Gradient thickness shim for curing molding of composite products and production process

Abstract

The present application relates to a kind of gradient thickness gaskets for the curing forming of composite products and production process, gradient thickness gasket includes multiple layers of semi-flexible gasket layers from top to bottom, fixedly connected between adjacent semi-flexible gasket layers, the width of each semi-flexible gasket layer is greater than or equal to 20mm, and the thickness is 0.1mm~0.3mm, the width of adjacent two semi-flexible gasket layers is different, and the single-side width difference of both at two side edges is greater than or equal to 20mm;The gradient thickness gasket is used to place between cover plate and composite product, and is located at the joint seam between adjacent cover plate, and the width of the semi-flexible gasket layer with minimum width in gradient thickness gasket is greater than the width of joint seam.Gradient thickness gasket can effectively solve the problem that indentation is generated at the joint seam between cover plate of composite product, and ensure the forming quality of surface.

Description

Technical Field

[0001] This invention relates to the field of composite material structure molding technology, specifically to a gradient thickness gasket and manufacturing process for curing composite material products. Background Technology

[0002] The fuselage of civil aircraft can be manufactured using a monolithic segment curing process. During the curing of the segmented fuselage, a pressure-equalizing cover plate (hereinafter referred to as the cover plate) is required to cover the surface skin to ensure the molding quality of the skin's aerodynamic surface. The skin is a composite material product. To ensure production operability, the curing of the segmented fuselage requires the use of segmented cover plates to cover the skin. See Appendix. Figure 1 As shown, the joint between the two cover plates requires special design treatment; otherwise, obvious indentations will appear on the skin at the edge of the cover plate, leading to product quality defects. To address the issue of indentations at the cover plate joint, new technologies need to be developed to solve this engineering challenge.

[0003] Chinese patent application CN2018108162110 discloses a method for preparing a composite material irregular skin structure, mentioning a "composite process thin layer" solution. This solution involves pouring resin onto non-woven fabric and curing under pressure, forming a "thin layer with both composite and non-composite areas." The "composite area" of this thin layer corresponds to the junction with the cover plate, and the "composite area has a structural boundary with a resin content gradient in the in-plane direction." The process thin layer mentioned in this patent is made by hand lay-up of liquid resin, which makes it difficult to guarantee the uniformity of the thin layer's thickness and width. Thin layers made from non-woven fabric lack structural strength and are easily crushed during curing. Furthermore, the joint dimensions between cover plates used in the curing of civil aircraft fuselages are generally several meters, making it difficult to produce thin layers of such size using hand lay-up methods. Therefore, the problem of indentations at the joints between large-sized cover plates during the curing of composite products is an urgent issue that needs to be addressed. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the technical problem to be solved by the present invention is to provide a gradient thickness gasket and production process for curing composite material products, which can effectively solve the problem of indentation at the splice seam between cover plates of composite material products.

[0005] To achieve the above object, the present application provides a gradient thickness gasket for curing and forming of a composite product, comprising a plurality of semi-flexible gasket layers from top to bottom, and adjacent semi-flexible gasket layers are fixedly connected, the width of each semi-flexible gasket layer is greater than or equal to 20 mm, and the thickness of each semi-flexible gasket layer is 0.1-0.3 mm, the width of adjacent two semi-flexible gasket layers is different, and the single-side width difference of the two at both sides is greater than or equal to 20 mm; the gradient thickness gasket is used to be placed between a cover plate and the composite product, and is located at a joint seam between adjacent cover plates, and the width of the semi-flexible gasket layer with the smallest width in the gradient thickness gasket is greater than the width of the joint seam.

[0006] Further, the center planes of all semi-flexible gasket layers in the width direction overlap.

[0007] Further, the semi-flexible gasket layers are three layers, the widths of the semi-flexible gasket layers from top to bottom decrease in turn, or the widths of the semi-flexible gasket layers from top to bottom increase in turn, or the widths of the uppermost and lowermost two semi-flexible gasket layers are both greater than the width of the semi-flexible gasket layer between them, or the widths of the uppermost and lowermost two semi-flexible gasket layers are both less than the width of the semi-flexible gasket layer between them.

