Data acquisition and analysis method for a profile method for residual stress testing

Abstract

This invention discloses a data acquisition and analysis method for residual stress testing using the contour method, belonging to the field of residual stress detection. The method includes: using a high-precision CNC machine tool to shape both sides of a pre-defined cut surface on a workpiece; using a contact coordinate measuring machine to establish two coordinate systems for the workpiece; cutting the workpiece at a pre-defined position; using a finite element mesh to determine the theoretical measurement point coordinates of the contour surface; using the contact coordinate measuring machine to measure the two cut surfaces according to the previously established coordinate systems and measurement points; and performing average error removal, noise removal, and background subtraction operations on the measured abnormal data. This invention, by pre-setting the coordinate systems before and after cutting and the theoretical test point coordinates, ensures that the obtained contour data corresponds one-to-one with the test points, eliminating the need for complex transformations and reducing data measurement errors.

Description

Technical Field

[0001] This invention relates to the field of residual stress detection, and more specifically to a method for data acquisition and analysis using the profile method for residual stress testing. Background Technology

[0002] With the rapid development of the aerospace industry, aluminum alloy structural components are shifting towards larger and more integrated designs. During the heat treatment process, the different heating and cooling rates at varying thicknesses of aluminum alloys can generate significant residual stress within the alloy. This can lead to unexpected deformation during subsequent processing, affecting the yield rate of aluminum alloy components. Furthermore, the internal residual stress is difficult to detect, thus impacting the prediction of material service life. Therefore, accurately understanding the residual stress within aluminum alloys is of great significance for improving processability and accurately predicting material life.

[0003] Current methods for residual stress testing mainly include X-ray diffraction, pinhole method, profilometry, ultrasonic method, and neutron diffraction. Among these, the profilometry method is a relatively low-cost method for measuring the residual stress distribution inside the cross-section of large-sized components. The basic principle of the profilometry method is as follows: cutting open the test surface of the sample releases stress, causing a certain deformation of the test surface. The amount of deformation is measured, and then a computer simulates the application of stress to make the deformation zero. The magnitude of this applied stress is the magnitude of the residual stress.

[0004] While the contour method has undergone significant development over the years, with substantial improvements in cutting methods and data fitting, it still suffers from the following shortcomings:

[0005] (1) The data of the two surfaces after cutting often cannot correspond accurately and require complex transformations to make them approximately correspond. For example, in the prior art, patent CN110487464B discloses a method for obtaining the cutting surface based on residual stress testing; using a coordinate measuring machine to measure the deformation profile of the cutting surface after residual stress release; wherein, the method of using a coordinate measuring machine to measure the deformation profile of the cutting surface after residual stress release includes: establishing multiple workpiece coordinate systems on the cutting surface; measuring the coordinate values ​​of the same preset position on the cutting surface based on different workpiece coordinate systems according to the multiple workpiece coordinate systems; and obtaining the deformation profile of the test piece based on residual stress according to the measurement data of different coordinate systems. This method establishes workpiece coordinate systems on the cutting surface and requires translation and rotation transformations of the measurement data before obtaining the profile data.

[0006] (2) The data processing method of the contour method is generally to unify the contour coordinates into a suitable mathematical model by fitting the data, but poor fitting method selection will lead to greater error. Summary of the Invention

[0007] This invention aims to address the shortcomings of existing technologies in the data acquisition and processing of residual stress testing using the profile method. It proposes a data acquisition and analysis method for residual stress testing using the profile method. By improving the data acquisition and processing methods, the data processing flow is simplified, while avoiding the introduction of additional data transformation and fitting errors.

[0008] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0009] A method for data acquisition and analysis using the profile method for residual stress testing includes the following steps:

[0010] Workpiece shaping: The CNC machine tool is used to shape the workpiece to be tested, so that the shaped workpiece forms a set of reference surfaces parallel to the preset cutting surface, a set of parallel side surfaces perpendicular to the preset cutting surface, and a set of top surfaces with the same horizontal height on both sides of the preset cutting surface.

