JP2011203055A - Method of measuring welded connection width, apparatus of measuring potential difference, and system of measuring welded connection width - Google Patents

Abstract

PROBLEM TO BE SOLVED: To nondestructively, accurately and readily measure a connection width of a lap joint welded portion, in a method of measuring a welded connection width.SOLUTION: In overlapping portions of an upper material and a lower material, a pair of current terminals 18 and 20 are brought into contact with both side positions across a welded portion 28 on one of surfaces of a lap joint test piece 26 welded and connected from an upper material side; and additionally, potential difference terminals 22 and 24 connected with a potentiometer 16 are brought into contact with two points on both sides across the welded portion 28, on a line coupled between contacts of the respective current terminals 18 and 20. A current is made to flow through the pair of current terminals 18 and 20, under the conditions such as to obtain potential difference between the two points on both sides, and a computer acquires the welded connection width W from the acquired potential difference and outputs the welded connection width W.

Description

  The present invention relates to a welded joint width measuring method, a potential difference measuring device, and a welded joint width measuring system for measuring a welded joint width of a lap joint welded portion obtained by welding and joining two metal plate overlapped portions.

  Conventionally, for example, in a state where two thin metal plates having a thickness of several millimeters are superposed, welding is performed by welding such as laser welding to produce a lap joint portion. In addition, various tests for evaluating the quality of the welded portion are performed at such a lap joint portion. For example, it is also performed to evaluate whether or not a desired joint strength can be secured by evaluating the joint strength of a welded portion.

  For example, using one sample of a lap joint part, it is made to fracture so that two metal plates may be separated, and the joint strength is evaluated. However, in this case, there is a problem that work is time-consuming and that 100% inspection cannot be performed.

  On the other hand, it has been found that the bonding width is greatly related to the strength of the welded joint. In other words, the strength of the welded joint is of course related to the presence or absence of defects in the welded part, but it is also closely related to the joint width, which is the width of the welded part. It is an important management item for evaluating

  For example, there may be a case where through welding is performed in which two metal plates are welded so as to penetrate from one side to the other side. In such a case, a welded joint portion is formed from either side of the two metal plates. And the width of the welded joint can be measured from either side. For this reason, there is a possibility that the strength of the weld joint can be predicted to some extent using the measured value of the joint width of the weld that appears on the surface.

On the other hand, an upper material and a lower material (the upper material is a plate material on the side where the welding means is provided during welding, and the lower material is a plate material on the anti-welding means side) which are two metal plates by laser welding or the like. In addition, when producing a lap joint part by welding together, the upper material and the lower material should be non-coated in order not to impair the construction restrictions and the appearance from the back side of the lap joint part, which is the lower material side. It may be joined by through welding. Non-penetrating welding is to provide a welded portion in the upper material and the lower material so as not to penetrate from the upper material to the lower material.
Note that Patent Documents 1 to 3 are prior art documents related to the present invention.

JP 2006-126085 A JP-A-7-83645 JP 2006-126068 A

  As described above, when two plate members are joined by non-penetrating welding, the joining width of the welded portion cannot be measured from both sides. Thus, it may not be easy to accurately measure the joint width of the joint portion, and in that case, it is not easy to evaluate the strength of the joint portion. Therefore, at present, particularly when a lap joint material is formed by non-penetrating welding, the lap joint material extracted as a sample is cut, that is, ruptured so as to separate two plate materials, and the fracture surface is specified. In many cases, the bonding width is measured by corroding with a solution and observing the fracture surface, and the bonding strength is evaluated using the measured bonding width. However, the method of breaking the lap joint material in this way is a kind of destructive test, and it takes a lot of time to measure the joint width, and there is a problem that 100% inspection cannot be performed. For this reason, realization of a method for measuring the joint width of a welded portion that is non-destructive and highly accurate is desired.

