FEATURE
Coriolis Composites utilises a standard off-the-shelf poly-articulating robot arm as the basis for a fibre placement system having eight axes of motion.
(Picture courtesy of Coriolis Composites.)
Automating
aerospace composites
production with
fibre placement
As with most automation, advanced fibre placement (AFP) requires
substantial investment, but it has shown its ability to cover its cost
in terms of saved labour and reduced material scrap, combined
with the ability to form laminates of exceptional quality with higher
accuracy and repeatability. George Marsh reports.
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0034-3617/11 ©2011 Elsevier Ltd. All rights reserved
FEATURE
T
o see an automated fibre placement
(AFP) system at work, its superarticulating head following an item’s
complex contour at miraculous speed, is
to wonder how such items could ever
have been laid up by hand.
Even were manual laminators able to lay
plies on complex curvatures with the
required fibre orientations and integrity,
they would not be able to do so repeatably in series production. Nor would
manual fabrication methods support the
production rates now needed by the
manufacturers of aircraft, ground vehicles
and other items for which composites are
now mainstream. Aircraft maker Boeing,
for example, plans a production rate for
its carbon composite B787 widebody
twinjet of 38 per month within a few
years.
AFP is one of the automated production technologies that will make this
and similar manufacturing feats possible.
Along with automated tape laying (ATL)
and filament winding, it will be key to
high-volume production of composite
items, promising reliable, consistent and
cost-effective fabrication.
Complex geometries
AFP has much in common with ATL but,
while the latter is best suited to plain,
relatively flat surfaces, AFP can be used
with much more complex geometries. This
is because it lays narrow tows, which can
be steered over sharply curved surfaces
whereas wider tapes cannot be so placed
without buckling some of the fibres and
potentially weakening the laminate.
When used with a rotating tool or mandrel,
AFP more closely resembles filament
winding, though use of tows tends to make
it a faster process.
In AFP, a number of prepreg tows or narrow
slit tapes are fed to placement heads that lay
them down to form a continuous prepreg
layer. Advanced machines can lay as many as
32 tows simultaneously, the tows being fed
from creels located at or near the head.
An AFP head can be mounted on a multiaxis articulating arm that moves around
the tool/mandrel, or can be carried by a
gantry. Alternatively, the tool can be rotated
under a static head or both the head and
the mandrel can move in a ‘dance’ choreographed by a software program.
As with most automation, AFP requires
substantial up-front investment, but it has
shown its ability to cover its cost in terms
of saved labour and reduced material scrappage alone, not to mention its ability to lay
tows accurately, reliably and repeatably to
form laminates of exceptional quality.
Tows can be laid in any pre-programmed
orientations and positions so that
laminate can be tailored to deliver the
strength and stiffness parameters required
by the designers at various parts of the
structure, fibres being aligned with the
local forces expected in service. Material is laid free of tension and folds,
with precisely defined pressure. Heads
can carry out all necessary cutting and
re-start operations plus consolidation with
compaction rollers.
Control of AFP has
much in common with
the computer numerical
control (CNC) of
machine tools.
Premium AEROTEC manufactures fuselage panels for the Airbus A350 XWB using MAG tape laying machines. (Picture © Premium AEROTEC GmbH.)
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FEATURE
Similar automation has subsequently
been applied by Hawker Beechcraft to the
production of carbon/epoxy composite
fuselages for its Premier 1 and Hawker
4000 business jets. Multiple VIPERS at the
company’s Wichita, Kansas, manufacturing
facility combine programmable 7-axis
dexterity with start/stop/cut control over
24 individual one-eighth inch wide fibre
tows. The machines are 90 ft long and
can accommodate long fuselage mandrels
for the larger, Horizon jet.
Complex nose sections, such as this one for the Boeing 787, are natural targets for AFP. (Picture © Boeing.)
Carrying out multiple synchronous functions at speed requires accurate machine
programming to ensure close coordination
of cutting, motion and position control
with highly dynamic reversal movements.
Control of AFP has much in common with
the computer numerical control (CNC) of
machine tools, so it is no surprise that
some of the heavyweight suppliers of AFP
systems are companies rooted in CNC
machine tools – such as MAG (formerly
Cincinnati Machine), Ingersoll and MTorres.
