Manufacturing method of "q" shaped section variable curvature complex skin with reinforced bent edge

Abstract

The present application belongs to the technical field of aircraft sheet metal part processing, and relates to a manufacturing method of a "U" shaped section variable curvature complex skin with reinforced bent edge. The present application uses a process flow of "stretch forming-numerical control milling-cutting-hand forming" to replace a single process flow of "straight line blanking-falling pressure forming-hand forming-cutting shape-drilling", and cooperates with two newly designed toolings for part forming and edge cutting, so as to solve the problems of size out-of-tolerance in the forming process of the "U" shaped section variable curvature complex skin part, high labor intensity, poor surface quality, high scrap rate and the like. In production, the part deformation and edge milling are completed by mechanical processing, the product precision is improved, the labor intensity of workers is significantly reduced, the part has no large area hammer mark, and the surface quality is significantly improved. The method can be used for processing large complex variable curvature parts, and can be widely applied in the field of aviation manufacturing.

Description

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[0001] The present invention belongs to the technical field of the processing of sheet metal parts of aircraft, and relates to a manufacturing method for a complex skin with a variable curvature of a "C" - shaped cross - section with reinforcing flanges. Background Art

[0002] There is a special - structure skin on an aircraft. Different from the traditional single - curvature or double - curvature large - arc skin structure, the typical characteristics of this kind of part are a complex variable - curvature outer shape with a "C" - shaped cross - section with reinforcing flanges, and the web has 10 - φ2.7 assembly holes. Since the fairing skin affects the aerodynamic shape of the aircraft, high requirements are imposed on the manufacturing precision and surface quality. The typical processing flow of this kind of part is "straight - line blanking - drop - forming - manual forming - cutting the outer shape - drilling holes", that is, the outer shape of the part is pressed by a drop - forming die in the blank state, then the reinforcing flanges are made manually, and finally the outer shape is cut and the assembly holes are drilled according to the template. Since the part has a slender structure, the size of the drop - forming die used for forming is large and it is easy to deform under the impact force of the drop hammer, resulting in errors in the part surface. During drop - forming, the blank deforms under the impact of the drop hammer, and the surfaces of different features are unevenly stressed, resulting in large springback and residual stress. After forming, manual repeated "material - gathering", "material - releasing" and "combination of material - gathering and material - releasing" methods are required for springback trimming and residual stress removal. Not only is the manufacturing precision of the part low, but also the labor intensity is large. A large amount of trimming and grinding etc. result in poor surface quality of the part, thus affecting the aerodynamic shape of the aircraft. In addition, the material thickness of this part is δ1.5mm, and the minimum value of the radius of the reinforcing flange is only R2.4mm. Cracks are likely to occur during the forming process, and the scrap rate usually exceeds 30%. The edge of the part is cut manually with low precision, and it cannot be quickly assembled with other parts during assembly, resulting in low assembly efficiency. The above problems make it very difficult to form this kind of part. Summary of the Invention

[0003] The purpose of the present invention is to invent a manufacturing method for a complex variable - curvature skin with a "C" - shaped cross - section with reinforcing flanges. The manufacturing method uses a newly designed set of form dies for forming parts and a set of fixtures for milling. The processing method of "straight - line blanking - drop - forming - manual forming - cutting the outer shape" is changed to "stretch - forming - CNC milling - manual forming". The form dies used in the present invention can achieve precise forming of the complex curvature of the part, and the milling fixture can achieve rapid cutting and drilling of the part edge, thereby achieving precise manufacturing of the complex variable - curvature skin with a "C" - shaped cross - section with reinforcing flanges, reducing the labor intensity and scrap rate, and improving the production efficiency.

[0004] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0005] A manufacturing method for a complex variable - curvature skin with a "C" - shaped cross - section with reinforcing flanges, the manufacturing method mainly consists of three processes: stretch - forming, CNC milling, and manual forming.

[0006] The first process is stretch forming.

[0007] The stretch forming and the manual forming share a set of mold tire, and the tooling is detachable, which can be used according to the forming requirements, so as to realize its function. The tooling includes a tire body, a local tire body, a positioning pin, a screw, a special positioning pin, a side cover plate, an integral cover plate, a special mold matching pin, a core, a fixed drill sleeve, a movable handle, and a lifting ring screw.

