Laser ultrasonic detection device and method for internal defects of shaft parts

Abstract

The invention relates to a laser ultrasonic detection device and method for internal defects of shaft parts, and solves the problem that the existing laser ultrasonic detection mostly focuses on plane detection and is difficult to evaluate the internal damage of a cylindrical body of the shaft parts. A precise rotating clamping table is arranged on a workbench of the device, the axis of a detected shaft part is clamped on the precise rotating clamping table, a liftable controllable single-source three-point reflection focusing device is arranged around the detected shaft part, and three uniformly distributed focusing points S1, S2 and S3 are formed on the circumference of the detected shaft part at the same horizontal height. A double-frequency laser interferometer for collecting ultrasonic reflection signals is arranged on one side of the shaft part to be detected on the workbench, and the double-frequency laser interferometer is aligned with the surface of the shaft part to be detected to form a detection point T0. The three-point laser ultrasonic thermoelastic mode detection is carried out on the detected shaft part, three-dimensional reconstruction is carried out on the internal defect, the approximate shape and position of the internal defect are obtained, and the shape and position information of the internal defect of the detected shaft part is mastered.

Description

Technical Field

[0001] The present invention belongs to the field of laser ultrasonic testing, and particularly relates to a laser ultrasonic testing device and method for internal defects of shaft parts. Background Art

[0002] Traditional non-destructive testing methods mainly rely on contact technologies, but in harsh environments such as high temperature and corrosive conditions, these methods have problems of insufficient adaptability. In recent years, laser ultrasonic non-destructive testing technology has developed rapidly as an emerging technology. Ultrasonic waves are generated inside the detected material by laser excitation and then detected. Laser ultrasonic technology has the advantages of being flexibly adaptable to various conditions, surface shapes, and materials, and can detect target objects in extreme environments such as high temperature and high pressure. It is widely used in fields such as defect detection and material state monitoring. In addition, laser ultrasound also has characteristics such as multimode, wide frequency band, and high time resolution, showing great development potential.

[0003] As key load-bearing components in industry, shaft parts often have defects such as holes and crystallization inside, which will seriously affect the performance and service life of the parts. If the internal defects and their positions of shaft parts can be effectively and quickly detected, their quality and reliability will be significantly improved. Therefore, applying laser ultrasonic technology to the internal defect detection of shaft parts has important application prospects. However, existing laser ultrasonic testing technologies mostly focus on planar testing, and the technology for evaluating internal damage of the cylindrical shape of shaft parts is still lagging behind. Moreover, the geometric characteristics of the cylindrical surface further increase the difficulty of defect detection, becoming a major challenge in the field of laser ultrasonic testing. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that current laser ultrasonic testing mostly focuses on planar testing and it is difficult to complete the evaluation of internal damage of the cylindrical shape of shaft parts, and to provide a laser ultrasonic testing device and method for internal defects of shaft parts.

[0005] A laser ultrasonic testing device for internal defects of shaft parts, including a workbench, is characterized in that a precision rotating chuck is arranged on the workbench, and the axis of the measured shaft part is vertically clamped on the precision rotating chuck. A liftable controllable single-source three-point reflection focusing device is arranged around the measured shaft part. The controllable single-source three-point reflection focusing device forms three uniformly distributed focusing points S1, S2, and S3 on the circumference at the same horizontal height of the measured shaft part. A dual-frequency laser interferometer for collecting ultrasonic reflection signals is arranged on one side of the workbench for the measured shaft part. The dual-frequency laser interferometer aligns with the surface of the measured shaft part to form detection points T0, and T0 is 180 degrees apart from S1 and at the same horizontal height.

[0006] Preferably, the controllable single-source three-point reflection focusing device is connected to a pulsed laser. The pulsed laser and the controllable single-source three-point reflection focusing device are jointly arranged on the same precision lifting platform, and the dual-frequency laser interferometer is arranged on the same or another precision lifting platform.

[0007] Preferably, the pulsed laser is connected to a laser power supply, the laser power supply is connected to a control handle, and the laser power supply is connected to a PC.

[0008] Preferably, the precision lifting platform is connected to a PC.

[0009] Preferably, the dual-frequency laser interferometer is connected to a data acquisition card, and the data acquisition card is connected to a PC.

