Multi-constraint combined net-size heatproof layer high-quality assembly method

Abstract

The invention discloses a multi-constraint combined net-size heat-proof layer high-quality assembly method. The method comprises the following steps: carrying out net-size forming on a heat-proof layer made of a heat-proof material; trying to sleeve a force bearing shell; model selection and blanking of the flexible heat insulation layer; performing surface treatment; a flexible heat insulation layer is bonded; the flexible heat insulation layer is partitioned; assembling the composite material heat-proof layer; assembling, adjusting and maintaining the shape; and pressurizing, curing and assembling. The composite material heat-proof layer is formed in a net size mode, the procedure that the outer surface is machined after sleeving is completed is omitted, and the development and production efficiency is improved. Based on the characteristics of a segmented combined type assembly structure, the problem of controlling gaps and aerodynamic shapes in the assembly process of the heat-proof layer is solved by designing and adjusting a shape maintaining tool. The flexible heat insulation layer is adopted as a buffer layer, the expansion stress of the shell is reduced, the problem of heat matching after the heat protection section is heated and expanded is solved, gaps are reserved in blocks of the flexible heat insulation layer, it is guaranteed that assembling glue liquid flows sufficiently, assembling defects are avoided, the assembling quality and reliability are improved, and finally high-quality and low-cost assembling is achieved.

Description

Technical Field

[0001] This invention relates to a high-quality assembly method for a multi-constraint combined net-size heat-resistant layer, belonging to the field of composite material heat-resistant layer assembly. Background Technology

[0002] Composite material heat shields are a crucial component of aircraft heat shields, undertaking both aerodynamic and thermal protection functions. Traditional heat shields utilize a single, integrated structure for the outer surface, assembled with an inner load-bearing shell using adhesives. This method is simple and involves minimal assembly constraints. However, traditional composite material heat shields employ a semi-raw structure with pre-existing allowances. Sufficient dimensional margins are left during the initial molding process, followed by machining to achieve the designed aerodynamic shape after assembly. This machining process is time-consuming and significantly impacts product development and production schedules. Furthermore, for large-scale heat shields with an axial length exceeding 2000mm, a direct double-layer assembly can lead to significant differences in the thermal expansion coefficients of the inner and outer layers, resulting in deformation mismatches between hot and cold environments. This can cause structural cracking and failure under prolonged flight conditions. To improve production efficiency and reduce costs, the new generation of heat shields utilizes a modular, irregularly shaped heat shield structure, with the outer composite material heat shield being molded to net dimensions. The composite material molding die is designed according to the aerodynamic shape of the final product. The final aerodynamic shape is formed during the molding of the composite material heat-insulating layer, followed by assembly. The outer surface is not machined after assembly. However, this method currently still has problems with gaps in the assembly process and low quality control of the aerodynamic shape. Summary of the Invention

[0003] The technical problem solved by the present invention is to overcome the shortcomings of the prior art and provide a high-precision assembly method for a non-circular, multi-constraint, composite material heat-resistant layer with net dimensions, so as to solve the problems of uncontrollable aerodynamic shape, incomplete assembly, or excessive assembly gaps during the heat-resistant layer assembly process.

[0004] The technical solution of this invention is:

[0005] A high-quality assembly method for a multi-constraint combined net-size heat-insulating layer includes the following steps:

[0006] Step 1: Perform net-dimensional molding of the multi-constraint combined net-dimensional heat insulation layer;

[0007] The multi-constraint combined net-size heat protection layer is a combined structure, which is spliced ​​together by a first composite material heat protection layer and a second composite material heat protection layer; the small end of the second composite material heat protection layer is formed with the large end of the first composite material heat protection layer in terms of net size, and the end face dimensions of the small end of the second composite material heat protection layer and the large end of the first composite material heat protection layer are consistent and fit together; the large end of the second composite material heat protection layer and the small end of the first composite material heat protection layer are reserved with end face allowance;

[0008] Step 2: Test fit the load-bearing shell;

[0009] Place the load-bearing shell vertically, and fit the second composite heat-insulating layer from the small end to the large end of the load-bearing shell onto the outer surface of the load-bearing shell. Measure the circumferential gap A between the second composite heat-insulating layer and the outer surface of the load-bearing shell.

