JP5450225B2 - Nondestructive inspection equipment - Google Patents

Description

  The present invention relates to a nondestructive inspection apparatus for nondestructively inspecting a welded part or the like of an object to be measured.

  Spot welding is generally used as welding used for assembling various thin metal products. Spot welding is a method in which a predetermined current is passed through both electrodes for a predetermined period of time by sandwiching them at a predetermined pressure from the top and bottom with an electrode whose tip is formed in a predetermined shape at the welded part of the metal plate that is overlapped. Thus, the welding site is locally heated and welded.

  Moreover, the surface of the welding site | part welded by spot welding is dented compared with the outside of a welding part by pressurization. This dent part is called an indentation part, and the dimension of the dent is called an indentation diameter.

  Moreover, the inside of a welding site | part is formed by the nugget part (welding part) and the crimping | compression-bonding part of the periphery. The nugget portion is a portion where the metal is once dissolved and solidified. On the other hand, a crimping | compression-bonding part is a part crimped | bonded by metal surfaces. The dimension of the nugget portion is referred to as the nugget diameter, the nugget portion and the crimping portion are collectively referred to as a joint portion, and the dimension of the joint portion is referred to as a joint diameter. In addition, a junction part is a part actually joined.

  Further, in spot welding, the overlapped metal plate materials are welded at points (spots), so it is necessary to inspect whether the welding strength is sufficient.

  As a method for measuring the welding strength in a non-destructive manner, a method for estimating the welding strength by measuring the nugget diameter is effective (see, for example, Patent Document 1). Conventionally, as a method for measuring a nugget diameter, a method is known in which a magnetic field generated by a coil through which a current is applied is applied to a welding site, and the nugget diameter is obtained from a change in the inductance of the coil generated as a result. In this conventional method, since the magnetic permeability (μ) varies between the nugget portion and the portion other than the nugget portion, this property is used to detect a change in the magnetic permeability (μ) as a change in inductance. Seeking the nugget diameter.

Japanese Patent No. 3098193

  Here, the sensor of the inspection apparatus is arranged with reference to a welded portion that can be visually recognized from the outside. By the way, the center position of the recessed part (indentation part) visually recognizable from the outside may not coincide with the center position of the nugget part. This occurs, for example, when the electrode tips do not face each other but face each other at a certain angle during spot welding.

  In this way, if the center position of the welded part and the center position of the nugget part are deviated, the nugget part is not formed or deviated immediately below where the sensor of the inspection apparatus is arranged. It becomes impossible to measure accurately. In such a case, the re-inspection must be repeated by shifting the sensor of the inspection device to various positions, and much labor is required to measure the nugget diameter.

  The present invention has been made in view of the above-described problems, and one of its purposes is to provide a nondestructive inspection apparatus capable of efficiently measuring a nugget portion.

In order to solve the above problems, the nondestructive inspection apparatus according to the present invention generates a magnetic flux density by applying a magnetic field to the object to be measured, and after the magnetic field is cut off, the magnetic flux emitted from a plurality of positions of the object to be measured. In the non-destructive inspection device that detects the internal structure of the object to be measured from the distribution state of the time constant, the detection result of the internal structure of the object to be measured is calculated. A moving direction determining unit that determines a moving direction of the magnetic flux detecting element, and a direction indicating unit that indicates the direction determined by the moving direction determining unit, the moving direction determining unit including the object to be measured When determining the moving direction of the magnetic flux detection element based on the detection result of the internal structure of the sensor, the previous detection result is compared with the current detection result, and the magnetic flux detection is performed in the direction in which the time constant of the transient change increases. Move the element It is preferable to determine the moving direction.

In order to solve the above problems, the nondestructive inspection apparatus according to the present invention generates a magnetic flux density by applying a magnetic field to the object to be measured, and after the magnetic field is cut off, the magnetic flux emitted from a plurality of positions of the object to be measured. In the non-destructive inspection device that detects the internal structure of the object to be measured from the distribution state of the time constant, the detection result of the internal structure of the object to be measured is calculated. A moving direction determining unit that determines a moving direction of the magnetic flux detecting element, and a direction indicating unit that indicates the direction determined by the moving direction determining unit, the moving direction determining unit including the object to be measured When determining the direction of movement of the magnetic flux detection element based on the detection result of the internal structure of, the previous detection result and the current detection result are compared, the time constant of the transient change is a predetermined value, When the change is in a certain range , Decided to discontinue the movement of the magnetic flux detecting element, said direction indicating section based on the determination of the cessation of movement by the moving direction determination section, it is preferable to perform an instruction to stop the movement.

