JP2011196862A - Method and device for inspection spot welding part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately inspect the quality of a spot welding portion.SOLUTION: An ultrasonic probe 10 transmits the ultrasonic signals propagated through an upper plate 2, which is the plate material on the outside of the spot welding part 4, from a plurality of the transmission positions of the upper plate 2, and an ultrasonic probe 20 receives at least the ultrasonic signals containing the spot welding part in a propagation route at a plurality of the receiving positions of the upper plate 2. An arithmetic unit 34 executes wavelet analysis of the ultrasonic signals received by the ultrasonic probe 20 and determines the quality of the spot welding part, on the basis of the analyzing result of the wavelet analysis.

Description

  The present invention relates to an inspection method and an inspection apparatus for spot welds for inspecting the quality of spot welds.

  The body of a vehicle such as an automobile is assembled by spot welding with thousands of points. The quality of spot welds directly affects the strength and durability of the vehicle body. For this reason, inspecting the quality of the spot weld is an extremely important operation. Thus, until now, a chisel inspection has been performed. The chisel inspection is an inspection method for inspecting the quality of the spot welded portion by inserting a chisel between the spot-welded metal plates and checking whether the spot welded portion is peeled off by the chisel.

  However, according to such an inspection method, when the chisel is inserted, the spot welded portion is destroyed by the chisel, and the quality of the spot welded portion may not be accurately inspected. Moreover, since the vehicle body in which the spot welded portion is destroyed cannot be used as a product, the manufacturing cost of the vehicle body increases. For this reason, in recent years, there has been proposed an inspection method for inspecting the quality of a spot welded portion in a non-contact manner using ultrasonic waves, as disclosed in Patent Document 1.

  In the inspection method described in Patent Document 1, the spot welded portion is merely a local weld at the interface between the fusion welded portion where the nugget, which is a melt-solidified structure, is formed, and the metal plate. It is determined which of the interface weld welds is not formed. Specifically, in this inspection method, when inspecting a spot weld formed by spot welding two metal plates, first, from a plurality of transmission positions on one metal plate surface, a plurality of directions. An ultrasonic wave propagating in one metal plate is transmitted toward Next, ultrasonic waves that have propagated through one metal plate are received at a plurality of reception positions on the surface of the one metal plate. And the presence or absence of the nugget in a spot welding part is detected by detecting attenuation | damping of the received ultrasonic wave, phase mixing, and attenuation | damping of a high frequency component.

  The nugget detection method based on ultrasonic attenuation, phase mixing, and high-frequency component attenuation will be described below.

[Attenuation of ultrasonic waves]
The melt-solidified structure forming the nugget is less likely to transmit ultrasonic waves than the metal structure of the metal plate. For this reason, when the ultrasonic wave passes through the nugget, the intensity of the ultrasonic wave is greatly attenuated. Therefore, by detecting the attenuation of the intensity of the received ultrasonic wave based on the transmitted ultrasonic wave, it is possible to determine whether or not a nugget exists on the ultrasonic wave propagation path.

[Phase mixing]
The propagation speed of ultrasonic waves in the nugget varies depending on the propagation direction. Moreover, the ultrasonic wave propagating in the metal plate has an ultrasonic component propagating in various angular directions. For this reason, when an ultrasonic wave passes through a nugget, the waveform of the received ultrasonic wave changes significantly from the waveform of the transmitted ultrasonic wave by mixing ultrasonic components having different phases. Therefore, whether or not there is a nugget on the propagation path of the ultrasonic wave is detected by detecting a change in the ultrasonic waveform by performing a cross-correlation operation between the received ultrasonic wave waveform and the transmitted ultrasonic wave waveform. Can be determined. It is also possible to determine whether or not there is a nugget on the ultrasonic wave propagation path by detecting a change in a specific frequency component due to mixing of ultrasonic components having different phases by frequency analysis.

[High-frequency component attenuation]
Since the nugget is formed of coarse crystal grains, the intensity of the ultrasonic wave that has passed through the nugget is greatly attenuated as the frequency increases. Therefore, it is possible to determine whether or not there is a nugget on the propagation path of the ultrasonic wave by detecting the attenuation of the intensity of the high frequency component of the ultrasonic wave received by the frequency analysis.

