Abstract
The first mass production of carbon fiber reinforces plastic parts (CFRP) produced in the high pressure resin transfer moulding process (HP-RTM) for implementation in the vehicle body was realized by BMW with the launch of the BMW i-series. The key for an economic and efficient HP-RTM production process for high volume CFRP part production is to characterize the cure behavior of the fast thermosetting epoxy resin matrix in detail. The objective of this work is to provide a new methodology for a comprehensive understanding of the curing behavior of fast curing epoxy resin systems applicable in high volume CFRP part production not only by laboratory analysis but also by direct investigation of the curing progress in the HP-RTM production process. In addition, a reaction kinetic model is derived to provide cure simulations. On this basis, a detailed examination of current processes is allowed to identify potential process optimizations. This also provides a benchmark method to compare the curing performance of future potential thermosetting matrix resins with prior art matrix systems. For this purpose, two fast curing epoxy resin systems, suitable for high volume CFRP part production in the HP-RTM process, were investigated exemplarily. Laboratory analysis was conducted by using differential scanning calorimetry (DSC), near-infrared (NIR) spectroscopy, rheometry and ultrasound technique. For online-cure-monitoring of the epoxy resin directly in the HP-RTM process also the ultrasound technique was applied. Furthermore a reaction kinetic model was developed to provide the prediction of the curing process and complement the comparison of laboratory and process investigations. This approach allows a comparison between theory and practice, which is absolutely necessary for a successful and efficient high volume CFRP manufacturing process. It could be demonstrated that a comprehensive understanding of the curing behavior of fast curing epoxy resins used in the HP-RTM process was achieved by both laboratory analysis and online-cure monitoring in the HP-RTM process. Also confident cure simulations could be achieved by the developed reaction kinetic models based on laboratory analytical data. The correlation of laboratory analysis, investigations of the curing progress in the HP-RTM process and the prediction of the curing progress was in good agreement. The developed methodology provides a comprehensive and consistent characterization strategy of the curing behavior of fast curing epoxy resin systems both in the laboratory and in the HP-RTM production process and a well-founded prediction of the curing progress depending on the applied cure temperatures is possible.
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