Nondestructive testing and three-dimensional visualization method for depth profile of hardening layer of linear guide rail

Abstract

The invention discloses a nondestructive testing and three-dimensional visualization method for the depth profile of a hardening layer of a linear guide rail, and belongs to the field of nondestructive testing. The method comprises the following steps: detecting a guide rail by using a multi-channel water immersion ultrasonic probe group to obtain hardening layer depth data and converting the hardening layer depth data into coordinate values; fitting a hardening layer contour curve by using the coordinate values to obtain a function expression; generating a hardening layer contour B scanning image by combining the guide rail contour and the hardening layer contour curve; according to the relation between the depth and the hardness, a hardening layer hardness B scanning image is generated through conversion; and finally, carrying out three-dimensional reconstruction on the depth contour of the hardening layer and the hardness B scanning image to realize three-dimensional observation of the hardening layer of the linear guide rail. According to the method, the depth profile curve of the hardening layer of the linear guide rail can be predicted by using a few points through an ultrasonic nondestructive testing method, three-dimensional observation is realized, and the visibility is improved.

Description

Technical Field

[0001] The 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] The traditional methods for measuring the depth of the hardened layer are microhardness method and metallographic method. The microhardness method requires measuring the hardness value point by point on the surface of the guide rail, which has low detection efficiency and high skill requirements for operators, and is prone to measurement errors due to human factors. The metallographic method requires destructive treatment such as cutting, polishing and acid etching of the guide rail, which not only damages the workpiece, but also has a cumbersome detection process and high cost. In addition, neither of these two methods can achieve intuitive visualization of the depth profile of the hardened layer, and it is difficult to meet the needs of efficient and non-destructive testing in modern industrial production. In contrast, ultrasonic backscattering technology uses the material characterization information carried by ultrasonic backscattering signals to achieve non-destructive and rapid detection of the depth of the hardened layer. However, the existing ultrasonic detection technology still faces many challenges when applied to complex cross-section guide rails. On the one hand, due to the coupling problem between the probe and the guide rail surface, the traditional contact ultrasonic detection method is difficult to obtain a stable ultrasonic signal on the complex shape cross section of the guide rail, resulting in a decrease in detection accuracy. On the other hand, the existing ultrasonic detection technology can usually only provide single-point or local hardened layer depth information, and cannot fully and intuitively display the distribution of the hardened layer depth profile. In addition, for guide rails with complex cross-sections, existing ultrasonic testing methods are difficult to achieve a comprehensive assessment of the entire cross-section, and the detection range is limited. Therefore, the present invention adopts ultrasonic backscattering detection technology to propose a non-destructive detection and three-dimensional visualization method for the depth profile of the guide rail hardening layer.

[0003] Linear guides need to bear loads and maintain high-precision and smooth linear reciprocating motion during use. The main failure forms are contact fatigue damage and plastic deformation. Therefore, the working surface of the guide must have characteristics such as high hardness, high strength, high toughness and high wear resistance, which requires the working surface of the guide to be quenched and heat treated to meet technical requirements such as surface hardness and hardened layer depth. After quenching, the organization and properties of the surface layer and the core of the steel differ, forming a hardened layer organization. In the hardened layer, the microhardness distribution is relatively uniform, and the microhardness changes in a gradient from the hardened zone to the transition zone and then to the substrate. The depth of the hardened layer is a key factor in determining the strength, load-bearing capacity and wear resistance of the guide. Its consistency is the basis of the geometric accuracy and guiding accuracy of the guide. Insufficient depth of the hardened layer will make the guide more prone to fatigue failure when subjected to alternating loads. Therefore, accurately and quickly detecting the depth of the hardened layer of the linear guide is an important technical issue to improve the quality of the guide, optimize the process flow and realize intelligent manufacturing.

