CN110363767B - Gridding ultrasonic tomography detection method for shaft workpiece defects - Google Patents
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Abstract
A gridding ultrasonic tomography detection method for shaft workpiece defects is characterized in that an end face area at one end of a workpiece is gridded and divided, a grid center is used as an ultrasonic probe sampling point, time domain signals of each sampling point are sequentially collected by an ultrasonic pulse echo method and then converted into depth signals in space, echo amplitude values corresponding to each depth are obtained, the positions of the defect echoes are clearly positioned, and the detection of the shaft workpiece internal defects is realized; the invention also considers the sound beam diffusivity, superposes all the amplitudes of the reflected signals capable of being diffused to a certain position, reconstructs the echo amplitudes of cross sections at different depths in the workpiece by adopting the amplitude data after superposition processing and displays the information of the cross sections in the workpiece by tomography, thereby not only effectively identifying the depth and two-dimensional distribution of the defects at the position, but also greatly improving the detection rate of the defects. The invention does not need to arrange a complex scanning array, realizes comprehensive, visual and effective detection and positioning imaging on the internal defects of shaft workpieces, reduces the difficulty of detection operation, and improves the operation efficiency, the detection rate and the reliability of detection results.
Description
Technical Field
The invention relates to the technical field of ultrasonic nondestructive testing, in particular to a gridding ultrasonic tomography detection method for shaft workpiece defects.
Background
The shaft workpiece is one of the most common parts and vulnerable parts in various mechanical equipment, and the defects of the shaft workpiece can cause a series of problems of severe vibration and noise generation of the machine, and even can cause damage to the equipment. The ultrasonic detection has strong penetrating power, high sensitivity, low cost and high speed, and can detect large steel forgings as long as several meters, so the ultrasonic nondestructive detection method is suitable for detecting shaft workpieces.
However, the traditional shaft ultrasonic detection mostly adopts a radial detection and continuous scanning along the circumference, and the mode has high labor intensity of detection personnel and low detection efficiency; meanwhile, the processing of the echo data is based on the assumption that the signals emitted by the probe are only radiated straightly from the axis of the probe, however, in the actual detection, the beams radiated by the ultrasonic wave source are not radiated straightly from the ultrasonic wave source, but are radiated outwards at a certain angle, so that the situation that the processed echo data cannot accurately reflect the defects fundamentally is caused by the assumption. In addition, conventional imaging for detecting defects is displayed by A, B, C, D scanning, and the defect position and range cannot be intuitively judged by traversing the detection condition of each detection surface.
Disclosure of Invention
In order to solve the technical problem, the invention provides an ultrasonic detection method of gridding tomography of shaft workpiece defects, which comprises the following steps:
step 3, sound path conversion treatment: converting the ultrasonic pulse echo signal into a depth signal, namely an echo signal on a half sound path;
and 4, superposition processing: performing square gridding superposition processing on the amplitude data of the echo signals on each sound path in the probe detection sound beam coverage circular area based on the sound beam half diffusion angle theta, which specifically comprises the following steps:
step 401, calculating a half diffusion angle theta of the sound beam of the probe, and calculating a diffusion distance and a coverage circle area of the detection sound beam corresponding to each echo signal according to theta, wherein the diffusion distance M is a distance between a boundary of the detection sound beam of the probe on the internal cross section of the workpiece corresponding to the echo signal and a central axis of the sound beam, the coverage circle area is a circular area with the diameter of 2 × M, and the center of the circle is a center of the coverage circle;
projecting the grids divided by the scanned end face on the covering circle area along the axial direction of the workpiece, so as to correspondingly grid the covering circle area, namely realizing the probe sound beam diffusion gridding; the grids at the center of the covering circle are central grids, and grids which are sequentially diffused outwards from the central grids at intervals of L in the covering circle region form a plurality of square-shaped regions;
step 402, calculating signal amplitudes corresponding to the central grids in the coverage circular area and the grids in each square-shaped area of the detection sound beam corresponding to each echo signal, thereby obtaining the gridded amplitude distribution data in the coverage circular area;
step 403: amplitude superposition: calculating the internal cross sections of the workpieces to be tested, where all echo signals are located, and converging echo signal data of corresponding different sampling points according to the same cross section; when the sound beam coverage circular areas of different sampling points on the same cross section are overlapped, the amplitude of the overlapped square grids is the superposition of the signal amplitudes corresponding to the grids in the different coverage circular areas;
step 5, normalization treatment: mapping the amplitude data in the ultrasonic echo superposition data obtained in the step 4 to a range of 0-1;
step 6, tomography: and (5) carrying out pseudo-color image processing on the echo signal data processed in the step (5), and presenting the condition of each echo signal cross section slice in the shaft workpiece to be detected by adopting tomography, so that ultrasonic detection tomography in the workpiece to be detected is realized and is used for identifying and positioning the defect signal.
