JP7435505B2 - Resistance spot welding method and resistance spot welding device - Google Patents

Description

The present disclosure relates to resistance spot welding techniques.

Conventionally, in the technology of resistance spot welding materials to be welded, when performing main welding under welding conditions of a preset master pattern, welding parameters such as welding voltage related to welding during preliminary energization and main welding are A technique is known for estimating the nugget diameter obtained by actual welding based on the amount of deviation from the welding parameters during actual welding. The material to be welded is a plurality of metal plates stacked one on top of the other.

JP2020-171942A

With conventional technology, if the electrical resistance value during actual welding is larger than the electrical resistance value during preliminary energization, it is predicted that the nugget diameter obtained during actual welding will be smaller than the target nugget diameter. are doing. Here, in the first case where there is a gap between the stacked metal plates, the nugget diameter is smaller than in the second case where there is no gap. However, in the first case, the welding material is pressurized by the pair of electrodes and curved, so that the contact area between the pair of electrodes and the welding material may increase. In this case, the value of electrical resistance in the first case is smaller than the value of electrical resistance in the second case. In other words, although the electrical resistance value becomes smaller, the nugget diameter also becomes smaller. As a result, when performing resistance spot welding on materials to be welded, the accuracy of estimating the nugget diameter may be reduced.

The present disclosure can be realized as the following forms.

(1) According to the first aspect of the present disclosure, a resistance spot welding method is provided. This resistance spot welding method is a method in which a material to be welded, which is a plurality of metal plates stacked on top of each other, is sandwiched between a pair of electrodes, and then electricity is applied between the pair of electrodes to melt and join the materials to be welded. a welding process, and a preparation process executed before the main welding process, in which the welding conditions are predetermined in order to obtain a nugget with a target nugget diameter in the main welding process, and the process corresponds to the material to be welded. A master resistance value, which is an electrical resistance value calculated using the welding voltage value and welding current value measured during the preliminary energization, is prepared as a master pattern in the main joining process. and a preparation step in which the main bonding step includes a correction value that is the difference between the master resistance value and the main resistance value, which is the value of the electrical resistance calculated in the main bonding step, in a predetermined determined interval. a resistance correction step of correcting the main resistance value in the main bonding step in a correction section after the determined section, and a corrected resistance value that is the main resistance value corrected in the resistance correction step; The method includes an estimating step of estimating a nugget diameter in the correction section using a difference from the master resistance value. According to this form, the main resistance value is corrected using the correction value in the resistance correction process to calculate the corrected resistance value, and the nugget diameter is estimated using the difference between the corrected resistance value and the master resistance value. This makes it possible to improve the estimation accuracy of the nugget diameter even when there are gaps between the plurality of metal plates.
(2) In the above embodiment, the difference between the master resistance value and the main resistance value in the resistance correction step may be an average value of the differences between the master resistance value and the main resistance value in the determination interval. According to this form, by setting the difference between the master resistance value and the main resistance value as the average value of the difference between the master resistance value and the main resistance value in the determination interval, even if the main resistance value locally fluctuates greatly, , the fluctuation can be smoothed out. This makes it possible to improve the accuracy of estimating the nugget diameter even when there is a gap between the plurality of metal plates.
(3) In the above embodiment, the resistance correction step may correct the main resistance value by adding the correction value to the main resistance value in the main bonding step in the correction section. According to this embodiment, when there is a gap between the plurality of metal plates, the value of the electrical resistance that has decreased due to the presence of the gap can be corrected by adding the correction value. This makes it possible to improve the accuracy of estimating the nugget diameter even when there is a gap between the plurality of metal plates.
(4) In the above embodiment, the section of the preliminary energization and the section of the energization in the main welding step are a pre-energization section for pre-treating the workpiece, and a pre-energization section of the pre-energization section, respectively. It has a subsequent main energization section in which the material to be welded is melted and the nugget grows, and the start time of the determination section is time t1, and the end time of the determination section is time t2. In this case, the following formula (1) may be satisfied.
ts≦t1<t2≦ts+0.3×(tf-ts)...(1)
Here, ts is the start time of the main energization section, and tf is the end time of the main energization section.
According to this form, since the interval before the nugget grows large can be set as the determination interval, it is possible to accurately calculate the value of electrical resistance that decreases due to gaps between multiple metal plates in the determination interval. . This makes it possible to improve the accuracy of estimating the nugget diameter even when there is a gap between the plurality of metal plates.
(5) In the above embodiment, the main joining step may further include a current adjustment step of adjusting the welding current value so that the nugget diameter estimated in the estimation step approaches the target nugget diameter. According to this embodiment, resistance spot welding can be performed to bring the nugget diameter closer to the target nugget diameter.
(6) According to the second aspect of the present disclosure, a resistance spot welding device is provided. According to this resistance spot welding device, the control device controls the operation of the resistance spot welding device, and the control device uses the measured welding voltage value and the measured welding current value. a resistance calculation unit that calculates the electrical resistance during welding; and a resistance calculation unit that calculates the electrical resistance during welding; a storage device that stores a master resistance value, which is the value of the electrical resistance calculated by the resistance calculation unit, as a master pattern during welding of the welded material; a resistance correction unit that corrects the main resistance value in a correction section after the determination section using a correction value that is a difference between the main resistance value that is the value of the electrical resistance calculated during welding of the welded material; and an estimating section that estimates a nugget diameter in the correction section using a difference between the corrected resistance value, which is the main resistance value corrected by the resistance correction section, and the master resistance value. According to this embodiment, the resistance correction section corrects the main resistance value using the correction value to calculate the corrected resistance value, and the estimation section calculates the nugget diameter using the difference between the corrected resistance value and the master resistance value. By estimating, it is possible to improve the accuracy of estimating the nugget diameter even when there is a gap between a plurality of metal plates.
The present disclosure can be realized in various forms, and in addition to the forms described above, it can be realized in the form of a computer program for executing a resistance spot welding method.

