Method for calculating diameter of nugget, method for determining quality of resistance spot welding, and welding method

Abstract

To provide a calculation method of a nugget diameter based on a stroke between electrodes, current value, voltage value, and applied pressure during weld.SOLUTION: A calculation method of a nugget diameter in a resistance spot welding is given which sandwiches, applies pressure to, and applies an electric current to overlapped multiple tabular weld materials between a pair of electrodes (101, 103) in an overlapped direction so as to weld the plurality of tabular weld materials (105, 107). The calculation method of a nugget diameter is based on measurement results of a stroke between a pair of electrodes, a current value, a voltage value, and applied pressure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for calculating the diameter of a nugget, a method for determining the quality of resistance spot welding, and a welding method.

Background Art

[0002] In resistance spot welding, methods for ensuring good products during spatter or splash generation have been developed. Patent Document 1 describes performing welding based on the time change curve and cumulative heat generation amount per unit volume at each step memorized as target values in test welding. In any step, if the amount of change over time in the instantaneous heat generation amount per unit volume deviates from the time change curve that is the reference, the amount of deviation is compensated within the remaining energization time of that step. Therefore, the energization amount is controlled so that the cumulative heat generation amount per unit volume in this welding matches the cumulative heat generation amount per unit volume obtained in advance in test welding. Further, when spatter generation is detected in any step, the target value of the cumulative heat generation amount per unit volume thereafter is reduced, and accordingly, the energization amount is controlled.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above document corrects the target value of adaptive control after spatter occurs, but it was not possible to estimate the diameter of the nugget, which is the size of the welded part, during spatter or splash generation. Therefore, an object of the present disclosure is to provide a method for measuring the stroke, current value, voltage value, and pressing force between electrodes during welding and calculating the diameter of the nugget.

Means for Solving the Problems

[0005] A method for calculating the diameter of the nugget of the present disclosure is a method for calculating the diameter of the nugget of resistance spot welding in which a plurality of stacked plate-shaped welding materials are sandwiched between a pair of electrodes in the stacking direction and pressed while passing an electric current to weld the plurality of plate-shaped welding materials, and calculating the diameter of the nugget using the measurement results of the stroke, current value, voltage value, and pressing force between the pair of electrodes.

[0006] During welding, the stroke, current value, voltage value, and pressing force between the electrodes can be measured, and the diameter of the nugget can be calculated.

[0007] Furthermore, the method for calculating the diameter of the nugget of the present disclosure is calculating a resistance waveform from the current value and voltage value between the pair of electrodes, calculating a dilation amount waveform from the pressing force and stroke between the pair of electrodes, and calculating the diameter of the nugget using the resistance waveform and the dilation amount waveform.

[0008] By calculating a resistance waveform from the current value and voltage value, calculating a dilation amount waveform from the pressing force and stroke, and using them, the diameter of the nugget can be calculated.

[0009] Furthermore, the method for calculating the diameter of the nugget of the present disclosure is wherein the dilation amount waveform is E = S + a×F ··· (1) and is calculated by, where E is the dilation amount, S is the stroke, a is the strain amount conversion coefficient, and F is the pressing force.

[0010] The dilation amount waveform can be calculated by the formula (1) with the stroke and pressing force as variables.

[0011] Furthermore, the method for calculating the diameter of the nugget of the present disclosure is The diameter of the nail is calculated using the change amount of the resistance waveform and the maximum value of the expansion amount of the expansion amount waveform or the integrated expansion amount value obtained by integrating the expansion amount with respect to time.

[0012] The diameter of the nail can be calculated using the change amount of the resistance waveform and the maximum value of the expansion amount of the expansion amount waveform or the integrated expansion amount value obtained by integrating the expansion amount with respect to time.

[0013] Further, the method for calculating the diameter of the nail of the present disclosure is The diameter of the nail is NI = C1×ΔR + C2×Emax + C4···(2) Or

Number

[0014] The diameter of the nail can be calculated by the above formula using the change amount of the resistance waveform and the maximum value of the expansion amount or the integrated expansion amount value obtained by integrating the expansion amount with respect to time.

[0015] Further, the method for calculating the diameter of the nail of the present disclosure is The formulas (2) and (3) are applied when the energization time is equal to or greater than a predetermined value.

[0016] When the energization time is equal to or greater than a threshold value which is a predetermined value, the above formulas (2) and (3) can be applied.

