SAMPE Journal - March/April 2017 - 37
Feature Article
mm/s (throughput 36 kg/h) to 350
mm/s (throughput 150 kg/h). The
anisotropy of the flexural strength
varies between 1.3 : 1 and 2.8 : 1.
The results show, that the fibers
can be aligned during the 3D Fiber
Spraying. For the comparison
study of the different materials, an
anisotropy ratio of 2 : 1 was selected
to compare parts with an anisotropic
behavior. This corresponds to the
parts with a throughput of 120 kg/h.
Figure 3. Flexural strength depending on different throughputs.
orientation of the fibers and high
fiber volume contents are required.
Material
For all preforms manufactured
by 3D Fiber Spraying, which
are presented in this paper, the
same materials were used. For
the preforms, a roving of the type
R63SX3 with a linear density of 4,800
Tex from Owens Corning, Battice,
Belgium, was used. To fix the fibers
permanently, a binder yarn from the
Company Heinrich KUPER GmbH,
Rietberg, Germany, was used. This
binder is made of a thin glass fiber,
which is coated with polyester and
a copolyamide. The Copolyamide
is the binding material. The binder
yarn has a linear density of 42 tex.
Overall, a binder content of 3% w/w
is incorporated into the preforms.
3D Fiber Spraying Process Parameters
To compare the fiber sprayed
preforms with commonly used
preforms made from fabrics,
fundamental
parameters
have
to be defined. Therefore, first
investigations were carried out
to determine the achievable fiber
orientation. In the investigations,
different process parameters of the 3D
Fiber Spraying process were varied
to analyze their influence on the
fiber orientation. The investigations
show, that the layup velocity (see
Figure 2) during the fiber spraying
process is a decisive parameter for
the fiber orientation. Figure 3 shows
the flexural strength (DIN EN ISO
14125, three point bending test)
of parts, manufactured in a RTMprocess with fiber sprayed preforms.
In the 3D Fiber Spraying process,
the throughput of the chopper unit
was varied. The throughput of the
chopper is corresponding with
an increasing layup velocity. The
increasing throughput causes higher
layup velocities to get the same fiber
weight distribution with the same
number of sprayed paths. The tested
parts have a thickness of 3 mm and
a fiber volume content of 40 %. For
the RTM-process, the resin system
EPIKOTE Resin 05475 / EPIKURE
Curing Agent 05443 (Momentive
Specialty
Chemicals
GmbH,
Duisburg, Germany) was used.
The results of the investigations are
summarized in Figure 3.
As shown in Figure 3, the
anisotropy of the material (relation
between the mechanical properties
parallel and perpendicular to the
aspired fiber orientation) increases
with increasing throughput. With
the increasing throughput, the layup
velocity has to be increased from 98
Preforming of Comparative Preforms
For the comparison study,
preforms and parts with commonly
used textiles were manufactured to
compare the mechanical properties
of the parts. As comparative textiles,
one non-crimped fabric and one
chopped stands mat was selected.
Non-crimped fabrics are typically
used for structural parts made in
the RTM-process. This comparison
with non-crimped fabrics allows for
quantifying the potential of the 3D
Fiber Spraying process for structural
applications. Chopped strands mats
are quasi-isotropic fabrics, which
typically do not allow for adjusting
the fiber orientation. But chopped
strands mats are fabrics which were
typically substituted by the first fiber
spraying technologies presented
within
previous
discussions.
Furthermore, chopped strands mats
are the comparative fabrics regarding
fiber length.
As mentioned above, the parts
should have an anisotropy ratio in
their flexural strength of 2 : 1. Only
the chopped strands mat cannot
fulfill this requirement due to their
fiber structure. Furthermore, the
parts should have a fiber volume
content of 40% at a thickness of 3
mm. With these requirements, two
materials were selected. For parts
with continuous fiber reinforcement,
a unidirectional non-crimped fabric
Table 1. Properties of the comparative performs.
SAMPE Journal, Volume 53, No. 2, March/April 2017
37
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