Method and apparatus for hot forming of aircraft skin

Abstract

The application discloses a kind of aircraft skin hot shaping method and device.In the present application, first, the geometric deviation of each target area is determined by calculating the point cloud of each target area on the skin to be shaped and the same position of the standard skin, and the shaping parameters of each target area are determined;Then, the hot shaping work is carried out using the shaping parameters of each target area, and the creep parameters are corrected based on experimental data;Then, the process of determining the shaping parameters of each target area, the hot shaping work of each target area and determining the target area is repeated, and the shaping parameters of each target area are obtained based on the corrected creep parameters, until there is no target area, and the hot shaping work of the skin to be shaped is completed.The present application constructs an aircraft skin hot shaping method based on material constitutive property and closed-loop feedback mechanism, which can significantly improve the accuracy, efficiency and process safety of the complex curved surface skin shaping process.

Description

Technical Field

[0001] This invention belongs to the field of aircraft skin manufacturing technology, specifically relating to a method and apparatus for thermally shaping aircraft skin. Background Technology

[0002] Aircraft skin, as a key component for aerodynamic shape and structural load transfer in aircraft, covers major structural areas including the fuselage, wings, and tail section. With the increasing size and complexity of next-generation aircraft, skin structures are becoming larger and more complex, placing higher demands on geometric accuracy and surface quality after forming. Skin shaping, as a crucial step in achieving high-precision forming, is one of the key technologies in skin manufacturing. However, existing skin shaping devices and methods still have limitations in terms of operational efficiency, control precision, and adaptability to complex surface morphologies, making it difficult to meet the stringent requirements of current high-performance aircraft structures for skin forming quality. Therefore, there is an urgent need to develop an efficient and high-precision skin shaping technology to improve overall manufacturing levels and ensure the reliability of aircraft structural performance. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and to propose a method and apparatus for thermally correcting aircraft skin.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention provides a method for thermally correcting aircraft skin, as detailed below:

[0006] S1. Fix the skin to be calibrated in the arc groove of the calibration platform. On the telescopic calibration thermal platform, set multiple telescopic thermal calibration components arranged in an array on the arc convex surface aligned with the arc groove. In the telescopic thermal calibration components, the electric telescopic rod drives the mounting plate. The side of the mounting plate away from the electric telescopic rod is an arc convex surface and a resistance heating element is fixed thereon. A pressure sensor is provided between the mounting plate and the resistance heating element. Divide the skin to be calibrated into multiple calibration areas aligned with each mounting plate, and number each calibration area and each telescopic thermal calibration component.

[0007] S2. The robotic arm drives the detection device to move, so that the detection device can detect each correction area and obtain the point cloud data of each correction area on the skin to be corrected. The target area is identified by the point cloud data of each correction area.

[0008] S3. Determine the thermal calibration parameters for each target area. The thermal calibration parameters include calibration temperature, holding time, and heating rate.

[0009] S4. Correction of creep parameters for the skin material to be shaped.

[0010] S5. Repeat step S3, and use the corrected creep parameters obtained in step S4 when repeating step S3, so as to obtain the corrected thermal correction parameters of each target area.

[0011] S6. Use the corrected thermal calibration parameters of each target area obtained in step S5 to perform thermal calibration on each target area; after completing the thermal calibration of each target area, repeat step S2. If there is no target area, complete the thermal calibration of the skin to be calibrated. If there is a target area, return to step S5 until the thermal calibration of the skin to be calibrated is completed.

[0012] Preferably, the numbering process is as follows: an array is used for numbering, where a one-dimensional parameter represents the platform type, a one-dimensional parameter of 1 indicates a calibration platform, a one-dimensional parameter of 2 indicates a scalable calibration thermal platform, a two-dimensional parameter represents the row position of each calibration area or each scalable thermal calibration component, and a three-dimensional parameter represents the column position of each calibration area or each scalable thermal calibration component.

[0013] Preferably, the specific process of step S2 is as follows:

[0014] (1) Point cloud data acquisition: The robotic arm drives the detection device to move, and the detection device scans each correction area to obtain the point cloud data of each correction area. During scanning, there is an overlapping area between each two adjacent correction areas.

[0015] (2) Establish the skin point cloud model to be corrected: Import the point cloud data collected in step (1) into the GeomagicControl X software in a unified format, use the denoising function in the software to remove isolated noise points generated during the scanning process, use the registration function to merge the point cloud data of each correction area into a unified coordinate system, and remove overlapping areas, thereby establishing the skin point cloud model to be corrected.

