JPH06265529A - Method and apparatus for evaluating spot-welded part - Google Patents

Abstract

PURPOSE:To evaluate a nugget of a spot-welded part highly accurately by means of an ultrasonic probe. CONSTITUTION:A spot-welded part is scanned by ultrasonic beams. At this time, a focal point of the ultrasonic beams is adjusted to be in the middle of a surface at the side of an upper plate 2 of a lower plate 3 and the bottom face of the lower plate 3. namely, inside the lower plate 3. A reflecting wave B1 at the bonded face of the upper and lower plates 2 and 3 is extracted, and the intensity distribution of the reflecting wave is obtained. A reflecting wave B2 at the bottom face of the lower plate 3 is extracted from the curve of the intensity distribution, and intensity distribution of the reflecting wave B2 is obtained. Two points (A), (B) where the increasing rate of the intensity distribution of the reflecting wave B2 at both sides becomes zero are detected. An area enclosed by the curve of the intensity distribution of the reflecting wave B1 and that of the reflecting wave B2 is calculated. A nuggety part or the bonding state is correctly and simply evaluated on the basis of the distance between the two points or the area.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding portion evaluation method and apparatus, and more particularly to a spot welding portion evaluation method and apparatus suitable for easily and highly accurately evaluating the nugget portion of the spot welding portion. .

[0002]

2. Description of the Related Art Spot welding is a type of resistance welding,
Two plates, an upper plate and a lower plate, are stacked, sandwiched by electrodes, and an electric current is applied while applying pressure, and a part of both plates is melted and joined by heat generation at a contact portion. The joint portion is a nugget portion at the central portion where both plates are fusion-bonded from the joint form,
It consists of the area where both plates are solid-phase bonded under the influence of heat on the outside, that is, the corona bond portion. The outside of the corona bond portion is a non-bonding portion. The size of the nugget correlates with the joint strength of the spot weld, so that
The quality of the spot welded portion is evaluated by the size (diameter) of the nugget portion.

As a conventional method for nondestructively inspecting the nugget diameter using ultrasonic waves, there is, for example, the one described in Japanese Patent Laid-Open No. 3-233352. In this conventional method, ultrasonic waves are transmitted and received while the ultrasonic probe is brought into contact with the spot welding portion to perform scanning. Then, due to the difference in the metal structure between the nugget portion and the corona bond portion, the attenuation of the ultrasonic wave passing through the nugget portion is greater than the attenuation degree of the ultrasonic wave passing through the corona bond portion, and at a preset time. With the height of the bottom plate bottom reflected wave as a reference value, compare the height of the measured bottom plate bottom reflected wave with this, and determine the location where the height of the measured reflected wave is smaller than the reference value as the nugget part, The part where the height of the measured reflected wave is larger than the reference value is determined as the corona bond part.

The Welding Society Papers (Vol. 10, 4
No. 1992, "Quality evaluation of spot welds by ultrasonic waves") focuses the ultrasonic focused beam in water at a position deeper than the bottom surface of the lower plate, and applies this ultrasonic focused beam to the spot weld. The spot welds are evaluated by scanning the image dimensionally and observing the image.

[0005]

However, in the former conventional method described above, since the ultrasonic probe scans while making contact with the spot welding surface having irregularities, the received signal strength becomes unstable, and spot welding is performed. Stable evaluation of parts is not possible. Further, since the ultrasonic waves that have entered the spot welded portion spread, the detection intensity of the reflected ultrasonic waves also becomes small, and there is a problem that highly accurate evaluation cannot be performed. In addition, the latter conventional method has a problem in that the range including only the nugget portion cannot be evaluated because the joint portion is evaluated in the range including the corona bond portion in the nugget portion.

It is an object of the present invention to provide a spot welding portion evaluation method and apparatus capable of accurately grasping the boundary between a corona bond portion and a nugget portion and evaluating the nugget portion easily and with high accuracy.

[0007]

Means for Solving the Problems The above-mentioned object is to provide a means for focusing the ultrasonic focused beam between the upper plate surface and the lower plate bottom surface of the spot welding portion, and the ultrasonic focused beam diameter of the spot welding portion. Means for scanning across the direction, means for transmitting and receiving ultrasonic waves to and from the spot weld along with the scanning, and obtaining the intensity of the bottom surface reflected wave of the spot weld lower plate at each transmit / receive position, and the transmit / receive position And a means for detecting a scanning distance between two points on both sides of the intensity distribution that increases toward the inner side of the spot welded portion and the rate of increase of the reflected wave intensity becomes zero first, and between the two points. And a means for evaluating the spot welds from the scanning distance of.

The above object is also to provide means for focusing the ultrasonic focused beam between the upper plate surface and the lower plate bottom surface of the spot weld, and the ultrasonic focused beam across the spot weld in the radial direction. Means for scanning, means for transmitting and receiving ultrasonic waves to and from the spot-welded portion along with the scanning to obtain the intensity of the bottom surface reflected wave of the spot-welded portion lower plate for each transmission / reception position, and reflected-wave intensity for the transmission / reception position A means for detecting the scanning distance between two points at the intensity positions where the intensity is a predetermined ratio of the maximum intensity on both sides of the distribution;
And a means for evaluating the spot weld from the scan distance between the points.