[0010] Preferably, the workbench is a self-balancing vibration isolation table, and the self-balancing vibration isolation table and the precision rotating chuck are both connected to a regulated and adjustable gas source.

[0011] A laser ultrasonic detection method for internal defects of shaft parts, using the above laser ultrasonic detection device, includes the following steps.

[0012] Step 1: Complete the installation and connection of the PC, laser power supply, pulsed laser, controllable single-source three-point reflection focusing device, dual-frequency laser interferometer, and data acquisition card, and install the shaft part to be measured on the precision rotating chuck.

[0013] Step 2: Turn on the experimental power supply, turn on the laser power supply and use the control handle to set the laser parameters. Adjust the controllable single-source three-point reflection focusing device so that the excitation beams are respectively located at three excitation points S1, S2, and S3 on the surface of the shaft part to be measured, and adjust the corresponding excitation spot sizes to match the shaft part to be measured. Turn on the dual-frequency laser interferometer and adjust the dual-frequency laser interferometer so that the detection beam is located at the detection point T0 on the surface of the shaft part to be measured.

[0014] Step 3: Open the detection and acquisition software on the PC, set the acquisition height H, the single-up height h0, and the single acquisition time t r , input the radius R of the shaft part to be measured and the internal ultrasonic shear wave velocity V S ;

[0015] Step 4: After the detection and acquisition software controls the precision rotating chuck to reset, control the pulsed laser to emit the excitation beam and control the dual-frequency laser interferometer to perform detection. Judge whether there is a defect echo. If all are regular echoes and there is no defect echo, return the defect-free information at this detection height, and adjust the rising height h0 of the two precision lifting platforms, and repeat the above detection; if a defect echo is detected, enter Step 5 and record the current adjusted rising times N until the total rising height reaches H.

[0016] Step 5: The acquisition software controls the controllable single-source three-point reflection focusing device to adjust the laser emitted by the pulsed laser to the excitation points S1, S2, and S3 in sequence and controls the dual-frequency laser interferometer for detection. Calculate and record the time intervals from excitation at each point to the arrival of the defect-reflected shear wave detected by the dual-frequency laser interferometer as t1, t2, and t3 respectively under the rising times N;

[0017] Step 6: Approximate the defect points in the shaft-like part to be measured as circular. According to the time of the defect-reflected shear wave from the excitation points S1, S2, and S3 to the detection point T0, calculate the three-reflection-point distribution elliptical curve of the defect circle;

[0018] Step 7: Establish a plane rectangular coordinate system x-y with the center of the cross-section of the shaft-like part to be measured as the origin 0,0-S1 as the Y-axis. Denote the center point of the defect circle as m and the radius as r, and establish a model in combination with the three-reflection-point distribution elliptical curve;

[0019] Step 8: Solve the coordinates of the center point m and the radius r of the defect circle in combination with the models in Steps 6 and 7, and save the data in the directory of the rising times N of the precision lifting table;

[0020] Step 9: Return to Step 4 and continue the detection.

[0021] Preferably, in Step 2, the excitation points S1, S2, S3, and the detection point T0 are at the same horizontal height. The excitation points S1, S2, S3 are spaced 120° from each other, and the detection point T0 is spaced 180 degrees from the excitation point S1.

[0022] Preferably, Step 6 is specifically: Approximate the defect points in the shaft-like part to be measured as circular. Excite at points S1, S2, and S3 in sequence, and obtain the detection signal at point T0 after each excitation; For the excitation point S1, the excited shear wave propagates inside the measured cylinder, encounters the edge of the defect circle and is reflected to the detection point T0. The reflection point of this reflected shear wave on the edge of the defect circle is K1. The propagation path P1 of this shear wave = L S1-K1 +L K1-T0 =V S t1. According to the acoustic reflection property, the normal line of the defect circle at point K1 bisects ∠S1K1T0. Then the reflection point K1 is distributed on an ellipse with S1 and T0 as the foci. Denote this ellipse as ellipse 1, with the origin as J1, and J1 coincides with the center of the cross-section of the shaft-like part to be measured. Its focal length c1 = 2R, the major axis minor axis And so on. When the excitation point is S2, the ultrasonic wave propagates inside the measured cylinder, encounters the defect circle and is reflected at the reflection point K2 and continues to propagate to the detection point T0. The path traveled by the ultrasonic wave P2 = L S2-K2 +L K2-T0 =VS t2. According to the reflection property of sound, the normal line passing through point K2 of the tangent line of the defect circle at point K2 bisects ∠S2K2T0. Then, the reflection points K2 are distributed on the ellipse edge with S2 and T0 as the foci. Denote this ellipse as ellipse 2, with the origin as J2, and its focal length c2 = R, major axis minor axis When the excitation point is S3, the ultrasonic wave propagates inside the measured cylinder, encounters the defect circle, reflects at the reflection point K3, and continues to propagate to the detection point T0. The distance traveled by the ultrasonic wave P3 = L S3-K3 +L K3-T0 =V S t3. According to the reflection property of sound, the normal line passing through point K3 of the tangent line of the defect circle at point K3 bisects ∠S3K3T0. Then, the reflection points K3 are distributed on the ellipse edge with S3 and T0 as the foci. Denote this ellipse as ellipse 3, with the origin as J3, and its focal length c3 = R, major axis minor axis

