Ultrasonic detection method for internal defects of aviation casting aluminum alloy bar and sensor assembly

Abstract

The invention discloses an aviation casting aluminum alloy bar internal defect ultrasonic detection method and a sensor assembly, and the method comprises the following steps: adjusting water distance through three water immersion focusing probes to realize focusing of different depth areas, which are respectively a near surface depth of 2mm, a 1 / 4 bar radius depth and a 3 / 4 bar radius depth, and carrying out ultrasonic C scanning imaging; the probe forms water coupling with the surface of a workpiece through a water jacket, so that high-precision layered focusing detection is ensured. The collected ultrasonic signals are subjected to noise reduction processing through a wavelet decomposition technology, a threshold function is improved, wavelet coefficients are screened, the signals are reconstructed, and a C scanning image is reconstructed. The method has the advantages that the detection sensitivity and accuracy of the internal defects of the aluminum alloy bar are improved, the method is particularly suitable for quality detection of the aluminum alloy bar in the aviation industry, and the method has the characteristics of full coverage, accuracy and high efficiency.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic detection technology, and in particular to a full-coverage high-precision ultrasonic detection method and an ultrasonic sensor assembly for internal defects of large-size aluminum alloy bars for aviation castings. Background Art

[0002] Aluminum alloy bars are important raw materials for aviation forgings, and the detection of internal defects is crucial to ensure the structural safety and performance of aircraft. The internal defects of aluminum alloy bars include pores, inclusions, cracks, segregation, etc. These defects may affect the mechanical properties of the material, leading to serious structural problems during use, and even affecting flight safety. Therefore, accurate and efficient defect detection technology is of great significance to the quality control of aviation castings.

[0003] Existing aluminum alloy bar defect detection technologies mainly include ultrasonic testing, visual testing, and penetration testing. Ultrasonic testing technology is widely used in aluminum alloy bar defect detection due to its advantages such as strong penetration, concentrated energy, and simple operation. However, the traditional ultrasonic testing method has the following shortcomings:

[0004] 1. Limited detection depth and coverage: Existing ultrasonic testing technology usually relies on a single-frequency probe for detection, and the detection depth and range are limited. Especially when performing defect detection on large-sized aluminum alloy bars, it is often difficult to cover the full size range, resulting in missed detection or low sensitivity.

[0005] 2. Insufficient detection accuracy: Traditional ultrasonic detection methods have difficulty in effectively distinguishing small-sized defects and noise, and in complex-shaped or multi-layered aluminum alloy bar structures, changes in the sound wave propagation path may also affect the accuracy of the detection results.

[0006] 3. The detection process is cumbersome and relies on manual operation: Existing ultrasonic detection mostly relies on manual operation. The detection process is time-consuming and labor-intensive and easily affected by human factors. The efficiency and accuracy are difficult to meet the needs of modern industrial production.

[0007] 4. Poor local water coupling effect: In existing ultrasonic testing technology, the design of the water coupling system often fails to fully consider the special needs of large-sized aluminum alloy bars, resulting in poor local water coupling effect, which in turn affects the quality of the detection signal and the detection accuracy. Summary of the invention

[0008] The present invention aims to solve the problems of insufficient depth coverage, low accuracy and excessive manual operation in the prior art, and provides an ultrasonic detection method and sensor assembly for internal defects of aluminum alloy bars for aviation castings. By improving water coupling technology and adopting automated and intelligent detection methods, the present invention can greatly improve the detection accuracy and efficiency of internal defects of aluminum alloy bars.

[0009] In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0010] An ultrasonic detection method for internal defects of aviation casting aluminum alloy bars comprises the following steps:

[0011] S1. An ultrasonic sensor assembly consisting of three water immersion focusing probes is used to perform three ultrasonic water immersion focusing C-scan imaging on the rod, and the focusing depth of the probe is controlled by adjusting the water distance;

[0012] S2. Install the probes in parallel on a special fixture for the probes, and perform layered C-scan automated testing on the rods. The height of each layer is equal to the focal height, and the focus of the sound beam is concentrated in the middle of each layer to collect the original data of each layer.

[0013] S3, applying wavelet decomposition technology to decompose the collected detection signal into four layers, and obtaining the wavelet coefficients of each decomposition layer;

[0014] S4. Use an improved threshold function to screen or retain specific wavelet coefficients, reconstruct and normalize the selected wavelet coefficients, and reconstruct the C-scan image based on the reconstructed signals.