The above-mentioned object is further to provide means for arranging an ultrasonic wave transmitter and an ultrasonic wave receiver so as to sandwich an upper plate and a lower plate of a spot weld portion, and at least the ultrasonic wave transmitter or the ultrasonic wave receiver. A means for focusing one of the ultrasonic focused beams between the upper plate surface and the lower plate bottom surface of the spot weld portion, and means for obtaining an ultrasonic intensity distribution transmitted through the spot weld portion at each transmission / reception position. By providing
To be achieved.

The above object is also to provide means for focusing the ultrasonic focused beam between the upper plate surface and the lower plate bottom surface of the spot weld portion, and for the ultrasonic focused beam to traverse the spot weld portion in the radial direction. A means for scanning, a means for transmitting and receiving ultrasonic waves to and from the spot-welded portion in association with the scanning, a means for obtaining a reflected wave intensity from the spot-welded joint surface for each transmitting / receiving position, and a reflected wave intensity for the transmitting / receiving position. On both sides of the distribution, means for detecting the scanning distance between two points of the intensity position where the intensity becomes a predetermined ratio of the maximum intensity, and the spot welded portion from the value obtained by adding a predetermined constant to the scanning distance between the two points This is achieved by providing means for evaluation.

The above object can be achieved by a configuration in which a spot weld is evaluated from an average value of the result of the above evaluation obtained from reflected ultrasonic waves and the result value of the above evaluation obtained from transmitted ultrasonic waves. To be done.

The above object is also to provide means for focusing the ultrasonic focused beam between the upper plate surface and the lower plate bottom surface of the spot welding portion, and the ultrasonic focused beam across the spot welding portion in the radial direction. And means for scanning, transmitting and receiving ultrasonic waves to and from the spot-welded portion along with the scanning, reflected wave intensity from the joining surface of the upper plate and the lower plate of the spot-welded portion at each transmitting / receiving position, and spot welding The means for obtaining the intensity of the reflected wave from the bottom surface of the lower plate and the transmitting and receiving positions between the two points of the two intensity distribution curves, at which the curves first intersect with each other toward the inner side of the spot weld. Provide a means to obtain the integrated value of the value obtained by subtracting the reflected wave intensity from the joint surface of the upper plate and the lower plate from the reflected wave intensity on the bottom plate bottom of each, and a means to evaluate the spot welded part from this integrated value. Achieved That.

The above object is further provided as means for forming and scanning an ultrasonic focused beam on a spot weld.
This is achieved by using an array type ultrasonic probe.

The above-mentioned object is to operate the above-mentioned spot welding portion evaluation device immediately after the spot welding process of the spot welding line, and when the spot welding portion is judged to be defective, the spot welding machine is so arranged that the same spot is spot-welded again. If the instruction is given and the instruction is repeated N times and it is determined to be defective, it is achieved by reviewing the welding conditions or excluding the products to be spot welded.

[0015]

In the present invention, in order to focus the ultrasonic focused beam between the upper plate surface and the lower plate bottom surface of the spot weld,
It is possible to increase the intensity of the bottom surface reflected wave of the spot welded lower plate. Generally, at the focus of the ultrasonic focused beam,
The best azimuth resolution and the highest reception intensity are obtained, and both are lowered as the distance from the focus is increased or decreased. Therefore, the focus is normally on the observation target surface, but in some cases, the bonding surface, which is the observation surface, and the lower plate bottom surface, which is the reflection surface, may be at different positions. In that case, as in the present invention, by focusing on the middle of the observation target surface and the ultrasonic reflection surface,
The spot beam to be observed can be received without increasing the ultrasonic beam diameter at the joining surface of the upper plate and the lower plate of the spot weld part and without lowering the intensity of the bottom reflected wave of the spot plate of the spot weld part. It is possible to obtain information for each minute range of the boundary between the corona bond portion and the nugget portion in a good S / N state.

According to the present invention, the spot welding is performed on both sides of the reflected wave intensity distribution from the scanning distance between the two points, which increases toward the inner side of the spot welded portion and the rate of increase of the reflected wave intensity is initially zero. Evaluate the department. With a thin ultrasonic focused beam, information for each minute range of the corona bond and nugget boundary of the spot weld is obtained as a continuous intensity distribution, so by detecting the intensity increase rate of the reflected wave intensity distribution, It is possible to accurately evaluate the position where the ultrasonic transmission intensity is not affected by the minute gap in the corona bond portion, that is, the boundary between the corona bond portion and the nugget portion.

Further, in the present invention, the spot welded portion is evaluated on the both sides of the reflected wave intensity distribution from the scanning distance between two points of the intensity position where the intensity becomes a predetermined ratio of the maximum intensity, and therefore the spot welded portion is evaluated at the joint surface. If there is a slight gap around the area where the plate and the lower plate are welded together and the strength contributes, a slightly larger area can be evaluated as the nugget portion.

Further, by adopting the two-probe method in which the ultrasonic transmitter and the ultrasonic receiver are arranged so as to sandwich the upper plate and the lower plate of the spot weld portion, the ultrasonic probe and the ultrasonic receiver are received by the single probe method. The influence of the reflected wave from the upper plate surface can be eliminated, and the optimum evaluation of the spot welded part of the thin plate becomes possible.

Further, in the present invention, the spot welded portion is evaluated from the scanning distance between two points at the intensity positions where the intensity is a predetermined ratio of the maximum intensity on both sides of the reflected wave intensity distribution. It is possible to eliminate the intensity fluctuation of the bottom plate bottom reflection echo due to the unevenness of the bottom plate bottom surface, and it becomes possible to stably evaluate the spot welded portion.

