Composite material sandwich structure forming process and sandwich structure

Abstract

The invention relates to the technical field of rail transit, in particular to a composite sandwich structure forming process and a sandwich structure. The forming process comprises the steps of part forming, wherein a plurality of profiles are sequentially spliced end to end to form an annular framework, and the annular framework is provided with a hollow cavity; the skin and the filler are cut, so that the skin and the filler are matched with the annular framework in size; composite molding: coating one side surface of the skin and two side surfaces of the framework with resin; the filler is put into the hollow cavity of the framework, then the skin fully coated with the resin is attached to the framework, the framework is turned over, the skin on the other side is attached to the framework, and a sandwich structure is formed; and the compounded sandwich structure is pressurized, the pressure is relieved after pressurization is conducted for preset time, and preparation of the sandwich structure is completed. By means of the method, the first-pass yield of the large-size composite material part is increased, and follow-up working hours such as repairing, shaping and polishing are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of rail transportation, and in particular to a composite material sandwich structure forming process and a sandwich structure. Background Art

[0002] In the field of rail transportation, composite materials are widely used in the manufacture of wall panels, cover panels, skirt panels and other components due to their light weight and high strength. These components play an important role in the appearance design and structural strength of the vehicle.

[0003] The traditional manufacturing process mainly uses vacuum infusion one-step molding technology, in which the entire structure is molded as a whole, including the skin, filler, skeleton and connectors. The working principle of this process is to laminate the composite material on the mold, introduce the resin by vacuum, make it evenly penetrate into the fiber layer, and then solidify and mold. However, this process has many problems in actual operation, such as large deformation of the product after molding, uneven resin introduction (resin accumulation affects product strength), delamination, local lack of glue and fiber leakage, poor appearance quality and other defects. In addition, due to the difficulty in controlling the amount of resin introduction, individual parts may have overweight problems, affecting delivery. The one-time pass rate is low, and most of them require repairing, shaping, polishing and other waste of work time.

[0004] Therefore, the existing molding process has the following technical problems:

[0005] Product deformation problem: Large-sized composite products are prone to deformation after the traditional one-time molding process, which affects the product dimensional accuracy.

[0006] Uneven distribution of resin: The resin is unevenly distributed in the composite material, resulting in partial lack of glue or fiber leakage in the product, affecting the strength of the product.

[0007] Delamination: Due to the loose bonding between the resin and fiber layers, the product is prone to delamination during use.

[0008] Poor appearance quality: Defects such as dry spots are prone to appear on the product surface, affecting the aesthetics.

[0009] Product overweight problem: Due to inaccurate control of resin introduction amount, individual parts may be overweight, affecting product delivery. Summary of the invention

[0010] In view of the shortcomings of the prior art, the purpose of the embodiments of the present invention is to provide a composite sandwich structure molding process, which solves the above technical problems through innovative molding processes, improves the first-time pass rate of large-size composite components, and reduces the subsequent work hours such as repair, shaping and polishing. By molding and recombining the components separately, the present invention can effectively control the resin distribution, reduce product deformation, improve the overall strength and appearance quality of the product, thereby extending the service life of the product, and meet the demand for high-performance composite components in the field of rail transit, which is of great significance to the promotion of composite materials in the field of rail transit.

[0011] In order to achieve the above object, the embodiment of the present invention provides the following technical solutions:

[0012] A composite sandwich structure forming process comprises: parts forming: a plurality of profiles are spliced ​​end to end in sequence to form an annular skeleton having a hollow cavity; a skin and a filler are cut so that the sizes of the skin and the filler match the annular skeleton; composite forming: a resin is coated on one side of the skin and on two sides of the skeleton; the filler is placed in the hollow cavity of the skeleton, and then the skin fully coated with the resin is attached to the skeleton, the skeleton is turned over, and the skin on the other side is attached to the skeleton to form a sandwich structure; the composite sandwich structure is pressurized, and the pressure is released after a predetermined time of pressurization to complete the preparation of the sandwich structure.

[0013] Optionally, when the parts are formed, the ends of adjacent profiles are connected by a connector, the connector is L-shaped, and the L-shaped connector is bonded and connected to two adjacent profiles.

[0014] Optionally, the environmental conditions are adjusted before operation, including an operating environment temperature of 15-30°C and a humidity of 30%-75%RH, and the resin is transported to the operating environment in advance to allow its temperature to be balanced before compounding.