[0008] The tooling "mold tire" can realize the stretching of the plate material into the variable curvature structure of the "U" section, and can form the structure to the final shape of the part. The structure tire body is designed according to the inner profile of the part, the local tire body is made in the unfolded state according to the corresponding position of the "several" shaped bending edge and is a detachable structure, the local tire body is aligned with the tire body by the positioning pin and is fixed by the screw, and the special positioning pin is used for positioning the part on the tire body. The side cover plate is designed according to the inner shape of the "several" shaped bending edge, and is aligned with the tire body by the positioning pin and is fixed by the screw. The integral cover plate is aligned with the tire body by the special mold matching pin, is used for clamping and fixing when trimming the part, and has a through hole at the reinforced bending edge to cooperate with the core for forming the reinforced bending edge. The core is manufactured according to the outer profile of the reinforced bending edge of the part, and is used for forming the reinforced bending edge. The fixed drill sleeve is installed on the cover plate, and is used for assembling hole position inspection. The movable handle is installed on the integral cover plate, and is convenient for installing and dismounting the integral cover plate. The lifting ring screw is installed on the tire body, and is used for lifting and hoisting the tooling. The above structure is manufactured according to the data set, the profile manufacturing tolerance is ±0.1mm, and the working profile roughness is not higher than Ra1.6.

[0009] During the stretch forming, the integral cover plate, the side cover plate, the core and the like are removed, and only the main body structure of the tire body and the local tire body is retained.

[0010] The second process is numerical control milling.

[0011] The tooling used in the numerical control milling process is "milling clamp", which includes a positioning pin, a vacuum adsorption device and a sealing strip, a non-plated steel wire sleeve, a lifting rod, and a vacuum clamp nozzle.

[0012] The tooling "milling clamp" can realize accurate milling and drilling of the edge and inner hole of the "U" section blank formed by the stretching process, and is used for subsequent sheet metal forming. The structure of the tool body is designed according to the part process data set, and the bottom of the tool body is widened to prevent the tooling from deforming and tilting during milling. The distance from the bottom is 40mm, and a pressing plate groove is added for tooling fixation during milling. The reference hole is arranged at the top of the tool body, which is used for tooling alignment and as the coordinate origin during numerical control milling. The positioning pin is installed at the top of the tool body, which is used for part positioning during milling. In order to ensure that the part and the clamp are tightly attached during milling, a vacuum suction device is added inside the tool body, and a sealing strip is laid near the milling edge. The non-plated steel wire sleeve is installed at a position about 150mm away from the edge of the part, which cooperates with the pressing plate to enhance the pressing effect of the blank during milling, preventing the vacuum suction device from failing during milling. The hanging rod penetrates the tool body, which is used for the lifting and handling of the tooling. The vacuum clamp connects the vacuum suction device inside the tool body with a nozzle, which is used for vacuum pumping during milling. The above structure is manufactured by using SAM-900-LX epoxy resin as the surface and SAM910 resin as the base, with a manufacturing tolerance of ±0.1mm and a working surface roughness of not more than Ra1.6.

[0013] The third process is hand forming.

[0014] The tooling used for hand forming is "mold body", which is the same as the tooling used for stretching forming. During hand forming and trimming, part of the tool body is removed, and the tool body is used in cooperation with the cover plate and side cover plate to form a "several" shaped structure. The tool body is used in cooperation with the core to form the reinforcing bend on the web.

[0015] The beneficial effects of the present application are:

[0016] By using the process flow of "stretch forming-numerical control milling-hand forming" instead of the single process flow of "straight line blanking-falling pressing forming-hand forming-cutting shape-drilling", and using two newly designed toolings for part forming and edge cutting, the problems of size tolerance, high labor intensity, poor surface quality and high scrap rate in the forming process of the "several" shaped cross section variable curvature skin part are solved. The main deformation of the part and the edge milling are completed by mechanical processing, the product precision is improved, the labor intensity of the workers is significantly reduced, the part has no large area hammer mark, and the surface quality is significantly improved.

[0017] The method can be used for processing large and complex variable curvature parts, and can be widely applied in the field of aviation manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 , part shape diagram;

[0019] Figure 2, Schematic diagram of a milled part;

[0020] Figure 3 , Overall structure diagram of the die blank;

[0021] Figure 4 , Detailed structure diagram of the die blank;

[0022] Figure 5 , Structure diagram of the milling fixture.

