JP2022134917A - Resistance spot welding method and resistance spot welding device - Google Patents

Abstract

To provide a technique that is able to improve the estimation accuracy of a nugget diameter in resistance spot welding.SOLUTION: A resistance spot welding method comprises: a main joining step of melting and joining a to-be-welded material; and a preparation step that is performed before the main joining step, the preparation step of preparing a master resistance value as a master pattern in the main joining step, wherein the main joining step includes: a resistance correction step of, by using a correction value in a predetermined decision interval that is a difference between the master resistance value and a main resistance value that is a value of an electric resistance calculated in the main joining step, correcting the main resistance value in the main joining step in a correction interval after the decision interval; and an estimation step of, by using a difference between a corrected resistance value which is the main resistance value corrected by the resistance correction step, and the master resistance value, estimating a nugget diameter in the correction interval.SELECTED DRAWING: Figure 7

Description

The present disclosure relates to the art of resistance spot welding.

Conventionally, in the technique of resistance spot welding of materials to be welded, when the main welding is performed under the welding conditions of a preset master pattern, welding parameters such as the welding voltage during the implementation of the preliminary energization and the welding parameters of the main welding A technique is known for estimating the nugget diameter to be obtained in the main welding based on the amount of deviation from the welding parameters during execution. A plurality of metal plates are superimposed on each other to be welded.

JP 2020-171942 A

According to conventional technology, if the electrical resistance value during main welding is greater than the electrical resistance value during pre-energization, it is predicted that the nugget diameter obtained by main welding will be smaller than the target nugget diameter. is doing. Here, in the first case where there is a gap between the overlapping metal plates, the nugget diameter is smaller than in the second case where there is no gap. However, in the first case, the material to be welded is bent by being pressed by the pair of electrodes, which may increase the contact area between the pair of electrodes and the material to be welded. In this case, the value of the electrical resistance in the first case is smaller than the value of the electrical resistance in the second case. In other words, the electric resistance value is decreased, but the nugget diameter is also decreased. As a result, the accuracy of estimating the nugget diameter may be lowered when welding the materials to be welded by resistance spot welding.

The present disclosure can be implemented as the following forms.

