Method for estimating nugget diameter in resistance spot welding, estimation device, and estimation system

Abstract

A nugget diameter estimation method includes: a step of acquiring time-series data including data before current application for each welding point with respect to two or more welding parameters including an expansion amount calculated based on displacement of an upper electrode and a lower electrode; a step of calculating: (i) a first difference between the expansion amount of a first point before current application and the expansion amount of an Nth point before current application, where N is an integer of two or more and M or less; and (ii) a second difference between the welding parameter of a first point after a current application start time point and the welding parameter of an Nth point after the current application start time point; and a step of estimating a nugget diameter of a Pth point using the welding parameter, where P is an integer of one or more and M or less.

Description

Technical Field

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

[0002] Previously, a technique was known in which the diameter of the weld nugget in resistance spot welding was estimated by creating approximate formulas related to the expansion or contraction of the base material based on the amount of thermal expansion of the base material during the application of welding current and the amount of contraction of the base material after the application of welding current was stopped (Japanese Patent Application Laid-Open No. 2003-181649). Summary of the Invention

[0003] In previous technologies, when resistance spot welding was performed sequentially on multiple weld points located at different positions on the base material, the accuracy of estimating the weld nugget diameter could be reduced.

[0004] This disclosure may be implemented in the following ways.

[0005] (1) According to a first aspect of this disclosure, a method for estimating the weld nugget diameter in resistance spot welding is provided. In the method for estimating the weld nugget diameter in resistance spot welding of a welded component held by an upper electrode and a lower electrode, the resistance spot welding is performed sequentially from the first point to the Mth point for M welding points existing at different positions of the welded component, where M is an integer of 2 or more. The estimation method includes: an acquisition step, acquiring timing data including data before the start of energizing the welding current for each welding point, with regard to two or more welding parameters that affect the size of the weld nugget diameter and which include expansion amounts calculated based on the displacement of the upper electrode and the lower electrode; and a differential calculation step, calculating: (i) a first difference, which is the difference between the weld nugget diameter of the first point before the start of energizing the weld nugget diameter. The expansion amount is the difference between the expansion amount at point N before the start of energization, where N is an integer greater than or equal to 2 and less than or equal to M; and (ii) a second difference, which is the difference between the welding parameters at point 1 after the start of energization and the welding parameters at point N after the start of energization; and an estimation step, which uses the welding parameters to estimate the weld nugget diameter at point P, where P is an integer greater than or equal to 1 and less than or equal to M. The estimation step uses the expansion amount at point P before the start of energization and the correlation between the first difference and the second difference to correct the calculated welding parameters at point P, and uses the corrected welding parameters to estimate the weld nugget diameter. According to this method, when welding is performed sequentially from point 1 to point M, the welding parameters tend to change at each welding point due to the influence of electrode heating. In contrast, according to this method, the welding parameters at point P, which is the object of estimation for the weld nugget diameter, are corrected using the expansion amount before the start of energization, which is related to the temperature of the electrode, and the weld nugget diameter is estimated. Therefore, when resistance spot welding is performed sequentially on multiple weld points located at different positions on the welded component, the weld nugget diameter can be estimated by taking into account the differences in welding parameters at each weld point caused by the difference in electrode temperature. Thus, when resistance spot welding is performed sequentially on multiple weld points located at different positions on the welded component, the reduction in the estimation accuracy of the weld nugget diameter can be suppressed. (2) Based on the above method, it may also include: a revision process for creating a revision form showing the aforementioned relationship; the aforementioned estimation process includes: substituting a third difference into the revision form to calculate the correction value of the aforementioned welding parameters when estimating the aforementioned weld nugget diameter at the aforementioned point P, wherein the third difference is the difference between the aforementioned expansion amount at the aforementioned point 1 before the start of energization and the aforementioned expansion amount at the aforementioned point P before the start of energization; and substituting the aforementioned welding parameters, which have been corrected by adding the aforementioned correction value to the aforementioned welding parameters at the aforementioned point P, into a predetermined estimation formula that uses the aforementioned welding parameters as explanatory variables and the estimated value of the aforementioned weld nugget diameter as the target variable, to calculate the aforementioned estimated value of the aforementioned weld nugget diameter. According to this method, a revision form for calculating the correction amount of the welding parameters substituted into the estimation formula for the weld nugget diameter can be created. Thus, by substituting the corrected welding parameters, which have been corrected using the revision form, into the estimation formula, the estimation accuracy of the weld nugget diameter can be improved. (3) Based on the above method, the aforementioned revision form can also be a linear equation calculated by performing linear regression on the aforementioned values ​​determined by the combination of the first difference and the second difference. According to this method, the correlation between the first difference and the second difference can be uniquely expressed. In addition, the revision form can be easily made based on the values ​​determined by the combination of the first difference and the second difference. (4) Based on the above method, the aforementioned revision formula can also be a higher-order equation calculated by performing nonlinear regression on the aforementioned values ​​determined by the combination of the first difference and the second difference. According to this method, compared with the case of making the revision formula through linear regression, a revision formula that reflects the correlation between the first difference and the second difference in more detail can be made. Therefore, the estimation accuracy of the melt core diameter can be further improved. (5) Based on the above method, if the expansion amounts at multiple time points before the start of energization are calculated at the same welding point, the first difference can be calculated using the average of the multiple expansion amounts before the start of energization. According to this method, it is possible to avoid calculating the first difference based solely on outliers when extreme changes occur in welding parameters before the start of energization. (6) According to a second aspect of this disclosure, an apparatus for estimating the weld nugget diameter in resistance spot welding is provided. In the apparatus for estimating the weld nugget diameter in resistance spot welding of a welded component held by an upper electrode and a lower electrode, the resistance spot welding is performed sequentially from the first point to the Mth point for M welding points located at different positions of the welded component, wherein M is an integer of 2 or more. The estimation apparatus comprises: an acquisition unit that acquires timing data including data before the start of energizing the welding current for each welding point, with regard to two or more welding parameters that affect the size of the weld nugget diameter and which include expansion amounts calculated based on the displacements of the upper electrode and the lower electrode; and a difference calculation unit that calculates: (i) a first difference, which is the difference between the weld nugget diameter of the first point before the start of energizing the weld nugget diameter. The expansion amount is the difference between the expansion amount at point N before the start of energization, where N is an integer greater than or equal to 2 and less than or equal to M; and (ii) a second difference, which is the difference between the welding parameters at point 1 after the start of energization and the welding parameters at point N after the start of energization; and an estimation unit, which uses the welding parameters to estimate the weld nugget diameter at point P, where P is an integer greater than or equal to 1 and less than or equal to M. The estimation unit uses the expansion amount at point P before the start of energization and the correlation between the first difference and the second difference to correct the calculated welding parameters at point P, and uses the corrected welding parameters to estimate the weld nugget diameter. According to this method, when welding is performed sequentially from point 1 to point M, the welding parameters tend to change at each welding point due to the influence of electrode heating. In contrast, according to this method, the welding parameters at point P, which is the object of estimation for the weld nugget diameter, are corrected using the expansion amount before the start of energization, which is related to the temperature of the electrode, and then the weld nugget diameter is estimated. Therefore, when resistance spot welding is performed sequentially on multiple weld points located at different positions on the welded component, the weld nugget diameter can be estimated by taking into account the differences in welding parameters at each weld point caused by the difference in electrode temperature. Thus, when resistance spot welding is performed sequentially on multiple weld points located at different positions on the welded component, the reduction in the estimation accuracy of the weld nugget diameter can be suppressed. (7) According to a third aspect of this disclosure, a system for estimating the weld nugget diameter in resistance spot welding is provided. In this system for estimating the weld nugget diameter in resistance spot welding of a welded component held by an upper electrode and a lower electrode, the resistance spot welding is performed sequentially from the first point to the Mth point at M different locations on the welded component, where M is an integer of 2 or more. The system includes an estimation device as described in the above-described method and a measuring mechanism for generating timing data of welding parameters. According to this method, the weld nugget diameter can be estimated using the timing data generated by the measuring mechanism. This disclosure can be implemented in various ways other than the estimation method, estimation device, and estimation system described above in resistance spot welding. For example, it can be implemented by a method for manufacturing the estimation device and estimation system, a method for controlling the estimation device and estimation system, a computer program for implementing the control method, and a non-transient recording medium on which the computer program is recorded. Attached Figure Description

