CN103245729B - Detection method and device for internal defects of welding seams - Google Patents

Abstract

The invention discloses a detection method and device for internal defects of a weld. Firstly, the corresponding relationship between the typical ultrasonic echo characteristics and the corresponding metallographic structure of the weld cross-section is established, and then the ultrasonic detection is performed on the surface of the welding test block. The comparative analysis of the ultrasonic echo characteristics and the characteristic waveform library kurtosis coefficient is used to determine whether there is a defect inside the weld. The device for implementing this method includes a sequentially connected test bench, a block to be tested, an ultrasonic flaw detector, a probe, and a coupling liquid. Test block ultrasonic testing device and PC system with MATLAB software installed. The technical scheme of the invention is simple, fast and effective, and can be applied to the non-destructive detection of welding seam defects.

Description

Method and device for detecting internal defects of weld seam

technical field

The invention relates to the field of non-destructive testing, in particular to the non-destructive testing of welding seam defects.

Background technique

At present, the non-destructive testing methods for weld quality mainly include magnetic particle testing, radiographic testing, electromagnetic eddy current testing, penetrant testing and ultrasonic flaw testing. The magnetic particle detection method is intuitive and quick to observe the defect, and can determine the size, range and shape of the defect. It has relatively high sensitivity, but it is only suitable for ferromagnetic materials. The ray detection method can intuitively display the image of the defect, which is convenient for qualitative and quantitative analysis; The electromagnetic eddy current method has a fast detection speed, has high sensitivity to near-surface defects, can detect flaws at high temperatures, and can be used for the detection of special-shaped materials and small parts; the penetrant detection method is simple to use, low in cost, realistic and intuitive, and has high detection sensitivity , but it can only detect opening defects on the surface of parts, it is not suitable for the detection of porous materials, and the materials are contaminated; ultrasonic flaw detection detection method, compared with the above detection methods, it has high sensitivity, good directivity, penetrating Strong force, fast detection speed, no harm to the human body and no pollution to the test piece and the environment, can locate and quantify defects, and has a wide range of applications, and the detection method based on ultrasonic is widely used in industrial production, medical and health, national defense technology, etc. field, the technology is mature.

The method of using ultrasonic waves to study the internal structure of objects began in 1930. By 1944 and 1946, the pulse reflection ultrasonic flaw detector was successfully developed in the United States and the United Kingdom, and then ultrasonic flaw detection widely entered the field of industrial testing and became an important non-destructive method. Detection method. Ultrasonic flaw detection is mainly to determine the distance between the defect and the surface by measuring the time for the signal to go back and forth to the defect, and to determine the size and position of the defect by measuring the amplitude of the echo signal and the position of the transmitting transducer. The characteristics of ultrasonic sound velocity, attenuation, impedance and scattering provide a wealth of information for the application of ultrasonic waves and become the conditions for its wide application

Laser welding has high energy concentration, extremely rapid heating and cooling process, and large depth-to-width ratio of weld seam, which can realize high-precision and anti-pollution vacuum environment welding, and can also be applied to many other technical occasions that cannot be completed by traditional welding methods. In the welding of some special materials and tiny contact points such as high-end automobile body and base, aircraft wing, and spacecraft, laser welding is replacing traditional welding. Laser welding is mainly divided into heat conduction welding and deep penetration welding. The laser power density level of the former is 10 ⁵ W/cm ² , and the power density level of deep penetration welding is 10 ⁶ W/cm ² .

Contents of the invention

The main purpose of the present invention is to provide a method and device for detecting internal defects of welds, and provide a simple, fast and effective non-destructive detection technology for internal defects of welded parts.

