QUALITY INSPECTION DEVICE, RESISTANCE SPOT WELDING SYSTEM, QUALITY INSPECTION PROGRAM, AND QUALITY INSPECTION METHOD

Abstract

To inspect weld quality with high accuracy even if dust occurs in resistance spot welding.SOLUTION: A quality inspection device for resistance spot welding in which energization is performed between a pair of electrodes sandwiching a welded material formed by multiple overlapping metal materials to melt and join the metal materials, includes: a measurement part which measures a voltage and a welding current during welding; a calculation part which calculates electric resistance based on the voltage and the welding current; and a nugget diameter calculation part which calculates a nugget diameter of a welding part obtained after welding based on the electric resistance.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a quality inspection device, a resistance spot welding system, a quality inspection program, and a quality inspection method. [Background technology]

[0002] Resistance spot welding is a highly efficient joining technique that is widely used by automakers and other manufacturers. The strength of a spot welded joint is closely related to the nugget diameter, which is the diameter of the weld metal formed inside the joint after welding. However, the nugget diameter cannot be directly observed from the outside of the joint. The nugget diameter is also called the weld diameter.

[0003] A chisel check is commonly used as a quality assurance method for resistance spot welding. In this method, a worker hits the material to be welded with a hammer to check the weld quality. Another quality assurance method for resistance spot welding is ultrasonic measurement.

[0004] Patent Document 1 describes a resistance spot welding apparatus. The resistance spot welding apparatus includes a pair of electrodes that sandwich a workpiece, which is made up of multiple overlapping metal plates. Electric current is passed between the electrodes sandwiching the workpiece to melt and join the metal plates. The resistance spot welding apparatus includes a measurement means, a resistance calculation unit, a master pattern registration unit, and a comparison unit. The measurement means includes a voltage measurement unit that measures the welding voltage and a pressure measurement unit that measures the pressure applied to sandwich the workpiece. The resistance calculation unit calculates the electrical resistance of the workpiece from the welding voltage and welding current measured by the voltage measurement unit. The master pattern registration unit registers, as a master pattern for the actual welding, the values ​​measured by the measurement means and the electrical resistance calculated by the resistance calculation unit when a pre-energization is performed under preset welding conditions to obtain a target weld nugget diameter. The comparison unit calculates a deviation between a measurement value measured by the measurement means during pre-energization and a measurement value measured by the measurement means during main welding, and calculates a deviation between a value of the electrical resistance calculated by the resistance calculation unit during pre-energization and a value of the electrical resistance calculated by the resistance calculation unit during main welding. The resistance spot welding device estimates the weld nugget diameter obtained in main welding based on the deviation calculated by the comparison unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-171942 Summary of the Invention [Problem to be solved by the invention]

[0006] Compared to conventional quality assurance methods, there is a demand for the establishment of technology that can automatically guarantee quality in-line, from the perspective of reducing labor costs and shortening lead times.

[0007] Although the quality assurance methods of the prior art had a certain degree of accuracy in determining the nugget diameter in a steady state, they had problems with the accuracy of determining the nugget diameter when spatter occurred, which is an unsteady state.

[0008] Therefore, an object of the present invention is to provide a quality inspection device, a resistance spot welding device, a quality inspection program, and a quality inspection method that can inspect welding quality with high precision even when spatter occurs during resistance spot welding. [Means for solving the problem]

