JP2009092601A - Nondestructive inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nondestructive inspection method for inspecting the state of a joint part of both components with high operation efficiency and reliability when joining a conductive component to another component. <P>SOLUTION: The nondestructive inspection method for inspecting the state of the joint part 2 of both components when joining the conductive component 3 formed of a conductive material, to another component 4, is characterized by applying a fluctuating magnetic field to the conductive component 3 to excite the whole conductive component 3 and determining the joined state based on the vibrating state of the conductive component after applying the magnetic field. It is preferable to arrange the conductive component 3 in the uniform magnetic field 7 and to apply the pulse-like fluctuating magnetic field 6 to the conductive component 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-destructive inspection method for inspecting the state of a joint portion between a conductive part formed of a conductive material and another component part, and more particularly to a non-contact method using a variable magnetic field. The present invention relates to a non-destructive inspection method for inspecting a joining state at a point.

Joining a conductive part formed of a conductive material such as metal to another component and inspecting the joining state is currently performed in various technical fields.
For example, the use of light metals such as aluminum alloys and magnesium alloys as housing materials for personal computers and mobile phones is expanding. Light metals are generally cast or thixomolding, but plastic processing of a thin plate material can greatly reduce the cost. When these thin plate materials are used, stud welding is indispensable for fixing electrical equipment. However, light metal welding conditions are severe and poor welding is likely to occur. For this reason, it is necessary to inspect the bonding state, and in particular, inspection means capable of performing non-destructive and high-speed inspection are required.

As a conventional nondestructive inspection method for stud welding or spot welding, there are the following methods.
(A) A method of estimating a welding state by measuring a welding current.
This is a method of measuring a welding current in a process of performing electric resistance welding and determining a mechanical welding state based on the welding current. However, since the welding current and the mechanical welding state do not necessarily have a fixed relationship, high-precision inspection is difficult.
JP-A-8-122286

(B) A method for evaluating based on the displacement of the stud in the stud welding process.
In stud welding, the stud itself is melted and welded to the base material. Therefore, the displacement of the stud in the welding process is related to the welding area, and the welding state is estimated from the relationship. However, welding defects occur due to accumulation of voids or components of different materials between the stud and the base material, despite the fact that the stud is melted. Therefore, only some defects can be detected from the displacement of the stud during the welding process. Further, in the case of a small stud, it is difficult to measure the displacement of the stud with high accuracy.
JP-A-5-23858

(C) Ultrasonic method.
A general inspection method is an ultrasonic flaw detection inspection. There are a water immersion method and a method using a contact type contactor. The water immersion method is a method in which a test object is immersed in a liquid, an ultrasonic wave is irradiated through water, and an inspection is performed based on the reflection. The water infiltration method requires low work efficiency because it is necessary to immerse the pair to be inspected in water, and is not practical for mass-produced products. Further, in the case of thin plate welding, it is difficult to distinguish between a welded portion and bottom surface reflection, and it is difficult to determine a welded portion. A method using a probe is also affected by bottom surface reflection, and a highly reliable inspection is difficult.

  The present invention relates to the inspection of the state of a joint portion between a conductive part and another component part, and intends to solve the above-described problems related to the prior art. In particular, an object of the present invention is to provide a non-destructive inspection method for a joint part of a conductive part with high work efficiency and high reliability.

  In order to solve the above-described problems, the present inventors have conducted intensive research. As a result, when the entire conductive part is vibrated, the vibration state of the part changes corresponding to the joining state of the part. The title and the present invention have been completed. In addition, a non-destructive and efficient inspection method can be realized by utilizing a local change in electromagnetic force when the conductive component is vibrated.

According to a first aspect of the present invention, there is provided a nondestructive inspection method for inspecting a state of a joint portion between a conductive component formed of a conductive material and another component when the conductive component is bonded to the conductive component. By applying a fluctuating magnetic field, the entire conductive component is vibrated, and a joining state is determined based on a vibration state of the conductive component after the magnetic field is applied.
In the present invention, “vibration of the entire conductive component” basically means that the entire conductive component including the joint is vibrated. Although it does not exclude the generation of elastic waves in the component, it does not mean that only the elastic wave is excited in the conductive component, such as excitation of ultrasonic waves.
In addition, the “vibration state of the conductive component” in the present invention basically means a state where the entire conductive component is oscillating and deforming, and only the elastic wave propagating through the conductive component is used. It does not mean that a part of the surface is vibrating.

  According to a second aspect of the present invention, in the nondestructive inspection method according to the first aspect, the conductive component is arranged in a uniform magnetic field, and the pulsed varying magnetic field is applied to the conductive component. It is characterized by.