[0010] Next, the first composite heat-insulating layer is fitted and assembled from the small end to the large end of the load-bearing shell onto the outer surface of the load-bearing shell, and the large end of the first composite heat-insulating layer is mated with the small end of the second composite heat-insulating layer. The circumferential gap B between the first composite heat-insulating layer and the outer surface of the load-bearing shell is measured.

[0011] Step 3: Selection and cutting of flexible insulation layer;

[0012] Based on the circumferential gaps A and B, select the appropriate thickness of the flexible insulation layer. According to the shape and structure of the load-bearing shell, the flexible insulation layer is attached to the outer surface of the load-bearing shell and cut into different blocks.

[0013] Step 4: Surface Treatment

[0014] The outer surface of the load-bearing shell and the inner surface of the composite heat-insulating layer are sandblasted.

[0015] Step 5: Bond the flexible insulation layer;

[0016] The pre-cut flexible thermal insulation layer is bonded to the outer surface of the load-bearing shell using adhesive.

[0017] Step Six: Divide the flexible insulation layer into sections;

[0018] The flexible insulation layer is segmented. Using a utility knife, the large flexible layer is divided into smaller pieces approximately 200mm wide and 400mm high. Excess flexible insulation layer is trimmed away, leaving gaps of 2-3mm between the segments. The natural gaps formed by splicing adjacent different flexible insulation segments are filled with fitting adhesive after assembly. After curing, this adhesive forms a mesh-like support between the insulation layer and the load-bearing shell. The gaps between the segments are used as pre-reserved channels for cable filling and are also insulated and protected.

[0019] Step 7: Assemble the second composite material heat-insulating layer;

[0020] The load-bearing shell is placed vertically. Adhesive is applied to the outer surface of the load-bearing shell with the second composite heat-insulating layer and the flexible heat-insulating layer. The second composite heat-insulating layer is fitted and assembled from the small end to the large end of the load-bearing shell to the outer surface of the load-bearing shell with the flexible heat-insulating layer, until the large end of the second composite heat-insulating layer protrudes to the reserved allowance.

[0021] Step 8: Assemble the first composite material heat-insulating layer;

[0022] The first composite heat-insulating layer is applied with adhesive, and the composite heat-insulating layer 1 is fitted and assembled from the small end to the large end of the load-bearing shell onto the outer surface of the load-bearing shell, so that the gap between the large end of the first composite heat-insulating layer and the small end of the second composite heat-insulating layer is less than 0.5mm, and the first composite heat-insulating layer protrudes from the small end of the load-bearing shell to the reserved allowance.

[0023] Step 9: Assemble and adjust the shaping fixture;

[0024] A shaping tool is assembled on the outer surface of the butt joint between the small end of the second composite heat protection layer and the first composite heat protection layer. The shaping tool is adjusted, and pressure is applied to the outer surface to correct the shape, so as to prevent the small end of the second composite heat protection layer from rotating relative to the first composite heat protection layer in the circumferential direction and to maintain the final aerodynamic shape after the sleeve assembly.

[0025] Step 10: Pressure curing and assembly;

[0026] Gradually apply pressure to the small end of the first composite heat-insulating layer. The gap between the small end of the first composite heat-insulating layer and the first composite heat-insulating layer should not exceed 0.50mm. During the pressure curing process, the glass cloth is squeezed into the load-bearing shell by the assembly adhesive, compressing the pre-embedded cable. The cable is pulled out while the assembly adhesive is in a semi-cured state. The pressure is kept constant until the adhesive is cured, and the assembly is completed.

[0027] Furthermore, the aforementioned multi-constraint combined net-size heat protection layer is a low-density composite material heat protection layer with the final aerodynamic shape as designed. During molding, the axial length of the large end of the first composite material heat protection layer and the small end of the second composite material heat protection layer has no allowance and is in net size state. The axial length of the end face of the small end of the first composite material heat protection layer and the large end of the second composite material heat protection layer has an allowance, and the outer surface does not need to be machined again after assembly.

[0028] Furthermore, the aforementioned multiple constraints refer to the constraint requirements on the assembly joint gaps of the composite material heat-insulating layer and the gaps between the composite material heat-insulating layer and the load-bearing shell structure.