Aircraft fuselages, with their pronounced
and complex curvatures, are a major
challenge for automation, but the VIPER,
with its seven axes of motion, successfully
placed carbon prepreg slit tapes for the
honeycomb cored structure, achieving a
near-net configuration complete with all the
necessary cut-outs and variable thicknesses.
Appropriate software programming ensured
that material wastage and removal operations were minimised.
AFP enables complete
fuselages to be made
in a fraction of the time
required for equivalent
metal structures.
Hawker claims that AFP enables complete
fuselages to be made in a fraction of the
time required for equivalent metal structures. This, together with vastly reduced
part count, simplified assembly, reduced
maintenance and the better performance
of the final product, makes the technology
a clear winner in the company’s view.
The use of AFP
CNC-controlled fibre placement machines
first became commercially available in the
late 1980s. By the mid-’90s, AFP production was becoming established, albeit on a
limited scale.
A significant milestone was the production by a European consortium of a
4.5 m long carbon composite fuselage
section under the Full-Barrel Composite
Fuselage (FUBA-COMP) research project.
This one piece section, up to 2 m wide,
was produced at BAE Systems in the UK
using a MAG VIPER 1200 CNC fibre placement system. This is one of three AFP
families produced by this company, the
others being the Viper 4000 and 6000
series.
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The composite fuselage of the Beechcraft Premier 1A business jet is manufactured using advanced fibre
placement.
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FEATURE
early next year to ATK’s facility in Clearfield, Utah, will have MAG’s ACES software
(Advanced Composites Environment Suite),
a modular programming and simulation
system that will be extended with features
to aid programming of existing machines at
the plant.
Automated Dynamics’ XT series fibre placement
robot processing unidirectional carbon fibre/PEEK
thermoplastic prepreg during the production of a
helicopter tailboom. Such robotic AFP processing
‘heads’ can fabricate with either thermoset or
thermoplastic materials. (Picture courtesy of
Automated Dynamics.)
Boeing has followed suit and is using VIPER
6000s for the barrel sections of its B787
fuselage.
A VIPER AFP system sold last year to Russia’s
United Aircraft Corporation is believed to be
the first automated composites processing
system sold into Russia. The equipment will
support production of UAC’s MS-21 series of
medium-range airliners.
On the military aviation front, in 1998 Alliant
Techsystems (ATK) demonstrated the ability
of AFP to manufacture a composite air inlet
duct for the Lockheed Martin F-22 Raptor
fighter. ATK had by then established a
track record in AFP manufacture including
certain other parts for the F-22, the work
taking place in a dedicated fibre placement
production facility in Virginia.
MAG is said to have won the contract on
cost, its ability to optimise the product for
the client’s particular application, and the
high lay-up rates achievable with difficult
bismaleimide (BMI) material - important,
apparently, in meeting cost reduction
targets for the F-35 programme.
VIPER attributes include independent control
over feed, clamp, cut and re-start for up
to 32 individual tows, automated ‘on the
fly’ adjustment of fibre band widths and
controlled placement of fibres over sharply
changing contours and around openings. The system allows wrinkle-free, near
net-shape lay-up of enclosed and deeply
contoured structures for the precision
manufacture of fuselage sections, panels,
cowls, ducts and nozzle cones for a range
of aerospace assets. The VIPER 6000 handles
tow widths of 3.2, 6.4 and 12.7 mm.
Spanish concern MTorres is another
machine tool specialist to have developed
AFP and ATL equipment. An early AFP
system from the company went to Japan
where Kawasaki Heavy Industries is using
MTorres supplied GKN Aerospace with automated
fibre placement machines to manufacture the
composite wing rear spar of the Airbus A350.
it to produce monolithic fuselage sections
for Boeing’s B787 programme. This system
can lay up to 24 half-inch tows simultaneously. By contrast, similar machines used
by GKN Aerospace and Spirit AeroSystems
to produce wing spars steer 16 quarterinch tows round the spars, including
their sharply curved edges. Dealing with
those edges requires careful attention to
the setting up of the TORRESFIBERLAYUP
machines, with fine tuning of multiple
parameters.
