Method for improving thickness uniformity of composite material based on VARI process

Abstract

The invention discloses a method for improving the thickness uniformity of a composite material based on a VARI technology, and relates to the technical field of composite material liquid forming. Comprising the following steps that a prefabricated part is laid on the surface of a tool, the surface of the prefabricated part is sequentially covered with demolding cloth and a flow guide net, and a composite body is formed; an inner-layer sealing bag is adopted to wrap the composite body and is connected with the glue injection pipe and the glue outlet pipe, and an inner bag packaging body is formed; after a breathable layer is laid on the periphery of the inner bag packaging body, the outer layer sealing bag is adopted for wrapping, a double-layer bag packaging body is formed, and the outer layer sealing bag is provided with an air outlet; the double-layer bag packaging body is vacuumized until the prefabricated part is compacted and the thickness is stable, and a compacted prefabricated part is obtained; measuring the net glue injection pressure range of the compacted prefabricated part without springback in thickness; and on the basis of the net glue injection pressure range, the net glue injection pressure is adjusted, glue is injected into the compacted prefabricated part till no bubble is discharged from the resin flowing out of the glue outlet pipe, and then the composite material product is obtained after curing. The defects of air holes and poor glue in the composite material can be avoided, the thickness rebound of the local area of the prefabricated part in the glue injection process is avoided, and the thickness uniformity of the composite material is good.

Description

Technical Field

[0001] This application relates to the field of liquid molding technology for composite materials, and in particular to a method for improving the thickness uniformity of composite materials based on the VARI process. Background Technology

[0002] The traditional vacuum-assisted resin infusion (VARI) process for preparing composite materials typically suffers from the following problems: (1) There are local permeability differences in the preforms, with significant differences in resin wetting speed between low-permeability areas and other areas. The resin is prone to forming rapid channels during the injection process, leading to insufficient resin wetting or air bubbles that cannot be expelled from the preforms, resulting in defects such as pores or poor resin content in the composite materials; (2) The traditional VARI process relies on atmospheric pressure to drive resin flow (i.e., net injection pressure = atmospheric pressure - vacuum bag pressure). When the altitude of the production site changes or the seasonal temperature difference is large, the atmospheric pressure fluctuates significantly, resulting in large deviations in the thickness and fiber volume fraction of different batches of products; (3) The traditional VARI process uses a single-layer vacuum bag, which cannot effectively disperse the upward rebound force generated in the low-permeability area of ​​the preforms, causing local thickness rebound and sudden increase in local thickness during the injection process, severely damaging the overall uniformity. Based on this, this application proposes a method for improving the thickness uniformity of composite materials based on the VARI process. Summary of the Invention

[0003] The main objective of this application is to provide a method for improving the thickness uniformity of composite materials based on the VARI process, aiming to solve the technical problem of uneven thickness of composite materials prepared by the existing VARI process.

[0004] To achieve the above objectives, this application proposes a method for improving the thickness uniformity of composite materials based on the VARI process, comprising the following steps: The prefabricated component is laid on the surface of the tooling, and a release cloth and a flow guide net are sequentially covered on the surface of the prefabricated component to form a composite; The composite is wrapped in an inner sealing bag and connected to a glue injection tube and a glue outlet tube to form an inner bag encapsulation body; then, after laying a breathable layer on the outer periphery of the inner bag encapsulation body, it is wrapped in an outer sealing bag to form a double-bag encapsulation body, wherein the outer sealing bag is provided with an air outlet. Vacuum the double-layer bag packaging body until the preform is compacted and the thickness is stable to obtain the compacted preform. Determine the range of net injection pressure required to prevent the thickness of the compacted precast component from rebounding; Based on the net injection pressure range, the net injection pressure is adjusted and the resin is injected into the compacted preform until no air bubbles are discharged from the resin flowing out of the injection pipe, thus obtaining a resin impregnated body. After curing the resin impregnated body, a composite material product with uniform thickness is obtained.