[0009] The present invention comprises the following configurations. (1) A quality inspection device for resistance spot welding, in which a current is passed between a pair of electrodes that sandwich a workpiece made of overlapping metal materials to melt and join the metal materials, a measuring unit for measuring a voltage and a welding current during welding; a calculation unit that calculates an electrical resistance based on the voltage and the welding current; and a nugget diameter calculation unit that calculates a nugget diameter of a welded portion obtained after welding based on the electrical resistance. Quality inspection equipment. (2) A quality inspection program for resistance spot welding, in which a current is passed between a pair of electrodes that sandwich a workpiece made of overlapping metal materials to melt and join the metal materials, comprising: A quality inspection device having a processor and a memory, A measurement function to measure the voltage and welding current during welding; a calculation function for calculating an electrical resistance based on the voltage and the welding current; a nugget diameter calculation function for estimating a nugget diameter of a welded portion obtained after welding based on the electrical resistance; A quality inspection program that achieves this. (3) Regarding resistance spot welding, in which a current is passed between a pair of electrodes that sandwich the workpieces made of overlapping metal materials to melt and join the metal materials, A quality inspection device having a processor and a memory executes a measuring step of measuring a voltage and a welding current during welding; a calculation step of calculating an electrical resistance based on the voltage and the welding current; and a nugget diameter calculation step of calculating a nugget diameter of a welded portion obtained after welding based on the electrical resistance. Quality inspection methods. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a quality inspection device, a resistance spot welding device, a quality inspection program, and a quality inspection method that can inspect welding quality with high accuracy even when spatter occurs during resistance spot welding. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a welding machine used for resistance spot welding. [Figure 2] 1 is a graph showing a current waveform in resistance spot welding between ultra-high tensile steel sheets. [Figure 3] 10 is a graph showing the accuracy of the predicted nugget diameter according to the first prediction model for resistance spot welding when expulsion occurs. [Figure 4] FIG. 1 is a schematic diagram illustrating a resistance spot welding system. [Figure 5] 10 is a flowchart illustrating an example of processing by the quality inspection device. [Figure 6] 10 is a graph showing the influence of dust generation on measured electrical resistance values. [Figure 7] FIG. 10 is a conceptual diagram illustrating the identification of a location where the electrical resistance suddenly drops. [Figure 8] 10 is a flowchart illustrating a process for calculating the amount of sudden drop in electrical resistance. [Figure 9] 10 is a graph showing the influence of dust on both sound pressure and electrode pressure. [Figure 10]10 is a scatter diagram showing the relationship between the difference between the maximum and minimum values ​​of sound pressure and electrode pressure and the presence or absence of dust. [Figure 11] 10 is a graph showing the accuracy of predicted nugget diameter using the second prediction model for resistance spot welding when expulsion occurs. [Figure 12] 10 is a graph showing the accuracy of the predicted nugget diameter using the second prediction model for resistance spot welding between galvannealed high-tensile steel sheets in the case where expulsion occurs. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0013] FIG. 1 is a schematic diagram of a welding machine used for resistance spot welding.

[0014] Welding machine 100 includes a pair of electrodes 113 and 115, a welding transformer unit 117 connected to the pair of electrodes 113 and 115, a control unit 119 that supplies welding power from a power supply unit 118 to welding transformer unit 117, and an electrode drive unit 120 that axially moves the pair of electrodes 113 and 115. Control unit 119 comprehensively controls the current value, welding time, electrode pressure, current application timing, pressure application timing, etc.

[0015] Welding machine 100 performs resistance spot welding. Welding machine 100 sandwiches multiple overlapping metal workpieces between a pair of electrodes 113 and 115. The metal workpieces are, for example, aluminum, but are not limited to this. In this embodiment, two overlapping sheets of metal material 21 and metal material 23 are resistance spot welded. However, the number of overlapping sheets is not limited to two.

[0016] Welding machine 100 applies current between a pair of sandwiched electrodes 113 and 115 to melt and join the metal materials. Additionally, electrode drive unit 120 drives electrodes 113 and 115 to apply pressure to the workpieces in the thickness direction. In this pressurized state, welding transformer unit 117 applies current between electrodes 113 and 115 based on a command from control unit 119. As a result, nugget 25 is formed between the multiple workpieces sandwiched between electrodes 113 and 115, resulting in a welded joint (joint) in which the multiple workpieces are integrated.

[0017] Each of the pair of electrodes 113 and 115 has a cooling unit inside the electrode. There are no particular limitations on the cooling method of the cooling unit, but in the configuration shown in Fig. 1, cooling pipes are placed in recesses formed in each of the electrodes 113 and 115, and a cooling medium such as water is supplied from the cooling pipes to cool the electrodes 113 and 115.

[0018] The control unit 119 causes the welding transformer unit 117 to apply electricity between the pair of electrodes 113 and 115 at a predetermined timing.

[0019] (Quality inspection of resistance spot welding when spatter occurs using the first prediction model) During resistance spot welding, expulsion may occur. The applicant predicted the nugget diameter during resistance spot welding when expulsion occurred using a first prediction model that uses the time-integrated value of the instantaneous heat generation during welding as a feature value.

[0020] The applicant conducted a quality inspection test on the prediction of nugget diameter by the first prediction model. The following materials to be welded, electrodes, and welding machines were used in the test.

