JP4756224B1 - Spot welding inspection equipment - Google Patents

Abstract

An inspection apparatus that non-destructively inspects the quality of a joint portion of a metal structure joined by spot welding or the like is provided.
In a spot welding inspection apparatus, a first probe and a second probe are arranged to face each other with a welded portion formed by spot welding by overlapping metal materials and inspecting the welded state of the welded portion. The first probe includes a rod-shaped first core material, a first application coil and a first detection coil wound around the first core material, and the second probe includes a rod-shaped second core material; A first mode in which a second application coil and a second detection coil wound around the second core material are provided, and a magnetic field generated by the second application coil is detected by the first detection coil; The second mode in which the generated magnetic field is detected by the second detection coil, the third mode in which the magnetic field generated by the first application coil is detected by the first detection coil, and the magnetic field generated by the second application coil are the first mode. 2 The fourth mode is detected by the detection coil. To be.
[Selection] Figure 1

Description

  The present invention relates to an inspection apparatus that inspects a joint formed by spot welding in a nondestructive manner.

  In manufacturing a metal structure, spot welding of metal materials is widely used. Spot welding is a method in which stacked metal materials are sandwiched between opposed electrodes and joined by passing a current between the electrodes. This method is widely used as a method of joining cases such as automobiles, home appliances, and electrical equipment.

  The reliability of the spot-welded part is an index of its joint strength. In other words, the higher the bonding strength, the higher the reliability. In spot welding, heat is generated at the time of energization using the electrical resistance of the metal material sandwiched between the electrodes, the metal materials are melted, then the energization is stopped, and the metal is rapidly cooled and joined. This melted portion is called a nugget, and it can be said that the larger the nugget diameter, that is, the joint surface, the higher the joint strength.

  For this reason, conventionally, the nugget diameter has been inspected as a quality inspection of spot welds. Since the nugget is spot welded inside, it cannot be visually observed from the surface. For this reason, various methods have been taken as methods for observing the internal structure.

  For example, a method is known in which a magnetic field is applied to a spot weld and its magnetic response characteristics are measured. Specifically, after applying a static magnetic field, it is cut off, and the magnetic field time change at a number of points on the surface of the spot weld is measured, and the nugget diameter is estimated from the position change of the change amount. . (Patent Document 1).

  As another method, there is a method in which an application coil is formed at both ends of a U-shaped yoke material, and a magnetic flux is applied so as to straddle each metal material spot-welded (Non-patent Document 1). That is, this is a method of detecting a magnetic flux leaking from the upper part of the spot welded portion by flowing a magnetic flux between the welded metal materials. In this method, the nugget diameter can be estimated from the magnetic field distribution, but since the correlation between the magnetic field strength and the bonding strength is high, the bonding strength can be directly estimated without estimating the nugget diameter.

  As another method, there is a method of performing a magnetic inspection during spot welding. That is, a high-frequency magnetic field application coil and a detection coil are attached to opposing electrodes used for spot welding, a magnetic field that passes through the spot weld is detected, and a temporal change in the detected magnetic field strength is measured after energization between the electrodes is completed. (Patent Document 2).

Japanese Patent No. 3098193 JP 2006-29882 A

`` A magnetic flux leakage methodusing a magnetoresistive sensor for nondestructive evaluation of spot welds '' K. Tsukada, M. Yoshioka, T. Kiwa, Y. Hirono, NDT & E International, Vol. 44 (2011) pp. 101-105

  Among the conventional magnetic measurement methods, the method of measuring the attenuation of the detection coil signal after applying a magnetic field from one side of the spot welded part, basically measures the eddy current generated by applying the magnetic field. The state of decaying later is measured.

  In this method, since the eddy current is generated near the surface layer, it was not possible to analyze even the deep state. Although the nugget diameter can be observed with information near the surface layer, changes in the nugget diameter generally require a resolution of 1 mm or less, so it is easy to inspect if the nugget is not formed, but the nugget is formed However, it is inaccurate to measure how much bonding strength is obtained.

