O o d h e a d p u b L i s h I n g L i m I t e d

Computer-aided design
The interface between the knitwear designer and the knit technician is critical
to the development of new samples. The designer’s concept sketch must
eventually be realised on the machine through the capabilities of the technician.
Until now computerised machine makers have been focusing on the knit
programming module where a trained technician creates a pattern on a dedicated
CAD system that saves the data on a diskette. This is then transferred to the
machine, and manufacturing starts. It is only in the past few years that the
two major computerised knitting machinery makers, i.e. Shima Seiki and
Stoll, have focused their energies on improving this interface.
Shima Seiki has enhanced the interpretative process in their SDS ONE
CAD integrated knit production system that allows all phases including
planning, design, evaluation and production. Knit designs are created in the
Paint program and are simultaneously converted to programming data. Various
combinations of knit structures and yarn selections are available in the design
system, which allow virtual simulation without actual knitting. There is also
a pattern structure database of knitted parts, such as collars, plackets and
cuffs, through which parts can be incorporated or changed at will. Alternatively,
Stoll’s M1 CAD system has tried to establish communication between designer
and technician by offering two different windows for designers and technicians
who need different information for the same design. The technical window
shows the developing design in the form of running yarn notations and
technical data, while the design window presents the design as a knitted
structure. Both windows are easily displayable and automatically convertible.
Shima Seiki, manufacturer of computerised Wholegarment
®
 knitting
machines has tested a fully integrated CAD concept in Japan. The company
offers ‘an original, one-of-a-kind sweater just for you’ in Japan’s knitwear
market through their Knit Factory Boutique – a production factory and retail
boutique combined in one facility. This revolutionary hybrid set-up offers
complete on-demand production of customised items designed and fitted
perfectly to each individual customer. The boutique is located in a three-
story building. One floor contains a couple of knitting machines. Another
floor has designs and samples to assist customers in making decisions regarding
the products they want. The third floor is a customer lounge where garments
can be tried on in a virtual CAD environment. The concept is for customers
to select a design and see how it might look in a particular setting. Changes
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are made, and the digital file used to drive the in-store knitting machines.
These steps take only about an hour or two, depending on the style, colours
and patterns selected. The completed product can be picked up by the consumer
at the agreed time. Prices range from 15 000 to 30 000 Japanese yen, which
are comparable to high-quality items sold in department stores.
The project is being considered one of the most promising forms of retail
fashion next to electronic shopping via the Internet. Once a customer places
an order, his or her measurements and preferred designs can be input into a
customer database, so the likelihood of repeat orders is very high. The project
is not just about a profitable retail store however. It is about integration of
cutting-edge technologies in knit designing, graphics programming, simulation,
whole-garment programming and manufacturing, and value-addition through
printing and/or embroidery. The recent innovations in CAD and seamless
manufacturing have made it possible.
5.5.3
Warp knitting
Warp knitting has emerged as the most versatile fabric production system
with a very favourable performance/cost ratio. Warp knitted fabrics can be
produced to be elastic or stable, with an open or closed structure. They can
be produced flat, tubular or three-dimensional. Fabric width of over 6 m is
available without seams or even up to a multiple of this width if it is a net
construction. The gamut of warp knitting includes Tricot, Raschel, Milanese
and Crochet knitting machines. Stitch bonding machines are also included
with warp knitting. These machines normally make flat fabrics. Knit-braiding
machine or the circular warp-knitting machine is a lesser-known but useful
member of the knitting machine family that can produce tubes of various
small diameters from 2 to 7 inches (5–18 cm).
Tricot is very common in lingerie. Milanese is stronger, more stable,
smoother and more expensive than tricot and hence is used in better quality
lingerie. Raschel knits do not stretch significantly and are often bulky;
consequently, they are often used as pile fabrics and as an unlined material
for coats, jackets, straight skirts and dresses.
By using weft insertion on warp knitting machines to insert length-wise
warp ends the extensibility of these fabrics in that direction can be reduced
and strength increased. Biaxial fabrics can be made by choosing the correct
structure and yarns of the same strength, to provide extensibility in both
directions. A ‘multi-axial’ structure can also be achieved by laying on additional
diagonal ends, rising both from right and from left. This complex structure
of yarn sheets is stitched through by compound needles and fixed together
by warp knitting. The combination of multi-directional fibre layers and matrices
has proved capable of absorbing and distributing extraordinarily high strain
forces and therefore find widespread industrial applications.
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Double needle-bar Raschel machines have been used to produce double-
sided fabrics, which are then slit to make warp knitted plush for upholstery.
When talking about upholstery most people think of home textiles and similar
applications for fabrics. However the automotive industry is also a huge
market for these textiles. In 2003 the European automotive industry alone
consumed nearly 45 500 tonnes of interior textiles for car seats, head-rests,
door covers, headliners and parcel shelves. Additionally, technical textiles
and semi-technical textiles are also used by the car industry in the form of
fabrics for air bags, seat belts, molded carpets, V- and timing belts, and
fabrics in the engine compartment (hoses, etc.). While woven fabrics dominate
this sector with 51% share, circular knits are the second largest fabric group
with a 19% share. Warp knitted fabrics hold the third largest share with a
12% of the market. This includes the Tricot family of knits (6%) brushed or
structured, with Tricot pile sinker fabrics having a 4% share. Raschel knits
represent just 0.79%. Brushed or structured Tricot fabrics are predominantly
used as headliners or are found in the seat wings. Owing to their fine dense
velour, Tricot pile sinker fabrics have a 4.73% share.
More recently, Raschel machines have been adapted to make spacer fabrics
where the two fabric surfaces are linked by relatively thick synthetic
monofilaments. Spacer knits are double-layered circular knits with a cushion
of air and ‘spring-like’ yarns between the two sides. Today, these fabrics can
reach a thickness of 60 mm and can be fashioned for diverse applications
ranging from helmets, boot soles, composites, medical products, body armour
and bedding. In another variant of this technique, conventional cotton or
wool yarns are used for linking the two fabric surfaces. The space between
the two fabrics can be filled with synthetic foam or sand to make insulators
or other special composites. Many recent models by European car
manufacturers (Citroen Grand, Lancia Argento, Smart Fortwo and Forfour,
and VW Polo Fun) have used spacer fabrics primarily as seat covers. Germany-
based Karl Mayer Textilmaschinenfabrik GmbH is the major machinery
supplier in this sector.
Another end use for spacer fabrics is moulded bra cups. A single spacer
fabric replaces three layers usually used in bra cups, i.e. the pretty ‘Face’
fabric, foam or fibrefill middle layer and the ‘lining’ fabric. Spacers mould
well and can be produced in different densities, allowing production of
matching wings and straps.