A method of forming a cylindrical skin of a cabin section

Abstract

The present application belongs to the technical field of metal plate processing, and provides a cabin section cylinder skin forming method. The forming process is divided into two stages of first constraint and second constraint. First heat treatment is carried out in the first constraint state, so that the stress relief and shape stabilization of the cylindrical preform are completed after the drum forming and before the welding, thereby providing a size-accurate butt joint reference for subsequent welding, effectively avoiding the joint gap misalignment and welding defects caused by the release of residual stress after drum forming in the welding process, and significantly improving the first-time weld pass rate. On this basis, the closed cylinder formed by welding is subjected to second heat treatment and simultaneously subjected to bulging force. The integral bulging tool is adopted, the uniform bulging is realized by using the thermal expansion difference between the bulging tool and the closed cylinder, the problems of uneven circumferential pressure and damaged cylinder roundness precision caused by the gap between the split parts in the split bulging structure in the prior art are avoided, and the welding deformation is further corrected to obtain the final size accuracy.

Description

Technical Field

[0001] This invention belongs to the field of metal sheet processing technology, and particularly relates to a method for forming the skin of a compartment cylinder. Background Technology

[0002] Thin-walled cylindrical components made of titanium alloys and other metals are widely used in aerospace, marine engineering, and chemical equipment due to their high specific strength and excellent corrosion resistance. Among them, the cylindrical skin of the compartment is a typical component of the aerospace vehicle compartment structure. It is usually manufactured by rolling, welding, and shaping thin metal sheets through multiple processes. The forming accuracy and weld quality control are key challenges that restrict the product qualification rate and reliability.

[0003] Application publication number CN103537876A discloses a processing method for a titanium alloy hyperbolic rotary cylinder. The process route is as follows: blanking, rolling and welding into a cone, cold expansion forming, crystallization annealing, hot expansion forming using a flap-type tooling, and internal stress relaxation straightening. This scheme combines cold expansion forming and hot expansion forming to straighten the welded cylinder, which improves the dimensional accuracy of the cylinder to a certain extent. However, this prior art has the following shortcomings: the titanium alloy plate is directly welded after rolling, without pre-controlling the opening gap and residual stress state of the rolled cylinder blank. The release of residual stress during rolling during welding can easily lead to misalignment of the joint and welding defects, affecting the first-pass yield of the weld; the crystallization annealing step is set after cold expansion forming and before hot expansion forming, and the process arrangement does not consider performing an independent shaping treatment on the cylinder blank before welding, which cannot provide a dimensionally stable reference for subsequent precision welding; hot expansion forming relies on flap-type tooling, and the flap structure has uneven circumferential pressure caused by the flap gap at high temperature, affecting the roundness accuracy of the cylinder.

[0004] The aforementioned shortcomings make it difficult for existing technologies to meet the requirements of engineered mass production in terms of product dimensional consistency, process reliability, and manufacturing cost when manufacturing compartment shell skins that have high requirements for weld quality and dimensional and positional accuracy such as roundness and straightness. Summary of the Invention

[0005] This invention provides a method for forming the skin of a compartment cylindrical body, aiming to solve the above-mentioned technical problems.

[0006] This invention is implemented as follows: a method for forming a cabin section shell skin, comprising the following steps: providing a titanium alloy sheet; applying a first constraint to the titanium alloy sheet and performing roll forming to form a cylindrical preform with an axially extending opening; performing a first heat treatment on the cylindrical preform under the first constraint; releasing the first constraint, applying a second constraint to both sides of the opening of the cylindrical preform, and welding along the opening to form a closed cylinder; releasing the second constraint, performing a second heat treatment on the closed cylinder, and applying an expansion force to the inner wall of the closed cylinder during the second heat treatment; cooling to room temperature and removing excess material to obtain a cabin section shell skin; applying the first constraint to the titanium alloy sheet and performing roll forming includes: placing the titanium alloy sheet between two layers of pads, with the titanium alloy sheet being sandwiched between the two layers of pads and jointly rolled to form a diameter of 0.7 to 0.9 times that of the cabin section shell skin; after roll forming, fixing the overlap of the two layers of pads by welding.

[0007] Furthermore, the first heat treatment of the cylindrical preform under the first constraint state includes: performing the first heat treatment together with the titanium alloy sheet and the two layers of the pad as an assembly; and removing the two layers of the pad after the first heat treatment is completed.

