JEC COMPOSITES MAGAZINE - Issue #94 - January/February 2015 - 43

LCM

Automated profile preforming
for aerospace applications
The utilization of modern liquid composite
moulding (LCM) processes for series production
of structural skin-stringer components requires
the development of automated manufacturing
methods. In this work, different approaches for
the efficient fabrication of near-net-shape profile preforms are identified and evaluated.

By

Christian Schillfahrt, Research Associate/PhD Candidate1
Ewald Fauster, Assistant Professor1
Ralf Schledjewski, Professor1,2
1 Chair of Processing of Composites, Montanuniversität Leoben
2 Christian-Doppler Laboratory for High Efficient Composite
Manufacturing

S

lightly curved skin-stringer elements are typical structural
FRP components in aeronautic applications. Up to now,
they have usually been manufactured separately using
prepreg materials followed by an elaborate assembly process or
by means of co-curing and co-bonding methods [1,2]. In order
to overcome the limitations of these autoclave-based techniques,
modern LCM methods have been of recent interest, focusing
on integral processing of dry near-net-shape preforms. As the
preforming chain is the crucial part of this out-of-autoclave approach, the development of automated preforming methods is
vital in terms of economic aspects, if higher production series
have to be achieved.
While skin structures with rather simple geometries can be efficiently manufactured through automated pick-&-place layup or
automated dry fibre placement (ADFP), the automated preforming of stringers is a more challenging task. Thus, applicable solutions for automated profile preforming are identified and evalu-

ated in this work with respect to a set of selected requirements:
- Flexibility in profile cross-section and curvature
- Flexibility in number of layers and architecture
- Realization of load-optimized fibre orientations
- In-line pre-compaction for enhanced preform stability and
reduced porosity
- High productivity and minimal (manual) reworking

Automated dry fibre placement
Automated dry fibre placement is characterized by the use of a
processing head that is automatically guided over a tool surface,
depositing multiple dry fibre tows in parallel [3]. In order to
obtain the required tack on the substrate, a binder material finely
dispersed among the fibres is thermally activated before compacting the fibres by means of a consolidation roller. The positioning
system, which carries the processing head, can either consist of an
anthropomorphic robot optionally extended by a linear axis, or
a gantry system. At present, several companies offer commercial
AFP systems, such as Coriolis Composites, MAG Composite
Technologies, Automated Dynamics, Electroimpact or MTorres.
This technique can be used for direct ADFP preform layup (see
Figure 1a), where the fibres are directly deposited on a profile
tooling. The additive path-by-path manufacturing makes this
process flexible in number of tows, layers and fibre orientations.
The major drawbacks of this approach are the inefficient layup
for fibre orientations predominant in directions transverse to the
major profile axis, the limited processing speed and the geometric limitations in concave cross-sections [4]. Furthermore, the
positioning system needs a high degree of movability. Alternatively, the following three-step procedure can be contemplated to
overcome these drawbacks. It consists in the automated layup of
one or multiple flat preforms (see Figure 1b), which are cut to the
required dimensions and draped onto a dedicated tool in order
to obtain the final stringer preform. Although this approach is
beneficial over direct layup in terms of layup paths and positioning system movability, the overall procedure is disadvantageous
because an additional cutting system and laborious manual
draping are required. The need for a separate cutting system can
be avoided by a modified approach, where the processing head's
cutting system is used to selectively cut the fibres along the layup
path (see Figure 1c). Therefore, a complex cutting system with
rotatable blades is needed to avoid an imprecise layup at the
profile ends. However, the labour-intensive manual draping step
is still required.

No94 January - February 2015 /

jec composites magazine 43
JEC COMPOSITES MAGAZINE - Issue #94 - January/February 2015

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