Special clamp for anodic oxidation of large-curvature aircraft skin and use method of special clamp

Abstract

The invention discloses a special clamp for anodic oxidation of a large-curvature aircraft skin and a using method of the special clamp, and belongs to the technical field of surface machining, two sets of clamp bodies in different clamping forms are adopted for common use, one set adopts a bottom clamping form with an adjustable clamping angle, and the other set adopts a side edge folding clamping form. In the anodizing process, the two sets of clamp bodies are clamped in curved edge arc top areas on the two sides of the skin correspondingly, the clamping angle of one set of clamp bodies is adjusted according to the curvature and size of the part, so that the part forms an inclined angle after being clamped, and it is avoided that no film layer exists locally due to formation of an air bag. The clamp is simple in structure and convenient to operate, the part is inclined in the bath solution, it is effectively guaranteed that the part is firmly clamped, overall electric conduction is good, and the defect of electricity striking caused by part shaking in the anodizing process is overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of surface processing and relates to a special fixture for anodizing large-curvature aircraft skin and a use method thereof. Background Art

[0002] Aircraft skin is an important component of the aircraft. It is a component that maintains the aircraft's shape, bears part of the aircraft's force, and provides good dynamic performance. Its manufacturing quality has an important impact on the aircraft's aerodynamic performance. The aircraft skin structure diagram is as follows: Figure 5 . Aircraft skin parts generally include composite skins and metal skins, among which metal skins are mainly thin-walled aluminum alloy materials, which are larger in size and have diverse structures depending on their location. In order to improve the service life of parts and meet the anti-corrosion requirements of products, aluminum alloy skin parts usually adopt the surface protection form of anodizing + painting. The anodizing process of aluminum alloy parts uses the principle of electrochemistry, with aluminum alloy parts as anodes and inert electrodes such as lead plates as cathodes. Both are placed in an electrolyte of a specific concentration at the same time, and an appropriate current is passed through to form a layer of aluminum oxide film with good mechanical properties and corrosion resistance on the surface of the aluminum alloy parts.

[0003] The anodizing process of aluminum alloys is a process in which the electrochemical generation and chemical dissolution of the oxide film occur simultaneously. The process is accompanied by the generation of a large amount of heat, and the solution needs to be continuously stirred by compressed air. Therefore, the anodizing fixture should have sufficient mechanical strength and rigidity to ensure that the parts are firmly mounted. In addition, the fixture should have good contact conductivity and be simple to operate and low-cost. Suitable tooling fixtures can not only improve the quality of the anodized film, but also reduce production costs and improve production efficiency. At present, the anodizing process of skin parts uses a medium-sized hanger fixture with a lower end facing each other, which is directly clamped in the reserved position on the long side of the part. For skin parts with large curvature, the ventilation and stirring of the bath liquid during the anodizing process of the parts causes the parts to shake severely in the bath liquid. The state of the parts needs to be observed at all times during the anodizing process, but there are still phenomena of parts being electrified and partially insulated, which greatly affects the film quality and product delivery progress. Summary of the Invention

[0004] To improve the quality of the anodized film on highly curved skin parts while accommodating the efficient and stable processing flow of automated anodizing production lines, the present invention provides a specialized fixture for the anodization of highly curved aircraft skins and its use method, based on the structural characteristics of highly curved skin parts and the state of the anodizing bath during the anodizing process. This fixture structure effectively ensures secure clamping and excellent electrical conductivity during the anodizing process of highly curved skin parts, avoiding defects such as electrical flashing and localized insulation during the anodizing process. Furthermore, the fixture offers advantages such as simple structure, easy operation, and low processing and maintenance costs, meeting the requirements of anodizing production lines.

