A nondestructive detection and 3D visualization method for the depth profile of the hardened layer of a linear guide

Abstract

The present invention discloses a method for non-destructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail, belonging to the field of non-destructive detection. The method detects the guide rail using a multi-channel water immersion ultrasonic probe group, obtains the hardened layer depth data and converts it into coordinate values; uses these coordinate values to fit the hardened layer contour curve to obtain a function expression; combines the guide rail outer contour and the hardened layer contour curve to generate a hardened layer contour B-scan image; according to the relationship between depth and hardness, converts and generates a hardened layer hardness B-scan image; finally, the hardened layer depth profile and the hardness B-scan image are three-dimensionally reconstructed to achieve three-dimensional observation of the hardened layer of the linear guide rail. The present invention can predict the hardened layer depth profile curve of the linear guide rail using a small number of points through ultrasonic non-destructive detection methods, and achieve three-dimensional observation to increase visibility.

Description

Technical Field

[0001] The present invention relates to the field of nondestructive testing, and in particular to a nondestructive testing and three-dimensional visualization method for the depth profile of a hardened layer of a linear guide rail. Background Art

[0002] Traditional methods for measuring the hardened layer depth are microhardness and metallography. The microhardness method requires point-by-point hardness measurements on the guide rail surface, resulting in low testing efficiency and high operator skill requirements, which can easily lead to measurement errors due to human error. The metallographic method requires destructive processing such as cutting, polishing, and acid etching on the guide rail, which not only damages the workpiece but also makes the testing process cumbersome and costly. Furthermore, neither method can directly visualize the hardened layer depth profile, making it difficult to meet the demand for efficient, non-destructive testing in modern industrial production. In contrast, ultrasonic backscattering technology utilizes the material characterization information carried by the ultrasonic backscattered signal to achieve non-destructive and rapid hardened layer depth measurement. However, existing ultrasonic testing technologies still face numerous challenges when applied to guide rails with complex cross-sections. First, traditional contact ultrasonic testing methods struggle to obtain stable ultrasonic signals across complex cross-sections due to coupling issues between the probe and the guide rail surface, resulting in reduced testing accuracy. Second, existing ultrasonic testing technologies typically only provide single-point or localized hardened layer depth information, failing to comprehensively and intuitively display the distribution of the hardened layer depth profile. Furthermore, for guide rails with complex cross-sections, existing ultrasonic testing methods struggle to fully assess the entire cross-section, resulting in a limited detection range. Therefore, this paper proposes a nondestructive testing and 3D visualization method for the depth profile of the guide rail's hardened layer, using ultrasonic backscatter testing technology.

[0003] During use, linear guides must withstand loads while maintaining high-precision, smooth linear reciprocating motion. Their primary failure modes are contact fatigue damage and plastic deformation. Therefore, the guide rail's working surface must exhibit high hardness, strength, toughness, and wear resistance. This requires a quenching heat treatment to meet technical requirements for surface hardness and hardened layer depth. After quenching, the microstructure and properties of the steel's surface and core differ, forming a hardened layer structure. Within the hardened layer, the microhardness distribution is relatively uniform, with a gradient from the hardened zone to the transition zone and then to the base material. The depth of the hardened layer is a key factor in determining the guide rail's strength, load-bearing capacity, and wear resistance. Its consistency is fundamental to the guide rail's geometric and guiding accuracy. Insufficient hardened layer depth makes the guide rail more susceptible to fatigue failure under alternating loads. Therefore, accurately and quickly measuring the hardened layer depth in linear guides is a critical technical issue for improving guide rail quality, optimizing process flows, and achieving intelligent manufacturing.

[0004] Conventional ultrasonic waves consist of longitudinal and shear waves. Shear waves are more sensitive to changes in the material's shear modulus, respond more strongly to microstructural changes, and decay more slowly within the material. Therefore, shear waves are more effective in distinguishing microstructural differences between the hardened layer and the base material. By analyzing signal characteristics such as time delay, amplitude, frequency, and phase changes, they can accurately assess the material's internal state and enable nondestructive testing.

[0005] During the inspection process, due to limitations in the rail model, the sections to be inspected were small in size and had complex geometric features. When using a contact flat probe, some sections of the rail could not generate effective shear waves. This was because the probe's coupling surface was small, while the wafer diameter was larger than the coupling surface width. This prevented the sound beam from fully entering the rail and caused it to reflect off the wedge bottom, resulting in turbulent sound waves and preventing the formation of effective ultrasonic shear waves.

[0006] When inspecting the depth of the guide rail's hardened layer, ultrasonic backscatter detection technology can be used to obtain ultrasonic A-scan signals indicating the depth of the guide rail's hardened layer. However, B-scan images provide a more intuitive display of workpiece cross-sectional information. Traditional B-scan images are generated using ultrasonic phased array probes by controlling the crystal excitation time to deflect and focus the acoustic beam. However, due to the complex cross-sectional shape of the guide rail, only a portion of the inspection surface receives the ultrasonic echo. Using multiple crystal deflection angles for scanning increases R&D and testing costs, making it impossible to directly obtain ultrasonic B-scan images of the guide rail cross-section using a phased array probe. Summary of the Invention

[0007] Therefore, it is necessary to provide a nondestructive detection and three-dimensional visualization method for the depth profile of the hardened layer of a linear guide rail, addressing the current inability to visually obtain the depth profile distribution of the hardened layer of the linear guide rail through nondestructive methods. Compared with existing methods, this invention not only overcomes the limitations of existing technologies through innovative detection technology and visualization methods, but also achieves significant improvements in detection accuracy, efficiency, visualization effect, scope of application, and cost-effectiveness. It has important industrial application value and broad application prospects.

