Automatic forming process method for variable-curvature composite stringer

Abstract

The invention belongs to the technical field of airplane composite material structural part manufacturing, and particularly relates to an automatic forming process method for a variable-curvature composite material stringer. Comprising the following steps that according to surface characteristic parameters of a variable-curvature composite material stringer mold, the surface characteristic parameters are approximately expanded through a geometric expansion method, then model reconstruction is conducted, and a profiling plane blank model is obtained; according to the profiling plane blank model, a laying path is planned through an automatic fiber laying path, the prepreg is laid on the laying mold, and a profiling plane blank is obtained; the profiling plane blank is positioned on a variable-curvature composite material stringer mold, and a variable-curvature stringer prefabricated body is obtained after rolling; and curing to obtain the variable-curvature composite material stringer. The shape of the prepreg blank is unfolded through a geometric unfolding method, a novel rolling forming technology is provided, the problem of wrinkles caused at the curvature change position in the forming process of the variable-curvature stringer is effectively solved, and finally the formed variable-curvature stringer is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of manufacturing aircraft composite material structural parts, and in particular relates to an automated forming process method for a variable curvature composite material long stringer. Background Art

[0002] As a key component of aircraft, composite long stringers are used in large quantities and have relatively regular cross-sectional shapes, which has prompted domestic and foreign aircraft manufacturers to focus on breakthroughs in their automated molding processes. Existing technologies have successfully developed automatic tape laying machines and automatic wire laying machines for carbon fiber composites, which have accelerated the upgrade of composite long stringer molding processes from manual laying to mechanical automated molding. However, due to the small cross-sectional area of ​​composite long stringers, they are not suitable for direct molding using automatic wire laying or automatic tape laying processes. Composite long stringers are mostly variable curvatures in the length direction. In addition, the existence of structural internal and external corners makes it difficult for traditional molding processes to accurately mold with high quality and efficiency. New molding processes have been proposed and practiced in large numbers.

[0003] At present, the mainstream composite long stringer forming processes include hot compression molding, hot diaphragm molding, laminated sliding molding, etc. However, since most of the long stringers used in aircraft have variable curvature, and the mold of the variable curvature composite long stringer is fixed, the composite material itself cannot be compressed and extended in the mold of the variable curvature composite long stringer like metal materials. In addition, due to the anisotropy, lamination and thermal sensitivity of the composite material matrix, the interlayer sliding is affected by the synergistic effects of the molding temperature, molding pressure, molding speed and layer angle, resulting in poor adhesion between the composite material and the variable curvature composite long stringer mold and uneven resin distribution. As a result, in various molding processes, the composite material is prone to wrinkles, bulges and tears at the curvature changes in the composite long stringer mold. In particular, wrinkle defects are almost unavoidable when the variable curvature long stringer is formed, so that the composite long stringer forming process is discontinuous and the quality is unstable due to wrinkles, bulges and tears when the variable curvature long stringer is formed. Summary of the invention

[0004] In order to solve the above problems, the present invention provides an automated forming process method for a long stringer of composite material with variable curvature. In order to overcome the defects of the composite stringer forming process, such as process discontinuity and unstable quality when forming a long stringer of variable curvature, which leads to the decrease of mechanical properties of the prepared long stringer of composite material and the difficulty of meeting the quality standards, the present invention unfolds the shape of the prepreg blank by a geometric unfolding method, and adopts roller forming, and finally realizes the long stringer of variable curvature after forming, forming a continuous process, effectively avoiding the problems such as wrinkles caused at the curvature change during the forming process of the long stringer of variable curvature, and finally realizes the long stringer of variable curvature after forming, with uniform resin distribution, excellent surface quality and meeting the mechanical properties standards.

[0005] The present invention solves the above technical problems through the following technical solutions.

[0006] The object of the present invention is to provide an automated forming process for a long stringer of a composite material with a variable curvature, comprising the following steps: According to the surface characteristic parameters of the variable curvature composite long stringer mold, the surface characteristic parameters are approximately unfolded using the geometric unfolding method, and then the model is reconstructed to obtain the contoured plane blank model.

[0007] According to the contoured flat blank model, the placement path is planned using the automatic wire placement path, and the prepreg is placed on the placement mold to obtain the contoured flat blank.