(1) According to a first aspect of the present disclosure, a resistance spot welding method is provided. In this resistance spot welding method, a material to be welded in which a plurality of metal plates are superimposed on each other is sandwiched between a pair of electrodes, and then an electric current is applied between the pair of electrodes to melt and join the material to be welded. A joining step and a preparatory step performed before the main joining step, wherein the welding conditions are predetermined in order to obtain a nugget with a target nugget diameter in the main joining step, and the material to be welded is supported. A preliminary energization is performed on the test material, and a master resistance value, which is an electrical resistance value calculated using the welding voltage value and the welding current value measured during the preliminary energization, is prepared as a master pattern in the main joining process. and 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 determination section. using a resistance correction step of correcting the main resistance value in the main bonding step in the correction section after the determination section, and a corrected resistance value that is the main resistance value corrected by the resistance correction step; an estimating step of estimating a nugget diameter in the correction section using the difference from the master resistance value. According to this aspect, the resistance correction step corrects the main resistance value using the correction value to calculate the corrected resistance value, and estimates the nugget diameter using the difference between the corrected resistance value and the master resistance value. Therefore, the nugget diameter estimation accuracy can be improved even when there are gaps between the plurality of metal plates.
(2) In the above aspect, 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 section. According to this aspect, by using the difference between the master resistance value and the main resistance value as the average value of the differences between the master resistance value and the main resistance value in the determination section, even if the main resistance value locally fluctuates significantly , 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.
(3) In the above aspect, 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 aspect, 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 aspect, the pre-energization section and the energization section in the main joining step are respectively a pre-energization section for performing pretreatment on the weld material and the pre-energization section. and a main energization section that melts the material to be welded and promotes the growth of the nugget, which is a later main energization section, and the start time of the determined section is time t1, and the end time of the determined section is time t2. In some cases, 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 aspect, since the section before the nugget grows large can be set as the determination section, the value of the electrical resistance that decreases due to the presence of the gap between the plurality of metal plates in the determination section can be calculated with high accuracy. . 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 aspect, the main joining step may further include a current adjusting step of adjusting the welding current value so that the nugget diameter estimated in the estimating step approaches the target nugget diameter. According to this aspect, resistance spot welding can be performed so that the nugget diameter is brought closer to the target nugget diameter.
(6) A resistance spot welding apparatus is provided according to a second aspect of the present disclosure. According to this resistance spot welding apparatus, a controller for controlling the operation of the resistance spot welding apparatus is provided, and the controller uses the measured welding voltage value and the measured welding current value to When a test material corresponding to the material to be welded is preliminarily energized using a resistance calculation unit that calculates the electrical resistance during welding and welding conditions that are predetermined to obtain a target nugget diameter, the a storage device that stores the master resistance value, which is the value of the electrical resistance calculated by the resistance calculation unit, as a master pattern for welding the materials to be welded; the master resistance value in a predetermined determination section; a resistance correction unit that corrects the main resistance value in the correction section after the determination section by using a correction value that is a difference from the main resistance value that is the value of the electric resistance calculated during welding of the weld material; and an estimating unit 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 unit, and the master resistance value. According to this aspect, the resistance correction unit corrects the main resistance value using the correction value to calculate the corrected resistance value, and the estimation unit 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 estimation accuracy of the nugget diameter even when there are gaps between the plurality of metal plates.
The present disclosure can be embodied in various forms, and in addition to the above forms, the present disclosure can be embodied in the form of a computer program for executing a resistance spot welding method.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic block diagram which shows the resistance spot welding apparatus which concerns on this embodiment. FIG. 2 is a diagram mainly for explaining a control device; A flowchart of a resistance spot welding method. Flowchart of the preparation process. FIG. 4 is a diagram showing an example of a welding current value, which is one of the welding conditions during preliminary energization in the preparation process; 7 is a graph showing values of electrical resistance between electrodes calculated during main energization. Flowchart of the main joining process. FIG. 5 is a diagram showing an example of changes 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. 5 is a diagram showing the relationship between the master resistance value of the master pattern, the main resistance value, and the corrected resistance value; FIG. 7 is a diagram for explaining the accuracy of estimating the nugget diameter when normal adaptive control is performed in a correction interval; FIG. 4 is a diagram schematically showing resistance values between electrodes during final welding when there is no gap in the welded material and when there is a gap in the welded material; FIG. 5 is a diagram for explaining the estimation accuracy of a nugget diameter when correction adaptive control is performed in a correction section; FIG. 5 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. 5 is a diagram for explaining the estimation accuracy of the nugget diameter when correction application control is performed on the material to be welded W; FIG. 5 is a diagram for explaining the estimation accuracy of the nugget diameter in the first case where the section condition is satisfied and the correction adaptive control is performed; FIG. 11 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 section 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 this embodiment. The resistance spot welding device 10 is a device that melts and joins a material to be welded W in which a plurality of metal plates W1 and W2 are superimposed. FIG. 1 shows a material W to be welded in which two aluminum plate materials W1 and W2 are superimposed. A resistance spot welding apparatus 10 includes a spot welding gun G, a robot arm RA, and a control device 100 .

A 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 . A gun body 1 is held by a robot arm RA. The upper electrode 2 is attached to the upper portion 1 a of the gun body 1 via an electrode lifting device 4 . The lower electrode 3 is attached to the lower portion 1b of the gun body 1. As shown in FIG. The tip of the upper electrode 2 and the tip of the lower electrode 3 are arranged to face each other. When welding the material W to be welded, the material W to be welded is sandwiched and pressurized by the upper electrode 2 and the lower electrode 3 , and an electric current is passed between the upper electrode 2 and the lower electrode 3 . As a result, the materials W to be welded are 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 and lifts the upper electrode 2 . The electrode lifting device 4 is attached to the tip of the upper portion 1 a of the gun body 1 . The electrode lifting device 4 includes a servomotor 41 and a lifting member 42 coupled to the drive shaft of the servomotor 41 . The electrode lifting device 4 raises and lowers the lifting member 42 by operating the servomotor 41 according to the command signal from the control device 100 . As a result, the material W to be welded is sandwiched between the upper electrode 2 and the lower electrode 3 .

