A method for forming a composite curved structure

Abstract

The application discloses a kind of forming methods of composite curved surface structure, comprising: selecting characteristic edge as ridge line and establishing coordinate system;Determine engineering boundary and expand processing allowance to form manufacturing boundary;Carry out manufacturability analysis and expand manufacturing boundary to two-dimensional profile;Lay and cut composite material layer;Hot diaphragm preforming and hot press tank solidification are mechanically processed into shape.The application adopts different processing allowance expansion ways and expansion strategies according to the symmetry of structure.Avoid preforming wrinkle through manufacturability analysis based on ridge line;Ensure that layer and tooling correspond accurately through ridge line projection and positioning structure design;Reduce transfer error by using hot diaphragm preforming and hot press tank solidification process.The method is suitable for hyperbolic stringer and other complex components in the field of aerospace, improves production efficiency and material utilization, reduces forming defect rate, and realizes stable manufacturing of high-quality composite structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite material manufacturing, in particular to a forming method of a composite material curved surface structure. BACKGROUND

[0002] Composite stringers are widely used in the longitudinal reinforcement structure design of aircraft fuselage panels. With the continuous development of computer technology and numerical control technology, the design and manufacturing of composite components are changing from the traditional "trial and error" mode to digital manufacturing mode. However, for complex-shaped composite structures such as double-curved hat-shaped stringers, one of the keys in the manufacturing process is to accurately unfold the three-dimensional structure model into a two-dimensional ply and ensure the forming quality.

[0003] Currently, there are two outstanding problems in the two-dimensional ply unfolding technology of composite curved surface structures: first, there is a lack of an unfolding method based on structural features, which makes it difficult to ensure that the fiber direction of the unfolded composite material ply is highly consistent with the design requirements when applied to complex curved surface structures, especially when dealing with different geometric features (such as symmetric and asymmetric structures) there is a lack of differentiated unfolding strategies; second, there is a lack of reliable positioning reference and manufacturability evaluation during the unfolding process, resulting in size deviation and wrinkle defects between the formed structure and the design model. These problems often require repeated trial production to verify and improve product quality, wasting a lot of resources and financial resources.

[0004] Although digital technology provides necessary means to improve product quality stability, efficiency and cost reduction, for complex curved surface structures, there is still a lack of a two-dimensional ply unfolding and forming method that can systematically solve the problems of ply unfolding, manufacturability analysis, positioning accuracy and forming quality. SUMMARY

[0005] To solve the above technical problems, the present application provides a forming method of a composite material curved surface structure, which can determine the ply reference direction by establishing a coordinate system with the feature edge line as the ridge line, thereby realizing high-quality forming of the composite material structure.

[0006] The application provides a forming method of a composite material curved surface structure, comprising the following steps: selecting a characteristic edge line in a three-dimensional geometric model of a composite material structure as a ridge line, defining a ply design origin at a starting position of the ridge line, and establishing a ridge line coordinate system based on the ply design origin; determining an engineering boundary of the composite material structure, and expanding a machining allowance to form a manufacturing boundary; based on the ridge line coordinate system, performing manufacturability analysis on the composite material structure with the machining allowance to evaluate whether wrinkles will be generated in a laying process, then using design software to expand the manufacturing boundary into a two-dimensional profile of a composite material ply; designing and running an automatic laying program according to the two-dimensional profile to complete laying of the composite material ply, and then using a cutting device to cut the laid composite material ply; and preforming and autoclave curing the cut composite material ply through a hot diaphragm device, and then performing mechanical processing to form a net size composite material structure.

[0007] Specifically, the composite material structure can be a hyperbolic stringer, and the characteristic edge line is a hat top external corner edge line.

[0008] Further, the step of establishing the ridge line coordinate system comprises: defining a ply reference direction as a tangent direction of the ridge line at the ply design origin; and setting other ply directions based on the reference direction at a predetermined angle.

[0009] Further, the range of the expanded machining allowance is 10-30 mm. The manufacturability analysis comprises: setting a maximum fiber deformation angle threshold; selecting a seed point on the composite material structure with the machining allowance as a starting point of fiber propagation along the circumferential direction; defining a radial radius and a weft radius of a fiber grid for simulating the laying behavior of the fiber in different directions; selecting a fiber propagation type and running an analysis simulation, wherein the fiber propagation type comprises a minimum distortion type and a symmetric type.

[0010] Notably, the application determines different machining allowance expansion modes according to the feature type of the composite material structure, wherein the feature type comprises a symmetric structure and an asymmetric structure. When the feature type is the symmetric structure, the two-dimensional profile of the composite material ply is expanded to form a composite material ply two-dimensional profile retaining the original feature profile; and when the feature type is the asymmetric structure, the two-dimensional profile of the composite material ply is expanded to form a regular shape composite material ply two-dimensional profile after simplification processing.

