Fraunhofer IPT develops automated production technology for CFRTP engine blades

       Aerospace materials need to have both high modulus and light weight at the same time. According to the British Rolls-Royce Company, carbon fiber composite materials (CFRP) have been used more and more widely in aero-engine fan blades due to their two excellent properties. At this stage, the production of many CFRP aviation components has been partially automated. Usually fiber-reinforced epoxy resin composite materials are used to make semi-finished prepregs, which are laid into thin sheets in a certain orientation according to design requirements, and then subjected to high energy consumption and high cost autoclave under certain temperature and pressure. The process takes a long time to solidify and shape, and the production process is time-consuming and costly.

 Recently, a research team from the Fraunhofer IPT in Germany has developed a more cost-effective automated production technology for aero-engine CFRP blades.

The team did not choose thermosetting epoxy resin-based composite materials, instead using carbon fiber reinforced thermoplastic composite materials (CFRTP). CFRTP has been used in aerospace structural parts for decades. It has good lightweight structural performance and excellent impact resistance. The automated molding process is fast and flexible. Because it is a thermoplastic material, there is no need for chemical cross-linking reaction to strengthen it. It only needs to be heated to melt and control the curing pressure during the cooling process, and it can also be heated to reshape.

       "Thermoplastic composites are more suitable for efficient manufacturing processes," said Dr. Henning Janssen, head of Fraunhofer's IPT fiber composites and laser system technology department. After a lot of experiments, the research team successfully combined the fully automatic tape laying and thermoforming process into one for the first time for the production of aircraft engine blades.

 Flexible process chain: automatic tape laying and thermoforming

       Through a set of fully automatic tape laying system that has obtained a commercial license, the thermoplastic unidirectional tape (UD) is stacked layer by layer along the required force direction of the structure, thereby obtaining a highly elastic multilayer organic board. Researchers monitor and record each automated process through various sensors.

       The organic board will be heated in the next process steps and will be nearly net shaped into the desired shape through a thermoforming process. The series of tests carried out in the early stage were first carried out on the 16mm thick carbon fiber fabric reinforced PA12 composite material, and quickly transferred to the carbon fiber unidirectional tape reinforced PEEK composite material.

       Series of tests for milling FRP parts

       After thermoforming, the leftover material of the organic board is cut and the parts are milled into the final shape. Due to the non-uniformity of the material structure, milling FRP is extremely challenging. At the same time, the carbon fiber composite material will have a serious sticking phenomenon on the edge of the milling cutter, resulting in severe tool wear and fluctuations in processing quality.

        A feasible way to extend tool life is to use milling cutters with polycrystalline diamond (PCD) coating. In the process of exploring the machining method of small CFRP blades, the researchers found that PCD coating can significantly extend the service life of the tool. At the same time, the custom-designed milling process will have a positive impact on the processing quality.

       Applications in various industrial fields

        Daniel Heinen, Head of Engine Mechanics Business Unit at Fraunhofer IPT, said: "The first application results of CFRTP show that the interrelated blade manufacturing and finishing processes are very effective, and the radial and front and rear edges of the blade have obtained good surface quality. Now we Each process link must be reviewed and optimized."

        In the coming months, several research projects will begin to study the application of new processes in different industrial fields. Researchers are very interested in high-performance thermoplastic PEEK-based composite materials and organic plate embedded sensor technology. Placing sensors inside the organic board can not only monitor the molding process, but also monitor the state of the blades during engine service. The project also studied the application of the new technology in aero-engine stator and nacelle components, as well as other industrial fields.

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