Expandable and contractible large-diameter sandwich structure mold and forming process method

Abstract

The invention discloses an expandable and contractible large-diameter sandwich structure mold and a forming process method, solves the process problem of continuous high-quality forming of inner and outer skins of a super-large-diameter rotary sandwich structure composite material, and belongs to the technical field of advanced manufacturing of structural composite materials. The invention is oriented to the manufacturing of large composite components, breaks through the splicing structure and the sealing method of the modular composite combined die, successfully solves the problem of matching of thermal expansion coefficients of the composite components and the die, and reduces the influence of the die on the dimensional accuracy of the composite component product as much as possible; a space frame structure scheme is adopted, the difficult problem of mold profile rigidity control is solved, a forming mold split airtight system is designed, and the airtight requirement in the composite material sandwich structure barrel forming process is met; the mold can be disassembled and assembled in a split mode and can be repeatedly used, and the manufacturing cost of the component mold is reduced.

Description

Technical Field

[0001] This invention relates to an expandable and contractible large-diameter sandwich structure mold and molding process, belonging to the field of advanced manufacturing technology of structural composite materials. Background Technology

[0002] Launch efficiency is a key indicator of a launch vehicle's advancement. Currently, one of the main technical approaches to addressing rocket launch efficiency is improving the lightweighting of the rocket body structure. With the development of the commercial aerospace sector both domestically and internationally, the demand for a synergistic optimization of lightweight rocket body structures and low-cost, rapid manufacturing is becoming increasingly prominent. This means achieving lightweight design and manufacturing of composite material structures while maintaining controllable manufacturing costs.

[0003] Traditional structural designs typically use aluminum alloys for the main load-bearing sections to meet requirements for weight reduction and structural strength and stiffness. This type of weight-reduction technology is quite mature and has essentially reached its weight-reduction limit. In recent years, advanced spacecraft structural designs abroad have addressed the issues of large structural scale and ultra-lightweight structures. Composite material sandwich structures have emerged as a response to this trend and have become the main structural form for advanced launch vehicle sections. Interstage sections, fairings, and fuel tanks all utilize composite material sandwich structures. As advanced spacecraft develop towards larger structural scales and ultra-lightweight structures, composite material sandwich structures, due to their excellent lightweight, high strength, and high stiffness characteristics, have become the main structural form for interstage sections, fairings, and fuel tanks in advanced foreign launch vehicles. Their application has also expanded from secondary load-bearing structures such as fairings, tail sections, and payload supports to primary load-bearing structures such as interstage sections. Based on the overall goal of improving carrying capacity, domestic launch vehicles have applied sandwich structures to replace metal semi-monocoque structures in components such as fairings, payload supports, and first-stage tail sections.

[0004] There is still a certain gap in the maturity of large-size composite sandwich structure technology: (1) In the rocket body sandwich composite structure, it is only applied to secondary load-bearing structure. (2) The axial compression design load of Falcon 9-level inter-section is 1036t, and the linear load-bearing capacity reaches 868kN / m. To achieve the leap from tens of tons of secondary load-bearing structure to hundreds of tons of main load-bearing structure, the existing sandwich composite material has insufficient compressive strength and shear resistance, and the cross-scale transfer law of mechanical properties of sandwich composite material is unclear. The theoretical methods and a series of key technologies such as integrated material structure design and overall automated manufacturing are lacking, and there is a gap in the application of main load-bearing structure. (3) The existing large sandwich composite materials are all made by manually laying skin + splitting inner and outer skins and assembling and bonding honeycomb + reinforcing the inter-segment seam with adhesive rivet. The reinforcing area needs to add redundant weight such as foam, reinforcing plate, adhesive, screw / rivet, etc. The weight reduction effect of sandwich structure is not obvious, and stress concentration is easy to occur at the seam, forming a source of failure, resulting in a decrease in load-bearing capacity.

[0005] With the development of commercial aerospace, there is an urgent need to seek design and manufacturing methods for large-scale structures and ultra-lightweight structures. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide an expandable and contractible large-diameter sandwich structure mold and molding process, which solves the process problem of continuous high-quality molding of inner and outer skins of ultra-large diameter rotary sandwich structure composite materials.

[0007] The technical solution of this invention is:

[0008] A large-diameter sandwich structure mold that can expand and contract includes: a mandrel, a front flange mechanism, a rear flange structure, a segmented module assembly, and an airtight system;

[0009] The segmented module assembly is fixedly connected to the mandrel through a front flange mechanism and a rear flange structure. The segmented module assembly is a large-diameter cylindrical structure composed of eight segmented modules fixedly connected through a front flange mechanism and a rear flange structure. It is the main structure of the mold surface and is used for product molding. At the same time, the gaps between adjacent modules are sealed by an airtight system.