[0011] In addition, the application further comprises designing a positioning structure at a feature position of the composite material structure to ensure that the two-dimensional profile of the composite material ply corresponds to the position of a forming tool, and projecting the ridge line onto the two-dimensional profile of the composite material ply, and marking a ridge line projection line by a marking device to serve as a positioning reference of the composite material ply on the tool.

[0012] The forming method of the composite curved surface structure provided by the technical scheme has the complete process flow of establishing a ridge line coordinate system through a feature edge line, determining an engineering boundary and expanding to form a manufacturing boundary, performing manufacturability analysis, expanding to a two-dimensional contour, automatic laying and cutting, pre-forming, and heat tank curing and mechanical processing, and realizes accurate forming of a complex curved surface structure. The method takes the feature edge line of the composite structure as the ridge line and establishes a coordinate system based on the ridge line, so that the reference direction of the layup is highly consistent with the structure feature; manufacturability analysis is performed before expansion, so that the risk of wrinkles in the laying process can be evaluated in advance; then, the two-dimensional contour accuracy is ensured by optimizing expansion according to the analysis result; and finally, the accurate correspondence between the composite layup and the forming tool is ensured by the positioning structure.

[0013] The application establishes a coordinate system based on the ridge line, so that the layup direction is consistent with the main stress direction of the structure, thereby improving the structure performance; meanwhile, manufacturability analysis is performed in advance and different expansion methods are adopted according to different structure features, thereby avoiding the quality problems caused by wrinkles and deformation in the traditional method; in addition, the application of the positioning structure and the ridge line projection solves the slippage problem of the composite layup in the forming process, thereby ensuring the consistency between the finally formed part and the design model. Through the organic combination of these technical measures, the application not only improves the forming quality of the composite structure, but also reduces the waste of material and financial resources caused by repeated trial production, thereby providing reliable technical support for efficient manufacturing of composite structures in the field of aviation and aerospace. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a flowchart of a forming method of a composite curved surface structure in an embodiment of the application;

[0015] Figure 2 is a schematic diagram of a double-curved stringer structure with symmetrical ear features on the edge strip in an embodiment of the application;

[0016] Figure 3 is a schematic diagram of a double-curved stringer structure with asymmetric ear features on the edge strip in an embodiment of the application.

[0017] Marked in the figure: 1, layup design origin; 2, ridge line; 3, ridge line projection line; 4, engineering boundary; 5, manufacturing boundary; 6, positioning structure. DETAILED DESCRIPTION

[0018] In the specific embodiments of the application, the terms used in the embodiments of the application are described below to make the purpose, technical scheme and advantages of the application more clear. It should be noted that the following term description is only used to help understanding and should not be regarded as a limitation on the protection scope of the application.

[0019] EEOP (Engineering Edge of Part) refers to the engineering design boundary, i.e. the theoretical boundary of the part.

[0020] MEOP (Manufacturing Edge of Part) refers to the manufacturing design boundary, which is usually the actual machining boundary designed on the basis of EEOP considering the manufacturing process requirements.

[0021] The ridge line refers to a characteristic line used to determine the long string unfolding reference. In the embodiments of the present application, the hat top sun angle edge line can be selected as the ridge line.

[0022] The ear refers to the protruding structure on the long string edge strip. According to the different structural characteristics, the ear can present various forms such as symmetrical distribution, asymmetrical distribution or staggered distribution, and the specific structural form of the ear is not limited in the present application.

[0023] The positioning hole refers to the hole structure used for positioning the material sheet, and the specific shape, size and position thereof can be designed according to the actual requirements, which is not limited in the present application.

[0024] The present application will be further described in detail below in combination with the drawings and specific embodiments, and it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. Those skilled in the art should understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and essence of the present application.

[0025] Embodiment one

[0026] With reference to Figure 1 , the present application relates to a forming method of a composite material curved surface structure, the composite material structure is a hyperbolic long string, comprising the following steps:

[0027] Step S1: selecting a characteristic edge line as a ridge line

[0028] The method of the present application is suitable for the forming of various composite material structures, preferably the composite material structure is a hyperbolic long string. The hyperbolic long string refers to a reinforcing structure with hyperbolic surface geometric characteristics, which is commonly used as a longitudinal reinforcing structure of a fuselage wall plate in the field of aerospace. Compared with a planar or single curved surface structure, the hyperbolic long string has a more complex geometric shape, and its unfolding forming is more difficult, and the method of the present application has a better technical effect.