[0029] Furthermore, the second composite heat-insulating layer has a 40mm margin in the axial length direction at the large end, and the first composite heat-insulating layer has a 50mm margin in the axial length direction at the small end.

[0030] Furthermore, the circumferential gap between the second composite heat-insulating layer and the outer surface of the load-bearing shell, and the circumferential gap between the first composite heat-insulating layer and the outer surface of the load-bearing shell are both 2±0.5mm.

[0031] Furthermore, the flexible insulation layer is made of high-temperature resistant polyurethane foam material with a thickness ranging from 2±0.5mm.

[0032] Furthermore, the pre-cut block-shaped flexible insulation layer is bonded to the outer surface of the load-bearing shell using a high-temperature resistant silicone rubber adhesive, specifically as follows:

[0033] High-temperature resistant silicone rubber adhesive is evenly applied to the surface of the block-shaped flexible insulation layer and the surface of the load-bearing shell. The block-shaped flexible insulation layer is then pasted along the generatrix and circumferential direction of the load-bearing shell to cover the surface of the load-bearing shell. During pasting, the longitudinal seams are aligned, and the longitudinal joints between the blocks are trimmed to naturally leave air channels, while the transverse joints are ensured to be in close contact. After pasting, a vacuum bag is placed to completely cover the load-bearing shell and the flexible insulation layer. Vacuum is drawn and pressurized at a pressure of 0.05-0.1 MPa. After curing for 24 hours, the heat protection layer is assembled. The longitudinal seam refers to the splicing gap along the generatrix direction of the shell.

[0034] Furthermore, the inner surfaces of the first composite heat-insulating layer and the second composite heat-insulating layer are coated with high-temperature resistant silicone rubber adhesive before being assembled onto the outer surface of the load-bearing shell, which has been pasted with a flexible heat-insulating layer. The curing time is 24 hours.

[0035] Furthermore, the shaped tooling consists of two semi-annular shaped arc plates (11). The inner surface shape of the shaped arc plate (11) matches the shape of the joint section between the second composite heat-insulating layer and the first composite heat-insulating layer. The adjusting screws (12) are evenly distributed on the shaped arc plate (11) and are divided into upper and lower rows. The end face of the upper row of adjusting screws matches the shape of the contact part of the first composite heat-insulating layer, and the end face of the lower row of adjusting screws matches the shape of the contact part of the second composite heat-insulating layer. The two semi-annular shaped arc plates (11) are connected and fixed into a ring whole by locking screws (13).

[0036] During assembly, install the adjusting tooling, and apply pressure to the outer surface of the upper and lower composite heat protection layers by adjusting the screw to correct the shape, so as to prevent the small end of the second composite heat protection layer from rotating relative to the large end of the first composite heat protection layer in the circumferential direction, and maintain the final aerodynamic shape after the sleeve assembly.

[0037] Furthermore, the pressure applied to the small end of the first composite material heat-insulating layer is controlled at 10-20 kN.

[0038] The advantages of this invention compared to the prior art are:

[0039] (1) The assembly method of the present invention can solve the problems of uncontrollable aerodynamic shape, incomplete assembly, or excessive assembly gaps during the assembly process of the heat-insulating layer. This process method can achieve high-precision assembly of irregularly shaped multi-constraint combined composite material heat-insulating layers, saving subsequent reprocessing steps after assembly and reducing costs.

[0040] (2) A flexible heat insulation layer is added between the composite heat insulation layer and the load-bearing shell. The gap between the composite heat insulation layer and the load-bearing shell is measured by trial assembly. The thickness of the flexible heat insulation layer is selected and the flexible heat insulation layer is bonded. This method can solve the problem of uneven gap and adhesive layer thickness between the composite heat insulation layer and the load-bearing shell.

[0041] (3) By reserving splicing gaps in the flexible insulation layer, the splicing adhesive can flow fully during the assembly process, ensuring that the adhesive is fully and evenly distributed on the surface of the heat insulation layer and the load-bearing shell. By dividing the flexible insulation layer into blocks, the problem of air pockets inside the flexible insulation layer during assembly compression is solved, thus avoiding debonding defects and improving assembly strength.