[0008] The present invention provides a method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail, the method comprising the following steps:

[0009] S1. Select multiple straight segments or curved segments with a fixed curvature as test points on the outer contour line of the cross section of the linear guide rail to be tested, place the linear guide rail to be tested in water, and use a multi-channel immersion ultrasonic probe group to synchronously transmit a focused acoustic beam to each test point in the form of scanning along the guide rail to perform shear wave detection. Calculate the hardened layer depth data of each test point based on the obtained ultrasonic backscattered detection signal, and then convert the hardened layer depth data of each test point into the coordinate value of the corresponding point on the hardened layer contour curve in the linear guide rail coordinate system;

[0010] S2. For each guide rail cross section, the hardened layer contour curve on each side of the guide rail is fitted according to the converted point coordinate value data to obtain a fitting curve expression for the hardened layer contour curve. Then, a B-scan image of the guide rail hardened layer contour at the current cross-sectional position is generated according to the hardened layer contour fitting curves on both sides of the guide rail and the outer contour line of the cross section. Finally, according to the pre-acquired mapping relationship between the hardened layer depth and hardness, the depth value of each pixel in the guide rail hardened layer contour B-scan image is converted into a hardness value to generate a B-scan image of the guide rail hardened layer hardness.

[0011] S3. The guide rail hardened layer contour B-scan images and guide rail hardened layer hardness B-scan images obtained from different guide rail cross sections are 3D reconstructed using image 3D visualization technology to achieve 3D observation of the linear guide rail hardened layer.

[0012] As a preferred embodiment of the above-mentioned first aspect, the linear guide rail to be tested only needs to arrange a multi-channel water immersion ultrasonic probe group on a single side to perform shear wave detection to obtain the corresponding point coordinate values on the hardened layer contour curve on this side, while the corresponding point coordinate values on the hardened layer contour curve on the other side are directly obtained through coordinate conversion in a mirror-symmetrical manner in the linear guide rail coordinate system.

[0013] As a preferred embodiment of the first aspect, multi-channel immersion ultrasonic probe groups need to be arranged on both sides of the linear guide rail to be tested to perform shear wave detection to obtain the corresponding point coordinate values on the hardened layer contour curve on this side.

[0014] As a preferred embodiment of the above-mentioned first aspect, when performing shear wave detection on the linear guide rail to be tested, the linear guide rail to be tested needs to be immersed in a water tank, and a multi-channel water immersion ultrasonic probe group is arranged on its side. Each water immersion ultrasonic probe is aimed at a detection point to emit a focused ultrasonic shear wave beam, and the ultrasonic shear wave enters the side of the linear guide rail at the first critical incident angle of the water-steel coupling interface. During the scanning process along the guide rail, all water immersion ultrasonic probes in the multi-channel water immersion ultrasonic probe group synchronously collect the backscattered detection signal of the ultrasonic shear wave.

[0015] As a preferred embodiment of the above-mentioned first aspect, in S1, when calculating the hardened layer depth data of each detection point based on the obtained ultrasonic backscatter detection signal, for any detection point, the acoustic time difference between the surface wave and the backscatter signal of the detection point is extracted from the ultrasonic backscatter detection signal, and the hardened layer depth of the detection point is calculated based on the shear wave propagation velocity and the shear wave propagation angle.

[0016] As a preferred embodiment of the above-mentioned first aspect, in S1, when converting the hardened layer depth data of each detection point into the corresponding point coordinate value on the hardened layer contour curve in the linear guide rail coordinate system, for any detection point, a linear guide rail coordinate system is established with the center point of the bottom edge of the cross section of the linear guide rail to be measured as the origin, the bottom edge of the cross section as the horizontal axis, and the symmetry center line of the cross section as the vertical axis, and then based on the chip center coordinates, water sound path and hardened layer depth of each ultrasonic probe, the point coordinates corresponding to the reflection point of the sound beam emitted by the ultrasonic probe on the hardened layer contour curve are obtained through coordinate transformation.

[0017] As a preferred embodiment of the first aspect, the mapping relationship between the hardened layer depth and the hardness is obtained by fitting the hardness values at different hardened layer depths of the linear guide rail cross section using a microhardness method.

[0018] As a preference of the first aspect above, the fitting function of the hardened layer profile curve adopts a 4th order polynomial or a 2nd order sine fitting function.

[0019] As a preferred embodiment of the above-mentioned first aspect, in the guide rail hardened layer contour B scanning image, the hardened layer area enclosed by the hardened layer contour fitting curve and the cross-section outer contour line needs to be discretized into a pixel matrix according to a preset resolution, and the hardened layer contour fitting curve is visualized as discrete points, and each row of pixels corresponds to one discrete point of visual display.

[0020] As a preferred embodiment of the first aspect, the hardness value of each pixel in the guide rail hardened layer hardness B scanning image is converted into a grayscale value and visually displayed according to a preset visualization effect.

[0021] By adopting the above technical solution, the beneficial effects of the present invention are:

[0022] (1) The present invention adopts ultrasonic backscattering technology, combined with a multi-channel water immersion focusing probe group, which can quickly and accurately obtain the hardened layer depth data without damaging the guide rail. The detection accuracy can reach millimeter level or even higher, which is significantly better than traditional methods.

