JP4663603B2 - Eddy current flaw detection method and eddy current flaw detection system - Google Patents

Description

  The present invention relates to an eddy current flaw detection method and an eddy current flaw detection system, and more particularly to an eddy current flaw detection method and an eddy current flaw detection system that can suppress edge noise.

  In various industrial fields, casting technology is used to manufacture parts and products having complicated shapes. As such an example, for example, a piston for an automobile can be cited. In the piston casting technique, a molten alloy (molten metal) is press-fitted into a mold, sufficiently spread in the mold, and then solidified. In the casting process, the location and speed at which the molten metal is pressed or the temperature of the molten metal and the mold are set in detail. However, there are cases where minute holes (cast holes) are formed in the surface layer portion of the piston due to the air entrained when pouring the molten metal or the contracting action during solidification. In order to guarantee the quality of the piston, it is indispensable to check for the presence of a cast hole.

  An eddy current flaw detection system is used to inspect for the presence or absence of such a cast hole. The problem here is the edge of the piston. At the edge portion, the distribution of eddy current changes and a large noise is generated, so that it becomes difficult to detect a casting hole in the vicinity of the edge.

  As this noise suppression method, a cross-point probe in which a probe is configured by one excitation coil and one detection coil is known (for example, see Non-Patent Document 1). In this method, the detection coil is arranged so that the edge noise is offset against the eddy current distribution by the exciting coil.

Eddy current testing III, P.53-55 (Japan Nondestructive Inspection Association)

  In the thing of a nonpatent literature 1, a detection coil is arrange | positioned orthogonally with respect to an exciting coil. When there is no flaw, the eddy current from the exciting coil is not detected by the detection coil, and if there is a flaw, the eddy current is disturbed by the flaw and a component in an orthogonal direction is generated, and is detected by the detection coil. . However, in the case where the excitation coil and the detection coil are arranged orthogonally as described above, there is a problem that the detected signal intensity is low and the S / N ratio is poor.

  An object of the present invention is to provide an eddy current flaw detection method and an eddy current flaw detection system which can suppress edge noise and have an improved S / N ratio.

(1) In order to achieve the above object, the present invention provides an eddy having an excitation coil to which a voltage is applied in order to generate an eddy current in an object to be inspected and a detection coil for detecting a magnetic flux due to the eddy current. In an eddy current flaw detection system that scans a current flaw detection probe on a surface to be inspected and obtains a flaw detection signal, the eddy current flaw detection probes have the same shape and are arranged so that their central axes are parallel to each other. A moving unit configured to move the eddy current flaw detection probe to a target position based on setting information from a computer, and move the eddy current flaw detection probe to a target position by the moving unit; after the application of the excitation voltage to one of the coils of the two coils, also a switching means for switching to apply an excitation voltage to the other coil, said at least Applying one to the excitation voltage of the number of coils to obtain a first flaw signal and the other of the coil as a detection coil, after being switched by said switching means, by applying an excitation voltage to the other coil, the one Difference detection means for acquiring a second flaw detection signal using the coil as a detection coil and acquiring a difference signal between the first flaw detection signal and the second flaw detection signal is provided.
With this configuration, edge noise can be suppressed and the S / N ratio can be improved.

  (2) In the above (1), preferably, the current flaw detection probe is composed of n coils (n> 2) having the same shape and having central axes parallel to each other, and the switching means. Is one of the two coils out of n coils as an excitation coil, the other as a detection coil, one as a detection coil, and the other as an excitation coil. The first and second flaw detection signals are acquired and the difference signal is acquired repeatedly.

(3) Further, in order to achieve the above object, the present invention provides an excitation coil to which a voltage is applied in order to generate an eddy current in an object to be inspected and a detection coil for detecting a magnetic flux due to the eddy current. In an eddy current flaw detection method for acquiring a flaw detection signal by scanning an eddy current flaw probe having a surface to be inspected, the eddy current flaw probe has the same shape and is arranged so that its central axes are parallel to each other. using at least two coils that, said moving the eddy current testing probe to the desired location based on the setting information from the computer, after said applying at least two one coil exciting voltage of the coil, also switching so as to apply an excitation voltage to the other coil, the applied either to the excitation voltage of at least two coils, the first flaw detection signal and the other of the coil as a detection coil Tokushi, wherein after switching by the switching means applies the excitation voltage to the other coil to obtain a second flaw signal one coil as a detection coil, the first testing signals and the second flaw detection A signal difference signal is obtained.
This method can suppress edge noise and improve the S / N ratio.

