A method for manufacturing a variable-thickness multi-flange thin-wall part with a reinforcing groove structure

Abstract

The present application belongs to the field of aircraft sheet metal part processing technology, and relates to a manufacturing method of a variable-thickness multi-flange thin-wall part with a reinforcing groove structure. The present application adopts a process method of "numerical control milling cutting + sheet metal forming + chemical milling" to replace "numerical control milling + sheet metal forming". By replacing mechanical cutting with chemical milling, and cooperating with two newly designed toolings for reinforcing groove and flange forming, the problems of wrinkle of the web plate caused by the reinforcing groove forming, and thickness area distortion and deviation are solved, and finally the accurate shape of the part is obtained and the surface quality is improved. The present application has generalizability, and can be widely applied to the processing of complex surface and variable-thickness thin-wall parts, and meets the structural use requirements while further reducing the weight of the aircraft body.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aircraft sheet metal part processing, and relates to a variable-thickness multi-flanged thin-wall part manufacturing method with a reinforcing groove structure. BACKGROUND

[0002] To adapt to the characteristics of light weight, most of the frame plates and skin parts of the aircraft select small-thickness aluminum alloy thin-wall structures, and even some parts adopt variable-thickness structures, so as to further reduce the weight, and the reinforcing grooves and reinforcing small flanges are arranged to improve the carrying capacity and meet the requirements of rigidity and strength. In the processing process, for the parts with small and uneven thickness, the error is large during thickness processing, and the stress of the reinforcing groove structure is uneven during the forming process, so that the overall manufacturing precision of the part is low.

[0003] The traditional processing method for the parts is "numerical control milling + sheet metal forming", that is, the edge and thickness of the part in the unfolded state are milled, and then sheet metal forming and heat treatment strengthening are adopted. Because the material thickness is small and the thickness milling area is large, the residual stress is large during the milling process, the deformation is serious and difficult to correct, and a large strain is generated during the forming process of the reinforcing groove, the surrounding material flows and tends to be uneven, which leads to serious wrinkling of the web after forming and difficulty in flattening, and finally leads to distortion and deviation of the thickness processing area, which cannot be corrected. In addition, due to the too thin thickness of the part, the surface hammer marks caused by sheet metal finishing are difficult to eliminate, and if the whole is polished, the aluminum layer of the part is damaged, thereby reducing the physical and chemical properties of the part. Based on the above reasons, the processing of the parts has great difficulty. SUMMARY

[0004] The purpose of the application is to invent a variable-thickness multi-flanged thin-wall part manufacturing method with a reinforcing groove structure, which uses two new designed toolings for part forming and uses the process method of "numerical control milling + sheet metal forming + chemical milling" to replace "numerical control milling + sheet metal forming". The processing method used in the application can solve the problems of wrinkling of the web caused by the forming of the reinforcing groove, which cannot be repaired, and the distortion and deviation of the thickness area, and finally achieve the purpose of obtaining the accurate shape of the part and improving the surface quality.

[0005] In order to achieve the above purpose, the technical scheme of the application is as follows:

[0006] A variable-thickness multi-flanged thin-wall part manufacturing method with a reinforcing groove structure, comprising three processes of numerical control milling, sheet metal forming and chemical milling.

[0007] The first process is numerical control milling.

[0008] The process uses two-dimensional spread data set of the part as medium, and mills the outer edge of the part in spread state for subsequent sheet metal forming. When designing the two-dimensional spread data set, four ear pieces are added on both sides of the part web, and φ5.2 positioning holes are drilled for subsequent sheet metal forming and positioning during chemical milling; considering that the material flows more during the forming of the reinforcing groove, in order to avoid local edge being too small, the process allowance can be increased for compensation, and the formed part is removed;

[0009] The second process: sheet metal forming.

[0010] The process forms the blank in flat plate state to the part shape, including the reinforcing groove, the bent edge and the reinforcing small bent edge forming. The sheet metal forming is divided into two times, the first forming adopts the hydraulic forming to form the reinforcing groove, and the used tooling is "mold I".

[0011] The mold I includes a body, a cover plate, positioning pins, a die pin, a movable handle and a lifting ring.

