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Indian Journal of Fibre & Textile Research
Vol. 33, September 2008, pp. 333-338
Robotic approach to textile preforming for composites
P Potluri a, T Sharif & D Jetavat
Textile Composites Group, School of Materials, Textiles and Paper, University of Manchester, Manchester M60 1QD, UK
Technical textiles offer high-value engineering applications for the traditional textile sector which is generally viewed
as a low-cost and high-volume commodity industry. This paper reviews the application of textiles in fibre-reinforced
composites and identifies key challenges to the textile industry in order to serve this market. While traditional textile
machinery may be adopted for producing 2D broadcloth reinforcements, novel machines/machine modifications are
necessary for producing 3D textile preforms. In this paper, a robotic approach to 3D textile preforming has also been
proposed.
Keywords: 3D weaving, Automation, Fibre-reinforced composites, Robotics, Textile composites
1 Introduction Fibre-reinforced composites (FRC) are popular in a
wind-range of applications including airframes, rocket
casings, ballistic armour, racing cars, high-end
passenger cars, wind turbines, racing & luxury yachts,
bridge decking and sporting equipment as
replacement for conventional engineering materials
such as steel, aluminium and concrete. For example,
Boeing 787 Dreamliner will have 50% by weight of
composites. Composites offer the advantages of high
specific stiffness and strength, improved fatigue life
and freedom from corrosion; they typically consist of
30-55% by volume of fibres such as carbon, glass &
kevlar and rest the matrix (typically an engineering
polymer such as epoxy). Aerospace composites are
traditionally manufactured using expensive prepreg
systems (fibres pre-impregnated with resin);
individual prepreg plies are cut to shape, stacked in
preferred orientations and subsequently cured in
autoclaves. This is an expensive and relatively slow
production process. In recent years, dry fibre
preforms in conjunction with liquid infusion
techniques (vacuum infusion, resin transfer moulding)
are becoming popular as a means of improving
productivity and reducing process costs. Reinforcing
fibres, in the form of yarn or roving, are arranged in
the required shape of the component (preform) prior
to infusion with a matrix material. Textile processes,
such as weaving, braiding, stitching, knitting and
embroidery, are employed in the manufacture of the
fibre preforms, and the resulting preforms are
generally referred to as ‘textile preforms’. The present
paper reviews the application of textiles in fibre-
reinforced composites and identifies challenges to
textile industries. A robotic approach to 3D textile
preforming has also been proposed.
1.1 Textile Preforms
Weaving, braiding and stitch-bonding are three
preferred methods for preforming as shown in Fig. 1.
These structures exhibit relatively small fibre
waviness. Weaving and stitch-bonding are commonly
used for manufacturing broadcloth (referred to as 2D
fabrics) while braiding is used for relatively narrow
seamless tubes. Knitting is less frequently used as the
resulting loops greatly reduce the strength and
stiffness. 2D broadcloth is subsequently converted
into a preform using a variety of manual or semi-
automated processes.1 Individual fabric panels are cut
in the preferred orientations using an automated
cutting table. Then these plies are stacked and
simultaneously draped on a mould surface.
Thermoplastic binders or stitching may be employed
to hold the layers together so that the preform can be
easily handled. Preforming is the most expensive and
labour intensive step in the composites manufacturing
process. Efforts have been made in the past to
automate the preforming process. Buckingham and
Newell2, and Zhang and Sarhadi
3 developed
automated preforming processes. However, these
systems are not widely used. Recently, 3D weaving
has received a lot of attention as a means of reducing
the preforming costs. 3D weaving process produces a
multi-layer preform consisting of several warp and
weft layers held together by ‘binding yarns.’ This
____________ aTo whom all the correspondence should be addressed.
E-mail: [email protected]
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2008
334
process is expected to produce a preform in one piece
for subsequent resin infusion.
