Pressure equalizing plate for improving flatness of composite material and forming method

Abstract

According to the pressure equalizing plate for improving the flatness of the composite material and the forming method, the pressure equalizing plate introduces a gradient compaction process to solve the process problem that a composite material laying layer is prone to wrinkling before curing, and the flatness of the composite material is remarkably improved. When the prepreg is paved, firstly, metal pressing blocks are arranged on the edge of each layer, and certain pre-tensioning force is applied to the material layer by utilizing the self weight of the metal pressing blocks, so that the paved layer is in an initial straight state. Then, the pressure equalizing plate designed by the invention is placed above the whole paving layer, and the pressure equalizing plate can apply non-uniform load distribution with a high central area and a low edge area to the surface of the composite material, so that a pushing effect from the center to the two sides is formed; the high pressure in the central area can drive residual tiny wrinkles or accumulated air to the edge areas of the two sides with the low pressure. The flatness and stability of the composite material can be remarkably improved, and the method is particularly suitable for high-performance composite material forming in the fields of aerospace, precision equipment and the like.

Description

Technical Field

[0001] This invention relates to the field of composite material molding technology, and in particular to a pressure equalizing plate and molding method for improving the flatness of composite materials. Background Technology

[0002] Due to the unique softness of the fiber-resin mixture in composite prepregs, each prepreg layer, due to its own weight, cannot achieve perfect straightness during the laying process, resulting in wrinkles between layers. Figure 1 As shown, curing significantly reduces the mechanical properties of composite structures, thus affecting the overall structural safety. This is a thorny issue in the field of composite manufacturing. Currently, it is impossible to control the size and probability of wrinkles within an ideal range. The only solution is to theoretically reduce the performance based on the dispersion of a large amount of manufacturing data, thereby greatly reducing the structural efficiency of composites and failing to achieve their lightweight advantages.

[0003] Currently, the method for controlling wrinkles during composite material laying involves vacuum-packing the composite with a maximum of four prepreg layers on a molding fixture. Atmospheric pressure is used to compact and shape the composite, eliminating the possibility of wrinkles. After all layers are laid, vacuum-packing is repeated, and the composite, along with the vacuum bags, is placed in an autoclave for curing. This method cannot effectively control the randomness of wrinkle occurrence, and the pressure distribution on the equalizing plate under the vacuum bag pressure is uneven and uncontrollable, failing to effectively control its compaction effect on the composite layers. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the present invention provides a pressure equalizing plate for improving the flatness of composite materials, comprising a frame and multiple pressure blocks. The frame is evenly divided into multiple rectangular grids arranged in the left-right direction, and each grid is equipped with a pressure block. When in use, the pressure equalizing plate is placed on the surface of the prepreg layer. By applying a load to the upper surface of the pressure block, the pressure is transmitted to the prepreg layer to achieve flattening. The load applied to each pressure block gradually decreases from the center of the pressure equalizing plate to the left and right edges.

[0005] Optionally, the load applied by each pressure block from the center of the equalizing plate to the left and right edges follows the following distribution formula:

[0006]

[0007] x represents the position number of the pressure block. The position number of each pressure block is defined using a coordinate system with the center of the pressure equalizing plate as the origin: the pressure block located at the center of the pressure equalizing plate corresponds to the position number x=0; from the center to the left, the numbers are x=-1, -2, -3, ..., and from the center to the right, the numbers are x=1, 2, 3, ...; P is the load applied by the pressure block located at the center of the pressure equalizing plate, and L is the total number of pressure blocks.

[0008] Alternatively, the total load for sealing and compacting the prepreg layer using only a vacuum bag is ΔP. .

[0009] Optionally, the load applied to the upper surface of the block is applied by weights or hydraulic pressure.

[0010] Optionally, the prepreg layer is multi-layered and laid on the surface of the molding tooling, and metal blocks are pressed on the left and right edges of each prepreg layer to make the prepreg layer taut.

[0011] Optionally, the metal block is clamped and fixed to the forming fixture by a C-clamp.

[0012] The present invention also provides a molding method for improving the flatness of composite materials, comprising the following steps:

[0013] S1. Lay the first layer of prepreg on the molding fixture. When laying the prepreg, try to make the prepreg layer as taut as possible. Use metal blocks to press down the left and right edges of the prepreg layer to achieve the maximum tension. Use C-clamps to clamp and fix the metal blocks to the molding fixture.