[0010] The front flange mechanism and the rear flange structure are fixed to the segmented module by locking bolts. At the same time, the front flange mechanism and the rear flange structure determine the positioning of the segmented module by front positioning protrusion and rear positioning protrusion, respectively. Reverse ejection bolts are set on the edges of the front flange mechanism and the rear flange structure to adjust the radial clearance of the segmented module connection position, and the connection area is sealed by the mold airtight system.

[0011] The segmented module assembly adopts an integral grid skin structure. The grid structure ensures the overall rigidity of the segmented module, and the skin ensures overall airtightness, thus ensuring the closure of the mold airtight system.

[0012] Limiting blocks are provided on both sides of the axial edge region of the segmented module assembly for limiting the honeycomb assembly and extending the outer skin.

[0013] Furthermore, the mold diameter is the same as the diameter of the segmented module assembly, ranging from 4m to 10m.

[0014] Furthermore, the front flange mechanism and the rear flange structure are required to control their radial thermal expansion deformation, with the radial expansion not exceeding 3mm.

[0015] Furthermore, the front flange mechanism, rear flange structure, and segmented module are all made of the same material, Invar alloy steel.

[0016] Furthermore, the airtight system includes a segmental airtight system, a flange airtight system, and a vacuum bag;

[0017] When the gaps between adjacent segmented modules are sealed by the inter-segment airtight system, a vacuum bag or airbag is used to cover the gaps between the segmented modules and is connected to the inner surface of the segmented module by a sealing strip.

[0018] When the gap between the front flange mechanism and the rear flange structure and the segmented module is sealed in the connection area through the flange airtight system, a vacuum bag or airbag is used to cover the gap between the front flange mechanism and the rear flange structure and the segmented module, and a sealing strip is used to connect with the inner surface of the front flange mechanism, the rear flange structure, and the segmented module.

[0019] The airtight system between the segments and the airtight system between the flanges are sealed by a sealing strip to achieve a sealed connection between the vacuum bag membrane or air bladder.

[0020] The vacuum bag is used for sealing the outer surface, and it needs to cover the segmented module, the front flange mechanism and the rear flange structure, and is connected to the outer surface of the front flange mechanism and the rear flange structure through a sealing strip.

[0021] Furthermore, the expandable and contractible mechanism adjusts the radial clearance of the connection position by using reverse ejector bolts, and then uses locking bolts to firmly fix the segmented module to the front flange mechanism and the rear flange structure. During the adjustment process, the front positioning protrusion and the rear positioning protrusion guide the movement direction of the segmented module.

[0022] Furthermore, during the radial clearance adjustment process, the adjustment of the gap by the segmented module requires the front flange mechanism and the rear flange structure to be carried out simultaneously. The single adjustment amount is within 1mm, and the total adjustment amount is within 1mm.

[0023] Furthermore, the expandable and contractible nature of the mold is used for secondary adjustment of the mold diameter during the molding process of large sandwich structures. The inner skin of the large sandwich structure is first cured, and then the honeycomb assembly and outer skin are formed. However, after the inner skin is cured, its coefficient of thermal expansion is different from that of the mold itself, resulting in a gap between the inner skin and the mold. The larger the component size, the larger the gap. It is necessary to adjust the radial position of the segmented module according to the gap between the inner skin and the mold to eliminate the gap between the inner skin and the mold and avoid the inner skin and the mold sliding and being difficult to position during the honeycomb molding and outer skin forming process.

[0024] Furthermore, the present invention also proposes a forming process for a large-diameter sandwich structure achieved through the aforementioned expandable and contractible large-diameter sandwich structure mold, comprising the following steps:

[0025] (1) Install large-diameter sandwich structure molds;

[0026] (2) The inner skin is automatically laid and formed, and after being wrapped, it is put into a hot autoclave for heating and pressure curing. The curing temperature is 120-140℃ and the curing pressure is 0.5-0.6MPa.

[0027] (3) Adjust the outer diameter of the large-diameter sandwich structure mold, tighten the inner skin, and install the limit block at the same time;

[0028] (4) Lay a film on the inner skin and install the honeycomb on the film;

[0029] (5) Lay the adhesive film on the honeycomb, then wrap the first layer of fabric strip by winding, and then lay and wrap the outer skin.

[0030] (6) After coating, it is placed in a hot autoclave for heating and pressurization curing. The curing temperature is 120-140℃ and the curing pressure is 0.2-0.3MPa.

[0031] (7) After curing, the mold is removed to obtain a large-diameter sandwich composite material shell.