[0015] Optionally, use sandpaper to polish the resin surface of all parts before laminating, and use masking tape to mask and protect the non-compounded areas.

[0016] Optionally, the main agent and the curing agent are mixed according to a set ratio, and glass beads are sprinkled in at the same time to prepare a two-component epoxy resin.

[0017] Optionally, after coating the resin on the skin, use a serrated scraper to evenly scrape the resin in sequence, and the latter scraping and the previous scraping should have an overlapping area; after the skin fully coated with the resin is attached to the frame, it is tied tightly with high-temperature tape.

[0018] Optionally, when pressurizing, two pads of equal thickness are placed on both sides of the sandwich structure.

[0019] Optionally, when pressurizing, the temperature is adjusted to 50° and the pressure is adjusted to 5.5 MPa, and the pressure is released after pressurizing and heating for 4 hours of curing.

[0020] An embodiment of the present invention also provides a sandwich structure prepared using the composite sandwich structure molding process as described above, comprising a frame, a filler and a skin; the frame comprises a profile and a connector, a plurality of profiles are spliced ​​end to end in sequence to form an annular frame, the connector is bonded to the ends of two profiles, and the annular frame has a hollow cavity; the filler is filled in the hollow cavity of the frame, and the skin covers both sides of the frame.

[0021] Optionally, the outer contour of the cross-section of the profile is a convex structure, which includes a small end and a large end, the small end of the convex structure faces inward, and the large end faces outward, and the inner side surface of the large end forms a positioning contour for installing the skin.

[0022] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0023] The molding method of the present invention is changed from one-time molding to multiple molding, and the traditional one-piece molding method is replaced by a method of secondary compounding after the components are molded separately, thereby avoiding the problem of local glue shortage or fiber leakage and improving the strength of the product. A low-temperature curing process is adopted to avoid thermal deformation and stress concentration, and after the compounding is completed, the flatness is excellent and no shaping is required. The combination of the resin and the fiber layer is more tightly, avoiding the problem of stratification of the product during use. The product qualification rate is effectively improved, the appearance quality is improved, and the process difficulties in the molding process are solved.

[0024] Single-sided brushing is used between the skin and the sandwich material, and double-sided brushing is used at the key positions where the skin and the frame are bonded to ensure that the resin is fully coated. The scraping tool uses an A2-type serrated scraper to remove bubbles and prevent local blistering after the sandwich panel is cured.

[0025] High-performance two-component epoxy resin is used in the sandwich structure composite, which has both high strength and sealing properties, effectively preventing the invasion of corrosive media around the sandwich panel, improving the overall corrosion resistance, and extending the service life of the product.

[0026] The skeleton adopts a convex structure, which can be accurately positioned when the skin is composited and will not deviate when pressurized, ensuring the accuracy of the overall shape and size.

[0027] Advantages of additional aspects of the present invention will be given in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In addition, the spacing or size between each other is exaggerated to show the position of each part, and the schematic diagram is only used for illustration.

[0029] Figure 1 is a schematic diagram of a sandwich structure provided by an embodiment of the present invention;

[0030] Figure 2 is a schematic diagram of a skeleton provided by an embodiment of the present invention;

[0031] Figure 3 is a schematic diagram of the installation of a connecting piece provided by an embodiment of the present invention;

[0032] Figure 4 is a schematic diagram of a profile provided by an embodiment of the present invention;

[0033] In the figure: 1, skeleton; 11, profile; 12, connector; 2, filler; 3, skin; DETAILED DESCRIPTION

[0034] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0035] Example 1

[0036] In order to solve the technical problems mentioned in the background technology, this embodiment proposes a composite material sandwich structure forming process.

[0037] In the composite sandwich structure forming process of this embodiment, firstly, a plurality of profiles 11 are spliced ​​end to end in sequence to form a ring-shaped skeleton 1 (such as Figure 1 , Figure 2 As shown). Each profile 11 is spliced ​​to form a stable annular structure, and the internal space of the annular skeleton 1 forms a hollow cavity for accommodating the filler 2. The selection of the profile 11 must ensure that it has sufficient strength and can maintain a stable shape in subsequent processes. The hollow cavity of the annular skeleton 1 plays a key role in the lightweight and strength of the sandwich structure, and plays a supporting and filling role.

[0038] The skin 3 and the filler 2 are cut into sizes that match the annular skeleton 1, ensuring that in the subsequent composite molding process, the skin 3 can be accurately attached to the surface of the skeleton 1 and the filler 2 can completely fill the hollow cavity.