Further, according to the present invention, firstly, means for obtaining the intensity of the reflected wave of the bottom surface of the lower plate of the spot welding portion at each transmitting / receiving position, and secondly, the reflection from the joint surface of the spot welding portion at each transmitting / receiving position. Means for obtaining the wave intensity, and means for calculating the average value of the scanning distances obtained by the first and second means. Therefore, the same portion of the spot weld is evaluated with double information by the first transmitted wave of the spot weld joint surface and the second reflected wave of the spot weld joint surface. The property is improved.

In the present invention, the intensity of the reflected wave from the joining surface of the upper plate and the lower plate of the spot welded portion and the intensity of the reflected wave from the bottom surface of the lower plate of the spot welded portion are obtained for each transmission / reception position, and these two intensity distributions are obtained. On both sides of the curve, between the two points where both curves first intersect toward the inner side of the spot weld, from the reflected wave intensity of the bottom plate bottom at each transmission / reception position, from the joint surface of the top plate and bottom plate Calculate the integrated value of the value obtained by subtracting the reflected wave intensity of, and evaluate the spot welds from this integrated value, so of course not only know the boundary between the nugget part and the corona bond part, but also the presence or absence of defects in the nugget part and the overall It is possible to double check the proper joining condition.

In the present invention, when the array type ultrasonic probe is used as a means for forming and scanning the ultrasonic focused beam with respect to the spot welded portion, the focus position can be freely set and the ultrasonic focused beam can be electronically focused. The high-speed scanning can be performed, and the spot-welded portion can be inspected efficiently in a short time.

Further, in the present invention, the above-mentioned evaluation of the spot-welded portion is executed immediately after the spot-welding process on the spot-welding line. If the spot-welded portion is judged to be defective, the spot-welded portion is spot-welded again. To the spot welder, repeat this feedback N times to the same spot welding point, and if it is determined that there is a defect, review the welding conditions or
In some cases, eliminate the product. That is, since the spot welding conditions are managed immediately after the spot welding, an abnormality in the spot welding can be immediately detected, and defects can be minimized.

[0024]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining an ultrasonic beam scanning method in a spot welded portion evaluation method according to an embodiment of the present invention, in which an ultrasonic focused beam 1 is passed through a center O of the diameter of the spot welded portion. It is sectional drawing of a board | plate material at the time of scanning in the X direction (radial direction). FIG. 2 is a flaw detection waveform obtained at each position of the spot weld portion, and FIG. 3 is an intensity distribution of the lower plate bottom surface echo obtained by scanning the ultrasonic focused beam.

In FIG. 1, the ultrasonic focused beam 1 is irradiated from the side of the upper plate 2 of the spot welded portion through the liquid and its focus is controlled so as to be at a position half the plate thickness t of the lower plate 3. ing. The joining surface 4 of the spot welded portion is affected by the heat from the nugget portion A where the upper plate 2 and the lower plate 3 at the center of the joint are welded and the upper plate 2 and the lower plate 3 around the nugget portion A due to the joining form. The corona bond portion B that is in close contact with the other can be distinguished from the other non-bonding portion C. Particularly, at the corona bond portion B, since it is considered that the upper plate 2 and the lower plate 3 are in contact with each other with a gap of several microns or less, ultrasonic waves are transmitted, and the reflected wave intensity from the joint surface 4 of the corona bond portion B is Very weak. However, the transmittance changes depending on the size of the gap. Therefore, in the present embodiment, the change in the transmittance of ultrasonic waves in the gap 4 of the corona bond portion B is detected to detect the boundary between the corona bond portion B and the nugget portion A.

FIG. 2 shows ultrasonic wave reception waveforms obtained at the nugget portion A, the corona bond portion B, and the non-joint portion C of the spot welded portion. At the non-joint portion C where the ultrasonic focused beam is at the position (a), the upper plate 2 and the lower plate 3 are completely separated from each other, so that after the reflected wave S on the surface of the upper plate 2, the bottom surface of the upper plate 2 is The reflected wave B1 at B. comes in, and then the multiple reflected wave B1-2 within the upper plate 2 of the reflected wave B1 is received. In the corona bond portion B and the nugget portion A, after the reflected wave S on the surface of the upper plate 2,
A gap between the upper plate 2 and the lower plate 3 (almost all ultrasonic waves are transmitted).
A weak reflected wave B1 at B comes, and then a reflected wave B2 transmitted to the lower plate 3 and reflected at the bottom surface 5 of the lower plate 3 is received. Therefore, when the upper plate 2 and the lower plate 3 have the same plate thickness, the time from the surface reflected wave S to the reflected wave B2 is the time from the surface reflected wave S to the reflected wave B1. It is about 2 times.

In FIG. 3, in order to extract the intensity change of the reflected wave B2 described in FIG. 2, the gate G is set at the time position where the reflected wave B2 appears, and the intensity P of the reflected wave B2 is set to the ultrasonic focused beam 1 3 is an intensity distribution graphed corresponding to the scanning position in the X direction. The reflected wave B2 is not received until the boundary (d) between the non-bonded portion C and the corona bond portion B, and the output value of the gate G should be low as shown by the dotted line, but in reality, the reflected wave B1 is generated. The second multiple reflection wave B1-2 of the gate G
The output value of the gate G is detected as shown by a solid line. The intensity of the multiple reflected waves B1-2 decreases as the focused ultrasonic beam 1 is scanned in the X direction from just before the boundary (d), and the boundary position (d) between the non-bonding portion C and the corona bond portion B is decreased. Then, the reflected wave B2 is also received, but its intensity shows a minimum value.

