Method for unfolding and forming two-dimensional material sheet of composite material curved surface structure

Abstract

The invention discloses a two-dimensional material sheet unfolding and forming method of a composite material curved surface structure. The method comprises the following steps: selecting a characteristic side line as a ridge line and establishing a coordinate system; determining an engineering boundary and expanding machining allowance to form a manufacturing boundary; carrying out manufacturability analysis and expanding a manufacturing boundary into a two-dimensional contour; laying and cutting the composite material laying layer; and performing thermal diaphragm preforming and autoclave curing, and then machining and forming. According to the structural symmetry, different machining allowance expansion modes and expansion strategies are adopted. Preforming wrinkles are avoided through manufacturability analysis based on ridge lines; through ridge line projection and positioning structure design, it is ensured that a laying layer accurately corresponds to a tool; and a thermal diaphragm preforming and autoclave curing process is adopted, so that the transfer error is reduced. The method is suitable for complex components such as hyperbolic stringers in the aerospace field, the production efficiency and the material utilization rate are improved, the forming defect rate is reduced, and stable manufacturing of a high-quality composite material structure is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of composite material manufacturing, and in particular to a method for unfolding and forming a two-dimensional sheet of a composite material curved surface structure. Background Art

[0002] Composite stringers are widely used in the design of longitudinal reinforcement structures 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 the digital manufacturing mode. However, for composite structures with complex shapes such as hyperbolic hat stringers, one of the keys in the manufacturing process is to accurately unfold the three-dimensional structural model into two-dimensional sheets and ensure the molding quality.

[0003] At present, there are two prominent problems in the two-dimensional sheet 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 composite material ply after unfolding is highly consistent with the design requirements when applied to complex curved surface structures, especially when dealing with different geometric features (such as symmetrical 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 dimensional deviations and wrinkle defects between the structure after molding and the design model. These problems often require product quality to be verified and improved through repeated trial production, wasting a lot of material and financial resources.

[0004] Although digital technology provides the necessary means to improve product quality stability, increase efficiency and reduce costs, for complex curved surface structures, there is still a lack of a two-dimensional sheet unfolding and forming method that can systematically solve problems such as layer unfolding, manufacturability analysis, positioning accuracy and forming quality. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a two-dimensional sheet unfolding and forming method for a composite material curved surface structure, which can determine the layup reference direction by establishing a coordinate system with the characteristic edge line as the ridge line, thereby achieving high-quality forming of the composite material structure.

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

[0007] Specifically, the composite material structure may be a hyperbolic long stringer, and the characteristic edge line is a positive angle edge line of the top of the hat.

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

[0009] Furthermore, the range of the extended machining allowance is 10-30mm. The manufacturability analysis includes: setting a threshold value for the maximum deformation angle of the fiber; selecting a seed point on the composite material structure with machining allowance as the starting point for the fiber to propagate outward in the circumferential direction; defining the radial radius and latitudinal radius of the fiber grid to simulate the laying behavior of the fiber in different directions; selecting the fiber outward propagation type and running the analysis simulation, the fiber outward propagation type including the minimum distortion type and the symmetric type.

[0010] It is worth noting that the present invention determines different machining allowance expansion methods according to the characteristic type of the composite material structure, and the characteristic type includes a symmetrical structure and an asymmetrical structure. When the characteristic type is the symmetrical structure, the two-dimensional profile of the composite material layer is expanded to retain the original characteristic profile; when the characteristic type is the asymmetrical structure, the two-dimensional profile of the composite material layer with a regular shape is expanded to be simplified.

[0011] In addition, the present invention 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 ply corresponds to the position of the forming tooling, and projecting the ridge line onto the two-dimensional contour of the composite material ply, and marking the ridge line projection line by a marking device, which is used as a positioning reference for the composite material ply on the tooling.

[0012] By adopting the above technical scheme, the two-dimensional sheet unfolding and forming method of the composite material curved surface structure provided by the present invention establishes the ridge coordinate system through the characteristic edge line, determines the engineering boundary and expands it to form the manufacturing boundary, performs manufacturability analysis, unfolds it into a two-dimensional contour, automatically lays and cuts, preforms, and autoclaves and cures it, and performs a complete process of machining, thereby realizing the precise forming of the complex curved surface structure. This method uses the characteristic edge line of the composite material structure as the ridge line and establishes a coordinate system based on it, so that the reference direction of the layer is highly consistent with the structural characteristics; by performing a manufacturability analysis before unfolding, the risk of wrinkles that may occur during the paving process can be pre-evaluated; then, the unfolding is optimized according to the analysis results to ensure the accuracy of the two-dimensional contour; finally, the positioning structure ensures the precise correspondence between the composite material layer and the forming tooling.

