Self-adaptive precision machining method for large-size thin-wall extruded skin

Abstract

The invention discloses a large-size thin-wall deformation skin self-adaptive precision machining method which comprises the steps that firstly, a thin-wall skin workpiece to be machined is fixed to a machining platform, an inner supporting rod is used for supporting an inner cavity of a skin to the position close to a theoretical position, a measuring head is used for detecting a skin machining area, and actual data of the workpiece machining area are obtained; 2, comparing according to a preset deformation threshold value, and calculating whether the deformation of the skin is within a machinable range or not; 3, calculating the actual center of the workpiece as a numerical control machining original point by measuring a skin machining area; 4, on the basis of multi-point on-machine measurement on a skin machining area, accurate cutting of a cutter movement track is achieved through measurement data processing, three-dimensional reconstruction and numerical control machining program compiling; and fifthly, the machined workpiece is subjected to surface treatment and quality detection. The problem that the thin-wall skin cannot be assembled with the corresponding end frame due to deformation, low machining precision and poor surface quality in the prior art is solved.

Description

Technical Field

[0001] The invention relates to an adaptive precision machining method for a large-size thin-wall extruded skin, belongs to precision machining technology, and is applicable to the technical fields of aerospace, automobile manufacturing and the like. Background Art

[0002] Thin-walled deformed skin processing is widely used in the manufacture of complex structural parts in the fields of aerospace, automobiles, etc. These thin-walled structural parts have the advantages of light weight and high strength, but their material thickness is thin and the structure is complex. They are prone to deformation during processing, making it difficult to control the processing accuracy and surface quality.

[0003] Traditional thin-walled skin processing methods mainly rely on fixed fixtures and simple measurement methods, which cannot effectively control the deformation of the skin. They usually have defects such as insufficient deformation control, low processing accuracy and difficult assembly. Summary of the invention

[0004] The technical problem solved by the present invention is: in order to overcome the shortcomings of the prior art, a method for adaptive precision machining of thin-walled deformed skin is proposed, which solves the problems of large deformation of thin-walled skin, low machining accuracy and poor surface quality, and realizes high-precision machining and surface quality control of thin-walled deformed skin.

[0005] The technical solution of the present invention is:

[0006] A method for adaptive precision machining of thin-walled deformable skin, comprising:

[0007] Fix the thin-walled skin workpiece to be processed on the processing platform, use the inner support rods to support the upper and lower surfaces of the inner cavity of the skin, and then use the probe to detect the contours of the front and rear ends of the skin after it is stabilized to obtain the actual data of the workpiece;

[0008] Compare the actual data of the workpiece obtained with the preset deformation threshold to calculate whether the skin deformation is within the processable range;

[0009] For workpieces within the machinable range, multi-point measurements are performed on the workpiece skin processing area to calculate the actual geometric center of the workpiece, and the actual geometric center is used as the origin of CNC machining;

[0010] Carry out multi-point on-machine measurement of the skin processing area, process the measurement data, reconstruct the three-dimensional structure, compile the CNC processing program, and machine the workpiece;

[0011] Carry out surface treatment and quality inspection on the processed workpiece.

[0012] Furthermore, multi-point on-machine measurement is performed on the skin processing area. The specific method is: the probe is installed on the spindle of the CNC machine tool, and a spherical probe is selected to comprehensively detect the skin surface to obtain surface geometric morphology data; the surface geometric morphology data is then analyzed and processed to generate three-dimensional measurement data of the skin surface.

[0013] Furthermore, the skin processing area is measured at multiple points on the machine, and then the measurement data is processed to find out the noise points and eliminate them. The method for finding out the noise points is as follows:

[0014] Statistics for each measurement point p i The number of neighborhood points n within the set radius i ;

[0015] If i is less than the threshold T1, then the corresponding measurement point p is determined i is a noise point, remove the measurement data of this point; if n i If it is greater than or equal to the threshold T1, the abnormal point is determined by the standard deviation threshold:

[0016]

[0017] Where N i is the measuring point p i Neighborhood range within a set radius;

[0018] If ‖p i -p j ||>d i +kσ i , then the measurement point p j Determined as the measuring point p i The abnormal point, when the measurement point p i If the ratio of surrounding abnormal points exceeds the threshold T2, then the measurement point p i Determined as a noise point.

[0019] Furthermore, based on the 3D model after 3D reconstruction, a CNC machining program is compiled, and the machining path design method is as follows: select the machining method and set the motion parameters of the tool; perform machining path simulation in CAM to verify whether the tool path is reasonable, ensure that no collision occurs during the machining process, and that the tool can effectively process each area that needs to be processed; finally, based on the 3D digital model of the workpiece and the tool path obtained by simulation, generate the NC code required by the CNC machine tool, and import the NC code into the machine tool for machining.

