Method for laying metal mesh composite film and method for representing the state of composite material parts by texture of metal mesh composite film

Abstract

The present invention proposes a method for laying a metal mesh composite film and a method for characterizing the state of a composite part using the texture of the metal mesh composite film. The laying method includes: pre-setting a metal mesh composite film on the surface of the part to be formed; wherein the parts to be formed include: parts to be co-cured and parts to be co-glued, and the metal mesh composite film is composed of a glue film and a ductile metal mesh; performing different laying treatments on composite skins of different configurations; packaging the laid parts in a vacuum bag, evacuating them, and performing vacuum value testing to form a complete vacuum state; and curing them according to the curing cycle of the metal mesh composite film and prepreg material resin system to generate a composite part. For the design verification and process verification required for large composite parts, the present invention provides a method for rapidly characterizing the internal state of composite parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber composite material parts manufacturing, and in particular relates to a method for laying a metal mesh composite film and a method for characterizing the state of a composite material part by using the texture of the metal mesh composite film. Background Art

[0002] During the development of large composite parts such as aircraft wings, control surfaces, and fuselage panels, the internal structure and quality of composite materials must be inspected. Ultrasonic testing is used to measure thickness and porosity, mechanical properties are measured by cutting and sampling, and porosity and fiber orientation are measured by metallographic photography. These methods lack intuitive inspection results and are time-consuming. When quality issues are discovered, re-sampling and re-inspection of the problematic area are necessary. Based on these test results, the type and cause of the problem can be determined.

[0003] Using a metal mesh composite film as the surface layer of a composite part, changes in the metal mesh pattern and color variation on the surface of the formed part can intuitively characterize areas of thickness variation within the composite part, the locations and edge ranges of overlaps, butt joints, multiple curves, and stringers, as well as fiber compression and resin flow. By comparing the texture and color differences of similar structures at different locations using image grayscale values, quality differences can be quickly identified. Compared to ultrasonic and X-ray detection methods, the metal mesh pattern and color variation can reveal areas of fiber thickness variation as small as 0.1 mm and the pressure distribution of stringers, beams, and ribs in the co-bonded area. Summary of the Invention

[0004] The purpose of the present invention is to propose a method for laying a metal mesh composite film and a method for characterizing the state of a composite material part by using the texture of the metal mesh composite film, which is used to quickly and qualitatively determine the quality state of the composite material part's ply configuration, co-curing, co-bonding, multiple curvatures and other positions.

[0005] To achieve the above object, the present invention provides a method for laying a metal mesh composite film, the method comprising:

[0006] A metal mesh composite film is preset on the surface of the part to be formed; wherein the part to be formed includes: a part to be co-cured and a part to be co-bonded, and the metal mesh composite film is composed of an adhesive film and a ductile metal mesh;

[0007] Different paving treatments are performed on the surfaces of parts with different configurations;

[0008] The parts after laying are packaged in vacuum bags, vacuumed and tested to form a complete vacuum state;

[0009] The metal mesh composite film and prepreg material resin system are cured according to the curing cycle to generate composite material parts.

[0010] Optionally, different paving treatments are performed on the surfaces of parts with different configurations, including:

[0011] For composite skins of different thicknesses and reinforced areas, 3-5 layers are laid and vacuum compacted according to the thickness of the prepreg.

[0012] Optionally, performing different paving treatments on the surfaces of parts with different configurations also includes:

[0013] For composite skins of different thicknesses and when the material width does not meet the designed width, overlapping or butting is required during laying. Depending on the thickness of the prepreg, 3-5 layers are laid and vacuum compacted once.

[0014] Optionally, performing different paving treatments on the surfaces of parts with different configurations also includes:

[0015] For composite material skins that are co-bonded, it is necessary to position the long stringers, ribs, etc. after the laying reaches the thickness of the layer, measure the gap between the laid skin and the long stringers and ribs, and lay the corresponding thickness of the film according to the size of the gap. After positioning, vacuum bag packaging is carried out to complete the bonding process.

[0016] Optionally, performing different paving treatments on the surfaces of parts with different configurations also includes:

[0017] For female mold products with multiple curvatures, vacuum compaction is required after the metal mesh composite film is laid on the tooling to eliminate bubbles between the tooling and the metal mesh composite film before subsequent layering.

[0018] Optionally, after curing according to the curing cycle of the metal mesh composite film and the prepreg material resin system, the following steps may also be performed:

[0019] The cured metal mesh composite membrane skin is demoulded and trimmed.