  In the nondestructive inspection apparatus, it is preferable that the direction indicating unit is configured to indicate the front-rear and left-right directions on the surface of the object to be measured.

  In the nondestructive inspection apparatus, it is preferable that the magnetic flux detection element is constituted by an array coil in which a plurality of coils are arranged.

  According to the present invention, the nugget portion can be measured efficiently.

It is a block diagram which shows the structure of the nondestructive inspection apparatus which concerns on this embodiment. It is a figure which shows the structure of the direction instruction | indication part of the nondestructive inspection apparatus which concerns on this embodiment. It is a figure where it uses for description at the time of applying a magnetic field with respect to a workpiece | work in two steps. It is a figure which shows typically a mode when a magnetic field is applied and magnetic flux density is generated. It is a figure which shows typically the disappearance process of a residual magnetism. It is a figure which shows the circuit diagram which replaced the closed loop of the magnetic flux density shown in FIG.5 (b) with the magnetic equivalent circuit. A closed loop C ₀ of the magnetic flux passing through any one of the array sensor immediately after blocking the static magnetic field is a diagram schematically illustrating. It is a figure where it uses for description about the change of the magnetic flux measured with an array sensor. It is a figure which shows the external appearance of a sensor probe. It is a figure where it uses for description about the measurement principle in the case of instruct | indicating the left-right direction. It is a figure with which it uses for description about the measurement principle in the case of indicating the front-back direction.

  As a method of melting and integrating two or more members, there is spot welding. An apparatus for spot welding welds members by passing a large current for a short time while sandwiching two metal plates between rod-like electrodes of pure copper or a copper alloy and pressing them strongly. Further, a slight dent pressed by the electrode is formed on the surface of the welded portion, and a nugget portion (a solidified weld metal) is formed in the inside. The nondestructive inspection apparatus 1 according to the present embodiment inspects the nugget portion by nondestructive. In addition, in a present Example, although the test | inspection of the welding site | part welded by spot welding is demonstrated, the welding method is not limited to spot welding. The “internal structure” means a structure that is chemically, physically and mechanically changed.

  The nondestructive inspection apparatus 1 is an apparatus for inspecting a welded part 3 of an object to be measured 2 (for example, an automobile body) made of a magnetic material, and applies a magnetic field to the welded part 3 to be emitted. A non-destructive inspection method is employed in which the nugget portion is inspected by measuring the magnetic flux density. Embodiments of the present invention will be described below.

  As shown in FIG. 1, the nondestructive inspection apparatus 1 includes a magnetic flux generation unit 16, an induced electromotive force detection unit 17, a sensor output switching unit 18, a sensor output control unit 19, a processing unit 20, and a moving direction determination. Unit 21 and direction indicating unit 22. The magnetic flux generation unit 16 includes an iron core 13 composed of the excitation magnetic pole 11 and the recovery magnetic pole 12, an excitation coil 14 that excites the iron core 13, and an excitation control unit 15 that controls the energization state and the interruption state of the excitation coil 14. .

  Here, the shape of the iron core 13 will be described. As schematically shown in FIG. 1, the iron core 13 is formed in a U shape in which an excitation magnetic pole 11 is formed on one end side and a recovery magnetic pole 12 is formed on the other end side. Further, coils C1 to Cn (n is a natural number of 2 or more) formed on the end face of the excitation magnetic pole 11 detect leakage magnetic flux generated from the welded part. In addition, the shape of the iron core 13 is not restricted to what was mentioned above.

  The magnetic flux generator 16 controls the excitation coil 14 to be energized by the excitation controller 15 to generate a magnetic flux between the excitation magnetic pole 11 and the recovery magnetic pole 12 and applies a magnetic field to the object 2 to be measured. In the exciting coil 14, a conductor is closely wound around a predetermined portion of the iron core 13 in a spiral shape, and is configured by a solenoid coil. In this embodiment, the direction in which the excitation coil 14 is wound will be described as the excitation magnetic pole 11. However, depending on the direction of the current flowing through the excitation coil 14, the direction in which the excitation coil 14 is wound becomes the excitation magnetic pole. Since it becomes a recovery magnetic pole, the direction around which the exciting coil 14 is wound may be used as the recovery magnetic pole.

