Lightweight low-scattering carbon fiber composite wedge and forming method thereof

Abstract

The invention provides a light-weight low-scattering carbon fiber composite material wedge and a forming method thereof, and belongs to the technical field of radar target characteristic testing. The low-scattering wedges are in a carbon fiber composite skin foam sandwich structure form, and the outer surfaces of the wedges have the characteristics of high precision, high strength and continuous electric conduction. The wedge outer skin is formed through the combination of a high-precision mold and an autoclave forming process, the temperature in the prepreg paving process and the curing forming process is accurately controlled, and the low-scattering special-shaped closed curved surface appearance with high profile precision is formed. Through the combination of a polyurethane foaming process and a positioning tool, the assemblability of the low-scattering wedges is realized, and the light weight of an interlayer composite material is kept. Compared with the prior art, the forming method of the light-weight low-scattering carbon fiber composite wedge has the advantages of being high in forming surface quality, light in weight, resistant to corrosion and integrated in structure and function, and has the long service life.

Description

Technical Field

[0001] The invention relates to the technical field of radar target characteristic testing, discloses a method for forming a low-scattering wedge, and particularly relates to a method for forming a lightweight low-scattering carbon fiber composite material wedge. Background Art

[0002] In electromagnetic scattering measurement, the performance of the target support structure wedge is very critical. It not only plays the role of structural support but also provides low scattering functionality, requiring its own scattering to be small and its interaction with the target to be small. To achieve low scattering, the shape of the wedge and its efficiency in reflecting electromagnetic waves play a very critical role.

[0003] So far, three types of wedge structures and corresponding manufacturing methods have been developed, which are foam wedges, high-strength non-metallic suspension wires and metal wedges in order of development. Among them, foam wedges and metal wedges are widely used. Foam wedges have low density, low scattering, and impact resistance, but low mechanical strength and poor bearing capacity. Foam wedges are usually formed by five-axis machining of low-scattering shapes or mold foaming. Five-axis machining of foam has poor precision, high cost and low efficiency. The mold direct foaming method gradually replaces foam machining. Metal wedges have strong bearing capacity and high reflectivity, but the shape is easy to bump, poor environmental adaptability, and heavy weight. In particular, the cutting cost of metal wedges with complex curved shapes is very high, but due to the strong machinability of metals, it can adapt to various complex shapes with low scattering characteristics and has a wider range of applications. The cross-section of a general wedge is a rhombus or an oval composed of two arc surfaces. The wedge shape features sharp leading and trailing edges and a smooth surface. These requirements determine the limitations of foam wedges, and it is difficult for general materials to meet this requirement.

[0004] In the current electromagnetic scattering measurement, the US National Test Site, Boeing's outdoor test site, the UK Underwood Quarry test site and the Brazilian test site all use a metal skin combined with a metal bracket structure. Domestic research on low-scattering wedges started relatively late. The Second Academy of Aerospace, Beijing University of Aeronautics and Astronautics, Shanghai University and other institutions have all carried out structural design, appearance design and material system design for low-scattering metal wedges.

[0005] There is no research on the use of carbon fiber reinforced resin-based composite sandwich structures to form low-scattering wedges in China. It is necessary to solve technical problems such as high-precision overall forming of complex curved surfaces, conductive and continuous outer surface, lightweight and high load-bearing capacity, so as to achieve integrated structural and functional forming. Summary of the invention

[0006] In view of the target support structure's demand for lightweight and high-load-bearing low-scattering wedges, while achieving low-cost and efficient production, the purpose of the present invention is to provide a molding method for a low-scattering wedge of a carbon fiber composite material, which can mold a low-scattering wedge with excellent properties such as lightweight, high precision, high load-bearing and continuous surface conductivity in one step.