[0021] The non-welded material consisted of two overlapping plates, an upper plate and a lower plate. Both plates were made of ultra-high tensile strength steel. Ultra-high tensile strength steel plates are also known as ultra-high tensile strength steel. The test specimens for the upper and lower plates were 40 mm wide and 125 mm long. The upper and lower plates were overlapped and resistance spot welded.

[0022] The electrodes used were of three types, shapes 1 to 3, as follows. (Shape 1) DR type electrode, φ16mm-6mm, tip R40, chromium copper (Shape 2) R-shaped electrode, φ16 mm, tip R8, chromium copper (Shape 3) R-shaped electrode, φ16 mm, tip R20, chromium copper

[0023] The welding machine used was a DC inverter type.

[0024] Figure 2 is a graph showing the current waveform during resistance spot welding of ultra-high-tensile steel sheets. In the graph, the horizontal axis represents time, and the vertical axis represents welding current or electrode pressure. The unit of welding current is kA, and the unit of electrode pressure is kN.

[0025] The time until the start of current application during pressure is T S The time from the start of current application to the end of current application is T W The time from the end of energization to the end of pressure is T H Let's say.

[0026] Table 1 shows the welding conditions for resistance spot welding in the test.

[0027] [Table 1]

[0028] FIG. 3 is a graph showing the accuracy of the predicted nugget diameter according to the first prediction model for resistance spot welding when expulsion occurs.

[0029] Figure 3 plots an excerpt from a case where the welding current was 12 kA and the target nugget diameter was 6√t (8.5 mm). The horizontal axis of the graph shown in Figure 3 represents the actual nugget diameter obtained by resistance spot welding. The vertical axis of the graph represents the predicted nugget diameter using the first prediction model. The diagonally extending dashed line represents an ideal line (hereinafter referred to as the ideal line) along which the actual nugget diameter obtained by resistance spot welding, which is the measured value, and the predicted nugget diameter using the first prediction model, which is the predicted value, match. When the predicted nugget diameter and the actual nugget diameter match, the points representing the welding results are plotted on this ideal line.

[0030] As can be seen from the graph in FIG. 3, in the case of prediction using the first prediction model, there was a certain degree of deviation between the predicted nugget diameter and the actual nugget diameter.

[0031] Therefore, the inventors have further devised a quality inspection method using a second prediction model, which will be described later, that uses resistance values ​​as feature quantities.

[0032] FIG. 4 is a schematic diagram illustrating a resistance spot welding system.

[0033] Resistance spot welding system 200 includes a quality inspection device 5, a welding machine 3, and a welding control device 1 that controls the welding machine 3. Resistance spot welding system 200 may further include a welding power source 2.

[0034] The welding machine 3 is equipped with a pair of electrodes (not shown). The pair of electrodes holds materials to be welded, which are made of overlapping metal materials. The welding machine 3 performs resistance spot welding by passing current between the pair of electrodes to melt and join the metal materials.

[0035] The welding power source 2 supplies power to a pair of electrodes provided in the welding machine 3 .

[0036] Welding control device 1 controls welding power source 2 and welding machine 3.

[0037] Welding control device 1 includes welding condition selection unit 11, welding current adjustment unit 12, welding time adjustment unit 13, time adjustment unit 14, and electrode pressure adjustment unit 15. Welding control device 1 may further include an input unit and an output unit (not shown). The input unit accepts user input. The output unit outputs information to the user.

[0038] The welding condition selection unit 11 sets welding conditions in response to user input, etc. For example, the welding conditions are T shown in Table 1. S , T W , T H , welding current I, electrode pressure F, plate gap, impact angle, electrode shape, etc. Welding conditions are not limited to these.

[0039] Welding current adjusting unit 12 adjusts the welding current in accordance with the welding conditions set by welding condition selecting unit 11. Welding time adjusting unit 13 adjusts the welding time in accordance with the welding conditions set by welding condition selecting unit 11.

[0040] The time adjusting unit 14 adjusts the squeeze, cool, hold, and other times in accordance with the welding conditions set by the welding condition selecting unit 11.

[0041] Electrode pressure adjusting unit 15 adjusts the electrode pressure applied by the pair of electrodes provided in welding machine 3 in accordance with the welding conditions set by welding condition selecting unit 11.