[0017] Further, the method for determining a good product in resistance spot welding of the present disclosure is The step of calculating the diameter of the nail by the method for calculating the diameter of the nail according to any one of claims 1 to 6, A step of determining whether the welded product of the resistance spot welding is a non-defective product by comparing the calculated diameter of the nugget with a predetermined value, When spatter occurs in the resistance spot welding, the diameter of the nugget is calculated using the measurement results of the stroke, current value, voltage value, and applied pressure immediately before the spatter occurs. This is a method for determining non-defective products in resistance spot welding.

[0018] When spatter occurs, it is possible to provide a method for determining non-defective products in resistance spot welding that calculates the diameter of the nugget using the measurement results of the stroke, current value, voltage value, and applied pressure immediately before the spatter occurs.

[0019] The welding method of the present disclosure is A first step of energizing between the pair of electrodes with a first current value, A second step of energizing between the pair of electrodes with a sinusoidal current higher than the first current value, A third step of energizing between the pair of electrodes while gradually increasing the current value from the center of the amplitude of the sinusoidal wave, A calculation step of calculating the diameter of the nugget by the method of calculating the diameter of the nugget according to any one of claims 1 to 6, In the calculation step, the diameter of the nugget is calculated using the measurement results of the stroke, current value, voltage value, and applied pressure in the first step to the third step. This is a welding method.

[0020] By combining the method of calculating the diameter of the nugget with the above energization pattern, it is possible to provide a welding method capable of calculating the diameter of the nugget.

Effects of the Invention

[0021] According to the present disclosure, it is possible to provide a method for measuring the stroke, current value, voltage value, and applied pressure between electrodes during welding and calculating the diameter of the nugget.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0023] Embodiment Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the invention according to the claims is not limited to the following embodiments. Also, not all of the configurations described in the embodiments are essential as means for solving the problems. For the sake of clarity of explanation, the following description and drawings have been appropriately omitted and simplified. In each drawing, the same elements are denoted by the same reference numerals, and duplicate explanations are omitted as necessary.

[0024] (Explanation of Resistance Spot Welding According to the Embodiment) FIG. 1 is a schematic diagram of resistance spot welding according to an embodiment. While referring to FIG. 1, resistance spot welding according to the embodiment will be described.

[0025] As shown in FIG. 1, a resistance spot welding system 100 according to an embodiment includes an upper movable electrode 101 and a lower fixed electrode 103, which are a pair of electrodes. A metal plate 105 and a metal plate 107 to be welded are arranged in an overlapping manner between the upper movable electrode 101 and the lower fixed electrode 103. Note that the movable electrode and the fixed electrode may be reversed vertically. The metal plate 105 and the metal plate 107 are a plurality of plate-like welding materials and are stacked vertically.

[0026] The upper movable electrode 101 moves up and down as indicated by the arrow to press the metal plate 105 and the metal plate 107. The upper movable electrode 101 and the lower fixed electrode 103 sandwich the metal plate 105 and the metal plate 107 from the direction in which the metal plate 105 and the metal plate 107 are overlapped. The upper movable electrode 101 and the lower fixed electrode 103 pass an electric current while pressing the metal plate 105 and the metal plate 107. Due to the resistance heat generated at the contact surface between the metal plate 105 and the metal plate 107, the metal plate 105 and the metal plate 107 are welded. The welded portion of the welding is called a nugget. In FIG. 1, two metal plates are depicted, but three or more metal plates may be used.

[0027] The amount by which the upper movable electrode 101 is pushed in after contacting the metal plate 105 is called the stroke. The stroke is measured by the upper movable electrode 101. The pressing force is measured by the lower fixed electrode 103. Also, the current value and the voltage value of the current flowing between the upper and lower electrodes during welding are measured. A processing device (not shown) such as a computer calculates the diameter of the nugget using these measured values.

[0028] (Explanation of a method for calculating the diameter of a nugget according to an embodiment) Figure 2 is a diagram showing the amount of expansion calculated from the stroke between the electrodes and the applied pressure. The graph on the left side of Figure 2 shows the time changes in the stroke and the applied pressure. The graph on the right side of Figure 2 shows the amount of expansion calculated from the measured values of the stroke and the applied pressure. Figure 3 is a diagram showing the calculation of the diameter of the slug by combining the maximum value or the time integral value of the amount of expansion and the change in resistance. The graph on the left side of Figure 3 is a graph showing the time changes in the current, resistance, and amount of expansion. The graph on the right side of Figure 3 plots the estimated value of the slug diameter and the measured value of the slug diameter. Figure 4 is a diagram showing the calculation of the diameter of the slug when there is a disturbance. Figure 5 is a diagram showing the quality determination of the diameter of the slug. With reference to Figures 2 to 5, a method for calculating the diameter of the slug according to the embodiment will be described.

