JP2008241419A - Method and device for measuring nugget diameter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring nugget diameter capable of simply and precisely measuring the nugget diameter formed on the spot-welded steel material. <P>SOLUTION: The diameter of the nugget formed on the steel material by the spot welding is obtained as follows: by using the searching probe provided with a pair of current electrode needles and a pair of voltage electrode needles, the surface of the steel is scanned along a prescribed line; according to the scanning, from the profile of the voltage variation detected by the pair of voltage electrode needles, two singular points exceeding the detection voltage at the part out of the welding region on the steel material are detected; and from the scanning position where the singular points are detected the diameter of the nugget formed on the steel material by the spot welding is obtained. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a nugget diameter measuring method and a nugget diameter measuring apparatus capable of nondestructively inspecting the diameter of a nugget formed on a steel material by spot welding.

  As means for detecting the depth d of the hardened layer B in the steel material A, for example, as shown in FIG. 6, a pair of current electrode needles 1 a and 1 b that pass a current I between any two points on the surface of the steel material and the current I A non-contact inspection method using a probe having at least a pair of voltage electrode needles 2a, 2b, 3a, 3b for detecting a difference (voltage) V1, V2 in the surface potential generated in the steel material A is known. (For example, refer to Patent Document 1). This non-contact inspection method using the probe probe is called a six-probe method, and is generated in the steel material A according to the information on the distances S, r1, r2 between the electrode needles and the potential differences V1, V2. The depth d of the hardened layer B is calculated according to the relationship between the electric potential distribution and the resistivity ρo, ρ of the steel material (base material) A and the hardened layer B.

Recently, an attempt has been made to measure the diameter of the nugget in the steel material spot-welded by applying the above-described 6-probe method. The nugget refers to a lump portion in which two steel materials are melted and solidified at the spot welded portion when two steel materials are overlapped and joined by spot welding.
JP 2004-39355 A

  By the way, in the conventional nugget diameter measurement, the inspection site using the probe probe described above is scanned across the formation region of the nugget N in the steel material A and detected via the pair of voltage electrode needles 2a and 2b. The change of the voltage V1 is detected over the scanning direction. Then, for example, as shown in FIG. 7, a detected voltage change profile obtained is discriminated by a predetermined threshold TH, and the width W of the profile detected thereby is obtained as the diameter D of the nugget N. However, the width W of the profile obtained as described above generally only represents the diameter D of the nugget N. Moreover, there remains a problem that the measured value (nugget diameter D) varies depending on how much the threshold TH is set.

  The present invention has been made in consideration of such circumstances, and its purpose is to provide a nugget diameter measuring method and nugget diameter that can easily and accurately nondestructively inspect the diameter of a nugget in a spot-welded steel material. It is to provide a measuring device.

In order to achieve the above object, the nugget diameter measuring method according to the present invention is:
<A> A pair of electrode needles that apply a constant current or voltage between any two points on the surface of the steel material that is a measurement object, and at least a pair of voltage electrode needles that detect a surface potential generated in the steel material by the current or voltage. Using the provided probe, scan the surface of the spot-welded steel along a predetermined line,
<B> From the profile of the change in the scanning direction of the voltage detected by the pair of voltage electrode needles with this scanning, the voltage exceeds the detection voltage at the site outside the spot welding region in the steel 2 One singular point is detected, and the diameter of the nugget formed on the steel material by the spot welding is obtained from the scanning position where these singular points are detected.

  Specifically, for example, when the scanning line by the probe is set as a straight line crossing the center of the spot welding region of the steel material, the diameter of the nugget is between two singular points detected in the scanning line. It is obtained as a distance. Alternatively, when the scanning lines by the probe are set as two straight lines crossing each other and crossing the spot welding region of the steel material, the diameter of the nugget is determined by each of the detected singular points in each scanning line. It is characterized in that it is obtained as a diameter of a circle indicating the outer shape of the nugget determined by the detection positions of at least three singular points.

  Incidentally, the probe probe is, for example, a plurality of probe needles arranged on a straight line at a constant pitch, and the scanning of the steel material by the probe probe is performed from the plurality of probe needles. The electrode needles and the probe needles to be used as the pair of voltage electrode needles are respectively selected, and the electrode needles and the probe needles to be selected as the voltage electrode needles are sequentially switched in the arrangement direction.