Furthermore, in order to ensure that the ultrasonic detection meets the requirement of coverage rate of not less than 20 percent, the side length L of the square grid is less than or equal to
On a scanned end face, a three-dimensional coordinate system is established by taking a vertex of a round circumscribed square where the scanned end face is located as a coordinate origin and the axial direction of the workpiece as a z-axis, and square grids are sequentially divided along an x-axis and a y-axis by taking the coordinate origin as a starting point and taking L as a side length.
Further, the sound path conversion treatment in step 3 specifically includes:
step 301: acquiring echo signal data, and acquiring an ultrasonic scanning signal according to the corresponding relation between the propagation time and the signal amplitude, namely a time domain signal of the echo signal with the propagation time as a horizontal axis and the signal amplitude as a vertical axis;
step 302: and calculating the corresponding relation between the half propagation sound path and the signal amplitude through the corresponding relation among the sound velocity, the propagation time and the propagation sound path to obtain a spatial depth signal, namely the spatial signal of the echo signal with the depth from the detection end surface as a horizontal axis and the signal amplitude as a vertical axis.
Further, in step 4, the half spread angle θ of the acoustic beam is 29(λ/D), where λ is the longitudinal ultrasonic wave wavelength.
Further, the normalization processing in step 5 specifically includes: in the amplitude superposition result data obtained in step 5, the maximum value of all the amplitudes V is taken as VmaxTaking the minimum value of all amplitude values as VminThen according to the normalization formula V ═ V-Vmin)/(Vmax-Vmin) All the magnitude data V are mapped to the range of 0-1.
Further, in step 6, the processing of the pseudo-color image on the echo signal data processed in step 5 is specifically: and 5, according to the amplitude normalization data of the ultrasonic echo signals obtained in the step 5, marking the color of the square grid of the internal cross section of the workpiece corresponding to each amplitude according to the conversion from the color A to the color B.
Further, in the step 6, the internal condition of each section cross section of the shaft workpiece to be detected is presented by adopting tomography, specifically,
step 601, mapping the V' obtained in the step 5 to RGB values, and performing pseudo-color coloring on corresponding grids;
and step 602, the distance between each cross section corresponding to all echo signals and the scanned end surface is z coordinate data of corresponding echo signal position coordinates, the sequence labels of corresponding sampling points represent (x, y) coordinate data of the corresponding sampling points, and amplitude distribution images of all echo corresponding to different depth cross sections are reconstructed in a three-dimensional coordinate system according to a pseudo-color coloring result, so that ultrasonic detection tomography inside the workpiece to be detected is realized and used for identifying and positioning defect signals.
For the cylindrical forging piece such as the shaft workpiece, the end surface of the shaft is detected by a pulse reflection method, and compared with the prior art, the invention has the beneficial effects that:
1. for the field detection of the service shaft type workpiece, the complexity and the complication of circumferential manual scanning are avoided, particularly when B, C, D scanning is carried out by a fixed mechanical scanning frame which is inconvenient to set due to the limitation of environment and surrounding space, the detection of the whole internal defect of the workpiece can be finished only by adopting a mode of manually traversing one end face of the scanned workpiece, the operation method is simple and easy to learn, and the detection efficiency is high.
2. The grid detection is adopted, the whole end face is divided in a grid dividing mode, the detection area of each probe is determined, and then the detection path of each probe can be controlled to comprehensively traverse the whole end face, so that the shaft internal defects can be comprehensively, visually and effectively detected and positioned and imaged without setting a complex multi-probe or multi-beam scanning array, the operation difficulty of detection personnel is reduced, and the detection speed is increased.