[0029] First, a method for calculating the amount of expansion of the metal plate will be described. The amount of expansion is obtained by the following formula (1). E = S + a×F ···(1) Here, E is the amount of expansion, S is the stroke, a is the strain conversion coefficient, and F is the applied pressure. The strain conversion coefficient a is a coefficient for converting the applied pressure into the strain amount and can be an arbitrary constant.

[0030] By using the stroke measured by the upper movable electrode 101 and the applied pressure measured by the lower fixed electrode 103 in this way, the amount of expansion can be calculated more accurately independently.

[0031] As shown in Figure 2, the amount of expansion was obtained from the stroke and the applied pressure using a sample without a gap and a sample with a gap. The ideal sample without a gap is shown by a solid black line, and the sample with a gap is shown by a solid gray line. The sample with a gap is said to have a so-called disturbance. Here, the strain conversion coefficient was set to 0.00048.

[0032] Next, a method for calculating the diameter of the slug will be described. The diameter of the slug can be calculated by the following formula (2) or (3). NI = C1×ΔR + C2×Emax + C4 ···(2) Or

Equation

[0033] As described above, the diameter of the nugget is calculated using the change amount of the resistance waveform and the maximum value of the expansion amount or the integrated expansion amount of the expansion amount waveform. The threshold value T in the left three figures of FIG. 3 is a predetermined value of the energization time to which the calculation method of the present disclosure can be applied. When it is below the threshold value, the method for calculating the diameter of the nugget of the present disclosure cannot be applied because it deviates from the actual measurement. Here, the threshold value follows 40% of the total energization time, but it is not limited thereto, and the threshold value also varies depending on the welding conditions.

[0034] The result of calculating the diameter of the nugget by ending the welding at the time indicated by the dotted line above the threshold value T in the left three figures of FIG. 3 is shown in the right figure of FIG. 3. The formula for calculating the diameter of the nugget is expressed as NI = 55.10×ΔR + 8526×Emax + 2.284 using (2).

[0035] The black solid line in the left figure of FIG. 3 is an ideal sample without a gap, and the gray solid line is a sample with a gap. As shown in the right figure of FIG. 3, for the ideal sample without a gap, the diameter of the nugget increases as the welding time increases from the initial stage to the final stage. The calculated estimated nugget diameter is shown by a straight line with a slope of 1 with the measured nugget diameter. The plot of the estimated nugget diameter and the measured nugget diameter falls between the straight lines drawn with at least ±20% of the upper and lower limits of the error.

[0036] For a sample with disturbances such as a gap, the diameter of the nugget also increases as the welding time increases. Also, the calculated estimated nugget diameter of the sample with a gap is shown by a straight line with a slope of 1 with the measured nugget diameter and falls between the straight lines drawn with at least ±20%.

[0037] Figure 4 is a diagram showing the calculation of the diameter of the nail when there is interference. Figure 4 shows the diameter of the nail when there are interferences of depression and face misalignment. Depression refers to the case where the upper movable electrode 101 is pushed in. Face misalignment refers to the case where the upper movable electrode 101 does not hit the metal plate vertically. In either case, the calculated estimated nail diameter is shown by a straight line with a slope of 1 from the actually measured nail diameter and falls between the straight lines drawn with at least ±20%. Therefore, it can be seen that the formula for calculating the diameter of the nail of the present disclosure can cope with interference.

[0038] Figure 5 is a diagram showing the quality determination of the diameter of the nail according to the embodiment. The upper left figure in Figure 5 shows the current value, the upper middle figure shows the resistance, and the lower left figure shows the calculated expansion amount. As shown in the lower left figure, in each of the three examples, sputtering occurred, so welding could only be performed up to a certain point. When sputtering occurs, the expansion amount and resistance drop rapidly, and the amount of change in resistance also changes rapidly. Therefore, the method for calculating the diameter of the nail cannot be applied even if the current value, voltage value, stroke, and pressing force are measured further.

