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

Abstract

The present invention provides a method for calculating a nugget diameter, which calculates a nugget diameter of resistance spot welding that is performed by pressing a plurality of plate-shaped welding materials (105, 107) by sandwiching the plurality of plate-shaped welding materials from a direction of overlap between a pair of electrodes (101, 103) while flowing a current, in the method for calculating the nugget diameter, a stroke between the pair of electrodes, a current value, a voltage value, and a pressing force are measured, and the nugget diameter is calculated using the measured results.

Description

Technical Field

[0001] This disclosure relates to a method for calculating the diameter of the weld nugget, a method for judging the quality of resistance spot welding, and a welding method. Background Technology

[0002] In resistance spot welding, a method has been developed to ensure good quality even when spatter or splatter occurs. International Publication No. 2016 / 174842 describes a method that uses the time-varying curve of the instantaneous heat generation per unit volume and the cumulative heat generation, stored as target values ​​in each step of a test weld, as a reference for welding. If, in any step, the time-varying amount of the instantaneous heat generation per unit volume deviates from the reference time-varying curve, this deviation is compensated for during the remaining energizing time of that step. Therefore, the energizing current is controlled so that the cumulative heat generation per unit volume in the actual weld matches the cumulative heat generation per unit volume predetermined in the test weld. Furthermore, if spatter is detected in any step, the target value of the cumulative heat generation per unit volume is reduced thereafter, and the energizing current is controlled accordingly. Summary of the Invention

[0003] In the aforementioned literature, the target value for adaptive control was corrected after spatter occurred, but the size of the weld, i.e., the weld nugget diameter, could not be estimated when spatter or sputtering occurred. Therefore, the object of this disclosure is to provide a method for calculating the weld nugget diameter by measuring the electrode travel, current value, voltage value, and applied pressure during welding.

[0004] The method disclosed herein for calculating the weld nugget diameter is a method for calculating the weld nugget diameter in resistance spot welding, which involves welding multiple overlapping plate-shaped welding materials by applying pressure and simultaneously flowing current between a pair of electrodes in the overlapping direction. In this calculation method, The diameter of the melt core is calculated using the measured results of the stroke, current, voltage, and applied pressure between the aforementioned pair of electrodes.

[0005] By measuring the stroke, current, voltage, and pressure applied between electrodes during welding, the diameter of the weld nugget can be calculated.

[0006] Furthermore, the method for calculating the diameter of the melt nugget disclosed herein is characterized in that... The resistance waveform is calculated based on the current and voltage values ​​between the aforementioned pair of electrodes. The expansion waveform is calculated based on the applied pressure and stroke between the aforementioned pair of electrodes. The diameter of the molten core is calculated using the aforementioned resistance waveform and the aforementioned expansion waveform.

[0007] The resistance waveform is calculated based on the current and voltage values, and the expansion waveform is calculated based on the applied pressure and stroke. By using these waveforms, the diameter of the molten core can be calculated.

[0008] Furthermore, the method for calculating the diameter of the melt nugget disclosed herein is characterized in that... The aforementioned expansion waveform is calculated using the following equation (1): E=S+a×F…(1) Where E is the expansion amount, S is the stroke, a is the deformation transformation coefficient, and F is the applied pressure.

[0009] The expansion waveform can be calculated using equation (1) with stroke and applied pressure as variables.

[0010] Furthermore, the method for calculating the diameter of the melt nugget disclosed herein is characterized in that... The diameter of the melt core can be calculated using the change in the aforementioned resistance waveform, the maximum value of the aforementioned expansion waveform, or the integral value of the expansion obtained by integrating the aforementioned expansion over time.

[0011] The diameter of the melt core can be calculated using the change in resistance waveform and the maximum value of expansion waveform or the integral value of expansion obtained by integrating the expansion over time.

[0012] Furthermore, the method for calculating the diameter of the melt nugget disclosed herein is characterized in that... The aforementioned molten core diameter is calculated using either equation (2) or equation (3): NI=C1×ΔR+C2×Emax+C4…(2), NI=C1×ΔR+C2×∫E+C4…(3), Where NI is the diameter of the melt core, ΔR is the change in the aforementioned resistance waveform, Emax is the maximum value of the aforementioned expansion, ∫E is the integral value of the expansion obtained by integrating the aforementioned expansion over time, and C1, C2, C3, and C4 are constants.

[0013] The diameter of the molten core can be calculated using the change in the resistance waveform, the maximum value of the expansion, or the integral value of the expansion obtained by integrating the expansion over time, and then using the above formula.

