Selcom is involved in the European Project MACH-to: Innovative components fot the textile machinery industry. Find the article here.

1. Innovative components for the
textile machinery industry
Within the MACH-to project, a new lightweight pattern guide bar of a knitting machine has been successfully
validated in the prepreg/autoclave process. The mass of the prototype composite component represents a
mass reduction of 36% compared to the benchmark of the current state-of-the-art aluminium component.
6 Compositi
Federico Meneghello, Andrea Pestarino, Daniele Pozzo - D’Appolonia S.p.A.
Olaf Heintze, Fabian Preller - INVENT GmbH
The interface is here presented by the
rods themselves, the connection be-tween
guide rods and pattern guide bar
can be modified if needed. In the cur-rent
design the interface is realised by
thread holes as well. So, the interface
‘pattern guide bar / guide rods’ can be
modified into a more material specific
and a more lightweight design.
Because of the close spatial alignment
of the pattern guide bars, the pre-set
design space of the new composite ver-sion
is very limited, especially concern-ing
the cross-section.
Figure 4 illustrates the cross-section
of the current design (state-of-the-art)
as well as a proposal for a more light-weight
design which would be still an
aluminium part. Important is that the
cross section of these designs can be
used by the machine supplier to inte-grate
into the warp knitting mechanism.
Besides the interfaces and the design
space, the mass of the pattern guide
bar is the third requirement of the new
composite parts.
As stated in figure 4, the state-of-the-art
design results in a total mass of 966
g for the bare aluminium pattern guide
bar. The version that is proposed by the
machine supplier as a lightweight al-uminium
alternative results in 793 g.
A new composite made pattern guide
bar shall bring a significantly reduction
of mass, which is at least m < 793 g,
while showing the same mechanical
performance. Because there are no de-tailed
specifications the components’
stiffness is chosen as a benchmark for
the mechanical performance.
CONCEPT
High end carbon fibre reinforced plas-tics
(CFRP) base on so called endless
fibres, which have lengths in the mag-nitude
of the components dimensions.
The endless fibre can be procured in
form of rovings which are yarns of thou-sands
of single carbon fibres or as a
semi-finished product in textile form.
Rovings can only be handled in few form
giving processes, e.g. filament winding
or pultrusion technique. Most CFRP
ACH-to (G.A. 315360) is a col-laborative
project, co-financed
by the European Union under
the Seventh Framework Pro-gramme,
for developing a textile ma-chines
Retrofit Kit, that would allow
end users to quickly and effectively re-place
the components responsible of
energy waste and losses in general.
The MACH-to Retrofit Kit will definitely
bring several advantages to the custom-ers
in terms of: energy saving, produc-tion
speed increase, less maintenance,
noise and vibration reduction and exten-sion
of machine specification. The pro-ject
team is composed by 7 partners
from 4 European countries, including re-search
centres and small-medium en-terprises:
INVENT GmbH, D’Appolo-nia
S.p.A., Alge Elastic GmbH, Naveta
Cz Sro, VUTS a.s., SELCOM S.r.l., Insti-tut
für Textiltechnik. The main output of
the project will be the design and pro-duction
of two Retrofit Kits (for two dif-ferent
textile machines). The paper will
describe one of them, i.e. a carbon fi-bre-
based pattern guide bar of a knit-ting
machine. The project starts from
the results of another EU project named
Nu-Wave (FP7project 218479 Jan2009-
Dec2011), which supported textile ma-chinery
SMEs in developing a new gen-eration
of high-performance machines.
The MACH-to project starts on the ba-sis
of Nu-Wave results and aims at fill-ing
the gap, that still separates them
from the market.
REQUIREMENTS ON A PATTERN
GUIDE BAR
Based on the promising results of the
previous project Nu-Wave, elementa-ry
composite components are going to
be up-scaled from laboratory scale to
industrial series application with all re-garding
requirements. The component
design of the Nu-Wave part is straight
from a technical point of view. To meet
the economic and manufacturing re-quirements
validated by an on-going
market analysis of the Mach-to pro-ject,
additional effort were spent in or-der
to revise the design of the compo-nent
itself, the manufacturing method
and the materials and semi-finished
products used. The fibre braiding tech-nology
combined with the resin infu-sion
technique which was the essen-tial
process of the Nu-Wave prototype,
has been switched into a process that
is much more attractive to medium lot
sizes on the one hand and that is more
applicable in standard SME workshops
that deal with composite manufactur-ing.