3. The inherent beam diffusivity of the probe is considered, and the signal amplitude is superposed in the coverage circle area of the probe beam by calculating the half-diffusivity angle, so that the actual working principle of the ultrasonic probe is better met; compared with the traditional signal processing mode without considering probe diffusion, the two-dimensional distribution imaging display after amplitude superposition is more favorable for detecting tiny defects; particularly, under the condition of long sound path of a large shaft, the detection rate of the defects is increased, the detection sensitivity of the defects and the reliability of the detection result are improved, and the imaging quality is improved;
4. by adopting tomography, the image of each cross section corresponding to the reflection echo of the shaft workpiece to be detected is accurately presented, the defect is positioned more visually, quickly and accurately, the signal amplitude is superposed, the imaging quality of defect detection is greatly improved, and the depth and the position of the defect can be effectively identified.
Drawings
FIG. 1 is a block diagram of the method steps of the present invention;
FIG. 2 is a schematic structural diagram of a shaft workpiece to be measured according to the present invention;
FIG. 3 is a schematic diagram of the meshing of the present invention;
FIG. 4 is a schematic diagram of the ultrasonic travel time and the ultrasonic sound path according to the present invention;
FIG. 5 is a schematic diagram of detecting acoustic beam dispersion distance and coverage circle according to the present invention;
FIG. 6 is a schematic diagram of the calculation of the corresponding amplitudes of each mesh in the detection sound beam coverage circle region corresponding to the echo signal according to the present invention;
FIG. 7 is a schematic diagram of the signal path transformation and the corresponding amplitude interval of the path interval according to the present invention;
FIG. 8 is a flow chart of the overlay process of the present invention;
FIG. 9 is a block diagram of a tomography step according to the present invention;
FIG. 10 is a tomographic image of a cross-section of the interior of a workpiece, the left image being the result of disregarding probe acoustic beam propagation, and the right image being the result of disregarding probe acoustic beam propagation and amplitude stacking according to the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made in order to clearly understand the objects, technical solutions and advantages of the present invention with reference to the accompanying drawings.
The invention relates to a grid-scribing ultrasonic tomography detection method for shaft workpiece defects, which comprises the following steps, wherein the method comprises the following steps in a block diagram as shown in figure 1:
Fig. 2 is a schematic structural diagram of a shaft workpiece to be measured, and 1 shows the shaft workpiece to be measured; 2 denotes the ultrasonic longitudinal wave straight probe, the length z of the workpiece2One end face of the scanning end face is used as a scanning end face, wherein the diameter 2R of the scanning end face is 4000 mm; an ultrasonic longitudinal wave straight probe with the frequency of 2.5MHz and the diameter D of 20mm is selected. To ensure that the ultrasound measurements meet a coverage of not less than 20% repetition rateThe requirement is met, the sampling point can be fully covered by the probe, and the side length L of the square grid is less than or equal to
For convenience of operation, in this embodiment, L is 11mm, a schematic diagram of grid division is shown in fig. 3, a three-dimensional coordinate system is established with a vertex of a circular circumscribed square where a scanned end face is located as a coordinate origin and an axial direction of the workpiece as a z-axis, square grids are sequentially divided along an X-axis and a Y-axis with 11mm as a side length L of the square grid and the coordinate origin as a starting point, that is, the scanned end face is subjected to square grid division to jointly divide X rows and Y columns of square grids, and the sequence of rows and columns is used as a reference number, for example: the first row and the first column are (1, 1), the first row and the second column are (1, 2) … …, and so on, as shown in fig. 3, the scanning end face is divided into 10 rows and 10 columns in the vertical and horizontal directions in the present embodiment.
according to the method, an ultrasonic pulse echo method is adopted for detection, according to the step 1, 60 sampling points are marked on a scanned end face, the sampling points are sequentially traversed by a probe, and corresponding ultrasonic pulse echo signals w (n) are collected; according to the sequence labels of the rows and the columns of the two-dimensional plane of the scanning end surface of the sampling points, enabling the sampling points to correspond to the echo signals obtained by the points one by one;
step 3, sound path conversion treatment: performing spatial sound path conversion processing on the obtained time domain echo signal w (n), so as to convert the time domain echo signal w (n) into a depth signal, namely an echo signal on a half sound path;
the schematic diagram is shown in FIG. 4, wherein z2Is the length of the workpiece, 2 times z2Is the sound path reflected by the bottom surface of the workpiece, travel time t2The time taken to go through the sound path; z is a radical of1The depth of the internal defect of the workpiece from the scanned end face is expressed by 2 times z1The acoustic path through the reflection of the defect, travel time t1The time taken to go through the sound path.