  According to the present invention, edge noise can be suppressed and the S / N ratio can be improved.

Hereinafter, the configuration and operation of an eddy current flaw detection system according to an embodiment of the present invention will be described with reference to FIGS.
First, the overall configuration of the eddy current flaw detection system according to the present embodiment will be described with reference to FIG.
FIG. 1 is a block diagram showing the overall configuration of an eddy current flaw detection system according to an embodiment of the present invention.

  The eddy current flaw detection probe 10 is attached to the stage 20. The stage 20 is controlled by the computer 40 via the position control circuit 30 to change the position of the probe 10. The stage 20, the position control circuit 30, and the computer 40 can be replaced with commercially available products. The eddy current flaw detection probe 10 is connected to the switching box 50 with a lead wire. The switching box 50 is an electronic circuit that switches between excitation and detection, and is electrically connected to the eddy current flaw detector 60 and controlled by the computer 40. The eddy current flaw detector 60 and the computer 40 can be replaced with general-purpose ones. Information such as information on position control and data from the eddy current flaw detector 60 can be monitored by the monitor 70.

Next, the configuration of the eddy current flaw detection probe 10 used in the eddy current flaw detection system according to the present embodiment will be described with reference to FIG.
FIG. 2 is a perspective view showing a configuration of an eddy current flaw detection probe used in the eddy current flaw detection system according to the embodiment of the present invention.

  The eddy current flaw detection probe 10 is composed of two coils 10A and 10B. The coils 10A and 10B have the same size and shape. For example, a lead wire having a diameter of 0.05 is wound into a cylindrical shape, and the number of turns is 200. The coils 10A and 10B have an inner diameter Φ1.3, an outer diameter Φ1.7, and a height of 2 mm. The two coils 10A and 10B are arranged such that the central axes of both the coils 10A and 10B are parallel and the distance between the centers of the two coils 10A and 10B is 3 mm. The positions of the coils 10A and 10B are fixed by a cylindrical case. The case is made of Duracon, and a cylindrical hole is machined at a position where the coils 10A and 10B are fixed. The coils 10A and 10B are placed in the holes, and a thin film sheet is attached to the outer surface of the case. The ends of the coils 10A and 10B are directly connected to lead wires and are electrically connected to the eddy current flaw detector 60.

  Here, the operation of the eddy current flaw detection system will be described. In all the controls, the state is monitored by the monitor 70 and the setting is changed by the computer 40. In the position control circuit 30, setting information (movement distance, movement speed, etc.) in the computer 40 is transmitted to the position control circuit 30, and electric power is sent to the stage 20 on the basis of the information. 10 moves to the target position. Setting information (transmission frequency, voltage, etc.) in the computer 40 is also transmitted to the eddy current flaw detector 60. An AC voltage having a set frequency is applied from the eddy current flaw detector 60 to the lead wire on the input side of the exciting coil of the eddy current flaw detection probe 10. The signal voltage from the lead wire on the output side of the detection coil of the eddy current flaw detection probe 10 is sent to the eddy current flaw detector 60. In the eddy current flaw detector 60, the output signal is transmitted to the computer 40 as a digital signal.

Next, the detailed operation of the eddy current flaw detection system according to the present embodiment will be described with reference to FIGS.
FIG. 3 is a flowchart showing the operation of the eddy current flaw detection system according to the embodiment of the present invention. 4 and 5 are operation explanatory diagrams of the eddy current flaw detection system according to the embodiment of the present invention.

  In step S <b> 10 of FIG. 3, the computer 40 outputs a position control signal to the position control circuit 30, whereby the position control circuit 30 moves the position of the stage 20.