[0005] Optionally, in the step of laying the preform on the tooling surface and sequentially covering the surface of the preform with a release cloth and a flow guide net, the size of the flow guide net is smaller than the preform to form a circumferentially uncovered edge area, and the width of the circumferentially uncovered edge area is 2.0cm-3.0cm.

[0006] Optionally, the breathable layer is a breathable felt strip, and the width of the breathable felt strip is 4.8cm-5.2cm.

[0007] Optionally, after the step of laying a breathable layer around the outer periphery of the inner bag packaging body and then wrapping it with an outer sealing bag to form a double-layer bag packaging body, the method further includes: After the breathable layer is laid around the double-layer bag packaging body, at least one additional extended sealing bag is added for wrapping, and the breathable layer is laid between each two adjacent extended sealing bags to form a multi-layer bag packaging body.

[0008] Optionally, the step of evacuating the double-layer bag packaging until the preform is compacted and its thickness is stable, to obtain a compacted preform, includes: The double-layer bag packaging body is evacuated to a maximum vacuum of -0.1 MPa. If no decrease in vacuum occurs within 25-30 minutes, evacuation continues. The thickness of the preform is measured every 1-3 minutes until the thickness change of the preform is ≤0.001 mm. When the compaction is stable, the compacted preform is obtained.

[0009] Optionally, the step of determining the net injection pressure range within which the compacted preform thickness does not spring back includes: The minimum net injection pressure critical value Δ for the compacted precast component thickness to prevent springback was determined, and Δ was set to 0.1 MPa as the net injection pressure range.

[0010] Optionally, the step of determining the minimum net injection pressure critical value Δ for preventing the compacted precast component thickness from springing back includes: The glue injection tube, the glue outlet tube, and the air outlet are all connected to a vacuum pump. The vacuum pump connected to the glue outlet tube and the air outlet is turned off, and the air pressure of the glue injection tube is gradually increased. When the thickness of the compacted preform increases by ≥0.003mm, the previous pressure value is recorded as the minimum net glue injection pressure critical value Δ.

[0011] Optionally, the step of adjusting the net injection pressure and injecting resin into the compacted preform until no air bubbles are discharged from the resin flowing out of the injection pipe to obtain the resin-impregnated body includes: The air pressure value of the dispensing tube and the air pressure value of the air outlet are both fixed at -0.1MPa; The pressure adjustment range of the dispensing tube is set to -(0.1MPa-Δ) to 0MPa; Resin is injected into the compacted preform until no air bubbles are discharged from the resin flowing out of the glue outlet for 5-10 minutes, thus obtaining a resin-impregnated body.

[0012] Optionally, in the step of curing the resin impregnated body, a stepped curing process is adopted, in which the resin impregnated body is kept at 75℃-85℃ for 1.5h-2.5h, and then the temperature is raised to 115℃-125℃ and kept at that temperature for 3.5h-4.5h.

[0013] Optionally, the preform is a carbon fiber plain weave fabric laminate, and the total number of layers in the preform is 6-10.

[0014] The beneficial effects of this application include: This application determines the minimum net injection pressure range within which the thickness of the preform does not rebound through actual measurement. Depending on the complexity of the preform structure, an appropriate net injection pressure can be selected within this range to avoid large differences in local permeability of the preform when the net injection pressure is too high, and to ensure that low-permeability areas can be completely wetted. This avoids the formation of rapid channels in the resin during the injection process due to excessive differences in resin wetting speed in different areas of the preform, which would lead to defects such as pores and resin deficiency in the composite material. At the same time, it also avoids the problem of excessively slow wetting speed of the preform, which would result in excessively high requirements for the resin process window time. This application employs a multi-layer sealed bag injection process, in which a breathable layer is laid between the inner and outer sealed bags. The discontinuous interface formed between the inner and outer sealed bags in the thickness direction is used to disperse the upward pressure in the low-permeability area of ​​the preform during the injection process and to diffuse the local rebound force laterally. This reduces the thickness rebound of the preform in the low-permeability area, maintains the uniformity of the overall thickness of the preform, and improves the consistency of the thickness deviation and fiber volume fraction of the composite material product. This application uses a vacuum pump to actively regulate pressure and control the net injection pressure to a constant level. It does not rely on atmospheric pressure to drive resin flow and can counteract atmospheric pressure interference. This avoids the problem of large deviations in thickness and fiber volume fraction of products from different origins and batches caused by external factors such as production site, season, and altitude in the traditional VARI process. As a result, it ensures the stability of product quality and significantly reduces the defect rate. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application 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 this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating the method for improving the thickness uniformity of composite materials based on the VARI process described in the embodiments of this application; Figure 2 The diagram shows the pressure distribution of the low-permeability zone in the sealed bag according to the embodiments of this application, wherein (a) is a schematic diagram of pressure concentration in a single-layer bag, and (b) is a schematic diagram of pressure distribution in a multi-layer bag; Figure 3 This is a schematic diagram of the preform injection process described in the embodiments of this application; Figure 4 This is a graph showing the change in thickness of the preform over time according to an embodiment of this application; Figure 5 This is a graph showing the thickness measurement results of the cured composite material product described in the embodiments of this application.

