JP4369699B2 - Inspection method for friction stir welds - Google Patents

Description

  The present invention relates to a method for inspecting a friction stir welding part that inspects whether or not a joining defect exists in a joint part joined by a friction stir welding method using an ultrasonic flaw detection apparatus equipped with an ultrasonic probe.

  In recent years, friction stir welding has attracted attention as a technique for joining the contacted end portions. The reason for this is that in seam welding, spot welding, and the like, a bulging portion is formed in which the bulging portion is formed in the joint portion, and for this reason, a finishing process for grinding the bulging portion is required. This is because there is an advantage that no finishing process is required.

  By the way, not only in general joining processes such as seam welding and spot welding, but also in friction stir welding, a joining defect may occur at the joint. That is, a hollow part may arise or an unjoined location may remain on the back side of the workpiece. Therefore, after the joining process is completed, an inspection for confirming whether or not such a joining defect exists is generally performed.

  As one of such inspection methods, as described in Patent Document 1, an ultrasonic flaw detection inspection method is widely adopted. In this inspection method, ultrasonic waves are oscillated from the ultrasonic probe toward the workpiece joint. For example, when there is no bonding defect in the bonded portion, the ultrasonic waves are reflected by the outer surface of the upper end surface and the inner surface of the lower surface of the bonded portion and return to the ultrasonic probe. That is, the ultrasonic probe detects ultrasonic waves reflected from the outer surface of the upper end surface of the joint and ultrasonic waves reflected from the inner surface of the lower end surface. As a result, the monitor constituting the inspection apparatus has a peak (S echo) attributed to the ultrasonic wave reflected on the outer surface of the upper end surface and a peak (B echo) attributed to the ultrasonic wave reflected on the inner surface of the lower end surface. The profile in which appears is displayed.

  On the other hand, when a bonding defect exists in the bonding portion, the ultrasonic wave incident on the inside of the bonding portion is also reflected by the bonding defect. For this reason, in the profile projected on the monitor, a peak (F echo) attributed to the ultrasonic wave reflected by the bonding defect further appears. The peak height, that is, the intensity of the F echo varies depending on the size of the bonding defect. Therefore, the size of the bonding defect can be inferred from the intensity of the F echo.

  In this way, by checking whether or not the F echo appears, it is possible to determine whether or not there is a bonding defect in the bonded portion, and infer the size of the bonding defect if it exists. You can also

JP 2000-180421 A (paragraphs [0035], [0036], FIGS. 3 and 4)

  By the way, when the friction stir welding is performed, the resulting bonding defects are usually extremely fine. For example, in the case of the hollow portion, the average value of the long diameter and the small diameter in the two-dimensional projection view, that is, the average diameter may be smaller than 0.1 mm.

  On the other hand, in the ultrasonic flaw detection inspection method, noise echo also appears in the profile. The intensity of this noise echo is said to be substantially equivalent to the intensity of the F echo that appears when an ultrasonic wave is reflected in a cavity having an average diameter of about 0.1 mm. For this reason, when the average diameter of a cavity part is less than 0.1 mm, the intensity | strength of F echo which appears by this cavity part becomes small compared with a noise echo. Therefore, when the presence or absence of a bonding defect is determined based on the intensity of the F echo as in the inspection method described in Patent Document 1, it is difficult to detect a remarkably small cavity.

  Moreover, when the unjoined part is inclined, a part of the ultrasonic wave incident on the inside of the joined part may be irregularly reflected. When such a situation occurs, the F echo does not appear with sufficient intensity because all of the reflected ultrasonic waves do not return to the ultrasonic probe. Eventually, the intensity of the F echo becomes smaller than that of the noise echo as described above, and it becomes difficult to detect the presence of an unjoined portion.

  Thus, when determining the presence or absence of a bonding defect based on the intensity of the F echo, it is extremely difficult to detect a remarkably fine bonding defect generated when the friction stir welding is performed.

  The present invention has been made to solve the above-described problems, and is a friction stir welded joint that can easily determine whether or not a joint defect exists in a joint formed by the friction stir welding method. The purpose is to provide an inspection method.