  On the other hand, in the method of measuring the magnetic flux leaking from the spot weld by introducing the magnetic flux across two welded metal materials, a very good correlation is obtained between the magnetic field strength and the joint strength. The applied magnetic field probe needs to contact or approach both of the two steel plates having a step. For this reason, the applied magnetic field probe may not be applied depending on the shape of the measurement object, and thus there is a limit to the applicable measurement object.

  In addition, an application coil and a detection coil are provided for each of the electrodes facing each other in spot welding, and an eddy current is generated by applying a high frequency of 10 kHz or higher. Even with the method of seeing, the change in the eddy current near the surface layer mentioned above could not be analyzed because of the change in the eddy current near the surface layer.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an inspection apparatus capable of diagnosing the reliability of a welded part by analyzing the structure from the surface layer to the deep part of the welded part by spot welding in a magnetic inspection method. To do.

  In the present invention, in a spot welding inspection apparatus that places the first and second probes facing each other across a welded portion formed by spot welding with overlapping metal materials, and inspects the welded state of the welded portion. The first probe includes a rod-shaped first core material, a first application coil and a first detection coil wound around the first core material, and the second probe includes a rod-shaped second core material; The second application coil and the second detection coil wound around the second core member are provided.

In particular, in the present invention, an input switch for switching whether the alternating current output from the alternating current power source is input to the first application coil or the second application coil, the signal output from the first detection coil, and the second detection coil A first mode in which a magnetic field generated by the second application coil is detected by the first detection coil by controlling an output switch that switches to and outputs any of the signals output from the first application coil; The second mode for detecting the magnetic field generated by the second detection coil, the third mode for detecting the magnetic field generated by the first application coil by the first detection coil, and the magnetic field generated by the second application coil. A control unit that executes the fourth mode detected by the second detection coil and analyzes the detection result is provided .

In the spot welding inspection apparatus of the present invention, the control unit executes the third mode and the fourth mode when the magnetic field strength detected in the first mode and / or the second mode is larger than a predetermined threshold. It is also characterized by ending without doing.

  According to the present invention, by using the first and second probes provided with the application coil and the detection coil, respectively, the welding state of the welded portion is inspected by detecting the magnetic field in the first to fourth modes. It is possible to efficiently and accurately detect the internal information of the nugget portion formed in the inside of the steel plate and properly inspect the welding state of the welded portion.

It is the schematic which shows the structure of the whole inspection apparatus. It is a graph of the measurement result in a 1st mode. It is a graph of the measurement result in a 2nd mode. It is the graph which showed the correlation with the magnetic field intensity in the center vicinity of the welding part obtained from FIG. 2, and the joining strength by a tensile strength test. It is a graph of the measurement result in a 3rd mode. It is a graph of the measurement result in the 4th mode.

  The inspection apparatus for spot welding according to the present invention has a first and second probes opposed to each other with a welded portion formed by spot welding with overlapping metal materials, and using these probes, the welded portion is arranged. We are going to inspect the welding state.

  In particular, the first probe includes a rod-shaped first core material, a first application coil and a first detection coil wound around the first core material, and the second probe has a rod-shaped second core material. And a second application coil and a second detection coil wound around the second core member.

  For the first core material and the second core material, it is desirable to use a material having high magnetic permeability, and specifically, ferrite having a relative magnetic permeability of 100 or more is desirable.

  In this way, by using the first core material and the second core material made of a high permeability material, the magnetic field is applied from the front of the welded portion and measured from the back, and the magnetic field is applied from the back to the front. Thus, the operation of measuring from the table can be performed, and the state of the deep part of the welded portion can be analyzed.

  A first application coil and a first detection coil are wound around the first core material, and a second application coil and a second detection coil are wound around the second core material, and measurement is performed without exchanging the probe arrangement. In addition, it is possible to perform measurement with higher accuracy than measurement on only one side.

  On the other hand, for example, by applying a magnetic field to the inspection object with the first application coil of the first probe and measuring with the first detection coil, vortices generated in the surface layer of the inspection object instead of the magnetic field penetrating the inspection object Current information can be detected. As a result, information in the depth direction from the surface to be inspected can be obtained.

