Braiding Machines and the Technique of Braiding Fibre - Essay Example

Braiding Machines The technique of braiding fibre is an old technology used in manufacturing a vast range of products such as cables, insulators, and surgical sutures. After discovering the high tolerance of braided structures to damages and their conformability, braids are now being used to produce composites for rocket launchers and aircraft structures (Peters, 1998 p 413). Adanur (1995) describes a circular braiding machine as one which is made up of two sets with even number of spools that contain braiding yarns. One set of yarn runs in a clockwise direction around the centre of the machine, while the other yarn set turns in a counterclockwise direction. While the yarn sets revolve in two opposite directions, the carriers are redirected to pass alternately inside and outside (under and over) one another. The clockwise and counterclockwise directions cause the two yarn sets to overlap, and produce a tubular braid. The yarns from the machine's bobbins are collected over the hub of the circular path where the bobbins move. As the speed of the yarn carriers set at constant, the fabric's openness is changed by when the take-up speed of the fabric changes (Adanur, 1995 pp 133-134). Three-dimensional rotary braiding uses horngears which are positioned in a flat arrangement. Each horngear has a special clutch-brake mechanism, and this allows a controlled stop or rotation of each horngear and the corresponding bobbins. The grooves in the machine working plate guide the bobbins which are driven by the horngears. The switches which are located between each pair of horn gears can be activated in order to transfer the bobbin to an adjacent horngear (Langer et. al., 2001 pp 1-2). There are two types of braiding looms used to produce three-dimensional braids, the rectangular and circular looms. Rectangular looms are used to manufacture solid structures, while the circular loom is used in producing thick tubular structures (Peters, 1998 p 415). The Maypole braiding machine is used in the manufacture of three-dimensional braid structures. Its mechanical components are grouped into four categories, namely, track plate, horn gears, spool carriers, and fabric take-up mechanism (Adanur, 1995 p 135). Braiding technology The technique of braiding materials is useful in manufacturing near-net-shaped preforms. Braided preforms can be fabricated using various configurations such as bending type, branching off type, and variable diameter type by using program control (Uozumi and Hirukawa, 1999 p2). Langer et. al. (2001 p 1) states that the technology of three-dimensional braiding is based on the concept of the more traditional two-dimensional braiding technique. In the University of Massachusetts Advanced Composite Materials and Textile Research Laboratory, a difference between two-dimensional braided fabric structures and the three-dimensional braiding technology has been indicated. A two-dimensional braided fabric composite is a combination of thread weaving and winding. This process lends the braided structure its unique features. two-dimensional braided fabrics are produced with the use of carbon, glass, or nylon fibres. The three-dimensional braiding technology is uses a unique process to produce the three-dimensional fibre architecture called the preform, which is impregnated with matrix material and fused together to produce the final product (Chen and Sherwood, 2006 [Online]). In three-dimensional braiding, there is more versatility in placing the yarn sets and interlacing them by moving the bobbins independently from one another and selectively in a flat arrangement of horngears. (Langer, et. al., 2001 p 1) According to Langer, using this technique allows the production of near-net shaped three-dimensional fabric preforms with a yarn architecture that is specifically designed for a required design criterium. (Langer, et. al., 2001 pp 1-2). The braiding technique uses a method where two sets of yarns in specific yarn carriers move in counter-rotation around a circular frame (Kruckenberg and Paton, 1998, p 98). According to Peters (1998), the most commonly used process in the production of three-dimensional braids is track and column braiding. He said further that the mechanism of these methods is different from traditional horngear method in the way that the carriers are displaced to produce the final braid design (Peters, 1998 p 414). Kruckenberg (1998) stated that the braiding process can also use mandrels to make more intricate preform shapes. Through suitable design of a mandrel and the selection of braiding parameters, braided structures are produced above the mandrels which vary in cross-sectional shape or dimension along their strength. (Kruckenberg, 1998, p 98). Characteristics of braids Braiding is a technique of forming fabrics and is believed to be even older than the process of weaving (Adanur, 1995 p 133). Braiding can be classified into two, two-dimensional and three-dimensional braiding. Adanur (1955 p 133-134) further classified two-dimensional braid structures into circular and flat braids. Three dimensional braid structures, however, has been developed mainly to produce composite structures. Two-dimensional circular or flat braids are produced through a