[0013] The present invention improves the structural performance by establishing a coordinate system based on the ridge line so that the direction of the ply is consistent with the main force direction of the structure; at the same time, by conducting a manufacturability analysis in advance and adopting differentiated unfolding methods according to different structural characteristics, the quality problems caused by wrinkles and deformation in the traditional method are avoided; in addition, the application of positioning structure and ridge line projection solves the slip problem of composite ply during the molding process, ensuring the consistency of the final molded part with the design model. Through the organic combination of these technical measures, the present invention not only improves the molding quality of composite material structures, but also reduces the waste of material and financial resources caused by repeated trial production, providing reliable technical support for the efficient manufacturing of composite material structures in the aerospace field. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic flow chart of a method for unfolding and forming a two-dimensional sheet of a composite material curved surface structure in one embodiment of the present invention; Figure 2 It is a schematic diagram of a hyperbolic long stringer structure having symmetrical ear features on the edge strip in one embodiment of the present invention; Figure 3 It is a schematic diagram of a hyperbolic long stringer structure with asymmetric ear structures on the edge strips in one embodiment of the present invention.

[0015] Markings in the figure: 1. Lamination design origin; 2. Ridge line; 3. Ridge line projection line; 4. Engineering boundary; 5. Manufacturing boundary; 6. Positioning structure. DETAILED DESCRIPTION

[0016] In the specific implementation of the present invention, in order to make the purpose, technical solution and advantages of the present invention clearer, the terms used in the implementation of the present invention are explained below. It should be noted that the following terminology description is only used to help understanding and should not be regarded as limiting the scope of protection of the present invention.

[0017] EEOP (Engineering Edge of Part) refers to the engineering design boundary, that is, the theoretical boundary of the part.

[0018] MEOP (Manufacturing Edge of Part) refers to the manufacturing design boundary, which is usually the actual processing boundary designed based on EEOP and considering the manufacturing process requirements.

[0019] The ridgeline refers to a characteristic line used to determine the datum of the long stringer expansion. In the embodiment of the present invention, the outer corner edge line of the top of the hat can be selected as the ridgeline.

[0020] The lugs refer to the protruding structures on the long stringer edge strips. According to different structural features, the lugs can be distributed in various forms such as symmetrical distribution, asymmetrical distribution or staggered distribution. The present invention does not limit the specific structural form of the lugs.

[0021] The positioning hole refers to a hole structure used for positioning the sheet, and its specific shape, size and position can be designed according to actual needs, and the present invention does not limit this.

[0022] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention. It should be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and essence of the present invention.

[0023] Embodiment 1 Reference Figure 1 The present invention relates to a method for unfolding and forming a two-dimensional sheet of a composite material curved surface structure, wherein the composite material structure is a hyperbolic long stringer, comprising the following steps: Step S1: Select the feature edge as the ridge line The method of the present invention is applicable to the molding of various composite material structures. Preferably, the composite material structure is a hyperbolic long stringer. The hyperbolic long stringer refers to a reinforcement structure with hyperbolic geometric features, which is commonly used in the longitudinal reinforcement structure of fuselage panels in the aerospace field. Compared with a plane or single-curved structure, a hyperbolic long stringer has a more complex geometric shape and is more difficult to unfold and mold. The method of the present invention has a better technical effect on it.

[0024] In step S1, a characteristic edge line in the three-dimensional geometric model of the composite material structure is selected as the ridge line. In this embodiment, the characteristic edge line is specifically selected as the outer corner edge line of the top of the hyperbolic long stringer. In the structure of the hyperbolic long stringer, the outer corner edge line of the top of the hat is located at the intersection of the top of the hat and the waist of the hat. It is a characteristic line that is almost parallel to the skin shape at this position, that is, the intersection of the long stringer surface and the skin profile surface, which is suitable as a reference for development and positioning. The ply design origin is defined at the starting position of the ridge line, and a ridge line coordinate system is established based on the ply design origin.