[0014] Furthermore, the method for calculating the diameter of the melt nugget disclosed herein is characterized in that... Equations (2) and (3) above apply to cases where the energizing time is above a specified value.

[0015] When the energizing time is above the threshold value specified above, equations (2) and (3) above can be applied.

[0016] In addition, the method for judging the quality of resistance spot welding disclosed herein includes: The step of calculating the aforementioned melt core diameter using the method described in any of the above technical solutions; and The process of determining whether a resistance spot weld is a good product involves comparing the calculated weld nugget diameter with a specified value. In the case of sputtering occurring during the aforementioned resistance spot welding, the aforementioned weld nugget diameter is calculated using the measured results of the aforementioned stroke, current value, voltage value, and applied pressure prior to the impending sputtering.

[0017] A method for judging the quality of resistance spot welding is provided, which calculates the weld nugget diameter by using the measured results of the stroke, current value, voltage value and pressure before the sputtering occurs.

[0018] The welding method disclosed herein has the following features: The first step of applying a first current value between a pair of electrodes; The second step is to apply a sinusoidal current higher than the first current value between the aforementioned pair of electrodes. The third step is to gradually increase the current value from the center of the amplitude of the aforementioned sine wave to energize the pair of electrodes; and The calculation steps for the aforementioned melt core diameter are derived using the method described in any of the above technical solutions. In the aforementioned calculation step, the aforementioned melt core diameter is calculated using the measured results of the aforementioned stroke, current value, voltage value, and applied pressure from the first to the third steps.

[0019] By combining the method for calculating the weld nugget diameter with the aforementioned energizing mode, a welding method capable of calculating the weld nugget diameter can be provided.

[0020] According to this disclosure, a method can be provided to calculate the diameter of the weld nugget by measuring the stroke, current value, voltage value, and pressure applied between electrodes during welding. Attached Figure Description

[0021] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements. Figure 1 This is a schematic diagram of the resistance spot welding involved in the implementation method. Figure 2 The expansion amount was calculated based on the stroke between the electrodes and the applied pressure. Figure 3 The diagram shows how the diameter of the molten core is calculated by combining the maximum value of the expansion or the integral value over time with the change in resistance. Figure 4 This is a diagram showing the calculated diameter of the molten core under the presence of interference. Figure 5 This is a diagram showing the quality assessment of the melt core diameter. Figure 6 This diagram shows the diameter of the molten core calculated during sputtering. Figure 7 This is a flowchart for calculating the diameter of the melt nugget and determining the quality of the product when sputtering occurs. Figure 8 This is a diagram illustrating the differences between the relevant power-on modes and the power-on modes involved in the implementation method. Figure 9 This is a flowchart of a method for calculating the diameter of the molten core applicable to the energizing mode involved in the implementation method. Detailed Implementation

[0022] Implementation Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, the technical solutions covered by the claims are not limited to the following embodiments. Furthermore, the configurations described in the embodiments are not necessarily all indispensable as technical means for solving the technical problems. For clarity, the following descriptions and drawings have been appropriately omitted and simplified. In the drawings, the same reference numerals are used to label the same elements, and repeated descriptions are omitted as necessary.

[0023] (Description of resistance spot welding involved in the implementation method) Figure 1 This is a schematic diagram of the resistance spot welding method described in the implementation embodiment. (Refer to...) Figure 1 The method of resistance spot welding involved in the implementation is explained.

[0024] like Figure 1 As shown, the resistance spot welding system 100 according to the embodiment includes an upper movable electrode 101 and a lower fixed electrode 103 as a pair of electrodes. Metal plates 105 and 107 to be welded are stacked between the upper movable electrode 101 and the lower fixed electrode 103. Furthermore, the movable electrode and the fixed electrode can also be reversed. The metal plates 105 and 107 are multiple plate-shaped welding materials stacked vertically.

[0025] The upper movable electrode 101 moves up and down as indicated by the arrow to apply pressure to metal plates 105 and 107. The upper movable electrode 101 and the lower fixed electrode 103 clamp metal plates 105 and 107 from the direction where they overlap. The upper movable electrode 101 and the lower fixed electrode 103 apply pressure to metal plates 105 and 107 while simultaneously allowing current to flow. Metal plates 105 and 107 are welded together by the resistance heat generated at the contact surface. The welded portion is called a weld nugget. Figure 1In the illustration, the metal plates are depicted as two pieces, but there can also be three or more pieces.

