Method for estimating nugget diameter of resistance spot welding

Abstract

A method for estimating a nugget diameter includes: a measured initial resistance value acquisition step of acquiring an initial resistance value during a current application period, i.e., a measured initial resistance value; a measured resistance value difference calculation step of calculating a difference between a main initial resistance value and the measured initial resistance value, i.e., a measured resistance value difference; a correction value calculation step of calculating a correction value for a welding parameter by substituting the measured resistance value difference calculated in the measured resistance value difference calculation step into a correction formula showing a correlation between the measured resistance value difference and the correction value for the welding parameter; a parameter correction step of correcting a value of the welding parameter by applying the correction value calculated in the correction value calculation step to the value of the welding parameter measured during a target welding; and a nugget diameter calculation step of calculating the nugget diameter by substituting the corrected value of the welding parameter into an estimation formula.

Description

Technical Field

[0001] This disclosure relates to a method for estimating the diameter of the weld nugget in resistance spot welding. Background Technology

[0002] Traditionally, resistance spot welding has been used in the manufacture of vehicle body frames and the like to join multiple metal plates together. This method involves clamping the workpieces (multiple metal plates) with a pair of electrodes while applying an electric current. The Joule heat generated by the resistance of the workpieces themselves melts the metal plates together. Furthermore, to improve the weld strength of the metal plates, it is necessary to ensure the diameter of the weld nugget obtained through resistance spot welding. Therefore, a method for estimating whether the weld nugget diameter has been sufficiently ensured is required.

[0003] The resistance welding method described in Japanese Patent Application Publication No. 2011-104628 establishes a database that corresponds to the cumulative value of electrical power applied to the workpiece and the diameter of the weld nugget. The diameter of the weld nugget can be estimated based on the actual cumulative electrical power. Summary of the Invention

[0004] However, in methods that estimate the weld nugget diameter solely based on its correlation with electrical power, as described in Japanese Patent Application Publication No. 2011-104628, there is a problem of poor accuracy in estimating the weld nugget diameter when various interferences exist at the welding site, such as gaps between steel plates, tilting of steel plates, and wear on the tip of the electrode pressed against the steel plate.

[0005] This disclosure may be implemented in the following ways.

[0006] (1) According to one aspect of this disclosure, a method for estimating the diameter of a weld nugget is provided. This method uses a predetermined estimation formula, with welding parameters that affect the size of the weld nugget diameter formed in resistance spot welding as the first explanatory variable and the estimated value of the weld nugget diameter as the first objective variable, to estimate the weld nugget diameter. The method comprises: a step of obtaining a measured initial resistance value, wherein the measured initial resistance value is the resistance value of the entire energized circuit of the object being welded, and is the initial resistance value during the energizing period of the weld corresponding to the weld nugget diameter being estimated; and a step of calculating a measured resistance value difference, wherein the measured resistance value difference is the difference between the initial resistance value during the energizing period of the main weld (i.e., the main initial resistance value) and the measured initial resistance value obtained in the step of obtaining the measured initial resistance value, wherein the main weld is a weld nugget diameter that does not have a weld nugget diameter. The welding process includes: welding under conditions that could affect the size of the weld nugget diameter, and welding that serves as the basis for the creation of the presumed formula; a correction value calculation step, in which the correction value of the welding parameter is calculated by substituting the measured resistance difference calculated in the measured resistance difference calculation step into a correction form that shows the correlation between the measured resistance difference and the correction value of the welding parameter, and which uses the measured resistance difference as a second explanatory variable and the correction value of the welding parameter as a second objective variable; a parameter correction step, in which the value of the welding parameter measured during welding of the object is corrected by applying the correction value calculated in the correction value calculation step; and a weld nugget diameter calculation step, in which the corrected value of the welding parameter is substituted into the presumed formula to calculate the weld nugget diameter. According to this method, the corrected value of the welding parameters is calculated by substituting the measured resistance difference into a predetermined correction formula that shows the correlation between the difference of measured resistance values ​​and the correction value of welding parameters, and the weld nugget diameter is calculated by substituting the corrected value of the welding parameters into a predetermined estimation formula. Compared to the main weld, which serves as the basis for the estimation formula and is free from interference that could affect the weld nugget diameter, interference can sometimes occur in the actual weld, i.e., the target weld, which is the estimation object for the weld nugget diameter. Furthermore, when interference actually occurs, using uncorrected welding parameter values ​​for the predetermined estimation formula can reduce the accuracy of the weld nugget diameter estimation. The inventors of this application have discovered that the presence or absence of interference in the weld is correlated with the difference between the primary initial resistance value and the measured initial resistance value, i.e., the measured resistance difference. Moreover, in the above method, the welding parameters are corrected using the measured resistance difference and the correction formula. Therefore, the weld nugget diameter calculated by substituting the corrected welding parameter values ​​into the estimation formula can be obtained as a highly accurate weld nugget diameter, thus improving the estimation accuracy of the weld nugget diameter. (2) In the above method, the revision form may also be made by including the following steps: (I) Parameter difference calculation step, calculating parameter difference, which is the difference between the value of the welding parameter in the main mode and the value of the welding parameter in the interference-related data, the main mode showing the correlation between the value of the welding parameter and the weld nugget diameter obtained by performing the main welding multiple times, the interference-related data showing the correlation between the value of the welding parameter and the weld nugget diameter obtained by performing welding in the state of interference, i.e., interference welding; (II) Interference resistance value difference calculation step, calculating interference resistance value difference, which is the difference between the main initial resistance value and the interference initial resistance value, the interference initial resistance value is the resistance value and is the initial resistance value during the energization period in the interference welding; and (III) Derivation step, using the correlation between the parameter difference and the interference resistance value difference, deriving the revision form. Based on this method, the correction formula can be easily derived by using the correlation between the parameter difference and the interference resistance value difference. (3) Alternatively, in the above method, the modified equation can be a linear equation calculated by performing linear regression on corresponding plotting points established between the interference resistance difference and the parameter difference. This method uniquely expresses the correlation between the interference resistance difference and the parameter difference. Furthermore, by establishing corresponding plotting points using the interference resistance difference and the parameter difference, it is easy to create a presumption. (4) In the above method, the estimation method may also include: an interference discrimination step, which determines the type of interference based on the characteristics of the resistance value during the energization period when the object is welded, and in the correction value calculation step, uses the correction form in the correction form made according to each type of interference that corresponds to the interference determined in the interference discrimination step to obtain the correction value of the welding parameters. According to this method, the type of interference is identified in the interference identification process, and the welding parameters are corrected using a correction formula corresponding to the type of interference. Therefore, an appropriate correction value corresponding to the type of interference can be calculated, thus further improving the estimation accuracy of the weld nugget diameter. (5) Alternatively, in the above method, the type of interference can be determined by comparing the resistance value during the object welding process with the resistance value during the main welding process. According to this method, the type of interference can be easily determined by comparing the resistance value with the resistance value during the main welding process. Attached Figure Description