[0016] (3) Registration of the skin point cloud model to be corrected with the standard skin design theory model: a. Import the standard skin design theory model; b. Perform initial rigid body registration of the skin point cloud model to be corrected and the standard skin design theory model obtained in step (2) using target feature points; c. Perform fine registration using the ICP algorithm; d. Calculate the RMS error value. If RMS ≤ 0.1 mm, the registration of the skin point cloud model to be corrected and the standard skin design theory model is qualified, and the registration is completed. If RMS > 0.1 mm, re-identify the target or adjust the target distribution, and return to step b.

[0017] (4) Deviation analysis and target area identification: Using the deviation analysis function in Geomagic Control X software, the shortest distance from each point in the point cloud within each correction area to the standard skin design theoretical model is calculated. It outputs the deviation distribution and statistics, and if the correction area exists... If the point is found, then the area of ​​the school's shape is designated as the target area; if the school's shape does not exist... If the point is found, the calibration area is determined to be a conforming area; then the number of each target area and its corresponding stretchable thermal calibration component is determined.

[0018] Preferably, the calibration temperature of each target region is determined by the following steps: performing local quadratic surface fitting on the point cloud data of each target region to obtain the curvature of each target region. Then, the target plastic strain of each target region is approximately calculated as follows:

[0019]

[0020] In the formula, This refers to the curvature deviation of the target area from the same position on the standard skin design theoretical model. The thickness of the skin to be calibrated.

[0021] Query the elastic modulus of the skin material to be shaped The curve of temperature variation and the yield stress of the skin material to be shaped. The curves showing the change with temperature indicate that the flow stress at which the target region undergoes corresponding plastic deformation is approximately...

[0022]

[0023] Solve The minimum temperature value that is established is taken as the minimum value of the safe calibration temperature range for the target area. ;

[0024] The maximum value of the safe straightening temperature range for the target area is the temperature at which the hardness of the skin material to be straightened decreases by 10%, minus the temperature of the safety margin. This allows us to obtain the safe calibration temperature range for the target area. Select the median value within the safe calibration temperature range. + ) / 2 is used as the calibration temperature for the target area.

[0025] Preferably, the heat preservation time for each target area is determined as follows: During the thermal straightening process, the controller controls the electric telescopic rod to drive the mounting plate to move the resistance heating element to press on the corresponding straightening area with a preset pressure value, applying constant pressure to the straightening area; the creep parameters of the skin material to be straightened are retrieved from the material database, including the pre-factor A, stress exponent n, and activation energy Q; the initial stress of each target area is determined. Approximate calculation is

[0026]

[0027]

[0028] In the formula, The initial strain of the target region, The curvature of the target region.

[0029] The total strain in each target region is

[0030] (1)

[0031] In the formula, The total strain in the target region, For the elastic strain of the target region, For the creep strain of the target region, The stress in the target area.

[0032] Under the condition of approximately constant total strain, differentiating equation (1) over time yields...

[0033]

[0034] but

[0035] (2)

[0036] in, The creep strain rate is calculated using Norton's power-law creep.

[0037]

[0038] In the formula, is the gas constant.

[0039] but

[0040] (3)

[0041] Integrating equation (3), we obtain the formula for stress decay over time:

[0042]

[0043] remember

[0044]

[0045] Then, under the corresponding calibration temperature, the stress in each target area will decrease to the target safe stress. The required time is

[0046] .

[0047] Preferably, the heating rate of each target area is determined by the following steps: specifying the maximum allowable temperature difference in the thickness direction of the skin to be shaped. The upper bound of the heating rate of each target region is approximated by the thermal diffusion equation.

[0048]

[0049]

[0050] In the formula, For correction coefficients, and The range of values ​​is ; The linear expansion coefficient of the skin material to be shaped at temperature T is obtained by consulting the standard handbook of metallic materials. The length of the skin feature to be corrected, and ; For safety factor, and The range of values ​​is .

[0051] The upper limit of the heating rate, which does not exceed the power limit of the heating equipment supplying the resistance heating element, is:

[0052]

[0053] In the formula, For heating equipment heating efficiency, For the power of the heating equipment, For the quality of the skin to be calibrated, The specific heat capacity of the skin material to be shaped is given.

[0054] Pick .

[0055] Preferably, the specific process of step S4 is as follows:

[0056] Ⅰ. Take a sample of the skin to be shaped, set strain gauges on the sample, and use the preset pressure value, holding time, heating rate, and multiple sets of different shaping temperatures obtained in step S3. A thermal calibration test was conducted on the strain gauge locations of the skin sample to be calibrated. The real-time strain measured by the strain gauges was extracted, and strain-time curves at different calibration temperatures were obtained. The stress at different calibration temperatures was calculated based on the final strain measured by the strain gauges after the thermal calibration test. .