And w (n) is expressed in the form of A scanning, namely w (n) is a two-dimensional curve with the horizontal axis as the receiving time of the echo signal and the vertical axis as the amplitude of the echo signal, and the ultrasonic travel time of the pulse echo is t, then:
2·z＝t·cL
wherein z is the axial distance between the echo reflection surface and the scanning end surface, i.e. the depth, 2. z is the corresponding sound path, cLThe sound velocity of the ultrasonic longitudinal wave on the shaft workpiece to be measured is used, and accordingly, the time domain signal w (n) is converted into a spatial sampling signal w (z) on a half sound path.
And 4, step 4: and (3) superposition processing: performing square gridding superposition processing on the amplitude data of the echo signals on each sound path in the probe detection sound beam coverage circular area based on the sound beam half diffusion angle theta, which specifically comprises the following steps:
step 401, when the sound pressure amplitude is reduced from the maximum value on the axis by a certain dB (for example, 3dB, 6dB, etc., in this embodiment, 3dB) the included angle between the sound beam boundary and the sound beam axis is the half-spread angle of the sound beam; a-3 dB half-spread angle θ of a circular wafer having a longitudinal wave wavelength λ and a diameter D of 29(λ/D);
calculating the distance z between the corresponding reflecting surface and the scanned end surface along the axial direction of the workpiece to be detected according to the travel time t of the reflected echo in the pulse echo signal, wherein the z is t.cLAnd/2, the diffusion distance M of the sound beam on the reflecting surface is z tan theta, the circular area covered by the sound beam is a circular area with the diameter of 2M, the center of the circle is hereinafter referred to as the center of the covered circle, and the center of the circle is the projection of the center of the probe on the inner cross section of the workpiece on which the reflecting surface is positioned.
Referring to fig. 5, when the detection sound beam encounters a defect inside a workpiece, the detection sound beam is reflected to form a defect echo, and on the cross section inside the workpiece where the defect is located, the distance between the diffusion boundary of the detection sound beam and the central axis of the detection sound beam is a diffusion distance M; in FIG. 5, the sound path 2 × p1And 2 x p4The included angle between the two is the half diffusion angle theta of the probe; 2 x p1Representing the path of the detection beam back and forth between the centre of the probe and the centre of the circle covered, 2 × p2Represents the middle point of the side length of the square grid at the center of the probe and the center of the circle covered by the probe (i.e. the side length from the center L/2 of the circle covered by the probeMidpoint of), 2 × p3Represents the sound path between the middle point of the side length of the adjacent square grid (namely the middle point of the side length of the square grid which is 3 × L/2 away from the circle center of the covering circle) which is diffused when the square grid at the circle center of the covering circle is diffused outwards4The sound path between the middle point of the side length of the adjacent square grid (that is, the middle point of the side length of the square grid which is 5 × L/2 away from the center of the circle covered by the circle) diffused when the square grid at the center of the circle covered by the probe diffuses two square grids outwards is shown, and fig. 5 only schematically shows the case that the covering distance of the detected sound beam only contains two grids diffused outwards, and the sound path is 2 × p1、2*p2、2*p3、2*p4The experienced travel times are t1、t2、t3、t4. By analogy, a plurality of grids covered by the sound beam in the detection sound beam coverage circular area corresponding to each echo signal can be calculated, the grids take the grid at the position of the center of the coverage circular circle as a central grid, and the grids which sequentially diffuse outwards at intervals of L form a plurality of square-shaped areas, so that the sound beam of the probe is diffused and meshed (see fig. 6).