[0007] 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 showing the configuration of a melting core diameter estimation system as a first embodiment of the present disclosure. Figure 2 This is a block diagram showing the general configuration of the control device in the first embodiment. Figure 3 This is a flowchart illustrating the steps in the method for estimating the diameter of the melt core. Figure 4 It is a graph that shows the change of resistance value over time. Figure 5 This is a flowchart illustrating the steps in the modified manufacturing method. Figure 6 This is a graph showing the correlation between the welding parameters before correction and the weld nugget diameter. Figure 7 This is a diagram illustrating an example of the modified formula. Figure 8 This is a graph showing the correlation between the corrected welding parameters and the weld nugget diameter. Figure 9 It is a graph used to compare the estimated error of the melt core diameter before and after the correction using the modified formula. Figure 10 This is a block diagram showing the general configuration of the control device in the second embodiment. Figure 11 This is a flowchart illustrating the steps in the method for estimating the diameter of the melt core in the second embodiment. Figure 12 It is a graph that shows the change of resistance value over time. Figure 13 It is a graph that shows the change of resistance value over time. Figure 14 It is a graph that shows the change of resistance value over time. Figure 15 The table shows a summary of the waveform characteristics of the resistance values ​​under various interference conditions. Figure 16 This is a graph showing the correlation between welding parameters and weld nugget diameter. Figure 17 This is a graph showing the correlation between welding parameters and weld nugget diameter. Figure 18 This is a graph showing the correlation between welding parameters and weld nugget diameter. Figure 19 This is a graph used to compare the estimated error of the melt core diameter before and after correction. Detailed Implementation

[0008] A. First implementation method: A1. Overall composition of the melting nugget diameter estimation system 1: Reference Figures 1-9 The first embodiment of this disclosure will now be described. When describing the method for estimating the diameter of the melt core in the first embodiment of this disclosure, the configuration of the melt core diameter estimation system 1 (hereinafter also simply referred to as "estimation system 1") will first be described. Figure 1 This is a schematic configuration diagram showing the weld nugget diameter estimation system 1 as a first embodiment of the present disclosure. The estimation system 1 is a system for estimating the diameter of the weld nugget formed on the welded part W by resistance spot welding performed by the resistance spot welding apparatus 10. The estimation system 1 includes the resistance spot welding apparatus 10, the control device 100, and the measuring mechanism 9.

[0009] The resistance spot welding apparatus 10 is a device that melts and joins multiple overlapping metal plates W1, W2 into a weldable component W. The resistance spot welding apparatus 10 includes a welding torch G and a robotic arm RA.

[0010] The welding torch G comprises a torch body 11, an upper electrode 2 and a lower electrode 3 as a pair of electrodes, an electrode lifting device 4, a pressurizing device 5, and a current adjusting device 6. The torch body 11 is held in place by a robotic arm RA. The lower electrode 3 is a fixed electrode disposed in a state fixed to the lower part 11b of the torch body 11. The upper electrode 2 is a movable electrode that can move in the direction relative to the lower electrode 3. The upper electrode 2 is mounted to the upper part 11a of the torch body 11 via the electrode lifting device 4. The upper electrode 2 and the lower electrode 3 each have internal flow paths (not shown) for the flow of cooling water.

