A microwave curing process for liquid-formed carbon fiber composite material preforms

Abstract

The present application belongs to the technical field of composite material curing process, and relates to a microwave curing process for carbon fiber composite material liquid forming preform, which realizes microwave efficient heating of the carbon fiber composite material liquid forming preform by introducing a metal film, a dielectric layer and a metal pattern on the carbon fiber composite material preform. During the heating and curing process, the periphery of the preform and the mold is covered with a heat preservation layer for heat preservation. After the heating and curing is completed, when the natural cooling rate of the carbon fiber composite material liquid forming preform is lower than the required cooling rate, the preform is directly moved to the outside of the curing equipment for natural cooling. The present application can realize microwave curing of the carbon fiber composite material liquid forming preform, and fully utilize the advantages of the two processes, so as to effectively reduce the curing energy consumption, reduce the occupancy rate of the curing equipment, further realize efficient and low-cost manufacturing of the carbon fiber composite material component, and provide technical support for industrial application of the carbon fiber composite material microwave curing technology.

Description

Technical Field

[0001] This invention relates to the field of composite material curing technology, and more particularly to a liquid molding process for carbon fiber composite materials, specifically a microwave curing process for liquid molding preforms of carbon fiber composite materials. Background Technology

[0002] Carbon fiber composites (i.e., carbon fiber reinforced resin matrix composites) possess advantages such as high specific strength, high specific modulus, good fatigue resistance, and designable material properties, leading to their widespread application in aerospace and other fields. However, the long manufacturing cycle and high production cost of carbon fiber composite components restrict the large-scale industrial application and promotion of composite materials. For example, the cost of materials such as carbon fiber and resin generally accounts for only 25% to 30%, while the manufacturing cost accounts for 70% to 75%. To enhance the overall competitiveness of carbon fiber composites and meet economic affordability requirements, improving manufacturing efficiency and reducing manufacturing costs are urgent needs and development goals for the application of carbon fiber composites. Liquid molding technology has advantages such as low equipment requirements, simple molding process, and low manufacturing cost, and is recognized in the industry as one of the low-cost manufacturing technologies. In particular, the vacuum-assisted resin transfer molding process in liquid molding technology has received widespread attention from the aerospace, automotive, and other manufacturing industries in recent years. In liquid molding processes, carbon fiber composites typically require heating and curing to form components with both mechanical properties and geometric shapes under high temperatures. Currently, this heating and curing process is mainly carried out in an oven. The heating principle is to heat the air and transfer the heat to the composite material through heat conduction, thereby achieving the heating and curing of the composite material. During the curing process, the air, composite material and mold in the oven are all heated, which has problems such as low curing efficiency, long curing cycle and high curing energy consumption.

[0003] In comparison, microwave curing offers advantages such as sensitive temperature control, rapid heating, and selective heating, effectively shortening the curing cycle and reducing energy consumption of composite materials. Its combination with liquid molding processes holds promise for further reducing manufacturing costs and improving efficiency. However, the high microwave reflectivity of highly conductive carbon fibers results in low microwave heating efficiency for liquid-molded carbon fiber preforms, limiting the development of microwave curing technology for carbon fiber composite liquid molding. Consequently, the microwave curing process for liquid-molded preforms is immature, and its engineering applications are progressing slowly.

[0004] To address the aforementioned problems, the inventors, through extensive theoretical analysis and experimental research, discovered that sequentially placing a metal thin film, a dielectric layer, and a metal pattern on a flow guide mesh can stably and efficiently absorb microwaves, thereby generating heat to directly heat and cure the liquid-formed carbon fiber composite preform. This is currently a reasonable, technologically advanced, and highly applicable method for achieving efficient and stable microwave heating and curing of liquid-formed carbon fiber composite preforms. Based on this, the present invention proposes a microwave curing process for liquid-formed carbon fiber composite preforms, achieving high-efficiency, low-energy-consumption, and low-cost microwave curing of these preforms. Summary of the Invention

[0005] The purpose of this invention is to address the problems of low microwave heating efficiency and immature microwave curing process in liquid molding preforms of carbon fiber composite materials. In the first aspect, it provides a microwave curing process for liquid molding preforms of carbon fiber composite materials, which can realize efficient microwave heating of liquid molding preforms of carbon fiber composite materials and high-efficiency, low-cost curing and manufacturing of liquid molding preforms of carbon fiber composite materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A microwave curing process for liquid-molded carbon fiber composite preforms includes the following steps:

[0008] Step 1) After cleaning the mold, spray a release agent or lay a release cloth on the mold surface, and then lay the carbon fiber preform on the upper surface of the mold.