FIG. 1 is a schematic configuration diagram showing a resistance spot welding device according to the present embodiment. A diagram mainly for explaining a control device. Flowchart of resistance spot welding method. Flowchart of the preparation process. The figure which shows an example of the welding current value which is one of the welding conditions at the time of preliminary energization in a preparation process. A graph showing the value of electrical resistance between electrodes calculated during main energization. A flowchart of the main bonding process. The figure which shows an example of the change of the welding current value of a master pattern, and the adaptive control value which is a welding current value in a main joining process. FIG. 3 is a diagram showing the relationship between a master resistance value of a master pattern, a main resistance value, and a corrected resistance value. FIG. 6 is a diagram for explaining the estimation accuracy of the nugget diameter when normal adaptive control is performed in the correction section. FIG. 3 is a diagram schematically showing the resistance value between electrodes during main welding in cases where there is no gap in the materials to be welded and cases where there is a gap. FIG. 7 is a diagram for explaining the estimation accuracy of the nugget diameter when correction adaptive control is performed in the correction section. FIG. 3 is a diagram for explaining the estimation accuracy of the nugget diameter when normal adaptive control is performed on the material to be welded. FIG. 4 is a diagram for explaining the estimation accuracy of the nugget diameter when correction application control is performed on the welded material W. FIG. 7 is a diagram for explaining the estimation accuracy of the nugget diameter in the first case where the interval condition is satisfied and correction adaptive control is performed. FIG. 7 is a diagram for explaining the estimation accuracy of the nugget diameter in a second case where correction adaptive control is performed without satisfying the interval condition.

A. Embodiment:
A-1: Configuration of resistance spot welding device 10:
FIG. 1 is a schematic configuration diagram showing a resistance spot welding apparatus 10 according to the present embodiment. The resistance spot welding device 10 is a device that melts and joins a welded material W in which a plurality of metal plates W1 and W2 are overlapped. FIG. 1 shows a welded material W in which two aluminum plate materials W1 and W2 are stacked on top of each other. The resistance spot welding device 10 includes a spot welding gun G, a robot arm RA, and a control device 100.

The spot welding gun G includes a gun body 1, a pair of electrodes, an upper electrode 2 and a lower electrode 3, an electrode lifting device 4, and a current adjusting device 5. Gun body 1 is held by robot arm RA. The upper electrode 2 is attached to the upper part 1a of the gun body 1 via an electrode lifting device 4. The lower electrode 3 is attached to the lower part 1b of the gun body 1. The tip of the upper electrode 2 and the tip of the lower electrode 3 are arranged at positions facing each other. When welding the material to be welded W, the material to be welded W is sandwiched between the upper electrode 2 and the lower electrode 3 and pressurized, and a current is passed between the upper electrode 2 and the lower electrode 3. As a result, the material to be welded W is melted by resistance heat generation and then solidified, thereby joining the plurality of metal plates W1 and W2.

The electrode lifting device 4 is an electric device that holds the upper electrode 2 and moves it up and down. The electrode lifting device 4 is attached to the tip of the upper portion 1a of the gun body 1. The electrode lifting device 4 includes a servo motor 41 and a lifting member 42 coupled to a drive shaft of the servo motor 41. The electrode lifting device 4 moves the lifting member 42 up and down by operating the servo motor 41 in accordance with a command signal from the control device 100 . Thereby, the workpiece W to be welded is held between the upper electrode 2 and the lower electrode 3.

Current adjustment device 5 adjusts the value of welding current (welding current value) flowing between upper electrode 2 and lower electrode 3 according to a current command signal transmitted from control device 100. As the current regulating device 5, for example, a known device such as a device including a variable resistor or a device including a converter is applied.

Control device 100 controls the operation of resistance spot welding device 10. In resistance spot welding using the resistance spot welding device 10, a test material is pre-energized to obtain a master pattern (not shown) for obtaining a target fused portion (nugget), that is, a nugget with a target nugget diameter. Store in storage device. Details of the master pattern 132 will be described later. The test material may be the material to be welded W, or may be a member having the same material, thickness, and other factors that affect welding as the material to be welded W. After the master pattern 132 is obtained by preliminary energization, the material to be welded W is energized by main welding. Preliminary energization and energization during main welding each include pre-energization performed in a pre-energization section and main energization performed in a main energization section after pre-energization. The pre-energization may, for example, cause at least the opposing surfaces of the metal plates W1, W2 to undergo a high-temperature reaction to remove or reduce the oxide film, which is a film with high electrical resistance, to prevent melting of the metal plates W1, W2 during the main energization. Implemented to facilitate. That is, the pre-energization section is a section for performing pretreatment on the workpiece W to be welded. This energization is performed to melt the metal plates W1 and W2 and grow a nugget. In other words, the main energization section is a section where the material to be welded W is melted and nugget growth is promoted. Generally, the welding current value is larger during main energization than during pre-energization. In addition, during preliminary energization, when looking at the spot welding gun G from above, the overlapping surfaces of the welded materials W are in close contact with each other without any gaps within the range where the tips of the electrodes 2 and 3 are located. is executed in the current state.

