One of the latest trends in automotive design involves the use of structural reinforcements made of injection-moulded plastic and structural foam. Although the number of production line applications is still small, BASF (Ludwigshafen / Germany; www.basf.com) and Lanxess (Leverkusen / Germany; www.lanxess.com), for example, see this as a potential high-growth business. Two cars that already feature such reinforcements instead of the usual welded steel are the 2009 model of the Peugeot 308 and the 2007 Citroën C4 Picasso. Audi, BMW and Opel are also using structural parts made of plastic, but predominantly only to solve problems that arise in the course of vehicle development – such as local buckling of the body and acoustic problems.

In the event of an accident, the insert elements increase the load resistance of the body and absorb some of the impact energy. In addition, they improve torsional rigidity, resulting in fewer troublesome vibrations to impair the driving characteristics.

Both BASF and Lanxess have opted for glass fibre-reinforced polyamide for the injection-moulded skeleton. Lanxess sees its “Durethan” BKV 35 H2.0 PA 6 as the carrier, while BASF has gone for “Ultramid” A3WG10 CR – a PA 6.6 GF 50 – one of the six grades of its crash (CR) range. These high-performance polyamides ensure that the parts can withstand the temperatures of 180-200 °C that occur during the drying of the finished body once cathodic electrodeposition coating (EDC) is complete. During this process, the blowing agent in the second component of the part is activated – a one-component expandable structural foam based on epoxy resin, which was previously applied to the polyamide skeleton in a two-component injection moulding process. The foam cures in the drying oven, expands and bonds the injection-moulded part permanently to the metal structure.

In the case of the C4 Picasso, nine insert elements are integrated specifically in crash-relevant parts of the body: the lower part of the A-post, the lower and bottom parts of the B-post and in the cross member above the rear axle. They afford greater rigidity and improved crash behaviour and also bring a weight saving of around 12 kg per vehicle compared with the usual welded metal reinforcement. The supplier is L&L Products Europe (Molsheim / France; www.llproducts.eu) – known as Core Products until 2007 – whose experts worked with Lanxess on the development.

Together with the automotive segment of Sika (Zurich / Switzerland; www.sika.ch), BASF has developed very similar parts that will be used as structural inserts on the rear flap hinge of the new Peugeot 308 SW. The Ultramid part will, as before, be encapsulated by a structural foam – in this case "SikaReinforcer" 911NT/2 – and anchored in the body during expansion of the foam.