[0017] Figure label: 1-Resin tank; 2-Conduit; 3-Wound tube; 4-Breathable felt strip; 5-Precast component; 6-Release cloth; 7-Flow guide net; 8-Inner sealing bag; 9-Outer sealing bag; 10-Tooling; 11-Collector; 12-Vacuum pump.

[0018] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0020] To address the technical problems existing in the prior art, embodiments of this application provide a method for improving the thickness uniformity of composite materials based on the VARI process, comprising the following steps: S1. The preform is laid on the surface of the tooling, and a release cloth and a flow guide net are sequentially covered on the surface of the preform to form a composite.

[0021] In the specific implementation process, the size of the guide net is smaller than that of the prefabricated part to form a circumferentially uncovered edge area, the width of which is 2.0cm-3.0cm.

[0022] When the guide net completely covers the preform, the wetting rate of the upper resin layer is greater than that of the lower resin layer, which can lead to defects such as porosity and insufficient resin in the final product. However, by controlling the dimensions of the guide net to be 2.0cm-3.0cm smaller than the preform, an uncovered edge area is formed around the preform. This prevents the resin from forming a fast channel in the upper layer during the injection process, balances the wetting rate of the upper resin layer with that of the lower resin layer, and thus avoids defects such as porosity and insufficient resin in the composite material.

[0023] Specifically, the preform is a carbon fiber plain weave fabric laminate, and the total number of layers in the preform is 6-10.

[0024] S2. The composite is wrapped with an inner sealing bag and connected to the glue injection tube and the glue outlet tube to form an inner bag encapsulation body; then, after laying a breathable layer on the outer periphery of the inner bag encapsulation body, it is wrapped with an outer sealing bag to form a double-layer bag encapsulation body, wherein the outer sealing bag is provided with an air outlet.

[0025] When impregnating precast components, especially complex ones, with resin, low-permeability areas often appear. During the resin injection process, the pressure in these low-permeability areas increases, causing the precast component to rebound. This, in turn, adds an upward force to the sealing bag. If a single-layer sealing bag is used, such as... Figure 2 As shown in (a), the thickness of the composite material at this location increases compared to other areas, leading to a decrease in the overall uniformity of the composite material. Therefore, this application employs a double-layer sealing bag. Utilizing the discontinuous interface formed between the inner and outer sealing bags in the thickness direction, the upward force, when transmitted to the interface between the inner and outer sealing bags, diffuses outwards around the preform, dispersing the upward pressure on the low-permeability areas of the preform during adhesive injection and allowing it to diffuse laterally. Figure 2 As shown in (b), the thickness of the precast component in this region will not rebound significantly, thereby reducing the amount of thickness rebound of the precast component in the low permeability region and maintaining the uniformity of the overall thickness of the precast component.

[0026] In the specific implementation process, the composite is wrapped by the inner sealing bag and then connected to the injection tube and the outlet tube to facilitate the injection and flow of resin in the subsequent injection process. The outer sealing bag only needs to have an air outlet and does not need to have an injection port, so that the air between the inner and outer sealing bags can be extracted during the subsequent injection process.