[0042] The quality inspection device 5 includes a processor 51 and a memory 52. ​​The quality inspection device 5 may further include a measurement device 53, a display device 54, and a communication device 55.

[0043] The processor 51 may include a microprocessing unit (MPU), a central processing unit (CPU), a digital signal processor (DSP), a graphical processing unit (GPU), or the like. The processor 51 may be configured with various integrated circuits (e.g., a large scale integration (LSI) or a field programmable gate array (FPGA)). The processor 51 executes a quality inspection program stored in the memory 52 to realize various functions, such as a calculation unit 511, a feature extraction unit 512, a chip determination unit 513, and a nugget diameter calculation unit 514.

[0044] The calculation unit 511 calculates the electrical resistance based on the voltage and the welding current. The calculation unit 511 may further calculate the instantaneous heat generation amount.

[0045] The feature extraction unit 512 extracts the feature.

[0046] The spatter determination unit 513 determines whether or not spatter occurs during welding.

[0047] The nugget diameter calculation unit 514 calculates the nugget diameter of the welded portion obtained after welding based on the electrical resistance.

[0048] The memory 52 includes a primary storage device (e.g., a random access memory (RAM) or a read only memory (ROM)). The memory 52 may include a secondary storage device (e.g., a hard disk drive (HDD) or a solid state drive (SSD)) or a tertiary storage device (e.g., an optical disk or an SD card). The memory 52 may also be an external storage medium. The memory 52 stores various data, information, programs, etc. The memory 52 stores a quality inspection program.

[0049] The measuring device 53 measures the voltage and welding current during welding. The measuring device 53 may further measure at least one of the electrode pressure and sound pressure of the electrode during welding.

[0050] The display device 54 is an information output device such as a display, and displays the information processed by the processor 51.

[0051] The communication device 55 communicates various data, information, etc. The communication device 55 communicates according to a wired or wireless communication method. The communication method may be a wide area network (WAN), a local area network (LAN), cellular communication for mobile phones (e.g., LTE, 5G), short-range communication (e.g., infrared communication or Bluetooth (registered trademark) communication), power line communication, etc.

[0052] FIG. 5 is a flowchart showing an example of processing by the quality inspection device.

[0053] The measuring device 53 measures various values ​​(St11). The various values ​​refer to the voltage and welding current during welding, etc. The measuring device 53 may further measure at least one of the electrode pressure and sound pressure of the electrode during welding.

[0054] The calculation unit 511 calculates the electrical resistance (St12). The electrical resistance can be calculated based on the voltage and welding current measured in step St11 according to Ohm's law, that is, electrical resistance = voltage / welding current.

[0055] The calculation unit 511 calculates the instantaneous heat generation amount (St13). The instantaneous heat generation amount can be calculated by multiplying the welding current by the voltage.

[0056] The feature extraction unit 512 extracts a feature (St14). More specifically, the feature extraction unit 512 extracts the amount of sudden drop in electrical resistance as the feature. This feature is used to predict the nugget diameter in step St18, which will be described later. A specific extraction algorithm for the amount of sudden drop in electrical resistance will be described later with reference to FIG. 8.

[0057] The feature quantity extraction unit 512 may further extract a time integral value of the electrical resistance and a time integral value of the electrode pressure as feature quantities. Then, the time integral value of the electrical resistance and the time integral value of the electrode pressure may be used as additional feature quantities to predict the nugget diameter in step St18 described below. The time integral value is a time integral value for a time period during welding.

[0058] The spatter determination unit 513 determines whether or not spatter has occurred during welding (St15). The determination of whether or not spatter has occurred will be described in detail later. If spatter has occurred (St16: YES), the process proceeds to step St18. If spatter has not occurred (St16: NO), the process proceeds to step St17.

[0059] In step St17, the nugget diameter calculation unit 514 determines that there is no expulsion and calculates the nugget diameter of the weld obtained after welding. In this case, either the first prediction model using the instantaneous heat generation amount as a feature value or the second prediction model using the electrical resistance as a feature value may be used. That is, if the expulsion determination unit 513 does not detect the occurrence of expulsion (St15: NO), the nugget diameter calculation unit 514 calculates the nugget diameter based on the instantaneous heat generation amount or the electrical resistance.