[0023] In the figure: 1. Matrix; 2. Local matrix; 3. Positioning pin; 4. Screw; 5. Special positioning pin; 6. Side cover plate; 7. Integral cover plate; 8. Special die-aligning pin; 9. Core; 10. Fixed drill bushing; 11. Movable handle; 12. Lifting eye bolt; 13. Structural matrix; 14. Positioning pin; 15. Vacuum adsorption device and sealing strip; 16. Non-plated wire screw sleeve; 17. Lifting rod; 18. Nozzle for vacuum fixture. Specific implementation mode

[0024] Example 1: ...

[0025] The specific manufacturing plan for the complex variable-curvature skin with a "C" - shaped cross-section and reinforced flanges is described as follows:

[0026] By using the process flow of "stretch forming - CNC milling - manual forming" to replace the single process flow of "straight blanking - drop forging - manual forming - cutting the outer shape - drilling", and cooperating with two newly designed toolings for part forming and edge cutting, problems such as out-of-tolerance of the profile size, high labor intensity, poor surface quality, and high scrap rate in the forming process of the complex variable-curvature skin parts with a "C" - shaped cross-section are solved. The specific steps are briefly introduced as follows.

[0027] Figure 3 , Figure 4 , Figure 5 As shown, the manufacturing of the complex variable-curvature skin with a "C" - shaped cross-section and reinforced flanges is realized based on the die blank and the milling fixture. The structure of the die blank includes: matrix 1, local matrix 2, positioning pin 3, screw 4, special positioning pin 5, side cover plate 6, integral cover plate 7, special die-aligning pin 8, core 9, fixed drill bushing 10, movable handle 11, lifting eye bolt 12. The structure of the milling fixture includes: positioning pin 14, vacuum adsorption device and sealing strip 15, non-plated wire screw sleeve 16, lifting rod 17, nozzle 18 for vacuum fixture.

[0028] The tooling "molding tire" can realize the stretching of the plate material to the variable curvature structure of "U" section, and can form the structure to the final shape of the part. The structure of the tire body 1 is designed according to the inner profile of the part, and the local tire body 2 is made in the unfolded state and is a detachable structure according to the corresponding position of the "J" shaped bending edge. The local tire body 2 is aligned with the tire body 1 by using positioning pins 3 and is fixed by using screws 4. Special positioning pins 5 are used for positioning the part on the tire body. The side cover plate 6 is designed according to the inner shape of the "J" shaped bending edge, and is aligned with the tire body 1 by using positioning pins 3 and is fixed by using screws 4. The whole cover plate 7 is aligned with the tire body by using special matching mold pins 8, which is used for clamping and fixing when trimming the part, and a through hole is made at the reinforced bending edge to cooperate with the core 9 for forming the reinforced bending edge. The core 9 is manufactured according to the outer profile of the reinforced bending edge of the part, which is used for forming the reinforced bending edge. The fixed drill sleeve 10 is installed on the cover plate, which is used for assembly hole position inspection. The movable handle 11 is installed on the whole cover plate, which is convenient for the installation and disassembly of the whole cover plate. The lifting ring screw 12 is installed on the tire body, which is used for lifting and hoisting the tooling. The above structure is manufactured according to the data set, the profile manufacturing tolerance is ±0.1mm, and the working profile roughness is not higher than Ra1.6.

[0029] When stretching and forming, remove the cover plate, side cover plate, core and other structures, and only keep the main body structure of the tire body 1 and the local tire body 2.

[0030] When manually forming and trimming, remove the local tire body 2, and the tire body is used in cooperation with the cover plate and the side cover plate to form the "J" shaped structure. The tire body is used in cooperation with the core, and then the reinforced bending edge on the web plate can be formed.

[0031] The tooling "milling clamp" can realize the accurate milling of the edge and inner hole of the "U" section blank formed by the stretching process and the drilling of the assembly hole, which is used for subsequent sheet metal forming. The structure of the tire body 13 is designed according to the part process data set, that is, the profile of the part bottom bending edge and the reinforced bending edge after unfolding according to the sheet metal unfolding algorithm. Considering the slender structure of the part, the bottom of the tire body is widened to prevent the tooling from deforming and tilting during milling. The whole is in the shape of "convex", and a pressing plate groove is added at a position 40mm away from the bottom for fixing the tooling on the platform during milling. A reference hole is provided at the top end of the tire body, which is used as the coordinate origin during tooling alignment and numerical control milling. The positioning pin 14 is installed at the top of the tire body, which is used for positioning the part during milling. In order to ensure that the part and the clamp are closely attached during milling, a vacuum suction device is added inside the tire body, and a sealing strip 15 is laid near the milling edge. The non-plated steel wire sleeve 16 is installed on the tire body about 150mm away from the edge of the part, which is used in cooperation with the pressing plate to enhance the pressing effect of the blank during milling, preventing the vacuum suction device from failing to cause the part to move during milling. The lifting rod 17 penetrates through the tire body, which is used for lifting and hoisting the tooling. The vacuum clamp connects the internal vacuum suction device of the tire body through the nozzle 18, which is used for vacuumizing during milling.