[0027] In the specific implementation process, the breathable layer is a breathable felt strip, and the width of the breathable felt strip is 4.8cm-5.2cm. By adding a breathable felt strip between the inner and outer sealed bags, it is possible to avoid the two sealed bags directly contacting and sticking together when vacuuming begins, which would prevent some air from being extracted and thus affect the vacuum level of the outer sealed bag.

[0028] After the step of forming the double-layer bag package, the method further includes: After the breathable layer is laid around the double-layer bag packaging body, at least one additional extended sealing bag is added for wrapping, and the breathable layer is laid between each two adjacent extended sealing bags to form a multi-layer bag packaging body.

[0029] For more complex structural components, multiple layers of sealed bags can be wrapped as needed to further disperse the pressure in the low-permeability areas of the precast components, prevent significant rebound in the thickness of the precast components in the low-permeability areas, and maintain the uniformity of the thickness of the precast components.

[0030] S3. Vacuum the double-layer bag packaging body until the preform is compacted and the thickness is stable to obtain the compacted preform.

[0031] In the specific implementation process, before compacting the double-layer bag packaging, the airtightness of the inner and outer sealing bags needs to be tested. If it is a multi-layer bag packaging, the airtightness of the extended sealing bag also needs to be tested. Specifically: By turning on the vacuum pump and waiting until each layer of sealed bags reaches the maximum vacuum level (i.e. -0.1MPa), turn off the vacuum pump and wait for 25-30 minutes. If the vacuum level of each layer of sealed bags does not decrease, it proves that the airtightness is good. The subsequent compaction step requires turning on the vacuum pump, continuing to evacuate the vacuum, and measuring the thickness of the preform every 1-3 minutes until the thickness of the preform no longer decreases. This application determines that when the thickness change is ≤0.001mm, the compaction is stable, and a compacted preform is obtained.

[0032] S4. Measure the range of net injection pressure within which the thickness of the compacted precast component does not rebound.

[0033] In the specific implementation process, firstly, the minimum net injection pressure critical value Δ for the compacted preform thickness to not rebound is determined. The injection tube, the outlet tube, and the air outlet are all connected to a vacuum pump. The vacuum pump connected to the outlet tube and the air outlet is turned off. The air pressure of the injection tube is gradually increased. Before the air pressure increases to a certain value, the preform thickness will not rebound. This value is recorded as the minimum net injection pressure critical value Δ.

[0034] Specifically, this application determines that when the thickness of the compacted precast component increases by ≥0.003mm, it is considered that the thickness has rebounded. That is, by gradually increasing the air pressure of the injection tube, when the thickness of the compacted precast component increases by ≥0.003mm, the previous pressure value is recorded as the minimum net injection pressure critical value Δ.

[0035] This application uses the measured Δ as the minimum net injection pressure to maintain the compacted thickness of the preform. Based on the minimum pressure required to prevent the compacted preform thickness from rebounding, Δ is set to a range of 0.1 MPa as the net injection pressure. Subsequently, an appropriate net injection pressure can be selected within this range according to the complexity of the preform structure, thereby reducing the net injection pressure and avoiding large differences in local permeability of the preform when the net injection pressure is too high. It also ensures that low-permeability areas can be completely wetted, thus avoiding the formation of rapid channels in the resin during the injection process due to excessive differences in resin wetting speed in different areas of the preform, which would lead to defects such as pores and resin deficiency in the composite material.

[0036] S5. Based on the net injection pressure range, adjust the net injection pressure and inject the resin into the compacted preform until no air bubbles are discharged from the resin flowing out of the injection pipe, thereby obtaining a resin impregnated body. After curing the resin impregnated body, a composite material product with uniform thickness is obtained.