[0029] In step S1, a characteristic edge line in a three-dimensional geometric model of a composite structure is selected as a ridge line. In this embodiment, the characteristic edge line is specifically selected as a hat top gable edge line of a hyperbolic long stringer. In the structure of the hyperbolic long stringer, the hat top gable edge line is located at the intersection of the hat top and the hat waist, is almost parallel to the skin shape at this position, that is, the intersection characteristic line of the long stringer surface and the skin surface, and is suitable as a reference for unfolding and positioning. A ply design origin is defined at the starting point of the ridge line, and a ridge line coordinate system is established based on the ply design origin.

[0030] Step S2: determining a ply reference direction and determining an engineering boundary based on the ridge line coordinate system

[0031] Based on the ridge line, the ply reference direction is defined as the tangent direction of the ridge line at the ply design origin. Specifically, first, the intersection point of the characteristic section of the long stringer and the ridge line is selected as the ply design origin, and the ridge line coordinate system is established at the ply design origin. Then, the first axis direction of the ridge line coordinate system is determined as the tangent direction of the ridge line at the ply design origin, and the second axis direction of the ridge line coordinate system is determined as perpendicular to the first axis direction. The establishment of this coordinate system fully considers the geometric characteristics of the hyperbolic long stringer, and provides a reliable reference for the subsequent control of the ply direction.

[0032] Other ply directions are set at predetermined angles based on the reference direction:

[0033] The first axis direction is defined as the 0° ply reference direction; the direction clockwise rotated by 45° relative to the 0° ply reference direction is defined as the +45° ply direction; the direction counterclockwise rotated by 45° relative to the 0° ply reference direction is defined as the -45° ply direction; and the second axis direction is defined as the 90° ply direction.

[0034] This definition method makes the ply direction well correspond to the geometric characteristics of the long stringer, while meeting the force requirements of the long stringer: the 0° ply direction is set along the tangent direction of the ridge line, which is the main force direction of the long stringer and can provide the required longitudinal strength; the ±45° ply direction is used to provide the required shear strength, meeting the force requirements of the long stringer under bending and torsion working conditions; and the 90° ply direction enhances the transverse strength and overall stability of the long stringer through transverse plies.

[0035] The engineering boundary of the composite structure is determined, and the machining allowance is expanded to form a manufacturing boundary. Different machining allowance expansion methods are determined according to the feature types of the composite structure, including symmetric structures and asymmetric structures. In this embodiment, the range of expanding the machining allowance is 10mm to 30mm, including 10mm, 20mm and 30mm, preferably 15mm to 25mm, and more preferably 20mm.

[0036] Specifically, when the feature type is a symmetric structure (e.g., a long stringer with a symmetric ear structure), the manufacturing boundary keeps the ear shape profile in the engineering boundary, only expanding the machining allowance; when the feature type is an asymmetric structure (e.g., a long stringer with an asymmetric ear structure), the ear line segment in the engineering boundary is straightened and extended to form the manufacturing boundary. This differentiated boundary determination method can better adapt to the development needs of long stringers with different structural features.

[0037] Step S3: manufacturability analysis and two-dimensional development

[0038] Based on the ridge line coordinate system, manufacturability analysis is performed on the composite structure with machining allowance to evaluate whether wrinkles will occur during the laying process. In the preferred embodiment, manufacturability analysis is completed using the CATIA CPD module, and the specific steps are as follows:

[0039] 1. Set the maximum fiber shear angle threshold, preferably ±15° as the warning value and ±30° as the limit value. When the fiber shear angle exceeds 15°, the system will issue a warning, indicating that wrinkles may occur in this area; when the shear angle exceeds 30°, the area will almost certainly have severe wrinkles and needs to be redesigned.

[0040] 2. Select a seed point on the composite structure with machining allowance as the starting point for the fiber to spread outward. In this embodiment, the seed point is preferably set in the center of the hat top area of the hyperbolic stringer, so that the fiber spread is more uniform.

[0041] 3. Define the radial radius and latitudinal radius of the fiber grid to simulate the laying behavior of the fiber in different directions. The radial radius is used to simulate the behavior of the fiber along the X-axis direction, and the latitudinal radius is used to simulate the behavior of the fiber along the Y-axis direction. In this embodiment, for a hyperbolic stringer with a length of 1500 mm and a width of 150 mm, the radial radius is set to 20 mm and the latitudinal radius is set to 10 mm.

[0042] 4. Select the fiber spread type and run the analysis simulation, including the minimum distortion type and the symmetric type. The minimum distortion type is the deformation scheme calculated by the system to minimize fiber distortion, and the symmetric type is the deformation scheme calculated symmetrically relative to the fiber direction.