[0042] (4) The small end of the composite heat protection layer 2 and the large end of the composite heat protection layer 1 are formed to the net size. The large end of the composite heat protection layer 2 and the small end of the composite heat protection layer 1 are reserved with end face allowance. When the two combined heat protection layers are assembled, the gap between them is controlled within 0.5mm by applying pressure.

[0043] (5) By designing a shape-forming tooling at the mating surface of composite heat-insulating layer 1 and composite heat-insulating layer 2, and by adjusting the pressure of the shape-forming tooling, the final pneumatic shape of the composite heat-insulating layer after assembly can be achieved, saving subsequent shape processing steps and reducing production costs. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of a combined net-size heat insulation layer structure;

[0045] Figure 2 A high-quality assembly process for multi-constraint combined net-size heat insulation layers;

[0046] Figure 3 This is a schematic diagram of filling the gaps between blocks;

[0047] Figure 4 This is a flowchart of the assembly method of the present invention. Detailed Implementation

[0048] The specific embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0049] This invention aims to achieve high-precision assembly of the irregularly shaped, multi-constrained, composite composite heat-resistant layer with net dimensions. Based on the characteristics of the composite assembly structure, it solves the problems of gap and aerodynamic shape control during the heat-resistant layer assembly process, achieving high-quality, low-cost assembly. To address the thermal compatibility issue, a flexible thermal insulation layer is added as a buffer layer between the circumferential load-bearing shell and the heat-resistant layer. When the load-bearing shell expands due to heat, the load-bearing shell and the heat-resistant layer compress the low-compression buffer layer, reducing the expansion stress of the shell. Furthermore, the flexible thermal insulation layer has pre-reserved splicing gaps and is segmented to ensure sufficient flow of the assembly adhesive, avoid assembly defects, and improve assembly quality and reliability.

[0050] In this invention, the multi-constraint composite net-size heat protection layer is a low-density composite material with the final designed aerodynamic shape. It is achieved through a net-size molding process. During molding, the axial length of the large end of composite heat protection layer 1 (i.e., the first composite heat protection layer) and the small end of composite heat protection layer 2 (i.e., the second composite heat protection layer) has no allowance, resulting in a net-size state. The axial length of the small end of composite heat protection layer 1 and the large end of composite heat protection layer 2 has allowance, so the outer surface does not require further machining after assembly. The "multi-constraint" refers to various constraint requirements, such as gaps in the assembly joints of the composite heat protection layers and gaps between the composite heat protection layer and the load-bearing shell structure. The "composite" refers to the composite heat protection layer adopting a segmented composite structure, consisting of composite heat protection layer 1 and composite heat protection layer 2, such as... Figure 1 As shown in the figure, the outer side of the load-bearing shell is a flexible heat insulation layer, and the outer side of the flexible heat insulation layer is a composite material heat protection layer. The composite material heat protection layer is divided into two parts, namely composite material heat protection layer 1 and composite material heat protection layer 2.

[0051] This invention proposes a high-quality assembly method for a multi-constraint combined net-size heat-insulating layer, comprising ten steps:

[0052] Step 1: Molding the heat-insulating material and heat-insulating layer to net dimensions;

[0053] Step 2: Test install the load-bearing shell;

[0054] Step 3: Selection and cutting of flexible insulation layer;

[0055] Step 4: Surface treatment.

[0056] Step 5: Bond the flexible insulation layer;

[0057] Step Six: Divide the flexible insulation layer into sections.

[0058] Step 7: Assemble the composite material heat-insulating layer 2;

[0059] Step 8: Assemble the composite material heat-insulating layer 1;

[0060] Step 9: Assemble and adjust the shaping fixture.

[0061] Step 10: Apply pressure for curing and assemble.

[0062] This invention utilizes a composite material heat-resistant layer with net-size molding, eliminating the need for machining the outer surface after assembly and improving research and production efficiency. Based on the segmented modular assembly structure, the design and adjustment of shaping tooling solve the problems of gap and aerodynamic shape control during the heat-resistant layer assembly process.

