Machining methods for thin-walled aluminum alloy parts with large curvature and narrow web

Abstract

The processing method for thin-walled aluminum alloy parts with large curvature and narrow webs belongs to the field of aerospace sheet metal parts processing technology. Based on the principle of profile bending, the sheet metal is bent into a profile section for shaping. The process involves CNC milling blanking, grate forming, bending forming, and manual finishing, combined with two newly designed sets of tooling for part forming and finishing. This solves problems such as high manual labor intensity during the forming process, inability to unload parts after forming, inaccurate profiles, and outer edge cutting dimensions exceeding allowable deviations, thereby improving product quality and production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of aerospace sheet metal parts processing technology, and relates to a processing device and method for thin-walled parts with large curvature and narrow web. Background Technology

[0002] In military aircraft research and development projects, the cockpit area contains numerous thin-walled parts with large curvature and narrow webs. These parts typically feature a channel-shaped cross-section, a semi-circular arc shape, a bending radius of up to R800mm, a channel width of 20mm, and a relatively thin material thickness, generally 1.5mm. The part dimensions relate to the theoretical outer edge of the aircraft cockpit canopy, requiring high manufacturing precision. Due to the small width of the channel cross-section and the absence of internal holes, accurate positioning of the part on the tooling is impossible during sheet metal forming. Therefore, it is not possible to pre-cut the part according to its unfolded dimensions before forming the shape; only raw material can be used for forming, followed by cutting the outer edge of the part along the tooling edge line. The typical process flow is "straight-line blanking – manual forming – cutting the outer shape." Because the part is positioned solely by two φ5.2mm pins added to both ends, positional movement is prone to occur during forming, causing deviations in the part's surface dimensions. These parts are closed-angle components with arc segments exceeding half a circle. After forming, they cannot be normally removed from the tooling; instead, they must be forcibly unloaded and their surfaces re-corrected according to a template. This process causes changes to the part's surface, and precise dimensional control is difficult when re-correcting the surface according to the template. Using straight-line blanking to form the part first, followed by manual cutting of the outer edge, results in a large workload and difficulty in controlling the edge dimensions, leading to poor dimensional accuracy. As typical convex curve bent-edge parts, forming requires repeated "feeding," "unfeeding," and "combined feeding" to force material flow, resulting in a large amount of manual work and numerous hammer marks on the part's surface, affecting surface quality and increasing the risk of fatigue damage. These problems make forming these parts extremely difficult. Summary of the Invention

[0003] The purpose of this invention is to develop a manufacturing method for thin-walled aluminum alloy parts with large curvature and narrow webs. This method utilizes two newly designed tooling sets for part forming and replaces the traditional "straight blanking – manual forming – shape cutting" process with a "CNC milling blanking – gantling forming – stretch bending forming – manual finishing" flow. The tooling used in this invention solves the problems of part positioning and unloading, avoiding issues such as parts being unable to be removed after forming and outer edge misalignment. Therefore, it allows for precise blanking according to the unfolded dimensions of the part, followed by forming the final shape according to the tooling. Except for cutting the stretch bending allowance at both ends, subsequent manual edge cutting in the width direction is no longer required. By CNC milling the unfolded part, followed by gantling forming and stretch bending forming, and finally manual finishing to shape the part to its final form, the invention achieves the desired part shape while improving production efficiency and processing accuracy. The main processes of CNC milling blanking, gantling forming, and stretch bending forming are all machined, resulting in low operator workload and high processing accuracy.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows:

[0005] A machining method for thin-walled aluminum alloy parts with large curvature and narrow web, the machining method including CNC milling blanking, gate forming, stretch bending forming and manual finishing.

[0006] Furthermore, the CNC milling blanking process is detailed as follows:

[0007] Milling uses the unfolded digital model of the part as a medium to mill out the outer edge in the unfolded state for subsequent forming. Considering the addition of bending process in subsequent forming, an allowance needs to be added to both ends of the part for clamping during milling. After the sheet metal is milled, the machined end face is filed and deburred with files and sandpaper. The edges are inspected by comparing the two-dimensional unfolded dataset with the sheet metal vision system to ensure that the shape limit deviation meets the inspection standard.

