Forming method of foam sandwich structure composite material

Abstract

The invention belongs to the technical field of composite material process manufacturing, and discloses a foam sandwich structure composite material forming method, which is characterized in that a lower skin prepreg, a metal connecting piece, a foam core material and an upper skin prepreg are laid in a mold cavity in sequence, so that accurate positioning and effective coating are realized; a cavity is wrapped in the root area of the blade body by utilizing the excellent in-plane mechanical property of the prepreg, a filling agent is injected through a glue injection port, the filling agent is heated to expand in the heating process, the size is remarkably increased, the irregular shape of the root area of the blade and the edge of a metal connecting piece can be automatically filled, and therefore the blade can be manufactured. And the shape follow-up supplement of the root structure is realized. The expanded microspheres form a uniform closed-cell foam structure, so that the thickness of an interlayer is effectively supported, structural collapse or insufficient local compaction is prevented, local accumulation of resin can be inhibited, the thickness consistency and the structural compactness are improved, the layering process is simplified, and the quality control is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of composite material manufacturing process, in particular to a method for forming a foam sandwich structure composite material. Background Art

[0002] Prepreg lamination is a very common, high-quality, and stable molding method for composite materials. It involves manually or automatically placing a pre-reinforced fiber material (prepreg) pre-filled with resin onto a mold. The prepreg is then vacuum-baked and heat-cured to create a structurally strong composite product. This process is widely used in aerospace, automotive, wind power, sports equipment, and other fields.

[0003] In water treatment equipment, composite blades are gradually replacing traditional metal blades and are being widely adopted due to their advantages such as light weight, high strength, and corrosion resistance. However, water treatment blades typically have large surface curvatures, complex structures, and metal connectors embedded at the blade roots for mechanical connection. This irregular structure complicates the core material structure and limits the layup path. This especially requires local reinforcement and cladding of the metal connector areas, making the laying of prepreg difficult and prone to quality defects such as wrinkles, voids, and resin accumulation. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for forming a foam sandwich structure composite material. When it comes to sandwich composite material structures such as water treatment blades with large curvature surfaces, locally embedded metal connectors, and complex core material structures, the method can simplify the layup process, improve the adaptability of composite material forming, and effectively improve the structural integrity and dimensional consistency of the composite material while ensuring material performance, thereby avoiding quality control problems such as wrinkling, voids, resin enrichment, and insufficient local compaction.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] A method for molding a foam sandwich composite material, wherein a blade includes a blade body and a metal connector embedded in the root of the blade body, the metal connector being used for mechanical connection to an external structure. The method for molding a foam sandwich composite material includes the following steps:

[0007] S1: Laying down the lower skin prepreg, the metal connector, and the foam core material located in the blade body region on the inner surface of the mold cavity in sequence, and laying down the upper skin prepreg on the surface of the foam core material; wherein the metal connector is provided at a predetermined position at the root and is wrapped between the lower skin prepreg and the upper skin prepreg; and simultaneously, reserving a glue injection port between the lower skin prepreg and the upper skin prepreg in the root region of the blade body;

[0008] S2: After the laying is completed, the mold is closed and sealed, and the microsphere foaming agent, foam stabilizer and epoxy resin are fully mixed according to the set ratio, and vacuum degassing is performed to prepare a filler; the filler is injected into the mold through the injection port to achieve conformal filling of the root area of ​​the blade body;

[0009] S3: After the filling is completed, the mold is heated and cured according to a preset temperature rising program to form a continuous and dense sandwich composite structure;

[0010] S4: After the curing is completed, the mold is cooled to room temperature, the cured blade is taken out, and the flash is cleaned.

[0011] Furthermore, a release agent is evenly coated on the inner surface of the mold cavity to facilitate subsequent demoulding operations.

[0012] Furthermore, before laying the lower skin prepreg, a gel coat is evenly sprayed on the inner surface of the mold cavity, and after the gel coat is cured, the lower skin prepreg is laid.

[0013] Furthermore, the metal connecting part includes a connecting bolt and a metal support leg, the connecting bolt and the metal support leg are movably connected, the metal support leg is embedded in the root of the blade body, and the connecting bolt can be threadedly connected to the external structure.

[0014] Furthermore, a reinforcement layer prepreg is laid on the metal leg portion, and the metal leg can be completely covered between the lower skin prepreg and the reinforcement layer prepreg to form a stable connection structure.

[0015] Furthermore, the matrix resins used in the lower skin prepreg, the upper skin prepreg and the reinforcement layer prepreg are all medium-temperature RTM resins.