[0012] The second forming adopts the manual forming to form the bent edge and the reinforcing small bent edge on both sides of the web, and the used tooling is "mold II",

[0013] The mold II includes a body, positioning pins, a die pin, a cover plate, a side cover plate, a movable handle and a lifting ring.

[0014] The mold I is used to press the milled blank to form the reinforcing groove. The tooling is designed and manufactured according to the process data, that is, the bent edge on both sides and the reinforcing small bent edge thereon are spread to the same plane as the web. The body of the mold I is made into a "concave" structure, that is, the reinforcing groove profile is embedded into the plane of the body, the thickness reduction area is compensated to the same thickness as other areas, the cover plate is made into a "convex" structure, the reinforcing rib protrudes below the plane of the cover plate, and the thickness reduction area is compensated to the same thickness as other areas. The positioning pins are installed between the body and the cover plate, and the positions thereof are consistent with the positions of the positioning holes of the numerically controlled milled part, for positioning the milled part on the tooling during forming. The die pin is installed between the body and the cover plate, for aligning the two and bearing the shear force of the cutting surface, preventing the relative position of the body and the cover plate from changing during hydraulic forming, causing the positioning pin to be bent and broken due to excessive force, and causing the part position to shift and deviate. The movable handle is installed on the upper surface of the cover plate, for facilitating the installation and removal of the cover plate during hydraulic forming, and the lifting ring is installed on the side of the body, for lifting and carrying the tooling. The manufacturing tolerance of the above structure profile is ±0.1 mm, and the roughness of the working profile is not higher than Ra1.6 μm

[0015] The aforementioned jig II is used to shape the blank with the reinforcing groove into the latest shape of the part, and can also be used for surface finishing of the part after heat treatment deformation. This tooling is manufactured according to the part's digital model. Its jig body adopts a split structure, with jig body I designed according to the inner surface of the part's web, and jig bodies II and III located on both sides of jig body I, their edges flush with jig body I. The positioning pins are aligned with the positioning holes of the CNC milled parts, used for positioning the part on the tooling during forming. The mold-closing pin is installed between the jig body and the cover plate, used for alignment and to withstand the shear force of the cutting surface, preventing the positioning pins from bending or breaking due to excessive force caused by changes in the relative position of the jig body and cover plate during forming, thus preventing deviations in the part's position. The cover plate is manufactured according to the outer surface of the part's web, and the side cover plates are manufactured according to the surface of the part's bent edges and the reinforcing small bent edges. When all three body parts (I, II, and III) are installed, they work in conjunction with cover plates to form the curved edges on both sides of the part. When body parts II and III are removed, body part I, cover plates, and side cover plates work together to reinforce the two small curved edges on the formed parts. Movable handles are installed on the upper surface of the cover plates for easy installation and removal during forming. Lifting rings are installed at appropriate positions on the sides of the body parts and cover plates for tooling lifting and handling. The manufacturing tolerance for the above structural surfaces is ±0.1mm, and the surface roughness of the working surfaces is no higher than Ra1.6μm.

[0016] The third process: chemical milling.

[0017] The area where the part is thinned from δ0.8mm to δ0.5mm is machined using chemical milling. Chemical milling is a processing technique that utilizes the principles of chemical or electrochemical corrosion to dissolve the surface of metallic or non-metallic materials with a chemical solution, thereby removing the material. It is suitable for surface machining of thin sheet parts, especially surfaces with complex geometries that are difficult to achieve the required thickness through machining, and it leaves no tool marks or chips on the surface. Specifically, in this part, chemical milling can achieve a uniform reduction in thickness.

[0018] Given that chemical milling releases internal material stress, leading to localized deformation, the chemical milling process used in this invention is arranged after sheet metal forming and heat treatment strengthening, specifically after the forming and heat treatment quenching of the web reinforcement groove, side bends, and small reinforcement bends. The advantages of this process are that the part thickness remains unchanged after the reinforcement groove is formed, and the web deformation caused by trimming the reinforcement groove does not result in thickness range shifts or distortions. Furthermore, compared to chemical milling of flat blanks, the reinforcement groove, bends, and small reinforcement bends have an inhibitory effect on chemical milling deformation, reducing it to a certain extent and helping to maintain the position of thickness variation areas while minimizing deformation trimming. Since chemical milling is performed after sheet metal forming, only simple trimming is needed to obtain the part's shape. Because sheet metal forming precedes thickness machining, the part surface quality is better, eliminating the need for overall grinding and thus ensuring the presence of the aluminum cladding layer and its excellent physicochemical properties.