[0032] Furthermore, the specific method for installing the molding die is as follows: the front flange mechanism and the rear flange structure are installed at fixed positions on the mandrel, and then the segmented modules of the segmented module assembly are installed one by one on the front flange mechanism and the rear flange structure, and fixed with locking bolts; the inter-segment airtight system and the flange airtight system are manufactured, and the sealing connection between the two is completed; thus, the molding die is obtained.

[0033] Furthermore, the specific method for dismantling the mold is as follows:

[0034] The first step is to remove the outer vacuum bag.

[0035] The second step is to loosen the connection between the front flange mechanism and the rear flange structure and the mandrel, and then remove the mandrel.

[0036] The third step involves manually entering the molding mold to remove the airtight system.

[0037] Fourth step, remove the front flange mechanism;

[0038] The fifth step is to begin disassembling the segmented module components, removing each segmented module one by one from inside the product;

[0039] Step 6: Move the product away from the rear flange mechanism. At this point, the mold removal is complete. Clean the product surface to obtain a large-diameter sandwich structure component.

[0040] The advantages of this invention compared to the prior art are:

[0041] (1) This invention proposes a design and manufacturing technology for a large-diameter sandwich structure mold that can expand and contract, which solves the process problem of continuous high-quality molding of inner and outer skins of ultra-large diameter rotary sandwich structures with a diameter of 5m or more, and lays a technical foundation for lightweight manufacturing of large composite rotary structures.

[0042] (2) Design and develop lightweight composite material combination molds with a length of 5 meters or more, while meeting the product demolding requirements and the convenience of mold installation and use. Design a composite material mold disassembly and assembly mechanism and optimize the airtightness of the composite material mold.

[0043] (3) By designing the expansion of the flange, the problem of excessive expansion difference between the mold and the carbon fiber composite skin is solved. Furthermore, by using the radial gap adjustment mechanism, the composite material is tightened, ensuring the overall assembly and molding of the inner and outer skins and honeycomb.

[0044] (4) The problem of air tightness control of the segmented mold parts was solved by the design of the sealing system, which met the air tightness requirements of the composite sandwich structure cylinder during the molding process, and at the same time controlled and coordinated its circumferential expansion difference.

[0045] (5) The mold can be disassembled and reassembled in sections and reused multiple times, which reduces the manufacturing cost of component molds. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the main structure of a large-size sandwich structure mold;

[0047] Figure 2 A schematic diagram of the structure for adjusting the expansion and contraction of the mold's outer diameter;

[0048] Figure 3 Schematic diagram of a zero-absorption pre-compacted coating structure;

[0049] Figure 4 This is a schematic diagram of the sealing of the inner surface of the mold. Detailed Implementation

[0050] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0051] Existing large-scale sandwich composite structures typically employ manual skin layup, segmented inner and outer skin assembly and bonding with honeycomb joints, and reinforcement with adhesive-riveted reinforcing plates at the inter-segment seams. Due to the added weight at the seams and the tendency for stress concentration under high compressive loads, the weight reduction effect of the sandwich structure is not significant, resulting in poor load-bearing capacity. The assembly and curing process leads to segmented panel bonding, and the panel seams are weak points in the load-bearing capacity of the composite sandwich structure, requiring structural reinforcement design to ensure the overall load-bearing capacity. A common reinforcement method involves filling a 20-30mm area around the panel seam with structural foam, while reinforcing plates and screws / rivets are used for reinforcement both inside and outside. This results in redundant weight added to the reinforced area by foam, reinforcing plates, adhesives, screws / rivets, etc. The larger the structure, the more significant the weight increase, ultimately affecting the weight reduction effect of the composite sandwich structure.

[0052] Although the current process of assembling and co-curing composite material sandwich structures for rocket bodies can meet the application requirements of existing launch vehicles, the existing process requires the panels to be decomposed into 6-8 pieces to manufacture composite material sandwich structures with a diameter of 5m or more. This greatly limits the load-bearing capacity and weight reduction effect of composite material sections. The existing assembly and curing process can no longer be used to manufacture large-size composite material rocket body load-bearing sections with a diameter of 5m or more. It is difficult to meet the application requirements of main load-bearing sections with a load capacity of thousands of tons. It is necessary to develop new technologies and solutions for automated molding of large-size carbon fiber composite shells.

[0053] Currently, the outer diameter of inter-stage sandwich load-bearing cylindrical sections is too large, reaching the 5m range, and thermal expansion issues prevent the continuous manufacturing of both inner and outer skins through layering. Patent No. 202310307260.2 discloses a composite material cylindrical section mold, preparation method, and composite material cylindrical section preparation method, which solves problems such as structural deformation and dimensional deviations caused by the mismatch of the thermal expansion coefficients between the mold and the product. However, its manufacturing scheme achieves mold expansion through circumferential expansion, which generates great friction between the mold and the product, directly affecting product quality. In addition, the hinged connection mechanism has low precision and cannot meet the precision requirements of automatic layering and forming.