The nugget diameter measuring apparatus according to the present invention is
<a> a probe having a plurality of probes arranged on a straight line at a constant pitch;
<b> A probe to be used as a pair of electrode needles and a pair of voltage electrode needles is selected from a plurality of probe needles in the probe probe, and a probe to be selected as the electrode needle and the voltage electrode needle is selected. Probe scanning means for sequentially switching the needles in the arrangement direction;
<c> Steel material inspection means for applying a constant current or voltage to the steel material through the pair of electrode needles and detecting a surface voltage generated in the steel material by the current or voltage through the pair of voltage electrode needles. ,
<d> The portion where the voltage deviates from the spot welding region of the steel material from the profile of the change in the scanning direction of the voltage detected by the steel material inspection means as the probe scanning means scans the probe An analysis means for detecting two singular points exceeding the detection voltage at
<e> Nugget diameter calculating means for obtaining the diameter of the nugget formed on the steel material by spot welding from the detected position in the scanning direction of the singular point obtained by the analyzing means.

  In particular, the probe probe is characterized in that a probe array in which a plurality of probe needles are linearly arranged at a constant pitch and provided so as to cross each other is used.

  In the nugget diameter measuring method according to the present invention, as described above, the surface of the spot-welded steel material is scanned along a predetermined line by using a probe having a pair of electrode needles and a pair of voltage electrode needles. As a result, a profile (potential distribution) of change in the scanning direction of the voltage detected by the pair of voltage electrode needles along with the scanning is obtained. Then, when the profile of the change in the detection voltage in the scanning direction was analyzed, it was noted that there exist two singular points that change in excess of the detection voltage at a part outside the spot welding region in the steel material. Yes.

  The voltage at these singular points is mainly due to the fact that the potential gradient in the nugget formation region is relatively steep, whereas the potential gradient in the region where the nugget is not formed is relatively slow. Thus, the potential gradient between the parts sandwiching the nugget edge is steep, and this is based on the result of consideration that it is caused by this steep potential gradient. Therefore, in the present invention, the above-described singular point in the profile is detected, for example, the width (distance) between two singular points is detected as the diameter of the nugget, thereby simplifying the diameter of the nugget formed on the steel material by spot welding. Therefore, it is possible to measure with high accuracy and reproducibility.

  The nugget diameter measuring apparatus according to the present invention uses a probe probe in which a plurality of probe needles are arranged in a straight line at a constant pitch, and a pair of electrode needles and Probe scanning means for scanning the probe probe by selecting the probe needles to be used as a pair of voltage electrode needles and sequentially switching the electrode needles and the probe needles to be selected as the voltage electrode needles in the arrangement direction; A steel material that applies a constant current or voltage to the steel material through the pair of current electrode needles in conjunction with the scanning and detects a surface potential generated in the steel material by the current or voltage through the pair of voltage electrode needles. Since the inspection means is provided, it is possible to easily scan the steel material that is the measurement object.

  Moreover, the point where the voltage exceeds the detection voltage at the part out of the spot welding region of the steel material is detected as a singular point from the profile of the change in the scanning direction of the voltage obtained by the scanning described above (analysis means), Since the diameter of the nugget formed on the steel material by spot welding is obtained from the detection position in the scanning direction of the two singular points obtained by the analyzing means (nugget diameter calculating means), the nugget diameter can be determined with a simple configuration. It can be detected with high accuracy and reproducibility.

  In other words, the diameter of the nugget formed on the steel material by spot welding can be easily and accurately measured with high reproducibility, simply by electrical scanning of the probe and simple analysis of the detected voltage change profile. It is possible to achieve a great effect in practical use.

Hereinafter, a nugget diameter measuring method and a nugget diameter measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings.
The nugget diameter measuring method according to the present invention measures, for example, the diameter of nugget N generated by superposing two steel materials A and spot welding the overlapped portion from the surface of the steel material by nondestructive inspection. For example, the nugget diameter measuring apparatus configured as shown in FIG. 1 is used.

