A method for forming carbon fiber sandwich structures and its application

Abstract

The present 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: spraying a gel coat on the forming surfaces and parting seams of an upper mold and a lower mold; after the gel coat is cured, applying an outer layer of epoxy resin liquid material on the surface of the gel coat, and then laying a carbon fiber cloth on the outer layer of epoxy resin liquid material, with the edge of the carbon fiber cloth located in the parting seam; mechanically processing to obtain a foam material inner core, 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; after applying an inner layer of epoxy resin liquid material on the surface of the foam material inner core, placing the foam material inner core between the upper mold and the lower mold, closing the mold and heating; demolding and polishing the parting seam of the product. Compared with conventional carbon fiber sandwich structures, since the glue injection pipeline is eliminated and the upper and lower forming molds are used for the preparation, the surface of the special-shaped structure can be formed smoothly. The front, back and surrounding inside of the structure with uneven thickness can all have the surface quality of the appearance surface.

Description

Technical Field

[0001] This invention belongs to the field of composite material molding technology, specifically relating to a molding method for carbon fiber sandwich structures and its application. Background Technology

[0002] The information disclosed in this background technology section is only intended to enhance 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 those skilled in the art.

[0003] With the rapid development of rail transit vehicles, one of the main factors affecting their speed and energy consumption will be their weight. Currently, seats and other components on rail vehicles are often made of fiberglass, manufactured using hand lay-up methods. However, this method suffers from problems such as heavy weight, burrs on the back, unevenness, and inconsistent thickness. Vacuum forming requires multiple injection lines to be pre-installed in the mold cavity for injection. Residual adhesive in these lines forms columnar structures on the product surface, requiring subsequent machining for removal, increasing the complexity of surface finishing. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for forming a carbon fiber sandwich structure and its application. A foam material core is placed between an upper mold and a lower mold. Epoxy resin is brushed onto the inner surface of the mold and carbon fiber cloth is laid. After mold closing, a curing treatment is applied to obtain a product with a smooth surface on both sides, reducing the complexity of subsequent processing.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

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

[0007] S1. Apply gel coat to the forming surfaces and parting seams of the upper and lower molds;

[0008] S2. After the gel coat has cured, apply an outer layer of epoxy resin liquid to the surface of the gel coat, and then lay carbon fiber cloth on the outer layer of epoxy resin liquid, with the edge of the carbon fiber cloth located in the parting seam.

[0009] S3. Obtain the foam material core by machining, and machine multiple through holes perpendicular to the surface of the foam material core according to a set density on the surface of the foam material core.

[0010] S4. After applying the inner layer of epoxy resin liquid to the surface of the foam core, place it between the upper and lower molds, then close the mold, and then heat the closed mold to cure the internal epoxy resin liquid.

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

[0012] During the preparation process, excess of both the outer and inner epoxy resin liquids creates a molding flash with a width of 20-40 mm at the parting line; and studs are formed in the through holes on the surface of the foam material core.

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

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

[0015] Optionally, in S2, the outer epoxy resin liquid is mixed with a curing agent according to the resin TDS and its viscosity is 500-1000 mPa.s at 25°C.

[0016] Optionally, in S2, the mass ratio of the outer 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, with each layer laid in a set direction.

[0018] Optionally, in S3, the pore size of the through holes on the surface of the foam material core is 1-3 mm, and the distribution density of the through holes is 100-150 pores / m².

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

[0020] Optionally, in S3, a metal embedded part is installed on the inner core of the foam material.

[0021] Optionally, S4, based on the positioning position of the metal embedded part in the mold, will process an opening in 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, the inner layer epoxy resin liquid is mixed with a curing agent according to the resin TDS and adjusted to a viscosity of 500-1000 mPa.s at 25°C.

[0025] Optionally, in S5, the grinding method for the parting seam includes: first using an angle grinder to cut, then using sandpaper to grind, to remove the carbon fiber cloth and epoxy resin inside the seam.

