A negative curvature composite material grid structure and forming method thereof

Abstract

The present invention discloses a method for forming a negative curvature composite mesh structure, wherein prepregs for forming negative curvature mesh ribs are laid in a mesh mold, and when the prepregs are laid, they are interrupted in the node area, and the ends of the prepregs are scattered and laid to the adjacent area of ​​the negative curvature mesh, and are laid alternately with the prepregs for forming end frames, thereby expanding the application scope of the mesh structure from a simple rotational structure to a quasi-rotational complex surface, breaking through the bridging and periodic limitations of the existing forming process, and realizing the automatic forming of negative curvature and non-periodic negative curvature mesh structures. The present invention also discloses a negative curvature composite mesh structure obtained by the forming method of the negative curvature composite mesh structure, which can be applied to the research and production of aerospace rocket body grid compartments, aircraft fuselages, wings, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of manufacturing resin-based structural composite materials, and relates to a negative curvature composite material grid structure component and a molding method thereof. Background Art

[0002] The automated forming of composite mesh structures mainly adopts the geodesic winding forming process. Due to the non-bridging, periodicity and geodesic constraints of the winding process, the existing mesh structures are generally used in simple rotational structures such as cones and columns, and the ribs are all uniformly distributed circumferentially. More complex curved or folded generatrix rotational meshes, especially mesh structures with local negative curvature, cannot be formed by winding or the winding forming is too difficult, which delays the application of mesh structures in this series of components. Summary of the invention

[0003] The purpose of the present invention is to overcome the above-mentioned defects and provide a method for forming a negative curvature composite mesh structure. Prepregs for forming negative curvature mesh ribs are laid in a mesh mold. When the prepregs are laid, they are interrupted in the node area. After the prepreg ends are scattered, they are laid to the adjacent area of ​​the negative curvature mesh and laid alternately with the prepreg for forming end frames. The application range of the mesh structure is expanded from a simple rotational structure to a quasi-rotational complex surface, breaking through the bridging and periodic limitations of the existing molding process, and can realize the automatic molding of negative curvature and non-periodic negative curvature mesh structures. The present invention also provides a negative curvature composite mesh structure obtained by the molding method of the negative curvature composite mesh structure, which can be applied to the research and production of aerospace rocket body grid compartments, aircraft fuselages, wings, etc.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] A method for forming a negative curvature composite material grid structure, wherein the negative curvature composite material grid structure comprises a negative curvature grid structure, an upper end frame and a lower end frame, comprising the following steps:

[0006] (1) manufacturing a mold having a structure corresponding to the negative curvature composite grid structural member to be formed, wherein the outer surface of the mold is provided with rib grooves corresponding to the negative curvature grid of the structural member;

[0007] (2) preparing a prepreg and cutting the prepreg to obtain prepreg filaments;

[0008] (3) Laying a layer of prepreg on the upper end frame and the lower end frame in the mold;

[0009] (4) laying a layer of prepreg in the groove of the rib provided in the mold, laying prepregs of equal thickness in different directions alternately, and heating and compacting them simultaneously;

[0010] (5) evenly breaking up the two ends of the prepreg laid in the groove and laying them on the layers of the upper end frame and the lower end frame in step (3);

[0011] (6) Repeating steps (3) to (5) to alternately lay prepregs of equal thickness in different directions, and performing interruption processing on the node areas, until the prepreg layers of the upper end frame and the lower end frame and the prepreg layers in the rib grooves reach a predetermined size; specifically, the interruption processing does not need to be performed after each layer of prepreg is laid, and the interruption processing can be performed again after multiple layers of prepreg are laid;

[0012] (7) Pre-compacting the mold and the layers on the mold after coating;

[0013] (8) Repeat steps (3) to (7) until the prepreg fills the rib grooves;

[0014] (9) The product obtained in the previous step is sequentially thermally cured, demolded, and polished to obtain a negative curvature composite mesh structure.

[0015] Furthermore, in the step (2), the prepreg is a hot-melt prepreg, and the hot-melt prepreg is cut by prepreg yarn cutting equipment to obtain prepreg yarns.

[0016] Furthermore, the hot melt prepreg includes an epoxy resin-based composite material system, a bismaleimide resin composite material system or a cyanate ester resin composite material system.

