Continuous inductive Preforming for RTM-Production

Abstract

The Institute of Composite Structures and Adaptive Systems (DLR) has invented together with the Institute of Joining and Welding (TU-Braunschweig) a technology to speed up the most time consuming step within the RTM Process chain. Weimer [1] and Herbeck [2] pointed out that the preforming step takes up to 60% of the overall efforts needed to produce a complex CFRP part. Two main reasons can be identi-fied: • Low process speed • Difficult to automate This paper will show a new technology which will help to overcome both problems: State of art technologies for production of dry preforms are the stitching and binder technol-ogy [2, 3]. Main disadvantage of the stitching technology is that the mechanical properties of the part will be lowered as with each stitch some fibres are cut or ondulated. The advan-tage of high degree of automation and speed are often not even considered as the mechani-cal properties are most important to get the maximum performance needed for nowadays low emission, high efficient airliners and vehi-cles. On the other hand, the binder technology is slow and up to now only poorly automated. Anyway, the performance of the overall part can be increased by alloying the matrix resin with special modified binder. It can be seen that the slowness of the binder technology is mainly caused by slow heat energy transfer due to conduction through bad heat-conduction material. The inductive heat-ing has a different characteristic: Here, the energy will be transferred volumetrically [3] directly into the preform (Fig. 1). Furthermore, only the area needed to consolidate will selec-tively be heated so that also the cool down rate is much faster. Within the paper, the influence of major pa-rameters will be shown and discussed. In the second part, a fully automated built and tested prototype production line with two induction stages will be shown to demonstrate some new approaches to automate the pre-forming step.

[1] Weimer C.: Harzinjektionstechniken für strukturelle Hubschrauberbauteile. 1.Materialica Kongress, München, 2005. [2] Herbeck L.: Faserverbundstrukturen - Von der Idee bis zum Prototypen, CCG-Seminar, Braunschweig, 2006. [3] Ströhlein T. Frauenhofer M.: Induktives Preformen. IB 131-2007/11, Braunschweig, 2007.