WO2008133216A1

WO2008133216A1 - Method and device for evaluating ultrasonic spot welded portion

Info

Publication number: WO2008133216A1
Application number: PCT/JP2008/057643
Authority: WO
Inventors: Hajime Takada; Hiroshi Adachi; Kousuke Tsuji
Original assignee: Jfe Steel Corporation; Toyota Shatai Kabushiki Kaisha
Priority date: 2007-04-19
Filing date: 2008-04-14
Publication date: 2008-11-06
Also published as: JP2008286792A; JP5421544B2

Abstract

A fusion welded portion is reliably discriminated from an interface deposit welded portion without being adversely influenced by the shape of the spot welded portion. Ultrasonic waves propagating along the surface of a subject are sent toward a plurality of directions from wave sending positions on outside plates (1a, 1b) of a spot welded portion(2). At wave receiving positions on the outside plate of the spot welded portion (2), ultrasonic waves propagating along the surface of the subject the propagation path of which does not include the spot welded portion (2) and the ultrasonic waves propagating along the surface of the subject the propagation path of which includes the spot welded portion (2) are received. The crosscorrelation between the signal of the received ultrasonic wave propagating through each of the propagation paths connecting the wave sending positions and the wave receiving positions and the signal of a reference ultrasonic wave is computed, and/or the frequency of the signal of the received ultrasonic wave propagating through each of the propagation paths is analyzed. The welded state is judged from the result of the crosscorrelation computation and/or the result of the frequency analysis.

Description

Method and apparatus for evaluating spot welded portion by ultrasonic wave

The present invention relates to a method and an apparatus for inspecting a joining state of a spot welded portion formed by superposing and welding a plurality of plate members by a nondestructive means using ultrasonic waves. Background art

In recent years, for example, in automobile body manufacturing factories, a spot welding inspection method that can be carried out simply has been awaited so that spot welds can be inspected with high efficiency on site. In particular, a spot welded part (hereinafter referred to as a fusion welded part) in which a melted and solidified part (nugget) is generated and the interface of the metal plate are only locally welded. There is a need for a spot welding inspection method that can easily determine spot welds (hereinafter referred to as “interfacial welds”) that have not been generated. The fusion weld is a good spot weld and the interface weld is a poor spot weld.

The body of an automobile is assembled by thousands of spot welds, and the quality of spot welds directly affects the strength and durability of the car body. It is very important to check whether spot welding is properly performed.

Conventionally, as a method for inspecting such spot welds, pass / fail was determined by inserting a chisel between the spot-welded metal plates and checking whether the spot welds peeled off. This is called a chisel inspection. However, since spot welds may break due to the chisel inspection, it is difficult to accurately determine whether or not spot welding is good by chisel inspection. In addition, if the spot welded part is destroyed by a chisel inspection, it will not be a product, resulting in a high cost. Therefore, in recent years, various apparatuses and methods for nondestructively inspecting the quality of spot welds using ultrasonic waves have been proposed.

For example, in Patent Documents 1 to 3, an ultrasonic probe is contacted perpendicularly to the plate surface in order to detect interface welding at a spot welded portion that is produced by superimposing and welding two plates. A method and apparatus for detecting a reflected wave by making the light incident is disclosed.

In Patent Documents 1 and 2, the ultrasonic wave (longitudinal wave) perpendicularly incident on the spot welded portion is observed on the bottom multiple reflection echo returning to the ultrasonic probe after multiple reflection between the front and back surfaces of the welded portion. This method makes use of the fact that the echo height of the bottom multiple reflection echo attenuates as it propagates between the fusion weld and the interface weld. The melt-solidified structure of the melt-solidified part (nugget) is also called a dendrite structure, and is a collection of coarse crystals extending in one direction. Therefore, the transmission of ultrasonic waves is poor and the attenuation is large compared to the metal structure of a steel sheet. In contrast, the metallographic structure of the interfacial welds has a fine crystal grain due to a temperature history close to normalization, so that the transmission of ultrasonic waves is good and the attenuation is small. Therefore, because of the large attenuation at the weld weld, the amplitude of the bottom echo drops sharply as the number of reflections at the bottom increases, whereas at the interface weld weld, the number of reflections at the bottom increases. The drop in the amplitude of the bottom echo accompanying this is gradual. This difference can be used to discriminate between the fusion weld and the interface weld weld.

