A large-angle skin flanging composite shell trajectory design and post-processing method

Abstract

The application provides a large-angle skin flanging composite shell trajectory design and post-processing method, first, according to the skin area trajectory planning, the center laying trajectory of the prepreg tows is obtained; then, the flanging area trajectory planning is carried out: first, the tow overlap rate of the skin area tow full coverage is set, and the intersection points of each prepreg tow and the flanging area boundary are obtained; the intersection points of the skin tow and the laying boundary are taken as the starting points of the flanging area trajectory, the intersection points with the lower boundary of the flanging area are obtained, and the flanging area trajectory line is obtained; finally, the flanging area tow coverage analysis and the tow cutting skin trajectory extension reserve the accurate calculation of the flanging tow length. The problems of poor skin-flanging continuity, flanging area wrinkle and lap joint defects during forming are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of automatic fiber placement forming of advanced composite materials, and particularly relates to a large-angle skin flanging composite shell trajectory design and post-processing method. BACKGROUND

[0002] Carbon fiber composite materials have become the main structural materials of aerospace vehicles due to their light weight and high strength, and their application sites and quantities have been increasing year by year, and they have been more widely used in the field of vehicle cabin sections. Among them, the complex special-shaped curved surface, cone, cylinder and other rotary body structures with flanging features are often used. The complex special-shaped curved surface, cylindrical and conical shell is a skin flanging structure as a whole, and the skin is flanged inward along the radial direction as the upper and lower end frames of the shell.

[0003] At present, the traditional forming method of the skin + flanged end frame of this type of composite component is to manually lay the wide pre-impregnated material. For complex special-shaped curved surfaces, conical shells and the like, the pre-impregnated material usually needs to be divided into blocks for laying and forming, so that it is difficult to form regular angle layers in the internal layers, and the fiber continuity is not good. The skin flanging has large curvature variation and non-developable characteristics, and the wide pre-impregnated material extended from the skin is prone to wrinkles and lap defects when manually flanged downward.

[0004] The automatic fiber placement technology has the advantages that the fiber continuity is good, the angle deviation is small, and the pre-impregnated narrow strip extended from the skin is easier to be flanged downward without defects.

[0005] The patent number CN 205272411 U, "Mold forming mold for internally flanged conical segment rotary body component", proposes a combined forming mold, designs a hanging yarn shoulder, realizes manual laying and spiral winding at the same time, and solves the problem of angle continuous fiber laying of the conical segment rotary body component. However, this winding process has small structure adaptability, and the skin and flanged part are difficult to be continuously formed as a whole.

[0006] The patent number CN 108859177 A, "Automatic fiber placement trajectory post-processing method for flanged area", proposes a post-processing method that the center trajectory of the flanged area is laid to extend a certain distance from the first surface, and then moves along the preset flanged trajectory to the second surface, which solves the problem that the pre-impregnated narrow strip cannot be compacted when the press roller encounters the flange. However, the flange involves large curvature variation and non-developable characteristics. The curvature variation of the curved surface and the fiber laying direction cause the geodesic orientation of the same roller trajectory flanged surface to be different. Directly flanging downward along the laying center trajectory leads to the problems of large degree of twist and R angle wrinkle of the actual laying fiber, and the interference between the winding head and the main shaft tail seat.

[0007] The patent of patent No. CN 103978698 A, a kind of composite material conical shell forming method with end frame, proposes the method of automatic laying and dry winding combination in laying process to realize the automatic forming of full lay angle and end frame of composite material conical shell, but the forming method is subject to the minimum yarn feeding length of filament laying equipment mechanism, when the height of end frame is less than the parameter, the yarn cutting action is performed before the filament laying head enters the corner of end frame and core mold, so the winding forming of composite material pre-impregnated yarn cannot be realized by using the tension of filament laying head. SUMMARY

[0008] The purpose of the present application is to provide a large-angle skin flanging composite shell trajectory design and post-processing method to solve the problem of poor skin-flanging continuity and flanging area wrinkle and lap joint defects in the forming of existing large-angle skin flanging composite structures, especially complex irregular curved surfaces, and ultimately improve the strength of the skin and flanging end frame of the structural member.

[0009] The technical solution to achieve the purpose of the present application is:

[0010] A large-angle skin flanging composite shell trajectory design method, comprising the following steps:

[0011] Step 1, according to the skin area trajectory planning, the center laying trajectory of the pre-impregnated yarn bundle is obtained;

[0012] Step 2, flanging area trajectory planning: first set the yarn overlap rate of the skin area yarn bundle full coverage, and find the intersection points of each pre-impregnated yarn bundle and the flanging area boundary; respectively, the intersection points of the skin yarn and the laying boundary are taken as the starting points of the flanging area trajectory, the flanging surface trajectory planning is converted into the problem of solving the natural path on the two patches of the tangent plane of the surface passing through the point and the flanging surface, the intersection points with the lower boundary of the flanging area are obtained, and the flanging area trajectory is obtained.