In order to solve the above technical problems, the technical scheme adopted in the present invention is as follows:

A method for detecting internal defects of a weld, characterized in that firstly establishing the corresponding relationship between typical ultrasonic echo features and the metallographic structure of the corresponding weld cross-section, and then performing ultrasonic testing on the surface of the welding test block, and passing the detected ultrasonic echo Features to judge whether there is a defect inside the weld, the specific steps are as follows:

(1) Use sandpaper to polish the surface of metal welded parts with a thickness between 5 mm and 15 mm, and clean the polished surface with acetone to remove oxide film, dirt, burrs and other sundries;

(2) Set the parameters of the ultrasonic flaw detector, respectively set the scanning mode, probe angle, probe type (single crystal or dual crystal probe), probe frequency, damping size, scanning range, delay time, detection mode, pulse type, etc., and then prepare coupling liquid;

(3) Calibrate the probe of the ultrasonic flaw detector to obtain the propagation speed of the ultrasonic wave in the metal welded part; at this time, use the propagation speed of the ultrasonic wave in the metal welded part and the thickness of the metal welded part to calculate the propagation speed of the ultrasonic wave in the test block time;

(4) Use double-crystal straight probes to detect flaws on the test block, place the probes on the test block, use an ultrasonic flaw detector to detect flaws in the weld area of the welded test block, obtain the ultrasonic waveform diagram of the metal welded part, and record the measurement position;

(5) Use wire cutting to cut perpendicular to the weld along the measurement points, and firstly grind the side perpendicular to the weld with sandpaper from coarse to fine grains to obtain the cross-section of the weld; clean the polished surface with acetone, Remove oxide film, dirt, burrs and other sundries on the surface, sand, polish and inlay the cross-section of the weld seam according to the standard metallographic sample preparation process, and put it under a laser confocal microscope to take a cross-sectional view of the weld seam;

(6) Use the empirical waveform analysis method to analyze the waveform diagram, establish the corresponding relationship between the typical ultrasonic echo characteristics and the corresponding weld section metallographic structure, and obtain the ultrasonic echo characteristics of the internal structure of the typical weld; use ultrasonic flaw detection The instrument performs flaw detection on other metal welded parts. According to the requirements of flaw detection accuracy, it detects equidistantly along the weld seam direction of the metal welded parts, and obtains the waveform diagram collection of the welding test block along the weld seam direction, and the ultrasonic echo characteristics of the internal structure of the typical defect weld seam. Comparative analysis to determine whether there are defects in the weld of the metal weldment.

The empirical waveform analysis method refers to the amplitude and pulse width of the first, second and third echoes of the ultrasonic wave, the propagation characteristics of the ultrasonic wave in the defective test block and the frequency of the received wave are essentially the attenuation value A characterization to judge weld quality and defect type.

The metal welds are of the same metal material.

The typical ultrasonic echo feature is characterized by the kurtosis coefficient eigenvalue KU calculated by taking time as the amplitude of the sampling point, and KU is the statistical value of the amplitude of the time sampling point, calculated by means of MATLAB.

Compare and analyze the waveform kurtosis coefficient of the metal weldment to be detected with the kurtosis coefficient of the characteristic waveform library to determine whether it is consistent with the typical ultrasonic echo characteristics, so as to determine whether there is a defect.

The thickness dimension of the metal weldment is determined based on the focus range of the ultrasonic probe as a reference, within the focus range.

A device for realizing the detection method of the internal defects of the weld is characterized in that: it includes a test bench 1, a metal weldment 2 positioned on the test bench 1, and a detection system; the detection system includes a software for installing MATLAB software. PC system 10, ultrasonic flaw detector 9, coupling liquid 3, double crystal straight probe 4, ultrasonic echo 5, weld 6 on metal weldment 2, welding area 7 and heat affected zone 8; among them, double crystal straight probe It is a dual-crystal longitudinal wave probe. The probe is both a transmitting probe and a receiving probe. It not only transmits ultrasonic pulses, but also receives ultrasonic pulses. The dual-crystal straight probe and the metal weldment are coupled by a universal coupling liquid.