[0008] The profiled plane blank is positioned on a variable curvature composite material long stringer mold, and then the profiled plane blank is rolled to obtain a variable curvature long stringer preform.

[0009] The variable curvature long stringer preform is cured and then demoulded to obtain a variable curvature composite material long stringer.

[0010] Furthermore, the surface characteristic parameters are the side length, perimeter, area and curvature of each side of the variable curvature composite material long stringer mold and surface defects of the variable curvature composite material long stringer mold, and the surface defects are wrinkles, protrusions and warping.

[0011] Furthermore, the geometric unfolding method is based on surface feature parameters, obtains the unfolding plane of the composite material long stringer mold based on three-dimensional design software, and then reconstructs the long stringer features based on the unfolding plane results, and reconstructs the unfolding plane features through feature recognition, feature mapping and feature reconstruction to obtain a contoured plane blank model.

[0012] Furthermore, the automatic wire placement path planning establishes a corresponding planning algorithm based on the prepreg placement process parameters, the shape surface geometric information characteristic parameters of the contoured flat blank and the component processing parameters to generate the center line of the automatic placement trajectory; wherein the prepreg placement process parameters are the prepreg tape width, the prepreg yarn width and the maximum lateral variability, and the component processing parameters are the placement direction, the stacking order and the number of placement layers.

[0013] Furthermore, the prepreg is a thermosetting or thermoplastic carbon fiber reinforced resin-based prepreg, and the width of the prepreg yarn is 3.0 mm to 13 mm, and the thickness is 0.1 mm to 0.5 mm.

[0014] Furthermore, before the profiling plane blank is positioned, the profiling plane blank is modified, and the profiling plane blank is positioned based on the bottom surface, end top surface and side curved surface contours of the modified profiling plane blank.

[0015] Furthermore, the width of the contoured plane blank is 100% to 105% of the width of the unfolded contoured plane blank model.

[0016] Furthermore, the curing temperature is 120° C. to 420° C., and the curing time is 1 h to 20 h.

[0017] Furthermore, when the contoured plane blank is placed on the variable curvature composite material long stringer mold, the variable curvature composite material long stringer mold is preheated. The variable curvature composite material long stringer mold is heated according to the single-layer thickness and number of layers of the laid contoured plane blank. When the blank thickness increases by 0.04mm to 0.08mm, the heating temperature increases by 6°C to 12°C.

[0018] Furthermore, the shape of the variable curvature composite material long stringer is L-shaped, hat-shaped or C-shaped.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention proposes an automated forming process method for a variable curvature composite long stringer. The shape of the prepreg blank is unfolded by a geometric unfolding method using the surface characteristic parameters of the variable curvature composite long stringer mold. After the model is reconstructed, the structural shape and size parameters of the high-precision variable curvature profiling plane blank obtained by the automatic wire laying path planning laying path are more in line with the mold. The profiling plane blank is positioned on the variable curvature composite long stringer mold and roller forming is adopted. During the rolling process, a tangential force along the rolling direction of the mold is generated, so that the rough profiling plane blank is deformed and fits the surface of the variable curvature composite long stringer mold, which can effectively eliminate wrinkles and gaps. The curvature long stringer is finally formed by curvature curvature, forming a continuous process, which not only saves resources and reduces production costs, but also effectively avoids the problems of wrinkles caused at the curvature change point during the forming process of the variable curvature long stringer. Finally, the resin of the formed variable curvature long stringer is evenly distributed, the surface quality is excellent, and the mechanical properties meet the standards.

[0020] (2) The present invention utilizes a geometric unfolding method to approximately unfold surface feature parameters such as wrinkles, protrusions, and warping on the surface, wherein the most important parameter is the wrinkle defect. Aiming at the demand for efficient unfolding of a variable curvature long stringer, a set of unfolding methods based on the geometric unfolding principle is established, an unfolding plane is obtained for a variable curvature composite material long stringer mold, and then the long stringer features are reconstructed based on the unfolding plane results. The long stringer features are reconstructed through three processes of feature recognition, feature mapping, and feature reconstruction to obtain an unfolded data model to obtain a contoured plane blank model. A corresponding planning algorithm is established according to prepreg laying process parameters, geometric information characteristic parameters of the outer surface of the contoured plane blank, and component processing parameters. The dynamic wire laying path is used to plan the laying path, and the structural shape and size parameters of the high-precision variable curvature contoured plane blank obtained are more in line with the mold.