[0057] II. Calculate the actual creep strain rate based on the strain-time curves at different calibration temperatures. .

[0058] III. Using the pre-factors of the skin material to be corrected, retrieved from the materials database. Stress index and activation energy As initial parameters, based on stress The predicted creep strain rate is obtained from the creep strain rate calculation formula:

[0059]

[0060] V. Constructing the objective function:

[0061]

[0062] In the formula, The number of temperature groups used for the thermal calibration test;

[0063] The objective function is solved iteratively using a nonlinear least squares fitting method until a preset number of iterations is reached, so that the creep parameter corresponding to the minimum objective function value is the corrected creep parameter.

[0064] Preferably, the thermal straightening process is as follows: according to the retractable thermal straightening components corresponding to each target area determined in step S2, the controller controls the electric telescopic rod to drive the mounting plate to move the resistance heating element to press on the corresponding target area with a preset pressure value. The resistance heating element works according to the thermal straightening parameters of each target area obtained in step S5, so that the material of the corresponding target area generates target plastic strain under the preset pressure.

[0065] This invention discloses an aircraft skin thermal calibration device, comprising a detection device, a robotic arm, a calibration platform, a retractable calibration thermal platform, and a base plate. The calibration platform and the retractable calibration thermal platform are spaced apart and both fixed to the base plate. The calibration platform has a concave arc surface with an arc groove on its side near the retractable calibration thermal platform, and a slot is formed near the outer edge of the bottom surface of the arc groove. The retractable calibration thermal platform has a convex arc surface on its side near the calibration platform and is equipped with multiple retractable thermal calibration components arranged in an array. Each retractable thermal calibration component includes an electric telescopic rod, a mounting plate, and a resistance heating element. The two ends of the electric telescopic rod are fixed to the retractable calibration thermal platform and the mounting plate, respectively. The mounting plate has a convex arc surface away from the electric telescopic rod and a resistance heating element is fixed thereon. A heat-insulating coating is applied between the mounting plate and the resistance heating element. A pressure sensor is also provided between the mounting plate and the resistance heating element. The robotic arm is mounted on the base plate and located outside the gap between the calibration platform and the retractable calibration thermal platform, driving the detection device to move. In the initial state, each electric telescopic rod is in the retracted state, and the side of each mounting plate closest to the calibration platform is spliced ​​together to form a convex arc surface that matches the arc groove.

[0066] Preferably, the robotic arm includes a base, a wrist, a forearm, and a large arm. The base and the base plate form a revolute joint that rotates about a vertical axis and are driven to rotate by a first drive motor. One end of the large arm and the base form a revolute joint that rotates about a horizontal axis and are driven to rotate by a second drive motor. One end of the forearm and the other end of the large arm form a revolute joint that rotates about a horizontal axis and are driven to rotate by a third drive motor. One end of the wrist and the other end of the forearm form a revolute joint that are driven to rotate by a fourth drive motor. A detection device is fixed at the other end.

[0067] The present invention has the following beneficial effects:

[0068] This invention constructs a thermal straightening method for aircraft skin based on material constitutive properties and a closed-loop feedback mechanism, which can significantly improve the accuracy, efficiency, and process safety of the straightening process for complex curved surface skins. Specifically, this invention first obtains the geometric deviation between the point cloud of each straightening region on the skin to be straightened and the same position on the standard skin by detection and calculation. The straightening region where the point cloud with geometric deviation exceeds the preset value is designated as the target region, and the straightening parameters of each target region are determined. The target plastic strain of each target region is obtained based on the deviation of the curvature of each target region from the curvature of the same position on the standard skin. Combined with the relationship between the elastic modulus and yield stress of the skin material to be straightened and temperature in the material database, the minimum temperature required to generate the corresponding target plastic strain in each target region is obtained. Finally, based on the hardness-temperature test of the skin material to be straightened, the temperature at which the hardness decreases by 10% is determined minus the safety margin. The highest temperature is used to determine the safe calibration temperature range for each target area. Based on this, the calibration temperature for each target area is determined. Using the Norton creep model and stress relaxation theory under constant strain conditions, the holding time required for the stress in each target area to decrease to the target safe stress at the corresponding calibration temperature is derived. Then, based on the maximum allowable temperature difference in the thickness direction of the skin to be calibrated, the upper limit of the heating rate of each target area at each calibration temperature is obtained through the thermal diffusion equation. The smaller value between this upper limit and the upper limit of the heating rate not exceeding the power limit of the heating equipment is taken as the heating rate of each target area. This effectively avoids thermal stress or local overheating damage caused by excessive thermal gradients and improves the service life of the heating equipment, thus obtaining the calibration parameters for each target area. Furthermore, to improve the accuracy of subsequent calibration parameter calculations, the creep parameters are corrected. Then, the process of determining the calibration parameters of each target area, performing thermal calibration on each target area, and determining the target area is repeated, with the calibration parameters of each target area based on the corrected creep parameters, until no target area exists, thus completing the thermal calibration of the skin to be calibrated. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0070] Figure 2This is a schematic diagram of the detection device and robotic arm in this invention;