[0011] Coordinate system establishment before cutting: On the non-cut surface after shaping, a contact measuring instrument is used to establish two coordinate systems that are mirror-symmetric about the preset cutting surface on the test piece, and the positioning points used to establish the coordinate systems are marked.

[0012] Cutting at the test position: The test piece is cut at a preset position to obtain two mirror-symmetrical cut surfaces;

[0013] Determination of the contour coordinates of the cut surface: The finite element method is used to mesh the contour surface to be measured on the cut surface, and the mesh nodes are used as the coordinates of the theoretical measurement points on the contour surface to be measured.

[0014] Cutting surface contour measurement: The two cut surfaces after cutting are measured using a contact coordinate measuring instrument according to the coordinate system established before cutting and the coordinates of the theoretical measurement points, to obtain two sets of contour coordinate points that are mirror images of each other about the cutting surfaces;

[0015] Contour data processing: The two sets of contour coordinate points are averaged to remove some errors, abnormal data steps caused by changes in cutting parameters are deducted from the background, and individual abnormal data points are denoised.

[0016] Preferably, in the workpiece shaping step, a high-precision machine tool is used to shape the workpiece to ensure that the shaped surface is flat, meets the roughness requirements, and can meet the surface accuracy required for establishing the coordinate system, and ensures that the three shaped surfaces on the same side of the preset cutting surface are perpendicular to each other.

[0017] Preferably, in the step of establishing the coordinate system before cutting, the origin and y-axis of the two established coordinate systems are on the same straight line, and the x-axis and z-axis have the same direction.

[0018] Preferably, the shaped workpiece forms a first top surface, a first side surface, and a second side surface on one side of the preset cutting surface, and a second top surface, a third side surface, and a fourth side surface on the other side of the preset cutting surface; the first top surface and the second top surface are on the same plane, the second side surface and the fourth side surface are on the same plane, and the first side surface and the third side surface are parallel reference planes; the first top surface, the first side surface, and the second side surface are perpendicular to each other, and the second top surface, the third side surface, and the fourth side surface are perpendicular to each other.

[0019] Preferably, in the step of establishing the coordinate system before cutting, a contact coordinate measuring instrument is used to randomly select three different points on the first top surface of the test piece to establish the xy plane of the first coordinate system; two points are randomly selected on the first side surface to establish the xz plane of the first coordinate system; and one point is randomly selected on the second side surface to establish the yz plane of the first coordinate system.

[0020] Preferably, in the step of establishing the coordinate system before cutting, the positioning point of the second coordinate system and the positioning point of the first coordinate system are located on both sides of the preset cutting surface, and the two are mirror symmetrical about the preset cutting surface, that is, the x-axis and z-axis are in the same direction, and the y-axis is in the opposite direction; the deviation between the mirror point of the origin of the second coordinate system and the origin of the first coordinate system is less than 0.004 mm.

[0021] Preferably, in the cutting step at the measured position, a contact measuring instrument is used to measure the two endpoints of the surface to be cut for positioning during cutting. During cutting, the four corners of the sample to be cut are firmly fixed on the cutting machine, and the cutting position of the cutting machine is set using the marked two endpoints. The cutting speed is maintained at 0.3 mm / min.

[0022] Preferably, in the contour data processing step, denoising a single abnormal data point includes replacing two abnormal points at both ends of the contour data with adjacent points.

[0023] Preferably, in the contour data processing step, denoising a single abnormal data point includes: treating contour data points whose difference from the average value of adjacent data is greater than 15% as abnormal data and replacing them with the average value of adjacent data.