[0063] Specifically, the assembly method flow of this invention is as follows: Figure 4 As shown, the specific steps are as follows:

[0064] Step 1: Molding the net dimensions of the heat-insulating material heat-insulating layer

[0065] The small end of composite heat-insulating layer 2 is formed to the net dimensions of the large end of composite heat-insulating layer 1. The end face dimensions of the small end of composite heat-insulating layer 2 and the large end of composite heat-insulating layer 1 are consistent and they fit together. A allowance is reserved on the end face of both the large end of composite heat-insulating layer 2 and the small end of composite heat-insulating layer 1.

[0066] Step 2: Test install the load-bearing shell

[0067] The load-bearing shell is placed vertically. The composite heat-insulating layer 2 is fitted onto the outer surface of the load-bearing shell from the small end to the large end. The circumferential gap A between the composite heat-insulating layer 2 and the outer surface of the load-bearing shell is measured. Then, the composite heat-insulating layer 1 is fitted onto the outer surface of the load-bearing shell from the small end to the large end, and the large end of the composite heat-insulating layer 1 is made to contact the small end of the composite heat-insulating layer 2. The circumferential gap B between the composite heat-insulating layer 1 and the outer surface of the load-bearing shell is measured.

[0068] Step 3: Selection and cutting of flexible insulation layer

[0069] Based on the circumferential gaps A and B, select the appropriate thickness of the flexible insulation layer. The flexible insulation layer is made of high-temperature resistant polyurethane foam material. According to the shape and structure of the load-bearing shell, the flexible insulation layer is attached to the outer surface of the load-bearing shell and cut into blocks with a cutting size of 400mm×400mm.

[0070] Step 4: Surface Treatment

[0071] To address the potential assembly delamination defects caused by the smooth outer surfaces of the load-bearing shell and the composite heat-insulating layer (the outer surface of the load-bearing shell is smooth due to the release agent, and the inner surface of the composite heat-insulating layer is coated with a waterproof adhesive layer), the outer surface of the load-bearing shell and the inner surface of the composite heat-insulating layer are sandblasted with a sand particle size of 20-40 and a sandblasting pressure of 0.2-0.4 MPa.

[0072] Step 5: Bond the flexible insulation layer

[0073] The cut flexible insulation layer blocks are bonded to the outer surface of the load-bearing shell using adhesive.

[0074] Prepare a high-temperature resistant silicone rubber adhesive. Apply the adhesive evenly to the surface of the flexible insulation layer and the surface of the load-bearing shell. Adhere the adhesive along the generatrix and circumferential direction of the load-bearing shell to completely cover the shell surface. When adhering, ensure that the longitudinal seams of two adjacent rows of flexible insulation layers along the generatrix are aligned (the longitudinal seam refers to the splicing gap along the generatrix of the shell). Adjacent different block-shaped flexible insulation layers are spliced ​​to form a longitudinal splicing gap with a width of about 2-3 mm. After trimming, this gap serves as a channel for adhesive flow. Ensure that the transverse butt joints are tight. Then, use a vacuum bag to completely cover the shell and the flexible insulation layer, apply vacuum and pressure at a pressure of 0.05-0.1 MPa, and cure for 24 hours before assembling the heat protection layer.

[0075] Step Six: Segmenting the Flexible Insulation Layer

[0076] To address the issues of sufficient adhesive flow and air release during the socket assembly process and prevent delamination defects, the flexible insulation layer is segmented. A utility knife is used to cut the large flexible layer into smaller pieces approximately 200mm wide x 400mm high, and excess flexible insulation layer is trimmed away. The gaps between the segments are 2-3mm wide. The natural gaps formed by splicing adjacent different flexible insulation blocks are filled with the socket assembly adhesive after assembly. After curing, this adhesive forms a mesh-like support between the insulation layer and the load-bearing shell. The gaps between the segmented flexible insulation layers serve as reserved channels for cable filling and are also insulated and protected. Figure 3 As shown. Use a cable with a diameter of approximately Φ2mm to fill the gaps between the sections, leaving 10cm at both ends for easy removal later; use a fiberglass cloth with a width of approximately 20mm to isolate and protect the exhaust channel to prevent the fitting adhesive from flowing into the channel during fitting assembly.