[0008] Further, the material of the semi-flexible gasket layer is carbon fiber composite material, glass fiber composite material or high polymer fiber reinforced composite material.

[0009] Further, the difference between the linear expansion rate of the semi-flexible gasket layer and the linear expansion rate of the composite product is within ±1×10-5 mm / m·℃.

[0010] The present application also provides a production process for curing and forming of a composite product, using the above gradient thickness gasket, comprising the following steps:

[0011] S1, placing a composite product to be cured and formed on a forming mold;

[0012] S2, determining the placement position of a cover plate on the surface of the composite product, and determining the gasket placement area corresponding to the joint seam between adjacent cover plates, and placing the gradient thickness gasket on the gasket placement area;

[0013] S3, placing the cover plate on the composite product, the side edges of the adjacent cover plates abutting each other are placed on one gradient thickness gasket, and are both located within the range of the semi-flexible gasket layer with the smallest width, and the width of the joint seam between the cover plates is less than the width of the semi-flexible gasket layer with the smallest width;

[0014] S4, after the cover plate is placed, filling the joint seam with an extensible pressure strip, and the pressure strip fills the joint seam;

[0015] S5, performing a curing forming work, and the cover plate and the gradient thickness pad apply pressure to the composite product during the curing forming process.

[0016] Further, in the step S3, the width of the joint between the adjacent cover plates is not less than 15mm.

[0017] Further, in the step S3, the center of the width direction of the joint between the adjacent cover plates coincides with the center of the width direction of the gradient thickness pad.

[0018] Further, in the step S4, the pressure strip material is raw butyl rubber.

[0019] Further, in the step S4, before the pressure strip is filled, a layer of isolation film is laid in the joint.

[0020] As described above, the gradient thickness pad and the production process of the present application have the following beneficial effects:

[0021] 1. During the curing forming of the composite product, the pressure can be uniformly transmitted to the joint between the cover plates through the gradient thickness pad, which can effectively solve the indentation problem caused by the joint and ensure that the surface quality of the composite product at and near the joint reaches the ideal effect; the gradient thickness pad has simple structure, is easy to use and has good technical effect.

[0022] 2. The production process can ensure that the pressure on the surface of the composite product during the curing forming is uniform, especially the stress on the joint of the cover plate is uniform, which can effectively improve the curing forming quality of the composite product compared with the prior art.

[0023] 3. It can be used for various types of composite products to ensure the forming of the skin aerodynamic surface, especially for the forming quality of the skin on the middle barrel section of the civil aircraft. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of the existing technology of the cover plate in the composite product.

[0025] Figure 2 It is a first structure schematic diagram of the semi-flexible pad layer in the present application.

[0026] Figure 3 It is a second structure schematic diagram of the semi-flexible pad layer in the present application.

[0027] Figure 4 It is a third structure schematic diagram of the semi-flexible pad layer in the present application.

[0028] Figure 5A fourth structure diagram of the semi-flexible gasket layer in the present application.

[0029] Figure 6 A diagram of curing and forming of the composite product in the production process of the present application.

[0030] Figure 7 A Figure 6 A circle in the present application.

[0031] Figure 8 A diagram of filling the pressure strip in the joint between the cover plates in the production process of the present application.

[0032] BRIEF DESCRIPTION OF DRAWINGS

[0033] 1 composite product

[0034] 2 cover plate

[0035] 201 joint

[0036] 3 gasket with gradient thickness

[0037] 301 semi-flexible gasket layer

[0038] 4 forming mold

[0039] 5 pressure strip

[0040] 6 release film

[0041] 7 air-permeable felt

[0042] 8 plastic vacuum bag

[0043] 9 sealing tape DETAILED DESCRIPTION

[0044] The embodiments of the present application are described below by specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification.

[0045] It should be noted that the structures, proportions, sizes, etc. shown in the drawings of the specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the implementation conditions of the present application, so they do not have technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects and purposes that can be achieved by the present application, should still fall within the scope of the technical content disclosed by the present application. At the same time, the terms such as "up", "down", "left", "right", "middle" and the like used in the specification are only for easy understanding and clarity, and are not used to limit the scope of the present application. The change or adjustment of the relative relationship without substantially changing the technical content is also considered as the implementation scope of the present application.