[0019] The beneficial effects of this invention are:

[0020] The application adopts a process method of "numerical control milling cutting + sheet metal forming + chemical milling" to replace "numerical control milling + sheet metal forming". By replacing mechanical cutting with chemical milling, and cooperating with two newly designed toolings for stiffener groove and edge bending forming, the problems of web wrinkling caused by stiffener groove forming, which cannot be repaired, and thickness area distortion and deviation are solved, so that the accurate shape of the part is finally obtained and the surface quality is improved. The application has generalizability and can be widely applied to the machining of complex surface and variable-thickness thin-walled parts, so as to meet the structural use requirements and further reduce the weight of the aircraft body. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a part shape diagram;

[0022] Figure 2 is a process data set schematic diagram;

[0023] Figure 3 is a mold tire I structure diagram;

[0024] Figure 4 is a mold tire II structure diagram.

[0025] In the figure: 1, tire body; 2, cover plate; 3, positioning pin; 4, mold pin; 5, movable handle; 6, lifting ring; 7, tire body; 8, positioning pin; 9, mold pin; 10, cover plate; 11, side cover plate; 12, movable handle; 13, lifting ring. DETAILED DESCRIPTION

[0026] The manufacturing method of the variable-thickness multi-edge thin-walled part with stiffener groove structure comprises the following steps:

[0027] Step one: numerical control milling cutting blanking.

[0028] This process uses the two-dimensional expanded data set of the part as the medium, and uses a numerical control three-axis machine tool to mill the outer edge of the part in the expanded state for subsequent sheet metal forming (thickness is not processed, and is processed by chemical milling later). When designing the two-dimensional expanded data set, four ear pieces are added on both sides of the part web and φ5.2 positioning holes are drilled for positioning during subsequent sheet metal forming and chemical milling; considering that there is more material flow during stiffener groove forming, to avoid local edge being too small, process allowance can be increased for compensation, which is removed after forming. When milling, a two-tooth milling cutter with a helix angle less than 45° is selected to facilitate chip removal, a drill bit with a top angle of 90°-110° and symmetrical on both sides of the top angle is selected, and the machining precision ensures that the shape limit deviation is not greater than 0.5mm. After the plate milling is completed, the processed end face is filed and deburred by using a file and sandpaper;

[0029] Step two: hydraulic forming.

[0030] This process is used to press the milled flat blank to form the reinforcing groove, using the tooling "mold I", and the equipment is a rubber bag press. First, lift the cover plate 2 of "mold I", place the milled flat blank on the mold body, and the φ5.2 positioning hole is fitted into the positioning pin 3 to fix the blank in the mold body. Close the cover plate and use the rubber pad to cover the workbench completely. Then, start the rubber bag press, and the "mold I" enters the working area with the workbench. Set the pressure value to 40 MPa for hydraulic forming. Under the action of the pressure transmitted by the rubber bag, the cover plate 2 and the mold body gradually approach until they are closed, the plate is deformed under stress, and the reinforcing groove shape is pressed. Finally, the "mold I" exits the working area with the workbench, the rubber pad is rolled up, the cover plate 2 is removed, the part is unloaded, and after the surface is inspected to confirm that there are no cracks, bruises, or other mechanical damage, it enters the next process;

[0031] Step three: manual forming.

[0032] This process forms the bending of both sides of the part and the reinforcing small bending on it. The tooling used is "mold II", and manual forming is used due to the thinness of the plate. First, form the bending of both sides. Connect the mold body II, III, and I through the mold pin 9, place the blank that has completed the reinforcing groove forming on the mold body I, fit the φ5.2 positioning hole into the positioning pin 8 to fix the blank in the mold body, close the cover plate 10, clamp the tooling with a universal clamp, and use rubber pads, beaters, and other tools to hit the plate to make the bending of both sides tightly adhere to the side of the mold body I, thereby completing the bending forming. Then, remove the mold body II, III, install the side cover plate 11, clamp the side cover plate and the mold body tightly with a universal clamp, and use rubber pads, beaters, and other tools to hit the bending position to make the ends of the bending of both sides tightly adhere to the side cover plate 11, thereby completing the reinforcing small bending forming. After completing the forming, remove the side cover plate and the cover plate, and take out the part;

[0033] Step four: part quenching.

