SAMPE Journal - November/December 2021 - 24

FEATURE / THICK ORGANO-SHEET
Figure 6b shows the temperature profiles for
induction heating process at a process velocity
of 1 m/min. The graph shows the temperatures
at several positions of the stack. At first, the
temperatures started to increase rapidly and
reached the melting temperature under induction
heating unit #1. Remarkably, the temperatures
inside the stack (7th
and 14th
and 21st
ply from the
top in the total 28-ply of fabrics) increased in the
same way. It means that the heating process wasn't
based on heat transfer but direct heating of carbon
fiber ply. The surface temperatures (1st
and 28th
ply) were kept lower, which was probably caused
by heat dissipation at physical contact with Teflon
belts. Before going inside double belt press, the
temperatures went down slightly due to the heat
dissipation through air, though the space was
enclosed with an insulation material. Inside double
belt press, the temperatures started to increase
again due to induction heating unit #2. Especially,
the surface temperatures increased significantly.
It is obvious that the thermal conduction between
steel belt and the material played a leading role in
this behavior. Consequently, all the temperatures
exceeded the melting temperature before press
zones. This outstanding heating capability enables
high rate manufacturing using double belt press.
Impregnation Quality of Composite Samples
The cross-sectional micrographs of composite
samples are shown in Figure 7. Few voids can be
seen in the cross-section for standard process at
a process velocity of 0.2 m/min. Measured void
content is 1.7%. On the other hand, a few voids are
observed inside fiber bundles in the cross-section
for induction heating process at 1 m/min. Void
content is 3.0% in this case. The value is slightly
higher. However, sufficient impregnation quality
was achieved, even for the high rate manufacturing.
Obviously, pre-heating of the material made a
major contribution to this result.
Mechanical Properties of Composite Samples
Figure 8 shows the flexural property of composite
samples. The flexural strength reached 600 MPa for
standard process. The value is close to the typical
one represented by normal compression molding.
The strength for induction heating process is
slightly lower, which can be attributed to the
higher void content mentioned above. The flexural
modulus was more than 50 GPa in either case. Some
modifications should be done in order to decrease
void content further, such as additional press zone
and reinforcing the insulation during the process.
It was demonstrated that the developed induction
Figure 6. Temperature profiles under manufacturing 6 mm thick CF/PA6
laminates using double belt press: a) standard process, b) novel induction
heating process. The temperatures were recorded with thermocouples at
different positions of stack.
Figure 7. Cross-sectional micrographs of the composites produced using
double belt press by a) standard process at a process velocity of 0.2 m/min,
and b) induction heating process at 1 m/min.
heating process using double belt press have a
great potential for high rate manufacturing of thick
organo-sheet. Photographs of composite sample
produced using double belt press at a process
velocity of 1 m/min is shown in Figure 9.
24 | SAMPE JOURNAL | NOVEMBER/DECEMBER 2021
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SAMPE Journal - November/December 2021

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