JP 2008-286792 A JP 2006-200901 A

  However, the inspection method described in Patent Document 1 has the following problems.

  First, the inspection method described in Patent Document 1 does not consider the presence of a heat-affected zone formed by the metal structure of the metal plate changing from the original metal structure due to heat applied during spot welding. In general, since crystal grains are coarsened in the heat-affected zone, the intensity of the ultrasonic wave propagating through the heat-affected zone is greatly attenuated, and the intensity of the high-frequency component may also be attenuated. For this reason, according to the inspection method described in Patent Document 1, there is a possibility that the nugget is erroneously determined even though the intensity of the ultrasonic wave is attenuated by the heat affected zone.

  2ndly, in an interface welding weld part, the waveform of the ultrasonic wave received by an ultrasonic wave propagating from one metal plate to the other metal plate via an interface changes. For this reason, according to the inspection method described in Patent Document 1, the waveform of the received ultrasonic wave is actually changed by the propagation of the ultrasonic wave from one metal plate to the other metal plate via the interface. Nevertheless, there is a possibility that the nugget is erroneously determined to be formed.

  This invention is made | formed in view of the said subject, The objective is to provide the inspection method and inspection apparatus of a spot-welded part which can test | inspect the quality of a spot-welded part correctly.

  In order to solve the above-described problems and achieve the object, the spot welded portion inspection method according to the present invention is a spot welder that inspects the quality of a spot welded portion formed by superposing and spot welding a plurality of plate materials. A method for inspecting a portion, a wave transmitting step for transmitting an ultrasonic signal propagating through a plate material from a plurality of wave transmitting positions of a plate material outside a spot welded portion, and a plurality of receiving waves of a plate material outside the spot welded portion At the position, receive the ultrasonic signal that includes at least the spot weld in the propagation path, and perform wavelet analysis of the ultrasonic signal received by the reception step, based on the analysis result of wavelet analysis And a determination step for determining the quality of the spot welded portion.

  In order to solve the above-described problems and achieve the object, the spot welded portion inspection apparatus according to the present invention is a spot welder that inspects the quality of a spot welded portion formed by spot welding by overlapping a plurality of plate materials. An inspection device for a portion, a wave transmitting means for transmitting an ultrasonic signal propagating through a plate material from a plurality of wave transmission positions of a plate material outside the spot welded portion, and a plurality of receiving waves of the plate material outside the spot welded portion At the position, the receiving means for receiving the ultrasonic signal including at least the spot weld in the propagation path, and the wavelet analysis of the ultrasonic signal received by the receiving means are executed, and based on the analysis result of the wavelet analysis Determining means for determining the quality of the spot welded portion.

  According to the inspection method and inspection apparatus for a spot welded portion according to the present invention, the quality of the spot welded portion is determined by performing wavelet analysis of an ultrasonic signal including the spot welded portion in the propagation path. It is possible to accurately check the quality.

FIG. 1 is a schematic diagram showing the configuration of a spot welded portion inspection apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a propagation path of an ultrasonic signal. FIG. 3 is a schematic diagram illustrating a propagation path of an ultrasonic signal, and FIGS. 3A and 3B are schematic diagrams illustrating a propagation path of an ultrasonic signal in a fusion welded portion and an interface weld weld, respectively. is there. FIG. 4 is a diagram illustrating an example of an ultrasonic signal to be transmitted. FIG. 5 is a diagram showing an ultrasonic signal. FIGS. 5A and 5B are diagrams showing the ultrasonic signal shown in FIG. 4 when a fusion welded portion and an interfacial weld weld are formed. It is a figure which shows the ultrasonic signal received when it is waved. FIG. 6 is a diagram illustrating an example of a mother wavelet. FIG. 7 is a diagram illustrating a mother wavelet, and FIGS. 7A to 7C are diagrams illustrating a change in the shape of the mother wavelet accompanying a change in expansion / contraction coefficient. FIG. 8 is a diagram showing a wavelet, and FIGS. 8A to 8C are cases where the ultrasonic signal includes an ultrasonic signal derived from a normal transmitted wave and an ultrasonic signal derived from a weld metal transmitted wave. It is a figure which shows the wavelet calculated by. FIG. 9 is a diagram illustrating a wavelet, and FIGS. 9A to 9C are diagrams illustrating wavelets that are calculated when the ultrasonic signal includes only an ultrasonic signal derived from a normal transmitted wave. FIG. 10 is a diagram illustrating an experimental example of wavelet analysis. FIG. 11 is a diagram for explaining the difference between the prior art and the present invention, and FIGS. 11A and 11B are diagrams showing the inspection results of the spot welds according to the prior art and the present invention, respectively. .