[0017] Furthermore, in the step (4), a single-filament laying head is used to lay a prepreg wire wider than a pressure roller in the rib groove, and a pressure roller is used simultaneously to compact the prepreg wire during the laying process. After the prepreg wire is laid, the edges on both sides of the prepreg wire are densified.

[0018] Furthermore, the edges of both sides of the prepreg layer are densified by the glue suction pre-compaction process;

[0019] In the step (4), the prepreg is in a viscoelastic state or a viscous fluid state.

[0020] Furthermore, in step (6), the node region includes nodes formed by cross-laying of two-way or three-way prepreg yarns;

[0021] The specific method for interrupting the node area is to remove the excess prepreg at the node and keep only the prepreg in a certain direction continuous. The number of prepreg layers removed in any direction at the node shall not exceed half of the total number of prepreg layers in that direction. The width of the prepreg is allowed to be widened locally to increase the proportion of continuous prepreg.

[0022] Furthermore, in the step (5), the two ends of the prepreg wire laid in the groove are scattered, and the scattered prepreg wire is evenly distributed within an angle range of 60°; the thickness of the prepreg wire at the scattered position is ≤1mm.

[0023] Furthermore, the material used for the mold is one or a combination of metal, silicone rubber, gypsum, wood or foam.

[0024] Furthermore, between step (8) and step (9), the method further includes using prepreg layers to form a structural component skin.

[0025] Furthermore, the curvature radius of the negative curvature grid in the negative curvature composite grid structure is ≥ 4.5 m.

[0026] Further, the negative curvature grid in the negative curvature composite grid structure is a rotational surface with local negative curvature, a rotational surface with overall negative curvature, a non-rotational surface with local negative curvature, or a non-rotational surface with overall negative curvature;

[0027] The mesh ribs in the negative curvature mesh are circumferentially distributed or non-circumferentially distributed; the mesh ribs in the negative curvature mesh are equally distributed or non-equally distributed.

[0028] A negative curvature composite material grid structure component is formed by using the above-mentioned forming method for a negative curvature composite material grid structure component.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) In a method for forming a negative curvature composite mesh structure of the present invention, a process method suitable for automatic placement of negative curvature mesh ribs is proposed, which breaks through the limitation that the mesh winding forming bridge area cannot be formed, and solves the problem of automatic forming of negative curvature mesh ribs;

[0031] (2) The present invention provides a method for forming a negative curvature composite mesh structure, which breaks the periodicity restriction and uniformity constraint of the mesh rib trajectory, and can realize the automatic forming of non-uniformly distributed mesh ribs, and the scrap rate is reduced from 50% of the mesh winding to about 10%;

[0032] (3) In a molding method of a negative curvature composite material grid structure of the present invention, a method for optimizing the processing of grid rib nodes is proposed. By interrupting the prepreg and breaking up the ends of the prepreg, the process problem of flat laying at the nodes is solved, and low-defect and high-quality molding of the node area is achieved;

[0033] (4) In the molding method of a negative curvature composite material grid structure of the present invention, high-quality solidification of the grid ribs without an external mold is achieved, thereby improving the degree of automation. The method of the present invention is suitable for the development of negative curvature grid structures, and is particularly suitable for the molding of negative curvature grids with a curvature radius of ≥4.5m. It can be applied to the development and production of aerospace rocket grid compartments, aircraft fuselages, wings, etc. Compared with traditional molding methods, it has obvious technical advantages, greatly improves the molding quality and molding efficiency of component composite materials, and has considerable prospects for economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of laying the prepreg in the rib groove of the present invention;

[0035] Figure 2 Schematic diagram of a conical negative curvature grid component in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0037] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0038] The present invention conducts research on local negative curvature grid structures and proposes a method for forming a negative curvature composite grid structure, comprising the following steps:

[0039] (1) manufacturing a mold having a structure corresponding to the negative curvature composite grid structural member to be formed, wherein the outer surface of the mold is provided with rib grooves corresponding to the negative curvature grid of the structural member;

[0040] (2) Based on the three-dimensional digital model of the product, the ply dimensions in the local negative curvature area are accurately calculated to obtain the predetermined dimensions of the ribs;

[0041] (3) Using hot melt prepreg, the prepreg wire size is obtained according to the rib width in the three-dimensional digital model of the product, and the prepreg wire is prepared by prepreg wire slitting equipment, which is used for mesh rib molding in subsequent steps and can also be used for skin molding;

[0042] (4) Using prepreg and a manual assisted laying process to lay the upper and lower end frames at the corresponding parts of the upper and lower end frames of the mold;