[0021] (3) Compared with the traditional automated manufacturing and forming processes of composite long girders, such as hot compression molding process, hot diaphragm molding process and laminated sliding molding process, all of which use a single mechanical force perpendicular to the mold surface or external force such as atmospheric pressure to form the long girders preform, the roller forming process adopted in the present invention not only has a force perpendicular to the mold surface, but also generates a tangential force along the rolling direction of the mold during the rolling process, which can effectively eliminate wrinkles and gaps, especially wrinkles caused by curvature changes during the forming process of variable curvature long girders. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figure is a process flow chart of the variable curvature composite material long stringer forming process of the present invention.

[0023] Figure 2 This is a schematic diagram of a long stringer mold of a composite material with variable curvature according to Example 1 of the present invention.

[0024] Figure 3 This is a profiled plane roughcast diagram of the variable curvature composite material long stringer after unfolding according to Example 1 of the present invention.

[0025] Figure 4 This is the path planning diagram of the contoured flat blank after unfolding according to Example 1 of the present invention.

[0026] Figure 5 This is the automatic wire laying diagram of the contoured flat blank after unfolding Example 1 of the present invention.

[0027] Figure 6 This is a schematic diagram of positioning and clamping the contoured flat blank after unfolding Example 1 of the present invention.

[0028] Figure 7 This is a schematic diagram of the rolling process of a long stringer of a variable curvature composite material in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Certain words are used in the present invention to refer to specific components. Those skilled in the art should understand that technicians will use different nouns to refer to the same component. The present invention does not distinguish between components by the difference in nouns, but by the difference in the functions of the components. As mentioned throughout the specification and claims, "including" is an open term and should be understood as "including but not limited to".

[0031] At present, the main processes for forming long stringers of composite materials include hot compression molding, hot diaphragm molding, and laminated sliding molding, all of which use a single mechanical force perpendicular to the mold surface or external forces such as atmospheric pressure to form the long stringer preform. However, since most of the long stringers used in aircraft have variable curvature, the composite material itself cannot be compressed and extended like metal materials. In addition, due to its anisotropy, lamination and thermal sensitivity of the resin matrix, the interlayer sliding is affected by the synergistic effects of molding temperature, molding pressure, molding speed, and laying angle. In various molding processes, it is easy to cause defects such as wrinkles, bulging, and tearing. As a result, when the composite long stringer molding process is used to form variable curvature long stringers, the process is discontinuous, the quality is unstable, and the prepreg sheets are wasted and the cost is high.

[0032] Based on the above problems, the present invention provides an automated forming process method for a long stringer of a composite material with a variable curvature, comprising the following steps: S1. According to the surface characteristic parameters of the variable curvature composite material long stringer mold 1, the surface characteristic parameters are approximately unfolded by using a geometric unfolding method, and then the model is reconstructed to obtain a contoured plane blank model.

[0033] S2. According to the contoured planar blank model, the placement path is planned by using the automatic wire placement path, and the prepreg is placed on the placement mold to obtain the contoured planar blank 2.

[0034] S3, positioning the contoured plane blank 2 on the variable curvature composite material long stringer mold 1, and then rolling the contoured plane blank 2 to obtain a variable curvature long stringer preform.

[0035] S4, curing the variable curvature long stringer preform and then demoulding it to obtain a variable curvature composite material long stringer.

[0036] The present invention provides an automated forming process method for variable-curvature composite stringers. By using the geometric unfolding method to unfold the shape of the prepreg blank, the structural shape and dimensional parameters of the high-precision variable-curvature profiling plane blank are more conforming to the mold. A new rolling forming process is proposed, which not only saves resources, reduces production costs, but also effectively avoids problems such as wrinkles caused by curvature changes during the forming process of variable-curvature stringers. Finally, the formed variable-curvature stringers have uniform resin distribution, excellent surface quality, and meet the mechanical property standards.