[0008] Furthermore, the temperature of the first heat treatment is lower than the temperature of the second heat treatment.

[0009] Furthermore, before applying the first constraint to the titanium alloy sheet and performing roll forming, the method further includes: opening through holes at both ends of the titanium alloy sheet near the edges; applying the second constraint to the two sides of the opening of the cylindrical preform includes: assembling the cylindrical preform onto a welding fixture, aligning the through holes with the positioning holes on the welding fixture; inserting positioning pins into the aligned positioning holes and through holes to position the two sides of the opening; and clamping and fixing the two sides of the opening using the welding fixture.

[0010] Furthermore, electron beam welding is used to weld along the opening.

[0011] Furthermore, applying a bulging force to the inner wall of the closed cylinder includes: assembling the closed cylinder onto a bulging fixture, the bulging fixture being a hollow cylindrical structure made of 06Cr19Ni10 stainless steel; and applying a bulging force to the inner wall of the closed cylinder using the thermal expansion difference between the bulging fixture and the closed cylinder.

[0012] Furthermore, the removal of excess material includes: circumferentially cutting the bulging closed cylinder to remove the annular process section with the through hole, thereby obtaining the compartment cylinder skin.

[0013] The beneficial effects of this invention are that the cabin shell skin forming method provided by this invention divides the forming process into two stages: a first constraint and a second constraint. Under the first constraint, a first heat treatment is performed, allowing the cylindrical preform to achieve stress relief and shape stabilization after roll forming and before welding. This provides a precise dimensional reference for subsequent welding, effectively avoiding misalignment and welding defects caused by the release of residual stress after roll forming during welding, significantly improving the first-pass yield of welds. Based on this, a second heat treatment is performed on the welded closed cylinder, and an expansion force is applied simultaneously. An integral expansion tooling is used, utilizing the thermal expansion difference between the tooling and the closed cylinder to achieve uniform expansion. This avoids the problems of uneven circumferential pressure and compromised cylinder roundness accuracy caused by the gaps between segments in the segmented expansion structure of existing technologies, further correcting welding deformation and obtaining final dimensional accuracy. This invention can significantly improve the dimensional consistency and process reliability of products, and is particularly suitable for aerospace and high-end equipment manufacturing fields with high requirements for cylinder roundness, straightness, and other dimensional and positional accuracy. Attached Figure Description

[0014] Figure 1 This is a structural schematic diagram of the cabin section's hull skin.

[0015] Figure 2 This is a schematic diagram of a titanium alloy sheet being subjected to a first constraint and then rolled into a roll.

[0016] Figure 3 This is a partial schematic diagram of the overlap between the two layers of pads after the roll is formed.

[0017] Figure 4 This is a schematic diagram of a cylindrical prefabricated component being assembled onto a welding fixture.

[0018] Figure 5 This is a structural diagram of the upper and lower clamping blocks of the welding fixture.

[0019] Figure 6 This is a schematic diagram showing the position of the cylindrical precast component on the lower clamping block.

[0020] Figure 7 This is a schematic diagram of a cylindrical precast component in a fixed state.

[0021] Figure 8 This is a schematic diagram of a closed cylinder assembled on an expansion fixture.

[0022] Figure 9 This is a schematic diagram of the removal of the annular process section from the expanded cylinder.

[0023] The numbers in the diagram represent: 01-section shell skin, 1-titanium alloy sheet, 2-pad plate, 3-cylindrical prefabricated part, 4-base, 5-column, 6-lower clamping block, 7-upper clamping block, 8-welding process hole, 9-positioning hole, 10-blind hole, 11-positioning pin, 12-through hole, 13-closed shell, 14-bulging tooling. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] See Figures 1-9 This invention provides a method for forming a section cylindrical skin. The method starts from a titanium alloy sheet 1 and proceeds sequentially through blanking, constraint rolling, first heat treatment, welding, second heat treatment, and bulging to finally obtain a section cylindrical skin 01 with dimensional accuracy requirements. The following describes each step in detail.

[0026] S1: Provide a titanium alloy sheet 1.