[0020] Furthermore, based on the processed measurement data, a three-dimensional digital model of the workpiece is generated using CAD / CAM. The generation method is: point cloud fitting is performed in CAD / CAM, the error between the point cloud and the fitting surface is calculated, and the smoothness and curvature are adjusted during the fitting process according to the complexity of the workpiece surface and the fitting accuracy requirements, so as to fit the processed measurement data into a new surface.

[0021] Furthermore, multi-point on-machine measurement is performed on the skin processing area, and at least 100 points are selected and evenly distributed on the skin processing area.

[0022] Furthermore, a plurality of measuring points are evenly arranged on the contour of the workpiece skin processing area, and multi-point measurement is performed on the workpiece skin processing area.

[0023] Furthermore, the inner support rod is designed according to the theoretical shape and size of the skin, and the length of the inner support rod is adjustable.

[0024] Furthermore, the three-dimensional reconstruction uses non-uniform rational B-splines for surface reconstruction.

[0025] Furthermore, the surface treatment includes polishing, cleaning and coating treatment.

[0026] The advantages of the present invention compared with the prior art are:

[0027] 1) The present invention uses internal support rods to support the inner cavity of the skin to a position close to the theoretical position, and combines it with a high-precision probe to perform morphology measurement. Compared with the traditional method that relies on fixed fixtures and simple measurement methods, this can significantly improve the processing accuracy of thin-walled skins.

[0028] 2) The present invention compiles a processing program through measurement data processing and three-dimensional reconstruction, reduces processing errors, and ensures processing accuracy.

[0029] 3) The present invention ensures that the skin can be accurately assembled with corresponding end frames and other components, solves the assembly difficulty problem caused by processing errors and poor surface quality, and improves assembly efficiency and overall performance.

[0030] 4) The present invention discloses a method for adaptive precision machining of thin-walled deformable skins, which has strong operability, can preset deformation thresholds according to skin machining requirements, and compile machining paths through multi-point on-machine measurement, and is adaptable to thin-walled skins of various complex shapes and structures, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The accompanying drawings are only used to illustrate some typical embodiments of the present invention and are not used to limit the scope of the present invention.

[0032] Figure 1This is a flow chart of a method for adaptive precision machining of thin-walled deformable skin according to an embodiment of the present invention;

[0033] Figure 2 is an overall schematic diagram of a thin-walled skin according to an embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of the front end surface of the skin according to an embodiment of the present invention;

[0035] Figure 4 2 is a schematic diagram of the rear end surface of the skin according to an embodiment of the present invention;

[0036] Figure 5 is a schematic diagram of eight-point measurement of a skin processing area according to an embodiment of the present invention;

[0037] Figure 6 is a schematic diagram of multi-point measurement of a skin processing area according to an embodiment of the present invention;

[0038] Figure 7 is a comparison diagram of the initial morphological data of the embodiment of the present invention and the theoretical morphological data;

[0039] Figure 8 is a schematic diagram of numerical control machining programming based on measurement data processing and three-dimensional reconstruction according to an embodiment of the present invention; DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0041] The present invention proposes a method for adaptive precision machining of large-size thin-wall extruded skins. The method process is as follows: Figure 1 As shown, specifically including:

[0042] S1: Fix the thin-walled skin workpiece to be processed on the processing platform, and use the inner support rod designed according to the theoretical shape of the workpiece to support the inner cavity of the skin to a position close to the theoretical position, thereby reducing the deformation of the skin. Then, use the high-precision probe installed on the spindle of the CNC machine tool to detect the skin and obtain the actual data of the workpiece.

[0043] S2: Compare the measured actual morphology data with the theoretical morphology data, and calculate whether the skin deformation is within the processable range according to the preset deformation threshold. If the deformation exceeds the preset threshold, the inner support rod needs to be readjusted until the deformation is within the processable range.

[0044] S3: Select multiple key measurement points in the skin processing area, which are points evenly arranged on the contour of the processing area. The number of measurement points will be determined according to the size of the processing area. In this embodiment, there are eight key measurement points, such as Figure 5The eight measuring points are measured using a probe, and the actual geometric center of the skin workpiece is calculated and used as the origin of CNC machining.

[0045] S4: Use a high-precision probe to measure 100 measurement points arranged in the skin processing area to obtain measurement data. The number of measurement points is adjusted according to the size of the measurement area to fully cover the surface of the entire processing area. The denser the measurement points, the higher the fitting accuracy. Use the statistical filtering method to process the collected measurement data. By calculating the point density around each point, detect and remove isolated points with low density or far away from the main surface to eliminate random noise points. The specific operations of the step of determining noise points are as follows: Process the collected measurement data to remove noise points and redundant data.