[0039] The resin is coated on one side of the skin 3 and two sides of the frame 1 to enhance the bonding strength between the skin 3 and the frame 1 and the filler 2 .

[0040] The filler 2 is placed in the hollow cavity of the skeleton 1. The filler 2 can be made of foam material, glass fiber, honeycomb material, etc. It has high lightness and strength, and can improve the mechanical properties of the sandwich structure after molding. Then, the resin-coated skin 3 is attached to the two sides of the skeleton 1. At this time, the connection between the skin 3 and the skeleton 1 is achieved through the bonding effect of the resin, ensuring the stability and strength of the sandwich structure. After turning over the skeleton 1 and attaching the skin 3 on the other side, the entire sandwich structure is preliminarily assembled.

[0041] Finally, the entire composite sandwich structure is pressurized. During the pressurization process, the pressure and time need to be controlled to ensure that the resin is completely cured and the skin 3 and the frame 1 are firmly bonded together to form the final form of the composite material. Pressurization enhances the density of the structure and fills all gaps through the flow of resin, thereby improving the mechanical properties of the composite structure.

[0042] In this embodiment, the ends of adjacent profiles 11 are connected by L-shaped connectors 12 (eg Figure 3 As shown). The L-shaped connector 12 has a right-angle structure, which can effectively fix the ends of two adjacent profiles 11 together to form a stable annular skeleton 1. The material of the connector 12 can be selected from the same composite material as the profile 11, or a metal material can be selected as needed to ensure the connection strength.

[0043] The L-shaped connector 12 is fixed to the end of the profile 11 by bonding. During bonding, the connection surface should be kept clean and smooth to ensure the bonding effect. Commonly used adhesives include epoxy resin, polyurethane glue, etc. The specific selection should be determined according to the material of the profile 11 and the operating environment conditions. The bonding process needs to control time and temperature to ensure that the bonding strength meets the requirements. This connection method has good assembly and adjustability, can achieve rapid assembly, and at the same time increases the overall strength of the skeleton 1 through the L-shaped connector 12.

[0044] Before composite molding, the temperature and humidity of the operating environment must be adjusted to ensure that the resin has optimal fluidity and adhesion during the curing process. The temperature of the operating environment should be controlled between 15℃ and 30℃, and the humidity should be controlled between 30% and 75% RH to avoid adverse effects of excessively high or low temperature and humidity on the resin curing and composite process. Before operation, the resin needs to be transported to the operating environment in advance and reach temperature balance to avoid performance fluctuations caused by temperature differences in the resin and ensure that the performance of the resin is always stable.

[0045] Before lamination, the surfaces of all parts should be polished with sandpaper. This treatment process helps to remove surface oxides or dirt and improve the adhesion between the resin and the surface of the parts. The coarseness of the sandpaper should be determined according to the material of the parts to ensure that the polished surface is smooth and has a certain degree of roughness to increase the adhesion of the resin. For areas that do not need to be laminated, masking tape can be used for masking protection to prevent unnecessary application of resin to these areas, ensuring that the resin coating is formed only on the parts that need to be laminated, while avoiding resin overflow that affects the appearance and performance of the product.

[0046] In this embodiment, the preparation of the resin requires mixing the main agent and the curing agent in a set ratio. This ratio should be optimized according to the type of resin used and the curing speed to ensure that the resin exhibits good fluidity and bonding properties during the curing process. At the same time, glass microspheres are added to enhance the filling performance of the resin, and the glass microspheres can increase the rigidity and impact resistance of the composite material.

[0047] When applying the resin to the skin 3 and the frame 1, a serrated scraper is used to evenly apply the resin. The scraper has a specific tooth shape, which can form a uniform resin coating during the coating process to avoid excessive resin accumulation or uneven coating. The latter scraping should have an overlapping area with the previous coating, which can ensure the continuity and uniformity of the resin coating and prevent the occurrence of local insufficient or excessive resin. After the skin 3 is coated, it needs to be immediately attached to the frame 1 to ensure the bonding effect of the resin.

[0048] During the pressurization process, two pads of equal thickness are placed on both sides of the sandwich structure. The function of these pads is to ensure that the sandwich structure is evenly stressed during the pressurization process, and to avoid deformation or damage of the structure due to excessive or insufficient local pressure. The material of the pads can be selected from rubber, foam or other materials with a certain degree of elasticity with moderate hardness.