FIG. 2 is a diagram mainly for explaining the control device 100. The control device 100 is capable of data communication with the welding material database WDB and the welding condition database TDB. The welded material database WDB is a database that stores information on a plurality of types of welded materials W. The welded material database WDB stores information on a plurality of types of welded materials W input from the input device 6 operated by the operator. The information on the material to be welded W is information that affects resistance spot welding, and includes, for example, a combination of the material of the material to be welded W, the plate thickness, the number of stacked sheets (plate set), etc.

The welding condition database TDB stores a plurality of welding conditions depending on the type of workpiece W to be welded. The welding conditions include a welding current value depending on the type of the material to be welded W, a lowering position of the upper electrode 2 by the lifting member 42, and the like. Specifically, a welding current value that can ensure a predetermined nugget diameter without causing molten metal to scatter during welding is determined experimentally depending on the type of the material W to be welded. The relationship between the type of material W to be welded and the welding current value is stored in advance in the welding condition database TDB.

The resistance spot welding device 10 further includes a measurement mechanism 200. The measurement mechanism 200 detects physical quantities necessary for welding using the resistance spot welding device 10. Measuring mechanism 200 is electrically connected to control device 100. Thereby, measurement information by the measurement mechanism 200 is transmitted to the control device 100. The measurement mechanism 200 includes a pressing force measurement section 201, an electrode displacement measurement section 202, a voltage measurement section 203, and a current measurement section 204.

The pressurizing force measurement unit 201 measures the pressurizing force exerted by each electrode 2 and 3 on the workpiece W to be welded. The pressurizing force measurement unit 201 is, for example, a load cell housed inside the electrode lifting device 4. When the main energization is executed, when the material to be welded W expands as it melts, a reaction force against the pressure applied by each of the electrodes 2 and 3 is generated in the material to be welded W. Thereby, the pressurizing force measured by the pressurizing force measurement unit 201 is obtained as a large value, so it can be determined whether the welded material W has melted to the target melting amount based on the change in the pressurizing force.

The electrode displacement measurement unit 202 measures the vertical position of the upper electrode 2. The electrode displacement measuring unit 202 is an encoder that is housed inside the electrode lifting device 4 and detects the rotation angle position of the output shaft of the servo motor 41 to measure the lifting position of the upper electrode 2.

The voltage measurement unit 203 is a voltage sensor that measures the voltage (potential difference) between the electrodes 2 and 3. In other words, voltage measuring section 203 measures the welding voltage value. Further, the current measurement unit 204 is a current sensor that measures the actual welding current value between each electrode 2 and 3.

The control device 100 includes a CPU 110, a storage device 130, and an input/output interface (not shown). The storage device 130 is composed of a RAM, a ROM, or the like, and stores a control program for the resistance spot welding device 10 and a master pattern 132.

The master pattern 132 includes an ideal welding current value change pattern to obtain a nugget with a target nugget diameter in the main welding process (main joining process), and welding voltage and welding current values measured during preliminary energization. , master resistance value calculated using welding voltage value and welding current value, pressurizing force, and electrode displacement. The master resistance value is an electrical resistance value calculated using a welding voltage value and a welding current value. The target nugget diameter is determined in advance through experiments, etc., depending on the thickness of the metal plates W1, W2, the number of stacked sheets, etc., as a value that can sufficiently increase the joint strength of the welded portion between the metal plates W1, W2. It is being

The CPU 110 functions as an information acquisition section 111, a condition selection section 112, an electrode adjustment section 113, and a current adjustment section 114 by executing a control program stored in the storage device 130. Further, the CPU 110 functions as a resistance calculation section 115, a resistance correction section 116, an estimation section 117, and a current correction section 118 by executing a control program stored in the storage device 130.

The information acquisition unit 111 acquires a captured image of the welded material W flowing on the manufacturing line, which is captured by an image capturing device (not shown). The information acquisition unit 111 then recognizes the welded material W using the acquired captured image. For example, the information acquisition unit 111 extracts identification information such as a tag attached to the welded material W from the captured image, and recognizes the welded material W based on the extracted identification information. The information acquisition unit 111 acquires information on the welded material W that matches the recognized welded material W from the welded material database WDB.

The condition selection unit 112 selects, from the welding condition database TDB, welding conditions corresponding to the type of the welded material W acquired from the welded material database WDB.

The electrode adjustment section 113 transmits an electrode position command signal to the electrode lifting device 4 in accordance with the electrode position conditions included in the welding conditions selected by the condition selection section 112 during preliminary energization or main welding energization. Further, current adjustment section 114 transmits a current command signal according to the welding current value to current adjustment device 5. For example, the current adjustment unit 114 transmits a current command signal according to the welding current value included in the welding conditions selected by the condition selection unit 112 to the current adjustment device 5 during preliminary energization.

The resistance calculation unit 115 calculates the value of electrical resistance using the welding voltage value and welding current value measured during energization. Specifically, the resistance calculation unit 115 calculates the value of electrical resistance by dividing the welding voltage value by the welding current value. The welding voltage value is a value measured by voltage measuring section 203. The welding current value is a value measured by the current measuring section 204.

The resistance correction unit 116 calculates the difference between the master resistance value of the master pattern 132 and the main resistance value, which is the electrical resistance value calculated by the resistance calculation unit 115 in the main bonding process, in a predetermined interval DT1 in the main bonding process. A resistance correction step is executed to correct the main resistance value in the correction section DT2 after the determined section DT1 using the correction value. Details of this resistance correction process will be described later.