Further, when the ultrasonic focused beam 1 is scanned toward the center O of the spot weld portion, the reflected wave B2 is less attenuated in the gap 4 as the gap 4 in the corona bond portion B is narrowed. , Its intensity increases. And the boundary position between the corona bond portion B and the nugget portion A (e)
To the welded state, and eventually the gap 4 of the corona bond part B
Becomes zero, the intensity of the reflected wave B2 becomes maximum and does not increase thereafter. In the nugget portion A, the reflected wave B2 shows a constant intensity or a tendency to slightly decrease. Therefore, the interval (d) between the minimum values on the left and right of the intensity distribution of FIG.
(G) corresponds to the diameter of the corona bond portion B. Also,
In the intensity distribution of the reflected wave B2 in FIG. 3, the distance (e) to (f) between the two points at which the increase rate of the intensity of the reflected wave B2, which increases toward the center O of the spot welded portion on the left and right, becomes zero. Corresponds to the diameter of the nugget portion A.

FIG. 4 is a circuit diagram of an apparatus for measuring the diameter of the nugget portion A described above. DUT 1 in water tank 7
9, the XY scanner 6 is driven by the scanner driving unit 8 to send the ultrasonic focused beam 1 to the feed pitch 0.
Scan at 05 mm. On the other hand, transmission / reception of the ultrasonic focused beam 1 is performed by the ultrasonic transmission / reception unit 9, and the transmission / reception timing is controlled by the control circuit 11 so as to be synchronized with the feed pitch of the XY scanner 6. The intensity of the bottom surface reflected wave B2 of the lower plate 3 at each scanning position is detected by the gate circuit 10, the scanning position and the intensity are stored in the memory circuit 12, and at the same time, displayed on the display unit 15 as an intensity distribution.

When the scanning of the ultrasonic focused beam 1 is completed,
As shown in FIG. 5, the increase rate calculation circuit 13 reads the intensity data X1 to XN stored in the memory circuit 12 from the X1 side and performs an increase rate calculation process (dP / dX).
X1 → XN curve is obtained. At this time, since the negative increase rate is not detected, the position data XS on the X1 → XN curve corresponding to the position S where the increase rate first becomes zero on the intensity distribution curve is known. Next, conversely to the above, the increase rate calculation circuit 13 reads the intensity data X1 to XN stored in the memory circuit 12 from the XN side and performs an increase rate calculation process (dP / dX) to obtain the intensity shown in FIG. XN corresponding to the position E where the rate of increase first becomes zero on the opposite side of the distribution curve →
Know the position data XE on the X1 curve. The scanning distance calculation circuit 14 calculates the scanning distance (XS-XE) between the points XS and XE at which the increase rate becomes zero first in each of the two curves,
Numerical values and images are displayed on the display unit 15. This distance becomes the diameter of the nugget portion A. Of course, if correction is necessary, such as when there are irregularities on the surface of the spot weld,
The value obtained by adding a predetermined constant to the calculated value of the nugget diameter is defined as the nugget diameter.

The above intensity distribution curve of the spot welded portion can also be obtained by a transmission method in which two probes are arranged so as to sandwich the spot welded portion, as shown in FIG. 6, and an evaluation method in that case. Is exactly the same as the above method. However,
Since the ultrasonic waves do not pass through the range C on both sides of the spot welded portion, both sides of the intensity distribution curve have low intensity as shown by the dotted line in FIG.

The spot-welded portion is not limited to the result of evaluation by the intensity of reflected ultrasonic waves described in FIGS.
By performing evaluation based on the average value of the evaluation result based on the intensity of the transmitted ultrasonic wave in FIG. 6, more accurate evaluation can be performed.

FIG. 7 (a) is a cross-sectional photograph of the actual spot-welded portion in the plate thickness direction, and FIG. 7 (b) is a cross-sectional position of the spot-welded portion where scanning is performed while transmitting and receiving an ultrasonic focused beam. It is the intensity distribution of the bonding surface reflected wave (B1) and the lower plate bottom surface reflected wave (B2) obtained. However, the surface of the spot welded portion is processed into a flat surface.

From the cross-sectional photograph of FIG. 7 (a), the nugget diameter, that is, the position where the gap between the joint surfaces of the upper plate and the lower plate disappears is 4.28 mm. In contrast, FIG. 7 (b)
When the nugget diameter is read from the intensity distributions of the joint surface reflected wave (B1) and the lower plate bottom reflected wave (B2), first, the intensity distribution of the lower plate bottom reflected wave (B2) is as shown in the figure. It has a trapezoidal shape in which the intensity of the reflected wave is high at the center of the. On both shoulders of the trapezoidal shape, the distance between the two points (a) and (b) where the increase rate of the reflected wave intensity becomes zero is 4.14 mm, which is slightly smaller than the value read from the cross-sectional photograph. become. In addition, in this intensity distribution,
The reason that the reflected wave intensity increases again outside (e) and (f), that is, on the non-joint side, is that the second multiple reflected wave on the bottom surface of the upper plate is detected by the same gate as described above.

