A trajectory design method for trapezoidal cross-section grid structures

Abstract

The present invention provides a trajectory design method for a trapezoidal cross-section grid structure, including: designing two circumferential and longitudinal basic trajectories that are completely fitted with the lower bottom surface of the trapezoidal cross-section grid structure rib; calculating the number of laying layers that are offset once according to the slope of the trapezoidal cross-section grid structure and the thickness of the single wire of the prepreg; obtaining the offset trajectories of the longitudinal reinforcement and the annular reinforcement respectively by changing the mold rotation angle and the axial position of the wire laying head; arranging the laying order and position at the grid structure node based on the number of offset cycles; dividing the node area into four areas: upper left, lower left, upper right, and lower right, and the annular reinforcement and the longitudinal reinforcement are alternately laid four times as one laying cycle; the next offset cycle laying starts to deviate from the position where the previous offset cycle laying process ends as a reference, repeating steps 2-4, and completing the laying process of the entire annular longitudinal reinforcement grid structure. The present invention has simple steps, does not destroy the continuity of the fiber, and can minimize the accumulation of the fiber.

Description

Technical Field

[0001] The invention belongs to the technical field of automatic placement and forming of advanced composite materials, and in particular relates to a trajectory design method for a trapezoidal cross-section grid structure. Background Art

[0002] Composite mesh structure is a composite material structure, which is widely used in the aerospace field due to its high specific strength, high specific stiffness and strong structural bending resistance. A major advantage of mesh structure is that it can be manufactured automatically at low cost. The use of automatic placement molding process to manufacture mesh structure can reduce a lot of manual operations and greatly improve production efficiency. According to the characteristics of fiber placement process, the structure of the node area and the trajectory of the fiber can be designed.

[0003] At present, there are many node trajectory planning algorithms: (1) Cut the fiber at the node, and achieve equal thickness at the node and the grid structure rib through the functions of cutting, stopping, and feeding, and adopt different cutting strategies for each layer. (2) Open equal volume grooves at the node position of the mold to change the trajectory of the fiber near the node. Each layer of fiber is alternately bent and offset in the direction of the fiber width to achieve equal thickness at the node and rib area.

[0004] However, the existing trajectory planning algorithms have the following problems: although cutting the fibers can achieve equal thickness of the node area and the ribs, it destroys the continuity of the fibers and increases the porosity in the node area, thereby reducing the performance of the structure; although turning the fibers at the nodes can ensure the continuity of the fibers, it introduces in-plane bending of the fibers, reducing the strength of the mesh reinforcement.

[0005] How to optimize the trajectory design process in the node area to minimize fiber accumulation while ensuring fiber continuity and reducing fiber bending has become an urgent problem to be solved in the industry. Summary of the invention

[0006] In order to solve the above problems, the present invention discloses a trajectory design method for a trapezoidal cross-section grid structure, which has simple steps and does not destroy the continuity of the fibers while minimizing the accumulation of the fibers.

[0007] The technical solution to achieve the purpose of the present invention is:

[0008] A trajectory design method for a trapezoidal cross-section grid structure comprises the following steps:

[0009] Step 1: Design the circumferential and longitudinal basic tracks that are completely in line with the lower bottom surface of the trapezoidal cross-section grid structure rib on the mold surface;

[0010] Step 2: Calculate the number of shifted layup layers N and the number of shift cycles k based on the slope of the trapezoidal cross-section grid structure, i.e., the trapezoidal busbar, and the thickness of the single filament of the prepreg;

[0011] Step 3: By changing the mold rotation angle and the axial position of the wire laying head, the positions of the offset trajectories of the longitudinal reinforcement and the annular reinforcement are obtained respectively;

[0012] Step 4: Based on the offset cycle number k, arrange the laying order and position at the grid structure nodes; divide the node area into four areas: upper left, lower left, upper right, and lower right. The circular reinforcement and longitudinal reinforcement are laid alternately four times for one laying cycle. After k cycles, one offset laying process is completed.

[0013] Step 5: The next offset cycle placement starts from the position where the previous offset cycle placement processing ended, repeating steps 2, 3, and 4 to finally complete the placement processing of the entire ring longitudinal reinforcement grid structure.

[0014] Compared with the prior art, the present invention has the following significant advantages:

[0015] This method ensures the fiber continuity of the longitudinal and annular reinforcements. At the same time, the reinforcements are laid in a straight line according to the fiber direction, solving the problem of fiber bending in the commonly used node steering method. By coordinating the placement and alternating sequence of the annular and longitudinal reinforcements, the fiber accumulation and overhead area are reduced, so that the resin flows more fully during curing, the interlayer bonding is closer, and the strength performance of the grid reinforcement is finally improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the front view of the trapezoidal cross-section grid structure mold.