  The induced electromotive force detection unit 17 is disposed on the end face of the excitation magnetic pole 11 and detects the induced electromotive force generated from the welded part 3. Moreover, the induced electromotive force detection part 17 is comprised by the array coil by which the some coil C is arrange | positioned. In the present embodiment, the induced electromotive force detection unit 17 is described as having 16 (C1 to C16) microcoils arranged uniformly in one row, but is not limited thereto, and is configured by a plurality of rows and a plurality of columns. May be.

  Moreover, in the welding site | part 3, the welded trace (henceforth a welding dent (nugget part)) can be visually recognized on the surface. In the inspection by the nondestructive inspection apparatus 1, a magnetic field is applied to the surface of the welding dent to generate a magnetic flux density, and the inside of the welding state is inspected by the coils C1 to C16.

  The sensor output control unit 19 sequentially selects outputs from the plurality of coils C1 to C16 included in the array coil. The sensor output switching unit 18 outputs a signal from the coil C selected by the sensor output control unit 19 to the processing unit 20.

The processing unit 20 calculates the decay time constant τ ₁ of magnetic energy and the decay time constant τ ₂ of eddy current loss based on the signal supplied from the sensor output switching unit 18. In addition, by measuring the distribution of the decay time constant τ ₁ of the magnetic energy of the weld dent (nugget part) and analyzing this, the shape and size of the part where the compositional change in the metal such as the nugget part occurs can be obtained. Can be sought. Therefore, the processing unit 20 may calculate the shape / dimension of the nugget part based on the calculated decay time constant τ ₁ of the magnetic energy and schematically display it on the display part.

The moving direction determination unit 21 generates an induced electromotive force on the surface of the DUT 2 on the surface of the measurement object 2 based on the processing results (magnetic energy decay time constant τ ₁ and eddy current loss decay time constant τ ₂ ). The moving direction of the detection unit 17 is determined. The direction instruction unit 22 instructs the direction determined by the movement direction determination unit 21.

  As shown in FIG. 2, the direction indicating unit 22 indicates four directions on the surface of the DUT 2: the front direction (22a), the rear direction (22b), the left direction (22c), and the right direction (22d). Is configured to do. In this embodiment, the direction instructing unit 22 instructs four directions every 90 degrees, but the number of directions to be instructed is not limited to this.

  Further, LEDs (a) to (d) having different emission colors are provided in each direction of the direction instruction unit 22. The direction instructing unit 22 appropriately controls the light emission of the LEDs (a) to (d) arranged in each direction in accordance with a command from the moving direction determining unit 21. Note that the light emission control is control such as lighting and blinking.

Here, a specific operation by the nondestructive inspection apparatus 1 will be described. Hereinafter, what the user moves with the hand on the object to be measured 2 is referred to as an inspection unit 5. The inspection unit 5 is a concept including an iron core 13, an excitation coil 14, an induced electromotive force detection unit 17, and a direction instruction unit 22.
In the nondestructive inspection apparatus 1, excitation is started by the excitation control unit 15 in accordance with a predetermined operation by the user, and the sensor output switching unit 18 is controlled by the sensor output control unit 19.

  For example, the sensor output control unit 19 performs detection control with the coils C1 to C16 arranged in a line as one set. The sensor output switching unit 18 switches according to the control of the sensor output control unit 19, for example, at a timing of 10 msec to 10 sec.

The processing unit 20 calculates the decay time constant τ ₁ of the magnetic energy of each coil and the decay time constant τ ₂ of the eddy current loss based on the signal supplied from the sensor output switching unit 18, and uses these values for sampling. Data (hereinafter referred to as nugget supplement data). The nugget supplemental data may be either one of the decay time constant τ ₁ of the magnetic energy of each coil and the decay time constant τ ₂ of the eddy current loss.

  The processing unit 20 may use one set of average values as nugget supplement data. Thus, the nondestructive inspection apparatus 1 has an advantage of being able to absorb the error of each coil C by using one set of average values as nugget supplemental data.

  The movement direction determination unit 21 determines the movement direction based on the processing result of the processing unit 20. If the processing result is immediately after the start of the inspection, the movement direction is determined to be forward (22a) for convenience. To decide.