[0005] The present invention adopts the following technical solutions:

[0006] A special fixture for anodizing large-curvature aircraft skins. The fixture consists of two sets of fixture bodies with different clamping configurations. One set uses a bottom clamping configuration with adjustable clamping angles, while the other uses a side-on clamping configuration. During the anodizing process, the two sets of fixture bodies are clamped to the top areas of the curved edges on either side of the skin. One set of fixture bodies adjusts the clamping angle based on the curvature and size of the part, creating an inclined angle after clamping to prevent the formation of air pockets that can lead to a localized film-free layer. The specific structure of the fixture is as follows:

[0007] The special clamps include left and right abutment clamps and top and bottom abutment clamps.

[0008] The left and right engaging clamps include a left engaging block 1 and a right engaging block 2. The left engaging block 1 is L-shaped, and the right engaging block 2 is U-shaped. When the two are engaged with each other, a hollowed-out Chinese character is formed in the middle. The upper end engaging portion of the left engaging block 1 and the right engaging block 2 is a connecting area, and the lower end engaging portion is a clamping surface 16. The connecting area adopts an assembly form of a concave and convex structure. A connecting boss 13 is provided in the connecting area of the right engaging block 2. A groove is formed in the connecting area of the left engaging block 1 to match the connecting boss 13. The connecting boss 13 and the groove are both provided with a coaxial axial center hole 14. After engagement, they are connected through the axis 8 to facilitate disassembly of the fixture and rotation to adjust the opening and closing angle of the clamping surface 16. The clamping surface 16 of the left engaging block 1 and the right engaging block 2 is used. In order to clamp large curvature skin parts, the clamping surfaces 16 of both adopt a U-shaped groove structure, which reduces the size of the fixture and reduces the weight of the fixture while ensuring good conductivity; coaxial fastening holes 15 are reserved in the middle of the left mating block 1 and the right mating block 2 to insert the fastening hook 11, and a threaded area is reserved at the tail end of the fastening hook 11, which is used in conjunction with the nut 9 and the fastening washer 10 to ensure firm clamping; a connecting hole 12 is made at the top of the right mating block 2, and the lower end of the copper hook 5 is connected by the fastening nut 6 and the bolt 7, and the upper end of the copper hook 5 is connected to the suspension beam. The connection angle between the copper hook 5 and the right mating block 2 is adjustable, so that the clamping angle between the left and right mating clamps and the large curvature skin parts can be adjusted.

[0009] The upper and lower engaging clamps include an upper engaging block 3 and a lower engaging block 4. The upper engaging block 3 is in the shape of a Chinese character with a hollow middle, and the lower engaging block 4 is in the shape of a U-shaped piece with an opening upward. The two adopt the upper and lower engaging form, and the engaging part on one side of the two is a connecting area, and the engaging part on the other side is a clamping surface 16; the connecting area of the upper engaging block 3 and the lower engaging block 4 also adopts an assembly form of a concave and convex structure. The connecting area of the lower engaging block 4 is also provided with a connecting boss 13, and the connecting area of the upper engaging block 3 is also made into a groove that matches the connecting boss 13. The connecting boss 13 and the groove are also reserved with a coaxial axial center hole 14 After alignment, they are connected by another axis 8. The clamping surfaces 16 of the left and right alignment blocks 1 and 2 are used to clamp skin parts with large curvature, and the clamping surfaces 16 of the two also adopt a U-shaped groove structure; the middle parts of the upper and lower alignment blocks 3 and 4 are also reserved with coaxial fastening holes 15 to penetrate another fastening hook 11, which is used in conjunction with the nut 9 and the fastening washer 10 to ensure firm clamping; a connecting hole 12 is also made on the top of the upper alignment block 3, which is connected to the lower end of another copper hook 5 through another fastening nut 6 and bolt 7. The length of the copper hook 5 is optional, and its upper end is connected to the suspension beam.

[0010] Furthermore, the left engaging block 1, the right engaging block 2, the upper engaging block 3 and the lower engaging block 4 are made of aluminum alloy.

[0011] Furthermore, the axis 8 is made of aluminum wire.

[0012] Furthermore, the fastening hook 11 is made of titanium alloy material.