[0007] The molding method proposed by the present invention is realized by the following technical solutions:

[0008] A lightweight, low-scattering carbon fiber composite material wedge, comprising a central metal support component c, a wedge outer skin a, a flange d, and a foamed body b; the central metal support component c is a cylindrical structure;

[0009] The central metal support assembly is located in the wedge outer skin, and both ends thereof are connected to the corresponding side wedge outer skins through flanges;

[0010] The area enclosed by the wedge outer skin a and the central metal support component c is filled with a foamed body b.

[0011] A method for forming a lightweight low-scattering carbon fiber composite material wedge is used to form a lightweight low-scattering carbon fiber composite material wedge as described above, and is characterized in that it specifically comprises the following steps:

[0012] Step 1, metallization spraying is performed on the left mold, the right mold and the end face flanging mold respectively, and a metal transfer method is adopted to realize the conductivity and continuous conductivity of the surface of the carbon fiber composite material;

[0013] Step 2, respectively covering the left mold, the right mold and the end face flanging mold with carbon fiber prepreg, and placing them in a vacuum bag for vacuum pre-compaction;

[0014] Step 3, after the left mold, the right mold and the end face flanging mold are molded together, the mold gap is processed, and the molded whole mold is placed in a vacuum bag, and heated, pressurized and solidified to form a wedge outer skin rough blank;

[0015] Step 4, taking the rough blank of the pointed wedge outer skin out of the integral mold, performing a surface transfer film removal treatment and a sharp edge deburring treatment to obtain the pointed wedge outer skin;

[0016] Step 5, placing the wedge outer skin in a foaming mold, installing a central metal support assembly, and performing polyurethane foaming. The polyurethane foaming is performed in multiple times depending on the foaming volume, and post-curing treatment is performed;

[0017] Step 6, after gluing the positioning metal flange of the wedge end face, install the assembly positioning tool.

[0018] Step 7, after stabilization, take the wedge out of the mold and perform post-processing into a finished wedge.

[0019] Furthermore, in step 1, the thickness of the metallized sprayed aluminum layer should be greater than 140 μm.

[0020] Furthermore, a carbon fiber / epoxy resin satin prepreg with a thickness of 0.25 mm and a carbon fiber / epoxy resin satin prepreg with a thickness of 0.50 mm are used, and the resin content is 38%-40%.

[0021] Furthermore, the edge transition of the prepreg paving is treated with symmetrical gradient paving, and after the mold is closed, the paving is overlapped to strengthen the sharp-angled and irregular-shaped areas.

[0022] Furthermore, carbon fiber unidirectional prepreg twist strips are used to fill the narrow area of ​​the sharp corner of the wedge, filled with foam glue, and overlapped in combination with the prepreg paving method in step 2.

[0023] Furthermore, an airbag is used to pre-compact the prepreg in the closed mold cavity. The airbag is slowly pressurized to 0.6 MPa at room temperature and maintained for 20-30 minutes to pre-compact the carbon fiber prepreg so that the prepreg and the mold fit tightly.

[0024] Furthermore, in order to improve the interfacial adhesive strength between the foam and the carbon fiber composite material, the foaming surface was polished, and cylindrical holes with a diameter of 5 mm and a depth of 10 mm were evenly processed on the foam bonding surface to increase the bonding area;

[0025] Further, in step 2, during the prepreg laying process, the pre-compacting times are no less than 3 times;

[0026] Further, the left mold and the right mold each include a wedge matching surface, two connecting surfaces and two end surfaces; the two connecting surfaces are respectively connected to the left and right sides of the wedge matching surface, and the connecting surfaces opposite to the left mold and the right mold are connected by bolts; the two end surfaces are respectively located on the upper and lower sides of the tip matching surface; the end surface of the left mold and the end surface of the right mold cooperate to form an annular support table surface;

[0027] The end surface is provided with a supporting vertical plate and a flanging rib, which are respectively used to cooperate with the assembly positioning tooling and the end surface flanging mold.