process where a number of yarns are diagonally crossed so that each yarn passes over and under one or more of the other. (Adanur, 1995, p 133). The most common patterns of two-dimensional braids include diamond braids, regular braids, and the Hercules braid. (Adanur, 1995 p 133) Two-dimensional braids have two layers of bias yarns which are linked together (Peters, 1998 p 415). In Adanur (1995 p 133) and Peters (1998 p 413), circular braids are produced as hollow structures around a core, and flat braids are formed as a flat strip or tape. Three-dimensional braids are constructed through a process where yarn sets are intertwined or interlaced in an orthogonal pattern to form a centre structure through position displacement. (Peters, 1998 p 413) Peters indicated further that the unique aspect of three-dimensional braids is their ability to provide through the thickness the reinforcement of composites as well as their instant adaptability to the manufacture of a wide range of complex shapes (Peters, 1998 p 413). Three-dimensional structures have three layers of yarn sets in a crisscross manner along a diagonal direction (Peters, 1998 p 415). Braided fabric composites are extensively used in various applications such as aerospace, automotive, biomedical, and recreational sports applications (Chen and Sherwood, 2006 [Online]). A braid is a fabric structure which is formed by interlacing two sets of filament or yarn in a way that their paths do not match the axis of the fabric. (Hristov, 2004, p ) Braided fabrics are processed using a system of two or more yarns which are intertwined in a way that all of the yarns are interlocked for most favourable distribution of load distribution ("American Composites Manufacturers Association", 2006 p 13). Braids can be classified into three main forms, namely, sleevings, flat braids, and overbraids. Sleevings has two sets of yarns which are continuous where fibres are set in a spiral pattern; flat braids have one yarn set, and this set is interwoven in a zig-zag pattern; in overbraids, fibres are braided directly to the cores which are placed during the braiding process (A&P Technology, 2006 p 5). The main braid architectures include biaxial, triaxial, and tailored structures. (A&P Technology, 2006 pp 5-6) Biaxial braids give reinforcement in the bias direction with fibre angles between 15 to 95, while triaxial braids give reinforcement in the bias direction with fibre angles of 10 to 80. ("American Composites Manufacturers Association", 2006 p 13) Advantages and disadvantages compared to knitted fabrics and woven fabrics Knitting, weaving, tufting, and braiding are the most common processes used in manufacturing fabrics. In knitting, a yarn system is interloped into columns (wales) and rows (courses) of loops. The two main types of knitting are weft knitting and warp knitting. The process of weaving uses interlacing and filling warps and yarns which are at right angles to each other. Different methods of interlacing and filling warps and yarn produce different fibre constructions. Braiding is considered to be the simplest process used to manufacture fabrics. In braiding, two sets of yarns are interlaced in a diagonal pattern and move in opposite directions (Adanur, 2000 p 1). Braided fabrics, especially those manufactured using the three-dimensional process, have several advantages over their knitted and woven counterparts, especially the three-dimensional braids. The near-net shape of braided fabrics give them structural integrity and unique design flexibility (Xiao et. al., 1994 p 1281). According to Xiao et. al. (1994 p 1281), braided composites have good mechanical behaviour, increased tensile and flexural strengths, and resistance to impact and fatigue. The various processes which use braided structures include autoclave, protrulsion, and various moulding processes such as compression, resin transfer, reaction injection, and open moulding (A&P Technology, 2006 p 4). The process of braiding reduces production costs, and has the versatility in producing composites which can be designed using various configuration, materials, and fibre orientation (Uozumi and Hirukawa, 1999 pp 5-8). Adanur (1995 p 134) states that braided structures fit well to the centre of the tubes and sleeves which make them easy to manufacture and produce, unlike knitted and woven structures which are difficult to mould. Three-dimensional preforms also have less crimp than knitted and woven fabrics, which make them highly effective in mechanical uses (Mallick, 1997 p 391). Mallick (1997 p 391) further state that knitted and woven structures are weak compared to their braided counterparts who has high tolerance for tension and damage. According to Hristov (2004), braided preforms show nonlinear behaviour under tensile loads in the axial direction. At higher tensile loads, the yarns crimp, swapping occurs, and the braid diameter is reduced due to the rearranged yarns. (Hristov, 2004 p 1) At this point the braid extends due to crimp reduction and the yarn's reorientation. If the load is increased, the braids elongate. (Hristov, 2004 p 1) Why is braided composite to be considered than other textile structures Uozumi and Hirukawa (1999) claim that braiding is a unique technology that can be used to different configurations, using