[0004] Conventional ultrasonic waves include longitudinal waves and shear waves. Shear waves are more sensitive to changes in the shear modulus of the material, respond more strongly to changes in the microstructure, and decay more slowly in the material. Therefore, shear waves can more effectively distinguish the microstructural differences between the hardened layer and the base material. By analyzing the time delay, amplitude, frequency, and phase change characteristics of the signal, the internal state of the material can be accurately evaluated to achieve non-destructive testing.

[0005] During the inspection process, due to the limitation of the rail model, the size of the part to be inspected is small and the geometric features are complex. When using a contact flat probe for inspection, some rail sections cannot generate effective shear waves. The reason is that the probe coupling surface is small, and the chip diameter is larger than the coupling surface width, resulting in the inability of the sound beam to fully enter and reflect at the bottom of the wedge, causing the sound wave to be turbulent and unable to form an effective ultrasonic shear wave.

[0006] In the detection of the depth of the hardened layer of the guide rail, the ultrasonic A-scan signal of the depth of the hardened layer of the guide rail can be obtained through ultrasonic backscatter detection technology. However, the B-scan image can more intuitively display the cross-sectional information of the workpiece. The traditional B-scan image uses an ultrasonic phased array probe to control the chip excitation time to achieve beam deflection and focusing. However, due to the complex shape of the guide rail cross section, only part of the detection surface can receive the ultrasonic echo. Scanning with multiple chip deflection angles will increase the cost of research and development and testing, so it is impossible to directly use the phased array probe to obtain the ultrasonic B-scan image of the guide rail cross section. Summary of the invention

[0007] Based on this, it is necessary to provide a non-destructive detection and three-dimensional visualization method for the depth profile of the hardened layer of a linear guide rail, in order to solve the problem that the depth profile distribution of the hardened layer of the linear guide rail cannot be intuitively obtained through non-destructive methods. Compared with the existing methods, the present invention not only solves the limitations of the existing technology through innovative detection technology and visualization methods, but also achieves significant improvements in detection accuracy, efficiency, visualization effect, scope of application and cost-effectiveness, and 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 steps of which include:

[0009] 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 to be tested, place the linear guide to be tested in water, and use a multi-channel immersion ultrasonic probe group to synchronously transmit a focused acoustic beam to each detection point in the form of scanning along the guide direction for 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 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 point coordinate value data obtained by conversion to obtain a fitting curve expression of the hardened layer contour curve, and then a guide rail hardened layer contour B scanning image 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, 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 a guide rail hardened layer hardness B scanning image;

[0011] S3. The B-scan images of the guide rail hardened layer contour and the B-scan images of the guide rail hardened layer hardness obtained from different guide rail cross sections are reconstructed in three dimensions using the three-dimensional image visualization technology to achieve three-dimensional observation of the linear guide 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 water immersion ultrasonic probe groups need to be arranged on two side surfaces of the linear guide rail to be tested to perform shear wave detection to obtain corresponding point coordinate values ​​on the hardened layer contour curve of this side.

[0014] As a preferred embodiment of the above-mentioned first aspect, when performing shear wave detection on the linear guide to be tested, the linear guide 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 at the first critical incident angle of the water-steel coupling interface, and during the scanning process along the guide direction, 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 the hardened layer depth data of each detection point is converted into the corresponding point coordinate value on the hardened layer contour curve in the linear guide coordinate system, 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 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 acoustic 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 cross section using a microhardness method.

[0018] As a preferred embodiment of the first aspect, the fitting function of the hardened layer profile curve adopts a 4th order polynomial or a 2nd order sinusoidal 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 visualized 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) The present invention 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, and combining VTK and Python for 3D reconstruction. Users can intuitively observe the distribution of the hardened layer from multiple angles and discover potential defects in a timely manner, 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 guides 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 reduces the testing cost. In addition, the fast testing speed and intuitive visualization results can help users make decisions faster, further improving economic benefits.