[0043] (5) using the prepreg slit in step (3) and using an automatic feeding device to accurately feed the prepreg to automatically place the prepreg in the rib groove;

[0044] Specifically, the hot melt prepreg is laid in each rib groove on the surface of the grid mold, and infrared heating lamp preheating and roller compaction are carried out simultaneously to ensure that the prepreg is in close contact with the bottom of the mold groove or the previous layer; prepregs of equal thickness in different directions are laid alternately, and interruption processing is allowed in the node area;

[0045] (6) Spread the prepreg laid in step (5) and lay it on the upper and lower end frame layers, ensuring that it is evenly dispersed as much as possible;

[0046] (7) Repeat steps (4) to (6) until the prepreg reaches a predetermined height and the upper and lower end frame layers reach a predetermined thickness;

[0047] (8) Coating the mold and the upper layer, and performing high temperature and high pressure pre-compaction in an autoclave after coating;

[0048] (9) Repeat steps (4) to (8) until the prepreg fills the mesh rib grooves;

[0049] (10) If there is a skin, the prepreg slit in step (3) is used to automatically lay the structure component skin according to the set laying order; if there is no skin, directly go to step (11);

[0050] (11) Wrapping the grid mold and the upper layer thereof, and curing them in an autoclave;

[0051] (12) After the can is taken out of the can, it is demolded, polished, and deburred to obtain a negative curvature grid structure.

[0052] Furthermore, in step (5), the automatic prepreg laying process uses a single-filament laying head to lay the hot-melt prepreg that is wider than the pressure roller in the rib grooves on the grid mold. During the laying process, the pressure roller compacts the prepreg into a compact state. After the prepreg is laid, the prepreg on both sides of the prepreg is densified through a glue suction pre-compaction process.

[0053] Furthermore, the method of the present invention can meet the needs of different types of prepregs, and the types of prepregs may include composite material systems such as epoxy, bismaleimide, and cyanate ester.

[0054] Furthermore, in step (5), the laying temperature is one of the important process parameters of automatic wire laying. The laying temperature of the prepreg mainly depends on the matrix resin formula and is also affected by the transmission temperature during the laying process. The matrix resins of the prepreg are different, and their viscosity changes with temperature in different patterns. In the automatic wire laying process, the prepreg is required to have a certain viscosity and a certain viscous flow property, that is, it is in a viscoelastic state or a viscous flow state. Therefore, prepregs of different resin systems have different laying temperatures during the automatic wire laying process. When the laying temperature is low, the poor fluidity of the matrix resin leads to too low viscosity of the prepreg resin, and the prepreg cannot fit well with the mold and the prepreg matrix, which ultimately leads to too high porosity of the product; when the laying temperature is too high, the matrix resin has good fluidity, and the prepreg is very easy to deform laterally under the pressure of the roller, resulting in wrinkles.

[0055] Further, in step (5), the laying pressure is an important process parameter for the automatic laying of prepreg, which directly affects the quality of the layer. During the automatic laying process, the laying pressure makes the layer being laid fit closely with the prepreg of the previous layer, which can effectively reduce the gap between layers and increase the interlayer adhesion. When the pressure of the pressure roller is too small, the prepreg cannot be firmly adhered to the mold surface by its own viscosity. At the same time, the prepreg layers cannot be compacted, which eventually leads to a large number of bubbles and protrusions in the laminate, reducing the quality of the product. When the pressure is too high, the prepreg will expand laterally during the laying process, there will be overlap between the tows, and the fibers will bend. At the same time, the excessive pressure causes the pressure roller to deform too much, causing the resistance of the yarn feeding channel to increase, which is not conducive to the reliable delivery of the prepreg.

[0056] Furthermore, in step (5), the interruption process is to remove excess prepreg yarns at the nodes where the two-directional or multi-directional prepreg yarns are cross-laid, so that only the prepreg yarns in one direction remain continuous, and the number of prepreg yarn layers removed at the nodes does not exceed half of the total number of prepreg yarn layers, and generally does not exceed the intersection of three aspects, and the capacity can be ensured by widening the local ribs.

[0057] Furthermore, in step (6), the prepreg yarn needs to be evenly distributed within a 60° angle range, and the thickness of the prepreg yarn distribution area after the prepreg yarn is scattered is not greater than 1 mm, so as to improve the continuity between the prepreg yarn and the end frame ply.