[0025] Step S2: Determine the ply reference direction and engineering boundary based on the ridge coordinate system A coordinate system is established based on the ridge line, and the ply reference direction is defined as the tangent direction of the ridge line at the ply design origin. Specifically, the intersection of the characteristic cross section of the long stringer and the ridge line is first selected as the ply design origin, and the ridge line coordinate system is established with the ply design origin. Then, the first axial direction of the ridge line coordinate system is determined to be the tangent direction of the ridge line at the ply design origin, and the second axial direction of the ridge line coordinate system is determined to be perpendicular to the first axial direction. The way this coordinate system is established fully considers the geometric characteristics of the hyperbolic long stringer, and provides a reliable reference for subsequent ply direction control.

[0026] Set other ply directions at predetermined angles based on the base direction: The first axial direction is defined as a 0° layup reference direction; the direction rotated 45° clockwise relative to the 0° layup reference direction is defined as a +45° layup direction; the direction rotated 45° counterclockwise relative to the 0° layup reference direction is defined as a -45° layup direction; the second axial direction is defined as a 90° layup direction.

[0027] This definition method ensures a good correspondence between the laying direction and the geometric characteristics of the long stringer, while meeting the stress requirements of the long stringer: the 0° laying direction is set along the tangent direction of the ridge line, which is the main stress direction of the long stringer and can provide the required longitudinal strength; the ±45° laying direction is used to provide the required shear strength to meet the stress requirements of the long stringer under bending and torsion conditions; the 90° laying direction enhances the lateral strength and overall stability of the long stringer through lateral laying.

[0028] Determine the engineering boundary of the composite material structure, and expand the processing allowance to form a manufacturing boundary. Determine different processing allowance expansion methods according to the characteristic type of the composite material structure, and the characteristic type includes a symmetrical structure and an asymmetrical structure. In this embodiment, the range of the expanded processing allowance is 10mm to 30mm, including 10mm, 20mm and 30mm, preferably 15mm to 25mm, and more preferably 20mm.

[0029] Specifically, when the feature type is a symmetrical structure (such as a long stringer with a symmetrical lug structure), the manufacturing boundary maintains the lug outline in the engineering boundary and only expands the processing allowance; when the feature type is an asymmetrical structure (such as a long stringer with an asymmetrical lug structure), the lug line segment in the engineering boundary is straightened and extended to form the manufacturing boundary. This differentiated boundary determination method can better meet the deployment requirements of long strings with different structural features.

[0030] Step S3: Manufacturability analysis and 2D development Based on the ridge coordinate system, a manufacturability analysis is performed on the composite material structure with processing allowance to evaluate whether wrinkles will be generated during the paving process. In this preferred embodiment, the manufacturability analysis is completed using the CATIA CPD module, and the specific steps are as follows: 1. Set the maximum fiber shear angle threshold, preferably ±15° as the alarm value and ±30° as the limit value. When the fiber shear angle exceeds 15°, the system will issue a warning, indicating that wrinkles may appear in the area; when the shear angle exceeds 30°, the area will almost certainly have severe wrinkles and need to be redesigned.

[0031] 2. Select a seed point on the composite material structure with machining allowance as the starting point for the fiber to propagate outward in the ring direction. In this embodiment, the seed point is preferably set at the center area of ​​the top of the hyperbolic long stringer, so that the fiber propagation can be more uniform.

[0032] 3. Define the radial radius and latitudinal radius of the fiber grid to simulate the placement behavior of the fiber in different directions. The radial radius is used to simulate the behavior of the fiber along the X-axis, and the latitudinal radius is used to simulate the behavior of the fiber along the Y-axis. In this embodiment, for a hyperbolic long 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.

[0033] 4. Select the fiber derivation type and run the analysis simulation. The fiber derivation types include minimum distortion type and symmetric type. The minimum distortion type is a deformation scheme calculated by the system to minimize fiber distortion, and the symmetric type is a deformation scheme calculated symmetrically relative to the fiber direction.