  On the other hand, Patent Document 1 describes a method of inspecting a weld using eddy current. In this method, in order to inspect the welded portion of the lap joint where the front material and the back material are joined by laser welding, the eddy current flaw detection sensor is moved along the surface of the back material or the front material, and the unjoined part and the joined part are detected. Changes in signal height at and are detected. Also, the relationship between the joint width and the change in signal height, the relationship between the change in signal height and the tensile strength, and the change in signal height are measured, so that the joint width and the tensile strength are predetermined. It can be estimated that this is the case. In the case of such an inspection method, there is a possibility that the joint width can be evaluated nondestructively, but since the eddy current method is applied, it is necessary to consider the change in lift-off, which is the distance between the measurement target and the bottom surface that is the sensor detection unit. Otherwise, there is a problem that the measurement result fluctuates greatly due to a slight lift-off change (for example, several μm). For example, when measuring the joint part of a lap joint from the weld surface side, since there exists a weld bead, lift-off changes with the unevenness | corrugation, and a measurement precision may deteriorate.

  Patent Document 2 discloses a method in which two metal plates are welded, and the joint width of the joint portion in the integrated test object is measured using ultrasonic waves. A method is described in which scanning is performed over a joint, a reflected echo is detected, a threshold is determined based on the detected reflected echo level pattern, and a joint width is measured based on the reflected echo level pattern and the threshold.

  Further, Patent Document 3 describes an inspection method for estimating the joint width of a welded portion of a lap joint and a strength of a lap joint, which are obtained by joining a front material and a back material by laser welding, using ultrasonic waves. In this case, there is a correlation between the amount of decrease in the bottom echo height of the backing material or the front material, and the joining width by laser welding and the tensile strength of the lap joint. It is said that the width or tensile strength can be estimated.

  In both cases of Patent Document 2 and Patent Document 3, the bonding width of the bonding portion is measured using ultrasonic waves. However, water, grease, or the like is interposed between the ultrasonic probe and the measurement target. A contact medium is required. For this reason, when this measurement method is used in an actual site, various restrictions may occur and measurement may be difficult. In addition, this measurement method requires measurement on a smooth surface, but the measurement accuracy may be greatly reduced when measurement is possible only from the weld surface where the weld bead exists. In addition, when the measurement target is a thin plate joint, the path of the ultrasonic beam is shortened, so that the signal to be detected is buried in the dead zone of the probe, and the measurement accuracy may be greatly reduced.

  The purpose of the welding joint width measuring method and the welding joint width measuring system of the present invention is to make it possible to measure the joint width at the lap joint welded portion with high accuracy and easily without breaking. In addition, the potential difference measuring device of the present invention is to realize a device for acquiring a potential difference for easily measuring a joint width at a lap joint welded portion with high accuracy and without destruction.

  A welding joint width measuring method according to the present invention is a measuring method for measuring a welding joint width of a lap joint welded portion obtained by welding and joining two metal plate overlapped portions, and is a one-side welded portion of a lap joint welded portion. A pair of current supply terminals are brought into contact with both sides of the electrode, and a potential difference measuring terminal connected to the potentiometer is contacted at two points on both sides of the welded portion on the straight line connecting the contact portions of the respective current supply terminals. In this state, a current is passed between the pair of current supply terminals to acquire (measure) a potential difference between two points on both sides, and a computer includes a step of acquiring a welding joint width from the acquired potential difference. This is a welding joint width measuring method characterized by the following.

  In the weld joint width measuring method according to the present invention, preferably, the step of acquiring the weld joint width is a calibration curve stored in the storage means by the computer and represents a relationship between the potential difference and the weld joint width. The welding joint width is acquired from the acquired potential difference while referring to the calibration curve data.

  The potential difference measuring device according to the present invention is a potential difference measuring device used in the welding joint width measuring method according to the present invention, and is connected to a DC power source capable of applying a DC current to the outside, a potentiometer, and a DC power source. And a pair of potential difference measurement terminals connected to a potentiometer.

  The welding joint width measuring system according to the present invention includes the potential difference measuring device according to the present invention and a computer, and the computer includes a potential difference acquiring unit that acquires a potential difference from the potential difference measuring device, and the potential difference and the welding joint width. A storage means for storing calibration curve data representing the relationship, and a joint width acquisition means for acquiring the weld joint width while referring to the calibration curve data read from the storage means based on the acquired potential difference. This is a welding joint width measuring system characterized by the following.

  According to the welding joint width measuring method and the welding joint width measuring system according to the present invention, the joint width at the lap joint welded portion can be measured with high accuracy and easily without destruction. In addition, according to the potential difference measuring apparatus according to the present invention, it is possible to realize an apparatus that acquires a potential difference for easily measuring a joint width at a lap joint welded portion with high accuracy and without destruction.