In order to achieve the above object, the present invention provides a cavity in a joint portion joined by a friction stir welding method in which a probe is inserted and processed so as to be positioned above a lower end surface of a joining surface of a member to be joined. Whether or not there is an unbonded part, a method for inspecting a friction stir welding part that is inspected by an ultrasonic flaw detection apparatus equipped with an ultrasonic probe,
Immersing the joint in a liquid medium;
While oscillating ultrasonic waves from the ultrasonic probe to the joint, the ultrasonic probe is connected to the joint while detecting the ultrasonic waves reflected from the joint with the ultrasonic probe. Scanning along the joining length direction of the part;
Have
When the ultrasonic wave reflected from the flat inner surface of the lower end surface at the joint is detected, the height of the measurement B echo appears when there is no cavity or unjoined part in the joint. When it is lower than the height of the theoretical B echo, it is determined that a hollow portion or an unjoined portion exists in the joint portion.

  In a joint formed by a welding method other than the friction stir welding method such as welding, the crystal grain size becomes coarse and the back surface is not flat. For this reason, even if an ultrasonic wave is incident on the joint, scattering or the like occurs. That is, since the ultrasonic wave is attenuated even though there is no bonding defect, the intensity of the B echo becomes smaller than the theoretical maximum value. In addition, the intensity of the B echo changes because the crystal grain size is not uniform and the back surface is not flat. For this reason, it is extremely difficult to determine whether or not a bonding defect exists by confirming that the intensity of the B echo is small in the case of other bonding methods.

  On the other hand, in the joint formed by the friction stir welding method, the crystal has a fine grain size and is arranged uniformly. And the back surface of a junction part becomes substantially flat. For this reason, when there is no bonding defect, the ultrasonic wave incident on the bonding portion is reflected by the inner surface of the back surface of the bonding portion with almost no attenuation. In other words, when there is no junction defect, the intensity of the B echo is constant and maximum.

  On the other hand, when a bonding defect exists, a part of the incident ultrasonic component is reflected by the bonding defect. For this reason, the intensity of the B echo is smaller than the intensity of the B echo when there is no bonding defect. Therefore, even if it is difficult to determine the presence / absence of a bonding defect from the F echo because the bonding defect is small and the intensity of the F echo is so small that it is substantially equal to the noise echo, the B echo By confirming that the strength of the material is small, it is possible to easily and easily detect the presence of a bonding defect.

  In this case, after the ultrasonic probe is scanned along the bonding length direction of the bonding portion, the ultrasonic probe is displaced in the bonding width direction of the bonding portion, and the ultrasonic probe is moved in the bonding length direction of the bonding portion. It is preferable to perform the step of scanning again along at least once. This is because it can be reliably determined whether or not there is a bonding defect.

  Furthermore, after the ultrasonic probe is scanned along the bonding length direction of the bonding portion, the ultrasonic probe is displaced in the bonding width direction of the bonding portion, and the ultrasonic probe is bonded to the bonding length of the bonding portion. More preferably, the step of scanning again along the direction is performed at least once within the range from the end of the probe buried region on the reading side to the end of the stirring region on the advanced side in the joining width direction. Accordingly, since it is only necessary to inspect only a region where a junction defect substantially occurs, the inspection range is narrowed, and the time for inspecting the junction defect can be shortened.

  Further, by recording and comparing the intensity of the B echo, it is possible to investigate the length direction and width direction dimensions of the bonding defect.

  As described above, according to the present invention, the intensity of the peak (measurement B echo) attributed to the ultrasonic wave reflected by the inner surface of the lower end surface of the joint is measured, and the theoretical B echo in the case where no joint defect exists. Compare with strength. For this reason, for example, the effect that an extremely small cavity having an average diameter of less than 0.1 mm and an unjoined portion with an inclined boundary surface can be detected easily and simply.