The estimating unit 117 compares the parameter values of the master pattern 132 at the time of preliminary energization with the parameter values at the time of energization for main welding, thereby determining the nugget diameter obtained by main welding and the nugget diameter obtained by preliminary energization. Estimate based on the diameter (target nugget diameter). Estimating unit 117 calculates the amount of deviation between at least one of the measurement values measured by measurement mechanism 200 during preliminary energization and at least one of the measurement values measured by measurement mechanism 200 during energization for main welding. The parameters for calculating the amount of deviation are appropriately selected depending on the material of the workpiece W to be welded. Furthermore, in place of or in addition to the above deviation amount, the estimation unit 117 uses a master resistance value calculated by the resistance calculation unit 115 during preliminary energization, and a master resistance value calculated by the resistance calculation unit 115 during energization for main welding. The amount of deviation from the main resistance value calculated by is calculated. Specifically, the estimation unit 117 estimates the nugget diameter obtained by main welding using the following equation (2). Equation (2) is stored in the storage device 130 as a program.

ここで、φは本溶接によって得られる推定されたナゲット径である。ｔは、ある時間を示す。φ_Ｍは予備通電によって得られるナゲット径であり、テスト材に予備通電を行ってナゲット径を実測することで得られる。ナゲット径はＪＩＳ Ｚ３１４４に従って実測される。Ｖは本溶接時の溶接電圧値［Ｖ］であり、Ｖ_Ｍは予備通電時（マスターパターン）の溶接電圧値［Ｖ］である。Ｆは本溶接時の加圧力［Ｎ］であり、Ｆ_Ｍは予備通電時（マスターパターン）の加圧力［Ｎ］である。Ｓは本溶接時の電極変位量［ｍｍ］であり、Ｓ_Ｍは予備通電時（マスターパターン）の電極変位量［ｍｍ］である。Ｒは本溶接時の電気抵抗の値である本抵抗値［μΩ］であり、Ｒ_Ｍは予備通電時（マスターパターン）の電気抵抗の値であるマスター抵抗値［μΩ］である。Ｃ_１～Ｃ_５は、任意の定数である。乖離量を算出するパラメーターである加圧力や電極変位や電圧値や電気抵抗の値は、ナゲット径に対する影響度の度合いが異なっている。よって、これらのパラメーターの乖離量とナゲット径の乖離量との関係を示すＣ_１～Ｃ_５は、実験やシミュレーションなどによって予め求められる。

Here, φ is the estimated nugget diameter obtained by main welding. t indicates a certain time. φ _M is the nugget diameter obtained by pre-energizing, and is obtained by pre-energizing the test material and actually measuring the nugget diameter. The nugget diameter is actually measured according to JIS Z3144. V is the welding voltage value [V] during main welding, and _VM is the welding voltage value [V] during preliminary energization (master pattern). F is the pressing force [N] during main welding, and _FM is the pressing force [N] during preliminary energization (master pattern). S is the electrode displacement amount [mm] during main welding, and _SM is the electrode displacement amount [mm] during preliminary energization (master pattern). R is the main resistance value [μΩ] which is the electrical resistance value during main welding, and _RM is the master resistance value [μΩ] which is the electrical resistance value during preliminary energization (master pattern). C ₁ to C ₅ are arbitrary constants. The pressure force, electrode displacement, voltage value, and electrical resistance value, which are parameters for calculating the amount of deviation, have different degrees of influence on the nugget diameter. Therefore, C ₁ to C ₅ indicating the relationship between the amount of deviation of these parameters and the amount of deviation of the nugget diameter are determined in advance through experiments, simulations, and the like.

If the pressing force during energization during main welding is smaller than the pressing force during preliminary energization, the nugget diameter obtained by main welding tends to be smaller than the target nugget diameter. Furthermore, if the voltage value during energization during main welding is higher than the voltage value during preliminary energization, the nugget diameter obtained during main welding tends to be smaller than the target nugget diameter. Furthermore, if the electrode displacement during energization during main welding is smaller than the electrode displacement during preliminary energization, the nugget diameter obtained during main welding tends to be smaller than the target nugget diameter. Furthermore, if the value of electrical resistance during energization during main welding is larger than the value of electrical resistance during preliminary energization, the nugget diameter obtained during main welding tends to be smaller than the target nugget diameter. This is because when the nugget diameter is small, the current path between the metal plates W1 and W2 is small, so the value of electrical resistance becomes large. In other words, a large value of electrical resistance indicates that the nugget diameter is small. C ₁ to C ₅ in the above equation (2) are set so as to reflect the relationship between each of the above indices and the nugget diameter. Note that in the above equation (2), if there is a factor that is not used for estimating the nugget diameter, the constants C ₁ to C ₅ of that factor are set to zero. In this embodiment, C ₁ , C ₂ , and C ₃ are set to zero.

On the other hand, when there is a gap between the metal plates W1 and W2, when the material to be welded W is held between the electrodes 2 and 3, the metal plates W1 and W2 are pressurized and curved, and the electrode 2 , 3 and the metal plates W1, W2 may increase in contact area. In this case, although the nugget diameter is small, the value of electrical resistance is small. Therefore, in this embodiment, the resistance correction unit 116 corrects the main resistance value in the correction section DT2 after the determination section DT1 in the resistance correction process, thereby suppressing a decrease in the estimation accuracy of the nugget diameter. Details of this resistance value correction will be described later.