[0054] This invention addresses the manufacturing of large composite material components, breaking through the limitations of modular composite material assembly mold splicing structures and sealing methods. It successfully solves the problem of matching the thermal expansion coefficients of composite material components and molds, minimizing the impact of molds on the dimensional accuracy of composite material components. A spatial frame structure is adopted to solve the problem of mold surface stiffness control, and a split airtight system for the forming mold is designed to meet the airtightness requirements during the forming process of composite sandwich structure cylinders. The mold can be disassembled and reassembled in sections for repeated use, reducing the manufacturing cost of component molds.

[0055] like Figure 1 As shown, the present invention proposes a large-diameter sandwich structure mold that can expand and contract, comprising: a mandrel 1, a front flange mechanism 2, a rear flange structure 3, a segmented module assembly 4, and an airtight system 5.

[0056] The segmented module assembly 4 is fixedly connected to the mandrel 1 through the front flange mechanism 2 and the rear flange structure 3. The segmented module assembly 4 is a large-diameter cylindrical structure formed by eight segmented modules 41 fixedly connected through the front flange mechanism 2 and the rear flange structure 3. It is the main structure of the mold surface and is used for product molding. At the same time, the gaps between adjacent modules of each segmented module 41 are sealed by the airtight system 5.

[0057] like Figure 2As shown, the front flange mechanism 2 and the rear flange structure 3 are fixed to the segmented module 41 by locking bolts 42. At the same time, the front flange mechanism 2 and the rear flange structure 3 determine the positioning of the segmented module 41 by the front positioning protrusion 21 and the rear positioning protrusion 31, respectively. Reverse ejection bolts 43 are provided on the edges of the front flange mechanism 2 and the rear flange structure 3 to adjust the radial clearance of the connection position of the segmented module 41, and the connection area is sealed by the mold airtight system 5.

[0058] The segmented module assembly 4 adopts an integral grid skin structure. The grid structure ensures the overall rigidity of the segmented module, and the skin ensures overall airtightness, ensuring the closure of the mold airtight system 5. Limiting blocks 6 are set on both sides of the axial edge area of ​​the segmented module assembly 4 for limiting the honeycomb assembly and extending the outer skin.

[0059] The mold diameter is the same as the diameter of the segmented module component 4, and the diameter is generally ≥3m; the optimal range is 4m-10m; the mold sandwich structure is formed by continuous molding of inner and outer skins, that is, both inner and outer skins maintain continuous fiber layup and have no splicing areas.

[0060] The front flange mechanism 2 and the rear flange structure 3 are required to control their radial thermal expansion deformation. The radial expansion is generally no more than 3 mm, and preferably less than 1 mm. They should be made of materials with sufficient structural strength and low coefficient of thermal expansion, preferably Invar alloy steel. The segmented module 41 should be made of a material with a coefficient of thermal expansion similar to or the same as that of the front flange mechanism 2 and the rear flange structure 3, preferably Invar alloy steel or composite materials.

[0061] The airtight system 5 includes a segmental airtight system 51, a flange airtight system 52, and a vacuum bag 53, such as Figure 3 and Figure 4 As shown.

[0062] When the gaps between adjacent segment modules 41 are sealed by the segment airtight system 51, a vacuum bag or airbag is used to cover the gaps between the segment modules 41 and is connected to the inner surface of the segment module 41 by a sealing strip 54.

[0063] When the gap between the front flange mechanism 2 and the rear flange structure 3 and the segmented module 41 is sealed by the flange airtight system 52, a vacuum bag or airbag is used to cover the gap between the front flange mechanism 2 and the rear flange structure 3 and the segmented module 41, and the sealing strip 54 is used to connect with the inner surfaces of the front flange mechanism 2, the rear flange structure 3 and the segmented module 41.

[0064] The airtight system 51 between the segments and the airtight system 52 between the flanges are sealed by a sealing strip 54 to achieve a sealed connection between the vacuum bag film or air bladder.

[0065] The vacuum bag 53 is used for sealing the outer surface. It needs to cover the split module 41, the front flange mechanism 2 and the rear flange structure 3, and is connected to the outer surface of the front flange mechanism 2 and the rear flange structure 3 through the sealing strip 54.

[0066] Expandable and contractible properties:

[0067] The expandable and contractible structure is achieved by adjusting the radial gap of the connection position using the reverse ejector bolt 43, and then using the locking bolt 42 to firmly fix the segmented module 41 to the front flange mechanism 2 and the rear flange structure 3. During the adjustment process, the positioning protrusions 21 and 31 guide the movement direction of the segmented module 41. The adjustment gap of the segmented module 41 needs to be adjusted synchronously by the front flange mechanism 2 and the rear flange structure 3. The single adjustment amount is within 1 mm, and the optimal total adjustment amount is within 1 mm.

