A molding process for composite materials

Abstract

The application provides a composite material forming process, which comprises the following steps: forming a first shell by using a first concave die and an inflatable inner die in cooperation, heating and pressurizing and curing; forming a second shell by using a first convex die and an inflatable outer die in cooperation, heating and pressurizing and curing; embedding the second shell in the first shell; adding a thermosetting resin between the two shells; and heating and pressurizing and curing to obtain the composite material. The process does not need a vacuum step, adopts a mode of separately preparing two shells and then combining the two shells, and can obtain the composite material with smooth surfaces on both sides and no pinholes, and can be applied to the forming and processing of the composite material with an open inner cavity structure, such as a helmet. The processing process is simple, the equipment demand is low, and the difficulty of the post-processing of the composite material is reduced.

Description

Technical Field

[0001] This invention relates to the field of material forming technology, and in particular to a forming process for composite materials. Background Technology

[0002] Composite material parts manufactured by prepreg molding are an important new material with a series of advantages such as light weight and low strength, and are widely used in load-bearing and functional structures. For example, most high-performance protective helmets on the market are made of carbon fiber composite materials.

[0003] However, there are certain difficulties in manufacturing composite products made from prepregs or fiber cloth. Since both prepregs and fiber cloths have fixed shapes, and in order for the parts to have the material properties of the prepregs or fiber cloths, they usually need to be made into the shape corresponding to the finished parts. The fiber material needs to be bonded to the mold surface for molding and curing. Conventional processes usually include molding, vacuum infusion, and vacuum hot pressing. For the production of complex components such as helmets, molding and vacuum hot pressing are generally used. In the molding process, a metal outer mold is required in conjunction with a rubber inner mold. Due to problems such as the flatness of the rubber inner mold surface and poor demolding effect, the inner surface of the final molded product is relatively rough and needs to be polished later. Although vacuum hot pressing can achieve good surface effects, its equipment and labor costs are high, making it difficult to mass-produce.

[0004] In view of this, for helmets or similar composite material products with internal cavities, how to improve the flatness of their inner surfaces while maintaining high production efficiency has become an urgent technical problem to be solved. Summary of the Invention

[0005] In view of this, the present invention proposes a molding process for composite materials, which aims to improve the flatness of the surface of the molded workpiece, while also making the process easier and more suitable for mass production.

[0006] The technical solution of this invention is implemented as follows: This invention provides a molding process for composite materials, particularly a molding process for reinforced fiber composite helmets, comprising the following steps:

[0007] Step 1: Cut the prepreg and attach it to the inner surface of the first cavity mold. Embed the inflatable inner mold into the first cavity mold with the prepreg attached. After the inflatable inner mold is inflated, heat and pressurize it to obtain the first outer shell.

[0008] Step 2: Cut the prepreg and attach it to the outer surface of the first punch. Place the inflatable outer mold on the outside of the first punch with the prepreg attached to its surface. Inflate the inflatable outer mold and then heat and pressurize it to obtain the second outer shell.

[0009] Step 3: Insert the first outer shell into the inner side of the first concave mold, insert the second outer shell into the inner side of the first outer shell, fill the space between the first and second outer shells with thermosetting resin, then insert the third inner mold into the inner side of the second outer shell, and after closing the mold, heat and pressurize to cure to obtain the molded composite material.

[0010] In some embodiments, step one further includes filling the space between the inner surface of the first mold cavity and the prepreg with thermosetting resin.

[0011] In some embodiments, step two further includes filling the space between the outer surface of the first punch and the prepreg with thermosetting resin.

[0012] In some embodiments, within the same composite material, there are no fewer than two second shells, and multiple second shells are spliced ​​together inside the first shell to cover the inner surface of the first shell.

[0013] In some implementations, before assembling multiple second housings, mortises or tenons are machined at the edges of the second housing assembly, and adjacent second housings are mortised and tenoned together by the mortises and tenons.

[0014] In some embodiments, the mortise or tenon extends in the same direction as the edge of the second housing on which the mortise or tenon is located.