[0023]

[0024] Step 7 is specifically as follows: Establish a plane rectangular coordinate system x - y with the center of the cross - section as the origin O and O - S1 as the y - axis. Denote the center point of the defect circle as m, with a radius of r. Let the coordinates of point m be (x m , y m ), the coordinates of point K1 be (x K1 , y K1 ), the coordinates of point K2 be (x K2 , y K2 ), the coordinates of point K3 be (x K3 , y K3 ). K1 satisfies the equation of ellipse 1:

[0025]

[0026] The normal slope of the tangent line of ellipse 1 at point K1 The normal slope of the tangent line of the defect circle at point K1

[0027] Satisfies G1 = G m1 , that is:

[0028]

[0029] K2 satisfies the equation of ellipse 2:

[0030]

[0031] The normal slope of the tangent line of ellipse 2 at point K2 The normal slope of the tangent line of the defect circle at point K2 Satisfies G2 = Gm2 That is

[0032]

[0033] K3 satisfies the equation of the ellipse 3:

[0034]

[0035] The normal slope of the tangent line of the ellipse 3 at point K3 The normal slope of the tangent line of the defective circle at point K3 Satisfies G3 = G m3 That is

[0036]

[0037] Points K1, K2, and K3 are located on the defective circle, then:

[0038]

[0039] Step 8 is specifically: substituting the values of a1, b1, a2, b2, a3, and b3 calculated in step 6 into Equation 1-7 in step 7 to solve for the coordinates (x m , y m ) of the center point m of the defective circle and the defective radius r, and saving the data in the directory of the number of times N that the precision lifting table rises.

[0040] Preferably, in step 4, after one detection is completed, control the precision rotating chuck to rotate by an angle, control the precision lifting table to reset, and use the same detection method to perform repeated verification detections 1-3 times. The rotation angle can be 30°, 60°, 90° or any other angle.

[0041] Preferably, summarize the detection information of each layer cross-section of the measured shaft-like part, and perform three-dimensional reconstruction on the internal defects of the measured shaft-like part.

[0042] The present invention performs detection on the measured shaft-like part in the three-point laser ultrasonic thermoelastic mode, extracts the arrival time of the reflected shear wave in the ultrasonic signal, approximates the shape of the defect on the cross-section of the measured shaft-like part as a circle, calculates the center and radius of the internal defect circle through an algorithm, performs three-dimensional reconstruction on the internal defect, and obtains the approximate shape and position of the internal defect. This technical solution can effectively detect internal defects, perform three-dimensional reconstruction on internal defects, and master the shape and position information of the internal defects of the measured shaft-like part. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below in conjunction with the drawings.

[0044] Figure 1 It is a schematic diagram of the connection relationship of a detection device of the present invention.

[0045] Figure 2 It is a schematic diagram of the physical position layout of a detection device of the present invention.

[0046] Figure 3 It is a two-dimensional schematic diagram of an algorithm for detecting cross-sectional defects of shaft parts of the present invention.

[0047] Figure 4 It is a schematic diagram of the internal defect location reconstruction of shaft parts of the present invention.

[0048] In the figure: 1. Precision rotating chuck, 2. Shaft part to be measured, 3. Pulse laser, 4. Laser power supply, 5. Control handle, 6. Dual-frequency laser interferometer, 7. Data acquisition card, 8. PC, 9. Controllable single-source three-point reflection focusing device, 10. Precision lifting table, 11. Self-balancing vibration isolation table, 12. Voltage-stabilized adjustable gas source. Specific embodiments

[0049] The present invention will be further described below through specific embodiments in conjunction with the drawings.

