SAMPE Journal - January/February 2025 - 18

FEATURE / INJECTION MOLDING
3.4 Quasi-static Torsion Test
Config 08 and config 09 are chosen for mechanical
testing in order to evaluate the part quality as
a function of the preheating temperature. Five
specimen per config have been tested. Figure 11
shows the testing setup, the torque and shear stress
boxplot of the tested specimen and an exemplary
fractured tooth of specimen config_08_01. All
failures of config 08 specimens occurred at the
interface of the TPC substrate and the overmolded
teeth of the splined shaft. In all cases the teeth are
sheared off the substrate. Adhesive failure in the
bonding zone dominates the fracture surface of the
config 08 specimen with minor TPC residue on the
teeth structure (see Figure 11c) and partially laid
bare fibers on the inside of the TPC-HP. The average
resultant shear strength at the interface area is
calculated to 13.4 N/mm² for config 08. All specimen
of config 09 failed outside of the joining zone. The
failure mechanism is splitting parallel to the fiber
direction of the laminate under torsion load. No
resultant strength values were identified for the
one-shot overmolding specimen with preheating
temperatures above the melting temperature of
the polymer, though the resultant shear stress
exceeds 32.4 N/mm² as no shear failure occurred for
specimen config_09_4 at a torque of 1508 Nm.
4. CONCLUSIONS
A novel manufacturing approach for thermoplastic
composite splined shafts by means of injection
overmolding on the inside of the TPC-HP has been
demonstrated in this study. With this technology, a
functionalization of TPC closed profiles made from
high-performance polymers can be performed
in a fast downstream process by which a wide
range of aerospace applications can be addressed.
With the chosen evaluation methods, good part
qualities were identified on optimized processing
parameters. The rough inner surface of the TPCHP
resulting from the CBM-process leads to flash
which can be reduced with a machined or smoother
inner surface.
The quasi-static torsion tests
revealed that the fusion bonding was insufficient
for a two-shot hybrid molding process, even with
relatively high preheating temperatures of the
TPC-HP. Only the specimens preheated above
melting temperature of the polymer were able to
withstand adequate loads. It is postulated that the
interface strength in the two-shot approach can
be improved and the shrinkage cavities reduced
with higher mold temperatures, a hot runner sprue
as well as an increased film cut height. In future
investigations, the torsion strength dependent
on the laminate surface preparation as well as
additional PEEK and PAEK interface films will be
further evaluated. Moreover, the process will be
enhanced by additional thermoforming of the TPC
in the overmolding process to further enhance the
design and manufacturing capabilities.
Figure 10. Photomicrograph images of longitudinal and cross-sections along
a sample of config 07.
Figure 11. Setup for the quasi-static torsion tests in a Zwick Roell Z250
testing machine (a), torque and shear stress boxplot of the tested specimens
(b), backside of a fractured splined shaft tooth of specimen config-08-01.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the funding
of this work by the Federal Ministry for Economic
Affairs and Climate Action, BMWK, within the
project InPro of the Federal Aviation Research
Programme LuFo VI-1 and for the support of the
associated partners Victrex Europa GmbH and the
Boeing Deutschland GmbH of the project.
5. REFERENCES
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[3]. Barfuss D, Würfel V, Grützner R, Gude M, Müller R.
Integral blow moulding for cycle time reduction of CFRTP
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[4]. Yassin K, Hojjati M. Processing of thermoplastic matrix
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18 | SAMPE JOURNAL | JANUARY/FEBRUARY 2025
www. sampe.org
https://www.doi.org/10.3390/polym13020180 https://www.doi.org/10.1063/1.5034876 https://doi.org/10.1177/0892705717738305 https://doi.org/10.1177/0892705717738305 http://www.sampe.org
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