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Composites Innovation: All-thermoplastic drive-shaft system for aerospace

A German company called herone GmbH was recently declared a top winner in the prestigious 2019 JEC Innovation Awards. The award was given in the aerospace application category for an all-thermoplastic drive-shaft system overmolded with an integral gear. Its unique design and manufacturing holds enormous potential to enable components to be made faster, in higher part counts, and with the potential for cost savings. The materials used are based on high-performing VICTREX PAEK polymer solutions. "Flying taxis" could be a beneficiary.

The drive shaft is formed from "organoTubes," which are braided preforms made from fully consolidated thermoplastic UD tapes. In this case, VICTREX AE 250 unidirectional tape (UDT), a carbon fiber PAEK composite, was used.

The process was developed by the Institute of Lightweight Engineering and Polymer Technology (TU Dresden) and herone for use in the manufacture of high-quality, continuous carbon fiber PAEK composite hollow profiles. The organoTubes are then overmolded with VICTREX PEEK 90HMF40, a carbon fiber PEEK composite, to incorporate the integral gear.

"The solution is a result of converging innovations: hollow profile technology and the hybrid overmolding technique developed by Victrex," said Daniel Barfuss, managing partner at herone GmbH.

By using thermoplastic tapes to form the organoTubes, the challenging and time-consuming process step of impregnating the carbon filaments with thermoplastic matrix material is already completed prior to preforming. This opens up the potential for significantly reduced cycle times and increases the process efficiency for the composite profile production within the hollow profile press process. Furthermore, braiding enables high deposition rates and makes the process suitable for large-scale industrial production.

For incorporating the gears, injection overmolding creates a cohesive molecular bond between the shaft and the gear, while the drive shaft is simultaneously thermoformed to create a form-lock between the gear and the drive shaft to further enhance the strength of the interface.

More about the materials
The VICTREX AE 250 composite has a melting temperature of around 40 C (104 F) lower than Victrex's short carbon fiber-reinforced PEEK 90HMF40. This means that, with the difference in the melting temperature, there is no need to pre-heat the matrix polymer of the shaft beyond its melting temperature prior to injection overmolding. This processing approach, on the part of Victrex, is known as "hybrid overmolding" and results in what the company deems "enormously improved resource efficiency, process reliability, and interface strength."

herone and Victrex expect the many advantages of the new thermoplastic solution to translate into tangible, real-world benefits, including:

• Enhanced part quality: In part, this is due to the textile preforming of the UD tapes.
• Fast cycle times: herone's consolidation technology enables cycle times measured in minutes.
• Cost reduction by smart design with integrated functionality, which reduces the number of parts and the assembly costs.
• Increased performance: Cohesive bonding and form-locking increase strength.
• Final forming of the composite tubing during the injection process creates the form-locking geometry and its unique features (e.g., an internal star shape).

"Innovative consolidation techniques of thermoplastic materials differ considerably from metal or thermoset processing," said Frank Schemm, Aerospace Sales team leader at Victrex. "Fully functional design features can be integrated in fewer manufacturing steps. ... In particular, the strongly growing branch of electrical vertical take-off and landing (eVTOL) vehicles, the so called flying taxis, demand much higher production rates than classical legacy programs."

The JEC Innovation Awards identify, promote, and reward the most innovative composite projects worldwide. In particular, they celebrate the cooperation between the different segments of the Composite Supply Chain. Learn more and view the winners in other categories here.

Source: Victrex

Published April 2019

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