[0068] In this invention, the expandable and contractible mold is mainly used for secondary adjustment of the mold diameter during the molding process of large sandwich structures. Large sandwich structures typically involve first curing the inner skin, followed by honeycomb assembly and outer skin molding. However, the coefficient of thermal expansion of the cured inner skin differs from that of the mold itself, resulting in gaps between the inner skin and the mold. The larger the component, the larger the gap, causing a misalignment and mispositioning between the mold rotation and the inner skin rotation. Therefore, it is necessary to adjust the radial position of the segmented modules based on the gap between the inner skin and the mold to eliminate the gap and avoid problems such as difficulty in positioning the inner skin and mold during honeycomb molding and outer skin molding.

[0069] Based on the above mold, the present invention also proposes a molding process for a large-diameter sandwich structure that can expand and shrink, the steps of which include:

[0070] (1) Install the molding mold;

[0071] The specific method for installing the molding die is as follows: install the front flange mechanism 2 and the rear flange structure 3 on the fixed position on the mandrel 1, and then install the segmented module assembly 4 and segmented module 41 one by one on the front flange mechanism 2 and the rear flange structure 3, and fix them with locking bolts 42; complete the fabrication of the segmented airtight system 51 and the flange airtight system 52, and complete the sealing connection between the two; thus obtaining the molding die.

[0072] (2) The inner skin is automatically laid and formed, and then wrapped and put into a hot autoclave for heating and pressure curing. The curing temperature is 120-140℃ and the curing pressure is 0.5-0.6MPa.

[0073] (3) Adjust the outer diameter of the mold, tighten the inner skin, and install the limit block at the same time;

[0074] (4) Lay the adhesive film on the inner skin and install the honeycomb on the adhesive film;

[0075] (5) Lay the adhesive film on the honeycomb, then wrap the first layer of fabric strip by winding, and then lay and wrap the outer skin;

[0076] (6) After coating, it is placed in a hot autoclave for heating and pressurization curing. The curing temperature is 120-140℃ and the curing pressure is 0.2-0.3MPa.

[0077] (7) After curing, the mold is removed to obtain a sandwich structure composite material shell.

[0078] The specific method for removing the mold is as follows:

[0079] The first step is to remove the outer vacuum bag 53, etc.;

[0080] The second step is to loosen the connection between the front flange mechanism 2 and the rear flange structure 3 and the mandrel 1, and then remove the mandrel 1.

[0081] The third step is for a person to manually enter the molding mold and remove the airtight system;

[0082] Step 4: Remove the front flange mechanism 2;

[0083] Step 5: Begin removing the segmented module component 4 one by one from inside the product.

[0084] Step 6: Move the product away from the rear flange mechanism 3. At this point, the mold removal is complete. Clean the product surface to obtain a large-diameter sandwich structure component.

[0085] For the manufacturing of composite material main load-bearing structural sections with a diameter of φ5m, controlling the weight of the molding die is one of the manufacturing challenges. The integral mold presents numerous obstacles in storage, transportation, assembly, and demolding. Furthermore, the gaps caused by the expansion difference between the inner and outer skins, formed on the same mold, are a significant manufacturing challenge. Compared to metal mold solutions, composite material mold solutions address issues such as matching the expansion coefficients of large components, minimizing mold weight, and controlling manufacturing costs. However, the reduced expansion coefficient of composite material molds also causes demolding and deformation problems after the sandwich structure shell has solidified. Modular mold design can solve the overall mold deformation problem by increasing the stiffness of smaller structural units, while also avoiding the difficulty of demolding integral molds. Therefore, it is necessary to develop breakthroughs in the modular composite material assembly mold splicing structure and sealing methods, establish a modular composite material assembly mold splicing structure, disassembly and assembly methods suitable for large sandwich structures, and formulate corresponding mold design and manufacturing specifications.

[0086] This invention proposes a design and manufacturing method for a large-diameter sandwich structure mold that can expand and contract, solving the technological challenge of continuous high-quality molding of the inner and outer skins of ultra-large diameter rotary sandwich structures (5m and above). This lays the technological foundation for the lightweight manufacturing of large composite rotary structures. The project results can be directly applied to 5m-class interstage sections and satellite supports, and can also be extended to the manufacturing of 10m-class composite sandwich structures, which is of great significance for the lightweighting of next-generation aerospace launch vehicles.

[0087] Example 1: Composite material cylindrical sandwich structure

[0088] The composite cylindrical sandwich structure has dimensions of φ5000mm×2000mm, with an inner skin thickness of 2mm and a ply of [45 / 02 / -45 / 90 / 0]s; and an outer skin thickness of 2.2mm and a ply of [carbon cloth /

[0089] (45 / 02 / -45 / 90 / 0)s]; The sandwich structure is aluminum honeycomb with a honeycomb height of 30mm; The skin is made of T800 / epoxy composite prepreg.