[0071] Figure 3 This is a schematic diagram of the structure during the thermal straightening process of the present invention;

[0072] Figure 4 This is a flowchart of a thermal straightening method for aircraft skin according to the present invention. Detailed Implementation

[0073] The present invention will now be further described with reference to the accompanying drawings.

[0074] like Figure 1 As shown, the present invention provides an aircraft skin thermal calibration device, comprising a detection device A1, a robotic arm A2, a calibration platform A3, a retractable calibration thermal platform A4, and a base plate A5.

[0075] like Figure 2 As shown, the robotic arm A2 includes a base B1, a wrist B2, a forearm B3, and a large arm B5. The base B1 and the base plate A5 form a revolute joint that rotates about a vertical axis, driven by a first drive motor. One end of the large arm B5 and the base B1 form a revolute joint that rotates about a horizontal axis a, driven by a second drive motor B6. One end of the forearm B3 and the other end of the large arm B5 form a revolute joint that rotates about a horizontal axis b, driven by a third drive motor B4. One end of the wrist B2 and the other end of the forearm B3 form a revolute joint that rotates by a fourth drive motor. A detection device A1 is fixed to the other end of the wrist, which is a 3D scanner.

[0076] The calibration platform A3 and the retractable calibration thermal platform A4, arranged at intervals, are both fixed to the base plate A5. The side of the calibration platform A3 closest to the retractable calibration thermal platform A4 is a concave arc surface with an arc groove, and a slot is formed on the bottom surface of the arc groove near the outer edge. The side of the retractable calibration thermal platform A4 closest to the calibration platform A3 is a convex arc surface and has multiple retractable thermal calibration components arranged in an array. The retractable thermal calibration components include electric telescopic rods, mounting plates, and resistance heating elements. The two ends of the electric telescopic rods are fixed to the retractable calibration thermal platform A4 and the mounting plate, respectively. The side of the mounting plate away from the electric telescopic rods is a convex arc surface and has a resistance heating element fixed thereon. A heat-insulating coating is applied between the mounting plate and the resistance heating element. A pressure sensor is also provided between the mounting plate and the resistance heating element. The base B1 is located outside the gap between the calibration platform A3 and the retractable calibration thermal platform A4. In the initial state, each electric telescopic rod is in a retracted state, and the sides of each mounting plate closest to the calibration platform A3 are spliced ​​to form an arc convex surface that matches the arc groove.

[0077] Among them, drive motor one, drive motor two B6, drive motor three B4, drive motor four and each electric telescopic rod are all controlled by the controller, and the signal output terminal of the pressure sensor is connected to the controller.

[0078] like Figure 4 As shown, the present invention provides a method for thermally correcting aircraft skin, which is detailed below:

[0079] S1. Install the skin to be calibrated into the arc groove of the calibration platform A3. The integrally formed protrusion on the skin to be calibrated is fixed to the slot (transition fit or interference fit, there is a gap between the skin to be calibrated and the side wall of the arc groove, the skin to be calibrated can be removed through the gap); Divide the skin to be calibrated into multiple calibration areas that are aligned with each mounting plate, and number each calibration area and each retractable thermal calibration component. The numbering process is as follows: use an array for numbering. Let the one-dimensional parameter represent the platform type. When the one-dimensional parameter is 1, it is the calibration platform A3. When the one-dimensional parameter is 2, it is the retractable thermal calibration platform A4. The two-dimensional parameter represents the row position of each calibration area or each retractable thermal calibration component. The three-dimensional parameter represents the column position of each calibration area or each retractable thermal calibration component. For example, the number (1, 1, 2) represents the calibration area in the first row and second column on the calibration platform A3, and the number (2, 1, 2) represents the retractable thermal calibration component in the first row and second column on the retractable thermal calibration platform A4.

[0080] S2. The robotic arm A2 drives the detection device A1 to move, enabling the detection device A1 to detect each correction area and obtain the point cloud data of each correction area on the skin to be corrected. The target area is identified through the point cloud data of each correction area. The specific process is as follows:

[0081] (1) Point cloud data acquisition: The robotic arm A2 drives the detection device A1 to move. The detection device A1 scans each correction area to obtain the point cloud data of each correction area. During the scanning, there is an overlapping area between each two adjacent correction areas.