[0009] Step 2) On the laid carbon fiber preform, lay the release cloth, flow guide net, metal film, dielectric layer and metal pattern in sequence, arrange the resin flow guide tubes in a reasonable manner, wrap it with a vacuum bag, seal it with sealing strip, perform vacuum treatment, and check the airtightness.

[0010] Step 3) Resin is injected under vacuum pressure difference, so that the resin flows into and permeates the dry carbon fiber preform. After the resin injection is completed, a carbon fiber composite liquid molding preform is formed, and an insulation layer is applied to the outside of the carbon fiber composite liquid molding preform and the mold.

[0011] Step 4) Transfer the liquid molding preform and mold of carbon fiber composite material into the microwave curing equipment for microwave heating and curing;

[0012] Step 5) After microwave curing is completed, once the natural cooling rate of the carbon fiber composite liquid molded part is lower than the required cooling rate of the material, move the carbon fiber composite liquid molded part and the mold outside the microwave curing equipment and place them in an open environment for natural cooling until the temperature of the part drops to the temperature required by the material curing process.

[0013] In step 2), the thickness of the metal film is 0.01 mm to 1 mm.

[0014] In step 2), the dielectric layer is made of one or more dielectric materials with a dielectric constant of less than 10 and a dielectric loss of less than 5, wherein the dielectric material is preferably one or more combinations of polymer materials.

[0015] In step 2), the thickness of the dielectric layer is 0.1 mm to 2 mm.

[0016] In step 2), the metal pattern is periodically arranged on the surface of the dielectric layer or in a local area of ​​the surface, and the circumcircle diameter d of the metal pattern satisfies the following relationship:

[0017]

[0018] Where c is the speed of light in a vacuum, and f is the frequency of the microwaves used for heating.

[0019] The microwave heating effect required for liquid molding preforms of carbon fiber composite materials can be adjusted by modifying the shape, size, spacing of the metal pattern and the thickness of the dielectric layer.

[0020] In step 3), the insulation layer is made of a flexible material with extremely low heat transfer coefficient and good wave transmission performance; the flexible material is preferably one or more of aerogel felt, glass fiber felt, glass wool felt and composite silicate felt insulation materials.

[0021] In step 3), the thickness of the insulation layer should be such that the natural cooling rate of the carbon fiber composite liquid molded part after microwave heating and curing is lower than the required cooling rate. At this time, during the cooling stage, the carbon fiber composite liquid molded part and the mold are moved directly outside the microwave curing equipment and placed in an open environment for natural cooling.

[0022] When the thickness of the insulation layer is limited and the natural cooling rate of the carbon fiber composite liquid molded part after microwave curing cannot be guaranteed to be lower than the required cooling rate, microwave power should be applied first during the cooling stage to make the cooling rate of the carbon fiber composite liquid molded part lower than the required cooling rate. After the natural cooling rate of the carbon fiber composite liquid molded part is lower than the required cooling rate of the material, the carbon fiber composite liquid molded part and the mold should be moved outside the microwave curing equipment and placed in an open environment for natural cooling.

[0023] Secondly, the present invention also provides a liquid-molded carbon fiber composite material part, which is prepared according to the above-mentioned microwave curing process for liquid-molded carbon fiber composite material preforms.

[0024] Thirdly, the present invention also provides applications of the above-mentioned carbon fiber composite liquid-molded parts in the fields of aerospace, automotive industry and shipbuilding.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The microwave curing process for liquid-molded carbon fiber composite preforms provided by this invention involves placing a metal film, a dielectric layer, and a metal pattern sequentially on a flow guide mesh. This process allows for stable and efficient microwave absorption, achieving efficient and stable microwave heating of liquid-molded carbon fiber composite preforms while ensuring processability and applicability.

[0027] This invention provides good insulation by applying an insulation layer to the periphery of the liquid molding preform and mold of carbon fiber composite material, which can reduce heat dissipation during the heating and curing process and further reduce curing energy consumption.

[0028] This invention, after microwave curing, when the natural cooling rate of the liquid-molded carbon fiber composite part is lower than the required cooling rate, directly moves the part outside the curing equipment for natural cooling. This significantly shortens the time the part remains within the curing equipment and greatly reduces equipment occupancy. Simultaneously, since the preform and mold have been removed from the microwave curing equipment, the next batch of liquid-molded carbon fiber composite preforms can be microwave-cured, improving production efficiency.

[0029] This invention can effectively realize and complete the microwave curing of liquid-molded carbon fiber composite parts. Compared with traditional curing processes, the manufacturing cost of carbon fiber composite components can be significantly reduced and the manufacturing efficiency can be effectively improved, providing important technical support for the industrial application of microwave curing technology for carbon fiber composites.