[0039] Therefore, the diameter of the nail was calculated using the amount of change in resistance and the expansion amount immediately before sputtering occurred. The result is shown in the right figure of Figure 5. Assuming that the lower limit value of quality is 3√t, the pass judgment threshold value is set to 3.6√t considering an error of 20%. When the samples are numbered 1, 2, and 3 from the left in the lower left figure of Figure 5, it can be calculated that sample 1 is 3.9√t, sample 2 is 3.9√t, and sample 3 is 4.1√t. All of them exceed the pass judgment threshold value, indicating that they are good products.

[0040] Actually, when cross-sectional photographs of the samples were taken, sample 1 was 4.3√t, sample 2 was 4.4√t, and sample 3 was 5.5√t. Therefore, it was found that all of them exceeded the calculated values and were good products. Thus, it can be seen that even when sputtering occurs, the diameter of the nail can be calculated by using the amount of change in resistance and the expansion amount immediately before.

[0041] (Explanation of the method for calculating the diameter of the nail at the time of sputtering occurrence according to the embodiment and performing pass judgment) FIG. 6 is a diagram for calculating the diameter of the spatters generated during the sputtering according to the embodiment. FIG. 7 is a flowchart for calculating the diameter of the spatters generated during the sputtering according to the embodiment and determining whether the product is good or not. A method for calculating the diameter of the spatters generated during the sputtering according to the embodiment and determining whether the product is good or not will be described with reference to FIGS. 6 and 7.

[0042] As shown in the upper diagram of FIG. 6, it is assumed that sputtering occurs at a value equal to or higher than the threshold value T. The threshold value T can be determined from experiments, for example, 40% of the total energization time. The estimated taget diameter NI is compared with a good product determination threshold value I, which is a predetermined value. When the estimated taget diameter NI exceeds the good product determination threshold value I, the welded product is regarded as a good product. The good product determination threshold value I is represented by the following formula (4). I≧Ndm×(100+X) / 100···(4) Here, Ndm is the lower limit value of the taget diameter quality, and X is the estimation error.

[0043] As shown in the lower diagram of FIG. 6, it is possible to determine whether the welded product is a good product or not based on whether the diameter of the taget estimated from the resistance waveform and the expansion amount waveform immediately before the spatters occur exceeds the good product determination threshold value I, that is, whether it is equal to or greater than a predetermined value.

[0044] As shown in FIG. 7, first, sputtering occurs (step S701). In resistance spot welding, sputtering may occur. In that case, this flowchart is executed. Then, it is determined whether the sputtering occurred before the threshold value T (step S702). When the sputtering occurred before the threshold value T at which the formulas (2) and (3) can be applied (in the case of YES in step S702), a taget inspection is performed (step S703). The taget inspection is an inspection for determining the quality of the welded part. When the sputtering occurred after the threshold value T (in the case of NO in step S702), the diameter of the taget is calculated from the waveforms immediately before the sputtering occurred (step S704). The waveforms used are the resistance waveform and the expansion amount waveform. The resistance waveform is calculated from the current value and the voltage value, and the expansion amount waveform is calculated from the stroke between the electrodes and the applied pressure.

[0045] After calculating the diameter of the splash, it is determined whether the diameter of the splash is smaller than the acceptable product determination threshold I (step S705). The acceptable product determination threshold I is the above-described predetermined value obtained from the quality lower limit value and the estimation error. If it is smaller than the acceptable product determination threshold I (in the case of YES in step S705), a tagane inspection is performed (step S706). If it is larger than the acceptable product determination threshold I (in the case of NO in step S705), it is determined that it is a good product and the process ends (step 707).

[0046] In this way, when sputtering occurs, it is possible to provide a method for determining the quality of resistance spot welding that calculates the diameter of the splash using the measurement results of the stroke, current value, voltage value, and applied pressure immediately before sputtering occurs. Therefore, an extra tagane inspection can be omitted.

[0047] (Explanation of an example of applying the energization pattern according to the embodiment to the method for calculating the diameter of the splash) FIG. 8 is a diagram showing the difference between the related energization pattern and the energization pattern according to the embodiment. FIG. 9 is a flowchart of applying the method for calculating the diameter of the splash to the energization pattern according to the embodiment. An example of applying the energization pattern according to the embodiment to the method for calculating the diameter of the splash will be described with reference to FIGS. 8 and 9.