  This nugget diameter measuring apparatus generally includes a probe probe 12 in which a plurality of (for example, 10 to 20) probe needles 11 are linearly arranged at a constant pitch, for example, 1 mm, to form an array structure, and the probe. An electronic switch 13 for selecting the probe 11 to be used as the pair of current electrode needles Ia and Ib and the pair of voltage electrode needles Va and Vb from among the plurality of probe needles 11 in the probe 12, and the operation of the electronic switch 13 And a scanning control unit (probe scanning means) 14 for sequentially switching the probe needles 11 selected as the current electrode needles Ia and Ib and the voltage electrode needles Va and Vb in the arrangement direction.

  The pair of current electrode needles Ia and Ib are for generating a potential distribution corresponding to the internal resistance of the steel material by causing the current I to flow through the steel material, for example, and the pair of voltage electrode needles Va , Vb is for detecting the surface potential generated in the steel material by the current I. Instead of passing a constant current I through the pair of current electrode needles Ia and Ib, a constant voltage E is applied between the pair of current electrode needles Ia and Ib to cause the internal resistance to the steel material. A potential distribution according to the above may be generated.

  Incidentally, the selection of the current electrode needles Ia, Ib and the voltage electrode needles Va, Vb is performed by changing the arrangement order of the plurality (n) of probe needles 11 to # 1, # 2, # 3, # 4, # 5. To #n, for example, the probe needles # 1 and # 4 are used as current electrode needles Ia and Ib, and the probe needles # 2 and # 3 are used as voltage electrode needles Va and Vb. The four probe needles 11 are regarded as one set, and the two outside electrodes are selected as current electrode needles Ia and Ib, and the two inside electrodes are selected as voltage electrode needles Va and Vb. The scanning of the probe 12 is performed by changing the set of the probes 11 to be selected as described above from [# 1, # 2, # 3, # 4] to [# 2, # 3, # 4, # 5]. The probe 11 is sequentially shifted one by one by repeating the procedure of changing to [# 3, # 4, # 5, # 6] and then changing to [# 3, # 4, # 5, # 6].

  The two probe needles 11 as the pair of current electrode needles Ia and Ib selected in this way are connected to the DC power supply 15. The pair of voltage electrode needles Va and Vb are connected to the voltage detector 16. That is, the probe probe 12 described above is used for nondestructive inspection of the steel material A by bringing the plurality of probe needles 11 into contact with the surface of the steel material A, which is an object to be inspected. The pair of current electrode needles Ia and Ib applies a constant voltage E from, for example, the DC power supply 15 described above between the contact points with the steel material A, so that a current I corresponding to the internal resistance of the steel material A flows between them. Take a role. As described above, a constant current I may flow from the DC power source 15 to the steel material A through the pair of current electrode needles Ia and Ib. Further, the pair of voltage electrode needles Va and Vb has a potential distribution generated in the steel material A by the constant voltage E or the constant current I applied between the pair of current electrode needles Ia and Ib. The voltage detector 16 plays a role of detecting the voltage V generated between the hands Va and Vb, and the voltage detector 16 detects the voltage. The DC power supply 15 and the voltage detector 16 serve as a steel material inspection unit that uses the probe probe 12 to obtain information that changes according to the internal state of the steel material A.

  The nugget diameter measuring apparatus according to the present invention sequentially records the voltage V detected via the voltage electrode needles Va and Vb in conjunction with the probe scanning described above in addition to the probe probe 11 and its driving means. And a memory 17 for obtaining a profile (voltage change pattern) of the voltage change over the scanning direction. Then, the singular point detection means (analysis means) 18 which is a characteristic processing function of this apparatus analyzes the profile of the change in the scanning direction of the detection voltage obtained in the memory 17, and the voltage V is the steel material A. The two singular points Xa and Xb exceeding the detection voltage Vo at the part out of the spot welding region (nugget formation region) of the above are detected, and the nugget diameter calculation means 19 is the singular point detection means (analysis means) 18 The diameter D of the nugget N formed on the steel material A by spot welding is obtained as the distance L between the detected positions on the surface of the steel material A at the two singular points Xa and Xb obtained by the above.