[0049] During pressurization, the temperature needs to be adjusted to 50°C and the pressure needs to be adjusted to 5.5MPa. The pressurization and heating processes need to be precisely controlled to ensure that the resin is fully cured while avoiding excessive temperature and pressure that may cause resin degradation or deformation.

[0050] After pressurization and heating, the curing time is maintained for 4 hours to ensure that the resin achieves the best connection between the frame 1 and the skin 3. When the pressure is released after pressurization, it is necessary to ensure that the sandwich structure is completely cooled to avoid deformation of the structure due to sudden temperature changes.

[0051] In order to make the technical solution provided in this embodiment clearer, the preparation process is further described:

[0052] 1. Parts molding:

[0053] ① Frame forming: The frame is spliced ​​at a 45° angle using "convex" profiles, and then bonded using L-shaped connectors.

[0054] Both the convex profile and the L-shaped connector are made using the pultrusion process. The mold needs to be processed in advance. The width of the cavity is determined according to the thickness of the skeleton. After the mold is processed, pultrusion is performed, and the pultruded profile is cut according to the required size. High-strength acrylic adhesive is used with L-shaped connectors for bonding. The theoretical adhesive layer thickness is 0.5mm. It can be quickly positioned in 15 minutes, and the strength of the fully cured joint can reach more than 20Mpa.

[0055] ② Skin molding: The skin is made of GFRP with a thickness of 1mm. It is formed on the platform using a vacuum introduction process and then cut after forming.

[0056] 2. Composite molding:

[0057] ① Preparation before compounding

[0058] Environmental conditions preparation: operating environment temperature 15-30℃, humidity 30%-75%RH.

[0059] The working area is clean and there is no dust or grinding.

[0060] The resin should be transported to the molding workshop at least 12 hours in advance to allow its temperature to balance before compounding.

[0061] Before all parts are composited, use 120# sandpaper to polish and brush the resin surface, and the polishing must be even without omissions.

[0062] Use masking tape to mask and protect non-composite areas to prevent glue overflow from contaminating the surface. Note that the masking tape must be firmly affixed.

[0063] ②Surface cleaning

[0064] The operator wears disposable rubber gloves and uses disposable wiping paper dipped in industrial alcohol to wipe the painted surface of each component in one direction. Wipe thoroughly without omission to ensure the cleaning quality. The wiping surface of the cleaning cloth should be changed frequently. Throw it away after it is dirty and do not reuse it.

[0065] After cleaning the surface with alcohol, let it dry for at least 5 minutes to ensure that the surface is completely dry, but not more than 4 hours, otherwise it must be cleaned again.

[0066] ③Combination

[0067] Mix the DP490 main agent and the curing agent in a mixing barrel at a ratio of 2:1, and sprinkle in 0.2mm glass beads (20g glass beads for every 600g resin). The mixing amount is 600g / ㎡, and the mixer speed is 120r / min.

[0068] Lay the cleaned skins on both sides flat on the workbench, then apply the resin on the skins in a serpentine shape, and use an A2 serrated scraper to evenly scrape the resin from left to right. Note that the last scraping should cover 1 / 3 of the previous scraping.

[0069] At the skeleton position, double-sided scraping method is used to ensure that the resin is fully coated.

[0070] Place the filler (foam / aramid honeycomb) into the frame cavity, then attach the fully resin-coated skin to the frame, and use high-temperature tape to tighten it to prevent dislocation. Then turn the frame over, attach the skin on the other side, and use high-temperature tape to tighten and secure the whole thing. Note that the high-temperature tape used for tightening can be stacked at most two layers.

[0071] The resin has a working life of 90 minutes, and all operations including mixing, painting, and pressurizing must be completed within 90 minutes.

[0072] ④ Pressurized curing

[0073] Move the composite sandwich panel to the hot press for pressurization. Note that two pads of equal thickness need to be placed on both sides of the sandwich panel to prevent the sandwich panel from being flattened by excessive pressure. Adjust the temperature to 50° and the pressure to 5.5Mpa (gauge pressure). After pressurization and heating for 4 hours, the pressure can be released. After the pressure is released, the masking tape can be torn off. After 24 hours, the residual glue can be polished.