[0015] In some embodiments, step three, before embedding the second housing inside the first housing, further includes laying reinforcing fibers on the inner surface of the first housing.

[0016] In some embodiments, the reinforcing fibers include organic fibers, natural fibers, and inorganic fibers. Organic fibers include aramid fibers, orlon fibers, polyester fibers, nylon fibers, vinylon fibers, polypropylene fibers, polyimide fibers, etc., natural fibers include cotton fibers, sisal fibers, etc., and inorganic fibers include glass fibers, carbon fibers, whiskers, etc.

[0017] In some embodiments, in step three, the third inner mold is a metal punch or an inflatable mold.

[0018] In some embodiments, the thermosetting resin includes thermosetting acrylic resins, etc.

[0019] In some embodiments, the heat curing temperature is 120-140℃, the heat curing pressure is 0.5-0.7MPa, and the curing time is 20-40min.

[0020] The molding process described above can be applied to the processing and molding of products with internal cavities, such as helmets.

[0021] The molding process of the composite material of the present invention has the following advantages over the prior art:

[0022] 1. The molding process of the composite material provided by the present invention uses at least two shells to be cured separately and then nested and cured together. Through this molding process, at least one smooth surface can be processed on the surface of each of the two shells. The smooth surface is used as the outer surface of the composite. This overcomes the problem of surface defects such as pinholes on one side of the product in conventional composite material processing. At the same time, since the two shells are composited, the defective surface can increase the contact area with the thermosetting material, thereby improving the connection strength between the two shells.

[0023] 2. Because the process of molding two shells separately and then bonding them together can reduce the number of overlapping layers of prepreg in a single shell, it helps to reduce the number of air bubbles between the layers of prepreg inside a single shell and improves the quality of a single shell.

[0024] 3. Due to the use of a two-shell composite process, the composite shell structure further improves the structural strength of the overall molded component. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the first die in step one of the present invention;

[0027] Figure 2 This is a schematic diagram of the structure of the first punch in step two of the present invention;

[0028] Figure 3 This is a schematic diagram of the third inner mold and the first concave mold structure in step three of the present invention;

[0029] Figure 4 This is a schematic diagram of the structure of the second outer shell prepared according to one embodiment of the present invention.

[0030] In the figure: 1-first concave mold, 2-first outer shell, 3-first convex mold, 4-second outer shell, 5-third inner mold, 41-mortise groove, 42-tenon end. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0033] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0034] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain. If any definition stated in this section is contrary to or otherwise inconsistent with a definition stated in a patent, patent application, published patent application, or other publication incorporated herein by reference, the definitions listed here shall prevail over those incorporated herein by reference.

[0036] The molding process of a carbon fiber composite helmet according to one embodiment of the present invention includes the following steps:

[0037] According to the design drawings of the composite helmet, its outer and inner surfaces are unfolded. The first shape is obtained after unfolding the outer surface, and the second shape is obtained after unfolding the inner surface.

[0038] According to the first drawing, the carbon fiber prepreg is cut, and several carbon fiber prepreg sheets are attached to the inner surface of the first mold 1. The inner surface of the first mold 1 is pre-coated with a release agent. The carbon fiber prepreg is stacked in at least two layers, and the seams of the carbon fiber prepreg sheets between adjacent layers are staggered. After attachment, polypropylene resin is filled between the first mold 1 and the carbon fiber prepreg layers. Then, a high-temperature resistant silicone inflatable inner mold is embedded inside the first mold. After inflation, the first mold 1 is heated. The pressure between the first mold 1 and the high-temperature silicone inflatable inner mold after inflation is 0.6 MPa, the heating temperature is 120°C, the holding time at 120°C is 40 min, and then the temperature is lowered to 60°C. The first outer shell 2 is then demolded.