[0046] Referring to Figures 1 to 8 , the present application provides a gradient thickness gasket 3 for curing forming of a composite product, the gradient thickness gasket 3 comprises a plurality of layers of semi-flexible gasket layers 301 from top to bottom, and adjacent semi-flexible gasket layers 301 are fixedly connected, the width of each semi-flexible gasket layer 301 is greater than or equal to 20 mm, and the thickness is 0.1 mm to 0.3 mm, the widths of adjacent two semi-flexible gasket layers 301 are different, and the single-side width difference of both at the two side edges is greater than or equal to 20 mm, that is, the total width difference of adjacent two semi-flexible gasket layers 301 is greater than or equal to 40 mm; the gradient thickness gasket 3 is used to be placed between the cover plate 2 and the composite product 1, and is located at the joint seam 201 between adjacent cover plates 2, and the width of the semi-flexible gasket layer 301 with the smallest width in the gradient thickness gasket 3 is greater than the width of the joint seam 201.

[0047] The gradient thickness gasket 3 relates to the present application, by setting a plurality of layers of semi-flexible gasket layers 301 with different widths, referring to Figures 2 to 5 , the width of the gradient thickness gasket 3 is changed from top to bottom, and changes in a gradient manner. In its cross section (cross section perpendicular to the length), the thickness of the gradient thickness gasket 3 is non-uniform, and the effective thickness decreases in a gradient manner from the middle to the two sides. In this application, the effective thickness of the gradient thickness gasket 3 at a certain position refers to the sum of the thicknesses of the semi-flexible gasket layers 301 at the position, for example, referring to Figure 2 , the gradient thickness gasket 3 has only one semi-flexible gasket layer 301 at the left and right side edges, and the effective thickness at the position is the thickness of the semi-flexible gasket layer 301, and has three semi-flexible gasket layers 301 at the middle, and the effective thickness at the position is the sum of the thicknesses of the three semi-flexible gasket layers 301. The semi-flexible gasket layers 301 of the gradient thickness gasket 3 are made of materials resistant to high temperature during curing of the composite product 1, and are required to have certain flexibility and can be bent and twisted to a certain extent to fit the surface of the product with curvature, and at the same time have certain structural rigidity and can withstand the pressure during curing of the composite product 1. The gradient thickness gasket 3 has a long strip structure, and its length is determined according to the length of the joint seam 201 between the cover plates 2,

[0048] When the composite product 1 is cured and formed by the cover plate 2, the gradient thickness gasket 3 is arranged between the cover plate 2 and the composite product 1, and is located at the joint seam 201 between adjacent cover plates 2, and the length direction of the gradient thickness gasket 3 is along the length direction of the joint seam 201, referring to Figure 7 and Figure 8As shown, the adjacent cover plates 2 are pressed on the gradient thickness gasket 3, and are located on the minimum width semi-flexible gasket layer 301 in the gradient thickness gasket 3, that is, the pressure of the edge of the cover plate 2 is applied on the area with the maximum effective thickness of the gradient thickness gasket 3. In the length direction, the gradient thickness gasket 3 is full of the joint seam 201, and the two ends are flush with or slightly protrude from the joint seam 201, which ensures that the entire edge of the cover plate 2 is pressed on the gradient thickness gasket 3. The width of each semi-flexible gasket layer 301 is greater than or equal to 20 mm, and the thickness is 0.1 mm to 0.3 mm, which can withstand the pressure from the cover plate 2 and ensure the structural strength at the joint seam 201 to prevent the gasket itself from producing obvious indentation on the surface of the product, and the single-side width difference of the two sides of the adjacent two layers of materials is not less than 20 mm, which provides good thickness transition. When the composite product 1 is cured and formed, the cover plate 2 transmits the pressure to the composite product 1 at the joint seam 201 through the gradient thickness gasket 3, which can apply corresponding pressure to the area, and at the same time, due to the large effective thickness in the middle of the gradient thickness gasket 3 and the small effective thickness on both sides, the pressure received by the composite product 1 in the area of the joint seam 201 can be similar to the pressure received by the composite product 1 in the area beside the joint seam 201, thereby effectively reducing the indentation caused by the joint seam 201 on the composite product 1, and ensuring that the surface quality of the composite product 1 at and near the joint seam 201 reaches the ideal effect.