Also, in Patent Document 3, using a focused ultrasonic probe with a large aperture angle, ultrasonic waves (longitudinal waves) are incident in the vertical direction of the spot weld and are generated by mode conversion in reflection at the bottom. By observing the amplitude of the generated transverse wave, it is possible to distinguish between the fusion welded part and the interfacial welded part by utilizing the phenomenon that the transverse wave does not easily pass through the solid-phase joint surface.

Patent Document 1: Japanese Patent Laid-Open No. 2-8700

Patent Document 2: Japanese Patent Laid-Open No. 4 2 6 5 8 5 4

Patent Document 3: Japanese Patent Laid-Open No. 2 0 0 0— 1 4 6 9 2 8

Patent Document 4: Japanese Patent Application Laid-Open No. 2 0 06-7 1 4 2 2

Disclosure of the invention As shown in FIG. 12, in spot welding, the upper plate 1 0 1 a and the lower plate 1 0 1 b are strongly pressed by an electrode tip (not shown). A depression 1 0 2 b is formed on the surface of the plate 1 0 1 b. The depression 1 2 b is roughly composed of an inclined surface 10 2 c and a flat part, but the flat part also has subtle irregularities. Therefore, the amplitude of the bottom multi-reflected echo that the ultrasonic wave perpendicularly incident on the spot welded part 102 reflects back and forth between the front and back of the welded part and returns to the ultrasonic probe is also affected by the subtle unevenness. Dependent. If the degree of the unevenness is large, the drop in the amplitude of the bottom echo accompanying the increase in the number of reflections on the bottom surface will also be abrupt. In addition, when ultrasonic waves are transmitted to the spot welded portion 102 using an ultrasonic probe, the ultrasonic waves are scattered by the unevenness, which makes it difficult to observe the bottom surface multiple reflection echo itself. Because of this, Patent Literature: ~

In the method disclosed in No. 2, it is difficult to accurately identify the fusion welded portion and the interfacial weld weld.

On the other hand, in the technique of Patent Document 3, since the amplitude of the transverse wave generated by the mode conversion depends on the incident angle of the ultrasonic wave to the bottom surface, the amplitude of the transverse wave changes depending on the shape of the weld described above. was there. However, in many cases, interfacial welds such as plating materials are often completely welded and joined to the metal used in the mesh. As a result, the transverse wave passes as in the case of fusion welds. With this technology, it was sometimes difficult to distinguish between fusion welds and interfacial welds.

The inventor of the present application has already proposed the following spot weld evaluation method in Patent Document 4. In other words, in the ultrasonic evaluation method for spot welds formed by superimposing and welding a plurality of metal plates, it propagates in the cross section formed by the direction along the surface of the metal plate or spot weld and the thickness direction. When the ultrasonic wave is referred to as an ultrasonic wave propagating along the surface of the subject, it propagates along the surface of the subject from a plurality of transmission positions of the metal plate outside the spot welded portion in a plurality of directions. Ultrasound is transmitted, and at multiple receiving positions on the metal plate outside the spot weld, the ultrasonic wave propagated along the surface of the subject not including the spot weld in the propagation path, and the propagation path spot An ultrasonic wave characterized by receiving ultrasonic waves propagating along the surface of the object including the welded portion and evaluating the soundness of the spot welded portion from the ultrasonic waves received at the plurality of positions. This is a method for evaluating spot welds using According to the present invention, the spot welded portion can be evaluated accurately in a non-destructive manner without being affected by the inclined surface formed around the recess formed in the spot welded portion, and limited to a short time. Even if measurement is performed, the spot welded part is highly reliable without being affected by the displacement of the position of the ultrasonic probe and the spot welded part or the contact state between the ultrasonic probe and the metal plate. Succeeded in evaluating the health. Also, in Patent Document 4, the amplitude profile of the ultrasonic wave transmitted using a transducer array and received using another transducer array is obtained, and the width of the amplitude profile below a predetermined threshold is calculated. Disclosed display as nugget diameter.

