Thermoplastic Drive Shaft System Developed for Aerospace Applications
herone GmbH, (Dresden, Germany) recently won the prestigious 2019 JEC Innovation Awards, in the Aerospace application category. The winning application was the company's all-thermoplastic drive-shaft system overmolded with an integral gear, designed for use in aerospace applications.
The drive shaft is formed from ‘organoTubes’, which are braided preforms made out of fully consolidated thermoplastic UD tapes, in this case, VICTREX AE™ 250 unidirectional tape (UDT), a carbon fiber PAEK composite. The process was developed by the Institute of Lightweight Engineering and Polymer Technology (TU Dresden) and herone GmbH 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.
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 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.
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 a difference of 40°C (104°F) 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 improved resource efficiency, process reliability and interface strength.
herone and Victrex expect the many advantages of the new thermoplastic solution to translate into tangible key benefits, including:
- Enhanced part quality - In part, this is due to 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 reduces the number of parts and 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)