[0082] (2) Establish the skin point cloud model to be corrected: Import the point cloud data collected in step (1) into the GeomagicControl X software in a unified format, use the denoising function in the software to remove isolated noise points generated during the scanning process, use the registration function to merge the point cloud data of each correction area into a unified coordinate system, and remove overlapping areas, thereby establishing the skin point cloud model to be corrected.

[0083] (3) Registration of the skin point cloud model to be corrected with the standard skin design theory model: a. Import the standard skin design theory model; b. Perform initial rigid body registration of the skin point cloud model to be corrected and the standard skin design theory model obtained in step (2) using target feature points; c. Perform fine registration using the ICP algorithm; d. Calculate the RMS error value. If RMS ≤ 0.1mm, the registration of the skin point cloud model to be corrected and the standard skin design theory model is qualified, and the registration is completed. If RMS > 0.1mm, re-identify the target or adjust the target distribution, and return to step b. In this regard, the error between the skin point cloud model to be corrected and the standard skin design theory model is not too large, so an RMS error threshold of 0.1mm is sufficient.

[0084] (4) Deviation analysis and target area identification: Using the deviation analysis function in Geomagic Control X software, the shortest distance from each point in the point cloud within each correction area to the standard skin design theoretical model is calculated. It outputs the deviation distribution and statistics, and if the correction area exists... If the point is found, then the area of ​​the school's shape is designated as the target area; if the school's shape does not exist... If the point is found, the calibration area is determined to be a conforming area; then the number of each target area and its corresponding scalable thermal calibration component is determined.

[0085] S3. Determine the thermal calibration parameters for each target area. The thermal calibration parameters include calibration temperature, holding time, and heating rate. The specific process is as follows:

[0086] ① Determine the calibration temperature for each target region: Perform local quadratic surface fitting on the point cloud data of each target region to obtain the curvature of each target region. (Gaussian curvature or mean curvature), and then calculate the target plastic strain of each target region using a small-slope linear approximation formula.

[0087]

[0088] In the formula, This refers to the curvature deviation of the target area from the same position on the standard skin design theoretical model. The thickness of the skin to be calibrated.

[0089] Query the elastic modulus of the skin material to be shaped The curve of temperature variation and the yield stress of the skin material to be shaped The curves showing the change with temperature indicate that the flow stress at which the target region undergoes corresponding plastic deformation is approximately...

[0090]

[0091] Solve The minimum temperature value that is established is taken as the minimum value of the safe calibration temperature range for the target area. In this embodiment, the yield stress is... The yield strength (σ0.2) index was used.

[0092] The temperature at which the hardness of the skin material to be shaped decreases by 10% (obtained through a hardness-temperature test) minus a safety margin. The temperature value is taken as the maximum value of the target area's safe calibration temperature range. This allows us to obtain the safe calibration temperature range for the target area. Select the median value within the safe calibration temperature range. + ) / 2 is used as the calibration temperature for the target area.

[0093] ② Determine the heat preservation time for each target area: During the thermal straightening process, the controller controls the electric telescopic rod to drive the mounting plate and the resistance heating element to press on the corresponding straightening area with a preset pressure value (measured by a pressure sensor). Applying a constant pressure to the straightening area, it can be approximately assumed that the total strain remains constant, and the material satisfies the linear elastic relationship and Norton's steady-state creep law. Therefore, the stress relaxation model under constant total strain conditions (the formula for stress decay over time) can be used to solve for the stress decay over time, so that the stress in each target area decreases to the target safe stress at the corresponding straightening temperature. The required time is the heat preservation time for each target area. The specific process is as follows: The creep parameters of the skin material to be shaped are retrieved from the material database. The creep parameters include the pre-factor A, stress exponent n, and activation energy Q; the initial stress of each target area... Approximate calculation is

[0094]

[0095]

[0096] In the formula, The initial strain of the target region, The curvature of the target region.

[0097] The total strain in each target region is

[0098] (1)

[0099] In the formula, The total strain in the target region, For the elastic strain of the target region, For the creep strain of the target region, The stress in the target area.

[0100] Under the condition of approximately constant total strain, differentiating equation (1) over time yields...

[0101]

[0102] but

[0103] (2)

[0104] in, The creep strain rate is calculated using Norton's power-law creep.

[0105]

[0106] In the formula, is the gas constant, with a value of 8.314 J / (mol·K).