[0037] In the specific implementation process, the steps for adjusting the net injection pressure include: Turn on the vacuum pump and fix the air pressure value of the dispensing tube and the air pressure value of the outlet to -0.1MPa; The pressure adjustment range of the dispensing tube is set to -(0.1MPa-Δ) to 0MPa; Resin is injected into the compacted preform until no air bubbles are discharged from the resin flowing out of the glue outlet for 5-10 minutes, thus obtaining a resin-impregnated body.

[0038] In the step of curing the resin impregnated body, a stepped curing process is adopted, in which the resin impregnated body is kept at 75℃-85℃ for 1.5h-2.5h, and then the temperature is raised to 115℃-125℃ and kept at that temperature for 3.5h-4.5h.

[0039] Specifically, if the net injection pressure is too high, rapid channels may form near the low-permeability zone of the preform, ultimately leading to defects such as porosity or resin deficiency in the composite material. If the net injection pressure is too low, the preform wetting speed will be too slow, the injection time will be too long, and the requirements for the resin's process window will be increased. Meanwhile, this application, after measuring and obtaining the net injection pressure range for maintaining the compacted thickness of the preform, uses a vacuum pump to adjust the resin tank pressure. By applying pressure to the resin, the net injection pressure is ensured to remain constant. This avoids the problem of different thicknesses and fiber volume fractions in different batches and from different origins caused by weather, altitude, and other factors affecting the injection process under atmospheric pressure conditions in traditional VARI processes.

[0040] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0041] Example 1 A method for improving the thickness uniformity of composite materials based on the VARI process, such as Figure 3 As shown, it includes the following steps: Step 1: Raw material preparation Precast component 5 is made of 8 layers of carbon fiber plain weave fabric and measures 40cm×50cm. The resin used is epoxy resin EPOLAM 2027 with a viscosity of 250 mPa·s; The flow guide net 7 is made of nylon mesh with a pore size of 1.5mm; Inner sealed bag 8, made of polyamide, with a thickness of 0.1mm; The outer sealed bag 9 is made of polyamide and is 0.15mm thick.

[0042] Step 2, Composite Preparation Clean tooling 10 and apply release agent to the side of it that contacts precast part 5. The preform 5 is laid on the surface of the tooling 10, and the release cloth 6 and the flow guide net 7 are sequentially covered on the surface of the preform 5. The size of the flow guide net 7 is smaller than that of the preform 5 to form a circumferential uncovered edge area λ with a width of 2.0cm-3.0cm, thus obtaining the composite.

[0043] Step 3: Double-layer sealing bag sealing The composite is wrapped with sealant and inner sealing bag 8. The inner sealing bag 8 is connected to resin tank 1 through conduit 2 to form a glue injection port. The conduit 2 is connected to liquid collector 11 to form a glue outlet. At the same time, the resin is guided by the winding tube 3, so that the point glue injection becomes line glue injection, forming an inner bag encapsulation body. A 5cm wide breathable felt strip 4 is laid around the outer periphery of the inner bag sealant, and then wrapped with sealant and an outer sealing bag 9. An air vent is reserved in the outer sealing bag 9 to form a double-layer bag sealant.

[0044] Step 4: Thickness compaction To test the airtightness of the inner sealing bag 8 and the outer sealing bag 9, close valves 1 and 3, and turn on vacuum pump 12 and valves 2, 4 and 5. When both the inner sealing bag 8 and the outer sealing bag 9 reach the maximum vacuum level of -0.1MPa, close valves 2 and 5 and wait for 30 minutes. If the vacuum level of the inner sealing bag 8 and the outer sealing bag 9 does not decrease, it proves that the airtightness is good. Reopen valves 2 and 5, continue evacuating, and measure and record the thickness of precast component 5 every 2 minutes. The results of the thickness change of precast component 5 over time are as follows: Figure 4 As shown, compaction is determined to be stable when the thickness variation of the preform 5 is ≤0.001mm, and the compacted preform 5 is obtained with a final thickness of 2.463±0.001mm.

