Processing method of double-curvature skin piece with local features

Abstract

The invention relates to a machining method for a double-curvature skin part with local features, and belongs to the technical field of aviation metal plate manufacturing. According to the combined forming machining method for the double-curvature skin local feature part, the consistency of skin stretching forming and local forming under the same positioning condition is guaranteed, the appearance precision of the skin in the manufacturing process is guaranteed, and the accuracy of skin forming machining and measuring is improved. A pneumatic forming structure device is additionally arranged on the tool structure, and the conventional process that a skin part needs two sets of independent tools to complete the machining process is broken through. The mode of two-time forming and one-time positioning is adopted, the width and the depth of a complex structure can be accurately manufactured, and uniform stress and smooth transition of the surface quality of a skin complex structure profile can be achieved.

Description

Technical Field

[0001] The invention relates to a method for processing a double-curvature skin part with local features, belonging to the technical field of aviation sheet metal manufacturing. Background Art

[0002] In the aviation industry, sheet metal parts are the main part of the shape and structure of modern aircraft. They have the characteristics of many types, complex structure, large outline size, low rigidity, etc., and they account for a considerable proportion of the whole machine. Generally speaking, the large-scale use of sheet metal parts can greatly reduce the weight of aircraft, aircraft engines, etc. under the premise of meeting the function and shape of the parts. Sheet metal parts are low in cost, can be mass-produced with high efficiency, and the economic benefits are very considerable. Since aircraft need to work for a long time under harsh conditions at high altitudes, high requirements are placed on the comprehensive performance of the materials of their parts. At present, most aviation companies formulate production processes for the manufacture of sheet metal parts based on their own experience, and there has been little innovation in the process, resulting in low production qualification rate and high cost. The most important factor affecting the cold forming performance of the sheet is the forming performance of the material itself. Therefore, if the processing technology is formulated without understanding the forming performance of the sheet itself and its basic parameters, it will not only fail to give full play to its maximum forming performance, but also affect the quality of the parts after forming.

[0003] There are multiple local features on the surface of aircraft curved skin parts. The assembly relationship of local features is to install finished parts. In order to meet the installation requirements of finished parts, local features need to be designed as raised rib structures. During the skin forming process, the raised position cannot be formed at one time. The raised position of the local features is stepped, and the width of the transition zone is 26 to 47 (mm). During the stretch forming process, agitation and warping deformation occur here. After being pressed by the upper pressing device, the transition zone depth is insufficient. There is basically no step shape during visual inspection. The conventional method is that workers use wooden hammers to knock out the stepped shape of the reinforcement ribs. After manual forming, there is poor surface quality of corrugation, which affects the appearance quality of the skin. The processing tolerance requirement is 0-0.3mm. Compared with the traditional aircraft skin part appearance tolerance of plus or minus 1mm, the inspection accuracy is increased by 3 times.

[0004] The present invention proposes a method for processing a hyperbolic skin part with local features, which takes the local features of the hyperbolic skin part as the research object, conducts a full process analysis of material properties, shape and structure characteristics, forming schemes, etc., and studies the influence of stretch forming process parameters on the tensile stress, shear stress, springback, etc. of the part. In combination with the shape characteristics of the part, tooling is designed and manufactured, and only one positioning with the part is achieved on two sets of tooling, so that the local features of the hyperbolic shape and the pressed protrusion can be manufactured quickly, accurately, and efficiently, and the fast and accurate positioning and the transition zone width meet the requirements of 26 to 47 (mm), and the surface quality of the transition zone is smooth without indentation. Summary of the invention

[0005] The present invention aims to solve a series of problems that the local features of the hyperbolic skin parts cannot be quickly and accurately positioned, the width of the transition zone cannot meet the requirements of 26 to 47 (mm), and the surface quality of the transition zone cannot be smooth and without indentations. A combined forming method is proposed. By adding a pneumatic local feature forming structure device, one-time precise positioning of the combined forming is achieved, which can not only ensure the accuracy of the hyperbolic skin stretch forming and the local feature forming under the same positioning conditions, but also ensure the shape accuracy of the hyperbolic skin during the manufacturing process. Take the typical local feature hyperbolic skin forming as an example.