[0008] Furthermore, the gate compression forming process is as follows:

[0009] The purpose of the guillotine forming process is to shape the milled flat blank into a shape with the same cross-section as the final groove cross-section of the part and a straight length, for subsequent stretch bending forming. The guillotine forming process can be completed using a CNC bending machine, general-purpose cutting tools, and templates.

[0010] Furthermore, the tooling used for stretch bending is a "stretch bending die", which is used to bend the straight strip material with a groove-shaped cross section after gate pressing into a "semi-ring shape"; the "stretch bending die" includes a die body 1, tool hole 2, clamp hole 3, pressure plate 4, mold closing screw 5 and lifting ring 6;

[0011] The surface of the die body 1 is designed according to the inner surface of the part, that is, the outer side is "convex". Tool holes 2 are provided on the die body 1 for alignment and connection between the pressure plate 4 and the die body 1. Through holes are provided at corresponding positions on the die body 1 and the pressure plate 4 for fixing the mold on the bending die platform using a clamp. The overall shape of the pressure plate 4 is similar to that of the die body 1, but the outer dimensions are larger than those of the die body 1. Two pressure plates 4 with the same structure are respectively installed on the upper and lower surfaces of the die body 1 to limit the blank during the bending process and prevent the blank from moving vertically. A gap is made between the die body 1 and the pressure plate 4 within 5mm of the bending edge height of the part to facilitate the flow of the blank during the bending process and prevent scratching the surface. The mold closing screws 5 pass through the die body 1 and the pressure plate 4 in sequence, and are aligned and tightened. Lifting rings 6 are respectively installed on the die body 1 and the pressure plate 4 for mold lifting and transportation.

[0012] Furthermore, for complex sheet metal parts, a springback angle is manufactured for the "bending die" tooling, that is, the structure of the jig 1 is locally adjusted to reduce the impact of springback on the bending forming of the parts.

[0013] Furthermore, the tooling used in the manual finishing process is a "molding jig," which is used to process the semi-finished product after bending to the final shape of the part, and to unload it from the tooling without changing the shape of the part; the "molding jig" includes a mold body 7, positioning pins 8, mold pins 9, pressure plates 10, pins 11, inner cover plates 12, screws 13, pressure plate nuts 14, outer cover plates 15, and tightening nuts 16; the mold body 7 includes mold body I, mold body II, and mold body III;

[0014] The mold 7 is used to determine the part's profile during forming. Mold 1 and mold 3 are arc-shaped structures, and their profiles are coordinated with the inner wall of the part's groove. Positioning pins 8 are installed at corresponding positions on both ends of the part for positioning during finishing. Four pin holes are distributed along the edge of the part, which cooperate with pins 11 to prevent the part from shifting during forming. Mold 2 is a strip structure, allowing the part to be pulled out from between mold 1 and mold 3 after forming, facilitating part unloading. Mold 1 and mold 3... II. After determining the relative position of the mold pin 9, the mold body III is fixed to the inner cover plate 12 using the pressure plate 10 and tightened with screws 13 and pressure plate nuts 14. A through hole is made in the middle of the mold body I, mold body III and inner cover plate 12 to facilitate tooling clamping and reduce the weight of the mold body. The outer cover plate 15 is shaped to match the outer wall of the part groove and is fixed to the mold body using tightening nuts 16 to ensure that the relative position between the mold body, part and cover plate remains unchanged during the part forming process, thereby ensuring the accuracy of the part shape and the ability to unload the part.