  Hereinafter, a spot welded portion inspection apparatus and inspection method according to an embodiment of the present invention will be described with reference to the drawings.

[Configuration of inspection equipment]
First, with reference to FIG. 1, the structure of the inspection apparatus of the spot weld part which is one Embodiment of this invention is demonstrated.

  FIG. 1 is a schematic diagram showing the configuration of a spot welded portion inspection apparatus according to an embodiment of the present invention. As shown in FIG. 1, the spot welded portion inspection apparatus 1 according to an embodiment of the present invention is a spot welded portion formed by spot welding two metal plates, an upper plate 2 and a lower plate 3. 4 is an apparatus for inspecting pass / fail of 4. The inspection apparatus 1 includes an ultrasonic probe 10, an ultrasonic probe 20, switch circuits 30 and 31, an ultrasonic transmitter / receiver 32, an A / D converter 33, and an arithmetic device 34. The ultrasonic probe 10, the ultrasonic probe 20, and the arithmetic unit 34 function as a wave transmitting unit, a wave receiving unit, and a determination unit according to the present invention, respectively.

The ultrasonic probe 10 and the ultrasonic probe 20 are arranged to face each other on the surface of the upper plate 2 that is a plate material outside the spot welded portion 4. A contact medium (not shown) is interposed between the ultrasonic probe 10 and the ultrasonic probe 20 and the upper plate 2. The ultrasonic probe 10 has a structure in which a transducer array 12 including a plurality of ultrasonic transducers 12 _{1 to} 12 _N is attached to a resin wedge 11. The ultrasonic probe 10 makes an ultrasonic signal transmitted from the ultrasonic transducers 12 _{1 to} 12 _N incident on the surface of the upper plate 2 in an oblique direction.

The ultrasonic probe 20 has a structure in which a transducer array 22 including a plurality of ultrasonic transducers 22 _{1 to} 22 _N is attached to a resin wedge 21. The ultrasonic probe 20 receives the ultrasonic signal propagating through the upper plate 2 by the ultrasonic transducers 22 _{1 to} 22 _N. In addition, as the number N of the ultrasonic transducers 12 _{1 to} 12 _N and the ultrasonic transducers 22 _{1 to} 22 _N , for example, the numbers of 4, 8, 16, 32, and the like can be used. In the present embodiment, the number N of ultrasonic transducers is 16. In the present embodiment, the ultrasonic probe 10 and the ultrasonic probe 20 are disposed on the upper plate 2 side. However, the ultrasonic probe is disposed on the lower plate 3 or both the upper plate 2 and the lower plate 3. The toucher 10 and the ultrasonic probe 20 may be disposed. In this embodiment, the transducer array is configured by a plurality of ultrasonic transducers. However, an ultrasonic signal may be transmitted / received by scanning one ultrasonic transducer.

The switch circuit 30 switches an ultrasonic transducer that transmits an ultrasonic signal among the ultrasonic transducers 12 _{1 to} 12 _N. The switch circuit 31 switches the ultrasonic transducer that receives the ultrasonic signal propagating through the upper plate 2 among the ultrasonic transducers 22 _{1 to} 22 _N. The ultrasonic transmitter / receiver 32 transmits an ultrasonic signal to the ultrasonic transducers 12 _{1 to} 12 _N and amplifies and outputs the ultrasonic signal received by the ultrasonic transducers 22 _{1 to} 22 _N. The A / D converter 33 performs analog / digital conversion on the ultrasonic signal amplified and output by the ultrasonic transmitter / receiver 32. The arithmetic unit 34 determines whether the spot welded portion 4 is a fusion welded portion where a nugget is formed or an interfacial welded portion where no nugget is formed by executing an analysis process described later. .