  The direction instruction unit 22 instructs the direction (forward direction (22a)) determined by the movement direction determination unit 21. Specifically, the direction instructing unit 22 turns on the LED (a) in the forward direction (22a). The nondestructive inspection device 1 may be configured to light the LED (a) in the forward direction (22a) of the direction indicating unit 22 immediately after the induced electromotive force detection unit 17 is disposed on the DUT 2. good.

  In this way, the nondestructive inspection apparatus 1 can guide the inspection unit 5 to the place where the nugget portion is formed by urging the movement of the inspection unit 5 in the direction indicated by the direction instruction unit 22. The nugget portion can be measured efficiently.

  Although details will be described later, a portion where the nugget portion is formed has a larger residual magnetism and a larger nugget supplement data than a portion where the nugget portion is not formed. The movement direction determination unit 21 determines the movement direction of the inspection unit 5 in the direction in which the nugget supplement data increases.

  Here, when determining the moving direction of the inspection unit 5 based on the processing result of the processing unit 20, the moving direction determination unit 21 compares the previous nugget supplemental data with the current nugget supplemental data to determine the nugget supplementation. The moving direction may be determined so that the inspection unit 5 is moved in the direction in which the data increases, that is, in the direction in which the time constant of the transient change increases.

  In addition, the movement direction determination unit 21 compares the previous nugget supplement data with the current nugget supplement data when determining the movement direction of the inspection unit 5 based on the detection result of the internal structure of the DUT 2. When the nugget supplement data decreases, it is determined that the inspection unit 5 has moved away from the nugget unit, and the moving direction is determined so as to return the inspection unit 5 to the previous position. Specifically, the direction instructing unit 22 lights the LED (b) in the rear direction (22b).

  In this way, the nondestructive inspection apparatus 1 can determine the moving direction of the inspection unit 5 where the nugget unit is accurately formed, and can efficiently measure the nugget unit.

  In addition, the movement direction determination unit 21 compares the previous nugget supplement data with the current nugget supplement data when determining the movement direction of the inspection unit 5 based on the detection result of the internal structure of the DUT 2. When the nugget supplement data is a predetermined value, that is, when the time constant of the transient change is a predetermined value and the change is in a certain range, the movement of the inspection unit 5 may be determined to be stopped. .

In the case of such a configuration, the direction instructing unit 22 gives an instruction to cancel the movement based on the determination to cancel the movement by the moving direction determining unit 21. Specifically, the direction instruction unit 22 lights the LEDs (a) to (d) in all directions at the same time.
In this way, the nondestructive inspection apparatus 1 can accurately tell the user the part where the nugget part is formed, and can efficiently measure the nugget part.

<Measurement principle>
Next, the measurement principle by the nondestructive inspection apparatus 1 will be described. The magnetic flux exits from the excitation coil 14 (excitation magnetic pole 11) for generating magnetism, passes through the induced electromotive force detection unit 17 disposed immediately below the excitation coil 14, enters the object to be measured 2 (workpiece), and is welded. It passes through the dent (nugget portion), passes through the recovery magnetic pole 12, and returns to the original excitation coil 14 (excitation magnetic pole 11).

  Here, paying attention to the coil C constituting the array coil, if the surface area of the coil C is S, the length of the magnetic path is L, and the magnetic permeability is μ, the magnetic resistance Rm is Rm = L / S × μ. Can be calculated. When a magnetic field is applied to generate a magnetic flux density (details will be described later with reference to FIG. 8), the magnetic field is slowly created and eventually becomes direct current. When the magnetic field is cut off at a predetermined timing to reduce the magnetism, a waveform of e = −dΦ / dt appears in the coil C in proportion to the change in the magnetic flux density (see FIG. 8A described later). ). Further, the magnetic resistance of the magnetic flux passing through each coil can be estimated by integrating the change in magnetic flux density generated in all the coils C1 to C16 and obtaining the intercept and time constant of the curve represented by the exponential function. . When the magnetic resistance of each coil is obtained, smoothed, and displayed on a display, the internal structure of the device under test 2 can be schematically visualized.

Factors affecting the magnetic resistance can be roughly divided into three (shape (air layer), residual stress, and hardness).
As shown in FIG. 3, the magnetic flux generated by the exciting coil 14 passes through the gap via the induced electromotive force detection unit 17 and enters the inside of the DUT 2 (work). Thereafter, the magnetic flux is affected by residual stress and hardness inside the workpiece.