The current correction unit 118 calculates a correction value (current correction value) for the welding current so that the nugget diameter (estimated nugget diameter) estimated by the estimation unit 117 approaches the target nugget diameter, and adjusts the welding current of the master pattern 132. Correct the value using the current correction value. Control in which the current correction unit 118 corrects the welding current value and the current adjustment unit 114 transmits the corrected welding current value as a command value to the current adjustment device 5 to perform welding is also referred to as adaptive control. The current correction unit 118 calculates a larger current correction value in the direction of increasing the welding current as it is estimated that the nugget diameter of the actual welding is smaller than the target nugget diameter. For example, if the pressure force during energization during main welding is smaller than the pressure force during preliminary energization, the current correction unit 118 adjusts the current correction value so that the greater the deviation, the higher the welding current value. calculate. In addition, for example, the current correction unit 118 corrects the resistance value in the correction period DT2 and the value of the electrical resistance during energization in main welding (main resistance value), compared to the value of the electrical resistance during preliminary energization (master resistance value). If the corrected resistance value corrected by section 116 is large, the following is performed. In other words, the current correction unit 118 calculates the current correction value such that the larger the deviation amount between the master resistance value and the main resistance value or the corrected resistance value, the higher the welding current value becomes. On the other hand, when the main resistance value or the corrected resistance value is smaller than the master resistance value, the current correction unit 118 calculates the current correction value so that the larger the deviation amount, the lower the welding current value. do.

A-2. Resistance spot welding method:
FIG. 3 is a flowchart of the resistance spot welding method. First, a preparation process is performed in step S10. In the preparation step, the master pattern 132 shown in FIG. 1 is prepared and stored in the storage device 130. After step S10, in step S20, the main joining process is performed by the resistance spot welding device 10. In this joining process, the materials to be welded W are joined by welding.

FIG. 4 is a flowchart of the preparation process. FIG. 5 is a diagram showing an example of welding current, which is one of the welding conditions during preliminary energization in the preparation process. FIG. 6 is a graph showing the value of the electrical resistance between the electrodes 2 and 3 calculated during main energization.

As shown in FIG. 4, first, in step S12, the information acquisition unit 111 of the resistance spot welding apparatus 10 acquires information on the workpiece W to be welded. As described above, in step S12, the information acquisition unit 111 acquires a captured image of the welded material W, and recognizes the welded material W based on the acquired captured image. Then, the information acquisition unit 111 acquires information on the welded material W that matches the recognized welded material W from the welded material database WDB.

After step S12, in step S14, the condition selection unit 112 selects a welding condition corresponding to the type of information on the welded material W acquired in step S14 from the welding condition database TDB.

In step S16 following step S14, the resistance spot welding apparatus 10 performs preliminary energization on the test material under the welding conditions selected in step S12. The welding conditions include conditions for pre-energization in the pre-energization section and conditions for main energization in the main energization section. For example, as shown in FIG. 5, the welding conditions include a welding current value in the pre-energization section and a welding current value in the main energization section. Further, in step S16, the CPU 110 obtains the measurement value measured by the measurement mechanism 200 during preliminary energization, and calculates the value of the electrical resistance. FIG. 6 schematically shows the value of the electrical resistance calculated by the resistance calculation unit 115 during main energization.

As shown in FIG. 4, in step S18, the CPU 110 registers the measured value obtained in step S16 and the calculated electrical resistance value by storing them in the storage device 130 as a master pattern 132.

FIG. 7 is a flowchart of the main bonding process. FIG. 8 is a diagram showing an example of a change in the welding current value of the master pattern and the adaptive control value which is the welding current value in the main joining process. FIG. 9 is a diagram showing the relationship between the master resistance value of the master pattern, the main resistance value, and the corrected resistance value. The welding current value pattern indicated by the dotted line in FIG. 8 is the welding current value pattern of the master pattern, and serves as a reference pattern in the main joining process. Moreover, the welding current value pattern shown by the solid line in FIG. 9 is a change pattern of the welding current value in the main joining process when adaptive control is performed based on the master pattern. The period from time t0 to time ts is the pre-energization section, and the period from time ts to time tf is the main energization section. The resistance value shown by the dotted line in FIG. 9 is the master resistance value, and the resistance value shown by the dashed-dotted line in FIG. 9 is the main resistance value when normal adaptive control, which will be described later, is performed among the adaptive controls. Moreover, the resistance value shown by the solid line in FIG. 9 is the corrected resistance value which is the main resistance value corrected by the resistance correction process described later.

As shown in FIG. 7, when the main bonding process is started, the CPU 110 performs normal adaptive control in step S34. In the normal adaptive control, the main resistance value calculated by the resistance calculation part 115 shown in FIG. is calculated, the current correction unit 118 corrects the welding current value based on this amount of deviation as described above, and welding is performed using the corrected welding current value. That is, the estimation unit 117 estimates the nugget diameter obtained by main welding using the above equation (2). Then, the current correction unit 118 calculates a current correction value of the welding current based on the difference between the estimated nugget diameter (estimated nugget diameter) and the target nugget diameter of the master pattern 132, and calculates the welding current of the master pattern 132. Correct the value. Then, current adjustment section 114 transmits a current command signal according to the corrected welding current value corrected by current correction section 118 to current adjustment device 5.

ここで、Ｒｃは補正値である。時間ｔ１は決定区間ＤＴ１の開始時間であり、時間ｔ２は決定区間ＤＴ１の終了時間である。上記式（３）から理解できるように、補正値は、決定区間ＤＴ１におけるマスター抵抗値と本抵抗値との差であり、本実施形態では、決定区間ＤＴ１におけるマスター抵抗値と本抵抗値の差の平均値である。 As shown in FIG. 8, when the main bonding process reaches a predetermined determination period DT1 in the main energization period, here, in the case of the period from time t1 to t2, as shown in FIG. , executes a correction value calculation step of calculating a correction value of the main resistance value (step S35). The correction value of this resistance value is calculated using the following equation (3).