[0011] The electrode lifting device 4 is an electrically powered device that holds and raises the upper electrode 2. The electrode lifting device 4 is mounted on the top of the upper part 11a of the gun body 11. The electrode lifting device 4 includes a servo motor 41 and a lifting component 42 coupled to the drive shaft of the servo motor 41. The electrode lifting device 4 raises and lowers the lifting component 42 by operating the servo motor 41 according to a lifting command from the control device 100.

[0012] The pressurizing device 5 presses the upper electrode 2 and the lower electrode 3 towards each other. Specifically, the pressurizing device 5 is a device that applies force to the upper electrode 2 and the lower electrode 3 respectively to press the welded part W with a predetermined pressure while the welded part W is held by the upper electrode 2 and the lower electrode 3. The pressurizing device 5 applies a predetermined force to the upper electrode 2 and the lower electrode 3 respectively according to the pressurizing command from the control device 100.

[0013] The current adjusting device 6 adjusts the value (hereinafter, current value) of the welding current flowing between the upper electrode 2 and the lower electrode 3 according to the current command sent from the control device 100. The current adjusting device 6 is, for example, a device equipped with a variable resistor or a device equipped with a converter.

[0014] Figure 2 This is a block diagram showing a general configuration of the control device 100. In this embodiment, in addition to controlling the operation of the resistance spot welding apparatus 10, the control device 100 also functions as a estimation device for estimating the diameter of the weld nugget in resistance spot welding. Furthermore, the estimation device may also be configured to be separate from the control device 100 and to communicate with it via wired or wireless means.

[0015] The control device 100 includes a communication unit 30, a display 40, an input operation unit 50, a storage unit 60, and a CPU 20. The control device 100 is, for example, a computer including the components 20 to 60. The communication unit 30 communicatively connects the resistance spot welding apparatus 10 and the measuring mechanism 9 to the control device 100. The display 40 is, for example, a liquid crystal display (LCD), which displays information according to instructions from the CPU 20. The input operation unit 50 includes, for example, a keyboard and a mouse, and receives instructions from the user.

[0016] The storage unit 60 stores various data, including programs for controlling the operation of the resistance spot welding apparatus 10, modification formulas 650, and estimation formulas 670. The storage unit 60 includes RAM, ROM, and rewritable non-volatile memory. Estimation formula 670 is a pre-prepared formula for calculating an estimated value for the weld nugget diameter. Specifically, estimation formula 670 is a formula that uses welding parameters that affect the size of the weld nugget diameter as the first explanatory variable and the estimated value of the weld nugget diameter as the first objective variable.

[0017] Revision 650 is a relational formula created to calculate the correction value of the welding parameters substituted into Estimated Formula 670. Revision 650 is a formula showing the correlation between the difference in measured resistance values ​​(described later) and the correction value of the welding parameters, and it is a predetermined formula that uses the difference in measured resistance values ​​as the second explanatory variable and the correction value of the welding parameters as the second objective variable. Here, in Estimated Formula 670 and Revision 650, for convenience, "first" and "second" are appended to distinguish their respective explanatory and objective variables.

[0018] The modified form 650 is shown by equation (1) of the following linear equation. Furthermore, a and b are constants determined by the combination of resistance difference and parameter difference, as described later. y is the correction value, and x is the measured resistance difference. Details regarding the derivation of modified form 650 are described later. y = ax + b (Equation 1)

[0019] The CPU 20 functions as the motion control unit 200, acquisition unit 210, differential calculation unit 220, correction production unit 230, correction value calculation unit 240, and estimation unit 290 by unfolding various programs stored in the storage unit 60.

[0020] The motion control unit 200 controls the operation of the resistance spot welding apparatus 10. The operation of the resistance spot welding apparatus 10 is controlled during welding based on preset parameters (hereinafter, welding parameters). That is, the welding parameters are welding conditions preset during welding. Welding parameters include, for example, current value, voltage value, resistance value, inter-electrode displacement, expansion amount, and pressure applied to electrodes 2 and 3. The motion control unit 200 comprehensively controls their operation. For example, the motion control unit 200 controls the operation of the resistance spot welding apparatus 10 based on the preset values ​​of the welding parameters set by the user via the input operation unit 50.

[0021] The acquisition unit 210 acquires various data used in the production of the revision form 650 and in the substitution into the estimation form 670. For example, the acquisition unit 210 acquires the initial measured resistance value, which will be described later, used when calculating the difference in measured resistance values. The difference calculation unit 220 calculates the difference in measured resistance values. The revision form production unit 230 produces the revision form 650. The correction value calculation unit 240 uses the revision form 650 to calculate the correction value of the welding parameters substituted into the estimation form 670. Specifically, the correction value calculation unit 240 calculates the correction value by substituting the difference in measured resistance values ​​into the revision form 650 (the above formula (1)).

[0022] The estimation unit 290 includes a parameter correction unit 291 and an estimation value calculation unit 292. The parameter correction unit 291 calculates corrected parameters that reflect the correction values ​​in the welding parameters. The estimation value calculation unit 292 uses the corrected welding parameters to calculate an estimated value for the weld nugget diameter in the weld. Details of each function and the estimation method for the weld nugget diameter will be described later. Furthermore, at least some of the functions of the CPU 20 can also be implemented by hardware circuitry.