  Here, as shown in FIG. 3, the nondestructive inspection apparatus 1 generates a magnetic field twice with respect to the workpiece by the exciting coil 14. Specifically, the exciting coil 14 applies a magnetic field for a short time as the first magnetic field, and generates a magnetic flux density by applying a shallow magnetic field to the workpiece by the skin effect (B1 in FIG. 3). Further, the exciting coil 14 applies a magnetic field for a sufficiently long time as the second magnetic field, and applies a magnetic field deeply to the workpiece to generate a magnetic flux density until it reaches the welding site 3 (FIG. 3). B2).

Then, the processing unit 20 shallowly applies a magnetic field to generate a magnetic flux density (magnetic resistance R ₀ ) and a measurement result obtained by applying a deep magnetic field to generate a magnetic flux density ( The differential magnetic resistance R of the magnetic resistance R ₂ ) is obtained.
R ₀ = R _f + R _a + R _w0
R ₂ = R _f + R _a + R _{w
R = R 2 -R 0 = R} w -R w0
Note that the R _f, shows a magnetic resistor having a core 13 from the induced electromotive force detecting portion 17 of configured sensor itself, R _a shows a magnetic resistance exists between the workpiece and the sensor. Also, R _w0 represents the magnetic resistance of the workpiece surface, R _w represents the magnetic resistance of the workpiece interior.

Therefore, the difference magnetic resistance R, a magnetic resistance R _f with the sensor itself, a magnetic resistance R _a existing between the workpiece and the sensor (canceled) was removed a resistance value. Thus, the nondestructive inspection apparatus 1 can obtain the magnetic resistance R with high accuracy regardless of the surface shape of the workpiece by obtaining the differential magnetic resistance R from the two-stage measurement results.

In the above description, the nondestructive inspection apparatus 1 first measures the magnetic resistance R ₀ by applying a shallow magnetic field to generate a magnetic flux density, and then applying a magnetic field deeply to generate the magnetic flux density to thereby generate the magnetic resistance. Although R ₂ is measured, the present invention is not limited to this, but the magnetoresistance R ₂ is measured by first applying a magnetic field deeply to generate a magnetic flux density, and then generating a magnetic flux density by applying a shallow magnetic field to thereby generate the magnetic resistance. R ₀ may be measured.

<Calculation method of time constant>
Next, a specific method for calculating the decay time constant τ ₁ of magnetic energy and the decay time constant τ ₂ of eddy current loss by the processing unit 20 will be described. The coils C <b> 1 to C <b> 16 of the nondestructive inspection apparatus 1 are disposed on the upper surface of the part to be inspected of the DUT 2. Then, the nondestructive inspection apparatus 1 energizes the exciting coil 14 and applies a magnetic field to the object 2 to be measured by the magnetic flux generated between the exciting magnetic pole 11 and the recovery magnetic pole 12 to generate a magnetic flux density. Here, FIG. 4A shows a schematic state when a magnetic field is applied to generate a magnetic flux density. As shown in FIG. 4A, the device under test 2 generates a magnetic flux density by applying a magnetic field to a magnetic flux passage portion according to the strength of the magnetic field.

  When the exciting coil 14 of the nondestructive inspection apparatus 1 is cut off, the magnetic flux loop is separated into a closed loop around the exciting coil 14 and a closed loop around the object to be measured 2 (FIG. 4 ( see b)). The closed loop of magnetic flux around the exciting coil 14 rapidly decreases and disappears. On the other hand, the closed loop of the magnetic flux around the object to be measured 2 does not disappear immediately (residual magnetism) but is held in the magnetic material as magnetic energy, gradually disappears, and finally returns to the state before applying the static magnetic field. .

  The nondestructive inspection apparatus 1 detects changes with time of the leakage magnetic flux of the DUT 2 using the coils C1 to C16. Although the change in the magnetic flux detected by the coils C1 to C16 after the static magnetic field is cut off is ideally monotonously decreased in an exponential function, it actually decreases, and thus decreases in a predetermined curve.