[0014] S2. Lay the subsequent prepreg layers one by one, and tension each prepreg layer with metal blocks in the same way as in step S1.

[0015] S3. After the prepreg layer is laid, the equalizing plate is placed on the surface of the top prepreg layer. The equalizing plate includes a frame and multiple pressure blocks. The frame is divided into multiple rectangular grids arranged in the left and right directions. Each grid is equipped with a pressure block. When in use, the equalizing plate is placed on the surface of the prepreg layer. By applying a load to the upper surface of the pressure blocks, the pressure is transferred to the prepreg layer to achieve flattening. The load applied to each pressure block gradually decreases from the center of the equalizing plate to the left and right edges.

[0016] Optionally, the load applied by each pressure block from the center of the equalizing plate to the left and right edges follows the following distribution formula:

[0017]

[0018] x represents the position number of the pressure block. The position number of each pressure block is defined using a coordinate system with the center of the pressure equalizing plate as the origin: the pressure block located at the center of the pressure equalizing plate corresponds to the position number x=0; from the center to the left, the numbers are x=-1, -2, -3, ..., and from the center to the right, the numbers are x=1, 2, 3, ...; P is the load applied by the pressure block located at the center of the pressure equalizing plate, and L is the total number of pressure blocks.

[0019] Alternatively, the total load for sealing and compacting the prepreg layer using only a vacuum bag is ΔP. .

[0020] Optionally, the process also includes step S4, which involves placing the molding fixture, along with the metal block and the equalizing plate, into an autoclave to cure the prepreg layer.

[0021] As described above, this invention provides a pressure equalization plate and molding method for improving the flatness of composite materials. This pressure equalization plate addresses the process challenge of wrinkles easily forming in composite material layups before curing by introducing a gradient compaction process, significantly improving the flatness of the composite material. During prepreg laying, metal pressure blocks are first placed at the edges of each layer, using their own weight to apply a certain pre-tension force to the material layer, thereby eliminating layup slack in the initial stage and suppressing wrinkle formation from the source, resulting in a preliminary flat state for the layup. Subsequently, the pressure equalization plate designed in this invention is placed on top of the overall layup. This pressure equalization plate can apply a non-uniform load distribution to the surface of the composite material, with a high load in the central region and a low load in the edge region, thus creating a pushing effect from the center to both sides. The higher pressure in the central region gradually drives residual micro-wrinkles or internally accumulated air to the lower pressure edge regions on both sides. The application of the pressure equalization plate and molding method in this invention can significantly improve the flatness and stability of composite materials, and is particularly suitable for high-performance composite material molding in aerospace, precision equipment, and other fields. Attached Figure Description

[0022] Figure 1 This diagram illustrates wrinkles that appear in composite materials in the prior art.

[0023] Figure 2 The diagram shows the placement of the equalizing plate in this invention.

[0024] Figure 3 This diagram illustrates the load application on the equalizing plate in this invention.

[0025] Component designation explanation

[0026] 10 equalizing plate, 11 forming tool, 12 prepreg layer, 13 metal block, 101 frame, 102 pressing block. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0029] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for the device in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or there may be one or more layers in between. The phrase “between” as used herein includes both endpoint values.

[0030] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0031] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0032] like Figures 1 to 3 As shown, the present invention provides a pressure equalizing plate 10 for improving the flatness of composite materials, including a frame 101 and a plurality of pressure blocks 102. The frame 101 is evenly divided into a plurality of rectangular grids arranged in the left and right directions. Each grid is equipped with a pressure block 102. When in use, the pressure equalizing plate is placed on the surface of the prepreg layer 12. By applying a load to the upper surface of the pressure block 102, the pressure is transmitted to the prepreg layer to achieve flattening. The load applied to each pressure block 102 gradually decreases from the center of the pressure equalizing plate to the left and right edges.

[0033] From the center of the equalizing plate outwards to the left and right edges, the loads applied by each pressure block follow the following distribution formula:

[0034]

[0035] x represents the position number of the pressure block. The position number of each pressure block is defined using a coordinate system with the center of the pressure equalizing plate as the origin: the pressure block located at the center of the pressure equalizing plate corresponds to position number x=0; from the center to the left, the numbers are x=-1, -2, -3, ...; from the center to the right, the numbers are x=1, 2, 3, ... . P is the load applied by the pressure block located at the center of the pressure equalizing plate, and L is the total number of pressure blocks. For ease of understanding, the width of each pressure block can be considered as a unit length of 1, then L is the sum of the widths of all pressure blocks, which is the total number of pressure blocks.

