Lightweight CFRP engine hoods in a jiffy
IKV, the Institute of Plastics Processing at RWTH Aachen University in Germany has worked together with the Institute of Automotive Engineering (ika) based at the same university and a number of industry partners to prototype an engine hood made of carbon fiber-reinforced plastic (CFRP) for the Ford Focus. Compared with a typical series-production steel hood, the CFRP hood is around 60% lighter, weighing less than 5 kg.
The prototype hood was formed using the gap impregnation process in the space of just a few minutes. In the process, a preform is inserted into a mold, then impregnated with a liquid resin, and finally cured. The innovative feature here is rapid impregnation through the creation of a temporary flow gap, followed by the subsequent compression of the impregnated preforms by means of pressing and squeezing.
The objective of the development partners is to produce a CFRP engine hood using the gap impregnation process and develop it to a stage where it is suitable for series production. In 2009, a gap impregnation unit was developed by IKV in conjunction with Hille Engineering (Aachen) for the automatic short-cycle production of high-performance parts made from fiber-reinforced plastics (FRP). Since then, IKV has been working continuously on extending the process. At present, high-quality parts measuring 50 x 50 cm can be manufactured with integrated functional elements in less than five minutes. For the CFRP engine hood for the Ford Focus, these findings have been transposed to dimensions of 105 x 158 cm. A time of less than 15 minutes has been calculated for the production.
Apart from the curved part and stiffening structures, the CFRP engine hood also contains the fixing elements for assembly of the engine hood. In terms of the design, the mechanical properties (e.g. pedestrian protection), materials selection, service temperature and surface quality of the part played a key role. After determining the mechanical data from the previously selected resin and prepreg systems, ika designed the hood by simulation, focusing primarily on the aspects of stiffness and crash properties. The actual properties of the hood were then determined in crash and rigidity tests. The test results confirm the final geometry of the part.
Based on these test results, a special mold is being designed for the gap impregnation unit installed in the IKV laboratory, which should enable automatic part production in less than 15 minutes. Following the start-up of the mold, further research will be carried out at IKV on process optimization with regard to process speed and surface quality of the finished part. Prototypes will be produced on the gap impregnation unit after it has been converted for engine hood production. These prototypes will then be subjected to special tests—for example, on head impact protection and temperature stresses —which are necessary to gain approval for series production.
Apart from IKV and ika, the industry partners involved in the joint project are the Ford Research Centre in Aachen, Composite Impulse, Toho Tenax Europe, Evonik Industries and Henkel. The project is financed by the German State of NRW as part of the Hightech.NRW project “Exterior body parts of CRP for large-volume production”. The aim is to conclude the project by September 2013 with the near-series, cycle time-optimized manufacture of the engine hood by the gap impregnation process.