[0046] For each point p in the point cloud i , count the number of neighboring points n within its radius r i :

[0047] n i =|N i |=|{p j ∈P|‖p i -p j || <r}|

[0048] For points with lower density, the number of neighboring points n i Usually small. i is less than the threshold T1, then p i Noise point. If n i If it is greater than or equal to the threshold T1, the abnormal point is determined by the standard deviation threshold:

[0049]

[0050] If ‖p i -p j ||>d i +kσ i Then p j Determined as p i The outlier point, when p i If the ratio of surrounding abnormal points exceeds the threshold T2, then p i Determined as a noise point.

[0051] S5: Based on the processed measurement data, use CAD / CAM software to generate a three-dimensional digital model of the workpiece and compare it with the ideal digital model. Specifically: Use the point cloud fitting function in the CAD / CAM software to calculate the error between the point cloud and the fitting surface, and adjust the smoothness and curvature during the fitting process according to the complexity of the workpiece surface and the fitting accuracy requirements, and fit the processed point data into a new surface. After fitting, save the generated surface as a surface file compatible with the CAD / CAM system (such as *.iges, *.step, etc.), import the fitted new surface into the CNC programming module for path planning.

[0052] S6: Based on the error analysis results, use CAD / CAM software to compile a CNC machining program to ensure that the tool path conforms to the actual shape of the workpiece. Specifically: select an appropriate machining strategy (such as rough machining, fine machining), and set the tool motion parameters (such as feed rate, cutting depth). Perform path simulation in the CAM software to verify whether the tool path is reasonable, ensure that no collision occurs during the machining process, and that the tool can effectively process each area that needs to be processed. Finally, based on the optimized tool path, generate the NC code required by the CNC machine tool, and import the NC code into the machine tool for machining.

[0053] S7: The surface of the workpiece after processing is mechanically polished, cleaned with high-pressure water and anodized to ensure the surface quality of the workpiece. After the surface treatment is completed, the workpiece is tested for dimensional accuracy and surface roughness.

[0054] Key points for implementation:

[0055] 1. Internal support rod: The length of the internal support rod can be adjusted to support the inner cavity of the skin to a position close to the theoretical position, reduce the deformation of the skin, and improve processing accuracy.

[0056] 2. Acquisition of initial morphology data: Use a high-precision contact probe to detect the skin surface and obtain initial morphology data.

[0057] 3. Eight-point measurement and actual center calculation: Select eight key measurement points in the processing area, measure the data of the eight points and calculate the actual workpiece center as the origin of CNC processing to ensure the accuracy of the processing path.

[0058] 4. Multi-point on-machine measurement: Arrange multiple measuring points in the processing area to fully cover the entire surface.

[0059] 5. Measurement data processing: Collect and process measurement data, and remove noise and redundant data.

[0060] 6. Three-dimensional reconstruction: Use the processed measurement data to generate a three-dimensional digital model, compare it with the ideal digital model, compile the processing path, and improve the processing accuracy.

[0061] 7. Surface treatment and quality inspection.

[0062] Example: Thin-wall skin processing in the aerospace industry

[0063] The following is a detailed introduction to the thin-wall deformable skin adaptive precision machining method of the present invention in conjunction with the accompanying drawings and embodiments:

[0064] The skin material is 6005A aluminum alloy, the product structure is a cylindrical structure, the length is 1.6m, the maximum width and height are 0.7m, such as Figure 2 , Figure 3 , Figure 4 As shown, the wall thickness is 3mm and the maximum wall thickness of the side wall is 4mm.

[0065] Step 1: Workpiece Fixing and Initial Probing

[0066] Workpiece fixing: Fix the thin-walled skin workpiece to be processed on the CNC machining platform to ensure the stability of the workpiece during the machining process.

[0067] Internal support rod installation: support the inner cavity of the skin to close to the theoretical position to reduce deformation.

[0068] Initial detection: Use a high-precision contact probe to detect the skin and processing area to obtain actual data.

[0069] Step 2: Deformation calculation

[0070] Deformation threshold judgment: According to the preset deformation threshold, judge whether the deformation is within the processable range. If it is beyond the range, make appropriate adjustments or readjust the inner support rod.

[0071] Step 3: Eight-point measurement and center calculation

[0072] Key measurement point selection: Select eight measurement points in the skin processing area, such as Figure 5 As shown, ensure that the measuring points are evenly distributed in the processing area.

[0073] Center calculation: Use the probe to detect eight measuring points and calculate the actual geometric center of the workpiece as the origin of CNC machining.

[0074] Step 4: Measurement data processing and 3D reconstruction

[0075] Measurement data processing: The measurement data of the skin workpiece is collected by a high-precision probe, and no less than 100 measurement points are arranged in the processing area of ​​the skin workpiece, such as Figure 6 As shown, the surface of the entire processing area is fully covered. CAD / CAM software is used to process the data, remove noise and redundant data, and ensure data accuracy.