Next, the intensity distribution of the joint surface reflected wave (B1) shows the upper plate 2 and the lower plate 3 toward the center of the spot weld.
Since the gap becomes smaller as the joining degree of No. 2 increases, the reflected wave at the bottom plate of the upper plate 2 becomes smaller, and the pot bottom shape is just opposite to the trapezoidal shape just before. The strength position where a predetermined ratio of the maximum strength of this pan bottom shape is reached, for example, the strength is 0.1
When the distance between the two points (C) and (D) of 5 is read, it becomes 4.64 mm, which is slightly larger than the value read from the cross-sectional photograph. The average of both values is 4.39 mm, which can be evaluated by the difference of about 0.1 mm from the value read from the cross-sectional photograph.

In the above-described embodiment, the scanning of the ultrasonic focused beam 1 was performed only for one line passing through the center of the spot welded portion. However, as shown in FIG.
It is also possible to perform two-dimensional scanning in the Y direction. In this case, of course, a means for obtaining the intensity distribution of the reflected wave B2 as a two-dimensional image with color gradation is provided. As a result, FIG.
As shown in FIG. 5, the entire state of the spot welded portion can be grasped by a color image, and the shape of the nugget portion, the presence / absence of defects F existing in the nugget portion, and the distribution thereof can be seen at a glance. Incidentally, FIG.
It is needless to say that the intensity distribution similar to that described above can be obtained by looking at the intensity on AA ′ across the two-dimensional image.

In a two-dimensional image in which the intensity distribution of the reflected wave B2 is color-graded, the area ratio of intensities above a certain level is calculated, and this area ratio is compared with that of a normal spot weld. The quality of spot welds can be determined. For example, as shown in FIG. 10A, if the area ratio NS of the intensity of 95% or more of the maximum intensity of the reflected wave B2 in the case of normal spot joining is “100”, it is shown in FIG. If there is unevenness in the bonding strength as a whole, the area ratio NS
Is "70", or as shown in FIG. 7C, when there is a defect inside the joint, the area ratio NS is "9".
In this way, the area ratio falls below “100” when there is an abnormality. Therefore, when the area ratio is below the allowable value, it can be determined that the bonding is defective. The spot welds are continuously inspected, and if the shape of the nugget is uneven in a certain direction as shown in FIG. 11, it is possible that the welding conditions such as electrode wear and partial contact are bad. It can also be used to manage welding conditions while watching a two-dimensional image of the part.

FIG. 12A shows an array type ultrasonic probe 1
It is a figure which shows the Example which scans the spot welding part with the ultrasonic focused beam 1 using 6. In the case of this embodiment, electronic scanning is performed in the X direction in which the arrays are arranged, and mechanical scanning is performed in the Y direction orthogonal to the electronic scanning. Since one axis of the two-dimensional scanning is electronically scanned, the scanning time is shortened to 1/30 and the spot welded portion can be inspected in a short time. The focusing of the ultrasonic beam uses both electronic focusing by controlling the transmission / reception timing of ultrasonic waves and focusing by the acoustic lens 18. Also,
By using a two-dimensional array probe, both axes can be electronically scanned, and higher-speed inspection can be realized.

FIG. 12B shows an example of inspection of an object that cannot be inspected by putting it in a water tank. A bag 17 containing a liquid is attached to the front surface of the array type ultrasonic probe 16 and spot welding is performed. It takes acoustic coupling with the surface of the part.

In each of the above-mentioned embodiments, an example in which the bottom surface reflected wave B2 of the lower plate is detected and imaged has been described. However, in the case of focusing on a defect occurring at the boundary between the upper plate and the lower plate, Needless to say, if the reflected wave B1 is visualized, the defect in the spot welded portion can be detected more reliably.

When the strength distribution curve is deformed due to the influence of the unevenness of the surface of the spot welded portion, the strength may be corrected.

FIG. 13 (a) shows the upper plate of the test piece welded with the energization time of the spot welding set to 4 cycles when the ultrasonic focused beam is scanned on the scanning line that crosses the center of the spot welding portion in the radial direction. It is a figure which shows the intensity distribution of the reflected wave B1 from the joint surface of a lower plate, and the reflected wave B2 from the bottom face of a lower plate. 13 (b) to 13 (e) similarly,
It is a strength distribution chart obtained from each test piece of energization time 5, 6, 7, and 8 cycles. As can be seen from these, energization time is long (the number of cycles is large) at spot welds.
It can be seen that the better the bonding state, the lower the intensity of the reflected wave B1 and the greater the intensity of the reflected wave B2. Therefore, the area surrounded by the reflected wave B1 from the joining surface of the upper plate and the lower plate and the reflected wave B2 from the bottom surface of the lower plate increases as the joining state improves. Therefore,
The area S surrounded by both curves is defined by the following equation 1 between two points ab where both curves first intersect when viewed from both ends of each intensity distribution in the figure.
According to the calculation, the result is as shown in FIG.

[0043]

[Equation 1]

Further, the test piece of 4 to 6 cycles shown by X in FIG. 14 was easily peeled off as a result of the peeling test, and the bonding strength could not be obtained at all. 7,8
As a result of the peeling test, the test piece of the cycle was found to have a button-like bonded portion and a certain bonding strength was obtained. As a result,
For example, if the threshold value of the area S is set to "30" to "40", it is possible to distinguish between the area where the bonding strength is not obtained at all and the area where the bonding portion remains in a button shape. You can evaluate the quality.