  That is, when the surface of the spot-welded steel A is scanned across the spot welding region (nugget formation region) using the probe probe 11 described above, the voltage V detected by the probe 11 is the spot welding. The region (nugget formation region) differs from the region outside the spot welding region (nugget formation region), and changes as shown in FIG. 2, for example. Specifically, the detection voltage V becomes a certain voltage Vo in a region deviating from the spot welding region (nugget formation region) at both ends on the scanning line, and the spot welding region at the center on the scanning line. In the (nugget formation region), the voltage of the central portion of the nugget N becomes lower than the voltage Vo. In particular, at the edge portion of the nugget N, the detected voltage is caused by the difference between the potential distribution in the spot welding region (nugget formation region) and the potential distribution in the region outside the spot welding region (nugget formation region). Is slightly higher than the constant voltage Vo.

  As shown in FIG. 2, the singular point detection means (analysis means) 18 detects the position where a voltage slightly higher than the constant voltage Vo detected in the area outside the spot welding area (nugget formation area) is detected. The nugget diameter calculating means 19 detects the singular points Xa and Xb by paying attention to the fact that the two singular points Xa and Xb indicate the edge positions of the nugget N, respectively. The diameter D of the nugget N is obtained as the distance L between the positions.

  More specifically, when two steel plates are overlapped and spot-welded, the two steel plates are melted and solidified in the spot welding region to form a nugget N. Therefore, the thickness of the steel sheet A in the nugget N formation region is a thickness in which the two steel sheets are overlapped and integrated. However, in the region outside the nugget N formation region, the two steel plates simply overlap each other, and it can be considered that these steel plates are physically separated. Therefore, when a constant voltage E is applied to the steel material A from the pair of current electrode needles Ia and Ib, or when a constant current I is passed between the pair of current electrode needles Ia and Ib, the steel material A The electric potential distribution generated in is different depending on which region of the steel A the contact position of the current electrode needles Ia and Ib is. That is, the potential distribution generated in the steel material A differs depending on the positional relationship between the positions of the current electrode needles Ia and Ib and the nugget N formation region, for example, as schematically shown in FIGS.

  Specifically, when the pair of current electrode needles Ia and Ib is positioned in a region outside the nugget N formation region, an electric field is generated only in the steel on the surface side where the current electrode needles Ia and Ib are in contact. Therefore, as shown in FIG. 3A, a potential distribution is generated only in the steel material on the surface side. Moreover, since the formation width of the electric field is narrow and the internal resistance in the electric field generating region is large, the equipotential lines indicating the state of the potential distribution generated in the steel material A are dense at substantially constant intervals, for example, as shown in FIG. Become. Therefore, the potential difference (voltage) detected by the pair of voltage electrode needles Va and Vb provided between the pair of current electrode needles Ia and Ib becomes high. The state of formation of the potential distribution between the pair of current electrode needles Ia and Ib of the steel material A is such that the position of the current electrode needles Ia and Ib is gradually shifted while one of the current electrode needles Ia and Ib is applied to the edge position of the nugget N. Even when it is moved, it hardly changes as shown in FIG. Therefore, even if the pair of current electrode needles Ia and Ib is moved in a region outside the nugget N formation region, the potential difference (voltage) detected by the pair of voltage electrode needles Va and Vb hardly changes, and the surface It is detected as a constant voltage Vo that is somewhat higher depending only on the internal resistance of the side steel.

  On the other hand, when one of the pair of current electrode needles Ia and Ib is positioned in the nugget N formation region across the edge of the nugget N as shown in FIG. The formed electric field extends to the steel material on the back side through the nugget N. In the nugget N formation region, the formation width of the electric field is widened and the internal resistance is also reduced. Therefore, an equipotential line indicating the potential distribution in the nugget N formation region is, for example, as shown in FIG. It becomes rough. However, in the peripheral region outside the nugget N formation region, there is a gap (space) between the steel material on the front side and the steel material on the back side (because there is no nugget N that integrates the front and back steel materials). As described above, the electric field extending to the back surface side does not extend to the steel material on the front surface side.