It is the schematic which shows a mode that the junction width of a welding part is measured using the welding junction width measuring system of embodiment of this invention. It is a figure which shows a mode that the terminal for electric current supply and the terminal for potential difference measurement which comprise the system of FIG. 1 were made to contact one example of a lap joint test piece. It is the figure which looked at the structure of FIG. 2 from the upper direction to the downward direction. It is a figure which shows the structure of the computer which comprises the system of FIG. It is a schematic diagram which shows the current density which flows through the lap joint test piece when the joining width of a welding part is large. It is a schematic diagram which shows the current density which flows through the lap joint test piece when the joining width of a welding part is small. It is a figure which shows the fracture surface of 1 board | plate material at the time of making the lap joint test piece of FIG. 3 fracture | rupture so that two board | plate materials may be isolate | separated. It is a figure which shows an example of the calibration curve showing the relationship between the junction width of a welding part and the potential difference obtained with the potentiometer used by this Embodiment. It is a flowchart which shows the welded joint width measuring method of embodiment of this invention.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. 1 to 8 show an example of an embodiment of the present invention.

  As shown in FIG. 1, the weld joint width measurement system used in the weld joint width measurement method of the present embodiment includes a computer 10 that is a personal computer and a potential difference measuring device 12. The potentiometer 12 includes a DC power source 14 that can apply a constant DC current to the outside, a potentiometer 16 such as a digital multimeter, and a current terminal 18 that is a pair of current supply terminals connected to the DC power source 14. , 20 and a pair of potential difference measuring terminals 22, 24 which are a pair of potential difference measuring terminals connected to the potentiometer 16. Such a potential difference measuring device 12 measures a potential difference between two points sandwiching the welded portion 28 in a state in which a relatively low constant direct current is passed through the lap joint test piece 26 having a welded joint. Used to output the measured potential difference.

  When measuring a potential difference using the potential difference measuring device 12, as shown in FIGS. 2 and 3, a lap joint test piece 26 is prepared, and a potential difference between two predetermined points of the test piece 26 is measured. . The lap joint test piece 26 is composed of two thin plates, which are an upper member 30 and a lower member 32, which are metal plates, and a weld portion 28 is provided by non-penetrating welding from the upper member 30 side by laser welding or the like. The lap joint test piece 26 which is a lap joint welded portion is formed by welding the 30 and the lower member 32 together. The “upper material” is a plate material on the side where the welding means is provided at the time of welding, and the “lower material” means a plate material on the anti-welding means side, and does not mean that the actual arrangement is limited.

  As shown in FIG. 3, two points Pi on both sides of the welded portion 28 of the welded surface 34, which is a surface of the upper member 30 where the welded portion 28 is located on the pair of current terminals 18, 20, The tips of the pair of current terminals 18 and 20 are brought into contact with Po. At the same time, the potentiometer 16 (see FIG. 3) is connected to two points Q1 and Q2 on both sides of the welded portion 28 on a straight line (dotted line L in FIG. 3) connecting the contact portions Pi and Po to the welding surface 34 of the current terminals 18 and 20. The tips of the potential difference terminals 22 and 24 connected to 1) are brought into contact with each other. In this case, each of the potential difference terminals 22 and 24 is in contact with the so-called directly above contact portions Pi and Po of the current terminals 18 and 20 of the welding surface 34. Further, the potential difference terminals 22 and 24 are arranged so that the welded portion 28 is located at the center between the terminals 22 and 24. Further, the current terminals 18 and 20 are configured so that when current flows, main current passes through the welded portion 28 in a direction (left and right direction in FIG. 3) orthogonal to the length direction (up and down direction in FIG. 3). To place.

  In this state, a constant and relatively low DC current is caused to flow from the contact portion Pi to the contact portion Po between the pair of current terminals 18 and 20, and a potential difference between the two points Q1 and Q2 is acquired, that is, measured. The measured potential difference is output to the computer 10 (FIG. 1). For this reason, as shown in FIG. 1, the potentiometer 16 and the computer 10 are connected by a cable 36. The computer 10 and the potential difference measuring device 12 can be connected wirelessly, and a signal representing the potential difference can be output to the computer 10 wirelessly, that is, transmitted. In the example shown in FIG. 1, the pair of current terminals 18, 20 and the pair of potential difference terminals 22, 24 are integrated with the sensor unit 38, and the terminals 18, 20, 22, 24 provided on the sensor unit 38 are connected. The measurement object can be touched at once. 1 and 2 and FIGS. 5A and 5B to be described later, the current terminals 18 and 20 and the potential difference terminals 22 and 24 are represented by arrows, and the current terminals 18 and 20 indicate the direction of current flow in the direction of the arrows. Represents.