[0006] The technical solution of the present invention is as follows:

[0007] The processing method is composed of transverse stretching, drilling positioning holes, and local feature forming. The principle of stretching is that the two ends of the sheet are clamped by the clamps of the stretching machine, and the stretching die lifted by the workbench contacts the sheet, generating uneven plane tensile strain to make the sheet fit with the stretching die. It is often used to form double-curved skin. Among them, transverse stretching is a forming method in which the sheet is clamped at both ends of the sheet along the transverse direction, and under the action of the top force of the stretching die lifted by the workbench, the sheet fits with the stretching die. It is generally used for forming skin parts with large transverse curvature. Drilling positioning holes refers to the operation of using a drill to position and process holes on the workpiece through a drilling template. Its advantages are high precision, high speed, and high efficiency. Local feature forming uses the flow and pressure of gas to generate power to drive the local feature forming die to work, which can realize complex parts processing. To complete the forming of local features of hyperbolic skin parts, a set of pneumatic local feature forming dies is required to realize the processing of local features of skin parts.

[0008] The typical parts processing process described is as follows Figure 5 shown.

[0009] The tooling designed for the combined processing method is a set of combined forming dies, including a stretching forming die and a pneumatic local feature forming die. The local feature forming die is used in conjunction with the stretching forming die to accurately, quickly and efficiently process the local features of the hyperbolic skin.

[0010] The stretching forming die comprises: a base, a movable drilling template and a hanging rod.

[0011] The pneumatic local feature forming mold includes: a Π-shaped fixing frame, a threaded positioning pin, a threaded connecting plate at both ends, a forming mold, a force block, a pressure nut, a support frame, a cylinder, an air inlet, and an air outlet. Among them, the base is made of SAM900 resin material. SAM900 resin is a non-metallic material, which is characterized by excellent chemical stability, electrical insulation, corrosion resistance, good bonding properties and high mechanical properties. In addition, it also has good mechanical processing properties, and its surface strength, wear resistance and impact resistance are very close to metal materials. There are 3 movable drilling templates, which are located on the upper surface of the base and are distributed in a triangular shape on different edges of the parts. They are used to drill positioning holes for parts. When in use, one side of each movable drilling template is connected to the base through Pin connection, with a fully drilled sleeve on the other side hole, The hole is a part positioning hole. The hanging rod is used to move the base, with a diameter of 80㎜ and a length of 350㎜. There are 4 of them, and each group of 2 is placed in the middle of the short side of the base, symmetrical to each other. There are 2 Π-shaped fixing frames, which are symmetrical to each other. Each is connected to the long side of the base through 6 bolts. There are 2 threaded connecting plates at both ends, which are symmetrical to each other. Their function is to connect the Π-shaped fixing frame and the forming mold. They are fixed by threaded locating pins. The forming mold frame is on the upper surface of the base, located above the local features of the hyperbolic skin, and the shape of the lower surface of the forming mold is the same as the shape of the local features of the hyperbolic skin. The force block is placed on the upper surface of the forming mold. Its shape is the same as the shape of the local features of the hyperbolic skin, and its size is the same as the size of the outermost edge of the local features of the hyperbolic skin. It is used to apply pressure. The lower surface of the pressure nut is connected to the force block, and the upper surface is connected to the cylinder. The main function of the support frame is to support the cylinder. Compressed air enters through the polyurethane hose and passes through the air inlet into the cylinder, and the change in gas pressure is used to generate power. The power is transmitted to the forming die through the pressure nut and the force block to form the local features of the skin. After the forming is completed, the compressed air is exhausted through the polyurethane hose through the air outlet. In order to better and more conveniently adjust the air pressure, an air regulating valve can be set. This finished product can be purchased separately.

[0012] A method for processing a double-curvature skin part with local features, the steps are as follows:

[0013] Step 1: Install the special platform and use a rail-mounted crane to place the special platform required for stretch forming in the center of the stretching machine.

[0014] Step 2: Install the base, use professional lifting ropes to wrap around the four lifting rods respectively, and use the rail crane again to place the base in the center of the platform to ensure that the base and the platform are well fixed, and position the base in the stretching direction to make it consistent with the direction of the jaws.

[0015] Step 3: Clamp the blank and place both ends of the blank in the jaws of the stretching machine so that the ends are in contact with the bottom of the jaws, ensuring that the clamping amount of the jaws on both sides is not less than 50mm.

[0016] Step 4: Close the jaws and clamp the blank, check the clamping status of the jaws to ensure that the jaws fully clamp the blank.

[0017] Step 5: Transverse pre-stretching, the base rises and contacts the blank, and the material begins to bend. When the material bends to contact the base × 1200mm = 1800mm 2 Due to the skin structure, the two sides are close to vertical in the final stage of stretching, the top force of the machine tool is the largest, and α = 90°α: the wrap angle of the sheet on the base. Therefore, the tensile force required for the sheet process in the stretching state is about 460N.