[0027] (6) The technical solution of the present invention has the potential to be integrated with an automated production line, and can achieve real-time monitoring and automated evaluation of the depth of the guide rail hardening layer. By combining with the industrial Internet and big data technology, the level of intelligence in the production process can be further improved, providing technical support for intelligent manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 2 Schematic diagram of the probe arrangement and detection point distribution for multi-channel water immersion focusing detection of complex-shaped cross-sections of guide rails.

[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.

[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 cross section of the linear guide, of which the left, middle and right are respectively the distribution diagram of the hardened layer of the linear guide cross section according to the metallographic method, the B-scan diagram of the contour of the hardened layer of the linear guide cross section, and the B-scan image of the hardness of the hardened layer of the linear guide.

[0034] Figure 7 It is the time series of the hardened layer profile and hardness B scanning image of the linear guide.

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

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

[0037] Fig.10 The three-dimensional visualization result of the hardened layer profile of the linear guide.

[0038] Fig.11 The three-dimensional reconstruction process of the hardness of the hardened layer of the linear guide.

[0039] Fig.12 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 purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with 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 different from 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 each embodiment 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 comprises 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 to be tested, place the linear guide to be tested in water, and use a multi-channel water immersion ultrasonic probe group to synchronously emit a focused acoustic beam to each detection point in the form of scanning along the guide direction for 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 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 too many required water immersion ultrasonic probes, and higher requirements for equipment and detection operations. 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 not actually 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 measured, in order to ensure the synchronization and accuracy of the measurement, a multi-channel water immersion ultrasonic probe group composed of multiple water immersion ultrasonic probes can be used. Each water immersion ultrasonic probe is aimed at a detection point to emit a focused ultrasonic shear wave sound beam. Different water immersion ultrasonic probes in the multi-channel water immersion ultrasonic probe group are synchronously transmitted and signal received, and ultrasonic backscatter detection signals at each detection point are obtained at the same time, thereby obtaining the corresponding hardened layer depth data at different detection points on the cross section. In addition, 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 sound beam will be synchronously emitted to each detection point for shear wave detection to obtain the ultrasonic backscatter detection signal on this cross section. Based on these ultrasonic backscatter detection signals, the distribution of the hardened layer thickness of each cross section can be reconstructed later, thereby realizing the three-dimensional visualization of the entire linear guide.

[0045] The reason for using a 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 comprehensive evaluation of the complex shape cross-section of the guide rail can be achieved. When performing the specific detection operation, the linear guide to be tested is placed in a water tank, and two groups of multi-channel water immersion focusing ultrasonic probe groups are used to respectively detect the important surfaces on both sides of the linear guide to be tested, and the obtained ultrasonic A-scan signals are saved in time to achieve a comprehensive evaluation of the complex shape cross-section of the linear guide.

[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 tested has two side surfaces, both of which are processed with hardened layers, the present invention needs to construct two hardened layer contour curves for a cross section, that is, the hardened layer contour curves on both sides need to be constructed 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 the practice of measuring both sides, a multi-channel immersion ultrasonic probe group needs to be arranged on both sides of the linear guide to perform shear wave detection to obtain the corresponding point coordinate values ​​on the hardened layer contour curve of this side. Then, the corresponding point coordinate values ​​on the hardened layer contour curves on both sides are used to fit the hardened layer contour curves of each side.

[0048] For the method of single-side measurement and then mirror-symmetric conversion, the linear guide to be tested only needs to arrange a multi-channel water immersion ultrasonic probe group on a single side for 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 by coordinate conversion in a mirror-symmetric manner in the linear guide coordinate system. Then, the corresponding point coordinate values ​​on the hardened layer contour curves on both sides are used to fit their respective hardened layer contour curves.

[0049] Below 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 a linear guide to be tested and fit the hardened layer profile curve.

