Engineers at the Fraunhofer Institute for Chemical Technology have developed a new technique for curing carbon fibre reinforced plastic (CFRP) that could hold the key to cost-effective small batch production.

Current CFRP production often involves large, expensive tooling and complicated, time-consuming heat cycles. Fraunhofer’s approach, however, uses infrared radiation to apply heat directly to the material in a vacuum.
For the mould wall, the researchers have found a material that transmits infrared radiation in the desired wavelength range, without experiencing any significant thermal expansion. As a result, they claim, a part that could take several hours to cure with a conventional vacuum-based variotherm process can now be done in less than 60 seconds.
“Our method is faster, more economical and more energy efficient than the current state of the art,” said Sebastian Baumgärtner, mechanical engineer at Fraunhofer. “Processing in a vacuum protects the material. The plastic does not oxidise, as it does in open procedures. Trapped air and any gases are sucked out. The process is very stable and easy to use.”
All forms of electromagnetic radiation are suitable for heating CFRP in this approach, Baumgärtner explained, including microwaves.
The system is described as being small enough to fit on ‘a normal shop floor’ with no large structures or special foundations. It’s also said to result in extremely low distortion.
“This is a major challenge when manufacturing with CFRP,” said Baumgärtner. “We heat and cool symmetrically, using a mould wall with minimal thermal expansion and operating at relatively low process pressures in order to avoid squeeze flow. The smooth surface of the mould wall also creates an almost reflective CFRP plate surface. This is a real advantage in the final component, particularly for applications in visible areas.”
The next step is to eliminate the use of the separating agent, which is currently used to remove the CFRP part from the moulds. At present, this tends to leave a residue on the parts, which can make further processing difficult, but the researchers are hoping to avoid this completely.
“Together with our colleagues from the Fraunhofer Institute for Manufacturing Technology and Advanced Materials Research IFAM in Bremen, we are developing a special, durable separation layer and our goal is to apply this to our mould wall,” said Baumgärtner.
Why is this new process suitable for “cost-effective small batch production” when it requires costly moulds operating in a vacuum? I’d have thought that reducing the cure process from hours to one minute would be just what’s needed to produce CFRP components in high volumes. . .
You are right. Basically this process has advantages for small and high volume processing of thermoplastic composites, as costs for the mould and heating equipment are low compared to a static/ continous press or an autoclave, as well as short cycle times can be reached. Because of the mould (pressing on both sides of the material) no time consuming vacuum bagging process is needed and the material can be processed in a very lean way. E.g. polyamide 6 carbon UD tape (2mm thickness) can be heated in less than 35 seconds over the melting point and cooled in 25 seconds. Therefore the whole consolidation step can be done in less than 60 seconds. Details on this study were presented yesterday at eccm17 conference. http://www.eccm17.org/
Best regards, Sebastian