  The invention according to claim 3 is the nondestructive inspection method according to claim 1, wherein the conductive component is a ferromagnetic material.

  According to a fourth aspect of the present invention, in the nondestructive inspection method according to any one of the first to third aspects, the vibration state of the conductive part is a reflected light of light irradiated on the conductive part or the conductive part. It measures using either of the electrostatic capacitance between a property component and a measurement electrode.

  According to a fifth aspect of the present invention, in the nondestructive inspection method according to any one of the first to fourth aspects, when determining the joining state, a spectrum analysis is performed on a measurement waveform related to a vibration state of the conductive part. By comparing the frequency spectrum obtained in this way with the frequency spectrum corresponding to the normal bonding state, the bonding state is determined.

  According to the first aspect of the present invention, in a nondestructive inspection method for inspecting the state of a joint portion between a conductive part formed of a conductive material and another component part, the conductive part is attached to the conductive part. Since the entire conductive component is vibrated by applying a fluctuating magnetic field, it is possible to efficiently vibrate the entire conductive component that is the object of measurement determination without contacting the conductive component. Become. In addition, since the bonding state is determined based on the vibration state of the conductive part after the magnetic field is applied, it is possible to provide a highly reliable nondestructive inspection method for the bonding part of the conductive part.

  According to the second aspect of the present invention, the conductive component is arranged in a uniform magnetic field, and the pulsed fluctuating magnetic field is applied to the conductive component, so that the conductive component is more efficiently vibrated. Therefore, a non-destructive inspection method with high work efficiency can be provided.

  According to the third aspect of the present invention, since the conductive component is a ferromagnetic material, the conductive component can be efficiently added by the magnetostriction effect in the conductive component simply by applying a varying magnetic field to the conductive component. Therefore, it is possible to provide a non-destructive inspection method with high work efficiency.

  According to the invention of claim 4, the vibration state of the conductive component uses either the reflected light of the light irradiated to the conductive component or the capacitance between the conductive component and the measurement electrode. Therefore, the vibration state of the conductive part can be measured nondestructively and efficiently.

  According to the fifth aspect of the present invention, when determining the joining state, the frequency spectrum obtained by spectrum analysis of the measurement waveform relating to the vibration state of the conductive part is compared with the frequency spectrum corresponding to the normal joining state. Therefore, it is possible to perform electrical automatic processing in order to determine the joining state, and it is possible to provide a non-destructive inspection method for joints of conductive parts with high work efficiency and reliability. .

Hereinafter, the nondestructive inspection method according to the present invention will be described in detail.
As shown in FIG. 1, the nondestructive inspection method of the present invention uses a magnetic field 6 that fluctuates in the inspection of a joint 2 between a conductive part 3 made of a conductive material and a base part 4 that is another component. Is used to vibrate the entire conductive component 3 and determine the bonding state of the bonding portion 2 from the vibration state of the conductive component.

  Specifically, in a uniform magnetic field 7, a fluctuating current is passed through the coil 5 disposed around the conductive component 3 to excite the fluctuating magnetic field inside the conductive component 3, and as a result An eddy current 8 is generated inside the conductive material 3, and the entire conductive component 3 is vibrated by the interaction between the uniform magnetic field 7 and the eddy current 8.

  The method for exciting the conductive component 3 is not limited to the method described above. For example, when the conductive component 3 is a ferromagnetic material, a uniform magnetic field is formed in the conductive component 3 before the changing magnetic field is applied, and the conductive component 3 is generated by the changing magnetic field 6. The conductive component 3 itself expands and contracts due to the magnetostrictive effect inside and vibrates.

  The state of the joint portion 2 between the conductive component 3 and the base portion 4 which is another component appears in the vibration state of the conductive member 3. For example, when the bonding areas are different, the vibration characteristics are also different. In addition, when a bonding material is used for the bonding portion, the vibration characteristics of the conductive parts change even when the bonding materials have different thicknesses.

Next, the vibration state of the conductive component 3 is measured by some measuring means, and the state of the joint 2 is estimated from the vibration characteristics.
In order to measure the vibration state of the conductive part 3, the vibration frequency and amplitude differ depending on various conditions such as the material and size of the conductive part, the area of the joined part and the joining material. It is necessary to select.

For example, when a stud is welded to a light metal thin plate used in the above-described personal computer or mobile phone, the vibration frequency is high and the amplitude is extremely small.
As a means of non-contact and high-speed measurement under such severe conditions, the reflected light of the light irradiated on the conductive parts such as laser Doppler vibrometer, position detection element (PSD), laser displacement meter, etc. The method used and the method of disposing a measuring electrode in the vicinity of the conductive component and measuring the capacitance between them can be suitably used.