[0024] Preferably, in the contour data processing step, background subtraction processing is performed on the abnormal data steps caused by changes in cutting parameters, including: sorting the points in the abnormal region according to their x-coordinate values, and setting the coordinates of the points at both ends of the abnormal region as (x1, y1) and (x2, y2) respectively. n y n Before correction, the coordinates of any point in the middle are (x, y), and the coordinates of the points immediately adjacent to the two ends of the anomaly region are (x0, y0) and (x0, y0) respectively. n+1 y n+1 Then, after the anomaly region is corrected, the coordinates of any point in the middle are (x′, y′), and y′ = y - (x - x1) * (yn -y n+1 -y1+y0) / (x n -x1)-y1+y0.

[0025] In summary, the present invention has the following advantages:

[0026] 1. This invention pre-sets the coordinate system before and after cutting and the coordinates of the theoretical test points, so that the obtained contour data is the point that corresponds one-to-one with the test point, without the need for complex transformations, thus reducing data measurement errors.

[0027] 2. This invention only performs simple smoothing on the abnormal parts of the measured contour data to obtain a relatively smooth data correction curve, avoiding the error introduced by fitting, and simplifying the data processing process.

[0028] 3. This invention improves the workpiece processing method by using three sets of reference planes after processing to establish two coordinate systems that are mirror-symmetric about the cutting surface, thus avoiding complex transformation processing when measuring the cutting surface contour data.

[0029] 4. This invention addresses the problem of poor surface quality caused by cutting parameters by setting the cutting speed to approximately 0.3 mm / min through experiments. Under this cutting parameter, the surface quality of the processed material is better, and the wire is less prone to breakage.

[0030] 5. This invention establishes a model of the cut sample in finite element software, enabling the design of the position of the test point on the contour surface before measurement. It also outputs the coordinates of the theoretical measurement points in the finite element simulation software as the coordinates used by the contact measuring instrument, ensuring that the measurement position is the same as the theoretical position. This facilitates the subsequent simulation of residual stress and simplifies the input and output process of data points. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating the data acquisition and analysis method based on residual stress profile method in an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of workpiece reshaping;

[0033] Figure 3 This is a schematic diagram of establishing a coordinate system before cutting;

[0034] Figure 4 A schematic diagram of the theoretical measurement points divided using finite element software;

[0035] Figure 5 The original measured contour and the averaged contour data;

[0036] Figure 6The outline data after background subtraction processing of abnormal data;

[0037] Figure 7 To Figure 6 The contour data after denoising the outlier data points.

[0038] In the picture:

[0039] 101. First top surface, 102. First side surface, 103. Second side surface, 104. Second top surface, 105. Third side surface, 106. Fourth side surface, 1001. Point 1, 1002. Point 2, 1003. Point 3, 1004. Point 4, 1005. Point 5, 1006. Point 6, 1007. Endpoint 1, 1008. Endpoint 2. Detailed Implementation

[0040] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0041] Reference Figure 1 This invention provides a method for data acquisition and analysis using the profile method for residual stress testing, comprising the following steps:

[0042] Step 1: Workpiece shaping.

[0043] A high-precision CNC machine tool is used to shape both sides of the preset cut surface on the workpiece to ensure that the coordinate system can be accurately established later. After shaping, the workpiece forms a set of reference planes parallel to the preset cut surface, a set of parallel side surfaces perpendicular to the preset cut surface, and a set of top surfaces with the same horizontal height on both sides of the preset cut surface.

[0044] like Figure 2 The diagram shows the workpiece structure after shaping. The shaped workpiece has a first top surface 101, a first side surface 102, and a second side surface 103 formed on one side of the preset cutting surface, and a second top surface 104, a third side surface 105, and a fourth side surface 106 formed on the other side of the preset cutting surface. The first top surface 101 and the second top surface 104 are on the same plane, the second side surface 103 and the fourth side surface 106 are on the same plane, and the first side surface 102 and the third side surface 105 are parallel reference surfaces. The first top surface 101, the first side surface 102, and the second side surface 103 are perpendicular to each other, as are the second top surface 104, the third side surface 105, and the fourth side surface 106.

[0045] Step 2: Establish coordinates before cutting.