[0006] 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 general structure of the estimation system. Figure 2 This is a schematic diagram illustrating the process of resistance spot welding. Figure 3 This is a block diagram showing the general structure of the estimation system. Figure 4 This is the first graph showing the timing data of the displacement between electrodes for each welding point. Figure 5 It is a graph showing the relationship between the amount of expansion in the region before energization begins and the electrode temperature. Figure 6 This is the second graph, showing the timing data of the displacement between electrodes for each welding point. Figure 7 It is a graph showing the timing data of the resistance values ​​in the energized interval for each weld point. Figure 8 This is a graph used to compare the estimated error of the melt core diameter before and after correction. Figure 9 This is a flowchart illustrating the method for estimating the diameter of the melt core. Figure 10 This is a flowchart showing the details of the differential calculation process. Figure 11 This is a diagram illustrating an example of the modified formula. Figure 12 This is a flowchart showing the details of the estimated process. Figure 13 It is a graph used to compare welding parameters before and after the application of the modified formula. Detailed Implementation

[0007] A. First implementation method: Figure 1This is a schematic diagram showing the general configuration of the estimation system 1. The estimation system 1 is a system for estimating the weld nugget diameter when resistance spot welding (hereinafter, welding) is performed sequentially from the 1st point to the Mth point at M welding points located at different positions on the welded component W (base material). In other words, the estimation system 1 estimates the weld nugget diameter when welding is performed two or more times consecutively at different welding points. The estimation system 1 includes a resistance spot welding apparatus 10, a control device 100, and a measuring mechanism 9.

[0008] 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.

[0009] 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.

[0010] 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 connected 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.

[0011] 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.

[0012] 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.

[0013] Figure 2 This is a schematic diagram illustrating the resistance spot welding process. In this embodiment, we will take the case of welding two metal plates W1 and W2 as an example, which is the component to be welded, W.

[0014] First, with the top 3a of the lower electrode 3 in contact with the second metal plate W2 and the first metal plate W1 placed on the second metal plate W2, the control device 100 sends a descent command to the electrode lifting device 4, causing the upper electrode 2 to descend toward the first metal plate W1. Thus, the upper electrode 2 descends from a predetermined initial position toward the part to be welded W, which is then held by the upper electrode 2 and the lower electrode 3. Next, the control device 100 sends a command to the pressurizing device 5 to initiate pressurization. As a result, the part to be welded W is pressurized by the pair of electrodes 2 and 3 with a predetermined pressure.

[0015] Next, while the component W to be welded is held and pressurized by the upper electrode 2 and the lower electrode 3 (hereinafter, the holding state), welding current flows between the upper electrode 2 and the lower electrode 3. The control device 100 sends a current command related to the start of energization to the current adjustment device 6, causing the welding current to continue for a predetermined energization time. As a result, utilizing the resistance heating generated during the energization of the welding current (hereinafter, during energization), the area near the interface WS of the first metal plate W1 and the second metal plate W2 in the component W to be welded melts. Figure 2 In the diagram, the molten portion M of the welded component W is shown by sparse shadow lines. Then, as the resistive heating increases and the molten portion M forms, the welded component W undergoes three-dimensional thermal expansion in a manner that pushes electrodes 2 and 3 back.

[0016] After a predetermined energizing time has elapsed since the start of energizing, the control device 100 sends a current command related to stopping energizing to the current adjusting device 6, maintaining a holding state while stopping the energizing of the welding current. Then, after a predetermined holding time, the control device 100 sends a command related to stopping pressure to the pressure applying device 5, stopping the pressure on the welded component W. In other words, after the energizing stop time, the holding state continues for a predetermined holding time. Next, the control device 100 sends a rising command to the electrode lifting device 4, causing the upper electrode 2 to separate from the first metal plate W1. As a result, the welded component W is released from electrodes 2 and 3.

[0017] At this time, due to the resistive heating generated during energization, the hardness (e.g., Brinell hardness) of the welded part W at the point where energization stops decreases compared to the point where energization begins. That is, the welded part W at the point where energization stops becomes softer than the welded part W at the point where energization begins. Moreover, during the period from the point where energization stops until the point after a predetermined holding time, the welded part W is continuously pressurized by a pair of electrodes 2 and 3. Consequently, the welded part W contracts in three dimensions in a way that it expands along the extension direction D2 of the plane orthogonal to the pressing direction D1 of electrodes 2 and 3.

[0018] Furthermore, in reality, the thermal expansion and contraction of the welded component W occur in three dimensions. However, in this disclosure, the degree of thermal expansion of the welded component W (hereinafter, component expansion amount) is calculated as the change in size of the welded component W in the expansion direction D3. The "expansion direction D3" referred to here is the direction orthogonal to the interface WS of the welded component W, the direction that pushes back the pair of electrodes 2 and 3, and the direction opposite to the pressure direction D1 of the electrodes 2 and 3. Additionally, in this disclosure, the degree of contraction of the welded component W (hereinafter, component contraction amount) is the change in size of the welded component W in the pressure direction D1, calculated as the change from the point when the energization was stopped.

[0019] Then, due to the cessation of power supply, the heat generated by resistance decreases, and the temperature of the welded component W drops, thereby causing the molten portion M of the welded component W to gradually solidify. Thus, multiple metal plates W1 and W2 are joined. A weld nugget N is formed at the joint interface WS where the multiple metal plates W1 and W2 are joined. The weld nugget N is the solidified joint portion after the metal plates W1 and W2 have melted. Figure 2 In the diagram, the weld nugget N is shown with densely drawn shadows. The shape of the weld nugget N is approximately the shape of a Go stone, passing through the center O of the joint and centered on the plane along the extension direction D2. Hereinafter, the dimension of the weld nugget N along the direction of the joint interface WS of the welded parts W will be referred to as the weld nugget diameter LN.

[0020] Figure 3 This is a block diagram showing the general configuration of the estimation system 1. In this embodiment, the control device 100, in addition to controlling the operation of the resistance spot welding device 10, also functions as an estimation device for estimating the weld nugget diameter LN in resistance spot welding. Furthermore, the estimation device may also be configured to be separate from the control device 100 and communicate with it via wired or wireless means.

[0021] 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.

[0022] The storage unit 60 stores various programs, including those controlling the operation of the resistance spot welding apparatus 10, and various data such as the modification formula 650 and the estimation formula 670. The estimation formula 670 is a pre-prepared formula for calculating the estimated value of the weld nugget diameter LN. Specifically, the estimation formula 670 is a formula that uses welding parameters that affect the size of the weld nugget diameter LN, and welding parameters after the energization start time, as explanatory variables, and the estimated value of the weld nugget diameter LN as the target variable. The modification formula 650 is a formula created to calculate the correction value of the welding parameters substituted into the estimation formula 670. The storage unit 60 includes RAM, ROM, rewritable non-volatile memory, etc.

[0023] 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.