[0018]

[0019] Step 6: heat-treat the pre-stretched blank, take the pre-stretched blank out of the jaws, and use an air furnace to quench the pre-stretched blank. The pre-stretched blank after quenching is in a "W" or "AQ" state.

[0020] Step 7: Second stretching and forming. Repeat the third and fourth steps to perform the second stretching and forming. The jaws clamp the pre-stretched blank to completely cover the working surface of the base until the blank and the base are completely fitted. Use a wooden hammer or rubber plate to knock on the surface of the part to check whether the part fits the base. During the stretching process, control the tension to ensure that the stretching rate does not exceed 6%. The blank is stretched in the newly quenched state, and the tensile strength is σ b =337MPa, and the tensile force required for stretching the newly quenched billet is about 764N.

[0021] Step 8: Install the movable drilling template at the designated position of the base and drill Locate the holes, remove the removable drilling template, and drill the holes in the Insert the positioning pin into the positioning hole, open the jaws, and remove excess material on both sides of the blank. Pay attention to protecting the surface of the part to prevent scratches or abrasions.

[0022] Step 9: Install the Π-shaped fixing frame, the threaded connecting plates at both ends, and the forming mold in sequence, and use polyurethane hoses to connect the compressed air, air inlet, and air outlet. After the installation is completed, open the compressed air regulating valve, and through air pressure transmission, the force block gives power to the forming mold to process the local feature shape.

[0023] Step 10: Five-coordinate milling shape, in order to ensure the manufacturing positioning accuracy, use the same The locating holes are used for positioning, and all edges and inner holes of the parts are milled using a five-coordinate CNC milling machine according to the verified CNC machining program.

[0024] Step 11: Check the shape, surface and edge accuracy of the parts. The shape tolerance is ±0.5mm, and the edge manufacturing accuracy tolerance is ±0.2mm.

[0025] Advantages of the present invention:

[0026] The combined forming processing method of the local characteristic parts of the hyperbolic skin ensures the consistency of the skin stretch forming and local forming under the same positioning conditions, ensures the shape accuracy of the skin during the manufacturing process, and improves the accuracy of the skin forming processing and measurement. The pneumatic forming structure device added to the tooling structure breaks through the conventional process of requiring two sets of independent tooling to complete the processing of a skin part. The method of two forming and one positioning can accurately manufacture the width and depth of the complex structure, and can achieve uniform force on the complex structural surface of the skin, and smooth transition of surface quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Front view of the combined forming die;

[0028] Figure 2 A top view of the combined forming die;

[0029] Figure 3 Top view of pneumatic local feature forming;

[0030] Figure 4 A three-dimensional diagram of a pneumatic local feature forming die;

[0031] Figure 5 Typical parts processing process flow chart.

[0032] In the figure: 1 base, 2 movable drilling template, 3 hanging rod, 4 Π-shaped fixing frame, 5 threaded positioning pin, 6 two-end threaded connecting plate, 7 forming die, 8 force block, 9 pressure nut, 10 support frame, 11 cylinder, 12 air inlet, 13 air outlet. DETAILED DESCRIPTION

[0033] According to the structure of the local features of the hyperbolic skin, a combined forming process flow is formulated. Taking the typical local features of the hyperbolic skin as an example, the implementation steps of the combined forming method are as follows:

[0034] Step 1: Install the special platform and use a rail-mounted crane to place the special platform required for stretch forming in the center of the stretching machine.

[0035] Step 2: Install the base 1, use professional lifting ropes to respectively cover the four lifting rods 3, and use the rail crane again to place the base 1 in the center of the platform, ensure that the base 1 and the platform are well fixed, and position the base 1 according to the stretching direction to make it consistent with the direction of the jaws.

[0036] Step 3: Clamp the blank and place both ends of the blank in the jaws of the stretching machine so that the ends are in contact with the bottom of the jaws, ensuring that the clamping amount of the jaws on both sides is not less than 50mm.

[0037] Step 4: Close the jaws and clamp the blank, check the clamping status of the jaws to ensure that the jaws fully clamp the blank.

[0038] Step 5: Transverse pre-stretching, base-1 rises and contacts the blank, and the material begins to bend. When the material bends to contact the surface of base-1, the jaws are released and the pre-stretched blank is taken out. The machine tool tonnage required for stretching can produce 0.9σ per unit area of ​​the blank. b The stress calculation is based on the top force P on the worktable during horizontal pulling. When the blank is pre-stretched, the tensile strength is σ b =203MPa, the cross-sectional area of ​​the blank is F = 1.5mm (blank thickness) × 1200mm (blank width) = 1800mm 2 Due to the skin structure, the two sides are close to vertical in the final stage of stretching, the top force of the machine tool is the largest, and α = 90°α: the wrap angle of the sheet on the base-1. Therefore, the tensile force required for the sheet process in the stretching state is about 460N.

