SAMPE Journal - March/April 2017 - 34

Feature Article
C. Hopmann, M. L. Fecher and K. Fischer
Institute of Plastics Processing (IKV), RWTH Aachen University
Aachen, Germany

3D Fiber Spraying - Development of an Automated,
High Volume-Capable Preforming Technology for
Structural RTM Parts
Abstract

Fiber reinforced composites are increasingly being applied in aircraft and automotive applications for structural lightweight
components. Accordingly, one of the central challenges for the application of thermoset composites in large series is the
development of preforming technologies for the automated, scrap-optimized production of components in short cycle times,
because the preforming process can cause up to 50% of the component costs. In order to reduce preforming costs and cycle times,
the 3D Fiber Spraying process is being developed at the Institute of Plastics Processing at RWTH Aachen University. This
process technology allows for the automated production of three dimensional shaped preforms in one process step. In the 3D
Fiber Spraying process, textile rovings are cut to a defined length (12-100 mm), oriented by an air jet in a fiber guiding unit and
sprayed on an air permeable layup mould. The fiber guiding unit, which is specifically developed for the process, facilitates an
adjustment of the local flexural strength with an anisotropic ratio of up to 2.8:1. Furthermore, functional elements like inserts
and stiffening profiles can be integrated without further sub processes. This allows for a precise adaption of the fiber structure
to the mechanical requirements for the envisaged component. Thereby, mechanical strengths comparable with continuous fiber
reinforced composites can be achieved. Conclusively, process steps like textile manufacturing and draping of textiles are avoided.
This paper presents the different fields of application, processing characteristics and current results of investigations regarding
the mechanical properties compared to commonly used preforms with continuous fiber reinforcement.
Introduction
In many fields of application,
fiber reinforces plastics (FRP) are
increasingly being applied for
structural lightweight components
in
aircraft
and
automotive
applications. FRP lead to a significant
weight reduction compared to
conventionally used construction
materials, coupled with their
outstanding mechanical properties1.
This allows for a reduction of the
energy consumption (e.g. fuel)
during the product lifetime, which
is necessary due to increasingly
strict regulations regarding CO2emissions in many parts of the
world1,2. Especially for structural
components, thermoset FRP offer the
highest potential for the reduction
of weight, fuel consumption and
emissions. Low viscosity thermoset
resin systems, enable a production
of FRP by impregnating near-net
shape
preforms.
Furthermore,
the large scale use of FRP in high
volume markets is enabled by new
production technologies (e.g. High
Pressure RTM, Gap-Impregnation).
34

These technologies allow for the
production of structural FRP-parts
in cycle times of 3-5 min.
Initial Situation
For
the
manufacturing
of
structural thermoset FRP parts
in the Resin Transfer Moulding
(RTM)-process or its derivates (High
Pressure RTM, Gap-Impregnation),
dry fiber preforms are necessary.
These preforms are impregnated
with a low viscosity resin system
in a closed RTM-mold. After the
impregnation, the curing of the resin
system takes places in the mold at
elevated temperatures. In general,
the preforms are made from noncrimped or woven fabrics, which are
cut, draped and thermoformed in a
multistage process, which leads to
high labor expenses and up to 30%
scrap from the cutting processes.
The costs for the preforming of
monolithic composite parts with
simple geometries may thus be up
to 50% of the entire manufacturing
costs3. Due to this cost distribution,
new cost saving and high volume

capable preforming technologies
are mandatory for high volume
production processes of structural
thermoset FRP-parts. Therefore,
different preforming technologies
were developed to reduce process
and part costs. One approach is
the preforming by fiber spraying
technologies. All fiber spraying
technologies have in common, that
a dry fiber roving is chopped in a
chopper unit and sprayed on an air
permeable layup mold. Together
with the fibers, a binder is sprayed
onto the mold. To temporary fix the
fibers on the layup mold, a vacuum
is applied. After the activation of the
binder, the preforms are manageable
and can be processed to structural
parts in a subsequent process. First
investigations and implementations
of the fiber spraying process were
done in 1950 by Chevrolet, Detroit,
USA, where the "Direct Fiber
Preform Process" was used to
manufacture shells of the Chevrolet
Corvette4. A further development of
this process is the "Programmable
Powdered Preform Process" (P4SAMPE Journal, Volume 53, No. 2, March/April 2017

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