[0015] The beneficial effects of this invention are as follows: Based on the principle of profile bending, the sheet metal is bent into a profile cross-section for forming. The process of "straight blanking - manual forming - cutting the shape" is replaced by the process of "CNC milling blanking - gating forming - bending forming - manual finishing". With the help of two newly designed tooling sets for part forming and finishing, the problems of high manual operation intensity in the forming process, inability to unload the parts after forming, inaccurate profile, and outer edge cutting dimensions exceeding the allowable deviation are solved, thereby improving product quality and production efficiency.

[0016] The manufacturing method involved in this invention can be extended to other parts in sheet metal manufacturing, solving the processing problem of parts with large curvature and bent edges. Considering factors such as strength, some sheet metal parts do not have structural holes such as pin holes designed inside. For sheet metal forming, especially for "thin and long" parts with bent edges, the lack of internal holes makes it impossible to position them. In hydroforming or manual forming, the blank is prone to movement, resulting in inaccurate shape. The manufacturing method involved in this invention uses a combination of "gantress forming - stretch bending forming" to replace hydroforming, and uses tooling structure assembly to solve the problem of part positioning, improve part processing accuracy, and reduce tooling manufacturing costs and cycle time. Attached Figure Description

[0017] Figure 1 This is the outline drawing of the part.

[0018] Figure 2 The image shows the external shape after guillotine forming, where (a) is the front view and (b) is the side view.

[0019] Figure 3 The diagram shows the structure of the bending die, where (a) is the front view and (b) is the side view.

[0020] Figure 4 The diagram shows the structure of a tire, where (a) is the front view and (b) is the side view.

[0021] In the diagram: 1. Carcass, 2. Tool hole, 3. Fixture hole, 4. Pressure plate, 5. Mold closing screw, 6. Lifting eye, 7. Mold body, 8. Positioning pin, 9. Mold pin, 10. Pressure plate, 11. Insert pin, 12. Inner cover plate, 13. Screw, 14. Pressure plate nut, 15. Outer cover plate, 16. Tightening nut. Detailed Implementation

[0022] The specific machining scheme for thin-walled aluminum alloy parts with large curvature and narrow web is explained below:

[0023] This processing method uses CNC milling for blanking and employs guillotine forming and stretch bending forming methods to manufacture thin-walled aluminum alloy parts with large curvature and narrow webs, thereby improving production efficiency and surface quality. The specific steps are briefly introduced below.

[0024] Figure 3 , 4 The diagram illustrates a machining method for thin-walled aluminum alloy parts with large curvature and narrow webs. This method is based on a bending die and a mold. The bending die structure includes a mold body 1, tool holes 2, clamping holes 3, a pressure plate 4, mold closing screws 5, and lifting rings 6. The mold structure includes a mold body 7, positioning pins 8, mold-aligning pins 9, a pressure plate 10, pins 11, an inner cover plate 12, screws 13, a pressure plate nut 14, an outer cover plate 15, and a tightening nut 16. The mold body 7 includes mold body I, mold body II, and mold body III.

[0025] The aforementioned "stretch bending die" is used to bend straight strips of material with a groove-shaped cross-section after grate forming into a "semi-ring" shape. Its structure 1, the die body, is designed according to the inner surface of the part, i.e., the outer side is "convex." Three tool holes 2 are made at appropriate positions on the die body for alignment and connection between the pressure plate and the die body. To facilitate the installation and fixation of the die on the stretch bending machine, 4 through holes of φ135mm are milled at corresponding positions on the die body and pressure plate for fixing the die to the stretch bending die platform using clamps. The pressure plate 4 has a similar overall shape to the die body, but its outer dimensions are slightly larger (generally 20mm is sufficient). Two identical structures are installed on the upper and lower surfaces of the die body to limit the blank during stretch bending, preventing vertical movement of the blank. A 0.5mm gap can be made between the die body and the pressure plate within 5mm of the bending edge height of the part, facilitating blank flow during stretch bending and preventing surface scratches. The die-clamping screws 5 align and tighten the die body and pressure plate. Lifting rings 6 are installed on the jig and pressure plate respectively, and are used for mold lifting and handling. For complex sheet metal parts, the tooling is manufactured with a springback angle (i.e., the jig structure 1 is locally adjusted) to reduce the impact of springback on the bending forming of the parts.