[0050] Embodiment 1: A laser ultrasonic detection device for internal defects of shaft parts, as Figure 1 , 2 shown. This device includes a workbench, on which a precision rotating chuck 1 is arranged, and the shaft part 2 to be measured is clamped vertically on the precision rotating chuck 1. The workbench is a self-balancing vibration isolation table 11, and both the self-balancing vibration isolation table 11 and the precision rotating chuck 1 are connected to a voltage-stabilized adjustable gas source 12.

[0051] A liftable controllable single-source three-point reflection focusing device 9 is arranged around the shaft part 2 to be measured. The controllable single-source three-point reflection focusing device 9 forms three evenly distributed focusing points S1, S2, and S3 on the circumference at the same horizontal height of the shaft part 2 to be measured. The controllable single-source three-point reflection focusing device 9 is connected to a pulse laser 3, and the pulse laser 3 and the controllable single-source three-point reflection focusing device 9 are jointly arranged on the same precision lifting table 10. The pulse laser 3 is connected to a laser power supply 4, the laser power supply is connected to a control handle 5, and the laser power supply 4 is connected to a PC 8.

[0052] On one side of the shaft part 2 to be measured on the workbench, there is a dual-frequency laser interferometer 6 for collecting ultrasonic reflection signals. The dual-frequency laser interferometer 6 aligns with the surface of the shaft part 2 to form a detection point T0. T0 is 180 degrees apart from S1 and at the same horizontal height. The dual-frequency laser interferometer 6 is connected to a data acquisition card 7, and the data acquisition card is connected to a PC 8. The dual-frequency laser interferometer 6 is arranged on another precision lifting table 10. The precision lifting table 10 is connected to a PC 8.

[0053] Embodiment 2: A laser ultrasonic detection method for internal defects of shaft parts, as follows Figure 3 、 4 shown. This method uses the laser ultrasonic detection device described in Embodiment 1, including the following steps

[0054] Step 1: Complete the installation and connection of the PC 8, laser power supply 4, pulsed laser 3, controllable single-source three-point reflection focusing device 8, dual-frequency laser interferometer 6, and data acquisition card 7, and install the shaft part 2 to be measured on the precision rotating chuck 1

[0055] Step 2: Turn on the experimental power supply, turn on the laser power supply 4, use the control handle 5 to set the laser parameters, adjust the controllable single-source three-point reflection focusing device 8 to make the excitation beams respectively located at three excitation points S1, S2, and S3 on the surface of the shaft part 2 to be measured and adjust the corresponding excitation spot sizes to match the shaft part 2 to be measured. Turn on the dual-frequency laser interferometer 6 and adjust the dual-frequency laser interferometer 6 to make the detection beam located at the detection point T0 on the surface of the shaft part 2 to be measured; the excitation points S1, S2, S3 and the detection point T0 are at the same horizontal height, the excitation points S1, S2, S3 are spaced 120° from each other, and the detection point T0 is spaced 180 degrees from the excitation point S1

[0056] Step 3: Open the detection and acquisition software on the PC 8, set the acquisition height H, single-rise height h0, and single acquisition time t r and input the radius R and the internal ultrasonic shear wave velocity V of the shaft part 2 to be measured S ;

[0057] Step 4: After the detection and acquisition software controls the precision rotating chuck 1 to reset, control the pulsed laser 3 to emit the excitation beam and control the dual-frequency laser interferometer 6 to perform detection, and judge whether there is a defect reflected echo. If all are regular reflected echoes and there is no defect reflected echo, return the defect-free information at this detection height, and adjust the rising height h0 of the two precision lifting tables 10, and repeat the above detection; if a defect reflected echo is detected, enter Step 5 and record the current adjusted rising times N until the total rising height reaches H; after one detection is completed, control the precision rotating chuck to rotate 60°, control the precision lifting table to reset, and perform repeated verification detection using the same detection method