[0034] Quench the part to improve the strength and hardness of the part. The specific operation is as follows: clean the part, load it into the air furnace heat treatment equipment, heat the temperature range: 495℃~505℃, and keep the temperature for 25min~30min. After completing the quenching, put it into flowing cold water of 10℃~40℃ to completely cool through, and the time is not less than 2min;

[0035] Step five: trimming of quenching deformation.

[0036] Put the quenched parts into "mold II" for finishing, use the tooling "mold II", remove the mold II, III, put the parts into the mold I, close the cover plate 10 and side cover plate 11, use hammer, aluminum hammer and other tools to knock the cover plate and side cover plate, the cover plate and side cover plate are stressed and the force is transmitted to the parts, forcing the deformed parts to adhere thereto, thereby completing the reinforcing groove, bending deformation finishing. For the reinforcing small bend on both sides of the bend, use hammer, aluminum hammer or rubber beating plate to knock the surface for finishing.

[0037] Step six: milling.

[0038] The purpose of this process is to reduce the thickness of the part from 0.8 mm to δ 0.5 mm and keep the rest of the area shape and thickness unchanged.

[0039] Main steps include:

[0040] 6.1 Cleaning: wipe the surface of the part with a cloth soaked in organic solvent, then wipe it dry with a clean cloth; the selected organic solvent should have no corrosive effect on the part;

[0041] 6.2 Apply protective glue: brush or spray chemical milling protective glue, the coating thickness is 0.20mm-0.50mm, check the quality of the glue film after the glue film is dry. There should be no place where the glue is not applied, as well as bubbles, pinholes and mechanical impurities;

[0042] 6.3 Marking: fix the chemical milling template on the part with positioning pins (the positioning pins are coordinated with the positioning pin positions of the part to be processed). According to the edge of the chemical milling template, use a scalpel to manually mark the outline of the etching area, remove the protective layer of the area to be etched, and protect the positioning holes;

[0043] 6.4 Chemical milling: put the part into the chemical milling tank, the chemical milling solution is NaOH, the distance between the part and the part, and the distance between the part and the tank wall is not less than 150mm, accurately measure the etching rate and record it. When the chemical milling time reaches 70%-90% of the calculated time, take out the part, measure the thickness of the chemical milling area, and calculate the remaining chemical milling time of the remaining thickness [chemical milling time = (measured thickness of the chemical milling area - δ 0.5mm) ÷ chemical milling rate], continue chemical milling until the required thickness is reached;

[0044] 6.5 Inspection: after completing the chemical milling, take out the part, clean it with cold water, and then remove the protective glue layer with a manual stripping method to check whether the chemical milling quality, the thickness of the chemical milling area and the surface roughness meet the engineering requirements;

[0045] Step seven: finishing chemical milling deformation.

[0046] When the part is chemically milled, the internal stress is released and the surface is locally twisted and deformed, which can be finished by manual method, as in step five;

[0047] Step eight: part surface treatment.

[0048] The parts are anodized and painted to improve their corrosion resistance.

[0049] 8.1 Anodizing: The parts are oxidized in a sulfuric acid anodizing tank at a temperature of 13-25°C and a voltage of 13-24V for 15-40 minutes, and then cleaned in a cold water tank for 1-2 minutes.

[0050] 8.2 Potassium dichromate sealing: The parts are treated in a potassium dichromate sealing tank at a temperature of 90-100°C for 15-20 minutes, cleaned in a warm water tank at 40-60°C for 1-2 minutes, blown dry with compressed air, or dried in a drying tank at 40-70°C for 10-20 minutes.

[0051] 8.3 Painting: The parts are painted with prepared paint within the effective period, and the thickness of the paint should be controlled within the range of 25-35μm. The painted parts are dried. The drying conditions are: room temperature, 7 days; or 40-50°C, 10-12 hours; or 65-75°C, 2-4 hours; or 100-110°C, 1-3 hours.