[0028] Furthermore, the assembly positioning tooling is an L-shaped structure, part of which is pressed on the top of the end face flanging mold, and part of which is connected to the supporting vertical plate; the end face flanging mold is a flat plate structure, which is pressed on the top of the flanging stop.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention provides a composite material molding method for complex conductive closed surfaces, and through the control of the molding process and the advantages of autoclave molding, the high precision of the composite material surface shape can be achieved, thereby achieving low scattering functionality; secondly, the continuity of metallization can be achieved through mold design and molding process, thereby improving production efficiency and product stability and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a cross-sectional view of the product structure of the present invention.

[0032] Figure 2 It is a process flow chart of the molding method of the present invention.

[0033] Figure 3 It is a product appearance structure diagram of the present invention.

[0034] Figure 4 This is the general assembly drawing of the wedge mold.

[0035] Figure 5 It is a schematic diagram of the assembly of the left and right molds in the wedge mold.

[0036] Figure 6 It is a schematic diagram of the structure of the end face flanging die in the wedge die.

[0037] Figure 7 It is a structural schematic diagram of the assembly and positioning tooling in the wedge mold.

[0038] In the figure: 1. left mold, 2. right mold, 3. assembly positioning tooling, 4. end face flanging mold, 1-1. end face, 1-2. wedge matching surface, 1-3. connecting surface, 1-4. flanging stop, 1-5. supporting vertical plate. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be described in detail and in full in combination with the drawings in the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0040] A lightweight, low-scattering carbon fiber composite material wedge, comprising a central metal support component c, a wedge outer skin a, a flange d, and a foamed body b; the central metal support component c is a cylindrical structure;

[0041] The central metal support assembly is located in the wedge outer skin, and both ends thereof are connected to the corresponding side wedge outer skins through flanges;

[0042] The area enclosed by the wedge outer skin a and the central metal support component c is filled with a foamed body b.

[0043] A method for forming a lightweight low-scattering carbon fiber composite material wedge is used to form a lightweight low-scattering carbon fiber composite material wedge as described above, and is characterized in that it specifically comprises the following steps:

[0044] Step 1, metallization spraying is performed on the left mold, the right mold and the end face flanging mold respectively, and a metal transfer method is adopted to realize the conductivity and continuous conductivity of the surface of the carbon fiber composite material;

[0045] Step 2, respectively covering the left mold, the right mold and the end face flanging mold with carbon fiber prepreg, and placing them in a vacuum bag for vacuum pre-compaction;

[0046] Step 3, after the left mold, the right mold and the end face flanging mold are molded together, the mold gap is processed, and the molded whole mold is placed in a vacuum bag, and heated, pressurized and solidified to form a wedge outer skin rough blank;

[0047] Step 4, taking the rough blank of the pointed wedge outer skin out of the integral mold, performing a surface transfer film removal treatment and a sharp edge deburring treatment to obtain the pointed wedge outer skin;

[0048] Step 5, placing the wedge outer skin in a foaming mold, installing a central metal support assembly, and performing polyurethane foaming. The polyurethane foaming is performed in multiple times depending on the foaming volume, and post-curing treatment is performed;

[0049] Step 6, after gluing the positioning metal flange of the wedge end face, install the assembly positioning tool.

[0050] Step 7, after stabilization, take the wedge out of the mold and perform post-processing into a finished wedge.

[0051] Furthermore, in step 1, the thickness of the metallized sprayed aluminum layer should be greater than 140 μm.

[0052] Furthermore, a carbon fiber / epoxy resin satin prepreg with a thickness of 0.25 mm and a carbon fiber / epoxy resin satin prepreg with a thickness of 0.50 mm are used, and the resin content is 38%-40%.

[0053] Furthermore, the edge transition of the prepreg paving is treated with symmetrical gradient paving, and after the mold is closed, the paving is overlapped to strengthen the sharp-angled and irregular-shaped areas.