[0020] The present invention also proposes a method for characterizing the state of a composite material part by using the texture of a metal mesh composite film, the method comprising:

[0021] defining grayscale values ​​of the resin area and the bright area of ​​the metal mesh for the image data of the metal mesh composite film, and defining grayscale value grading;

[0022] According to the grayscale value, the thickness change area, overlap, docking, and co-curing positions are confirmed, and compared with the 3D digital model to confirm the dimensional conformity of the paving position and the stress conditions of the paving and bonding areas.

[0023] The present invention has the following beneficial effects:

[0024] The significance of this invention lies in providing a method for rapidly characterizing the internal quality of large composite parts, which is essential for design and process verification. This method provides a visually intuitive method for assessing and confirming process plans, design compliance, and internal quality. Using image processing software, the images are quantitatively analyzed based on grayscale values ​​to identify areas of thickness variation, overlaps, butt joints, and co-curing. These areas are then compared with 3D digital models to confirm dimensional conformity of placement locations and stress conditions in bonding areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0026] Figure 1 Schematic diagram of an extended copper metal mesh according to an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of the internal structure of the cross-section of the ply thickness variation region and a schematic diagram of a product photo of an embodiment of the present invention;

[0028] Figure 3 A schematic diagram of the internal structure of the ply overlap area cross section and a product photo of an embodiment of the present invention;

[0029] Figure 4 Schematic diagram of the girder bonding area, photos, and thermal deformation diagram of the girder R corner according to an embodiment of the present invention;

[0030] Figure 5 Schematic diagram, photo, and schematic diagram of the wrinkle formation mechanism of the female molded product according to an embodiment of the present invention;

[0031] Figure 6 Schematic diagram of metallographic photographs of typical ply and resin triangle area with ply directions of ±45°, 90°, and 0° in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0034] During the curing process of thermosetting resin-based composites, the resin softens and flows, and the fiber bed with a high fiber volume content bears and transmits pressure. A metal mesh composite film is applied to the surface of the composite part. During the curing process, the pressure carried and transmitted by the fiber bed acts on the metal mesh, which moves toward the mold surface, thinning the resin composite film layer and creating a noticeable metal mesh texture and color difference.

[0035] Composite parts have varying fiber bed thicknesses in areas with varying thicknesses, overlaps, butt joints, and co-curing. Thermal deformation of the bonded parts during co-bonding causes localized pressure differences, and multi-curvature surfaces are subjected to nonlinear forces. This can cause the metal mesh composite film on the surface of composite parts to exhibit metallic streaks, color differences, and resin banding. These variations in the metal mesh are manifestations of the pressure transfer from resin flow and the fiber bed / layup configuration. Using image processing software to quantitatively analyze images based on grayscale values, we can identify areas with varying thicknesses, overlaps, butt joints, and co-curing. Comparing these images with the 3D digital model of the part quickly confirms the dimensional conformity of the placement locations and the stress conditions in the bonding area.

[0036] This embodiment proposes a method for laying a composite film of a mesh, and the laying method includes:

[0037] A metal mesh composite film is preset on the surface of the part to be formed; wherein the part to be formed includes: a part to be co-cured and a part to be co-bonded, and the metal mesh composite film is composed of an adhesive film and a ductile metal mesh;

[0038] Different paving treatments are performed on the surfaces of parts with different configurations;

[0039] The parts after laying are packaged in vacuum bags, vacuumed and tested to form a complete vacuum state;

[0040] The metal mesh composite film and prepreg material resin system are cured according to the curing cycle to generate composite material parts.

[0041] Furthermore, different paving treatments are performed on the surfaces of parts with different configurations, including:

[0042] For composite skins of different thicknesses and reinforced areas, 3-5 layers are laid and vacuum compacted according to the thickness of the prepreg.

[0043] Furthermore, different paving treatments are performed on the surfaces of parts with different configurations, including:

[0044] For composite skins of different thicknesses and when the material width does not meet the designed width, overlapping or butting is required during laying. Depending on the thickness of the prepreg, 3-5 layers are laid and vacuum compacted once.

[0045] Furthermore, different paving treatments are performed on the surfaces of parts with different configurations, including:

[0046] For composite material skins that are co-bonded, it is necessary to position the long stringers, ribs, etc. after the laying reaches the thickness of the layer, measure the gap between the laid skin and the long stringers and ribs, and lay the corresponding thickness of the film according to the size of the gap. After positioning, vacuum bag packaging is carried out to complete the bonding process.

[0047] Furthermore, different paving treatments are performed on the surfaces of parts with different configurations, including:

[0048] For female mold products with multiple curvatures, vacuum compaction is required after the metal mesh composite film is laid on the tooling to eliminate bubbles between the tooling and the metal mesh composite film before subsequent layering.