[0060] In step St18, the nugget diameter calculation unit 514 determines that there is expulsion and calculates the nugget diameter of the weld obtained after welding based on the electrical resistance. Specifically, if the expulsion determination unit 513 detects the occurrence of expulsion (St16: YES), the nugget diameter calculation unit 514 calculates the nugget diameter based on the amount of sudden drop in electrical resistance.

[0061] More specifically, when the spatter determination unit 513 detects the occurrence of spatter (St16: YES), the nugget diameter calculation unit 514 calculates the nugget diameter based on the amount of sudden drop in electrical resistance.

[0062] The nugget diameter calculation unit 514 may calculate the nugget diameter based on the integral value of the electrical resistance and the integral value of the electrode pressure force in addition to the amount of sudden drop in the electrical resistance.

[0063] The display device 54 displays the welding quality (St19). The displayed welding quality may be information indicating the calculated nugget diameter, or information generated based on the nugget diameter.

[0064] (Calculation of nugget diameter when there is a flash) As described above with reference to Fig. 3, in resistance spot welding when expulsion occurs, a certain degree of discrepancy is observed between the nugget diameter predicted by the first prediction model and the actual nugget diameter. Therefore, in an embodiment of the present disclosure, a method for calculating the nugget diameter when expulsion occurs has been further devised.

[0065] Figure 6 is a graph showing the effect of spatter generation on measured electrical resistance. The horizontal axis of the graph represents time, and the vertical axis of the graph represents welding current or resistance.

[0066] As a result of the inventor's diligent research, it was observed that when dust is generated, the electrical resistance drops suddenly. The graph shows three phases P1, P2, and P3 in which the electrical resistance drops suddenly.

[0067] Therefore, the quality inspection device 5 according to one or more embodiments of the present disclosure determines whether or not the value of electrical resistance calculated from the measured values ​​of voltage and welding current has suddenly dropped, and if there is such a sudden drop, determines that expulsion has occurred (step St15), and calculates the nugget diameter assuming the presence of expulsion (step St18). Note that the expulsion determination unit 513 may determine that the value of electrical resistance has suddenly dropped if the amount of sudden drop in electrical resistance, which will be described later, is equal to or greater than a predetermined value.

[0068] (amount of sudden drop in electrical resistance) Fig. 7 is a conceptual diagram illustrating the identification of a location where the electrical resistance suddenly drops. Fig. 8 is a flowchart illustrating the calculation process of the amount of sudden drop in electrical resistance. An example of the calculation process of the amount of sudden drop in electrical resistance will be described with reference to Figs. 7 and 8 together.

[0069] The processor 51 smoothes the measured value of the electrical resistance R (St21), thereby canceling noise contained in the measured value.

[0070] The processor 51 obtains the differential value R' of the electric resistance R (St22). The processor 51 extracts the portion of the electric resistance R where the electric resistance R is decreasing (St23).

[0071] The processor 51 excludes a continuous decrease from the decrease in the electrical resistance R (St24). "Continuous" means, for example, a continuous decrease for 15 milliseconds or more, but 15 milliseconds is merely an example, and other numbers of seconds may be used as the threshold for determining whether or not the decrease is continuous.

[0072] The processor 51 extracts points where the differential value R' of the electrical resistance R is equal to or less than a threshold value from the extracted portion that has not been excluded (St25). For example, assuming that the electrical resistance decreases by 0.0025 mΩ in 5 ms, the electrical resistance is −0.5×10 -3 (Ω / sec), the threshold is -0.5×10 -3 Note that this set threshold is merely an example, and other values ​​may be used.

[0073] The processor 51 identifies the start and end points of the sudden drop, including the point extracted in step St25 (St26). The start point of the sudden drop is the first data point in time when the differential value R' of the electrical resistance R changes from positive to negative. Note that, because it is not always possible to obtain a measurement value exactly at the timing when the differential value R' becomes 0, the first data point when the differential value R' changes from positive to negative is identified as the start point. The end point of the sudden drop is the first data point in time when the differential value R' of the electrical resistance R changes from negative to positive.

[0074] The processor 51 acquires the resistance value of the sudden drop start region (St27). For example, the resistance value of the sudden drop start region is the average value of the resistance values ​​for 2 milliseconds before the start of the sudden drop identified in step St26.

[0075] The processor 51 acquires the resistance value of the sudden drop end region (St28). For example, the resistance value of the sudden drop end region is the average value of the resistance values ​​1 millisecond before and after the end point of the sudden drop identified in step St26.