[0054] Furthermore, carbon fiber unidirectional prepreg twist strips are used to fill the narrow area of ​​the sharp corner of the wedge, filled with foam glue, and overlapped in combination with the prepreg paving method in step 2.

[0055] Furthermore, an airbag is used to pre-compact the prepreg in the closed mold cavity. The airbag is slowly pressurized to 0.6 MPa at room temperature and maintained for 20-30 minutes to pre-compact the carbon fiber prepreg so that the prepreg and the mold fit tightly.

[0056] Furthermore, in order to improve the interfacial bonding strength between the foam and the carbon fiber composite material, the foaming surface is polished, and cylindrical holes with a diameter of 5 mm and a depth of 10 mm are evenly processed on the foam bonding surface to increase the bonding area; in step 2, during the prepreg paving process, the pre-compacting times are not less than 3 times.

[0057] Further, the left mold and the right mold each include a wedge matching surface, two connecting surfaces and two end surfaces; the two connecting surfaces are respectively connected to the left and right sides of the wedge matching surface, and the connecting surfaces opposite to the left mold and the right mold are connected by bolts; the two end surfaces are respectively located on the upper and lower sides of the tip matching surface; the end surface of the left mold and the end surface of the right mold cooperate to form an annular support table surface;

[0058] The end surface is provided with a supporting vertical plate and a flanging rib, which are respectively used to cooperate with the assembly positioning tooling and the end surface flanging mold.

[0059] Furthermore, the assembly positioning tooling is an L-shaped structure, part of which is pressed on the top of the end face flanging mold, and part of which is connected to the supporting vertical plate; the end face flanging mold is a flat plate structure, which is pressed on the top of the flanging stop.

[0060] Furthermore, the curing process of the wedge outer skin autoclave is to evacuate the vacuum so that the vacuum degree is stable at above -0.092MPa throughout the entire heating, insulation and cooling process; the mold is heated from room temperature to 85-90℃, the heating rate is 2±0.5℃ / min, and the insulation is for 60min. After completion, the pressurization is increased to 0.2MPa, the mold is heated to 130℃, the heating rate is 2±0.5℃ / min, and the insulation is for 150min. The pressure can be released to maintain the vacuum; the temperature is reduced from 130℃ to below 70℃, the cooling rate is more than 3℃ / min, pay attention to the cooling rate, and the vacuum is released after it drops to room temperature.

[0061] Furthermore, the thickness of the wedge outer skin is 1.5 mm, and the polyurethane foam density is 50 kg / m 3 .

[0062] The following is a further description in conjunction with the accompanying drawings and specific implementations:

[0063] Mold metallization spraying, protect the unsprayed area, apply release agent on the mold surface, use a robotic arm to automatically spray, the thickness of the sprayed metal aluminum layer is greater than 140μm, and spray the cavity surface of molds 1-4.

[0064] For the outer skin, 0.25mm thick carbon fiber / epoxy resin satin prepreg and 0.50mm thick carbon fiber / epoxy resin satin prepreg are used, with a resin content of 38%-40%. First, a layer of adhesive film and a layer of 0.25mm thick prepreg are laid on the mold cavity surface. The edge area of ​​the first layer of prepreg completely overlaps with the mold cavity, and vacuum pre-compacted for 20-30 minutes; then 1 layer of 0.25mm prepreg and 2 layers of 0.5mm prepreg are laid in sequence. The prepreg laying treatment of the edge of the left and right molds adopts symmetrical gradient laying. After the mold is closed, the butt laying is overlapped to strengthen the sharp corners and special-shaped areas.

[0065] The left mold and the right mold are combined, and the mold is completely closed with a positioning locking device to form the shape of the sharp corner area, ensuring the sharpness R ≤ 1mm. The narrow area of ​​the sharp corner is filled with 6mm wide carbon fiber unidirectional prepreg twisted strips and filled with foam glue, and the butt-jointed carbon fiber prepreg described in the previous step is used for overlap treatment. An airbag is placed in the closed mold cavity, and the mold cavity is closed with a baffle. The room temperature airbag is slowly pressurized to 0.6MPa for 20-30 minutes to pre-compact the carbon fiber prepreg so that the prepreg and the mold fit tightly (especially the narrow area of ​​the mold sharp corner).