  Next, in step S <b> 20, the computer 40 outputs a control command to the eddy current flaw detector 60, and the eddy current flaw detector 60 controls the switching box 50 in accordance with the control command, and the eddy current flaw detector 10. An excitation voltage is applied to one of the coils 10A and 10B, and the coil to which the excitation voltage is applied is operated as an excitation coil.

  Here, the operation of the exciting coil will be described with reference to FIG. As shown in FIG. 4A, the test specimen TS is a thick flat plate. The specimen TS has an edge EG in a part thereof. Further, there is a scratch W near the edge EG. In step S20, for example, when an exciting voltage is applied to the coil 10A and the coil 10A operates as an exciting coil, an eddy current EC is generated inside the specimen TS.

  Next, in step S30, the eddy current flaw detector 60 acquires a signal from the other coil of the coils 10A and 10B operating as the detection coil via the eddy current flaw detector 60, and transmits the data to the computer 40. Hold. Here, FIG. 5A shows the acquired signal. In the drawing, a black circle portion W1 'is a signal obtained from the scratch W, and a hatched portion EG1' is a signal obtained from the edge EG.

  Next, in step S40, the switching box 50 electrically switches excitation and detection of the coils 10A and 10B.

  After switching, in step S50, a voltage is applied so that the other of the coils 10A and 10B operates as an exciting coil. As shown in FIG. 4B, in step S50, when an exciting voltage is applied to the coil 10B and the coil 10B operates as an exciting coil, an eddy current EC is generated inside the specimen TS.

  Next, in step S60, the eddy current flaw detector 60 acquires a signal from the coil 10A, which operates as a detection coil, via the eddy current flaw detector 60, and transmits the data to the computer 40 to hold it. Here, FIG. 5B shows the acquired signal. In the drawing, a black circle portion W2 'is a signal obtained from the scratch W, and a hatched portion EG2' is a signal obtained from the edge EG.

  Next, in step S70, the computer 40 calculates the difference between both signals, and then displays the result on the monitor 70 as a signal at the stage 20 position in step S80. FIG. 5C illustrates a difference signal between the signal in FIG. 5A and the signal in FIG. Since the noise signal EG1 ′ from the edge in FIG. 5A is equal to the noise signal EG2 ′ from the edge in FIG. 5B, the difference between the signal in FIG. 5A and the signal in FIG. By taking this, the influence of edge noise can be removed. On the other hand, the positional relationship between the scratch W and the detection coil 10B shown in FIG. 4A is different from the positional relationship between the scratch W and the detection coil 10A shown in FIG. Since the flaw detection signal W1 ′ in FIG. 5 and the flaw detection signal W2 ′ from the flaw in FIG. 5B are not equal, the difference between the signal in FIG. 5A and FIG. W1 ′ and W2 ′ remain as flaw detection signals.

  As described above, in the present embodiment, the two coils 10A and 10B are arranged so that the central axes of both the coils 10A and 10B are parallel to each other, compared to the case where the two conventional coils are orthogonal to each other. The level of the flaw detection signal, that is, the signal level is increased. On the other hand, since the edge noise can be sufficiently suppressed, the S / N ratio can be increased as compared with the conventional case.

  Next, it returns to step S1, moves the stage 20 position, and repeats said procedure.

  As described above, according to the present embodiment, edge noise can be suppressed and the S / N ratio can be increased.

Next, the configuration and operation of an eddy current flaw detection system according to another embodiment of the present invention will be described with reference to FIGS. 6 and 7. The overall configuration of the eddy current flaw detection system according to this embodiment is the same as that shown in FIG.
FIG. 6 is a perspective view showing a configuration of an eddy current flaw detection probe used in an eddy current flaw detection system according to another embodiment of the present invention.

  In this embodiment, the eddy current flaw detection probe 10 is composed of n coils 10 (1), 10 (2),..., 10 (i),. Here, the coils 10 (1), 10 (2),..., 10 (i),... 10 (n) have parallel central axes, and the distance between the centers of the coils is constant. Placed in.

Next, the detailed operation of the eddy current flaw detection system according to the present embodiment will be described with reference to FIG.
FIG. 7 is a flowchart showing the operation of the eddy current flaw detection system according to another embodiment of the present invention. The same step numbers as those in FIG. 3 indicate the same processing contents.