The present invention has principle innovation and technological innovation, establishes the corresponding relationship between the typical ultrasonic echo characteristics and the corresponding weld section metallographic structure according to the metal weldment of specific materials, obtains the ultrasonic echo characteristics of the internal structure of the typical defect weld, and then according to Flaw detection accuracy needs to be detected equidistantly along the direction of the weld of the metal weldment, and the waveform diagram collection of the welding test block along the direction of the weld is obtained, compared with the ultrasonic echo characteristics of the internal structure of the typical defect weld, and the weld of the metal weldment is judged Whether there is a defect, that is, the non-destructive testing is associated with the metallographic structure of the weld section, and the internal microstructure characteristics of the metal welded part weld can be obtained, forming a new principle and technology of ultrasonic echo non-destructive testing.

The invention has beneficial effects. The invention is based on the detection method of ultrasonic echo flaw detection weld internal defects, which is a new method for non-destructive flaw detection along the direction of the weld seam of the metal weldment on the basis of obtaining the ultrasonic echo characteristics of the internal structure of the typical defect weld of the metal weldment of a specific material , is a supplement to the existing internal defect detection method of metal welded parts. Ultrasonic is used to detect the flaws of the butt welding test block. It is simple and easy to operate, with high sensitivity, good directivity, strong penetration, fast detection speed, and no harm to the human body. damage and no pollution to the specimen and the environment.

Description of drawings

Figure 1 is the ultrasonic testing device for the metal butt welding test block

Figure 2 is a cross-sectional view of the weld without defects inside the 7075-T6 aluminum alloy laser butt welding weld

Fig. 3 is the ultrasonic wave diagram of 7075-T6 aluminum alloy laser butt welding without defects inside the weld seam

Figure 4 is a cross-sectional view of the weld with shrinkage cavity defects inside the 7075-T6 aluminum alloy laser butt welding weld

Figure 5 is the ultrasonic waveform diagram of shrinkage cavity defects inside the 7075-T6 aluminum alloy laser butt welding weld

In the figure, 1. Test platform 2. Metal weldment 3. Coupling liquid 4. Double crystal straight probe 5. Ultrasonic echo in workpiece 6. Weld seam 7. Butt welding area 8. Heat affected area 9. Ultrasonic flaw detector display equipment 10. PC system with MATLAB program installed.

Detailed ways

The details and working conditions of the specific device proposed by the present invention will be described in detail below in conjunction with the accompanying drawings.

Embodiment one:

A method for detecting internal defects of welds based on the ultrasonic echo flaw detection, the specific operation steps are as follows:

1. Use sandpaper to smooth the surface of the metal weldment, and clean the polished surface with acetone to remove oxide film, dirt, burrs and other sundries;

2. Set the parameters of the ultrasonic flaw detector, respectively set the scanning mode, probe angle, probe type (single crystal or dual crystal probe), probe frequency, damping size, scanning range, delay time, detection mode, pulse type, etc., and then prepare for coupling liquid;

3. Calibrate the probe of the ultrasonic flaw detector, and obtain the propagation speed of the ultrasonic wave in the metal welded part; at this time, use the propagation speed of the ultrasonic wave in the metal welded part and the thickness of the metal welded part to calculate Medium propagation time;

4. Use double-crystal straight probes to detect flaws on the test block, place the probe on the test block, use an ultrasonic flaw detector to detect flaws in the weld area of the welded test block, obtain the ultrasonic waveform diagram of the metal welded part, and record the measurement position;

5. Use line cutting to cut perpendicular to the weld seam along the measurement points, and first use 200#, 500#, 800#, 1200#, 1500# sandpaper to grind the sides perpendicular to the weld seam in sequence; Clean the polished surface with acetone to remove oxide film, dirt, burrs and other sundries on the surface. According to the standard metallographic sample preparation process, the cross-section of the weld is polished, polished, and inlaid with sandpaper, and placed in an OLYMPUS OSL3000 laser confocal microscope. Take a cross-sectional view of the weld below;

6. Use the empirical waveform analysis method to analyze the waveform diagram, establish the corresponding relationship between the typical ultrasonic echo characteristics and the corresponding weld section metallographic structure, and select the ultrasonic wave of the weld with pores, slag inclusions and crack defects in the internal structure. The echo, and the ultrasonic echo with a good internal structure of the weld are used as the characteristic waveform;

