Forming and milling integrated skin processing method

Abstract

The invention belongs to the technical field of aviation aircraft sheet metal machining, and relates to skin part forming and appearance machining. The forming process and the milling process are integrated on one die, multiple times of transferring and repositioning between the processes are avoided, the machining period is greatly shortened, the production efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of aviation aircraft sheet metal processing and relates to the forming and shape processing of skin parts. Background Art

[0002] In the aerospace field, skin is an important component of the aircraft body structure, and its processing accuracy and quality directly affect the performance and safety of the aircraft. In traditional skin processing technology, two different sets of molds are usually used for forming and milling the shape, which is a cumbersome process and costly. During the forming stage, mold stretching, rolling and other methods are generally used to make the sheet material reach the designed curved surface shape. However, this method has many problems. Due to the manufacturing accuracy of the mold and wear during use, it is difficult to ensure that the shape accuracy of the skin is highly consistent each time it is formed. In addition, the forming process will generate a complex residual stress distribution inside the sheet material. These residual stresses may cause skin deformation during subsequent processing and use, affecting product quality.

[0003] During the milling phase, the formed skin is fixed to a milling machine for milling to achieve the desired contours, hole patterns, and other features. However, due to the irregular shape of the formed skin, it is difficult to ensure accurate positioning during the clamping process. Improper clamping can cause displacement and vibration of the skin during milling, which in turn affects milling accuracy. Furthermore, multiple transfers and repositioning steps are required between machining operations, which not only increases the machining cycle but also introduces further cumulative errors.

[0004] Therefore, there is an urgent need for an integrated skin processing method that can organically combine the forming and milling processes, improve processing accuracy and efficiency, and reduce production costs. Summary of the Invention

[0005] The purpose of the present invention is to provide a skin processing method that integrates forming and milling, so as to solve the problems of low processing accuracy, low production efficiency and high cost caused by the separation of forming and milling processes in the existing skin processing technology, and to achieve high-precision, high-efficiency and high-quality processing of the skin.

[0006] According to one aspect of the present application, a method for integrated forming and milling of a skin is provided, comprising the following steps:

[0007] 1. Raw material preparation: According to the design requirements of the skin, select suitable metal sheets as raw materials, strictly test the chemical composition and mechanical properties of the sheets to ensure that they meet the use standards of aerospace parts, pre-treat the surface of the metal sheets to remove oil stains, oxide layers and other impurities on the surface, improve the surface quality of the metal sheets, and lay a good foundation for subsequent processing to obtain pre-treated metal sheets;

[0008] 2. Use a heat treatment fixture to clamp the metal sheet for quenching to reduce deformation and residual stress to obtain a quenched metal sheet;

[0009] 3. Stretch forming: Using stretch control algorithms, combined with finite element analysis and real-time monitoring data from the CNC skin stretching machine, we can achieve precise control of the stretching process and obtain the formed metal sheet.

[0010] 4. Milling the outer shape to obtain the skin.

[0011] The heat treatment fixture comprises a frame (1), a lower clamping plate (2), an upper clamping plate (3), and an adaptive clamping block (4).

[0012] The main body of the frame (1) is made of a high-strength heat-resistant alloy material with a heat-resistant temperature of not less than 1000° C. The outer shape is rectangular to facilitate the placement of pre-treated metal plates;

[0013] The frame (1) is provided with an upper clamping plate (3) and a lower clamping plate (2) mounted on the upper and lower parts;

[0014] The upper clamping plate (3) and the lower clamping plate (2) are connected by a plurality of adjustable adaptive clamping blocks (4). The height of the adaptive clamping blocks (4) can be adjusted according to the width of the pre-treated metal sheet. The adaptive clamping blocks (4) can also adapt to the clamping requirements of pre-treated metal sheets of different thicknesses, thereby achieving uniform clamping of the pre-treated metal sheet and avoiding deformation of the pre-treated metal sheet due to uneven force during the quenching process.

[0015] The upper clamping plate (3) and the lower clamping plate (2) are provided with universal positioning grooves and positioning pins. By adjusting the position of the positioning pins in the positioning grooves, pre-treated metal plates of different sizes and shapes can be positioned quickly and accurately, thereby improving the versatility of the clamp.