[0090] Design a large-diameter sandwich structure mold that can expand and contract according to the product size, such as Figure 1 As shown, the mold includes a mandrel 1, a front flange mechanism 2, a rear flange structure 3, a segmented module assembly 4, and an airtight system 5;

[0091] The segmented module assembly 4 is fixedly connected to the mandrel 1 through the front flange mechanism 2 and the rear flange structure 3. The segmented module assembly 4 is composed of 8 segmented modules 41 fixedly connected through the front flange mechanism 2 and the rear flange structure 3 to form the main structure of the mold surface, which is used for the surface of product molding. At the same time, the gaps between adjacent modules of each segmented module 41 are sealed by the segmented airtight system 51.

[0092] The front flange mechanism 2 and the rear flange structure 3 are fixed to the segmented module 41 by locking bolts 42. At the same time, the front flange mechanism 2 and the rear flange structure 3 determine the positioning of the segmented module 41 on it by positioning protrusions 21 and 31. A reverse ejection bolt 43 is provided to adjust the radial clearance of the connection position, and the connection area is sealed by the flange airtight system 52.

[0093] The segmented module 41 adopts an integral grid skin structure. The grid structure ensures the overall rigidity of the segmented module, and the skin is required to ensure overall airtightness and ensure the closure of the mold airtight system 5.

[0094] The segmented module 41 is provided with limiting blocks 6 on both sides of the axial edge region for limiting the honeycomb assembly and extending the outer skin.

[0095] The mold has a diameter of 5000mm, and its diameter can be adjusted within a range of 2mm; the mold sandwich structure is formed by continuous molding of inner and outer skins, that is, both inner and outer skins maintain continuous fiber layup and have no splicing areas.

[0096] The front flange mechanism 2 and the rear flange structure 3 are required to control their radial thermal expansion deformation. The radial expansion is generally 1 mm. The front flange mechanism 2 and the rear flange structure 3 are made of Invar alloy steel.

[0097] The segmented module 41 should be made of a material with a coefficient of thermal expansion similar to or the same as that of the front flange mechanism 2 and the rear flange structure 3. In this embodiment, Invar alloy steel is used.

[0098] The airtight system 5 includes a segmental airtight system 51, a flange airtight system 52, and a vacuum bag 53.

[0099] When the gaps between adjacent segment modules 41 are sealed by the segment airtight system 51, a vacuum bag film is used to cover the gaps between the segment modules 41 and is connected to the inner surface of the segment module 41 by a sealing strip 54.

[0100] When the gap between the front flange mechanism 2 and the rear flange structure 3 and the segmented module 41 is sealed by the flange airtight system 52, a vacuum bag film is used to cover the gap between the front flange mechanism 2 and the rear flange structure 3 and the segmented module 41, and is connected to the inner surface of the front flange mechanism 2, the rear flange structure 3 and the segmented module 41 by the sealing strip 54.

[0101] The airtight system 51 between the segments and the airtight system 52 between the flanges are sealed by a sealing strip 54 to achieve a sealed connection between the vacuum bag film and the two.

[0102] The vacuum bag 53 is used for sealing the outer surface. It needs to cover the split module 41, the front flange mechanism 2 and the rear flange structure 3, and is connected to the outer surface of the front flange mechanism 2 and the rear flange structure 3 through the sealing strip 54.

[0103] The expandable and contractible mechanism adjusts the radial clearance of the connection position by using the reverse ejector bolt 43, and then uses the locking bolt 42 to firmly fix the segmented module 41 to the front flange mechanism 2 and the rear flange structure 3. During the adjustment process, the positioning protrusions 21 and 31 guide the movement direction of the segmented module 41. The adjustment of the clearance of the segmented module 41 during the adjustment process requires the front flange mechanism 2 and the rear flange structure 3 to be carried out synchronously. The single adjustment amount is 0.5mm, and it is adjusted in 1-2 times to reach the position.

[0104] The expandable and contractible mold is mainly used for secondary adjustment of the mold diameter during the molding process of large sandwich structures. In large sandwich structures, the inner skin is typically cured first, followed by honeycomb assembly and outer skin molding. However, the coefficient of thermal expansion of the cured inner skin differs from that of the mold itself, resulting in gaps between the inner skin and the mold. The larger the component, the larger the gap, causing a misalignment and mispositioning between the mold rotation and the inner skin rotation. Therefore, it is necessary to adjust the radial position of the segmented modules based on the gap between the inner skin and the mold to eliminate the gap and avoid problems such as difficulty in positioning the inner skin and mold during honeycomb molding and outer skin molding.