The current adjusting device 5 adjusts the value of the welding current (welding current value) that flows between the upper electrode 2 and the lower electrode 3 according to the current command signal transmitted from the control device 100 . As the current adjusting device 5, for example, a known device such as a device provided with a variable resistor or a device provided with a converter is applied.

A control device 100 controls the operation of the resistance spot welding device 10 . In the resistance spot welding by the resistance spot welding device 10, preliminary energization is performed on the test material to obtain a target fusion zone (nugget), that is, a master pattern for obtaining a nugget with a target nugget diameter, not shown. Store in memory. 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 factors as those of the material to be welded W, such as material and thickness, which affect welding. After the master pattern 132 is acquired by the preliminary energization, the material W to be welded is energized for the main welding. Preliminary energization and energization during main welding respectively include pre-energization performed in a pre-energization section and main energization performed in a main energization section after pre-energization. In the pre-energization, for example, at least the opposing surfaces of the metal plates W1 and W2 are reacted at a high temperature to remove or reduce the oxide film, which is a film with high electric resistance, so that the metal plates W1 and W2 are not melted in the main energization. implemented for ease. That is, the pre-energization section is a section for pre-processing the material W to be welded. The main energization is performed to melt the metal plates W1 and W2 and grow a nugget. In other words, the main energizing section is a section in which the material to be welded W is melted to promote nugget growth. In general, the welding current value is larger in main energization than in pre-energization. Further, the preliminary energization is performed so that, when the spot welding gun G is viewed from above, the superimposed surfaces of the materials W to be welded W are in close contact with each other within the range where the respective tips of the electrodes 2 and 3 are positioned. is executed in the

FIG. 2 is a diagram mainly for explaining the control device 100. As shown in FIG. The control device 100 is capable of data communication with a material-to-be-welded database WDB and a welding condition database TDB. The welding target material database WDB is a database that stores information on a plurality of types of welding target materials W. FIG. The welding target material database WDB stores information on a plurality of types of welding target 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, plate thickness, number of layers of the material to be welded W (plate assembly), and the like.

The welding condition database TDB stores a plurality of welding conditions corresponding to the types of materials W to be welded. Welding conditions include a welding current value corresponding to the type of material W to be welded, a lowering position of the upper electrode 2 by the elevating member 42, and the like. Specifically, a welding current value that can ensure a predetermined nugget diameter without scattering molten metal during welding is experimentally obtained according to the type of 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.

Resistance spot welding apparatus 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, the measurement information by the measurement mechanism 200 is transmitted to the control device 100 . The measuring mechanism 200 includes a pressure measuring section 201 , an electrode displacement measuring section 202 , a voltage measuring section 203 and a current measuring section 204 .

The pressure measuring unit 201 measures the pressure applied to the material W to be welded by the electrodes 2 and 3 . The applied force measuring unit 201 is, for example, a load cell housed inside the electrode lifting device 4 . When the main energization is performed, when the material W to be welded expands as it melts, a reaction force against the pressure applied by the electrodes 2 and 3 is generated in the material W to be welded. As a result, the applied pressure measured by the applied pressure measuring unit 201 is obtained as a large value, so whether or not the material to be welded W has melted to the target melting amount can be determined based on the change in the applied pressure.

The electrode displacement measuring section 202 measures the vertical position of the upper electrode 2 . The electrode displacement measuring unit 202 is an encoder that is accommodated inside the electrode lifting device 4 and measures the lifting position of the upper electrode 2 by detecting the rotation angle position of the output shaft of the servomotor 41 .

The voltage measurement unit 203 is a voltage sensor that measures the voltage (potential difference) of each electrode 2,3. That is, the voltage measurement unit 203 measures the welding voltage value. A current measuring unit 204 is a current sensor that measures the actual welding current value between the electrodes 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 RAM, ROM, etc., and stores a control program for the resistance spot welding apparatus 10 and a master pattern 132 .