[0058] Step 5: The detection and acquisition software controls the controllable single-source three-point reflection focusing device 8 to adjust the laser emitted by the pulsed laser 3 to the excitation points S1, S2, and S3 in sequence and control the dual-frequency laser interferometer 6 to perform detection, and calculate and record the time intervals from the excitation at each point to the arrival of the defect-reflected shear wave detected by the dual-frequency laser interferometer 6 as t1, t2, and t3 respectively under the rising times N

[0059] Step 6: Approximate the defect points in the shaft part 2 to be circular, sequentially excite at points S1, S2, and S3, and obtain the detection signals at point T0 after each excitation; for the excitation point S1, the ultrasonic shear wave excited propagates inside the measured cylinder, reflects from the defect circular edge, and reaches the detection point T0. The reflection point of this reflected ultrasonic shear wave on the defect circular edge is K1, and the propagation path P1 of this ultrasonic shear wave is P1 = L S1-K1 + L K1-T0 = V S t1. According to the sound reflection property, the normal line of the defect circle at point K1 bisects ∠S1K1T0. Then the reflection point K1 is distributed on the ellipse with S1 and T0 as the foci. Denote this ellipse as ellipse 1, with the origin as J1, and J1 coincides with the center of the cross-section of the measured shaft part (2). Its focal length c1 = 2R, major axis minor axis And so on. When the excitation point is S2, the ultrasonic wave propagates inside the measured cylinder, encounters the defect circle, reflects at the reflection point K2, and continues to propagate to the detection point T0. The path traveled by the ultrasonic wave is P2 = L S2-K2 + L K2-T0 = V S t2. According to the sound reflection property, the normal line passing through point K2 of the tangent line of the defect circle at point K2 bisects ∠S2K2T0. Then the reflection point K2 is distributed on the ellipse edge with S2 and T0 as the foci. Denote this ellipse as ellipse 2, with the origin as J2, and its focal length c2 = R, major axis minor axis When the excitation point is S3, the ultrasonic wave propagates inside the measured cylinder, encounters the defect circle, reflects at the reflection point K3, and continues to propagate to the detection point T0. The path traveled by the ultrasonic wave is P3 = L S3-K3 + L K3-T0 = V S t3. According to the sound reflection property, the normal line passing through point K3 of the tangent line of the defect circle at point K3 bisects ∠S3K3T0. Then the reflection point K3 is distributed on the ellipse edge with S3 and T0 as the foci. Denote this ellipse as ellipse 3, with the origin as J3, and its focal length c3 = R, major axis minor axis

[0060]

[0061] Step 7 is specifically as follows: Establish a plane rectangular coordinate system x - y with the center of the cross-section as the origin O and O - S1 as the y-axis. Denote the center point of the defect circle as m and the radius as r. Let the coordinates of point m be (x m , y m ), the coordinates of point K1 be (x K1 , y K1 ), the coordinates of point K2 be (x K2 , y K2 ), and the coordinates of point K3 be (x K3 , yK3 ), K1 satisfies the equation of ellipse 1:

[0062]

[0063] The normal slope of the tangent line of ellipse 1 at point K1 The normal slope of the tangent line of the defective circle at point K1

[0064]

[0065] Satisfy G1 = G m1 , that is:

[0066]

[0067] K2 satisfies the equation of ellipse 2:

[0068]

[0069] The normal slope of the tangent line of ellipse 2 at point K2 The normal slope of the tangent line of the defective circle at point K2 Satisfy G2 = G m2 That is

[0070]

[0071] K3 satisfies the equation of ellipse 3:

[0072]

[0073] The normal slope of the tangent line of ellipse 3 at point K3 The normal slope of the tangent line of the defective circle at point K3 Satisfy G3 = G m3 That is

[0074]

[0075] Points K1, K2, and K3 are located on the defective circle, then there is:

[0076]

[0077] Step 8 is specifically: Substitute the values of a1, b1, a2, b2, a3, and b3 calculated in step 6 into Equation 1-7 in step 7 to solve for the coordinates (x m , y m ) of the center point m of the defective circle and the defective radius r, and save the data in the directory of the rising times N of the precision lifting table 10.

[0078] Step 9: Return to step 4 and continue the detection.

[0079] Such as Figure 4As shown, after summarizing the detection information of each layer cross-section of the shaft part to be measured, a three-dimensional reconstruction of the internal defects of the shaft part to be measured is carried out.