[0013] Step 3, flanging area yarn coverage analysis and yarn cutting: set the overlap parameter and yarn cutting strategy, set the minimum yarn length after cutting the flanging area, get the jth yarn cutting point of the ith center trajectory of the flanging area, and form the trajectory of the jth yarn of the ith center trajectory of the flanging area.

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

[0015] (1) The algorithm of the present application is good in universality, and is suitable for skin flanging whole trajectory design and post-processing of single-end-face flanging, double-end-face flanging complex irregular curved surface, cone, cylinder and other composite rotary body structures, especially for complex irregular curved surfaces.

[0016] (2) The two-step method is used for overall trajectory planning of the skin and the flanging area, which improves the continuity of the skin and the flanging fiber and improves the strength of the flanging end frame.

[0017] (3) Based on the automatic cutting function of the fiber laying, according to the geometric information of the inner and outer boundaries of the component flanging and the characteristics of the automatic fiber laying device, the corresponding algorithm is established to accurately calculate the cutting information of the pre-impregnated fiber tows in the flanging area, effectively solving the problems of wrinkles and lap defects in the flanging area.

[0018] (4) The two-step method is used for trajectory key point information post-processing of the skin and the flanging area. This post-processing method mainly solves the problem that the automatic fiber laying device cannot directly lay the flanging surface. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a side view of a large-angle flanged composite cone shell.

[0020] Figure 2 It is a schematic diagram for solving the trajectory direction of the flanging area.

[0021] Figure 3 It is a schematic diagram of overall trajectory planning of the skin flanging.

[0022] Figure 4 It is a schematic diagram of tow cutting and key point calculation in the flanging area.

[0023] Figure 5 It is a schematic diagram of path post-processing key point calculation. DETAILED DESCRIPTION

[0024] The present application will be further described below in combination with the drawings and specific embodiments.

[0025] A large-angle skin flanging composite shell trajectory design and post-processing method of the present embodiment takes a composite cone shell with large-angle flanging as an example. The shell has end frames with the skin flanging inward layer by layer along the radial direction, such as Figure 1 , which are the large end frame and the small end frame, respectively. The skin lay-up sequence is [45 / 0 / -45 / 90] 2s . The specific steps are as follows:

[0026] Step 1: Trajectory planning for the skin area is performed using a trajectory algorithm. According to the geometric information of the component surface and the device characteristics information, considering the constraints of the laying angle and the process (curvature constraint, tow width, number of tows, etc.), a trajectory strategy algorithm is used for skin trajectory planning based on the component surface or surface triangular mesh, forming the initial center trajectory and the center laying trajectory at other positions formed by offset, finally covering the entire cone shell surface. The center trajectory sequence is N1, N2…N i …N m (i is the center trajectory sequence number, and m is the total number of center trajectories). For example,Figure 3 The trajectory generation and offset for the 45° skin area center are generated, the number of filaments n laid by the filament laying device is 8, and the filament width d is 6.35 mm.

[0027] Step 2: Perform the flange area trajectory planning. The flange area laying path directly formed by the conventional skin filament center trajectory planning has the following problems: (1) the laying device may interfere with the mold, spindle tail seat box; (2) due to the curvature change of the curved surface and the curve laying angle, the actual laying filament is twisted and the R angle wrinkle is large due to the different natural path orientations of the filaments of the same roller trajectory. Therefore, a two-step method is used to plan and post-process the trajectory of the rotary curved surface flange area:

[0028] a) Skin area filament full coverage and intersection point calculation of each prepreg filament and boundary. After full coverage of the prepreg filaments, the two non-parallel filaments intersect and need to be cut. The filament overlap rate is set to 50%, and the number of filaments and filament serial numbers corresponding to the center trajectory are marked after full coverage calculation, denoted by the letter combination N ij Mark the prepreg filaments, and lay the filaments to cover the entire conical shell curved surface. The filaments are N 11 , N 12 , … N 1j , N 21 … N ij … N mn (i is the center trajectory serial number; j is the filament serial number, 1 ≦ j ≦ n, and the maximum value of j depends on the device parameters (n is the number of filaments laid by the filament laying device), N ij is the jth filament of the ith center trajectory; then the intersection point of each filament N ij of the skin and the large end boundary of the skin (i.e. the upper boundary of the large end flange area) is Ρ ij , and the intersection point of each filament N ij of the skin and the small end boundary of the skin (i.e. the upper boundary of the small end flange area) is Γ ij .