various materials and moulding methods for optimum use. Braiding is a useful and versatile method used in producing near-net shaped structures, which can be fabricated under different configurations, e.g., bending type, branching off, and variable diameter, to produce different braided products. Various materials such as carbon, aramid, glass, and silicon, together with yarn, can be used to produce hybrid fibres (Uozumi and Hirakawa, 1999 pp 1-3). Compared to knitted and woven materials, braided structures are cost-effective and least expensive. This is due to recent technological developments in braiding process, the material's superior conformability, and the unique predictability of the material's design. This design makes braided structures ideal because braids conform to the exact shape of the material that it needs to reinforce. This also reduces the time for labour devoted to manufacturing, and therefore reduces manufacturing costs. ("American Composites Manufacturers Association", 2006 pp 12-13). Three-dimensional braids also show less stiffness and superior strength quality compared to other composite structures. Compared to standard braids which have limited stability, three-dimensional structures can be easily moulded to other materials, thus, eliminating other costly processes such as cutting and sewing. Three-dimensional braids also have high bearing capacity compared to other braided fibres which were manufactured using other techniques. (Langer et. al., 2001 pp 7-8) The current and future capability of braided fabrics in aerospace industry Braids are preferred as reinforcement materials in a wide range of applications including industrial, medical, recreational, and aerospace. In its industrial value, braids are used as the main load bearing reinforcement material in cross beams, car air bags, furniture, and lamp poles. These are also used as partial reinforcement in boat hulls and shipping containers. For medical uses, braided structures and preforms are extensively used for prosthetic limbs, orthotic braces, surgical tools like endoscopes and catheters, and implant devices like splints and stents. Recreational tools which use braided materials include wind bicycle components, baseball bats, surfing mats, snowboards, water skis, sail masts, hockey sticks, and tennis racquets (A&P Technology, 2006 pp 3-4). In the aerospace industry, braided structures are used in applications such as: aircraft engine containment, jet and airplane propeller blades, engine stator vanes, ducts and tubes, and various satellite components (A&P Technology, 2006 p 3). The United States National Aeronautics and Space Administration (NASA) have been conducting extensive research and development using three-dimensional braided preforms. A study on woven, knitted, stitched, and braided composites was done from 1985 to 1997 and the results have been published in a technical paper. Composite preforms as structural components have been studied and NASA states that multi-axial composite preforms provide through-the-thickness reinforcement which in turn produces laminates with superior damage tolerance. It was also deducted from the NASA study that after extensive cost analyses were performed, braided frames have significant cost advantage (Dow and Dexter, 1997 pp 2-3, 13). Bibliography A&P Technology. 2006. Braid FAQs. [Primer] Adanur, S. 1995. Wellington Sears Handbook of Industrial Textiles. Switzerland: Wellington Sears Company. Adanur, S. 2000. Handbook of Weaving. Florida: CRC Press LLC. American Composites Manufacturers Association. 2006. Composites Basics: Materials. [Primer]. Buckley, J.D. and Dandy Dale Edie (eds). 1993. Carbon-carbon materials and composites. New Jersey: Noyes Publication. Chen, Julie and James Sherwood. 2006. Braiding. [Online] Advanced Composite Materials and Textile Research Laboratory, University of Massachusetts Lowell. Available: http://m-5.uml.edu/acmtrl/research-Braiding.htm Dow, Marvin B. and H. Benson Dexter. 1997. Development of Stitched, Braided and Woven Composite Structures in the ACT Program and at Langley Research Center (1985 to 1997) Summary and Bibliography. Virginia: National Aeronautics and Space Administration. Hristov, K. 2004. Mechanical Behavior of Circular Hybrid Braids Under Tensile loads. Textile Research Journal. January 2004. Kruckenberg, T. and R. Paton. (eds.) 1998. Resin Transfer Moulding for Aerospace Structure. Langer, H. A. Pickett, B. Obolenski, H. Schneider, M. Schneider, and E. Jacobs. 2001. Computer Controlled, Automated Manufacture of 3D-Braids for Composites. National Science Foundation Workshop on Composite Sheet Forming, Lowell, Massachusetts, 5-7 September, 2001. Mallick, P.K. (ed). 1997. Composites Engineering Handbook. New York: Marcel Dekker Inc. Peters, S.T. (ed.). 1998. Handbook of Composites. 2nd Ed. London: Chapman and Hall. Uozumi, Tadashi and M. Hirukawa. 1999. Braiding Technologies for Commercial Applications. Oral Paper in the 6th International SAMPE Symposium and Exhibition, Tokyo, 26-29 October 1999. Xiao, L., J. Li, and F. Dong. 1994. The Properties of 5-D Reinforced Organic Silicon Composites. Proceedings of the American Society for Composites, University of Delaware, 20-22 September 1994, pp. 1281-1282. Newark: Technomic Publishing Company. Read More