A preform molding method based on directional gradient expansion

Abstract

The present application relates to the technical field of preform forming, and particularly relates to a preform forming method based on directional gradient expansion. In the technical solution, at least one interlacing core is arranged, and a basic framework is interlaced at each interlacing core. The basic framework is used as a starting position, and subsequent yarns are introduced in a preset direction around the basic framework in sequence to realize directional gradient expansion, so that the preform is obtained by interlacing. Since the yarns constituting the basic framework are in a curved form, the yarn form of the subsequent yarns and the existing yarns at the interlacing points is controllable. Therefore, the preform is suitable for high-curvature curved surfaces or special-shaped components with requirements for deformation coordination in different directions.

Description

Technical Field

[0001] This invention relates to the field of preform molding technology, and in particular to a preform molding method based on directional gradient expansion. Background Technology

[0002] In aerospace, rail transportation and other fields, the demand for high-performance composite material components with complex stress structures (such as cylindrical shells and shaped tubes) is increasing. The commonly used three-dimensional fabrics mainly have orthogonal triaxial and 2.5D structures. The orthogonal triaxial structure is composed of orthogonal combinations of yarns in the X, Y and Z directions (i.e., including axial yarns, circumferential yarns and radial yarns). The 2.5D structure usually refers to a shallow cross-bending or shallow cross-straight-bending structure (i.e., including axial yarns and circumferential yarns). Among them, the axial yarn is also called warp yarn, the circumferential yarn is also called weft yarn, and the radial yarn is also called normal yarn.

[0003] In the field of fiber preform molding, whether it is an orthogonal triaxial structure or a 2.5D structure, the molding method is relatively simple: first, yarns in one direction are laid, and then yarns in the other direction are laid. However, this molding method is not suitable for irregularly shaped components (such as dome-shaped or dumbbell-shaped components), especially for irregularly shaped components with high curvature surfaces or requirements for deformation coordination in different directions (i.e., the deformation coordination between straight yarns that play a load-bearing role and curved yarns that play a deformation role).

[0004] Therefore, there is an urgent need to provide a preform forming method and a preform based on directional gradient expansion to solve the above-mentioned technical problems. Summary of the Invention

[0005] This invention provides a preform forming method based on directional gradient expansion, which can be effectively applied to irregularly shaped components with high curvature surfaces or deformation coordination requirements in different directions.

[0006] In a first aspect, embodiments of the present invention provide a preform forming method based on directional gradient expansion, comprising: Identify at least one entangled core of the preform; A basic skeleton is woven at each of the said weaving cores; wherein, the basic skeleton includes at least interlocked axial yarns and circumferential yarns, and the yarns constituting the basic skeleton are in a curved shape; Using the basic skeleton as the starting position, subsequent yarns are introduced sequentially around the basic skeleton in a predetermined direction for directional gradient expansion to weave a preform; wherein, the yarn shape of the subsequent yarns and the existing yarns at the interlacing point is controllable, and the yarn shape includes a straight shape and a curved shape, and two adjacent basic skeletons can be interlaced by expanding the weaving.

[0007] Secondly, embodiments of the present invention provide a preform formed by winding using the method mentioned in the above embodiments.

[0008] Beneficial effects: According to the embodiments of the present invention, a preform forming method and a preform based on directional gradient expansion are provided. This involves setting at least one winding core and winding a basic skeleton at each winding core. Using this basic skeleton as the starting point, subsequent yarns are successively introduced around the basic skeleton in a predetermined direction for directional gradient expansion to obtain the preform. Because the yarns constituting the basic skeleton are curved, the yarn shape of subsequent and existing yarns at the interlacing points is controllable. Therefore, this preform is suitable for high-curvature surfaces or irregularly shaped components requiring deformation coordination in different directions. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 A schematic flowchart of the preform forming method based on directional gradient expansion provided in an embodiment of the present invention; Figure 2 A schematic diagram of a basic skeleton provided for an embodiment of the present invention; Figure 3 This is a schematic diagram of a hybrid bending structure provided in an embodiment of the present invention. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0012] like Figure 1 As shown, this embodiment of the invention provides a preform forming method based on directional gradient expansion, comprising: Step S1: Determine at least one woven core of the preform; Step S2: Weave a basic skeleton at each weaving core; wherein, the basic skeleton includes at least interlocked axial yarns and circumferential yarns, and the yarns constituting the basic skeleton are in a curved shape. Step S3: Using the basic skeleton as the starting position, introduce subsequent yarns one by one along a preset direction around the basic skeleton to carry out directional gradient expansion in order to weave a preform; wherein, the yarn shape of the subsequent yarns and the existing yarns at the interlacing point is controllable, and the yarn shape includes straight shape and curved shape, and two adjacent basic skeletons can be interlaced by expanding the weaving method.