[0052] After the above steps, the final state parts are obtained.

Claims

1. A method of manufacturing a variable thickness multi-flange thin-walled part with a reinforcing slot structure, characterized by, Comprising the following steps: Step one: CNC milling cutting blank; This process uses the two-dimensional development data set of the part as the medium, and uses a numerical control three-axis machine tool to mill the outer edge of the part in the developed state for subsequent sheet metal forming; Step two: hydraulic forming; This process is used to press the strengthened groove out of the milled flat blank. The tooling is "mold Ⅰ", and the equipment is a rubber bladder press. First, lift the cover plate (2) of "mold Ⅰ", place the milled flat blank on the mold body, and position the φ5.2 locating hole in the locating pin (3) to fix the blank in the mold body. Close the cover plate and use rubber pads to cover the workbench completely. Then start the rubber bladder press, and the "mold Ⅰ" enters the working area with the workbench. Set the pressure value to 40MPa for hydraulic forming. Under the action of the pressure transmitted by the rubber bladder, the cover plate (2) and the mold body gradually approach until they are closed. The sheet metal deforms under stress and forms a strengthened groove shape. Finally, remove the "mold Ⅰ" from the working area with the workbench, roll up the rubber pad, remove the cover plate (2), unload the part, and check the surface of the part to confirm that there are no cracks, pressure marks, or other mechanical damage before entering the next process. Step three: manual forming; This process forms the bend on both sides of the part and the small reinforcing bend on it. The tooling is "mold Ⅱ". Due to the thinness of the sheet metal, manual forming is used. First, form the bend on both sides. Connect the mold body Ⅱ, Ⅲ with the mold body Ⅰ through the mold pin (9), place the blank that has completed the forming of the strengthened groove on the mold body Ⅰ, position the φ5.2 locating hole in the locating pin (8) to fix the blank in the mold body, close the cover plate (10), and clamp the tooling with a universal clamp. Use rubber pads and a beating plate tool to beat the sheet metal, so that the bends on both sides are tightly attached to the side of the mold body Ⅰ, thereby completing the bend forming. Then, remove the mold body Ⅱ, Ⅲ, install the side cover plate (11), clamp the side cover plate and the mold body tightly with a universal clamp, use rubber pads and a beating plate tool to beat the bend position, so that the ends of the bends on both sides are tightly attached to the side cover plate (11), thereby completing the small reinforcing bend forming. After forming, remove the side cover plate and the cover plate, and take out the part. Step four: part quenching; Quench the part to improve its strength and hardness. Step five: trimming of quenching deformation; Place the quenched part into "mold Ⅱ" for trimming. The tooling is "mold Ⅱ". Remove the mold body Ⅱ and Ⅲ, place the part into the mold body Ⅰ, close the cover plate (10) and the side cover plate (11), use a hammer and an aluminum hammer tool to strike the cover plate and the side cover plate, which will transmit the force to the part, forcing the deformed part to be tightly attached to it, thereby completing the deformation trimming of the strengthened groove and the bend. For the small reinforcing bend on both sides of the bend, use a hammer, an aluminum hammer, or a rubber beating plate to strike its surface for trimming. Step six: chemical milling; Step seven: trimming of chemical milling deformation; Trim the surface deformation of the part after chemical milling. The method is the same as step five. Step eight: surface treatment of the part; Anodize and paint the part to improve its corrosion resistance.

2. A method of manufacturing a variable thickness multi-flange thin-walled part with a reinforcing slot structure according to claim 1, wherein The specific operation of step six is as follows: 6.1 Cleaning: wipe the surface of the part with a cloth soaked in organic solvent, then wipe dry with a clean cloth; the selected organic solvent should have no corrosive effect on the part; 6.2 Apply protective glue: brush or spray the protective glue, the coating thickness is 0.20mm-0.50mm, and the glue film quality is checked after drying; there should be no place without coating, as well as bubbles, pinholes and mechanical impurities; 6.3 Etching: fix the etching template on the part with positioning pins; according to the edge of the etching template, use a scalpel to manually etch the contour line of the etching area, remove the protective layer of the etching area, and protect the positioning hole; 6.4 Milling: place the part in the milling tank, the milling solution is NaOH, the distance between the parts and the distance between the part and the tank wall should not be less than 150mm, accurately measure the etching rate and record it; when the milling time reaches 70%-90% of the calculated time, take out the part, measure the thickness of the milling area, and calculate the remaining milling time of the remaining thickness [milling time=(measured thickness of the milling area-δ0.5mm)÷milling rate], continue to mill until the required thickness is reached; 6.5 Inspection: after completing the milling, take out the part, clean it with cold water, and then remove the protective glue layer by hand stripping method to check whether the milling quality, thickness of the milling area and surface roughness meet the engineering requirements.

