Braiding Techniques for Fibre Preform Manufacturing: Advantages and Limitations in Composite Materials
Fibre preforms are an essential component in the manufacturing of composite materials. There are two major ways of manufacturing fibre preforms: weaving and braiding. While weaving involves the interlacing of warp and weft yarns, braiding is a process that involves the interlacing of yarns at different angles to produce fabrics with varying properties. In this article, we will explore the different types of braiding used in the production of fibre preforms.
Braiding is suited to the manufacture of narrow width flat or tubular fabric and is not as capable as weaving in the production of large volumes of wide fabrics. Unlike standard weaving, braiding can produce fabric that contains fibres at 45-degree angles to one another, which makes it a valuable manufacturing process for composite materials. Braiding is done over top of mandrels that vary in cross-sectional shape or dimension along their length. Braiding is limited to objects about a brick in size.
There are three main types of braiding: four-step, two-step, and multilayer interlock braiding. Four-step or row and column braiding utilizes a flat bed containing rows and columns of yarn carriers that form the shape of the desired preform. 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 are four separate sequences of row and column motion, which act to interlock the yarns and produce the braided preform. The yarns are mechanically forced into the structure between each step to consolidate the structure, as a reed is used in weaving.
Two-step braiding is unlike the four-step process because the two-step process includes a large number of yarns fixed in the axial direction and a lesser number of braiding yarns. The process consists of two steps in which the braiding carriers move completely through the structure between the axial carriers. This relatively simple sequence of motions is capable of forming preforms of essentially any shape, including circular and hollow shapes. Unlike the four-step process, the two-step process does not require mechanical compaction: the motions involved in the process allow the braid to be pulled tight by yarn tension alone.
Multilayer interlocking braiding is another type of braiding that consists of a number of standard circular braiders being joined together to form a cylindrical braiding frame. This frame has a number of parallel braiding tracks around the circumference of the cylinder but the mechanism allows the transfer of yarn carriers between adjacent tracks forming a multilayer braided fabric with yarns interlocking to adjacent layers. The multilayer interlock braid differs from both the four-step and two-step braids in that the interlocking yarns are primarily in the plane of the structure and thus do not significantly reduce the in-plane properties of the preform.
The four-step and two-step processes produce a greater degree of interlinking as the braiding yarns travel through the thickness of the preform, but therefore contribute less to the in-plane performance of the preform. A disadvantage of the multilayer interlock equipment is that due to the conventional sinusoidal movement of the yarn carriers to form the preform, the equipment is not able to have the density of yarn carriers that is possible with the two-step and four-step machines.
In conclusion, braiding is a valuable manufacturing process for composite materials that produces fabrics with fibres at different angles, which increases the strength and stiffness of the composite in all three dimensions. There are three main types of braiding: four-step, two-step, and multilayer interlock braiding, each with its unique advantages and disadvantages.