However, in a busy manufacturing site inspection that requires judgment in a short time, depending on the spot welded area, it may be necessary to simply identify and display good and defective parts. In such cases, it is preferable to display the distinction between fusion welds and interfacial welds rather than nugget diameters.

The present invention has been made in order to solve the drawbacks of Patent Document 4, and the problem is that it is not affected by the shape of the spot welded portion and is highly reliable with the fusion welded portion. It is to identify and display the interface weld weld. In other words, the present invention is an improvement over Patent Document 4 that enables instant determination of the quality of spot welds.

The present invention relates to an ultrasonic evaluation method of a spot welded portion formed by superposing and welding a plurality of plate materials, and propagating in a cross section formed by a direction along the surface of the plate material or spot welded portion and a thickness direction. The ultrasonic wave that propagates along the surface of the subject is propagated along the surface of the subject in multiple directions from multiple wave transmission positions on the plate material outside the spot weld. Ultrasound is transmitted, and spot welds are not included in the propagation path at the multiple receiving positions of the plate material outside the spot welds. Receiving the ultrasonic wave propagating along the surface of the subject and the ultrasonic wave propagating along the surface of the subject including the spot weld in the propagation path. A cross-correlation operation between an ultrasonic signal received in each of the propagation paths connecting the received wave positions and a reference ultrasonic signal, and the plurality of transmitting positions and the plurality of receiving positions. At least one of the frequency analysis of the ultrasonic signals received in each of the propagation paths connecting the two, and determining the welding state based on at least one of the cross-correlation calculation results and the frequency analysis results The above-mentioned problem is solved.

The present invention also relates to an ultrasonic evaluation apparatus for a spot welded portion formed by superposing and welding a plurality of plate materials, according to the direction along the surface and the thickness direction of the plate material or spot welded portion. When the ultrasonic wave propagating in the cross section to be formed is referred to as the ultrasonic wave propagating along the surface of the subject, the subject is directed toward the plural directions from the plurality of transmission positions of the plate material outside the spot welded portion. The ultrasonic wave that propagates along the surface of the subject that does not include spot welding in the propagation path at the multiple receiving positions of the plate material outside the spot welded part , And means for receiving ultrasonic waves propagating along the surface of the subject including spot welds in the propagation path, and a propagation path connecting the plurality of transmission positions and the plurality of reception positions Supersonic waves received in each of And cross-correlation between the signal of the reference ultrasonic signal and the reference ultrasonic signal, and frequency analysis of the ultrasonic signal received in each of the propagation paths connecting the plurality of transmission positions and the plurality of reception positions A means for discriminating a welding state based on at least one of the cross-correlation calculation result and the frequency analysis result, and an ultrasonic spot welded portion characterized by comprising: An evaluation device is provided.

As the reference ultrasonic signal, an ultrasonic signal that has propagated along the surface of the subject that does not include a spot weld in the propagation path can be used. The means for transmitting ultrasonic waves propagating along the surface of the subject from the plurality of transmission positions in a plurality of directions can be an ultrasonic probe including a transducer array.

The means for receiving ultrasonic waves at the plurality of receiving positions may be an ultrasonic probe equipped with a transducer array.

According to the present invention, it is possible to reliably distinguish between a fusion welded portion and an interface weld welded portion without being affected by the shape of the spot welded portion. Brief Description of Drawings

FIG. 1 is a perspective view showing a basic configuration of an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an ultrasonic propagation path for explaining the principle of the present invention. Figure 3 is also a plan view.

Figure 4 is a cross-sectional view of the spot weld.

FIG. 5 is a perspective view including a partial block diagram showing an example of an apparatus for carrying out the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a cross-correlation calculation value profile.

FIG. 7 is a diagram showing the accuracy of measurement results obtained by the method of the present invention.