[0037] Compared with traditional automated manufacturing and forming processes for composite stringers, such as hot compression molding process, hot diaphragm molding process, and laminated slip forming process, all of which use an external force such as a single mechanical force or atmospheric pressure perpendicular to the mold surface to form the stringer preform. The rolling forming process adopted in the present invention not only has a force perpendicular to the mold surface, but also generates a tangential force along the rolling direction of the mold during the rolling process, which can effectively eliminate wrinkles and voids, especially the wrinkles at the curvature change during the forming process of variable-curvature stringers.

[0038] In some specific embodiments, the surface feature parameters are the side length, perimeter, area of the variable-curvature composite stringer mold 1, and the curvature of each side and the surface defects of the variable-curvature composite stringer mold 1. The surface defects include wrinkles, protrusions, and warping. It should be noted that during the stringer forming process, defects such as wrinkles, protrusions, and warping will appear on the surface. Using the geometric unfolding method to approximately unfold the surface feature parameters such as the wrinkles, protrusions, and warping that appear on the surface, and the most important parameter is the wrinkle defect, with the aim of making the structural shape and dimensional parameters of the high-precision variable-curvature profiling plane blank more conforming to the mold.

[0039] In some specific embodiments, the geometric unfolding method is based on the surface feature parameters, and the unfolding plane of the composite long stringer mold is obtained based on the three-dimensional design software, and then the long stringer features are reconstructed based on the unfolding plane results, and the unfolding plane is reconstructed through feature recognition, feature mapping and feature reconstruction to obtain a contour plane blank model. It should be noted that the present invention aims at the efficient unfolding requirements of the variable curvature long stringer, and establishes a set of unfolding methods based on the geometric unfolding principle. First, the unfolding plane is obtained through the variable curvature composite long stringer mold 1, that is, the three-dimensional surface feature parameters of the composite long stringer mold 1 are unfolded into two-dimensional plane feature parameters, and the two-dimensional plane feature parameters of the variable curvature composite long stringer mold 1 are obtained with reference to the surface feature parameters of the long stringer curvature, length and width of the three-dimensional feature, and then the long stringer unfolding plane is obtained based on the three-dimensional design software, and then the long stringer features are reconstructed based on the unfolding plane results, and the long stringer is reconstructed through the three processes of feature recognition, feature mapping and feature reconstruction, and the unfolded CAD data model is obtained based on the secondary development function of the CATIA three-dimensional design software to obtain a contour plane blank model, so that the structural shape and size parameters of the obtained high-precision variable curvature contour plane blank are more in line with the mold.

[0040] In some specific embodiments, the automatic wire placement path planning placement path establishes a corresponding planning algorithm based on the prepreg placement process parameters, the geometric information characteristic parameters of the outer shape surface of the contoured plane blank 2, and the component processing parameters to generate the center line of the automatic placement trajectory; wherein the prepreg placement process parameters are the prepreg tape width, the prepreg yarn width, and the maximum lateral variability, and the component processing parameters are the placement direction, the stacking sequence, and the number of layers. It should be noted that in the automatic wire placement path planning placement path of the present invention, it is mainly based on the input prepreg tape placement process information such as the prepreg tape width, the prepreg yarn width, the maximum lateral variability, etc., the geometric information characteristics of the component outer shape surface, and the characteristic information of the placement equipment such as the maximum number of layable tows, etc., and the component processing information such as the placement direction, the stacking sequence, and the number of layers are used to establish a corresponding planning algorithm to generate the center line of the automatic placement trajectory.

[0041] It should be noted that in the automatic wire laying path planning placement path, the prepreg is laid out in N layers step by step to obtain the contoured plane blank 2, where N≥1. The thickness of the contoured plane blank 2 is determined by reconstructing the surface features of the wall panel based on the original feature thickness and the mapped bottom contour line. The surface features are divided into equal thickness features and unequal thickness features, which need to be reconstructed using two different methods. Equal thickness features do not require the thickness to remain unchanged, and thickness fluctuations within a certain range are allowed. At this time, the blank thickness needs to be determined by stretching based on the bottom wheel line; if the current feature is an unequal thickness feature, the blank thickness needs to be determined based on the distance information between the surface control point and the base surface of the original model feature.