Claims

1. A laser ultrasonic detection device for internal defects of shaft parts, including a workbench, characterized in that, A precision rotating chuck (1) is provided on the workbench. The axis of the shaft part (2) to be measured is vertically clamped on the precision rotating chuck (1). A liftable controllable single-source three-point reflection focusing device (9) is arranged around the shaft part (2) to be measured. The controllable single-source three-point reflection focusing device (9) forms three uniformly distributed focusing points S1, S2, and S3 on the circumference at the same horizontal height of the shaft part (2) to be measured. On one side of the shaft part (2) to be measured, a dual-frequency laser interferometer (6) for collecting ultrasonic reflection signals is provided on the workbench. The dual-frequency laser interferometer (6) aligns with the surface of the shaft part (2) to be measured to form a detection point T0. T0 is 180 degrees apart from S1 and at the same horizontal height.

2. The laser ultrasonic detection device for internal defects of a shaft part according to claim 1, characterized in that, The controllable single-source three-point reflection focusing device (9) is connected to a pulsed laser (3). The pulsed laser (3) and the controllable single-source three-point reflection focusing device (9) are jointly arranged on the same precision lifting table (10). The dual-frequency laser interferometer (6) is arranged on the same or another precision lifting table (10).

3. The laser ultrasonic detection device for internal defects of a shaft part according to claim 2, characterized in that, The pulsed laser (3) is connected to a laser power supply (4). The laser power supply is connected to a control handle (5). The laser power supply (4) is connected to a PC (8).

4. The laser ultrasonic detection device for internal defects of a shaft part according to claim 2, characterized in that The precision lifting table (10) is connected to a PC (8).

5. The laser ultrasonic detection device for internal defects of a shaft part according to claim 1, characterized in that, The dual-frequency laser interferometer (6) is connected to a data acquisition card (7). The data acquisition card is connected to a PC (8).

6. The laser ultrasonic detection device for internal defects of a shaft part according to claim 1, characterized in that, The workbench is a self-balancing vibration isolation table (11). Both the self-balancing vibration isolation table (11) and the precision rotating chuck (1) are connected to a regulated and adjustable air source (12).

7. A laser ultrasonic detection method for internal defects of shaft parts, using the laser ultrasonic detection device according to any one of claims 1-6, characterized in that: It includes the following steps. Step 1: Complete the installation and connection of each component of the detection device, and install the shaft part (2) to be measured on the precision rotating chuck (1). Step 2: Turn on the experimental power supply and adjust the detection parameters. Step 3: Open the detection and acquisition software on the PC (8), set the acquisition height H, the single-upward height h0, and the single acquisition time t r , input the radius R and the internal ultrasonic shear wave velocity V of the shaft part (2) to be measured S ; Step 4: After the detection acquisition software controls the precision rotating chuck (1) to reset, control the pulsed laser (3) to emit an excitation beam and control the dual-frequency laser interferometer (6) to conduct a detection. Judge whether there is a defect reflected echo. If all are regular reflected echoes and there is no defect reflected echo, return the defect-free information at this detection height, and adjust the rising height h0 of the two precision lifting tables (10), and repeat the above detection. If a defect reflected echo is detected, enter Step 5 and record the current adjustment rising times N until the total rising height reaches H. Step 5: The detection acquisition software controls the controllable single-source three-point reflection focusing device (8) to adjust the laser emitted by the pulsed laser (3) to the excitation point S1, the excitation point S2, and the excitation point S3 in turn and control the dual-frequency laser interferometer (6) to conduct a detection, and calculate and record the time intervals from the excitation at each point to the arrival of the defect reflected shear wave detected by the dual-frequency laser interferometer (6) as t1, t2, and t3 respectively under the rising times N. Step 6: Approximate the defect point in the shaft part (2) to be measured as a circle, and calculate the three-reflection-point distribution elliptical curve of the defect circle according to the time of the defect reflected shear wave from the excitation points S1, S2, and S3 to the detection point T0. Step 7: Taking the center of the cross-section of the shaft part (2) under test as the origin O, and O-S1 as the Y-axis, establish a plane rectangular coordinate system x-y. Denote the center point of the defect circle as m and the radius as r, and establish a model by combining the elliptic curves where the three reflection points are distributed. Step 8: Combine the models in Steps 6 and 7 to solve the coordinates of the center point m and the radius r of the defect circle, and save the data under the directory of the rising times N of the precision lifting table (10). Step 9: Return to Step 4 and continue the detection.