[0013] In this embodiment, at least one winding core is set, and a basic skeleton is woven at each winding core. Using this basic skeleton as the starting point, subsequent yarns are introduced sequentially around the basic skeleton in a predetermined direction for directional gradient expansion, thus obtaining a preform. Because the yarns constituting the basic skeleton are curved, the yarn shape of subsequent and existing yarns at the interlacing points is controllable. Therefore, this preform is suitable for high-curvature surfaces or irregularly shaped components requiring deformation coordination in different directions.

[0014] Understandably, directional gradient expansion can be either surface expansion or volume expansion. Surface expansion refers to expansion along any plane formed by X / Y / Z during the weaving process, such as expansion along the XY plane, the YZ plane, or the XZ plane. Volume expansion refers to simultaneous expansion along the planes formed by X / Y / Z. For example, when weaving a cylinder, the axial (Z-direction) yarn increases slowly to control the length, while the radial (X, Y-direction) yarns increase rapidly and synchronously to achieve diameter expansion; at the spherical end of a dumbbell shape, the three-dimensional yarns need to be accelerated to form a spherical profile.

[0015] For the expansion molding method of 2.5D structural preforms, the traditional 2.5D woven preform preparation method usually adopts the "bent warp yarns, straight weft yarns" approach, where the bent warp yarns run through the thickness direction to bind the straight weft yarns. This structure has only one system of fiber bending, i.e., single bending. When facing preforms with large curvature, there are inherent limitations: only the warp yarns can provide limited bending adaptability, while the straight weft yarns, which are the main load-bearing direction, are difficult to slide and redistribute in-plane. This results in poor shape adjustability when the preform needs to deform in multiple directions, and wrinkles, buckling, or resin-rich areas are easily generated on the surface of the preform, making it difficult to form complex Gaussian curvature surfaces with high quality.

[0016] Currently, the manufacturing of complex curved fiber preforms such as spheres and domes, both domestically and internationally, mainly involves near-net-shape weaving of simple curved surfaces. A fundamental limitation exists: existing near-net-shape weaving techniques struggle to simultaneously and controllably achieve bending and area expansion of the fiber network in both warp and weft directions, making it impossible to directly "grow" high-curvature surfaces with high quality. The directional gradient expansion molding method proposed in this invention uses a basic skeleton as the starting point, successively introducing subsequent yarns along a predetermined direction to achieve directional gradient expansion. This weaving process yields a preform with controllable yarn morphology at the interlacing points, allowing each yarn to provide a certain degree of bending adaptability. This provides an innovative solution for obtaining a preform with optimal fiber structure and no defects in a single operation.

[0017] Traditional molding processes for expanding orthogonal triaxial preforms have the following problems: 1) Subtractive process: mechanical processing from large 3D woven blocks, cutting fibers, severely damaging performance; 2) Molding and filling process: molding short fibers or preform fragments with resin, resulting in discontinuous fibers and low performance; 3) Additive manufacturing process: current composite material 3D printing has limited fiber length, coarse orientation control, and poor interlayer performance. This invention proposes a "volume-expandable and shape-adjustable preform molding" method. Its purpose is to control the yarns in three orthogonal directions (X, Y, Z) to grow and extend in a gradient direction during the weaving process, continuously increasing the number of fibers involved in the weaving. This allows the preform to gradually expand its volume from an initial core point or small volume and precisely shape into a target three-dimensional solid shape, achieving "weaving as shaping".