[0042] In some embodiments, the prepreg is a thermosetting or thermoplastic carbon fiber reinforced resin-based prepreg, the prepreg wire width is 3.0 mm to 13 mm, and the thickness is 0.1 mm to 0.5 mm. Preferably, the prepreg is a thermosetting CFRP prepreg, the prepreg wire width is 6.35 mm, and the thickness is 0.13 mm.

[0043] In some embodiments, before the profiling plane blank 2 is positioned, the profiling plane blank 2 is trimmed, and the profiling plane blank 2 is positioned based on the bottom surface, end top surface and side curved surface contours of the modified profiling plane blank 2. It should be noted that the present invention uses an automatic wire laying device to achieve automated and efficient manufacturing of the profiling plane blank 2, and then fixes the profiling plane blank 2 on a rolling workbench through a positioning clamping device, and then completes the roll forming of the profiling plane blank 2 through an automated rolling device, and finally completes the final curing forming of the composite material long stringer through a curing process. Before the profiling plane blank 2 is positioned, the profiling plane blank 2 needs to be trimmed to facilitate the positioning of the profiling plane blank 2, and the profiling plane blank 2 is positioned based on the bottom surface, end top surface and side curved surface contours of the modified profiling plane blank 2, such as Figure 6 As shown, two side pins 3 are used to limit two degrees of freedom on the top curved surface of the profiling plane blank 2, an end positioning pin 4 is used to clamp the end on one end side to limit one degree of freedom, and a bottom positioning pin 5 is used in the middle of the bottom curved surface contour to elastically constrain the profiling plane blank 2. The end positioning pins 4 and the bottom positioning pins 5 are used to limit three freedoms of the profiling plane blank, and the profiling plane blank is positioned on the variable curvature composite material long stringer mold.

[0044] In some embodiments, the width of the profiling plane blank is 100% to 105% of the width of the profiling plane blank model after unfolding. The width of the profiling plane blank is not less than the width of the profiling plane blank model after unfolding, the purpose of which is to compensate for the accuracy of the laying misalignment and rolling track, and to facilitate later trimming. The upper limit of the width of the profiling plane blank is 105% of the original width of the mold.

[0045] In some specific embodiments, the curing includes thermosetting and thermoplastic resin systems, the curing temperature is 120°C to 420°C, and the curing time is 1h to 20h. Preferably, in a specific embodiment, the prepreg is a thermosetting CFRP prepreg, the curing temperature is 180°C, and the curing time is 3h.

[0046] In some specific embodiments, when the profiled plane blank is placed on the variable curvature composite long stringer mold 1, the profiled plane blank 2 is then rolled, and the variable curvature composite long stringer mold 1 is preheated first. The temperature is heated according to the single-layer thickness and number of layers of the laid profiled plane blank. When the blank thickness increases by 0.04mm-0.08mm, the heating temperature increases by 6℃-12℃, and the blank edge is trimmed to align the profiled plane blank 2 with the edge of the variable curvature composite long stringer mold 1. The profiled plane blank laid on the variable curvature mold is rolled using a profiled roller head to obtain a variable curvature long stringer preform; the stress concentration effect at the R angle position of the variable curvature long stringer preform is affected by the rolling pressure, wherein the R angle refers to the top angle or corner angle of the long stringer preform. Since the thickness of the blank will increase the bonding force, rigidity and hardness between the blank layers, the rolling is to deform the blank and fit the mold surface.

[0047] In some specific embodiments, the variable curvature composite material stringer is in an L-shape, a hat-shape or a C-shape.

[0048] The invention is further described below through specific examples.

