Cost Efficiency through Load-optimised and Semi-impregnated Prepregs
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The manufacturing of prepreg based fibre composite parts generally requires multiple process steps and curing via autoclave. This leads to long cycle times and high investment costs. RWTH Aachen University demonstrates how to overcome these problems by the usage of novel partially impregnated prepregs based on tailored textiles.
High Component Prices
In the steadily growing market for carbon fibre reinforced plastics (CFRP), pre-impregnated reinforcement textiles, so-called prepregs, play a major role. With a market share of approximately 45 %, prepreg-based processes generated a worldwide turnover in 2015 of approximately € 4.4 billion . The technology is mainly applied for the production of parts with high quality requirements and for series smaller than 10.000 pieces/year . For up to 1000 pieces/year, the deposition and the stacking of the prepregs are generally done manually. For this, UD-prepregs or prepregs based on woven fabrics are cut into shape and then layered to form the specific component. For quantities greater than 1000 pieces/year, automated deposition systems can be used. In general, the layers are then cured under the influence of temperature and pressure using an autoclave. This allows fibre volume contents of about 60 %. In combination with the specific alignment of the reinforcement fibres within the individual layers, the manufactured components show high quality and excellent mechanical properties. In return, the coating process, the deposition and the use of the autoclave cause high investment and energy costs and require long cycle times. In addition, the waste resulting from the stacking process is expensive to recycle due to the already applied matrix system. These circumstances lead to high process costs and component prices. For that, the use of prepregs is currently only suitable for certain high-performance applications . For instance, the estimated costs of carbon fiber reinforced plastic within the aerospace sector, which is currently the main user of the prepreg technology, averaged 260 €/kg in 2016 .
Production of Tailored Non-Crimp Fabrics
The process costs can be reduced by up to 20 % compared to the conventional prepreg process.
Due to the transfer coating, the necessary flow path is only a few mm depending on the thickness of the buildup. Compared to conventional infusion methods, in which the entire textile layer has to be penetrated, the time for complete impregnation is thus significantly reduced. Moreover, the precise introduction of the required amount of resin onto a resinous base in a vacuum construction can be dispensed with. On top of that, the use of an autoclave becomes unnecessary.
Summary and Outlook
Within the research project “Tailored Prepreg”, a new process chain is being developed at the Institut für Textiltechnik at the RWTH Aachen University, in which load-optimised non-crimp fabrics are produced by singlestep manufacturing and are then partially impregnated in a continuous coating process and subsequently consolidated. For this purpose, the existing process for the manufacturing of TNCF is extended by a continuous draw-off, which allows a distortion-free winding of fabrics with local reinforcements. In a subsequent transfer coating process, the reinforcement fabrics are partially impregnated, which ensures rapid consolidation with a high fibre volume ratio without the use of an autoclave. The investigated process chain allows the reduction of manual effort, fibre waste and investment costs, which considerably reduces the costs for prepreg components.
The IGF project “Tailored Prepreg” (No. 19441 N) of Forschungsvereinigung Forschungskuratorium Textil eV, Reinhardtstraße 12-14, 10117 Berlin is funded by AiF within the program for the promotion of industrial joint research (IGF) by the Federal Ministry of Economics and Energy BMWi on the basis of a decision of the German Bundestag. We would like to thank the participating project partners as well as the members of the project accompanying committee for their cooperation and the support of the research work.
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