[0030] The carbon fiber composite liquid molding parts prepared by the above-mentioned microwave curing process for liquid molding preforms can be widely used in aerospace, automotive and shipbuilding industries. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the material placement sequence and curing equipment in this invention;

[0032] Figure 2 This is a schematic diagram of the three-layer structure of the present invention, consisting of a metal thin film, a dielectric layer, and a metal pattern.

[0033] Figure 3 The results are test and simulation results of the microwave absorption performance of the three-layer structure composed of a metal thin film, a dielectric layer and a metal pattern of the present invention.

[0034] Figure 4 The test results show the absorption rate of the three-layer structure consisting of a metal thin film, a dielectric layer, and a metal pattern of the present invention as a function of temperature at a microwave frequency of 2.45 GHz.

[0035] Figure 5 These are microwave heating effect diagrams of carbon fiber composite liquid molding preforms, where (a) is a microwave heating effect diagram of a carbon fiber composite liquid molding preform with a three-layer structure consisting of a metal film, a dielectric layer, and a metal pattern; and (b) is a microwave heating effect diagram of a carbon fiber composite liquid molding preform without a three-layer structure consisting of a metal film, a dielectric layer, and a metal pattern.

[0036] Figure 6 These are actual images of carbon fiber reinforced epoxy resin composite flat panel components, where (a) is an actual image of a carbon fiber reinforced epoxy resin composite flat panel component cured by microwave curing process of carbon fiber composite liquid molding preform; and (b) is an actual image of a carbon fiber reinforced epoxy resin composite flat panel component cured by oven curing process.

[0037] Figure 7 These are the curing degree test results of carbon fiber reinforced epoxy resin matrix composite plate components, where (a) is the curing degree test result of carbon fiber reinforced epoxy resin matrix composite plate components cured by microwave curing process of carbon fiber composite liquid molding preforms; and (b) is the curing degree test result of carbon fiber reinforced epoxy resin matrix composite plate components cured by oven curing process.

[0038] Figure 8 This is a physical image of a carbon fiber reinforced epoxy resin composite flat panel component cured by microwave curing of a carbon fiber composite liquid molding preform with two layers of chopped glass fiber mat.

[0039] Figure 9 The results are the degree of curing test results of carbon fiber composite flat plate components cured by microwave curing process for carbon fiber composite liquid molding preforms with two layers of chopped glass fiber mat.

[0040] In the diagram: 1. Magnetron; 2. Rectangular waveguide; 3. Microwave curing equipment; 4. Insulation layer; 5. Vacuum bag; 6. Metal pattern; 7. Dielectric layer; 8. Metal film; 9. Flow guide net; 10. Release cloth; 11. Carbon fiber preform; 12. Release cloth / release agent; 13. Mold; 14. Resin flow guide tube; 15. Sealing strip. Detailed Implementation

[0041] The technical solution of the present invention will be clearly and thoroughly described and explained below with reference to the accompanying drawings and specific embodiments.

[0042] A microwave curing process for liquid-molded carbon fiber composite preforms, the key steps of which include the following:

[0043] Step 1) After cleaning the mold 13, spray a release agent on the surface of the mold or lay a release cloth 12, and then lay the carbon fiber preform 11 on the upper surface of the mold.

[0044] Step 2) On the laid carbon fiber preform 11, lay the release cloth 10, the flow guide net 9, the metal film 8, the medium layer 7, and the metal pattern 6 in sequence, and arrange the resin flow guide tubes 14 in a reasonable manner. Finally, wrap it with a vacuum bag 5, seal it with sealing strips 15, perform vacuum treatment, and check the air tightness.

[0045] Step 3) Resin is injected under vacuum pressure difference, so that the resin flows into and permeates the dry carbon fiber preform 11. After the resin injection is completed, a carbon fiber composite liquid molding preform is formed, and a heat insulation layer 4 is applied to the periphery of the carbon fiber composite liquid molding preform and the mold 13.

[0046] Step 4) Transfer the carbon fiber composite liquid molding preform and mold 13 into the microwave curing equipment 3 for microwave heating and curing;

[0047] Step 5) After microwave heating and curing is completed, once the natural cooling rate of the carbon fiber composite liquid molded part is lower than the cooling rate required by the material, move the carbon fiber composite liquid molded part and mold 13 outside the microwave curing equipment 3 and place them in an open environment for natural cooling until the temperature of the part drops to the temperature required by the material curing process.