[0016] Furthermore, the foam core material is interference-fitted with the lower skin prepreg and the upper skin prepreg so as to provide pressure during curing.

[0017] Furthermore, the particle size of the expandable microspheres in the microsphere foaming agent ranges from 20 microns to 25 microns.

[0018] Furthermore, the expansion ratio of the expandable microspheres in the microsphere foaming agent ranges from 4 to 5 times.

[0019] Furthermore, the lower skin prepreg, the upper skin prepreg and the foam core material can be cured and expanded simultaneously.

[0020] Beneficial effects of the present invention:

[0021] The present invention provides a method for forming a composite material with a foam sandwich structure, which is suitable for the field of water treatment by spraying a waterproof gel coat on the inner surface of the mold cavity first, so as to form a waterproof coating on the blade shell. After that, the skin prepreg is laid in sequence, and then the metal connector and the foam core material are placed, and finally the upper skin prepreg is laid. Through structural presetting, the metal connector is embedded between the upper and lower skins to achieve precise positioning and effective coating, and a cavity is wrapped in the root area of ​​the blade body using the excellent in-plane mechanical properties of the prepreg. Secondly, a filler composed of a mixture of a microsphere foaming agent, a foam stabilizer and an epoxy resin is used, and is injected into the mold cavity through a reserved glue injection port. During the heating process, the microspheres of the filler expand due to heat, and the volume increases significantly, which can automatically fill the irregular shape of the root area of ​​the blade and the edge of the metal connector, which are difficult to compact using traditional processes, thereby realizing the form-fitting supplement of the root structure. The expanded microspheres form a uniform closed-cell foam structure, which not only effectively supports the thickness of the interlayer and prevents structural collapse or local insufficient compaction, but also inhibits local accumulation of resin, improves thickness consistency and structural density. This thermal expansion and pressure process can significantly reduce the complexity of the core material design in the root area of ​​the blade body, simplify the layering process, improve the flexibility and stability of the molding process, and ensure the structural integrity and mechanical properties of the root area of ​​the composite material. Next, a preset temperature rise program is used for staged heating and curing to control the reaction rate, improve the control accuracy of the curing process, avoid warping or deformation due to local heat release, and improve the dimensional consistency and geometric accuracy of the product. Finally, after cooling and demolding, the flash is cleaned, and the mold can be directly demolded in one piece after curing is completed, which improves the yield rate, ensures the stability of the finished product quality, and avoids quality control problems such as wrinkling, degassing, resin enrichment, and local insufficient compaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of the blade in the present invention;

[0023] Figure 2 It is a structural schematic diagram of the metal connector in the present invention;

[0024] Figure 3 The present invention is a flow chart of the foam sandwich structure composite material forming method.

[0025] In the picture:

[0026] 1. Propeller blade; 2. Propeller body; 3. Metal connector; 4. Connecting bolt; 5. Metal support leg. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0028] In the description of the present invention, unless otherwise expressly specified or limited, the terms "connected," "connected," and "fixed" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention in specific circumstances.

[0029] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0030] In the description of this embodiment, terms such as "upper," "lower," "left," and "right" are used to refer to positions or locations based on those shown in the accompanying drawings. These terms are intended solely to facilitate description and simplify operation, and are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first" and "second" are used solely for descriptive purposes and have no special meaning.

[0031] Currently, composite blades 1 used in the water treatment field are widely used due to their light weight, high strength and excellent corrosion resistance. However, this type of blade 1 usually has a large surface curvature and a complex three-dimensional structure, and a metal connector 3 for mechanical connection is embedded at the root of the blade, further increasing the irregularity of the structure. The complex geometric shape places high demands on the core material structure design and limits the prepreg laying path. When it is necessary to reinforce or cover the metal connector 3 in a local area, the difficulty of the prepreg laying operation increases significantly, and quality defects such as wrinkles, gaps and resin accumulation are very likely to occur, affecting the quality of the finished product.

[0032] Please refer to Figures 1 to 3As shown, to solve the above problems, this embodiment provides a method for molding a foam sandwich structure composite material, wherein a blade 1 includes a blade body 2 and a metal connector 3 embedded in the root of the blade body 2, and the metal connector 3 is used to mechanically connect to an external structure; the method for molding a foam sandwich structure composite material includes the following steps:

[0033] S1: Lay down the lower skin prepreg, the metal connector 3, and the foam core material located in the blade area of ​​the blade body 2 in sequence on the inner surface of the mold cavity, and lay down the upper skin prepreg on the surface of the foam core material; the metal connector 3 is located at a predetermined position at the root and is wrapped between the lower skin prepreg and the upper skin prepreg; at the same time, a glue injection port is reserved between the lower skin prepreg and the upper skin prepreg in the root area of ​​the blade body 2;

[0034] S2: After the laying is completed, the mold is closed and sealed. The microsphere foaming agent, foam stabilizer and epoxy resin are fully mixed according to the set ratio, and vacuum degassing is performed to prepare a filler. The filler is injected into the mold through the injection port to achieve form-fitting filling of the root area of ​​the blade body 2.