[0076] The processor 51 calculates the amount of sudden drop in the electrical resistance R (St29). The amount of sudden drop in the electrical resistance R is obtained by subtracting the resistance value in the sudden drop end region acquired in step St28 from the resistance value in the sudden drop start region acquired in step St27.

[0077] (Determining the presence or absence of dust) Figure 9 is a graph showing the effect of spatter on both sound pressure and electrode pressure. In each graph, the horizontal axis represents time. The vertical axis represents resistance and sound pressure for the sound pressure graph, and welding current and electrode pressure for the electrode pressure graph. Some of the welding conditions are listed above each graph. For example, the welding conditions for the sound pressure graph when there is no spatter are a welding current of 5.0 kA, a gap of 0 mm, and an impact angle of 0 degrees.

[0078] When comparing the sound pressure when there is no dust with the sound pressure when there is dust, the sound pressure fluctuates up and down more when there is dust. When comparing the electrode pressure when there is no dust with the electrode pressure when there is dust, the electrode pressure fluctuates up and down more when there is dust. Therefore, the applicant decided to use this fluctuation range to determine the presence or absence of dust.

[0079] Fig. 10 is a scatter plot showing the relationship between the difference between the maximum and minimum values ​​of sound pressure and electrode pressure and the presence or absence of expulsion. The horizontal axis shows the test resistance spot welding results, and the vertical axis shows the calculated value obtained by subtracting the maximum value from the minimum value.

[0080] For resistance spot welding without a flash, the difference between the maximum and minimum sound pressure values ​​was less than 0.2. On the other hand, for resistance spot welding with a flash, the difference between the maximum and minimum sound pressure values ​​exceeded 0.2.

[0081] In resistance spot welding without a gap, the difference between the maximum and minimum electrode pressure was approximately 2. On the other hand, in resistance spot welding with a gap, the difference between the maximum and minimum electrode pressure was significantly greater than 2.

[0082] Based on the above test results, the inventors discovered that the maximum-minimum values ​​of the sound pressure or electrode pressure are strongly correlated with the presence or absence of dust.

[0083] 5, the dust determination unit 513 determines whether dust has occurred based on the difference between the maximum and minimum values ​​of the electrode pressure or sound pressure. More specifically, the dust determination unit 513 determines whether dust has occurred based on whether the difference between the maximum and minimum values ​​of the electrode pressure or sound pressure is larger or smaller than a predetermined threshold value.

[0084] (Quality inspection of resistance spot welding when spatter occurs using a second predictive model) The inventors created a second prediction model using the sudden drop in electrical resistance as a feature. As a prediction model, a generalized additive model of the form nugget diameter = b1 + f(x1) + f(x2) + ... was adopted. b1 is a constant and f is a function. When n is an integer equal to or greater than 1, x n means the feature value in the nth phase where the electrical resistance drops sharply. For example, in the example in Figure 6, the electrical resistance drops sharply in three phases, P1, P2, and P3, so the prediction model as a generalized additive model will have the following format: Nugget diameter = b1 + f(x1) + f(x2) + f(x3)

[0085] The prediction accuracy of the second prediction model for resistance spot welding when spatter occurs was as follows:

[0086] FIG. 11 is a graph showing the accuracy of the predicted nugget diameter according to the second prediction model for resistance spot welding when expulsion occurs.

[0087] Figure 11 plots an excerpt from a case where the welding current was 12 kA and the target nugget diameter was 6√t (8.5 mm). The horizontal axis of the graph shown in Figure 11 represents the actual nugget diameter obtained by resistance spot welding. The vertical axis of the graph represents the predicted nugget diameter using the second prediction model. The diagonally extending dashed line represents the ideal line. When the predicted nugget diameter and the actual nugget diameter match, the points representing the welding results are plotted on this ideal line.

[0088] As can be seen from the graph in Fig. 11, in resistance spot welding when expulsion occurs, the plots for the second prediction model are closer to the ideal line than those for the first prediction model. In other words, it was confirmed that the second prediction model has higher prediction accuracy than the first prediction model in resistance spot welding when expulsion occurs.

[0089] (Spot welding of galvannealed high-tensile steel sheets when spatter occurs) The inventors also used the second prediction model to predict the nugget diameter in resistance spot welding when expulsion occurs in galvannealed high-tensile steel sheet, commonly known as plated high-tensile steel sheet.