The master pattern 132 is the ideal change pattern of the welding current value for obtaining a nugget with a target nugget diameter in the main welding process (main bonding process), and the welding voltage value and the welding current value measured during preliminary energization. , the master resistance value calculated using the welding voltage value and the welding current value, the applied force, and the electrode displacement. The master resistance value is the electrical resistance value calculated using the welding voltage value and the welding current value. Note that the target nugget diameter is a value that can sufficiently increase the joint strength of the welded portion between the metal plates W1 and W2, and is determined in advance by experiments according to the thickness of the metal plates W1 and W2, the number of layers, etc. It is

CPU 110 functions as information acquisition section 111 , condition selection section 112 , electrode adjustment section 113 , and current adjustment section 114 by executing control programs stored in storage device 130 . Further, CPU 110 functions as resistance calculator 115 , resistance corrector 116 , estimator 117 , and current corrector 118 by executing control programs stored in storage device 130 .

The information acquisition unit 111 acquires a captured image of the material to be welded W flowing on the production line captured by an imaging device (not shown). Then, the information acquisition unit 111 recognizes the workpiece W using the acquired captured image. For example, the information acquisition unit 111 extracts identification information such as a tag attached to the material to be welded W from the captured image, and recognizes the material to be welded W based on the extracted identification information. The information acquisition unit 111 acquires information on the weld materials W that match the recognized weld materials W from the weld material database WDB.

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

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

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

The resistance correction unit 116 calculates the difference between the master resistance value of the master pattern 132 in the predetermined determination section DT1 in the main bonding process and the main resistance value, which is the electrical resistance value calculated by the resistance calculation unit 115 in the main bonding process. is used to perform the resistance correction step of correcting the main resistance value in the correction section DT2 after the determination section DT1. The details of this resistance correction process will be described later.

Estimating unit 117 compares the parameter values of master pattern 132 during preliminary energization with the parameter values during final welding energization, thereby estimating the nugget diameter obtained by final welding. Estimated based on the diameter (target nugget diameter). Estimating unit 117 calculates the amount of deviation between at least one measurement value measured by measurement mechanism 200 during preliminary energization and at least one measurement value measured by measurement mechanism 200 during main welding energization. A parameter for calculating the deviation amount is appropriately selected according to the material of the material to be welded W and the like. Further, the estimating unit 117 calculates the master resistance value calculated by the resistance calculating unit 115 during preliminary energization, and the resistance calculating unit 115 Calculate the amount of divergence from this resistance value calculated by Specifically, the estimator 117 estimates the nugget diameter obtained by the final welding using the following equation (2). Formula (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 the main welding. t indicates a certain time. φ _M is the nugget diameter obtained by preliminary energization, and is obtained by actually measuring the nugget diameter after preliminarily energizing a test material. The nugget diameter is actually measured according to JIS Z3144. V is the welding voltage value [V] at the time of main welding, and VM is the welding voltage value [V] at the time of preliminary _energization (master pattern). F is the pressure [N] during the main welding, and FM is the pressure [N] during the preliminary _energization (master pattern). S is the electrode displacement amount [mm] at the time of main welding, and SM is the electrode displacement amount [mm] at the time of preliminary _energization (master pattern). R is the main resistance value [ _μΩ ] which is the value of the electrical resistance at the time of final welding, and RM is the master resistance value [μΩ] which is the value of the electrical resistance at the time of preliminary energization (master pattern). C ₁ -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 obtained in advance by experiments, simulations, or the like.

When the applied pressure during energization during main welding is smaller than the applied pressure during preliminary energization, the nugget diameter obtained in main welding tends to be smaller than the target nugget diameter. Further, when the voltage value during the main welding energization is higher than the voltage value during the preliminary energization, the nugget diameter obtained in the main welding tends to be smaller than the target nugget diameter. Further, when the electrode displacement during main welding energization is smaller than the electrode displacement during preliminary energization, the nugget diameter obtained in main welding tends to be smaller than the target nugget diameter. Further, when the electrical resistance during main welding is larger than the electrical resistance during preliminary energization, the nugget diameter obtained in 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, resulting in a large electrical resistance value. In other words, a larger electrical resistance value indicates a smaller nugget diameter. C ₁ to C ₅ in the above equation (2) are set so as to reflect the relationship between each index and the nugget diameter. 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 W to be welded is sandwiched between the electrodes 2 and 3, the metal plates W1 and W2 are pressurized and bent, so that the electrode 2 , 3 and the metal plates W1, W2 may increase. In this case, although the nugget diameter is small, the electric resistance value is small. Therefore, in the present embodiment, the resistance correction unit 116 corrects the main resistance value in the correction section DT2 subsequent to the determination section DT1 in the resistance correction step, thereby suppressing deterioration in nugget diameter estimation accuracy. The details of the correction of this resistance value will be described later.