[0048] The placement order of the above materials and the schematic diagram of the microwave curing equipment are shown below. Figure 1As shown. The microwave curing equipment 3 generates microwaves through the magnetron 1, which are transmitted through the rectangular waveguide 2 and then emitted by the slot antenna into the microwave curing equipment 3 to microwave heat the liquid-molded preform of carbon fiber composite material.

[0049] It should be noted that in this invention, the metal film 8 can be made of pure metals such as iron, copper, aluminum, silver, gold, and zinc, or alloys such as steel, copper alloys, aluminum alloys, and zinc alloys. The metal film 8 in the following specific embodiments is described using stainless steel, which is resistant to high temperatures and has stable electromagnetic properties, but it is by no means limited to stainless steel.

[0050] The dielectric layer 7 is preferably made of one or more polymer materials, and more preferably, materials with good dielectric properties such as polyimide and polytetrafluoroethylene are selected. The dielectric layer 7 in the following specific embodiments is described as a flexible polyimide film, but the material of the dielectric layer 7 is by no means limited to polyimide.

[0051] The metal pattern 6 can be made of pure metals such as iron, copper, aluminum, silver, gold, and zinc, or alloys such as steel, copper alloys, aluminum alloys, and zinc alloys. In the specific embodiments described below, the metal pattern 6 is described using stainless steel, but it is by no means limited to stainless steel. The metal pattern 6 can be square, circular, elliptical, fan-shaped, or some combinations thereof. The form of the pattern is not the core of this invention. Through the reasonable design of the thickness of the dielectric layer 7, and the shape, size, and arrangement of the metal pattern 6, the desired microwave absorption efficiency can be ultimately obtained, achieving the required microwave heating effect. The metal pattern 6 in the specific embodiments described below uses... Figure 2 The shape shown is arranged in a periodic array.

[0052] In this invention, the thickness of the dielectric layer 7, and the shape, size, and arrangement of the metal pattern 6 can all be determined using the finite element method. In the specific embodiments described below, the microwave heating frequency is 2.45 GHz, the dielectric constant of the polyimide film used to fabricate the dielectric layer 7 is 3.044, the dielectric loss is 0.008, and both the metal film 8 and the metal pattern 6 are made of stainless steel foil with a conductivity of 1.1 × 10⁻⁶. 6 S / m, with a thickness of 0.03mm, the form, size, arrangement, and thickness of the dielectric layer 7, determined by the finite element method, are as follows: Figure 2 As shown. The metal pattern 6 is preferably etched and attached to the dielectric layer 7 by means of etching, electroplating, photolithography, electron / ion etching, molding, chemical etching, etc. The metal thin film 8 can be attached to the lower surface of the dielectric layer 7 by means of molding, bonding, etc.

[0053] After the three-layer structure consisting of metal thin film 8, dielectric layer 7, and metal pattern 6 was fabricated, its absorption curve was tested using a vector network analyzer (VNA) via the free space method. The finite element simulation and test results are as follows: Figure 3 As shown in the figure, the test results of the absorption curves of the three-layer structure composed of metal film 8, dielectric layer 7, and metal pattern 6 are in good agreement with the simulation results. Furthermore, the absorption rate reaches 94% at the microwave heating frequency of 2.45 GHz, indicating that the three-layer structure can achieve efficient microwave heating. Further, a vector network analyzer (VNA) was used to test the change in the absorption rate of the three-layer structure at 2.45 GHz during the heating process. The test results are shown in the figure. Figure 4 As shown, the three-layer structure consisting of the metal film 8, the dielectric layer 7, and the metal pattern 6 exhibits a relatively stable microwave absorption effect at 2.45 GHz during the heating process, with the absorption rate varying from 86% to 98%. This indicates that the three-layer structure can achieve stable and efficient microwave heating, providing important technical support for the efficient microwave curing of liquid-formed carbon fiber composite preforms.

[0054] In this invention, the insulation layer 4 is composed of a flexible material with extremely low heat transfer coefficient and good wave transmission performance, preferably one or more combinations of aerogel felt, glass fiber felt, glass wool felt, and composite silicate felt. In the specific embodiments described below, the insulation layer 4 is preferably described as chopped glass fiber felt, but the material of the insulation layer 4 is by no means limited to chopped glass fiber felt. The thickness of the insulation layer 4 is determined by the finite element method, which is calculated using heat transfer simulation software.

[0055] Example 1

[0056] A liquid molding preform of carbon fiber reinforced epoxy resin matrix composite material was prepared by microwave heating and curing. Its dimensions are 300mm×300mm×2.5mm (length×width×thickness). The carbon fiber preform 11 is made of plain weave carbon fiber cloth, of which the carbon fiber cloth model is SYT49S-12K and a total of 6 layers are laid.

