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

Abstract

The application discloses a large-size thin-wall deformed skin self-adaptive precision machining method, which comprises the following steps: 1, fixing the thin-wall skin workpiece to be machined on a machining platform, supporting the skin inner cavity to a position close to a theoretical position by using an inner supporting rod, and detecting the skin machining area by using a measuring head to obtain actual data of the workpiece machining area; 2, comparing the preset deformation threshold value to calculate whether the skin deformation is within the machinable range; 3, calculating the actual center of the workpiece as a numerical control machining origin by measuring the skin machining area; 4, based on the in-machine measurement of the skin machining area, processing the measurement data, three-dimensional reconstruction, and preparing a numerical control machining program to realize accurate cutting of the tool movement track; and 5, performing surface treatment and quality detection on the machined workpiece. The application solves the problem that the thin-wall skin cannot be assembled with a corresponding end frame due to deformation, low machining precision and poor surface quality in the prior art.

Description

TECHNICAL FIELD

[0001] The application relates to a large-size thin-wall extrusion skin self-adaptive precision machining method, and belongs to the technical field of precision machining. BACKGROUND

[0002] The thin-wall deformed skin machining is widely applied to the manufacturing of complex structural parts in the fields of aerospace and automobile, etc. The thin-wall structural parts have the advantages of light weight and high strength, but the material thickness is thin and the structure is complex, and deformation is prone to occur in the machining process, so that the machining precision and surface quality are difficult to control.

[0003] The traditional thin-wall skin machining method mainly depends on fixed clamps and simple measuring means, and the deformation amount of the skin cannot be effectively controlled, and the defects of insufficient deformation control, low machining precision and assembly difficulty usually exist. SUMMARY

[0004] The application solves the technical problems that the thin-wall skin has large deformation, low machining precision and poor surface quality, and realizes high-precision machining and surface quality control of the thin-wall deformed skin.

[0005] The technical solution of the application is as follows:

[0006] A thin-wall deformed skin self-adaptive precision machining method comprises the following steps:

[0007] The thin-wall skin workpiece to be machined is fixed on a machining platform, an inner support rod is used to support the upper and lower surfaces of the skin inner cavity, and then a probe is used to detect the front and rear end profiles of the skin to obtain actual data of the workpiece;

[0008] The obtained actual data of the workpiece is compared with a preset deformation threshold value, and whether the skin deformation is within a machinable range is calculated;

[0009] For the workpiece within the machinable range, a plurality of points are measured in the skin machining area of the workpiece, the actual geometric center of the workpiece is calculated, and the actual geometric center is taken as the origin of numerical control machining;

[0010] The skin machining area is measured at a plurality of points in the machine, and after measurement data processing and three-dimensional reconstruction, a numerical control machining program is compiled to machine the workpiece;

[0011] The machined workpiece is subjected to surface treatment and quality detection.

[0012] Further, the skin processing area is measured by multi-point in-machine, the specific method is: the measuring head is installed on the spindle of the numerical control machine tool, the spherical probe is selected, the surface is fully detected to obtain the surface geometric appearance data; the surface geometric appearance data is analyzed and processed to generate the three-dimensional measurement data of the skin surface.

[0013] Further, the skin processing area is measured by multi-point in-machine, the specific method is: the measuring head is installed on the spindle of the numerical control machine tool, the spherical probe is selected, the surface is fully detected to obtain the surface geometric appearance data; the surface geometric appearance data is analyzed and processed to generate the three-dimensional measurement data of the skin surface.

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

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

[0016]

[0017] In the formula, N i is the neighborhood range of the measurement point p i within the set radius;

[0018] If ‖p i -p j ||>d i +kσ i , the measurement point p j is determined as an abnormal point of the measurement point p i , and when the proportion of abnormal points around the measurement point p i exceeds the threshold T2, the measurement point p i is determined as a noise point.

[0019] Further, based on the three-dimensional model reconstructed by three dimensions, a numerical control machining program is compiled, and the machining path design method is: the machining method is selected, and the motion parameters of the tool are set; machining path simulation is carried out in CAM to verify whether the tool path is reasonable, to ensure that no collision occurs in the machining process, and the tool can effectively machine each area that needs to be machined; finally, according to the three-dimensional digital model of the workpiece and the tool path obtained by simulation, the NC code required by the numerical control machine tool is generated, and the NC code is imported into the machine tool for machining.

[0020] Further, based on the processed measurement data, a three-dimensional digital model of the workpiece is generated using CAD / CAM, and 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 requirement, and the processed measurement data is fitted into a new surface.

[0021] Further, the skin processing area is measured by multiple points on the machine, and the selected points are at least 100 points or more, uniformly distributed on the skin processing area.

[0022] Further, a plurality of measurement points are uniformly arranged on the contour of the workpiece skin processing area, and the workpiece skin processing area is measured by multiple points.

[0023] Further, 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] Further, the three-dimensional reconstruction adopts non-uniform rational B-spline for surface reconstruction.

