JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 40

manufacturing

AFPT GmbH is installed in the Institute
for Carbon Composites (LCC) at the
Technische Universität München (TUM).
This head can process tapes from 0.25 inch
(6mm) to 2 inch (51mm) wide, allowing
the manufacture of composites with reduced
scrap. Narrow tapes can be steered along
curved geometries whereas wide tapes are
used when high material output for large but
less curved parts is required. The placement
head can be mounted on an industrial robot
placed on a 3.5m-long linear axis to manufacture large parts. The TP-AFP equipment
with all of the machinery components is
shown in Fig. 1.
The energy input for heating the thermoplastic matrix material is provided by a 4kW
diode laser. The laser ensures heat application with a very short reaction time, good
controllability and high efficiency [1]. An
infrared camera mounted on the TP-AFP
head ensures permanent temperature
measurement over the focal spot of the laser
during processing. The maximum temperature measured by the infrared camera is used
to control the laser power in order to prevent
overheating. Simultaneously, the angle of
the laser optics is controlled to distribute the
heat input by the laser between the incoming tape and the substrate. Using this closed
loop control (CLC), an even heating of the
incoming tape and substrate during TPAFP within the polymer's process window
enables in-situ consolidation. The CLC principle is shown schematically in Fig. 2.

Fig. 3: Combined manufacturing approach using laser-assisted TP-AFP and thermoforming for the production of hollow structures

In comparison to the consolidation of plies
in an autoclave, the process cycle times, the
energy consumption and the required consumables can be reduced by consolidating
tapes in-situ with the TP-AFP process.

Assembling possibilities
with TP-AFP
As aircraft or automotive structures consist
of multiple parts, the individual components need to be joined traditionally in a
subsequent step by mechanical fastening
or adhesive bonding. Mechanical fastening

Fig. 2: Principle of closed loop control during TP-AFP X

40 jec composites magazine / No97 May - June 2015

can lead to increased weight due to the use
of bolts and the need for locally reinforced
laminates around the holes to increase
bearing strength [2]. Additionally, the long
curing times of most high-performance
adhesives and extensive surface preparation
can be challenging during adhesive bonding
due to the chemical inertness of certain
polymers [3].
Since the molecular structure of thermoplastic matrix materials allows fusion bonding,
they offer an alternative to conventional
assembly methods. Several fusion bonding
techniques such as ultrasonic welding, resistance welding and induction welding can be
used to join and repair thermoplastics. With
commonly used fusion bonding techniques,
the parts to be joined have to be fabricated
in a previous step. In addition, the assembly
steps require additional processing equipment, leading to higher investment costs.
Besides the production of composite parts,
the TP-AFP technology can be employed
for the assembly of components. There are
two possibilities for assembly. One way is to
manufacture single composite parts separately and join them in a subsequent step by
applying laser energy only to the bond zone
without tape feed. This functional principle
is known from laser transmission welding,

JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015

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