[0026] The amount by which the upper movable electrode 101 is pressed in from the point of contact with the metal plate 105 is called the stroke. The stroke is measured using the upper movable electrode 101. The applied pressure is measured using the lower fixed electrode 103. In addition, the current and voltage values ​​of the current flowing between the upper and lower electrodes during welding are measured. A processing device such as a computer (not shown) uses these measured values ​​to calculate the weld nugget diameter.

[0027] (Explanation of the method for calculating the diameter of the melt core involved in the implementation) Figure 2 The expansion amount was calculated based on the stroke between the electrodes and the applied pressure. Figure 2 The chart on the left shows the changes in travel and pressure over time. Figure 2 The chart on the right shows the expansion calculated based on the measured values ​​of stroke and applied pressure. Figure 3 The diagram shows how the diameter of the molten core is calculated by combining the maximum value of the expansion or the integral value over time with the change in resistance. Figure 3 The graph on the left shows the changes in current, resistance, and expansion over time. Figure 3 The chart on the right plots the estimated and measured values ​​of the melt core diameter. Figure 4 This is a diagram showing the calculated diameter of the molten core under the presence of interference. Figure 5 This is a diagram showing the quality assessment of the melt core diameter. (Refer to...) Figures 2 to 5 The method for calculating the diameter of the melt core involved in the implementation method will be explained.

[0028] First, the method for calculating the expansion of the metal plate will be explained. The expansion is calculated using the following formula (1). E=S+a×F…(1) Here, E is the expansion amount, S is the stroke, a is the deformation transformation coefficient, and F is the applied pressure. The deformation transformation coefficient 'a' is the coefficient that transforms the applied pressure into deformation, and can be set to any constant.

[0029] 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 expansion amount can be calculated with better accuracy compared to the case where they are calculated separately.

[0030] like Figure 2 As shown, the expansion was calculated based on stroke and applied pressure using both gapless and gapped samples. The ideal gapless sample is shown as a solid black line, while the gapped sample is shown as a solid gray line. The gapped sample is considered to have interference. Here, the deformation transformation coefficient was set to 0.00048.

[0031] Next, the method for calculating the diameter of the melt core will be explained. The diameter of the melt core can be calculated using the following formula (2) or (3). NI=C1×ΔR+C2×Emax+C4…(2), NI=C1×ΔR+C3×∫E+C4…(3), Here, NI is the diameter of the melt core, ΔR is the change in resistance waveform, and Emax is the maximum value of the expansion. ∫E is the integral value of the expansion obtained by integrating the expansion over time, and C1, C2, C3, and C4 are constants.

[0032] As mentioned above, the diameter of the melt core is calculated using the change in the resistance waveform and the maximum value of the expansion waveform or the time integral of the expansion. Figure 3 The threshold T in Figure 3 on the left is a specified value for the energizing time for which the calculation method of this disclosure is applicable. Below this threshold, the calculation method for the weld nugget diameter deviates from actual measurements and is therefore inapplicable. Here, the threshold is set to 40% of the total energizing time, but it is not limited to this; the threshold varies depending on the welding conditions.

[0033] In Figure 3 The results of calculating the weld nugget diameter, shown by the dotted lines above the threshold T in the three figures on the left, are presented below. Figure 3 The right figure shows the formula for calculating the diameter of the melt core, which is (2), and is given as NI = 55.10 × ΔR + 8526 × Emax + 2.284.

[0034] Figure 3 In the left image, the black solid line represents an ideal sample without gaps, while the gray solid line represents a sample with gaps. (Example:) Figure 3 As shown in the right figure, for an ideal sample with no gap, the longer the welding time from the beginning to the end, the larger the weld nugget diameter. The calculated estimated weld nugget diameter is shown as a straight line with a slope of 1 relative to the measured weld nugget diameter. The plots of the estimated and measured weld nugget diameters fall between straight lines drawn with upper and lower limits of error of at least ±20%.

[0035] For samples with interference such as gaps, the longer the welding time, the larger the weld nugget diameter. Furthermore, the calculated estimated weld nugget diameter for samples with gaps is shown as a straight line with a slope of 1 relative to the measured weld nugget diameter, falling within a straight line drawn at least ±20%.

[0036] Figure 4 This is a diagram showing the calculated diameter of the molten core under the presence of interference. Figure 4The diagram shows the weld nugget diameter when interferences such as downward pushing and deviation from the perpendicular surface are present. Downward pushing refers to the case where the upper movable electrode 101 is pressed in. Deviation from the perpendicular surface refers to the case where the upper movable electrode 101 is not perpendicularly in contact with the metal plate. In either case, the calculated estimated weld nugget diameter is shown as a straight line with a slope of 1 relative to the measured weld nugget diameter, falling within the range of straight lines drawn at least ±20%. Therefore, it can be seen that the formula for calculating the weld nugget diameter in this disclosure addresses the interferences.