FIG. 8 is an explanatory diagram showing the magnitude profile of the specific frequency component of the received ultrasonic wave. FIG. 9 is a diagram showing the accuracy of measurement results obtained by the method of the present invention.

FIG. 10 is an explanatory diagram showing a determination method using the feature amount space.

Figure 11 shows a display example of the identification result between the fusion weld and the interface weld.

Fig. 12 is a cross-sectional view illustrating the spot weld.

The description of the reference numerals in the figure is as follows.

1 a, 1 0 1 a… Upper plate

1 b, 1 0 1 b ... Lower plate

2, 1 0 2 ... Spot weld 2 a, 1 0 2 a… nuggets

2 b… Melt solidified structure> (welded metal)

1 0, 2 0 ... Ultrasonic probe

1 1, 2 1 ... vibrator array

2 5, 2 6 ... switch circuit

3 0… Ultrasonic transceiver

3 1 "'A, D converter

3 2... Arithmetic unit BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Here, an example of the evaluation of a spot weld where two metal plates are joined will be described. The upper plate of the two metal plates is called the upper plate, and the lower plate is called the lower plate. In the present invention, as shown in FIG. 1, an ultrasonic probe 10 having a transducer array 11 and an ultrasonic probe 20 having a transducer array 21 are connected to an upper plate 1. a Make contact with the spot welding part 2 on the opposite side. An appropriate contact medium is interposed between the ultrasonic probe 10 and the ultrasonic probe 20 and the upper plate 1a.

Using an ultrasonic probe 10 having the transducer array 11, ultrasonic waves are transmitted from a plurality of positions to the upper plate 1 a. The ultrasonic probe 10 has a structure in which the transducer array 1'1 is attached to the resin wedge 1 2, and the ultrasonic wave transmitted from the transducer array 1 1 is obliquely formed on the upper plate 1 Incident on a.

As shown in FIG. 2, the ultrasonic waves traveling obliquely with respect to the surface of the upper plate la are transmitted into the upper plate la by the obliquely incident ultrasonic waves. The ultrasonic wave traveling diagonally includes longitudinal waves and transverse waves, and propagates through the upper plate: la while repeating reflection and mode conversion on the bottom surface and surface of the upper plate 1a (hereinafter, along the surface of the subject). Also referred to as ultrasonic waves propagating to the surface). In Fig. 2, the solid line is the transverse wave and the broken line is the longitudinal wave. Ultrasonic When the incident angle to the upper plate 1a is an appropriate value, the ultrasonic wave that propagates by repeating the reflection is a wave called a Lamb wave.

The propagating ultrasonic waves are received by the ultrasonic probe 20 having the transducer array 21. The ultrasonic probe 20 has a structure in which a transducer array 21 is attached to a resin wedge 22.

The plane path shown in Fig. 3 (viewed from the top surface of the metal plate) is obtained by the ultrasonic probe 1 0 equipped with the transducer, ray 1 1 and the ultrasonic probe 2 0 equipped with the transducer array 2 1. (Path) can be received. Ultrasound probe 1 0 transducer array 1 1 represents individual transducers 1 1 i to l 1 _N , ultrasound probe 2 0 transducer array 2 1 individual transducers 2 1 We denote it as ~ 2 1 ₁ ^. As N, for example, the number of 4, 8, 16 or 32 can be used. Figure 3 shows the case where N is 16. Since the ultrasonic waves transmitted from the transducers 11 1 to 11 _N of the vibrator array have a spatial spread, the plane path shown in Fig. 3 is passed from the transducers 1 li to l 1 _N. It can transmit ultrasonic waves.

The ultrasonic wave transmitted from the transducer 1 1 i of the ultrasonic probe 10 is received by the transducers 2 1 i to 2 1 _{N of the} ultrasonic probe 2 0. Next, the ultrasonic wave transmitted from the transducer 1 1 _{2 of the} ultrasonic probe 10 is received by the transducers 2 1 i to 2 1 _{N of the} ultrasonic probe 20. This process is repeated until the ultrasonic waves transmitted from the transducer 1 1 _{N of the} ultrasonic probe 10 are received by the transducers 2 1 i to 2 1 _{N of the} ultrasonic probe 2 0. This is done by sequentially changing the oscillator ll _n (N = l, 2,. As a result, ultrasonic waves transmitted from a plurality of positions and propagating in a plurality of directions can be received by the transducer 2 1!-. 2 1 N of the ultrasonic probe 20.