[0057] After cleaning mold 13, a three-layer structure consisting of release cloth 12, 6 layers of plain weave carbon fiber cloth, release cloth 10, flow guide net 9, metal film 8, dielectric layer 7, and metal pattern 6 is sequentially laid on top of mold 13. Resin flow guide pipe 14 is then arranged, wrapped with vacuum bag 5, sealed with sealing strip 15, and vacuumed to check airtightness. Subsequently, epoxy resin is injected into the dry carbon fiber cloth preform under vacuum pressure difference to form a carbon fiber reinforced epoxy resin-based composite liquid molding preform, which is then placed in microwave curing equipment 3 for microwave heating. Microwave curing equipment 3 uses magnetron 1 to generate microwaves, which are transmitted through rectangular waveguide 2 and then emitted by a slotted antenna into microwave curing equipment 3 to microwave heat the carbon fiber reinforced epoxy resin-based composite liquid molding preform. The heating effect is shown in the figure. Figure 5 As shown in (a), it can be seen that the carbon fiber reinforced epoxy resin matrix composite liquid molding preform is heated efficiently by microwaves under the three-layer structure composed of metal film 8, dielectric layer 7 and metal pattern 6.

[0058] In contrast, the three-layer structure consisting of the metal film 8, the dielectric layer 7, and the metal pattern 6 is not introduced in the above-mentioned preparation process of the carbon fiber reinforced epoxy resin matrix composite liquid molding preform; other settings and processes remain consistent with the above process. The carbon fiber reinforced epoxy resin matrix composite liquid molding preform without the three-layer structure consisting of the metal film 8, the dielectric layer 7, and the metal pattern 6 is placed in the microwave curing equipment 3 for microwave heating. The heating effect is shown in the figure below. Figure 5 As shown in (b), the carbon fiber reinforced epoxy resin matrix composite liquid molding preform without the introduction of the three-layer structure consisting of the metal film 8, the dielectric layer 7, and the metal pattern 6 hardly absorbs microwaves for heating in the microwave environment, and the heating effect is weak. This shows that the carbon fiber composite liquid molding preform has the characteristic of almost total microwave reflection, and further demonstrates the role of the three-layer structure consisting of the metal film 8, the dielectric layer 7, and the metal pattern 6, which can realize the efficient and stable microwave heating of the carbon fiber composite liquid molding preform.

[0059] Example 2 (Microwave curing of carbon fiber reinforced epoxy resin composite liquid molding flat plate components)

[0060] This embodiment uses the microwave curing process for liquid molding preforms of carbon fiber composite materials proposed in this invention to cure and mold a carbon fiber reinforced epoxy resin matrix composite flat panel component with dimensions of approximately 500mm × 500mm × 3.2mm (length × width × thickness). The carbon fiber preform 11 used is made of plain weave carbon fiber cloth, wherein the carbon fiber cloth model is SYT49S-12K, and the recommended curing process for the epoxy resin used is to hold at 120℃ for 90 minutes with a cooling rate of less than 1.5℃ / min.

[0061] In this embodiment, the heating rate in the microwave curing process of the carbon fiber composite liquid molding preform is set to 1℃ / min, and the liquid molding microwave curing steps of the carbon fiber reinforced epoxy resin matrix composite flat plate component are as follows:

[0062] Step 1) Clean the glass mold 13 (650mm×650mm×5mm) with alcohol, and lay the release cloth 12 on the surface of the mold 13. Then, lay 8 layers of plain carbon fiber cloth with a size of 500mm×500mm (length×width) on the upper surface of the mold 13 with the release cloth.

[0063] Step 2) On the stacked carbon fiber preform 11, lay out the three-layer structure consisting of release cloth 10, flow guide net 9, prepared metal film 8, dielectric layer 7 and metal pattern 6 in sequence, arrange the resin flow guide tube 14 in a reasonable manner, wrap it with vacuum bag 5, seal it with sealing strip 15, perform vacuum treatment, and check the air tightness.

[0064] Step 3) Resin is infused under vacuum pressure difference, allowing epoxy resin to flow into and permeate the pre-laid dry carbon fiber preform 11. After resin infusion, a carbon fiber reinforced epoxy resin-based composite liquid molding preform is formed. Short-cut glass fiber mat is then covered on the upper surface (outside the vacuum bag 5) and lower surface of the mold 13 for insulation. Based on the thermal conductivity and heat transfer simulation model of the short-cut glass fiber mat, the number of layers is set to 4, ensuring that the natural cooling rate of the liquid molding part is lower than the required cooling rate of the material.