[0026] Secondly, the above-mentioned method for forming carbon fiber sandwich structures is applied in the preparation of seats or skirt panels.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. This invention provides a method for forming carbon fiber sandwich structures. Compared with conventional carbon fiber sandwich structures, this method eliminates the need for glue injection pipelines and uses two molding dies to achieve smooth surface forming of irregularly shaped structures. It can ensure that the front, back, and inner sides of structures with uneven thickness all have the surface quality of an aesthetically pleasing surface.

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

[0030] 3. This invention forms a composite material consisting of foam material and epoxy resin studs within a certain range on the surface of the foam material core, which produces a synergistic effect to improve compressive strength, so that the strength is not reduced while the weight is reduced. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 This is a schematic diagram of the carbon fiber sandwich structure in Example 1.

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

[0034] Among them, 1. Upper mold; 2. Lower mold; 3. Parting seam; 4. Gel coat; 5. Foam material core; 6. Fiber reinforcement layer; 7. Metal embedded part; 8. Bolt. Detailed Implementation

[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate 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 includes the following steps.

[0039] S1, such as Figure 1 As shown, gel coat 4 is sprayed onto 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 of the thickness direction of the product. Since both the upper mold 1 and the lower mold 2 have forming surfaces, the multiple surfaces of the product have the surface quality of the appearance surface. The thickness of gel coat 4 is 0.3 mm, and the spray gun pressure is controlled at 0.6-0.7 MPa.

[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 using a scraper. Then, carbon fiber cloth is laid on the outer layer of epoxy resin liquid. The outer layer of epoxy resin liquid has a curing agent added according to the resin TDS and is prepared to obtain a liquid with a viscosity of (800 mPa.s, 25℃). The carbon fiber cloth consists of two layers: a 200g twill carbon cloth close to the gel coat 4 and a 400g twill carbon cloth further away from the gel coat 4. 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 permeates the carbon fiber cloth.

[0041] S3. CNC machining is used to obtain the foam material core 5, and multiple φ1 through holes perpendicular to the surface of the foam material core 5 are machined on the surface of the foam material core 5 at a density of 100 holes / square meter; during the machining process, grooves are machined at the position of the metal embedded part 7; the through holes serve to accommodate the epoxy resin liquid to form an anchoring structure, while increasing the foam strength.

[0042] S4. After installing the metal embedded part 7 on the surface of the foam material core 5, apply an inner layer epoxy resin liquid with a viscosity of (800 mPa.s, 25℃) (the mass ratio of epoxy resin liquid to carbon fiber cloth is 1:1). According to the position of the metal embedded part as positioned by the mold, cut the opening of the metal embedded part on the carbon fiber cloth. Install the metal embedded part 7 on the foam material core 5. Then, place the foam material core 5 coated with the inner layer epoxy resin liquid between the upper mold 1 and the lower mold 2. After closing the mold, use bolts to fix the upper mold 1 and the lower mold 2 together. Heat the mold to the curing temperature of the outer layer epoxy resin liquid and the inner layer epoxy resin liquid and keep it warm to cure the inner layer epoxy resin liquid and the outer layer epoxy resin liquid, which then combines with the carbon fiber cloth to form the fiber reinforcement layer 6.

[0043] S5. Demold and sand the excess material at the parting seam 3 of the product. The sanding method is as follows: first use an angle grinder to cut, then use sandpaper to sand and remove the carbon fiber cloth and epoxy resin in the seam.

[0044] The obtained carbon fiber sandwich structure mainly consists of an inner foam material core 5 and an outer 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. Excess liquid enters the through holes on the surface of the foam material core 5 to form a stud 8 structure with a length of 3-5 mm, ensuring that the foam material core 5 and the skin are firmly bonded 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. Excess liquid enters the parting seam 3 to form a forming flash with a width of 20 mm. Therefore, it is not necessary to add a glue injection pipeline to the mold or use negative pressure to assist forming inside the mold, so that the shape, size and surface quality of the product can meet the requirements.