FIG. 5 shows the disappearance process of the remanent magnetism. This magnetic energy loss process, as shown in FIG. 5 (a), the magnetic flux density passing through any one of the coils C1 to C16 and phi _1. In addition, eddy currents induced by changes in the magnetic flux density φ ₁ are In ₁ , In ₂ , In ₃ ..., And their induction coefficients are M ₁ , M ₂ , M ₃ . It is considered that the eddy currents In ₁ , In ₂ , In ₃ ... Induced from the change of the magnetic flux density φ ₁ are independent. At this time, the eddy currents In ₁ , In ₂ , In ₃ ... Are induced with an induction coefficient M = ΣMi (i = 1, 2, 3,...) According to the change of the magnetic flux density φ _1. It can be replaced with one eddy current i ₂ . Namely, disappearance process of the magnetic flux passing through any one of the coils C1 to C16 has a magnetic flux density phi _1, can be represented by an eddy current i ₂ induced by induction factor M from the magnetic flux density phi _1. FIG. 5B shows an equivalent circuit of FIG. Here, R ₂ represents the electrical resistance of the eddy current i ₂ , and L ₂ represents the inductance of the eddy current i ₂ .

In FIG. 6, the closed loop of the magnetic flux density φ is replaced with a magnetic equivalent circuit. Here, i ₁ indicates the magnetic flux density, R ₁ indicates the difficulty of returning the magnetic flux at the measurement site holding the magnetic flux (resistance), and L ₁ is the inductance of the magnetic flux space holding the magnetic flux. I ₂ indicates the eddy current at the measurement site, R ₂ indicates the electric resistance of the eddy current loop, and L ₂ indicates the volume of the space in which the eddy current is generated.

FIG. 7 shows a closed loop C ₀ of the magnetic flux i ₁ (= φ ₁ ) that passes through any one of the coils C 1 to C 16 immediately after blocking the static magnetic field. At this time, the magnetic energy stored during the application of the static magnetic field does not immediately disappear but gradually disappears. This magnetic energy is held in the closed loop space of the magnetic flux, and it is considered that it gradually disappears depending on the difficulty of returning the magnetic flux given to the space. The magnetic energy W can be expressed by equation (1). Note that L in FIG. 7 indicates the length of magnetic flux density generated by applying a magnetic field.

Here, L is a value proportional to the volume of the space holding the magnetic flux (that is, the space holding the magnetic energy). On the other hand, the expression (1) is the same expression as the energy accumulated when the current i ₁ is passed through the coil having the inductance L. From these, the inductance L ₁ of FIG. 6, it can be seen that correspond to the volume of the whole space that holds the magnetic flux.

Further, when the equivalent circuit shown in FIG. 6 is expressed by equations, equations (2a) and (2b) are obtained.

  Solving equations (2a) and (2b) yields equations (3a) and (3b).

Here, as an initial condition, when the static magnetic field interrupting the magnetic flux density _{i 1} of (t = 0) as _{I 0,} define the constants of equation (3). At this time, when the induction coefficient M is small and the eddy current i ₂ induced from the change of the magnetic flux density i ₁ is small, that is, when L1 · L2 >> M · M, the following results are obtained.

  Substituting equations (4a) and (4b) into equation (3a) yields the following equation (5).

The value that can be actually measured is the magnetic flux density i ₁ on the left side of equation (5). FIG. 8A shows a transient change of the magnetic flux density i ₁ given by the equation (5). Here, as is clear from the equation (4d), the second term on the right side of the equation (5) can be ignored and can be approximated only by the first term. On the other hand, the voltage measured by a loop coil generally used as a magnetic sensor is a value proportional to the rate of change of magnetic flux density, that is, the differential magnetic flux density. Therefore, the equation (5) is differentiated by the time t, and the equation of the differential magnetic flux density shown in the equation (6) is obtained.

FIG. 8B shows a transient change in the differential magnetic flux density given by equation (6). The expression (5) is an expression indicating a change in the magnetic flux density i ₁ obtained by the coils C1 to C16, and the expression (6) is an expression indicating a change in the differential magnetic flux density (di ₁ / dt).

Here, the time constant τ ₁ of the first term on the right side of the equation (6) is equal to “L1 / R1” as given by the equation (4a). Further, the first term on the right side of the equation (6) is a term indicating the magnetic flux density reduction characteristic in the vicinity of the DUT 2 after the static magnetic field is interrupted, that is, the magnetic energy attenuation characteristic. In spot welds, the nugget part (where the metal composition or structural strength changes) and the parts other than the nugget part (where the metal composition or structural strength does not change) A change occurs in the time constant τ ₁ . Therefore, if the distribution of the time constant τ ₁ in the spot welded portion is measured and analyzed, the shape / dimension of the portion such as the nugget portion where the compositional change in the metal occurs can be obtained.