[0034] In this preferred embodiment, for the hyperbolic long stringer with symmetrical structure, symmetrical external diffraction is selected; for the hyperbolic long stringer with asymmetrical structure, minimum distortion external diffraction is selected. In the forming process of a certain type of hyperbolic long stringer adopted in this embodiment, a seed point is set in the cap top area, the radial radius is set to 15mm, the latitudinal radius is set to 8mm, and symmetrical external diffraction is selected for analysis. The analysis results show that, using the method provided by the present invention, the average shear angle is generally within 3°, and the local deviation may be as large as 6.33°; the average deviation angle is within 3°, and the local maximum deviation reaches 12.64°, so that the deformation characteristics of the component are improved, so that the fiber deformation angles in all areas are controlled within the range allowed by the manufacturing process.

[0035] Then, the manufacturing boundary is unfolded into a two-dimensional profile of the composite material ply using design software. In this preferred embodiment, the CATIA composite material design (CPD) module is used for unfolding design, and the software supports functions such as coordinate system establishment based on feature edges, manufacturability analysis, and two-dimensional profile unfolding. Specifically, when the feature type is the symmetrical structure, the two-dimensional profile of the composite material ply is unfolded to retain the original feature profile; when the feature type is the asymmetrical structure, the two-dimensional profile of the composite material ply is unfolded to form a simplified regular shape.

[0036] During the production verification process in this embodiment, it was found that when the hyperbolic long stringer is a symmetrical structure, the two-dimensional sheet unfolding method that retains the original characteristic contour can effectively reduce material waste and improve the efficiency of automatic laying. In a batch of a certain model of fuselage cap-shaped long stringers produced, the material utilization rate increased from 78% to 91% by 13 percentage points compared with the traditional rectangular unfolding method. For asymmetric structures, the regular shape unfolding method reduces the risk of wrinkles during the preforming process. In the production of a certain model of asymmetric long stringers used in this embodiment, after unfolding using this method, the preforming defect rate was reduced from 22% to 4%, and the quality pass rate was improved.

[0037] The specific implementation of the unfolding process in this embodiment is as follows: the design software divides the composite material structure surface into multiple small pieces according to the material properties (polytetrafluoroethylene resin-based composite material, elastic modulus of 70GPa, Poisson's ratio of 0.3), and corrects the unfolded pieces according to the theory of elastic mechanics to maintain the continuity between the regions and avoid wrinkles or overlaps. Through the isometric mapping algorithm, the small pieces are spliced ​​on the two-dimensional plane to match the manufacturing boundary, ensuring that the ply direction of each region is consistent with the ply reference direction determined above, and the deviation of the ply direction is controlled within the range of -1° to +1°.

[0038] In addition, a positioning structure is designed at a characteristic position of the composite material structure to ensure that the two-dimensional profile of the composite material layer corresponds to the position of the forming tool. The characteristic position includes the top position of the cap of the long stringer or the middle position of the cap of the long stringer. At the same time, the ridge line is projected onto the two-dimensional profile of the composite material layer, and the ridge line projection line is marked by a marking device, which is used as the positioning reference of the composite material layer on the tooling.

[0039] Step S4: Automatic placement and cutting The composite material ply is laid out according to the two-dimensional contour design and the automatic laying program is run, and then the laid composite material ply is cut using a cutting device. Due to the use of an unfolding method based on a ridge coordinate system, the unfolded sheet can achieve a deviation of the fiber angle from the theoretical model within the range of ±1°, greatly improving the accuracy of the fiber angle.

[0040] Step S5: Hot diaphragm preforming and autoclave curing The cut composite material ply is preformed and autoclaved by a hot diaphragm device, and then machined to form a net-size composite material structure. The present invention maps the ridges and positioning holes on the three-dimensional model onto the two-dimensional plane sheet after expansion, which can achieve accurate positioning of the sheet and the molding tool, reducing errors in the molding process.

[0041] The above method can improve the deployment accuracy and preforming quality of the hyperbolic long stringer, improve material utilization, and reduce preforming defects. Compared with the prior art, the method of the present invention improves production efficiency and reduces manufacturing costs while ensuring product quality.