As shown in FIG. 4, the nugget 2 a generated in the spot weld 2 is a molten and solidified structure 2 b having a direction substantially parallel to the plate thickness direction. This molten and solidified structure 2b force is a weld metal as referred to in the present invention. This melt-solidified structure 2b, also called a dendrite structure, is a collection of coarse crystals extending in one direction. Compared to other metal structures, the transmission of ultrasonic waves is poor (attenuation is large). Therefore, the ultrasonic wave propagating in the path shown in Fig. 3 is attenuated according to the length of the melt-solidified structure 2b existing in the propagation path when the path contains the melt-solidified structure 2b. The amplitude is reduced and received by the ultrasonic probe 20. In addition, the melt-solidified structure 2b has a property that the speed of propagation of the ultrasonic wave is considerably different from that of the metal structure of the metal plate. In the melt-solidified structure 2b, as shown in the schematic diagram of the micro metal structure shown in Fig. 4, the specific orientation of the metal crystal (shown using the dashed arrows in Fig. 4) is almost aligned in the thickness (z) direction. Therefore, the structure has inertial anisotropy. Therefore, the propagation speed of ultrasonic waves changes depending on the propagation direction (azimuth dependence of propagation speed). On the other hand, in the metal structure of a metal plate (steel plate), since the metal crystal is oriented in a random direction, the propagation speed of the ultrasonic wave does not depend on the propagation direction and is a constant value. As described above, the propagation speed of the ultrasonic wave propagating along the surface of the object is determined when the propagation path includes the molten solidified structure 2 b and when the propagation path does not include the molten solidified structure 2 b (metal Generally, it is different from (propagating only the metal structure of the plate). Furthermore, the ultrasonic wave propagating in the subject while repeating reflection and mode conversion on the bottom and surface of the subject has ultrasonic components propagating in various angular directions, so it melts in the propagation path. When solidified tissue 2b is included, the propagation velocity changes for each component due to the azimuth dependence of the propagation velocity, resulting in a significant change in the waveform of the received ultrasonic signal (phase mixing). . .

Width of ultrasonic probe 10 used for transmission (total width of transducers 1 li to l 1 _N ) and width of ultrasonic probe 20 used for reception (transducers 2 1 i to 2 1 _{By making} the overall width of _N ) larger than the planar size of the melt-solidified structure 2b, the path located at the end of the planar path shown in Fig. 3 (eg 1 1 1 2 1 1 _N → It is possible to prevent the melted and solidified structure 2b from being contained in 1 2 _N ). In this path that does not include the melt-solidified structure, there is only a metal structure of the metal plate (steel plate) and a fine crystal structure that has undergone a temperature history close to normalization. b attenuation and phase Mixing of does not appear. Similarly, because the microstructure of the interface weld weld is subject to a temperature history close to normalization, the crystal grains are fine, so the attenuation and phase mixing due to the melt-solidified structure 2b are not applied to the received ultrasonic waves. Does not appear. In addition, since the melt-solidified structure 2b is composed of coarse crystal grains, the higher the frequency of the ultrasonic wave, the more the ultrasonic wave is attenuated. Therefore, in the plane path shown in FIG. 3, when the received ultrasonic wave of the path including the molten solidified structure 2 b and the received ultrasonic wave of the path not including the molten solidified structure 2 b are compared, the molten solidified structure 2 The received wave of the path that does not include b contains more high-frequency components. Similarly, when the received ultrasonic wave of the path including the interface weld is compared with the received ultrasonic wave of the path including the molten solidified structure 2b, the received ultrasonic wave of the path including the interface weld is higher in frequency. Contains a lot of ingredients. '

Further, the received ultrasonic wave of the path including the melt-solidified structure 2 b also changes its low frequency component as a result of the mixing of the ^: phase. Therefore, comparing the received ultrasonic wave of the path including the melt-solidified structure 2b and the received sound wave of the path not including the molten-solidified structure 2b in the planar path shown in Fig. 3, A difference appears. Similarly, when the received ultrasonic wave of the path including the interface weld and the received ultrasonic wave of the path including the melted solidified structure 2.b are compared, there is a difference in the low frequency component.