[0016] The heat treatment fixture is provided with cooling pipes in a mesh distribution, which can ensure that the coolant is evenly sprayed on the surface of the pretreated metal plate, thereby achieving uniform cooling of the plate and improving the quenching quality.

[0017] Before stretching, the stretching process is simulated and analyzed using finite element software to predict the deformation of different parts and the required stretching force; based on the simulation results, a stretching process curve is formulated, including the relationship between the stretching force, stretching speed and stretching path over time; during the stretching process, the force, deformation and displacement of the quenched metal sheet are monitored in real time through force sensors, displacement sensors and strain sensors installed on the stretching equipment; the stretching control algorithm dynamically adjusts the stretching process curve based on the real-time monitoring data to ensure that the quenched metal sheet is always in the optimal stress state during the stretching process, avoiding excessive or insufficient stretching.

[0018] In the stretch forming and milling of the outline, a special die is used.

[0019] The special mold consists of a support body (5), a lower positioning member (6), a support rod (7), a mold bracket (8), a stretching profile (9), a positioning plate (10), a rotating wheel (11), a transmission shaft sleeve (12), a milling profile (13), a vacuum suction nozzle (14), a reference hole (15), and a pressing threaded hole (16).

[0020] The support body (5) is made of Q235 or metal of the same strength and is used for support during stretching, forming and milling.

[0021] A row of lower positioning members (6) is installed on each side of the support body (5), and the number is calculated according to the length of the support body (5), and is usually set to be installed at intervals of 300 mm;

[0022] A support rod (7) is installed on the lower positioning member (6), and the support rod (7) is used to ensure the position of the pulling profile 9 in the horizontal direction to prevent it from rotating;

[0023] The stretching profile 9 is supported by four mold brackets (8), which are installed on both sides of the support body (5) without affecting the direction of stretching, with two mold brackets installed in each direction;

[0024] The surface of the drawing profile 9 is provided with 2 to 3 positioning plates (10) for drilling positioning holes in the quenched metal sheet after forming, for use in the next milling process;

[0025] A rotating wheel (11) is installed on each side of the drawing profile 9 in the non-drawing direction. The function of the rotating wheel (11) is to rotate the drawing profile 9 180 degrees with force after the first forming process is completed, and use another profile to carry out the next process;

[0026] In order to save the force during the rotation process, each rotating wheel (11) is equipped with a transmission sleeve (12). The transmission sleeve (12) can be equipped with multiple gears or other structures to transmit torque and reduce the loading force during the rotation process, making it easier to change direction.

[0027] During the milling process of the special mold, the support rods (7) on both sides are completely opened using a hexagonal wrench, and then the rotating wheel (11) is turned to rotate the support body (5) 180 degrees;

[0028] The other side corresponding to the stretching profile (9) is a milling profile (13), and a vacuum suction nozzle (14) is installed on the side of the milling profile (13) for installing a rubber tube and a vacuum pump during the milling process to provide adsorption force, thereby ensuring that each position of the formed metal sheet can obtain sufficient adsorption loading force, so that it can be tightly fitted with the milling profile (13);

[0029] After the formed metal sheet is tightly adsorbed on the die, a pressing block and a threaded pin are used to tighten the threaded pin into the tightening threaded hole (16) so that the edge of the formed metal sheet to be milled is pressed, thereby achieving a milling state;

[0030] The coordinate system is established by using two reference holes (15) on the surface of the milling profile (13). The two reference holes (15) should be set on both sides of the profile and kept on the same horizontal plane, so as to reduce errors and improve processing accuracy. The compiled program is used to complete the processing steps of the metal sheet shape after forming, so that one set of molds can complete two processing steps, reducing multiple positioning in the middle and reducing the number of tooling.

[0031] The skin also needs to be inspected and controlled, and the outer dimensions, surface shape and key features of the skin are comprehensively inspected by non-contact measuring equipment such as laser scanners and three-dimensional coordinate measuring machines. The inspection data is compared and analyzed with the digital model to determine whether the processing accuracy meets the design requirements. For products that fail the inspection, the reasons are found out through data analysis, such as improper processing parameter settings, equipment failure, etc., and corresponding corrective measures are taken to rework them. A complete quality traceability system is established to record the parameters, operators, inspection data and other information of each processing link, so that when quality problems occur, the root cause of the problem can be traced quickly and accurately, and effective improvement measures can be taken to continuously improve the processing quality.