FIG. 15 is a diagram showing an embodiment in which the above-described evaluation method is applied to a spot welding line, and FIG. 16 is a diagram.
It is a flow chart which shows a processing procedure. When the spot welding target component 24 reaches the position (a) on the belt conveyor 23, the spot welding machine 20 and the ultrasonic inspection machine 21 are incorporated in the welding robot 22 (the welding machine 20 and the inspection machine 21).
May be installed separately), and spot welding is performed at a predetermined location. After that, the target component 24 advances to the position (b), and the ultrasonic welder 21 inspects the spot welded portion. As the detection unit of the ultrasonic inspection machine 21, it is preferable to use a robot 22 having the electronic scanning ultrasonic probe of FIG.

Evaluation results of spot welds are good (YE
If S), the spot welder 20 spot welds the next target component. If defective (NO), the robot 22 moves from the current position (c) to the position (d) (the robot 22 may not move and the upper part may rotate).
Then, spot welding of the defective part is performed again. Then, the ultrasonic inspection machine 21 performs ultrasonic inspection of the spot welded portion. The re-welding and re-inspection are repeated N times, and when it is still determined that the spot welded portion is defective, the series of operations is stopped and the spot welding conditions such as the electrode consumption of the spot welding machine 20 are checked. In some cases, reject defective products.

As described above, by performing the inspection immediately after the spot welding process, it is possible to quickly detect the variation in the spot welding conditions.

[0048]

According to the present invention, the focus of the ultrasonic focused beam is set between the joining surface of the upper plate and the lower plate of the spot weld and the bottom surface of the lower plate. The bottom plate bottom reflected wave can be detected with a good S / N ratio without significantly deteriorating the azimuth resolution and the strength of the bottom plate bottom reflected wave. Also, by scanning the ultrasonic focused beam, it is possible to detect the position where the minute gap in the corona bond part of the spot weld part disappears from the increase rate of the bottom reflected wave intensity of the bottom plate of the spot weld part. Can be evaluated accurately.

Further, since the influence of the surface reflected wave of the spot welded portion can be eliminated by the transmission method, especially the size of the nugget portion of the thin plate can be evaluated.

Further, if the method of not using the bottom surface reflected wave of the lower plate of the spot welded portion is adopted, stable spot welded portion can be evaluated without being affected by the unevenness of the bottom surface of the lower plate.

If the same portion of the spot weld is evaluated with double information by the transmitted wave of the spot weld and the reflected wave of the spot weld joint surface, the reliability of the evaluation is improved. Furthermore, if the quality of the spot welded portion is determined from the area surrounded by both reflected waves, information such as voids and the overall joining state can be obtained, and simple evaluation can be performed.

Further, when the ultrasonic focused beam is scanned at high speed by the electronic scanning method using the array type ultrasonic probe, the spot welded portion can be evaluated in a short time.

Further, by performing the inspection immediately after the spot welding process on the spot welding line, it is possible to detect a variation in the spot welding conditions quickly and to minimize defects in the spot welding.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an ultrasonic focused beam scanning method in a spot welded portion evaluation method according to an embodiment of the present invention.

FIG. 2 is a transmission / reception waveform diagram at each scanning position in FIG.

FIG. 3 is an intensity distribution diagram of reflected ultrasonic waves obtained by scanning an ultrasonic focused beam.

FIG. 4 is a circuit configuration diagram of a spot welding portion evaluation apparatus according to an embodiment of the present invention.

FIG. 5 is an operation explanatory diagram of the increase rate operation circuit of FIG. 4;

FIG. 6 is an explanatory diagram of scanning an ultrasonic focused beam by a transmission method.

FIG. 7 is a correspondence diagram between a reflected wave intensity distribution and a nugget diameter.

FIG. 8 is an explanatory diagram of two-dimensional scanning with an ultrasonic focused beam.

FIG. 9 is a two-dimensional image diagram of intensity distribution.

FIG. 10 is a two-dimensional image diagram of the intensity distribution of various spot welds.

FIG. 11 is a two-dimensional image diagram of the intensity distribution in the case of a single contact of an electrode.

FIG. 12 is a diagram illustrating the use of an array type ultrasonic probe.

FIG. 13 is a strength distribution diagram obtained for test pieces having different energization times.

FIG. 14 is a diagram showing the relationship between energization time and area evaluation value.

FIG. 15 is an explanatory diagram of a spot welding robot.

16 is a flowchart showing a processing procedure of the welding robot of FIG.

[Explanation of symbols]

1 ... Ultrasonic focused beam, 2 ... Upper plate, 3 ... Lower plate, 4 ... Bonding surface, 5 ... Lower plate bottom surface, 6 ... XY scanner, 7 ... Water tank, 8
... Scanner drive section, 9 ... Ultrasonic wave transmitting / receiving circuit, 10 ... Gate circuit, 11 ... Control circuit, 12 ... Memory circuit, 13 ... Increasing rate calculation circuit, 14 ... Scanning distance calculation circuit, 15 ... Display section, 16 ... Array type Ultrasonic probe, 17 ... Rubber bag, 18
... Acoustic lens, 19 ... Inspected object, 20 ... Spot welding machine, 21 ... Ultrasonic inspection machine, 22 ... Device, 23 ... Conveyor, A ... Nugget part, B ... Corona bond part, C ... Non-bonding part, B1 ... Bonding surface reflected wave, B2 ... Lower plate bottom surface reflected wave.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Fuminobu Takahashi 7-2-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Energy Research Laboratory, Ltd.