[0045] Because the foam core 5 is made of elastic material and has a relatively long through-hole, the gas inside the through-hole has a certain compression margin. Therefore, when the epoxy resin on the surface of the foam core 5 is subjected to mold closing pressure, it can enter the through-hole even without a negative pressure device and solidify into a stud 8 structure. The length of the stud 8 in different parts varies with the thickness of different parts of the foam core 5. When the thickness is thinner, a stud structure with a through-hole length can be formed (e.g., Figure 1 (The anchor 8 on the left side). After the epoxy resin is cured, the anchor 8 structure and the fiber reinforcement layer 6 become a whole. When the fiber reinforcement layer 6 is subjected to pressure during use, the anchor 8 tends to move into the through hole. However, the adhesion between the side wall of the anchor 8 and the hole wall resists this tendency. Therefore, the numerous anchors 8 arranged perpendicularly to the surface of the fiber reinforcement layer 6 can prevent the fiber reinforcement layer 6 from deforming under pressure. This is equivalent to forming a composite material composed of anchors 8 of foam material and epoxy resin within a certain range of the surface of the foam material core 5, which produces a synergistic effect to improve the compressive strength. This makes the pressure resistance of the product higher than that of the fiber reinforcement layer 6 and the foam material core 5 alone.

[0046] Example 2

[0047] This embodiment uses the carbon fiber sandwich structure forming method described in Example 1 to prepare the seat, such as... Figure 2 As shown.

[0048] The inner core of the foam material is made of low-density foam with a density of 60-100 kg / m³. 3 3. Lightweight and with a certain degree of compressive strength

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

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

[0051] The resulting product can reduce weight by more than 70% compared to the original fiberglass split bonding structure (3mm thick hollow shell structure), without reducing strength.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for forming a carbon fiber sandwich structure, characterized in that, Includes the following steps: S1. Apply gel coat to the forming surfaces and parting seams of the upper and lower molds; S2. After the gel coat has cured, apply an outer layer of epoxy resin liquid to the surface of the gel coat, and then lay carbon fiber cloth on the outer layer of epoxy resin liquid, with the edge of the carbon fiber cloth located in the parting seam. S3. Obtain the foam material core by machining, and machine multiple holes perpendicular to the surface of the foam material core according to a set density on the surface of the foam material core. S4. After applying the inner layer of epoxy resin liquid to the surface of the foam core, place it between the upper and lower molds, then close the mold, and then heat the closed mold to cure the internal epoxy resin liquid. S5. Demold and polish the parting seam of the product; During the preparation process, excess of both the outer and inner epoxy resin liquids creates a molding flash with a width of 20-40 mm at the parting line; and studs are formed in the holes on the surface of the foam material core.

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

3. The method for forming a carbon fiber sandwich structure as described in claim 1, characterized in that, In S2, the outer epoxy resin liquid is mixed with curing agent according to the resin TDS and adjusted to make its viscosity 500-1000 mPa.s at 25℃. Optionally, the mass ratio of the outer epoxy resin liquid to the carbon fiber cloth is (1.0~1.5):

1.

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

5. The method for forming a carbon fiber sandwich structure as described in claim 1, characterized in that, In S3, the pore size of the pores on the surface of the foam material core is 1-3 mm, and the pore distribution density is 100-150 pores / m².

6. The method for forming a carbon fiber sandwich structure as described in claim 1, characterized in that, The length of the stud is 3-5 mm.

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

8. The method for forming a carbon fiber sandwich structure as described in claim 1, characterized in that, In S4, the amount of epoxy resin liquid used in the inner layer is such that the mass ratio of epoxy resin liquid to carbon fiber cloth is (1.0~1.5):

1. Optionally, in S4, the inner layer epoxy resin liquid is mixed with a curing agent according to the resin TDS and adjusted to a viscosity of 500-1000 mPa.s at 25°C.

9. The method for forming a carbon fiber sandwich structure as described in claim 1, characterized in that, In S5, the grinding method for the parting seam includes: first, using an angle grinder to cut, and then using sandpaper to grind to remove the carbon fiber cloth and epoxy resin inside the seam.

10. The application of a method for forming a carbon fiber sandwich structure as described in any one of claims 1-9 in the preparation of seats or skirt panels.

Images