[0015] Preferably, in step S1, a 15 MHz probe is used to detect the surface and near-surface area, and a 10 MHz probe is used to detect the internal area. The water layer thickness H is not greater than 110 mm, and the focal length F-focus L is expressed as:

[0016]

[0017] The probe chip radius r-focal area q can be expressed as:

[0018]

[0019] Among them, L is the focal position of the probe, H is the thickness of the water layer, C2 is the sound speed in water, and C3 is the sound speed in the workpiece.

[0020] Preferably, the three inspection areas planned in step S1 are achieved by adjusting the water distance and the focus position to achieve layered coverage inspection within the full thickness range of the rod. Inspection area 1: by adjusting the water distance, the focus of probe A is 2 mm away from the surface of the aluminum rod, and a focusing area is formed on the surface of the rod and its near surface to avoid missed inspections; Inspection area 2: the water distance is adjusted so that the focus of probe B is 1 / 4R away from the surface of the rod and the scanning area is 0 to 1 / 2R; Inspection area 3: the water distance is adjusted so that the focus of probe C is 3 / 4R away from the depth of the rod surface, and the scanning area is 1 / 2R to R.

[0021] Preferably, the specific process of step S2 includes:

[0022] S201, install multiple sensor components on the gimbal, and fine-tune the angle to ensure that the probe is perpendicular to the workpiece surface;

[0023] S202, adjusting the center and height adjustment device to change the vertical and horizontal positions of the sensor assembly, thereby achieving the required water distance for detection to meet the needs of different detection depths;

[0024] S203, the roller rotating shaft drives the rod to rotate at a constant speed in situ, and the transverse motion shaft drives the probe to step transversely, and the combination of the two realizes spiral scanning of the entire rod;

[0025] S204. Repeat the above steps according to different layered scanning schemes to achieve full coverage scanning.

[0026] Preferably, three immersion ultrasonic probes with different parameters are used, and the probe parameters are as follows:

[0027] Center frequency 15MHz, chip diameter 6.35mm, focal length 13.9mm;

[0028] Center frequency 10MHz, chip diameter 25.4mm, focal length 154mm;

[0029] The center frequency is 10MHz, the chip diameter is 25.4mm, and the focal length is 300mm.

[0030] Preferably, the specific process of step S3 includes:

[0031] The 'Sym8' wavelet base is used to decompose the ultrasonic signal collected by S2 into 4 layers to obtain multi-scale wavelet coefficients. The wavelet coefficients are reconstructed by improving the soft threshold function to obtain the filtered detection signal.

[0032] Preferably, the specific process of step S4 includes:

[0033] S401, the wavelet transform threshold function expression is:

[0034]

[0035] Among them, d j,k represents the wavelet coefficient, d 0 j,k is the wavelet coefficient after threshold processing, sign(d j,k ) is a sign function.

[0036] The improved threshold function expression is:

[0037]

[0038] Where: γ is the threshold, N is the signal length, j is the decomposition scale, σ is the standard deviation of the signal at different scales, and fi is the decomposition coefficient at the i-th decomposition scale, median is the median of the function, and 0.6745 is the adjustment coefficient of the standard deviation of Gaussian white noise.

[0039] S402, setting a threshold for the detail wavelet coefficients obtained by decomposition at each scale, retaining only the wavelet coefficients greater than the threshold and reconstructing them into a denoised detection signal;

[0040] S403, setting a search window for the reconstructed A-scan signal according to the layered scanning focus position and the focal area, performing a pulse peak search within the window, and reconstructing a detection image based on the pulse peak value after noise reduction;

[0041] S404. Repeat the above steps according to different layered scanning schemes to achieve full coverage scanning.

[0042] The present invention also discloses an ultrasonic sensor assembly for implementing the above-mentioned ultrasonic detection method for internal defects of aluminum alloy bars of aviation castings. The ultrasonic sensor assembly includes: a water spray probe, a special water jacket is installed at the front end of the water spray probe, the end of the water jacket is in contact with the bar, and a thread is designed on the upper part of the water jacket to match the thread machined in the water spray probe, thereby achieving good water coupling and reducing probe wear.

[0043] Preferably, the gap between the water jacket and the rod is set to 0.5 mm to achieve the best water coupling effect.