[0027] A titanium alloy sheet 1 meeting the grade and thickness requirements was selected and laser-cut to the required dimensions. After cutting, any remaining burrs at the cut were removed. The cut sheet 1 was then milled using a machining center to ensure its length and width met the unfolded dimensions of the cylindrical preform 3. Specifically, the length L of the titanium alloy sheet 1 satisfied 0.9965πD ≤ L ≤ 0.9975πD, where D is the design inner diameter of the cabin section skin 01. Any remaining burrs at the milled area were removed after milling. The surface roughness, dimensional tolerances, shape, and positional tolerances of the milled titanium alloy sheet 1 met the precision requirements for subsequent electron beam welding assembly.

[0028] After milling, four through holes 12 are made at both ends of the titanium alloy sheet 1 near the edges. Two through holes 12 are made at each end, located on both sides near the edges. The through holes 12 are used for subsequent positioning on the welding fixture, and their positions and dimensions are determined based on the positions of the positioning holes 9 and the diameter of the positioning pins 11 in the welding fixture. After making the through holes 12, any remaining burrs at the hole openings are removed.

[0029] S2: Apply a first constraint to the titanium alloy sheet 1 and roll it into shape to form a cylindrical preform 3 with an axially extending opening.

[0030] Two layers of pads 2 are prepared as constraint fixtures for roll forming. Both pads 2 are made of stainless steel, and the thickness of pad 2 is greater than the thickness of titanium alloy sheet 1. Optionally, the thickness of pad 2 is 2 to 3 times the thickness of titanium alloy sheet 1. The length and width of pad 2 are greater than the length and width of titanium alloy sheet 1, respectively. Optionally, the length of pad 2 is the length of titanium alloy sheet 1 + 80 mm, and the width of pad 2 is the width of titanium alloy sheet 1 + 50 mm, to ensure that pad 2 can completely cover titanium alloy sheet 1 and effectively constrain it during roll forming. The stainless steel pad 2 can be made of 06Cr19Ni10 stainless steel. The contact surfaces of stainless steel pad 2 and titanium alloy sheet 1 are clean and free of oil to prevent contamination of the surface of titanium alloy sheet 1 during subsequent heat treatment.

[0031] A titanium alloy sheet 1 with pre-drilled through holes 12 is placed between two upper and lower pads 2. The titanium alloy sheet 1 is held between the upper and lower pads 2, and the three layers of sheet material are fed together into a three-roll mill for roll forming. During roll forming, an over-rolling allowance is reserved to compensate for subsequent springback. Optionally, the titanium alloy sheet 1 together with the upper and lower pads 2 is rolled to 0.7 to 0.9 times the design diameter of the cabin section skin, forming a cylindrical preform 3 with an axially extending opening. At this time, the cylindrical preform 3 remains cylindrical under the first constraint state.

[0032] After the roll is formed, the upper and lower pads 2 form a cylindrical shape and wrap around the outer periphery of the cylindrical precast part 3, with the two ends of the pads 2 overlapping at the openings. For example... Figure 3 As shown, in this state, the two ends of the titanium alloy sheet 1 do not contact each other, nor do the two ends of the titanium alloy sheet 1 contact the surface of the titanium alloy sheet 1. The overlap of the upper and lower pads 2 is firmly fixed by argon arc welding, so that the constraint fixture formed by the pads 2 maintains the constraint state on the cylindrical preform 3 during subsequent heat treatment, preventing irregular deformation or springback of the cylindrical preform 3 during heat treatment.

[0033] S3: Perform the first heat treatment on the cylindrical preform 3 under the first constraint state.

[0034] After completing the rolling and welding of the overlap of the pad 2, the titanium alloy sheet 1 and the upper and lower pads 2 are sent together into a vacuum heat treatment furnace for the first heat treatment. The target temperature for the first heat treatment is 600℃, the heating rate is 5~10℃ / min, the holding time is 90~120min, and the furnace is cooled after the holding time is completed.

[0035] During the first heat treatment process, such as Figure 2 , 3As shown, the upper and lower backing plates 2 maintain the constraint on the cylindrical preform 3. Since the stainless steel backing plates 2 form a closed constraint ring through welding at the overlap after the roll forming, and stainless steel still possesses sufficient strength and rigidity at 600℃, they can continuously apply circumferential constraint to the titanium alloy cylindrical preform 3 throughout the entire heat treatment process, preventing springback deformation or instability. Simultaneously, the heat treatment temperature of 600℃ effectively eliminates residual stress generated during the titanium alloy roll forming process, allowing the cylindrical preform 3 to complete stress relaxation and shape stability under constraint, providing a dimensionally accurate butt joint reference for subsequent welding.