[0037] Figure 5 This is a diagram showing the quality determination of the melt core diameter involved in the implementation method. Figure 5 The top left figure shows the current value, the middle left figure shows the resistance, and the bottom left figure shows the calculated expansion. As shown in the bottom left figure, sputtering occurred in all three embodiments, so welding could only be stopped halfway through. When sputtering occurs, the expansion and resistance drop sharply, and the change in resistance also changes drastically. Therefore, even if the current, voltage, stroke, and pressure are continuously measured, the method for calculating the weld nugget diameter cannot be applied.

[0038] Therefore, the diameter of the melt nugget is calculated using the resistance change and expansion prior to sputtering. The results are shown below. Figure 5 The right image shows the lower limit of quality. The threshold for judging good products is then set to account for a 20% error. t. If from Figure 5 Starting from the left side of the lower left figure, the samples are numbered 1, 2, and 3 sequentially. Sample 1 is calculated as... Sample 2 was calculated as Sample 3 was calculated as All of them exceeded the threshold for judging good products, indicating that they are all good products.

[0039] In fact, cross-sectional photographs of the samples were taken; sample 1 was... Sample 2 is Sample 3 is Therefore, it can be concluded that all values ​​exceeded the calculated values, indicating that all products are of good quality. Thus, it can be concluded that even in the case of sputtering, the diameter of the melt nugget can be calculated by using the resistance change and expansion before the process begins.

[0040] (Description of the method for calculating the weld nugget diameter and determining the quality of the product during sputtering as described in the embodiments) Figure 6 It is a diagram in which the diameter of the melt core is calculated when sputtering occurs as described in the implementation method. Figure 7 This is a flowchart illustrating the calculation of the melt core diameter and the determination of good product quality during sputtering, as described in the implementation method. (Refer to...) Figure 6 and Figure 7 The method for calculating the diameter of the melt nugget when sputtering occurs and determining the quality of the product, as described in the implementation method, will be explained.

[0041] like Figure 6 As shown in the figure above, sputtering occurs when the threshold T is above the threshold. The threshold T can be, for example, 40% of the total energizing time, and is determined experimentally. The weld nugget diameter NI is estimated to be greater than the good product judgment threshold I, and if it exceeds the good product judgment threshold I, the weld is considered to be good. The good product judgment threshold I is expressed by the following equation (4). I≧Ndm×(100+X) / 100…(4) Here, Ndm is the lower limit of the melt core diameter quality, and X is the estimated error.

[0042] like Figure 6 As shown in the figure below, the welded product can be judged as good by using the resistance waveform and expansion waveform up to the moment sputtering occurs to estimate whether the weld nugget diameter exceeds the good product judgment threshold I, that is, whether it is above the specified value.

[0043] like Figure 7 As shown, first, sputtering occurs (step S701). Sputtering sometimes occurs in resistance spot welding. In this case, the flowchart is executed. Then, it is determined whether it occurred before the threshold T (step S702). If sputtering occurred before the threshold T for which equations (2) and (3) are applicable (if step S702 is yes), a chisel inspection is performed (step S703). The chisel inspection is an inspection to determine the quality of the weld. If sputtering occurred after the threshold T (if step S702 is no), the weld nugget diameter is calculated using the waveform up to just before sputtering occurs (step S704). The waveforms used are the resistance waveform and the expansion waveform. The resistance waveform is calculated based on the current and voltage values, and the expansion waveform is calculated based on the travel and pressure between the electrodes.

[0044] After calculating the weld nugget diameter, it is determined whether the weld nugget diameter is smaller than the good product judgment threshold I (step S705). The good product judgment threshold I is the aforementioned specified value calculated based on the lower quality limit and the estimated error. If it is smaller than the good product judgment threshold I (if yes in step S705), a chisel inspection is performed (step S706). If it is larger than the good product judgment threshold I (if no in step S705), it is determined to be a good product and the process ends (step S707).

[0045] This provides a method for judging the quality of resistance spot welding, which calculates the weld nugget diameter using measurements of the stroke, current, voltage, and pressure applied before sputtering occurs. Therefore, additional chisel inspection can be omitted.