[0066] The paving method of the baffle is the same as that of the left mold and the right mold. After paving, the baffle is assembled to the end faces of the left mold and the right mold of the mold, filling the sharp corner area of ​​the end face, transitioning and overlapping the carbon fiber prepreg, and performing secondary pre-compaction.

[0067] The pre-compacted parts are laid in the order of demoulding cloth, pressure strip, porous isolation film, breathable felt and vacuum bag. Place them in the autoclave and evacuate them to stabilize the vacuum degree above -0.092MPa throughout the entire heating, insulation and cooling process; the mold is heated from room temperature to 85-90℃ at a heating rate of 2±0.5℃ / min and kept warm for 60min. After completion, the pressure is increased to 0.2MPa, the mold is heated to 130℃ at a heating rate of 2±0.5℃ / min and kept warm for 150min. The pressure can be released to maintain the vacuum; the temperature is reduced from 130℃ to below 70℃ at a cooling rate of more than 3℃ / min. Pay attention to the cooling rate and release the vacuum after it drops to room temperature.

[0068] After the sharp split product is solidified and formed, the thickness of the outer skin after solidification is 1.5mm, and the auxiliary materials are removed. The inner surface of the outer skin is polished to improve the bonding strength between the outer skin and the foam.

[0069] For the foaming of the wedge product, the outer skin does not need to be removed from the mold. The baffle of the mold is removed. After installing the central metal support component of the wedge, the baffle and the positioning center metal component are assembled. Note that the surface of the metal parts is sandblasted to improve the bonding strength between the metal parts and the foam. The polyurethane foaming agent is mixed evenly in a weight ratio of 1:1, and the inner cavity of the wedge is foamed and filled with foam using a foaming machine. Note that the foaming is divided into zones and the aging process is carried out. The aging process is maintained at 60℃ for 2 hours. After sufficient aging, the baffle is removed.

[0070] Assemble the wedge to position the metal flange. In order to improve the interface bonding strength, grind the foamed surface, evenly process cylindrical holes with a diameter of 5mm and a depth of 10mm on the foam bonding surface, apply epoxy structural adhesive, and fill the cylindrical holes with the adhesive. The coating thickness is 0.2mm. Place the metal flange and install assembly tools 7 and 8 to ensure the position accuracy of the central axis of the metal flange. Curing at 60℃ for 2 hours, and after curing and completely cooling to room temperature, demold and repair burrs to obtain a low-scattering composite material wedge.

[0071] The mold involved in the embodiment of the present invention requires high precision, and a low expansion coefficient material is selected as the mold material.

[0072] The composite material wedge prepared by the preparation method of the present invention has the advantages of light weight and corrosion resistance, and has high surface shape precision and continuous conductivity, can efficiently achieve the target demand of low scattering, and the product has a long service life and excellent assemblability. The molding method is simple and easy to operate, the product size is precisely controllable, the surface is smooth and low in roughness, and it is easy to perform various surface treatments later, and is suitable for mass production.

[0073] The molding method of the present invention is applicable to special-shaped closed curved surface structures with high requirements for surface accuracy and structural parts with strict requirements for surface conductivity continuity. Such structural parts adopt a carbon fiber composite skin foam sandwich structure, combined with a metal positioning center support, and have both the precise positioning and assemblability of metal structural parts and the light weight and high strength of carbon fiber sandwich composite materials.