[0043] In the preferred embodiment, for the hyperbolic stringers of symmetric structure, the symmetric type of lofting is selected; for the hyperbolic stringers of asymmetric structure, the minimum distortion type of lofting is selected. In the forming process of a certain type of hyperbolic stringer adopted in the embodiment, a seed point is arranged in the hat top area, the radial radius is set to 15 mm, the weft direction radius is set to 8 mm, and the symmetric type of lofting is selected for analysis. The analysis result shows that, by using the method provided by the application, the average value of the shear angle is generally within 3°, and the local deviation can be as large as 6.33°; the average deviation angle is within 3°, and the maximum local deviation is 12.64°, so that the deformation characteristics of the component are improved, and the fiber deformation angle in all areas is controlled within the range allowed by the manufacturing process.

[0044] Then the manufacturing boundary is unfolded into a two-dimensional profile of the composite material layup by using a design software. In the preferred embodiment, the CATIA composite material design (CPD) module is used for unfolding design, which supports functions such as coordinate system establishment based on feature lines, manufacturability analysis, and two-dimensional profile unfolding. Specifically, when the feature type is the symmetric structure, the unfolding forms a two-dimensional profile of the composite material layup that retains the original feature profile; when the feature type is the asymmetric structure, the unfolding forms a two-dimensional profile of the composite material layup of a regular shape after simplification processing.

[0045] In the production verification process in the embodiment, it is found that when the hyperbolic stringer is of symmetric structure, the two-dimensional sheet unfolding method that retains the original feature profile can effectively reduce material waste and improve automatic laying efficiency. In a batch of a certain type of fuselage hat-shaped stringer, compared with the traditional rectangular unfolding method, the material utilization rate is increased from 78% to 91% by using the method for unfolding, which is increased by 13 percentage points. For the asymmetric structure, the regular shape unfolding method reduces the risk of wrinkles in the preforming process. In the production of a certain type of asymmetric stringer adopted in the embodiment, after unfolding by using the method, the preforming defect rate is reduced from 22% to 4%, and the quality first pass yield is increased.

[0046] The specific implementation of the unfolding process in the embodiment is that the design software approximately divides the composite material structure surface into a plurality of small sheets according to the material properties (polytetrafluoroethylene resin-based composite material, elastic modulus of 70 GPa, and Poisson's ratio of 0.3), corrects the unfolded sheets according to the theory of elasticity, maintains the continuity between the regions, and avoids wrinkles or overlaps. The small sheets are spliced on a two-dimensional plane by using the equidistant mapping algorithm, so that they match the manufacturing boundary, and the layup direction of each region is kept consistent with the aforementioned determined layup reference direction, and the deviation of the layup direction is controlled within the range of -1° to +1°.

[0047] In addition, a positioning structure is designed at a feature position of the composite structure to ensure that the two-dimensional profile of the composite ply corresponds to the position of the forming tool. The feature position includes a hat top end position of the stringer or a middle position of the hat top of the stringer. Meanwhile, the ridge line is projected onto the two-dimensional profile of the composite ply, and a ridge line projection line is marked by a marking device to serve as a positioning reference for the composite ply on the tool.

[0048] Step S4: automatic laying and cutting

[0049] The automatic laying program is designed and run according to the two-dimensional profile to complete the laying of the composite ply, and then the laid composite ply is cut by a cutting device. Since the unfolding method based on the ridge line coordinate system is adopted, the deviation of the fiber angle from the theoretical model can be controlled within ±1°, greatly improving the accuracy of the fiber angle.

[0050] Step S5: hot diaphragm preforming and autoclave curing

[0051] The cut composite ply is preformed and autoclaved by a hot diaphragm device, and then machined to form a net size composite structure. The ridge line and positioning hole on the three-dimensional model are unfolded and mapped onto the two-dimensional flat sheet, which can realize accurate positioning of the sheet and the forming tool, and reduce the error in the forming process.

[0052] By using the above method, the unfolding accuracy and preforming quality of the hyperbolic stringer can be improved, the material utilization rate can be improved, and the preforming defects can be reduced. Compared with the prior art, the method of the present application improves the production efficiency while ensuring the product quality and reduces the manufacturing cost.

[0053] Example two

[0054] Reference Figure 2 Another embodiment of the present application provides a forming method for a composite curved structure, the composite structure being a hyperbolic stringer with symmetrical ear features on the edge strip of the hyperbolic stringer. The method comprises the following steps:

[0055] Step S1: selecting a feature edge as a ridge line

[0056] According to the foregoing technical solution, the embodiment selects a feature edge line in a three-dimensional geometric model of the composite structure as the ridge line 2, defines the layup design origin 1 at a starting position of the ridge line 2, and establishes a ridge line coordinate system based on the layup design origin 1. In the embodiment, the feature edge line is specifically selected as a corner edge line of a hat top of a double-curved stringer, and the corner edge line is located at an intersection of the hat top and a stringer. The reason for selecting the corner edge line as the ridge line 2 is that the corner edge line is a feature line at the intersection of the hat top and the stringer, has stable geometric characteristics, and has small deformation in a pre-forming process, and is more suitable as a reference for unfolding and positioning.