  In the present embodiment, step S90 is added which is a condition (i = n?) That is repeated by the number of coils 10 (1), 10 (2),..., 10 (i),. Therefore, as shown in steps S20 and S30, the coil 10 (i-1) is an excitation coil, the coil 10 (i) is a detection coil, and as shown in steps S50 and S60, the coil 10 (i) is turned on. The process of using the exciting coil and the coil 10 (i-1) as the detection coil is repeated n times.

As described above, according to this embodiment, edge noise can be suppressed and the S / N ratio can be increased.

Further, in this embodiment, the number of coils used for the eddy current flaw detection probe is not two but n, which is more than two, so that the range in which flaw detection can be performed at a time can be widened. Since the number of movements can be reduced, the flaw detection time can be shortened.

1 is a block diagram showing an overall configuration of an eddy current flaw detection system according to an embodiment of the present invention. It is a perspective view which shows the structure of the eddy current test probe used for the eddy current test system by one Embodiment of this invention. It is a flowchart which shows operation | movement of the eddy current test system by one Embodiment of this invention. It is operation | movement explanatory drawing of the eddy current flaw detection system by one Embodiment of this invention. It is operation | movement explanatory drawing of the eddy current flaw detection system by one Embodiment of this invention. It is a perspective view which shows the structure of the eddy current test probe used for the eddy current test system by other embodiment of this invention. It is a flowchart which shows operation | movement of the eddy current test system by other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Eddy current flaw detection probe 10A, 10B ... Coil 20 ... Stage 30 ... Position control circuit 40 ... Computer 50 ... Switching box 60 ... Eddy current flaw detector 70 ... Monitor

Claims (3)

An eddy current flaw detection probe having a coil for excitation to which voltage is applied to generate an eddy current in the inspection target and a detection coil for detecting a magnetic flux due to the eddy current is scanned on the surface to be inspected. In an eddy current flaw detection system that acquires signals,
The eddy current flaw detection probe is composed of at least two coils having the same shape and arranged so that their central axes are parallel to each other,
Moving means for moving the eddy current flaw detection probe to a target position based on setting information from a computer;
The eddy current probe is moved to the desired position by the moving means, after the application of the excitation voltage to one of the coils of said at least two coils, also switches to apply an excitation voltage to the other coil Switching means;
An excitation voltage is applied to one of the at least two coils, a first flaw detection signal is acquired using the other coil as a detection coil, and after switching by the switching means , an excitation voltage is applied to the other coil. An eddy current flaw detection system comprising: a difference signal means for obtaining a second flaw detection signal using one coil as a detection coil and obtaining a difference signal between the first flaw detection signal and the second flaw detection signal. . The eddy current flaw detection system according to claim 1,
The current flaw detection probe is composed of n (n> 2) coils having the same shape and arranged so that their central axes are parallel to each other.
The switching means repeats that one of two coils out of n coils is an excitation coil, the other is a detection coil, one is a detection coil, and the other is an excitation coil.
The difference signal means obtains the first and second flaw detection signals, and repeats obtaining the difference signal. An eddy current flaw detection probe having a coil for excitation to which voltage is applied to generate an eddy current in the inspection target and a detection coil for detecting a magnetic flux due to the eddy current is scanned on the surface to be inspected. In an eddy current flaw detection method for acquiring a signal,
As the eddy current flaw detection probe, using at least two coils having the same shape and arranged so that their central axes are parallel to each other,
The eddy current flaw detection probe is moved to a target position based on setting information from a computer,
After the application of the excitation voltage to one of the coils of said at least two coils, also switched so as to apply an excitation voltage to the other coil,
An excitation voltage is applied to one of the at least two coils, a first flaw detection signal is acquired using the other coil as a detection coil, and after switching by the switching means , an excitation voltage is applied to the other coil. An eddy current flaw detection method characterized in that a second flaw detection signal is obtained using one coil as a detection coil, and a difference signal between the first flaw detection signal and the second flaw detection signal is obtained.

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