[0050] exist Figure 2 In the exemplary linear guide shown, there are symmetrical hardened layers on both sides. During the use of the linear guide, the hardened layer on its side needs 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 according to specific detection requirements. Figure 2 Six detection points on the outer contour curve on the right side of the cross section were selected, and corresponding ultrasonic backscatter detection probes were set to detect the depth of the hardened layer. Among the six detection points of the cross section, there are 4 straight segments and 2 curved segments with fixed curvature, the straight segments are III, IV, V, VI, and the curved segments are I and II. Since the linear guide is a continuous strip, the above 4 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. Combined with the working state of the guide, the two surfaces I and IV are mainly the contact surfaces of the rollers in the guide slider, which need to have high wear resistance; at the same time, I and III are also important 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 certain tensile and compressive deformations.

[0051] Based on the 6 detection points selected above, shear wave detection is performed on the linear guide to be tested. The specific method is: immerse the linear guide to be tested in a water tank, and arrange a 6-channel water immersion ultrasonic probe group 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 at the first critical incident angle of the water-steel coupling interface (the contact surface between the side wall of the guide and the water). During the scanning process along the guide direction, 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 depth of the hardened layer 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 of 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 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 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.

[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 this Cartesian coordinate system, the midpoint of the bottom side of the cross section of the guide rail is taken as the origin, the bottom side of the cross section is taken as the X-axis, and the symmetric center line of the cross section is taken as the Y-axis. According to the requirements of the detection 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. The respective detection water acoustic paths are recorded as H1, H2, H3, H4, H5, and H6, respectively. The center position of the probe wafer can be obtained by using the fixed outer dimensions of the linear guide rail, and the coordinates of the probe wafer center are recorded. 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). 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 to obtain the depth of the hardened layer at each detection point.

[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 ultrasonic shear waves is almost unobservable. However, when the ultrasonic wave passes through the transition zone, the sound wave is significantly scattered due to the change in the microstructure. Assuming that the acoustic time difference between the surface wave and the backscattered signal is t, t is the acoustic wave flight time between the surface wave and the backscattered signal at the detection point, then the depth (HD) of the hardened layer at the detection point can be obtained 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] In the formula, c 1 is the propagation speed of ultrasound in water, c 2 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 impinges on the water-steel coupling interface), and β is the shear wave propagation angle in the hardened layer.

[0062] Based on the above hardened layer depth calculation method, the hardened layer depths 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 used to calculate the center coordinates of the wafer 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 in the manner of "the horizontal coordinates are opposite numbers and the vertical coordinates remain unchanged", thereby obtaining 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; then, according to the hardened layer contour fitting curves on both sides of the guide rail and the outer contour line of the cross section, a guide rail hardened layer contour B scanning image at the current cross-sectional position is generated; 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 a guide rail hardened layer hardness B scanning image.

[0066] It should be noted that, since a series of data at different guide rail cross sections are detected during the probe scanning process, each guide rail cross section can obtain point data on the hardened layer profile curve on both sides, so it is necessary to fit the hardened layer profile curve on both sides of each guide rail cross section respectively. The fitting function of the hardened layer profile curve needs to be optimized and selected according to the actual profile curve. In an 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] In the formula: 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] In the formula: p1, p2, p3, p4, p5 are the fitting coefficients respectively.

[0073] In addition, the mapping relationship between the depth of the hardened layer and the hardness can be obtained by fitting according to the actual experimental data. In the traditional hardened layer depth detection method, the hardness value of the guide rail section is often measured by the microhardness method, and the depth of the hardened layer is judged by distinguishing the hardness changes of the hardened layer and the core structure. In the embodiment of the present invention, the hardness value of the linear guide rail section at different hardened layer depths can be measured by the microhardness method and then fitted to obtain the above mapping relationship. Figure 5 The figure shows the mapping relationship obtained by fitting after the microhardness measurement of a linear guide rail in the present invention. 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, its hardness gradually decreases. Figure 5 It can be seen that 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 hardened layer of the guide rail using water immersion ultrasonic shear wave detection, the mutation boundary of the hardness value can be confirmed, and then the hardness value can be determined according to the change of the hardened layer depth. 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 B-scan images of the guide rail hardened layer contour and the B-scan images of the guide rail hardened layer hardness obtained from different guide rail cross sections are reconstructed in three dimensions using the three-dimensional image visualization technology to achieve three-dimensional observation of the linear guide hardened layer.

