Forming method and application of carbon fiber sandwich structure

Abstract

The invention relates to a forming method and application of a carbon fiber sandwich structure, and belongs to the technical field of composite material forming. The forming method comprises the following steps: spraying gel coats on forming surfaces and parting seams of the upper mold and the lower mold; after the gel coat is cured, the surface of the gel coat is coated with an outer-layer epoxy resin liquid material, then carbon fiber cloth is laid on the outer-layer epoxy resin liquid material, and the edge of the carbon fiber cloth is located in the parting seam; a foam material inner core is obtained through machining, and a plurality of through holes perpendicular to the surface of the foam material inner core are machined in the surface of the foam material inner core; brushing an inner layer epoxy resin liquid material on the surface of the foam material inner core, putting the foam material inner core between an upper mold and a lower mold, closing the mold and heating; and demolding and polishing the parting seam of the product. Compared with a conventional carbon fiber sandwich structure, a glue injection pipeline is eliminated, and upper and lower forming molds are used for mold closing preparation, so that smooth surface forming of a special-shaped structure can be realized. And the front surface, the back surface and the peripheral inner surface of the structure with the non-uniform thickness have the surface quality of an appearance surface.

Description

Technical Field

[0001] The invention belongs to the technical field of composite material forming, and in particular relates to a forming method of a carbon fiber sandwich structure and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] With the rapid development of rail vehicles, one of the main factors affecting the speed and energy consumption of rail vehicles will be the weight of the vehicle itself. Seats and other devices on existing rail vehicles are often made of fiberglass. The fiberglass devices are prepared by hand lay-up, which has problems such as heavy product weight, burrs on the back, unevenness, and uneven product thickness. When using the vacuum forming method, multiple injection lines need to be reserved in the mold cavity for injection. The residual glue in the injection line will form a columnar structure and remain on the surface of the product, which needs to be removed by mechanical processing, increasing the complexity of surface processing. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a forming method of a carbon fiber sandwich structure and its application, wherein a foam material core is placed between an upper mold and a lower mold, epoxy resin is brushed on the inner surface of the mold and carbon fiber cloth is laid, and a curing treatment is performed after the mold is closed to obtain a product with smooth surfaces on both sides, thereby reducing the complexity of subsequent processing.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] In a first aspect, a method for forming a carbon fiber sandwich structure comprises the following steps:

[0007] S1. Spraying gel coat on the forming surface and parting seam of the upper mold and the lower mold;

[0008] S2. After the gel coat is cured, an outer layer of epoxy resin liquid is applied on the surface of the gel coat, and then a carbon fiber cloth is laid on the outer layer of epoxy resin liquid, with the edge of the carbon fiber cloth being located in the parting seam;

[0009] S3, obtaining a foam material inner core by mechanical processing, and processing a plurality of through holes perpendicular to the surface of the foam material inner core on the surface of the foam material inner core according to a set density;

[0010] S4, after brushing the inner layer of epoxy resin liquid on the surface of the inner core of the foam material, put it between the upper mold and the lower mold, then close the mold, and then heat the mold after closing the mold to solidify the epoxy resin liquid inside;

[0011] S5. Demould and polish the parting seam of the product;

[0012] During the preparation process, the outer layer epoxy resin liquid material and the inner layer epoxy resin liquid material are excessive, forming a molding flash with a width of 20 to 40 mm at the parting seam position; and forming a bolt in the through hole on the surface of the inner core of the foam material.

[0013] Optionally, in S1, the parting seam is located in the middle of the product in the thickness direction.

[0014] Optionally, in S1, the gel coat thickness is 0.3-0.5 mm.

[0015] Optionally, in S2, a curing agent is added to the outer layer epoxy resin liquid according to the resin TDS, and the mixture is prepared so that its viscosity is 500 to 1000 mPa.s at 25°C.

[0016] Optionally, in S2, the mass ratio of the outer layer epoxy resin liquid to the carbon fiber cloth is (1.0-1.5):1.

[0017] Optionally, in S2, the carbon fiber cloth includes multiple layers of twill carbon fiber cloth, and each layer of the carbon fiber cloth is laid in a set direction.

[0018] Optionally, in S3, the diameter of the through holes on the surface of the inner core of the foam material is 1 to 3 mm, and the distribution density of the through holes is 100 to 150 holes per square meter.

[0019] Optionally, the length of the bolt is 3 to 5 mm.

[0020] Optionally, in S3, metal embedded parts are installed on the foam material core.

[0021] Optionally, S4, according to the positioning position of the metal embedded part in the mold, a metal embedded part opening is processed on the carbon fiber cloth to expose the metal embedded part.

[0022] Optionally, in S4, bolts are used to fix the upper mold and the lower mold together when the mold is closed.

[0023] Optionally, in S4, the mass ratio of the inner layer epoxy resin liquid to the carbon fiber cloth is (1.0-1.5):1.

[0024] Optionally, in S4, a curing agent is added to the inner layer epoxy resin liquid according to the resin TDS, and the mixture is adjusted so that its viscosity is 500-1000 mPa.s at 25°C.