[0017] Figure 2 It is a schematic diagram of the basic trajectory of the grid structure; (the area enclosed by the two dotted lines 1 is the placement of longitudinal reinforcement prepreg, the area enclosed by the two dotted lines 2 is the placement of annular reinforcement prepreg, the area enclosed by the two thin solid lines is the bottom surface of the trapezoidal section, the area enclosed by the two thick solid lines is the upper surface of the trapezoidal section, and the shaded part is the overlapping area at the rib nodes) where: ------- is dotted line 1; …………… is dotted line 2.

[0018] Figure 3 Schematic diagram of the position of an offset trajectory of the grid structure.

[0019] Figure 4 Schematic diagram of the laying sequence at the grid structure nodes.

[0020] (a) is a top view with the circular reinforcement on the left and the longitudinal reinforcement on the top;

[0021] (b) is a top view with the circular reinforcement on the right and the longitudinal reinforcement on the bottom;

[0022] (c) is a top view with the circular reinforcement on the left and the longitudinal reinforcement on the bottom;

[0023] Among them, (d) is a top view with the circular reinforcement on the right and the longitudinal reinforcement on the top. DETAILED DESCRIPTION

[0024] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. It should be noted that the words "front", "rear", "left", "right", "upper" and "lower" used in the following description refer to directions in the accompanying drawings, and the words "inner" and "outer" refer to directions toward or away from the geometric center of a specific component, respectively.

[0025] Step 1: According to Figure 1 The mold shown in the figure has grid rib grooves intersecting with longitudinal rings on the mold surface, and the cross-section of the grid rib groove is an isosceles trapezoid. The grid structure information of the trapezoidal cross-section is obtained, and the prepreg tow width b is automatically laid, which is the same as the bottom width of the trapezoidal groove. According to the upper side length a, lower side length b and height h of the rib groove trapezoidal cross-section, the sine formula θ=arctan[2h / (ab)] is used to obtain the bottom angle θ of the long side of the trapezoid, where the upper side length a does not exceed twice the lower side length b, and the groove depth h is 10 to 15 mm. According to the rib groove information, the circumferential and longitudinal basic trajectories that are completely in contact with the lower bottom surface of the trapezoidal cross-section grid structure rib are designed, as shown in FIG. Figure 2 ;

[0026] Step 2: When the distance x between the edge of the track placement area and the waistline of the trapezoidal section is greater than 0.5 mm, the placement track is offset. According to the bottom angle θ of the long side of the trapezoidal section and the thickness t of the single filament of the prepreg, the number of offset cycles k and the number of offset placement layers N are calculated, k = xtanθ / 4t, k is an integer, N = 4k;

[0027] Step 3: By changing the mold rotation angle and the axial position of the wire laying head, the offset trajectory positions of the longitudinal reinforcement and the annular reinforcement are obtained. The mold rotation axis in the laying structure rotates a certain angle to offset the longitudinal reinforcement trajectory. The rotation angle is α = 180 × x / πR. Based on the centerline of the longitudinal reinforcement standard trajectory, the mold is rotated clockwise and counterclockwise by α to obtain two longitudinal reinforcement offset trajectories, where R is the mold radius; the annular reinforcement trajectory is offset by adjusting the axial position of the wire laying head. The wire laying head is moved left by x and right by x relative to the centerline of the annular reinforcement standard trajectory to obtain two annular reinforcement offset trajectories.

[0028] Step 4: Arrange the laying order and position of the grid structure nodes based on the number of offset cycles; divide the node area into four areas: upper left, lower left, upper right, and lower right. The circular reinforcement and longitudinal reinforcement are laid alternately four times for one laying cycle, such as Figure 4As shown, the first layer of circular reinforcement is laid on the left side, and the first layer of longitudinal reinforcement is laid on the upper side, so as to obtain an overlapping area on the upper left position; the second layer of circular reinforcement is laid on the right side, and the second layer of longitudinal reinforcement is laid on the lower side, so as to obtain an overlapping area on the lower right position; the third layer of circular reinforcement is laid on the left side, and the third layer of longitudinal reinforcement is laid on the lower side, so as to obtain an overlapping area on the lower left position; the fourth layer of circular reinforcement is laid on the right side, and the fourth layer of longitudinal reinforcement is laid on the upper side, so as to obtain an overlapping area on the upper right position; four layers of longitudinal circular reinforcement constitute a cycle, which is repeated k times to complete an offset cycle; and so on, the entire reinforcement groove is laid.

[0029] Step 5: The next offset cycle placement starts from the position where the previous offset cycle placement processing ended, repeating steps 2, 3, and 4 to finally complete the placement processing of the entire ring longitudinal reinforcement grid structure.