[0018] It should be noted that winding is a technology that uses dry fibers to create a three-dimensional preform through the synergy of textile technologies. Compared to weaving, it places greater emphasis on winding and weaving. In other words, winding is a forming process that combines winding and weaving, introducing continuous fibers or yarns into an interwoven yarn system and winding them along a mandrel or spatial path.

[0019] In one embodiment of the present invention, the preform is a 2.5D structure, and the basic skeleton includes an axial yarn and a circumferential yarn that are interlocked and fixed.

[0020] like Figure 2 As shown, in one embodiment of the present invention, the preform is a 2.5D structure, and the basic skeleton includes two axial yarns and two circumferential yarns, both of which are curved. The two axial yarns are parallel to each other, and the two circumferential yarns are parallel to each other. Each axial yarn is interlocked and fixed with the two circumferential yarns respectively.

[0021] In one embodiment of the present invention, the preform is an orthogonal three-dimensional structure, and the basic skeleton includes an interlocked and fixed axial yarn, a circumferential yarn and a radial yarn.

[0022] In one embodiment of the present invention, at least one subsequent yarn is introduced each time.

[0023] like Figure 3 As shown, in one embodiment of the present invention, the number of subsequent yarns introduced each time is an even number, and the two subsequent yarns are symmetrically arranged relative to the basic skeleton.

[0024] Please continue reading. Figure 3 In one embodiment of the present invention, when the subsequent yarn passes through the existing yarn, the existing yarn has an opening at the interlacing point, and the subsequent yarn can pass through the opening. At this time, the subsequent yarn is in a straight shape and the existing yarn is in a curved shape, so that the subsequent yarn and the existing yarn form a mixed curved structure.

[0025] Please continue reading. Figure 3 In one embodiment of the present invention, the hybrid bending structure is bent and extended along its diagonal direction.

[0026] In one embodiment of the present invention, in the hybrid bending structure, the length of the bent yarn between two adjacent yarns is 5~50mm.

[0027] Taking a 2.5D structure of warp and weft yarns as an example, the core of this invention lies in changing the way and order in which the warp and weft yarns are introduced, so that both the warp and weft yarns can be periodically bent in the structure, thereby greatly improving the deformation coordination ability and overall expansion performance of the preform in both warp and weft directions. The expansion direction of the preform in this invention is formed by the interweaving of multiple weft yarns and multiple warp yarns. When the preform is formed by winding, the warp and weft yarns are introduced alternately, one by one, and interwoven with each other, and the forming direction is to expand outward from the center starting point.

[0028] Specifically, within the plane of the preform, a warp yarn is first introduced. The weft yarn introduced immediately after it does not simply pass over or under the warp yarn, but rather forms an interlocking, curved interlacing point with the warp yarn and the yarns of adjacent layers. Then, the next warp yarn interlaces with the weft yarn in a similar manner, and this process is repeated alternately. Through this alternating, sequential introduction of each warp and weft yarn, each yarn exhibits a periodic, wavy, curved shape within the preform. All interlacing points together constitute a three-dimensional, uniformly distributed spatial grid connection structure, giving the warp and weft yarns good sliding and redistribution properties in both in-plane directions.

[0029] Furthermore, this invention defines and controls key parameters of yarn bending: Bending length: The length of each warp or weft yarn within a complete bending cycle is called the bending length, which ranges from 5mm to 50mm and is adjusted according to the curvature of the target surface. The smaller the bending length, the denser the interlacing points, and the stronger the structural adaptability.

[0030] Bending curvature: The radius of curvature of the yarn at the bend apex. The smaller the radius of curvature, the greater the degree of bending, and the stronger the expansion capability of the preform in the corresponding direction.

