JEC COMPOSITES MAGAZINE - Issue #89 - May 2014 - 52

process
neously via gas pressure without extra barriers such as
diaphragms. Directly after the shaping process, the two halves
are fusion-bonded using the residual temperature from the
shaping process inside the mould. After fusion-bonding, the
cooling step starts and the part edges are enclosed by injection
moulding so that a net-shaped part can be ejected after cooling
to the ejection temperature.

Experiments and material
For all experiments, 1 mm organo-sheets based on polyamide
6 (PA 6) reinforced with 45 vol.% woven (twill weave) glass
fibres were used (TEPEX® 102-RG600(2)/45% from BondLaminates GmbH). Earlier research has shown that a special
modification is required to ensure the gas density of the organosheets is above the melting temperature of the matrix polymer
[8]. Without an adequate gas density, the gas pressure cannot
be transformed into a shaping force. To provide the required
gas density, films of a commercial polyamide 6 (Durethan®
B30S from Lanxess Deutschland GmbH) with and without 3
weight % of triallyl isocyanurate (TAIC) were produced via
flat film extrusion. For this work, the films containing TAIC
were crosslinked by electron-beam irradiation (2 kGy) by Beta
Gamma Service.
The radiation-crosslinked films were then applied on the gas
injection side of the organo-sheet at 225°C and 25 bar by Neue
Materialien Fürth GmbH. To prevent extensive warpage during
the heating process, non-crosslinked films without TAIC were
applied on the opposite side of the sheet. The radiation-crosslinked layer on the injection side provides a gas density above
the melting temperature while the unlinked layer prevents
warpage. For injection moulding, a 30 weight % glass fibre
reinforced PA6 (Durethan® BKV 30 from Lanxess Deutschland
GmbH) was used.
Using the process steps shown in Fig. 1, specimens were produced with the parameters shown in Fig. 2. To inject the gas

No.
1

Temperature
Fibre
Forming Welding Injection
Separation
Mould pressure pressure moulding
orientation Sheets
plane
0/90°

0/90°

no
220°C

196°C

39 bar
80°C
4.5 sec

5 N/
mm²

45/45°

Fig. 2: Specimens and design of experiments

52 jec composites magazine / No89 May 2014

yes
yes

Fig. 3: Test setup for torsion test and stiffness calculation according to [9]

(nitrogen), an Airmould modular system (Wittmann Battenfeld GmbH) was used on a 2K injection moulding machine
(ENGEL Austria GmbH). The used mould was produced by C.
K. Siebenwurst GmbH & Co. KG and developed in cooperation
within the Twin-O-Sheet funded research project. A custom IR
heater array (Bielomatik Leuze GmbH + Co. KG) was used to
heat the sheets. During the process, the organo-sheet temperature on both sides of the part was measured with thermocouples
at five positions using a data recording system (OMB-DAQ-56,
Omega).
To determine the stiffness and energy absorption of the
specimens, quasi-static torsion tests were performed with the
setup shown in Fig. 3. The free clamping length L was 140 mm.
During the tests, the specimens were twisted with a constant
speed ω of 1.5 °/s up to an angle ϕ of max. 90° and the resulting
torque M was measured. All tests were performed on dry technical specimens (70°C/vacuum). The stiffness was analyzed at
a 6° torsion angle. To determine the maximum energy absorption, the curve progression until 30° was integrated.

Results
The average temperatures of the organo-sheets in the flange
area during the process are shown in Fig. 4. At the end of the
heating step, the organo-sheet temperature reaches an average
of about 240°C after 26 seconds. During the ascending of the
heater, the running-in of the injection needle and the closing of
the mould to 0.9 N/mm², the temperature drops about 20 K.
Over the injection phase of 4.5 seconds, the temperature drops
to 195°C due to the temperature of the separation plane. This
temperature is held during the 30 second welding step where a
5 N/mm² welding pressure is applied at the flange. Afterwards,
the electric heaters in the separation plane are shut off to cool
the flange down to about 180°C for enclosing the edges via
injection moulding. This temperature was empirically determined by decreasing the flange temperature systematically step
by step in multiple trials. If the temperature within the flange
is above 180°C during the moulding step, the resulting hollow
body is not rigid enough and collapses under the pressure of the
melt. This can be explained by the recrystallization peak temperature of the PA6 matrix, which is about 192°C (DSC). Above

JEC COMPOSITES MAGAZINE - Issue #89 - May 2014

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