JEC COMPOSITES MAGAZINE - Issue #117 - November/December 2017 - 32

MANUFACTURING fibre placement

Fig. 1: Vertical deposition of approximately 400 kg of unidirectional dry fibre material with an infrared heating system

development of larger components with
more integral shapes is possible without
restricting the layup rate. For the subsequent impregnation and curing steps,
shorter process times can be achieved
using heatable tools that enable higher
heating rates. Additional cost savings
are possible due to the lower cost of
ovens compared to autoclaves and the
need for less refrigerated transport and
warehouses.
Layup process development
To meet the set productivity requirements for the future production of
large-scale
composite
structures,
new plant concepts have to be used.
Therefore, DLR in Stade developed
a new production approach based on
compact industrial robots that are
compatible with the fibre layup process
and can move autonomously on a rail
system. To improve the accessibility
of the robot units, the fibres are laid
on a vertically positioned mould. To
increase productivity, several layup
robots will be used simultaneously -

either for simultaneous fibre layup or as
redundant units in the event of errors.
To this end, DLR developed the GroFi®
research platform, on which large composite structures can be manufactured
and different technologies such as AFP,
ATL and DFP can be compared. [9]
The GroFi® fibre layup research facility
at DLR Stade was used to layup the
pre-trial preforms and the full-scale
demonstrator. In a previous project
funded by the German Federal Ministry
of Economic Affairs and Energy
(BMWi), a dry fibre placement unit
from Coriolis Composites with 16 ¼"
tows was modified and integrated into
the GroFi® platform. The machine is
installed on a compact platform with a
minimized footprint of 2.5 m to 2.8 m.
Contrary to most DFP machines, it uses
three infrared lamps instead of a laser
system to activate the binder.
To get a better understanding of the dry
fibre tows used, several manufacturing
trials where performed at the beginning
of the project. In a first step, studies were

jec composites magazine / N°117 November - December 2017

conducted in the field of vertical layup
of quasi-isotropic preforms with variations of heating energy and compaction
force. To enable sufficient tack between
the first ply and the mould, a standard
release film was applied on the tool
surface. Unlike standard release agents,
the film allows better control of the first
ply adhesion with no or less cleaning
required after infusion and curing. Due
to the fact that, as in prepreg processes,
an additional vacuum-assisted debulking process at room temperature does
not increase the first ply tack, this is the
most critical step, especially for vertical
layup processes. Furthermore, the
influence of heating versus compaction
force was investigated, and it was shown
that heat management of IR lamps is a
crucial factor for a secure and stable
layup process. Several tests showed that
the temperature process window for
the binder applied on the tapes is very
narrow.
Based on the first trials, the main focus
of the ongoing manufacturing trials is

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #117 - November/December 2017