[0023] (2) The present invention realizes a comprehensive evaluation of the complex cross-section of the guide rail through a multi-channel water immersion ultrasonic probe group, which greatly improves the detection speed and can complete the detection of the entire guide rail cross-section in a short time, greatly shortening the detection cycle and improving production efficiency.

[0024] (3) This paper achieves 3D visualization of the hardened layer depth profile and hardness distribution by fitting the hardened layer contour curve and generating a B-scan image, combined with VTK and Python for 3D reconstruction. Users can intuitively observe the distribution of the hardened layer from multiple angles and promptly identify potential defects, providing strong support for quality control and process optimization.

[0025] (4) The present invention adopts a water immersion focusing probe group, which can flexibly adjust the probe position and detection parameters. It is suitable for linear guide rails of various complex shapes and has wide applicability to meet the needs of different industrial scenarios.

[0026] (5) The nondestructive testing method of the present invention avoids workpiece loss, reduces the complexity of the testing equipment and the difficulty of operation, and lowers the testing cost. In addition, the fast testing speed and intuitive visual results can help users make decisions more quickly, further improving economic benefits.

[0027] (6) The technical solution of the present invention has the potential to be integrated with automated production lines, enabling real-time monitoring and automated assessment of the depth of the guide rail hardened layer. By combining it with industrial Internet and big data technologies, it can further enhance the intelligence level of the production process and provide technical support for intelligent manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the steps for the linear guide hardened layer depth profile detection and three-dimensional visualization method.

[0029] Figure 2 Schematic diagram of the probe layout and detection point distribution for multi-channel water immersion focused testing of complex-shaped guide rail sections.

[0030] Figure 3 Schematic diagram of the guide rail coordinate system for guide rail cross-section detection.

[0031] Figure 4 This is a schematic diagram of the shear wave detection principle.

[0032] Figure 5 Schematic diagram of the mapping relationship between the depth of the hardened layer and the hardness of the hardened layer.

[0033] Figure 6 These are various images of the linear guide rail cross section, of which the left, middle, and right images are respectively the metallographic method of the linear guide rail cross section hardened layer distribution diagram, the linear guide rail cross section hardened layer contour B-scan diagram, and the linear guide rail hardened layer hardness B-scan image.

[0034] Figure 7 The time series of B scanning images of the hardened layer profile and hardness of the linear guide.

[0035] Figure 8 Flowchart of method steps in an embodiment of the present invention.

[0036] Figure 9 The 3D reconstruction process of the hardened layer profile of a linear guide.

[0037] Figure 10 This is the three-dimensional visualization result of the hardened layer profile of the linear guide.

[0038] Figure 11 The 3D reconstruction process of the hardness of the hardened layer of the linear guide.

[0039] Figure 12 This is the three-dimensional visualization result of the hardness of the hardened layer of the linear guide. DETAILED DESCRIPTION

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in the various embodiments of the present invention can be combined accordingly without conflicting with each other.

[0041] In a preferred embodiment of the present invention, a method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail is provided, which includes the following steps:

[0042] S1. Select multiple straight segments or curved segments with fixed curvature as detection points on the outer contour line of the cross section of the linear guide rail to be tested, place the linear guide rail to be tested in water, and use a multi-channel water immersion ultrasonic probe group to synchronously transmit a focused acoustic beam to each detection point in the form of scanning along the guide rail direction to perform shear wave detection. Calculate the hardened layer depth data of each detection point based on the obtained ultrasonic backscattered detection signal, and then convert the hardened layer depth data of each detection point into the corresponding point coordinate value on the hardened layer contour curve in the linear guide rail coordinate system.

[0043] It should be noted that the number of detection points in the present invention needs to meet the requirements of the number of coordinate points of the subsequent curve fitting. In theory, the more detection points there are, the higher the accuracy of the subsequent curve fitting. However, too many detection points will result in an excessive number of required water-immersion ultrasonic probes, and the requirements for equipment and detection operations will also be higher. Therefore, it is necessary to reasonably select an appropriate number of detection points based on the shape of the outer contour line of the cross section of the actual linear guide. Each detection point on the outer contour line of the cross section is actually not a single point, but a straight line segment or a curve segment with a fixed curvature, because no matter how the ultrasonic beam is focused, it still has a certain focus area range. When performing subsequent coordinate calculations, the midpoint of each straight line segment or curve segment can be equivalent to a detection point.

[0044] Since there are multiple detection points on the cross-section of the linear guide to be tested, in order to ensure the synchronization and accuracy of the measurement, a multi-channel water immersion ultrasonic probe group consisting of multiple water immersion ultrasonic probes can be used. Each water immersion ultrasonic probe emits a focused ultrasonic shear wave beam at a detection point. The different water immersion ultrasonic probes in the multi-channel water immersion ultrasonic probe group synchronously transmit and receive signals, and simultaneously obtain ultrasonic backscatter detection signals at each detection point, thereby obtaining the corresponding hardened layer depth data at different detection points on the cross-section. Moreover, since the linear guide is strip-shaped, the hardened layer thickness at different cross-sections may be different. Therefore, in order to comprehensively detect the hardened layer thickness at different positions of the linear guide, the multi-channel water immersion ultrasonic probe group needs to scan along the guide direction. During the scanning process, for any scanned cross-section, a focused ultrasonic beam will be synchronously emitted to each detection point for shear wave detection, obtaining the ultrasonic backscatter detection signal on this cross-section. Based on these ultrasonic backscatter detection signals, the hardened layer thickness distribution of each cross-section can be reconstructed, thereby achieving three-dimensional visualization of the entire linear guide.

