Progress in the forming process of the hottest res

Progress in forming technology of resin matrix composites (III)

(4) weaving

weaving is a basic textile process, which can make more than two yarns interweave with each other in an oblique or longitudinal direction to form a preform with an overall structure. This process can usually produce preforms with complex shapes, but its size is limited by the size of equipment and yarn. In the aviation industry, at present, this technology mainly focuses on weaving equipment, production and geometric analysis. The ultimate goal is to achieve fully automated production, and integrate equipment and technology with cad/cam. This technology is generally divided into two categories, one is two-dimensional knitting technology, and the other is three-dimensional knitting technology

the traditional two-dimensional weaving process can be used to manufacture preforms of complex tubular, concave or planar parts, and its cost is relatively low compared with other textile technologies. Its research mainly focuses on the research and development of automatic knitting machines to reduce production costs and expand the scope of application. Its key technologies include quality control, fiber direction and distribution, mandrel design and so on. Its applications in the aviation industry include the manufacture of aircraft inlet and fuselage J-shaped spacer frames. This technology is usually used in combination with RTM and RFI technology. In addition to the three intelligent basic configurations: host computer, microcomputer and printer, it can also be used in combination with extrusion and molding. Its application level can best reflect its progressiveness in the manufacturing of F-35 fighter inlet manufactured by Lockheed Martin company by setting a movable jaw seat on the frame. The stiffener and the inlet shell are an integral structure, reducing 95% of fasteners, improving aerodynamic performance and signal characteristics, and simplifying the assembly process. In order to overcome the problem of low strength in the thickness of two-dimensional braiding, three-dimensional braiding technology is developed, which makes it possible to manufacture non residual preforms. However, this technology is also limited by the size of the equipment

at present, general weaving equipment can only produce preforms with a cross-section of less than 100mm, while the large-scale of aircraft parts requires large-size and expensive knitting machines. Although this technology has been developed since the 1960s, it has experienced four-step weaving, two-step weaving and multi-layer interlocking weaving technology. With the development of 3D braiding machine, it still has great application potential in the future of aircraft manufacturing. The three-dimensional braided C, J, t plates, I-beam, connecting rod, body girder, F-frame, barrel parts of the body, etc. have been verified

(5) knitting

the reinforced structure of knitted composites began in the 1990s. Because its directional strength and impact resistance are better than those of woven composites, and the coil structure of knitted fabrics has great extensibility, it is easy to manufacture non load bearing components with complex shapes. At present, advanced industrial knitting machines have been produced abroad, which can quickly produce complex near zero allowance structures with less material waste. The preform made by this method can be selectively used in some parts to enhance the mechanical properties of the structure by adding directional fibers. In addition, the knitted structure of this coil is easy to deform when subjected to external forces, so it is suitable for forming holes in composite materials, which has great advantages over drilling. However, its low mechanical properties also affect its wide application

(6) warp knitting

knitting has great potential in the aerospace industry. The multi axial and multi-layer warp knitted fabric made by using warp knitting technology and combining with the concept of fiber placement is generally called warp knitted fabric. Because this material does not bend, the fiber can be arranged in the best form by a tool developed by NASA. Warp knitting technology can obtain thick multi-layer fabrics and determine the fiber direction as expected. Because there is no need to lay more layers, it greatly improves economic benefits. At present, a variety of wide width glass and carbon fiber warp knitted fabrics can be obtained in the market abroad. This preform has two advantages: first, it has low cost compared with other textile composite preforms; Second, it has the potential to surpass the traditional two-dimensional prepreg laminate. Because the products are mainly used in the leaf filter, filter, filter press, belt filter and other equipment of alumina and copper smelting enterprises, its fiber is straight, which can be strengthened in the thickness direction, so as to improve the interlaminar performance of the material. But at present, the main reasons that restrict its application are the high cost of raw materials and the insufficient degree of marketization. Foreign aerospace industry departments are studying the application of this technology to secondary and main load-bearing components, which has been verified on aircraft wing stringers and wing panels, and it is expected to be widely used in aircraft manufacturing in the future

in view of the above preform manufacturing technology, foreign countries have also carried out a variety of research in recent years, such as the US Air Force implementing the oblique weave preform development plan for composite structures and canceling the layering process, so as to reduce the complexity and cost of processing the overall composite structure