[0044] Compared with the prior art, the advantages of the present invention are:

[0045] Non-contact detection: The ultrasonic sensor assembly of the present invention realizes local water coupling by means of water spray coupling, and can perform detection without contacting the object to be detected, thereby reducing the damage caused by probe wear during the detection process and solving the problem of difficult detection of internal defects in large-sized aluminum alloy bars of aviation castings.

[0046] High degree of automation: The present invention realizes automatic detection of aviation bars by building a high-precision scanning device, reduces human operation errors and improves detection efficiency.

[0047] Wide scope of application: The solution of the present invention is not only suitable for the detection of large-size aluminum alloy bars for aviation, but can also be used for the detection and analysis of internal defects of other tubes and bars with similar regular diameters.

[0048] High resolution: The present invention uses improved soft threshold wavelet decomposition technology to perform four-layer wavelet decomposition on the signal. By setting the threshold function and the number of decomposition layers, the interference of noise on the detection signal can be reduced, thereby improving the resolution of small defects. By setting the search window according to the layered scanning focus position and the focal range of the de-noised echo signal, the pulse peak search is performed within the window range. And the peak value of the pulse wave after noise reduction is reconstructed for detection image. A high-resolution C-scan image of large-size aviation aluminum alloy bars can be obtained. This image can clearly show the details of large-size aviation aluminum alloy bars, so that the inspection personnel can accurately and more accurately evaluate the details of the internal defects of the bars.

[0049] High sensitivity: The water-immersion ultrasonic probe is used to detect large-size aluminum alloy bars for aviation. The full coverage scan inside the aluminum alloy bar is achieved through the focused sound field. The detection sensitivity can reach 0.1% within the bar depth range of 0 to 60 mm. Equivalent size of flat bottom hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The present invention is a flowchart of an ultrasonic detection method for internal defects of aluminum alloy bars for aviation castings according to an embodiment of the present invention.

[0051] Figure 2 This is a structural diagram of the arrangement of the ultrasonic sensor assembly according to an embodiment of the present invention in a specific application.

[0052] Figure 3 It is an overall schematic diagram of the mechanical structure of the present invention.

[0053] In the figure, 1-circumferential rotation device; 2-axial stroke device; 3-center and height adjustment device; 4-ultrasonic sensor assembly.

[0054] Figure 4 It is a schematic diagram of the ultrasonic sensor assembly of the present invention.

[0055] Figure 5 The image is a comparison of the A scan signal of the step test block before and after filtering of the present invention; wherein (a) Flat bottom hole A scan signal, (b) Flat bottom hole A scan signal, (c) Flat-bottom hole A-scan signal.

[0056] Figure 6 This is a comparison diagram of the C-scan image of the flat-bottom hole step test block of the present invention; wherein (a) is The original C-scan image of the flat-bottom hole, (b) The original C-scan image of the flat-bottom hole, (c) Raw C-scan image of a flat-bottom hole.

[0057] Figure 7 The following are comparison diagrams of the C-scan images before and after filtering of the layered coverage scanning of the large-size aluminum alloy bars for aviation castings of the present invention; wherein (a) is the image focused at 2 mm, (b) is the image reconstructed after focusing at 15 mm, and (c) is the image reconstructed after focusing at 45 mm. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0059] like Figure 1 As shown, the fully covered high-precision ultrasonic detection method for internal defects of a Φ120 mm large-size aluminum alloy bar for aviation castings in an embodiment of the present invention comprises the following steps:

[0060] S1. Use three water immersion focusing probes to perform three ultrasonic water immersion focusing C-scan imaging on the rod. By adjusting the water distance, the focusing depth is set to 2 mm near the surface, 1 / 4 rod radius depth, and 3 / 4 rod radius depth respectively.

[0061] S2. Three probes are installed in parallel on a special probe fixture, and a water jacket is installed at the front end of the probe. The gap between the water jacket and the cylinder is set to 0.5mm. The bar is automatically inspected by layered C scanning through a self-built layered focusing detection system. The height of each layer is equal to the focal area height, and the focus of the sound beam is concentrated in the middle of each layer to collect the original data of each layer.

[0062] S3. Apply wavelet decomposition technology to decompose the collected detection signal into four layers to obtain the wavelet coefficients of each decomposition layer.

[0063] S4. Use an improved threshold function to screen or retain specific wavelet coefficients, reconstruct and normalize the selected wavelet coefficients, and reconstruct the C-scan image based on the reconstructed signals.