[0024] 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, contraction amount, and pressure applied to electrodes 2 and 3. The motion control unit 200 comprehensively controls the operation of the resistance spot welding apparatus 10 based, for example, on the preset values ​​of the welding parameters set by the user via the input operation unit 50.

[0025] The acquisition unit 210 acquires timing data (described later) for each welding point. The differential calculation unit 220 uses the timing data to calculate the differential data (described later). The revision form production unit 230 uses the differential data to produce a 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 formula 670. The estimation unit 290 includes a parameter correction unit 291 and an estimation value calculation unit 292. The parameter correction unit 291 calculates the corrected parameters that reflect the correction values ​​in the welding parameters. The estimation value calculation unit 292 uses the corrected welding parameters to calculate the estimated value of the weld nugget diameter LN at point P (P is an integer greater than or equal to 1 and less than or equal to M, and so on). Details of each function are described later. Figure 9 The method for estimating the melting core diameter LN shown later will be described in conjunction with the following. Furthermore, at least a portion of the functions of CPU 20 can also be implemented via hardware circuitry.

[0026] 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 ​​calculated based on the measured values ​​obtained from the welding condition instructions sent from the motion control unit 200, that is, when welding is performed according to the preset welding parameter settings. When welding is performed sequentially from point 1 to point M for the component W to be welded, the actual values ​​of each welding parameter are measured separately for each welding point. The measured values ​​of the welding parameters measured by the measuring mechanism 9 are sent to the CPU 20 via the communication unit 30.

[0027] 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, a 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.

[0028] Each component 91 to 97 of the measuring mechanism 9 measures the actual values ​​of welding parameters at predetermined measurement times during the welding process (hereinafter, during welding). "During welding" refers to the period from the point when the welded component W is held and pressurized by a pair of electrodes 2 and 3 and enters a holding state (hereinafter, welding start time) to the point when the pressure on the welded component W is released and the welded component W enters a non-holding state (hereinafter, non-holding state) (hereinafter, welding end time). In this embodiment, the time point at which the measurement of welding parameters begins (hereinafter, measurement start time) is set to be the same as the welding start time. Furthermore, the time point at which the measurement of welding parameters ends (hereinafter, measurement end time) is set to be the same as the welding end time.

[0029] 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.

[0030] The voltage measuring unit 92 measures the voltage value (potential difference) between the upper electrode 2 and the lower electrode 3. The voltage measuring unit 92 is, for example, a voltage sensor.

[0031] 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.

[0032] 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.

[0033] The displacement measuring unit 96 includes a first displacement measuring unit 961 for measuring the displacement of the upper electrode 2 (hereinafter, the first displacement) and a second displacement measuring unit 962 for measuring the displacement of the lower electrode 3 (hereinafter, the second displacement).

[0034] 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.

[0035] 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.

[0036] 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 in the energized interval by adding the first and second displacements during the energized interval. However, the method for calculating the inter-electrode displacement is not limited to this.

[0037] Figure 4 The first figure shows the timing data DH1 to DH6 of the displacement between electrodes for each welding point. Figure 4 The horizontal axis represents the elapsed time from the start time point T1 of the measurement of the displacement between the electrodes. Figure 4The vertical axis represents the measured value of the displacement between the electrodes. Figure 4 The diagram shows the timing data DH1 to DH6, representing the inter-electrode displacement at each weld point from point 1 to point 6, welded sequentially. The term "timing data" here refers to data obtained by arranging the measured values ​​of welding parameters in chronological order. In other words, the timing data represents the progression of multiple measured values ​​for each welding parameter during the welding process. Furthermore, the set values ​​of the welding parameters are identical at each weld point from point 1 to point 6. Additionally, the timing data DH1 to DH6 can be... Figure 4 It can be generated as a chart, or as a collection of numerical data such as a table.

[0038] In this embodiment, the energizing start time T2, which begins energizing the component W to be welded, is 100 milliseconds elapsed from the welding parameter measurement start time T1. The energizing stop time T3, which stops energizing the component W to be welded, is 400 milliseconds elapsed from the welding parameter measurement start time T1. The measurement end time T4, which ends the welding parameter measurement, is a predetermined holding time elapsed from the energizing stop time T3. Figure 4 In the example shown, the measurement end time T4 is approximately 900 milliseconds elapsed from the energization stop time T3. Therefore, in this embodiment, the interval from the welding parameter measurement start time T1, from 0 milliseconds to slightly earlier than 100 milliseconds, is the "pre-energization start interval," and the interval from 100 milliseconds to slightly earlier than 400 milliseconds is the "energization in progress interval." Furthermore, the interval from the welding parameter measurement start time T1, after 400 milliseconds, is the "energization stop interval." Hereinafter, the inter-electrode displacement in the pre-energization start interval and the inter-electrode displacement in the energization in progress interval, specifically the inter-electrode displacement from the initial positions of electrodes 2 and 3, are also referred to as "expansion amount." Additionally, the inter-electrode displacement in the post-energization stop interval, specifically the inter-electrode displacement from the positions of electrodes 2 and 3 at the energization stop time T3, is also referred to as "contraction amount."

[0039] When welding is performed continuously from point 1 to point M, multiple weld points exist at different locations on the welded parts W. Therefore, at time points earlier than the energization start time T2, no thermal expansion occurs in the welded parts W near each weld point, and the expansion of the parts in the interval before energization is considered to be approximately zero. That is, the expansion of the parts does not affect the expansion (inter-electrode displacement) in the interval before energization. Therefore, assuming that an increase in the number of consecutive welds does not affect the measured values ​​of the welding parameters, the expansion in the interval before energization is considered to be independent of the weld points and approximately constant. However, in reality, as... Figure 4As shown, the time-series data DH1–DH6 regarding the expansion amount in the interval before energization show differences after points 1, 2, and 3. Based on this, the increase in the number of consecutive welding operations affects the measured values ​​of the welding parameters.

[0040] Figure 5 It is shown Figure 4 The graph shows the relationship between the expansion amount in the interval before energization begins and the electrode temperature. Figure 5 The horizontal axis represents the measured value of the expansion in the interval before the energization begins. Figure 5 The vertical axis represents the measured value of the electrode temperature (upper electrodes 2 and 22). For example... Figure 5 As shown, in terms of electrode temperature, point 2 is higher than point 1, and points 3 and beyond are higher than point 2. This is because the electrode temperature that rose during the previous welding did not completely decrease. Furthermore, after point 3, the electrode temperature at any welding point is in the range of 100 degrees Celsius or higher and 150 degrees Celsius or lower, indicating a high level of electrode temperature rise. In other words, when welding each welding point from point 1 to point 3, the electrode temperature rises accordingly with the increase in the number of consecutive welding operations. In contrast, when welding each welding point after point 4, the electrode temperature at point 3 is approximately maintained. Therefore, there is a correlation between the welding point (number of consecutive welding operations) and the electrode temperature. In addition, in this embodiment, the increase in electrode temperature due to the increase in the number of consecutive welding operations after point 4 is high, but the way the electrode temperature changes is not limited to this.