[Inspection method for spot welds]
Next, referring to FIG. 2 to FIG. 9, when the spot weld portion 4 is determined to be a fusion weld portion where a nugget is formed or an interfacial weld portion where a nugget is not formed. The operation of the inspection apparatus 1 will be described. This determination operation is broadly divided into two processes: an ultrasonic transmission / reception process for transmitting / receiving an ultrasonic signal and an analysis process for analyzing the received ultrasonic signal. Therefore, in the following, for ease of explanation, the operation of the inspection apparatus 1 will be described separately for ultrasonic transmission / reception processing and analysis processing. However, in an actual operation, the ultrasonic transmission / reception process and the analysis process may be executed in parallel, or the analysis process may be executed after the ultrasonic transmission / reception process is completed.

[Ultrasonic transmission / reception processing]
First, the ultrasound transmission / reception process will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating a propagation path of ultrasonic waves transmitted from the ultrasonic transducers 12 _{1 to} 12 ₁₆ . As shown in FIG. 2, the ultrasonic signals W transmitted from the ultrasonic transducers 12 _{1 to} 12 ₁₆ propagate in a plurality of directions through a plane path, and the ultrasonic transducers 22 _{1 to} 22 ₁₆ receive the ultrasonic waves. The ultrasonic signals W transmitted from the transducers 12 _{1 to} 12 ₁₆ are received. Therefore, in this ultrasonic transmission / reception process, first, the switch circuit 30 transmits the ultrasonic signal W from the ultrasonic transducer 12 ₁ , and the switch circuit 31 transmits the ultrasonic wave transmitted from the ultrasonic transducer 12 _1. The signal W is received by the ultrasonic transducers 22 _{1 to} 22 ₁₆ . The ultrasonic signals received by the ultrasonic transducers 22 _{1 to} 22 ₁₆ are amplified and output by the ultrasonic transmitter / receiver 32, A / D converted by the A / D converter 33, and stored in the arithmetic unit 34. The

Next, the switch circuit 30 transmits an ultrasonic signal W from the ultrasonic transducer 12 _2, switching circuit 31 an ultrasonic signal W which is transmitting from the ultrasonic transducer 12 _second ultrasonic vibrator 22 ₁ the reception by to 22 _16. The ultrasonic signals received by the ultrasonic transducers 22 _{1 to} 22 ₁₆ are amplified and output by the ultrasonic transmitter / receiver 32, A / D converted by the A / D converter 33, and stored in the arithmetic unit 34. The This process until ultrasonic signals transmitting from the ultrasonic transducer 12 ₁₆ is received wave by the ultrasonic vibrator 22 _{1-22 16,} by sequentially changing the ultrasonic transducers that transmit ultrasonic signals Do. As a result, the calculation device 34 stores ultrasonic signal data propagating from a plurality of positions in a plurality of directions.

[Analysis processing]
Next, analysis processing will be described with reference to FIGS. FIGS. 3A and 3B are schematic diagrams showing propagation paths of ultrasonic signals in the fusion welded portion and the interfacial weld weld portion, respectively. As shown in FIG. 3 (a), in the fusion welded portion in which the nugget R1 is formed, two types of superconducting waves W1 that do not pass through the nugget R1 and a weld metal transmitted wave W2 that propagates in the nugget R1 are used. A sound wave signal is detected by the ultrasonic probe 20. Further, since the propagation speed of the ultrasonic signal is different between the nugget R1 and the metal region other than the nugget R1, the reception timing of the normal transmitted wave W1 and the reception timing of the weld metal transmitted wave W2 in the ultrasonic probe 20 are different. . On the other hand, as shown in FIG. 3B, since there is no nugget in the interface welded portion, the ultrasonic signal received by the ultrasonic probe 20 is only the normal transmitted wave W1. The actual propagation path of the ultrasonic signal is complicated with reflection and mode conversion on the bottom and surface of the metal plate, but is not shown in FIG.