[0030] For example, in a typical grid structure, the number of offset cycles for a certain offset is 5, and the number of offset laying layers is 20. Then the first layer of offset circular reinforcement is laid on the left side, and the first layer of longitudinal reinforcement is laid on the upper side; the second layer of offset circular reinforcement is laid on the right side, and the second layer of longitudinal reinforcement is laid on the lower side; the third layer of offset circular reinforcement is laid on the left side, and the third layer of longitudinal reinforcement is laid on the lower side; the fourth layer of offset circular reinforcement is laid on the right side, and the fourth layer of longitudinal reinforcement is laid on the upper side; continue the cycle, the seventeenth layer of offset circular reinforcement is laid on the left side, and the seventeenth layer of longitudinal reinforcement is laid on the upper side; the eighteenth layer of offset circular reinforcement is laid on the right side, and the eighteenth layer of longitudinal reinforcement is laid on the lower side; the nineteenth layer of offset circular reinforcement is laid on the left side, and the nineteenth layer of longitudinal reinforcement is laid on the lower side; the twentieth layer of offset circular reinforcement is laid on the right side, and the twentieth layer of longitudinal reinforcement is laid on the upper side; 4 layers of longitudinal circular reinforcement are a group, and the cycle is repeated 5 times. After a total of 20 layers are laid, the offset ends. Then repeat step 2, step 3, step 4, and so on until the placement process of the entire grid structure is completed.

[0031] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include any combination of the above-mentioned technical features.

Claims

1. A trajectory design method for a trapezoidal cross-section grid structure, characterized in that: The following steps are involved: Step 1: Design the circumferential and longitudinal basic tracks that are completely in line with the lower bottom surface of the trapezoidal cross-section grid structure rib on the mold surface; Step 2: Calculate the number of shifted layup layers N and the number of shift cycles k based on the slope of the trapezoidal cross-section grid structure, i.e., the trapezoidal busbar, and the thickness of the single filament of the prepreg; Step 3: By changing the die rotation angle and the axial position of the wire laying head, the positions of the offset trajectories of the longitudinal reinforcement and the annular reinforcement are obtained respectively; specifically: The mold rotation axis rotates a certain angle to offset the longitudinal reinforcement trajectory. The rotation angle is α=180×x / πR. Based on the centerline of the longitudinal reinforcement standard trajectory, the mold is rotated clockwise and counterclockwise by α to obtain two longitudinal reinforcement offset trajectories. The circular reinforcement trajectory is offset by adjusting the axial position of the wire laying head. The wire laying head is moved left by x and right by x relative to the centerline of the circular reinforcement standard trajectory to obtain two circular reinforcement offset trajectories. R is the mold radius, and x is the distance from the boundary of the trajectory laying area to the waistlines on both sides of the trapezoidal section of the rib groove. Step 4: Based on the offset cycle number k, arrange the laying order and position at the grid structure nodes; divide the node area into four areas: upper left, lower left, upper right, and lower right. The circular reinforcement and longitudinal reinforcement are laid alternately four times for one laying cycle. After k cycles, one offset laying process is completed. Specifically: The first layer of circular reinforcement is laid on the left side, and the first layer of longitudinal reinforcement is laid on the upper side, so as to obtain an overlapping area on the upper left position; the second layer of circular reinforcement is laid on the right side, and the second layer of longitudinal reinforcement is laid on the lower side, so as to obtain an overlapping area on the lower right position; the third layer of circular reinforcement is laid on the left side, and the third layer of longitudinal reinforcement is laid on the lower side, so as to obtain an overlapping area on the lower left position; the fourth layer of circular reinforcement is laid on the right side, and the fourth layer of longitudinal reinforcement is laid on the upper side, so as to obtain an overlapping area on the upper right position; four layers of longitudinal circular reinforcement constitute a cycle, which is repeated k times to complete an offset cycle; and so on, the entire reinforcement groove is laid; Step 5: The next offset cycle placement starts from the position where the previous offset cycle placement processing ended, repeating steps 2, 3, and 4 to finally complete the placement processing of the entire ring longitudinal reinforcement grid structure.

2. The trajectory design method of a trapezoidal cross-section grid structure according to claim 1, characterized in that: When the distance x between the boundary of the trajectory laying area and the waistlines on both sides of the trapezoidal section is greater than 0.5mm, the laying trajectory is offset. The number of offset cycles k and the number of offset laying layers N are calculated based on the thickness t of a single fiber and the bottom angle θ of the long side of the trapezoidal section, and k is rounded to an integer.

3. The trajectory design method of a trapezoidal cross-section grid structure according to claim 2, characterized in that: k=xtanθ / 4t, N=4k.

4. The trajectory design method of a trapezoidal cross-section grid structure according to claim 1, characterized in that: The bottom width of the groove of the trapezoidal cross-section grid structure is the same as the width b of the laid prepreg band, the upper side length a is no more than twice the lower side length b, and the groove height is 10 to 15 mm.

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