[0057] Step S2: determining a layup reference direction and determining an engineering boundary based on the ridge line coordinate system

[0058] In this step, the layup reference direction is defined as a tangent direction of the ridge line at the layup design origin, and other layup directions are set at predetermined angles based on the reference direction. Specifically, an intersection of a feature section of the stringer and the ridge line is selected as the layup design origin, and a ridge line coordinate system is established at the layup design origin. A first axis direction of the ridge line coordinate system is determined as a tangent direction of the ridge line at the layup design origin, and a second axis direction of the ridge line coordinate system is determined as perpendicular to the first axis direction.

[0059] Based on the established ridge line coordinate system, the first axis direction is defined as a 0° layup reference direction, a direction rotated clockwise by 45° relative to the 0° layup reference direction is defined as a +45° layup direction, a direction rotated counterclockwise by 45° relative to the 0° layup reference direction is defined as a -45° layup direction, and the second axis direction is defined as a 90° layup direction. This way of establishing a coordinate system and defining a layup direction not only considers the geometric characteristics of the stringer, but also facilitates the control of the layup direction.

[0060] The engineering boundary 4 of the composite structure is determined, and a machining allowance is expanded to form a manufacturing boundary 5. In the embodiment, the stringer stringer has left-right symmetrical ear features. When the shape and size of the ears on the left and right sides of the stringer stringer differ by no more than 2 mm, it is determined as a symmetrical ear feature, which belongs to the foregoing symmetrical structure type. First, the engineering boundary 4, i.e., a theoretical contour profile considering engineering tolerances, is determined, and then a machining allowance is expanded based on the engineering boundary 4 to form the manufacturing boundary 5. In the preferred embodiment, the range of the expanded machining allowance is 10 mm to 30 mm, including 10 mm, 20 mm and 30 mm, and preferably 20 mm. The selection of the allowance can ensure sufficient machining allowance, and also avoid excessive waste of materials.

[0061] Different processing allowance expanding methods are determined according to the characteristic type of the composite structure. In the embodiment, for the symmetric structure, the ear shape profile in the MEOP is maintained, and such an expanding design can improve the material utilization rate of automatic laying, and the ear shape profile of the two-dimensional sheet can play a role similar to that of a cut slit, reducing the pre-forming wrinkles in the long stringer region.

[0062] Step S3: manufacturability analysis and two-dimensional expansion

[0063] Based on the ridge line coordinate system, manufacturability analysis is performed on the composite structure with processing allowance to evaluate whether wrinkles will be generated in the laying process. As described above, the manufacturability analysis includes steps such as setting a maximum fiber deformation angle threshold, selecting a seed point, defining the radial radius and the weft radius of the fiber grid, selecting a fiber extrapolation type, and running an analysis simulation, which will not be described here again.

[0064] In the preferred embodiment, the CATIA V5 CPD module is used for manufacturability analysis, and a symmetric type of extrapolation is selected for analysis due to the symmetric structure of the stringer. In the hyperbolic stringer forming of the embodiment, the seed point is set in the central region of the cap, the radial radius is set to 12 mm, and the weft radius is set to 6 mm. The analysis result shows that, using the method provided by the application, the average shear angle is generally within 2.8°, and the local deviation can be as large as 5.92°; the average deviation angle is within 2.9°, and the local maximum deviation is as large as 11.85°, which improves the deformation characteristics of the component and controls the fiber deformation angle in all regions within the range allowed by the manufacturing process.

[0065] Then, the manufacturing boundary is expanded into a two-dimensional profile of the composite layup using the CATIA V5 CPD module. According to the foregoing embodiment, when the characteristic type is the symmetric structure, the expansion forms a two-dimensional profile of the composite layup that retains the original characteristic profile. For the symmetric ear structure stringer of the embodiment, the expanded two-dimensional sheet retains the original ear profile, and the material utilization rate reaches 93%, which is 15 percentage points higher than that of the conventional rectangular expansion method.

[0066] The specific implementation of the expansion process is that the CATIA software approximately divides the composite structure surface into a plurality of small sheets according to the material properties (in the embodiment, carbon fiber epoxy resin prepreg with an elastic modulus of 135 GPa and a Poisson's ratio of 0.32), corrects the expanded sheets according to the theory of elasticity, maintains the continuity between the regions, and avoids wrinkles or overlaps. The small sheets are spliced on a two-dimensional plane by equidistant mapping algorithm, so that they match the manufacturing boundary, and the layup direction of each region is kept consistent with the layup reference direction determined as described above, and the deviation of the layup direction is controlled within the range of -1° to +1°. The specific analysis and processing process has been described above and will not be described here again.