[0039]

[0040] Step 6: heat-treat the pre-stretched blank, take the pre-stretched blank out of the jaws, and use an air furnace to quench the pre-stretched blank. The pre-stretched blank after quenching is in a "W" or "AQ" state.

[0041] Step 7: Second stretching and forming. Repeat the third and fourth steps to perform the second stretching and forming. The jaws clamp the pre-stretched blank to completely cover the working surface of the base-1 until the blank and the base-1 are completely fitted. Use a wooden hammer or rubber plate to knock on the surface of the part to check whether the part fits the base-1. During the stretching process, control the tension to ensure that the stretching rate does not exceed 6% (the stretching rate is tested using elongation test paper). The blank is stretched in the newly quenched state, and the tensile strength is taken as σ b =337MPa, and the tensile force required for stretching the newly quenched billet is about 764N.

[0042] Step 8: Install the movable drilling template-2 at the specified position of the base-1 and drill Locate the holes, remove the removable drilling template-2, and drill the holes in the Insert the positioning pin into the positioning hole, open the jaws, and remove excess material on both sides of the blank. Pay attention to protecting the surface of the part to prevent scratches or abrasions.

[0043] Step 9: Install the Π-shaped fixing frame-4, the two-end threaded connecting plate-6, and the forming mold-7 in sequence, and use a polyurethane hose to connect the compressed air, the air inlet-12, and the air outlet-13. After the installation is completed, open the compressed air regulating valve, and through the air pressure transmission, the force block-8 gives power to the forming mold-7 to process the local feature shape.

[0044] Step 10: Five-coordinate milling shape, in order to ensure the manufacturing positioning accuracy, use the same The locating holes are used for positioning, and all edges and inner holes of the parts are milled using a five-coordinate CNC milling machine according to the verified CNC machining program.

[0045] Step 11: Check the shape, surface and edge accuracy of the parts. The shape tolerance is ±0.5mm, and the edge manufacturing accuracy tolerance is ±0.2mm.

Claims

1. A combined forming die for processing a double-curvature skin part with local features, characterized in that: Including stretch forming dies and pneumatic local feature forming dies; The stretch forming die comprises: a base (1), a movable drilling template (2), and a hanging rod (3); The pneumatic local feature forming die comprises: a Π-shaped fixing frame (4), a threaded positioning pin (5), a threaded connecting plate at both ends (6), a forming die (7), a force block (8), a pressure nut (9), a support frame (10), a cylinder (11), an air inlet (12), and an air outlet (13); The movable drilling templates (2), 3 in number, are located on the upper surface of the base (1) and are distributed in a triangular shape on different edges of the parts, and are used to drill positioning holes for the parts. When in use, one side of each movable drilling template (2) is connected to the base (1) via a 2-φ5 pin, and the other side has a φ5 hole with a drill sleeve inserted therein, and the φ5 hole is a positioning hole for the part; The hanging rod (3) is used to move the base (1), has a diameter of 80 mm, a length of 350 mm, and is 4 in number. Each group of 2 is placed in the middle of the short side of the base (1) and is symmetrical to each other. Two threaded connecting plates (6) are symmetrical to each other and are used to connect the Π-shaped fixing frame (4) and the forming die (7). The two connecting plates are fixed by threaded positioning pins (5). The forming die (7) is mounted on the upper surface of the base (1) and is located above the local feature of the hyperbolic skin. The shape of the lower surface of the forming die (7) is the same as the shape of the local feature of the hyperbolic skin. The force block (8) is placed on the upper surface of the forming mold (7), has the same shape as the local characteristic shape of the hyperbolic skin, and has the same size as the outermost edge size of the local characteristic of the hyperbolic skin, and is used to apply pressure.

2. A combined forming die for processing a double-curvature skin part with local features as claimed in claim 1, characterized in that: The base (1) is made of SAM900 resin material.

3. A combined forming die for processing a double-curvature skin part with local features as claimed in claim 1 or 2, characterized in that: The lower surface of the pressure nut (9) is connected to the force block (8), and the upper surface is connected to the cylinder (11).

4. A combined forming die for processing a double-curvature skin part with local features as claimed in claim 1 or 2, characterized in that: The Π-shaped fixing frames (4) are two in number and are symmetrical to each other, and each is connected to the long side of the base (1) via 6 bolts.