[0035] S3: After filling is completed, the mold is heated and cured according to a preset temperature rise program to form a continuous and dense sandwich composite structure;

[0036] S4: After the curing is completed, the mold is cooled to room temperature, the cured blade 1 is taken out, and the flash is cleaned.

[0037] By laying down the skin prepreg on the inner surface of the mold cavity in sequence, then placing the metal connector 3 and the foam core material, and finally laying the upper skin prepreg, the metal connector 3 is embedded between the upper and lower skins through structural presetting to achieve precise positioning and effective covering, and a cavity is wrapped in the root area of ​​the blade body 2 using the excellent in-plane mechanical properties of the prepreg. Secondly, a filler composed of a mixture of microsphere foaming agent, foam stabilizer and epoxy resin is used and injected into the mold cavity through a reserved injection port. During the heating process of the filler, the microspheres expand due to heat and increase in volume significantly, which can automatically fill the irregular shape of the root area of ​​the blade 1 and the edge of the metal connector 3 and other areas that are difficult to compact using traditional processes, thereby achieving form-fitting supplementation of the root structure. The expanded microspheres form a uniform closed-cell foam structure, which not only effectively supports the thickness of the interlayer and prevents structural collapse or local insufficient compaction, but also inhibits local accumulation of resin, improves thickness consistency and structural density. This thermal expansion and pressure process can significantly reduce the complexity of the core material design in the root area of ​​the blade body 2, simplify the layering process, improve the flexibility and stability of the molding process, and ensure the structural integrity and mechanical properties of the root area of ​​the composite material. Next, a preset temperature rise program is used for staged heating and curing to control the reaction rate, improve the control accuracy of the curing process, avoid warping or deformation due to local heat release, and improve the dimensional consistency and geometric accuracy of the product. Finally, after cooling and demolding, the flash is cleaned, and the mold can be directly demolded in one piece after curing is completed, which improves the yield rate, ensures the stability of the finished product quality, and avoids quality control problems such as wrinkling, voids, resin enrichment, and local insufficient compaction.

[0038] In order to facilitate the demolding of the blade 1, in some optional embodiments, a release agent is evenly coated on the inner surface of the mold cavity, wherein the release agent forms a thin isolation film between the mold and the product, effectively reducing the adhesion between the gel coat and the mold surface, making the demolding process smoother, and avoiding defects such as surface tearing of the blade 1, damage to the gel coat, or edge chipping caused by forced demolding.

[0039] For example, the release agent may be, but is not limited to, a silicone release agent or a solvent release agent, which is not specifically limited herein.

[0040] Optionally, before laying out the lower skin prepreg, a gel coat is evenly sprayed on the inner surface of the mold cavity, and after the gel coat is cured, the lower skin prepreg is laid out; wherein, the setting of the gel coat can be flexibly selected according to different use environments. When the blades are used in more complex working conditions such as sewage treatment, there may be chemical corrosion ranging from weak acid to strong alkali. At this time, a gel coat with chemical corrosion resistance can be selected to enhance the surface density and corrosion resistance of the molded product, thereby improving the service life and stability of the composite blades in harsh environments.

[0041] For example, the gel coat may be, but is not limited to, epoxy gel coat or vinyl ester gel coat, etc., which is not specifically limited here.

[0042] like Figure 2 As shown, specifically, the metal connector 3 includes a connecting bolt 4 and a metal support leg 5, the connecting bolt 4 and the metal support leg 5 are movably connected, the metal support leg 5 is embedded in the root of the blade body 2, and the connecting bolt 4 can be mechanically connected to the external structure; wherein, the metal support leg 5 is embedded in the composite material body as a structural insert, which can realize the effective transmission of load and the enhancement of the connection position; the connecting bolt 4 and the metal support leg 5 are movably connected, and the connecting bolt 4 provides a rigid mechanical connection with the external structure (such as a bushing, a coupling, a transmission part, etc.), so that the blade 1 can flexibly adjust the connection direction during the installation process, which is convenient for alignment with the external structure, improves the installation convenience and connection reliability, ensures that it is not easy to loosen or deflect during long-term operation, and avoids assembly errors or maintenance difficulties caused by the limitations of integrated molding.