[0067] In addition, positioning structure 6 is designed at the feature position of the composite structure to ensure that the two-dimensional profile of the composite ply corresponds to the position of the forming tool. Specifically, positioning holes with a diameter of 6 mm ± 0.2 mm and a distance of 25 mm ± 2 mm from the end of the material sheet are arranged at the hat top end position of the stringer or the middle position of the hat top. Two positioning holes are arranged for a stringer with a length less than 1000 mm, and one additional positioning hole is arranged every 500 mm for a stringer with a length greater than 1000 mm. The positioning holes are processed by a special punching tool or ultrasonic cutting to ensure that the hole edges are clean and free of burrs. At the same time, the ridge line 2 is projected onto the two-dimensional profile of the composite ply, and the ridge line projection line 3 is marked by a laser projection system as a positioning reference for the composite ply on the tool.

[0068] Step S4: automatic laying and cutting

[0069] The automatic laying program is designed and run according to the two-dimensional profile to complete the laying of the composite ply, and then the laid composite ply is cut by a cutting device. In this embodiment, the automatic laying is performed by an AFP (automatic fiber placement) device, and the cutting is performed by an ultrasonic cutting device.

[0070] Step S5: hot diaphragm preforming and autoclave curing

[0071] The cut composite ply is preformed and autoclave cured by a hot diaphragm device, and then machined to form a net size composite structure. In this embodiment, the hot diaphragm preforming and autoclave curing are completed at one time in an autoclave, and then the cured product is machined.

[0072] In terms of quality control, a three-coordinate measuring instrument is used to detect the unfolded size, a special protractor is used to detect the fiber laying angle, and the positioning hole position accuracy and hole diameter size are checked to ensure the manufacturing quality of the composite structure.

[0073] The beneficial effects of this embodiment are that for a hyperbolic stringer with symmetrical ear structures, the material utilization is improved by retaining the unfolded mode of the original ear profile; the positioning accuracy of the composite ply on the tool is improved by arranging reasonable positioning holes and ridge line projections; and the positioning error caused by process transfer is reduced by completing preforming and autoclave curing at one time, thereby improving production efficiency and product quality.

[0074] Example Three

[0075] Reference Figure 3Yet another embodiment of the present application provides a forming method of a composite material curved structure, the composite material structure being a hyperbolic stringer, the stringer in this embodiment being a hyperbolic stringer with asymmetric ear structure of stringer rib. The asymmetric structure of the ears on the left and right sides of the stringer in shape and size increases the difficulty of the unfolding design. The forming method provided by this embodiment comprises the following steps:

[0076] Step S1: selecting a characteristic edge line as a ridge line

[0077] According to the foregoing basic principle, this embodiment selects a characteristic edge line in the three-dimensional geometric model of the composite material structure as the ridge line 2. Specifically, the acute angle edge line at the intersection of the cap top and the stringer rib is selected as the ridge line 2. In this embodiment, although the ear structure of the stringer rib is asymmetric, the characteristics of the acute angle edge line at the cap top are still stable, so it is still selected as the unfolding reference. The layup design origin 1 is defined at the starting point position of the ridge line 2, and the ridge line coordinate system is established based on the layup design origin 1.

[0078] Step S2: determining a layup reference direction and determining an engineering boundary based on the ridge line coordinate system

[0079] According to the technical solution of the present application, the layup reference direction is defined as the tangent direction of the ridge line at the layup design origin, and other layup directions are set at predetermined angles based on the reference direction. First, the intersection of the characteristic cross section of the stringer and the ridge line is selected as the layup design origin, and the ridge line coordinate system is established at this point. The tangent direction of the ridge line at the layup design origin is determined as the first axial direction of the ridge line coordinate system, and the second axial direction perpendicular to the first axial direction is established.

[0080] On this basis, the layup reference direction is determined: the first axial direction is defined as the 0° layup reference direction, the direction clockwise rotating 45° relative to the 0° layup reference direction is defined as the +45° layup direction, the direction counterclockwise rotating 45° is defined as the -45° layup direction, and the second axial direction is defined as the 90° layup direction. This definition ensures accurate control of the layup direction under asymmetric structure.

[0081] The engineering boundary 4 of the composite material structure is determined, and the machining allowance is expanded to form the manufacturing boundary 5. In this embodiment, for the stringer with asymmetric ear structure of stringer rib, the engineering boundary 4 is first determined, and then the machining allowance is expanded to form the manufacturing boundary 5. In this preferred embodiment, the range of expanding the machining allowance is 10mm to 30mm, including 10mm, 18mm and 30mm, and the preferred value is 18mm. Compared with the 20mm machining allowance in the foregoing embodiment, the selection of 18mm in this embodiment takes into account the optimization of material utilization under asymmetric structure.