2 3D Weaving
Figure 2 compares 3D weaving process with
conventional 2D weaving. In 2D weaving, warp is
typically supplied from a single warp beam (or a creel
in case of carbon weaving). The weft is inserted by a
variety of devices including a shuttle, projectile,
rapier, air jet or a water jet; rapier weft insertion
appears to be the most popular choice for composite
preforming. 3D weaving on conventional looms is
shown in Fig. 2b. Several ground or stuffer warps are
supplied from one or more warp beams and the
binding yarns from a separate beam. In case of
carbon fibres, it is usual to supply individual warp
yarns from a large creel. The binding yarns are
supplied under relatively low tension to enable them
to interlace around several warp layers without
causing excessive distortion to the warp yarns. As
can be seen in Fig. 2b, weft yarns are introduced one
at a time through a shed created between two adjacent
warp layers. Since the sheds are created one at a time,
3D weaving on conventional looms is a slow process. 2.1 Limitations of 3D Weaving on Conventional Looms
There are a number of limitations to 3D weaving on
conventional looms. These limitations must be
overcome in order to produce near-net preforms for
composites. First of all, the preform is produced as a
rectangular billet with constant width and thickness.
Repeated shedding (to insert several picks in each
plane) can lead to local distortions and hence the
resulting preform geometry may not be optimum. For
example, 3D orthogonal preform shown in Fig. 3
requires six shed changes in order to insert one set of
picks. Distortion to warp may also occur at the take-
up rollers. Another major limitation is the inability of
conventional weaving machines to insert non-
orthogonal yarns. A vast majority of composite
preforms require quasi-isotropic lay-up having 0o,
±45o and 90
o plies. This is not possible with
conventional 3D weaving.
2.2 Extension of 3D Weaving
Capabilities of conventional weaving must be
further expanded in order to create near-net shapes.
Recently, a number of machine modifications have
been made (Fig. 4) to improve the preforming
capability of conventional looms.4 Figure 4a shows
an on-loom cutting device for trimming off the excess
weft yarns in order to create a multi-stepped preform
shown in Fig. 4b. The weft yarns are locked in
position by leno mechanisms (Fig. 4b). While multi-
step preform is suitable for creating lap joints, a
Fig. 1—Various methods of preforming [(a) woven fabrics, (b) braided fabric, and (c) stitch-bonded fabric]
Fig. 3 —Orthogonal 3D weave
Fig. 2—Weaving processes [(a) 2D weaving, and (b) 3D weaving
on conventional looms]
Main wrap beam
POTLURI et al.: ROBOTIC APPROACH TO TEXTILE PERFORMING FOR COMPOSITES
335
number of other applications require a gradual taper.
Here, we have developed an improved weaving
process by controlling the degree of compaction
applied to the weft tow, gradual taper can be achieved
without dropping individual warp layers. Of course,
degree of taper is limited with this process. The idea
is to incorporate this tapering technique along with
the multi-step preforming method (Fig. 5) in order to
obtain gentle transition at each step.
2.3 Mechatronic Approach
Conventional weaving machines are optimised for
producing 2D broadcloth with cotton and poly-cotton
yarns. Over the years, these machines were
developed to increase the productivity. However, for
3D weaving of carbon fibres, important issues are:
(i) ability to create thick multi-layer fabrics, (ii) little
or no crimp in most of the yarn systems, (iii) ability to
change width and thickness in order to produce near-
net shapes, and (iv) ability to place yarns at bias
orientations. Rather than trying to modify
conventional looms, it may be prudent to develop
completely new looms for the purpose of 3D weaving.
Since weaving involves a multiple degrees of freedom
in shedding, picking, beat-up, let-off, take-up and
selvedge formation, a mechatronic /robotic approach
may be appropriate to build suitable 3D weaving
machines. Mohamed et al. 5 described a purpose built
machine in which several weft yarns are inserted
simultaneously around pre-arranged warp layers by
creating multiple sheds. This multi-weft insertion
system is efficient for producing relatively thick
fabrics. Additionally, distortion in individual warp
yarns can be minimized due to the fact that the sheds
are produced locally and the shed size is small.