[0013] A method for using the above-mentioned special fixture for anodizing large-curvature aircraft skins comprises the following steps:

[0014] The first step is to select two copper hooks 5 of appropriate length, connect the two copper hooks 5 to the right mating block 2 in the left and right mating clamps and the upper mating block 3 in the upper and lower mating clamps respectively, adjust the connection angle between the copper hooks 5 and the right mating block 2, and then fix them firmly with nuts 6 and bolts 8.

[0015] In the second step, the connection areas of the left and right engaging blocks 1 and 2 as well as the upper and lower engaging blocks 3 and 4 are assembled and the shaft 8 is inserted.

[0016] The third step is to clamp the clamping ear area of the arc top on one side of the large curvature skin part between the clamping surfaces 16 of the left and right matching clamps, and clamp the clamping ear area of the arc top on the other side between the clamping surfaces 16 of the upper and lower matching clamps, and then use the fastening hook 11 to connect the fastening hole 15 of the matching surface, install the fastening washer 10 and the nut 9 in sequence and tighten them to ensure that the clamping is firm.

[0017] In the fourth step, a copper hook 5 is attached to the suspension beam, and a crane is used to move the highly curvatured skin part through the entire anodizing process. By adjusting the angle of the copper hook 5 and the clamp, the highly curvatured skin part is tilted after attachment, preventing air pockets during the anodizing process and ensuring overall clamping stability.

[0018] Step 5: After the large curvature skin parts are anodized and dried, they are moved to the parts unloading area by the production line crane, the copper hook 5 is removed from the suspension beam, the nuts 9 on the two matching fixtures are loosened, and the large curvature skin parts are removed.

[0019] Furthermore, the left joining block 1, the right joining block 2, the upper joining block 3 and the lower joining block 4 need to be subjected to anodizing film removal treatment before being reused to ensure that the joining surfaces are flat and have good electrical conductivity.

[0020] Furthermore, before anodizing, 40mm×50mm arc top ears are reserved on both sides of the arc top area of the large curvature aircraft skin parts to avoid fixture marks on the surface of the parts after anodizing.

[0021] Beneficial effects of the present invention: The fixture of the present invention has a simple structure and is easy to operate. During the anodizing process, two sets of fixtures are used to clamp the arc top areas on both sides of the skin parts respectively, and the parts are tilted in the tank liquid, which effectively ensures that the parts are firmly clamped and the overall conductivity is good, avoiding electrical defects caused by the shaking of the parts during the anodizing process. The hooks, bolts, nuts and other structures used for fastening the fixture are made of titanium alloy, which avoids repeated film stripping and erosion damage, and effectively increases the service life of the fixture. The fixture body is easy to disassemble, the connecting device is highly versatile, easy to process and manufacture, and the cost of fixture processing and subsequent maintenance is low, meeting the needs of industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the fixture structure.

[0023] Figure 2 Schematic diagram of the left and right matching fixture structure.

[0024] Figure 3 Schematic diagram of the upper and lower matching fixture structure.

[0025] Figure 4 It is a schematic diagram of the structure of the right engaging block of the fixture.

[0026] Figure 5 Schematic diagram of the structure of large curvature skin parts.

[0027] Figure 6 This is a top view of a skin part with large curvature.

[0028] Figure 7 This is a schematic diagram of the installation process during the anodizing process of large-curvature aircraft skin parts.

[0029] In the figure, 1 is the left mating block; 2 is the right mating block; 3 is the upper mating block; 4 is the lower mating block; 5 is the copper hook; 6 is the fastening nut; 7 is the bolt; 8 is the axis; 9 is the nut; 10 is the fastening washer; 11 is the fastening hook; 12 is the connecting hole; 13 is the connecting boss; 14 is the axis hole; 15 is the fastening hole; 16 is the clamping surface. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clear, the specific implementation methods of the present invention will be described in detail below based on the technical solutions.

[0031] A special fixture for anodizing large-curvature aircraft skins, the specific structure is as follows:

[0032] The special fixtures include left and right fixtures and upper and lower fixtures. Figure 1 shown.