Therefore, by observing the waveform change (attenuation and phase mixing) and frequency components of the received ultrasonic wave, it is possible to identify whether the propagation path contains a molten solidified structure or an interface welded part. Can be performed. Specifically, the cross-correlation calculation is performed with the signal waveform of the received ultrasonic wave on the other path, using the signal waveform of the received ultrasonic wave on the path located at the end as a reference waveform. If the propagation path contains a melt-solidified structure, the cross-correlation calculation value becomes a relatively small value due to a change in the waveform of the received ultrasonic wave. In addition, frequency analysis is performed on the ultrasonic signals received in each of the propagation paths connecting a plurality of transmission positions and a plurality of reception positions. When the solidification structure is included in the propagation path, phenomena such as large attenuation of high frequency components and changes in low frequency components are observed. In this embodiment, since the ultrasonic probe 10 and the ultrasonic probe 20 are not brought into contact with the recesses of the spot welded portion 2, spotting is performed in ultrasonic transmission and reception. The effect of the dent in the weld does not appear. Furthermore, the ultrasonic wave propagating along the surface of the subject does not lose the property of propagating along the surface even if the incident angle and reflection angle with respect to the subject front and back surfaces are slightly changed due to a few depressions and irregularities. For this reason, in this embodiment, it is possible to identify whether the propagation path includes a force including a melt-solidified structure or whether an interface weld weld is included without being affected by the shape of the spot weld. Can be done.

As shown in FIG. 5, as described above, the ultrasonic probe 10 and the ultrasonic probe were applied to the sample on which two metal plates (steel plates) having a thickness of 0.6 mm were overlapped and spot-welded. The ultrasonic probe 10 is driven sequentially from the ultrasonic transmitter / receiver 30 through the switch circuit 25 to the transducer 1 1 to 1 1 _The ultrasonic wave transmitted from _{N is} received by the ultrasonic probe 2 Q transducers 2 1 i to 2 1 _{N, and} is amplified by the ultrasonic transmitter / receiver 30 through the switch circuit 26. The AZD converter 31 converts the received signal to AZD, and then uses the arithmetic unit 3 2 to transmit the received ultrasonic wave transmitted from the vibrator 1 1 i and received by the vibrator 2 1] as a reference signal. As a result, cross-correlation calculation was performed with the received ultrasonic signals of other paths. Here, N is 1 6, and the maximum value of the signal waveform after calculation is detected as the cross-correlation calculation result. In addition, the frequency analysis (Fast Fourier Transform: FFT) of the received ultrasonic signal received by the transducers 2 1 i to 2 1 _N of the ultrasonic probe 20 is performed using the arithmetic device 3 2. It was.

Figure 6 compares the cross-correlation calculation profile measured using a spot weld sample containing a melt-solidified structure and an interfacial weld sample. The profile of the cross-correlation calculation value is the received ultrasonic signal transmitted from the transducer 1 1 _{n and} received by the transducer 2 1 _n (n = 1, 2, 3,-, 1 6). The result of cross-correlation with the reference signal is displayed in the order of the path number n. As shown in Fig. 6, there is a clear difference in the cross-correlation calculation value profile between the spot weld sample containing the melt-solidified structure and the interfacial weld sample. Figure 7 shows the average value of the specific frequency components of the received ultrasonic waves measured using the spot weld sample including the melt-solidified structure and the interface weld weld sample (for example, in this experiment, the ultrasonic probe 1 0 The center frequency of ultrasonic waves transmitted and received by 20 and 20 is in the range of 10%, and if the center frequency is 10 MHz, the range is 9 to 11 MHz, spot welds including melt-solidified structures and interface weld spots. Any frequency component that can be observed to be different from the welded part is shown in comparison with the magnitude profile of the received ultrasonic wave. Is the magnitude of the specific-frequency component of the received ultrasonic signal transmitted from the vibrator 1 1 _{η and} received by the vibrator 2 1 _η (η = 1, 2, 3,…, 1 6). The path numbers are arranged in the order of η, as shown in Fig. 7. There is a clear difference in the magnitude profile of the specific frequency component of the received ultrasonic wave between the weld weld sample and the interface weld welded sump nore. Is an abbreviation for arbitrary unit and indicates a relative value.