[0045] The reason for adopting the water immersion ultrasonic backscatter detection system in the present invention is that the probe used in the contact method is a flat probe, and the width of the sound beam is equal to the diameter of the probe chip, which causes the sound beam to be scattered on the complex shape cross-section of the guide rail, thereby causing the received sound waves to be disordered. Therefore, the present invention will adopt ultrasonic backscatter detection based on the water immersion method, and use the water immersion focusing probe to have a more concentrated sound beam to solve the problem of divergence caused by excessive sound beam width. By utilizing the focusing advantage of the water immersion probe, a full-scale evaluation of the complex shape cross-section of the guide rail can be achieved. When performing the specific detection operation, the linear guide rail to be tested is placed in a water tank, and two groups of multi-channel water immersion focusing ultrasonic probe groups are used to detect the important surfaces on both sides of the linear guide rail to be tested respectively, and the obtained ultrasonic A-scan signals are saved in time to achieve a full-scale evaluation of the complex shape cross-section of the linear guide rail.

[0046] It should be noted that the hardened layer contour curve in the present invention refers to the contour line inside the hardened layer, that is, the interface line between the hardened layer and the steel structure matrix inside the guide rail. Since the linear guide rail to be measured has two side surfaces, both of which are processed with hardened layers, the present invention needs to construct two hardened layer contour curves for one cross section, that is, it is necessary to construct the hardened layer contour curves on both sides separately. Generally speaking, the two sides of a linear guide rail are mirror-symmetrical, so in order to construct the hardened layer contour curves on both sides, the present invention can use the actual measurement method to construct them separately or only measure one side, and the other side is converted in a mirror-symmetrical manner.

[0047] For those requiring actual measurements on both sides, a multi-channel immersion ultrasonic probe set is deployed on each side of the linear guide rail for shear wave testing to obtain the corresponding point coordinates on the hardened layer profile curve for that side. The corresponding point coordinates on the hardened layer profile curves on both sides are then used to fit the hardened layer profile curves for each side.

[0048] For single-sided measurement followed by mirror-symmetric conversion, the linear guide rail only needs to be tested by deploying a multi-channel immersion ultrasonic probe set for shear wave testing on a single side. The corresponding coordinate values of the points on the hardened layer profile curve on that side are obtained. The corresponding coordinate values of the points on the hardened layer profile curve on the other side are directly converted in a mirror-symmetric manner within the linear guide rail coordinate system. The corresponding coordinate values on the hardened layer profile curves on both sides are then used to fit their respective hardened layer profile curves.

[0049] Below is Figure 2 The example shown is used to specifically describe how to use a multi-channel water immersion ultrasonic probe set to perform shear wave detection on the linear guide to be tested and fit the hardened layer profile curve.

[0050] exist Figure 2 In the exemplary linear guide rail shown, there are symmetrical hardened layers on both sides. During the use of the linear guide rail, the hardened layers on its sides need to bear the load brought by the slider roller and the load. In this embodiment, a 6-channel water immersion ultrasonic probe group is used to detect the right side surface of the linear guide rail according to specific detection requirements. Figure 2 Six detection points were selected on the outer contour curve on the right side of the cross section, and corresponding ultrasonic backscatter detection probes were set up to detect the depth of the hardened layer. Among the six detection points of the cross section, there are four straight segments and two curved segments with fixed curvature. The straight segments are III, IV, V, and VI, and the curved segments are I and II. Since the linear guide is a continuous bar, the above four straight segments are actually a plane on the side of the guide, and the curved segments are actually a curved surface on the side of the guide. Considering the working state of the guide, surfaces I and IV are mainly the contact surfaces of the rollers in the guide slider, and they need to have high wear resistance. At the same time, I and III are also important load-bearing surfaces of the guide. When the guide is loaded, the two working surfaces need to directly bear the pressure brought by the slider and its load, and the other working surfaces also need to withstand a certain amount of tensile and compressive deformation.

[0051] Based on the six test points selected above, shear wave testing is performed on the linear guide rail to be tested. The specific method is as follows: the linear guide rail to be tested is immersed in a water tank, and a six-channel water immersion ultrasonic probe group is arranged on its side. Each water immersion ultrasonic probe is aimed at a test point to emit a focused ultrasonic shear wave beam. The ultrasonic shear wave enters the side of the linear guide rail at the first critical incident angle of the water-steel coupling interface (the contact surface between the guide rail side wall and the water). During the scanning process along the guide rail, all water immersion ultrasonic probes in the multi-channel water immersion ultrasonic probe group synchronously collect the backscattered detection signal of the ultrasonic shear wave.

[0052] Based on the synchronous acquisition of ultrasonic shear wave backscatter detection signals by all immersion ultrasonic probes, the hardened layer depth at each detection point is calculated. The specific method is as follows:

[0053] For any detection point, the acoustic time difference between the surface wave and the backscattered signal at the detection point is extracted from the ultrasonic backscattered detection signal, and the hardened layer depth at the detection point is calculated based on the shear wave propagation velocity and shear wave propagation angle.