[0036] After the first heat treatment, once the assembly has cooled to room temperature in the furnace, the upper and lower backing plates 2 are removed, and the titanium alloy cylindrical preform 3, whose shape has stabilized, is taken out. At this point, the cylindrical preform 3, formed from the flat structure of the titanium alloy sheet 1 through rolling and heat treatment, has become a stable near-cylindrical structure. Within the range of 0.7 to 0.9 times the design diameter of the cabin section skin, the near-cylindrical structure is a partially spiral overlapping structure or a C-shaped structure, forming an opening extending axially. The two end faces on both sides of the opening can be brought closer together by applying a small external force. Thus, the opening gap and roundness of the cylindrical preform 3 have been effectively controlled, providing a good foundation for subsequent welding and assembly.

[0037] S4: Release the first constraint, apply the second constraint to both sides of the opening of the cylindrical precast part 3, and weld along the opening to form a closed cylinder 13.

[0038] After releasing the first constraint, the cylindrical prefabricated part 3 is transferred to the welding fixture for the second constraint. In this embodiment of the invention, as... Figures 4-7 As shown, the welding fixture includes a base 4, two columns 5, and a clamping assembly. The clamping assembly includes a lower clamping block 6 and an upper clamping block 7. The two ends of the lower clamping block 6 are detachably mounted to the tops of the two columns 5 via bolts. The main body of the lower clamping block 6 extends horizontally, spanning between the two columns 5. The two ends of the upper clamping block 7 are detachably mounted to the two ends of the lower clamping block 6 via bolts. The upper clamping block 7 is located directly above the lower clamping block 6, forming a clamping space between them. The upper surface of the lower clamping block 6 is a convex arc-shaped surface, the curvature of which matches the inner wall curvature of the cylindrical preform 3. The lower surface of the upper clamping block 7 is a concave arc-shaped surface, the curvature of which matches the curvature of the cylindrical preform 3, and its radius is equal to or greater than the theoretical outer diameter of the cylindrical preform 3. Welding process holes 8 are provided through the upper clamping block 7 and the lower clamping block 6 at the positions of the weld joints to be welded on the cylindrical precast part 3. The welding process holes 8 pass through both the lower clamping block 6 and the upper clamping block 7, and are directly opposite the weld joints to be welded at both ends of the sheet metal when clamped. Positioning holes 9 are provided on both sides of the welding process holes 8 of the upper clamping block 7, and blind holes 10 are provided on both sides of the welding process holes 8 of the lower clamping block 6. The positioning holes 9 and the blind holes 10 are coaxial and have the same diameter, and positioning pins 11 are inserted into them.

[0039] Four through holes 12 are pre-drilled on both sides of the opening of the cylindrical precast component 3. The position and size of the through holes 12 are determined according to the process requirements. The through holes 12 are aligned with the blind holes 10, and the positioning pins 11 are inserted. Then, the positioning holes 9 of the upper clamping block 7 are aligned with the positioning pins 11 and inserted to clamp the cylindrical precast component 3. In this way, the relative position between the cylindrical precast component 3 and the upper clamping block 7 and the lower clamping block 6 is completely fixed, thus completing the second constraint on the cylindrical precast component 3.

[0040] After completing the second constraint, electron beam welding is performed along the opening. The welding fixture and the cylindrical preform 3 are placed together in the vacuum chamber of the electron beam welding machine. The electron beam gun is fixed directly above the welding process hole 8. The working platform moves the welding fixture and the cylindrical preform 3 along the extension direction of the welding process hole 8 to perform continuous welding on the butt joint to be welded, forming a closed cylinder 13. After welding is completed, the weld is inspected by X-ray. The closed cylinder 13 that passes the inspection proceeds to the next process.

[0041] S5: Release the second constraint and perform a second heat treatment on the closed cylinder 13. During the second heat treatment, apply an expansion force to the inner wall of the closed cylinder 13.