Here, with reference to FIG. 4, FIG. 5, the difference in the ultrasonic signal received when the fusion welding part and the interface welding part are formed is demonstrated in detail. FIG. 4 is a diagram illustrating an example of ultrasonic signals transmitted from the ultrasonic transducers 12 _{1 to} 12 ₁₆ . FIGS. 5A and 5B show ultrasonic signals received when the ultrasonic signal shown in FIG. 4 is transmitted when the fusion welded portion and the interface weld weld are formed. FIG.

When the transmission of an ultrasound signal S _IN as shown in FIG. 4, when the fusion weld is formed, as shown in FIG. 5 (a), derived from the normal transmission wave W1 received timing different Ultra The sound wave signal S _out1 and the ultrasonic signal S _out2 derived from the weld metal transmitted wave W2 are received. On the other hand, when the interface welded portion is formed, only the ultrasonic signal _Sout1 derived from the normal transmitted wave W1 is received as shown in FIG. 5B. Therefore, by analyzing the ultrasonic signals received by the ultrasonic transducers 22 _{1 to} 22 ₁₆ , it is determined whether or not the received ultrasonic signals are formed by one or a plurality of ultrasonic signals. Thus, it can be determined whether a fusion weld or an interface weld weld is formed on the propagation path of the received ultrasonic wave.

In the present embodiment, the arithmetic unit 34 performs wavelet analysis on the ultrasonic signals corresponding to the ultrasonic waves received by the ultrasonic transducers 22 _{1 to} 22 ₁₆ , thereby receiving the received ultrasonic signals. It is determined whether or not it is formed by one or a plurality of ultrasonic signals. Here, the wavelet analysis is a kind of continuous wavelet transform for calculating a wavelet W (a, b) obtained by the following Equation 1 when the original signal is represented by x (t) and the mother wavelet is represented by Ψ (t). Means processing.

This equation (1) can be modified as the following equation (2).

Therefore, when the parameter a (hereinafter referred to as expansion / contraction coefficient) a is assumed to be a constant value, the wavelet analysis is performed by using Ψ (t / a), that is, a waveform obtained by expanding / contracting the mother wavelet Ψ (t) by a times in the time direction. It can be regarded as a cross-correlation calculation with the signal x (t). Therefore, the arithmetic unit 34 resembles an ultrasonic signal received by each of the ultrasonic transducers 22 _{1 to} 22 ₁₆ as an original signal x (t) and a normal transmitted wave in which ultrasonic components having different phases are not mixed. Wavelet analysis is performed using an ultrasonic signal (hereinafter referred to as a basic signal) as a mother wavelet Ψ (t). Thereby, the arithmetic unit 34 can calculate how many components of the basic signal are included in the ultrasonic signals received by the ultrasonic transducers 22 _{1 to} 22 ₁₆ . Note The basic signal, an ultrasonic signal propagating through the along the surface of the upper plate 2 that the propagation path does not include a spot weld, and more specifically, is the ultrasonic transducer 12 ₁ transmitting ultrasonic transducer 22 it can be exemplified ultrasonic signals received by _{1-22 16.}

  Here, in order to facilitate understanding of the wavelet analysis, the wavelet analysis will be schematically described with reference to FIGS. In the wavelet analysis, a mother wavelet Ψ (t) as shown in FIG. 6 is defined. First, the arithmetic unit 34 fixes the value of the parameter τ as shown in FIGS. 7 (a) to (c). The mother wavelet Ψ (t) is expanded / contracted by changing the value of the expansion / contraction coefficient a. In the example shown in FIGS. 7A to 7C, the value of the expansion / contraction coefficient a increases in the order of a1, a2, and a3, and the mother wavelet Ψ (t / a) expands / contracts according to the value of the expansion / contraction coefficient a. . Next, the computing device 34 performs a cross-correlation computation process with the original signal x (t) by changing the value of the parameter τ for a plurality of mother wavelets Ψ (t / a) having different values of the expansion coefficient a.