  Preferred embodiments of the method for inspecting a friction stir welding portion according to the present invention will be described below and described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a friction stir welding tool 14 for friction stir welding the end faces of two workpieces 10 and 12 is a cylindrical rotating body 16 fixed to a spindle of a friction stir welding apparatus (not shown). And a probe 18 provided at the tip of the rotating body 16. First, the friction stir welding is performed on the end surfaces of the workpieces 10 and 12 with the friction stir welding tool 14.

  Specifically, after the end surfaces of the workpieces 10 and 12 are brought into contact with each other, the probe 18 is brought into contact with one end of the contact portion. In this state, when the rotating body 16 and the probe 18 are rotated along with the rotation of the spindle, frictional heat is generated as the probe 18 comes into sliding contact with the vicinity of the end faces of the workpieces 10 and 12. The vicinity of the end surface is softened. Due to this softening, the tip of the probe 18 is buried.

  Then, the buried probe 18 is displaced along the contact portion. At this time, the softened meat plastically flows as it is stirred by the probe 18, and then the meat hardens as the probe 18 moves away from the stirring location. The phenomenon is sequentially repeated following the displacement of the friction stir welding tool 14 along the contact portion, whereby the end faces of the workpieces 10 and 12 are integrally solid-phase bonded, and as a result, A joint 20 is formed.

  In the following description, an end surface in which the probe 18 is buried and subjected to friction stir welding is referred to as an upper end surface 22, and an end surface opposite to the upper end surface 22 is referred to as a lower end surface 24.

  Next, the configuration of an inspection apparatus for inspecting whether or not there is a bonding defect in the bonding portion 20 formed as described above will be schematically described with reference to FIG. The inspection device 30 is a water immersion type ultrasonic flaw detection inspection device, and includes a control unit 32 and an ultrasonic probe 34. Among these, the control unit 32 includes a pulse signal transmission unit 36, a pulse signal reception unit 38, an echo analysis unit 40, and a displacement control unit 42.

  The pulse signal transmission unit 36 generates, for example, a 15 MHz pulse signal and transmits the pulse signal to the ultrasonic probe 34. The pulse signal receiving unit 38 receives, for example, a 15 MHz pulse signal from the ultrasonic probe 34, amplifies the pulse signal as necessary, and transmits the pulse signal to the echo analysis unit 40.

  The echo analyzer 40 analyzes the pulse signal received by the pulse signal receiver 38, converts the pulse signal into a peak, and causes it to appear as a profile on a monitor (not shown).

  The displacement control unit 42 is a mechanism for displacing the ultrasonic probe 34 and controlling the direction and the amount of displacement. That is, the displacement control unit 42 directs the ultrasonic probe 34 in the joining length direction (arrow X direction), the joining width direction (arrow Y direction), and the vertical direction (arrow Z direction) for a predetermined distance. It plays a role of displacement.

  The ultrasonic probe 34 can be immersed in water, and an ultrasonic transducer for oscillation (not shown) that oscillates ultrasonic waves, and detection ultrasonic waves that detect ultrasonic waves reflected from the joint 20. And a vibrator (not shown). The oscillating ultrasonic transducer generates an ultrasonic wave by vibrating the piezoelectric element by the 15 MHz pulse signal transmitted from the pulse signal transmission unit 36. The detection ultrasonic transducer converts the ultrasonic wave received by the piezoelectric element into a pulse signal and transmits the pulse signal to the pulse signal receiving unit 38.

  Next, a method for inspecting the friction stir welding portion according to the present embodiment performed using the inspection device 30 will be described. In this inspection method, as shown in the flowchart in FIG. 3, a state in which the first step S <b> 1 in which the joint portion 20 is immersed in water and the ultrasonic probe 34 that oscillates an ultrasonic wave face the joint portion 20. And a second step S2 for displacing along the length direction of the joint portion 20. The processing procedure shown in this flowchart is sequenced, and is stored in a storage unit such as a memory (not shown) constituting the control unit 32 and executed by a control unit such as a CPU (central processing element) (not shown). .