  When determining the bonding state, directly compare the vibration state of the conductive component, for example, the change in displacement of the conductive component over time and the change in displacement speed and acceleration with the vibration characteristics corresponding to the normal bonding state. However, it is highly possible that the measurement result (measurement waveform) includes various noises for each component, and also results in comparison with vibration that is not related to the joint. Furthermore, the vibration change of the joint part of interest may appear very small with respect to other factors, and it is not preferable to directly compare the measurement results.

In the non-destructive inspection method of the present invention, the measurement waveform result related to the vibration state of the conductive part is subjected to spectrum analysis using Freee transform, wavelet transform, linear prediction method, maximum entropy method, Hartley transform, etc. Is determined to be a frequency spectrum, and further, compared with a frequency spectrum corresponding to a normal bonding state, the bonding state is determined.
With this configuration, more accurate determination can be made. In addition, these processes can be electrically automatically performed and work efficiency can be improved.

FIG. 2 is a logical block diagram showing a nondestructive inspection apparatus for performing the nondestructive inspection method of the present invention.
In order to examine the joining state of the conductive component 3 and the base portion 4, both are arranged on the inspection table 31.
A uniform magnetic field 7 is applied to the conductive component 3 in advance by a magnet 32 such as an electromagnet installed at the lower part of the inspection table 31. The installation location of the magnet 32 is not limited to, for example, the lower part of the inspection table 31, and can be arbitrarily installed in a place where a uniform electric field can be formed on the conductive component 3, and the number and shape can also be set as appropriate. It is.

  The memory 11 in the computer system 10 stores a pulse waveform, a burst waveform, and other fluctuation waveforms corresponding to the fluctuating magnetic field applied to the conductive component 3. The electrical signals related to these waveforms are sent to the coil 5 via the D / A converter 21 and the amplifier 22, and a varying magnetic field is applied to the conductive component 3.

The vibration state of the conductive component 3 is measured by the laser Doppler vibrometer 25 and is taken into the computer system 10 via the controller 24 and the A / D converter 23.
Next, a frequency spectrum corresponding to the vibration state is obtained by the fast Fourier transform (FFT) means 12 for spectral analysis of the measured waveform. This frequency spectrum is displayed on the CRT monitor 14 via the video device 13.

  In FIG. 2, the frequency spectrum corresponding to the vibration state is only displayed on the CRT monitor 14 or the like. However, in order to automatically determine the bonding state of the conductive parts, the frequency corresponding to the normal bonding state in advance. The spectrum is accumulated and stored in another storage means, and compared with the frequency spectrum to be inspected. For example, the frequency spectrum value of a specific band, the shape of the entire waveform, and the like are compared to determine the joining state.

  In particular, when a change appears in the frequency spectrum of a specific band in the case of a defective bonding state, it is possible to determine the bonding state by comparing the frequency spectrum values of the specific band (or only a specific frequency). is there. Also, if the waveform size or amount of change in a specific band is relatively small in the overall waveform, the relative value of the size of the specific band and another waveform of interest within the same waveform is calculated. It is also possible to determine the joining state by comparing the relative values.

As an example of the conductive component, the welding state of the magnesium stud shown in FIG. 3 was determined. FIG. 3 is a cross-sectional view showing a state in which a substantially cylindrical stud having a cylindrical recess at the center is joined to a magnesium thin plate, and the numerical values shown in the figure are in mm units.
Three studs welded under appropriate conditions and three studs welded under inappropriate conditions with insufficient welding energy were inspected. A coil (diameter: about 7 mm, number of turns: 25 times) is arranged so as to surround the stud in FIG. 3, a uniform magnetic field is applied, and a pulse current (1 μs width, peak current: about 1 A) is periodically applied to the coil. Washed away.

The pulse current was input 1000 times, the damping vibration generated immediately after the input was measured 1000 times, and the frequency spectrum was obtained by the FFT means as the result of averaging the vibrations.
FIG. 4 is the result of a proper weld stud and FIG. 5 is the result of an improper weld stud. At the peak occurring at several tens of kHz, a difference in frequency and a difference in amplitude can be confirmed.
Therefore, it is possible to easily determine whether the bonding state is good or bad by comparing the magnitudes of the frequency spectra of such specific bands or specific frequencies.
In this way, considering that the difference in the bonding state appears at a low frequency of several tens of kHz, the non-contact inspection method of the present invention captures the reflection mode of the ultrasonic wave or the like from the bonding portion. It is presumed that the change in the vibration state of the entire conductive part including the joint (including other components in some cases) is captured.