[0041] like Figure 2 As shown, when the electrode temperature rises, the upper electrode 2 and the lower electrode 3 undergo thermal expansion. Specifically, the higher the electrode temperature of the upper electrodes 2 and 22, the longer their lengths L10 and L20 (dimensions along the long side). In other words, the upper electrodes 2 and 22 extend towards the part W being welded as the electrode temperature rises. Figure 2In the diagram, the shape of the upper electrode 2 at point 1 during welding is shown in solid line. The shape of the upper electrode 22 at point N (where N is an integer between 2 and M) after point 1 during welding is shown in dashed line. Due to the increase in electrode temperature, the length L20 of the upper electrode 22 at point N becomes longer than the length L10 of the upper electrode 2 at point 1, and thus the separation distance L2 at point N becomes shorter than the separation distance L1 at point 1. Here, "separation distances L1 and L2" refer to the shortest straight-line distance between the tips 2a and 22a of the upper electrodes 2 and 22 and the welded component W, which is the distance traveled from the initial position of the upper electrodes 2 and 22 to the welded component W. Therefore, the difference between the separation distance L1 at point 1 and the separation distance L2 at point N represents the degree of thermal expansion of the upper electrodes 2 and 22 caused by the increase in electrode temperature due to resistive heating (hereinafter, the first electrode expansion amount). Furthermore, in this embodiment, the separation distances L1 and L2 are defined by the difference in the first displacement amount.

[0042] Furthermore, similar to the upper electrode 2, the higher the electrode temperature of the lower electrodes 3 and 33, the longer the length (dimension along the long side) of the lower electrode 3. Figure 2 In the diagram, the shape of the lower electrode 3 at point 1 during welding is shown in solid line. The shape of the lower electrode 33 at point N, which is further back than point 1, is shown in dashed line. As a result, the length of the lower electrode 3 at point N becomes longer than that at point 1, causing deformation in the lower electrode 3 during welding at point N. Therefore, the difference between the second displacement at point 1 and the second displacement at point N represents the degree of thermal expansion of the lower electrodes 3 and 33 caused by the rise in electrode temperature due to resistive heating (hereinafter, second electrode expansion).

[0043] Based on the above, by continuously performing welding on multiple different welding points, the electrode temperature rises while the lengths L10 and L20 of electrodes 2 and 3 change. Therefore, it is assumed that... Figure 4 As shown, the trend of the time series data DH1~DH6 of the inter-electrode displacement varies for each welding point. In fact, as... Figure 5 As shown by the straight line GS, the amount of expansion in the pre-energization interval is correlated with the electrode temperature. Specifically, the amount of expansion in the pre-energization interval increases in response to an increase in electrode temperature. Therefore, there is a correlation between the number of weld points (in consecutive welds) and the amount of expansion in the pre-energization interval.

[0044] Furthermore, as mentioned above, during the period before energization begins, the component expansion does not affect the inter-electrode displacement. Therefore, the inter-electrode displacement during the period before energization begins represents the degree of thermal expansion of the two electrodes 2 and 3 accompanying the rise in electrode temperature (hereinafter, electrode expansion). The "electrode expansion" referred to here is the value obtained by adding the first electrode expansion and the second electrode expansion.

[0045] Figure 6 The second figure shows the timing data DH1 and DH25 of the inter-electrode displacement for each welding point. Figure 7 It is a graph showing the timing data DT1 and DT25 of the resistance value in the energized interval for each weld point. Figure 6 The horizontal axis and Figure 7 The horizontal axis represents the elapsed time from the start time T1 of the welding parameter measurement. Figure 6 The vertical axis represents the measured value of the displacement between the electrodes. Figure 7 The vertical axis represents the measured resistance value. Figure 6 and Figure 7 In order to facilitate comparison of the difference in measured welding parameters after the energization start time T2 due to the increase in the number of consecutive welding operations, a chart is shown that has been pre-adjusted so that the measured values ​​of welding parameters in the interval before energization start are approximately the same at points 1 and 25. Furthermore, Figure 6 and Figure 7 The welding parameter settings shown are used when the timing data is obtained. Figure 4 same.

[0046] like Figure 6 As shown, the time-series data of inter-electrode displacement DH1 and DH25 show different tendencies at points 1 and 25. The following reasons can be considered as evidence of this difference in tendency based on the weld point.

[0047] like Figure 5 As shown, during welding from point 1 to point 3, the electrode temperature rises corresponding to the increase in the number of consecutive welds. That is, during welding at point 1, the electrode temperature continuously rises during the energized interval, so it is assumed that the electrode expansion increases during the energized interval. Therefore, in Figure 6 In the timing data DH1 of the electrode displacement during welding at point 1, it is assumed that both the component expansion and the electrode expansion contribute to the expansion during the energized interval.

[0048] In addition, such as Figure 5As shown, the expansion amount in the interval before the start of energization at point 2 is greater than that in the interval before the start of energization at point 1. Furthermore, since resistive heating is generated due to energization, the resistive heat generation does not increase during the period when energization is stopped, so it is difficult to conclude that the electrode temperature rises significantly in the interval after energization stops. Therefore, it is assumed that during welding at point 1, the electrode temperature at the energization stop time point T3 is approximately maintained in the interval after energization stops. Therefore, in Figure 6 In the timing data DH1 of the electrode displacement during welding at point 1, it is assumed that both the component shrinkage and the electrode shrinkage have an effect on the shrinkage in the interval after the power is turned off.

[0049] On the other hand, such as Figure 5 As shown, during welding after point 4, the electrode temperature remains approximately the same as during the third welding attempt, independent of the number of welding cycles. Therefore, it is assumed that during welding at point 25, the electrode expansion does not change in either the energized or energized intervals. Thus, in Figure 6 In the time series data DH25 of the electrode displacement during welding at point 25, it is believed that the component expansion mainly affects the expansion during the energized interval, and the component contraction mainly affects the contraction after the energization stops.

[0050] In fact, such as Figure 6 As shown, in the energized interval, for example, at a time point immediately before the energization stop time T3, where the expansion amounts are significantly different at points 1 and 25, the expansion amount at point 25 is smaller than that at point 1. Furthermore, in the interval after energization stops, the contraction amount at point 25 is smaller than that at point 1.

[0051] Moreover, such as Figure 7 As shown, the timing data DT1 and DT25 of the resistance values ​​show different tendencies at points 1 and 25. That is, it is assumed that the electrode temperatures differ within the interval before energization begins, thus resulting in differences in resistance values. In this case, the estimated nugget diameter LN, Equation 670, is based on the assumption that welding is performed using electrodes 2 and 3 at temperatures near room temperature, i.e., the nugget diameter LN at the welding point at point 1. Therefore, if the number of consecutive welding operations is not considered, i.e., if the welding parameters are not corrected before substituting into Equation 670, the estimated accuracy of the nugget diameter LN may decrease.

[0052] Figure 8 This graph is used to compare the estimated error of the weld nugget diameter LN 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 LN and the estimated value of the weld nugget diameter LN calculated using revision formula 670. Figure 8The left figure shows the estimation error of the weld nugget diameter LN when the welding parameters are not corrected by substituting into the opposite estimation formula 670, but the weld nugget diameter LN is estimated. Figure 8 The right figure shows the estimation error of the weld nugget diameter LN when the welding parameters, modified using formula 650, are substituted into formula 670 to estimate the weld nugget diameter LN. Figure 8 The horizontal axis in the left and right figures represents the estimated error of the melt core diameter LN. Figure 8 The vertical axis in the left and right figures is the measured diameter of the melt core, LN.

[0053] exist Figure 8 In this paper, data related to the estimated error for welding performed under four different welding conditions are plotted. For the welding under the first condition, the welding point at point 1 was performed with 2.0 liters of cooling water flowing through electrodes 2 and 3. For the welding under the second condition, the welding point at point 25 was performed with 2.0 liters of cooling water flowing through electrodes 2 and 3. For the welding under the third condition, the welding point at point 1 was performed with 1.3 liters less cooling water than under the first condition flowing through electrodes 2 and 3. For the welding under the fourth condition, the welding point at point 25 was performed with 1.3 liters less cooling water than under the first condition flowing through electrodes 2 and 3. Under each condition, the welding point to be welded and the cooling water flow rate (e.g., the set values ​​of welding parameters such as current) are the same. For any given condition, in Figure 8 In each case, multiple data points are displayed for each condition.