[0064] (1) Three focus areas are planned for large-size aluminum alloy bars for aviation castings, marked as test areas 1 to 3. Three immersion ultrasonic probes with different parameters are used. The key parameters of probe A are: center frequency 15MHz, chip diameter 6.35mm, focal length 13.9mm; the key parameters of probe B are: center frequency 10MHz, chip diameter 25.4mm, focal length 154mm; the key parameters of probe C are: center frequency 10MHz, chip diameter 25.4mm, focal length 300mm. The probe layout is as follows Figure 2As shown. In the detection area 1, by adjusting the water distance H1 = 5.4mm, the focal distance of probe A from the aluminum rod surface is T1 = 2mm, the focal length L1 ≈ 4.4mm, the focal diameter Φ1 ≈ 0.05mm, and the scanning area is 0-4.2mm; detection area 2: adjusting the water distance H2 = 90.25mm, the focal distance of probe B from the rod surface is T2 = 15mm, the focal length L2 ≈ 24mm, the focal diameter Φ2 ≈ 0.21mm, the scanning area is 3-27mm, and the overlapping coverage area ΔL1 of probes A and B is 3mm; detection area 3: adjusting the water distance H3 = 108.8mm, the depth of probe C focal distance from the rod surface is T3 = 45mm, the focal length L3 ≈ 42mm, the focal diameter Φ3 ≈ 0.41mm, the scanning area is 24-60mm, and the overlapping coverage area of ​​probes B and C is ΔL2 = 3mm.

[0065] (2) The mechanical structure of the present invention is as follows Figure 3 As shown, the water jet focused ultrasonic testing process is as follows:

[0066] S201. Install multiple sensor components on the gimbal and fine-tune the angle to ensure that the probe is incident perpendicularly on the workpiece surface.

[0067] S202, adjusting the center and height adjustment device to change the vertical and horizontal positions of the sensor assembly, thereby achieving the required water distance for detection to meet the needs of different detection depths.

[0068] S203, the roller rotating shaft drives the rod to rotate at a constant speed in situ, and at the same time the transverse motion shaft drives the probe to step transversely, and the combination of the two realizes the spiral scanning of the entire rod.

[0069] S204. Repeat the above steps according to different layered scanning schemes to achieve full coverage scanning.

[0070] (3) Extract the ultrasonic signal collected in S2, and use the Sym8 wavelet basis to perform four-layer wavelet decomposition on the detection signal to obtain the wavelet coefficients of the detection signal; set a threshold for the detail wavelet coefficients obtained by decomposition at each scale, and only retain the wavelet coefficients greater than the threshold and reconstruct them into the denoised detection signal. According to the above method, wavelet decomposition and signal reconstruction are performed, and the detection signal is compared. Figure 5 As shown in the figure, the signal-to-noise ratio is increased by 114.01%, 67.08% and 389.71% respectively. Figure 6 As shown, the noise in the image is effectively removed, the edges of the defective image become clearer, and the image resolution is effectively improved.

[0071] (4) Setting a search window for the reconstructed A-scan signal according to the layered scanning focus position and the focal range, performing a pulse peak search within the window range, and reconstructing the detection image based on the pulse peak value after noise reduction.

[0072] (5) Repeat the above steps according to different probes and scanning schemes to achieve full coverage scanning. The layered coverage detection results are as follows: Figure 7 shown.

[0073] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the implementation methods of the present invention, and should be understood that the protection scope of the present invention is not limited to such special statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. An ultrasonic detection method for internal defects of aluminum alloy bars for aviation castings, characterized in that: The following steps are involved: S1. An ultrasonic sensor assembly consisting of three water immersion focusing probes is used to perform three ultrasonic water immersion focusing C-scan imaging on the rod, and the focusing depth of the probe is controlled by adjusting the water distance; S2. Install the probes in parallel on a special fixture for the probes, and perform layered C-scan automated testing on the rods. The height of each layer is equal to the focal height, and the focus of the sound beam is concentrated in the middle of each layer to collect the original data of each layer. S3, applying wavelet decomposition technology to decompose the collected detection signal into four layers, and obtaining the wavelet coefficients of each decomposition layer; S4. Use an improved threshold function to screen or retain specific wavelet coefficients, reconstruct and normalize the selected wavelet coefficients, and reconstruct the C-scan image based on the reconstructed signals.