[0026] The aforementioned "molding kit" comprises seven mold bodies used to determine the part's profile during forming. Mold bodies I and III are arc-shaped structures, with their profiles coordinated with the inner wall of the part's groove. One φ5 locating pin 8 is installed at each corresponding position on both sides of the part for positioning during finishing. Four pin holes are distributed along the part's edge line, engaging with pins 11 to prevent positional shifting during forming. Mold body II is a strip structure, allowing the part to be extracted from between mold bodies I and III after forming, facilitating unloading. After determining their relative positions using mold pins 9, mold bodies I, II, and III are fixed to the inner cover plate 12 using pressure plates 10 and tightened with screws 13 and pressure plate nuts 14. Through holes are formed in the middle of mold bodies I, III, and the inner cover plate 12 to facilitate tooling clamping and reduce the kit's weight. All of the above structures constitute the kit body. The outer cover plate 15 is coordinated with the outer wall of the part's groove shape and is fixed to the jig by tightening nuts 16 to ensure that the relative positions of the jig, part and cover plate remain unchanged during the part forming process, thereby ensuring the accuracy of the part's shape and the ability to unload the part.

[0027] Furthermore, the above structure is manufactured according to the dataset, with a surface manufacturing tolerance of ±0.1mm, and the surface roughness of the working surface is not higher than Ra1.6. The lifting ring is used for mold lifting and handling.

[0028] The machining method for thin-walled aluminum alloy parts with narrow webs and curvature includes the following steps:

[0029] Step 1: Milling and cutting the material.

[0030] The unfolded shape of the part (rectangular strip with a 200mm allowance at each end) is milled using CNC milling based on the 2D unfolded dataset, ensuring that the external shape deviation does not exceed 0.5mm. A two-tooth milling cutter with a helix angle of less than 45° is selected for milling to facilitate chip removal. The drill bit is selected with a 90°–110° apex angle, symmetrical on both sides. After milling, the machined end face is filed and deburred using sandpaper. A sheet metal vision system is used to inspect the edges against the 2D unfolded dataset to ensure that the external shape deviation meets the inspection standards.

[0031] Step 2: Gantry forming.

[0032] This process is used to shape the milled flat blank into a shape with a cross-section identical to the final groove cross-section of the part and a straight length, for subsequent stretch bending. Forming is accomplished using a CNC bending machine and general-purpose cutting tools. The first clamping action bends the flat blank into an "L" shape, and the second forming action bends it into a "concave" shape. First, a suitable clamping tool and corresponding tool holder slot are selected based on the bending radius and angle of the part's cross-section. The clamping tool is then installed on the CNC bending machine's fixed block, connecting it to the bending machine's slide. Based on the bending height and angle shown in the template, the position of the bending machine's backstop and the bottom dead center of the slide stroke are set. Then, the flat blank is fed in, with the bottom surface of the sheet metal against the upper surface of the tool holder and the end face against the backstop. The machine's mold closing switch is pressed, and the slide slides down to close the mold. Release the mold closing switch. After the slider moves up, remove the part and measure the bending height and bending angle. If the dimensions meet the requirements, proceed to the next process. If the dimensions do not meet the requirements, adjust the position of the back baffle of the bending machine and the bottom dead center of the slider stroke and reshape until the dimensions meet the requirements.

[0033] Step 3: Bending and shaping.

[0034] First, fix the bending die to the bending machine platform using fixing pins. Then, select a concave jaw according to the groove cross-sectional shape of the part, clamping both ends of the blank in the jaws with a clamping distance of not less than 100mm, and ensuring the center of the blank is against the bending center of the bending die. Adjust the tension value; the blank moves with the jaws, creating relative displacement between the jaws and the bending die, bending the blank until it is completely flush with the bending die. After completing the above steps, unload the tension and remove the part (semi-finished product) along a direction perpendicular to the bending die's profile.