In the apparatus of the embodiment shown in FIG. 5, the wedge members 1 2 and 22 of the ultrasonic probes 10 and 20 are made of polystyrene, and the transducer arrays 1 1 1 ₁₆ and 2 1 to 2 1 ₁₆ are arranged in an array. The spot weld 2 was measured so that the width of the vibrator in the direction was 0.8 mm and the incident angle of the ultrasonic wave on the top plate surface was 25.4 °. 'As a measurement target, 30 samples prepared by spot welding two steel sheets with a thickness of 0.6 mm were used. 20 are spot weld sample containing melt-solidified structure, and 10 are interface weld spot weld sample.

For each sample, normalize so that the maximum value of the cross-correlation calculation value (the cross-correlation calculation value of the reference signal and the signal of path 1 li → l 2, is usually the maximum) is 1 28, and other paths ( Oscillator 1 1 _n → Oscillator 2 1 _n , n = 2, 3, ..., 1 6) The cross-correlation calculated value and the absolute value of the difference between 1 did. Figure 8 shows the correlation calculation evaluation index for each sample. Spot welded sun containing molten solidified structure It can be seen that there is a clear difference in the correlation calculation evaluation index between the pull and the interface weld spot weld sample. By setting an appropriate threshold value for the correlation calculation evaluation index, it is possible to determine a spot weld including a melt-solidified structure and an interface weld spot weld.

For each sample, the frequency of the specific frequency component of the received ultrasonic wave was determined by fast Fourier transform (FFT). The average value of the specific frequency components of multiple paths was calculated and used as a frequency evaluation index. For example, vibrator 1 l _n → vibrator 2 1 _n , n = 6, 7,-, 11, and there is a difference between spot welds containing molten solidified structures and interface weld spot welds Any route can be selected as long as it is observed, and any number can be selected. Figure 9 shows the frequency evaluation index for each sample. It can be seen that there is a clear difference in the frequency evaluation index between the spot weld sample containing the molten and solidified structure and the interface weld spot weld sample. By setting an appropriate threshold value for the frequency evaluation index, it is possible to determine a spot weld including a melt-solidified structure and an interfacial weld spot weld. As a frequency evaluation index, in addition to the average value of the specific frequency component in the predetermined route, the maximum value of the specific frequency component in the predetermined route, the center of gravity frequency, the center frequency, and the change in the low-frequency ultrasonic component Indices such as condition can be used. The frequency evaluation index may be configured using two or more indices.

In the actual determination, the determination may be made using either the correlation calculation evaluation index or the frequency evaluation index. Note that, when both evaluation indexes are combined, the reliability of the determination result is improved.

Furthermore, as shown in Fig. 1Q, two or more evaluation indexes are selected from the correlation calculation evaluation index and the frequency evaluation index to be feature quantity A, feature quantity B, and so on. The center of gravity of the spot welded part group (healthy group) and interfacial weld spot welded part group (defective group) is obtained in advance, and when measuring a new spot welded part, the feature value space of the spot welded part measured value Position (measurement value position) and sound collection The distance between the group (healthy distance) and the distance between the measured value position and the defective group (defect distance) are obtained and compared, and it is determined that the spot weld is included in the smaller group. Moyore.

Figure 11 shows a display example of the identification result between the fusion weld and the interface weld. The case of a fusion weld is shown in (a) in Fig. 11. The case of an interfacial weld is shown in (b) in Fig. 11. In this way, it is possible to simply show the distinction between fusion welds and interfacial welds, so there is no doubt in the inspection results and it is suitable for inspections in busy manufacturing sites.