  The potential distribution formed in the steel material A changes greatly at the edge of the nugget N as shown in FIG. 3C. In the nugget N formation region, the equipotential line interval becomes rough, and the nugget N In the peripheral region outside the formation region of the nugget N, the equipotential line interval in the nugget N formation region is increased, so that the equipotential line interval is shown in FIGS. 3A and 3B, respectively. It becomes narrower than the interval between the potential lines. As a result, the voltage detected by the pair of voltage electrode needles Va and Vb positioned across the edge of the nugget N may become higher than the above-described constant voltage Vo. In particular, when the voltage detection position by the pair of voltage electrode needles Va and Vb is moved across the edge of the nugget N, as described above, the voltage in a region where the interval between equipotential lines is narrowed is detected. Therefore, the detected voltage is slightly higher than the above-described constant voltage Vo.

  Thereafter, when the pair of current electrode needles Ia and Ib is positioned in the nugget N formation region, the potential distribution formed between the current electrode needles Ia and Ib of the steel material A as shown in FIG. These equipotential lines spread widely through the nugget N to the steel material on the back surface side, and the interval between the equipotential lines becomes rough. Only in the vicinity of the current electrode needles Ia and Ib, the interval between the equipotential lines is slightly narrowed due to the influence of the surroundings. As a result, the pair of voltage electrode needles Va and Vb described above detects the potential difference in the potential distribution region where the equipotential lines in the nugget N formation region are widely spaced. It becomes lower than Vo. Thus, the position where the voltage detected by the pair of voltage electrode needles Va and Vb is the lowest is the center of the nugget N where the influence of the edge of the nugget N is minimized.

  As a result, when the probe probe 11 scans across the nugget N formation region and detects the voltage change (surface potential distribution), it corresponds to the nugget N formation region as shown in FIG. Then, the detection voltage becomes lower, and the detection voltage at the edge of the nugget N becomes slightly higher than the voltage Vo detected around the nugget N. The position where the detection voltage is slightly higher than the ambient voltage Vo, that is, the above-described singular point in the change profile (change pattern) of the detection voltage indicates the edge position of the nugget N.

  The nugget diameter measuring method and the nugget diameter measuring apparatus according to the present invention are based on the above-described consideration, and spot welding is performed using the probe probe 11 described above as shown in FIG. It starts by scanning across the formation position of the nugget N of the steel material A [step S1]. Preferably, scanning with the probe 11 is performed so as to pass through the center of the nugget N formation region. The scanning of the probe 11 is performed by sequentially switching the connection of the plurality of probes 11 constituting the probe 11 as described above.

  Thereafter, a voltage change profile (change pattern) is detected in the scanning direction by developing the voltage detected by the scanning of the probe 11 in conjunction with the scanning [Step S2]. As described above, the two singular points Xa and Xb having a voltage slightly higher than the voltage Vo detected at the periphery of the nugget N are detected [step S3]. Then, the diameter D of the nugget N corresponding to the distance L between the singular points Xa and Xb is obtained from the relationship between the distance L between these singular points Xa and Xb and the scanning width of the steel material A by the probe probe 11 [Step] S4].

  If it is difficult to set the scanning position of the steel material A by the probe probe 11 so as to pass through the center of the nugget N formation region, for example, a plurality of probe needles are linearly arranged at a constant pitch. Spot probe regions (nugget formation regions) of the steel material A are used in the above-mentioned two sets of probe arrays as shown in FIG. 5 using probe probes provided by crossing two sets of probe arrays 21 and 22 with each other. It is sufficient to scan across each. Then, the outer shape of the nugget N is determined from the detection positions of at least three singular points among the singular points (edge positions of the nugget N) xa, xb, ya, yb detected by these two sets of probe arrays. The circle shown may be obtained, and the nugget diameter D may be obtained as the diameter of this circle. However, in this case, it goes without saying that the driving and scanning are controlled so that the two probe arrays do not interfere with each other.

  According to the method and apparatus of the present invention for measuring the diameter D of the nugget N as described above, the focus is on the singular point of the voltage change obtained when the nugget region is scanned. Simple and accurate measurement is possible. Moreover, since the voltage change pattern obtained when the nugget region is scanned as in the prior art is different from the case where the nugget diameter is obtained by discriminating with a certain threshold TH as shown in FIG. 7, the reliability of the measured value is high. In addition, effects such as high measurement reproducibility can be achieved.