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

[0026] Compared with the prior art, the present application has the following advantages:

[0027] 1) The inner support rod is used to support the inner cavity of the skin close to the theoretical position, and the topography is measured by a high-precision probe, which can significantly improve the machining accuracy of the thin-walled skin compared with the traditional method of relying on fixed clamps and simple measurement means.

[0028] 2) The present application processes and reconstructs the measurement data to prepare the machining program, reduces the machining error and ensures the machining accuracy.

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

[0030] 4) The present application discloses a thin-walled deformed skin self-adaptive precision machining method, which has strong operability, can preset the deformation threshold according to the skin machining requirements, and can prepare the machining path through multiple on-machine measurements, which is suitable for various complex shape and structure thin-walled skin, and has a wide application range. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to better understand the technical scheme of the present application, the embodiments of the present application will be described in detail below with reference to the drawings, and the drawings are only used to illustrate some typical embodiments of the present application and do not limit the scope of the present application.

[0032] Figure 1is a flow chart of a thin-walled deformed skin self-adaptive precision machining method according to an embodiment of the present application;

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

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

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

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

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

[0038] Figure 7 is a comparison diagram of initial topography data and theoretical topography data according to an embodiment of the present application;

[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 application; DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings.

[0041] The present application proposes a large-size thin-walled extruded skin self-adaptive precision machining method, the method flow is as shown in Figure 1 , specifically comprising:

[0042] S1: fixing a thin-walled skin workpiece to be machined on a machining platform, using an inner support rod designed according to the theoretical shape of the workpiece to support the skin inner cavity close to the theoretical position, thereby reducing the deformation amount of the skin. Then, using a high-precision probe installed on the spindle of a numerical control machine tool to detect the skin and obtain the actual data of the workpiece.

[0043] S2: comparing the measured actual topography data with the theoretical topography data, and according to a pre-set deformation threshold, calculating whether the skin deformation is within the machinable range. If the deformation exceeds the pre-set threshold, the inner support rod needs to be adjusted again until the deformation is within the machinable range.

[0044] S3: selecting multiple key measurement points in the skin machining area, which are points uniformly arranged on the machining area contour. The number of measurement points will be determined according to the size of the machining area. In this embodiment, there are eight key measurement points, as shown in Figure 5As shown. The probe is used to measure these eight measurement points, and the actual geometric center of the skinned workpiece is calculated and used as the origin of CNC machining.

[0045] S4: Measure 100 points arranged in the skin processing area using a high-precision probe to obtain measurement data. The number of measurement points is adjusted according to the size of the measurement area to fully cover the entire surface of the processing area; the denser the measurement points, the higher the fitting accuracy. Statistical filtering is used to process the collected measurement data. By calculating the point density around each point, isolated points with low density or far from the main surface are detected and removed to eliminate random noise. The specific steps for identifying noise points are as follows: process the collected measurement data to remove noise 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 low density, the number of neighboring points n i Usually small. If n i If the value is less than the threshold T1, then p is determined to be... i Noise point. If n i If the value is greater than or equal to the threshold T1, then outliers are identified using the standard deviation threshold.

[0049]

[0050] If ||p i -p j ||>d i +kσ i Then p j Determined as p i Anomalies, when p i If the proportion of surrounding outliers exceeds the threshold T2, then p i This point has been identified as a noise point.

[0051] S5: Based on the processed measurement data, generate a three-dimensional digital model of the workpiece using CAD / CAM software and compare it with the ideal model. Specifically: In the CAD / CAM software, use the point cloud fitting function, calculate the error between the point cloud and the fitting surface, and according to the complexity of the workpiece surface, fitting accuracy requirements, etc., adjust the smoothness and curvature in the fitting process, 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 numerical control programming module, and plan the path.

[0052] S6: According to the error analysis results, use CAD / CAM software to compile numerical control machining program to ensure that the tool path conforms to the actual shape of the workpiece. Specifically: Select appropriate machining strategy (such as rough machining, finishing), and set the motion parameters of the tool (such as feed speed, cutting depth). In the CAM software, perform path simulation to verify whether the tool path is reasonable, ensure that no collision occurs during machining, and the tool can effectively process each area that needs to be processed. Finally, according to the optimized tool path, generate the NC code required by the numerical control machine tool, and import the NC code into the machine tool for processing.

[0053] S7: Perform mechanical polishing, high-pressure water cleaning and anodic oxidation coating treatment on the machined workpiece surface to ensure the surface quality of the workpiece. After completing the surface treatment, detect the size accuracy and surface roughness of the workpiece.

[0054] Key points of implementation:

[0055] 1. Inner support rod: The length of the inner support rod can be adjusted to support the inner cavity of the skin close to the theoretical position, reducing the deformation of the skin and improving the machining accuracy.

[0056] 2. Initial topography data acquisition: Use high-precision contact probe to detect the skin surface and acquire initial topography data.

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

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

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

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

[0061] 7. Surface treatment and quality inspection.