The process, that is chosen here,
is the prepreg / autoclave process along
with a design concept that omits a com-ponent’s
core. Omitting the core saves
weight and process costs. This paper
gives a review of the revision of the
main concept of the composite com-ponents.
It deals with the design of the
components – beginning at the general
idea up to the calculation of mechanical
properties – the design of an intelligent
mould concept for economical produc-tion
and the manufacturing itself.
To achieve the technical and econom-ic
targets of the project an elementa-ry
machine part has been chosen to be
substituted by a lightweight composite
pendant. This part is the pattern guide
bar, which is subjected to high accel-erations
and velocity. So the mass re-duction
affected by the new compos-ite
lightweight design has full impact on
the energy saving targets of the project.
Figure 1 illustrates the warp knitting
machine in which the composite parts
are to be integrated. The pattern guide
bar is one of eight components that hold
the needles (fig.2) and fulfil the move-ment
pattern of the needles.
The needles are stacked together into
groups of about ten needles each that
are put on a needle guide plate. These
needle guides are connected to the pat-tern
bar via thread hole interfaces (fig.3
and 4).
To use these needles guides as non-vari-able
parts furthermore, these interfaces
shall not be modified or shall be adapted
in a new pattern guide bar, respective-ly.
On the other hand, the pattern guide
bars are connected to the machine by
the use of adjustable guide rods (fig.3).
M

2. - Innovative components for the textile machinery industry -
chosen in terms of mechanical proper-ties,
thermal stability and chemical sta-bility
concerning machine lubricants
and cleaning agents, as well as eco-nomic
Compositi 7
aspects.
Furthermore the processing properties
of the adhesive, i.e. the viscosity and
the pot life, are well applicable for the
bonding. A jig is used to fix both the
shells and to assure a constant thick-ness
of the adhesive.
Integrating COTS inserts
The inserts are integrated in bore holes
that are machined before. The holes ex-hibit
a set-off and so two diameters.
This way, the inserts have form-fit to-wards
the direction of load application
in the installation procedure. The set-off
is also used to assure the fixation of the
inserts by adhesive.
For this process, a different epoxy ad-hesive
is used as for the bonding of
the shells, because the viscosity of the
material needs to be lower (lower gap
thicknesses and a different application
process). Figure 14 (a) illustrates the
position of the holes for the 50 COTS
(‘commercial off-the-shelf’). In figure
14 (b) the set-off of the bore holes is
shown.
Summary of manufacturing
The prototype composite component
has been finished with a surface treat-ment
to be robust for presentation and
marketing purposes (fig. 16).
In terms of an economic series produc-tion
this last processing step can be
omitted.
All the mentioned figures
refer to the italian version
Fig.1
Fig.2: Composition of pattern guide bars
Fig.3: Pattern guide bar and its interface sto the needle
guides and the guides rods
Fig.4: Design space and interface (IF) of two solutions made
by the machine supplier
Fig.5: Clamping concept for the interface “pattern guide bar
/ guide rods”
Fig.6: FE models of the state-of-the-art pattern guide bar
and the new concept (stage 1)
Fig.7: Boundary conditions of the 4-points-bending FE
analyses
Fig.8: Boundary conditions of the torsional bending FE
analyses
Fig.9: Comparison of stiffness in 4-point-bending loading
Fig.10: Comparison of stiffness at torsional loading
Fig.11: Lay-up of the CFRP shells under vacuum bag before
entering the autoclave
Fig.12: Mould (left) and CFRP shells (right) after curing
Fig.13: Shells after demoulding and before trimming
Fig.14: Bar after machining the holes for positioning the
metallic inserts
Fig.15: Bar after integrating the metallic insert
Fig.16: Bar after surface finishing
parts are made with processes based
on textile pre-forms. Nearly all textiles
are plane and so, CFRP components of-ten
have thin walled architectures. An-other
characteristic of composite mate-rials
is the polymer matrix that embeds
the fibres. Therefore, these materials
do not have rigid surfaces and they ex-hibit
relatively low stiffness in direction
transverse to the fibres plane. Those ar-eas
of CFRP parts that require rigid sur-faces
or that cannot be reinforced by
fibres in the directions of load are com-monly
strengthened by additional metal
components. In the following, the con-cept
of a composite pattern guide bar
deals with these challenges.