  As shown in FIG. 4, the computer 10 includes a potential difference acquisition unit 40, a storage unit 42, a junction width acquisition unit 44, an output unit 46, and an operation unit (not shown). The computer 10 includes a CPU, a memory, and the like, and has a function of recording and evaluating data such as a potential difference and a junction width. Further, the potential difference acquisition unit 40 acquires the potential difference measured from the potential difference measuring device 12 by wire or wirelessly. The storage means 42 includes a hard disk drive device or the like as a memory or an external storage device, and stores in advance calibration curve data representing the relationship between the potential difference and the weld joint width. Such a calibration curve is used to obtain the weld joint width from the potential difference. That is, the potential difference obtained when the potential difference between two points of the test piece 26 (FIG. 1 and the like) is measured as described above corresponds to the joining width W of the welded portion 28 (FIG. 1) on a one-to-one basis.

  The reason for this will be described with reference to FIGS. 5A and 5B. FIG. 5A is a schematic diagram showing a current density flowing through the test piece 26 when the joining width W of the welded portion 28 is large. FIG. 5B is a schematic diagram showing a current density flowing through the test piece 26 when the joining width W of the welded portion 28 is small. 5A and 5B each show a cross section cut at a portion including the welded portion 28, and the current density is represented by a plurality of striped lines. In addition, the joining width W means the joining width W by welding in the joining part of the upper material 30 and the lower material 32. For example, as illustrated in FIG. 5A, when a current is passed from the point Pi to the point Po when the joining width W is large, the current flows only in the thickness of one upper material 30 in the unwelded portion. However, in the joint portion including the welded portion 28, the current flows by the thickness of the upper material 30 and the lower material 32. In this case, the current flows out and flows also in part of the lower member 32 at the joint. For this reason, the current density around the contact portions Q1 and Q2 between the potential difference terminals 22 and 24 and the test piece 26 decreases, and the potential difference of the welded portion 28 becomes smaller than that of the unwelded portion.

  Further, as shown in FIG. 5B, even when the joining width W is small, as in the case shown in FIG. The current density around the contact portions Q1 and Q2 between the potential difference terminals 22 and 24 and the test piece 26 decreases, and the potential difference of the welded portion 28 becomes smaller than that of the unwelded portion. However, in the case shown in FIG. 5B, since the joining width W is smaller than that in the case of FIG. 5A, the protrusion of the current to the lower member 32 at the joining portion is reduced. Therefore, the decrease in current density around the contact portions Q1, Q2 between the potential difference terminals 22, 24 and the test piece 26 is smaller than that in the case of FIG. 5A, and the decrease in potential difference with respect to the unwelded portion in the welded portion 28. Is smaller than in the case of FIG. 5A. From this, the inventor considered that there is a one-to-one correspondence between the joint width W of the welded portion 28 and the potential difference. That is, since the low current density region (the range indicated by α in FIGS. 5A and 5B) formed on the surface of the welded portion 28 corresponds to the bonding width W, the potential difference reflecting the current density is measured, so that the bonding It was thought that the width W could be estimated, that is, measured. That is, it was considered that the junction width W can be accurately measured from the measured potential difference using a calibration curve representing the relationship between the junction width W and the potential difference.

  Next, a method for obtaining this calibration curve will be described. In the following description, the same or equivalent elements as those shown in FIGS. 1 to 4 are denoted by the same reference numerals. First, in a state where two upper members 30 and lower members 32 constituting each of a plurality of test pieces 26 are overlapped, welding is joined by laser welding, and the output at the time of laser irradiation is changed by each test piece 26. Thus, a plurality of test pieces 26 having different joining widths W of the welded portions 28 were produced. Then, in the same manner as described above, with each test piece 26, the potential difference between the two points corresponding to each other is measured in the state where current is passed using the potential difference measuring device 12, and the potential difference at each test piece 26 is obtained. It was. Thereafter, each test piece 26 is broken so that the two upper members 30 and the lower member 32 are separated. FIG. 6 is a view showing a fracture surface that is the back surface of the upper member 30 that is one plate member when the test piece 26 of FIG. 3 is broken so as to separate two plate members.