8. The laser ultrasonic detection method for internal defects of a shaft part according to claim 7, characterized in that, In Step 2, the excitation point S1, the excitation point S2, the excitation point S3, and the detection point T0 are at the same horizontal height. The excitation point S1, the excitation point S2, and the excitation point S3 are spaced 120° from each other, and the detection point T0 is spaced 180° from the excitation point S1.

9. A laser ultrasonic detection method for internal defects of a shaft part according to claim 7, wherein Step 6 is specifically as follows: Approximate the defect points in the shaft-like part to be measured (2) as circles, sequentially excite at points S1, S2, and S3, and obtain detection signals at point T0 after each excitation; for the excitation point S1, the ultrasonic shear wave excited propagates inside the measured cylinder, reflects from the defect circle edge to the detection point T0, the reflection point of this reflected ultrasonic shear wave on the defect circle edge is K1, and the distance P1 traveled by this ultrasonic shear wave this time is P1 = L S1-K1 +L K1-T0 =V S t1. According to the sound reflection property, the normal line of the defect circle at point K1 bisects ∠S1K1T0, then the reflection point K1 is distributed on the ellipse with S1 and T0 as foci. Denote this ellipse as ellipse 1, the origin is J1, J1 coincides with the center of the cross-section of the shaft-like part to be measured (2), and its focal length c1 = 2R, major axis minor axis And so on. When the excitation point is S2, the ultrasonic wave propagates inside the measured cylinder, encounters the defect circle, reflects at the reflection point K2, and continues to propagate to the detection point T0. The distance P2 traveled by the ultrasonic wave is P2 = L S2-K2 +L K2-T0 =V S t2. According to the sound reflection property, the normal line passing through point K2 of the tangent line of the defect circle at point K2 bisects ∠S2K2T0, then the reflection point K2 is distributed on the ellipse edge with S2 and T0 as foci. Denote this ellipse as ellipse 2, the origin is J2, and its focal length c2 = R, major axis minor axis When the excitation point is S3, the ultrasonic wave propagates inside the measured cylinder, encounters the defect circle, reflects at the reflection point K3, and continues to propagate to the detection point T0. The distance P3 traveled by the ultrasonic wave is P3 = L S3-K3 +L K3-T0 =V S t3. According to the sound reflection property, the normal line passing through point K3 of the tangent line of the defect circle at point K3 bisects ∠S3K3T0, then the reflection point K3 is distributed on the ellipse edge with S3 and T0 as foci. Denote this ellipse as ellipse 3, the origin is J3, and its focal length c3 = R, major axis minor axis Step 7 is specifically as follows: Taking the center of the cross-section as the origin O and O-S1 as the Y-axis, a plane rectangular coordinate system x-y is established. Denote the center point of the defective circle as m, with a radius of r. Let the coordinates of point m be (x m , y m ), the coordinates of point K1 be (x K1 , y K1 ), the coordinates of point K2 be (x K2 , y K2 ), the coordinates of point K3 be (x K3 , y K3 ). K1 satisfies the equation of ellipse 1: Normal slope of the tangent line of ellipse 1 at point K1 Normal slope of the tangent line of the defective circle at point K1 Satisfy G1 = G m1 , that is: K2 satisfies the equation of ellipse 2: Normal slope of the tangent line of ellipse 2 at point K2 Normal slope of the tangent line of the defective circle at point K2 Satisfy G2 = G m2 Namely K3 satisfies the equation of ellipse 3: Normal slope of the tangent line of the ellipse 3 at point K3 Normal slope of the tangent line of the defective circle at point K3 Satisfy G3 = G m3 Namely Since the points K1, K2, and K3 are located on the defect circle, then: Step 8 specifically is: Substitute the values of a1, b1, a2, b2, a3, and b3 obtained in Step 6 into Equation 1-7 in Step 7 to solve for the coordinates (x m , y m ) of the center point m of the defective circle and the defective radius r, and save the data in the directory of the number of ascents N of the precision lifting table (10).

10. The laser ultrasonic detection method for internal defects of a shaft part according to claim 7, characterized in that In Step 4, after one detection is completed, control the precision rotating chuck to rotate by an angle, control the precision lifting table to reset, and use the same detection method to perform a verification detection 1-3 times repeatedly.

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