Here, Rc is a correction value. Time t1 is the start time of decision section DT1, and time t2 is the end time of decision section DT1. As can be understood from the above equation (3), the correction value is the difference between the master resistance value and the main resistance value in the determination interval DT1, and in this embodiment, the difference between the master resistance value and the main resistance value in the determination interval DT1. is the average value of

As shown in FIG. 7, after step S35, the CPU 110 executes correction adaptive control in steps S36 to S40 instead of normal adaptive control. As shown in FIG. 8, the correction adaptive control is executed in a correction section DT2 subsequent to the decision section DT1.

ここで、Ｒ（ｔ）は補正前の本補正値であり抵抗算出部１１５によって算出される値である。 In the correction adaptive control, first, the resistance correction unit 116 executes a resistance correction step of correcting the main resistance value using the correction value (step S36). The resistance correction unit 116 corrects the main resistance value by adding a correction value to the main resistance value in the correction period DT2. That is, the corrected main resistance value R'(t) is calculated using the following equation (4). The corrected resistance value R'(t) is also referred to as the corrected resistance value R'(t).

Here, R(t) is the main correction value before correction, and is a value calculated by the resistance calculation unit 115.

As described above, in step S36, as shown in FIG. 9, the corrected resistance value is derived by adding the correction value calculated in the determination period DT1 to the main correction value in the correction period DT2.

As shown in FIG. 7, after step S36, the estimation unit 117 executes an estimation process (step S38). The estimation unit 117 estimates the nugget diameter obtained by main welding using the following equation (5) instead of the above equation (2). Equation (5) differs from Equation (2) in that the corrected resistance value is used instead of the actual resistance value. Note that in this embodiment, C1, C2, and C3 are set to zero. Equation (5) is stored as a program in the storage device 130.

As can be understood from the above equation (5), the estimation unit 117 uses the difference between the master resistance value and the corrected resistance value, which is the main resistance value corrected in the resistance correction process of step S36, to calculate the correction interval. Estimate the nugget diameter at each time point of DT2.

After step S38, a current adjustment process is performed by the current correction section 118 and the current adjustment section 114 (step S40). In the current adjustment step, a correction value of the welding current is calculated so that the estimated nugget diameter estimated in step S38 approaches the target nugget diameter of the master pattern 132, and the welding current value of the master pattern 132 is corrected. Adjust the welding current value when In the current adjustment step, current adjustment section 114 transmits a current command signal according to the corrected welding current value corrected by current correction section 118 to current adjustment device 5. Thereby, welding of the welded material W using the corrected welding current value is performed.

The correction adaptive control is executed until the estimated nugget diameter reaches a predetermined nugget diameter.

A-3. Estimation accuracy of nugget diameter:
FIG. 10 is a diagram for explaining the estimation accuracy of the nugget diameter when normal adaptive control is performed without performing correction adaptive control in correction period DT2. FIG. 11 is a diagram schematically showing the resistance value between the electrodes 2 and 3 during main welding when there is no gap in the material to be welded W and when there is a gap. In FIG. 10, the vertical axis is the actually measured nugget diameter, and the horizontal axis is the estimated nugget diameter estimated by the estimation unit 117. The ideal line shown in FIGS. 10 and 11 is a line where the estimated nugget diameter and the actually measured nugget diameter match.

In the material to be welded W, if there is no gap (plate gap) between the stacked metal plates W1 and W2, and if the main resistance value is smaller than the master resistance value, the target nugget diameter of the master pattern 132 There is a relationship in which the nugget diameter in the main welding becomes smaller than that in the actual welding. Therefore, as shown in FIG. 10, when there is no gap between the metal plates W1 and W2, by performing normal adaptive control based on this relationship, a white circle indicating the correspondence between the estimated nugget diameter and the measured nugget diameter is created. The plot indicated by is located on or near the ideal line.

On the other hand, if there is a gap (plate gap) between the overlapping metal plates W1 and W2 in the welded material W, when the welded material W is held between the electrodes 2 and 3, the metal plates W1, When W2 is pressurized and curved, the contact area between the electrodes 2 and 3 and the metal plates W1 and W2 may increase. In this case, as shown in FIG. 11, the value of electrical resistance becomes small despite the small nugget diameter. Therefore, as shown in FIG. 10, when there is a gap (plate gap) between the overlapping metal plates W1 and W2 and normal adaptive control is performed, the correspondence between the estimated nugget diameter and the measured nugget diameter is shown. Plots marked with a cross are located away from the ideal line. In other words, the accuracy of estimating the estimated nugget diameter decreases.

FIG. 12 is a diagram for explaining the estimation accuracy of the nugget diameter when correction adaptive control is performed in the correction period DT2. In FIG. 12, the horizontal axis is the estimated nugget diameter estimated by the estimation unit 117. The ideal line shown in FIG. 12 is a line where the estimated nugget diameter and the actually measured nugget diameter match. In the correction adaptive control, the correction value calculated in the determination period DT1 shown in FIG. 9 is used to correct the main correction value in the correction period DT2. In other words, the correction adaptive control is a control that uses a correction value to cancel fluctuations in the electrical resistance value due to factors other than the growth of the nugget that affect the electrical resistance value, in this case, the gap between the metal plates W1 and W2. Therefore, the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter is on the ideal line or near the ideal line in both cases where there is a gap between the overlapped metal plates W1 and W2 and when there is no gap. Located in In other words, the estimated nugget diameter can be estimated with high accuracy.