[0074] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention may be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the present invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the present invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A lightweight, low-scattering carbon fiber composite material wedge, characterized in that: It comprises a central metal support component (c), a wedge outer skin (a), a flange (d) and a foam body (b); the central metal support component (c) is a cylindrical structure; The central metal support assembly is located in the wedge outer skin, and both ends thereof are connected to the corresponding side wedge outer skins through flanges; The area enclosed by the wedge outer skin (a) and the central metal support assembly (c) is filled with a foamed body (b).

2. A method for forming a lightweight low-scattering carbon fiber composite material wedge, used to form a lightweight low-scattering carbon fiber composite material wedge as claimed in claim 1, characterized in that: The specific steps include: Step 1, metallization spraying is performed on the left mold, the right mold and the end face flanging mold respectively, and a metal transfer method is adopted to realize the conductivity and continuous conductivity of the surface of the carbon fiber composite material; Step 2, respectively covering the left mold, the right mold and the end face flanging mold with carbon fiber prepreg, and placing them in a vacuum bag for vacuum pre-compaction; Step 3, after the left mold, the right mold and the end face flanging mold are molded together, the mold gap is processed, and the molded whole mold is placed in a vacuum bag, and heated, pressurized and solidified to form a wedge outer skin rough blank; Step 4, taking the rough blank of the pointed wedge outer skin out of the integral mold, performing a surface transfer film removal treatment and a sharp edge deburring treatment to obtain the pointed wedge outer skin; Step 5, placing the wedge outer skin in a foaming mold, installing a central metal support assembly, and performing polyurethane foaming. The polyurethane foaming is performed in multiple times depending on the foaming volume, and post-curing treatment is performed; Step 6, gluing the positioning metal flange of the wedge end surface and then installing the positioning tool; Step 7, after stabilization, take the wedge out of the mold and perform post-processing into a finished wedge.

3. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: In step 1, the thickness of the metallized sprayed aluminum layer should be greater than 140 μm.

4. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: Carbon fiber / epoxy resin satin prepreg with a thickness of 0.25 mm and carbon fiber / epoxy resin satin prepreg with a thickness of 0.50 mm are used, and the resin content is 38%-40%.

5. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: Symmetrical gradient ply is used for edge transition of prepreg paving, and after mold closing, the paving is overlapped to strengthen the sharp-angled and irregular-shaped areas.

6. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: The narrow area of ​​the sharp corner of the wedge is filled with carbon fiber unidirectional prepreg twisted strips, filled with foam glue, and overlapped in combination with the prepreg laying method in step 2.

7. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: The airbag is used to pre-compact the prepreg in the closed mold cavity. The airbag is slowly pressurized to 0.6MPa at room temperature and maintained for 20-30 minutes to pre-compact the carbon fiber prepreg so that the prepreg and the mold fit tightly.

8. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: In order to improve the interfacial bonding strength between the foam and the carbon fiber composite material, the foaming surface is polished, and cylindrical holes with a diameter of 5 mm and a depth of 10 mm are evenly processed on the foam bonding surface to increase the bonding area; in step 2, during the prepreg paving process, the pre-compacting times are not less than 3 times.

9. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: The left mold and the right mold each include a wedge matching surface, two connecting surfaces and two end surfaces; the two connecting surfaces are respectively connected to the left and right sides of the wedge matching surface, and the connecting surfaces opposite to the left mold and the right mold are connected by bolts; the two end surfaces are respectively located on the upper and lower sides of the tip matching surface; the end surface of the left mold and the end surface of the right mold cooperate to form an annular support table surface; The end surface is provided with a supporting vertical plate and a flanging stopper, which are respectively used to cooperate with the assembly positioning tooling and the end surface flanging mold.

10. The method for forming a lightweight low-scattering carbon fiber composite material wedge according to claim 2, characterized in that: The assembly positioning tooling is an L-shaped structure, part of which is pressed on the top of the end face flanging mold, and part of which is connected with the supporting vertical plate; the end face flanging mold is a plate-shaped structure, which is pressed on the top of the flanging stop.

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