JP2016044998A - Measuring method for contact dimension between steel sheets/plates, and measuring device for contact dimension between steel sheets/plates - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method and a measuring device for contact dimensions between steel sheets/plates that can more accurately measure the contact dimension in a shorter period of time.SOLUTION: Paired electrodes 11a and 11b are brought into contact with the respective surfaces of two steel sheets/plates 1a and 1b, and a direct current is caused to flow between the two electrodes 11a and 11b by potential difference measuring means 12, which measures the potential difference ΔV between the electrodes 11a and 11b at the time. Memory means 27 keeps in store the contact dimension C between the steel sheets/plates 1a and 1b and the potential difference ΔV between the electrodes 11a and 11b, measured in advance by numerical analysis or measurement with the electric resistivity rates ρ of the respective contact parts between the electrodes 11a and 11b and the steel sheets/plates 1a and 1b taken into consideration. Contact dimension calculating means 28 figures out the contact dimension C between the steel sheets/plates 1a and 1b from the potential difference ΔV measured by the potential difference measuring means 12 on the basis of the relationship between the contact dimension C stored in the memory means 27 and the potential difference ΔV.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for measuring a contact dimension between steel plates for measuring a contact dimension between two steel plates, and an apparatus for measuring a contact dimension between steel plates.

  Steel plates are widely used as structural materials for automobiles, home appliances, etc., and joining of the steel plates is a kind of resistance welding, and quick and inexpensive spot welding is generally used. For example, in an automobile, thousands of spot welds exist per vehicle. Conventionally, in order to evaluate the quality and dimensions of contact portions between steel plates such as spot welds, a method using ultrasonic waves (for example, see Patent Document 1), a method of measuring a potential difference, and the like have been used. ing.

  As a method of measuring the potential difference and evaluating the quality and dimensions of the contact portion between the steel plates, for example, a pair of electrode needles that apply a constant current or voltage between any two points on the steel plate surface, and the current or voltage By using a probe probe having a pair of voltage electrode needles for detecting the surface potential generated on the steel sheet by the use of a probe probe, the surface potential change detected when the surface of the spot welded steel material is scanned along a predetermined line Based on this, the probe is applied to the nugget (contact part) diameter formed on the steel (see, for example, Patent Document 2), the spot welded area and the non-welded area away from the welded area. There is one that measures electrical resistance by contact, and evaluates joint strength based on the ratio of the electrical resistance (see, for example, Patent Document 3).

  However, in the method using ultrasonic waves as described in Patent Document 1 and the method of measuring a potential difference using a probe probe as described in Patent Documents 2 and 3, compared with the working time of spot welding. Since it takes a long time to install the torch and probe for ultrasonic generation at a predetermined position and scan the probe, the measurement time becomes very long. When it has, there was a problem that it was not practical. For example, in an automobile manufacturing process, spot welding is performed in only a few seconds, and it is difficult to apply to such a site. For this reason, in the automobile manufacturing process, the quality of spot welds is guaranteed by accurately controlling the three factors of welding current, current application time, and applied pressure. Welding using chisel An unsuccessful inspection of the part has been carried out.

  Therefore, in order to shorten the measurement time, a method has been developed in which each electrode for welding arranged with a steel plate interposed therebetween is used as an electrode for voltage measurement. As such a method, for example, the welding current applied between the electrodes and the voltage between the electrodes are measured, and using this measurement value, the temperature distribution based on the heat conduction model and the current distribution diameter are numerically analyzed, Estimate the diameter of the nugget (contact part) generated by welding (see, for example, Patent Document 4), measure the voltage by passing a current between the electrodes after welding, and use the obtained electrical resistance value as a reference value There is one that discriminates the quality of welding by comparing with (for example, see Patent Document 5).

JP 2011-220714 A Japanese Patent No. 4822545 JP 2008-254005 A Japanese Patent Laid-Open No. 11-47945 JP 2010-234424 A

  However, the method using the numerical analysis as described in Patent Document 4 does not consider the possibility that the surface roughness of the steel sheet changes during resistance welding or the like, so that an error occurs in the calculation of the size of the contact portion (nugget). There has been a problem that accurate contact dimensions may not be calculated. The method described in Patent Document 5 does not determine the contact dimension between the steel plates, and the reference value greatly affects the determination of pass / fail, so the determination of pass / fail may change depending on how to take the reference value. There was a problem that an accurate judgment could not be made.

  The present invention has been made paying attention to such a problem, and a contact dimension measuring method between steel sheets and a contact dimension measuring apparatus between steel sheets capable of measuring the contact dimension between steel sheets more accurately in a short time. The purpose is to provide.