[0054] In addition, it is also necessary to convert the hardened layer depth data of each detection point into the corresponding point coordinate value on the hardened layer contour curve in the linear guide coordinate system. The specific method is:

[0055] For any detection point, a linear guide coordinate system is established with the center point of the bottom edge of the cross section of the linear guide to be tested as the origin, the bottom edge of the cross section as the horizontal axis, and the symmetry center line of the cross section as the vertical axis. Then, based on the chip center coordinates, water acoustic path and hardened layer depth of each ultrasonic probe, the coordinates of the point corresponding to the reflection point of the sound beam emitted by the ultrasonic probe on the hardened layer contour curve are obtained through coordinate transformation.

[0056] The above coordinate transformation needs to be converted based on the specific coordinates of the linear guide rail coordinate system. In the embodiment of the present invention, an exemplary Cartesian coordinate system based on the midpoint of the bottom of the guide rail is given, such as Figure 3As shown in Figure 2 . In this Cartesian coordinate system, the midpoint of the bottom edge of the guide rail's cross section is used as the origin, the bottom edge of the cross section is used as the X-axis, and the centerline of symmetry of the cross section is used as the Y-axis. According to the requirements of the testing process, the detection water acoustic path of each ultrasonic probe is pre-set and accurately recorded when arranging the multi-channel water immersion ultrasonic probe group. The six ultrasonic probes numbered ①, ②, ③, ④, ⑤, and ⑥ correspond to a total of six detection points I, II, III, IV, V, and VI. Their respective detection water acoustic paths are recorded as H1, H2, H3, H4, H5, and H6, respectively. The fixed external dimensions of the linear guide rail can be used to obtain the probe's wafer center position and record the coordinates of the probe wafer center. The wafer center coordinates of the six ultrasonic probes numbered ① to ⑥ are represented by (x1, y1), (x2, y2), (x3, y3), (x4, y4), (x5, y5), and (x6, y6), respectively. Therefore, a multi-channel water immersion shear wave detection system is used to detect the depth of the hardened layer at six detection points on the guide rail cross section, and the depth of the hardened layer at each detection point is obtained.

[0057] For each detection point, the backscattered signal of the ultrasonic shear wave can be processed using the acoustic time difference measurement technology to obtain the depth information of the hardened layer. The principle of this detection method is that in the very dense and delicate hardened layer structure on the surface, the scattering of the ultrasonic shear wave is almost unobservable. However, when the ultrasonic wave passes through the transition zone, due to the change in the microstructure, the sound wave is significantly scattered. Let the acoustic time difference between the surface wave and the backscattered signal be t, and t is the acoustic wave flight time between the surface wave and the backscattered signal at the detection point. Then the depth of the hardened layer at the detection point (HD) can be calculated by the following formula:

[0058]

[0059] where v T is the shear wave propagation velocity in the hardened layer, and β is the shear wave propagation angle in the hardened layer. Figure 4 As shown, according to the schematic principle of shear wave detection, the shear wave propagation angle β in the hardened layer satisfies the following relationship:

[0060]

[0061] Where c1 is the propagation speed of ultrasound in water, c2 is the propagation speed of ultrasound in the hardened layer, ɑ is the ultrasonic incident angle in water (i.e., the first critical incident angle when the acoustic shear wave enters the water-steel coupling interface), and β is the shear wave propagation angle in the hardened layer.

[0062] Based on the above calculation method of the depth of the hardened layer, the depth of the hardened layer at the six detection points Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, and Ⅵ can be calculated and recorded as D1, D2, D3, D4, D5, and D6 respectively. Figure 3The coordinate system shown in the figure can be obtained by using the coordinates of the center of the chip of the i-th ultrasonic probe (x i ,y i ), the water sound path H corresponding to the detection point i And the depth D of the corresponding detection point i , the coordinates of the fitting points on the hardened layer contour curve are obtained by coordinate transformation (m i ,n i ), the coordinate transformations of the six detection points are as follows:

[0063]

[0064] The above coordinate transformation method is only for the hardened layer on the right side of the guide rail. Since the left and right sides are mirror-symmetrical, the coordinate transformation of the hardened layer detection point on the left side of the guide rail can be based on the center coordinates of the probe chip on the left. The above coordinate transformation method is converted according to the method of "the horizontal coordinates are opposite numbers and the vertical coordinates remain unchanged", so as to obtain the point data on the hardened layer contour curve on the left side.

[0065] S2. For each guide rail cross section, the hardened layer contour curve on each side of the guide rail is fitted according to the point coordinate value data obtained by conversion to obtain the fitting curve expression of the hardened layer contour curve, and then the guide rail hardened layer contour B scanning image of the current cross-sectional position is generated according to the hardened layer contour fitting curves on both sides of the guide rail and the outer contour line of the cross section, and finally, according to the mapping relationship between the hardened layer depth and hardness obtained in advance, the depth value of each pixel in the guide rail hardened layer contour B scanning image is converted into a hardness value to generate the guide rail hardened layer hardness B scanning image.

[0066] It should be noted that since the probe scans a series of data at different guide rail cross sections, each guide rail cross section can obtain point data on the hardened layer profile curve on both sides. Therefore, it is necessary to fit the hardened layer profile curve on both sides of each guide rail cross section separately. The fitting function of the hardened layer profile curve needs to be optimized based on the actual profile curve. In the embodiment of the present invention, a 4th order polynomial or a 2nd order sine function can be used, where:

[0067] The fitting curve model of the second-order sine function is as follows:

[0068]

[0069] Where: a1, b1, c1, a2, b2, c2 are fitting coefficients respectively.