[0029] b) Flange area trajectory planning. The large end and small end flange surface trajectory planning is performed respectively, and the intersection points Ρ ij and Γ ij of the skin filaments and the laying boundary are taken as the starting points of the flange area trajectory, which can be converted into a problem of solving the natural path on the two patches of the tangent plane of the point and the flange surface: taking the small end flange surface as an example, as shown in Figure 2 , the tangent plane of the point Γ ij is S1, the flange surface is S2, and the two planes intersect on a straight line l, L is the tangent vector of the straight line l passing through the point Γ ij , V1 and N1 are the tangent vectors of the filament trajectory N ij passing through the point Γ ij , and N2 is the normal vector of the two planes S1 and S2. Then the following conclusions can be drawn:

[0030] L = N1 x N2 (1)

[0031] To ensure the same direction of laying, we can get:

[0032] V1·L = V2·L (2)

[0033] At the same time, because V2 and N2 are perpendicular, we can get:

[0034] V2·N2 = 0 (3)

[0035] Solving (1), (2), and (3), we can get vector V2, which is the natural path direction of the point on the flanging surface Γ ij . When laying along this direction, the flanging at the edge is well laid. At the same time, the flanging surface is a plane, and the intersection point with the lower boundary of the small-end flanging region can be obtained from this direction. The flanging region trajectory is as follows Figure 3 .

[0036] Step 3: Analysis of flanging region filament coverage and filament cutting. Due to the complexity of the core mold shape, the curved surface skin is folded and collected along the axis at the end frame. The distance between the center lines of adjacent filaments after flanging of the same roller cannot always remain constant, and the filaments overlap too much, so filament cutting is required. The filament cutting scheme meets two conditions: (1) Set the overlap parameter and filament cutting strategy. When adjacent filaments intersect, the yarn is cut to ensure that the triangular area (overlap / gap) formed by filament cutting is uniformly distributed; (2) To ensure the continuity of the skin and the flanging fiber as much as possible, the minimum filament length after cutting in the flanging region is ≥ 20 mm. The jth filament cutting point of the ith center trajectory in the small-end flanging region is M ij , and the flanging region trajectory formed is ΓM 11 …ΓM 1j , ΓM 21 …ΓM ij …ΓM mn , and the cutting effect is as follows Figure 4 .ΓM ij The trajectory of the jth filament of the ith center trajectory.

[0037] Similarly, the large-end frame flanging region trajectory planning repeats steps 2 and 3. The filament cutting points of the large-end flanging region are N ij , and the paths of the flanging filaments after cutting are ΡN 11 , ΡN 12 , …ΡN 1j , …ΓN ij …ΓN mn .

[0038] Step 4: Post-processing of the skin flanging laying path. To address the issues of varying surface curvature and different geodesic orientations of the filament bundles along the same roller track, directly flanging along the center track of the ribbon results in significant twisting and R-angle wrinkling of the laid filament bundles, and may also cause equipment interference. Therefore, during post-processing, the skin track is extended to allow for the flanging length of each roller filament bundle, followed by a second flanging. The post-processing steps are as follows:

[0039] a) Obtain the length of each filament bundle in the flanged area. Calculate the path ΓM of the filament bundles after trimming in the small-end flanged area. 11 …ΓM 1j ,ΓM 21 、…ΓM ij …ΓM mn The length of each filament bundle N at the small end boundary point of the skin is used as the reference. ij Extend the length of the filament bundle in the reserved small-end flange area, respectively L 11 ...L 1j L 21 ...L ij ...L mn ; Calculate the path PN after cutting the yarn bundle in the large-end flange area. 11 , PN 12 ...ΡN 1j , PN 21 …ΡN ij …ΡN mn The length of each filament bundle N of the skin ij Extend the length of the filament bundle in the reserved large end flange area, respectively, by K 11 K 12 ...K 1j K 21 …K ij …K mn L ij The length of the filament bundle reserved for the small end flange area of ​​the j-th filament bundle of the i-th center trajectory, K. ij The length of the filament bundle reserved for the large end flange area of ​​the j-th filament bundle of the i-th center trajectory.

[0040] b) Extend the skin area laying path and calculate key points. This invention modifies the post-processing method for curved skin flanging structures compared to traditional methods. The main idea is: the large end is the laying start point, and the large end reserves the prepreg material required for the flanging area through pre-feeding wire; the small end follows the skin center trajectory N. i The extended trajectory line in the tangential direction is the reserved path for the filament bundle in the flanged area. For example... Figure 5 As shown, the key calculation is as follows: Based on the principle of the automatic yarn placement machine, the pre-impregnated yarn bundle is first pre-fed at position 00 at a height h away from 01, and the pre-fed yarn lengths are fs+K. ij(fs is the shortest laying length of the fiber laying device, i.e. the distance from the cutter to the position below the compression roller), the 01 position is the position where the large end laying starts, and the skin laying starts; before the end of a track, the fiber needs to be cut; in order to ensure that the fiber laying ends at the 03 position, the fiber needs to be cut at the 02 position before the 03 position (the length of the advance cutting is fs), so the 02 is the position where the cutter cuts the fiber. The laying path 03 position of the present application is Γ ij The distance L of the position extension curve ij The point Γ ij The point Γ ij The position of the projection of the point Γ i to the center track N

[0041] c) output the track NC file. According to the track process information, the track NC file is generated, including the number of laying layers, the number of track strips, the track motion path point position information, key point instructions and the like.