[0077] This invention employs a flexible heat insulation layer as a buffer layer between the circumferential load-bearing shell and the heat-insulating layer to reduce the shell expansion stress, solve the thermal compatibility problem after the heat-insulating section expands due to heat, and reserve gaps in the flexible heat insulation layer to ensure sufficient flow of the assembly adhesive, avoid assembly defects, improve assembly quality and reliability, and ultimately achieve high-quality, low-cost assembly.

[0078] Step 7: Assemble the composite material heat-insulating layer 2

[0079] The load-bearing shell is placed vertically. Adhesive is applied to the outer surface of the load-bearing shell with the composite heat-insulating layer 2 and the flexible heat-insulating layer. The composite heat-insulating layer 2 is fitted and assembled from the small end to the large end of the load-bearing shell onto the outer surface of the load-bearing shell with the flexible heat-insulating layer, until the large end of the composite heat-insulating layer 2 protrudes to the reserved allowance.

[0080] Step 8: Assemble the composite material heat-insulating layer 1

[0081] Apply adhesive to the composite heat-insulating layer 1 and fit it onto the outer surface of the load-bearing shell from the small end to the large end, so that the gap between the large end of the composite heat-insulating layer 1 and the small end of the composite heat-insulating layer 2 is less than 0.5mm, and the composite heat-insulating layer 1 protrudes beyond the small end of the load-bearing shell to the reserved allowance.

[0082] Step 9: Assemble and adjust the shaping fixture

[0083] The small end of the composite heat protection layer 2 is fitted with a shaping tool on the outer surface of the butt joint of the composite heat protection layer 1. The shaping tool is adjusted, and pressure is applied to the outer surface to correct the shape, so as to prevent the small end of the composite heat protection layer 2 from rotating relative to the composite heat protection layer 1 in the circumferential direction and maintain the final aerodynamic shape after the fitting assembly.

[0084] A shape-fitting tool is assembled between the small end of composite heat-insulating layer 2 and the outer surface of the butt joint of composite heat-insulating layer 1. For example... Figure 2 As shown, the weft-shaped fixture consists of two semi-annular weft-shaped arc plates 11. The inner surface shape of the weft-shaped arc plate 11 matches the shape of the joint section between the second composite heat-insulating layer and the first composite heat-insulating layer. Adjusting screws 12 are evenly distributed on the weft-shaped arc plates 11 and are divided into upper and lower rows. The end face of the upper row of adjusting screws matches the shape of the contact part of the first composite heat-insulating layer, and the end face of the lower row of adjusting screws matches the shape of the contact part of the second composite heat-insulating layer. The two semi-annular weft-shaped arc plates 11 are connected and fixed into a ring shape by locking screws 13. During assembly, the weft-shaped fixture is installed, and the adjusting screws apply pressure to the outer surfaces of the upper and lower composite materials to correct the shape, preventing the small end of the composite heat-insulating layer 2 from rotating relative to the composite heat-insulating layer 1 in the circumferential direction, thus maintaining the final aerodynamic shape after the fitting assembly.

[0085] Step 10: Pressure curing and assembly

[0086] Gradually apply pressure to the small end of the composite heat-insulating layer 1 (the pressure at the small end is controlled at 10-20kN). The gap between the small ends of the upper and lower composite heat-insulating layers 2 and the composite heat-insulating layer 1 should not exceed 0.50mm. When the two products are pressed and cured, the glass cloth is squeezed into the load-bearing shell under the pressure of the assembly adhesive, compressing the pre-embedded cable. When the assembly adhesive is in a semi-cured state (curing for 3-6 hours), pull it out and keep the pressure constant until the adhesive is cured to complete the assembly.