[0062] Example: Thin-walled skin processing in the field of aerospace

[0063] The thin-walled deformed skin self-adaptive precision machining method of the present application will be described in detail below in combination with the drawings and examples:

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

[0065] Step one: workpiece fixing and initial detection

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

[0067] Inner support rod installation: Support the inner cavity of the skin to approach the theoretical position to reduce the deformation amount.

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

[0069] Step two: deformation amount calculation

[0070] Deformation threshold judgment: According to the preset deformation threshold, judge whether the deformation amount is within the machinable range. If it exceeds the range, adjust or re-adjust the inner support rod appropriately.

[0071] Step three: eight-point measurement and center calculation

[0072] Key measurement point selection: Select eight measurement points in the skin machining area, as shown in Figure 5 , to ensure that the measurement points are evenly arranged in the machining area.

[0073] Center calculation: Use the probe to detect the eight measurement points to calculate the actual geometric center of the workpiece as the origin of numerical control machining.

[0074] Step four: measurement data processing and three-dimensional reconstruction

[0075] Measurement data processing: Collect the measurement data of the skin workpiece through a high-precision probe, and arrange no less than 100 measurement points in the machining area of the skin workpiece, as shown in Figure 6 , to fully cover the surface of the entire machining area. Use CAD / CAM software to process the data, remove noise and redundant data, and ensure data accuracy.

[0076] Three-dimensional reconstruction: Based on the processed measurement data, a non-uniform rational B-spline surface reconstruction is used to generate a three-dimensional digital model of the workpiece, accurately reflecting the actual geometric shape of the workpiece.

[0077] NC machining program: Based on the generated three-dimensional model, a NC machining program is compiled to ensure that the tool path accurately conforms to the actual shape of the workpiece, as shown in Figure 7 、 Figure 8 , to achieve accurate cutting.

[0078] Step five: surface treatment and quality detection

[0079] Polishing: Adopting mechanical polishing method, the surface of the machined workpiece is treated to remove small burrs and surface roughness, improve surface finish and flatness.

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

[0081] Coating treatment: Anodizing coating is applied to the workpiece to improve its corrosion resistance, wear resistance and aesthetics.

[0082] Quality detection: Using roughness meter equipment to detect the quality of the workpiece surface after treatment, to ensure the polishing and cleaning effect, detect the uniformity and defect-free of the coating, meet the design requirements.

[0083] The above is only the best specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

[0084] The contents not described in detail in the specification of the present application belong to the known technology of the person skilled in the art.

Claims

1. A method for adaptive precision machining of thin-walled deformable skin, characterized in that, include: The thin-walled skin workpiece to be processed is fixed on the processing platform. The inner cavity of the skin is supported on the upper and lower surfaces using internal struts. After it is stabilized, the probe is used to detect the front and rear contours of the skin to obtain the actual data of the workpiece. Based on the comparison between the actual data of the workpiece and the preset deformation threshold, it is calculated whether the deformation of the skin is within the machinable range. For workpieces within the machinable range, multi-point measurements are performed on the workpiece skin machining area to calculate the actual geometric center of the workpiece, and the actual geometric center is used as the origin of CNC machining. Multi-point on-machine measurement is performed on the skin processing area. After measurement data processing and three-dimensional reconstruction, a CNC machining program is compiled, and the workpiece is machined. Surface treatment and quality inspection are performed on the processed workpieces; Multi-point on-machine measurement of the skin processing area is performed as follows: the probe is installed on the spindle of the CNC machine tool, a spherical probe is selected, and the skin surface is fully probed to obtain surface geometric morphology data; then the surface geometric morphology data is analyzed and processed to generate three-dimensional measurement data of the skin surface. Based on the reconstructed 3D model, a CNC machining program is developed. The machining path design method is as follows: select the machining method and set the tool motion parameters; perform machining path simulation in CAM to verify whether the tool path is reasonable, ensure that no collisions occur during machining, and that the tool can effectively machine each area that needs to be machined; finally, based on the 3D digital model of the workpiece and the simulated tool path, generate the NC code required by the CNC machine tool, and import the NC code into the machine tool for machining. Based on the processed measurement data, a three-dimensional digital model of the workpiece is generated using CAD / CAM. The generation method is as follows: point cloud fitting is performed in CAD / CAM, the error between the point cloud and the fitted 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 that the processed measurement data is fitted into a new surface.

2. The adaptive precision machining method for thin-walled deformable skin according to claim 1, characterized in that, Perform multi-point on-machine measurements on the skin processing area, selecting more than 100 points evenly distributed across the skin processing area.

3. The adaptive precision machining method for thin-walled deformable skin according to claim 1, characterized in that, Multiple measurement points are evenly set on the outline of the workpiece skin processing area to perform multi-point measurement on the workpiece skin processing area.

4. The adaptive precision machining method for thin-walled deformable skin according to claim 1, characterized in that, The inner struts are designed to conform to the theoretical shape and size of the skin, and their length is adjustable.

5. The adaptive precision machining method for thin-walled deformable skin according to claim 1, characterized in that, The 3D reconstruction uses non-uniform rational B-splines for surface reconstruction.

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

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