A-4. Estimation accuracy of nugget diameter using specific welded material W:
FIG. 13 is a diagram for explaining the estimation accuracy of the nugget diameter when normal adaptive control is performed on the workpiece W to be welded without performing correction adaptive control. FIG. 14 is a diagram for explaining the estimation accuracy of the nugget diameter when correction application control is performed on the workpiece W to be welded. 13 and 14, the vertical axis is the actually measured nugget diameter, and the horizontal axis is the estimated nugget diameter estimated by the estimation unit 117. The ideal line shown in FIGS. 13 and 14 is a line where the estimated nugget diameter and the actually measured nugget diameter match. The material to be welded W is formed by overlapping two metal plates W1 and W2. One metal plate W1 is a bare steel plate with a thickness of 1.6 mm. The other metal plate W2 is a galvanized steel plate with a thickness of 1.2 mm. The material to be welded W was subjected to resistance spot welding using the resistance spot welding device 10 with a gap of 2 mm between the two metal plates W1 and W2.

As shown in Fig. 13, when normal application control is performed without correction application control, the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter is located far away from the ideal line, and the estimated nugget diameter The estimation accuracy was low. On the other hand, as shown in Fig. 14, when correction application control is performed, the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter is located close to the ideal line, indicating that the estimation accuracy of the estimated nugget diameter is high. It became.

According to the above embodiment, as shown in FIG. 7, the main resistance value is corrected using the correction value in the resistance correction process to calculate the corrected resistance value, and the difference between the corrected resistance value and the master resistance value is calculated. By using this method to estimate the nugget diameter, the accuracy of estimating the nugget diameter can be improved even when there are gaps between the plurality of metal plates. Further, according to the above embodiment, the difference between the master resistance value and the main resistance value is set as the average value of the difference between the master resistance value and the main resistance value in the determination interval, as in the above formula (3), so that the main resistance value Even if there is a large local variation, the variation can be smoothed out. This makes it possible to improve the accuracy of estimating the nugget diameter even when there is a gap between the plurality of metal plates W1 and W2. Further, according to the above embodiment, as shown in the above equation (4), in the resistance correction process, the main resistance value is corrected by adding the correction value to the main resistance value in the main bonding process in the correction interval DT2. . Thereby, when there is a gap between the plurality of metal plates W1 and W2, the value of the electrical resistance that has decreased due to the presence of the gap can be corrected by adding the correction value. This makes it possible to improve the accuracy of estimating the nugget diameter even when there is a gap between the plurality of metal plates W1 and W2. Further, according to the embodiment described above, as shown in FIG. 7, a current adjustment step is performed in which the welding current is adjusted so that the nugget diameter estimated in the estimation step approaches the target nugget diameter. Thereby, resistance spot welding can be performed to bring the nugget diameter closer to the target nugget diameter.

B. Preferred form of decision interval DT1:
Although the determined section DT1 is not particularly limited, it is preferably set in the main energization section, and particularly preferably set so as to satisfy the following section conditions. That is, it is preferable that the determination period DT1 is set to a period before the main energization period starts and the growth of the nugget progresses significantly. By satisfying this interval condition, the interval before the nugget grows significantly is set as the determination interval DT1, so that changes in the electrical resistance value due to the growth of the nugget can be reduced. Thereby, the difference between the master resistance value and the main resistance value, which is caused by the gap between the overlapping metal plates W1 and W2, can be calculated with high accuracy in the determination interval DT1.
<Section conditions>
ts≦t1<t2≦ts+0.3×(tf-ts)
Here, time ts is the start time of the main energization section, and time tf is the end time of the main energization section. Time t1 is the start time of decision section DT1, and time t2 is the end time of decision section DT1.

FIG. 15 is a diagram for explaining the estimation accuracy of the nugget diameter in the first case where the interval condition is satisfied and correction adaptive control is performed. FIG. 16 is a diagram for explaining the estimation accuracy of the nugget diameter in the second case where the correction adaptive control is performed without satisfying the interval condition. The material to be welded W, which is the target for calculating the data shown in FIGS. 15 and 16, is made up of three galvanized steel plates stacked one on top of the other. The thickness of each of the three galvanized steel plates is 1.4 mm. In addition, in FIGS. 15 and 16, the correspondence between the estimated nugget diameter and the measured nugget diameter is plotted using a welded material W with a gap between three galvanized steel plates and a welded material W with no gap. did. The welding time and the timing of the determination section DT1 in the first case shown in FIG. 15 and the second case shown in FIG. 16 are as follows. The main energization section ends 468 ms after the start of the pre-energization section.
<Welding time>
Pre-energization period time: 218ms
Main energization section time: 250ms
Start time of the determination interval in the first case t1: 220 ms after the start of the main energization interval End time of the determination interval in the first case t2: 225ms after the start of the main energization interval Start time of the determination interval in the second case t1: 270 ms after the start of the main energization section End time of the determination section in the second case t2: 260 ms after the start of the main energization section

As shown in FIG. 15, in the first case where the determined interval DT1 satisfies the interval condition, the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter in the correction adaptive control is located in a range close to the ideal line. do. That is, when the determined interval DT1 satisfies the interval conditions, the accuracy of the estimated nugget diameter estimated by the estimation unit 117 in the correction adaptive control is higher. On the other hand, as shown in FIG. 16, in the second case where the determined interval DT1 does not satisfy the interval condition, a part of the plot (encircled by a dotted line) showing the correspondence between the estimated nugget diameter and the measured nugget diameter in the corrective adaptive control (plot) is located slightly away from the ideal line. Therefore, since the determined interval DT1 satisfies the interval condition, the accuracy of the estimated nugget diameter can be further improved.