[0049] As a preferred design, in the present embodiment, referring to Figures 2 to 5 , the center surfaces of all semi-flexible gasket layers 301 in the gradient thickness gasket 3 overlap in the width direction, referring to Figure 2 , for any two adjacent semi-flexible gasket layers 301, the single-side width difference at the two sides is the same, denoted as L, L≥20 mm, and the cross section of the entire gradient thickness gasket 3 is a left-right symmetrical structure. Of course, the center surfaces of the adjacent semi-flexible gasket layers 301 can also have a slight deviation. The lengths of the semi-flexible gasket layers 301 in the gradient thickness gasket 3 are determined according to the length of the joint seam 201 between the cover plates 2, and preferably the lengths of the semi-flexible gasket layers 301 are the same, and the two ends are aligned. Of course, there can also be a small distance between the end surfaces of the adjacent semi-flexible gasket layers 301.

[0050] In the present application, the number of semi-flexible gasket layers 301 in the gradient thickness gasket 3 can be set according to actual needs, and the total thickness of the gradient thickness gasket 3 in the middle is X-Y mm. Referring to Figures 2 to 5 , taking three semi-flexible gasket layers as an example, the width of each semi-flexible gasket layer 301 in the gradient thickness gasket 3 can be selected in the following ways: (1) referring to Figure 2 , the width of the middle semi-flexible gasket layer 301 is the largest, and the widths of the upper and lower semi-flexible gasket layers 301 are small, and the cross section of the gradient thickness gasket 3 as a whole is spindle-shaped with the upper and lower narrow and the middle wide; (2) referring to Figure 3The width of the semi-flexible pad layer 301 decreases from top to bottom, and the cross section of the gradient-thickness pad 3 is in the shape of an inverted pyramid. Figure 4 The width of the semi-flexible pad layer 301 increases from top to bottom, and the cross section of the gradient-thickness pad 3 is in the shape of a normal pyramid.

[0051] In the present application, the gradient-thickness pad 3 is used in the production of a composite product 1, which includes but is not limited to carbon fiber reinforced composite, glass fiber reinforced composite, and high polymer fiber reinforced composite, etc. The semi-flexible pad layer 301 of the gradient-thickness pad 3 is also made of composite material, and as a preferred design, in the present embodiment, the material can be but is not limited to carbon fiber composite, glass fiber composite, and high polymer fiber reinforced composite, and the materials of different semi-flexible pad layers 301 can be the same or different. With the above design, the gradient-thickness pad 3 can have a certain structural rigidity to support the pressure from the cover plate 2 during the curing of the composite product 1, while having a certain flexibility to fit the surface of the composite product 1 with curvature. Further, the difference between the linear expansion rate of the semi-flexible pad layer 301 of the gradient-thickness pad 3 and the linear expansion rate of the composite product 1 is within ±1×10^5 mm / m·℃, so as to prevent the difference in thermal expansion coefficient from being too large and causing deformation of the product surface.

[0052] In the present application, the gradient-thickness pad 3 can be made by ordinary manual layering and autoclave curing method, and the connection between the semi-flexible pad layers 301 is stable. The upper and lower surfaces of the gradient-thickness pad 3 are smooth.

[0053] The present application also provides a production process for the curing and forming of a composite product, which uses the above-mentioned gradient-thickness pad 3, and refers to Figure 6 and Figure 7 , which includes the following steps:

[0054] S1, placing the composite product 1 to be cured and formed on the forming mold 4.

[0055] S2, determining the placement position of the cover plate 2 on the surface of the composite product 1, and determining the pad placement area corresponding to the splicing joint 201 between adjacent cover plates 2, and placing the gradient-thickness pad 3 on the pad placement area. Preferably, before placing the gradient-thickness pad 3, a layer of plastic film is laid on the composite product 1 as a separation film 6 for isolating the composite product 1 from the cover plate 2 and other auxiliary materials.