According to this cross-correlation calculation process, when the received ultrasonic signal includes the ultrasonic signal S _out1 derived from the normal transmitted wave W1 and the ultrasonic signal S _out2 derived from the weld metal transmitted wave W2, A wavelet W (a, τ) including two peaks corresponding to the ultrasonic signal S _out1 and the ultrasonic signal S _out2 as shown in FIGS. 8A to 8C is calculated. On the other hand, when the received ultrasonic signal includes only the ultrasonic signal S _out1 derived from the normal transmitted wave W1, it corresponds to the ultrasonic signal S _out1 as shown in FIGS. A wavelet W (a, τ) including one peak is calculated.

  The wavelets W (a, τ) shown in FIGS. 8A to 8C and FIGS. 9A to 9C are respectively mother wavelets Ψ (t / t) shown in FIGS. 7A to 7C. The wavelet W (a, τ) calculated using a) is shown. In the present embodiment, the cross-correlation calculation processing is performed for a plurality of mother wavelets Ψ (t / a) having different values of the expansion coefficient a. However, the value of the expansion coefficient a may be determined in advance or for each measurement. An optimal value may be selected by calculating a plurality of expansion / contraction coefficients a.

As described above, in the wavelet W (a, τ) calculated when the fusion welded portion is formed, peaks corresponding to the normal transmitted wave and the weld metal transmitted wave are observed adjacent to each other. On the other hand, in the wavelet W (a, τ) calculated when the interface weld weld is formed, only the peak corresponding to the normal transmitted wave is observed. Accordingly, for the wavelet W (a, τ) having the highest correlation obtained by the wavelet analysis, the wavelet analysis is performed by calculating the interval between adjacent peaks or the intensity ratio between the peak of interest and the peak in the vicinity thereof. It can be determined whether the obtained wavelet W (a, τ) is derived from the fusion welded portion or the interfacial welded portion. That is, it is possible to determine whether a fusion welded portion or an interfacial weld weld portion is formed on the propagation path of the ultrasonic signal received by each of the ultrasonic transducers 22 _{1 to} 22 ₁₆ .

  As is apparent from the above description, in the spot welded portion inspection method and inspection apparatus according to an embodiment of the present invention, the ultrasonic probe 10 is an upper plate 2 that is a plate material outside the spot welded portion 4. An ultrasonic signal propagating through the upper plate 2 is transmitted in a plurality of directions from a plurality of transmission positions, and the ultrasonic probe 20 is spotted on at least a propagation path at a plurality of reception positions on the upper plate 2. An ultrasonic signal including a weld is received. Then, the computing device 34 performs wavelet analysis of the ultrasonic signal received by the ultrasonic probe 20, and determines the quality of the spot welded portion based on the analysis result of the wavelet analysis. According to such a configuration, since the quality of the spot welded portion 4 is determined by executing wavelet analysis of an ultrasonic signal including the spot welded portion 4 in the propagation path, the quality of the spot welded portion 4 is accurately inspected. be able to.

A technique for applying wavelet transform when measuring an ultrasonic signal is disclosed in Patent Document 2, for example. However, until now, wavelet analysis has been used to calculate frequency components of ultrasonic signals for each time. On the other hand, the wavelet analysis in the present embodiment is for calculating how much of the basic signal component is included in the ultrasonic signals received by the ultrasonic transducers 22 _{1 to} 22 ₁₆ . Therefore, its usage is greatly different from the conventional wavelet analysis.

[Experimental example]
Finally, an experimental example of wavelet analysis is shown.

FIGS. 10A and 10B are diagrams showing an example of an experiment of wavelet analysis. In this experiment, the ultrasonic transmission / reception processing is performed by setting the resin wedges 11 and 21 to polystyrene, the width in the arrangement direction of the ultrasonic transducers to 0.8 mm, and the incident angle of the ultrasonic signal with respect to the upper plate 2 surface to 25.4 °. went. Further, analysis processing is transmitting from the ultrasonic transducer 12 _1, the ultrasonic signals received by the ultrasonic transducer 22 _first mother wavelet [psi (t), the value of the scale factor a performed with 1.075 It was.