[0039] According to the second drawing, the carbon fiber prepreg is cut, and several carbon fiber prepreg sheets are attached to the outer surface of the first punch 3. The outer surface of the first punch 3 is pre-coated with a release agent. The carbon fiber prepreg is stacked in at least two layers, and the seams of the carbon fiber prepreg sheets between adjacent layers are staggered. After attachment, polypropylene resin is filled between the first punch 3 and the carbon fiber prepreg layers. Then, a high-temperature resistant silicone inflatable outer mold is fitted on the outside of the first punch. After inflation, the first punch is heated. After inflation, the pressure between the first punch and the high-temperature silicone inflatable inner mold is 0.6 MPa. The heating temperature is 120°C, and the holding time at 120°C is 40 minutes. Then, the temperature is lowered to 60°C, and the second outer shell 4 is demolded.

[0040] The first outer shell 2 is embedded inside the first concave mold 1, and then the second outer shell 4 is embedded inside the first outer shell 2. Then, acrylic resin is filled between the first outer shell 2 and the second outer shell 4. Then, the third inner mold 5 of aluminum alloy is embedded inside the second outer shell 4. The edge of the third inner mold 5 and the first concave mold 1 can be closed. After the two are closed, they are heated to 120°C and kept warm for 40 minutes. Then, they are cooled to 60°C and demolded to obtain the blank of the carbon fiber composite helmet.

[0041] The above embodiments can be used for the molding of helmets or other composite materials with internal cavities that can be directly demolded from the third inner mold 5. The first concave mold 1, the first convex mold 3, and the third inner mold 5 can all be made of metal or ceramic materials. After molding, the surface of the composite material close to the metal or ceramic mold has a relatively smooth surface, while the surface of the composite material in contact with the silicone inflatable mold is rough after molding. Therefore, during the process of the first outer shell 2 and the second outer shell 4 being joined, the smoother side of the first outer shell 2 is located on the side away from the second outer shell 4, and the smoother side of the second outer shell 4 is located on the side away from the first outer shell 2. The rough sides of both can not only be eliminated by the mold closing method, but also the contact area between the first outer shell 2 and the second outer shell 4 can be increased, thereby improving the bonding strength between the two.

[0042] In some embodiments, if the third inner mold 5 cannot be directly embedded into the second outer shell 4, the third inner mold 5 can be an inflatable inner mold, such as a high-temperature silicone inflatable inner mold. In this case, at least two second outer shells 4 are provided on the inner side of the same carbon fiber composite helmet. Multiple second outer shells 4 are made separately, and then embedded into the first outer shell 2 respectively and spliced ​​together to form the inner layer structure of the composite material.

[0043] The above embodiments can be used for the processing and production of composite material workpieces with cavity openings smaller than the internal cross-sectional size of the cavity. However, since the second outer shell 4 needs to be spliced ​​later, cracks may appear in the spliced ​​parts. Cracks may cause the thermosetting resin to leak before pressure heating. During the curing process, the gaps between multiple second outer shells 4 may be uneven or the distribution of multiple second outer shells 4 may be uneven, or the thickness of the thermosetting resin on the inner surface of the second outer shell 4 may be uneven, thereby affecting the overall structural performance and aesthetics.

[0044] To address the potential subsequent problems mentioned above, some embodiments further include machining a mortise 41 or tenon 42 at the splicing edge of the second outer shell 4, with adjacent second outer shells 4 being connected by mortise and tenon joints using the mortise 41 and tenon 42.

[0045] In the above embodiments, a tenon 41 is opened at the connecting edge of the two interconnected second shells 4 or a tenon 42 is machined. The tenon 42 is embedded in the tenon 41 to complete the limiting connection. On the one hand, multiple second shells 4 can be connected to form a whole in the first shell 2, thereby avoiding gaps between two adjacent second shells 4. On the other hand, it is conducive to forming a flatter and more uniform inner surface and improving the inner surface quality of the final workpiece.

[0046] Preferably, the extension direction of the tenon 41 or the tenon 42 is the same as the extension direction of the edge of the second outer shell 4 where the tenon 41 or the tenon 42 is located.

