transfer moulding (HP-RTM) supply reactive resin components for the supporting structures, for example the side frame, at BMW’s 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.

In order to produce fibrr-reinforced parts with an epoxy matrix in larger series, KraussMaffei enhanced high-pressure resin transfer moulding (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. KraussMaffei says 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.

KraussMaffei says another advantage is that 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.

“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 fibre composite production and is our competitive edge for other projects", summarised Josef Renkl, Head of Research, Development and Application Technology.