[0032] Further, the above milling fixture is made of SAM-900-LX epoxy resin for surface and SAM 910 resin for base body, with a manufacturing tolerance of ±0.1 mm for the profile, and a working profile roughness of no more than Ra1.6.

[0033] Example 2:

[0034] The specific method for the "K" shaped section complex variable curvature skin with reinforced bent edge includes the following steps:

[0035] Step one: blanking

[0036] The part is made of aluminum alloy sheet material with a material grade of 7B04, an OB state, and a thickness of δ1.5 mm, and the size is 1750 mm X 1200 mm, wherein the length direction is parallel to the fiber direction of the sheet material, which is beneficial to the stretch forming and the maximum utilization of the forming performance of the material during manual bending edge forming,

[0037] Step two: stretch forming

[0038] Firstly, the special platform required for stretching is placed in the center position of the stretching machine using a crane, the side cover plate 6, the overall cover plate 7, the core 9 and other structures are removed, only the main body structure of the mold tire including the tire body 1 and the partial tire body 2 is retained and placed in the center position of the platform, and the mold tire and the platform are fixed well and the stretching direction is consistent with the clamping direction of the jaw; then the mold tire is cleaned and lubricating oil is applied to the surface of the mold tire for material flow during the drawing. During the stretch forming, the two ends of the raw material of the part are placed in the jaws of the stretching machine, the end is in contact with the bottom end of the jaw to ensure sufficient clamping, the jaw is closed, the raw material is clamped, the jaw is operated by the control system to stretch, the raw material is gradually deformed to the mold tire surface until it is tightly attached, and the top action of the platform can be matched during the process. After the stretching is completed, the surface of the stretched part is knocked by using a wooden hammer or a rubber pad, and whether the part is attached to the tire is checked. After the first stretching of the qualified part, the load and the jaw track are saved for use in subsequent part forming. After the stretching is completed, the jaw is opened, the part is unloaded from the jaw, and the part is taken out from above the mold tire. Compared with the drop press forming, in this process, the material flows uniformly on the surface of the mold tire under the action of the stretching force and finally attaches to it, so that the thickness change of the stretched part is uniform, the surface quality is good, and the wrinkling, material thinning and even cracking caused by excessive local deformation in the drop press forming are avoided, which improves the production efficiency and reduces the labor intensity;

[0039] Step three: numerical control milling

[0040] Milling preparation: first use the crane to hoist the milling fixture to the numerical control five-axis milling platform, accurately measure the X, Y, Z of the milling fixture and the origin of the coordinate system by using the dial gauge and ruby probe, and manually adjust the position of the tooling, and then fix the milling fixture on the milling platform through the pressing plate; then cut off the clamping part of the "U" shaped piece and install it on the tire body 13, ensure the relative position of the profile and the fixture, and then fix it with the positioning pin 14, and install the movable pressing plate at the corresponding position of the non-plated steel wire sleeve 16 to prevent the vacuum suction device from failing during milling, causing the part to move;

[0041] Milling processing: straighten the coordinate system and make the coordinate system of the machine coincide with the programming coordinate system, connect the vacuum clamp nozzle 18, start the vacuum suction equipment, ensure that the part is tightly adsorbed to the surface of the milling fixture under the action of the sealing strip 15, run the numerical control milling program, complete the milling of the outer edge and the inner edge of the developed hole, and drill the assembly hole. After completing the milling, turn off the machine button, clean the aluminum chips on the surface of the part, and check whether the edge size and surface of the part are damaged or mechanically damaged; after completing the above operation, turn off the vacuum suction equipment, remove the movable pressing plate, and take out the part;