  The present invention is not limited to the embodiment described above. For example, the configuration of the probe 11, that is, the number of the plurality of probes 12 and the arrangement pitch thereof may be set according to the required measurement specifications. It is of course possible to redefine the diameter of the nugget N based on the interval between the two singular points Xa and Xb and the center position of the nugget N forming the bottom point of the voltage profile. Of course, the output of the voltage detector 16 can be taken into a personal computer (PC) and the above-described processing can be executed by software. Further, the two pairs of probe needle arrays 21 and 22 described above are not necessarily provided so that the arrangement directions of the probe needles 11 are orthogonal to each other. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

The schematic block diagram of the nugget diameter measuring apparatus which enforces the nugget diameter measuring method which concerns on one Embodiment of this invention. The figure which shows the example of the change pattern of the electrical potential distribution calculated | required by scanning the spot-welded steel materials, and the relationship between the singular point and nugget diameter in this change pattern. The figure which shows typically the mode of the electric potential distribution inside the steel materials which changes with scanning positions. The figure which shows the rough process sequence of the nugget diameter measuring method which concerns on this invention. The figure for demonstrating the principle of the nugget diameter measurement using two sets of probe needle arrays. The figure for demonstrating the principle of the state detection of the inside of steel materials by a six-probe method. The figure for demonstrating the measurement principle of the conventional general nugget diameter measurement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Probe probe 12 Probe 13 Electronic switch 14 Scan control part 15 DC power supply 16 Voltage detector 17 Memory 18 Singular point detection part 19 Nugget diameter calculation part 21, 22 Probe array Ia, Ib Current electrode needle Va, Vb Voltage electrode needle

Claims (6)

Using a probe probe provided with a pair of electrode needles for applying a constant current or voltage between any two points on the surface of the steel material and at least a pair of voltage electrode needles for detecting a surface potential generated in the steel material by the current or voltage Scan the surface of the spot-welded steel along a predetermined line,
From the profile of the change in the scanning direction of the voltage detected by the pair of voltage electrode needles along with this scanning, two singular points where the voltage exceeds the detected voltage at the site outside the spot welding region in the steel material The nugget diameter measuring method is characterized in that the diameter of the nugget formed on the steel material by the spot welding is obtained from the scanning position where these singular points are detected. The scanning line by the probe probe is set as a straight line across the center of the spot welding region of the steel material,
The nugget diameter measuring method according to claim 1, wherein the diameter of the nugget is obtained as a distance between two singular points detected in the scanning line. The scanning line by the probe probe is set as two straight lines crossing each other and crossing each spot welding region of the steel material,
2. The diameter of the nugget is obtained as a diameter of a circle indicating an outer shape of the nugget determined by detection positions of at least three singular points among the singular points detected in each scanning line. Nugget diameter measurement method. The probe probe is a linear arrangement of a plurality of probe needles at a constant pitch,
The scanning of the steel material by the probe probe selects the probe needles to be used as the pair of electrode needles and the pair of voltage electrode needles from the plurality of probe needles, respectively, and the electrode needles and the voltage electrodes The nugget diameter measuring method according to claim 1, wherein the probe is selected by sequentially switching probe needles to be selected as needles in the arrangement direction. A probe probe in which a plurality of probe needles are linearly arranged at a constant pitch;
A probe to be used as a pair of electrode needles and a pair of voltage electrode needles is selected from a plurality of probe needles in the probe probe, and the probe to be selected as the electrode needle and the voltage electrode needle is Probe scanning means for sequentially switching in the arrangement direction;
A steel material inspection means for applying a constant current or voltage to the steel material through the pair of electrode needles, and detecting a surface potential generated in the steel material by the current or voltage with the pair of voltage electrode needles,
Detection at a site where the voltage deviates from the spot welding region of the steel material from the profile of change in the scanning direction of the voltage detected by the steel material inspection means as the probe scanning means scans the probe. An analysis means for detecting two singularities exceeding the voltage;
1. A nugget diameter measuring device comprising: a nugget diameter calculating means for obtaining a diameter of a nugget formed on the steel material by spot welding from a detected position in the scanning direction of the singular point obtained by the analyzing means.   6. The nugget diameter measuring apparatus according to claim 5, wherein the probe probe is provided by crossing two sets of probe arrays in which a plurality of probe needles are linearly arranged at a constant pitch.

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