[0043] Furthermore, the metal connector 3 also includes a locating pin connected to the metal leg, which is used to pre-position the metal connector 3 and the external structure during installation. After achieving preliminary alignment with the locating pin, the metal connector 3 and the external structure are reliably fixed together using the connecting bolt 4, thereby improving installation accuracy and assembly efficiency.

[0044] In some optional embodiments, a reinforcement layer prepreg is laid on the metal leg 5, and the metal leg 5 can be completely covered between the lower skin prepreg and the reinforcement layer prepreg to form a stable connection structure; wherein, by additionally laying the reinforcement layer prepreg on the surface of the metal leg 5, a sandwich-type covering of the metal leg 5 is achieved (i.e., sandwiched between the lower skin and the reinforcement layer), thereby improving the bonding area and interface strength of the metal and composite material interface, and significantly reducing the risk of structural failure caused by interface peeling, slippage, etc.; and, the reinforcement layer prepreg, as a local reinforcement material, enhances the overall stiffness and shear resistance of the root structure in the force concentrated area at the connection, thereby improving the impact resistance and fatigue resistance of the composite structure during connection, transportation, installation and service.

[0045] Specifically, the matrix resins used in the lower skin prepreg, upper skin prepreg and reinforcement layer prepreg are all medium-temperature RTM resins; among them, medium-temperature RTM (Resin Transfer Molding) resins usually have a curing temperature range of 80°C to 120°C, avoiding the risk of thermal damage to the mold system and foam core material caused by high temperature. At the same time, it is also more conducive to complete reaction than the low-temperature system and is suitable for the composite molding of precision sandwich structures; RTM special resins have the characteristics of low viscosity and good fluidity, and can fully infiltrate the reinforcing fibers in the prepreg during the processes of injection, pressurization, and laying, thereby improving the internal density and interface adhesion of the finished product and enhancing the mechanical properties and integrity of the composite material.

[0046] More specifically, before preparing the lower skin prepreg, the upper skin prepreg and the reinforcement layer prepreg, the matrix resin is prepolymerized at a temperature of 90°C for 3 minutes to increase its initial viscosity; wherein, moderate prepolymerization can convert the matrix resin from a low-viscosity state to a medium initial viscosity, so that the prepared prepreg is easier to maintain its shape, and is not easy to flow, accumulate or slip when laid on complex curved surfaces such as the blade 1 profile or the root insert edge, and can reduce excessive flow of the matrix resin in the initial stage of heating, thereby effectively controlling the resin-rich area or dry point (empty point) problem caused by resin loss, and enhancing the operability and positioning accuracy of the laying process.

[0047] In some embodiments, the foam core material is interference fit with the lower skin prepreg and the upper skin prepreg to provide pressure during curing; wherein, by making the foam core material slightly larger than the wrapping space, a certain compression stress is generated during assembly, so that the lower skin prepreg and the upper skin prepreg are tightly fitted with the foam core material. During the hot pressing or curing process, the foam core material in the interference state will continue to exert a reaction force on the upper and lower layers, and a good interface can be formed without additional pressure, effectively preventing delamination, bubbling or voids between the interlayers due to thermal expansion and contraction or resin flow, thereby improving the density of the interlayer and enhancing the structural bonding strength and integrity.

[0048] Optionally, the foam core material can be, but is not limited to, PMI foam (PolyMethacrylimide Foam). PMI foam has low density, high compressive and shear strength and modulus, and can significantly reduce the overall weight while ensuring structural strength. The specific type of foam used is not specifically limited here.

[0049] Specifically, the particle size of the expandable microspheres in the microsphere foaming agent ranges from 20 microns to 25 microns. Among them, expandable microspheres with smaller particle sizes are selected because they have good dispersibility and fluidity. The smaller the microspheres, the easier it is to evenly distribute in the epoxy matrix, avoiding local agglomeration and ensuring the uniformity of the composite system. In addition, since the small-diameter microspheres have a large specific surface area at the interface with the resin, the interface can be more tightly bonded, which is beneficial to enhancing the bonding force of the microscopic interface and improving the strength and stability of the final composite material.

[0050] Optionally, the foaming rate of the microsphere foaming agent is in the range of 4 to 5 times, wherein after the microspheres expand, a closed-cell structure is formed, which can significantly reduce the density of the material and effectively reduce the overall weight of the blade 1; and, the foaming rate of 4 to 5 times is relatively mild, and a moderate foaming rate can reduce the internal stress caused by resin shrinkage, improve the dimensional stability of the product, and avoid warping or cracking.