2. The method for ultrasonic detection of internal defects of aluminum alloy bars for aviation castings according to claim 1, characterized in that: In step S1, a 15MHz probe is used to detect the surface and near-surface area, and a 10MHz probe is used to detect the internal area. The water layer thickness H is not greater than 110mm, and the focal length F-focus L is expressed as: Among them, L is the focal position of the probe, H is the thickness of the water layer, C2 is the sound speed in water, and C3 is the sound speed in the workpiece.

3. The method for ultrasonic detection of internal defects of aluminum alloy bars for aviation castings according to claim 1, characterized in that: The three inspection areas planned in step S1 are to achieve layered coverage inspection within the full thickness range of the bar by adjusting the water distance and the focus position. Inspection area 1: by adjusting the water distance, the focus of probe A is 2 mm away from the surface of the aluminum bar, and a focusing area is formed on the surface of the bar and its near surface to avoid missed inspection; Inspection area 2: the water distance is adjusted so that the focus of probe B is 1 / 4R away from the surface of the bar and the scanning area is 0~1 / 2R; Inspection area 3: the water distance is adjusted so that the focus of probe C is 3 / 4R away from the depth of the bar surface, and the scanning area is 1 / 2R~R.

4. The method for ultrasonic detection of internal defects of aluminum alloy bars for aviation castings according to claim 1, characterized in that: The specific process of step S2 includes: S201, install three ultrasonic sensor assemblies on the pan-tilt platform, and fine-tune the angle to ensure that the probes are incident perpendicularly on the workpiece surface; S202, adjusting the center and height adjustment device to change the vertical and horizontal positions of the sensor assembly, thereby achieving the required water distance for detection; S203, the roller rotating shaft drives the bar to rotate at a constant speed in situ, and the transverse motion shaft drives the probe to step transversely, and the combination of the two realizes spiral scanning of the entire bar; S204. Repeat the above steps according to different layered scanning schemes to achieve full coverage scanning.

5. The method for ultrasonically detecting internal defects of aluminum alloy bars for aviation castings according to claim 4, characterized in that: The ultrasonic sensor assembly has three immersion ultrasonic probes with different parameters. The probe parameters are as follows: Center frequency 15MHz, chip diameter 6.35mm, focal length 13.9mm; Center frequency 10MHz, chip diameter 25.4mm, focal length 154mm; The center frequency is 10MHz, the chip diameter is 25.4mm, and the focal length is 300mm.

6. The method for ultrasonically detecting internal defects of aluminum alloy bars for aviation castings according to claim 1, characterized in that: The specific process of step S3 includes: The ultrasonic signal collected by S2 is decomposed into four layers by wavelet basis function to obtain multi-scale wavelet coefficients. The wavelet coefficients are reconstructed by improving the soft threshold function to obtain the filtered detection signal.

7. The method for ultrasonic detection of internal defects of aluminum alloy bars for aviation castings according to claim 1, characterized in that: The specific process of step S4 includes: S401, the wavelet transform threshold function expression is: Among them, d j,k represents the wavelet coefficient, d 0 j,k is the wavelet coefficient after threshold processing, sign(d j,k ) is a sign function. The improved threshold function expression is: Where: γ is the threshold, N is the signal length, j is the decomposition scale, σ is the standard deviation of the signal at different scales, and f i is the decomposition coefficient at the i-th decomposition scale, median is the median of the function, and 0.6745 is the adjustment coefficient of the standard deviation of Gaussian white noise. S402, setting a threshold for the detail wavelet coefficients obtained by decomposition at each scale, retaining only the wavelet coefficients greater than the threshold and reconstructing them into a denoised detection signal; S403, setting a search window for the reconstructed A-scan signal according to the layered scanning focus position and the focal area, performing a pulse peak search within the window, and reconstructing a detection image based on the pulse peak value after noise reduction; S404. Repeat the above steps according to different layered scanning schemes to achieve full coverage scanning.

8. An ultrasonic sensor assembly, used for implementing the ultrasonic detection method for internal defects of aluminum alloy bars for aviation castings according to any one of claims 1 to 6, characterized in that: The ultrasonic sensor assembly comprises a water jet probe, a special water jacket is installed at the front end of the water jet probe, the end of the water jacket is fitted with the rod, and a thread is designed on the upper part of the water jacket to match the thread processed in the water jet probe.

9. The method for ultrasonically detecting internal defects of aluminum alloy bars for aviation castings according to claim 8, characterized in that: The gap between the water jacket and the water jet probe was set to 0.5 mm.

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