  In order to achieve the above object, a method for measuring a contact dimension between steel plates according to the present invention is a method for measuring a contact dimension between steel plates, which measures a contact dimension between two steel plates, each contacting a surface of each steel plate. A potential difference measuring step for measuring a potential difference between the electrodes when a DC current of a constant magnitude is passed between the pair of electrodes, and a contact dimension between the steel plates and each of the currents when the DC current is passed. The relationship between the potential difference between the electrodes was determined in the relationship evaluation step obtained in advance by numerical analysis and / or measurement in consideration of the electrical resistivity of the contact portion between each electrode and each steel plate, and the relationship evaluation step. And a contact dimension calculating step of obtaining a contact dimension between the steel plates from the potential difference measured in the potential difference measuring step based on the relationship.

  A contact dimension measuring apparatus between steel plates according to the present invention is a contact dimension measuring apparatus between steel plates for measuring a contact dimension between two steel plates, and is provided with a pair of contacts provided on the surface of each steel plate. Considering the electrical resistivity of the contact part between each electrode and each steel plate in advance, a potential difference measuring means for measuring a potential difference between each electrode by passing a direct current of a certain magnitude between the electrode and each electrode. Storage means for storing the relationship between the contact dimension between the steel plates and the potential difference between the electrodes when the direct current is passed, which has been obtained by numerical analysis and / or measurement, and stored in the storage means Contact size calculating means for obtaining a contact dimension between the respective steel plates from the potential difference measured by the potential difference measuring means based on the relationship between the contact dimension and the potential difference.

  The apparatus for measuring a contact dimension between steel plates according to the present invention can suitably implement the method for measuring a contact dimension between steel plates according to the present invention. The contact dimension measuring method between steel sheets and the contact dimension measuring apparatus between steel sheets according to the present invention are the relationship between the contact dimension between the steel sheets and the potential difference between the electrodes when a constant direct current is passed between the electrodes. Considering the electrical resistivity of the contact portion between each electrode and each steel plate when obtaining in advance, it is possible to flexibly when the surface roughness of the steel plate changes (increases) during resistance welding. Can respond. For this reason, the contact dimension between steel plates can be measured more accurately. Further, when measuring the contact dimension, it is sufficient to measure the potential difference between the electrodes once, and the measurement can be performed in a shorter time compared to the case of performing scanning or measurement at a plurality of points.

  In the contact dimension measuring method between steel sheets according to the present invention, the relation evaluation step obtains the potential difference as a function of the contact dimension and the electrical resistivity by numerical analysis, and further, between each steel sheet at a plurality of different potential differences. By measuring a contact dimension of the plurality of measurement results, a relationship between the electrical resistivity and the contact dimension is obtained by numerical analysis using the plurality of measurement results, and based on the relationship and a function of the potential difference, the contact dimension and A relationship with the potential difference may be obtained. In the contact dimension measuring apparatus between steel plates according to the present invention, the storage means obtains the potential difference as a function of the contact size and the electrical resistivity by numerical analysis, and further, between each steel plate at a plurality of different potential differences. By measuring a contact dimension, a relationship between the electrical resistivity and the contact dimension is obtained by numerical analysis using the plurality of measurement results, and the contact is obtained based on the relationship and a function of the potential difference. You may memorize | store the relationship between a dimension and the said electrical potential difference. In this case, even when the surface roughness of the steel plate is increased during resistance welding and the electrical resistivity of the contact portion between each electrode and each steel plate is increased, the contact dimensions and the potential difference are taken into consideration. The contact dimension between the steel plates can be measured more accurately.

  Further, in the contact dimension measuring method between steel plates according to the present invention, the relationship evaluation step may obtain the relationship between the contact dimension and the potential difference only by measurement without using numerical analysis. In the contact dimension measuring apparatus between steel plates according to the present invention, the storage means may store the relationship between the contact dimension and the potential difference obtained only by measurement without using numerical analysis. Also in this case, the contact dimension between the steel plates can be accurately measured.

  Further, in the contact dimension measuring method between steel plates according to the present invention, the relation evaluation step can be assumed that the electrical resistivity of the contact portion between each electrode and each steel plate can be assumed to be constant. You may obtain | require the relationship with an electrical potential difference. In the apparatus for measuring a contact dimension between steel plates according to the present invention, the storage means can be assumed to have a constant electrical resistivity of a contact portion between each electrode and each steel plate, and the contact dimension obtained by numerical analysis and the above-mentioned The relationship with the potential difference may be stored. In this case, even if resistance welding is performed, when the electrical resistivity of the contact portion between each electrode and each steel plate does not change, the relationship between the contact dimension and the potential difference can be obtained efficiently.