Current correction unit 118 calculates a welding current correction value (current correction value) so that the nugget diameter (estimated nugget diameter) estimated by estimating unit 117 approaches the target nugget diameter. value is corrected by the current correction value. The control in which current correction unit 118 corrects the welding current value and current adjustment unit 114 transmits the corrected welding current value as a command value to current adjustment device 5 to perform welding is also called adaptive control. The current correction unit 118 calculates a larger current correction value in the direction of increasing the welding current as the nugget diameter of the main welding is estimated to be smaller than the target nugget diameter. For example, the current correction unit 118 adjusts the current correction value so that the larger the divergence, the higher the welding current value when the applied pressure during main welding is smaller than the applied pressure during preliminary energization. calculate. In addition, for example, the current correction unit 118 compares the electrical resistance value (master resistance value) during the preliminary energization with the electrical resistance value (main resistance value) during the main welding energization and the resistance correction in the correction section DT2. If the corrected resistance value corrected by the unit 116 is large, the following is performed. That is, the current correction unit 118 calculates the current correction value so that the welding current value increases as the divergence amount between the master resistance value and the main resistance value or the corrected resistance value increases. On the other hand, the current correction unit 118 calculates the current correction value so that the larger the divergence, the lower the welding current value when the main resistance value and the corrected resistance value are smaller than the master resistance value. do.

A-2. Resistance spot welding method:
FIG. 3 is a flow chart of the resistance spot welding method. First, a preparation process is performed in step S10. In the preparation process, 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 by the resistance spot welding device 10 is performed. In the main joining step, the materials W to be welded are joined by welding.

FIG. 4 is a flow chart 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 material W to be welded. As described above, in step S12, the information acquisition unit 111 acquires the captured image of the material to be welded W, and recognizes the material to be welded W based on the acquired captured image. Then, the information acquisition unit 111 acquires information on the weld materials W that match the recognized weld materials W from the weld material database WDB.

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

After step S14, in step S16, 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 the welding current value in the pre-energization section and the welding current value in the main energization section. Further, in step S16, the CPU 110 acquires the measured value measured by the measuring mechanism 200 during the preliminary energization, and calculates the value of the electrical resistance. FIG. 6 schematically shows the electrical resistance values calculated by the resistance calculator 115 during the main energization.

As shown in FIG. 4, in step S18, the CPU 110 stores the measured value obtained in step S16 and the calculated electrical resistance value as the master pattern 132 in the storage device 130 for registration.

FIG. 7 is a flow chart of the main joining process. FIG. 8 is a diagram showing an example of changes 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 the reference pattern in the main joining process. The pattern of the welding current value indicated by the solid line in FIG. 9 is the change pattern of the welding current value in the main joining process when the 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 indicated by the dotted line in FIG. 9 is the master resistance value, and the resistance value indicated by the one-dot chain line in FIG. Further, the resistance value indicated 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 step is started, the CPU 110 performs normal adaptive control in step S34. The normal adaptive control does not correct the main resistance value calculated by the resistance calculation unit 115 shown in FIG. is calculated, the current correction unit 118 corrects the welding current value based on the amount of deviation as described above, and welding is performed with the corrected welding current value. That is, the estimating unit 117 estimates the nugget diameter obtained by the final 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. Current adjusting unit 114 then transmits a current command signal according to the corrected welding current value corrected by current correcting unit 118 to current adjusting 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 step reaches a predetermined determination section DT1 in the main energization section, here, in the case of the section from time t1 to t2, as shown in FIG. , a correction value calculation step for calculating a correction value of the resistance value is executed (step S35). The correction value of this resistance value is calculated using the following formula (3).

where Rc is a correction value. Time t1 is the start time of the decision interval DT1, and time t2 is the end time of the decision interval DT1. As can be understood from the above formula (3), the correction value is 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, 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 the correction interval DT2 after the determination interval 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 section 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 the correction value to the main resistance value in the correction section DT2. That is, the corrected main resistance value R'(t) is calculated using the following equation (4). The main resistance value R′(t) after correction is also called a corrected resistance value R′(t).