[0036] Here, taking the center of the equalizing plate as a reference, the pressure load on the symmetrical grids on both sides is parabolically distributed. The load is large at the center, resulting in greater deformation of the equalizing plate caused by the pressing blocks, and thus greater pressure on the prepreg layer. Conversely, the load is small at the left and right edges, resulting in smaller deformation of the equalizing plate caused by the pressing blocks, and thus less pressure on the prepreg layer. Figure 3 As shown, the load applied to the prepreg layer by the equalizing plate exhibits a distribution that is high in the center and low at the edges. Due to the flexibility of the material, wrinkles can be effectively pushed outward from the center, resulting in a straight layup. At the same time, this distribution also helps the resin to flow evenly from the high-pressure zone in the center to the low-pressure zones on both sides, and pushes air bubbles to the edges for discharge, further improving the smoothness.

[0037] Since this application uses a pressure equalizing plate instead of a vacuum bag for sealing and compaction, it is necessary to ensure that the total load applied by the pressure equalizing plate to the prepreg layer is consistent with the total load applied by using only a vacuum bag for sealing and compacting the prepreg layer.

[0038] That is, ΔP = The solution is obtained .

[0039] Wherein, ΔP is the total load of sealing and compacting the prepreg layer using a vacuum bag.

[0040] Furthermore, the load applied to the upper surface of the pressure block 102 is applied by weights or hydraulic loading. Weight loading is a static gravity loading method, which involves directly placing standardized weights on the upper surface of the pressure block and using their gravity to provide continuous and stable pressure. It has the advantages of being simple, reliable, and inexpensive. Hydraulic loading, on the other hand, applies force to the upper surface of the pressure block through a small hydraulic cylinder. The hydraulic system consists of a pump station, control valves, and pipelines, and can precisely control the pressure, loading rate, and holding time according to a preset program. It is suitable for composite material components with complex molding processes or strict requirements on the pressure curve.

[0041] Furthermore, the prepreg layer 12 is multi-layered and laid on the surface of the molding fixture 11. Each prepreg layer 12 has a metal block 13 pressed on its left and right edges to keep the prepreg layer 12 taut. The metal block 13 can be clamped and fixed to the molding fixture 11 with a C-clamp. The weight of the metal block applies a certain lateral tension to the prepreg layer along the edge, making it flat and firm on the surface of the fixture, avoiding wrinkles caused by looseness.

[0042] The prepreg layer mentioned in this invention is the core semi-finished material constituting the composite material, generally referring to fiber fabric that has been pre-impregnated with a resin system (such as epoxy resin) and has reached a certain curing stage. Before compaction, the prepreg layer is in a soft, uncured or partially gelled state, possessing both the strength of fibers and the viscosity of resin. Its interlayer adhesion allows it to be laid layer by layer, but external pressure is still needed to expel air between layers and within the fibers, compact the fiber structure, and ensure uniform resin distribution. After layup, the prepreg layer, due to its softness and viscosity, is prone to loosening and wrinkling, and local bulges may also occur between layers due to inaccurate placement. If these defects are not initially constrained before compaction, they will form problems such as pores or uneven thickness after curing, seriously affecting the mechanical properties and surface quality of the component. Therefore, before applying the equalizing plate, metal blocks need to be regularly placed at the edges of the layers to apply lateral tension and local pressure to the edges of the material layer, allowing it to be initially flattened and positioned on the tooling surface, providing a stable and flat initial state for the subsequent main compaction process.

[0043] The metal blocks 13 are typically made of high-density, non-deformable steel, and are mostly rectangular in shape. Their weight and spacing are determined based on the characteristics of the prepreg and process requirements. The compaction of the metal blocks 13 is part of the pre-compaction stage, which is connected with the subsequent main compaction using the equalizing plate 10, together ensuring that the composite material obtains a uniform and dense structural morphology before curing.

[0044] Based on the above-described pressure equalization plate structure, the present invention also provides a molding method for improving the flatness of composite materials, comprising the following steps:

[0045] S1. Lay the first layer of prepreg 12 on the molding fixture 11. When laying, try to make the prepreg layer taut. Use metal blocks 13 to press the left and right edges of the prepreg layer to achieve maximum tension. Use C-clamps to clamp and fix the metal blocks 13 to the molding fixture.