[0025] Optionally, in S5, the grinding method of the parting seam includes: first cutting with an angle grinder, and then grinding with sandpaper to remove the carbon fiber cloth and epoxy resin in the seam.

[0026] In a second aspect, the above-mentioned carbon fiber sandwich structure forming method is used in the preparation of seats or skirts.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention provides a forming method for a carbon fiber sandwich structure. Compared with a conventional carbon fiber sandwich structure, the present invention eliminates the injection pipeline and uses two upper and lower forming molds for preparation, so that the surface of the special-shaped structure can be formed smoothly. The front, back and surrounding inner parts of the structure with uneven thickness can all have the surface quality of the appearance surface.

[0029] 2. The foam material inner core of the present invention is prepared by mechanical processing, which can embed metal parts in the product, effectively eliminating the problem of metal part bonding failure and the cost involved in bonding.

[0030] 3. The present invention forms a composite material composed of foam material and epoxy resin bolts within a certain range on the surface of the foam material inner core, which produces a synergistic effect to improve the compression resistance, so that the strength is not reduced while the weight is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0032] Figure 1 Schematic diagram of the structure of the carbon fiber sandwich structure in Example 1.

[0033] Figure 2 This is a schematic diagram of the appearance of the seat in Example 2.

[0034] Among them, 1. upper mold; 2. lower mold; 3. parting seam; 4. gel coat; 5. foam material inner core; 6. fiber reinforcement layer; 7. metal embedded parts; 8. bolt. DETAILED DESCRIPTION

[0035] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] Example 1

[0038] A method for forming a carbon fiber sandwich structure comprises the following steps.

[0039] S1, such as Figure 1 As shown, gel coat 4 is sprayed on the forming surfaces and parting seam 3 of the upper mold 1 and the lower mold 2. The parting seam 3 is located in the middle position of the thickness direction of the product. Since both the upper mold 1 and the lower mold 2 have forming surfaces, multiple surfaces of the obtained product have the surface quality of the appearance surface; the thickness of the gel coat 4 is 0.3mm, and the spray gun pressure is controlled at 0.6-0.7Mpa.

[0040] S2. After the gel coat 4 is cured, an outer layer of epoxy resin liquid is applied to the surface of the gel coat 4 with a scraper, and then carbon fiber cloth is laid on the outer layer of epoxy resin liquid. A curing agent is added to the outer layer of epoxy resin liquid according to the resin TDS, and a liquid with a viscosity of (800mPa.s, 25°C) is prepared; the carbon fiber cloth includes two layers, a layer close to the gel coat 4 is a 200g twill carbon cloth, and a layer away from the gel coat 4 is a 400g twill carbon cloth. The application range of the outer layer of epoxy resin and the laying range of the carbon fiber cloth both include the parting seam 3. During the application process, the mass ratio of the outer layer of epoxy resin liquid to the carbon fiber cloth is 1:1, so that the outer layer of epoxy resin liquid penetrates the carbon fiber cloth.

[0041] S3. Obtain the foam material inner core 5 by CNC machining, and process a plurality of φ1 through holes perpendicular to the surface of the foam material inner core 5 at a density of 100 holes / square meter on the surface of the foam material inner core 5; process a groove at the position of the metal embedded part 7 during the machining process; the function of the through hole is to accommodate the epoxy resin liquid to form an anchoring structure and increase the foam strength at the same time.

[0042] S4. After installing the metal embedded parts 7 on the surface of the foam material inner core 5, an inner layer of epoxy resin liquid with a viscosity of (800mPa.s, 25°C) is applied to the entire surface (the mass ratio of epoxy resin liquid to carbon fiber cloth is 1:1). According to the position of the metal embedded parts positioned by the mold, a metal embedded part opening is cut out on the carbon fiber cloth. The metal embedded parts 7 are installed on the foam material inner core 5. Then, the foam material inner core 5 coated with the inner layer of epoxy resin liquid is placed between the upper mold 1 and the lower mold 2. After the molds are closed, the upper mold 1 and the lower mold 2 are fixed together with bolts. The mold is heated to the curing temperature of the outer layer of epoxy resin liquid and the inner layer of epoxy resin liquid and kept warm, so that the outer layer of epoxy resin liquid and the inner layer of epoxy resin liquid are cured and combined with the carbon fiber cloth to form a fiber reinforced layer 6.

[0043] S5. De-mould and polish the excess material at the parting seam 3 of the product. The polishing method is: first cut with an angle grinder, then polish with sandpaper to remove the carbon fiber cloth and epoxy resin in the seam.

[0044] The obtained carbon fiber sandwich structure is mainly composed of an inner layer of foam material core 5 and an outer layer of skin (fiber reinforcement layer 6). The skin is formed by fusing and curing an outer layer of epoxy resin liquid, carbon fiber cloth and an inner layer of epoxy resin liquid. The epoxy resin reacts with the curing agent to form a strong cross-linked structure, and excess liquid enters the through holes on the surface of the foam material core 5 to form a bolt 8 structure with a length of 3 to 5 mm, ensuring that the foam material core 5 and the skin are firmly combined together. The outer surface of the skin is cured and formed under the action of the forming surfaces of the upper mold 1 and the lower mold 2, and excess liquid enters the parting seam 3 to form a forming flash with a width of 20 mm. Therefore, there is no need to add a glue injection pipeline to the mold, and there is no need to use negative pressure inside the mold to assist in forming, so that the shape, size and surface quality of the product can meet the requirements.