[0107] but

[0108] (3)

[0109] Integrating equation (3), we obtain the formula for stress decay over time:

[0110]

[0111] remember

[0112]

[0113] Then, under the corresponding calibration temperature, the stress in each target area will decrease to the target safe stress. The required time is

[0114]

[0115] ③ Determine the heating rate of each target area: To avoid thermal stress or localized burns, specify the maximum allowable temperature difference in the thickness direction of the skin to be shaped. The upper bound of the heating rate of each target region is approximated by the thermal diffusion equation.

[0116]

[0117]

[0118] In the formula, For correction factors, and The range of values ​​is ; The linear expansion coefficient of the skin material to be shaped at temperature T can be obtained by consulting the standard handbook of metallic materials. The length of the skin feature to be corrected, and ; For safety factor, and The range of values ​​is .

[0119] The upper limit of the heating rate, which does not exceed the power limit of the heating equipment supplying the resistance heating element, is:

[0120]

[0121] In the formula, Heating efficiency of heating equipment that supplies power to resistance heating elements. For the power of the heating equipment, For the quality of the skin to be calibrated, The specific heat capacity of the skin material to be shaped is given.

[0122] Pick The heating rate for each target region.

[0123] S4. The creep parameter correction for the skin material to be shaped is as follows:

[0124] Ⅰ. Take a sample of the skin to be shaped, set strain gauges on the sample, and use the preset pressure value, holding time, heating rate, and multiple sets of different shaping temperatures obtained in step S3. (Measured using an infrared thermometer) A thermal calibration test is performed on the strain gauge positions on the skin sample to be calibrated. The real-time strain detected by the strain gauges is extracted to obtain strain-time curves at different calibration temperatures. The stress at different calibration temperatures is then calculated based on the final strain detected by the strain gauges after the thermal calibration test. .

[0125] II. Calculate the actual creep strain rate based on the strain-time curves at different calibration temperatures. .

[0126] III. Using the pre-factors of the skin material to be corrected, retrieved from the materials database. Stress index and activation energy As initial parameters, based on stress The predicted creep strain rate is obtained from the creep strain rate calculation formula:

[0127]

[0128] V. Constructing the objective function:

[0129]

[0130] In the formula, The number of temperature groups used for the thermal calibration test;

[0131] The objective function is solved iteratively using a nonlinear least squares fitting method until a preset number of iterations is reached, so that the creep parameter corresponding to the minimum objective function value is the corrected creep parameter.

[0132] S5. Repeat step S3, and use the corrected creep parameters obtained in step S4 when repeating step S3, so as to obtain the corrected thermal correction parameters of each target area.

[0133] S6. Use the corrected thermal calibration parameters of each target area obtained in step S5 to perform thermal calibration on each target area; after completing the thermal calibration of each target area, repeat step S2. If there is no target area, complete the thermal calibration of the skin to be calibrated. If there is a target area, return to step S5 until the thermal calibration of the skin to be calibrated is completed.

[0134] The thermal calibration process is as follows: Figure 3 As shown, the robotic arm A2 drives the detection device A1 to move, so that both the robotic arm A2 and the detection device A1 are located outside the gap between the calibration platform A3 and the retractable calibration thermal platform A4, so as to avoid affecting the movement of each retractable thermal calibration component. Then, according to the retractable thermal calibration components corresponding to each target area determined in step S2, the controller controls the electric telescopic rod to drive the mounting plate to move the resistance heating element to press on the corresponding target area with a preset pressure value. The resistance heating element works according to the thermal calibration parameters of each target area obtained in step S5, so that the corresponding target area generates target plastic strain under the action of preset pressure, so that the shape of the corresponding target area conforms to the target shape.

Claims

1. A method for thermally correcting aircraft skin, characterized in that: Specifically as follows: S1. Fix the skin to be calibrated in the arc groove of the calibration platform. On the telescopic calibration hot platform, set multiple telescopic thermal calibration components arranged in an array on the arc convex surface aligned with the arc groove. In the telescopic thermal calibration components, the electric telescopic rod drives the mounting plate. The side of the mounting plate away from the electric telescopic rod is an arc convex surface and a resistance heating element is fixed thereon. A pressure sensor is provided between the mounting plate and the resistance heating element. Divide the skin to be calibrated into multiple calibration areas aligned with each mounting plate and number each calibration area and each telescopic thermal calibration component. S2. The robotic arm drives the detection device to move, so that the detection device can detect each correction area and obtain the point cloud data of each correction area on the skin to be corrected. The target area is identified by the point cloud data of each correction area. S3. Determine the thermal calibration parameters for each target area. The thermal calibration parameters include calibration temperature, holding time, and heating rate. S4. Correction of creep parameters for the skin material to be shaped; S5. Repeat step S3, and use the corrected creep parameters obtained in step S4 when repeating step S3, so as to obtain the corrected thermal correction parameters of each target area. S6. Use the corrected thermal calibration parameters of each target area obtained in step S5 to perform thermal calibration on each target area; after completing the thermal calibration of each target area, repeat step S2. If there is no target area, complete the thermal calibration of the skin to be calibrated. If there is a target area, return to step S5 until the thermal calibration of the skin to be calibrated is completed.

