Method for estimating nugget diameter

Abstract

To provide a method for estimating a nugget diameter, that can suppress deterioration in estimation accuracy although a plate thickness deviates from a nominal plate thickness.SOLUTION: A method for estimating a nugget diameter in resistance welding includes the steps of: estimating a plate thickness of an object to be welded, from an initial position of an electrode in resistance welding; calibrating an expansion amount of the object to be welded in resistance welding by using the estimated plate thickness to acquire a calibrated expansion amount; and estimating a nugget diameter by using the acquired calibrated expansion amount.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for estimating a nugget diameter. [Background technology]

[0002] Various techniques for inspecting workpieces in resistance welding have been disclosed. For example, Patent Document 1 discloses a technique for detecting an abnormality in the plate thickness of workpieces. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-019039 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have found that the nugget diameter and the expansion amount of the workpiece during welding are correlated, and that the nugget diameter can be estimated using the expansion amount. The expansion amount of the workpiece during welding is correlated with the plate thickness of the workpiece. Here, the plate thickness of the workpiece may deviate from the nominal plate thickness at the time of design due to processing errors during processing such as pressing. In Patent Document 1, such variations in the plate thickness of the workpiece before welding are not taken into consideration. When the expansion amount varies from the assumption at the time of design due to such plate thickness variations, there is a problem that the estimation accuracy decreases when the nugget diameter is estimated using the expansion amount. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms. According to one embodiment of the present disclosure, there is provided a method for estimating a nugget diameter in resistance welding, the method comprising: a step of identifying an expansion amount of a workpiece in the resistance welding; a step of estimating a sheet thickness of the workpiece from an initial position of an electrode in the resistance welding; a step of estimating an expansion amount of the workpiece using master information including information indicating a correlation between the sheet thickness and the expansion amount of the workpiece and a reference expansion amount corresponding to a reference sheet thickness and the estimated sheet thickness; a step of comparing the estimated expansion amount with the reference expansion amount; a step of correcting the expansion amount identified in the resistance welding using a result of the comparison; and a step of estimating the nugget diameter using the corrected expansion amount, the step of estimating the nugget diameter including a step of applying the corrected expansion amount to a multiple regression equation obtained for the reference sheet thickness, the multiple regression equation having at least the expansion amount of the workpiece as an explanatory variable and the nugget diameter as a response variable.

[0006] According to one aspect of the present disclosure, there is provided a method for estimating a nugget diameter in resistance welding, the method including the steps of: estimating a sheet thickness of a workpiece from an initial position of an electrode in the resistance welding; correcting an expansion amount of the workpiece in the resistance welding using the estimated sheet thickness to obtain a corrected expansion amount; and estimating the nugget diameter using the corrected expansion amount. According to this form of method, the plate thickness of the workpieces to be welded is estimated, the amount of expansion of the workpieces from the estimated plate thickness is estimated, and the estimated plate thickness is used to correct the amount of expansion during resistance welding. Therefore, even if the plate thickness deviates from the nominal plate thickness at the time of design, the nugget diameter is estimated after correcting for the variation in the amount of expansion, thereby suppressing a decrease in estimation accuracy. The present disclosure may be realized in various forms other than the method for estimating a nugget diameter, for example, a computer program for implementing the method for estimating a nugget diameter, a non-transitory recording medium on which the computer program is recorded, or the like. [Brief description of the drawings]

[0007] [Figure 1] 1 is a diagram showing a schematic configuration of a resistance welding device according to an embodiment of the present invention; [Diagram 2] FIG. 4 is a process diagram showing a method for estimating a nugget diameter in the first embodiment. [Diagram 3] 1 is a graph showing the relationship between the initial position of the electrode and the plate thickness of the workpiece. [Figure 4] 1 is a graph showing the correspondence relationship between the plate thickness of the workpiece and the amount of expansion. [Diagram 5] 13 is a graph showing estimated values ​​and actual measured values ​​of nugget diameters when the nugget diameter is estimated according to a comparative example. [Figure 6] 1 is a graph showing estimated values ​​and actual measured values ​​when the nugget diameter is estimated by the method of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A. First embodiment: A1: Equipment configuration: 1 is a diagram showing a schematic configuration of a resistance welding apparatus 100 in this embodiment. The resistance welding apparatus 100 is an apparatus that applies a current to a plurality of overlapping workpieces W1, W2 to generate Joule heat and join the workpieces W1, W2. The resistance welding apparatus 100 includes a welding gun 10, a robot 20, a resistance measuring device 30, and a control unit 40.