[0082] Different processing allowance expansion methods are determined according to the characteristic types of the composite structure. In the embodiment, for the asymmetric structure, the ear line segment in the engineering boundary is straightened and extended to form a manufacturing boundary. The purpose of straightening the ear line segment is to simplify the unfolding process of the asymmetric structure and reduce stress concentration during preforming.

[0083] Step S3: manufacturability analysis and two-dimensional unfolding

[0084] Based on the ridge line coordinate system, manufacturability analysis is performed on the composite structure with processing allowance to evaluate whether wrinkles will be generated during the laying process. The basic steps of manufacturability analysis have been described above. In the embodiment, since the longeron is an asymmetric structure, the minimum distortion type outer deviation is selected for analysis.

[0085] In the preferred embodiment, CATIA V5 CPD module is used for manufacturability analysis. For the asymmetric hyperbolic longeron of the embodiment, the seed point is set in the central front area of the cap, the radial radius is set to 10 mm, and the latitudinal radius is set to 5 mm. The analysis results show that using the method provided by the application, the average shear angle is generally within 3.2°, and the local deviation can be as large as 6.78°; the average deviation angle is within 3.4°, and the maximum local deviation is 13.15°, which improves the deformation characteristics of the component and controls the fiber deformation angle in all areas within the allowable range of the manufacturing process.

[0086] Then the manufacturing boundary is unfolded into a two-dimensional profile of the composite layup using the CATIA V5 CPD module. According to the foregoing technical solution, when the characteristic type is the asymmetric structure, a simplified regular shape composite layup two-dimensional profile is formed. For the asymmetric ear structure longeron of the embodiment, the two-dimensional sheet after unfolding is in a regular rectangular shape. Although the material utilization rate is slightly lower than that of the scheme that retains the ear shape (87% vs. 93%), the preforming defect rate is reduced from 22% to 3.5%, and the quality stability is greatly improved.

[0087] The specific implementation of the unfolding process in this embodiment is that CATIA software approximately divides the composite structure surface into multiple small pieces according to the material properties (T800 carbon fiber / high modulus epoxy resin prepreg is used in this embodiment, the elastic modulus is 165 GPa, and the Poisson's ratio is 0.28), corrects the unfolded pieces according to the theory of elasticity, maintains the continuity between the regions, and avoids wrinkles or overlaps. Through the equidistant mapping algorithm, the small pieces are spliced on the two-dimensional plane to match the manufacturing boundary, and it is ensured that the layup direction of each region is consistent with the aforementioned determined layup reference direction. Due to the asymmetry of the stringer structure, the angle deviation in the layup process needs to be specially controlled. In this embodiment, the deviation of the layup direction is controlled within the range of-0.8° to +0.8°, which is more stringent than the requirement of-1° to +1° in the foregoing embodiment.

[0088] In addition, a positioning structure 6 is designed at the feature position of the composite structure to ensure that the two-dimensional profile of the composite layup corresponds to the position of the forming tool. Considering the characteristics of the asymmetric structure, in addition to being provided at the end, the positioning hole in this embodiment is also increased at the asymmetric ear. The diameter of the end positioning hole is 6 mm±0.2 mm, and the distance from the end of the piece is 30 mm±2 mm, which is increased compared with 25 mm±2 mm in the foregoing embodiment, in order to improve the positioning accuracy under the asymmetric structure. The diameter of the auxiliary positioning hole is 4 mm±0.2 mm, and its position is determined according to the specific position of the asymmetric ear. All positioning holes are processed by special punching tools or ultrasonic cutting to ensure smooth hole edges without burrs. At the same time, the ridge line 2 is projected onto the two-dimensional profile of the composite layup, and the ridge line projection line 3 is marked by a laser projection marking system, which is used as the positioning reference of the composite layup on the tool.

[0089] Step S4: automatic laying and cutting

[0090] According to the two-dimensional profile, an automatic laying program is designed and run to complete the laying of the composite layup, and then the laid composite layup is cut using a cutting device. In this embodiment, the automatic laying is performed by AFP (automatic fiber placement) equipment, the laying speed is 25 m / min, the tape width is 6.35 mm, and the laying accuracy is controlled within ±0.3 mm; the cutting is performed by an ultrasonic cutting device, and the cutting accuracy is controlled within ±0.15 mm. These indicators are more stringent than those in the foregoing embodiment.