[0045] Step 5: Determination of net injection pressure range Close valve 5 and gradually increase the air pressure in the glue injection tube. Before the air pressure increases to -0.07MPa, the thickness of the preform 5 will not rebound. Therefore, the minimum net glue injection pressure critical value Δ is 0.07MPa. Set the net glue injection pressure range as 0.07MPa-0.1MPa. Subsequently, the net glue injection pressure can be selected between 0.07MPa-0.1MPa according to the actual situation. Considering that the structure of the preform 5 is simple in this embodiment, the net glue injection pressure can be appropriately increased. Finally, the net glue injection pressure is selected as 0.08MPa.

[0046] Step 6: Adhesive application and curing The air pressure values ​​of both the dispensing hose and the air outlet are fixed at -0.1MPa; Open valve 5, close valve 2, adjust the air pressure of the glue injection hose to -0.02MPa, open valves 1 and 3, connect vacuum pump 12 to resin tank 1, then the net glue injection pressure is 0.08MPa, start glue injection; After the resin flows out of the dispensing tube 2, observe the air bubbles in the resin inside the dispensing tube 2. If no air bubbles are discharged for 10 minutes, close valves 1, 4, and 5 and vacuum pump 12 to complete the dispensing process and obtain the resin-impregnated body. A stepped curing process was adopted, in which the resin impregnated body was kept at 80℃ for 2 hours, and then the temperature was raised to 120℃ and kept for 4 hours to obtain a composite material product with uniform thickness.

[0047] Step 7: Thickness Inspection The thickness of the above composite material product was measured using a 16-point (4×4 grid) measurement method. The test results are as follows: Figure 5As shown in the figure, the thickness at the intersection of the dashed lines is in mm. It can be seen that the average thickness of the composite material product is 2.534 mm, and the CV value (coefficient of variation) is 1.39%, indicating that its thickness uniformity is good.

[0048] Example 2 Compared with Example 1, after obtaining the double-layer bag packaging body, a 5cm wide breathable felt strip is laid again, and it is wrapped with sealant and a third layer of sealing bag. The third layer of sealing bag has a new air outlet. When vacuuming, the third layer of sealing bag is controlled simultaneously, and the air pressure value is maintained at -0.1MPa. The remaining steps are the same as in Example 1.

[0049] Thickness testing revealed that the composite material product had a thickness of 2.532 mm and a CV value of 1.31%, indicating good thickness uniformity.

[0050] In summary, this application determines the minimum net injection pressure range within which the preform thickness does not rebound through actual measurement. Depending on the complexity of the preform structure, an appropriate net injection pressure can be selected within this range to avoid large local permeability differences in the preform when the net injection pressure is too high, and to ensure complete wetting of low-permeability areas. This avoids the formation of rapid channels in the resin during injection due to excessive differences in resin wetting rates in different areas of the preform, which could lead to defects such as pores and resin deficiency in the composite material. It also avoids the problem of excessively slow preform wetting rates, which would impose excessively high requirements on the resin process window time. This application employs a multi-layer sealed bag injection process, laying a breathable layer between the inner and outer sealed bags. The discontinuous interface formed between the inner and outer sealed bags in the thickness direction disperses the injection pressure. During the adhesive bonding process, the upward pressure in the low-permeability areas of the preform diffuses the local rebound force laterally, thereby reducing the thickness rebound of the preform in the low-permeability areas and maintaining the uniformity of the overall thickness of the preform. This improves the consistency of the thickness deviation and fiber volume fraction of the composite material product. After testing, the coefficient of variation (CV) of the thickness of the cured composite material product is ≤1.5%, indicating good thickness uniformity. This application uses a vacuum pump to actively regulate the pressure and control the net injection pressure to a constant value. It does not rely on atmospheric pressure to drive the resin flow and can offset atmospheric pressure interference. This avoids the problem of large deviations in thickness and fiber volume fraction of products from different origins and batches caused by external factors such as production site, season, and altitude in the traditional VARI process. This ensures the stability of product quality and significantly reduces the defect rate.