[0046] Two coordinate systems are established on the test piece using a contact coordinate measuring machine, and the positioning points used to establish the coordinate systems are marked. The origin and y-axis of these two coordinate systems are on the same straight line, and the x-axis and z-axis have the same direction.

[0047] Specifically, such as Figure 3 As shown, a contact coordinate measuring machine is used to randomly select three different positioning points on the first top surface 101 of the test piece: point 1001, point 2 1002 and point 3 1003, to establish the xy plane of the first coordinate system, and the positions of point 1001, point 2 1002 and point 3 1003 are marked on the first top surface 101 with a marker pen.

[0048] Two positioning points, 1004 and 1005, are randomly selected on the first side surface 102 to establish the xz plane of the first coordinate system. The positions of 1004 and 1005 are marked on the first side surface 102 with a marker.

[0049] Randomly select a positioning point on the second side 103: point six 1006, establish the yz plane of the first coordinate system, and mark the position of point six 1006 on the second side 103 with a marker.

[0050] The method for establishing the second coordinate system is similar to that of the first coordinate system. However, the positioning points of the second coordinate system must be located on opposite sides of the theoretically cut surface, and the two coordinate systems must be mirror-symmetric about the theoretically cut surface, meaning that the x-axis and z-axis directions are the same, while the y-axis directions are opposite. Furthermore, the positioning points of the second coordinate system require multiple trials to ensure that the deviation between the mirror image of the origin of the second coordinate system and the origin of the first coordinate system is less than 0.004 mm. This ensures that the y-axis of both coordinate systems lies on the same straight line. The positions of the six positioning points used to establish the second coordinate system are also marked.

[0051] Use a contact measuring instrument to measure the two endpoints of the surface to be cut: endpoint one 1007 and endpoint two 1008, and mark them for positioning during cutting.

[0052] Step 3: Cut the surface to be tested.

[0053] Cut the test piece at the preset position. In practice, the four corners of the sample to be cut are firmly fixed on the cutting machine. The cutting position of the cutting machine is set using the marked endpoint 1007 and endpoint 2 1008. The cutting speed is kept at about 0.3 mm / min. At this cutting speed, it can be ensured that aluminum chips are smoothly discharged during the cutting process while the surface roughness is low.

[0054] Step 4: Determine the coordinates of the cutting surface contour.

[0055] The finite element mesh generated by finite element simulation software or mesh generation software is used to directly or indirectly determine the coordinates of the theoretical measurement points on the profile surface to be measured, and then imported into the contact coordinate measuring instrument as the preset measurement points.

[0056] In practice, the digital model of the test piece after being cut according to the theoretical cutting surface is imported into the finite element software. The finite element simulation software is used to mesh the cut contour surface to be tested. The mesh nodes are used as the coordinates of the theoretical measurement points on the contour surface to be tested. The coordinate data of the theoretical measurement points are then imported into the contact coordinate measuring machine as preset measurement points. A schematic diagram of the preset measurement points is shown below. Figure 4 As shown.

[0057] By establishing a model of the test piece in finite element software, the positions of the test points on the contour surface are designed before measurement. Using self-developed software, the coordinates of the theoretical measurement points in the finite element simulation software are output as coordinates for the contact measuring instrument, ensuring that the measured positions are the same as the theoretical positions. This facilitates subsequent residual stress simulation and simplifies the input and output process of data points.

[0058] Step 5: Measure the profile of the cut surface.

[0059] The two cut contour surfaces were measured using a contact coordinate measuring machine according to the two previously established coordinate systems and preset measurement points. The (x, z) coordinates of the two sets of data corresponded one-to-one, and the y-axis was on the same straight line.

[0060] In this step, coordinate systems are established for the two cut samples using the points marked in step two, resulting in two coordinate systems identical to those before cutting. The y-axis of both systems lies on the same straight line, and the x and z axes have the same direction, thus ensuring a one-to-one correspondence between the (x, z) coordinates of the two sets of data. Then, contact measurements are performed on the contours of the two cut surfaces according to the preset measurement points determined in step four.