[0070] The fitting curve model of the 4th order polynomial is as follows:

[0071]

[0072] Where: p1, p2, p3, p4, and p5 are fitting coefficients respectively.

[0073] Furthermore, the aforementioned mapping relationship between hardened layer depth and hardness can be obtained by fitting actual experimental data. Traditional methods for measuring the depth of the hardened layer often employ microhardness testing to measure the hardness of the guide rail cross section, determining the depth of the hardened layer by distinguishing the hardness variations between the hardened layer and the core structure. In embodiments of the present invention, the aforementioned mapping relationship can be obtained by fitting the hardness values of the linear guide rail cross section at different hardened layer depths using microhardness testing. Figure 5 The mapping relationship obtained by fitting the microhardness measurement of a linear guide rail by the present invention is shown. It can be found that there is a clear mapping relationship between the hardness distribution on the guide rail cross section and the distribution of the hardened layer. As the depth of the detection point from the surface increases, the hardness gradually decreases. Figure 5 As can be seen from the figure, the relationship between the depth of the hardened layer and the hardness of the hardened layer is not linear, and there is a sudden change in the change. When the hardness value drops sharply, the current distance is the depth of the hardened layer. Therefore, after obtaining the depth information of the guide rail hardened layer by using water immersion ultrasonic shear wave detection, the sudden change boundary of the hardness value can be confirmed, and then the hardness value can be determined according to the Figure 5 The fitting curve shown can be used to infer the hardness distribution at different depths in the vertical area below a certain point on the guide rail surface.

[0074] S3. The guide rail hardened layer contour B-scan images and guide rail hardened layer hardness B-scan images obtained from different guide rail cross sections are 3D reconstructed using image 3D visualization technology to achieve 3D observation of the linear guide rail hardened layer.

[0075] It should be noted that the three-dimensional image visualization technology required for three-dimensional reconstruction can be selected according to actual needs. However, when performing three-dimensional visualization, the display is often displayed at a fixed resolution. Therefore, in the above-mentioned guide rail hardened layer contour B-scan image, the hardened layer area enclosed by the hardened layer contour fitting curve and the cross-section outer contour line needs to be discretized into a pixel matrix according to the preset resolution. The hardened layer contour fitting curve is visualized as discrete points, and each row of pixels corresponds to one discrete point of visualization. Similarly, the hardness value of each pixel in the guide rail hardened layer hardness B-scan image can be converted into a grayscale value and visualized according to the preset visualization effect.

[0076] In an embodiment of the present invention, each pixel in a single B-scan image contains the following information: the current pixel's x-coordinate, y-coordinate, and corresponding hardness value. Furthermore, by converting the hardness value to a grayscale value, the guide rail cross-section hardness B-scan image is grayscaled, and the hardness information is represented by grayscale intensity. This hardness B-scan image thus serves the same purpose as an ultrasonic B-scan image, providing a more intuitive representation of the hardness distribution across the guide rail cross-section. Figure 6 The guide rail hardened layer profile B-scan image and the rail hardened layer hardness B-scan image, which are finally converted from the actual cross-section of a linear guide rail, are exemplarily shown. It can be seen that the guide rail hardened layer profile B-scan image and the rail hardened layer hardness B-scan image reconstructed by the above method of the present invention can well reflect the actual distribution of the hardened layer on the cross-section of the linear guide rail.

[0077] In addition, the above Figure 6 The figure shows the B-scan image of the hardened layer profile of the guide rail and the B-scan image of the hardened layer hardness of the guide rail of a single cross section. However, since the ultrasonic probe is moved along the guide rail for scanning, when the scanning position changes, the characteristics of the hardened layer profile on different cross sections of the linear guide rail can be reflected over time. The generated time series of the B-scan image of the hardened layer profile of the linear guide rail and the time series of the B-scan image of the hardened layer of the linear guide rail are shown in Figure 2. Figure 7 In the present invention, the 3D reconstruction method and the 3D observation display effect can be selected according to the actual visualization effect requirements.

[0078] The following is a specific example to demonstrate the specific approach and technical effects of the above-mentioned linear guide rail hardened layer depth profile non-destructive detection and three-dimensional visualization method.

[0079] Example

[0080] In this embodiment, a linear guide rail of model 20 is used as a detection workpiece, and a method for detecting and three-dimensionally visualizing the depth profile of the hardened layer of the linear guide rail is described in detail.

[0081] like Figure 8 As shown, the linear guide hardened layer depth profile detection and 3D visualization method includes the following sequential steps:

[0082] Step 1: Refer to the above step S1 and use a set of 6-channel water immersion ultrasonic probes to detect the right surface of the linear guide rail. The specific detection method is as follows: put the guide rail to be tested into the water tank, use the water immersion probe holder to fix the position of the water immersion ultrasonic probe, and align the 6 ultrasonic probes respectively. Figure 2 There are 6 detection points in total, namely Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, and Ⅵ.

[0083] In order to avoid severe ultrasonic shear wave scattering and poor detection results, shape analysis was performed on the above six detection points. An investigation of the guide rail's processing drawings revealed that the curvature of surfaces I and II is fixed, with a curvature radius of 1.86mm and a central angle of 56.32°. Plane III is 45° to the bottom of the guide rail and is 1.16mm long; plane IV is perpendicular to the bottom of the guide rail and is 1.61mm long; plane V is 45° to the bottom of the guide rail and is 4.09mm long; plane VI is perpendicular to the bottom of the guide rail and is 2.5mm long. After confirming the shape characteristics of the above detection planes, a reasonable water immersion focusing probe is set so that the sound beam can be focused and incident on the surface to be tested, while minimizing the scattering of the sound waves.