[0046] (Example of applying the energizing mode described in the implementation method to the method for calculating the diameter of the molten core) Figure 8 This is a diagram illustrating the differences between the relevant power-on modes and the power-on modes involved in the implementation method. Figure 9 This is a flowchart illustrating a method for calculating the molten core diameter applicable to the energizing mode involved in the embodiment. (Refer to...) Figure 8 and Figure 9 An example of applying the energizing mode involved in the implementation method to the calculation method of the melting core diameter will be explained.

[0047] The relevant multi-segment power-on modes are shown in Figure 8 The left figure shows the probability of sputtering occurring before the threshold T is 74%. The average sputtering time is 200 ms. On the other hand, the multi-segment power-on mode of this disclosure is shown in... Figure 8 The right figure shows the power-on mode. With this power-on mode applied, the probability of sputtering occurring before the threshold T is 0%. The average sputtering time is 370 ms.

[0048] Therefore, regarding the energizing mode of this disclosure, which delays the sputtering time, if combined with the method for calculating the melt core diameter of this disclosure, the melt core diameter can be roughly calculated.

[0049] like Figure 9 As shown, regarding this energizing mode, firstly, as a first step, energizing is performed with a low first current value (step S901). That is, in the first step, a constant current value is supplied to the electrodes. Next, as a second step, energizing is performed with a sinusoidal current that is higher than the first current value (step S902). A sinusoidal current higher than the first current value means a sinusoidal wave whose minimum value is higher than the first current value. Then, as a third step, energizing is performed by gradually increasing the current value from the center of the amplitude of the sinusoidal wave (step S903). Figure 8 During the process, the current value increases linearly. Finally, as a calculation step, the diameter of the molten core is calculated (step S904). The diameter of the molten core is calculated based on the current and voltage values ​​obtained from the energizing conditions in steps 901 to S903.

[0050] By combining the method for calculating the weld nugget diameter with the aforementioned energizing mode, a welding method capable of calculating the weld nugget diameter can be provided.

[0051] Furthermore, this disclosure is not limited to the above-described embodiments, and appropriate modifications can be made without departing from the spirit of the invention. For example, in resistance spot welding, the upper part can be a movable electrode and the lower part a fixed electrode, but the upper part can also be a fixed electrode and the lower part a movable electrode.

Claims

1. A method for calculating the weld nugget diameter, wherein the weld nugget diameter for resistance spot welding is calculated by applying pressure and simultaneously flowing current to weld multiple overlapping plate-shaped welding materials between a pair of electrodes from the overlapping direction, wherein in the calculation method, The resistance waveform is calculated based on the current and voltage values ​​between the pair of electrodes. The expansion waveform is calculated based on the applied pressure and stroke between the pair of electrodes. The expansion waveform is calculated using the following formula (1): E=S+a×F･･･(1) in, E is the expansion amount, S is the stroke, a is the deformation transformation coefficient, and F is the applied pressure. The diameter of the melt core is calculated using the change in the resistance waveform and the maximum value of the expansion waveform, or the integral value of the expansion obtained by integrating the expansion over time. The diameter of the melting core is calculated using either equation (2) or equation (3): NI=C1×ΔR+C2×Emax+C4･･･(2), ･･･（3）， Wherein, NI is the diameter of the melt core, ΔR is the change in the resistance waveform, and Emax is the maximum value of the expansion. The integral value of the expansion is obtained by integrating the expansion over time, and C1, C2, C3, and C4 are constants.

2. The method for calculating the diameter of the melt core according to claim 1, wherein, Equations (2) and (3) are applicable to situations where the energizing time is above a specified value.

3. A method for judging the quality of resistance spot welds, comprising: The step of calculating the diameter of the melt core using the method for calculating the melt core diameter according to claim 1 or 2; and The step of determining whether the resistance spot welded product is a good product is to compare the calculated weld nugget diameter with a specified value. In the event of sputtering during resistance spot welding, the diameter of the weld nugget is calculated using the measurements of the stroke, current, voltage, and applied pressure prior to the occurrence of the sputtering.

4. A welding method, comprising: The first step of applying a first current value between a pair of electrodes; The second step is to apply a sinusoidal current higher than the first current value between the two electrodes. The third step of gradually increasing the current value from the center of the amplitude of the sine wave to energize the pair of electrodes; and The calculation step of the melt core diameter is obtained by using the method for calculating the melt core diameter as described in claim 1 or 2. In the calculation step, the diameter of the melt core is calculated using the measured results of the stroke, current value, voltage value, and applied pressure from the first to the third steps.

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