[0090] The welded materials were both galvannealed high-tensile steel sheets. The test specimens for the upper and lower sheets were 40 mm wide and 125 mm long. The upper and lower sheets were overlapped and resistance spot welded.

[0091] The electrodes and welding machine used were the same as those described above for the ultra-high strength steel plate.

[0092] The current waveform was the same as that shown in Figure 2. Table 2 shows the welding conditions for resistance spot welding of galvannealed high-tensile steel sheets.

[0093] [Table 2]

[0094] FIG. 12 is a graph showing the accuracy of predicted nugget diameter using the second prediction model for resistance spot welding between galvannealed high-tensile steel sheets in the case where expulsion occurs.

[0095] The horizontal axis of the graph shown in FIG. 12 represents the actual nugget diameter obtained by resistance spot welding. The vertical axis of the graph represents the predicted nugget diameter using the second prediction model. The diagonal line represents the ideal line. When the predicted nugget diameter and the actual nugget diameter match, the points representing the welding results are plotted on this ideal line.

[0096] As can be seen from the graph in Fig. 12, in resistance spot welding when expulsion occurs, the plots for the second prediction model are concentrated close to the ideal line. In other words, it was confirmed that the second prediction model has high prediction accuracy even in resistance spot welding between galvannealed high-tensile steel sheets.

[0097] The present invention is not limited to the above-described embodiments, and the present invention also contemplates the mutual combination of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the description in the specification and well-known techniques, and these modifications and applications are included in the scope of protection sought.

[0098] As described above, the present specification discloses the following: (1) A quality inspection device for resistance spot welding, in which a current is passed between a pair of electrodes that sandwich a workpiece made of overlapping metal materials to melt and join the metal materials, a measuring unit for measuring a voltage and a welding current during welding; a calculation unit that calculates an electrical resistance based on the voltage and the welding current; and a nugget diameter calculation unit that calculates a nugget diameter of a welded portion obtained after welding based on the electrical resistance. Quality inspection equipment. This quality inspection device makes it possible to inspect the welding quality with high accuracy even when spatter occurs during resistance spot welding.

[0099] (2) The quality inspection device according to (1), further comprising a spatter determination unit that determines whether or not spatter has occurred during welding. According to this quality inspection device, by performing quality inspection using different features depending on whether or not flash has occurred, it is possible to inspect welding quality with high accuracy whether or not flash has occurred.

[0100] (3) The measuring unit further measures at least one of an electrode pressure and a sound pressure of the electrode during welding, The quality inspection device according to (2), wherein the dust determination unit determines whether dust has occurred based on the difference between the maximum and minimum values ​​of the electrode pressure or the sound pressure. This quality inspection device can accurately determine whether or not dust has occurred based on the electrode pressure or sound pressure, which has a high correlation with the presence or absence of dust.

[0101] (4) The quality inspection device according to (3), wherein, when the spatter determination unit detects the occurrence of spatter, the nugget diameter calculation unit calculates the nugget diameter based on the amount of sudden drop in the electrical resistance. This quality inspection device makes it possible to estimate the nugget diameter with high accuracy based on the amount of sudden drop in electrical resistance, which is correlated with the occurrence of spatter.

[0102] (5) The quality inspection device according to (4), wherein the nugget diameter calculation unit calculates the nugget diameter based on an integral value of the electrical resistance and an integral value of the electrode pressure. According to this quality inspection device, the nugget diameter is calculated based on a larger number of feature quantities, thereby enabling more accurate quality inspection.

[0103] (6) A quality inspection device according to any one of (1) to (5) above; a welding machine including the pair of electrodes, which applies current between the pair of electrodes that sandwich the workpieces to melt and join the metal materials together; a welding control device that controls the welding machine; A resistance spot welding system comprising: This resistance spot welding system allows resistance spot welding to be performed, and further allows for highly accurate inspection of weld quality even when spatter occurs during resistance spot welding.

[0104] (7) A quality inspection program for resistance spot welding in which a current is passed between a pair of electrodes that sandwich a workpiece made of overlapping metal materials to melt and join the metal materials, the program comprising: A quality inspection device having a processor and a memory, A measurement function to measure the voltage and welding current during welding; a calculation function for calculating an electrical resistance based on the voltage and the welding current; a nugget diameter calculation function for estimating a nugget diameter of a welded portion obtained after welding based on the electrical resistance; A quality inspection program that achieves this. According to this quality inspection program, even if spatter occurs during resistance spot welding, it is possible to inspect the welding quality with high accuracy.