[0042] Embodiment 2 Reference Figure 2 Another embodiment of the present invention provides a method for unfolding and forming a two-dimensional sheet of a composite material curved surface structure, wherein the composite material structure is a hyperbolic long stringer, wherein the edge strip of the hyperbolic long stringer has symmetrical ear features. The method comprises the following steps: Step S1: Select the feature edge as the ridge line Following the aforementioned technical solution, this embodiment selects the characteristic edge line in the three-dimensional geometric model of the composite material structure as the ridge line 2, defines the ply design origin 1 at the starting position of the ridge line 2, and establishes a ridge line coordinate system based on the ply design origin 1. In this embodiment, the characteristic edge line is specifically selected as the positive angle edge line of the hyperbolic long truss cap top, and the positive angle edge line is located at the intersection of the cap top and the edge strip. The reason for selecting the positive angle edge line as the ridge line 2 is that: as the intersection characteristic line of the cap top and the edge strip, the positive angle edge line has stable geometric features and is less deformed during the preforming process, and is more suitable as a reference for unfolding and positioning.

[0043] Step S2: Determine the ply reference direction and engineering boundary based on the ridge coordinate system In this step, the ply reference direction is defined as the tangent direction of the spine at the ply design origin, and other ply directions are set at a predetermined angle based on the reference direction. Specifically, the intersection of the characteristic cross section of the long stringer and the spine is selected as the ply design origin, and the spine coordinate system is established with the ply design origin. The first axial direction of the spine coordinate system is determined to be the tangent direction of the spine at the ply design origin, and the second axial direction of the spine coordinate system is determined to be perpendicular to the first axial direction.

[0044] Based on the established spine coordinate system, the first axial direction is defined as the 0° ply reference direction, the direction rotated 45° clockwise relative to the 0° ply reference direction is defined as the +45° ply direction, the direction rotated 45° counterclockwise relative to the 0° ply reference direction is defined as the -45° ply direction, and the second axial direction is defined as the 90° ply direction. This method of establishing the coordinate system and defining the ply direction not only takes into account the geometric characteristics of the long stringer, but also facilitates the control of the ply direction.

[0045] Determine the engineering boundary 4 of the composite material structure, and expand the processing allowance to form a manufacturing boundary 5. In this embodiment, the long stringer edge has left-right symmetrical ear features. When the difference in shape and size between the ears on the left and right sides of the long stringer edge does not exceed 2mm, it is determined to be a symmetrical ear feature, which belongs to the aforementioned symmetrical structure type. First, determine the engineering boundary 4, that is, the theoretical shape profile taking into account the engineering tolerance, and then expand the processing allowance on the basis of the engineering boundary 4 to form a manufacturing boundary 5. In this preferred embodiment, the range of the expanded processing allowance is 10mm to 30mm, including 10mm, 20mm and 30mm, preferably 20mm. The selection of this allowance can ensure sufficient processing margin without causing excessive material waste.

[0046] Different processing allowance expansion methods are determined according to the characteristic type of the composite material structure. In this embodiment, for the symmetrical structure, the outer contour of the ear piece in the MEOP is maintained. Such an unfolding design can improve the material utilization rate of the automatic placement, and the outer contour of the ear piece of the two-dimensional sheet can play a role similar to a cut, reducing the preformed wrinkles in the long stringer edge area.

[0047] Step S3: Manufacturability analysis and 2D development Based on the ridge coordinate system, a manufacturability analysis is performed on the composite material structure with machining allowance to evaluate whether wrinkles will be generated during the paving process. As mentioned above, the manufacturability analysis includes setting the maximum fiber deformation angle threshold, selecting seed points, defining the radial radius and latitudinal radius of the fiber grid, selecting the fiber outward derivative type and running the analysis simulation, etc., which will not be repeated here.

[0048] In this preferred embodiment, CATIA V5 CPD module is used to perform manufacturability analysis. Since the long stringer is a symmetrical structure, the symmetrical external derivation is selected for analysis. In the forming of the hyperbolic long stringer in this embodiment, the seed point is set in the central area of ​​the cap top, the radial radius is set to 12mm, and the latitudinal radius is set to 6mm. The analysis results show that using the method provided by the present invention, the average shear angle is generally within 2.8°, and the local possible deviation is as large as 5.92°; the average deviation angle is within 2.9°, and the local maximum deviation reaches 11.85°, so that the deformation characteristics of the component are improved, so that the fiber deformation angles in all areas are controlled within the range allowed by the manufacturing process.