[0033] like Figure 2 As shown, the left and right joining fixtures include a left joining block 1 and a right joining block 2, both of which are made of aluminum alloy. The left joining block 1 is L-shaped, and the right joining block 2 is U-shaped (such as Figure 4 ), the left and right sides of the two are matched to form a hollowed-out Chinese-character form in the middle, which ensures the clamping strength on the one hand and reduces the overall weight on the other hand for easy operation; the upper end of the left matching block 1 and the right matching block 2 are matched for the connection area, and the lower end is matched for the clamping surface 16. The connection area adopts a concave and convex structure assembly form, and the right matching block 2 connection area is provided with a connecting boss 13, and the left matching block 1 connection area is made of a groove that matches the connecting boss 13. The connecting boss 13 and the groove are both reserved with a coaxial axial hole 14 with a diameter of 5mm. After matching, the axis 8 is inserted into the axis hole 14 to achieve connection, so as to facilitate the disassembly of the fixture and the rotation to adjust the opening and closing angle of the clamping surface 16. The axis 8 is made of aluminum wire, and the clamping surfaces 16 of the left matching block 1 and the right matching block 2 are used To clamp large curvature skin parts, the clamping surfaces 16 of both blocks adopt a U-shaped groove structure, which reduces the size of the clamp and reduces the weight of the clamp while ensuring good conductivity; coaxial fastening holes 15 are reserved in the middle of the left and right blocks 1 and 2 to insert the fastening hooks 11. The fastening hooks 11 are made of titanium alloy and have a 50mm threaded area reserved at the tail end. They are used in conjunction with nuts 9 and fastening washers 10 to ensure firm clamping; a connecting hole 12 is made on the top of the right block 2, which is connected to the lower end of the copper hook 5 by fastening nuts 6 and bolts 7. The upper end of the copper hook 5 is connected to the suspension beam. The connection angle between the copper hook 5 and the right block 2 is adjustable, thereby making the clamping angle between the left and right clamps and the large curvature skin parts adjustable.

[0034] like Figure 3As shown, the upper and lower mating fixtures include an upper mating block 3 and a lower mating block 4, both of which are made of aluminum alloy. The upper mating block 3 is in a hollowed-out middle Chinese-shaped shape, and the lower mating block 4 is in a U-shaped shape with an opening upward. The two adopt the upper and lower mating form, and the mating part on one side of the two is a connection area, and the mating part on the other side is a clamping surface 16; the connection area of the upper mating block 3 and the lower mating block 4 also adopts an assembly form of a concave and convex structure, and the connection area of the lower mating block 4 is also provided with a connecting boss 13, and the connection area of the upper mating block 3 is also made into a groove that matches the connecting boss 13, and the connecting boss 13 and the groove are also reserved with a coaxial axis. Hole 14, after alignment, is connected by another axis 8. The clamping surfaces 16 of the left and right alignment blocks 1 and 2 are used to clamp large curvature skin parts, and the clamping surfaces 16 of the two also adopt a U-shaped groove structure; the middle part of the lower end surface of the upper alignment block 3 and the middle part of the lower alignment block 4 are also reserved with coaxial fastening holes 15 to penetrate another fastening hook 11, which is used in conjunction with the nut 9 and the fastening washer 10 to ensure firm clamping; a connecting hole 12 is also made on the top of the upper alignment block 3, which is connected to the lower end of another copper hook 5 through another fastening nut 6 and bolt 7. The length of the copper hook 5 is optional, and its upper end is connected to the suspension beam.

[0035] A method for using the above-mentioned special fixture for anodizing large-curvature aircraft skins comprises the following steps:

[0036] The first step is to select two copper hooks 5 of appropriate length, connect the two copper hooks 5 to the right mating block 2 in the left and right mating clamps and the upper mating block 3 in the upper and lower mating clamps respectively, adjust the connection angle between the copper hooks 5 and the right mating block 2, and then fix them firmly with nuts 6 and bolts 8.

[0037] In the second step, the connection areas of the left and right engaging blocks 1 and 2 as well as the upper and lower engaging blocks 3 and 4 are assembled and the shaft 8 is inserted.

