JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013 - 66

tow placement

Fig. 6: Stamp-formed CFRTP structure with an insert integrated during the thermoforming process

selected process temperature is suitable for both joining partners.
The more thermally stable material needs to be fused without
degrading the joining partner that is less thermally stable.
When using optical heating, the absorption properties of the
material used with respect to the wavelength of the laser system
is important. Different fibre reinforcements can result in different
optical absorption properties. The process can be adapted to join
two materials with different optical properties by adjusting the
laser power distribution via proper setting of the laser angle.
The fact that the PA66/GF blank could not be joined in the given
test plan is due to its low absorption degree in the near infrared
spectrum, in conjunction with a high welding temperature, high
lay-up rate and limited laser power available. Welding a PA66/CF
tape on a PA66/CF blank in the same process conditions can be
done with ease since both joining partners absorb 85% to 90% of
the laser energy used close to the surface.
A good joint would be achieved by reducing the lay-up rate or
using more laser power. The utilization of carbon black particles
in the laminate polymer for greater absorption is also an option.
The application of a CO2 laser system to tape placement is also
investigated in FibreChain as, due to its longer wavelength, the
absorption of the laser radiation by the GFRP is higher even
without carbon black particles. To make this approach more efficient, Trumpf developed, as part of FiberChain, a new q-switched
nanosecond pulsed CO2 laser system in the kW range that can also
operate in a continuous wave mode. Therefore, this system can be
used for joining, tape placement and cutting operations.

Combined forming and functionalization process
The tailored thermoplastic composite sheets produced by laser-assisted tape laying can be moulded to the final shape in a thermoforming process. Stamp forming of thermoplastic composites is a
fast process with cycle times shorter than 1 minute, and is hence
suitable for high-volume production. The Fraunhofer IPT team
combined thermoforming with a simultaneous functionalization
process. Inserts and fasteners can be integrated during the thermoforming process (Figure 6).

As the thermoplastic matrix material is molten prior to the thermoforming process, inserts can be integrated into the structure by a
local forming process. One of the main benefits of this integration
is that the additional process step usually required to integrate the
insert becomes redundant. Additionally, the mechanical properties
of moulded-in joints are superior in comparison to joints with drilled
holes as the fibres are not damaged but squeezed to the boundary
area of the joint area. In contrast to injection moulding or thermoplastic welding, the load is carried not only by the matrix material
but also by the fibres. The increased joint strength was demonstrated
at Fraunhofer IPT for both fabric-based thermoplastic composites
and composite sheets made out of unidirectional tapes. Furthermore, complex geometries such as undercuts can be achieved during
the thermoforming process, so that appropriate inserts can lead to
even higher joint strengths.
After the integration of inserts is completed and the matrix material
is cooled down below the melting temperature, in-mould trimming
of the CFRTP structure can be performed. Hence the conventional
process chain of forming, trimming and joining can be shortened to
one integrated process step.

Development and implementation
of production processes and systems
Besides its research activities, Fraunhofer IPT also develops and
implements production processes and systems for automated manufacturing of lightweight fibre-reinforced thermoset and thermoplastic components. A new laser-assisted fibre-placement system will be
launched this summer (Figure 7).
The “hybridTLK” (hybridAFP) is a laser-assisted fibre-placement
system which can be added as an end effector to jointed-arm and
linear-gantry industrial robots in variable manufacturing cells. It
makes it possible to handle different types of fibre-reinforced goods
such as thermoplastic tapes, thermoset prepregs and dry-fibre
placement material. The material storage and guiding units need
to be adapted to the different material properties, e.g. they have

66 jec composites magazine / No83 August - September 2013

JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013

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