[0023] The measuring mechanism 9 is a mechanism that measures the actual values ​​of welding parameters as physical quantities required for welding using the resistance spot welding device 10. The "actual values ​​of welding parameters" referred to here are the values ​​of the welding parameters actually observed when welding is performed according to the welding condition instructions sent from the motion control unit 200, that is, when welding is performed using preset welding parameter settings. The actual values ​​of the welding parameters measured by the measuring mechanism 9 are sent to the CPU 20 via the communication unit 30.

[0024] In this embodiment, the measuring mechanism 9 includes a current measuring unit 91, a voltage measuring unit 92, a resistance calculating unit 93, a pressure measuring unit 95, an inter-electrode displacement measuring unit 96, and an inter-electrode displacement calculating unit 97. Furthermore, the configuration and function of the measuring mechanism 9 are not limited to this. For example, the measuring mechanism 9 may also include other mechanisms for measuring welding parameters. Additionally, at least a portion of the functions of the measuring mechanism 9 can be implemented as a function of the CPU 20.

[0025] Each component 91 to 97 of the measuring mechanism 9 measures the actual values ​​of welding parameters at predetermined measurement times during welding. The current measuring unit 91 measures the current flowing between the upper electrode 2 and the lower electrode 3. The current measuring unit 91 is, for example, a current sensor. The voltage measuring unit 92 measures the voltage (potential difference) between the upper electrode 2 and the lower electrode 3. The voltage measuring unit 92 is, for example, a voltage sensor.

[0026] The resistance calculation unit 93 calculates the resistance value (hereinafter, resistance value) using the measured values ​​of the current and voltage measured when the power is applied. Specifically, the resistance calculation unit 93 calculates the resistance value by dividing the voltage value by the current value. In this case, the current value and voltage value at the same measurement time point are used in the calculation of the resistance value.

[0027] The pressure measuring unit 95 measures the pressure applied by each electrode 2, 3 to the welded component W. The pressure measuring unit 95 is, for example, a force sensor housed inside the electrode lifting device 4. The inter-electrode displacement measuring unit 96 includes a first displacement measuring unit 961 that measures the displacement of the upper electrode 2 (hereinafter, the first displacement) and a second displacement measuring unit 962 that measures the displacement of the lower electrode 3 (hereinafter, the second displacement).

[0028] The first displacement measuring unit 961 measures, for example, the lifting position of the upper electrode 2 at a first measuring time point and the lifting position of the upper electrode 2 at a second measuring time point after a predetermined measuring time has elapsed from the first measuring time point, and calculates the first displacement based on the difference between the measured values. The first displacement measuring unit 961 is, for example, an encoder housed inside the electrode lifting device 4 that measures the lifting position of the upper electrode 2 by detecting the rotational angle position of the output shaft of the servo motor 41.

[0029] The second displacement measuring unit 962 measures a second displacement. Specifically, it is fixed to the lower part 11b of the gun body 11. Therefore, when a force is applied due to thermal expansion, the lower electrode 3 deforms without moving. Thus, the second displacement measuring unit 962 measures the force (deformation value) applied to the lower electrode 3 as the second displacement. The second displacement measuring unit 962 is, for example, a deformation sensor that measures the deformation value of the lower electrode 3.

[0030] The inter-electrode displacement calculation unit 97 uses the first displacement measured and calculated by the first displacement measuring unit 961 and the second displacement measured by the second displacement measuring unit 962 to calculate the displacement between the upper electrode 2 and the lower electrode 3 (hereinafter, the inter-electrode displacement). In this case, the value at the same measurement time point is used in the calculation of the inter-electrode displacement. For example, the inter-electrode displacement calculation unit 97 calculates the inter-electrode displacement during energization by adding the first and second displacements during the energization period. However, the method for calculating the inter-electrode displacement is not limited to this.

[0031] A2. Method for estimating the diameter of the molten core: Next, the method for estimating the diameter of the melt core in the first embodiment of this disclosure, which uses the estimation system 1 described in detail above, will be explained. Figure 3 This is a flowchart illustrating the steps in the method for estimating the diameter of the melt nugget. For example... Figure 3 As shown, the method for estimating the diameter of the melt nugget includes the steps of obtaining the measured initial resistance value (S110), calculating the difference of the measured resistance value (S120), calculating the correction value (S130), correcting the parameters (S140), and calculating the diameter of the melt nugget (S150), and each step is executed in sequence.

[0032] In the measured resistance value difference calculation process (S120), the acquisition unit 210 acquires the initial measured resistance value during the energizing period of the weld, i.e., the welding of the target object, corresponding to the diameter of the weld nugget that is being estimated. Here, "initial energizing period" in this embodiment refers to the time from the start of energizing to one-quarter of the total energizing period. However, it is not limited to one-quarter and can be any period within the first half of the energizing period. Hereinafter, "resistance value" refers to the resistance value of the entire energizing circuit including the welded object. Figure 4 It is a graph that shows the change in resistance value over time. Figure 4 In the figure, the resistance value Rm (hereinafter also referred to as the main resistance value Rm) in the main weld is shown in thin solid line, while the resistance value Ra (hereinafter also referred to as the measured resistance value Ra) in the interfering weld is shown in dashed line as an example of object weld.

