SAMPE Journal - March/April 2017 - 36

Feature Article
thickness steps and a variable and
adjustable fiber orientation is the 3D
Fiber Spraying process which has
been developed by the Institute of
Plastics Processing (IKV) in Industry
and the Skilled Crafts at RWTH
Aachen
University,
Germany.
3D stands for the manufacturing
of 3D-shaped preforms without
thermoforming
processes.
The
orientation of the fibers during the
3D Fiber Spraying process enables an
increase of the mechanical properties
of parts with fiber sprayed preforms
without further sub-processes. In
combination with the RTM-process
structural FRP-parts with a fiber
volume contents (FVC) of over 40 %
can be manufactured.
3D Fiber Spraying Process Technology
As
mentioned
above,
the
preforming with non-crimped or
woven fabrics causes high work
efforts and multiple sub-processes
like cutting, fiber layup and forming.
Furthermore, the use of fabrics leads
to high scrap rates (up to 30%) and
a three dimensional draping of the
fabrics is limited11,12. The integration
of functional elements is complex
and often combined with manual
work efforts. The 3D Fiber Spraying
process is one possible approach
to achieve a reduction in process
steps and process costs for the high
volume capable manufacturing of
structural RTM-parts. In general, the
part manufacturing in the 3D Fiber
Spraying process can be divided in
three steps (Figure 1).

In the first step, a three dimensional
preform is manufactured using the
3D Fiber Spraying process. In the
3D Fiber Spraying process, glass or
carbon fiber rovings are chopped to
a defined length (adjustable between
12.5 mm and 100 mm) and sprayed
on an air permeable layup mould.
For the spraying, the fibers are
accelerated by an air jet, which is
provided by a venturi nozzle placed
below the chopper unit. With this
air jet, the fibers are transported
to the layup mold. During this
transportation, the fibers pass a fiber
guide unit, immediately before the
fibers impinge on the surface of the
layup mold (Figure 2). In the fiber
guide unit, the fibers are orientated
which enables the orientation of the
fibers in the preform.
To temporarily fix the fibers, a
vacuum is applied at the layup
mould. To fix the fibers permanently,
a binder is necessary. Therefore,
two different technologies were
investigated at IKV. The first binder
is a thermoplastic binder yarn. This
binder yarn is fed to the chopper
together with the reinforcing fibers.
After the chopping of binder and
reinforcing fibers, both are sprayed
on the layup mold. Hot-air, provided
by a hot-air gun, activates the
thermoplastic binder. The second
binder system is a UV-curing
thermoset binder. This binder is
sprayed on the fibers after the layup
and is activated via UV-light. For the
investigations presented in this paper,
the thermoplastic binder yarn was

Figure 2. Functional principle (left) and process technology of the 3D fiber spraying.
36

used, because it is easier to process.
Both binder systems lead to the same
mechanical properties and have no
influence on the parts behavior. In
the second step, the preforms are
further processed to structural FRPparts by means of RTM. The nearnet shaped manufacturing of the
preforms with integrated functional
elements, thickness steps and
adjusted fiber orientations allows
for direct processing of the preforms
without additional process steps like
draping or thermoforming. Due to
the RTM-process, parts with high
fiber volume contents (> 40%), good
surface qualities and a good laminate
quality. In a last step a small post
processing of the parts can take
place, if it is necessary.
Paper's Intent and Aim
The possibility to orientate the
fibers during the 3D Fiber Spraying
process, leads to higher mechanical
properties of the parts with
aligned fibers compared to parts
with randomly orientated fibers.
Reference parts are made from noncrimped fabrics or chopped strands
mats, depending on the parts and
the expected loads. The aim of the
investigations presented in this paper
is the comparison of the mechanical
properties of RTM-parts with 3D
Fiber sprayed preforms, preforms
made from non-crimped fabrics
and preforms made from chopped
strands mats. This comparison will
show the potential of the 3D Fiber
Spraying process, compared to
competitive and commonly used
technologies, in quasi static and
dynamic testing.
Experimentation
3D Fiber Spraying
As mentioned above, the 3D Fiber
Spraying enables an orientation
of the chopped fibers during the
fiber spraying process. Due to this
fiber orientation, the properties of
the preforms (e.g. permeability)
and the mechanical properties
of the manufactured parts can
be influenced. To achieve high
mechanical properties, a high
SAMPE Journal, Volume 53, No. 2, March/April 2017

Table of Contents for the Digital Edition of SAMPE Journal - March/April 2017