[0049] Furthermore, after curing according to the curing cycle of the metal mesh composite film and the prepreg material resin system, the following steps are further included:

[0050] The cured metal mesh composite film parts are demoulded and trimmed.

[0051] Specifically, in this embodiment, before laying the first layer of prepreg: Method 1, laying the metal mesh composite film on the tooling surface coated with a release agent, the laying of the metal mesh composite film needs to be butt-jointed, and when the overlapping position is a double-layer mesh, it needs to be cut into one layer; after laying the metal mesh composite film on the tooling, vacuum compaction is required to eliminate bubbles between the tooling and the film, and the metal mesh needs to be flattened.

[0052] Alternatively, before laying the first layer of prepreg: Method 2, lay the adhesive film, which is transparent, translucent, or opaque, and then stick a ductile copper mesh or aluminum mesh on the film surface, such as Figure 1 As shown in the figure, lay the film or metal mesh in a butt-jointed manner to ensure smooth laying. After laying the film and metal mesh on the tooling, use a vacuum method to compact them to eliminate bubbles between the tooling and the film and to make the metal mesh flat.

[0053] For skins of different thicknesses and reinforced areas, depending on the thickness of the prepreg, lay 3-5 layers and perform vacuum compaction to eliminate bubbles. Figure 2 shown.

[0054] For skins of different thicknesses and when the material width does not meet the design width, overlapping or butting is required during layer laying. Depending on the thickness of the prepreg, 3-5 layers are laid and vacuum compacted once. Figure 3 shown.

[0055] For the skin to be glued together, after the pavement reaches the thickness, the long stringers and ribs need to be positioned, the gap between the pavement skin and the long stringers and ribs needs to be measured, and the appropriate thickness of the adhesive film needs to be laid according to the size of the gap. After positioning, vacuum bag packaging is performed to complete the bonding process. Figure 4 shown.

[0056] For products with multiple curvatures, vacuum compaction is required after laying the film and metal mesh on the tooling to eliminate bubbles between the tooling and the film and make the metal mesh flat before proceeding with subsequent layering to reduce wrinkles generated during the laying of vacuum auxiliary materials, thereby avoiding or reducing metal mesh textures and stripes caused by vacuum auxiliary materials. Figure 5 shown.

[0057] The composite parts after laying are packaged in vacuum bags, vacuumed and tested for vacuum value to form a complete vacuum state.

[0058] The metal mesh composite film and prepreg material resin system are cured according to the curing cycle to form composite material parts.

[0059] After curing, demoulding and edge trimming are carried out, and subsequent identification of metal mesh stripes and color differences is carried out.

[0060] This embodiment also proposes a method for characterizing the resin flow and co-bonding interface state during the curing process of the prepreg by the metal mesh composite film texture. The identification method includes:

[0061] Defining grayscale values ​​of the resin area and the bright area of ​​the metal mesh for the image data of the metal mesh composite film, and defining grayscale value grading;

[0062] According to the grayscale value, the thickness change area, overlap, docking, and co-curing positions are confirmed, and compared with the 3D digital model to confirm the dimensional conformity of the paving position and the stress conditions of the paving and bonding areas.

[0063] Confirm and identify the surface status of composite parts, various metal mesh textures, metal mesh color differences, resin strips, and compare them with various configurations of the layup diagram to confirm the consistency or difference between the metal mesh characteristics and the theoretical layup.

[0064] Quantitatively analyze the image and use image processing software to define the grayscale values ​​of the resin area and the bright area of ​​the metal mesh, and define the grayscale value classification. According to the grayscale value, confirm the thickness change area, overlap, docking, co-curing and other positions, and compare with the 3D digital model to confirm the dimensional conformity of the paving position and the stress condition of the paving and bonding areas.

[0065] This embodiment uses a metal mesh on the surface of a composite part to characterize the internal pressure distribution, fiber bed movement, resin flow results and curing quality of the composite part by forming different textures, color differences and other surface phenomena on the surface of the part after molding.

[0066] The mechanism of the metal mesh being pressed out during the curing process is that during the curing process of the part, the air pressure and vacuum pressure in the autoclave are applied to the prepreg layer packaged in the vacuum bag. The pressure is transmitted layer by layer from the auxiliary material on the surface through the surface prepreg to the mold surface. The resin matrix and the fiber bundle share the pressure. The pressure inside the resin matrix is ​​P r , see formula (1). When the resin softens due to heat, high points are formed on the fiber bed at the edges of the prepregs of different layers and at the overlaps of the layers. When the prepregs are glued together, the rebound deformation of the stringer edges and other factors will generate pressure on the fiber bundle / bed. The stress is transmitted through the fiber bed, pressing the metal mesh to the tooling surface, the composite film becomes thinner, and the metal mesh is pressed out, showing metal and resin stripes and color differences.