[0038] The third step is to reserve 40mm×50mm arc top ears (such as Figure 6 ), wipe the surface of the large curvature skin parts with a part soaked in GLX-40 cleaning agent organic solvent, and then dry the parts with a clean cloth; clamp the arc top ear piece on one side of the large curvature aircraft skin parts between the clamping surfaces 16 of the left and right matching clamps, and clamp the arc top ear piece on the other side between the clamping surfaces 16 of the upper and lower matching clamps, and then use the fastening hook 11 to connect the fastening hole 15 of the matching surface, install the fastening washer 10 and the nut 9 in sequence and tighten them to ensure that the clamping is firm.

[0039] In the fourth step, the copper hook 5 is mounted on the suspension beam, and the large curvature skin parts are moved by the crane to undergo the full anodizing process. By adjusting the connection angle between the copper hook 5 and the matching fixture, the large curvature skin parts are kept at an inclination angle of 20° to 30° on both sides after being mounted (such as Figure 7) to avoid air pockets during the anodizing process and ensure the stability of the overall clamping.

[0040] The fifth step is to use the pre-treatment form of polishing-alkali corrosion-polishing to pre-treat the large curvature skin parts in nitric acid-sodium hydroxide-nitric acid bath in sequence. The surface of the pre-treated parts should maintain a continuous water film for 30 seconds without breaking; using the constant pressure method, immerse the large curvature skin parts in sulfuric acid electrolyte, at a temperature of 13-25 ° C, increase the voltage to the specified range within 5 minutes, and maintain the voltage for the required time. In order to prevent local overheating during anodizing, compressed air is used to stir the bath liquid; at 90 ° C -100 ° C, the large curvature skin parts are immersed in sulfuric acid electrolyte. The curvature skin parts are immersed in potassium dichromate bath for sealing treatment; the large curvature skin parts are dried in a drying tank at 40℃-70℃; the large curvature skin parts are moved to the parts unloading area by the production line crane, and wearing clean cotton gloves, the copper hook 5 is removed from the suspension beam, and the nuts 9 on the two matching clamps are loosened to remove the large curvature skin parts; after anodizing, the appearance of the film layer is continuous, smooth and uniform. The color of the film layer after sealing is usually light yellow to yellow-green. Due to different materials and surface conditions, the surface color is allowed to be different.

[0041] The left joining block 1, the right joining block 2, the upper joining block 3 and the lower joining block 4 need to be de-anodized before being used again to ensure that the joining surfaces are flat and have good conductivity.

[0042] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A special fixture for anodizing large-curvature aircraft skins, characterized in that: The described special fixture consists of two groups of fixture bodies with different clamping forms used together. One group adopts a bottom clamping form with adjustable clamping angles, and the other group adopts a side mating clamping form. During the anodizing process, the two groups of fixture bodies are respectively clamped on the curved edge arc top areas on both sides of the skin. One group of fixture bodies adjusts the clamping angle according to the curvature and size of the part, so that the part forms an inclined angle after clamping, avoiding the formation of air bags and resulting in local film-free areas.

2. The special fixture for anodizing large-curvature aircraft skin according to claim 1, characterized in that: The described special fixture includes a left-right mating fixture and an up-down mating fixture; The left-right mating fixture includes a left mating block (1) and a right mating block (2). The left mating block (1) is L-shaped, and the right mating block (2) is U-shaped. After they are mated left and right, they form a hollowed-out square shape in the middle. The upper mating part of the left mating block (1) and the right mating block (2) is the connection area, and the lower mating part is the clamping surface (16). The connection area adopts an assembly form with concave and convex structures. The clamping surface (16) is used to clamp large-curvature skin parts. Coaxial fastening holes (15) are reserved in the middle of both the left mating block (1) and the right mating block (2), and a fastening hook (11) is inserted to achieve firm clamping. A copper hook (5) is connected to the top of the right mating block (2) to connect to the suspension beam, and the connection angle between the copper hook (5) and the right mating block (2) is adjustable; The up-down mating fixture includes an upper mating block (3) and a lower mating block (4). The upper mating block (3) is in a hollowed-out square shape in the middle, and the lower mating block (4) is U-shaped with an upward opening. They adopt an up-down mating form. One side mating part of them is the connection area, and the other side mating part is the clamping surface (16). The connection area also adopts an assembly form with concave and convex structures. The clamping surface (16) is used to clamp large-curvature skin parts. Coaxial fastening holes (15) are also reserved in the middle of both the upper mating block (3) and the lower mating block (4), and another fastening hook (11) is inserted to achieve firm clamping. Another copper hook (5) is connected to the top of the upper mating block (3) to connect to the suspension beam, and the length of the copper hook (5) is optional.