[0061] Step 6: Contour data processing.

[0062] After measurement using the coordinate system designed according to this invention, the contour data of the two cutting surfaces should theoretically be mirror-symmetrical about the theoretically cut surface. However, actual measurement results may produce some abnormal data. To address these abnormal data, a combination of methods including average error removal, noise removal, and background subtraction of abnormal regions can be used for processing.

[0063] First, for some errors caused by lateral vibration or arc displacement during the cutting process, an averaging process is used to remove the errors and obtain the average contour curve.

[0064] like Figure 5As shown, some values ​​on the right side of the average contour curve after averaging are significantly bulging. This is due to the narrowing of the cutting area caused by parameter changes during the cutting process. This abnormal area is removed using a background subtraction operation. The specific operation method is as follows: Sort the points in the abnormal area according to their x-coordinate values. The two endpoints are points 4001 and 400n, respectively. Point 400x is any point in the middle, and the two points immediately adjacent to the abnormal area are points 4000 and 400n+1. Let the coordinates of points 4000, 4001, 400n, and 400n+1 be (x0, y0), (x1, y1), (x2, y2), (x3, y3), (x4, y4), (x5, y5), (x6, y6), (x7, y7), (x8, y8), (x9, y9), (x1, y1), (x1, y1), (x2, y2), (x3, y1), (x2, y2), (x3, y1), (x2, y2), (x3, y3), (x4, y4), (x5, y1), (x2, y2), (x3, y3), (x4, y4), (x5, y5), (x6, y6), (x7, y7), (x8, y8), (x9, y9), (x1, y1), (x2, y2), (x3 ...2), (x3, y2), ( n y n ) and (x n+1 y n+1 If the coordinates of point 400x are (x, y), then the calculated coordinates of point 400x are (x′, y′), and y′ = y - (x - x1) * (y n -y n+1 -y1+y0) / (x n -x1)-y1+y0, where y1 and y0 are the points at both ends of the anomaly region. n Alternatively, it can be processed using this formula. The calculated contour curve is as follows. Figure 6 As shown, the abnormal area has been eliminated.

[0065] Furthermore, since the points at both ends of the contour data generally have larger errors, the two abnormal points at both ends of the contour are replaced with adjacent points.

[0066] Furthermore, contour data points that differ from the average of adjacent data by more than 15% are considered outliers and replaced with the average of adjacent data.

[0067] After processing using the above methods, the final contour data curve is as follows: Figure 7 As shown in the figure. Using the processing method in this step, only abnormal data is smoothed, without the need for curve fitting, and the final processed result is more representative of the actual contour data.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for data acquisition and analysis using the profile method for residual stress testing, characterized in that, Includes the following steps: Workpiece shaping: The CNC machine tool is used to shape the workpiece to be tested, so that the shaped workpiece forms a set of reference surfaces parallel to the preset cutting surface, a set of parallel side surfaces perpendicular to the preset cutting surface, and a set of top surfaces with the same horizontal height on both sides of the preset cutting surface. Coordinate system establishment before cutting: On the non-cut surface after shaping, a contact measuring instrument is used to establish two coordinate systems that are mirror-symmetric about the preset cutting surface on the test piece, and the positioning points used to establish the coordinate systems are marked. Cutting at the test position: The test piece is cut at a preset position to obtain two mirror-symmetrical cut surfaces; Determination of the contour coordinates of the cut surface: The finite element method is used to mesh the contour surface to be measured on the cut surface, and the mesh nodes are used as the coordinates of the theoretical measurement points on the contour surface to be measured. Cutting surface contour measurement: The two cut surfaces after cutting are measured using a contact coordinate measuring instrument according to the coordinate system established before cutting and the coordinates of the theoretical measurement points, to obtain two sets of contour coordinate points that are mirror images of each other about the cutting surfaces; Contour data processing: First, the two sets of contour coordinate points are averaged to remove some errors. Then, the abnormal data steps caused by the change of cutting parameters are subjected to background subtraction. Finally, the individual abnormal data points are denoised.