[0076] 3D reconstruction: Based on the processed measurement data, the 3D digital model of the workpiece is generated using non-uniform rational B-spline surface reconstruction to accurately reflect the actual geometric shape of the workpiece.

[0077] Programming NC machining: Based on the generated 3D model, program the NC machining to ensure that the tool path accurately conforms to the actual shape of the workpiece, such as Figure 7 , Figure 8 As shown, accurate cutting is achieved.

[0078] Step 5: Surface treatment and quality inspection

[0079] Polishing: Use mechanical polishing method to process the surface of the processed workpiece to remove tiny burrs and surface roughness and improve surface smoothness and flatness.

[0080] Cleaning: Use ultrasonic cleaning and high-pressure water cleaning methods to remove oil, dust and other impurities on the surface of the workpiece to ensure a clean surface.

[0081] Coating treatment: Anodize the workpiece to improve its corrosion resistance, wear resistance and aesthetics.

[0082] Quality inspection: Use roughness tester equipment to inspect the surface quality of the processed workpiece to ensure the polishing and cleaning effect, check the uniformity and defect-freeness of the coating, and meet the design requirements.

[0083] The above description is only the best specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0084] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for adaptive precision machining of thin-walled deformable skin, characterized in that: include: Fix the thin-walled skin workpiece to be processed on the processing platform, use the inner support rods to support the upper and lower surfaces of the inner cavity of the skin, and then use the probe to detect the contours of the front and rear ends of the skin after it is stabilized to obtain the actual data of the workpiece; Compare the actual data of the workpiece obtained with the preset deformation threshold to calculate whether the skin deformation is within the processable range; For workpieces within the machinable range, multi-point measurements are performed on the workpiece skin processing area to calculate the actual geometric center of the workpiece, and the actual geometric center is used as the origin of CNC machining; Carry out multi-point on-machine measurement of the skin processing area, process the measurement data, reconstruct the three-dimensional structure, compile the CNC processing program, and machine the workpiece; Carry out surface treatment and quality inspection on the processed workpiece.

2. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: Perform multi-point on-machine measurement on the skin processing area. The specific method is: install the probe on the spindle of the CNC machine tool, select the spherical probe, conduct a comprehensive detection of the skin surface, and obtain the surface geometric morphology data; then analyze and process the surface geometric morphology data to generate three-dimensional measurement data of the skin surface.

3. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: Perform multi-point on-machine measurement on the skin processing area, and then process the measurement data to find and eliminate the noise points. The method for finding the noise points is as follows: Statistics for each measurement point p i The number of neighborhood points n within the set radius i ; If i is less than the threshold T1, then the corresponding measurement point p is determined i is a noise point, remove the measurement data of this point; if n i If it is greater than or equal to the threshold T1, the abnormal point is determined by the standard deviation threshold: Where N i is the measuring point p i Neighborhood range within a set radius; If ‖p i -p j ||>d i +kσ i , then the measurement point p j Determined as the measuring point p i The abnormal point, when the measurement point p i If the ratio of surrounding abnormal points exceeds the threshold T2, then the measurement point p i Determined as a noise point.

4. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: Based on the 3D model after 3D reconstruction, the CNC machining program is compiled, and the machining path design method is as follows: select the machining method and set the motion parameters of the tool; perform machining path simulation in CAM to verify whether the tool path is reasonable, ensure that no collision occurs during the machining process, and that the tool can effectively process each area that needs to be processed; finally, based on the 3D digital model of the workpiece and the tool path obtained by simulation, generate the NC code required by the CNC machine tool, and import the NC code into the machine tool for machining.

5. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: Based on the processed measurement data, CAD / CAM is used to generate a three-dimensional digital model of the workpiece. The generation method is: point cloud fitting is performed in CAD / CAM, the error between the point cloud and the fitting surface is calculated, and the smoothness and curvature are adjusted during the fitting process according to the complexity of the workpiece surface and the fitting accuracy requirements, and the processed measurement data is fitted into a new surface.

6. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: Perform multi-point on-machine measurement on the skin processing area, and select at least 100 points evenly distributed on the skin processing area.

7. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: Multiple measuring points are evenly set on the contour of the workpiece skin processing area, and multi-point measurement is performed on the workpiece skin processing area.

8. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: The inner support rod is designed according to the theoretical shape and size of the skin, and the length of the inner support rod is adjustable.

9. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: The three-dimensional reconstruction uses non-uniform rational B-splines for surface reconstruction.

10. The method for adaptive precision machining of thin-walled deformable skin according to claim 1, characterized in that: The surface treatment includes polishing, cleaning and coating.

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