  In the first step S1, the workpieces 10 and 12 that have been friction stir welded as described above are transported to the top of a water tank (not shown) under the action of a transport mechanism (not shown), and are then immersed in water by being lowered. The At this time, the upper end surface 22 subjected to the friction stir welding process is directed upward.

  After that, the ultrasonic probe 34 (see FIG. 2) is connected to the scanning start point P0 facing the one end of the joint 20 shown in FIG. Arranged and lowered so as to be separated by a predetermined distance.

  Then, a pulse signal of 15 MHz is supplied from the pulse signal transmission unit 36 to the ultrasonic probe 34, and an ultrasonic wave Q1 is generated when the piezoelectric element of the oscillating ultrasonic transducer is vibrated by the pulse signal. . The ultrasonic wave Q1 travels from the ultrasonic probe 34 toward the joint 20.

  In this state, in the second step S2, the ultrasonic probe 34 is displaced in the joining length direction of the friction stir welding, that is, the arrow X direction in FIGS. 2 and 4 under the control action of the displacement control unit 42. .

  Here, as shown in FIG. 5, when there is no bonding defect in the bonding portion 20, the ultrasonic wave Q <b> 1 is reflected on the outer surface of the upper end surface 22 or the inner surface of the lower end surface 24 in the bonding portion 20. The reflected ultrasonic waves Q2 and Q3 generated by this reflection enter the piezoelectric element of the ultrasonic transducer for detection that constitutes the ultrasonic probe 34. The piezoelectric element converts the incident reflected ultrasonic waves Q2 and Q3 into pulse signals, and then transmits the pulse signals to the pulse signal receiving unit 38. The pulse signal is further transmitted from the pulse signal receiver 38 to the echo analyzer 40.

  As a result, in the profile displayed on the monitor constituting the echo analysis unit 40, as shown in FIG. 6, a peak (S echo) attributed to the reflected ultrasonic wave Q2 reflected on the outer surface of the upper end surface 22, A peak (B echo) attributed to the reflected ultrasonic wave Q3 reflected by the inner surface of the lower end surface 24 appears. Hereinafter, the B echo when there is no junction defect is referred to as a theoretical B echo, and its intensity is T1. In FIG. 6, all peaks other than S echo and B echo are noise echoes.

  In the friction stir welding, the probability of occurrence of joint defects is extremely small. For this reason, most of the profiles shown in FIG. 6 are obtained.

  On the other hand, as shown in FIG. 7, when the cavity 50 having an average diameter of less than 0.1 mm exists as a bonding defect, the ultrasonic wave Q <b> 1 that has entered the joint 20 is also reflected by the cavity 50. As a result, a reflected ultrasonic wave Q4 is generated, and a profile in which a peak (F echo) belonging to the reflected ultrasonic wave Q4 appears is obtained as shown in FIG. Since the average diameter of the cavity 50 is as small as less than 0.1 mm, the F echo intensity T3 is also small, which is approximately the same as the maximum noise echo intensity T0.

  Therefore, in the present embodiment, attention is focused on the intensity of the B echo. That is, as can be understood from FIG. 7, in a portion where the cavity 50 is present, a part of the component of the incident ultrasound Q1 is reflected by the cavity 50 to generate the reflected ultrasound Q4. Reflected ultrasonic waves Q3 are generated by the remaining components being reflected from the inner surface of the lower end surface. For this reason, as shown in FIG. 8, the intensity T2 of the measured B echo measured at this time is smaller than the intensity T1 of the theoretical B echo by the intensity T3 of the F echo.

  Thus, when the cavity 50 exists, the intensity of the measurement B echo becomes smaller than the theoretical B echo as the F echo appears. In other words, by confirming that the intensity of the measured B echo is smaller than that of the theoretical B echo, even the very small cavity 50 can be reliably detected.

  Thus, according to the present embodiment, it is determined whether or not a junction defect exists based on whether or not the intensity of the measurement B echo is smaller than that of the theoretical B echo. Accordingly, since the cavity 50 is extremely fine, the presence of the F echo can be detected even when the intensity of the F echo is approximately equal to or smaller than that of the noise echo.