  In the contact dimension measuring method and the contact dimension measuring apparatus between steel sheets according to the present invention, the contact dimension is a contact dimension between the steel plates when the steel plates are connected by resistance welding, and each electrode is the resistance welding It is preferable to comprise an electrode for performing the above. In this case, since the electrode used for resistance welding can be used as it is as an electrode for measuring the contact dimension, the electrode positioning and installation time can be omitted, and the contact dimension can be measured in a shorter time. It can be performed.

  ADVANTAGE OF THE INVENTION According to this invention, the contact dimension measuring method between the steel plates and the contact dimension measuring apparatus between steel plates which can measure the contact dimension between steel plates more correctly in a short time can be provided.

It is a side view which shows the contact dimension measuring apparatus between the steel plates of embodiment of this invention. It is an analytical model of FEA when it can be assumed that the electrical resistivity of the contact part of each electrode and each steel plate regarding the contact dimension measuring method between the steel plates of embodiment of this invention is constant. The results of FEA analysis using the analysis model shown in FIG. 2 are: (a) current density distribution when the electrode diameter D = 6 mm, Fe disk diameter (contact dimension of each steel plate) C = 3 mm, (b) D = 6 mm , Current density distribution when C = 6 mm, (c) distribution of potential ψ with respect to various C values when D = 6 mm. 3 is a graph showing (a) the relationship between the potential difference ΔV and C for various values of D, and (b) the relationship between ∂ (ΔV) / ∂C and C, in the FEA analysis result based on the analysis model shown in FIG. 2. (A) FEA analysis model modeling actual electrode shape, (b) measurement of potential difference ΔV (Experiment), and analysis shown in (a) It is a graph which shows the relationship between the diameter of Shim (contact dimension of each steel plate) C and potential difference ΔV obtained by FEA analysis using a model. It is a flowchart in the case where it can be assumed that the electrical resistivity of the contact part of each electrode and each steel plate is constant showing the contact dimension measuring method between the steel plates of the embodiment of the present invention. The results of FEA analysis using the analysis model shown in FIG. 2 are as follows: (a) Current density distribution when a current is applied locally (Local), (b) Current density distribution when a current is applied sufficiently far away (Uniform) , (C) is a graph showing the distribution of potential ψ in each case. It is an analysis model of FEA in case the electrical resistivity of the contact part of each electrode and each steel plate changes regarding the contact dimension measuring method between the steel plates of the embodiment of the present invention. FIG. 9 is a graph showing the distribution of potential ψ with respect to the value of electrical resistivity ρ of various contact portions when the physical contact portion (contact dimension of each steel plate) C = 3 mm, as a result of FEA analysis using the analysis model shown in FIG. 8. is there. It is a graph which shows the relationship between C and electric potential difference (DELTA) V with respect to the value of various (rho) of the FEA analysis result by the analysis model shown in FIG. It is a graph which shows the relationship between the measured contact dimension C of each steel plate, and (rho) calculated by the FEA analysis by the analysis model shown in FIG. A contact dimension C ^E obtained from the measured value of the potential difference [Delta] V, which is a graph showing the relationship between the contact dimension C ^M obtained by actual measurement. It is a flowchart in case the electrical resistivity of the contact part of each electrode and each steel plate which shows the contact dimension measuring method between the steel plates of embodiment of this invention changes.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 thru | or FIG. 13 has shown the contact dimension measuring method and the contact dimension measuring apparatus between steel plates of embodiment of this invention.
As shown in FIG. 1, a contact dimension measuring device 10 between steel plates is a device for measuring a contact size between steel plates 1a and 1b when two steel plates 1a and 1b are connected by resistance welding. And a pair of electrodes 11a and 11b, a potential difference measuring means 12, and a control analysis terminal 13.

  Each of the electrodes 11a and 11b is made of copper and includes an electrode for performing spot welding which is a kind of resistance welding. Each electrode 11a, 11b has a shell shape having a flat surface at the tip. Each electrode 11a, 11b presses the flat surface at the tip with a predetermined pressure from both sides of the two steel plates 1a, 1b, which are overlapped with each other, to the opposite position of the surface of each steel plate 1a, 1b. It is provided so that contact is possible.