Step 402, calculating signal amplitudes corresponding to the central grids in the coverage circle region and the grids in the square-shaped region of the detection sound beam corresponding to each echo signal:
comparing M with L/2 of each echo signal, (1) when M < ═ L/2 represents that the detection sound beam has no diffusion at the cross section of the defect, and the coverage circle region only comprises a central grid, and the corresponding amplitude of the grid is the maximum amplitude of the echo signal; (2) when L/2< M < ═ n +1) L/2, n is M divided by L/2 to get integer, detecting that the sound beam covered circle region contains central grid and n/2 square regions which are outwards diffused in sequence from the central grid at intervals of L, the amplitude corresponding to the grid in each square region is the maximum amplitude value in the sound path region corresponding to the region, thereby obtaining the gridded amplitude distribution data in the covered circle region;
schematic diagram of acoustic beam diffusion gridding referring to fig. 6, wherein the probe is located at (x, y) of the scanned end face, and the defects are respectively located at different depths in the workpieceOnly the internal cross sections (three sections from left to right) of the workpiece to be detected where the defects of three different depths are located are illustrated in fig. 6, the circular area with the diameter D corresponding to the central grid of the coverage circular area is a beam coverage area based on the assumption that a beam is not vertically propagated in the conventional ultrasonic detection, based on the assumption, the amplitude corresponding to the central grid of the coverage circular area is the maximum amplitude of the defect echo time domain signal, other areas of the coverage circular area are not covered by the detected acoustic beam, and the corresponding amplitude is zero; after the half diffusion angle theta of the sound beam is considered, three covering circular areas corresponding to three defect echoes are calculated according to the theta, and at the moment, the detection sound beam of the defect echo sequentially covers circular areas with the diameters of 1, 3 and 5 square grid side lengths; (1) burying the shallowest defect, wherein only a central grid is arranged in the coverage circle region, and the amplitude corresponding to the grid is the maximum amplitude of the echo time domain signal; (2) burying deeper defect, wherein the amplitude corresponding to the central grid in the coverage circle region is the maximum amplitude of the echo time domain signal, the interval 1 × L is diffused outwards from the central grid to form a square region, the amplitude corresponding to the eight grids in the region is the maximum amplitude in the corresponding sound path region in the echo time domain signal, namely the sound path 2 × p in fig. 52And 2. sup. p3Corresponding ultrasonic travel time interval (t)2，t3) The maximum value of the corresponding amplitude interval in the echo time domain signal; (3) burying the deepest defect, wherein the amplitude corresponding to the central grid in the coverage circle region is the maximum amplitude of the echo time domain signal; the interval 1 x L is diffused outwards from the central grid to form a first square-shaped area, and the amplitude values corresponding to the eight grids contained in the area are the amplitude maximum values in the corresponding sound path interval in the echo time domain signal, namely the sound path 2 x p in figure 52And 2. sup. p3Corresponding ultrasonic travel time interval (t)2，t3) The maximum value of the corresponding amplitude interval in the echo time domain signal; similarly, the distance 2 × L is spread outward from the central grid to form a second square-shaped region, and the amplitude values corresponding to the sixteen grids contained in the region are the maximum amplitude values in the corresponding acoustic path interval in the echo time domain signal, that is, the acoustic path 2 × p in fig. 53And 2. sup. p4Corresponding ultrasonic travel time interval (t)3，t4) In the echo time domainThe maximum value of the corresponding amplitude interval in the signal. And the depth of each cross section from the scanning end face is the z coordinate data of the corresponding echo signal data.
The detection beam of the deepest buried defect in fig. 6 and its diffusion distance M are shown in fig. 5; the echo time domain signal schematic diagram of the defect is shown in the upper diagram of fig. 7, four different sound paths, four different travel times and a travel time interval (t) can be seen after amplification through a capture window2，t3) And interval (t)3，t4) Schematic diagram of amplitude interval versus acoustic path interval is shown in the lower graph of fig. 7.
Step 403: amplitude superposition: calculating the internal cross sections of the workpieces to be tested, where all echo signals are located, and converging echo signal data of corresponding different sampling points according to the same cross section; when the sound beam coverage circular areas of different sampling points on the same cross section are overlapped, the amplitude of the overlapped square grids is the superposition of the signal amplitudes corresponding to the grids in different coverage circular areas. A flowchart of the overlay processing is shown in fig. 8;
step 5, normalization treatment: mapping the amplitude data in the ultrasonic echo superposition data obtained in the step 4 to a range of 0-1;
and (3) carrying out normalization processing on the superposed data: after the amplitude data are superposed, taking the maximum value in all the amplitudes V as VmaxTaking the minimum value of all amplitude values as VminThen according to the formula V' ═ V (V-V)min)/(Vmax-Vmin) All the magnitude data V are mapped to the range of 0-1.