[0032] The advantages of this application are:

[0033] The forming and milling processes are integrated into one mold, avoiding multiple transfers and repositioning between processes, greatly shortening the processing cycle, improving production efficiency and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Heat treatment fixture structure diagram.

[0035] Figure 2 This is a special mold structure diagram.

[0036] Figure 3 This is a special mold structure diagram.

[0037] Among them, 1 frame, 2 lower clamping plate, 3 upper clamping plate, 4 adaptive clamping block, 5 support body, 6 lower positioning piece, 7 support rod, 8 mold bracket, 9 stretching surface, 10 positioning plate, 11 rotating wheel, 12 transmission shaft sleeve, 13 milling surface, 14 vacuum suction nozzle, 15 reference hole, 16 tightening threaded hole. DETAILED DESCRIPTION

[0038] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0039] Example 1

[0040] The first step is sheet quenching.

[0041] Sheet clamping: The aluminum alloy sheet is placed on the lower clamping plate 2 and accurately positioned by adjusting the positioning pins in the positioning slots. The upper clamping plate 3 then descends, and the adaptive clamping block 4, driven by elastic connectors, automatically conforms to the sheet surface, achieving uniform clamping of the sheet.

[0042] Quenching: The quenching equipment is activated to heat and cool the aluminum alloy sheet. During the heating process, the fixture ensures the stability of the sheet. During the cooling process, coolant is evenly sprayed onto the sheet surface through the cooling pipe, achieving rapid and uniform cooling. Sheet removal: After quenching is complete, the upper clamp is released and the aluminum alloy sheet is removed, completing the entire quenching process.

[0043] The second step is stretch forming.

[0044] The blanked aluminum alloy sheet is stretched using a skin stretching machine. To ensure the sheet adheres to the mold after stretching, the aluminum alloy sheet is quenched and the forming is completed within 20 minutes after quenching. During the forming process, the surface of the drawing surface 9 should be lubricated to increase the elongation of the sheet during the forming process and reduce friction between the part surface and the tooling.

[0045] Pre-stretching: The metal sheet to be stretched is fixed to the stretching equipment and a small initial tensile force is applied to the sheet to induce initial plastic deformation, eliminate residual stress within the sheet, and initially conform the sheet to the stretching profile 9, preparing for subsequent formal stretching. During this stage, the stretching speed and tensile force are precisely controlled to ensure uniform stress distribution across the sheet.

[0046] Zoned stretching: The sheet material is divided into multiple zones based on the skin's shape and design requirements. Different stretching parameters, such as stretching speed, force, and direction, are applied to each zone. For areas with complex shapes and high deformation requirements, the force and number of stretches are appropriately increased to ensure sufficient deformation. For relatively flat areas, a relatively small force and faster stretching speed are used to improve overall stretching efficiency. By controlling stretching in these zones, each section of the sheet material deforms in the desired manner, effectively improving the uniformity of the skin's thickness distribution.

[0047] Synchronous Compensatory Stretching: During the stretching process, the sheet's deformation is monitored in real time, and sensors are used to obtain strain data from various parts of the sheet. Based on this monitoring data, the stretching equipment is adjusted in real time, performing additional compensatory stretching in areas with insufficient deformation. This ensures uniform deformation across the entire sheet, minimizing defects such as wrinkles and springback caused by differential deformation. Simultaneously, the shape and position of the stretching die are adjusted to apply an appropriate counterforce to the sheet, further optimizing its deformation.

[0048] Post-processing: After stretching is complete, the skin undergoes heat treatment and shape correction. Heat treatment eliminates residual stress within the skin caused by stretching, improving its mechanical properties. Shape correction fine-tunes the skin's shape to better meet design requirements and ensure dimensional accuracy.

[0049] At the same time, based on the stretching process curve obtained through finite element simulation analysis, parameters such as stretching force, stretching speed, and stretching path are input into the stretching equipment's control system. The stretching equipment is started, and the stretching die begins stretching the skin. During the stretching process, force sensors monitor the stretching force in real time, displacement sensors monitor the skin's stretching displacement, and strain sensors monitor the skin's strain. The intelligent stretching control algorithm compares and analyzes the real-time monitoring data with the preset stretching process curve. If the monitoring data deviates from the process curve, the algorithm automatically adjusts the stretching equipment's operating parameters, such as increasing or decreasing the stretching force and adjusting the stretching speed, to ensure that the skin is stretched according to the predetermined process curve.