  The potential difference measuring means 12 has two current terminals 21a and 21b, two voltage measurement terminals 22a and 22b, a measurement power source 23, and a voltage measuring device 24. The current terminals 21a and 21b are provided so as to be in contact with the side surfaces of the electrodes 11a and 11b, respectively. The voltage measuring terminals 22a and 22b are provided so as to be able to contact the side surfaces on the rear end side of the current terminals 21a and 21b of the electrodes 11a and 11b, respectively. The measurement power source 23 is connected to each of the current terminals 21a and 21b, and is provided so that a DC current having a constant magnitude flows between the electrodes 11a and 11b through the current terminals 21a and 21b. The voltage measuring device 24 is connected to the voltage measuring terminals 22a and 22b. When a direct current is passed between the electrodes 11a and 11b by the measuring power source 23, the potential difference between the voltage measuring terminals 22a and 22b. It is provided to measure

  The control analysis terminal 13 includes a computer and is connected to a measurement power source 23 and a voltage measuring device 24. The control analysis terminal 13 has a control means 25, a voltage input means 26, a storage means 27, and a contact dimension calculation means 28 as its functions. The control means 25 can control the magnitude of the direct current that flows between the electrodes 11a and 11b from the measurement power supply 23 and the timing at which the direct current flows. Further, the control means 25 can control the measurement timing of the voltage measuring device 24 so that the voltage measuring device 24 measures the potential difference when a direct current is passed between the electrodes 11a and 11b by the measuring power source 23. ing. The voltage input means 26 can input a potential difference between the voltage measuring terminals 22a and 22b measured by the voltage measuring device 24.

  The storage means 27 is a contact between the steel plates 1a and 1b, which has been obtained in advance by numerical analysis and / or measurement in consideration of the electrical resistivity of the contact portion between the electrodes 11a and 11b and the steel plates 1a and 1b. The relationship between the dimensions and the potential difference between the electrodes 11a and 11b when a direct current is passed is stored. The contact dimension calculation means 28 obtains the contact dimension between the steel plates 1a and 1b from the potential difference input from the voltage input means 26 based on the relationship between the contact dimension stored in the storage means 27 and the potential difference. ing.

  The contact dimension measuring apparatus 10 between steel plates can suitably implement the contact dimension measuring method between steel plates according to the embodiment of the present invention. Hereinafter, based on an Example, the effect of the contact dimension measuring method between the steel plates of embodiment of this invention and the contact dimension measuring apparatus 10 between steel plates is demonstrated.

[When it can be assumed that the electrical resistivity of the contact portion between each electrode and each steel plate is constant-numerical analysis]
In the case where the electrical resistivity of the contact portion between each electrode 11a, 11b and each steel plate 1a, 1b can be assumed to be constant, the contact dimension measurement between the steel plates was examined by numerical analysis.

First, the potential distribution on the electrodes 11a and 11b when current flows from the electrodes 11a and 11b to the two steel plates 1a and 1b is calculated by finite element analysis (FEA), and the contact between the steel plates 1a and 1b is calculated. The change of the potential distribution with the change of the situation was investigated.
The flow of current inside each steel plate 1a, 1b and each electrode 11a, 11b is governed by the Laplace equation shown below.
Δψ = 0 (1)
Here, ψ is a potential, and Δ is a Laplace operator. By solving Equation (1) by FEA analysis, ψ can be obtained. In the following, FEA analysis was performed using the general-purpose nonlinear analysis program Marc.

A 1/2 analysis model of FEA is shown in FIG. As shown in FIG. 2, the steel plates 1a and 1b made of Fe are discs having a diameter of 17.5 mm and a thickness of 1.2 mm, and the thickness is set at the center of the two steel plates 1a and 1b. A 0.7 mm, diameter C Fe disk (Contact) was inserted as a physical contact. Moreover, each Cu electrode (Electrode) 11a, 11b of diameter D was pressed to the position of 20 mm in length from the outer surface of each steel plate 1a, 1b. In the FEA analysis, the range of C is 1-6 mm, the range of D is 3-9 mm, the electrical resistivity of each Cu electrode 11a, 11b is 1.68 × 10 ⁻⁸ Ω · m, each steel plate 1a, 1b and Fe The electric resistivity of the disk was set to 1.42 × 10 ⁻⁷ Ω · m. Moreover, the electrical resistivity of the contact part between each electrode 11a, 11b and each steel plate 1a, 1b was made constant at 6.0 × 10 ⁻⁶ Ω · m. The electrical resistivity between the same Fe steel plates 1a and 1b and the Fe disk was set to zero. In addition, current was input / output from a position 4 mm away from the surface of each steel plate 1a, 1b on the side surface of each electrode 11a, 11b, and the applied current was 1A. The x-axis was defined on the surfaces of the electrodes 11a and 11b, and the origin was the center between the steel plates 1a and 1b.