  At this time, the signal of the first detection coil is detected by lock-in detection means for detecting at the same frequency as the first application coil. In magnetic measurement, errors are likely to occur due to environmental magnetic noise such as magnetic noise from a commercial power supply. However, by using this lock-in detection means, only the detection signal synchronized with the first application coil can be extracted. And a weaker signal can be extracted. The same applies to the second probe.

  The magnetic field applied from the first application coil and the second application coil is pulsed, and can be applied to the inspection object as a magnetic field including various frequencies. Here, when the signals detected by the first detection coil and the second detection coil are Fourier transformed, they can be decomposed as signals for the applied magnetic field at each frequency.

The difference in the frequency of the applied magnetic field can be expressed as the difference in the depth of the eddy current generated by applying the magnetic field. The depth at which this eddy current can be generated is expressed as the skin depth δ of the following equation.
δ = (1 / πμfσ) ^1/2
Here, μ is magnetic permeability, σ is conductivity, and f is frequency.
Therefore, information on the depth direction from the surface of the inspection target to which the magnetic field is applied can be extracted from the frequency of the applied magnetic field.

  The signal for lock-in detection by the lock-in detection means can obtain the result for each frequency by scanning the frequency of the applied magnetic field, and the signal detected by applying the pulsed magnetic field can be Fourier transformed. The result for each frequency can be obtained.

  Since the detection sensitivity of the first detection coil and the second detection coil varies depending on the frequency, it is necessary to correct the sensitivity for each frequency. In addition, the detection sensitivity of the first detection coil and the second detection coil is generally such that the applied magnetic field intensity also varies depending on the frequency, and in particular, the intensity of each frequency included in the pulsed magnetic field differs.

  For this reason, the detection signal intensity at each frequency when the inspection object is measured is normalized by the detection signal intensity at each frequency measured when there is no inspection object. By this normalization, it is possible to obtain a signal that is not affected by a difference in applied magnetic field intensity due to a difference in frequency. Also, since each phase information is measured based on the phase when there is no inspection object, the amount of phase change when measuring the inspection object is measured, so that accurate phase information of the inspection object for each frequency can be obtained. .

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

  FIG. 1 is a schematic diagram of an inspection apparatus according to an embodiment of the present invention.

  The inspection apparatus includes a first probe 1-1 and a second probe 1-2, and the first probe 1-1 and the second probe 1-2 are spot welded with metal materials 5 overlapped. It is supposed to be arranged with the formed welded portion interposed therebetween. In this embodiment, a steel plate having a thickness of 1.2 mm is used as the metal material 5.

  Although not shown, the first probe 1-1 and the second probe 1-2 are mounted on the support members, respectively, and are directly opposed to each other with the welded portion interposed therebetween. 1-2 are arranged. In the present embodiment, the support member is a C-shaped member as viewed from the side, and has a shape that does not contact the spot-welded metal material 5.

  The first probe 1-1 includes a rod-shaped first core member 2-1, a first application coil 3-1 and a first detection coil 4-1 wound around the first core member 2-1. ing. Similarly, the second probe 1-2 includes a rod-shaped second core member 2-2, a second application coil 3-2 and a second detection coil 4-2 wound around the second core member 2-2. It has.

  Each of the first core material 2-1 and the second core material 2-1 is a ferrite bar having a relative magnetic permeability of 800, and in the present embodiment, has a round bar shape of φ3 mm. The first application coil 3-1 and the second application coil 3-2 are formed by winding copper wires around the first core material 2-1 and the second core material 2-2, respectively. The number is 30 times. The first detection coil 4-1 and the second detection coil 4-2 are also formed by winding copper wires around the first core material 2-1 and the second core material 2-2, respectively. The number is 15 times. The design conditions of each core material and each coil may be appropriately adjusted according to the material of the metal material 5 to be spot welded and the size of the welded portion formed by spot welding.

