Greater freedom of design and improved component quality Manufacturing processes and materials optimized further
Leverkusen - Their combination of light weight and high flexural strength has played a key role in the breakthrough of polyurethane fiber composite materials in automotive construction. One current example is that of the trunk floor of the new Mercedes-Benz A Class produced by Intier Automotive Näher GmbH in Rastatt, Germany. Other large series production runs include the support for the loading floors of the Opel Vectra Caravan and the Golf Plus which are produced by HONSA KFT, a subsidiary of Koller Formenbau und Kunststoff GmbH, in Pécs, Hungary. In all three moldings, the sandwich construction is bonded with the Baypreg® F polyurethane system from Bayer MaterialScience AG. "Thanks to advances in materials and processes, it has been possible to further improve the performance of the polyurethane fiber composite materials used for these components," says Dr. Dirk Wegener, expert in polyurethane composites at Bayer MaterialScience.
The basic work of designing the Opel Vectra and Golf Plus loading floors was performed by the polyurethane processing development team from Bayer MaterialScience in conjunction with HONSA. The ready-to-use process for series production was developed at Hennecke GmbH, a subsidiary of Bayer MaterialScience. Hennecke GmbH, a manufacturer of polyurethane processing machinery based in Sankt Augustin near Bonn, Germany, markets this continuously optimized version of its CSM (Composite Spray Molding) spray technology under the name CompurTec.
The manufacture of a lightweight sandwich component made of polyurethane fiber composite materials involves spraying a package consisting of a light honeycomb core (e.g. cardboard) and two fiber outer layers on both sides with the heat-activated 2-component polyurethane system Baypreg® F and compressing it in a compression mold at approximately 130 °C. This enables components to be manufactured with weights of significantly less than three kilograms per square meter, i.e. up to 60 percent lighter than corresponding components made of conventional materials such as wood or sheet metal. The high flexural strength of the sandwich components is a result of the 0.4 to 0.6 millimeter thick, fiber-reinforced outer layers. The modulus of elasticity of the outer layers is around 13,000 MPa, as a result of which only moderate deformation takes place even under heavy load.
"The aim of our work was to improve the overall plasticity and component quality in critical areas such as edges and supporting points so that moldings could be produced in attractive designs without the need for finishing," says Hans-Guido Wirtz, an expert in polyurethane processing technology at Bayer MaterialScience. To achieve this, the polyol formulation for Baypreg® F was further improved and the means provided to insert additional cut glass fibers locally during the polyurethane spraying process. "These measures enable large wall thickness variations of up to 50 millimeters, for example. It is also easier to produce large components with complex three-dimensional geometry. It is even possible to achieve a pronounced deformation of surfaces as in the case of domes. Sharp-edged areas can also be produced with great precision," concludes Wegener. He sees the potential for further applications for polyurethane fiber composite materials in automobile interiors: "Applications under consideration include multi-dimensional, contoured vehicle floors, trough-shaped trunk floors, seat wells and rear seat backs as well as cabin floors in truck construction."