ADVANCED MATERIALS & PROCESSES | MARCH 2025 26 and the braid may be taken up from the braiding machine along a horizontal axis. Both orientations are illustrated in Fig. 2. With regard to other machine styles, a maypole braiding machine may be altered such that a flat braided structure, or tape, may be formed instead of a cylindrical braid. Another option is a 3D braiding machine, which is comprised of multiple adjacent braiding machine tracks between which carriers of one track may interact with carriers of other tracks to create braided structures with increased thickness (Fig. 5). FIBER MATERIALS AND SIZES Braided structures may be formed with fibers of a wide range of sizes, including from 1K carbon and below to 60K carbon or greater fiber sizes; 1K carbon is a single bundle (or tow) of carbon fiber containing 1000 individual filaments. Materials that can be these slots. A typical maypole braiding machine features two sets of spool carriers—one that travels clockwise and one that travels counterclockwise around the machine. To form a braided structure, bobbins or spools are filled with material and placed onto spool carriers. The material is then threaded through a series of yarn guides attached to the spool carrier. These carriers not only support the bobbins but also apply tension to each individual tow, or fiber bundle, as the braid is being formed. They also control the amount of fiber released as the spool carrier moves around the machine track. Typical spool carriers use springs to control the tension applied to each tow. Spool carriers generally feature a ratcheting mechanism that controls the amount of material released from the spool. As spool carriers move around the sinusoidal path of a standard maypole braiding machine, they move nearer and further from the vertical axis, or center, of the machine. The radial change in position of spool carriers allows for the intertwining of tows. Additionally, the yarn length supplied by each carrier must change in relation to each radial position such that each tow remains under tension. This yarn length is controlled by the spool carrier mechanisms. The structure of a braid formed by a maypole-style braiding machine is determined by the relationship of the speed with which the braided structure is taken up and the speed at which the horn gears turn. Additionally, the structure can be affected by the number of spool carriers loaded into the braiding machine. If two of the slots of the horn gear are filled, a 2 x 2 braided structure will be formed. In this 2 x 2 twill structure, each tow of material passes over two tows and under two tows as the spool carrier moves around the braiding machine track (Fig. 3b). If only one of the slots of the horn gear is filled, a 1 x 1 plain weave braided structure will be formed (Fig. 3a). In a 1 x 1 structure, each tow passes over one tow and under another tow in the braided structure. It is possible to form different braided structures, including 3 x 3, 4 x 4, and so on, by increasing the number of slots in the horn disk. For example, a 3 x 3 Hercules braid could be formed by increasing the number of horn gear slots from four to six slots (Fig. 3c). Formation of a braided structure will naturally occur at a formation point above the spool carriers (Fig. 4). The fiber interaction below the formation point is referred to as the braid shed. The formation of a braided structure is considered the point in the braiding process at which the inter- twining tows have become configured into the desired angles and coverage factor. Coverage is the degree to which gaps between the braided yarns in a braided structure are observed. High coverage indicates little to no gaps are observed, while low coverage indicates more space between fibers. A formation device may be placed at the formation point to aid in braid formation. Additionally, a formation device may be used in combination with a mandrel, which would be fixed in place and upon which the braid would form before being pulled up by a take-up device. While some maypole-style braiding machines are oriented such that the spool carriers move in a plane normal to a vertical axis, other machines may be constructed such that the track plates are oriented in a vertical plane (a) (b) (c) Fig. 3 — Braid architectures: (a) 1 x 1 plain weave; (b) 2 x 2 twill; and (c) 3 x 3 Hercules. Courtesy of A&P Technology. Fig. 4 — Formation of braided sleeving. Courtesy of A&P Technology.
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