[0075] It should be noted that the three-dimensional visualization technology of the image required for three-dimensional reconstruction can be selected according to actual needs. However, in three-dimensional visualization, the display is often displayed at a fixed resolution. Therefore, in the above-mentioned 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 the preset resolution, and the hardened layer contour fitting curve is visualized as discrete points, and each row of pixels corresponds to 1 discrete point of visualization. Similarly, the hardness value of each pixel in the guide rail hardened layer hardness B scanning image can be converted into a grayscale value and visualized according to the preset visualization effect.

[0076] In the embodiment of the present invention, in a single B-scan image, each pixel point has the following information: the x-coordinate, y-coordinate and corresponding hardness value of the current pixel. Furthermore, by converting the hardness value and the grayscale value, the guide rail cross section hardness B-scan image is grayscaled, and the hardness information is expressed by the grayscale intensity. In this way, the hardness B-scan image has the same function as the ultrasonic B-scan image, and can characterize the hardness distribution on the guide rail cross section from a more intuitive perspective. Figure 6 The guide rail hardened layer contour B-scan image and the guide 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 contour B-scan image and the guide 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 of a single cross section and the B-scan image of the hardened layer hardness of the guide rail. However, since the ultrasonic probe is moved along the direction of 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 1. Figure 7 In the present invention, the 3D reconstruction method and the display effect of 3D observation can be selected according to the actual visualization effect requirements.

[0078] The specific method and technical effect of the above-mentioned linear guide hardened layer depth profile non-destructive detection and three-dimensional visualization method are demonstrated below through a specific embodiment.

[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 a hardened layer depth profile of the linear guide rail is described in detail.

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

[0082] Step 1: Referring to the above step S1, a set of 6-channel water immersion ultrasonic probes is used to detect the right surface of the linear guide rail to be tested. 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 effect, shape analysis is performed on the above 6 detection points. The processing drawings of the guide rail are investigated and it is known that the curvatures of the two curved surfaces Ⅰ and Ⅱ are fixed, with a curvature radius of 1.86mm and a central angle of 56.32°. Plane Ⅲ is 45° to the bottom surface of the guide rail and is 1.16mm long; plane Ⅳ is perpendicular to the bottom surface of the guide rail and is 1.61mm long; plane Ⅴ is 45° to the bottom surface of the guide rail and is 4.09mm long; plane Ⅵ is perpendicular to the bottom surface 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 sound waves.

[0084] In this embodiment, in order to meet such detection requirements, the sound beam width of the focusing probe needs to be strictly set to be less than or equal to the width of the detection surface. Here, 1 mm is set as the reference standard for the sound beam width. Combined with the focal zone diameter calculation formula 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, satisfying:

[0087]

[0088] Where: c 1 is the speed of ultrasound in water, c 3 is the speed of ultrasound in the chip, and R is the radius of curvature of the chip cylinder 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 is 20 MHz, and its wavelength in water is 0.075 mm. The relationship between the probe chip diameter and the focal length can be calculated as follows:

[0090]

[0091] Therefore, the focal length of the probe can be set as needed according to the established probe wafer diameter, so as to achieve the shear wave depth measurement of the measured surface. For example, if the probe wafer diameter is set to 6mm, the focal length of the probe 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] When the guide rail is tested for underwater shear wave, the immersion probe is fixed and the guide rail to be tested moves in a straight line, so that the multi-channel immersion ultrasonic probe group synchronously transmits a focused acoustic beam to each detection point in the form of scanning along the guide rail direction for shear wave detection, obtains an ultrasonic backscatter detection signal, and completes the detection of the entire guide rail. After the detection is completed, the obtained ultrasonic A-scan signal (i.e., the aforementioned ultrasonic backscatter detection signal) is analyzed and processed, and the signal data of each guide rail cross section during the scanning process is extracted based on the signal timestamp, and the hardened layer depth data of each detection point on the cross section is calculated based on the extracted data, and the coordinate values ​​of each fitting point in the hardened layer contour curve on both sides in the guide rail coordinate system are converted.