[0042] Release the second constraint and assemble the qualified closed cylinder 13 onto the bulging fixture 14, as follows. Figure 8 As shown. The bulging fixture 14 is a hollow cylindrical structure made of 06Cr19Ni10 stainless steel. The mating surfaces of the bulging fixture 14 are uniformly coated with a 0.01~0.02mm thick solder resist coating. The outer diameter d of the bulging fixture 14 satisfies:

[0043] Where T is the bulging temperature, α1 is the linear expansion coefficient of titanium alloy at the bulging temperature, and α2 is the linear expansion coefficient of 06Cr19Ni10 stainless steel at the bulging temperature.

[0044] The titanium alloy enclosed cylinder 13 and the bulging tooling 14 are fed together into a vacuum heat treatment furnace for a second heat treatment. The target temperature for the second heat treatment is 750℃, the heating rate is 5~10℃ / min, the holding time is 90~120min, and the furnace is cooled after the holding time is completed.

[0045] During the heating and heat preservation process, since the linear expansion coefficient of the 06Cr19Ni10 stainless steel bulging tool 14 is greater than that of the titanium alloy closed cylinder 13, the radial thermal expansion of the bulging tool 14 is greater than that of the titanium alloy cylinder. A thermal expansion difference is generated between the outer peripheral surface of the bulging tool 14 and the inner wall surface of the titanium alloy closed cylinder 13. As a result, the bulging tool 14 applies a continuous and uniform radial bulging force to the inner wall of the titanium alloy cylinder. This bulging force causes the titanium alloy closed cylinder 13 to gradually bulge to the inner hole design size of the compartment cylinder skin 01.

[0046] Compared with the segmented expansion structure used in the prior art, the expansion tool 14 used in this embodiment of the invention is an integral hollow cylindrical structure with a continuous radial expansion surface. It can uniformly apply expansion force to the entire inner circumference of the closed cylinder 13, avoiding the problems of uneven radial pressure and damage to the roundness accuracy of the cylinder caused by the segmented expansion structure, and significantly improving the roundness and dimensional consistency of the cylinder after expansion.

[0047] S6: Cool to room temperature and remove excess material to obtain section shell skin 01.

[0048] After the second heat treatment, once the assembly has cooled to room temperature in the furnace, the bulged cylinder is removed from the bulging fixture 14. The bulged cylinder is then circumferentially cut, as shown below. Figure 9 As shown, the annular process section with through hole 12 is removed. Based on this, other forms of excess material removal can be performed on the bulged cylinder according to actual process requirements. For example, the weld excess height can be ground or machined to make the weld area flush with the base material surface, ensuring the smoothness of the outer surface of the cylinder and the aerodynamic shape requirements. The axial ends of the cylinder can be trimmed to remove minor deformations or irregular edges generated during rolling and bulging, ensuring that the axial length and end face flatness of the cylinder meet the final design requirements. After completing the above excess material removal processes, the compartment cylinder skin 01 is obtained.

[0049] The present invention will be further described below with reference to specific embodiments.

[0050] Example 1 This invention provides a method for forming a section cylindrical skin, wherein the section cylindrical skin is designed with a diameter D of 496 mm and a thickness of 2 mm. The method includes the following steps: A 2mm thick TC4 titanium alloy sheet is provided, which is laser-cut and milled to a length L of 1553.5mm and a width of 600mm. Four through holes are formed at both ends of the titanium alloy sheet according to the blind hole positions of the welding fixture in this embodiment of the invention. Residual burrs at the cuts and hole openings are removed to ensure that the surface roughness Ra of the mating surface of the titanium alloy sheet is ≤3.2μm, the flatness is ≤0.01mm, and the dimensional tolerance is 1553.5±0.1mm.

[0051] Two pads, each 1633.5 mm long and 650 mm wide, are provided. A titanium alloy sheet is sandwiched between the two pads and rolled on a plate rolling machine to obtain a cylindrical preform. The inner diameter of the rolled cylindrical preform, including the two pads, is 446.4 mm. The overlapping ends of the two pads are securely fixed by argon arc welding to obtain the first assembly.

[0052] The assembly is sent into a vacuum heat treatment furnace for the first heat treatment. The target temperature for the heat treatment is 600℃, the heating rate is 6℃ / min, the holding time is 100min, and the assembly is cooled with the furnace after the holding time is completed.