[0049] Then, the manufacturing boundary is unfolded into a two-dimensional profile of the composite material ply using the CATIA V5 CPD module. According to the aforementioned implementation scheme, when the feature type is the symmetrical structure, the two-dimensional profile of the composite material ply is unfolded to retain the original feature profile. For the symmetrical ear structure long stringer of this embodiment, the unfolded two-dimensional sheet retains the original ear profile, and the material utilization rate reaches 93%, which is 15 percentage points higher than the traditional rectangular unfolding method.

[0050] The specific implementation of the unfolding process is as follows: CATIA software divides the composite material structure surface into multiple small pieces according to the material properties (carbon fiber epoxy resin prepreg is used in this embodiment, the elastic modulus is 135GPa, and the Poisson's ratio is 0.32), and the unfolded pieces are corrected according to the theory of elastic mechanics to maintain the continuity between the regions and avoid wrinkles or overlaps. Through the isometric mapping algorithm, the small pieces are spliced ​​on the two-dimensional plane to match the manufacturing boundary, ensuring that the ply direction of each region is consistent with the ply reference direction determined above, and the deviation of the ply direction is controlled within the range of -1° to +1°. The specific analysis and processing process has been described above and will not be repeated.

[0051] In addition, a positioning structure 6 is designed at a characteristic position of the composite material structure to ensure that the two-dimensional contour of the composite material ply corresponds to the position of the forming tooling. Specifically, a positioning hole is set at the top end of the cap of the long stringer or the middle position of the cap top. The diameter of the positioning hole is 6mm±0.2mm and the distance from the end of the sheet is 25mm±2mm. For long stringers with a length of less than 1000mm, two positioning holes are set. For those with a length greater than 1000mm, one intermediate positioning hole needs to be added every 500mm. The positioning holes are processed with a special punching tool or ultrasonically cut to ensure that the edges of the holes are neat and burr-free. At the same time, the ridge line 2 is projected onto the two-dimensional contour of the composite material ply, and the ridge line projection line 3 is marked by a laser projection system, which is used as a positioning reference for the composite material ply on the tooling.

[0052] Step S4: Automatic placement and cutting The composite material ply is laid out according to the two-dimensional contour design and an automatic laying program is run, and then the laid composite material ply is cut using a cutting device. In this embodiment, the automatic laying is performed using an AFP (automatic fiber placement) device, and the cutting is performed using an ultrasonic cutting device.

[0053] Step S5: Hot diaphragm preforming and autoclave curing The cut composite material plies are preformed and autoclaved by a hot diaphragm device, and then machined to form a net-size composite material structure. In this embodiment, the hot diaphragm preforming and autoclave curing are completed in the autoclave at one time, and the machining is performed after curing.

[0054] In terms of quality control, a three-coordinate measuring machine is used to detect the unfolded dimensions, a special protractor is used to detect the fiber laying angle, and the positioning accuracy and hole size of the locating holes are checked at the same time to ensure the manufacturing quality of the composite structure.

[0055] The beneficial effects of this embodiment are as follows: for a hyperbolic long stringer with a symmetrical ear structure, the material utilization rate is improved by retaining the unfolding method of the original ear contour; the positioning accuracy of the composite material ply on the tooling is improved by setting reasonable positioning holes and ridge 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.

[0056] Embodiment 3 Reference Figure 3 Another embodiment of the present invention provides a method for unfolding and molding a two-dimensional sheet of a composite material curved surface structure, wherein the composite material structure is a hyperbolic long stringer, and the long stringer in this embodiment is a hyperbolic long stringer with an asymmetric edge strip ear structure. The asymmetric structure of the ears on the left and right sides of the long stringer in shape and size increases the difficulty of unfolding design. The molding method provided in this embodiment includes the following steps: Step S1: Select the feature edge as the ridge line According to the above basic principles, this embodiment uses the characteristic edge line in the three-dimensional geometric model of the composite material structure as the ridge line 2. Specifically, the outer corner edge line of the hyperbolic long stringer cap top is selected as the ridge line 2, and the outer corner edge line is located at the intersection of the cap top and the edge strip. In this embodiment, although the ear piece structure of the long stringer edge strip is asymmetric, the characteristics of the outer corner edge line of the cap top are still stable, so it is still selected as the development reference. The ply design origin 1 is defined at the starting position of the ridge line 2, and the ridge line coordinate system is established based on the ply design origin 1.