  The above-described scanning is performed until the arrival point P1 shown in FIG. 4 is reached along the joining length direction (arrow X direction in FIGS. 2 and 4) in the joining portion 20. Thereafter, the ultrasonic probe 34 is displaced by the width D2 within the bonding width D1 along the bonding width direction (arrow Y direction) under the control action of the displacement control unit 42. The above scanning from the arrival point P2 to the arrival point P3 along the arrow X direction is performed again. The above scanning is repeated until the ultrasonic probe 34 reaches the final point Pn.

  That is, in the present embodiment, the scanning of the ultrasonic probe 34 is repeatedly performed along the length direction of the joint portion 20. Of course, the comparison of the intensities of the measured B echo and the theoretical B echo is investigated in all the scans, and it is determined that a junction defect exists when the intensity T2 of the measured B echo becomes smaller than the intensity T1 of the theoretical B echo. Is done. Thereby, it can be determined reliably whether the cavity part 50 exists.

  In addition, by recording and comparing the intensity of the measurement B echo, the length direction and width direction dimensions of the cavity 50 can be investigated.

  In the above-described embodiment, the case where the cavity 50 is detected has been described as an example. However, the bonding defect may be an unbonded portion 60 illustrated in FIG. In this case, a part of the component of the ultrasonic wave Q1 incident on the joint 20 may be diffusely reflected, and the reflected ultrasonic wave Q4 may not be directed toward the ultrasonic probe 34. As a result, the reflected ultrasonic wave Q3 is reduced, so that the intensity T2 of the measurement B echo is smaller than the intensity T1 of the theoretical B echo as shown in FIG. Thereby, it can be detected that the unjoined portion 60 exists.

  That is, even in this case, it can be determined that a junction defect exists by confirming that the intensity T2 of the measured B echo is smaller than the intensity T1 of the theoretical B echo.

  Furthermore, the workpieces 10 and 12 may be immersed in another liquid other than water, such as glycerin. In any case, it is not particularly necessary to immerse the entire workpieces 10 and 12, and only the joint portion 20 may be immersed.

  By the way, as shown in FIG. 1, the direction which the vector component V1 of the rotation direction (arrow W direction) points in the location most spaced from the boundary line L1 of the end surfaces of the workpieces 10 and 12 of the rotary body 16 on the workpiece 12 side. Is opposite to the displacement direction of the rotator 16 (arrow X1 direction). The side in which the direction in which the vector component V1 is directed in this way is opposite to the displacement direction of the rotating body 16 is referred to as a retrieving side. In this case, the retreading side is the workpiece 12 side.

  On the other hand, in FIG. 1, the direction in which the vector component V2 in the rotation direction (arrow W direction) at the position farthest from the boundary line L1 of the rotary body 16 on the workpiece 10 side is directed is the displacement direction (arrow) of the rotary body 16. X1 direction). The side in which the direction in which the vector component V2 is directed in this way is the same as the displacement direction of the rotating body 16 is referred to as an advance side. In this case, the advancing side is the work 10 side.

  Here, as shown in FIG. 11, when the center line of the probe 18 is buried so as to overlap the boundary line L1, the agitation region R1 on the advanced side is smaller than the agitation region R2 on the retreading side. For this reason, there is a concern that an unstirred portion is generated at the lower end of the boundary line L1. In this case, this unstirred portion becomes the unjoined portion 60.

  The reason why the agitation region R1 on the advancing side is smaller than the agitation region R2 on the retreading side is presumed to be that plastic flow occurs densely on the retreading side and plastic flow is sparse on the advancing side. Is done. Therefore, the cavity 50 as shown in FIG. 7 is easily formed in the stirring region R1 on the advanced side.

  As can be understood from the above, the bonding defect (cavity 50 or unbonded portion 60) in the bonding portion 20 is buried in the probe 18 on the reading side in the bonding width direction (arrow Y direction) as shown in FIG. It can be said that it substantially occurs within the range Y1 from the end of the region to the end of the agitating region R1 on the advancing side.