  As a result of FEA analysis, current density distributions in the case of C = 3 mm and 6 mm when D = 6 mm are shown in FIGS. 3A and 3B, respectively. As shown in FIGS. 3A and 3B, when C = 3 mm, it is confirmed that a relatively high current density is formed in the vicinity of the Fe disk compared to the case of C = 6 mm. It was done. This suggests that the electrical resistance at the Fe disk increases with decreasing C, and this is considered to be because the current path becomes longer as C decreases.

  FIG. 3C shows the distribution of ψ for various C values when D = 6 mm. As shown in FIG. 3C, it can be seen that as C decreases, the absolute value of ψ increases. For example, paying attention to the potential difference ΔV between two points A and B at a position of 12 mm from the outer surface of each steel plate 1a, 1b, ΔV when C = 6 mm is 123 μV, whereas when C = 1 mm ΔV is 592 μV, and ΔV increases as C decreases.

  The relationship between ΔV and C for various values of D is shown in FIG. As shown in FIG. 4A, it can be seen that ΔV decreases as C increases in all D cases. It can also be seen that in a certain C, the value of ΔV increases as the value of D decreases. In order to accurately evaluate C from the measured ΔV, the relationship between ∂ (ΔV) / ∂C and C is obtained and shown in FIG. As shown in FIG. 4B, the smaller the value of C, the larger the value of ∂ (ΔV) / ∂C, and the maximum is D = 9 mm. From this, it can be said that C can be accurately evaluated by using a thicker electrode.

  From the above FEA analysis results, it can be seen that when current is input between the electrodes 11a and 11b, C can be evaluated by paying attention to the potential distribution between the electrodes 11a and 11b. In order to confirm this, an experiment using the contact dimension measuring apparatus 10 between steel plates was performed below.

[When it can be assumed that the electrical resistivity of the contact portion between each electrode and each steel plate is constant-measurement experiment]
In the experiment, as the two steel plates 1a and 1b, 60 mm square steel plates each having a thickness of 1.2 mm were used. Further, a disk-shaped shim was extracted from the same steel plate by punching and used as a contact portion between the steel plates 1a and 1b. The shim diameter C is 3-6 mm. As shown in FIG. 1, each steel plate 1a, 1b was inserted between two Cu electrodes 11a, 11b, and the pressing force of each electrode 11a, 11b was 2.35 kN (constant). Each current terminal 21a, 21b is brought into contact with the surface of each electrode 11a, 11b via a spring at a position 4 mm from the surface of each steel plate 1a, 1b, and a current of 2A is provided between each current terminal 21a, 21b. Shed. Moreover, each voltage measurement terminal 22a, when a current is passed using each voltage measurement terminal 22a, 22b installed at a position 12 mm from the surface of each steel plate 1a, 1b on the surface of each electrode 11a, 11b. The potential difference ΔV between 22b was measured.

In addition, an actual electrode shape was modeled, and FEA analysis was also performed using the analysis model shown in FIG. In the analysis, the contact resistance between each Cu electrode 11a, 11b and each steel plate 1a, 1b was made constant at 6.0 × 10 ⁻⁶ Ω · m. In addition, it is thought that contact resistance (rho) ₁ between each steel plate 1a, 1b and shim changes with the surface pressure between both. Here, since the applied pressure between the electrodes 11a and 11b is constant, the surface pressure varies with C. Considering the above, ρ ₁ is given by the following equation.
ρ ₁ = ρ ₀ + Q (C−C ₀ ) ² (2)
Here, ρ ₀ is a contact resistance that becomes a constant value under application of sufficient surface pressure (C ₀ ), and Q is a constant. In the analysis, it was assumed that C ₀ = 3 mm, ρ ₀ = 1.35 × 10 ⁻⁵ Ω · m, and Q = 1.8 Ω / m. For comparison, an analysis was also performed when the contact resistance between the steel plates 1a and 1b and the shim was constant at ρ ₂ = 1.6 × 10 ⁻⁵ Ω · m.

FIG. 5B shows the relationship between the shim diameter C and the potential difference ΔV obtained by measuring the potential difference and FEA analysis. As shown in FIG. 5 (b), it was confirmed from the actual measurement result (Experiment) that the measured value of ΔV decreased as C increased. This tendency is similar to the result of FEA analysis. In particular, the analysis result in the case (the case of [rho ₁₎ of each steel sheet 1a, the contact resistance between the 1b and the shim changes are in good agreement with the measured values. In the actual spot welded portion inspection, since the welded portion is physically joined to the steel plates 1a and 1b, the contact resistance at both contact portions may be constant (in the case of ρ ₂ ). As shown in FIG. 5B, the change in ΔV with respect to the change in C becomes more remarkable.