[0065] Step 4) The carbon fiber composite liquid molding preform and mold 13 are transferred into the microwave curing equipment 3 for microwave heating and curing. The preform is microwave heated and cured according to the set curing process (i.e., heated from room temperature to 120℃ and held at 1℃ / min for 90min).

[0066] Step 5) After the heating and curing are completed, turn off all microwave sources directly. The natural cooling rate of the carbon fiber composite liquid molded part is about 0.8℃ / min, which is lower than the cooling rate required by the material. At this time, move the carbon fiber reinforced epoxy resin-based composite liquid molded part and mold 13 directly to the outside of the microwave curing equipment 3 and place them in an open environment for natural cooling until the temperature drops below 60℃.

[0067] The carbon fiber reinforced epoxy resin matrix composite flat panel component cured by the microwave curing process of the above-mentioned carbon fiber composite liquid molding preform is as follows: Figure 6As shown in (a), the surface of the flat component is smooth and without obvious defects, indicating that the microwave curing process for liquid-molded carbon fiber composite preforms proposed in this invention can achieve the curing and molding of carbon fiber composite components. Furthermore, the readings of the three-phase four-wire electronic energy meter on the microwave curing equipment 3 were recorded before and after the start and end of the microwave curing process for the aforementioned liquid-molded carbon fiber composite preforms, and the curing energy consumption of this microwave curing process was calculated. The calculation results are shown in Table 1. It can be seen that the curing energy consumption of the microwave curing process for the liquid-molded carbon fiber composite preforms is 6.27 kW·h.

[0068] Furthermore, the degree of cure of the carbon fiber reinforced epoxy resin matrix composite flat panel component, formed using the microwave curing process for liquid molding preforms of carbon fiber composite materials proposed in this invention, was measured using differential scanning calorimetry. To ensure the validity and reliability of the degree of cure measurement results, samples were taken from four different locations on the flat panel component and the degree of cure was tested. The measurement results of the degree of cure are as follows: Figure 7 As shown in (a), the DSC curve of the carbon fiber composite material sample cured by the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention did not show an obvious exothermic peak, indicating that the flat plate component cured by the microwave curing process proposed in this invention has been completely cured. Based on this, a universal testing machine was used to conduct four mechanical property tests on the carbon fiber reinforced epoxy resin matrix composite liquid molding flat plate component cured by the microwave curing process proposed in this invention, according to mechanical property testing standards. These tests included tensile strength, compressive strength, flexural strength, and interlaminar shear strength. Five test samples were taken for each mechanical property test, and the average value was calculated. The test results are shown in Table 2. The tensile strength of the composite plate component cured by the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention is 702.7 MPa, the compressive strength is 415.9 MPa, the flexural strength is 767.8 MPa, and the interlaminar shear strength is 48.3 MPa.

[0069] Comparative Example 1 (Oven curing of liquid-molded flat plate components made of carbon fiber reinforced epoxy resin matrix composites)

[0070] This comparative example uses a traditional oven curing method to cure and mold a liquid-molded flat panel component of carbon fiber reinforced epoxy resin matrix composite material. The curing conditions, curing settings, and materials are the same as in Example 2, and the heating rate during the curing process is 1℃ / min. The specific steps for oven curing and molding the liquid-molded flat panel component of carbon fiber reinforced epoxy resin matrix composite material are as follows:

[0071] Step 1) Clean the glass mold 13 (650mm×650mm×5mm) with alcohol, and lay a release cloth on the surface of the mold 13. Then, lay carbon fiber cloth with a size of 500mm×500mm (length×width) on the upper surface of the mold 13 with the release cloth, for a total of 8 layers.

[0072] Step 2) Lay out the release cloth 10 and the flow guide net 9 on the stacked carbon fiber preform 11 in sequence, arrange the resin flow guide tube 14 in a reasonable manner, and finally wrap it with a vacuum bag 5, seal it with sealing strip 15, perform vacuum treatment, and check the air tightness.

[0073] Step 3) Resin is injected under vacuum pressure difference, so that epoxy resin flows into and permeates the above-laid dry carbon fiber preform 11. After the resin injection is completed, a carbon fiber reinforced epoxy resin matrix composite liquid molding preform is formed.

[0074] Step 4) The prepared carbon fiber reinforced epoxy resin matrix composite liquid molding preform and mold 13 are transferred together into an oven for heat curing. The preform is heated and cured in the oven according to the set curing process (i.e., heated from room temperature to 120℃ at a heating rate of 1℃ / min and held at that temperature for 90min).

[0075] Step 5) After heating and curing, the liquid molded carbon fiber reinforced epoxy resin composite material is slowly cooled by natural cooling in the oven. The part is removed from the oven when the temperature drops to 60°C, and the curing is completed.