[0091] Step S5: hot diaphragm preforming and autoclave curing

[0092] The cut composite material layer is preformed and autoclaved by a hot diaphragm device, and then is mechanically processed to form a net size composite material structure. In this embodiment, the hot diaphragm preforming and autoclaving are completed at one time, the curing temperature is 180°C, the pressure is 0.7 MPa, and the holding time is 2 hours. After curing, mechanical processing is performed, and the processing tolerance is controlled within ±0.08 mm.

[0093] The quality inspection standard of this embodiment is more strict: the three-coordinate measuring instrument is used to detect the unfolded key size, and the allowable deviation is ±0.3 mm; the special protractor is used to detect the fiber laying angle, and the allowable deviation is ±1.5°. These more strict standards are considered in view of the higher requirement of the asymmetric structure on the forming quality.

[0094] The beneficial effect of this embodiment is that: for the asymmetric double-curved stringer with the ear piece structure, the ear piece line segment is straightened and extended to form a regular shape of the manufacturing boundary, and the minimum distortion type outer deviation is selected for manufacturability analysis, so that the special problem faced by the asymmetric structure in the unfolding process is effectively solved; by adding auxiliary positioning holes and using a laser projection system to mark the ridge line projection, the positioning accuracy of the asymmetric structure is improved; by using more strict quality control standards, the stability of the forming quality under the asymmetric structure is ensured. It has been proved in practice that this method can reduce the forming defect rate of the asymmetric structure stringer from 22% to 3.5%, which is reduced by 84%, and the product quality and production efficiency are improved.

[0095] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that various changes, replacements and modifications can be made to the present application without departing from the spirit and scope of the technical solutions of the present application, and these all belong to the scope of protection of the present application. The technical solutions not described in detail in the present application are all conventional technical solutions known by those skilled in the art.

Claims

1. A method for forming a composite material curved surface structure, characterized in that: The steps include: S1: Selecting a characteristic edge line in a three-dimensional geometric model of a composite material structure as a ridge line, defining a ply design origin at the starting point of the ridge line, and establishing a ridge line coordinate system based on the ply design origin; the composite material structure is a hyperbolic long stringer, and the characteristic edge line is a positive corner edge line of a cap top; S2: determining the engineering boundary of the composite material structure and expanding the processing allowance to form a manufacturing boundary; S3: Based on the ridge coordinate system, a manufacturability analysis is performed on the composite material structure with a machining allowance to evaluate whether wrinkles will be generated during the layup process, and then the manufacturing boundary is unfolded into a two-dimensional outline of the composite material layup using design software; S4: Designing and running an automatic placement program according to the two-dimensional contour to complete the placement of the composite material layer, and then using a cutting device to cut the laid composite material layer; S5: The cut composite material layers are preformed and cured in an autoclave using a hot diaphragm device, and then machined to form a net-size composite material structural component.

2. The method according to claim 1, characterized in that The step S1 of establishing the ridge coordinate system includes: The ply reference direction is defined as the tangent direction of the ridge line at the ply design origin; Other ply directions are arranged at predetermined angles based on the reference direction.

3. The method according to claim 1, characterized in that The range of the expanded machining allowance in step S2 is 10-30 mm.

4. The method according to claim 1, wherein In step S2, expanding the machining allowance to form a manufacturing boundary includes: Different machining allowance expansion methods are determined according to the characteristic types of the composite material structure, wherein the characteristic types include symmetrical structures and asymmetrical structures.

5. The method according to claim 4, characterized in that In step S3, using design software to unfold the manufacturing boundary into a two-dimensional outline of the composite material layup includes: When the characteristic type is the symmetrical structure, unfolding to form a two-dimensional profile of the composite material ply that retains the original characteristic profile; When the feature type is the asymmetric structure, a simplified two-dimensional outline of a composite material ply with a regular shape is formed by unfolding.

6. The method according to claim 1, characterized in that The manufacturability analysis of the composite material structure with machining allowance in step S3 includes: Set the maximum fiber deformation angle threshold; Selecting a seed point on the composite material structure with machining allowance as a starting point for fiber propagation outward along the ring direction; Define the radial radius and weft radius of the fiber grid to simulate the placement behavior of fibers in different directions; Select the fiber extension type and run the analysis simulation, the fiber extension type includes minimum distortion type and symmetric type.

7. The method according to claim 1, characterized in that In the step S2, it also includes designing a positioning structure at a characteristic position of the composite material structure to ensure that the two-dimensional contour of the composite material layer corresponds to the position of the forming tool.

8. The method according to claim 7, characterized in that The method also includes projecting the ridge line onto the two-dimensional contour of the composite material layer, and marking the ridge line projection line by a marking device for use as a positioning reference for the composite material layer on a tool.

9. The method according to claim 1, characterized in that The composite material structure is a reinforced structure used in the aerospace field.

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