Claims (15)

[Claims] 1. An ultrasonic beam is transmitted from a surface of an upper plate to a lower plate and a reflected ultrasonic wave is received with respect to a plate material in which an upper plate and a lower plate are spot-welded, and the ultrasonic beam is relative to the plate material. In the evaluation method of the spot welding part to inspect the size in the scanning direction of the spot welding part from the intensity change of the reflected ultrasonic waves obtained while scanning the ultrasonic beam to be transmitted, the ultrasonic beam to be transmitted to the upper plate side surface and the back surface of the lower plate. While focusing, the ultrasonic beam is scanned relative to the plate material, and the intensity of the reflected ultrasonic wave from the joint between the upper and lower plates and the reflected ultrasonic wave from the back surface of the lower plate changes the intensity of the spot weld. A method for evaluating spot welds, characterized in that the size in the scanning direction of is measured. 2. An ultrasonic beam is transmitted from a surface of the upper plate to a lower plate with respect to a plate material in which an upper plate and a lower plate are spot-welded, and reflected ultrasonic waves are received, and the ultrasonic beam is relative to the plate material. In the spot welding portion evaluation device that inspects the size of the spot welding portion in the scanning direction from the intensity change of the reflected ultrasonic waves obtained while scanning, the ultrasonic beam to be transmitted is transmitted between the upper plate side surface and the back surface of the lower plate. A means for focusing between the spot and the spot welding part by changing the intensity of the reflected ultrasonic wave from the upper plate / lower plate joint and the reflected ultrasonic wave from the lower plate back surface by scanning the ultrasonic beam relative to the plate material. And a means for determining the size in the scanning direction of the spot welded portion evaluation apparatus. 3. An ultrasonic beam is transmitted from a surface of the upper plate to a lower plate and a reflected ultrasonic wave is received with respect to a plate material in which an upper plate and a lower plate are spot-welded, and the ultrasonic beam is relative to the plate material. In the evaluation method of the spot welding part to inspect the size in the scanning direction of the spot welding part from the intensity change of the reflected ultrasonic waves obtained while scanning the ultrasonic beam to be transmitted, the ultrasonic beam to be transmitted to the upper plate side surface and the back surface of the lower plate. The ultrasonic beam is relatively scanned with respect to the plate material while focusing between the two, and the scanning enters the spot welding portion and the intensity change rate becomes zero after the intensity of the ultrasonic wave reflected from the lower surface of the lower plate increases. A point and a second point at which the rate of change in the intensity of reflected ultrasonic waves from the back surface of the lower plate starts changing from zero when the scan deviates from the spot welded portion, and the distance between the first point and the second point is calculated. Basically, the large spot welding part in the scanning direction Evaluation method for spot welds characterized by determining the size. 4. An ultrasonic beam is transmitted from a surface of an upper plate to a lower plate and a reflected ultrasonic wave is received with respect to a plate material in which an upper plate and a lower plate are spot-welded, and the ultrasonic beam is relative to the plate material. In the spot welding portion evaluation device that inspects the size of the spot welding portion in the scanning direction from the intensity change of the reflected ultrasonic waves obtained while scanning, the ultrasonic beam to be transmitted is transmitted between the upper plate side surface and the back surface of the lower plate. Means for focusing between, means for obtaining a first point at which the rate of change in the intensity of ultrasonic waves reflected from the back surface of the lower plate becomes zero after scanning of the ultrasonic beam enters the spot welding portion, A means for obtaining a second point at which the rate of change of the intensity of reflected ultrasonic waves from the lower surface of the lower plate starts changing from zero when the scan deviates from the spot-welded portion, and the distance between the first point and the second point is basically used. In the scanning direction of the spot weld Spot weld evaluation apparatus characterized by comprising means for determining is come. 5. An ultrasonic beam is transmitted from a surface of the upper plate to a lower plate and a reflected ultrasonic wave is received with respect to a plate material in which an upper plate and a lower plate are spot-welded, and the ultrasonic beam is relative to the plate material. In the evaluation method of the spot welding part to inspect the size in the scanning direction of the spot welding part from the intensity change of the reflected ultrasonic waves obtained while scanning the ultrasonic beam to be transmitted, the ultrasonic beam to be transmitted to the upper plate side surface and the back surface of the lower plate. While focusing, the ultrasonic beam is scanned relative to the plate material, the ultrasonic wave intensity curve reflected from the joint between the upper and lower plates is obtained by scanning, and is obtained by scanning. A method for evaluating spot welds, characterized in that a reflected ultrasonic wave intensity curve from the back surface of the lower plate is obtained, and the size in the scanning direction of the spot welds is obtained from the area surrounded by both reflected wave intensity curves. 6. An ultrasonic beam is transmitted from a surface of the upper plate to a lower plate and a reflected ultrasonic wave is received with respect to a plate material in which an upper plate and a lower plate are spot-welded, and the ultrasonic beam is relative to the plate material. In the spot welding portion evaluation device that inspects the size of the spot welding portion in the scanning direction from the intensity change of the reflected ultrasonic waves obtained while scanning, the ultrasonic beam to be transmitted is transmitted between the upper plate side surface and the back surface of the lower plate. A means for relatively scanning the ultrasonic beam with respect to the plate material while focusing between them, a means for obtaining a reflected ultrasonic intensity curve from the joint between the upper and lower plates obtained by scanning, and a means for scanning A spot characterized by comprising means for obtaining a reflected ultrasonic wave intensity curve from the back surface of the lower plate obtained in accordance with the above, and means for obtaining the size in the scanning direction of the spot weld from the area surrounded by both reflected wave intensity curves. Welding part evaluation device. 