A spokesman for MTorres noted that its
machines must be able to run a wide
range of materials, some of which are challenging. For instance, the Toray Torayca 3900
series epoxy prepreg used for most B787
components and the Hexcel Hexply M21
material chosen by Airbus for A350 parts
Since then, ATK has used AFP to produce
35 ft long composite skins for the upper
wing surfaces of the F-35 Lightning II joint
strike fighter (JSF), bringing unprecedented
precision to the manufacturing process.
Tows for the skins are laid down on a large
mandrel fashioned in heavy invar metal for
thermal stability and durability.
Recently ATK ordered two more MAG VIPER
AFP systems for F-35 production, adding to
five VIPERS it already has at North American
sites. The new machines, due for delivery
www.reinforcedplastics.com
MAG IAS is supplying two VIPER® 6000 Fibre Placement Systems to Alliant Techsystems’ Clearfield, Utah,
facility, for use on the F-35 programme. The order includes MAG's ACES® software (Advanced Composites
Environment Suite), a modular programming and simulation system. The two systems will ship in early 2012.
(Picture courtesy of MAG IAS.)
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FEATURE
Thermoplastic prepreg is easier to handle
than thermoset. Because resin transfer is
not the issue it can be with thermosets, an
enclosed feed chamber with active cooling
is not needed. However, component wear
may be substantial so hard surface finishes
are provided on contact parts. Compaction
roller heating is applied, in the same way
as with thermoset prepreg, to reduce resin
matrix viscosity at the feed point.
CGTech supplies machine independent off-line NC programming software for AFP machines. Current
projects include a large one-piece fuselage barrel on an Electroimpact multi-machine AFP fabrication cell.
A simulation of this is shown in the picture.
both have low resin viscosity – this offering
the best structural properties after curing.
These materials therefore require higher
temperatures and pressures at the point of
compaction than the average.
Tows and prepreg
The simultaneous laying of multiple tows
by fibre placement is widely seen as the
supreme composite automation discipline.
According to Automated Dynamics, a
New York-based company that produces
advanced composite structures as well as
production automation, AFP tows some
3 mm to 6 mm thick are used to conquer
‘difficult’ geometry challenges while tapes of
double this width may serve on less severe
curvatures, thus improving throughput.
Thermoplastic tapes as wide as 50 mm can
be laid singly in operations still referred to
as AFP because the tapes are considered to
be narrower than those traditionally used
for tape laying. Tow/tape can be placed
in any axial orientation between 0 and
90 degrees, allowing stiffness and strength
to be optimised within a low weight and at
an affordable cost.
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Automated Dynamics says its head technology enables it to offer the advantage of
in-situ consolidation, each precision placement
head being associated with an elastomeric
compaction roller that may be heated or
cooled for consolidation purposes. In-situ
consolidation is said to result in structures
having low void content, a superior finish,
good fibre concentricity and minimal buckling.
The drape and high tack of most thermosetting resins under normal ambient conditions
raises difficulties for automatic handling,
including unwanted resin migration. This is
mitigated partly by using prepreg materials
having reduced drape and tack and partly
by providing a cooled feed environment so
that resin migration and build-up are avoided.
The prepreg resin can be softened prior to
consolidation by using an infrared (IR) lamp to
apply heat to the nip point of the compaction
roller. Surfaces in the feed system that have
high contact with prepreg, such as rollers
and guide chutes, are specially coated to
combat resin ‘stiction’. Tape guidance systems
maintain close geometric tolerances relative
to the prepreg cross section so as to prevent
buckling during the feed sequence.
Coriolis Composites in France was originally
founded by three competition sailors who
sought affordable series production of boats.
Nowadays, major clients are in commercial
aerospace, wind turbine and automotive
sectors as well as performance yachting.
Coriolis’ innovative system, developed over
ten years, utilises a standard off-the-shelf
poly-articulating robot arm as the basis
for a fibre placement system having eight
axes of motion. Use of standard robotic
components makes the system flexible and
economically attractive, says the company.
Coriolis is also proud of its AFP system’s
low head weight and hence low inertia
which, together with powerful drive
motors, make high lay-down rates possible.
Hardware refinements include flexible
pipes to protect and guide the fibres, and
a creel-mounted tension reduction and
equaliser system. CADfiber for Windows
and Catia V5 CATfiber software is used for
command programming and composite
design optimisation. The two-module
stand-alone package helps users optimise
the laminate design and the placement of
fibres on a range of curves, both geodesic
and non-geodesic, as well as curve offsets.