3. A method of manufacturing a variable thickness multi-flange thin-walled part with reinforced slot structure according to claim 1, wherein, The step eight is specifically operated as follows: 8.1 Anodizing: under the conditions of temperature 13℃-25℃ and voltage 13V-24V, the part is placed in a sulfuric acid anodizing tank for oxidation treatment for 15min-40min, and then cleaned in a cold water tank for 1min-2min; 8.2 Potassium dichromate sealing: under the condition of temperature 90℃-100℃, the part is treated in a potassium dichromate sealing tank for 15min-20min, cleaned in a 40℃-60℃ warm water tank for 1min-2min, dried with compressed air, or dried in a 40℃-70℃ drying tank for 10min-20min; 8.3 Spraying: use the prepared paint within the effective period for spraying, and the thickness of the paint should be controlled within the range of 25μm-35μm; the painted part is dried; the drying conditions are: room temperature: dried for 7 days; or 40℃-50℃, dried for 10h-12h; or 65℃-75℃, dried for 2h-4h; or 100℃-110℃, dried for 1h-3h.

4. A method of manufacturing a variable thickness multi-flange thin-walled part with reinforced slot structure according to claim 1 or 2, characterized in that, The step four is specifically operated as follows: The part is cleaned and loaded into an air furnace heat treatment equipment, the heating temperature range is 495℃-505℃, and the holding time is 25min-30min; after quenching, it is completely cooled in flowing cold water of 10℃-40℃ for not less than 2min.

5. A method of manufacturing a variable thickness multi-flange thin-walled part with a reinforcing slot structure as defined in claim 3, wherein, The step four is specifically operated as follows: The part is cleaned and loaded into an air furnace heat treatment equipment, the heating temperature range is 495℃-505℃, and the holding time is 25min-30min; after quenching, it is completely cooled in flowing cold water of 10℃-40℃ for not less than 2min.

6. A method of manufacturing a variable thickness multi-flange thin-walled part with reinforced slot structure according to claim 1 or 2 or 5, wherein, The moulding tyre I includes a tyre body (1), a cover plate (2), a positioning pin (3), a clamp pin (4), a movable handle (5), and a lifting ring (6); the moulding tyre II includes a tyre body (7), a positioning pin (8), a clamp pin (9), a cover plate (10), a side cover plate (12), a movable handle (12), and a lifting ring (13); the tyre body (1) of the moulding tyre I is made into a "concave" structure, and the cover plate (2) is made into a "convex" structure.

7. A method of manufacturing a variable thickness multi-flange thin-walled part with reinforced slot structure as defined in claim 3, wherein, The moulding tyre I includes a tyre body (1), a cover plate (2), a positioning pin (3), a clamp pin (4), a movable handle (5), and a lifting ring (6); the moulding tyre II includes a tyre body (7), a positioning pin (8), a clamp pin (9), a cover plate (10), a side cover plate (12), a movable handle (12), and a lifting ring (13); the tyre body (1) of the moulding tyre I is made into a "concave" structure, and the cover plate (2) is made into a "convex" structure.

8. A method of manufacturing a variable thickness multi-flange thin-walled part with reinforced slot structure according to claim 4, wherein, The moulding tyre I includes a tyre body (1), a cover plate (2), a positioning pin (3), a clamp pin (4), a movable handle (5), and a lifting ring (6); the moulding tyre II includes a tyre body (7), a positioning pin (8), a clamp pin (9), a cover plate (10), a side cover plate (12), a movable handle (12), and a lifting ring (13); the tyre body (1) of the moulding tyre I is made into a "concave" structure, and the cover plate (2) is made into a "convex" structure.

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