Fukuta et al.6
described a three-dimensional weaving
machine consisting of longitudinal, vertical and
horizontal yarns. Longitudinal or warp yarns (Y) are
arranged as an array through a perforated comber
board. Vertical yarns (Z) are inserted as double picks
with bent needles that would provide space for
inserting horizontal yarns. Horizontal yarns (X) are
inserted using a number of rapiers through the gaps
created by the vertical bent needles. Using this
process, a relatively thick block of fabric can be
created
Figure 6 shows the conceptual design of a
mechatronic 3D weaving machine being developed at
the University of Manchester. A number of straight/
Fig. 4—(a) Cutting device, and (b) multiple steps
Fig. 6—3D weaving machine concept
Fig. 5—Gradual tapering with weave modifications
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2008
336
stuffer yarn systems are arranged in such a way that
they form permanent sheds. All the weft yarns are
inserted simultaneously with the aid of bent needles; a
selvedge forming mechanism operates through the
weft loops formed by the bent needles in order to
simultaneously lock them at the right selvedge.
Shedding is required to be performed only on the
binding yarn. The beat-up is achieved by a
mechanism with two degrees of freedom – a series of
needles (not a conventional reed) is inserted just
behind the newly inserted picks in order to push them
into cloth fell position. The degree of beat-up may be
changed, if needed, in order to achieve a gentle taper
(Fig. 5). Additional mechanisms to drop certain
stuffer yarns are under development in order to create
multiple steps (Fig. 4b). There are three advantages
with this approach, namely (i) yarn distortions are
minimised since the stuffer yarns form permanent
sheds and need not be subjected to repeated shedding,
(ii) since all the weft yarns are inserted
simultaneously, this machine needs to run at the
fraction of the speed of a conventional weaving
machine, (iii) mechatronic concepts easily lend
themselves to near-net weaving because of flexible
motions.
3 Robotic Preforming Mechatronic 3D weaving concept still has a
number of limitations in relation to near-net
preforming, such as (i) non-orthogonal yarn
orientations are not possible, (ii) there is a lot of fibre
wastage due to cutting/trimming of ends and picks,
(iii) it is not easy to create local features, and (iv)
preforms made using 3D weaving are essentially flat
and it is difficult to mould them into complex shapes.
Here, a robotic approach is proposed to preforming
near-net shapes. This concept combines the merits of
3D weaving and fibre placement (FP) processes.
3.1 Automated Fibre Placement
Automated tape laying and fibre placement are
currently used in the aerospace industry to
manufacture large composite parts. Grant7 presented
a detailed review of the automated tape layers (ATL)
and fibre placement (FP) machines. These are
essentially machine tools to deposit thin layers of
prepreg tape precisely on a mould surface. This
process of building-up material on a mould surface
may be viewed as inverse of CNC machining of solid
metal blocks. These ATL and FP machines are
hugely expensive machines, each costing several
million dollars. In addition, the prepreg material is
expensive and has a limited shelf life. In this work,
we have developed fibre placement system in relation
to dry fibre yarns.
3.2 Robotic System
Extending the concept of mechatronic weaving
further, a modular gantry robotic system has been
developed in order to deposit fibres in a completely
flexible manner, as shown in Fig. 7. This gantry robot
consists of 4 –axis of freedom, i.e. X- axis, Y-axis, Z-
axis and rotation axis; however, the additional axes
can be added if required. The work envelope is [3m,
2m, 0.6 m]. Additionally, a number of pneumatic
valves are available for controlling cutters and other
devices.