5. The combined forming die for processing a double-curvature skin part with local features as claimed in claim 3, characterized in that: The Π-shaped fixing frames (4) are two in number and are symmetrical to each other, and each is connected to the long side of the base (1) via 6 bolts.

6. A combined forming die for processing a double-curvature skin part with local features as claimed in claim 1, 2 or 5, characterized in that: The support frame (10) supports the cylinder (11), and compressed air enters through the polyurethane hose and passes through the air inlet (12) into the cylinder (11). The change in gas pressure is used to generate power, and the power is transmitted to the forming mold (7) through the pressure nut (9) and the force block (8) to form the local features of the skin. After the forming is completed, the compressed air is exhausted through the polyurethane hose and the air outlet (13).

7. A combined forming die for processing a double-curvature skin part with local features as claimed in claim 3, characterized in that: The support frame (10) supports the cylinder (11), and compressed air enters through the polyurethane hose and passes through the air inlet (12) into the cylinder (11). The change in gas pressure is used to generate power, and the power is transmitted to the forming mold (7) through the pressure nut (9) and the force block (8) to form the local features of the skin. After the forming is completed, the compressed air is exhausted through the polyurethane hose and the air outlet (13).

8. A combined forming die for processing a double-curvature skin part with local features as claimed in claim 4, characterized in that: The support frame (10) supports the cylinder (11), and compressed air enters through the polyurethane hose and passes through the air inlet (12) into the cylinder (11). The change in gas pressure is used to generate power, and the power is transmitted to the forming mold (7) through the pressure nut (9) and the force block (8) to form the local features of the skin. After the forming is completed, the compressed air is exhausted through the polyurethane hose and the air outlet (13).

9. A method for processing a double-curvature skin part with local features, characterized in that: Here are the steps: Step 1: Install the special platform and use the rail crane to place the special platform required for stretch forming at the center of the stretching machine; Step 2: Install the base (1), use professional lifting ropes to respectively cover the four lifting rods (3), and use the rail-mounted crane again to place the base (1) at the center of the platform, ensure that the base (1) and the platform are well fixed, and position the base (1) according to the stretching direction so that it is consistent with the direction of the jaws; Step 3: Clamp the blank and place both ends of the blank in the jaws of the stretching machine so that the ends are in contact with the bottom of the jaws, ensuring that the clamping amount of the jaws on both sides is not less than 50mm; Step 4: Close the jaws and clamp the blank, check the clamping state of the jaws to ensure that the jaws fully clamp the blank; Step 5: Transverse pre-stretching and forming, the base (1) rises and contacts the blank, and the material begins to bend; when the material is bent to contact the surface of the base (1), the jaws are released and the pre-stretched blank is taken out; Step 6: heat-treat the pre-stretched blank, take the pre-stretched blank out of the jaws, and use an air furnace to quench the pre-stretched blank. The pre-stretched blank after quenching is in "W" or "AQ" state; Step 7: Second stretching and forming, repeat the processing steps of step 3 and step 4 to perform the second stretching and forming, the jaws clamp the pre-stretched blank to completely cover the working surface of the base (1), until the blank and the base (1) are completely fitted, use a wooden hammer or a rubber plate to knock the surface of the part to check whether the part fits the base (1), and control the tension during the stretching process to ensure that the stretching rate does not exceed 6%; Step 8: Install the movable drilling template (2) at the designated position of the base (1), drill a 3-φ5.2 positioning hole, remove the movable drilling template (2), insert the positioning pins into the 3-φ5.2 positioning holes, open the jaws, remove the excess material on both sides of the blank, and pay attention to protecting the surface of the part to prevent scratches or abrasions; Step 9: sequentially install the Π-shaped fixing frame (4), the threaded connecting plate (6) at both ends, and the forming mold (7), and use a polyurethane hose to connect the compressed air, the air inlet (12), and the air outlet (13); after the installation is completed, open the compressed air regulating valve, and through the air pressure transmission, the force block (8) provides power to the forming mold (7) to process the local characteristic shape; Step 10: Five-coordinate milling of the shape. In order to ensure the manufacturing positioning accuracy, the same 3-φ5.2 positioning holes are used for positioning. According to the verified CNC machining program, a five-coordinate CNC milling machine is used to mill all the edges and inner holes of the parts; Step 11: Check the shape, surface and edge accuracy of the parts. The shape tolerance is ±0.5mm, and the edge manufacturing accuracy tolerance is ±0.2mm.

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