[0051] Optionally, the lower skin prepreg, upper skin prepreg and microsphere foaming agent can be cured and expanded at the same time, wherein synchronous curing can effectively ensure that the lower skin prepreg, upper skin prepreg and foam core structure reach a cured and bonded state at the same time, avoiding interface dislocation, delamination or poor bonding due to inconsistent molding rhythms, and significantly improving the integrity and shear strength of the overall sandwich structure. Synchronous expansion can dynamically adapt to the complex structure inside the mold and the dead corners around the metal connector 3, improve the filling density of irregular areas, and avoid internal voids or local insufficient compaction. Simultaneous expansion and curing can eliminate the need for step-by-step heating or secondary molding processes, improve overall production efficiency, reduce energy consumption and mold occupancy time, and is more suitable for mass production.

[0052] It is understandable that a foam sandwich structure composite material molding method is not only applicable to the molding of blades, but also applicable to the molding of any foam sandwich composite material with complex structure and difficult prepreg laying operation, and is not specifically limited here.

[0053] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. A person skilled in the art would be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for forming a foam sandwich structure composite material, wherein a blade (1) comprises a blade body (2) and a metal connector (3) embedded in the root of the blade body (2), wherein the metal connector (3) is used for mechanical connection with an external structure, and is characterized in that: The foam sandwich structure composite material forming method comprises the following steps: S1: laying down the lower skin prepreg, the metal connector (3) and the foam core material located in the blade area of ​​the blade body (2) in sequence on the inner surface of the mold cavity, and laying down the upper skin prepreg on the surface of the foam core material; wherein the metal connector (3) is located at a predetermined position at the root and is coated between the lower skin prepreg and the upper skin prepreg; and at the same time, a glue injection port is reserved between the lower skin prepreg and the upper skin prepreg in the root area of ​​the blade body (2); S2: After the laying is completed, the mold is closed and sealed, the microsphere foaming agent, the foam stabilizer and the epoxy resin are fully mixed according to the set ratio, and the filler is prepared after vacuum degassing; the filler is injected into the mold through the injection port to achieve the shape-conforming filling of the root area of ​​the blade body (2); S3: After the filling is completed, the mold is heated and cured according to a preset temperature rising program to form a continuous and dense sandwich composite structure; S4: After the solidification is completed, the mold is cooled to room temperature, the solidified blade (1) is taken out, and the burrs are cleaned.

2. The method for forming a foam sandwich structure composite material according to claim 1, wherein: A release agent is evenly coated on the inner surface of the mold cavity to facilitate subsequent demoulding operations.

3. The method for forming a foam sandwich structure composite material according to claim 2, wherein: Before laying the lower skin prepreg, a gel coat is evenly sprayed on the inner surface of the mold cavity, and after the gel coat is cured, the lower skin prepreg is laid.

4. The method for forming a foam sandwich structure composite material according to claim 1, wherein: The metal connecting member (3) comprises a connecting bolt (4) and a metal leg (5), wherein the connecting bolt (4) and the metal leg (5) are movably connected, the metal leg (5) is embedded in the root of the blade body (2), and the connecting bolt (4) can be threadedly connected to the external structure.

5. The method for forming a foam sandwich structure composite material according to claim 4, characterized in that: A reinforcement layer prepreg is laid on the metal leg (5), and the metal leg (5) can be completely covered between the lower skin prepreg and the reinforcement layer prepreg to form a stable connection structure.

6. The method for forming a foam sandwich structure composite material according to claim 5, characterized in that: The matrix resins used in the lower skin prepreg, the upper skin prepreg and the reinforcement layer prepreg are all medium-temperature RTM resins.

7. The method for forming a foam sandwich structure composite material according to claim 1, wherein: The foam core material is interference-fitted with the lower skin prepreg and the upper skin prepreg so as to provide pressure during curing.

8. The method for forming a foam sandwich structure composite material according to claim 7, characterized in that: The particle size of the expandable microspheres in the microsphere foaming agent ranges from 20 microns to 25 microns.

9. The method for forming a foam sandwich structure composite material according to claim 8, characterized in that: The expansion ratio of the expandable microspheres in the microsphere foaming agent ranges from 4 to 5 times.

10. The method for forming a foam sandwich structure composite material according to claim 9, characterized in that: The lower skin prepreg, the upper skin prepreg and the foam core material can be cured and expanded simultaneously.

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