[0087] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A high-quality assembly method for a multi-constraint combined net-size heat-insulating layer, characterized in that, include: Step 1: Perform net-dimensional molding of the multi-constraint combined net-dimensional heat insulation layer; The multi-constraint combined net-size heat protection layer is a combined structure, which is spliced ​​together by a first composite heat protection layer (1) and a second composite heat protection layer (2); the small end of the second composite heat protection layer (2) is formed with the large end of the first composite heat protection layer (1) in net size, and the end face dimensions of the small end of the second composite heat protection layer (2) and the large end of the first composite heat protection layer (1) are consistent and fit together; the large end of the second composite heat protection layer (2) and the small end of the first composite heat protection layer (1) are reserved with end face allowance; Step 2: Test fit the load-bearing shell; The load-bearing shell is placed vertically, and the second composite heat-insulating layer (2) is fitted and assembled from the small end to the large end of the load-bearing shell onto the outer surface of the load-bearing shell. The circumferential gap A between the second composite heat-insulating layer (2) and the outer surface of the load-bearing shell is measured. Then, the first composite heat-insulating layer (1) is fitted and assembled from the small end to the large end of the load-bearing shell onto the outer surface of the load-bearing shell, and the large end of the first composite heat-insulating layer (1) is mated with the small end of the second composite heat-insulating layer (2), and the circumferential gap B between the first composite heat-insulating layer (1) and the outer surface of the load-bearing shell is measured. Step 3: Selection and cutting of flexible insulation layer; Based on the circumferential gaps A and B, select the appropriate thickness of the flexible insulation layer. According to the shape and structure of the load-bearing shell, the flexible insulation layer is attached to the outer surface of the load-bearing shell and cut into different blocks. Step 4: Surface Treatment The outer surface of the load-bearing shell and the inner surface of the composite heat-insulating layer are sandblasted. Step 5: Bond the flexible insulation layer; The pre-cut flexible thermal insulation layer is bonded to the outer surface of the load-bearing shell using adhesive. Step Six: Divide the flexible insulation layer into sections; The flexible insulation layer is divided into sections. A utility knife is used to cut the large area of ​​the flexible insulation layer into smaller sections with an area of ​​200mm wide and 400mm high. Excess flexible insulation layer is also cut off. The natural gaps formed by splicing adjacent different sections of flexible insulation layer are filled with fitting adhesive after fitting and assembly. After curing, a mesh support is formed between the heat insulation layer and the load-bearing shell. The gaps between the flexible insulation layer sections are used as reserved channels for cable filling and isolation protection. A certain length is reserved at both ends of the cable for easy removal later, to prevent the adhesive from flowing into the channels during the assembly process. Step 7: Assemble the second composite material heat-insulating layer; The load-bearing shell is placed vertically. Adhesive is applied to the outer surface of the load-bearing shell with the second composite heat-insulating layer and the flexible heat-insulating layer. The second composite heat-insulating layer is fitted and assembled from the small end to the large end of the load-bearing shell to the outer surface of the load-bearing shell with the flexible heat-insulating layer, until the large end of the second composite heat-insulating layer protrudes to the reserved allowance. Step 8: Assemble the first composite material heat-insulating layer; The first composite heat-insulating layer is applied with adhesive, and the composite heat-insulating layer 1 is fitted and assembled from the small end to the large end of the load-bearing shell onto the outer surface of the load-bearing shell, so that the gap between the large end of the first composite heat-insulating layer and the small end of the second composite heat-insulating layer is less than 0.5mm, and the first composite heat-insulating layer protrudes from the small end of the load-bearing shell to the reserved allowance. Step 9: Assemble and adjust the shaping fixture; A shaping tool is assembled on the outer surface of the butt joint between the small end of the second composite heat protection layer and the first composite heat protection layer. The shaping tool is adjusted, and pressure is applied to the outer surface to correct the shape, so as to prevent the small end of the second composite heat protection layer from rotating relative to the first composite heat protection layer in the circumferential direction and to maintain the final aerodynamic shape after the sleeve assembly. Step 10: Pressure curing and assembly; Gradually apply pressure to the small end of the first composite heat-insulating layer. The gap between the small end of the first composite heat-insulating layer and the first composite heat-insulating layer should not exceed 0.50mm. During the pressure curing process, the glass cloth is squeezed into the load-bearing shell by the assembly adhesive, compressing the pre-embedded cable. The cable is pulled out while the assembly adhesive is in a semi-cured state. The pressure is kept constant until the adhesive is cured, and the assembly is completed.