[0049] Example 1 This embodiment provides an L-shaped curvature composite material long stringer automatic forming process method, the process flow is as follows Figure 1 As shown, the following steps are included: S1. Continuous development of variable curvature long stringer profiling: The variable curvature composite material long stringer mold 1 is as follows Figure 2 As shown, according to the surface feature parameters of the variable curvature composite long stringer mold 1, that is, according to the geometric features of the variable curvature composite long stringer mold 1, wherein the geometric features are the side length, perimeter and area of ​​the variable curvature composite long stringer mold 1, as well as the curvature information of each side, the surface defects of wrinkles, protrusions and warping of the variable curvature composite long stringer mold, the surface features of the variable curvature composite long stringer mold 1 are approximately unfolded by using the geometric unfolding method through the plug-in secondary developed by CATIA, the long stringer features are reconstructed based on the unfolded plane results, the long stringer features are reconstructed through feature recognition, feature mapping and feature reconstruction, and the model is reconstructed to obtain a contoured plane blank model. The contoured plane blank model of the variable curvature composite long stringer after unfolding is as shown in FIG. Figure 3 shown.

[0050] S2. Automatic wire laying path planning on a contoured plane: CFRP prepreg is selected as the laying raw material. The prepreg wire width is 6.35mm and the thickness is 0.125mm. Based on the obtained high-precision square blank model, the laying path is planned using the path planning software. The equidistant translation method is used. The laying margin is greater than 20mm, which is convenient for trimming. The laying path is as follows: Figure 4As shown, a corresponding planning algorithm is established based on the prepreg laying process parameters, the geometric information characteristic parameters of the outer surface of the contoured plane blank 2, and the component processing parameters. According to the input prepreg tape laying process information such as prepreg tape bandwidth, prepreg yarn width, maximum lateral variability, etc., component outer surface geometric information characteristics and characteristic information of the laying equipment such as the maximum number of layable filament bundles, etc., a corresponding planning algorithm is established according to the component processing information such as laying direction, stacking sequence and laying layer number, etc., to generate the center line of the automatic laying trajectory, and reasonable planning is performed according to the width of the prepreg yarn. The width stroke of the automatically laid blank is extended by a certain margin to ensure that the width of the laid contoured plane blank is not less than 102% of the width of the unfolded high-precision contoured plane blank model.

[0051] S3. Profiling plane blank manufacturing: According to the profiling plane blank model, use a tape laying machine or a wire laying machine to automatically lay it on a neat flat plate onto the laying mold. The automatic wire laying diagram of the profiling plane blank is as follows: Figure 5 As shown, the prepreg is laid step by step in a layering manner with [0 / +45 / -45 / 90] as a unit, and a total of 4 [0 / +45 / -45 / 90] layers are laid with a total thickness of 2 mm, to obtain a contoured plane blank 2, and the contoured plane blank 2 is shaped to facilitate the positioning of the contoured plane blank 2.

[0052] S4, positioning of the profiling plane blank: positioning the profiling plane blank 2 based on the bottom surface, end top surface and side curved surface contours of the modified profiling plane plate blank 3. The schematic diagram of positioning and clamping the profiling plane blank 2 is shown in FIG. Figure 6 As shown, two side pins 3 are used to limit two degrees of freedom on the top curved surface of the contoured plane blank, an end positioning pin 4 is used to clamp the end on the side of one end to limit one degree of freedom, and a bottom positioning pin 5 is used in the middle of the bottom curved surface contour to elastically constrain the contoured plane blank. The end positioning pins 4 and the bottom positioning pins 5 are used to limit three freedoms of the contoured plane blank, and the contoured plane blank is positioned on the L-shaped curvature composite material long stringer mold, and the ends are fixed and the sides are elastically constrained.

[0053] S5, roll forming preform: after positioning the profiled flat blank 2, heating the mold, the mold is an upper mold 6 and a lower mold 7, the upper mold 6 clamps the lower mold 7, the profiled flat blank 2 is clamped between the upper mold 6 and the lower mold 7, the mold temperature is heated to an appropriate temperature according to the single layer thickness and number of layers of the laid profiled flat blank 2, and the blank edge is trimmed to align the profiled flat blank 2 with the mold edge, such as Figure 7As shown, a profiling roller head is then used to roll the profiling plane blank 2 laid on the variable curvature mold. The rolling pressure during the rolling process is 0.3 MPa. When the blank thickness increases by 0.06 mm, the heating temperature increases by 10°C, and the edge of the blank is trimmed to align the profiling plane blank with the edge of the variable curvature composite material long stringer mold to obtain an L-shaped variable curvature long stringer preform, that is, a roll-formed preform is obtained.