  As is clear from the comparison between FIG. 10A and FIG. 10B, the peak interval observed from the wavelet W (a, τ) shown in FIG. 10A is the wavelet shown in FIG. It is narrower than the peak interval observed from W (a, τ). Accordingly, a fusion weld is formed in the propagation path of the ultrasonic signal from which the wavelet W (a, τ) shown in FIG. 10A is calculated, and the wavelet W (a, τ) shown in FIG. 10B. It can be seen that an interface weld weld is formed in the propagation path of the ultrasonic signal for which is calculated. The reason why a plurality of peaks are observed in the wavelet W (a, τ) derived from the interfacial weld weld is that the ultrasonic signals propagating through the plurality of paths by reflection on the front and back surfaces and mode conversion are received. Because it is waved.

  FIGS. 11 (a) and 11 (b) are diagrams showing the inspection results of the spot welds according to the prior art (cross-correlation calculation) and the present invention, respectively. In this experiment, the ultrasonic transmission / reception processing is performed by setting the resin wedges 11 and 21 to polystyrene, the width in the arrangement direction of the ultrasonic transducers to 0.8 mm, and the incident angle of the ultrasonic signal with respect to the upper plate 2 surface to 25.4 °. went. In addition, as samples to be inspected, twelve samples prepared by spot welding with two steel plates having an upper plate 2 having a thickness of 0.55 mm and a lower plate 3 having a thickness of 1.2 mm were used. Of the twelve samples, four are samples of fusion welds and eight are samples of interfacial welds.

In the inspection using the prior art, for each sample, the ultrasonic signals transmitted by the ultrasonic transducers 12 _{1 to} 12 ₈ are transmitted from the reference signal and the ultrasonic transducer 12 ₁ , and the ultrasonic transducer 22 is transmitted. ₁ is normalized so that the correlation mutual operation value with the ultrasonic signal received by ₁ is 128, and the ultrasonic signal transmitted by the ultrasonic transducers 12 _{9 to} 12 ₁₆ is the reference signal and the ultrasonic transducer. The correlation mutual operation value with the ultrasonic signal transmitted from 12 ₁₆ and received by the ultrasonic transducer 22 ₁₆ was normalized to 128. (1) A propagation path of an ultrasonic signal transmitted from the ultrasonic transducer 12 _n (n = 1 to 16) and received by the ultrasonic transducer 22 _n (n = 1 to 16), (2 ) Propagation path of an ultrasonic signal transmitted from the ultrasonic transducer 12 _n (n = 1 to 7) and received by the ultrasonic transducer 22 _{n + 1} (n = 1 to 7), and (3) ultrasonic wave Cross-correlation calculation values for the propagation paths of ultrasonic signals transmitted from the transducer 12 _n (n = 9 to 16) and received by the ultrasonic transducer 22 _n−1 (n = 9 to 16) The sum of the absolute values of the difference from 128 (however, when the difference is larger than 128, the difference is 0) was used as the correlation calculation evaluation index.

In the inspection using the present invention, the transmitting from the ultrasonic transducer 12 _8, transmits an ultrasound signals received by the ultrasonic transducer 22 ₈ original signal x (t), from the ultrasonic transducer 12 ₁ is a portion of the ultrasonic signals received by the ultrasonic transducer 22 _first mother wavelet [psi (t), were wavelet analysis the value of scale factor a as 1.075. And about the obtained wavelet W (a, (tau)), it becomes the 1st peak among the 1st peak which becomes the maximum value within the designated range, and the peak which becomes 0.5 times or more of the intensity of the 1st peak. A near second peak was detected, and the interval between the first peak and the second peak was calculated as an evaluation index.

  As shown in FIG. 11A, in the inspection using the conventional technique, the value of the correlation calculation evaluation index is approximated between the sample of the interfacial welded portion and the sample of the fusion welded portion where the size of the heat affected zone is large. It was. For this reason, in the inspection using the prior art, it was not possible to distinguish between the sample of the interfacial weld and the sample of the fusion weld. In contrast, in the inspection using the invention of the present application, the peak-to-peak interval was greatly different between the interface weld weld sample and the fusion weld sample. Therefore, according to the inspection using the invention of the present application, it was possible to accurately distinguish between the sample of the interfacial weld and the sample of the fusion weld.