Further, the time constant τ ₂ of the second term on the right side of the equation (6) is equal to “L ₂ / R ₂ ” as given by the equation (4b). Therefore, this term corresponds to the time constant of the equivalent circuit of the eddy current i ₂ shown in FIG. That is, the second term on the right side of the equation (6) is a term indicating the attenuation characteristic of the eddy current loss. As shown in FIG. 7, when the length of the magnetic flux density in the DUT 2 is L and the magnetic flux passage area is ds, L ₂ can be expressed by the equation (7).

Therefore, from the equations (4b) and (7), the time constant τ ₂ of the attenuation characteristic of the eddy current loss passes through the magnetic path where the eddy current is generated, that is, the steel plate, as shown in the equation (8). It is proportional to the length of the magnetic path.

That is, the change in the length of the magnetic path of the magnetic flux passing near the spot welded portion can be detected as the change in the time constant τ ₂ of the attenuation characteristic of the second term on the right side of the equation (6).

  The nondestructive inspection apparatus 1 has a time constant when a magnetic field is generated by applying a shallow magnetic field and a time constant when a magnetic field is generated by applying a deep magnetic field as shown in the measurement principle described above. Based on this, the magnetic resistance Rf of the sensor itself and the time constant of canceling the magnetic resistance Ra existing between the workpiece and the sensor are calculated, and the user is accurately ascertained where the nugget portion is formed. Can be efficiently guided.

  Further, by using the nondestructive inspection apparatus 1, the user can grasp at a glance the moving direction to proceed next, and can efficiently perform the nondestructive inspection on the object 2 to be measured. it can.

<Application example>
Here, an application example of the nondestructive inspection apparatus 1 will be described with reference to FIG. Hereinafter, what the user moves with the hand on the object 2 is referred to as a sensor probe 5. The sensor probe 5 is a concept including an iron core 13, an excitation coil 14, an induced electromotive force detection unit 17, and a direction instruction unit 22. In the present embodiment, the sensor probe 5 is described as a handy type that can be freely operated by the user's hand, but is not limited thereto, and may be operated by machine control. The size can be freely changed according to the application.

  As shown in FIG. 9, the sensor probe 5 is brought close to the object to be measured 2 (may be brought into contact with it) and starts measurement. In the case of the first measurement, the sensor probe 5 indicates a predetermined direction (for example, the forward direction (22a)), and then compares the previous nugget supplement data with the current nugget supplement data, and the nugget supplement data. The direction instructing unit 22 instructs to move in the direction in which the time constant increases, that is, in the direction in which the time constant of the transient change increases.

  In this way, the direction indicating unit 22 can guide the sensor probe 5 to the welding site 3.

  Here, the measurement principle when the left direction (22c) or the right direction (22d) is instructed by the direction instructing unit 22 will be described with reference to FIG. For example, when the welded part 3 is located directly below a part of the induced electromotive force detection unit 17 (coils C2 to C4), if the nugget waveform is drawn based on the value detected from each coil, the nugget waveform is From C2 to the coil C3, the magnetic path length becomes the shortest so that it becomes closer to the reference line, and from the coil C3 to the coil C4, the magnetic path length becomes longer, so it moves away from the reference line.

  Accordingly, in the present embodiment, the sensor probe 5 has the maximum value of the nugget waveform located on the left side (near the coil C3), and therefore, as shown in FIG. (C) is turned on. The user can move the sensor probe 5 to the welding site 3 by moving the sensor probe 5 in accordance with an instruction from the direction instruction unit 22.

  Next, the measurement principle when the front direction (22a) or the rear direction (22b) is instructed by the direction instructing unit 22 will be described with reference to FIG. In the following, it is assumed that the sensor probe 5 is moved on the DUT 2 and the induced electromotive force detection unit 17 is in the position shown in FIG.