[0057] Step S2: Determine the ply reference direction and engineering boundary based on the ridge coordinate system According to the technical solution of the present invention, the ply reference direction is defined as the tangent direction of the ridge line at the ply design origin, and other ply directions are set at a predetermined angle based on the reference direction. First, the intersection of the characteristic cross 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 this point. The tangent direction of the ridge line at the ply design origin is determined as the first axial direction of the ridge line coordinate system, and a second axial direction perpendicular to the first axial direction is established.

[0058] On this basis, the layup reference direction is determined: the first axial direction is defined as the 0° layup reference direction, the direction rotated 45° clockwise relative to the 0° layup reference direction is defined as the +45° layup direction, the direction rotated 45° counterclockwise is defined as the -45° layup direction, and the second axial direction is defined as the 90° layup direction. This definition method ensures accurate control of the layup direction under asymmetric structures.

[0059] The engineering boundary 4 of the composite material structure is determined, and the processing allowance is expanded to form a manufacturing boundary 5. In this embodiment, for the long stringer with an asymmetric edge strip and ear structure, the engineering boundary 4 is first determined, and then the processing allowance is expanded to form a manufacturing boundary 5. In this preferred embodiment, the range of the expanded processing allowance is 10mm to 30mm, including 10mm, 18mm and 30mm, preferably 18mm. Compared with the 20mm processing allowance in the previous embodiment, the selection of 18mm in this embodiment is to optimize the material utilization rate under the asymmetric structure.

[0060] Different processing allowance expansion methods are determined according to the characteristic type of the composite material structure. In this 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.

[0061] Step S3: Manufacturability analysis and 2D development Based on the ridge coordinate system, a manufacturability analysis is performed on the composite material structure with processing allowance to evaluate whether wrinkles will be generated during the paving process. The basic steps of the manufacturability analysis have been described above. In this embodiment, since the long stringer is an asymmetric structure, the minimum distortion type is selected for analysis.

[0062] In this preferred embodiment, CATIA V5 CPD module is used for manufacturability analysis. For the asymmetric hyperbolic long stringer of this embodiment, the seed point is set in the front area of ​​the center of the cap top, the radial radius is set to 10mm, and the latitudinal radius is set to 5mm. The analysis results show that, using the method provided by the present invention, the average shear angle is generally within 3.2°, and the local possible deviation is as large as 6.78°; the average deviation angle is within 3.4°, and the local maximum deviation reaches 13.15°, so that the deformation characteristics of the component are improved, so that the fiber deformation angles in all areas are controlled within the range allowed by the manufacturing process.

[0063] Then, the manufacturing boundary is unfolded into a two-dimensional profile of the composite material ply using the CATIA V5 CPD module. According to the aforementioned technical solution, when the feature type is the asymmetric structure, the two-dimensional profile of the composite material ply with a regular shape is unfolded and simplified. For the asymmetric ear structure long stringer of this embodiment, the unfolded two-dimensional sheet is in a regular rectangular shape. Although the material utilization rate is slightly lower than that of the solution retaining the ear shape (87% vs. 93%), the preforming defect rate is reduced from the original 22% to 3.5%, and the quality stability is greatly improved.

[0064] The specific implementation of the unfolding process in this embodiment is as follows: CATIA software divides the composite material structure surface into multiple small pieces according to the material properties (T800 grade carbon fiber / high modulus epoxy resin prepreg is used in this embodiment, with an elastic modulus of 165GPa and a Poisson's ratio of 0.28), and corrects the unfolded pieces according to the theory of elastic mechanics to maintain the continuity between the regions and avoid wrinkles or overlaps. Through the isometric mapping algorithm, the small pieces are spliced ​​on the two-dimensional plane to match the manufacturing boundary, ensuring that the ply direction of each region is consistent with the ply reference direction determined above. Due to the asymmetry of the long stringer structure, it is necessary to control the angle deviation during the ply process. In this embodiment, the deviation of the ply direction is controlled within the range of -0.8° to +0.8°, which is more stringent than the -1° to +1° requirement of the previous embodiment.