In the present experiment, the transmitting from the ultrasonic transducer 12 _8, although the ultrasonic signals received by the ultrasonic transducer 22 ₈ to the original signal x (t), fused weld and surface welding welding Other propagation paths may be used as long as a difference is observed with respect to the part, and wavelet analysis may be performed on the propagation paths of a plurality of ultrasonic signals. In addition to the method of calculating the interval between the first peak and the second peak, the determination may be made by calculating the intensity ratio between the first peak and the second peak or the maximum value of the first peak.

  When discriminating by the peak intensity ratio, by setting the range for detecting the second peak so that the peak derived from the interface weld weld is not included, the interface weld weld (the second peak intensity / first The value of the peak intensity is small. In addition, a plurality of evaluation indexes may be calculated by wavelet analysis, and the determination may be performed by combining a plurality of evaluation indexes, or a combination of the evaluation indexes calculated by the prior art and the evaluation indexes calculated by the present invention may be combined. A determination may be made.

  Although the embodiment to which the invention made by the present inventor is applied has been described above, the present invention is not limited by the description and the drawings that form a part of the disclosure of the present invention according to this embodiment. For example, in the present embodiment, the quality of a spot welded portion formed by spot welding two metal plates (steel plates) is inspected, but the plate material to be inspected is limited to a steel plate. The present invention can also be applied to other plate materials such as aluminum, inorganic materials, and organic materials. Further, the number of plates to be spot welded is not limited to two. Moreover, the judgment of the quality of the spot welded part is not limited to only the identification between the fusion welded part and the interface welded part. That is, other embodiments, examples, operational techniques, and the like made by those skilled in the art based on the present embodiment are all included in the scope of the present invention.

1 test device 2 upper 3 lower plate 4 spot welds 10, 20 ultrasonic probe 11, 21 resin wedge 12 and 22 the transducer array _{12 1 ~12 N, 22 1 ~22} N ultrasonic transducers 30 and 31 Switch circuit 32 Ultrasonic transceiver 33 A / D converter 34 Arithmetic unit

Claims (4)

A method for inspecting a spot welded portion for inspecting the quality of a spot welded portion formed by spot welding by overlapping a plurality of plate materials,
A wave transmitting step of transmitting an ultrasonic signal propagating through the plate material from a plurality of transmission positions of the plate material outside the spot welded portion;
A wave receiving step of receiving an ultrasonic signal including the spot welded portion at least in the propagation path at a plurality of wave receiving positions of the plate material outside the spot welded portion;
A wavelet analysis of the ultrasonic signal received by the wave receiving step is performed, and a determination step of determining the quality of the spot weld based on the analysis result of the wavelet analysis;
A method for inspecting a spot welded portion.   The wave receiving step includes a step of receiving an ultrasonic signal that does not include a spot weld in the propagation path, and a spot welded portion in the propagation path received in the wave receiving step as a mother wavelet used in the wavelet analysis. The method for inspecting a spot weld according to claim 1, wherein a part or all of an ultrasonic signal not including a mark is used.   The determining step uses at least one of a peak position and intensity included in the wavelet calculated by the wavelet analysis to determine whether the spot weld is a fusion weld or an interfacial weld. The method for inspecting spot welds according to claim 1 or 2, further comprising a step of determining. A spot welded portion inspection device for inspecting the quality of a spot welded portion formed by spot welding with overlapping a plurality of plate materials,
A wave transmitting means for transmitting an ultrasonic signal propagating through the plate material from a plurality of transmission positions of the plate material outside the spot welded portion;
Wave receiving means for receiving an ultrasonic signal including the spot welded portion at least in the propagation path at a plurality of wave receiving positions of the plate material outside the spot welded portion;
Performing wavelet analysis of the ultrasonic signal received by the wave receiving means, and determining means for determining the quality of the spot weld based on the analysis result of the wavelet analysis;
An inspection apparatus for spot welds, comprising:

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