[0054] like Figure 8 As shown in the left figure, without correcting the welding parameters substituted into the reverse estimation formula 670, and estimating the weld nugget diameter LN, the estimation error of the weld nugget diameter LN at point 25 becomes more than 10%, regardless of the cooling water flow rate. In other words, without considering the rise in electrode temperature resulting from continuous welding from point 1 to point M, the estimation accuracy of the weld nugget diameter LN at point 25 is lower than that at point 1.

[0055] Therefore, the inventors of this application have studied a modification formula 650 that uses the amount of expansion in the pre-energization interval, which is related to the weld point (number of consecutive welds), to calculate the welding parameters to be substituted into the presumption formula 670.

[0056] Figure 9This is a flowchart illustrating a method for estimating the weld nugget diameter LN. Each step from S1 to S9 is performed by the estimation system 1. In the method for estimating the weld nugget diameter LN, the following steps are performed sequentially: obtaining the weld nugget diameter LN (step S1), differential calculation (step S3), refining the weld nugget (step S5), and estimating the weld nugget diameter (step S9). In this embodiment, an example is given of correcting a welding parameter A that differs from the amount of expansion. That is, in this embodiment, at least the welding parameter A, which differs from the amount of expansion, is included as an explanatory variable in estimation formula 670.

[0057] The acquisition process (step S1) involves acquiring timing data for each welding point, including data from the period before the start of energization of the welding current. In this embodiment, timing data for two or more welding parameters, including the expansion amount calculated based on the displacement of the upper electrode 2 and the lower electrode 3, is acquired.

[0058] In the acquisition process (step S1), the acquisition unit 210 acquires the measured values ​​of the welding parameters and generates a list of parameters for each welding parameter. Figure 4 The timing data shown is displayed on the display 40 and stored in the storage unit 60.

[0059] like Figure 9 As shown, after obtaining the process (step S1), the process is calculated by difference (step S3). Figure 10 This is a flowchart showing the details of the differential calculation process (step S3). The differential calculation process (step S3) is the process of calculating the first difference and the second difference separately. The first difference is the difference between the expansion amount at point 1 in the interval before the start of energization and the expansion amount at point N in the interval before the start of energization. The second difference is the difference between the welding parameter A at point 1 after the start of energization time T2 and the welding parameter A at point N after the start of energization time T2. At this time, the welding parameter A, which becomes the source data for calculating the second difference, is a value under the same selection conditions as the welding parameter A included as an explanatory variable in the presumed formula 670 for the weld nugget diameter LN. The "selection conditions" mentioned here include the selection conditions for the measured values, which time point or interval among the multiple measured values ​​of the welding parameter A after the start of energization time T2, and whether some numerical processing is performed on each measured value. Numerical processing refers to, for example, the processing of calculating the integral value of multiple measured values ​​or the processing of calculating the average value based on multiple measured values.

[0060] For example, when the welding parameter A in Estimated Formula 670, which is included as an explanatory variable in the weld nugget diameter LN, is the integral value of the measured value (e.g., expansion) for the entire energized interval, the second difference is the difference between point 1 and point N of the integral value of the measured value for the entire energized interval. For example, when the welding parameter A in Estimated Formula 670, which is included as an explanatory variable in the weld nugget diameter LN, is the maximum value of the measured value for the energized interval, the second difference is the difference between point 1 and point N of the maximum value of the measured value for the energized interval. For example, when the welding parameter A in Estimated Formula 670, which is included as an explanatory variable in the weld nugget diameter LN, is the average value of the measured values ​​within a predetermined selected time range in the energized interval, the second difference is the difference between point 1 and point N of the average value of the measured values ​​within the selected time range.

[0061] Here, the difference calculation unit 220 calculates the first difference and the second difference at at least two weld points from point 1 to point M. For example, if timing data exists for each weld point from point 1 to point 25, the first difference and the second difference can be calculated for all weld points from point 1 to point 25, or for each weld point from point 1 to any weld point (e.g., point 6). Figure 10 The diagram illustrates the method for calculating the differences at each weld point from point 1 to point N, from point 1 to point M.

[0062] In step S310, the differential calculation unit 220 refers to the timing data of the expansion amount and welding parameter A, and obtains the expansion amount in the interval before the start of energization and the welding parameter A after the start time point T2 for each welding point.

[0063] After step S310, the combination value calculation process (steps S321 to S335) is performed. The combination value calculation process (steps S321 to S335) involves calculating a first difference and a second difference for each weld point, and then calculating the combination value determined by the combination of the first and second differences. In the combination value calculation process (steps S321 to S335), the difference calculation unit 220 calculates the combination value for each weld point as difference data. The calculated difference data is appropriately displayed on the display 40 and stored in the storage unit 60.

[0064] In the combined value calculation process (steps S321 to S335), steps S321 and S322 are first executed. In step S321, the difference calculation unit 220 calculates the first difference at point 1. For example... Figure 4As shown, when the measured values ​​of the expansion amount at multiple time points in the interval before the start of energization are calculated at the same welding point, the difference calculation unit 220 calculates the first difference by averaging the measured values ​​of the expansion amount at each time point in the interval before the start of energization, for example.

[0065] In step S322, the difference calculation unit 220 calculates the second difference at point 1. At this time, both the first and second differences represent the difference between point 1 and point N. Therefore, both the first and second differences at point 1 are zero. Furthermore, steps S321 and S322 can be executed either first or in parallel after step S310.

[0066] After steps S321 and S322, step S325 is executed. In step S325, the difference calculation unit 220 calculates a first combination value determined by the combination of the first difference at point 1 and the second difference at point 1. In this embodiment, the combination value is a coordinate value in a coordinate system where the first difference is set as the x-coordinate value and the second difference is set as the y-coordinate value. Alternatively, the combination value can be defined by other indicators.

[0067] After step S325, steps S331 and S332 are executed. In step S331, the difference calculation unit 220 calculates the first difference at the second point. Specifically, the difference calculation unit 220 calculates the first difference, for example, by subtracting the average expansion amount of the second point in the interval before energization from the average expansion amount of the first point in the interval before energization. In step S332, the difference calculation unit 220 calculates the second difference at the second point. Specifically, the difference calculation unit 220 calculates the second difference, for example, by subtracting the maximum value of the welding parameters of the second point in the interval during energization from the maximum value of the welding parameters of the first point in the interval during energization. Furthermore, after step S325, steps S331 and S332 can be executed either one first or simultaneously. Alternatively, the difference calculation unit 220 can also calculate the difference between the first and second points using methods other than those described above.

[0068] After steps S331 and S332, step S335 is executed. In step S335, the difference calculation unit 220 calculates the second combination value determined by the combination of the first difference at the second point and the second difference at the second point.

[0069] Furthermore, the processing of each welding point from point 3 to point M, performed by the differential calculation unit 220, is the same as that of each step from S331 to S335. The calculated first difference, second difference, and combined value are stored as differential data in the storage unit 60.

[0070] like Figure 9As shown, after the difference calculation process (step S3), a revision process (step S5) is performed. The revision process (step S5) is a process of creating a revision form 650 that shows the correlation between the first difference and the second difference calculated in the difference calculation process (step S3). In other words, the revision form 650 is a relational expression that uses the first difference as the explanatory variable and the second difference as the target variable.