  When the sensor probe 5 is moved from the position shown in (c) in FIG. 11 (hereinafter referred to as (c) position) to the position shown in (b) in FIG. 11 (hereinafter referred to as (b) position). , (C), the welded part 3 is formed only directly under the coil C3. However, in the (b) position, the welded part 3 is directly under the coils C2, C3 and C4. Is formed. Therefore, the average value nugget supplement data in which the coils C1 to C16 are set as one set increases in the case of being in the (b) position than in the case of being in the (c) position. Therefore, as shown in FIG. 11, the sensor probe 5 lights the LED (a) in the forward direction (22 a) of the direction indicating unit 22.

  Further, when the sensor probe 5 is moved from the position (c) to the position (a) in FIG. 11 where the welded portion 3 is not formed (hereinafter referred to as the position (a)), the coils C1 to C16 are moved. The average value of nugget supplement data for one set is reduced in the position (a) than in the position (c). Therefore, the sensor probe 5 lights the LED (b) in the rear direction (22b) of the direction instruction unit 22. Further, the sensor probe 5 is referred to as a position (hereinafter referred to as (d)) shown in (d) in FIG. 11 where the welded part 3 is not formed from the (c) position. ), The average nugget supplement data with the coils C1 to C16 as one set is reduced in the position (d) rather than the position (c). Therefore, the sensor probe 5 turns on the LED (a) in the forward direction (22a) of the direction indicating unit 22.

  In this way, the user can move the sensor probe 5 to the welding site 3 by moving the sensor probe 5 in accordance with an instruction from the direction instruction unit 22.

  In the above description, the detection values of all the coils C1 to C16 before and after the movement of the sensor probe 5 are sampled, the nugget supplement data is calculated, and depending on whether the nugget supplement data increases or decreases before and after the movement. Although the moving direction is determined, the present invention is not limited to this, and the number of coils showing a detection value greater than or equal to a predetermined value may be calculated, and the moving direction may be determined depending on whether the calculated value increases or decreases before and after the movement. .

DESCRIPTION OF SYMBOLS 1 Nondestructive inspection apparatus 5 Inspection part 11 Excitation magnetic pole 12 Recovery magnetic pole 13 Iron core 14 Excitation coil 15 Excitation control part 16 Magnetic flux generation part 17 Inductive electromotive force detection part (Flux detection element)
18 Sensor output switching unit 19 Sensor output control unit 20 Processing unit 21 Moving direction determination unit 22 Direction instruction unit

Claims (4)

A magnetic field is applied to the object to be measured to generate a magnetic flux density.After the magnetic field is interrupted, the magnetic flux emitted from a plurality of positions of the object to be measured is measured by the magnetic flux detection element, and the time constant of the transient change is calculated. In non-destructive inspection equipment that detects the internal structure of the object to be measured from the distribution of time constants,
Based on the detection result of the internal structure of the object to be measured, a moving direction determining unit that determines the moving direction of the magnetic flux detecting element;
A direction indicating unit that indicates the direction determined by the moving direction determining unit ,
The movement direction determination unit compares the previous detection result with the current detection result when determining the movement direction of the magnetic flux detection element based on the detection result of the internal structure of the object to be measured, and changes transiently. A non-destructive inspection apparatus characterized by determining a moving direction so as to move the magnetic flux detecting element in a direction in which the time constant increases . A magnetic field is applied to the object to be measured to generate a magnetic flux density.After the magnetic field is interrupted, the magnetic flux emitted from a plurality of positions of the object to be measured is measured by the magnetic flux detection element, and the time constant of the transient change is calculated. In non-destructive inspection equipment that detects the internal structure of the object to be measured from the distribution of time constants,
Based on the detection result of the internal structure of the object to be measured, a moving direction determining unit that determines the moving direction of the magnetic flux detecting element;
A direction indicating unit that indicates the direction determined by the moving direction determining unit,
The movement direction determination unit compares the previous detection result with the current detection result when determining the movement direction of the magnetic flux detection element based on the detection result of the internal structure of the object to be measured, and changes transiently. When the time constant is a predetermined value and the change is in a certain range, it is determined to stop the movement of the magnetic flux detection element,
The non-destructive inspection apparatus , wherein the direction instructing unit gives an instruction to cancel the movement based on the determination to cancel the movement by the moving direction determining unit . The non-destructive inspection apparatus according to claim 1, wherein the direction instructing unit is configured to instruct a front / rear / right / left direction on the surface of the object to be measured . The non-destructive inspection apparatus according to claim 1, wherein the magnetic flux detection element is configured by an array coil in which a plurality of coils are arranged .

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