[0054] S6, preform curing and demoulding: the long stringer preform in S5 is placed in an autoclave or a high-temperature drying oven for curing, heated to 180°C, kept warm for 3 hours, and then cooled to room temperature and taken out and demoulded.

[0055] S7, variable curvature composite material long stringer: demoulding to obtain an L-shaped variable curvature composite material long stringer component.

[0056] In summary, the present invention provides an automated forming process method for a variable curvature composite material long stringer to overcome the problems of wrinkles caused by out-of-plane buckling at the curvature change and uneven resin distribution leading to discontinuity of the variable curvature long stringer forming process, unstable quality, waste of prepreg sheets, decreased mechanical properties of the prepared composite long stringer, and difficulty in meeting quality standards. The present invention unfolds the prepreg blank shape through a geometric unfolding method, and proposes a new roller forming process, which effectively avoids the problems of wrinkles caused at the curvature change during the forming process of the variable curvature long stringer, and ultimately achieves a variable curvature long stringer after forming with uniform resin distribution, excellent surface quality, and qualified mechanical properties.

[0057] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0058] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An automated forming process for a variable curvature composite long stringer, characterized in that: The following steps are involved: According to the surface characteristic parameters of the variable curvature composite material long stringer mold (1), the surface characteristic parameters are approximately unfolded using a geometric unfolding method, and then the model is reconstructed to obtain a contoured plane blank model; According to the contoured plane blank model, the placement path is planned by using the automatic wire placement path, and the prepreg is placed on the placement mold to obtain the contoured plane blank (2); Positioning the contoured plane blank (2) on the variable curvature composite material long stringer mold (1), and then rolling the contoured plane blank (2) to obtain a variable curvature long stringer preform; The variable curvature long stringer preform is cured and then demoulded to obtain a variable curvature composite material long stringer.

2. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: The surface characteristic parameters are the side length, perimeter, area and curvature of each side of the variable curvature composite material long stringer mould (1) and surface defects of the variable curvature composite material long stringer mould (1), and the surface defects are wrinkles, protrusions and warping.

3. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: The geometric unfolding method is based on surface feature parameters, obtains the unfolding plane of the composite material long stringer mould (1) based on three-dimensional design software, and then reconstructs the long stringer features based on the unfolding plane result, and reconstructs the features of the unfolding plane through feature recognition, feature mapping and feature reconstruction to obtain a contoured plane blank model.

4. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: The automatic wire placement path planning method establishes a corresponding planning algorithm for the placement path based on the prepreg placement process parameters, the geometric information characteristic parameters of the outer surface of the contoured plane blank (2), and the component processing parameters, and generates the center line of the automatic placement trajectory; wherein the prepreg placement process parameters are the prepreg tape width, the prepreg yarn width, and the maximum lateral variability, and the component processing parameters are the placement direction, the stacking order, and the number of placement layers.

5. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: The prepreg is a thermosetting or thermoplastic carbon fiber reinforced resin-based prepreg, and the width of the prepreg yarn is 3.0mm to 13mm and the thickness is 0.1mm to 0.5mm.

6. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: Before the profiling plane blank (2) is positioned, the profiling plane blank (2) is reshaped, and the profiling plane blank (2) is positioned based on the bottom surface, end top surface and side curved surface contours of the reshaped profiling plane blank (2).

7. The automatic forming process of a variable curvature composite long stringer according to claim 1, characterized in that: The width of the profiling plane blank (2) is 100% to 105% of the width of the unfolded profiling plane blank model.

8. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: The curing temperature is 120° C. to 420° C., and the curing time is 1 hour to 20 hours.

9. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: When the profiled plane blank (2) is placed on the variable curvature composite material long string mold (1), the variable curvature composite material long string mold (1) is preheated. The variable curvature composite material long string mold (1) is heated at a temperature according to the single layer thickness and the number of layers of the laid profiled plane blank (2). When the blank thickness increases by 0.04 mm to 0.08 mm, the heating temperature increases by 6° C. to 12° C.

10. The automatic forming process of a variable curvature composite material long stringer according to claim 1, characterized in that: The variable curvature composite material long stringer has an L-shape, a hat-shape or a C-shape.

Images