2. The high-quality assembly method for a multi-constraint combined net-size heat-insulating layer according to claim 1, characterized in that: The aforementioned multi-constraint combined net-size heat protection layer is a low-density composite heat protection layer with the final aerodynamic shape as the outer dimensions. During molding, the axial length of the large end of the first composite heat protection layer (1) and the small end of the second composite heat protection layer (2) has no allowance and is in net size state. The axial length of the end face of the small end of the first composite heat protection layer (1) and the large end of the second composite heat protection layer (2) has an allowance, and the outer surface does not need to be machined again after assembly.

3. The high-quality assembly method for a multi-constraint combined net-size heat-resistant layer according to claim 2, characterized in that: The aforementioned multiple constraints refer to the constraint requirements on the assembly joint gaps of the composite material heat-insulating layer and the gaps between the composite material heat-insulating layer and the load-bearing shell structure.

4. The high-quality assembly method for a multi-constraint combined net-size heat-insulating layer according to claim 1, characterized in that: The second composite heat insulation layer (2) has a 40mm margin in the axial length direction of the large end, and the first composite heat insulation layer (1) has a 50mm margin in the axial length direction of the small end.

5. The high-quality assembly method for a multi-constraint combined net-size heat-insulating layer according to claim 1, characterized in that: The circumferential gap between the second composite heat-insulating layer (2) and the outer surface of the load-bearing shell, and the circumferential gap between the first composite heat-insulating layer (1) and the outer surface of the load-bearing shell are both 2±0.5mm.

6. The high-quality assembly method for a multi-constraint combined net-size heat-insulating layer according to claim 1, characterized in that: The flexible insulation layer is made of high-temperature resistant polyurethane foam material with a thickness ranging from 2±0.5mm.

7. A high-quality assembly method for a multi-constraint combined net-size heat-insulating layer according to claim 1, characterized in that: The pre-cut, block-shaped flexible insulation layer is bonded to the outer surface of the load-bearing shell using high-temperature resistant silicone rubber adhesive. Specifically: High-temperature resistant silicone rubber adhesive is evenly applied to the surface of the block-shaped flexible insulation layer and the surface of the load-bearing shell. The block-shaped flexible insulation layer is then pasted along the generatrix and circumferential direction of the load-bearing shell to cover the surface of the load-bearing shell. During pasting, the longitudinal seams are aligned, and the longitudinal joints between the blocks are trimmed to naturally leave air channels, while the transverse joints are ensured to be in close contact. After pasting, a vacuum bag is placed to completely cover the load-bearing shell and the flexible insulation layer. Vacuum is drawn and pressurized at a pressure of 0.05-0.1 MPa. After curing for 24 hours, the heat protection layer is assembled. The longitudinal seam refers to the splicing gap along the generatrix direction of the shell.

8. A high-quality assembly method for a multi-constraint combined net-size heat-insulating layer according to claim 1, characterized in that: The inner surfaces of the first composite heat-insulating layer (1) and the second composite heat-insulating layer (2) are coated with high-temperature resistant silicone rubber adhesive and then assembled onto the outer surface of the load-bearing shell that has been pasted with a flexible heat insulation layer. The curing time is 24 hours.

9. A high-quality assembly method for a multi-constraint combined net-size heat-insulating layer according to claim 1, characterized in that: The shaped tooling consists of two semi-annular shaped arc plates (11). The inner surface shape of the shaped arc plate (11) matches the shape of the joint section between the second composite heat-insulating layer and the first composite heat-insulating layer. The adjusting screws (12) are evenly distributed on the shaped arc plate (11) and are divided into upper and lower rows. The end face of the upper row of adjusting screws matches the shape of the contact part of the first composite heat-insulating layer, and the end face of the lower row of adjusting screws matches the shape of the contact part of the second composite heat-insulating layer. The two semi-annular shaped arc plates (11) are connected and fixed into a ring whole by locking screws (13). During assembly, install the adjusting tooling, and apply pressure to the outer surface of the upper and lower composite heat protection layers by adjusting the screw to correct the shape, so as to prevent the small end of the second composite heat protection layer from rotating relative to the large end of the first composite heat protection layer in the circumferential direction, and maintain the final aerodynamic shape after the sleeve assembly.

10. A high-quality assembly method for a multi-constraint combined net-size heat-resistant layer according to claim 1, characterized in that: The pressure at the small end of the first composite heat-insulating layer (1) is controlled at 10-20 kN.

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