[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] In order to verify the accuracy of the hardened layer contour curve obtained by fitting in the present invention, the actual linear guide rail cross section is further polished and acid-etched in this embodiment, and the hardened layer distribution diagram of the guide rail cross section is photographed. The hardened layer contour is extracted using a computer vision algorithm, and the curve equation that best fits the contour points is found using a curve fitting tool. The specific steps are as follows:

[0098] First, the acid-etched image was grayed and denoised using Gaussian filtering (σ=1.5). Secondly, the image segmentation method used was based on the Otsu adaptive threshold algorithm to divide the distribution map of the hardened layer of the guide rail section into multiple objects and regions, and to separate the boundaries of the hardened layer regions. Next, the Canny algorithm (threshold 50~150) was used to accurately extract the boundaries of the hardened layer. Then, cv2.findContours() in OpenCV was used to obtain the hardened layer boundary point set and complete the contour point extraction. Finally, the 8th-order polynomial fitting (least squares method) was used to obtain the fitting curve equation; when there were missing boundary points, B-spline interpolation was used for smoothing.

[0099] Finally, a comparison was made on the consistency of 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, thereby 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 the above step S3, based on the 3D visualization technology of VTK and Python, the B-scan image sequence of the hardened layer depth profile is 3D reconstructed to generate the 3D visualization result of the hardened layer profile of the linear guide, and the 3D observation of the hardened layer profile of the linear guide is realized. At the same time, based on the 3D visualization technology of VTK and Python, the B-scan image sequence of the hardness of the hardened layer depth is 3D reconstructed to generate the 3D visualization result of the hardness of the linear guide, and the 3D observation of the hardness of the linear guide is realized.

[0101] In this embodiment, the exemplary linear guide rail hardened layer profile 3D reconstruction process is as follows: Fig. 9 The three-dimensional visualization result of the hardened layer profile of the linear guide obtained by using Python and VTK toolkit is shown in the figure. Fig.10 In an embodiment of the present invention, an exemplary linear guide rail hardened layer hardness three-dimensional reconstruction process is as follows: Fig.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. Fig.12 In the three-dimensional visualization result of the hardness of the hardened layer of the linear guide obtained in this example, the hardness value of the hardened layer is distinguished by color, where orange represents a larger 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 all fall within the protection scope 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, characterized in that: The following steps are involved: 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 to be tested, place the linear guide to be tested in water, and use a multi-channel immersion ultrasonic probe group to synchronously transmit a focused acoustic beam to each detection point in the form of scanning along the guide direction for 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 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 of the hardened layer contour curve, and then a guide rail hardened layer contour B scanning image 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, 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 a guide rail hardened layer hardness B scanning image; S3. The B-scan images of the guide rail hardened layer contour and the B-scan images of the guide rail hardened layer hardness obtained from different guide rail cross sections are reconstructed in three dimensions using the three-dimensional image visualization technology to achieve three-dimensional observation of the linear guide hardened layer.

2. A linear guide rail hardened layer depth profile nondestructive detection and three-dimensional visualization method as claimed in claim 1, characterized in that: The linear guide 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 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: The two side surfaces of the linear guide rail to be tested need to be respectively arranged with a multi-channel water immersion ultrasonic probe group to perform shear wave detection to obtain the corresponding point coordinate values ​​on the hardened layer contour curve of 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: When performing shear wave detection on the linear guide to be tested, the linear guide 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 at the first critical incident angle of the water-steel coupling interface. During the scanning process along the guide direction, 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.

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: 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.

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 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 acoustic 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.

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 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 cross section using a microhardness method.

8. 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.

9. 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-section 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 the visual display.

10. 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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