Here, R(t) is a main correction value before correction, which is a value calculated by the resistance calculator 115 .

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

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

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

After step S38, a current adjustment step is performed by current correction unit 118 and current adjustment unit 114 (step S40). In the current adjustment step, a welding current correction value is calculated so as to bring the estimated nugget diameter estimated in step S38 closer to 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 Then, in the current adjustment process, the current adjustment unit 114 transmits a current command signal according to the corrected welding current value corrected by the current correction unit 118 to the current adjustment device 5 . As a result, welding of the welded material W using the corrected welding current value is performed.

Correction adaptive control is performed until the estimated nugget diameter reaches a predetermined nugget diameter.

A-3. Accuracy of nugget diameter estimation:
FIG. 10 is a diagram for explaining the estimation accuracy of the nugget diameter when the normal adaptive control is performed without performing the correction adaptive control in the correction interval DT2. FIG. 11 is a diagram schematically showing resistance values between the electrodes 2 and 3 at the time of main welding when there is no gap in the material W to be welded 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 lines shown in FIGS. 10 and 11 are lines where the estimated nugget diameter and the actually measured nugget diameter match.

If there is no gap (plate gap) between the superimposed metal plates W1 and W2 in the material W to be welded, and if this resistance value is smaller than the master resistance value, the target nugget diameter of the master pattern 132 It has a relationship that the nugget diameter in the main welding becomes smaller than that. Therefore, as shown in FIG. 10, when there is no gap between the metal plates W1 and W2, normal adaptive control is performed on the premise of this relationship. Plots marked with are located on or near the ideal line.

On the other hand, in the material to be welded W, if there is a gap (plate gap) between the metal plates W1 and W2 that are superimposed, when the material to be welded W is sandwiched between the electrodes 2 and 3, the metal plates W1 and W2 The contact area between the electrodes 2 and 3 and the metal plates W1 and W2 may increase because W2 is pressed and bent. In this case, as shown in FIG. 11, although the nugget diameter is small, the electric resistance value is small. Therefore, as shown in FIG. 10, when there is a gap (plate gap) between the superimposed metal plates W1 and W2, when normal adaptive control is performed, the correspondence between the estimated nugget diameter and the measured nugget diameter is shown. Plots marked with crosses lie away from the ideal line. That is, the estimation accuracy of the estimated nugget diameter is lowered.

FIG. 12 is a diagram for explaining the estimation accuracy of the nugget diameter when the correction adaptive control is performed in the correction interval 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 section DT1 shown in FIG. 9 is used to correct the main correction value in the correction section DT2. In other words, the correction adaptive control is a control that cancels fluctuations in the electric resistance value due to the gap between the metal plates W1 and W2, factors other than the nugget growth, that affect the electric resistance value. Therefore, the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter is on or near the ideal line in both cases with and without a gap between the superimposed metal plates W1 and W2. Located in That is, the estimated nugget diameter is estimated with high accuracy.

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

As shown in FIG. 13, when the normal application control is performed without performing the correction application control, the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter is at a position greatly deviated from the ideal line, and the estimated nugget diameter The estimation accuracy of was low. On the other hand, as shown in FIG. 14, when the correction application control is performed, the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter is located near the ideal line, and the estimation accuracy of the estimated nugget diameter is high. became.

According to the above embodiment, as shown in FIG. 7, the corrected resistance value is calculated by correcting the main resistance value using the correction value in the resistance correction step, and the difference between the corrected resistance value and the master resistance value is calculated. By estimating the nugget diameter using this, it is possible to improve the estimation accuracy of the nugget diameter even when there is a gap 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 the average value of the differences between the master resistance value and the main resistance value in the determination section as in the above equation (3), so that the main resistance value Even if there is a large local variation, the variation can be smoothed out. As a result, even when there is a gap between the plurality of metal plates W1 and W2, the nugget diameter estimation accuracy can be improved. Further, according to the above embodiment, in the resistance correction step, the main resistance value is corrected by adding the correction value to the main resistance value in the main bonding step in the correction section DT2, as in the above formula (4). . Accordingly, when there is a gap between the plurality of metal plates W1 and W2, the value of electrical resistance that has decreased due to the gap can be corrected by adding the correction value. As a result, even when there is a gap between the plurality of metal plates W1 and W2, the nugget diameter estimation accuracy can be improved. Further, according to the above-described embodiment, as shown in FIG. 7, the current adjusting step is performed to adjust the welding current so that the nugget diameter estimated in the estimating step approaches the target nugget diameter. Thereby, resistance spot welding can be performed so that the nugget diameter is closer to the target nugget diameter.