[0042] Step four: manual forming

[0043] First, remove the partial tire body 2 of the mold tire, place the milled "U" shaped blank on the tire body 1, fix it at both ends with the special positioning pin 5, and use the special counter-mold pin 8, screw 4, and whole cover plate 7 and side cover plate 6. Use a hammer, a board and other tools to knock the blank, forcing the blank to fit the side cover plate, and complete the "J" shaped bending edge forming. Then, remove the whole cover plate, place the core at the reinforced bending edge position, use an aluminum hammer to knock the core, and the core moves downward under the pressure, and the blank bends under the pressure of the core, thereby completing the reinforced bending edge forming. Since the part profile is mainly formed by stretching, the material flowability is good, the residual stress is small, and the workload of later manual finishing is reduced. In addition, the core forming plate is uniformly stressed, so the reinforced bending edge is not easy to crack, thereby reducing the risk of cracking. After completing the above forming, remove the cover plate and check whether the gap between the part and the tire body and the side cover plate meets the design requirements. If the gap does not meet the requirements, repeat the process to repair it;

[0044] Step five: quenching

[0045] The parts are quenched, the purpose is to improve the strength and hardness of the parts. The specific operation is as follows: the parts are cleaned, the surface is free of visible dirt, and the air furnace heat treatment equipment is loaded. When loading, the parts should be placed in the effective heating area of the air furnace, and the gap between the parts should be left, and the tight packing, stacking or tightening is not allowed. Quenching temperature range: 465-475℃, holding time 30-45min, after quenching, the parts are cooled in flowing cold water of 10-40℃ to complete cooling, the cooling time is not less than 2min;

[0046] Step six: trimming

[0047] The parts are placed on the mold tire body, the overall cover and side cover are installed, and the quenching deformation trimming is performed manually to ensure that the gap between the parts and the tool fitting is not greater than 0.5mm;

[0048] Step seven: artificial aging

[0049] The purpose of artificial aging is to eliminate internal stress, stabilize the organization and size. First, clean the parts to ensure that the surface is dry, free of dirt, oil and grease, etc. Then load the furnace, when all temperature sensors of the equipment reach the required temperature range, the parts enter the furnace, or cold state, but the furnace temperature recovery time is not more than 2h. The parts should be placed in the effective heating area of the equipment, the parts can be stacked, the stacking thickness is not more than 25mm, and the spacing between the layers is at least 25mm. First aging: heating temperature range: 115±5℃, aging holding time: 7-8h; after the first aging, the parts do not exit the furnace and directly enter the second aging, heating temperature range: 165±5℃, holding time: 15-16h. After completing the aging, the parts are cooled by air cooling;

[0050] Step eight: physical and chemical property detection

[0051] After aging, the parts are sent to the physical and chemical department for conductivity or hardness inspection according to the standard, the hardness value is 450-530MPa, and the conductivity is ≥21MS / m. If the conductivity and hardness detection are not qualified, repeat the heat treatment, and then perform the detection of this step again until the physical and chemical properties are qualified and can enter the subsequent process;

[0052] After the above steps are completed, the final shape of the parts is obtained.

Claims

1. A manufacturing method for a complex skin with a "Ji" - shaped cross - section and variable curvature with reinforced flanges, characterized in that, The steps are as follows: The first process is stretch forming; The stretch forming and manual forming share a set of die blanks. This tooling adopts a detachable structure and can be disassembled and used according to the forming requirements, so as to realize its functions; This tooling includes: a carcass (1), a partial carcass (2), a positioning pin (3), a screw (4), a special positioning pin (5), a side cover plate (6), an integral cover plate (7), a special die-aligning pin (8), a core (9), a fixed drill bushing (10), a movable handle (11), a lifting eye bolt (12); The "die blank" of the said tooling realizes stretching a sheet material into a variable-curvature structure with a "U" cross-section and forming this structure into the final shape of the part; the carcass (1) is designed according to the inner surface of the part, the partial carcass (2) is made in an unfolded state corresponding to the position of the "J" - shaped flange and is of a detachable structure, the partial carcass (2) and the carcass (1) are aligned with each other by a positioning pin (3) and fixed with a screw (4), and the special positioning pin (5) is used for positioning the part on the carcass; the side cover plate (6) is designed according to the inner shape of the "J" - shaped flange, and is aligned with the carcass (1) by a positioning pin (3) and fixed with a screw (4); the integral cover plate (7) is aligned with the carcass by a special die-aligning pin (8), and is used for clamping and fixing when trimming the part, and through holes are made at the strengthening flange to cooperate with the core (9) for forming the strengthening flange; the core (9) is manufactured according to the outer surface of the strengthening flange of the part and is used for forming the strengthening flange; the fixed drill bushing (10) is installed on the cover plate and is used for inspecting the hole positions of the assembly holes, the movable handle (11) is installed on the integral cover plate for facilitating the installation and disassembly of the integral cover plate; the lifting eye bolt (12) is installed on the carcass and is used for handling and hoisting the tooling; The second process is numerical control milling and cutting; The tooling used in the numerical control milling and cutting process is a "milling and cutting fixture". This tooling includes: a structural carcass (13), a positioning pin (14), a vacuum adsorption device and a sealing strip (15), a non-plated wire screw sleeve (16), a lifting rod (17), a nozzle for vacuum fixture (18); The said "milling and cutting fixture" realizes precise milling and cutting of the edges and inner holes of the "U" - section blank formed in the stretching process and drilling of the assembly holes, and is used for subsequent sheet metal forming; the positioning pin (14) is installed at the top of the carcass and is used for positioning the part during milling and cutting; to ensure that the part and the fixture are closely fitted during milling and cutting, a vacuum adsorption device is added inside the carcass, and a vacuum adsorption device and a sealing strip (15) are laid near the milling edge; the lifting rod (17) penetrates through the carcass and is used for handling and hoisting the tooling; the nozzle for vacuum fixture (18) is connected to the vacuum adsorption device inside the carcass and is used for evacuating during milling and cutting; The third process is manual forming; The tooling used in manual forming is a "die blank". This tooling uses the same set of tooling as that used in stretch forming; during manual forming and trimming, the partial carcass (2) is removed, and the carcass is used in cooperation with the cover plate and the side cover plate to form a "J" - shaped structure; when the carcass is used in cooperation with the core, the strengthening flange on the web can be formed.