[0050] The third step is milling. By rotating the rotating wheel 11, the stretching surface 9 is rotated 180°, and then the support rods 7 on both sides are tightened to ensure that they are level. The coordinate system of the reference hole 15 is established using the CNC machine tool probe, completing the preparatory work before milling. The skin processed in the above steps is then placed on the milling surface 13. The vacuum adsorption system is activated to ensure that the skin is completely in contact with the workbench. At the same time, the threaded pins are tightened to tightly fit the clamping block on the sheet to prevent vibration during the milling process. Based on the material type of the skin (such as aluminum alloy 7075) and the design requirements, the CNC system retrieves the corresponding cutting parameters from the cutting parameter database, such as setting the cutting speed to 2000m / min, the feed rate to 0.15mm / r, and the cutting depth to 0.5mm. The milling equipment is activated, and the new coated carbide milling cutter begins milling the skin. During the processing, the cutting force sensor, vibration sensor, and position sensor collect data in real time and transmit it to the monitoring and error compensation system. When the cutting force sensor detects a sudden increase of 15% in the cutting force, the system determines that tool wear or abnormal cutting status may occur, and automatically reduces the cutting speed by 10%. At the same time, it adjusts the feed rate to restore the cutting force to the normal range, ensuring the stability and accuracy of the machining process.

[0051] The fourth step is quality inspection. After milling, the milled skin profile is thoroughly inspected using a high-precision three-dimensional coordinate measuring machine. The skin's contour, key dimensions, and surface accuracy are measured according to the design drawings. The measured data is compared and analyzed with the design standards. For minor deviations (e.g., dimensional deviations within ±0.3mm), the CNC system fine-tunes the processing equipment to compensate, ensuring that the milled skin profile meets manufacturing standards.

[0052] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art may make various modifications or substitutions within the technical scope disclosed in the present invention, and all such modifications or substitutions shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A skin processing method integrating forming and milling, characterized in that: The following steps are involved:

1. Raw material preparation: According to the design requirements of the skin, select suitable metal sheets as raw materials, strictly test the chemical composition and mechanical properties of the sheets to ensure that they meet the use standards of aerospace parts, pre-treat the surface of the metal sheets to remove oil stains, oxide layers and other impurities on the surface, improve the surface quality of the metal sheets, and lay a good foundation for subsequent processing to obtain pre-treated metal sheets; 2. Use a heat treatment fixture to clamp the metal sheet for quenching to reduce deformation and residual stress to obtain a quenched metal sheet; 3. Stretch forming: Using stretch control algorithms, combined with finite element analysis and real-time monitoring data from the CNC skin stretching machine, we can achieve precise control of the stretching process and obtain the formed metal sheet.

4. Milling the outer shape to obtain the skin.

2. The forming and milling integrated skin processing method according to claim 1, characterized in that: The heat treatment fixture comprises a frame (1), a lower clamping plate (2), an upper clamping plate (3), and an adaptive clamping block (4).

3. The forming and milling integrated skin processing method according to claim 2, characterized in that: The main body of the frame (1) is made of a high-strength heat-resistant alloy material with a heat-resistant temperature of not less than 1000° C. The outer shape is rectangular to facilitate the placement of pre-treated metal plates; The frame (1) is provided with an upper clamping plate (3) and a lower clamping plate (2) mounted on the upper and lower parts; The upper clamping plate (3) and the lower clamping plate (2) are connected by a plurality of adjustable adaptive clamping blocks (4). The height of the adaptive clamping blocks (4) can be adjusted according to the width of the pre-treated metal sheet. The adaptive clamping blocks (4) can also adapt to the clamping requirements of pre-treated metal sheets of different thicknesses, thereby achieving uniform clamping of the pre-treated metal sheet and avoiding deformation of the pre-treated metal sheet due to uneven force during the quenching process. The upper clamping plate (3) and the lower clamping plate (2) are provided with universal positioning grooves and positioning pins. By adjusting the position of the positioning pins in the positioning grooves, pre-treated metal plates of different sizes and shapes can be positioned quickly and accurately, thereby improving the versatility of the clamp.