  From the above numerical analysis and experimental results, when it can be assumed that the electrical resistivity of the contact portion between each electrode 11a, 11b and each steel plate 1a, 1b can be assumed to be constant, using the contact dimension measuring device 10 between steel plates, Thus, the method for measuring the contact dimension between the steel plates according to the embodiment of the present invention can be implemented. That is, as shown in FIG. 6, first, in the relationship evaluation step, the relationship between the contact dimension C and the potential difference ΔV between the steel plates is obtained by numerical analysis as shown in FIGS. 4 (a) and 5 (b). And stored in the storage means 27 (step 31). Thereafter, the potential difference measuring means 12 measures the potential difference ΔV between the electrodes 11a and 11b (step 32), and the contact dimension calculating means 28 calculates the potential difference ΔV based on the relationship stored in the storage means 27. Thus, the contact dimension C between the steel plates 1a and 1b can be obtained (step 33).

  In the above numerical analysis and experiment, a current is locally applied between two points on the surface of each electrode 11a, 11b. Here, when a current is applied locally and when a current is applied sufficiently far from the ends of the electrodes 11a and 11b, current density distributions are obtained by FEA analysis, and FIGS. Shown in b). In addition, the distribution of ψ at that time is shown in FIG. As shown in FIG. 7C, the values of ΔV when C = 6 mm and 1 mm when current is applied locally (Local) are 123 μV and 592 μV, respectively. On the other hand, when current is applied from a sufficiently far distance and the current density is uniform inside each electrode 11a, 11b (Uniform), the values of ΔV when C = 6 mm and 1 mm are 147 μV and 616 μV, respectively. It is the same level as when a current is applied locally. For this reason, it can be said that the input / output method of the current may be selected according to the situation.

[When the electrical resistivity of the contact portion between each electrode and each steel plate changes-Numerical analysis]
In actual welding such as spot welding, since the surface roughness of the steel plates 1a and 1b increases after welding, the contact resistance (electric resistivity) between the electrodes 11a and 11b and the steel plates 1a and 1b is not constant. It seems that there are many things that change. In general, the diameter of the contact portion between the steel plates 1a and 1b is increased by increasing the welding current, but the surface roughness of the steel plates 1a and 1b is increased, and the electrodes 11a and 11b and the steel plates 1a and 1b are increased. Since contact resistance with 1b increases, it is necessary to obtain | require the contact dimension between each steel plate 1a, 1b in consideration of this. Therefore, first, the potential difference at each electrode 11a, 11b when the contact resistance between each electrode 11a, 11b and each steel plate 1a, 1b and the contact dimension between each steel plate 1a, 1b are changed. It was calculated by numerical analysis, and the effect of both on the potential difference was examined.

As in the case of FIG. 2, the finite element method was used for the numerical analysis. The FEA analysis model is shown in FIG. As shown in FIG. 8, two steel plates (Sheet) 1a and 1b are made into discs having a diameter of 17.5 mm and a thickness of 1.2 mm, and the thickness is set at the center of the two steel plates 1a and 1b. A physical contact (Weld) of 0.1 mm and diameter C was provided. In the FEA analysis, the electrical resistivity of each Cu electrode (Electrode) 11a, 11b was set to 1.68 × 10 ⁻⁸ Ω · m, and the electrical resistivity of Fe was set to 1.42 × 10 ⁻⁷ Ω · m. Each Cu electrodes 11a, 11b and the steel plate 1a, the electrical resistivity of the contact portion ρ between 1b, was changed in the range of ^{1 × 10 -6 Ω · m~50 ×} 10 -6 Ω · m .

  Similarly to the model shown in FIG. 2, current input / output was performed from a position 4 mm away from the surface of each steel plate 1a, 1b on the side surface of each electrode 11a, 11b, and the applied current was 1A. Further, the x-axis was defined on the surfaces of the electrodes 11a and 11b, and the origin was the center between the steel plates 1a and 1b. In the FEA analysis, by solving Equation (1), the surface potential ψ at each electrode 11a, 11b was obtained, and the potential difference ΔV between the points A and B on the surface of each electrode 11a, 11b was obtained. In the following, FEA analysis was performed using the general-purpose nonlinear analysis program Marc.