[0056] S3, the cover plates 2 are placed on the composite product 1, the side edges of the adjacent cover plates 2 are placed on a gradient-thickness gasket 3, and are located within the range of the half-soft gasket layer 301 with the smallest width, and the joint 201 between the cover plates 2 has a width smaller than the width of the half-soft gasket layer 301 with the smallest width in the gradient-thickness gasket 3, that is, the edges of the cover plates 2 are pressed on the position with the largest effective thickness in the middle of the composite product 1, see Figure 6 and Figure 7 . Preferably, the width of the joint 201 between the adjacent cover plates 2 is not less than 15 mm, so as to prevent the shear force of the cover plates 2 on the gradient-thickness gasket 3 from being too large and damaging the gasket. At the same time, the center plane of the joint 201 between the adjacent cover plates 2 in the width direction coincides with the center plane of the gradient-thickness gasket 3 in the width direction, so as to ensure that the pressure of the two cover plates 2 on the gradient-thickness gasket 3 is uniform.

[0057] S4, after the cover plates 2 are placed, an extensible pressure strip 5 is filled in the joint 201, and the pressure strip 5 fills the joint 201. Before the pressure strip 5 is filled, a layer of plastic film is laid in the joint 201 as a separation film 6, which is used to separate the pressure strip 5 from the cover plates 2 and the gradient-thickness gasket 3. The pressure strip 5 is made of flexible rubber material, which is resistant to high temperature during curing of the composite product 1 and has a certain fluidity, so as to ensure that it can fill all the gaps in the joint 201 during curing, and at the same time has a certain structural strength, so as to ensure that it can effectively transmit pressure during curing. The pressure strip 5 can use unvulcanized butyl rubber raw material, or other suitable flexible rubber materials with similar properties. After the pressure strip 5 is filled, its volume matches the volume of the joint 201, see Figure 8 , so as to ensure that the pressure in the joint 201 area during curing is consistent with the non-joint 201 area.

[0058] In this step, preferably, after the pressure strip 5 is filled, the entire composite product 1 is covered with a breather fabric 7, see Figure 6 and Figure 7 , the breather fabric 7 is covered on the cover plates 2, covering the cover plates 2, the pressure strip 5, the composite product 1, etc., and the breather fabric 7 is used to exhaust the gas generated during the curing process of the product.

[0059] S5, curing and forming work is performed, and the cover plates 2 and the gradient-thickness gasket 3 apply pressure to the composite product 1 during the curing and forming process. Specifically, in this embodiment, see Figure 6 and Figure 7, the curing and molding work can be performed in the following manner: the entire structure assembled at the end of step S4 is wrapped and sealed by using a plastic vacuum bag 8, the plastic vacuum bag 8 is wrapped on the air-permeable felt 7, the edges are connected to and sealed with the molding mold 4 by using sealing rubber strips 9, then vacuumizing, and the composite product 1 to be molded is put into a hot press tank to be subjected to high temperature and high pressure, so that the composite product 1 is changed from a blank to a finished product, and the curing and molding work is completed. During the curing and molding process, the cover plate 2 and the pressure strip 5 bear the pressure, and the gradient thickness gasket 3 is subjected to the pressure transmitted from the cover plate 2 and the pressure strip 5, so that the pressure is applied to the composite product 1 through the cover plate 2 and the gradient thickness gasket 3.

[0060] Through the above steps, after the curing and molding work is completed, the composite product 1 with good surface quality is obtained.

[0061] The gradient thickness gasket 3 and the production process of the present application have the following beneficial effects:

[0062] 1. During the curing and molding of the composite product 1, the pressure can be uniformly transmitted to the position of the spliced joint 201 of the composite product 1 located between the cover plates 2 through the gradient thickness gasket 3, the indentation problem caused by the spliced joint 201 can be well solved, and the surface quality of the composite product 1 at and near the spliced joint 201 can reach the ideal effect; the gradient thickness gasket 3 has simple structure, is easy to use, and has good technical effect.

[0063] 2. The production process can ensure that the pressure on the surface of the composite product 1 is uniform during the curing and molding, and compared with the prior art, the curing and molding quality of the composite product 1 can be effectively improved.