[0071] Figure 11 This is a diagram showing an example of revision 650. Figure 11 The horizontal axis represents the first difference. Figure 11 The vertical axis represents the second difference. Figure 11 The figure shows an example of a modified form 650 of welding parameter A, which is created using the combined values ​​at each weld point from point 1 to point 6. Welding parameter A is a welding parameter included as an explanatory variable in the presumed formula 670 of the weld nugget diameter LN, and is the welding parameter that is the subject of modification in this embodiment.

[0072] For example, when using the combined values ​​(x1, y1) to (x6, y6) at each welding point from point 1 to point 6 to create a revision form 650 for welding parameter A, the revision form creation unit 230 performs regression on the combined values ​​(x1, y1) to (x6, y6) at each welding point from point 1 to point 6. Thus, the revision form 650 for welding parameter A is created.

[0073] To be more specific, the formal production department 230, for example... Figure 11 As shown by the regression line GC, a linear regression is performed on the combined values ​​(x1, y1) to (x6, y6) at each welding point from point 1 to point 6. From this, the revision production unit 230 calculates the following linear equation (1) as revision form 650. Furthermore, a and b are constants determined by the combined values ​​of the first and second differences. y = ax + b (Equation 1) The generated modified form 650 is appropriately displayed on the display 40 and stored in the storage unit 60. Furthermore, the method for calculating the modified form 650 is not limited to this. The modified form 650 can also be generated using methods other than linear regression of the combined values. Additionally, the constants a and b, and the combined values ​​of the modified form 650 are not limited to this.

[0074] like Figure 9 As shown, after the formal manufacturing process (step S5), the estimation process (step S9) is performed. Figure 12This is a flowchart showing the details of the estimation process (step S9). In the estimation process (step S9), the correction value calculation process (step S7), the parameter correction process (step S91), and the estimation value calculation process (step S95) are executed sequentially. The correction value calculation process (step S7) is a process of calculating the correction value of welding parameter A using the correction form 650, which is the welding parameter A to be corrected. In the correction value calculation process (step S7), first, step S71 is executed.

[0075] In step S71, the correction value calculation unit 240 obtains the timing data of the welding process, which is the estimated target of the weld nugget diameter LN, and the timing data of the expansion amount (displacement between electrodes) and the welding parameter A, which is the target of correction.

[0076] After step S71, step S73 is executed. When estimating the weld nugget diameter LN at point P during welding, in step S73, the correction value calculation unit 240 obtains the expansion amount at point 1 and point P within the interval before energization begins. Then, the correction value calculation unit 240 calculates the difference (hereinafter, the third difference) between the expansion amount at point 1 and point P within the interval before energization begins. Afterward, the correction value calculation unit 240 substitutes the third difference into the correction formula 650. Thus, the correction value for the welding parameter A, which is the object of correction, is calculated (step S75). Furthermore, the correction value can be positive, negative, or zero.

[0077] After the correction value calculation process (step S7), the parameter correction process (step S91) is performed. In the parameter correction process (step S91), first, step S911 is performed. The parameter correction process (step S91) is a process of correcting the calculated welding parameter value of point P using the correlation between the first difference and the second difference, and the expansion amount of point P in the interval before the start of energization.

[0078] In step S911, the parameter correction unit 291 adds a correction value to the welding parameter A calculated at point P after the energization start time T2, i.e., the value before correction. Thus, the corrected welding parameter A is obtained (step S915). In other words, the corrected welding parameter A is defined by the relationship shown in the following formula (2). Corrected welding parameters = original welding parameters + corrected value (Equation 2)

[0079] Figure 13 This is a graph used to compare welding parameters A before and after using the modified version 650. Figure 13 The left figure shows the welding parameters A before correction, arranged in the order of the welding points. Figure 13The right figure shows the corrected welding parameters A in the order of the welding points. Figure 13 The vertical axis in the left and right figures represents the value of welding parameter A. Figure 13 The horizontal axis in the left and right figures represents the welding points.

[0080] exist Figure 13 In this paper, data from welding points 1 to 25 were plotted under three different welding conditions. For welding under the baseline condition, each welding point was welded with 2.0 liters of cooling water flowing through electrodes 2 and 3. In this case, welding under the baseline condition was performed with the influence of the previous welding point largely eliminated. Specifically, for example, welding for the next welding point began after a predetermined standby time (e.g., 10 seconds) had elapsed since the energization stop time T3 of the previous welding point. For welding under condition 5, each welding point was welded with 2.0 liters of cooling water flowing through electrodes 2 and 3. For welding under condition 6, each welding point was welded with 1.3 liters less cooling water than under condition 5 flowing through electrodes 2 and 3. Under conditions 5 and 6, no standby time was set between welding points, and welding was performed continuously for each welding point. In other words, conditions 5 and 6 simulate welding under conditions where the electrode temperature rises due to an increase in the number of consecutive welding passes. The welding parameter settings are the same under all conditions. Therefore, the data for the baseline conditions are comparative examples of the data for conditions 5 and 6.

[0081] like Figure 13 As shown in the left figure, during welding after point 2, the welding parameter A before correction shows a significant difference between the drawings related to the reference condition and those related to conditions 5 and 6. In particular, the difference ΔE6 between the drawing related to condition 6 and the drawing related to the reference condition is larger than the difference ΔE5 between the drawing related to condition 5 and the drawing related to the reference condition. That is to say, in the welding under condition 6, the cooling water flow rate is reduced, resulting in a greater rise in electrode temperature compared to the welding under condition 5, and the difference ΔE in welding parameter A is considered to be significant.

[0082] In contrast, regarding the modified welding parameter A, regardless of the cooling water flow rate, the difference ΔE between the drawing related to the baseline condition and the drawings related to the fifth and sixth conditions decreases at any welding point after point 2. Based on this, at least when the cooling water flow rate is in the range of 1.3 liters to 2.0 liters, the welding parameter A substituted into the presumed formula 670 for the weld nugget diameter LN can be well modified regardless of the cooling water flow rate.

[0083] like Figure 12 As shown, after the parameter correction process (step S91), the estimated value calculation process (step S95) is performed. The estimated value calculation process (step S95) is a process of calculating the estimated value of the weld nugget diameter LN at point P using the corrected welding parameters A.

[0084] In step S951, the estimation calculation unit 292 substitutes the corrected welding parameter A into the estimation formula 670 for the weld nugget diameter LN. Thus, the estimated value of the weld nugget diameter LN at point P is obtained (step S955).

[0085] In fact, such as Figure 8 As shown, by modifying the welding parameter A by substituting the estimation formula 670 for the weld nugget diameter LN into the modified formula 650, the weld nugget diameter LN was successfully estimated with good accuracy when welding multiple weld points at different locations on the welded component W was performed continuously. Furthermore, through... Figure 9 and Figure 12 The execution of each process up to step S955 (steps S1 to S9) concludes the method for estimating the weld nugget diameter LN in this embodiment. Furthermore, the weld point at point P, which is the object of the estimation of the weld nugget diameter LN, may also be a weld point on a welded component that exists in a different part than the welded component W used in the fabrication of the revision form 650.