[0076] Carbon fiber reinforced epoxy resin composite flat panel components cured by oven curing method, such as Figure 6 As shown in (b), the surface of the flat panel component is smooth and without obvious defects. Furthermore, the readings of the three-phase four-wire electronic energy meter on the oven were recorded before and after the start and end of the oven curing process for the aforementioned carbon fiber composite liquid-molded flat panel component, and the curing energy consumption of this oven curing process was calculated. The calculation results are shown in Table 1. It can be seen that the curing energy consumption of the oven curing process for this carbon fiber composite liquid-molded flat panel preform is 29.0 kW·h.

[0077] Furthermore, the degree of curing of the carbon fiber reinforced epoxy resin composite flat plate component cured by the oven curing method was measured using differential scanning calorimetry. The measurement results are as follows: Figure 7As shown in (b), the DSC curve of the carbon fiber composite material sample cured by the traditional oven curing process did not show an obvious exothermic peak, indicating that the flat plate component cured by the oven curing process was completely cured. Based on this, a universal testing machine was used to conduct four mechanical property tests on the liquid-molded flat plate component of carbon fiber reinforced epoxy resin matrix composite material cured by the oven curing process, according to the mechanical property testing standards. These tests included tensile strength, compressive strength, flexural strength, and interlaminar shear strength. Five test samples were taken for each mechanical property test, and the average value was calculated. The test results are shown in Table 2. The tensile strength of the composite material flat plate component cured by the traditional oven curing method was 709.3 MPa, the compressive strength was 368.2 MPa, the flexural strength was 673.1 MPa, and the interlaminar shear strength was 48.5 MPa.

[0078] Table 1. Curing energy consumption of carbon fiber composite liquid molding preforms during microwave curing process (Example 2) and oven curing process (Comparative Example 1) for curing carbon fiber reinforced epoxy resin matrix composite flat components.

[0079] Table 2. Mechanical property test results of carbon fiber reinforced epoxy resin composite flat plate components cured by microwave curing process (Example 2) and oven curing process (Comparative Example 1) for liquid-molded carbon fiber composite preforms.

[0080]

[0081] Comparing the results of Example 2 and Comparative Example 1 in Tables 1 and 2 above, the carbon fiber composite flat panel component cured by the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention exhibits comparable mechanical properties (tensile strength, compressive strength, flexural strength, and interlaminar shear strength) to the traditional oven curing process, without affecting the degree of curing of the carbon fiber composite material. This demonstrates that the microwave curing process proposed in this invention can meet the requirements of industrial applications. Furthermore, while ensuring the mechanical properties and degree of curing of the carbon fiber composite component, the energy consumption of the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention is reduced by 78.7% compared to the oven curing process. In addition, since the carbon fiber composite liquid molding preform can be directly removed from the curing equipment after microwave heating and curing, whereas in the oven curing process, the part must be removed only after the temperature drops to 60°C, the equipment occupancy rate of the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention is effectively reduced.

[0082] Example 3

[0083] Example 3 follows the same experimental setup and arrangement as Example 2, employing the microwave curing process for liquid-molded carbon fiber composite preforms proposed in this invention to cure and mold carbon fiber reinforced epoxy resin composite flat panels. In this example, the number of chopped glass fiber mat layers is reduced from 4 to 2, meaning the thickness of insulation layer 4 is reduced. After the carbon fiber reinforced epoxy resin composite flat panel has been incubated at 120°C, as cooling begins, all microwave sources are turned off. The natural cooling rate of the flat panel is 1.7°C / min, higher than the required cooling rate (1.5°C / min). At this point, the microwave sources are turned on again, applying a certain amount of microwave power to the carbon fiber reinforced epoxy resin composite flat panel to maintain its cooling rate below 1.5°C / min. When the temperature of the flat panel drops to 100°C, its natural cooling rate decreases to 1.4°C / min. At this point, all microwave sources are turned off, and the liquid-molded carbon fiber reinforced epoxy resin composite preform and mold 13 are moved outside the microwave curing equipment 3 and placed in an open environment for natural cooling until the temperature drops below 60°C.

[0084] The carbon fiber composite liquid molding preforms proposed in this invention are cured by microwave curing process, resulting in carbon fiber reinforced epoxy resin matrix composite flat panel components, such as... Figure 8 As shown, the surface of the flat component is smooth and without obvious defects, indicating that the microwave curing process for liquid molding preforms of carbon fiber composite materials proposed in this invention can achieve the curing and molding of carbon fiber composite components.