[0048] The left diagram of FIG. 8 shows the related multi-stage energization pattern. At this time, the probability of sputtering occurring before the threshold T was 74%. The average sputtering timing was 200 ms. On the other hand, the right diagram of FIG. 8 shows the multi-stage energization pattern of the present disclosure. When energized with such an energization pattern, the probability of sputtering occurring before the threshold T was 0%. The average sputtering timing was 370 ms.

[0049] Therefore, the energization pattern of the present disclosure delays the sputtering timing, and when combined with the method for calculating the diameter of the splash of the present disclosure, it becomes possible to substantially calculate the diameter of the splash.

[0050] As shown in Fig. 9, this energization pattern first energizes at a low first current value as the first step (step S901). That is, in the first step, a constant current value is supplied to the electrodes. Next, as the second step, it energizes with a sinusoidal current higher than the first current value (step S902). A sinusoidal current higher than the first current value means a sinusoidal wave whose minimum value in the sinusoidal wave is higher than the first current value. Then, as the third step, it energizes while gradually increasing the current value from the center of the amplitude of the sinusoidal wave (step S903). In Fig. 8, the current value is increasing linearly. Finally, as the calculation step, the diameter of the nugget is calculated (step S904). The diameter of the nugget is calculated by calculating the current value and the voltage value from the energization conditions from step 901 to step S903.

[0051] By combining the method of calculating the diameter of the nugget with the above energization pattern, a welding method capable of calculating the diameter of the nugget can be provided.

[0052] Note that the present disclosure is not limited to the above embodiments, and can be appropriately changed without departing from the gist. For example, in resistance spot welding, the upper part is a movable electrode and the lower part is a fixed electrode, but the upper part may be a fixed electrode and the lower part may be a movable electrode.

Explanation of Reference Numerals

[0053] 100 Resistance spot welding system 101 Upper movable electrode 103 Lower fixed electrode 105 Metal plate 107 Metal plate

Claims

1. A method for calculating the diameter of a nugget in resistance spot welding, which welds a plurality of stacked plate-shaped welding materials by sandwiching them between a pair of electrodes in the stacking direction and applying pressure while passing an electric current, comprising: calculating a resistance waveform from the current value and voltage value between the pair of electrodes; calculating a dilation amount waveform from the applied pressure and stroke between the pair of electrodes; wherein the dilation amount waveform is calculated by E = S + a×F... (1), where E is the dilation amount, S is the stroke, a is the strain amount conversion coefficient, and F is the applied pressure; calculating the diameter of the nugget using the change amount of the resistance waveform and the maximum dilation amount value of the dilation amount waveform or the dilation amount integral value obtained by integrating the dilation amount over time.

2. The diameter of the nugget is calculated by the formula NI = C1×ΔR + C2×Emax + C4... (2) or NI = C3×∫E dt + C4... (3) 【Number 3】 where NI is the diameter of the nugget, ΔR is the change amount of the resistance waveform, Emax is the maximum dilation amount value, ∫E dt is the dilation amount integral value obtained by integrating the dilation amount over time, and C1, C2, C3, C4 are constants. The method for calculating the diameter of the nugget according to Claim 1. 【Number】

3. The formulas (2) and (3) are applicable when the energization time is equal to or greater than a predetermined value. The method for calculating the diameter of the nugget according to Claim 2.

4. A method for determining whether a welded product of the resistance spot welding is a good product, comprising: calculating the diameter of the nugget by the method for calculating the diameter of the nugget according to any one of Claims 1 to 3; comparing the calculated diameter of the nugget with a predetermined value to determine whether the welded product of the resistance spot welding is a good product; and when spatter occurs in the resistance spot welding, calculating the diameter of the nugget using the measurement results of the stroke, current value, voltage value, and applied pressure immediately before the spatter occurs.

5. a first step of energizing between the pair of electrodes with a first current value; a second step of energizing between the pair of electrodes with a sinusoidal current higher than the first current value; a third step of energizing between the pair of electrodes while gradually increasing the current value from the center of the amplitude of the sinusoidal wave; and a calculation step of calculating the diameter of the nugget by the method for calculating the diameter of the nugget according to any one of Claims 1 to 3. In the calculating step, a welding method for calculating the diameter of the nugget using the measurement results of the stroke, current value, voltage value, and pressing force from the first step to the third step.

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