[0086] According to the first embodiment described above, such as Figure 5 As shown, when resistance spot welding is continuously performed on multiple weld points located at different positions on the component W being welded, the electrode temperature changes with the increase in the number of consecutive welds. Therefore, as... Figure 6 and Figure 7 As shown, due to the increase in the number of consecutive welds, the measured values ​​of welding parameters at each weld point sometimes differ. When this difference in welding parameter values ​​occurs, instead of correcting the welding parameters included in Estimated Formula 670 as explanatory variables, the values ​​are substituted into Estimated Formula 670 for the weld nugget diameter LN, as follows: Figure 8 As shown, the estimation accuracy of the melt core diameter LN sometimes decreases. In contrast, according to the first embodiment described above, as... Figure 11As shown, the welding parameter A, which is derived from the expansion amount in the pre-energization interval that is related to the electrode temperature, is modified using formula 650. This modified formula is then substituted into the estimation formula 670 for the weld nugget diameter LN to correct the welding parameter A. The corrected welding parameter A is then substituted into formula 670 for the estimation formula of the weld nugget diameter LN to estimate the weld nugget diameter LN. Therefore, when resistance spot welding is performed continuously on multiple weld points located at different positions of the welded component W, even if differences in the welding parameter A arise at each weld point due to the increase in the number of consecutive welds, the estimation accuracy of the weld nugget diameter LN can be suppressed. In other words, even when resistance spot welding is performed continuously on multiple weld points located at different positions of the welded component W, the estimation accuracy of the weld nugget diameter LN can be maintained at the same level as when welding is performed only on the first weld point.

[0087] Furthermore, according to the first embodiment described above, such as Figure 11 As shown, the modified form 650 is a linear equation calculated by performing linear regression on multiple combined values ​​determined by the combination of the first and second differences. This uniquely expresses the correlation between the first and second differences. Furthermore, the modified form 650 can be easily constructed from multiple combined values.

[0088] Furthermore, according to the first embodiment described above, such as Figure 4 As shown, when the expansion amounts at multiple time points within the pre-energization interval are calculated for the same welding point, the first difference is calculated using the average of the expansion amounts at each time point within the pre-energization interval. This avoids calculating the first difference solely based on outliers during the period from the start time point T1 of welding parameter measurement to the start time point T2 of energization. Therefore, when resistance spot welding is continuously performed on multiple welding points at different locations on the welded component W, the reduction in the estimated accuracy of the weld nugget diameter LN can be further suppressed.

[0089] Furthermore, according to the first embodiment described above, the estimation system 1 can generate timing data based on the welding parameters measured by the measuring mechanism 9 to estimate the weld nugget diameter LN.

[0090] B. Second implementation method: In this embodiment, a method for estimating the weld nugget diameter LN at point P by modifying both welding parameter A and expansion amount when the welding parameter A and expansion amount are included as explanatory variables in the estimation formula 670 of the weld nugget diameter LN are used. When multiple welding parameters exist in the estimation formula 670 of the weld nugget diameter LN as explanatory variables, and multiple welding parameters are used as the modification targets, the modification formula 650 is manufactured for each welding parameter. Furthermore, the configuration of the estimation system 1 is the same as in the first embodiment (…). Figure 1 , Figure 3 The same applies to steps and configurations as those in the first embodiment. The same reference numerals are used for these steps, and descriptions are omitted.

[0091] In this embodiment, the following steps are also performed sequentially. Figure 9 The steps shown are: acquisition process (step S1), difference calculation process (step S3), revision process (step S5), and estimation process (step S9). The processing content in the acquisition process (step S1) is the same as in the first embodiment.

[0092] In the differential calculation process (step S3), the differential calculation unit 220 calculates the first differential, the second differential related to welding parameter A, and the second differential related to expansion amount. The calculation methods for the first differential and the second differential related to welding parameter A are the same as in the first embodiment. Regarding the second differential related to expansion amount, it is the difference between the expansion amount at the first point after the energization start time T2 and the expansion amount at the Nth point after the energization start time T2. Specifically, for example, if the expansion amount included as an explanatory variable in the presumption formula 670 for the weld nugget diameter LN is the maximum value of the measured value during the energization interval, the second differential related to expansion amount is the difference between the first point and the Nth point with respect to the maximum value of the measured value during the energization interval.

[0093] Next, in Figure 12 In the modification form manufacturing process (step S5) shown, the modification form manufacturing unit 230 calculates a first modification form for calculating the correction value of welding parameter A and a second modification form for calculating the correction value of expansion amount. The manufacturing method of the first modification form is the same as the modification form 650 in the first embodiment (e.g., Figure 11 The same applies. The second revision is revision 650, which shows the correlation between the first difference and the second difference related to the expansion. The method for making the second revision is the same as that for the first revision.

[0094] Next, in the correction value calculation process (step S7), the correction value calculation unit 240 calculates the correction value of welding parameter A at point P and the correction value of expansion at point P, respectively. The method for calculating the correction value of welding parameter A is the same as... Figure 12The first embodiment shown is the same. The correction value for the expansion amount is calculated by substituting the third difference into the second correction formula.

[0095] Next, the estimation unit 290 sequentially performs the parameter correction process (step S91) and the estimation value calculation process (step S95).

[0096] Specifically, in the parameter correction process (step S91), the parameter correction unit 291 adds the correction value of the welding parameter A calculated through the first revision to the calculated welding parameter A at point P, which is the welding parameter A after the energization start time T2. This yields the corrected welding parameter A. Then, the parameter correction unit 291 adds the correction value of the expansion amount calculated through the second revision to the calculated expansion amount at point P, which is the expansion amount after the energization start time T2. This yields the corrected expansion amount. Then, in the estimated value calculation process (step S95), the estimated value calculation unit 292 substitutes the corrected welding parameter A and the corrected expansion amount into the estimated formula 670 for the weld nugget diameter LN. This yields the estimated value of the weld nugget diameter LN at point P.

[0097] According to the second embodiment described above, the estimation formula 670 for the weld nugget diameter LN includes welding parameters A and expansion amount, which are different from the expansion amount, as explanatory variables. In this case, according to the second embodiment, two revision formulas 650 are created: a first revision formula 650 for welding parameter A and a second revision formula 650 for expansion amount. Then, the welding parameters A and expansion amount are corrected using the first and second revision formulas. Therefore, when the estimation formula 670 for the weld nugget diameter LN includes welding parameters and expansion amount, which are different from the expansion amount, as explanatory variables, the weld nugget diameter LN can be estimated using the corrected welding parameters A and the corrected expansion amount. Thus, even when the estimation formula 670 for the weld nugget diameter LN includes welding parameters and expansion amount, which are different from the expansion amount, as explanatory variables, the estimation accuracy of the weld nugget diameter LN can be improved.

[0098] C. Other implementation methods: C-1. Other implementation methods 1: In the above embodiments, such as Figure 11As shown, the revision equation 650 is a linear equation calculated by performing a linear regression on multiple combined values ​​determined by the combination of the first difference and the second difference. However, this disclosure is not limited to this. The revision equation 650 can also be a higher-order equation calculated by performing a nonlinear regression on multiple combined values ​​determined by the combination of the first difference and the second difference. In this way, compared with the case where the revision equation 650 is a linear equation, a revision equation 650 that reflects the correlation between the first difference and the second difference in more detail can be produced. As a result, the estimation accuracy of the weld nugget diameter LN can be further improved when resistance spot welding is continuously performed on multiple weld points existing at different locations of the welded component W.

[0099] C-2. Other implementation methods 2: In the above embodiments, such as Figure 1 As shown, the welded component W consists of two overlapping metal plates W1 and W2. However, this disclosure is not limited to this. The welded component W can also consist of three or more overlapping metal plates. Even in this manner, it is possible to suppress the reduction in the estimated accuracy of the weld nugget diameter LN.

[0100] C-3. Other implementation methods 3: In the above embodiment, the first difference is calculated using the average of the measured values ​​of the expansion at multiple time points in the period before energization. However, this disclosure is not limited to this. The first difference may also be calculated using welding parameters expressed by indicators other than measured values ​​and averages, such as the integral value of the measured values ​​of welding parameters in the period before energization. In this way, a modified formula 650 expressing welding parameters with appropriate indicators can be made based on the type of welding parameters included as explanatory variables in the presumption formula 670 for the weld nugget diameter LN, the number of metal plates W1 and W2 as the welded parts W, the growth mode of the weld nugget N, etc.