[0058] Furthermore, the composite material grid structure mold may be made of metal, or silicone rubber, gypsum, wood, foam or a mixture of the above materials.

[0059] In practical applications, the grid ribs of cabin components have local negative curvature characteristics. The process of the present invention is suitable for the molding of such cabin components. The curvature radius range of the negative curvature grid applicable to the process of the present invention is not less than 1m, and the optimal range is above 4.5m radius.

[0060] The negative curvature grid ribs in the negative curvature composite grid structure applicable to the present invention can be distributed in equal or unequal degrees along the circumferential direction (with uneven distribution angles), or in equal or unequal degrees along the non-circumferential direction, and different rib grooves can be evenly distributed circumferentially, or have different laying trajectories or angles. The negative curvature grid structure can be a traditional rotational surface, or a quasi-revolutionary complex surface, or a non-developable free-form surface.

[0061] Embodiment 1:

[0062] This embodiment adopts a negative curvature composite material grid structure forming method of the present invention to prepare a conical negative curvature grid component:

[0063] The outer diameter of the lower end frame 1 of the conical negative curvature grid component is 1000mm, the outer diameter of the upper end frame 2 is 750mm, the cone angle is 50°, the curvature radius of the negative curvature grid 3 busbar is 5m, the upper and lower end frames are both inward-turned L end frames, the thickness is 8.4mm, the flange length is 45mm, and the ply adopts quasi-isotropic ply [-45 / 0 / 45 / 90] 7S The cross section of the rib 4 is an isosceles trapezoid, the upper base length of the trapezoid is 6mm, the lower base length is 7.5mm, the height of the trapezoid is 8mm, the upper base is the inner surface of the product, the helix angle of the rib 4 is ±30°, and the 40 ribs 4 are distributed along the circumference with equal helix angles. For specific structure, see Figure 2 .

[0064] The conical negative curvature grid component is made of TG800 / 603B carbon fiber reinforced epoxy resin based prepreg with a thickness of 0.15mm.

[0065] The specific steps of this embodiment are as follows:

[0066] (1) manufacturing a mold having a structure corresponding to the negative curvature composite grid structural member to be formed, wherein the outer surface of the mold is provided with rib grooves 5 corresponding to the negative curvature grid of the structural member;

[0067] (2) Based on the three-dimensional digital model of the product, the ply dimensions in the local negative curvature area are accurately calculated to obtain the predetermined dimensions of the ribs;

[0068] (3) Using hot melt prepreg, according to the three-dimensional digital model of the product, a prepreg slitting device is used to prepare a 6.5 mm wide prepreg for mesh rib forming in the subsequent steps, and can also be used for skin forming;

[0069] (4) Laying the upper and lower end frames on the mold using prepreg using a manual assisted laying process;

[0070] (5) Figure 1, using the prepreg slit in step (3), the prepreg automatic placement technology is used to lay the prepreg in the rib groove 5, and the hot melt prepreg is laid layer by layer in each groove on the surface of the grid mold, and infrared heating lamp preheating and pressure roller 6 compaction are performed simultaneously to ensure that the prepreg is in close contact with the bottom of the mold groove or the previous layer; ribs of equal thickness in different directions are laid alternately, and interruption processing is allowed in the node area; the laying process parameters of 6.5mm wide TG800 / 603B prepreg are shown in Table 1.

[0071] Table 1 Component reinforcement laying process parameters

[0072] parameter describe Laying pressure 0.30MPa Laying temperature 23-28℃ Tow tension 0.02-0.04MPa Laying rate 10m / min Prepreg Width 6.5mm

[0073] During the prepreg laying process, the yarn bundles in the compacted area are laid flat without obvious wrinkles, the fibers are well straightened, fit tightly, and the molding quality is good.

[0074] (6) Spread the prepreg laid in step (5) and lay it on the upper and lower end frame layers, ensuring that it is evenly dispersed as much as possible;

[0075] (7) Repeat steps (4) to (6) until the prepreg reaches a predetermined height and the upper and lower end frame layers reach a predetermined thickness;

[0076] (8) coating the mold, and performing high temperature and high pressure pre-compaction in an autoclave after coating;

[0077] (9) Repeat steps (4) to (8) until the prepreg fills the mesh rib grooves;

[0078] (10) If there is a skin, the prepreg slit in step (3) is used to automatically lay the component skin according to the set laying order; if there is no skin, the process directly proceeds to step (11);

[0079] (11) Coating the mesh mold and curing it in an autoclave;

[0080] (12) After the can is taken out of the can, it is demolded, polished, and deburred to obtain a conical negative curvature grid component.