[0084] In this embodiment, in order to meet such detection requirements, the beam width of the focused probe needs to be strictly set to be less than or equal to the width of the detection surface. Here, 1mm is set as the reference standard for the beam width. Combined with the calculation formula of the focal zone diameter and the wavelength λ of the ultrasonic wave in water, 水 , it can be determined that the probe needs to meet the following conditions:

[0085]

[0086] Where D is the wafer diameter, is the wavelength of ultrasound in water, F is the theoretical focal length, and it satisfies:

[0087]

[0088] Where: c1 is the speed of ultrasound in water, c3 is the speed of ultrasound in the chip, and R is the chip cylindrical curvature radius of the line focusing probe or the spherical curvature of the chip of the point focusing probe.

[0089] The wavelength of ultrasound in water The frequency of the probe and the speed of sound in water determine the frequency of the water immersion focusing probe used in this embodiment. The wavelength of the probe in water is 0.075 mm, and the relationship between the probe's chip diameter and focal length can be calculated as follows:

[0090]

[0091] The probe's focal length can be adjusted based on the probe's crystal diameter, enabling shear wave depth measurement of the surface under test. For example, if the probe's crystal diameter is 6mm, the probe's focal length needs to be less than or equal to 79.8mm.

[0092] In this embodiment, the parameters of the water immersion focusing probe are set as follows: the probe frequency is 20 MHz, the probe wafer diameter is 10 mm, and the focal length of the probe needs to be less than or equal to 133 mm.

[0093] During underwater shear wave testing of a guide rail, the immersion probe is stationary while the rail moves linearly. A multi-channel immersion ultrasonic probe assembly simultaneously scans along the rail, emitting focused acoustic beams at each test point for shear wave testing. This generates ultrasonic backscatter signals, completing the entire guide rail inspection. After testing, the ultrasonic A-scan signals (i.e., the aforementioned ultrasonic backscatter signals) are analyzed and processed. Signal data for each rail cross section during the scanning process is extracted based on the signal timestamps. Based on this extracted data, the hardened layer depth data for each test point on that cross section is calculated, and the coordinates of each fitting point in the hardened layer profile curve on both sides are converted to the guide rail coordinate system.

[0094] Step 2. Referring to the aforementioned step S2, based on the coordinate values of the fitting points obtained in step 1, use MATLAB software to use a 4th-order polynomial or a 2nd-order sine fitting function to perform curve fitting on the coordinates of each point on the hardened layer contour curve on both sides of the guide rail to obtain the function expression of the hardened layer contour curve.

[0095] Then, for each cross-section, the obtained hardened layer contour curve function expression is used to discretize the points on the hardened layer contour curve using Python software, and the coordinates of 1000 points on the hardened layer contour curve on both sides of the guide rail are generated respectively; according to the guide rail outer contour characteristics and the coordinates of 1000 points on the hardened layer contour curve on both sides, the guide rail hardened layer contour B-scan image is generated.

[0096] At the same time, Python software is also needed to convert and generate a B-scan image of the hardness of the hardened layer based on the relationship between depth and hardness, that is, the curve of the guide rail hardness changing with the vertical distance from the surface.

[0097] To verify the accuracy of the hardened layer profile curve obtained through fitting in the present invention, this embodiment further polished and acid-etched the actual linear guide rail cross section and photographed the hardened layer distribution diagram of the guide rail cross section. A computer vision algorithm was used to extract the hardened layer profile, and a curve fitting tool was used to find the curve equation that best fits the profile points. The specific steps are as follows:

[0098] First, the post-etching image was grayscaled and denoised using a Gaussian filter (σ = 1.5). Next, an image segmentation method based on the Otsu adaptive threshold algorithm was used to divide the hardened layer distribution map of the guide rail cross section into multiple objects and regions, isolating the hardened layer region boundaries. Next, the Canny algorithm (threshold 50-150) was used to accurately extract the hardened layer boundaries. Finally, the cv2.findContours() function in OpenCV was used to obtain the hardened layer boundary point set and complete the contour point extraction. Finally, an 8th-order polynomial fitting (least squares method) was used to obtain the fitting curve equation. When boundary points were missing, B-spline interpolation was used for smoothing.

[0099] Finally, a consistency comparison was performed between the hardened layer depth profile curve fitted according to the ultrasonic backscattering detection method and the hardened layer depth profile curve obtained by processing the actual guide rail cross-section according to the image detection algorithm, proving that the hardened layer depth profile curve fitted by the present invention is consistent with the actual hardened layer depth profile curve, proving the effectiveness of the ultrasonic backscattering detection method for the guide rail hardened layer depth profile of the present invention.

[0100] Step 3. Referring to step S3 above, based on VTK and Python's 3D image visualization technology, the B-scan image sequence of the hardened layer depth profile is 3D reconstructed to generate a 3D visualization of the linear guide's hardened layer profile, enabling 3D observation of the linear guide's hardened layer profile. Simultaneously, based on VTK and Python's 3D image visualization technology, the B-scan image sequence of the hardened layer depth profile is 3D reconstructed to generate a 3D visualization of the linear guide's hardness, enabling 3D observation of the linear guide's hardness.