3. The special fixture for anodizing large-curvature aircraft skin according to claim 2, characterized in that: The connection area of the left mating block (1) and the right mating block (2) adopts an assembly form with concave and convex structures. Specifically: a connection boss (13) is set in the connection area of the right mating block (2), and a groove for fitting the connection boss (13) is made in the connection area of the left mating block (1). Coaxial axis holes (14) are reserved in both the connection boss (13) and the groove. After mating, they are connected by an axis (8).

4. The special fixture for anodizing large-curvature aircraft skin according to claim 2, characterized in that: The connection area of the upper mating block (3) and the lower mating block (4) adopts an assembly form with concave and convex structures. Specifically: a connection boss (13) is set in the connection area of the lower mating block (4), and a groove for fitting the connection boss (13) is made in the connection area of the upper mating block (3). Coaxial axis holes (14) are also reserved in both the connection boss (13) and the groove. After mating, they are connected by an axis (8).

5. The special fixture for anodizing large-curvature aircraft skin according to claim 2, characterized in that: The clamping surfaces (16) of both the left-right mating fixture and the up-down mating fixture adopt a U-shaped groove structure.

6. The special fixture for anodizing large-curvature aircraft skin according to claim 2, characterized in that: The left mating block (1), the right mating block (2), the upper mating block (3) and the lower mating block (4) are made of aluminum alloy.

7. The special fixture for anodizing large-curvature aircraft skin according to claim 2, characterized in that: The described fastening hook (11) is made of titanium alloy material.

8. A method for using the special fixture for anodizing large-curvature aircraft skin according to any one of claims 1 to 7, characterized in that: It includes the following steps: The first step is to select two copper hooks (5) of appropriate length, connect the two copper hooks (5) to the right joining block (2) in the left and right joining fixtures and the upper joining block (3) in the upper and lower joining fixtures, and adjust the connection angle between the copper hooks (5) and the right joining block (2); The second step is to assemble the connection areas of the left and right engaging blocks (1) and the upper and lower engaging blocks (3) and (4); The third step is to clamp the clamping ear piece area of the arc top on one side of the large curvature skin part between the clamping surfaces (16) of the left and right matching clamps, and clamp the clamping ear piece area of the arc top on the other side between the clamping surfaces (16) of the upper and lower matching clamps, and then use the fastening hooks (11) to clamp the two matching clamps firmly. In the fourth step, the copper hook (5) is mounted on the suspension beam, and the large curvature skin part is moved to perform the full process of anodizing; by adjusting the connection angle between the copper hook (5) and the matching fixture, the large curvature skin part is tilted after being mounted to avoid the generation of air pockets; Step 5: After the large curvature skin part is anodized and dried, the copper hook (5) is removed from the suspension beam, the two matching clamps are removed, and the large curvature skin part is removed.

9. The method for using the special fixture for anodizing large-curvature aircraft skin according to claim 8, characterized in that: The left joining block (1), the right joining block (2), the upper joining block (3) and the lower joining block (4) need to be subjected to anodizing film removal treatment before being used again.

10. The method for using the special fixture for anodizing large-curvature aircraft skin according to claim 8, characterized in that: Before anodizing, 40mm×50mm arc top ears are reserved in the arc top areas on both sides of the large curvature aircraft skin parts.

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