  As shown in FIG. 6, both end edges in the width direction (left and right direction in FIG. 6) of the joint mark 48 appearing on the fracture surface may actually be slightly wavy and not be a complete straight line. Also, assuming that the test piece 26 is configured, the current flowing between the two points A and B sandwiching the welded portion 28 is not only in the direction of the straight arrow α, but also according to the change in the joining width W1 due to the swell. There is also the possibility of flowing slightly off the direction. For this reason, the average joint width as a whole is obtained as the joint width used for the calibration curve. That is, as shown in FIG. 6, the joint area of the welded portion 28 is obtained from the joint trace 48 that appears on the fracture surface of the upper member 30 by measurement or the like. In this case, for example, the bonding area can be obtained from an image obtained by photographing the fractured surface using an appropriate area measuring device. And the average joining width W was calculated | required by remove | dividing the obtained joining area by the width direction length La of the upper material 30 which is joining length. Of course, a person measures the bonding width W1 at a plurality of equally spaced positions separated in the width direction (vertical direction in FIG. 6) of the upper member 30, and obtains an average bonding width W from the plurality of bonding widths W1, Other means such as calculating the bonding area can also be used.

  FIG. 7 shows an example of a calibration curve representing the relationship between the average junction width W thus obtained and the potential difference obtained by the experiment with the potentiometer 16. In the case of FIG. 7, calibration curves are obtained from the four test pieces 26. Thus, the junction width W and the potential difference have a one-to-one relationship, and it can be confirmed that the junction width W can be measured from the potential difference obtained by using the calibration curve. This calibration curve can also be used to convert the potential difference into the junction width W.

  In the computer 10 shown in FIG. 4, the calibration curve obtained in this way is stored in the storage means 42 in advance. 4 obtains the weld joint width W while referring to the calibration curve data read from the storage means 42 based on the potential difference obtained from the potential difference measuring device 12. The output means 46 outputs the weld joint width W acquired by the joint width acquisition means 44 to an output unit such as a display.

  Such a potential difference measuring device 12 and a welded joint width measuring system include, for example, a welded joint width of a test piece 26 that is a lap joint welded part in which two upper members 30 and a lower member 32 are welded together by non-through welding by laser welding. Used in a measurement method for measuring W. FIG. 8 is a flowchart showing this measurement method. That is, when carrying out the method of measuring the weld joint width W, first, in step S10 (hereinafter, step is simply referred to as S), the sensor unit 38 is installed as shown in FIG. 1, that is, the sensor unit. The step of arranging the 38 terminals 18, 20, 22, 24 on the test piece 26 is performed. In this case, as described with reference to FIGS. 2 and 3 above, the pair of current terminals 18 and 20 are brought into contact with both side positions sandwiching the welded portion 28 of the welding surface 34 of the test piece 26, and each current terminal 18. , 20 are brought into contact with two potential points 22 and 24 connected to the potentiometer 16 at two points on both sides of the welded portion 28 on a straight line connecting the contact portions.

  Next, in this state, a step of applying a constant DC current between the pair of current terminals 18 and 20 using the DC power source 14 is performed (S12), and the potential difference between the two points on both sides is obtained by the potentiometer 16. That is, the step of measuring and outputting to the computer 10 and storing the data representing the potential difference in the storage means 42 is performed (S14). Next, in the computer 10, the welding joint width W is obtained from the obtained potential difference, that is, measured and stored in the storage means 42, and the welding joint width W is displayed on an output unit such as a display and output. (S16). In this step, the welding joint width W is calculated from the acquired potential difference while referring to the calibration curve data that the computer 10 stores in advance in the storage means 42 and represents the relationship between the potential difference and the welding joint width W. To get. In this case, for example, data representing a calibration curve is stored in the storage means 42 as a map, and the weld joint width W is acquired while referring to the map. The acquired weld joint width W is output to the output unit.