[0105] A process for forming a large-diameter sandwich structure that can expand and shrink includes the following steps:

[0106] (1) Install the molding mold;

[0107] (2) The inner skin is automatically laid and formed, and then wrapped and put into a hot autoclave for heating and pressure curing. The curing temperature is 140℃ and the curing pressure is 0.6MPa.

[0108] (3) Adjust the outer diameter of the mold, tighten the inner skin, and install the limit block at the same time;

[0109] (4) Lay J47 medium-temperature adhesive film on the inner skin and install the honeycomb on the J47 medium-temperature adhesive film;

[0110] (5) Lay J47 medium-temperature adhesive film on the honeycomb, then complete the winding of the first layer of fabric strip by winding, and then lay and wind the outer skin;

[0111] (6) After coating, it is placed in a hot autoclave for heating and pressurization curing. The curing temperature is 140℃ and the curing pressure is 0.3MPa.

[0112] (7) After curing, the mold is removed to obtain a sandwich structure composite material shell.

[0113] In step 1 of the molding process for a large-diameter sandwich structure that can expand and contract, the specific method for installing the molding mold is as follows: the front flange mechanism 2 and the rear flange structure 3 are installed at fixed positions on the mandrel 1, and then the segmented module assembly 4 and segmented modules 41 are installed one by one on the front flange mechanism 2 and the rear flange structure 3, and fixed with locking bolts 42; the inter-segment airtight system 51 and the flange airtight system 52 are made, and the sealing connection between the two is completed; the molding mold is obtained.

[0114] In step 7 of the molding process for a large-diameter sandwich structure that can expand and shrink, the specific method for removing the mold is as follows:

[0115] The first step is to remove the outer vacuum bag 53, etc.;

[0116] The second step is to loosen the connection between the front flange mechanism 2 and the rear flange structure 3 and the mandrel 1, and then remove the mandrel 1.

[0117] The third step is for a person to manually enter the molding mold and remove the airtight system;

[0118] Step 4: Remove the front flange mechanism 2;

[0119] Step 5: Begin removing the segmented module component 4 one by one from inside the product.

[0120] Step 6: Move the product away from the rear flange mechanism 3. At this point, the mold removal is complete. Clean the product surface to obtain a large-diameter sandwich structure component.

[0121] The above steps yield a composite cylindrical sandwich structure and its molding die. After molding, its internal quality was subjected to infrared non-destructive testing, and no debonding defects were found.

[0122] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A large-diameter sandwich structure mold that can expand and contract, characterized in that, include: Mandrel (1), front flange mechanism (2), rear flange structure (3), segmented module assembly (4), and airtight system (5); The segmented module assembly (4) is fixedly connected to the mandrel (1) through the front flange mechanism (2) and the rear flange structure (3); the segmented module assembly (4) is a large-diameter cylindrical structure formed by eight segmented modules (41) fixedly connected through the front flange mechanism (2) and the rear flange structure (3), which is the main structure of the mold surface and is used for product molding. At the same time, the gaps between adjacent modules of each segmented module (41) are sealed by the airtight system (5); The front flange mechanism (2) and the rear flange structure (3) are fixed to the segmented module (41) by locking bolts (42). At the same time, the front flange mechanism (2) and the rear flange structure (3) determine the positioning of the segmented module (41) by the front positioning protrusion (21) and the rear positioning protrusion (31) respectively. Reverse ejection bolts (43) are set on the edges of the front flange mechanism (2) and the rear flange structure (3) to adjust the radial clearance of the connection position of the segmented module (41) and to seal the connection area by the mold airtight system (5). The segmented module assembly (4) adopts an integral grid skin structure. The grid structure ensures the overall rigidity of the segmented module, and the skin ensures overall airtightness, thus ensuring the closure of the mold airtight system (5). The segmented module assembly (4) has limiting blocks (6) on both sides of its axial edge region for limiting the honeycomb assembly and extending the outer skin.

2. The expandable and contractible large-diameter sandwich structure mold according to claim 1, characterized in that: The mold diameter is the same as the diameter of the segmented module component (4), ranging from 4m to 10m.

3. The expandable and contractible large-diameter sandwich structure mold according to claim 1, characterized in that: The front flange mechanism (2) and the rear flange structure (3) are required to control their radial thermal expansion deformation, with the radial expansion not exceeding 3 mm.

4. The expandable and contractible large-diameter sandwich structure mold according to claim 3, characterized in that: The front flange mechanism (2), the rear flange structure (3), and the split module (41) are made of the same material, Invar alloy steel.