[0101] C-4. Other implementation methods 4: In the above embodiment, the first difference is calculated using the average of the measured values ​​of expansion at multiple time points within the period before energization begins. However, this disclosure is not limited to this. The first difference may also be calculated, for example, based on the measured value of expansion at any time point within the period before energization begins, without using an average. Even in this manner, it is possible to suppress the reduction in the estimation accuracy of the weld nugget diameter LN. Furthermore, in this manner, even if the timing data of the welding parameters contains outliers, it is possible to select any time point other than the time point where the outlier appears and calculate the first difference.

[0102] C-5. Other implementation methods 5: In the above embodiments, such as Figure 9As shown, after the estimation device produces the repair template 650 through the execution of each step up to the repair template production step (step S5), it estimates the weld nugget diameter LN. However, this disclosure is not limited to this. The estimation device may also estimate the weld nugget diameter LN, for example, using the repair template 650 pre-stored in the storage unit 60. In this way, the predetermined produced repair template 650 can be used to calculate the correction value of the welding parameters.

[0103] C-6. Other implementation methods 6: In other embodiments, the estimation device may use two or more combined values ​​that serve as the calculation source for the correction form 650, which are pre-stored in the storage unit 60, and a combined value calculated based on timing data obtained when estimating the melt core diameter LN at point P, to calculate a new correction form 650. That is, in other embodiments, the estimation device may update the coefficients of the correction form 650 each time the melt core diameter LN is estimated. In this manner, the calculation accuracy of the correction value can be improved.

[0104] C-7. Other implementation methods 7: In the above embodiment, a correction form 650 showing the correlation between the first difference and the second difference is created, and the correction value of the welding parameters is calculated using the correction form 650. However, this disclosure is not limited to this. The correction value of the welding parameters can also be calculated, for example, by referring to a correlation table showing the correlation between the first difference and the second difference. Even in this way, the correction value of the welding parameters can be calculated. As a result, the reduction in the estimation accuracy of the weld nugget diameter LN can be suppressed.

[0105] C-8. Other implementation methods 8: In the second embodiment described above, the estimation formula 670 for the weld nugget diameter LN includes welding parameter A and expansion amount, which are different from the expansion amount, as explanatory variables. Therefore, in the second embodiment described above, the welding parameter A and expansion amount substituted into the estimation formula 670 for the weld nugget diameter LN are modified respectively. However, this disclosure is not limited to this. For example, if the estimation system 1 includes three or more welding parameters as explanatory variables in the estimation formula 670 for the weld nugget diameter LN, a modification form 650 can be made for each welding parameter, the modified value can be calculated, and the weld nugget diameter LN can be estimated based on this. In this case, the modification form 650 for each welding parameter can be made using the same method as the method for making the modification form 650 related to welding parameter A shown in the first embodiment. In addition, if the estimation formula 670 for the weld nugget diameter LN includes three or more welding parameters as explanatory variables, any welding parameter can be selected, and a modification form 650 can be made only for the selected welding parameter. In this manner, when three or more welding parameters are included as explanatory variables in the estimating formula 670 for the weld nugget diameter LN, the estimation accuracy of the weld nugget diameter LN can be improved by modifying any selected welding parameter. Furthermore, it is possible to create a modification formula 650 for each welding parameter without limiting the type of welding parameter.

[0106] 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 of the embodiments 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 estimation method, which uses the diameter of the weld nugget in resistance spot welding of a component held by an upper electrode and a lower electrode, wherein, Regarding the aforementioned resistance spot welding For M welding points located at different positions on the component being welded, the welding is performed sequentially from point 1 to point M, where M is an integer greater than or equal to 2. The estimation method comprises: In the process of obtaining two or more welding parameters that affect the size of the weld nugget diameter, time-series data including the welding current before the start of energization is obtained for each weld point, wherein the two or more welding parameters include the amount of expansion calculated based on the displacement of the upper electrode and the lower electrode; The differential calculation process calculates: (i) a first difference, which is the difference between the expansion amount at point 1 before the start of energization and the expansion amount at point N before the start of energization, where N is an integer greater than 2 and less than M; and (ii) a second difference, which is the difference between the welding parameters at point 1 after the start of energization and the welding parameters at point N after the start of energization; and In the estimation process, the diameter of the weld nugget at point P is estimated using the welding parameters, where P is an integer greater than or equal to 1 and less than or equal to M. The estimation process uses the expansion amount at point P before the start of energization and the correlation between the first difference and the second difference to correct the calculated welding parameters at point P, and uses the corrected welding parameters to estimate the weld nugget diameter.

2. The estimation method according to claim 1, wherein, It also includes: a revision process for creating a revision document that illustrates the aforementioned relationships. The estimation process includes: In the process of substituting the third difference into the correction formula when estimating the diameter of the weld nugget at point P, the correction value of the welding parameters is calculated, wherein the third difference is the difference between the expansion amount at point 1 before the start of energization and the expansion amount at point P before the start of energization; and The process involves substituting a predetermined formula, which uses the welding parameters as explanatory variables and the estimated value of the weld nugget diameter as the objective variable, into the corrected welding parameters, which have been modified by adding the correction value to the calculated welding parameters at point P, to calculate the estimated value of the weld nugget diameter.

3. The estimation method according to claim 2, wherein, The modified equation is a linear equation calculated by performing linear regression on multiple combined values ​​determined by the combination of the first difference and the second difference.

4. The estimation method according to claim 2, wherein, The modified equation is a high-order equation calculated by performing nonlinear regression on multiple combined values ​​determined by the combination of the first difference and the second difference.

5. The estimation method according to claim 1 or 2, wherein, If the expansion amount is calculated at multiple time points before the start of energization at the same welding point, The first difference is calculated using the average of the multiple expansion amounts prior to the start of the power-on.

6. A estimation device for estimating the diameter of the weld nugget in resistance spot welding of a component being welded, which is held by an upper electrode and a lower electrode, wherein... Regarding the aforementioned resistance spot welding For M welding points located at different positions on the component being welded, the welding is performed sequentially from point 1 to point M, where M is an integer greater than or equal to 2. The estimation device includes: The acquisition unit acquires timing data for each weld point, including data prior to the start of energization of the welding current, for two or more welding parameters that affect the size of the weld nugget diameter, wherein the two or more welding parameters include the amount of expansion calculated based on the displacement of the upper electrode and the lower electrode. The difference calculation unit calculates (i) a first difference, which is the difference between the expansion amount at point 1 before the start of energization and the expansion amount at point N before the start of energization, where N is an integer greater than or equal to 2 and less than or equal to M; and (ii) a second difference, which is the difference between the welding parameters at point 1 after the start of energization and the welding parameters at point N after the start of energization; and The estimation section uses the welding parameters to estimate the diameter of the weld nugget at point P, where P is an integer greater than or equal to 1 and less than or equal to M. The estimation unit uses the expansion amount at point P before the start of energization and the correlation between the first difference and the second difference to correct the calculated welding parameters at point P, and uses the corrected welding parameters to estimate the weld nugget diameter.

7. An estimation system for estimating the diameter of the weld nugget in resistance spot welding of components held by upper and lower electrodes, wherein, Regarding the aforementioned resistance spot welding For M welding points located at different positions on the component being welded, the welding is performed sequentially from point 1 to point M, where M is an integer greater than or equal to 2. The estimation system has the following features: The estimating device as claimed in claim 6; and The measuring agency generates time-series data of welding parameters.

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