[0042] The present application is based on the automatic fiber laying technology, and adopts a two-step method to carry out the overall track planning and design and post-processing of the skin and the flanging area, and accurately calculates the cutting information of the pre-impregnated fiber bundle in the flanging area, so as to solve the problems that the existing large-angle skin flanging composite structure is prone to poor continuity of the skin and the flanging, and the flanging area is prone to wrinkle and lap joint defects, especially when the complex special-shaped curved surface is formed, and finally improves the strength of the skin and the flanging end frame of the structure.

Claims

1. A method for trajectory design of a large-angle skin-flap composite shell, characterized in that, The method comprises the following steps: Step 1, obtaining the center laying track of the prepreg bundle according to the skin area track planning; Step 2, carrying out the flanging area track planning: firstly, setting the bundle overlap rate of the skin area bundle full coverage, and obtaining the intersection points of each prepreg bundle and the flanging area boundary; taking the intersection points of the skin bundle and the laying boundary as the starting points of the flanging area track, converting the flanging surface track planning into the problem of solving the natural path on the two surface patches of the tangent plane of the curved surface passing through the points and the flanging surface, obtaining the intersection points with the lower boundary of the flanging area, and obtaining the flanging area track line; The specific process of the flanging surface trajectory planning is as follows: taking each wire beam corresponding to the skin laying center trajectory and intersecting with the skin two end boundary as the flanging region trajectory starting point, making the skin skinning plane as S1, the flanging surface as S2, and the two planes intersecting with a straight line l, L being the tangent vector of the straight line l passing through the boundary intersection point; the tangent vector V1 of the wire beam trajectory N passing through the boundary intersection point, N1 and N2 being the normal vectors of the two planes S1 and S2 respectively; then there are: ij ​ (1) (2) (3) Obtaining the vector V2, which is the natural path direction of the intersection point of the upper boundary of the flanging surface; the intersection point with the lower boundary of the flanging area at the other end can be determined in the same way; Step 3, flanging area bundle coverage analysis and bundle cutting: setting the overlap parameter and the bundle cutting strategy, and setting the minimum bundle length after cutting the flanging area; Obtaining the jth bundle cutting point of the ith center track of the flanging area, and forming the track line of the jth bundle of the ith center track of the flanging area. The intersection points of each prepreg bundle and the flanging area boundary are obtained, and the specific process is as follows:

2. The large angle skin flange composite case trajectory design method of claim 1, wherein, The method further comprises post-processing of the skin flanging laying path, firstly, obtaining the length of each bundle in the flanging area, and prolonging the laying path of the skin area according to the principle of the automatic fiber placement machine. The number and serial number of the tows corresponding to the center trajectory after full coverage calculation are marked with the letter combination N ij The tow of the prepreg is marked, and the tows are laid to finally cover the entire conical shell surface, and the tows are N 11 , N 12 , …N 1j、 N 21 …N ij …N mn , N ij is the jth tow of the ith center trajectory; then the tows N ij of the skin intersect with the boundary points of the skin at Γ ij .

3. The method of claim 1, wherein, The length of each bundle in the flanging area is obtained, and the specific process is as follows: calculating the length of the path after cutting the bundle of the flanging area at both ends as the bundle length reserved for the flanging area at both ends of the boundary points of the skin.

4. The method of claim 3, wherein, The composite shell is a conical shell, the large end is the laying starting end, and the small end is prolonged along the tangent direction of the skin center track to form the flanging area reserved bundle path.

5. The large-angle skin-stretch composite shell trajectory design method according to claim 4, wherein, The specific process of extending the skin area laying path is as follows: firstly, the pre-fed yarn operation is performed on the upper end of the laying starting position 01 on the pre-impregnated tows, the pre-fed yarn length is divided into ƒs+K ij , the skin laying is started, the tow cutting needs to be performed before the position 02 which is away from the position 03 of stopping, the cutting length is ƒs, the position 02 is the position of cutting the tows by the cutter, and the position 03 is the position of stopping Γ ij ’ The position of the point of the laying boundary intersection point of the end is projected to the corresponding center track. ij ij ’ The point is the position of the laying boundary intersection point of the end projected to the corresponding center track.​ where K ij is the length of the tows reserved for the end-flanging of the start end of the jth tow of the ith central trajectory, and ƒs is the minimum deposition length of the fiber placement equipment.

6. The large-angle skin-stretch composite shell trajectory design method of claim 4, wherein, ​

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