[0047] Since the first shell 2 and the second shell 4 are formed separately, and when there are multiple second shells 2, the integrity of the multiple second shells 4 is not high. Therefore, the improvement of the overall structural strength of the helmet mainly depends on the first shell 2. In order to compensate for the strength of the multiple second shells 4 forming an integrated structure, in some embodiments, reinforcing fibers can be laid between the first shell 2 and the second shell 4 in advance. After the reinforcing fibers are heated and pressurized with thermosetting resin, they can form a composite material layer in the middle layer, which further improves the structural strength of the overall composite material.

[0048] In the above scheme, before the second outer shell 4 is embedded into the inner side of the first outer shell 2, reinforcing fibers are laid on the inner surface of the first outer shell 2. In order to improve the laying stability and directional stability of the reinforcing fibers, some thermosetting resin can be applied to the inner surface of the first outer shell 2 during laying.

[0049] Preferably, the direction of laying the reinforcing fiber between the first outer shell 2 and the second outer shell 4 is not parallel to the joint direction of the second outer shell 4 at the corresponding position of the reinforcing fiber. More preferably, the direction of laying the reinforcing fiber is perpendicular to the joint direction of the second outer shell 4 at the corresponding position of the reinforcing fiber.

[0050] It should be understood that when decomposing the first and second graphics to obtain the corresponding cutting schemes for the carbon fiber prepreg, the cutting scheme for each layer of carbon fiber prepreg will take into account the unsealing direction of the two adjacent carbon fiber layers in advance to meet the requirements of non-parallel or perpendicular to each other. The above cutting schemes can be designed with the assistance of drawing unfolding software.

[0051] The carbon fiber composite helmet prepared by the above method has a smooth and flat surface structure on both the inner and outer surfaces, without pinholes or burrs. At the same time, this process does not require vacuum processing, vacuum coating, or heating in an autoclave. After the workpiece is processed, the surface polishing requirement is reduced, which can reduce the processing time, reduce the processing difficulty, and reduce material waste.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A molding process for a composite material, characterized in that, Includes the following steps: Step 1: Cut the prepreg and attach it to the inner surface of the first cavity mold. Embed the inflatable inner mold into the first cavity mold with the prepreg attached. After the inflatable inner mold is inflated, heat and pressurize it to obtain the first outer shell. Step 2: Cut the prepreg and attach it to the outer surface of the first punch. Place the inflatable outer mold on the outside of the first punch with the prepreg attached to its surface. Inflate the inflatable outer mold and then heat and pressurize it to obtain the second outer shell. Step 3: Insert the first outer shell into the inner side of the first concave mold, insert the second outer shell into the inner side of the first outer shell, fill the space between the first and second outer shells with thermosetting resin, then insert the third inner mold into the inner side of the second outer shell, and after closing the mold, heat and pressurize to cure to obtain the molded composite material. Both the first die and the first punch are made of metal or ceramic.

2. The molding process of the composite material as described in claim 1, characterized in that, Step one also includes filling the space between the inner surface of the first mold cavity and the prepreg with thermosetting resin.

3. The molding process of the composite material as described in claim 1, characterized in that, Step two also includes filling the space between the outer surface of the first punch and the prepreg with thermosetting resin.

4. The molding process of the composite material as described in claim 1, characterized in that, Within the same composite material, there are no fewer than two second shells, and multiple second shells are spliced ​​together inside the first shell to cover the inner surface of the first shell.

5. The molding process of the composite material as described in claim 4, characterized in that, Before splicing multiple second shells, mortises or tenons are machined at the edges of the spliced ​​second shells, and adjacent second shells are mortised and tenoned together by mortises and tenons.

6. The molding process of the composite material as described in claim 5, characterized in that, The extension direction of the mortise or tenon is the same as the extension direction of the edge of the second housing on which the mortise or tenon is located.

7. The molding process of the composite material as described in claim 1, characterized in that, Step three, before embedding the second housing inside the first housing, also includes laying reinforcing fibers on the inner surface of the first housing.

8. The molding process of the composite material as described in claim 1, characterized in that, In step three, the third inner mold is a metal punch or an inflatable mold.

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