Control functions include tow steering,
minimum fibre length check, roller compliance, fibre position on the roller, cut and
restart for each tow, and automatic trim for
contours.
System maturity coincided with the desire of
aerospace and other fabricators to industrialise their composites production and this
has taken Coriolis into the aerospace market.
Significant airframer clients include Airbus
and Bombardier Aerospace. Bombardier
recently ordered AFP systems from the French
company for manufacturing parts for its new
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FEATURE
C-Series, an extensively composite regional
aircraft expected to enter the market in 2013.
A faster future
The future for AFP probably lies with
machines that are considerably faster than
those in use today. Increases in manufactured part size and complexity, together
with the high rates at which the aerospace industry needs to fabricate those
composite parts, have created the need for
on-the-fly fibre placement at 2000 inches
per minute and more, several times faster
than current-generation machines can
achieve. Such speeds are required to avoid
the need for multiple slower machines
working in parallel. While re-engineering of
systems for feeding, cutting and machinery
control has resulted in machines that
can deliver rates of this order, progress
continues and further refinement is likely
to push speeds even higher.
Raising the speed bar to these levels places
high demands on mechanical systems,
servos, controls and programming systems.
A realistic lay-down includes many short
courses (a course is a single pass of the
machine, which can be laying down
multiple materials tows or tapes) over sharp
contours, and bi-directional lay-down for
speed. The machine will continually be
accelerating and decelerating in multiple
axes to maintain the surface parameters
required. Within the feed system, spool
dynamics are closely controlled with associated ‘dancer’ rollers and pneumatic disc
brakes. High-speed computing is needed to
maintain precision in positioning, cut placement and timing.
American company Electroimpact Inc,
self-billed as a world leader in design and
manufacture of aerospace tooling and
automation, has developed AFP technology
for laying tow at up to 2000 inches per
minute over complex items, whilst allowing
cutting and adding within customer-defined
end placement tolerances. Its system can
dispense multiple tows or slit films ranging
from a quarter inch in high contour areas to
two inches or wider over lower curvatures.
All lay-ups can be performed bidirectionally
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Fibre placement machine for carbon fibre reinforced plastic (CFRP) aerostructures at Premium AEROTEC’s
plant in Nordenham, Germany. (Picture © Premium AEROTEC.)
and operators can control the feed rate
without affecting end cut accuracy.
contracted CGTech to develop a variant of its
VERICUT suite specifically for its AFP system.
A particular challenge the company faced
was that of on-the-fly cutting. Cutting a
tape that is moving fast through the guide
system requires careful timing of blade
and shear edge arrivals so that a ragged
cut – or worse, failure to sever – are
avoided. Electroimpact developed a new
guide chute system to secure this, as well
as high-speed cutter actuation to avoid
the blade exerting drag on the moving
material. Accurately timed cuts are made
in less than one millisecond. Extremely
tight integration of the CNC motion
control and the timing of cut and add
commands is achieved.
Also in demand is FiberSIM from VISTAGY
Inc. This, and associated modules from
the company’s Aero Suite, are used by a
number of aerospace contractors including
Tier 1 suppliers like GKN Aerospace. Recently
the SOLVER Company of Russia purchased
Vistagy software for use with a VIPER 1200
fibre placement system.
Demand for high-precision software programming has led to another trend in AFP/ATL
circles. There is growing reliance on specialist
program developers as high placement
speeds increasingly outrun the capability of
control software engineered by AFP machine
tool vendors. Rigorous programming can
avoid the end placement errors sometimes
seen with less effective programs.
Electroimpact, for one, has taken the
specialist out-sourcing route, having
Electroimpact AFP machines are used,
inter alia, by Spirit AeroSystems in Wichita,
Kansas, to produce composite fuselage
nose sections for the Boeing B787. SOLVER
will use the Viper/FiberSIM combination to
design and manufacture composite parts for
various projects being undertaken by the
Voronezh Aircraft Plant (VASO).
In summary, AFP is progressively becoming
a highly capable automation platform.
Joining ATL and filament winding as the
primary tools for laying down quality
composite laminates, it has become a
standard process for fabricating large
complex carbon-epoxy skins and shells. As
such, it is in the process of revolutionising
the high-volume production of complex
aerospace structures. ■
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