[0033] Here, the main weld is a weld in a state free from interference that could affect the size of the weld nugget diameter, and it serves as the reference weld for manufacturing the estimated type 670. Furthermore, it means a weld that serves as the reference for obtaining the main data when obtaining the difference between the estimated weld nugget diameter and the measured resistance value. Interferences include, for example, the gap between the steel plates (hereinafter, also simply "plate gap"), the tilt of the steel plates, and wear on the tips of the electrodes 2 and 3 pressed against the steel plates. Furthermore, "free from interference" is not limited to the situation where the plate gap, the tilt of the steel plates, and the wear on the tips are completely absent (zero), but also has a broad meaning including situations where there are trace amounts that can be considered to be completely absent. For example, if the plate gap is 0.1 mm or less, the tilt angle is 0.1° or less, and the wear is 0.1% or less, then it can be said to be a state of "free from interference". Figure 4 In the diagram, the change in current value is shown as a solid line. Figure 4 In the process, the power-on start time is 100ms and the power-on end time is 470ms.

[0034] In this embodiment, the "initial power-on Ti" is set between 170ms and 200ms. This is to avoid the period immediately following the unstable power-on process, during which interference is easily detected. Research by the inventors of this application has shown that during the first half of the power-on period, the resistance value in the initial power-on Ti is also prone to capturing interference characteristics, and in the event of interference, it becomes lower than the resistance value during the main soldering. The measured initial resistance value uses the average value from the initial power-on Ti.

[0035] In the measured resistance difference calculation process (S120), the difference calculation unit 220 calculates the measured resistance difference. The measured resistance difference is the difference between the main initial resistance value and the measured initial resistance value. The main initial resistance value is the initial resistance value in the main weld, and here, like the measured initial resistance value, the average value in the initial energized Ti is used. Furthermore, the main initial resistance value is obtained from data in a previously executed main weld before the target weld is performed, for example, stored in the storage unit 60.

[0036] In the correction value calculation process (S130), the correction value calculation unit 240 substitutes the measured resistance difference into the correction form 650 to calculate the correction value of the welding parameters. In the parameter correction process (S140), the parameter correction unit 291 corrects the value of the welding parameters. Specifically, the correction is performed by adding the correction value calculated in the correction value calculation process (S130) to the value of the welding parameters measured during welding of the object. That is, the corrected welding parameters are defined by the relationship shown in the following formula (2). Corrected welding parameters = original welding parameters + corrected value (Equation 2)

[0037] In the weld nugget diameter estimation step (S150), the weld nugget diameter is calculated by the estimation value calculation unit 292. Specifically, the corrected welding parameter values ​​are substituted into the estimation formula to calculate the weld nugget diameter.

[0038] A3. Method for making the modified version 650: Next, the manufacturing method of the modified version 650 will be explained. Figure 5 This is a flowchart illustrating the steps in the manufacturing method of the revision piece 650 performed by the revision piece manufacturing department 230. Furthermore, Figure 5 The flowchart shown is in Figure 3 Execute before the flowchart shown. Figure 5 As shown, the manufacturing method of the modified form 650 includes a parameter differential calculation process (S201), an interference resistance value differential calculation process (S202), and a derivation process (S203), and each process is executed sequentially.

[0039] In the parameter difference calculation process (S201), the difference between the welding parameter values ​​in the main mode and the welding parameter values ​​in the interference-related data is calculated, i.e., the parameter difference. The main mode shows the correlation between the welding parameter values ​​and the weld nugget diameter obtained by performing the main welding multiple times. The interference-related data shows the correlation between the welding parameter values ​​and the weld nugget diameter obtained by performing interference welding multiple times under interference conditions.

[0040] Figure 6 This is a graph showing the correlation between the welding parameters before correction and the weld nugget diameter. Figure 6The vertical axis represents the values ​​of welding parameters, and the horizontal axis represents the diameter of the weld nugget. Figure 6 In the diagram, the main pattern is plotted using blacked-out circles, and the interference-related data is plotted using blacked-out squares. In this embodiment, the interference is set to generate plate gaps, and the average resistance value during the latter half of the welding process is used as the welding parameter. Figure 6 The straight line in the equation is a linear equation calculated by performing linear regression on plotting points corresponding to the values ​​of welding parameters and the diameter of the weld nugget during the main welding process. This is equivalent to Estimated Equation 670. For example... Figure 6 As shown, in the presence of interference, the plotting point deviates downwards from the presupposition. This "deviation" is the difference Pd between the welding parameter values ​​in the master mode and the welding parameter values ​​in the interference-related data, i.e., the "parameter difference".