[0009] The workpieces W1 and W2 are metal materials such as aluminum or steel. The workpieces W1 and W2 may be the same type of metal material or different types of metal materials. The workpieces W1 and W2 are not limited to two sheets, and may be three or more sheets.

[0010] The welding gun 10 includes a gun body 1, a pair of electrodes, that is, an upper electrode 2 and a lower electrode 3, and an actuator 4.

[0011] The upper electrode 2 and the lower electrode 3 include shanks 5a, 5b, tips 6a, 6b, and strain sensors 7a, 7b. The upper electrode 2 is attached to the upper part 1a of the gun body 1 via an actuator 4. The lower electrode 3 is disposed in the lower part 1b of the gun body 1. In this embodiment, the upper electrode 2 is a moving electrode, and the lower electrode 3 is a fixed electrode. The tips 6a, 6b are attached to the tips of the shanks 5a, 5b, respectively. The tips 6a, 6b come into contact with the workpieces W1, W2 when resistance welding is performed. The strain sensors 7a, 7b are attached to the sides of the shanks 5a, 5b, respectively. The strain sensors 7a, 7b measure the amount of expansion and contraction of the workpieces W1, W2 from a state where they are overlapped during resistance welding. The strain sensors 7a, 7b are sensors that can optically detect the amount of displacement of the workpieces W1, W2, for example. The measured amounts of expansion and contraction are transmitted to the control unit 40.

[0012] The actuator 4 is attached to the upper part 1a of the gun body 1, and moves the upper electrode 2 in a direction to contact the lower electrode 3 or in a direction to move the upper electrode 2 away from the lower electrode 3. As a result, the workpieces W1, W2 are pressed and clamped between the upper electrode 2 and the lower electrode 3 when resistance welding is performed. The actuator 4 is, for example, an electric actuator, a hydraulic actuator, or a pneumatic actuator.

[0013] The robot 20 is, for example, an articulated robot, etc. The robot 20 moves the welding gun 10 in the horizontal and vertical directions and operates to rotate the welding gun 10 about an arbitrary rotation axis, thereby changing the position and angle of the welding gun 10.

[0014] The resistance measuring device 30 measures the circuit resistance value in the resistance welding apparatus 100. In this embodiment, the circuit resistance value is the resistance value of the entire system including the welding gun 10, the robot 20, the resistance measuring device 30, and the control unit 40. The circuit resistance value measured by the resistance measuring device 30 is transmitted to the control unit 40.

[0015] The control unit 40 controls the operation of the welding gun 10 and the robot 20. Specifically, the control unit 40 adjusts the current value flowing through the upper electrode 2 and the lower electrode 3, adjusts the pressure applied to the workpieces W1 and W2 by the operation of the actuator 4, and adjusts the positions of the welding points of the upper electrode 2 and the lower electrode 3 on the workpieces W1 and W2. The control unit 40 can also estimate the plate thickness of the workpieces W1 and W2 from the positions of the upper electrode 2 and the lower electrode 3 when the workpieces W1 and W2 are sandwiched between the upper electrode 2 and the lower electrode 3. The control unit 40 is realized by, for example, a computer having a processor and a memory. The processor is, for example, a central processing unit (CPU), and the memory is, for example, a read only memory (ROM), a random access memory (RAM), and a storage.