[0035] Step 4: Manual finishing.

[0036] First, place the mold horizontally on the platform, remove the tightening nut 16, and separate the outer cover plate 15 from the mold body (composed of mold body I, mold body II, mold body III, pressure plate 10, and inner cover plate 12). Tighten the pressure plate nut 14 to ensure that mold body I, mold body II, mold body III, pressure plate 10, and inner cover plate 12 remain clamped. Place the bent blank between the outer cover plate and the mold body (composed of mold body I, mold body II, mold body III, pressure plate 10, and inner cover plate 12). Drill φ5.2 positioning holes at the positions of positioning pins 9 on both ends and fix them with positioning pins. Tighten the tightening nut 16 to ensure that the position between the cover plate and the mold body remains unchanged during the forming process.

[0037] Secondly, the blank is trimmed manually until it fits snugly against mold body 7 (mold body I, mold body II, mold body III) and the two ends of the part are recessed. During the trimming process, it is necessary to observe the distance between the two sides of the part and the pins 11 on the mold body. If both sides are in contact with the pins, it means that the blank has not shifted during the forming process and the external dimensions of the part can be guaranteed. If there is a gap between one side of the part and the pin, and the other side is embedded in the pin, it means that the blank has shifted and needs to be readjusted.

[0038] After the parts are tightly fitted to the tooling, pull out the tightening nut 16, and the outer cover plate 15 will separate from the body by a certain distance. Remove the outer cover plate from above the tooling. Loosen the pressure plate nut 14, remove the pressure plate 10, and pull out the mold body II from the side. Then move the mold body I and mold body III inward by a certain distance. At this time, the parts can be removed from the tooling in a free state.

[0039] Step 5: Part quenching.

[0040] The purpose of quenching the parts is to improve their strength and hardness. After quenching, the parts are kept at room temperature for 120-240 hours and then sent to the physical and chemical department for conductivity or hardness testing according to standards. The acceptable conductivity value is 18.5 MS / m-20 MS / m. If the conductivity is unqualified, hardness testing is allowed, with an acceptable value ≥62 HRB. If both conductivity and hardness tests are unqualified, this step is repeated for heat treatment until the physical and chemical properties are qualified before proceeding to the next process.

[0041] Step Six: Trim quenching deformation.

[0042] The quenched part is placed between the outer cover plate and the fixture (composed of mold body I, mold body II, mold body III, pressure plate 10, and inner cover plate 12), and positioning pins 8 are inserted at both ends. Tighten the tightening nut 16 to ensure that the relative position between the cover plate and the fixture remains unchanged during the part trimming process; use tools such as a hammer, aluminum hammer, or rubber beater to manually trim the deformed parts to ensure that the parts fit tightly with the fixture. After trimming, pull out the tightening nut 16, and the outer cover plate 15 separates from the fixture by a certain distance. Remove the outer cover plate from above the fixture. Loosen the pressure plate nut 14, remove the pressure plate 10, pull out mold body II from the side, and then move mold body I and mold body III inward a certain distance respectively. At this time, the part can be taken out of the fixture in a free state.

[0043] Step 7: Remove the ear flap.

[0044] Cut off the lugs used for positioning on both ends of the part, and file and deburr it to make the surface roughness of the machined end meet the requirements of the design drawings;

[0045] Step 8: Surface treatment of parts.

[0046] The purpose of anodizing and painting the parts is to improve their corrosion resistance; after completing the above steps, the final physical part is obtained.

