JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015 - 41

too. Another method to assemble composite
parts with TP-AFP is to directly place tapes
on a second composite part. Thus, the joint
is produced during manufacturing of the
skin layers.
At the LCC, two main manufacturing
technologies - TP-AFP and thermoforming
- were combined to produce hollow skinstiffener structures as they can be prevalently
found in aircraft applications. The process
steps of this combined manufacturing approach are schematically presented in Fig. 3.
First, laminates tailored to future load
paths are manufactured with laser-assisted
TP-AFP using unidirectional carbon fibrereinforced tapes (Fig. 3a). The laminates are
then thermoformed into three-dimensional
(3D) profiles (Fig. 3b). A removable core
system with high compressive strength and
good thermal stability is inserted into the 3D
profile. The even plane generated allows the
placement of skin layers on top of the flanges
using laser-assisted TP-AFP (Fig. 3c). During TP-AFP of the skin layers, in-situ joining
to the flanges is enabled (Fig. 3d), resulting
in a fully bonded skin-stiffener structure.
After completion of the skin layers, the
water-soluble core system is removed. The
low thermal expansion of the core material and the locally concentrated heat input
by the laser prevent deformations in the
composite part.
Following this combined manufacturing approach, an in-situ joined hollow structure is
produced without further machining other
than trimming. Fig. 4 shows a demonstrator
produced by the combined approach and
in-situ joined skin layers [4]. The process
development and the demonstrator manufacturing was conducted in a joint research
project together with Dutch Thermoplastic
Components and AFPT GmbH.
Due to labour-intensive processes, conventional assembly of parts by mechanical
fastening and adhesive bonding amounts
up to 40% of the total manufacturing costs
of airframes [5]. Joining by in-situ consolidation with TP-AFP can reduce assembly
costs significantly since no elaborate surface
preparation, additional equipment and
materials are required anymore. In addition

to the general advantages of fusion bonding
techniques, the benefit of this approach is
the elimination of an additional process step
to manufacture the skin component prior
to assembly. Thus, faster process cycle times
are possible due to a more efficient process
chain.

Hybrid joining
Beyond in-situ consolidation of tapes onto
tapes, the TP-AFP process is also suitable
for hybrid joining. Tapes can be joined
in-situ to metals such as aluminium or
titanium. The CFRTP tape and the metal
surface are heated by the laser source of the
TP-AFP head. Due to a surface treatment,
the metallic surface absorbs the laser light
and is heated too. No separate pre-heating
of the metal part is necessary. To improve
the mechanical properties of the joint,
special surface pretreatments are used for the
metallic partner. Besides chemical or physical pretreatment, surface coating showed
promising results. Due to the high intensity
of the laser source, the heating time is very
short. Only the surface of the metal is heated
and, therefore, the overall heat input and accordingly, the heat-affected zone are low. In
addition, the locally concentrated heat input
and the overall low resulting temperature of
the metal contribute to reducing the residual
stresses arising from the different thermal
expansion between CFRP and metal. Several combinations of metal and CFRP have
been successfully joined by TP-AFP. For
instance, combining aluminium with carbon
fibre-reinforced polyamide 6 (PA 6) resulted

in single lap shear strengths up to 20MPa.
Of course, injection-moulded core systems
can be combined with tapes laid-up by TPAFP. This requires the matrix material of the
tapes and the core material to be identical
or chemically similar. Fig. 5 shows a hybrid
joint of CFRTP to aluminium and to an
injection-moulded core.

Booster casing demonstrator
Due to an unlimited part thickness and
the elimination of intermediate debulking
steps or final consolidation in an autoclave,
the TP-AFP technology is well suited for
large and thick-walled pressure vessels. To
judge the feasibility of the TP-AFP process,
a booster casing demonstrator for future
launch vehicles was produced. A tooling for
the booster casing was mounted on a winding axis, thus allowing tape winding and
placement within one production process.
The segmented aluminium mandrel was
designed to enable demoulding by reducing
the inner diameter due to inner kinematics.
The research on the process parameters and
demonstrator manufacturing was carried out
as part of a joint research project together
with MT Aerospace AG, the University of
Augsburg and the Deutsche Zentrum für
Luft- und Raumfahrt (DLR) in Augsburg.
The demonstrator component consists of
three main parts (schematically shown in
Fig. 6 on the left): the skirt, the pressure
vessel comprising the cylindrical shell and
the dome, and the segment connection area.
The wound vessel laminate is designed to
withstand inner pressures. The segment con-

Fig. 4: Demonstrator manufactured by thermoforming and TP-AFP using carbon fibre-reinforced tapes with
a polyether sulfone matrix

Fig. 5: Hybrid joint made from CFRTP to aluminium (left); skin plies in-situ bonded to an injection-moulded
core (right)

No97 May - June 2015 /

jec composites magazine 41

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

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #97 - Special JEC Americas - May/June 2015