[0016] When welding the workpieces W1, W2 using the resistance welding apparatus 100 described above, the upper electrode 2 and the lower electrode 3 clamp the workpieces W1, W2 and apply pressure while passing current between them. The workpieces W1, W2 melt due to resistance heat generated by the current passing through them and then solidify, thereby joining the workpieces W1, W2. A nugget is formed at the joint interface of the joined workpieces W1, W2. The nugget is a portion where the molten parts of the workpieces W1, W2 are cooled and solidified. The nugget has a go stone shape with the joint interface as the center plane.

[0017] A2. Method for estimating nugget diameter: 2 is a process diagram showing a method for estimating a nugget diameter in the first embodiment. The method for estimating a nugget diameter is performed to evaluate the reliability of resistance welding. For example, if the nugget diameter obtained by this estimation method is within a normal range, the reliability of the resistance welding is evaluated as high. On the other hand, if the nugget diameter is out of the normal range, the reliability of the resistance welding is evaluated as low.

[0018] The amount of expansion of the workpieces W1, W2 during resistance welding is identified (step S105). In this embodiment, the amount of expansion is the amount of displacement of the workpieces W1, W2 from the start of current flow from the electrodes to the workpieces W1, W2 to the end of current flow. The amount of expansion can be identified by measuring using the strain sensors 7a, 7b when the workpieces W1, W2 are resistance welded.

[0019] The plate thickness of the workpieces W1 and W2 is estimated from the initial position of the electrode in resistance welding (step S110). FIG. 3 is a graph showing the relationship between the initial position of the electrode and the plate thickness of the workpieces W1 and W2. The horizontal axis shows the initial position of the electrode, and the vertical axis shows the plate thickness of the workpieces W1 and W2. In this embodiment, the initial position of the electrode refers to the height of the electrode when the tips 6a and 6b contact the workpieces W1 and W2 in a non-energized state. The thickness of the workpieces W1 and W2 can be estimated from the initial position of the electrode. The reference for the initial position of the electrode is determined by the position of the electrode when the resistance welding device 100 is started. "Nominal" in FIG. 3 indicates the initial position of the electrode corresponding to the plate thickness specified in the nominal drawing. "Reduced plate thickness" indicates an example of the initial position of the electrode when the plate thickness is thinner than the plate thickness specified in the nominal drawing.

[0020] The expansion amounts of the workpieces W1 and W2 are estimated using information indicating the correlation between the plate thickness and the expansion amount of the workpieces W1 and W2, master information including a reference expansion amount corresponding to the reference plate thickness, and the estimated plate thickness (step S115). In this embodiment, the reference plate thickness refers to the plate thickness of the workpieces W1 and W2 specified in the design drawing. The reference expansion amount refers to the expansion amount measured when the workpieces W1 and W2 having the reference plate thickness are welded. FIG. 4 is a graph showing the correspondence relationship between the plate thickness and the expansion amount of the workpieces. Such a graph can be obtained, for example, by performing a simple regression analysis with the expansion amount as the objective variable and the plate thickness as the explanatory variable. Specifically, resistance welding is performed on the workpieces W1 and W2 having various plate thicknesses, and data on the plate thickness and the expansion amount are accumulated. Next, the accumulated data is plotted and the least squares method is performed to obtain a regression equation. The expansion amounts of the workpieces W1 and W2 are estimated using the correspondence relationship between the plate thickness and the expansion amount thus obtained and the plate thickness estimated in step S110.

[0021] The expansion amount estimated in step S115 is compared with the standard expansion amount included in the master information (step S120). As shown in FIG. 4, by comparing the estimated expansion amount with the standard expansion amount, the change in the expansion amount due to the variation in plate thickness can be investigated. Note that "nominal" in FIG. 4 indicates an example of the expansion amount corresponding to the plate thickness specified in the nominal drawing, that is, the standard expansion amount. "Thickness reduction" indicates an example of the expansion amount estimated when the plate thickness is thinner than the plate thickness specified in the nominal drawing. In step S120, the estimated expansion amount is divided by the standard expansion amount to calculate the ratio of the estimated expansion amount to the standard expansion amount (estimated expansion amount / standard expansion amount).