[0041] In the interference resistance value difference calculation process (S202), the difference between the main initial resistance value and the initial interference resistance value during the energization period in the interference welding is calculated, namely the interference resistance value difference. Figure 7 This is a diagram illustrating an example of revision 650. In Figure 7 In the graph, the horizontal axis represents the difference in measured resistance values, and the vertical axis represents the correction value. Additionally, in... Figure 7 In the diagram, the horizontal axis corresponds to the aforementioned difference in interference resistance values, and the vertical axis corresponds to the aforementioned difference in parameters. Figure 7 In the diagram, black circles were used to plot data without interference, and black squares were used to plot data with interference. Figure 7 The straight line in the equation is a linear equation approximating the line, calculated by performing linear regression on each plotting point. This equation is equivalent to a modified equation 650.

[0042] That is, in this embodiment, a correction form 650 is created using the correlation between the parameter difference and the interference resistance value difference. By substituting the measured resistance value difference into x in the created correction form 650 (the above formula (1)), the correction value is calculated as y. Figure 8 This is a graph showing the correlation between the corrected welding parameters and the weld nugget diameter. Figure 8 The vertical axis represents the corrected welding parameter values, and the horizontal axis represents the weld nugget diameter. Figure 8 In the diagram, the main pattern is plotted using blacked-out circles, and the data with interfering information is plotted using blacked-out squares. For example... Figure 8 As shown, there is interference-related data and Figure 6 In comparison, a correction was made to bring the data closer to the approximate line. That is, the data was corrected to be treated the same as the main pattern.

[0043] Figure 9This graph is used to compare the estimated error of the weld nugget diameter before and after using revision formula 650. The "estimated error" referred to here is the degree of deviation between the measured value of the weld nugget diameter and the estimated value of the weld nugget diameter calculated using revision formula 670. Figure 9 The left figure shows the estimation error of the weld nugget diameter when the welding parameters are not corrected by substituting into the opposite estimation formula 670, but the weld nugget diameter is estimated. Figure 9 The right figure shows the estimation error of the weld nugget diameter when the welding parameters, which have been modified using modified formula 650, are substituted into the estimation formula 670 to estimate the weld nugget diameter. Figure 9 The horizontal axis in the left and right figures represents the estimated error of the melt core diameter. Figure 9 The vertical axis in the left and right figures represents the measured diameter of the molten core.

[0044] In addition, Figure 9 In the diagram, blacked-out circles represent data obtained from multiple uninterrupted welding operations, while blacked-out squares represent data obtained from multiple interfering welding operations. For example... Figure 9 As shown in the left figure, when the welding parameters substituted into the opposing estimation formula 670 are not corrected, and the weld nugget diameter is estimated, the estimation error of the weld nugget diameter under interference conditions is mostly above 10%. On the other hand, as... Figure 9 As shown in the right figure, when the weld nugget diameter is estimated by substituting the values ​​of the welding parameters corrected using the modification formula 650 into the estimation formula 670, even in the presence of interference, the estimation error of the weld nugget diameter converges to within 10%. That is, according to the first embodiment described above, by correcting the welding parameters substituted into the estimation formula 670 for the weld nugget diameter using the modification formula 650, the weld nugget diameter can be estimated with good accuracy.

[0045] Furthermore, in the aforementioned estimation method, the primary initial resistance value and the correction form 650 are pre-stored in the storage unit 60. Therefore, when estimating the weld nugget diameter, the measured initial resistance value at the moment of energization is obtained. Based on this, the difference between the measured resistance value and the registered primary initial resistance value is calculated. The calculated measured resistance value difference is then substituted into the correction form 650, and through this simple process, the correction value can be calculated. In addition, the correction form 650 is manufactured considering the influence of interference, and the correlation between the deviation from the main weld (i.e., the interference resistance value difference) and the parameter difference is obtained. Therefore, by using the correction value obtained using the correction form 650 to correct the value of the welding parameters, the influence of interference can be corrected.

[0046] B. Second implementation method: Next, refer to Figures 10-19The second embodiment of this disclosure will be described below. Furthermore, in the second embodiment, the overall configuration of the melt core diameter estimation system 1 ( Figure 1 ) and the general configuration of the control device 100 Figure 2 The embodiments described above are largely the same as the first embodiment, so the same reference numerals are used for substantially the same parts and descriptions are omitted. Figure 10 This is a block diagram showing the general configuration of the control device 100. (Example) Figure 10 As shown, in the second embodiment, the CPU 20 differs from the first embodiment in that it also has an interference detection unit 250. The other configurations are the same.

[0047] The interference discrimination unit 250 determines the type of interference based on the characteristics of the resistance value during the energization period of the object during welding. In the second embodiment, the interference discrimination unit 250 distinguishes three types of interference. The first type of interference is "plate gap," the second is "upward / downward push," and the third is "vertical surface breakage." "Upward / downward push" occurs when the welding surface is pushed up or down due to errors or misalignment in the position control of the robot of the lower electrode 3, or wear on the tips of electrodes 2 and 3. In "upward push," the upper electrode 2 makes weak contact, and the lower electrode 3 makes strong contact. In "downward push," the upper electrode 2 makes strong contact, and the lower electrode 3 makes weak contact. "Vertical surface breakage" occurs when the perpendicular relationship between the electrode and the contact surface breaks down due to errors in the position control of the robot of the lower electrode 3.