Step 6: mapping the amplitude data to a pseudo-color value, performing pseudo-color image processing, and adopting tomography to present the internal condition of each section cross section of the shaft workpiece to be detected; the method comprises the following specific steps:
step 601, mapping the V' obtained in the step 5 to RGB values, and performing pseudo-color coloring on corresponding grids;
and step 602, the distance between each cross section corresponding to all echo signals and the scanned end surface is z coordinate data of corresponding echo signal position coordinates, the sequence labels of corresponding sampling points represent (x, y) coordinate data of the corresponding sampling points, and amplitude distribution images of all echo corresponding to different depth cross sections are reconstructed in a three-dimensional coordinate system according to a pseudo-color coloring result, so that ultrasonic detection tomography inside the workpiece to be detected is realized and used for identifying and positioning defect signals. The gridded three-dimensional coordinates are shown in FIG. 3 for a cross-sectional depth of 3900mm, for example: the 3900mm position of the 7 th column in the 1 st row is (1,7,3900), the 3900mm position of the 8 th column in the 2 nd row is (2,8,3900), … …, and so on, and the spatial position data of the grid is set for data reconstruction.
Aiming at the detection situation of the shaft type object, the invention divides each sampling point by using a grid, acquires an ultrasonic echo signal of each sampling point through a straight probe, obtains a coverage circle area of a detection sound beam on the internal cross section of a workpiece corresponding to the echo based on a diffusion angle, superposes the amplitudes of different 'square' -shaped diffusion grids in the range, thereby obtaining the echo intensity after the superposition of the grid amplitudes, presents slice cross section tomography through a false color image of the grid corresponding to the amplitudes, and compares the imaging results of not considering probe sound beam diffusion and carrying out amplitude superposition, referring to figure 10, which shows that the defect imaging effect is more obvious under the condition of considering sound beam diffusion, the detection sensitivity to tiny defects is higher, and the invention is more suitable for the detection of large-scale shaft type tiny defects.
Compared with the traditional detection mode, the mode of scanning the end surface of the single probe point by point reduces the operation difficulty of detection personnel and improves the detection efficiency; meanwhile, the amplitude superposition processing of the probe diffusion reality is considered, the detection rate of small defects is improved, and the reliability of the detection result is improved.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (7)
1. A gridding ultrasonic tomography detection method for shaft workpiece defects is characterized by comprising the following steps:
step 1, grid division: dividing square grids with the side length of L on the scanned end face of the workpiece according to the diameter D of the ultrasonic straight probe and the size of the end face of the shaft workpiece to be detected, wherein each grid corresponds to a sampling point;
step 2, echo acquisition: taking the center of the square grid as a probe central point, sequentially placing the probes at the sampling points, and receiving ultrasonic pulse echo signals;
step 3, sound path conversion treatment: converting the ultrasonic pulse echo signal into a depth signal, namely an echo signal on a half sound path;
and 4, superposition processing: performing square gridding superposition processing on the amplitude data of the echo signals on each sound path in the probe detection sound beam coverage circular area based on the sound beam half diffusion angle theta, which specifically comprises the following steps:
step 401, calculating a half diffusion angle theta of the sound beam of the probe, and calculating a diffusion distance and a coverage circle area of the detection sound beam corresponding to each echo signal according to theta, wherein the diffusion distance M is a distance between a boundary of the detection sound beam of the probe on the internal cross section of the workpiece corresponding to the echo signal and a central axis of the sound beam, the coverage circle area is a circular area with the diameter of 2 × M, and the center of the circle is a center of the coverage circle;
projecting the grids divided by the scanned end face on the covering circle area along the axial direction of the workpiece, so as to correspondingly grid the covering circle area, namely realizing the probe sound beam diffusion gridding; the grids at the center of the covering circle are central grids, and grids which are sequentially diffused outwards from the central grids at intervals of L in the covering circle region form a plurality of square-shaped regions;
step 402, calculating signal amplitudes corresponding to the central grids in the coverage circular area and the grids in each square-shaped area of the detection sound beam corresponding to each echo signal, thereby obtaining the gridded amplitude distribution data in the coverage circular area;
step 403: amplitude superposition: calculating the internal cross sections of the workpieces to be tested, where all echo signals are located, and converging echo signal data of corresponding different sampling points according to the same cross section; when the sound beam coverage circular areas of different sampling points on the same cross section are overlapped, the amplitude of the overlapped square grids is the superposition of the signal amplitudes corresponding to the grids in the different coverage circular areas;
step 5, normalization treatment: mapping the amplitude data in the ultrasonic echo superposition data obtained in the step 4 to a range of 0-1;
step 6, tomography: and (5) carrying out pseudo-color image processing on the echo signal data processed in the step (5), and presenting the condition of each echo signal cross section slice in the shaft workpiece to be detected by adopting tomography, so that ultrasonic detection tomography in the workpiece to be detected is realized and is used for identifying and positioning the defect signal.