[0074] In summary, in this molding method, the parts are assembled after being molded separately, and the skin is coated with epoxy resin for secondary composite molding. The composite process uses high-strength epoxy resin DP490, with a mixing amount of 600g / ㎡, and 20g of glass beads are mixed per ㎡ to control the coating thickness. The scraper uses an A2 type serrated scraper. In view of the high thermal expansion coefficient of the composite material, a curing process of 50 degrees hot pressing for 4 hours is selected to prevent the product from deforming during the curing process. The overall flatness is ensured by applying pressure with a hot press or vacuum negative pressure, and the hot press is pressurized to 5.5Mpa (displayed).

[0075] Example 2

[0076] This embodiment provides a sandwich structure prepared by the above-mentioned molding process, which is composed of a skeleton, a filler and a skin. The skeleton includes profiles and connectors, and the profiles are spliced ​​into a ring skeleton through the connectors, and have a hollow cavity for filling the filler. The filler has the characteristics of light weight and high strength, which can effectively improve the mechanical properties and impact resistance of the sandwich structure. The skin covers both sides of the skeleton, which plays a role in enhancing the overall structural strength and aesthetics.

[0077] The cross-sectional outer contour of the profile is a convex structure, such as Figure 4 As shown in Figure 1, the design of the convex structure helps to improve the positioning accuracy of the skin. The convex structure includes a small end ( Figure 4 in the right side) and the big endian ( Figure 4 The left side of the frame, with the small end facing the inside of the frame and the large end facing the outside. The inner side of the large end forms the positioning contour when installing the skin, which can effectively guide the fit between the skin and the frame, thereby ensuring the precise shape and stability of the sandwich structure. The frame adopts a "convex" structure, which can be accurately positioned when the skin is bonded, and will not deviate when pressurized, ensuring the accuracy of the overall shape and size.

[0078] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A composite sandwich structure forming process, characterized in that: include: Part forming: Multiple profiles are spliced ​​end to end to form a ring skeleton with a hollow cavity; the skin and filler are cut to match the size of the skin and filler with the ring skeleton; Composite molding: apply resin on one side of the skin and on both sides of the frame; put the filler into the hollow cavity of the frame, then fit the skin fully coated with resin to the frame, turn the frame over, and fit the other side of the skin to the frame to form a sandwich structure; pressurize the composite sandwich structure, and release the pressure after a predetermined time to complete the preparation of the sandwich structure.

2. The composite sandwich structure forming process according to claim 1, characterized in that: When the parts are formed, the ends of adjacent profiles are connected by a connector, which is L-shaped and is bonded and connected to two adjacent profiles.

3. The composite sandwich structure forming process according to claim 1, characterized in that: Before operation, adjust the environmental conditions, including operating environment temperature of 15-30℃ and humidity of 30%~75%RH. Transport the resin to the operating environment in advance to balance its temperature before compounding.

4. The composite sandwich structure forming process according to claim 1, characterized in that: Before compounding all parts, use sandpaper to polish the resin surface and use masking tape to mask and protect the non-compounded areas.

5. The composite sandwich structure forming process according to claim 1, characterized in that: The main agent and the curing agent are mixed according to a set ratio, and glass beads are sprinkled in at the same time to prepare a two-component epoxy resin.

6. The composite sandwich structure forming process according to claim 1, characterized in that: After coating the resin on the skin, use a serrated scraper to evenly scrape the resin in sequence. The last scraping should have an overlapping area with the previous scraping. After the skin fully coated with resin is attached to the frame, use high-temperature tape to tie it tightly.

7. The composite sandwich structure forming process according to claim 1, characterized in that: When pressurizing, two pads of equal thickness are placed on both sides of the sandwich structure.

8. The composite sandwich structure forming process according to claim 1, characterized in that: When pressurizing, adjust the temperature to 50° and the pressure to 5.5Mpa. After pressurizing and heating for 4 hours, remove the pressure.

9. A sandwich structure prepared by the composite sandwich structure forming process according to any one of claims 1 to 8, characterized in that: Includes skeleton, filling and skin; The skeleton comprises profiles and connectors, a plurality of profiles are spliced ​​end to end in sequence to form an annular skeleton, the connectors are bonded to the ends of two profiles, and the annular skeleton has a hollow cavity; The filler is filled in the hollow cavity of the frame, and the skin covers both sides of the frame.

10. The sandwich structure according to claim 9, characterized in that: The cross-sectional outer contour of the profile is a convex structure, which includes a small end and a large end. The small end of the convex structure faces inward, and the large end faces outward. The inner side surface of the large end forms a positioning contour for installing the skin.

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