[0065] In addition, a positioning structure 6 is designed at a characteristic position of the composite material structure to ensure that the two-dimensional contour of the composite material ply corresponds to the position of the forming tooling. Taking into account the characteristics of the asymmetric structure, in addition to the positioning holes set at the end, auxiliary positioning holes are added at the asymmetric ear pieces in this embodiment. The diameter of the end positioning hole is 6mm±0.2mm, and the distance from the end of the sheet is 30mm±2mm, which is increased from 25mm±2mm in the previous embodiment. This is to improve the positioning accuracy under the asymmetric structure. The diameter of the auxiliary positioning hole is 4mm±0.2mm, and its position is determined according to the specific position of the asymmetric ear piece. All positioning holes are processed by special punching tools or ultrasonic cutting to ensure that the edges of the holes are smooth and free of burrs. At the same time, the ridge line 2 is projected onto the two-dimensional contour of the composite material ply, 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 material ply on the tooling.

[0066] Step S4: Automatic placement and cutting The composite material ply is laid out according to the two-dimensional contour design and the automatic laying program is run, and then the laid composite material ply is cut using a cutting device. In this embodiment, the automatic laying is performed using an AFP (automatic fiber placement) device, the laying speed is 25m / min, the tape width is 6.35mm, and the laying accuracy is controlled within the range of ±0.3mm; the cutting is performed using an ultrasonic cutting device, and the cutting accuracy is controlled within the range of ±0.15mm. These indicators are more stringent than those in the previous embodiments.

[0067] Step S5: Hot diaphragm preforming and autoclave curing The cut composite material ply is preformed and autoclaved by a hot diaphragm device, and then machined to form a net size composite material structure. In this embodiment, hot diaphragm preforming and autoclave curing are completed at one time, the curing temperature is 180°C, the pressure is 0.7MPa, and the insulation time is 2 hours. After curing, mechanical processing is performed, and the processing tolerance is controlled within the range of ±0.08mm.

[0068] The quality inspection standards of this embodiment are more stringent: a three-coordinate measuring machine is used to detect the key dimensions of the unfolding, with an allowable deviation of ±0.3mm; a special protractor is used to detect the fiber laying angle, with an allowable deviation of ±1.5°. These stricter standards take into account the higher requirements of the asymmetric structure on the molding quality.

[0069] The beneficial effects of this embodiment are as follows: for the hyperbolic long stringer with asymmetric edge strip ear structure, by straightening and extending the ear segment to form a regular manufacturing boundary, and selecting the minimum distortion type external derivative for manufacturability analysis, the special difficulties faced by the asymmetric structure during the deployment process are effectively solved; by adding auxiliary positioning holes and using a laser projection system to mark the ridge projection, the positioning accuracy of the asymmetric structure is improved; by stricter quality control standards, the stability of the molding quality under the asymmetric structure is guaranteed. Practice has proved that this method can reduce the molding defect rate of the asymmetric structure long stringer from 22% to 3.5%, a reduction of 84%, and improve product quality and production efficiency.

[0070] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention is described in detail with reference to the above embodiments, it should be understood by those skilled in the art that various changes, substitutions and modifications may be made to the present invention without departing from the spirit and scope of the technical solutions of the present invention, which all belong to the scope of protection claimed by the present invention. The techniques not described in detail in the present invention are all conventional techniques well known to those skilled in the art.

Claims

1. A method for unfolding and forming a two-dimensional sheet of a composite material curved surface structure, characterized in that: The steps include: S1: Select a characteristic edge line in a three-dimensional geometric model of a composite material structure as a ridge line, define a ply design origin at a starting point of the ridge line, and establish a ridge line coordinate system based on the ply design origin; 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 processing allowance to evaluate whether wrinkles will be generated during the laying process, and then the manufacturing boundary is unfolded into a two-dimensional contour of the composite material layer 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 by a hot diaphragm device, and then mechanically processed to form a net-size composite material structural part.

2. The method according to claim 1, characterized in that The composite material structure is a hyperbolic long stringer, and the characteristic edge line is a positive angle edge line of the top of the hat.

3. 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.

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

5. The method according to claim 1, characterized in that In step S2, expanding the machining allowance to form a manufacturing boundary includes: Different machining allowance expansion methods are determined according to the characteristic type of the composite material structure, wherein the characteristic type includes a symmetrical structure and an asymmetrical structure.

6. The method according to claim 5, characterized in that In step S3, using design software to unfold the manufacturing boundary into a two-dimensional outline of the composite material ply 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.

7. 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 the fiber to propagate outward along the ring direction; Define the radial radius and latitudinal 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.

8. 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.

9. The method according to claim 8, 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.

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

Images