[0081] After the conical negative curvature grid component was solidified, the forming quality was tested by ultrasonic testing. The test showed that the forming quality of the test piece was good, and no defects such as delamination, inclusions, and pores were found.

[0082] The present invention is described in detail above in conjunction with specific implementation methods and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The protection scope of the present invention shall be subject to the attached claims.

[0083] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for forming a negative curvature composite material grid structure, wherein the negative curvature composite material grid structure comprises a negative curvature grid structure, an upper end frame and a lower end frame, characterized in that: The following steps are involved: (1) manufacturing a mold having a structure corresponding to the negative curvature composite grid structural member to be formed, wherein the outer surface of the mold is provided with rib grooves corresponding to the negative curvature grid of the structural member; (2) preparing a prepreg and cutting the prepreg to obtain prepreg filaments; (3) Laying a layer of prepreg on the upper end frame and the lower end frame in the mold; (4) placing a layer of prepreg in the groove of the ribs in the mold, and simultaneously heating and compacting the prepreg; (5) evenly breaking up the two ends of the prepreg laid in the rib grooves and laying them on the layers of the upper end frame and the lower end frame in step (3); (6) Repeating steps (3), (4) and (5) to alternately lay prepregs of equal thickness in different directions and interrupting the node area until the prepreg plies at the upper end frame and the lower end and the prepreg plies in the rib grooves reach a predetermined size; (7) Pre-compacting the mold and the layers on the mold after coating; (8) Repeat steps (3) to (7) until the prepreg fills the rib grooves; (9) thermally curing, demolding and polishing the product obtained in the previous step in sequence to obtain a negative curvature composite grid structure; In the step (4), a single-filament placement head is used to place a prepreg wire wider than a pressure roller in the rib groove, and a pressure roller is used to compact the prepreg wire during the placement process. After the prepreg wire is placed, the edges on both sides of the prepreg wire are densified; The curvature radius of the negative curvature grid in the negative curvature composite grid structure is ≥4.5m; In the step (6), the node region includes nodes formed by cross-laying of two-way or three-way prepreg yarns; The specific method of interrupting the node area is to remove the excess prepreg at the node, so that only the prepreg in a certain direction remains continuous. The number of prepreg layers removed in any direction at the node does not exceed half of the total number of prepreg layers in that direction. The width of the prepreg is allowed to be widened locally to increase the proportion of continuous prepreg. In the step (5), the two ends of the prepreg wire laid in the rib groove are broken up, and the broken up prepreg wire is evenly distributed within a 60° angle range; the thickness of the prepreg wire at the broken up position is ≤1 mm.

2. The method for forming a negative curvature composite material grid structure according to claim 1, characterized in that: In the step (2), the prepreg is a hot-melt prepreg, and the hot-melt prepreg is cut by prepreg yarn cutting equipment to obtain prepreg yarns.

3. The method for forming a negative curvature composite material grid structure according to claim 2, characterized in that: The hot-melt prepreg comprises an epoxy resin-based composite material system, a bismaleimide resin composite material system or a cyanate ester resin composite material system.

4. The method for forming a negative curvature composite material grid structure according to claim 1, characterized in that: In step (4), the edges of both sides of the prepreg layer are densified by a glue suction pre-compaction process; In step (4), the prepreg is in a viscoelastic state or a viscous fluid state.

5. The method for forming a negative curvature composite material grid structure according to claim 1, characterized in that: The material used for the mold is one or a combination of metal, silicone rubber, gypsum, wood or foam.

6. The method for forming a negative curvature composite material grid structure according to claim 1, characterized in that: Between step (8) and step (9), the method also includes using prepreg yarn plies to form the structural component skin.

7. The method for forming a negative curvature composite material grid structure according to claim 1, characterized in that: The negative curvature grid in the negative curvature composite grid structure is a rotational surface with local negative curvature, a rotational surface with overall negative curvature, a non-rotational surface with local negative curvature, or a non-rotational surface with overall negative curvature; The mesh ribs in the negative curvature mesh are circumferentially distributed or non-circumferentially distributed; the mesh ribs in the negative curvature mesh are equally distributed or non-equally distributed.

Images