[0067]

[0068] Where: σ is the external pressure; is the effective stress borne by the fiber network; P r is the resin pressure.

[0069] The thickness of the composite skin involved in this embodiment ranges from 2.6mm to 14.2mm, and the metal mesh can present different stripes. Due to the difference in the thickness of the fiber bed, the resin-rich area, etc., different areas of V f The V of the fiber bed in the sample is different. f The calculated value is between 0.588-0.607%. Combined with the metallographic photos Figure 6 The relaxation and buckling of the upper and lower fibers in the middle black resin triangle area, and the acting force The calculation formula is expressed as formula (2)

[0070]

[0071] Where: V f Fiber volume content, V f0 Initial fiber volume content, E f Fiber flexural modulus, β fiber curvature, V0 maximum fiber volume content.

[0072] The metal mesh is used to lay the first layer of the product on the forming tooling. The metal mesh appearance texture of the composite part after forming can be used to analyze the process and results, and qualitatively judge the internal quality of the part.

[0073] The appearance of the composite part after molding represents the resin flow conditions and pressure transmission conditions and results.

[0074] After molding, the same configuration area of ​​the composite part shows different metal mesh color differences, which represents the resin flow condition and the pressure distribution of the bonding interface.

[0075] The thickness of the metal strips of the ductile metal mesh is approximately 0.03-0.05, and the thickness of the film is approximately 0.1mm. The movement range of the metal strips of the metal mesh in the film is between 0.05-0.10mm. The result of the movement of the metal strips is reflected on the surface of the product. The metal mesh presents different brightness. The brightness of the metal strips ranges from an invisible clear grid to an inversely proportional to the thickness of the film coverage.

[0076] The thickness variation area of ​​the composite skin after molding shows different stripes, which show the thickness difference and position of the fiber bed of the laminate. Figure 2 The number of layers in the reinforcement area changes, and the thickness of the fiber bed changes by more than 0.11 mm, such as Figure 3 As shown, the pressure of the fiber bed is transmitted to the metal mesh, and the metal mesh is pressed out.

[0077] After forming, the composite skin has overlapping areas and butt joints. Figure 3 The overlapped areas of the resin and metal mesh strips correspond to thicker fiber beds. The fiber bed thickness is thinner in the wider areas of the docking area, resulting in darker resin strips. For example, when the unidirectional tape overlaps, where the fiber bed thickness varies by more than 0.11mm, the pressure from the fiber bed is transferred to the metal mesh, causing it to be pressed out and revealing the color of the metal strips.

[0078] Lay-up of the formed composite skin in the stringer bonding area, see Figure 4 (a) reflects the rebound deformation of the long stringer during heating, and the pressure difference on the edge strips, which causes the resin stripes and metal mesh stripes, as well as the color difference of the metal mesh due to the mismatch of the bonding surface. Figure 4 (b) If the long stringer edge undergoes rebound deformation, which causes the local movement of the fiber bed to change by more than 0.11mm, etc. Figure 4 As shown in (c), the pressure of the fiber bed is transmitted to the metal mesh, and the metal mesh is pressed out.

[0079] Due to the deformation of the fiber bed in the above situation, a resin-enriched strip is formed around the deformation. Figure 6 .

[0080] Composite parts formed by negative molding, see Figure 5The wrinkles of the auxiliary materials during the curing process cause the fiber bed to be subjected to illegal forces during the pressurization process, resulting in the displacement of the fibers, which in turn generates different pressures on the metal mesh, causing the local metal mesh to be pressed out, resulting in strips and color differences between the resin and the metal mesh.

[0081] After curing, the different film thicknesses on the metal mesh and the metal strips show different brightness. Using imaging software, it is possible to identify areas of variable thickness, overlaps, butt joints, co-curing and other locations.

[0082] The significance of this embodiment is that, for the design verification and process verification required for large composite parts, a method for quickly characterizing the internal state of composite parts is provided.

[0083] Composite autoclave molding processes include co-curing and co-bonding. Composite aerodynamic parts often utilize stringers and ribs to enhance strength and rigidity. The interface between the stringers, ribs, and the skin during co-curing or co-bonding can affect the quality of the finished composite. Process parameters during the curing process also influence quality.

[0084] Evaluate and confirm the process plan, design compliance and internal quality. The current quality inspection and verification method is to confirm the thickness, porosity and detect FOD through A-scan or C-scan, then perform dimensional measurement, and then cut and sample various parts of the composite parts to test thickness, porosity, etc. Finally, through metallographic inspection, compare the A-scan or C-scan test results to confirm quality compliance.