C. Other embodiments:
C-1. Other embodiment 1:
In the above embodiment, as shown in equation (3) above, the correction value that is the difference between the master resistance value and the main resistance value in the resistance correction process is the average value of the difference between the master resistance value and the main resistance value in the determination interval DT1. However, it is not limited to this. For example, the correction value may be the difference between the master resistance value and the main resistance value at any point in the decision section DT1, or the difference between the master resistance value and the main resistance value at each point in the decision section DT1. It may be the total value obtained by multiplying the difference by a weighting coefficient. Even in this case, similarly to the above embodiment, the main resistance value is corrected using the correction value in the resistance correction process to calculate the corrected resistance value, and the difference between the corrected resistance value and the master resistance value is used. By estimating the nugget diameter using the metal plates, the accuracy of estimating the nugget diameter can be improved even when there are gaps between the plurality of metal plates.

C-2. Other embodiment 2:
In the above embodiment, the resistance correction process corrects the main resistance value by adding a correction value to the main resistance value in the main bonding process in the correction interval DT2, as shown in the above equation (4). It is not limited to this. For example, in the resistance correction step, the main correction value may be corrected by adding a value obtained by multiplying the correction value by a weighting coefficient to the main resistance value in the main bonding step in the correction section DT2. Even in this case, similarly to the above embodiment, the main resistance value is corrected using the correction value in the resistance correction process to calculate the corrected resistance value, and the difference between the corrected resistance value and the master resistance value is used. By estimating the nugget diameter using the metal plates, the accuracy of estimating the nugget diameter can be improved even when there are gaps between the plurality of metal plates.

The present disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from the spirit thereof. For example, the technical features of the embodiments corresponding to the technical features in each form described in the column of the summary of the invention may be Alternatively, in order to achieve all of the above, it is possible to perform appropriate replacements or combinations. Further, unless the technical feature is described as essential in this specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 1... Gun body, 1a... Upper part, 1b... Lower part, 2... Upper electrode, 3... Lower electrode, 4... Electrode lifting device, 5... Current adjustment device, 6... Input device, 10... Resistance spot welding device, 41... Servo Motor, 42... Lifting member, 100... Control device, 110... CPU, 111... Information acquisition section, 112... Condition selection section, 113... Electrode adjustment section, 114... Current adjustment section, 115... Resistance calculation section, 116... Resistance correction section Section, 117... Estimation section, 118... Current correction section, 130... Storage device, 132... Master pattern, 200... Measurement mechanism, 201... Pressure force measurement section, 202... Electrode displacement measurement section, 203... Voltage measurement section, 204... Current measuring section, DT1...Decision section, DT2...Correction section, G...Spot welding gun, RA...Robot arm, TDB...Welding condition database, W...Welded material, W1, W2...Metal plate, WDB...Welded material database

Claims (6)

A resistance spot welding method, comprising:
a main joining step of sandwiching a welded material made of a plurality of metal plates stacked on top of each other between a pair of electrodes, and then applying electricity between the pair of electrodes to melt and join the welded materials;
A preparatory step executed before the main joining step, in which a test material corresponding to the material to be welded is welded using predetermined welding conditions in order to obtain a nugget with a target nugget diameter in the main joining step. a preparatory step in which a master resistance value, which is an electrical resistance value calculated using the welding voltage value and welding current value measured during the preliminary energization, is prepared as a master pattern in the main bonding process; , comprising;
The main bonding step is
Using a correction value that is the difference between the master resistance value and the main resistance value, which is the value of the electrical resistance calculated in the main bonding step, in the predetermined determination interval, the correction value in the correction interval after the determination interval is used. a resistance correction step of correcting the main resistance value in the main bonding step;
A resistance spot welding method comprising: estimating a nugget diameter in the correction section using the difference between the corrected resistance value, which is the main resistance value corrected in the resistance correction step, and the master resistance value. . The resistance spot welding method according to claim 1,
The resistance spot welding method, wherein the difference between the master resistance value and the main resistance value in the resistance correction step is an average value of the differences between the master resistance value and the main resistance value in the determination interval. The resistance spot welding method according to claim 1 or 2,
In the resistance spot welding method, the resistance correction step corrects the main resistance value by adding the correction value to the main resistance value in the main joining step in the correction section. The resistance spot welding method according to any one of claims 1 to 3,
The section of the preliminary energization and the section of the energization in the main joining process are a pre-energization section for pre-treating the workpiece to be welded, and a main energization section after the pre-energization section, respectively. and a main energized section that melts the material to be welded and promotes the growth of the nugget,
A resistance spot welding method that satisfies the following formula (1), where the start time of the determined section is time t1, and the end time of the determined section is time t2.
ts≦t1<t2≦ts+0.3×(tf-ts) (1)
Here, ts is the start time of the main energization section, and tf is the end time of the main energization section. The resistance spot welding method according to any one of claims 1 to 4,
The main joining step further includes a current adjustment step of adjusting the welding current value so that the nugget diameter estimated in the estimation step approaches the target nugget diameter. A resistance spot welding device,
a pair of electrodes for sandwiching a welded material made of multiple metal plates stacked on top of each other;
a voltage measuring section that measures a welding voltage value;
a current measuring section that measures a welding current value;
A control device that controls the operation of the resistance spot welding device,
The control device includes:
a resistance calculation unit that calculates electrical resistance during welding using the measured welding voltage value and the measured welding current value;
When the test material corresponding to the welded material is pre-energized using predetermined welding conditions to obtain the target nugget diameter, the electrical resistance value calculated by the resistance calculation section is used. a storage device that stores a certain master resistance value as a master pattern when welding the material to be welded;
Using a correction value that is the difference between the master resistance value and the main resistance value, which is the value of the electrical resistance calculated during welding of the material to be welded, in the predetermined determination interval, a resistance correction section that corrects the main resistance value in the correction section;
A resistance spot welding device, comprising: an estimating section that estimates a nugget diameter in the correction section using the difference between the corrected resistance value, which is the main resistance value corrected by the resistance correction section, and the master resistance value. .

Images