[0022] Using the result of the comparison in step S120, the amount of expansion during resistance welding is corrected (step S125). In step S125, the amount of expansion measured by the strain sensors 7a and 7b during resistance welding is corrected. Specifically, the amount of expansion identified in step S105 is multiplied by the inverse of the "ratio of the estimated amount of expansion to the reference amount of expansion" calculated in step S120 (reference amount of expansion / estimated amount of expansion). Note that the above-mentioned steps S105, S115 to S125 can also be said to be processes of correcting the amount of expansion of the workpieces W1 and W2 during resistance welding using the estimated plate thickness to obtain the corrected amount of expansion.

[0023] The nugget diameter is estimated using the corrected expansion amount (step S130). The nugget diameter is estimated by a multiple regression equation with the nugget diameter as the objective variable and the expansion amount, contraction amount, and circuit resistance value of the welded objects W1 and W2 during resistance welding as explanatory variables. Here, the larger the expansion amount and contraction amount, the larger the estimated nugget diameter, and the larger the resistance value, the smaller the estimated nugget diameter. Such a multiple regression equation is obtained by collecting the expansion amount, contraction amount, and circuit resistance value during resistance welding as experimental data and performing multiple regression analysis. When estimating the nugget diameter using such a multiple regression equation, if the expansion amount measured by the strain sensors 7a and 7b is used, the fluctuation in the expansion amount due to the fluctuation in the plate thickness is not taken into consideration, so there is a risk that the estimation accuracy of the nugget diameter will decrease. Therefore, the measured expansion amount is corrected as described in step S125, and the nugget diameter is estimated using the corrected expansion amount.

[0024] According to the method for estimating the nugget diameter according to the embodiment described above, when the plate thickness of the workpieces W1 and W2 deviates from the nominal value in the drawing, the nugget diameter is estimated by correcting the change in the expansion amount caused by the fluctuation in the plate thickness. Therefore, even if the plate thickness deviates from the nominal value in the drawing, it is possible to suppress a decrease in the estimation accuracy of the nugget diameter.

[0025] FIG. 5 is a graph showing the estimated value and the actual measurement value of the nugget diameter when the nugget diameter is estimated by the comparative example. In the comparative example, the expansion amount is not corrected and is used in the multiple regression equation for estimating the nugget diameter. FIG. 6 is a graph showing the estimated value and the actual measurement value when the nugget diameter is estimated by the method of the embodiment. In FIG. 5 and FIG. 6, the horizontal axis indicates the estimated value of the nugget diameter, and the vertical axis indicates the actual measurement value of the nugget diameter. In addition, in FIG. 5 and FIG. 6, the solid line L1 is a line where the estimated value and the actual measurement value match, that is, a line indicating that the estimation accuracy is 100%. The broken line L2 is a line indicating that the estimated value is 10% short of the actual measurement value. The broken line L3 is a line indicating that the estimated value is 10% over the actual measurement value. Here, the estimation accuracy refers to the ratio of the estimated value based on the actual measurement value. It is preferable that the estimation accuracy is within a range of -10% to +10%. As shown in FIG. 5, in the case of the comparative example, the estimation accuracy was within the range of -19% to 0%. The reason why there are many data in which the estimated value is smaller than the actual measured value is that when the plate thickness is thinner than the nominal value in the drawing, the expansion amount is small, and the estimated value is estimated to be smaller than the actual value. As shown in FIG. 6, according to the method of the embodiment, the nugget diameter is estimated after correcting the fluctuation in the expansion amount due to the deviation of the plate thickness from the nominal plate thickness, so the estimation accuracy was within the range of -14% to +3%. This shows that the decrease in estimation accuracy is suppressed by the method of estimating the nugget diameter of the embodiment.

[0026] In addition, according to the method of the present embodiment, since it is possible to suppress the deterioration of the estimation accuracy of the nugget diameter, it is possible to calculate the reliability of the weld while maintaining a certain level. This makes it possible to omit the process of ultrasonic inspection by an inspector to check the reliability of the weld, thereby realizing a reduction in manufacturing costs.