2. The manufacturing method of the "ji" - shaped cross - section variable - curvature complex skin with reinforced flanges as described in claim 1, wherein, The described carcass (1), partial carcass (2), positioning pin (3), screw (4), special positioning pin (5), side cover plate (6), integral cover plate (7), special die-aligning pin (8), core (9), fixed drill bushing (10), movable handle (11), lifting eye bolt (12) are manufactured according to the dataset, with the profile manufacturing tolerance of ±0.1 mm and the working surface roughness not higher than Ra1.

6.

3. The manufacturing method of the "Ji" - shaped cross - section variable - curvature complex skin with reinforced flanges according to claim 1 or 2, wherein, The described positioning pin (14), vacuum adsorption device and sealing strip (15), non-plated wire screw insert (16), lifting rod (17), nozzle for vacuum fixture (18) are manufactured with SAM-900-LX epoxy resin on the surface and SAM910 resin as the matrix, with the profile manufacturing tolerance of ±0.1 mm and the working surface roughness not higher than Ra1.

6.

4. The manufacturing method of the "ji"-shaped cross-section variable curvature complex skin with reinforced bent edges as described in claim 1 or 2, wherein, The described structural carcass (13) is integrally in a "convex" shape, with a pressing plate groove added at a position 40 mm from the bottom for fixing the tooling on the platform during milling; a reference hole is provided at the top of the structural carcass (13) for tooling alignment and as the coordinate origin during CNC milling.

5. The manufacturing method of the "Ji"-shaped cross-section variable curvature complex skin with reinforced flanges as described in claim 3, characterized in that, The described structural carcass (13) is integrally in a "convex" shape, with a pressing plate groove added at a position 40 mm from the bottom for fixing the tooling on the platform during milling; a reference hole is provided at the top of the structural carcass (13) for tooling alignment and as the coordinate origin during CNC milling.

6. The manufacturing method of the "ji"-shaped cross-section variable-curvature complex skin with reinforced bent edges as claimed in claim 1 or 2 or 5, characterized in that, The described non-plated wire screw insert (16) is installed at the carcass position about 150 mm from the edge of the part, and during milling, it cooperates with the pressing plate to enhance the pressing effect on the blank and prevent the part from shifting during milling due to the failure of the vacuum adsorption device.

7. The manufacturing method of the "ji" - shaped cross - section variable - curvature complex skin with reinforced bent edges as described in claim 3, characterized in that, The described non-plated wire screw insert (16) is installed at the carcass position about 150 mm from the edge of the part, and during milling, it cooperates with the pressing plate to enhance the pressing effect on the blank and prevent the part from shifting during milling due to the failure of the vacuum adsorption device.

8. The manufacturing method of a complex skin with a "ji" - shaped cross - section and variable curvature with strengthened bent edges as claimed in claim 4, wherein The described non-plated wire screw insert (16) is installed at the carcass position about 150 mm from the edge of the part, and during milling, it cooperates with the pressing plate to enhance the pressing effect on the blank and prevent the part from shifting during milling due to the failure of the vacuum adsorption device.

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