2. The method as claimed in claim 1, wherein the side length L of the square grid is less than or equal to 20% to ensure that the ultrasonic inspection satisfies the requirement of not less than 20% coverage rate
On a scanned end face, a three-dimensional coordinate system is established by taking a vertex of a round circumscribed square where the scanned end face is located as a coordinate origin and the axial direction of the workpiece as a z-axis, and square grids are sequentially divided along an x-axis and a y-axis by taking the coordinate origin as a starting point and taking L as a side length.
3. The gridding ultrasonic tomography detection method for the shaft workpiece defects according to claim 1, wherein the acoustic path conversion treatment in step 3 is specifically:
step 301: acquiring echo signal data, and acquiring an ultrasonic scanning signal according to the corresponding relation between the propagation time and the signal amplitude, namely a time domain signal of the echo signal with the propagation time as a horizontal axis and the signal amplitude as a vertical axis;
step 302: and calculating the corresponding relation between the half propagation sound path and the signal amplitude through the corresponding relation among the sound velocity, the propagation time and the propagation sound path to obtain a spatial depth signal, namely the spatial signal of the echo signal with the depth from the detection end surface as a horizontal axis and the signal amplitude as a vertical axis.
4. The method for detecting the shaft workpiece defect by gridding ultrasonic tomography according to claim 1, wherein the half divergence angle θ of the sound beam in step 4 is 29(λ/D), wherein λ is the wavelength of the ultrasonic longitudinal wave.
5. The gridding ultrasonic tomography detection method for the shaft workpiece defects according to claim 1, wherein the normalization processing in step 5 specifically comprises: in the amplitude superposition result data obtained in step 4, the maximum value of all the amplitudes V is taken as VmaxTaking the minimum value of all amplitude values as VminThen according to the normalization formula V ═ V-Vmin)/(Vmax-Vmin) All the magnitude data V are mapped to the range of 0-1.
6. The gridding ultrasonic tomography detection method for shaft workpiece defects according to claim 1, wherein in step 6, the echo signal data processed in step 5 is subjected to pseudo-color image processing, specifically: and 5, according to the amplitude normalization data of the ultrasonic echo signals obtained in the step 5, marking the color of the square grid of the internal cross section of the workpiece corresponding to each amplitude according to the conversion from the color A to the color B.
7. The method for detecting the defects of the shaft workpieces through the gridding ultrasonic tomography is characterized in that in the step 6, the tomography is adopted to present the internal conditions of the cross sections of all the slices of the shaft workpieces to be detected, specifically,
step 601, mapping the V' obtained in the step 5 to RGB values, and performing pseudo-color coloring on corresponding grids;
step 602, sequentially labeling sampling points according to the spatial positions of the sampling points on the two-dimensional plane of the scanned end surface, so that the sampling points correspond to echo signals obtained by the sampling points one by one, and the sequential labels of the sampling points represent (x, y) coordinate data of the sampling points; the distance between each cross section corresponding to all echo signals and the scanned end face is z coordinate data of corresponding echo signal position coordinates; and reconstructing amplitude distribution images of all the echoes corresponding to different depth sections in a three-dimensional coordinate system according to the pseudo-color coloring result, thereby realizing ultrasonic detection tomography inside the workpiece to be detected and being used for identifying and positioning the defect signals.
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