[0064] 3. It can be used for various types of composite products 1 to ensure the molding of the skin aerodynamic surface, and especially can be used for the molding quality of the skin on the barrel section fuselage of a civil aircraft.

[0065] In summary, the present application effectively overcomes the shortcomings of the prior art and has high industrial utilization value.

[0066] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A gradient thickness gasket for curing composite material products, characterized in that: The structure consists of multiple layers of semi-flexible gaskets (301) from top to bottom. Adjacent semi-flexible gaskets (301) are fixedly connected. The width of each semi-flexible gasket (301) is greater than or equal to 20 mm, and the thickness is 0.1 mm to 0.3 mm. The widths of two adjacent semi-flexible gaskets (301) are different, and the difference in width between the two on each side is greater than or equal to 20 mm. The thickness of the gradient thickness gasket (3) is non-uniform, and the effective thickness decreases gradually from the middle to the sides. The effective thickness of the gradient thickness gasket (3) at a certain point refers to the sum of the thicknesses of the semi-flexible gaskets (301) at that point. The gradient thickness gasket (3) is used to be placed between the cover plate (2) and the composite material product (1) and is located at the splice seam (201) between adjacent cover plates (2). The width of the semi-flexible gasket (301) with the smallest width in the gradient thickness gasket (3) is greater than the width of the splice seam (201).

2. The gradient thickness gasket according to claim 1, characterized in that: All semi-flexible gasket layers (301) overlap at their center planes in the width direction.

3. The gradient thickness gasket according to claim 1, characterized in that: The semi-flexible gasket layer (301) consists of three layers. The width of the semi-flexible gasket layer (301) decreases sequentially from top to bottom, or the width of the semi-flexible gasket layer (301) increases sequentially from top to bottom, or the width of the top and bottom two semi-flexible gasket layers (301) is greater than the width of the semi-flexible gasket layer (301) between them, or the width of the top and bottom two semi-flexible gasket layers (301) is less than the width of the semi-flexible gasket layer (301) between them.

4. The gradient thickness gasket according to claim 1, characterized in that: The semi-flexible gasket layer (301) is made of carbon fiber composite material, glass fiber composite material or polymer fiber reinforced composite material.

5. The gradient thickness gasket according to claim 1 or 4, characterized in that: The difference between the linear expansion rate of the semi-flexible gasket layer (301) and the linear expansion rate of the composite material product (1) is within ±1×10^-5 mm / m·℃.

6. A production process for curing and molding composite material products, characterized in that: Using the gradient thickness pad (3) as described in any one of claims 1 to 5, the method includes the following steps: S1. Place the composite material product (1) to be cured on the molding die (4); S2. Determine the placement position of the cover plate (2) on the surface of the composite material product (1), and determine the gasket placement area corresponding to the splice seam (201) between adjacent cover plates (2). Place the gradient thickness gasket (3) on the gasket placement area. S3. A cover plate (2) is placed on the composite material product (1). The sides of the adjacent cover plates (2) are placed on a gradient thickness gasket (3) and are all within the range of the narrowest semi-flexible gasket layer (301). The width of the splice seam (201) between the cover plates (2) is less than the width of the narrowest semi-flexible gasket layer (301). S4. After the cover plate (2) is placed, the stretchable pressure strip (5) is filled into the splice seam (201). The pressure strip (5) fills the splice seam (201). S5. The curing process is carried out. During the curing process, the cover plate (2) and the gradient thickness gasket (3) apply pressure to the composite material product (1).

7. The production process according to claim 6, characterized in that: In step S3, the width of the splice seam (201) between adjacent cover plates (2) is not less than 15mm.

8. The production process according to claim 6, characterized in that: In step S3, the center plane of the splice seam (201) between adjacent cover plates (2) in the width direction coincides with the center plane of the gradient thickness gasket (3) in the width direction.

9. The production process according to claim 6, characterized in that: In step S4, the pressure strip (5) is made of uncured butyl rubber raw material.

10. The production process according to claim 6, characterized in that: In step S4, before the pressure strip (5) is filled, a layer of isolation film (6) is laid in the splice seam (201).

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