[0046] S2. Lay the subsequent prepreg layers 12 one by one, and tension each prepreg layer 12 by the metal block 13 in the same way as in step S1.

[0047] It should be noted that to ensure the prepreg maintains its processing properties during storage, transportation, and laying, it is usually equipped with a double-sided protective film (also known as release film or release paper). During laying, first peel off the lower film, lay the prepreg sheet flat, and slowly and steadily peel off the lower protective film completely, exposing the adhesive resin side. This side will directly contact the already laid layer or mold surface below. Then, use a scraper or roller to gently roll from the center outwards to remove air and ensure complete adhesion, avoiding wrinkles or bridging. Next, peel off the upper film. After the prepreg is laid flat and its position is confirmed, slowly peel off the upper protective film. Repeat this "peel off film—lay out—peel off film" sequence layer by layer until the required number of layers is reached.

[0048] S3. After the prepreg layer 12 is laid, the frame 101 of the pressure equalizing plate 10 is placed on the surface of the uppermost prepreg layer 12. Pressure blocks 102 are arranged in each grid of the frame 101. Then, a load is applied to the upper surface of the pressure blocks 102 to transfer the pressure to the prepreg layer to achieve flattening. The load applied to each pressure block gradually decreases from the center of the pressure equalizing plate to the left and right edges.

[0049] From the center of the equalizing plate outwards to the left and right edges, the loads applied by each pressure block follow the following distribution formula:

[0050]

[0051] 'x' represents the position number of the pressure block. The position number of each pressure block is defined using a coordinate system with the center of the pressure equalizing plate as the origin: the pressure block located at the center of the pressure equalizing plate corresponds to position number x=0; from the center to the left, the numbers are x=-1, -2, -3, ...; from the center to the right, the numbers are x=1, 2, 3, ... . P is the load applied by the pressure block located at the center of the pressure equalizing plate, and L is the total number of pressure blocks. Here, taking the center of the pressure equalizing plate as the reference, the pressure load on the symmetrical grid on both sides is parabolically distributed. The load is large at the center, the deformation caused by the pressure block pressing down on the pressure equalizing plate is large, and the pressure applied to the prepreg layer is large; the load is small at the left and right edges, the deformation caused by the pressure block pressing down on the pressure equalizing plate is small, and the pressure applied to the prepreg layer is small. Figure 3 As shown, the load applied to the prepreg layer by the equalizing plate exhibits a distribution that is high in the center and low at the edges. Due to the flexibility of the material, wrinkles can be effectively pushed outward from the center, resulting in a straight layup. At the same time, this distribution also helps the resin to flow evenly from the high-pressure zone in the center to the low-pressure zones on both sides, and pushes air bubbles to the edges for discharge, further improving the smoothness.

[0052] Since this application uses a pressure equalizing plate instead of a vacuum bag for sealing and compaction, it is necessary to ensure that the total load applied by the pressure equalizing plate to the prepreg layer is consistent with the total load applied by the vacuum bag to the prepreg layer for sealing and compaction.

[0053] That is, ΔP = The solution is obtained

[0054] Wherein, ΔP is the total load of sealing and compacting the prepreg layer using a vacuum bag.

[0055] Finally, in step S4, the molding fixture, along with the metal block and the equalizing plate, is placed into an autoclave to cure the prepreg layer. Since the equalizing plate is used instead of the vacuum bag for sealing and compaction in step S3, this step does not require the vacuum bag sealing and compaction process.

[0056] Furthermore, in steps S1 and S2, when manual laying is used, the prepreg layer needs to be manually flattened, and after laying several layers (usually 2 to 4 layers) in succession, the prepreg layer needs to be compacted and shaped by sealing with a vacuum bag to avoid the formation of wrinkles.