3.3 Control System
The robotic control system consists of four AC
servo drives and several I/O ports. The main software
platform used here is CoDeSys8, which stands for
Controlled Development System. This software
supports all languages described by the standard IEC-
61131, i.e. instruction list (IL), structural text (ST),
sequential function chart (SFC), function block
diagram (FBD), ladder diagram (LD) and continuous
fuction (CFC). The motion of the drives can be
controlled by different methods like by function
blocks, CNC editor or CAM editor; however, CNC
editor provides multi-dimensional motions
graphically and textually. To interpret these motions,
their specified libraries must be included in the
CoDeSys program. These libraries will automatically
create the corresponding data structures (CNC Data,
CAM Data), which can be accessed by the IEC
program. However, for the communication of this IEC
program with the hardware, structure of drives is first
mapped in the PLC configuration and the appropriate
parameters of these drives will be set. This structure
Fig. 7—Robotic system
POTLURI et al.: ROBOTIC APPROACH TO TEXTILE PERFORMING FOR COMPOSITES
337
then will be made accessible for the application with
the aid of the drive interface libraries. The internal
library SM Drivebasic.lib provides IEC data
structures and global variables, which will represent
the drives, axisgroups and bus interfaces which have
been configured in the PLC configuration. With the
aid of <BusinterfaceName> Drive.lib the data get
exchanged in the structure and hardware. Figure 8
presents the general structure of the control system.
3.4 Robotic Preforming Concept
Robotic preforming aims to overcome the
limitations of 3D weaving by achieving the following
objectives:
• To produce preforms with any arbitrary geometry
length-wise and width-wise,
• To produce a preform with a large number of
layers in 0o, 90
o and ±θ
o directions,
• To produce a preform with single or double
curvatures,
• To produce taper in thickness in any direction,
and
• To incorporate through thickness reinforcement.
The robotic system has an end-effector for
depositing carbon yarn continuously on a mould
surface. The yarn is supplied from a spool attached to
the robot arm (Fig. 9). Unlike prepreg material, dry
carbon yarn does not have any tackiness to stick on
the mould surface. Alternate concepts are required for
securing individual tow. Cahuzac9 proposed the use
of pins for securing the yarns – similar approach has
been adopted here. It can be seen from Fig. 9 that
carbon fibres are deposited around pins in order to
create a large number of warp, weft and bias layers.
The component need not be flat and the fibres can be
deposited on a curved tooling.
3.5 Resin Impregnation
The mould surface and the holding pins were
covered with a release film so that resin infusion can
be conducted without disturbing the yarns. Figure 10a
shows the arrangement for vacuum infusion process.
The pins can be removed once the resin is fully
infused and starts to gel. This process can be used not
only for flat but also for curved parts as well.
Fig. 10—(a) Vacuum infusion process, and (b) multi-axial panel
produced by vacuum infusion
Fig. 11—(a) Circular panel with edge taper, and (b) cross-
sectional view
Fig. 8—Control structure
Fig. 9—Deposition of carbon fibre yarns on a mould surface
INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2008
338
Figure 11 shows a circular panel with taper at the
ends. Additional pins were required on the tapered
section in order to terminate the yarn in the region.
This circular panel demonstrates the advantage of
robotic preforming over 3D weaving. A 3D woven
preform would require a significant amount of cutting
and trimming in order to produce a circular preform.
At present, the robotic preforming system does not
introduce through thickness reinforcement. Currently,
we are developing a tufting head that will incorporate
through thickness reinforcement to the preform. Once
tufted, the preform can be lifted off the tool surface
and placed in an RTM tool.
4 Conclusions
The work reported in this paper looked at the gap
between textile preforming and automated fibre
placement systems. Textile preforming techniques
including 3D weaving are efficient methods for
producing dry fibre assemblies. However, these
techniques have limitations for near-net preforming.
Automated fibre placement systems are capable of
producing near-net shapes; however, these systems
can deposit prepreg materials. It has been
demonstrated that the robotic preforming technique
can create complex near-net preforms using dry
fibres. Since dry fibre preforms lead to significant
cost reduction in comparison to prepreg systems,
robotic preforming methods are likely to succeed
commercially, once sufficiently developed.
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