[0027] B. Other embodiments: (B1) In step S110 of the first embodiment, the sheet thicknesses of the workpieces W1, W2 are estimated from the initial positions of the electrodes, but the sheet thicknesses of the workpieces W1, W2 may be estimated from the initial positions of the tips 6a, 6b instead of the initial positions of the electrodes. Also, the sheet thicknesses of the workpieces W1, W2 may be estimated from the distance between the tips 6a, 6b.

[0028] (B2) In step S120 of each embodiment, the reference expansion amount is an expansion amount estimated from the plate thickness specified in the nominal drawing, but instead, it may be an expansion amount estimated from an arbitrary plate thickness.

[0029] (B3) In each embodiment, the nugget diameter may be estimated by the control unit 40. In such a case, the control unit 40 may estimate the nugget diameter by executing a program recorded in the memory. Furthermore, the master information may be recorded in the memory of the control unit 40.

[0030] (B4) In each embodiment, the resistance welding apparatus 100 has been described in which the upper electrode 2 is a moving electrode and the lower electrode 3 is a fixed electrode, but instead of this configuration, the upper electrode 2 may be a fixed electrode and the lower electrode 3 may be a moving electrode. Also, both the upper electrode 2 and the lower electrode 3 may be moving electrodes.

[0031] (B5) In each embodiment, the amount of expansion and contraction is measured by the strain sensors 7a, 7b. However, instead of this, the amount of expansion and contraction may be measured using the amount of displacement of the movable electrode.

[0032] (B6) In each embodiment, the amount of expansion used to estimate the nugget diameter may be the maximum value of the displacement of the workpieces W1 and W2 in the time range from the start of energization to the end of energization. Also, instead of the maximum value of the displacement, an integral value or an average value of the displacement may be used. Also, instead of the time range from the start of energization to the end of energization, any time range may be used.

[0033] The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features of the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention 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. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0034] The present disclosure may be realized, for example, in the following forms. [Form 1] A method for estimating a nugget diameter in resistance welding, comprising: determining an expansion amount of a workpiece during the resistance welding; estimating a plate thickness of the workpiece from an initial position of an electrode in the resistance welding; A step of estimating the expansion amount of the workpiece using master information including information indicating a correlation between the plate thickness and the expansion amount of the workpiece and a reference expansion amount corresponding to a reference plate thickness, and the estimated plate thickness; comparing the estimated expansion amount with the reference expansion amount; using the results of the comparison to correct the amount of expansion determined during the resistance welding; estimating the nugget diameter using the corrected expansion amount; Equipped with The step of estimating the nugget diameter includes a step of applying the corrected expansion amount to a multiple regression equation obtained for the reference plate thickness, the multiple regression equation having at least the expansion amount of the welded object as an explanatory variable and the nugget diameter as a response variable, A method for estimating nugget diameter. [Explanation of symbols]

[0035] 1...gun body, 1a...upper part, 1b...lower part, 2...upper electrode, 3...lower electrode, 4...actuator, 5a, 5b...shank, 6a, 6b...tips, 7a, 7b...sensors, 10...welding gun, 20...robot, 30...resistance measuring device, 40...control unit, 100...resistance welding device, W1, W2...workpieces to be welded

Claims

[Claim 1] A method for estimating a nugget diameter in resistance welding, comprising: determining an expansion amount of a workpiece during the resistance welding; estimating a plate thickness of the workpiece from an initial position of an electrode in the resistance welding; A step of estimating the expansion amount of the workpiece using master information including information indicating a correlation between the plate thickness and the expansion amount of the workpiece and a reference expansion amount corresponding to a reference plate thickness, and the estimated plate thickness; comparing the estimated expansion amount with the reference expansion amount; using the results of the comparison to correct the amount of expansion determined during the resistance welding; estimating the nugget diameter using the corrected expansion amount; Equipped with The step of estimating the nugget diameter includes a step of applying the corrected expansion amount to a multiple regression equation obtained for the reference plate thickness, the multiple regression equation having at least the expansion amount of the welded object as an explanatory variable and the nugget diameter as a response variable, A method for estimating nugget diameter.

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