2. The data acquisition and analysis method for residual stress testing using the profile method according to claim 1, characterized in that, In the workpiece shaping step, a high-precision machine tool is used to shape the workpiece to ensure that the shaped surface is flat, meets the roughness requirements, and can meet the surface accuracy required for coordinate system establishment, and ensures that the three shaped surfaces on the same side of the preset cutting surface are perpendicular to each other.

3. The data acquisition and analysis method for residual stress testing using the profile method according to claim 1, characterized in that, In the step of establishing the coordinate system before cutting, the origin and y-axis of the two established coordinate systems are on the same straight line, and the x-axis and z-axis have the same direction.

4. The data acquisition and analysis method for residual stress testing using the profile method according to claim 1, characterized in that, After shaping, the workpiece forms a first top surface, a first side surface, and a second side surface on one side of the preset cutting surface, and a second top surface, a third side surface, and a fourth side surface on the other side of the preset cutting surface; the first top surface and the second top surface are on the same plane, the second side surface and the fourth side surface are on the same plane, and the first side surface and the third side surface are parallel reference planes; the first top surface, the first side surface, and the second side surface are perpendicular to each other, and the second top surface, the third side surface, and the fourth side surface are perpendicular to each other.

5. The data acquisition and analysis method for residual stress testing using the profile method according to claim 4, characterized in that, In the coordinate system establishment step before cutting, a contact coordinate measuring instrument is used to randomly select three different positioning points on the first top surface of the test piece to establish the xy plane of the first coordinate system; two positioning points are randomly selected on the first side surface to establish the xz plane of the first coordinate system; and one positioning point is randomly selected on the second side surface to establish the yz plane of the first coordinate system.

6. The data acquisition and analysis method for residual stress testing using the profile method according to claim 5, characterized in that, In the step of establishing the coordinate system before cutting, the positioning point of the second coordinate system and the positioning point of the first coordinate system are located on both sides of the preset cutting surface, and the two are mirror symmetrical about the preset cutting surface, that is, the x-axis and z-axis are in the same direction, and the y-axis is in the opposite direction; the deviation between the mirror point of the origin of the second coordinate system and the origin of the first coordinate system is less than 0.004 mm.

7. The data acquisition and analysis method for residual stress testing using the profile method according to claim 1, characterized in that, During the cutting step at the measured position, a contact measuring instrument is used to measure the two endpoints of the surface to be cut for positioning during cutting. During cutting, the four corners of the sample to be cut are firmly fixed on the cutting machine. The cutting position of the cutting machine is set using the two marked endpoints, and the cutting speed is maintained at 0.3 mm / min.

8. The data acquisition and analysis method for residual stress testing using the profile method according to claim 1, characterized in that, In the contour data processing step, noise reduction is performed on individual abnormal data points, including replacing two abnormal points at both ends of the contour data with adjacent points.

9. The data acquisition and analysis method for residual stress testing using the profile method according to claim 1, characterized in that, In the contour data processing step, noise reduction is performed on individual abnormal data points, including: treating contour data points whose difference from the average value of adjacent data is greater than 15% as abnormal data and replacing them with the average value of adjacent data.

10. The data acquisition and analysis method for residual stress testing using the profile method according to claim 1, characterized in that, In the contour data processing step, background subtraction is performed on abnormal data steps caused by changes in cutting parameters. This includes: sorting the points in the abnormal region according to their x-coordinate values, and setting the coordinates of the points at both ends of the abnormal region as (x1, y1) and (x2, y2) respectively. n y n Before correction, the coordinates of any point in the middle are (x, y), and the coordinates of the points immediately adjacent to the two ends of the anomaly region are (x0, y0) and (x0, y0) respectively. n+1 y n+1 Then, after the anomaly region is corrected, the coordinates of any point in the middle are (x′, y′), and y′ = y - (x - x1) * (y n -y n+1 -y1+y0) / (x n -x1)-y1+y0.

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