7. An apparatus for inspecting a spot weld by transmitting and receiving an ultrasonic focused beam, and means for focusing the ultrasonic focused beam between an upper plate surface and a lower plate bottom of the spot weld. Means for scanning an ultrasonic focused beam so as to traverse the spot welding portion in the radial direction, and ultrasonic waves are transmitted / received to / from the spot welding portion along with the scanning, and a bottom surface reflected wave of the spot welding portion lower plate at each transmission / reception position Between the two points on the both sides of the reflected wave intensity distribution with respect to the transmission / reception position and increasing toward the inner side of the spot weld, and the rate of increase of the reflected wave intensity is initially zero. Spot weld evaluation, comprising means for obtaining a scan distance and means for evaluating the spot weld from a value obtained by adding a predetermined constant to the scan distance between the two points. apparatus. 8. An apparatus for inspecting a spot weld by transmitting and receiving an ultrasonic focused beam, and means for focusing the ultrasonic focused beam between an upper plate surface and a lower plate bottom of the spot weld. Means for scanning an ultrasonic focused beam so as to traverse the spot welding portion in the radial direction, and ultrasonic waves are transmitted / received to / from the spot welding portion along with the scanning, and a bottom surface reflected wave of the spot welding portion lower plate at each transmission / reception position And a means for detecting the scanning distance between two points at intensity positions on both sides of the reflected wave intensity distribution with respect to the transmission / reception position where the intensity has a predetermined ratio of maximum intensity, and between the two points. And a means for evaluating the spot-welded portion from a value obtained by adding a predetermined constant to the scanning distance of 1. 9. The intensity distribution according to claim 7 or 8, wherein the ultrasonic wave transmitter and the ultrasonic wave receiver are arranged so as to sandwich an upper plate and a lower plate of a spot weld portion, Alternatively, the focus of at least one of the ultrasonic focused beams of the ultrasonic wave receiver is set between the upper plate surface and the lower plate bottom surface of the spot weld, and the ultrasonic intensity transmitted through the spot weld is measured. An apparatus for evaluating spot welds, which is a strength distribution obtained by 10. An apparatus for inspecting a spot weld by transmitting and receiving an ultrasonic focused beam, and means for focusing the ultrasonic focused beam between an upper plate surface and a lower plate bottom of the spot weld. Means for scanning the focused ultrasonic beam so as to traverse the spot weld in the radial direction;
A means for transmitting and receiving ultrasonic waves to and from the spot weld along with the scanning to obtain a reflected wave intensity from the spot weld joint surface for each transmitting and receiving position; and both sides of the reflected wave intensity distribution for the transmitting and receiving position. A means for detecting the scanning distance between two points of the intensity position where the intensity becomes a predetermined ratio of the maximum intensity, and a means for evaluating the spot welded portion from the value obtained by adding a predetermined constant to the scanning distance between the two points are provided. Spot weld evaluation device characterized by the above. 11. The spot weld is evaluated from an average value of the evaluation value obtained by the spot weld evaluation device according to claim 7 and the evaluation value obtained by the spot weld evaluation device according to claim 10. Spot weld evaluation device characterized by the above. 12. An apparatus for inspecting a spot weld by transmitting and receiving an ultrasonic focused beam, and means for focusing the ultrasonic focused beam between an upper plate surface and a lower plate bottom of the spot weld. Means for scanning the focused ultrasonic beam so as to traverse the spot weld in the radial direction;
The ultrasonic wave is transmitted / received to / from the spot welding portion along with the scanning, and the reflected wave intensity from the bottom plate bottom plate of the spot welding part for each transmission / reception position and the reflection wave intensity from the joint surface of the upper plate and the lower plate of the spot weld part are displayed. Means for obtaining and the reflection of the bottom plate bottom surface of each transmission / reception position between two points on both sides of the two intensity distribution curves for the transmission / reception position, where the two curves first intersect toward the inside of the spot weld. A spot-welded portion evaluation device, comprising means for evaluating a spot-welded portion from an integrated value of a value obtained by subtracting a reflected wave intensity from a joint surface between an upper plate and a lower plate from a wave intensity. 13. The array type ultrasonic probe according to claim 7, wherein the array type ultrasonic probe is used as a means for forming and scanning an ultrasonic focused beam on the spot weld portion. Spot weld evaluation device. 14. A spot welder, and the spot welded portion evaluation device according to claim 7.
When the spot-welded portion evaluation device determines that the spot-welded portion is defective, control means for instructing the spot-welding machine to feed back spot-welding again to the same portion and spot-welding instruction for the same portion by the control means are repeated N times. A spot welding robot comprising: means for revising welding conditions when the spot welded portion evaluation apparatus determines that the spot welding portion is defective even after the removal, or means for excluding a target product of the spot welding. 15. An electronic scanning ultrasonic probe is used as a means for forming and scanning an ultrasonic focused beam.
13. The spot welded portion evaluation device according to claim 12, a robot having the electronic scanning ultrasonic probe at its hand, and the electronic scanning ultrasonic probe at the hand liquid-tightly covered. A spot welding inspection robot, comprising: a bag body for contacting an object, the bag body containing an ultrasonic wave propagating liquid medium therein.