Concept stage 1: two-shells-body
To use only minimum material mass and
simultaneously gain the same stiffness
as the aluminium benchmark, the ma-terial
has to be put on the outer edg-es
of the design space. So, in forming
a closed cross-section of material with
the biggest possible diameter, the bend-ing
stiffness and torsional stiffness of
the components acquires a maximum.
The cross-section is formed by two
shells. Because none of these shells has
an undercut, they are relatively easy to
manufacture in standard CFRP process-es,
e.g. vacuum infusion or prepreg/au-toclave
technique. The shells are bond-ed
together to close the cross-section
and gain full stiffness. In this stage 1
of the concept, the interfaces are real-ised
with metallic inserts. The interface
to the needles guides is one metallic in-sert
per thread hole. The interface to the
guide rods is also realised with a metal-lic
insert for each connecting screw as
set up in the aluminium state-of-the art
design. The mass of this concept is cal-culated
to 675 g.
To lower the manufacturing effort for the
latter interface and to reduce weight, the
concept is further developed in a next
stage, described in the following.
Concept stage 2: clamping interface
The further development of the inter-face
between pattern guide bar and
guide rods requires a revision of the pat-tern
guide bar geometry and the guide
rod elements, as illustrated in figure 5.
The two shells of the CFRP component
are formed to a flange in which the al-uminium
part can grasp. The alumini-um
part has a cap that is to be fixed via
screws and avoids the CFRP part to slip
out the form closure.
This concept reduces the manufactur-ing
effort of integrating 28 metallic in-serts
used in the concept stage 1. Fur-thermore,
the mass is reduced to 623
g (not concerning changes at the guide
rod elements).
Dimensioning
The use of composite material and the
reduction of mass is valid only if the
component exhibit the same mechan-ical
behaviour. A practical benchmark
is the stiffness at bending loading and
torsional loading. To choose a suita-ble
CFRP material and to design prop-er
shell thicknesses two finite element
(FE) models are built up to represent
the properties of both the aluminium
component that is currently used by the
machine supplier and the CFRP concep-tual
component (fig.6). A 4-point-bend-ing
test set-up is modelled with arbi-trary
values for the length of the bearing
distances and loading distances as well
as arbitrary values for the bending forc-es
(fig.7). The aim of the test is a com-parison
of the component properties
that shall be nearly equal. The same is
valid for the torsional bending test set-up,
illustrated in figure 8.The bounda-ry
conditions of the tests are kept con-stant
for the aluminium benchmark and
the CFRP concept component. As it can
be seen in the following images (fig.9
and 10), a combination of different ma-terial
properties and shell thicknesses
has been found, to provide nearly equal
properties for the composite pattern
guide bar. The maximum 4-point-bend-ing
deflection of the CFRP bar is quite
lower than the benchmark (fig.9). In the
torsional bending test the overall defor-mation
is in the same range for both the
benchmark and the new concept.
Remark: In the FE model of the com-posite
pattern guide bar the very outer
corner exhibits a massive deformation
because of a very local acting force ap-plication
point.
MANUFACTURING
OF THE DEMONSTRATOR
For the manufacturing of the shells a
prepreg material is used. A biaxial car-bon
fibre fabric and an epoxy resin are
chosen which are procured pre-impreg-nated.
The fabrics are cut precisely with
an automated cutting machine and laid
up into a single-sided mould. The pre-cise
cutting is important to an end-con-tour
of the shells which is nearly free
of post-processing. The mould and the
prepreg lay-up are covered with a vacu-um
bag and cured in an autoclave. Fig-ure
11 illustrates the lay-up under the
vacuum bag before entering the auto-clave.
After curing the shells exhibit a good
laminate quality with edges that need to
be trimmed by grinding (fig. 12 and 13).
Bonding of the shells
The shells are bonded together with an
epoxy adhesive that is appropriate for
industrial applications. The adhesive is