7. Import the four characteristic waveform data extracted by the ultrasonic flaw detector into the PC system with MATLAB software installed, establish the characteristic waveform library and use MATLAB to calculate the kurtosis coefficient KU of the four waveforms;

8. Use an ultrasonic flaw detector to detect flaws in other metal welded parts. According to the requirements of flaw detection accuracy, detect equidistantly along the weld direction of the metal welded parts, obtain the waveform diagram set of the welding test block along the weld direction, and calculate the peak value of the waveform The coefficient KU is compared with the ultrasonic echo characteristics of the internal structure of typical defective welds to judge whether there are defects and the types of defects in the welds of metal weldments.

Embodiment two:

The ultrasonic testing device for internal defects of metal laser butt welding welds of the present invention comprises: a test bench 1 connected in sequence, a metal weldment 2, and a detection system, wherein the detection system includes an ultrasonic flaw detector 9, a double-crystal straight probe 4, a coupling Liquid 3, ultrasonic echo 5, PC system 10 with MATLAB software installed, weld 6, welding area 7 and heat-affected zone 8. Use the test block ultrasonic detection system to detect the flaws of the butt welded metal weldment 2, use the double crystal straight probe 4 to scan the test block, use the coupling liquid 3 to couple the probe and the test block, and scan the results on the display screen of the ultrasonic flaw detector 9 above shows that the data stored by the ultrasonic flaw detector is exported to the PC system 10, and the kurtosis value coefficient KU is calculated by MATLAB software programming, and compared with the characteristic waveform library to determine whether there is a defect and the type of defect.

The following is an example of the internal defect detection method and device of the 7075-T6 aluminum alloy laser butt welding weld. The laser is used to conduct the laser butt welding test on the 7075-T6 aluminum alloy, and the ultrasonic flaw detector is used to detect the flaws of the butt welding test block and obtain the welding test block Waveform diagram, and the waveform analysis, the preparation of the metallographic structure observation sample, placed in the OLYMPUS OSL3000 laser confocal microscope to take the cross-sectional view of the weld.

Figure 3 is the ultrasonic wave diagram of the 7075-T6 aluminum alloy laser butt welding seam without defects, and Figure 2 is the sectional view of the 7075-T6 aluminum alloy laser butt welding seam without defects. Figure 2 shows that the ultrasonic echoes are clearly visible, the distance between adjacent echoes is almost equal, and the corresponding welds have no obvious cracks and shrinkage cavities when the amplitude of multiple echoes decreases, and the welding quality is high;

Fig. 5 is an ultrasonic wave diagram of defects inside a 7075-T6 aluminum alloy laser butt welding seam, and Fig. 4 is a cross-sectional view of a defect inside a 7075-T6 aluminum alloy laser butt welding seam. Figure 4 shows that the waveforms of the first, second, and third echoes of the ultrasonic wave are very low in amplitude, gentle in the first wave, small in amplitude, and delayed backwards compared with the flawless ultrasonic waveform in Figure 5. After the second echo, the echo cannot be detected, which indicates that the ultrasonic wave encountered a large defect in the propagation of the test block, and there was obvious scattering and frequency attenuation. Observation found that the corresponding metallographic structure diagram has obvious wide and deep cracks and shrinkage cavities.

Experiments show that the microstructure characteristics of laser butt welding seam can be reflected in the corresponding ultrasonic echo images, and different defect echoes have their own unique waveform characteristics, and there is a corresponding relationship to a certain extent.