[0057] In summary, this invention provides a pressure equalization plate and molding method for improving the flatness of composite materials. This pressure equalization plate addresses the process challenge of wrinkles easily forming in composite material layups before curing by introducing a gradient compaction process, significantly improving the flatness of the composite material. During the prepreg laying, metal pressure blocks are first placed at the edges of each layer, using their own weight to apply a certain pre-tension force to the material layer, thereby eliminating layup slack in the initial stage and suppressing wrinkle formation from the source, resulting in a preliminary flat state for the layup. Subsequently, the pressure equalization plate designed in this invention is placed on top of the overall layup. This pressure equalization plate can apply a non-uniform load distribution to the surface of the composite material, with a high load in the central region and a low load in the edge region, thus creating a pushing effect from the center to both sides. The higher pressure in the central region gradually drives residual micro-wrinkles or internally accumulated air to the lower pressure edge regions on both sides. The application of the pressure equalization plate and molding method in this invention can significantly improve the flatness and stability of composite materials, and is particularly suitable for high-performance composite material molding in aerospace, precision equipment, and other fields.

[0058] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A pressure equalizing plate for improving flatness of a composite material, characterized by, The frame is divided into multiple rectangular grids arranged along the left-right direction, and each grid is equipped with a pressing block. The self-leveling plate is placed on the surface of the prepreg layer during use, and the load is applied to the upper surface of the pressing block to transfer the pressure to the prepreg layer to flatten it. The load applied to each pressing block gradually decreases from the center of the self-leveling plate to the left and right edges.

2. The pressure equalizing plate for improving flatness of a composite material according to claim 1, characterized by, The load applied to each pressing block from the center of the self-leveling plate to the left and right edges follows the distribution formula: x represents the position number of the pressing block, and the position number of each pressing block is defined using a coordinate system with the center of the self-leveling plate as the origin: the pressing block located at the center of the self-leveling plate corresponds to the position number x=0; from the center to the left, the position numbers are x=-1, -2, -3, …, and from the center to the right, the position numbers are x=1, 2, 3, …; P is the load applied to the pressing block located at the center of the self-leveling plate, and L is the total number of pressing blocks.

3. The pressure equalizing plate for improving flatness of a composite material according to claim 2, characterized by, The total load to pack the compacted pre-preg layers using only vacuum bag is ΔP, .

4. The pressure equalizing plate for improving flatness of a composite material according to claim 1, characterized by: The load applied to the upper surface of the pressing block is loaded by a weight or hydraulic loading.

5. The pressure equalizing plate for improving flatness of a composite material according to claim 1, characterized by: The prepreg layer is multi-layered and laid on the surface of the forming tool, and the left and right edges of each prepreg layer are pressed with metal blocks to tension the prepreg layer.

6. The pressure equalizing plate for improving flatness of a composite material according to claim 5, characterized by: The metal blocks are clamped and fixed to the forming tool by C-clamps.

7. A forming method for improving flatness of a composite material, characterized by, The method comprises the following steps: S1, lay the first layer of prepreg on the forming tool, try to tension the prepreg during laying, and use metal blocks to press the left and right edges of the prepreg to achieve maximum tension. The metal blocks are clamped and fixed to the forming tool by C-clamps; S2, lay the subsequent prepreg layer by layer, and tension each prepreg layer by metal blocks according to the method of step S1; S3, after the prepreg layer is laid, place the self-leveling plate on the surface of the uppermost prepreg layer. The self-leveling plate comprises a frame and multiple pressing blocks. The frame is divided into multiple rectangular grids arranged along the left-right direction, and each grid is equipped with a pressing block. The self-leveling plate is placed on the surface of the prepreg layer during use, and the load is applied to the upper surface of the pressing block to transfer the pressure to the prepreg layer to flatten it. The load applied to each pressing block gradually decreases from the center of the self-leveling plate to the left and right edges.

8. The molding process for improving flatness of a composite material according to claim 7, wherein The load applied to each pressing block from the center of the self-leveling plate to the left and right edges follows the distribution formula: x represents the position number of the pressing block, and the position number of each pressing block is defined using a coordinate system with the center of the self-leveling plate as the origin: the pressing block located at the center of the self-leveling plate corresponds to the position number x=0; from the center to the left, the position numbers are x=-1, -2, -3, …, and from the center to the right, the position numbers are x=1, 2, 3, …; P is the load applied to the pressing block located at the center of the self-leveling plate, and L is the total number of pressing blocks.

9. The molding process for improving flatness of a composite material according to claim 8, wherein, The total load to pack the compacted pre-preg layers using only vacuum bag is ΔP, .

10. The molding process for improving flatness of a composite material according to claim 7, wherein, The method further comprises step S4: placing the forming tool together with the metal blocks and the self-leveling plate into a hot press tank for curing of the prepreg layer.

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