[0101] In this embodiment, the exemplary linear guide rail hardened layer profile 3D reconstruction process is as follows: Figure 9 The three-dimensional visualization results of the hardened layer profile of the linear guide obtained by using Python and VTK toolkit are shown in the figure. Figure 10 In an embodiment of the present invention, an exemplary three-dimensional reconstruction process of the hardness of the linear guide hardened layer is as follows: Figure 11 The three-dimensional visualization results of the hardness of the linear guide hardened layer obtained by using Python and VTK toolkit are shown in the figure. Figure 12 In this example, the three-dimensional visualization of the hardness of the linear guide rail's hardened layer is shown. The hardness values of the hardened layer are distinguished by color, where orange represents a higher hardness value and blue represents a lower hardness value.

[0102] The above-described embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail, characterized in that: The following steps are involved: S1. Select multiple straight segments or curved segments with fixed curvature on the outer contour line of the cross section of the linear guide rail to be tested as detection points, place the linear guide rail to be tested in water, and use a multi-channel water immersion ultrasonic probe group to synchronously transmit a focused acoustic beam to each detection point in the form of scanning along the guide rail direction for shear wave detection. When performing shear wave detection on the linear guide rail to be tested, the linear guide rail to be tested needs to be immersed in a water tank, and a multi-channel water immersion ultrasonic probe group is arranged on its side. Each water immersion ultrasonic probe is aimed at a detection point to emit a focused ultrasonic shear wave beam, and the ultrasonic shear wave enters the water-steel coupling interface at the first critical incident angle. On the side of the linear guide rail, all water-immersion ultrasonic probes in the multi-channel water-immersion ultrasonic probe group synchronously collect backscattered detection signals of ultrasonic shear waves during scanning along the guide rail direction; based on the obtained ultrasonic backscattered detection signals, the hardened layer depth data of each detection point is calculated; for any detection point, the acoustic time difference between the surface wave and the backscattered signal at the detection point is extracted from the ultrasonic backscattered detection signal, and the hardened layer depth of the detection point is calculated based on the shear wave propagation velocity and the shear wave propagation angle; the hardened layer depth data of each detection point is then converted into the corresponding point coordinate value on the hardened layer contour curve in the linear guide rail coordinate system; S2. For each guide rail cross section, the hardened layer contour curve on each side of the guide rail is fitted according to the point coordinate value data obtained by conversion to obtain a fitting curve expression for the hardened layer contour curve; then, based on the hardened layer contour fitting curves on both sides of the guide rail and the outer contour line of the cross section, a B-scan image of the guide rail hardened layer contour at the current cross-sectional position is generated; finally, based on the pre-acquired mapping relationship between the hardened layer depth and the hardness, the depth value of each pixel in the guide rail hardened layer contour B-scan image is converted into a hardness value to generate a B-scan image of the guide rail hardened layer hardness; the mapping relationship between the hardened layer depth and the hardness is obtained by fitting the hardness values at different hardened layer depths of the linear guide rail cross section using a microhardness method; S3. The guide rail hardened layer contour B-scan images and guide rail hardened layer hardness B-scan images obtained from different guide rail cross sections are 3D reconstructed using image 3D visualization technology to achieve 3D observation of the linear guide rail hardened layer.

2. The method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail according to claim 1, characterized in that: The linear guide rail to be tested only needs to arrange a multi-channel water immersion ultrasonic probe group on a single side to perform shear wave detection to obtain the corresponding point coordinate values on the hardened layer contour curve on this side, while the corresponding point coordinate values on the hardened layer contour curve on the other side are directly obtained through coordinate conversion in a mirror-symmetrical manner in the linear guide rail coordinate system.

3. The method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail according to claim 1, characterized in that: Multi-channel water immersion ultrasonic probe groups need to be arranged on the two side surfaces of the linear guide rail to be tested to perform shear wave detection to obtain the corresponding point coordinate values on the hardened layer contour curve on this side.

4. The method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail according to claim 1, characterized in that: In said S1, when converting the hardened layer depth data of each detection point into the corresponding point coordinate value on the hardened layer contour curve in the linear guide rail coordinate system, for any detection point, a linear guide rail coordinate system is established with the center point of the bottom edge of the cross section of the linear guide rail to be measured as the origin, the bottom edge of the cross section as the horizontal axis, and the symmetry center line of the cross section as the vertical axis. Then, based on the chip center coordinates, water sound path and hardened layer depth of each ultrasonic probe, the point coordinates corresponding to the reflection point of the sound beam emitted by the ultrasonic probe on the hardened layer contour curve are obtained through coordinate transformation.

5. The method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail according to claim 1, characterized in that: The fitting function of the hardened layer profile curve adopts a 4th order polynomial or a 2nd order sine fitting function.

6. The method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail according to claim 1, characterized in that: In the B-scan image of the guide rail hardened layer contour, the hardened layer area enclosed by the hardened layer contour fitting curve and the cross-sectional outer contour line needs to be discretized into a pixel matrix according to a preset resolution. The hardened layer contour fitting curve is visualized as discrete points, and each row of pixels corresponds to one discrete point of visual display.

7. The method for nondestructive detection and three-dimensional visualization of the depth profile of the hardened layer of a linear guide rail according to claim 1, characterized in that: The hardness value of each pixel in the guide rail hardened layer hardness B scanning image is converted into a grayscale value and visualized according to a preset visualization effect.

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