[0085] The significance of this embodiment lies in providing a method for rapidly characterizing the internal quality of large composite parts, which require design and process verification. This method provides a visually intuitive method for assessing and confirming process plans, design compliance, and internal quality. Using image processing software, the images are quantitatively analyzed based on grayscale values ​​to identify areas of thickness variation, overlaps, butt joints, and co-curing. These areas are then compared with 3D digital models to confirm dimensional conformity of placement locations and stress conditions in bonding areas.

[0086] Composite autoclave molding processes include co-curing and co-bonding. Composite aerodynamic parts often utilize stringers and ribs to enhance strength and rigidity. The interface between the stringers, ribs, and the skin during co-curing or co-bonding can affect the quality of the finished composite. Process parameters during the curing process also influence quality.

[0087] Evaluate and confirm the process plan, design compliance and internal quality. The current quality inspection and verification method is to confirm the thickness, porosity and detect FOD through A-scan or C-scan, then perform dimensional measurement, and then cut and sample various parts of the composite parts to test thickness, porosity, etc. Finally, through metallographic inspection, compare the A-scan or C-scan test results to confirm quality compliance.

[0088] This embodiment can effectively shorten the inspection time, cycle and number of inspections, and optimize the current quality inspection and verification methods, that is, reduce the distribution of A-scan or C-scan points, and reduce the number of cutting samples (testing thickness, porosity, metallographic inspection, etc.) and measurement workload of various parts of composite parts.

[0089] Compared with ultrasonic and X-ray detection methods, the pattern and color difference of the metal mesh can show the area of ​​fiber thickness variation of 0.1mm and the pressure distribution of the long stringers, beams and ribs in the co-bonded area.

[0090] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for characterizing the state of a composite material part by using a metal mesh composite film texture, characterized in that: The method for identifying the resin flow and co-bonding interface state of a metal mesh composite film prepreg laid using a metal mesh composite film laying method during the curing process, wherein the metal mesh composite film texture characterizes the state of a composite material part, includes: defining grayscale values ​​of the resin area and the bright area of ​​the metal mesh for the image data of the metal mesh composite film, and defining grayscale value grading; Confirm the thickness change area, overlap, butt joint, and co-curing position based on the grayscale value, and compare it with the 3D digital model to confirm the dimensional conformity of the paving position, as well as the stress condition of the paving and bonding areas; The method for laying the metal mesh composite film comprises: A metal mesh composite film is preset on the surface of the part to be formed; wherein the part to be formed includes: a part to be co-cured and a part to be co-bonded, and the metal mesh composite film is composed of an adhesive film and a ductile metal mesh; Different paving treatments are performed on the surfaces of parts with different configurations; The parts after laying are packaged in vacuum bags, vacuumed and tested to form a complete vacuum state; The metal mesh composite film and prepreg material resin system are cured according to the curing cycle to generate composite material parts.

2. The method for characterizing the state of a composite material part by using a metal mesh composite film texture according to claim 1, wherein: Different paving treatments are performed on the surfaces of parts with different configurations, including: For composite skins of different thicknesses and reinforced areas, 3-5 layers are laid and vacuum compacted according to the thickness of the prepreg.

3. The method for characterizing the state of a composite material part by using a metal mesh composite film texture according to claim 1, wherein: Different paving treatments for parts with different configurations also include: For composite skins of different thicknesses and when the material width does not meet the designed width, overlapping or butting is required during laying. Depending on the thickness of the prepreg, 3-5 layers are laid and vacuum compacted once.

4. The method of characterizing the state of a composite material part by using a metal mesh composite film texture according to claim 1, wherein: Different paving treatments for parts with different configurations also include: For composite material skins that are co-bonded, it is necessary to position the long stringers, ribs, etc. after the laying reaches the thickness of the layer, measure the gap between the laid skin and the long stringers and ribs, and lay the corresponding thickness of the film according to the size of the gap. After positioning, vacuum bag packaging is carried out to complete the bonding process.

5. The method for characterizing the state of a composite material part by using a metal mesh composite film texture according to claim 1, characterized in that: Different paving treatments for parts with different configurations also include: For female mold products with multiple curvatures, vacuum compaction is required after the metal mesh composite film is laid on the tooling to eliminate bubbles between the tooling and the metal mesh composite film before subsequent layering.

6. The method for characterizing the state of a composite material part by using a metal mesh composite film texture according to claim 1, wherein: After curing according to the curing cycle of the metal mesh composite film and prepreg material resin system, it also includes: The cured metal mesh composite membrane skin is demoulded and trimmed.

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