[0105] (8) Regarding resistance spot welding, in which a current is passed between a pair of electrodes that sandwich the workpieces made of overlapping metal materials to melt and join the metal materials, A quality inspection device having a processor and a memory executes a measuring step of measuring a voltage and a welding current during welding; a calculation step of calculating an electrical resistance based on the voltage and the welding current; and a nugget diameter calculation step of calculating a nugget diameter of a welded portion obtained after welding based on the electrical resistance. Quality inspection methods. According to this quality inspection method, even if spatter occurs during resistance spot welding, it is possible to inspect the welding quality with high accuracy. [Explanation of symbols]

[0106] 1 Welding control device 11 Welding condition selection section 12 Welding current adjustment unit 13 Welding time adjustment unit 14 Time Adjustment Section 15 Electrode pressure adjustment unit 2 Welding power source 3. Welding machine 5 Quality inspection equipment 51 processors 511 Calculation Unit 512 Feature Extraction Unit 513 Chili Judgment Department 514 Nugget diameter calculation section 52 memory 53 Measuring Devices 54 Display Devices 55 Communication Devices 100 welding machine 113, 115 electrode 117 Welding transformer section 118 Power supply section 119 Control Unit 120 Electrode drive unit 200 Resistance Spot Welding System

Claims

1. 1. A quality inspection device for resistance spot welding in which current is passed between a pair of electrodes that sandwich a workpiece made of overlapping metal materials to melt and join the metal materials, a measuring unit for measuring a voltage and a welding current during welding; a calculation unit that calculates an electrical resistance based on the voltage and the welding current; a nugget diameter calculation unit that calculates a nugget diameter of a welded portion obtained after welding based on the electrical resistance; a flash determination unit that determines whether flash occurs during welding, The measurement unit further measures at least one of an electrode pressure and a sound pressure of the electrode during welding, the dust determination unit determines whether dust has occurred based on a difference between a maximum value and a minimum value of the electrode pressure or the sound pressure. Quality inspection equipment.

2. When the expulsion determination unit detects the occurrence of expulsion, the nugget diameter calculation unit calculates the nugget diameter based on the amount of sudden drop in the electrical resistance. The quality inspection device according to claim 1 .

3. The nugget diameter calculation unit calculates the nugget diameter further based on an integral value of the electrical resistance and an integral value of the electrode pressure. The quality inspection device according to claim 2.

4. A quality inspection device according to any one of claims 1 to 3; a welding machine including the pair of electrodes, which applies current between the pair of electrodes that sandwich the workpieces to melt and join the metal materials together; a welding control device that controls the welding machine; A resistance spot welding system comprising:

5. 1. A quality inspection program for resistance spot welding in which current is passed between a pair of electrodes that sandwich a workpiece made of overlapping metal materials to melt and join the metal materials, A quality inspection device having a processor and a memory, A measurement function to measure the voltage and welding current during welding; a calculation function for calculating an electrical resistance based on the voltage and the welding current; a nugget diameter calculation function for estimating a nugget diameter of a welded portion obtained after welding based on the electrical resistance; A flash detection function that determines whether flash occurs during welding; To achieve this, The measuring function further measures at least one of an electrode pressure and a sound pressure of the electrode during welding; the dust determination function determines whether dust has occurred based on a difference between a maximum value and a minimum value of the electrode pressure or the sound pressure; Quality inspection program.

6. Resistance spot welding is a method of welding workpieces made of overlapping metal materials by passing current between a pair of electrodes that sandwich the workpieces, melting and joining the metal materials together. A quality inspection device having a processor and a memory executes a measuring step of measuring a voltage and a welding current during welding; a calculation step of calculating an electrical resistance based on the voltage and the welding current; a nugget diameter calculation step of calculating a nugget diameter of a welded portion obtained after welding based on the electrical resistance; a flash determination step of determining whether or not flash has occurred during welding, The measuring step further measures at least one of an electrode pressure and a sound pressure of the electrode during welding, the dust determination step determines whether dust has occurred based on a difference between a maximum value and a minimum value of the electrode pressure or the sound pressure; Quality inspection methods.

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