[0045] Since the material of the foam material inner core 5 is elastic and the length of the through hole is long, the gas inside the through hole has a certain compression margin. Therefore, when the epoxy resin on the surface of the foam material inner core 5 is subjected to the mold clamping pressure, it can enter the through hole even without a negative pressure device and solidify into a bolt 8 structure. The length of the bolt 8 at different parts varies with the thickness of the foam material inner core 5 at different parts. When the thickness is thin, a bolt structure with the length of the through hole can be formed (such as Figure 1 The bolt 8 on the left in the middle). After the epoxy resin is cured and formed, the bolt 8 structure and the fiber reinforcement layer 6 become an integral whole. When the fiber reinforcement layer 6 is subjected to pressure during use, the bolt 8 tends to move into the through hole, and the bonding effect between the side wall of the bolt 8 and the hole wall will resist this tendency. Therefore, the numerous bolts 8 arranged vertically to the surface of the fiber reinforcement layer 6 can prevent the compression deformation of the fiber reinforcement layer 6, which is equivalent to forming a composite material composed of the bolts 8 of the foam material and the epoxy resin within a certain range on the surface of the foam material inner core 5, producing a synergistic effect to improve the compressive resistance, so that the pressure bearing capacity of the obtained product is higher than that of the single fiber reinforcement layer 6 and the foam material inner core 5.

[0046] Example 2

[0047] This embodiment adopts the forming method of the carbon fiber sandwich structure in embodiment 1 to prepare the seat. Figure 2 shown.

[0048] The inner core of the foam material is made of low-density foam with a density of 60-100kg / m 3 3. Lightweight and has certain pressure resistance

[0049] The outer layer epoxy resin liquid material is selected from BST-E760 epoxy resin.

[0050] The inner layer epoxy resin liquid material is selected from BST-E760 epoxy resin.

[0051] The product can reduce weight by more than 70% compared with the original glass fiber reinforced plastic split bonding structure (3mm thick hollow shell structure) without reducing strength.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for forming a carbon fiber sandwich structure, characterized in that: The following steps are involved: S1. Spraying gel coat on the forming surface and parting seam of the upper mold and the lower mold; S2. After the gel coat is cured, an outer layer of epoxy resin liquid is applied on the surface of the gel coat, and then a carbon fiber cloth is laid on the outer layer of epoxy resin liquid, with the edge of the carbon fiber cloth being located in the parting seam; S3, obtaining a foam material inner core by mechanical processing, and processing a plurality of holes perpendicular to the surface of the foam material inner core on the surface of the foam material inner core according to a set density; S4, after brushing the inner layer of epoxy resin liquid on the surface of the inner core of the foam material, put it between the upper mold and the lower mold, then close the mold, and then heat the mold after closing the mold to solidify the epoxy resin liquid inside; S5. Demould and polish the parting seam of the product; During the preparation process, the outer layer epoxy resin liquid material and the inner layer epoxy resin liquid material are excessive, forming a molding flash with a width of 20 to 40 mm at the parting seam position; and forming a plug in the hole on the surface of the inner core of the foam material.

2. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: In S1, the parting seam is located in the middle of the product in the thickness direction; Optionally, in S1, the gel coat thickness is 0.3-0.5 mm.

3. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: In S2, the outer layer epoxy resin liquid material is added with a curing agent according to the resin TDS and is formulated so that its viscosity is 500 to 1000 mPa.s at 25°C; Optionally, the mass ratio of the outer layer epoxy resin liquid to the carbon fiber cloth is (1.0-1.5):

1.

4. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: In S2, the carbon fiber cloth includes multiple layers of twill carbon fiber cloth, and each layer of the carbon fiber cloth is laid in a set direction.

5. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: In S3, the diameter of the holes on the surface of the inner core of the foam material is 1 to 3 mm, and the distribution density of the holes is 100 to 150 holes / square meter.

6. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: The length of the bolt is 3-5 mm.

7. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: In S3, metal embedded parts are installed on the foam material core.

8. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: In S4, the amount of the inner layer epoxy resin liquid material is such that the mass ratio of the epoxy resin liquid material to the carbon fiber cloth is (1.0-1.5):1; Optionally, in S4, a curing agent is added to the inner layer epoxy resin liquid according to the resin TDS, and the mixture is adjusted so that its viscosity is 500 to 1000 mPa.s at 25°C.

9. The method for forming a carbon fiber sandwich structure according to claim 1, characterized in that: In S5, the grinding method of the parting seam includes: first cutting with an angle grinder, and then grinding with sandpaper to remove the carbon fiber cloth and epoxy resin in the seam.

10. Use of the forming method of the carbon fiber sandwich structure according to any one of claims 1 to 9 in the preparation of seats or skirts.

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