5. The expandable and contractible large-diameter sandwich structure mold according to claim 1, characterized in that: The airtight system (5) includes a segment airtight system (51), a flange airtight system (52), and a vacuum bag (53); When the gaps between adjacent segment modules (41) are sealed by the segment airtight system (51), a vacuum bag or airbag is used to cover the gaps between the segment modules (41), and a sealing strip (54) is used to connect with the inner surface of the segment module (41). When the gap between the front flange mechanism (2) and the rear flange structure (3) and the segmented module (41) is sealed by the flange airtight system (52), a vacuum bag or airbag is used to cover the gap between the front flange mechanism (2) and the rear flange structure (3) and the segmented module (41), and the sealing strip (54) is used to connect with the inner surface of the front flange mechanism (2), the rear flange structure (3), and the segmented module (41); The inter-segment airtight system (51) and the flange airtight system (52) are sealed by a sealing strip (54) to achieve a sealed connection between the two vacuum bag membranes or air bladders. The vacuum bag (53) is used for sealing the outer surface, which needs to cover the split module (41), the front flange mechanism (2) and the rear flange structure (3), and is connected to the outer surface of the front flange mechanism (2) and the rear flange structure (3) by a sealing strip (54).

6. The expandable and contractible large-diameter sandwich structure mold according to claim 1, characterized in that: The expandable and contractible structure is achieved by adjusting the radial gap of the connection position using the reverse ejector bolt (43), and then using the locking bolt (42) to firmly fix the segmented module (41) on the front flange mechanism (2) and the rear flange structure (3). During the adjustment process, the front positioning protrusion (21) and the rear positioning protrusion (31) guide the movement direction of the segmented module (41).

7. The expandable and contractible large-diameter sandwich structure mold according to claim 6, characterized in that: During the radial clearance adjustment process, the split module (41) needs to adjust the clearance simultaneously with the front flange mechanism (2) and the rear flange structure (3). The single adjustment amount is within 1 mm, and the total adjustment amount is within 1 mm.

8. The expandable and contractible large-diameter sandwich structure mold according to claim 6, characterized in that: The expandable and contractible mold is used for secondary adjustment of the mold diameter during the molding process of large sandwich structures. The inner skin of large sandwich structures is first cured, and then the honeycomb assembly and outer skin are formed. However, after the inner skin is cured, its coefficient of thermal expansion is different from that of the mold itself, resulting in a gap between the inner skin and the mold. The larger the component size, the larger the gap. It is necessary to adjust the radial position of the segmented module according to the gap between the inner skin and the mold to eliminate the gap between the inner skin and the mold and avoid the inner skin and the mold sliding and being difficult to position during the honeycomb molding and outer skin forming process.

9. A method for forming a large-diameter sandwich structure using an expandable and contractible large-diameter sandwich structure mold as described in any one of claims 1-8, characterized in that, include: (1) Install large-diameter sandwich structure molds; (2) The inner skin is automatically laid and formed, and after being wrapped, it is put into a hot autoclave for heating and pressure curing. The curing temperature is 120-140℃ and the curing pressure is 0.5-0.6MPa. (3) Adjust the outer diameter of the large-diameter sandwich structure mold, tighten the inner skin, and install the limit block at the same time; (4) Lay a film on the inner skin and install the honeycomb on the film; (5) Lay the adhesive film on the honeycomb, then wrap the first layer of fabric strip by winding, and then lay and wrap the outer skin. (6) After coating, it is placed in a hot autoclave for heating and pressurization curing. The curing temperature is 120-140℃ and the curing pressure is 0.2-0.3MPa. (7) After curing, the mold is removed to obtain a large-diameter sandwich composite material shell.

10. The forming process method for a large-diameter sandwich structure according to claim 9, characterized in that: The specific method for installing the molding mold is as follows: the front flange mechanism (2) and the rear flange structure (3) are installed at fixed positions on the mandrel (1), and then the segment modules (41) of the segment module assembly (4) are installed one by one on the front flange mechanism (2) and the rear flange structure (3), and fixed with locking bolts (42); the segment airtight system (51) and the flange airtight system (52) are made, and the sealing connection between the two is completed; the molding mold is obtained.

11. The forming process method for a large-diameter sandwich structure according to claim 9, characterized in that: The specific method for dismantling the mold is as follows: First step, remove the outer vacuum bag (53); The second step is to loosen the connection between the front flange mechanism (2) and the rear flange structure (3) and the mandrel (1), and remove the mandrel (1); The third step involves manually entering the molding mold to remove the airtight system. Step 4: Remove the front flange mechanism (2); Fifth step, begin disassembling the segmented module assembly (4), and remove the segmented modules (41) one by one from inside the product; Step 6: Move the product away from the rear flange mechanism (3). At this point, the mold is completely removed. Clean the surface of the product to obtain a large-diameter sandwich structure.

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