In this embodiment, since the ultrasonic probe provided with the transducer array is used on both the transmission side and the reception side, the configuration is simple. It is also possible to use a plurality of probes in juxtaposition to either one or both, or to scan and use a single probe. .

Furthermore, in the above description, the present invention is applied to welding inspection of a metal plate (steel plate), but the application target of the present invention is not limited to this. It can also be applied to welding inspection of aluminum plates and other inorganic and organic materials. Also, the number of welds is not limited to two, and the evaluation of the soundness of spot welds is not limited only to the identification of spot welds containing a melt-solidified structure and spot welds containing an interface weld. Les.

Claims

The scope of the claims

1. In the ultrasonic evaluation method for spot welds formed by superposing and welding a plurality of plate materials, the cross section formed by the direction along the surface of the plate material or spot weld and the thickness direction When the propagating ultrasonic wave is referred to as the ultrasonic wave propagating along the surface of the subject,,.

The ultrasonic wave propagating along the surface of the subject is transmitted from multiple wave transmission positions of the plate material outside the spot weld in multiple directions,

The ultrasonic wave propagating along the surface of the subject not including the spot weld in the propagation path at a plurality of receiving positions of the plate material outside the spot weld, and the subject including the spot weld in the propagation path Receives ultrasonic waves propagating along the surface,

A cross-correlation operation between a signal of an ultrasonic wave received in each of propagation paths connecting the plurality of transmission positions and the plurality of reception positions and a reference ultrasonic signal; and At least one of the frequency analysis of the ultrasonic signal received in each of the propagation paths connecting the wave position and the plurality of reception positions is performed, and at least one of the cross-correlation calculation result and the frequency analysis result A method for evaluating a spot weld by ultrasonic waves, characterized in that a welding state is discriminated based on the ultrasonic wave.

2. The ultrasonic wave signal according to claim 1, wherein the reference ultrasonic signal is a signal including a spot weld in a propagation path and an ultrasonic signal propagating along the surface of the subject. Evaluation method of spot welds by ultrasonic waves.

3. In an ultrasonic evaluation apparatus for spot welds formed by superposing and welding a plurality of plates, the cross section formed by the direction along the surface of the plate or spot weld and the thickness direction When the ultrasonic wave that propagates is called ultrasonic wave that propagates along the surface of the subject, Means for transmitting ultrasonic waves propagating to the surface along the surface of the subject from a plurality of transmission positions of the plate material outside the spot welded portion in a plurality of directions;

Ultrasonic waves that have propagated along the surface of the subject that does not include the spot weld in the propagation path, and the subject that includes the spot weld in the propagation path at a plurality of receiving positions on the plate material outside the spot weld. Means for receiving ultrasonic waves propagating along the surface of the surface, and ultrasonic signals received in each of the propagation paths connecting the plurality of transmission positions and the plurality of reception positions and a reference At least one of a cross-correlation calculation with the ultrasonic signal and a frequency analysis of the ultrasonic signal received in each of the propagation paths connecting the plurality of transmission positions and the plurality of reception positions Means for determining the welding state based on at least one of the cross-correlation calculation result and the frequency analysis result;

An apparatus for evaluating spot welds using ultrasonic waves.

4. The ultrasonic wave signal according to claim 3, wherein the reference ultrasonic signal is a signal including a spot weld in a propagation path and an ultrasonic signal propagated along the surface of the subject. Evaluation equipment for spot welds using ultrasonic waves.

5. The ultrasonic probe according to claim 3 or 4, wherein the means for transmitting ultrasonic waves propagating along the surface of the subject from the plurality of transmission positions in a plurality of directions includes a transducer array. An apparatus for evaluating spot welds by ultrasonic waves, characterized by being a child.

6. The ultrasonic spot according to any one of claims 3 to 5, wherein the means for receiving ultrasonic waves at the plurality of receiving positions is an ultrasonic probe including a transducer array. Evaluation equipment for welds.