Claims

1. A method for machining thin-walled aluminum alloy parts with large curvature and narrow web, characterized in that, The processing method includes CNC milling blanking, gating forming, stretch bending forming, and manual trimming; The CNC milling blanking process is as follows: Milling uses the unfolded digital model of the part as a medium to mill out the outer edge in the unfolded state for subsequent forming. Considering the addition of bending process in subsequent forming, an allowance needs to be added to both ends of the part for clamping during milling. After the sheet metal is milled, the machined end face is filed and deburred with files and sandpaper. The edges are inspected by comparing the two-dimensional unfolded dataset with the sheet metal vision system to ensure that the shape limit deviation meets the inspection standard. The tooling used in the manual finishing process is a "form jig", which is used to process the semi-finished product after bending and shaping to the final shape of the part, and to unload it from the tooling without changing the shape of the part. The "molding" includes a mold body (7), positioning pins (8), mold pins (9), a second pressure plate (10), pins (11), an inner cover plate (12), screws (13), pressure plate nuts (14), an outer cover plate (15), and tightening nuts (16); the mold body (7) includes mold body I, mold body II, and mold body III; The mold (7) is used to determine the part profile during forming. Mold I and Mold III are arc-shaped structures. The profiles of Mold I and Mold III are coordinated with the inner wall of the part groove. Positioning pins (8) are installed at corresponding positions on both sides of the part for part positioning during trimming. Four pin holes are distributed along the edge of the part, which cooperate with the pins (11) to prevent the part from shifting during forming. Mold II is a strip structure. After forming, the part can be pulled out between Mold I and Mold III for easy unloading. Mold I, Mold II, and Mold III are connected by... After determining the relative position of the mold pin (9), the second pressure plate (10) is used to fix it to the inner cover plate (12), and screws (13) and pressure plate nuts (14) are used to tighten it. Through holes are made in the middle of the mold body I, mold body III and inner cover plate (12) to facilitate tooling clamping and reduce the weight of the mold body. The outer cover plate (15) is coordinated with the outer wall of the part groove and is fixed to the mold body by tightening nuts (16) to ensure that the relative position between the mold body, part and cover plate remains unchanged during the part forming process, thereby ensuring the accuracy of the part profile and the ability to unload the part.

2. The processing method for thin-walled aluminum alloy parts with large curvature and narrow web according to claim 1, characterized in that, The specific details of gate compression forming are as follows: The purpose of the guillotine forming process is to shape the milled flat blank into a shape with the same cross-section as the final groove cross-section of the part and a straight length, for subsequent stretch bending forming. The guillotine forming process can be completed using a CNC bending machine, general-purpose cutting tools, and templates.

3. The processing method for thin-walled aluminum alloy parts with large curvature and narrow web according to claim 1, characterized in that, The tooling used for stretch bending is called a "stretch bending die", which is used to bend the straight strip material with groove cross section after guillotine forming into a "semi-ring" shape; the "stretch bending die" includes a die body (1), tool hole (2), clamp hole (3), first pressure plate (4), mold closing screw (5) and lifting ring (6); The surface of the die body (1) is designed according to the inner surface of the part, that is, the outer side is "convex". Tool holes (2) are provided on the die body (1) for the alignment and connection of the first pressure plate (4) and the die body (1). Through holes are provided at corresponding positions of the die body (1) and the first pressure plate (4) for fixing the mold on the bending die platform using a clamp. The overall shape of the first pressure plate (4) is similar to that of the die body (1), but the outer dimensions are larger than those of the die body (1). Two first pressure plates (4) with the same structure are installed on the die body (1) respectively. The upper and lower surfaces of the die body (1) are used to limit the blank during the bending process and prevent the blank from moving vertically. A gap is made between the die body (1) and the first pressure plate (4) within 5mm of the bending height of the part, so as to facilitate the flow of the blank during the bending process and prevent the surface from being scratched. The mold closing screws (5) pass through the die body (1) and the first pressure plate (4) in sequence, and are aligned and tightened. The lifting rings (6) are installed on the die body (1) and the first pressure plate (4) respectively, for mold lifting and transportation.

4. The processing method for thin-walled aluminum alloy parts with large curvature and narrow web according to claim 3, characterized in that, For complex sheet metal parts, the springback angle is manufactured for the "bending die" tooling, that is, the structure of the die body (1) is locally adjusted to reduce the impact of springback on the bending forming of the parts.

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