  Therefore, the scanning with the ultrasonic probe 34 already described with reference to FIG. 4 may be performed within the range Y1 in the joining width direction (arrow Y direction) as shown in FIG. . As a result, the inspection range is narrowed, and it is possible to substantially detect a bonding defect (cavity 50 or unbonded portion 60) in the bonding portion 20 in a short time.

It is principal part perspective explanatory drawing which shows the state which is friction stir welding the end surfaces of two workpieces with the tool for friction stir welding. It is a schematic block diagram of the test | inspection apparatus for performing the test | inspection method which concerns on this Embodiment. It is a flowchart of the inspection method of the friction stir welding part which concerns on this Embodiment. It is plane explanatory drawing which shows the scanning pattern of an ultrasonic probe. It is explanatory drawing of the detection principle explaining the advancing condition of the ultrasonic wave and reflected ultrasonic wave in case a joining defect does not exist in a junction part. It is the profile formed from the echo which appears by the ultrasonic wave and reflected ultrasonic wave which are shown in FIG. It is explanatory drawing of the detection principle explaining the advancing condition of the ultrasonic wave and reflected ultrasonic wave in case a cavity part exists in a junction part. It is the profile formed from the echo which appears by the ultrasonic wave and reflected ultrasonic wave which are shown in FIG. It is explanatory drawing of the detection principle explaining the advancing condition of an ultrasonic wave and a reflected ultrasonic wave in case an unjoined location exists in a junction part. It is the profile formed from the echo which appears by the ultrasonic wave and reflected ultrasonic wave which are shown in FIG. It is the principal part expanded sectional view seen from the displacement direction of the probe which shows the state where the centerline of the probe was buried in the contact part in the state which overlapped with the boundary line formed when the end surfaces of a workpiece | work contact | abut.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 12 ... Work 14 ... Friction stir welding tool 18 ... Probe 20 ... Joining part 30 ... Inspection apparatus 32 ... Control part 34 ... Ultrasonic probe 36 ... Pulse signal transmission part 38 ... Pulse signal receiving part 40 ... Echo analysis Part 42 ... Displacement control part 50 ... Cavity part 60 ... Unjoined part Q1 ... Ultrasound Q2-Q4 ... Reflected ultrasonic wave R1, R2 ... Stirring area

Claims (3)

Whether there is a hollow portion or an unjoined portion in the joint portion joined by the friction stir welding method in which the probe is inserted and processed so as to be positioned above the lower end surface of the joint surface of the member to be joined, A method of inspecting a friction stir joint that is inspected by an ultrasonic flaw detection apparatus equipped with an ultrasonic probe,
Immersing the joint in a liquid medium;
While oscillating ultrasonic waves from the ultrasonic probe to the joint, the ultrasonic probe is connected to the joint while detecting the ultrasonic waves reflected from the joint with the ultrasonic probe. Scanning along the joining length direction of the part;
Have
When the ultrasonic wave reflected from the flat inner surface of the lower end surface at the joint is detected, the height of the measurement B echo appears when there is no cavity or unjoined part in the joint. When the height of the theoretical B echo is lower than the height, it is determined that a hollow portion or an unjoined portion exists in the joint portion. The inspection method according to claim 1,
After the ultrasonic probe is scanned along the bonding length direction of the bonding portion, the ultrasonic probe is displaced in the bonding width direction of the bonding portion, and the ultrasonic probe is moved in the bonding length direction of the bonding portion. A method of inspecting a friction stir welded portion, wherein the step of performing scanning again along at least once is performed. The inspection method according to claim 2,
After the ultrasonic probe is scanned along the bonding length direction of the bonding portion, the ultrasonic probe is displaced in the bonding width direction of the bonding portion, and the ultrasonic probe is moved in the bonding length direction of the bonding portion. And the step of performing scanning again along the width direction of the joining is performed at least once within a range from the end of the buried region of the probe on the side of the leading side to the end of the stirrer of the advancing side. Part inspection method.

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