[0048] In the second embodiment, the correction template 650 is manufactured separately for each type of interference. In this embodiment, three correction templates 650 are stored in the storage unit 60. The manufacturing of the correction templates 650 is the same as in the first embodiment, using different types of interference to obtain data.

[0049] Figure 11 This is a flowchart illustrating the steps in the method for estimating the diameter of the melt nugget in the second embodiment. For example... Figure 11 As shown, in the second embodiment, the difference from the first embodiment lies in the inclusion of an interference discrimination step (S121) between the measured resistance value difference calculation step (S120) and the correction value calculation step (S130). In the interference discrimination step (S121), the interference discrimination unit 250 determines which of three types of interference is presumed to be generated during the object welding. This determination is performed by comparing the waveform of the resistance value during object welding with the waveform of the resistance value during main welding.

[0050] Figures 12-14This is a graph showing the change in resistance value over time. In each graph, the resistance value Rm in the main weld (hereinafter referred to as the main resistance value Rm) is shown by a thick solid line, and the resistance values ​​Rg1 and Rg2 in the interfering welds are shown by dashed lines and double-dotted lines. Additionally, in Figure 12 The changes in current value are shown as thin solid lines in the diagram. In each diagram, the start of energization is 100ms, and the end of energization is 300ms.

[0051] Figure 12 This data is based on the condition where a gap is created as a disturbance. Figure 12 In the diagram, resistance value Rg1 is the resistance value with a plate gap of 1mm, and resistance value Rg2 is the resistance value with a plate gap of 2mm. Figure 13 This refers to data generated as a disturbance, resulting in push-up and push-down. Figure 13 In the diagram, resistance value Rg1 is the resistance value during the 2mm upward push, and resistance value Rg2 is the resistance value during the 2mm downward push. Figure 14 This data pertains to situations where vertical surface collapse occurs as a disturbance. Figure 14 In the diagram, resistance values ​​Rg1 and Rg2 show the respective data for two cases that resulted in a 3° vertical surface collapse.

[0052] like Figures 12-14 As shown in the figures, the waveform characteristics of the resistance value during welding differ depending on the type of interference. Figure 15 The table presents a summary of the waveform characteristics of the resistance values ​​under various interference conditions. Here, "initial power-on T1" is set as... Figures 12-14 The 140ms to 160ms range is used for "the first half of formal power-on (T2)" and "the second half of formal power-on (T3)" ranges from 140ms to 178ms. Furthermore, for convenience, the characteristic quantities are differentiated as described above, but "the first half of power-on" indicates the range from the beginning of the power-on period to the middle of the power-on period. Additionally, the "initial power-on" here can be set differently from the "initial power-on" when the measured initial resistance value is obtained.

[0053] like Figures 12-14 and Figure 15As shown in the figures, for the interference being a gap between plates, the waveform of the resistance value is smaller than the main resistance value Rm at the initial stage of formal power-on, the slope is greater than 0 in the first half of formal power-on, and smaller than the main resistance value Rm in the second half of formal power-on. For the interference being an upward / downward push, the waveform of the resistance value is smaller than the main resistance value Rm at the initial stage of formal power-on, the slope is almost 0 in the first half of formal power-on, and almost the same as the main resistance value Rm in the second half of formal power-on. For the interference being a vertical surface collapse, the waveform of the resistance value is smaller than the main resistance value Rm at the initial stage of formal power-on, the slope is greater than 0 in the first half of formal power-on, and greater than the main resistance value Rm in the second half of formal power-on.

[0054] In the above example, the fact that the resistance is smaller than the main resistance value Rm at the initial stage of formal power-on is the same for all interferences. However, the slope during the first half of formal power-on and the comparison with the main resistance value Rm during the second half of formal power-on can distinguish between different interferences. Specifically, in order to use such characteristics to identify the type of interference, a specific threshold in the welding process is predetermined, and the interference can be identified based on whether it exceeds the threshold.

[0055] In the second embodiment, after identifying the type of interference, the correction value of the welding parameters is calculated using the correction form 650 made according to each type of interference, which corresponds to the interference identified in the interference identification process (S121). Figures 16-18 These are graphs showing the correlation between welding parameters and weld nugget diameter. In each graph, the vertical axis represents the values ​​of the welding parameters, and the horizontal axis represents the weld nugget diameter. In each graph, the main pattern is plotted with a hollow quadrilateral, the uncorrected data with triangles, and the corrected data with crosses.

[0056] Figure 16 This data is based on the condition where a gap is created due to interference. Figure 17 This refers to data generated as an interference, resulting in push-up and push-down. Figure 18 This data represents the situation where vertical surface collapse occurred due to interference. The straight lines in each figure are derived from a linear regression of plotting points corresponding to the welding parameter values ​​and the weld nugget diameter, equivalent to Estimation 670. As shown in the figures, in the presence of interference, the plotting points in the uncorrected data deviated downwards from the Estimation. However, by using various correction equations 650, the plotting points in the corrected data were adjusted to a position almost identical to the Estimation.