  In addition to the first probe 1-1 and the second probe 1-2, the inspection apparatus includes an AC power source 6 that applies a predetermined AC current to the first application coil 3-1 and the second application coil 3-2, A first amplifier 7-1 that amplifies and outputs the signal output from the first detection coil 4-1, and a second amplifier 7-2 that amplifies and outputs the signal output from the second detection coil 4-2. And.

  Furthermore, the inspection apparatus includes a control unit 10 that controls the execution of the inspection performed by the inspection apparatus and analyzes the detection result using the first probe 1-1 and the second probe 1-2.

  The control unit 10 controls the input switch 11 that switches whether the alternating current output from the alternating current power source 6 is input to the first application coil 3-1 or the second application coil 3-2.

  The AC power source 6 outputs an AC current having a predetermined frequency based on a signal having a predetermined frequency input from the oscillator 8, and the oscillator 8 generates a signal having a predetermined frequency based on the control of the control unit 10. And input to the AC power source 6.

  Further, in the control unit 10, a signal output from the first detection coil 4-1 via the first amplifier 7-1 and a signal output from the second detection coil 4-2 via the second amplifier 7-2. The output switch 12 that switches which signal of the signals is input to the control unit 10 is controlled.

  The signal output from the output switch 12 is input not only to the control unit 10 but also to the lock-in detector 9 which is lock-in detection means. The lock-in detector 9 inputs a signal having a predetermined frequency output from the oscillator 8, extracts the same frequency component as the frequency of this signal, and inputs it to the control unit 10.

  Further, the input switch 11 is output from a pulse signal generation power source 13 that outputs not only the alternating current output from the alternating current power source 6 but also a predetermined pulsed current signal based on the control of the control unit 10. A current signal may also be input. That is, the first application coil 3-1 and the second application coil 3-2 may be input with a current signal input from either the AC power supply 6 or the pulse signal generation power supply 13.

  Although not shown, the inspection apparatus is provided with a stage for fixing and supporting the spot-welded metal material 5 to be inspected and horizontally moving in the plane direction. This stage is controlled based on the control of the control unit 10. The weld is inspected while moving. Note that the inspection apparatus may be configured to move a support member that supports the first probe 1-1 and the second probe 1-2 instead of the stage.

  In the inspection apparatus configured as described above, the control unit 10 performs the inspection by executing the following four modes when inspecting the welded portion. In the first mode, the control unit 10 detects the magnetic field generated by applying an alternating current to the second application coil 3-2 by the first detection coil 4-1. In the second mode, the control unit 10 detects the magnetic field generated by passing an alternating current through the first application coil 3-1 with the second detection coil 4-2. In the third mode, the control unit 10 detects the magnetic field generated by passing an alternating current through the first application coil 3-1 with the first detection coil 4-1. In the fourth mode, the control unit 10 detects the magnetic field generated by applying an alternating current to the second application coil 3-2 with the second detection coil 4-2.

  In the first mode and the fourth mode, since the magnetic field is generated by the second application coil 3-2, detection is simultaneously performed by the first detection coil 4-1 and the second detection coil 4-2 in some cases. In the second mode and the third mode, since the magnetic field is generated by the first application coil 3-1, in some cases, the first detection coil 4-1 and the second detection coil 4-2 simultaneously detect the magnetic field. May be performed. Alternatively, the third mode and the fourth mode may be performed at the same time because they are inspections on one side only.

  In the first mode and the second mode, among the signals output from the first detection coil 4-1 and the second detection coil 4-2, the control unit 10 is input from the oscillator 8 in the lock-in detector 9. Only the signal of the component synchronized with the frequency reference signal is input, and the magnetic field strength information and the phase information obtained from this signal are analyzed.

  Below, the result of having measured with respect to the welding part formed by spot welding is demonstrated. Here, what was spot-welded with respect to the metal material 5 which consists of a steel plate with a thickness of 1.2 mm is used for a test | inspection object.

