Page 30 - 3D Fibre Reinforced Polymer Composites

Manufacture of 30 Fibre Preforms 19

In spite of some limitations in preform design with the multilayer weaving process, its
greatest advantage is that it can be performed upon conventional weaving looms and
does not require significant costs to develop specialised machinery. It appears suited
primarily to the manufacture of large volumes of flat or simply shaped preforms with a
basic 0" and 90" yarn architecture.

2.2.3 3D Orthogonal Non-Wovens
There is still some argument as to what constitutes the distinction between multilayer
(or 3D weaving) and 3D orthogonal non-wovens. The traditional definition of weaving
requires the yams to be interlaced with each other, thus processes that produce preforms
with the yams in orthogonal, non-interlaced architectures are generally referred to as 3D
orthogonal non-wovens (Khokar, 1996). These processes generally differ from
multilayer weaving in that multiple yarns that are separate from the warp yarns (X
direction) are inserted in the Y and Z directions in a highly controlled manner. The
production of a 3D fibre architecture using a 3D non-woven process therefore does not
solely rely upon the warp yam lifting sequence. Confusion can sometimes occur due to
the fact that 3D weaving equipment is also capable of producing orthogonal non-woven
preforms through the selection of a suitable lifting sequence. It would therefore be better
to define the style of preform produced rather than the equipment used in manufacture,
however this is not yet the case in the majority of the literature.
Since the 1970's a wide range of processes have been developed to produce 3D
orthogonal preforms. These vary from techniques utilising relatively conventional
weaving mechanisms but with multiple weft insertion (Mohamed et a]., 1988), to
processes (Mohamed et al., 1988; KO, 1989a) that have very little in common with the
traditional weaving process. Some of the earliest work in 3D orthogonal nonwovens
was pioneered in France by Aerospatiale and Brochier who licensed their separately
developed technology in the USA to Hercules (Btuno et al., 1986) and Avco Speciality
Materials (Rolincik, 1987; Mullen and Roy, 1972; McAllister, and Taverna, 1975)
respectively. Both processes are similar in that they use an initial framework around
which radial and circumferential yarns (for cylindrical preforms) or Y and Z yarns (for
rectangular billets) are placed. For the Brochier process (AutoweaveTM) this framework
consists of pre-cured reinforcements inserted into a phenolic foam mandrel whilst the
Aerospatiale process uses a network of metallic rods and plates that are removed during
the placement of the axial yarns (see Figure 2.8). Both processes are capable of
producing shaped preforms by suitable shaping of the initial framework and can be used
to construct 4D and 5D preforms, that is with architectures containing fibres laid in
directions other than X, Y or Z. These two processes have been mostly used for the
production of carbodcarbon composites for use as components in rocket motors and
exit cones.
Significant development of machinery to manufacture 3D non-woven preforms has
also been undertaken within Japan since the 1970's, particularly at the Three-D
Composites Research Corporation (a subsidiary of the Mitsubishi Electric Corporation).
Methods for the production of non-woven preforms have been developed by Fukuta et
al. (1974) and Kimbara et a1 (1991), an example of which is shown in Figure 2.9. Again
these processes rely upon the insertion of yam or cured composite rods along pre-set
directions, the main difference between these methods and others being the mechanisms
to control that insertion.