  According to the joint width measuring method using such a weld joint width measuring system, the joint width W of the test piece 26 that is a lap joint welded part can be measured with high accuracy and easily without destruction. That is, by preparing calibration curve data corresponding to the difference in thickness and material of each of the two upper members 30 and the lower member 32 in the test piece 26, the current 2 can be passed while non-destructively. The junction width W can be accurately measured simply by measuring the potential difference between the points. That is, as apparent from the above description, the degree of decrease in the current density changes according to the weld joint width W. Therefore, by measuring the change in current density as a potential difference, the joint width W can be easily and accurately measured. be able to. In addition, unlike the conventional structure in which the joint width of the welded portion is measured using the eddy current (Patent Document 1), the measurement accuracy of the joint width W can be increased regardless of the unevenness of the surface of the welded portion 28. In addition, unlike the conventional structure in which the welding joint width is measured using the above ultrasonic waves (Patent Documents 2 and 3), the measurement accuracy can be increased without requiring a special contact medium. In addition, since the resistivity does not change greatly when the material of the metal plate changes, it is possible to measure the bonding width W regardless of the material difference by preparing calibration curve data according to the plate thickness. .

  Further, in S16 of FIG. 8 described above, the quality of the joint width W is evaluated by comparing the reference joint width preset by the computer 10 with the measured joint width W, and together with the joint width W, or The evaluation can be output to the output unit in place of the bonding width W.

  Further, the bonding width W is closely related to the bonding strength of the test piece 26. For this reason, a calibration curve representing the relationship between the bonding width W and the bonding strength is stored in the computer 10 in advance, and the bonding strength is output from the measured bonding width W while referring to the data of the calibration curve. By comparing the strength with a preset reference value, it is possible to evaluate the quality of the bonding strength and output the evaluation.

  Further, according to the potential difference measuring device 12, it is possible to realize a device for acquiring a potential difference for easily and accurately measuring the joining width W of the test piece 26 which is a lap joint welded portion without breaking.

  In the present embodiment, the potential difference is measured by bringing the current terminals 18 and 20 and the potential difference terminals 22 and 24 into contact with the weld surface 34 side of the test piece 26, but the present invention is not limited to this. . For example, the potential difference between two points on both sides of the welded portion 28 is measured by bringing the current terminals 18 and 20 and the potential difference terminals 22 and 24 into contact with the non-welded surface side of the test piece 26, that is, the lower surface side of FIGS. You can also Also in this case, the measured potential difference changes in accordance with the change in the weld joint width W, so that the weld joint width W can be measured using the measured value of the potential difference.

  10 Computer, 12 Potentiometer, 14 DC power supply, 16 Potentiometer, 18, 20 Current terminal, 22, 24 Potentiometer terminal, 26 Lap joint test piece, 28 Welded part, 30 Upper material, 32 Lower material, 34 Weld surface, 36 cables, 38 sensor units, 40 potential difference acquisition means, 42 storage means, 44 bonding width acquisition means, 46 output means, 48 bonding traces.

Claims (4)

It is a measuring method for measuring the weld joint width of a lap joint welded portion obtained by welding and joining the overlapping portions of two metal plates,
A pair of current supply terminals are brought into contact with both side positions sandwiching the welded portion on one side of the lap joint welded portion, and a potentiometer is attached to two points on both sides of the welded portion on the straight line connecting the contact portions of the current supply terminals. A current is passed between a pair of current supply terminals in a state where the connected potential difference measurement terminals are in contact with each other, and a potential difference between two points on both sides is acquired;
A computer comprising a step of obtaining a weld joint width from the obtained potential difference. In the welding joint width measuring method according to claim 1,
The step of acquiring the weld joint width is a calibration curve stored in the storage means by the computer, and referring to the calibration curve data representing the relationship between the potential difference and the weld joint width, the weld joint width from the acquired potential difference. A method for measuring a welded joint width, characterized in that: A potential difference measuring device used in the welding joint width measuring method according to claim 1,
A DC power supply capable of applying a DC current to the outside, a potentiometer, a pair of current supply terminals connected to the DC power supply, and a pair of potential difference measurement terminals connected to the potentiometer Potential difference measuring device. The potential difference measuring device according to claim 3,
With a computer,
Computer
A potential difference acquiring means for acquiring a potential difference from the potential difference measuring device;
Storage means for storing calibration curve data representing the relationship between the potential difference and the weld joint width;
A welding joint width measuring system comprising: a joining width obtaining unit that obtains a welding joint width while referring to the calibration curve data read from the storage unit based on the obtained potential difference.

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