Page 36 - 3D Fibre Reinforced Polymer Composites

Manufacture of 30 Fibre Preforms 25

that are capable of being manufactured. In particular, unlike the standard weaving
process, braiding can produce fabric that contains fibres at k45O (or other angles) as
well as O", although fibres placed in the 90' direction are not possible with the standard
braiding process.
The primary difficulty with the traditional braiding technique is that it cannot make
thick-walled structures unless the mandrel is repeatedly braided over. This can be done
but it only produces a multilayer structure without through-thickness reinforcement. TO
manufacture true three-dimensional braided preforms it was necessary for new braiding
techniques to be developed.

Figure 2.12 Illustration of standard braiding process using horn gears

2.3.2 Four-Step 3D Braiding
The late 1960's saw an interest in the use of three-dimensional braiding to construct
carbodcarbon aerospace components and a number of processes were developed to
achieve this goal (KO, 1982; Brown, 1985). One of the first three-dimensional braiding
processes (Omniweave) was developed by General Electric (Stover et al., 1971), and
further developed and patented by Florentine (1982) under the name of Magnaweave.
This process (known as 4-step, or row-and-column) utilises a flat bed containing rows
and columns of yarn carriers that form the shape of the required preform (see Figure
2.15). Additional carriers are added to the outside of the array, the precise location and
quantity of which depends upon the exact preform shape and structure required. There