[0031] Bending areas: The bending of yarns is not limited to the warp and weft axes, but can also be set along diagonal directions (i.e., directions forming a 45° angle with the warp and weft directions), forming "diagonal bending areas". Such bending areas can significantly improve the deformation coordination of precast structures under oblique forces and avoid stress concentration.

[0032] Yarn tension: During the introduction of each yarn, a constant tension is applied through the end fixing device. The tension value is adjusted according to the yarn material, diameter, and target curvature. Excessive tension can easily lead to yarn breakage, while insufficient tension will loosen the bending structure, increase the porosity of the structure, and reduce the expansion effect.

[0033] Hybrid bending structure: During the weaving process, some yarns remain straight between interlacing points, while others remain bent, forming a hybrid bending structure. The lengths of the straight and bent sections are adjustable to achieve a balance between local rigidity and overall expansion performance.

[0034] Please continue reading. Figure 2 Using the central area at the top of the prefabricated structure as a positioning reference, two warp yarns and two weft yarns, for a total of four yarns, are introduced. These four yarns are arranged in an orthogonal, staggered pattern and interlocked at the central interlacing point. Each yarn is tensioned along a pre-defined target curved surface, and its two ends are fixed. Because each yarn is tensioned along the curved path, all four yarns exhibit a periodic wavy bending shape after fixing, i.e., a double-bending structure (both warp and weft yarns are bent). These initial four yarns form the basic framework for the expansion of the prefabricated structure.

[0035] After the initial four yarns are fixed, subsequent yarns (single or multiple) are introduced sequentially. A position is selected in the existing yarn network where the yarn to be introduced is called the warp. An opening is created in this warp to allow the subsequent yarn to enter. The newly introduced yarn, called the weft, is passed through the opening formed by the existing yarn in a straight line, remaining straight after entering the opening. After passing through the opening, the new yarn interlocks with the existing yarn at the interlacing point. This interlocking transforms the existing yarn from a straight state to a curved state. Due to the constraint of the curvature of the opening space during the passage, the new yarn will experience slight local bending near the interlacing point, but its main body remains straight, and both ends of the new yarn are fixed. If the existing yarn is not open, and the subsequent yarn is simply laid flat on top of it, the existing yarn will not bend. Thus, the bending shape during the expansion process can be controlled by adjusting whether the existing yarn is open.

[0036] Please continue reading. Figure 3When each introduced yarn reopens, the newly introduced yarn remains straight within the existing yarns, while the introduced yarn remains curved at the subsequent opening. This results in both straight and curved states, known as mixed curvature. Furthermore, the ratio of straight to curved lengths in the mixed curvature structure can be adjusted according to design requirements. A higher proportion of straight lengths results in greater rigidity and dimensional stability in the corresponding direction; a higher proportion of curved lengths results in greater surface expansion capability and surface adaptability. Mixed curvature regions can be locally located at the edges or curvature transition zones of the preform to achieve a performance gradient distribution.

[0037] During the subsequent alternating introduction of yarns, if yarns are added sequentially along the four directions (i.e., the front, back, left, and right sides of the preform plane), yarns located diagonally (at approximately 45° angles to both warp and weft directions) will automatically appear in the hybrid bending structure. Due to the alternating compression and interlocking effect of the yarns from the four orthogonal directions, a periodic bending state will naturally form without the need for additional pre-setting of bending paths. Since the yarns in the diagonal direction are all in a bent state, when the preform is subjected to oblique loads, the bent yarns can absorb energy and disperse stress through their own deformation (elongation or compression) and relative sliding, thereby significantly improving the deformation coordination ability and expansion performance of the preform in the diagonal direction.