[0057] Figure 19 This graph is used to compare the estimated error of the melt core diameter before and after using the modified version 650. Figure 19The left figure shows the estimation error of the weld nugget diameter when the welding parameters are not corrected by substituting into the opposite estimation formula 670, but the weld nugget diameter is estimated. Figure 19 The right figure shows the estimation error of the weld nugget diameter when the welding parameters, which have been modified using modified formula 650, are substituted into the estimation formula 670 to estimate the weld nugget diameter. Figure 19 The horizontal axis in the left and right figures represents the estimated error of the melt core diameter. Figure 19 The vertical axis in the left and right figures represents the measured diameter of the molten core.

[0058] like Figure 19 As shown, for data whose estimated accuracy deviates significantly by more than ±20% without correction, it can be estimated to be within ±20% with correction. That is, according to the second embodiment described above, the same effect as the first embodiment described above can be achieved. Moreover, since the type of interference is identified and the welding parameters are corrected using the correction formula 650 corresponding to the type of interference, a suitable correction value corresponding to the type of interference is calculated, thus further improving the estimated accuracy of the weld nugget diameter.

[0059] C. Other implementation methods: (C1) In the above embodiments, the measured initial resistance value and the main initial resistance value use the average value of the initial energization Ti, but the value at any time during the initial energization Ti can also be used.

[0060] (C2) In the above embodiments, the estimation formula 670 is a relational expression that uses the welding parameters as the first explanatory variable and the estimated value of the weld nugget diameter as the first objective variable. Here, when multiple welding parameters are included as the first explanatory variable, a modification formula 650 can be created for each of the welding parameters, the modified value can be calculated, and the weld nugget diameter can be estimated based on this. Alternatively, any welding parameter can be selected, and a modification formula 650 can be created only for the selected welding parameter.

[0061] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in each embodiment corresponding to the technical features in the various methods described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-mentioned problems, or to achieve some or all of the above-mentioned effects. In addition, any technical feature that is not described as an essential technical feature in this specification can be appropriately deleted.

Claims

1. A method for estimating the diameter of a weld nugget, comprising estimating the diameter of a weld nugget using a predetermined estimating formula that takes welding parameters that affect the size of the weld nugget diameter formed in resistance spot welding as the first explanatory variable and the estimated value of the weld nugget diameter as the first objective variable, wherein, The estimation method comprises: The process of obtaining the measured initial resistance value involves obtaining the measured initial resistance value, which is the resistance value of the entire energized circuit of the welding object and the initial resistance value during the energized period of the welding process, corresponding to the weld nugget diameter of the presumed object. The measured resistance difference calculation process calculates the measured resistance difference, which is the difference between the initial resistance value during the energization period in the main welding, i.e., the main initial resistance value, and the measured initial resistance value obtained in the measured initial resistance value acquisition process. The main welding is welding in a state where there is no interference that may affect the size of the weld nugget diameter, and it is the welding that serves as the manufacturing reference for the presumed formula. The correction value calculation process involves substituting the correction form, which shows the correlation between the measured resistance difference and the correction value of the welding parameter, and which is a predetermined correction form that uses the measured resistance difference as a second explanatory variable and the correction value of the welding parameter as a second objective variable, into the measured resistance difference calculated in the measured resistance difference calculation process to calculate the correction value of the welding parameter. The parameter correction step corrects the value of the welding parameters by applying the correction value calculated in the correction value calculation step to the value of the welding parameters measured during welding of the object; and The process of calculating the weld nugget diameter involves substituting the corrected values ​​of the welding parameters into the estimated formula to calculate the weld nugget diameter.

2. The method for estimating the diameter of the melt nugget according to claim 1, wherein, The repair form is produced through the following processes: (I) Parameter difference calculation process: Calculate the parameter difference, which is the difference between the value of the welding parameter in the main mode and the value of the welding parameter in the interfering related data. The main mode shows the correlation between the welding parameter values ​​obtained by performing the main weld multiple times and the weld nugget diameter. The interference-related data shows the correlation between the values ​​of the welding parameters obtained by performing welding under the condition of interference, i.e., interference welding, and the weld nugget diameter; (II) Interference resistance value difference calculation process, calculate the interference resistance value difference, the interference resistance value difference is the difference between the main initial resistance value and the interference initial resistance value, the interference initial resistance value is the initial resistance value during the energization period in the interference welding; as well as (III) Derivation process: using the correlation between the parameter difference and the interference resistance value difference, the correction form is derived.

3. The method for estimating the diameter of the melt nugget according to claim 2, wherein, Regarding the aforementioned revisions. The equation is a linear equation calculated by establishing corresponding plotting points based on the difference in the interference resistance value and the difference in the parameters.

4. The method for estimating the diameter of the melt core according to any one of claims 1 to 3, wherein, The estimation method also has the following features: The interference detection process identifies the type of interference based on the characteristics of the resistance value during the energizing period of the object during welding. In the correction value calculation process, the correction value of the welding parameters is obtained by using the correction form corresponding to the interference identified in the interference discrimination process, which is produced according to each type of interference.

5. The method for estimating the diameter of the melt nugget according to claim 4, wherein, In the interference detection process, The type of interference is determined by comparing the resistance value of the object during welding with the resistance value of the main welding.

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