[0051] The above description is merely an optional embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made based on the inventive concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for improving the thickness uniformity of composite materials based on the VARI process, characterized in that, Includes the following steps: The prefabricated component is laid on the surface of the tooling, and a release cloth and a flow guide net are sequentially covered on the surface of the prefabricated component to form a composite; The composite is wrapped in an inner sealing bag and connected to a glue injection tube and a glue outlet tube to form an inner bag encapsulation body; then, after laying a breathable layer on the outer periphery of the inner bag encapsulation body, it is wrapped in an outer sealing bag to form a double-bag encapsulation body, wherein the outer sealing bag is provided with an air outlet. Vacuum the double-layer bag packaging body until the preform is compacted and the thickness is stable to obtain the compacted preform. Determine the range of net injection pressure required to prevent the thickness of the compacted precast component from rebounding; Based on the net injection pressure range, the net injection pressure is adjusted and the resin is injected into the compacted preform until no air bubbles are discharged from the resin flowing out of the injection pipe, thus obtaining a resin impregnated body. After curing the resin impregnated body, a composite material product with uniform thickness is obtained.

2. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 1, characterized in that, In the step of laying the preform on the tooling surface and sequentially covering the surface of the preform with a release cloth and a flow guide net, the size of the flow guide net is smaller than the preform to form a circumferentially uncovered edge area, and the width of the circumferentially uncovered edge area is 2.0cm-3.0cm.

3. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 1, characterized in that, The breathable layer is a breathable felt strip, and the width of the breathable felt strip is 4.8cm-5.2cm.

4. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 3, characterized in that, After the step of laying a breathable layer around the outer periphery of the inner bag packaging body and then wrapping it with an outer sealing bag to form a double-layer bag packaging body, the method further includes: After the breathable layer is laid around the double-layer bag packaging body, at least one additional extended sealing bag is added for wrapping, and the breathable layer is laid between each two adjacent extended sealing bags to form a multi-layer bag packaging body.

5. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 1, characterized in that, The step of evacuating the double-layer bag-encapsulated body until the preform is compacted and its thickness is stable, to obtain the compacted preform, includes: The double-layer bag packaging body is evacuated to a maximum vacuum of -0.1 MPa. If no decrease in vacuum occurs within 25-30 minutes, evacuation continues. The thickness of the preform is measured every 1-3 minutes until the thickness change of the preform is ≤0.001 mm. When the compaction is stable, the compacted preform is obtained.

6. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 1, characterized in that, The step of determining the net injection pressure range within which the thickness of the compacted precast component does not rebound includes: The minimum net injection pressure critical value Δ for the compacted precast component thickness to not rebound was determined, and Δ to 0.1 MPa was set as the net injection pressure range.

7. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 6, characterized in that, The step of determining the minimum net injection pressure critical value Δ for preventing the compacted precast component thickness from rebounding includes: The glue injection tube, the glue outlet tube, and the air outlet are all connected to a vacuum pump. The vacuum pump connected to the glue outlet tube and the air outlet is turned off, and the air pressure of the glue injection tube is gradually increased. When the thickness of the compacted preform increases by ≥0.003mm, the previous pressure value is recorded as the minimum net glue injection pressure critical value Δ.

8. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 7, characterized in that, The step of adjusting the net injection pressure and injecting resin into the compacted preform until no air bubbles are discharged from the resin outlet pipe to obtain the resin-impregnated body includes: The air pressure value of the dispensing tube and the air pressure value of the air outlet are both fixed at -0.1MPa; The pressure adjustment range of the dispensing tube is set to -(0.1MPa-Δ) to 0MPa; Resin is injected into the compacted preform until no air bubbles are discharged from the resin flowing out of the glue outlet for 5-10 minutes, thus obtaining a resin-impregnated body.

9. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 1, characterized in that, In the step of curing the resin impregnated body, a stepped curing process is adopted, in which the resin impregnated body is kept at 75℃-85℃ for 1.5h-2.5h, and then the temperature is raised to 115℃-125℃ and kept at that temperature for 3.5h-4.5h.

10. The method for improving the thickness uniformity of composite materials based on the VARI process according to claim 1, characterized in that, The preform is a carbon fiber plain weave fabric laminate, and the total number of layers in the preform is 6-10.

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