[0053] After cooling, the welding fixation at the end overlap of the two pads is removed, and the cylindrical precast component is unrolled using a plate rolling machine.

[0054] The cylindrical prefabricated component is installed on the welding fixture in this embodiment of the invention. The through hole on the cylindrical prefabricated component is aligned with the blind hole of the welding fixture. A positioning pin is inserted, and the two end faces of the cylindrical prefabricated component are aligned and abutted to form a butt joint to be welded. The upper clamping block and the lower clamping block are joined together and connected by bolts to clamp and fix the cylindrical prefabricated component.

[0055] In a vacuum chamber, electron beam welding is used to weld the joints to be welded through welding process holes to form a closed cylinder.

[0056] Provide an bulging fixture and calculate its outer diameter d, where α1 = 11.2 × 10⁻⁶ at 750℃. -6 K -1 α² = 19.5 × 10 -6 K -1 The diameter d was found to be 493 mm. The closed cylinder was then assembled onto the bulging fixture, and a boron nitride coating with a thickness of 0.01 mm was uniformly applied to the mating surfaces of the bulging fixture to obtain the second assembly.

[0057] The second assembly is sent into a vacuum heat treatment furnace for a second heat treatment. The target temperature for the heat treatment is 750℃, the heating rate is 5℃ / min, the holding time is 100min, and the assembly is cooled with the furnace after the holding time is completed.

[0058] Remove the annular process section with through holes, and trim any minor deformations or irregular edges to obtain the compartment shell skin.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for forming the skin of a compartment shell, characterized in that, Includes the following steps: Provide a titanium alloy sheet; The titanium alloy sheet is subjected to a first constraint and rolled into a cylindrical preform with an axially extending opening. The cylindrical preform is subjected to a first heat treatment under the first constraint state; Release the first constraint, apply a second constraint to both sides of the opening of the cylindrical preform, and weld along the opening to form a closed cylinder; Release the second constraint and perform a second heat treatment on the closed cylinder, during which an expansion force is applied to the inner wall of the closed cylinder; Cool to room temperature and remove excess material to obtain the compartment shell skin; Applying a first constraint to the titanium alloy sheet and performing roll forming includes: The titanium alloy sheet is placed between two layers of pads, and the titanium alloy sheet is held between the two layers of pads and rolled together to form a cylinder. The titanium alloy sheet is rolled to 0.7 to 0.9 times the design diameter of the cabin section skin. After the roll is formed, the overlap of the two layers of pads is fixed by welding.

2. The method for forming the skin of a compartment shell according to claim 1, characterized in that, The first heat treatment of the cylindrical preform under the first constraint state includes: The titanium alloy sheet and the two layers of the pad are combined and subjected to the first heat treatment; After the first heat treatment is completed, the two layers of pads are removed.

3. The method for forming the skin of a compartment shell according to claim 1, characterized in that, The temperature of the first heat treatment is lower than the temperature of the second heat treatment.

4. The method for forming the skin of a compartment shell according to claim 1, characterized in that, Before applying a first constraint to the titanium alloy sheet and performing roll forming, the method further includes: Through holes are made at both ends of the titanium alloy sheet near the edges; Applying a second constraint to the two sides of the opening of the cylindrical preform includes: The cylindrical prefabricated part is assembled onto the welding fixture, so that the through hole is aligned with the positioning hole on the welding fixture; Insert the positioning pin into the aligned positioning hole and through hole to position the two sides of the opening; The two sides of the opening are clamped and fixed by the welding fixture.

5. The method for forming the shell skin of a compartment according to claim 4, characterized in that, Electron beam welding is used to weld along the opening.

6. The method for forming the skin of a compartment hull according to claim 1, characterized in that, Applying a bulging force to the inner wall of the closed cylinder includes: The closed cylindrical body is assembled onto the bulging fixture, which is a hollow cylindrical structure and is made of 06Cr19Ni10 stainless steel. The thermal expansion difference between the forming tool and the closed cylinder is used to apply a forming force to the inner wall of the closed cylinder.

7. The method for forming the skin of a compartment shell according to claim 4, characterized in that, The removed excess includes: The enlarged closed cylinder is then circumferentially cut to remove the annular process section with the through hole, thus obtaining the compartment cylinder skin.

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