Claims (7)

1. the detection method of a weld seam inherent vice, be characterised in that the corresponding relation first setting up typical ultrasonic echo feature and corresponding section of weld joint metallographic structure, then ultrasound examination is carried out on the surface of welding test block, judge weld seam inside whether defectiveness by the ultrasonic echo feature detected, concrete steps are as follows:

(1) be that metal welding fitting surface finish between 5 mm ~ 15 mm is smooth by gauge with sand paper, and with acetone cleaning polishing surface, to remove the foreign material such as oxide film, dirt, burr;

(2) UT (Ultrasonic Testing) instrument parameter is set, arrange the probe of scan mode, head angle, monocrystalline or twin crystal type, frequency probe, damping size, sweep limit, time delay, pickup mode, pulse pattern respectively, next gets out coupling solution;

(3) ultrasonic fault detector probe is calibrated, obtain the velocity of propagation of ultrasound wave in metal welding fitting; Now, with the velocity of propagation of ultrasound wave in metal welding fitting and the thickness of metal welding fitting, ultrasound wave travel-time in test block is calculated;

(4) adopt double-crystal normal probe to detect a flaw to test block, probe is placed on above test block, utilize ultra-sonic defect detector to detect a flaw to welding test block welded seam area, obtain the ultrasound wave oscillogram of metal welding fitting, and record measuring position;

(5) adopt Linear cut along measuring everywhere perpendicular to weld seam cutting, the seam cross-section of acquisition is first polished to the side perpendicular to weld seam successively with the sand paper of particle from coarse to fine; With the surface after acetone cleaning polishing, the foreign material such as oxide film, dirt, burr on removing surface, according to the sand papering of standard metallographic specimen preparation section butt welded seam xsect, polishing, inlay, take section of weld joint figure under being put in laser confocal microscope;

Utilize experience Waveform Analysis Method, oscillogram is analyzed, set up typical ultrasonic echo feature and the corresponding relation of corresponding section of weld joint metallographic structure, obtain the ultrasonic echo feature of typical weld seam inner structure; Ultra-sonic defect detector is utilized to detect a flaw to other metal welding fittings, according to flaw detection precision needs, equidistantly detect along metal welding fitting bead direction, obtain the oscillogram set of welding test block along bead direction, analyze with the ultrasonic echo Characteristic Contrast of typical defect weld seam inner structure, judge the weld seam whether existing defects of metal welding fitting.

2. the detection method of a weld seam inherent vice as claimed in claim 1, it is characterized in that: described experience Waveform Analysis Method refer to by hyperacoustic first time, second time and third time the wave amplitude of echo and pulsewidth, ultrasound wave propagation characteristic and to receive ripple frequency be in fact that a sign of pad value is to judge weldquality and defect type in defective test block.

3. a detection method for weld seam inherent vice as claimed in claim 1, is characterized in that: described metal welding fitting is same metal material.

4. the detection method of a weld seam inherent vice as claimed in claim 1, it is characterized in that: described exemplary ultrasonic ripple echo character is that the coefficient of kurtosis eigenwert KU that the amplitude being sampled point in order to the time calculates characterizes, KU is the statistics numerical value of time-sampling point amplitude, is calculated by MATLAB means.

5. the detection method of a weld seam inherent vice as claimed in claim 1, it is characterized in that: the coefficient of kurtosis compare of analysis that the waveform coefficient of kurtosis of metal welding fitting to be detected and signature waveform storehouse are carried out, differentiate and whether conform to exemplary ultrasonic ripple echo character, thus determine whether there is defect.

6. a detection method for weld seam inherent vice as claimed in claim 1, is characterized in that: described metal welding fitting gauge determines that according to the focusing range of ultrasonic probe be reference, within focusing range.

7. realize a device for the detection method of weld seam inherent vice as claimed in claim 1, it is characterized in that: comprise test bench (1), metal welding fitting (2), the detection system be positioned on test bench (1); Described detection system comprise MATLAB software is installed PC system (10), ultra-sonic defect detector (9), coupling liquid (3), double-crystal normal probe (4), ultrasonic echo (5), the weld seam (6) be positioned on metal welding fitting (2), welding region (7) and heat-affected zone (8); Wherein double-crystal normal probe is twin crystal longitudinal wave probe, and probe is transmitting probe and receiving transducer simultaneously, both launches ultrasonic pulse, and receives ultrasonic pulse again, is to adopt general coupling liquid to be coupled between double-crystal normal probe and metal welding fitting.