[0038] Taking an orthogonal three-dimensional structure as an example, based on the contour and internal structural requirements of the target shape at its current position, the number of yarns involved in the weaving in the X, Y, and Z directions is increased synchronously and in a controlled manner. For example, when weaving a solid sphere, starting from the core, the number of three-dimensional yarns increases proportionally to the increase in the radius of the sphere in each radial direction towards the sphere. Each newly introduced yarn moves along a predetermined three-dimensional spatial trajectory and interweaves with the existing yarn network in space (such as orthogonal interlacing, angular interlocking, etc.) to form a solid overall structure. By precisely controlling the rate and number of yarns introduced at different positions and in different directions (which can be six directions), the expansion rate and direction of the local volume of the prefabricated body are dynamically adjusted, thereby shaping its shape in real time. This process continues, with the X, Y, Z and corresponding circumferential yarns continuously introduced from the outside and integrated into the outer boundary of the prefabricated body, pushing the boundary to expand outward, while the internal yarn density increases uniformly, ultimately forming a completely solid prefabricated body with continuous fiber penetration, no internal seams, and a shape consistent with the design model.

[0039] The advantages of the directional gradient expansion of this invention can be summarized as follows: 1) By incorporating bionic principles, plants can achieve the entanglement and shaping of complex, irregular three-dimensional structures based on the direction of sunlight (directional gradient).

[0040] 2) Expanding from a point to an area and then to a volume: fibers in different directions form different openings according to the fabric structure, achieving 2.5D, orthogonal three-dimensional, reinforced structure customized design and molding. "Volume expansion" involves increasing the size in six directions, and when the size in a certain direction (such as the ZZ direction) does not increase, it can be transformed into the "area expansion" method.

[0041] 3) By leveraging the concept of spatial discrete points, multiple cores can "grow" simultaneously, improving forming efficiency.

[0042] In addition, embodiments of the present invention also provide a preform formed by winding as described in any of the above embodiments.

[0043] It should be noted that the preform provided in this embodiment has the same inventive concept as the method embodiment described above, and therefore the two have the same beneficial effects. The beneficial effects of the preform will not be elaborated here.

[0044] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0045] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A preform forming method based on directional gradient expansion, characterized in that, include: Identify at least one entangled core of the preform; A basic skeleton is woven at each of the said weaving cores; wherein, the basic skeleton includes at least interlocked axial yarns and circumferential yarns, and the yarns constituting the basic skeleton are in a curved shape; Using the basic skeleton as the starting position, subsequent yarns are introduced sequentially around the basic skeleton in a predetermined direction for directional gradient expansion to weave a preform; wherein, the yarn shape of the subsequent yarns and the existing yarns at the interlacing point is controllable, and the yarn shape includes a straight shape and a curved shape, and two adjacent basic skeletons can be interlaced by expanding the weaving.

2. The method according to claim 1, characterized in that, The preform has a 2.5D structure, and the basic skeleton includes an axial yarn and a circumferential yarn that are interlocked and fixed.

3. The method according to claim 1, characterized in that, The preform has a 2.5D structure. The basic skeleton includes two axial yarns and two circumferential yarns, both of which are curved. The two axial yarns are parallel to each other, and the two circumferential yarns are parallel to each other. Each axial yarn is interlocked and fixed with the two circumferential yarns respectively.

4. The method according to claim 1, characterized in that, The preform is an orthogonal three-dimensional structure, and the basic skeleton includes an interlocked and fixed axial yarn, a circumferential yarn and a radial yarn.

5. The method according to claim 1, characterized in that, Each subsequent yarn introduced must be at least one.

6. The method according to claim 5, characterized in that, Each time an even number of subsequent yarns are introduced, the subsequent yarns are arranged symmetrically with respect to the basic skeleton.

7. The method according to any one of claims 1-6, characterized in that, An opening is provided at the interlacing point of the existing yarn, allowing the subsequent yarn to pass through the opening. At this point, the subsequent yarn is in a straight shape, while the existing yarn is in a curved shape, so that the subsequent yarn and the existing yarn form a mixed curved structure.

8. The method according to claim 7, characterized in that, The hybrid bending structure bends and extends along its diagonal direction.

9. The method according to claim 7, characterized in that, In the hybrid bending structure, the length of the bent yarn between two adjacent yarns is 5~50mm.

10. A prefabricated body, characterized in that, The method described in any one of claims 1-9 is used for winding and forming.

Images