2. The aircraft skin thermal straightening method according to claim 1, characterized in that: The numbering process is as follows: an array is used for numbering. A one-dimensional parameter represents the platform type. When the one-dimensional parameter is 1, it is a calibration platform. When the one-dimensional parameter is 2, it is a scalable calibration thermal platform. A two-dimensional parameter represents the row position of each calibration area or each scalable thermal calibration component. A three-dimensional parameter represents the column position of each calibration area or each scalable thermal calibration component.

3. The aircraft skin thermal straightening method according to claim 1, characterized in that: The specific process of step S2 is as follows: (1) Point cloud data acquisition: The robotic arm drives the detection device to move, and the detection device scans each correction area to obtain the point cloud data of each correction area. During the scanning, there is an overlapping area between each two adjacent correction areas. (2) Establish the point cloud model of the skin to be corrected: import the point cloud data collected in step (1) into the Geomagic Control X software in a unified format, use the denoising function in the software to remove isolated noise points generated during the scanning process, use the registration function to merge the point cloud data of each correction area into a unified coordinate system, and remove overlapping areas, thereby establishing the point cloud model of the skin to be corrected. (3) Registration of the point cloud model of the skin to be corrected with the standard skin design theory model: a. Import the standard skin design theory model; b. Perform initial rigid body registration between the point cloud model of the skin to be corrected obtained in step (2) and the design theory model of the standard skin using target feature points; c. Perform fine registration using the ICP algorithm; d. Calculate the RMS error value. If RMS ≤ 0.1mm, the registration between the point cloud model of the skin to be corrected and the design theory model of the standard skin is deemed qualified and the registration is completed. If RMS > 0.1mm, re-identify the target or adjust the target distribution and return to step b. (4) Deviation analysis and target area identification: Using the deviation analysis function in Geomagic Control X software, the shortest distance from each point in the point cloud within each correction area to the standard skin design theoretical model is calculated. It outputs the deviation distribution and statistics, and if the correction area exists... If the point is found, then the area of ​​the school's shape is designated as the target area; if the school's shape does not exist... If the point is found, the calibration area is determined to be a conforming area; then the number of each target area and its corresponding scalable thermal calibration component is determined.

4. The aircraft skin thermal straightening method according to claim 1, characterized in that: The steps to determine the calibration temperature for each target region are as follows: Perform local quadratic surface fitting on the point cloud data of each target region to obtain the curvature of each target region. Then, the target plastic strain for each target region is approximately calculated as follows: In the formula, This refers to the curvature deviation of the target area from the same position on the standard skin design theoretical model. The thickness of the skin to be shaped; Query the elastic modulus of the skin material to be shaped The curve of temperature variation and the yield stress of the skin material to be shaped The curves showing the change with temperature indicate that the flow stress at which the target region undergoes corresponding plastic deformation is approximately... Solve The minimum temperature value that is established is taken as the minimum value of the safe calibration temperature range for the target area. ; The maximum value of the safe straightening temperature range for the target area is the temperature at which the hardness of the skin material to be straightened decreases by 10%, minus the temperature of the safety margin. This allows us to obtain the safe calibration temperature range for the target area. Select the median value within the safe calibration temperature range. + ) / 2 is used as the calibration temperature for the target area.