As an FEA analysis result, the distribution of ψ with respect to various values of ρ when C = 3 mm is shown in FIG. As can be seen from FIG. 9, the larger the value of ρ, the larger the absolute value of ψ. FIG. 10 shows the relationship between C and ΔV for various values of ρ. As shown in FIG. 10, ΔV takes a larger value as C is smaller and as ρ is larger. Here, when ΔV is approximated as a linear sum of functions each having C and ρ as independent variables, the following equation is obtained.
ΔV = 6.88 × 10 ^-8 C ^-1.2 + 14.2ρ + 1.07 × 10 ^-5 (3)
The square value (R ² value) of the correlation coefficient R in Expression (3) is 0.9995.

[When the electrical resistivity of the contact portion between each electrode and each steel plate changes-measurement experiment]
Each steel plate 1a, 1b is actually spot-welded, and ΔV at that time is measured, and after welding, each steel plate 1a, 1b is cut to observe the cross section of the welded portion, and the contact dimension between each steel plate 1a, 1b C was measured. Further, the electrical resistivity ρ of the contact portion between each Cu electrode 11a, 11b and each steel plate 1a, 1b was calculated from the actually measured ΔV and C by FEA analysis using the analysis model shown in FIG. Here, the FEA analysis was performed from the measured ΔV and C to calculate the electrical resistivity ρ of the contact portion. However, the measured ΔV and C were substituted into the equation (3) to obtain the electrical resistivity ρ of the contact portion. You may ask for it.

The relationship between the calculated ρ and the actually measured C is shown in FIG. As shown in FIG. 11, ρ increases as C increases. This is because the surface roughness of the steel plates 1a and 1b increases as C increases. The relationship between ρ and C in the case of FIG. 11 can be approximated by the following equation (solid line in FIG. 11).
ρ = 2.14 × 10 ⁻⁷ × exp (947 × C) (4)

From Formula (3) and Formula (4),
ΔV = 6.88 × 10 ^-8 C ^-1.2 + 3.04 × 10 ^-6 exp (947 × C) + 1.07 × 10 ^-5 (5)
Is obtained. From equation (5), C can be evaluated by measuring ΔV. In addition, since the relationship of Formula (4) is dependent on welding conditions, the same evaluation formula can be obtained by obtaining this relationship anew under different welding conditions.

In order to evaluate the formula (5), 52 spot weldings were newly performed, and the spot weld samples were measured with the contact dimension ^CE obtained by using the formula (5) from the measured value of the potential difference ΔV. comparison between the obtained contact dimension C ^M were performed. The result is shown in FIG. As shown in FIG. 12, ^CE and ^CM are in good agreement, and it has been confirmed that the contact dimension between the steel plates 1a and 1b can be accurately measured by using the equation (5).

  From the above numerical analysis and experimental results, when the electrical resistivity of the contact portion between each electrode 11a, 11b and each steel plate 1a, 1b changes, using the contact dimension measuring apparatus 10 between the steel plates, the following is performed. Thus, the method for measuring the contact dimension between the steel plates according to the embodiment of the present invention can be carried out. That is, as shown in FIG. 13, first, in the relational evaluation step, the contact of the contact portion between each electrode 11a, 11b and each steel plate 1a, 1b as shown in Expression (3) obtained from FIG. 10 by numerical analysis. A potential difference ΔV is determined as a function of the dimension C and the electrical resistivity ρ (step 34). Next, the contact dimension C between the respective steel plates 1a and 1b at a plurality of different potential differences ΔV is measured, and numerical analysis is performed using the plurality of measurement results as shown in Expression (4) obtained from FIG. The relationship between the electrical resistivity ρ and the contact dimension C is obtained (step 35). Further, based on the relationship between the electrical resistivity ρ and the contact dimension C and the function of the potential difference ΔV, the relationship between the contact dimension C and the potential difference ΔV as shown in equation (5) is obtained and stored in the storage means 27. (Step 36).

  After obtaining the relationship between the contact dimension C and the potential difference ΔV in the relationship evaluation step, the potential difference ΔV between the electrodes 11a and 11b is measured by the potential difference measuring means 12 as in FIG. Based on the measured potential difference ΔV, the calculation means 28 can determine the contact dimension C between the steel plates 1a and 1b based on the relationship stored in the storage means 27 (step 33).

  From the above examples, the contact dimension measuring method between steel plates and the contact dimension measuring apparatus 10 between steel plates according to the embodiment of the present invention are the contact dimensions between the steel plates 1a and 1b and the electrodes 11a and 11b. When the relationship between the potential difference between the electrodes 11a and 11b when a constant direct current is passed through is previously determined, the electrical resistivity of the contact portion between the electrodes 11a and 11b and the steel plates 1a and 1b is determined. By considering it, not only when the electrical resistivity is constant, but also when the electrical resistivity changes due to changes (increases) in the surface roughness of the steel plates 1a, 1b during resistance welding, etc. can do. For this reason, the contact dimension between the steel plates 1a and 1b can be measured more accurately.