  When performing spot welding, the spot welding electrode diameter is φ6.5mm, and AC current is applied to the electrode to perform spot welding. However, in order to create samples with different weld joint strength, AC current The number of cycles was 5 cycles, 7.5 cycles, 12.5 cycles, 15 cycles, and 17.5 cycles, and an alternating current was applied to the electrodes to create welds.

  When measuring the weld, the metal material 5 is moved with respect to the first probe 1-1 and the second probe 1-2, and the measurement position is changed and the measurement is sequentially performed at a plurality of positions. In particular, the measurement position was provided on a straight line passing through the center of the weld.

  FIG. 2 shows the result of detecting the magnetic field generated in the first mode, that is, by applying the alternating current output from the alternating current power supply 6 to the second application coil 3-2 by the first detection coil 4-1. The frequency of the alternating current is 20 Hz. It can be seen that the magnetic field strength is the smallest at a position of 4 mm, which is near the center of the weld, and the magnetic field strength is reduced as the number of spot welding cycles is increased. Here, in this 1st mode, it can measure without being influenced by an eddy current by measuring a frequency at an extremely low frequency of 100 Hz or less.

  FIG. 3 shows the result of detection by the second detection coil 4-2 in the second mode, that is, the magnetic field generated by energizing the first application coil 3-1 with the alternating current output from the alternating current power supply 6. The frequency of the alternating current is 20 Hz. In the second mode, similarly to the first mode, it can be seen that the magnetic field strength is the smallest at the position of 4 mm in the vicinity of the center of the weld, and the magnetic field strength is reduced as the number of spot welding cycles is increased.

  FIG. 4 is a graph showing the correlation between the magnetic field strength and the tensile strength, and is plotted with the value of the magnetic field strength at the 4 mm point in FIG. 2 as a representative value. The tensile strength is the maximum value until the spot-welded metal material 5 is pulled by a tensile tester and broken.

  In FIG. 4, the correlation coefficient is -0.94. Similarly, even if the tensile strength is evaluated using Fig. 3, the correlation coefficient is -0.94 and there is no difference between the first mode and the second mode. You can see that Moreover, from this result, it was confirmed that the magnetic field strength (magnetic permeability) was lower as the spot welding with higher tensile strength was obtained, and it was found that a very high correlation was obtained between the two.

  Therefore, in the inspection apparatus, the weld is inspected in the first mode and / or the second mode, and when the magnetic field strength is larger than a predetermined threshold value, it is immediately determined as “welding failure”, The inspection may be terminated without executing the third mode and the fourth mode. Thus, by not performing the inspection in the third mode and the fourth mode at the joint where it is considered that a bonding failure is occurring, unnecessary inspection execution is suppressed and the inspection efficiency is improved. Can do.

  FIG. 5 shows the result of detection by the first detection coil 4-1 in the third mode, that is, the magnetic field generated by energizing the first application coil 3-1 with the alternating current output from the alternating current power supply 6. The frequency of the alternating current is larger than that in the first mode and the second mode, and is 1 kHz, so that the surface layer of the welded portion can be inspected. As described above, since the difference in the frequency of the applied magnetic field appears as a difference in the depth of the eddy current generated by applying the magnetic field, in the third mode, the frequency of the AC current output from the AC power supply 6 is appropriately changed. It is desirable to measure while.

  FIG. 6 shows the result of detection by the second detection coil 4-2 in the fourth mode, that is, the magnetic field generated by energizing the second application coil 3-2 with the alternating current output from the alternating current power supply 6. The frequency of the alternating current is set to 1 kHz, and the surface layer of the welded portion can be inspected, and it is desirable to measure while appropriately changing the frequency of the alternating current output from the alternating current power source 6 as in the third mode.

  As is clear from the comparison between FIG. 5 and FIG. 6, in the third mode, there is a correlation between the number of cycles at the time of spot welding and the magnetic field strength, whereas in the fourth mode, the correlation at the time of spot welding. It can be seen that there is no correlation between the number of cycles and the magnetic field strength, and the internal structure is different between the front and back of the weld.