  FIG. 6 shows an embodiment in which the coil 5 is arranged on the back surface of the base part 4. Note that when the conductive component is a ferromagnetic material, the constant magnetic field 7 is not necessary, and therefore a coil 5 that applies a varying magnetic field can be arranged as shown in FIG.

  FIG. 7 shows an example of a current that flows through the coil 5 when the constant magnetic field 7 and the variable magnetic field 6 are generated using one coil 5. A variable magnetic field 6 can be generated by generating a constant magnetic field 7 in a constant current portion and superimposing pulse currents. By utilizing this, it is not necessary to use the two magnetic field forming means of the magnet 32 and the coil 5 for forming the magnetic field as shown in FIG. 2, and it is possible to use one coil as shown in FIG. It becomes.

  FIG. 8 shows an example in which the vibration of the conductive component 3 is measured from the change in capacitance. A measurement electrode 19 is disposed on the conductive part 3. When the conductive part 3 vibrates, the distance between the conductive part 3 and the electrode 19 changes. The change in the interval can be electrically measured as a change in capacitance.

  FIG. 9 shows an example in which the conductive component is a plate-like body 30. The joining method is an example of spot welding. Reference numeral 1 denotes a spot weld. The coil 5 is disposed above the conductive component 30 in the constant magnetic field 7, and a varying current flows through the coil 5. As a result, a fluctuating eddy current 8 is generated in the conductive component 30, and the conductive material vibrates due to the interaction between the constant magnetic field 7 and the fluctuating eddy current 8. The vibration is measured using a laser 9. The subsequent processing can be performed in the same manner as the stud welding described above.

  As described above, according to the nondestructive inspection method of the present invention, when a conductive part and another component are joined, the state of the joint part of both can be inspected with high work efficiency and reliability. Possible non-destructive inspection methods can be provided.

It is the figure which showed the method of exciting an electroconductive component with the magnetic field which fluctuates. 1 is a logical block diagram of an inspection apparatus that performs a nondestructive inspection method according to the present invention. It is sectional drawing which shows a mode that the electroconductive component was joined to the thin plate which is a base part. It is the frequency spectrum of the vibration of the electroconductive member welded on the appropriate conditions. It is a frequency spectrum of the vibration of the electroconductive member welded on the unsuitable conditions. It is a figure at the time of arrange | positioning the coil which generate | occur | produces the magnetic field which fluctuates to the back surface of an electroconductive component. It is the figure which showed the example of the electric current sent through a coil in the case of generating a fixed magnetic field and a fluctuating magnetic field with a single coil. It is a figure in the case of calculating | requiring the vibration of an electroconductive component from the electrostatic capacitance between an electroconductive component and an electrode using the electrode for a measurement. It is the figure which showed the example in case an electroconductive component is a plate-shaped object.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spot welding part 2 Joint part 3 Conductive component 4 Base part 5 Coil 6 Fluctuating magnetic field 7 Constant magnetic field 8 Fluctuating eddy current 9 Laser 10 Computer system 11 Memory 12 FFT means 13 Video device 14 CRT monitor 21 D / A converter 22 Amplifier 23 A / D Converter 24 Controller 25 Laser Doppler Vibrometer 30 Conductive Parts (Plate)
31 Inspection table 32 Magnet

Claims (5)

In the non-destructive inspection method for inspecting the state of the joint portion between the conductive component formed of the conductive material and other component parts,
Applying a magnetic field that fluctuates to the conductive component to vibrate the entire conductive component, and determining a joining state based on a vibration state of the conductive component after the magnetic field is applied. Destructive inspection method.   2. The nondestructive inspection method according to claim 1, wherein the conductive component is disposed in a uniform magnetic field, and the pulsed varying magnetic field is applied to the conductive component. .   The nondestructive inspection method according to claim 1, wherein the conductive component is a ferromagnetic material.   4. The nondestructive inspection method according to claim 1, wherein the vibration state of the conductive component is a reflected light of light irradiated on the conductive component, or between the conductive component and the measurement electrode. A non-destructive inspection method characterized by being measured using any one of the capacitances between.   5. The nondestructive inspection method according to claim 1, wherein when determining the joining state, a frequency spectrum obtained by performing spectrum analysis on a measurement waveform related to a vibration state of the conductive part is set to be normal. A non-destructive inspection method characterized in that a joining state is determined by comparing with a frequency spectrum corresponding to a particular joining state.

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