SAMPE Journal - January/February 2025 - 34

FEATURE / LONG-FIBER THERMOPLASTIC COMPOSITES
lost as heat goes directly into the laminate except
for the sections that protrude from the laminate
for facilitating electrical connections. As the part
size scales up, those protruding sections will
become a smaller percentage of the length which
will further increase efficiency. Resistive mesh
heating elements have some drawbacks, including
bulky electrical connections, forming areas that
need to be designated before manufacturing,
and increases the stiffness of the forming region
by the mesh. To address these challenges, two
approaches were taken; the first was to develop
metal wires as an alternative heating element to the
mesh, and the second, which is currently an active
area of research, is to investigate other localized
heating methods such as convection, infrared, and
induction.
Work to extend the embedded resistive heating
to wire heating elements has been completed,
where a jig was used to space 0.51 mm diameter,
304 stainless steel wires at 3.94 wires per centimeter
as shown in Figure 5. A sheet of neat PETG resin,
0.5 mm in thickness, was then heated and pressed
onto the wires to hold them in place for transferring
to the laminate stack. After consolidation, the ends
of the wires protruding from the laminate were
twisted and attached to a ring terminal for electrical
connection.
Experiments were
conducted
to
evaluate the heating capabilities of the wire heating
elements and compare them to the mesh heating
elements. Numerical tools previously developed
for the design and analysis of the mesh heating
elements were also extended to the wires to assist
in the comparison.
The results of a comparison between the wire
and mesh heating elements are shown in Figure 6.
Transient temperatures measured by the embedded
thermocouples and power inputs are shown. The
solid lines represent the mesh heating elements
and dashed lines represent the wire heating
elements. The locations for the thermocouples
(TC) are shown in Figure 7 to highlight their
positions relative to the heating element. TC4 is
adjacent to the heating element, TC2 is within the
heating zone, TC1 is on the edge of the heating
zone, and TC8 is outside of the heating zone.
These two test runs were comparable because for
their given power inputs, 87 W for the wire heating
element and 44 W for the mesh, they reached the
target temperature of 148.9°C within the same time
of 17 minutes. The difference in power inputs was
due to the difference in the electrical resistance
of the two heating element types. The wires had
twice the diameter of the wires in the mesh which
greatly reduced the heat generation per wire for a
given power input. For a mesh and wire heating
element of the same volume and material, the
power input should all be equal. Figure 6 shows
that at everywhere but the edge of the heating
zone the mesh and wires performed similarly. This
Figure 5. An aluminum jig was used for placing stainless steel wires in CFRTP
specimens.
Figure 6. A comparison of the embedded resistive wire heating elements to
the embedded resistive mesh heating elements.
Figure 7. The general thermocouple locations for the two specimens
compared in Figure 6.
difference was likely due to minor lateral shifting
of the wires during initial consolidation, which did
not impact the mesh as much due to its transverse
wires.
2.2.3 Methods for the Localized Thermoforming
of Thick-Gauge CFRTP Laminates
To enable the widespread use of large-scale,
long-fiber reinforced thermoplastic laminates for
34 | SAMPE JOURNAL | JANUARY/FEBRUARY 2025
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SAMPE Journal - January/February 2025

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