4. The forming and milling integrated skin processing method according to claim 3, characterized in that: The heat treatment fixture is provided with cooling pipes in a mesh distribution, which can ensure that the coolant is evenly sprayed on the surface of the pretreated metal plate, thereby achieving uniform cooling of the plate and improving the quenching quality.

5. The forming and milling integrated skin processing method according to claim 1, characterized in that: Before stretching, finite element software is used to simulate and analyze the stretching process to predict the deformation of different parts and the required stretching force. Based on the simulation results, a stretching process curve is developed, including the relationship between the stretching force, stretching speed and stretching path over time. During the stretching process, the force, deformation and displacement of the quenched metal sheet are monitored in real time through force sensors, displacement sensors and strain sensors installed on the stretching equipment; the stretching control algorithm dynamically adjusts the stretching process curve based on the real-time monitoring data to ensure that the quenched metal sheet is always in the optimal stress state during the stretching process, avoiding excessive or insufficient stretching.

6. The forming and milling integrated skin processing method according to claim 1, characterized in that: In the stretch forming and milling of the outline, a special die is used.

7. The forming and milling integrated skin processing method according to claim 6, characterized in that: The special mold consists of a support body (5), a lower positioning member (6), a support rod (7), a mold bracket (8), a stretching profile (9), a positioning plate (10), a rotating wheel (11), a transmission shaft sleeve (12), a milling profile (13), a vacuum suction nozzle (14), a reference hole (15), and a pressing threaded hole (16).

8. The forming and milling integrated skin processing method according to claim 7, characterized in that: The support body (5) is made of Q235 or metal of the same strength and is used for support during stretching, forming and milling. A row of lower positioning members (6) is installed on each side of the support body (5), and the number is calculated according to the length of the support body (5), and is usually set to be installed at intervals of 300 mm; A support rod (7) is installed on the lower positioning member (6), and the support rod (7) is used to ensure the position of the pulling profile 9 in the horizontal direction to prevent it from rotating; The stretching profile 9 is supported by four mold brackets (8), which are installed on both sides of the support body (5) without affecting the direction of stretching, with two mold brackets installed in each direction; The surface of the drawing profile 9 is provided with 2 to 3 positioning plates (10) for drilling positioning holes in the quenched metal sheet after forming, for use in the next milling process; A rotating wheel (11) is installed on each side of the drawing profile 9 in the non-drawing direction. The function of the rotating wheel (11) is to rotate the drawing profile 9 180 degrees with force after the first forming process is completed, and use another profile to carry out the next process; In order to save the force during the rotation process, each rotating wheel (11) is equipped with a transmission sleeve (12). The transmission sleeve (12) can be equipped with multiple gears or other structures to transmit torque and reduce the loading force during the rotation process, making it easier to change direction.

9. The forming and milling integrated skin processing method according to claim 8, characterized in that: During the milling process of the special mold, the support rods (7) on both sides are completely opened using a hexagonal wrench, and then the rotating wheel (11) is turned to rotate the support body (5) 180 degrees; The other side corresponding to the stretching profile (9) is a milling profile (13), and a vacuum suction nozzle (14) is installed on the side of the milling profile (13) for installing a rubber tube and a vacuum pump during the milling process to provide adsorption force, thereby ensuring that each position of the formed metal sheet can obtain sufficient adsorption loading force, so that it can be tightly fitted with the milling profile (13); After the formed metal sheet is tightly adsorbed on the die, a pressing block and a threaded pin are used to tighten the threaded pin into the tightening threaded hole (16) so that the edge of the formed metal sheet to be milled is pressed, thereby achieving a milling state; The coordinate system is established by using two reference holes (15) on the surface of the milling profile (13). The two reference holes (15) should be set on both sides of the profile and kept on the same horizontal plane, so as to reduce errors and improve processing accuracy. The compiled program is used to complete the processing steps of the metal sheet shape after forming, so that one set of molds can complete two processing steps, reducing multiple positioning in the middle and reducing the number of tooling.

10. The forming and milling integrated skin processing method according to claim 1, characterized in that: The skin also needs to be inspected and controlled, and the skin's external dimensions, surface shape and key features must be comprehensively inspected using non-contact measuring equipment such as laser scanners and three-coordinate measuring machines. The inspection data must be compared and analyzed with the digital model to determine whether the processing accuracy meets the design requirements.

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