5. The aircraft skin thermal straightening method according to claim 1, characterized in that: The heat preservation time for each target area is determined as follows: During the thermal straightening process, the controller controls the electric telescopic rod to drive the mounting plate, which in turn moves the resistance heating element to press against the corresponding straightening area at a preset pressure value, applying constant pressure to the straightening area; the creep parameters of the skin material to be straightened are retrieved from the material database, including the pre-factor A, stress exponent n, and activation energy Q; the initial stress of each target area is determined. Approximate calculation is In the formula, The initial strain of the target region, The curvature of the target region; The total strain in each target region is （1） In the formula, The total strain in the target region, For the elastic strain of the target region, For the creep strain of the target region, The stress in the target area; Under the condition of approximately constant total strain, differentiating equation (1) over time yields... but （2） in, The creep strain rate is calculated using Norton's power-law creep. In the formula, It is the gas constant; but （3） Integrating equation (3), we obtain the formula for stress decay over time: remember Then, under the corresponding calibration temperature, the stress in each target area will decrease to the target safe stress. The required time is 。 6. The aircraft skin thermal straightening method according to claim 1, characterized in that: The steps to determine the heating rate of each target area are as follows: Specify the maximum allowable temperature difference in the thickness direction of the skin to be shaped. The upper bound of the heating rate of each target region is approximated by the thermal diffusion equation. In the formula, For correction factors, and The range of values ​​is ; The linear expansion coefficient of the skin material to be shaped at temperature T is obtained by consulting the standard handbook of metallic materials. The length of the skin feature to be corrected, and ; For safety factor, and The range of values ​​is ; The upper limit of the heating rate, which does not exceed the power limit of the heating equipment supplying the resistance heating element, is: In the formula, For heating equipment heating efficiency, For the power of the heating equipment, For the quality of the skin to be calibrated, The specific heat capacity of the skin material to be shaped; Pick .

7. The aircraft skin thermal straightening method according to claim 1, characterized in that: The specific process of step S4 is as follows: Ⅰ. Take a sample of the skin to be shaped, set strain gauges on the sample, and use the preset pressure value, holding time, heating rate, and multiple sets of different shaping temperatures obtained in step S3. A thermal calibration test was conducted on the strain gauge locations of the skin sample to be calibrated. The real-time strain measured by the strain gauges was extracted, and strain-time curves at different calibration temperatures were obtained. The stress at different calibration temperatures was calculated based on the final strain measured by the strain gauges after the thermal calibration test. ; II. Calculate the actual creep strain rate based on the strain-time curves at different calibration temperatures. ; III. Using the pre-factors of the skin material to be corrected, retrieved from the materials database. Stress index and activation energy As initial parameters, based on stress The predicted creep strain rate is obtained from the creep strain rate calculation formula: V. Constructing the objective function: In the formula, The number of temperature groups used for the thermal calibration test; The objective function is solved iteratively using a nonlinear least squares fitting method until a preset number of iterations is reached, so that the creep parameter corresponding to the minimum objective function value is the corrected creep parameter.

8. The aircraft skin thermal straightening method according to claim 1, characterized in that: The thermal straightening process is as follows: According to the retractable thermal straightening components corresponding to each target area determined in step S2, the controller controls the electric telescopic rod to drive the mounting plate to move the resistance heating element to press on the corresponding target area with a preset pressure value. The resistance heating element works according to the thermal straightening parameters of each target area obtained in step S5, so that the material of the corresponding target area generates target plastic strain under the preset pressure.

9. The apparatus used in the aircraft skin thermal alignment method according to any one of claims 1 to 8, comprising a detection device, a robotic arm, a calibration platform, and a base plate, characterized in that: It also includes a retractable calibration thermal platform; the calibration platform and the retractable calibration thermal platform are spaced apart and fixed to the base plate. The side of the calibration platform near the retractable calibration thermal platform is a concave arc surface with an arc groove, and a slot is formed on the bottom surface of the arc groove near the outer edge. The side of the retractable calibration thermal platform near the calibration platform is a convex arc surface and has multiple retractable thermal calibration components arranged in an array. The retractable thermal calibration components include an electric telescopic rod, a mounting plate, and a resistance heating element. The two ends of the electric telescopic rod are fixed to the retractable calibration thermal platform and the mounting plate, respectively. The side of the mounting plate away from the electric telescopic rod is a convex arc surface and has a resistance heating element fixed thereon. A heat insulation coating is applied between the mounting plate and the resistance heating element. A pressure sensor is also provided between the mounting plate and the resistance heating element. The robotic arm is mounted on the base plate and located outside the gap between the calibration platform and the retractable calibration thermal platform, driving the detection device to move. In the initial state, each electric telescopic rod is in a retracted state, and the sides of each mounting plate near the calibration platform are spliced ​​to form an arc convex surface that matches the arc groove.

10. The apparatus used in the aircraft skin thermal straightening method according to claim 9, characterized in that: The robotic arm includes a base, a wrist, a forearm, and a main arm. The base and the base plate form a revolute joint that rotates about a vertical axis and is driven by a drive motor. One end of the main arm and the base form a revolute joint that rotates about a horizontal axis and is driven by a drive motor. One end of the forearm and the other end of the main arm form a revolute joint that rotates about a horizontal axis and is driven by a drive motor. One end of the wrist and the other end of the forearm form a revolute joint that is driven by a drive motor. A detection device is fixed at the other end.

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