[0085] Furthermore, the degree of cure of the carbon fiber reinforced epoxy resin composite flat plate component was measured using differential scanning calorimetry. The measurement results of the degree of cure are as follows: Figure 9 As shown, the carbon fiber composite sample cured by the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention did not exhibit a significant exothermic peak, indicating that the flat plate component was completely cured. The microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention does not affect the degree of curing of the carbon fiber composite. Based on this, a universal testing machine was used to test the tensile strength, compressive strength, flexural strength, and interlaminar shear strength of the carbon fiber reinforced epoxy resin matrix composite liquid molding flat plate component cured by the microwave curing process according to mechanical property testing standards. Five test samples were taken for each mechanical property test, and the average value was calculated. The test results are shown in Table 3. Compared with the mechanical property test results of the oven-cured flat plate component in Table 2, the flat plate component cured by the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention is comparable to the traditional oven-curing process in all four mechanical properties. This indicates that the microwave curing process of the carbon fiber composite liquid molding preform proposed in this invention does not reduce the mechanical properties of the carbon fiber composite component and meets the requirements of industrial applications.

[0086] Table 3. Mechanical property test results of carbon fiber reinforced epoxy resin composite flat plate components cured by microwave curing process (Example 3) for carbon fiber composite liquid molding preforms with 2 layers of chopped glass fiber mat.

[0087]

[0088] All parts not covered in this invention are existing technologies and will not be described in detail here. Alternatively, they may be implemented using the same or similar technologies as existing technologies.

[0089] The above are merely preferred embodiments of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A microwave curing process for liquid-molded carbon fiber composite preforms, characterized in that: The curing process includes the following steps: 1) After cleaning the mold, spray a release agent or lay a release cloth on the mold surface, and then lay carbon fiber cloth on the upper surface of the mold. 2) Lay out the release cloth, flow guide net, metal film, dielectric layer and metal pattern in sequence on the stacked carbon fiber preform, arrange the resin flow guide tubes in a reasonable manner, wrap it with a vacuum bag, seal it with sealing strip, perform vacuum treatment, and check the air tightness. 3) Resin is injected under vacuum pressure difference, so that the resin flows into and permeates the dry carbon fiber preform. After the resin injection is completed, a carbon fiber composite liquid molding preform is formed, and an insulation layer is applied to the outside of the carbon fiber composite liquid molding preform and the mold. 4) Transfer the liquid molding preform and mold of carbon fiber composite material into the microwave curing equipment for microwave heating and curing; 5) After microwave curing is completed, once the natural cooling rate of the carbon fiber composite liquid molded part is lower than the required cooling rate of the material, move the carbon fiber composite liquid molded part and the mold outside the microwave curing equipment and place them in an open environment for natural cooling until the temperature of the part drops to the temperature required by the material curing process. The thickness of the metal film is 0.01 mm to 1 mm; The dielectric layer is made of one or more dielectric materials with a dielectric constant of less than 10 and a dielectric loss of less than 5, wherein the dielectric material is one or more combinations of polymer materials; The thickness of the dielectric layer is 0.1mm to 2mm; The metal patterns are periodically arranged on the surface of the dielectric layer or in a local area of ​​the surface, and the circumcircle diameter d of the metal patterns satisfies the following relationship: ， The speed of light in a vacuum. The frequency of the microwaves used for heating; The thickness of the insulation layer should be sufficient to ensure that the natural cooling rate of the carbon fiber composite liquid molded part after microwave curing is lower than the required cooling rate of the material. In this case, the carbon fiber composite liquid molded part and the mold should be moved outside the microwave curing equipment and placed in an open environment for natural cooling during the cooling stage. When there are limitations on the thickness of the insulation layer, or the thickness of the insulation layer cannot ensure that the natural cooling rate of the carbon fiber composite liquid molded part after microwave curing is lower than the required cooling rate of the material, microwave power should be applied first during the cooling stage to make the cooling rate of the carbon fiber composite liquid molded part lower than the required cooling rate of the material. After the natural cooling rate of the carbon fiber composite liquid molded part is lower than the required cooling rate of the material, the carbon fiber composite liquid molded part and the mold should be moved outside the microwave curing equipment and placed in an open environment for natural cooling.

2. The microwave curing process for liquid-formed carbon fiber composite preforms according to claim 1, characterized in that: The microwave heating effect required for liquid molding preforms of carbon fiber composite materials can be adjusted by modifying the shape, size, spacing of the metal pattern and the thickness of the dielectric layer.

3. The microwave curing process for liquid-formed carbon fiber composite preforms according to claim 1, characterized in that: The insulation layer is made of a flexible material with extremely low heat transfer coefficient and good wave transmission performance; the flexible material is one or more of aerogel felt, chopped glass fiber felt, glass wool felt or composite silicate felt.

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