JEC COMPOSITES MAGAZINE - Issue #89 - May 2014 - 53

Conclusion

Fig. 4: Temperature in the Twin-O-Sheet process without active cooling

Fig. 5: Torsion test results (IM = injection moulding)

this temperature, most of the matrix is still in the molten state and
has hardly any stiffness. With about 180°C within the flange and
the 80°C mould temperature, the hollow body is rigid enough to
be enclosed by injection moulding. If the flange temperature is too
low, no accurate bonding strength will be gained between the organo-sheet part and the injection moulded part [6]. Since no active
cooling system was used for these experiments, the time to cool
down the parts to the ejection temperature was about 150 seconds.
With an active cooling system, the complete cycle time in this setup
can be shortened to 180 seconds.
The analysis results of the torsion tests are shown in Fig. 5 left. By
enclosing the edges of the 0/90° specimens by injection moulding,
the maximum average energy absorption and average torque can
be increased. The energy absorption increases from an average
of 0.027 to 0.04 kJ and the torque from 83 to 133 Nm. While the
enclosed specimens collapse at the transition to the mountings
within the hollow body, the specimens without injection moulding collapse in the weld at about 10° as can be seen in Fig. 5 right.
The stiffness at the 6° torsion angle stays almost constant through
enclosing the edges. An increase in stiffness to an average of 97.5
Nm² can be gained with the 45/45° orientation of the fibres within
the specimen.
The 45/45° fibre orientation in Fig. 5 left tends to show a lower
maximum torque and energy absorption compared to the 0/90°
orientation. This is due to imperfections in two of the three specimens. The optimal specimen shows a higher maximum torque
(167 Nm) and a higher energy absorption (0.066 kJ) compared to
the 0/90° orientation.

Functionalized hollow bodies were produced using the Twin-OSheet process. Without active cooling, the cycle time was 5 minutes.
At the current state of research, a complete part can be manufactured
in 3.5 minutes using active cooling after the fusion bonding of the organo-sheets. But this cycle time also remains an area of improvement.
Cooling the parts before injection moulding is necessary since the
hollow body gets destroyed when it is too hot due to the low matrix
viscosity and thus low stiffness. With injection moulding, the process
control becomes more complex but the mechanical performance
of the parts can be clearly increased by enclosing the part edges and
thus decreasing stress concentrations. In the performed experiments,
the maximum energy absorption and the maximum torque could be
increased through enclosing the edges by injection moulding. The
part stiffness was also increased by changing the fibre orientation.
The 45/45° fibre orientation needs further investigation with a higher
number of specimens. The influence of different process parameters,
e.g. sheet temperature, is subject to current research.
We would like to thank all our partners within the Twin-O-Sheet
project (Fkz. 02PJ2103), the German Federal Ministry of Education
and Research (BMBF) and the Karlsruhe Institute of Technology
(PTKA - KIT). Further thanks go to PTS Plastic-Technologie-Service Marketing und Vertriebs GmbH and BGS Beta-Gamma-Service
GmbH & Co. KG. n
Contact: info@lkt.uni-erlangen.de
More information: www.lkt.uni-erlangen.de
References
[1] D. Drummer, T. Müller: Thermoplastische Hochleistungsfaserverbunde
stehen vor einer großen Renaissance, Intelligenter Produzieren 3 (2010)
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[2] M. Hou, L. Ye, Y. W. Mai: Manufacturing process and mechanical
properties of thermoplastic composite components, Journal of Materials
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[3] M. Hou: Stamp forming of continuous glass fibre reinforced polypropylene, Composites Part A: Applied Science and Manufacturing 28 (1997) 8,
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[4] J. Nowacki, J. Schuster, P. Mitschang, M. Neitzel: Thermoformen von
GFK - Vergleich zwischen Metall- und Silikonstempeln, KU Kunststoffe 89
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[5] G. D. Smith, C. J. G. Plummer, P.-E. Bourban, J.-A. E. Månson: Nonisothermal fusion bonding of polypropylene, Polymer 42 (2001) 14, S.
6247-6257.
[6] P. E. Bourban, A. Bögli, F. Bonjour, J. A. E. Månson: Integrated processing of thermoplastic composites, Composites Science and Technology 58
(1998) 5, S. 633-637.
[7] P. E. Bourban, N. Bernet, J. E. Zanetto, J.-A. E. Månson: Material phenomena controlling rapid processing of thermoplastic composites, Composites Part A: Applied Science and Manufacturing 32 (2001) 8, S. 1045-1057.
[8] D. Drummer, C. Gröschel, A. Seefried: Direct Forming of Organosheets
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[9] «Festigkeitslehre,» in Handbuch Maschinenbau - Grundlagen und
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JEC COMPOSITES MAGAZINE - Issue #89 - May 2014

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