  In spot welding, one of the electrodes through which current flows is generally tapered or rounded at the tip, and the tip of the other electrode is flat. This is probably because the distribution of current flowing in the welded portion is different between the front and back of the welded portion, and as a result, the shape of the nugget formed in the welded portion and the depth distribution from the surface are different. In particular, when a weld is formed by abutting an electrode having a rounded tip, a depression called an indentation is likely to occur, and current also concentrates here, so that the nugget is at a shallower position. Is supposed to be formed.

  In the third mode and the fourth mode, since detection is performed by the detection coil on the application coil side, the first detection coil 4 is driven simultaneously with the first application coil 3-1 and the second application coil 3-2. -1 and the second detection coil 4-2 can be used to examine the structure of the surface layer of the weld. That is, the third mode and the fourth mode can be performed simultaneously.

  In the 3rd mode and the 4th mode mentioned above, in order to detect the depth distribution of a welding part, it is necessary to change the frequency of the alternating current output from alternating current power supply 6 variously, and based on control of control part 10 Measurement is performed by sequentially inputting a signal having a predetermined frequency from the oscillator 8 to the AC power supply 6, but by using the pulse signal generation power supply 13, the measurement can be performed more easily.

  That is, a pulsed alternating current output from the pulse signal generation power source 13 is input to the first application coil 3-1 and the second application coil 3-2, and the first detection coil 4-1 and the second detection coil 4 are input. By decomposing the signal output from -2 into each frequency by Fourier transform, multiple types of frequency can be measured at once. Therefore, measurement time can be shortened.

  In addition, in the third mode and the fourth mode, the applied magnetic field intensity differs depending on the frequency and the sensitivity of each detection coil also differs. In particular, when an alternating current having a pulse waveform is used, the magnetic field intensity at each frequency varies greatly. ing. For this reason, it is desirable to perform background measurement when there is no metal material 5 to be inspected in advance and analyze the signal intensity and phase of each detection coil at each frequency.

  Then, the metal material 5 to be inspected is measured, the signal strengths of the first detection coil 4-1 and the second detection coil 4-2 are normalized, and the amount of phase change is calculated, thereby spot welding. The internal structure from the surface of the part can be analyzed.

  The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications, design changes, and the like within the technical scope of the present invention are included in the technical scope.

  INDUSTRIAL APPLICABILITY The present invention can be applied to non-destructive estimation of joint strength of joints such as spot welds that are widely used in the manufacture of metal structures that are casings for automobiles, home appliances, and electrical equipment.

1-1 First probe
1-2 Second probe
2-1 First core material
2-2 Second core material
3-1 First applied coil
3-2 Second applied coil
4-1 First detection coil
4-2 Second detection coil 5 Metal material 6 AC power supply
7-1 First amplifier
7-2 Second amplifier 8 Oscillator 9 Lock-in detector
10 Control unit
11 Input selector
12 Output selector
13 Pulse signal generator

Claims (2)

In a spot welding inspection apparatus that places the first and second probes facing each other across a welded portion formed by spot welding with overlapping metal materials, and inspecting the welded state of the welded portion,
The first probe includes a rod-shaped first core member, a first application coil and a first detection coil wound around the first core member,
The second probe includes a rod-shaped second core member, a second application coil and a second detection coil wound around the second core member,
From an input switch for switching whether the AC current output from the AC power source is input to the first application coil or the second application coil, the signal output from the first detection coil, and the second detection coil By controlling the output switcher to switch to any of the output signals,
A first mode in which a magnetic field generated by the second application coil is detected by the first detection coil;
A second mode in which a magnetic field generated by the first application coil is detected by the second detection coil;
A third mode in which a magnetic field generated by the first application coil is detected by the first detection coil;
A spot welding inspection apparatus including a control unit that executes a fourth mode in which a magnetic field generated by the second application coil is detected by the second detection coil and analyzes a detection result . The controller is
2. The spot according to claim 1, wherein when the magnetic field intensity detected in the first mode and / or the second mode is larger than a predetermined threshold, the spot is terminated without executing the third mode and the fourth mode. Welding inspection device.

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