  Moreover, the contact dimension measuring method between the steel plates and the contact dimension measuring apparatus 10 between the steel plates according to the embodiment of the present invention use the electrodes used for spot welding as the electrodes 11a and 11b for measuring the contact dimensions. Since the electrodes 11a and 11b are used as they are, the time required for positioning and installation of the electrodes 11a and 11b can be omitted, and the contact dimensions can be measured in a shorter time. Further, when measuring the contact dimension, the potential difference between the electrodes 11a and 11b may be measured once, and the measurement can be performed in a shorter time compared to the case of performing scanning or measurement at a plurality of points. .

DESCRIPTION OF SYMBOLS 1a, 1b Steel plate 10 Contact size measuring apparatus 11 between steel plates 11a, 11b Electrode 12 Potential difference measuring means 21a, 21b Current terminal 22a, 22b Voltage measuring terminal 23 Measuring power supply 24 Voltage measuring device 13 Control analysis terminal 25 Control means 26 Voltage Input means 27 Storage means 28 Contact dimension calculation means

Claims (8)

A method for measuring a contact dimension between two steel plates, which measures a contact dimension between two steel plates,
A potential difference measuring step for measuring a potential difference between the electrodes when a direct current of a constant magnitude is passed between a pair of electrodes in contact with the surfaces of the respective steel plates,
The relationship between the contact dimension between the steel plates and the potential difference between the electrodes when the direct current is applied is determined in advance by numerical analysis and / or measurement in consideration of the electrical resistivity of the contact portion between each electrode and each steel plate. The relationship evaluation process to be requested,
Based on the relationship obtained in the relationship evaluation step, a contact size calculation step for obtaining a contact size between the steel plates from the potential difference measured in the potential difference measurement step,
A method for measuring a contact dimension between steel plates, comprising:   The relation evaluation step obtains the potential difference as a function of the contact dimension and the electrical resistivity by numerical analysis, and further measures the contact dimension between the steel plates at a plurality of different potential differences, thereby measuring the plurality of measurements. A relationship between the electrical resistivity and the contact size is obtained by numerical analysis using a result, and a relationship between the contact size and the potential difference is obtained based on the relationship and a function of the potential difference. Item 1. A method for measuring a contact dimension between steel plates according to Item 1.   2. The relationship evaluation step of obtaining a relationship between the contact dimension and the potential difference by numerical analysis when it can be assumed that the electrical resistivity of the contact portion between each electrode and each steel plate is constant. Of measuring contact dimensions between steel plates. The contact dimension is a contact dimension between each steel plate when each steel plate is connected by resistance welding,
The method for measuring a contact dimension between steel plates according to any one of claims 1 to 3, wherein each electrode comprises an electrode for performing the resistance welding. A contact dimension measuring device between steel sheets for measuring a contact dimension between two steel sheets,
A pair of electrodes each provided in contact with the surface of each steel plate;
A potential difference measuring means for passing a direct current of a certain magnitude between the electrodes and measuring a potential difference between the electrodes at that time,
The contact dimension between the steel plates and the potential difference between the electrodes when the direct current is passed, which are obtained in advance by numerical analysis and / or measurement in consideration of the electrical resistivity of the contact portion between each electrode and each steel plate. Storage means for storing the relationship between
Based on the relationship between the contact dimension stored in the storage means and the potential difference, contact dimension calculation means for obtaining a contact dimension between the steel plates from the potential difference measured by the potential difference measuring means,
An apparatus for measuring a contact dimension between steel plates, comprising:   The storage means obtains the potential difference as a function of the contact size and the electrical resistivity by numerical analysis, and further measures the contact size between the steel plates at a plurality of different potential differences, thereby obtaining a plurality of measurement results. The relationship between the electrical resistivity and the contact size is obtained by numerical analysis using the, and the relationship between the contact size and the potential difference obtained based on the relationship and the function of the potential difference is stored. The apparatus for measuring a contact dimension between steel plates according to claim 5.   The storage means stores the relationship between the contact dimension and the potential difference obtained by numerical analysis when the electrical resistivity of the contact portion between each electrode and each steel plate can be assumed to be constant. The apparatus for measuring a contact dimension between steel plates according to claim 5. The contact dimension is a contact dimension between each steel plate when each steel plate is connected by resistance welding,
The contact dimension measuring device between steel plates according to any one of claims 5 to 7, wherein each electrode comprises an electrode for performing the resistance welding.