B. Preferred form of decision interval DT1:
Although the determination section DT1 is not particularly limited, it is preferably set in the main energization section, and more preferably set so as to satisfy the following section conditions. In other words, the determination section DT1 is preferably set to a section after the start of the main energization section and before the nugget grows significantly. By satisfying this section condition, the section before the nugget grows large is set as the determination section DT1, so that the change in the electric resistance value caused by the growth of the nugget can be reduced. Thereby, the difference between the master resistance value and the main resistance value due to the gap between the metal plates W1 and W2 superimposed can be accurately calculated in the determination section 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 the decision interval DT1, and time t2 is the end time of the decision interval DT1.

FIG. 15 is a diagram for explaining the estimation accuracy of the nugget diameter in the first case where the section condition is satisfied and the 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 superimposed galvanized steel sheets. Each of the three galvanized steel sheets has a thickness of 1.4 mm. In FIGS. 15 and 16, the correspondence between the estimated nugget diameter and the measured nugget diameter is plotted using the welded material W with a gap between three galvanized steel sheets and the welded material W without a gap. did. The welding time and the timing of the decision interval 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 section time: 218 ms
Time of main energization section: 250ms
Start time t1 of the decision section in the first case: 220 ms after the start of the main energization section End time t2 of the decision section in the first case: 225 ms after the start of the main energization section Start time of the decision section in the second case t1: 270 ms after the start of the main energization section End time of the determined 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 determination interval DT1 satisfies the interval conditions, 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 determination section DT1 satisfies the section condition, 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 determination interval DT1 does not satisfy the interval condition, a part of the plot showing the correspondence between the estimated nugget diameter and the measured nugget diameter in the correction adaptive control (surrounded by the dotted line plot) is located slightly away from the ideal line. Therefore, the determination section DT1 satisfies the section condition, so that the accuracy of the estimated nugget diameter can be further improved.

C. Other embodiments:
C-1. Alternative Embodiment 1:
In the above embodiment, the correction value, which is the difference between the master resistance value and the main resistance value in the resistance correction process, is the average value of the differences between the master resistance value and the main resistance value in the determination section DT1, as in the above equation (3). 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 interval DT1, or the difference between the master resistance value and the main resistance value at each point in the decision interval DT1. may be the total value obtained by multiplying the difference by a weighting factor. Even in this case, as in the above embodiment, the corrected resistance value is calculated by correcting the main resistance value using the correction value in the resistance correction step, and the difference between the corrected resistance value and the master resistance value is used. By estimating the nugget diameter by using the nugget diameter, it is possible to improve the estimation accuracy of the nugget diameter even when there is a gap between the plurality of metal plates.

C-2. Alternative 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 section 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 factor to the main resistance value in the main bonding step in the correction section DT2. Even in this case, as in the above embodiment, the corrected resistance value is calculated by correcting the main resistance value using the correction value in the resistance correction step, and the difference between the corrected resistance value and the master resistance value is used. By estimating the nugget diameter by using the nugget diameter, it is possible to improve the estimation accuracy of the nugget diameter even when there is a gap 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 scope of the present disclosure. For example, the technical features of the embodiments corresponding to the technical features in each form described in the outline of the invention are used to solve some or all of the above problems, or Alternatively, replacements and combinations can be made as appropriate to achieve all. Also, if the technical features are not described as essential in this specification, they can be deleted as appropriate.

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

Claims (6)

A resistance spot welding method comprising:
A main joining step of sandwiching a plurality of metal plates to be welded together by a pair of electrodes, and then energizing between the pair of electrodes to melt and join the materials to be welded;
A preparatory step that is executed before the main joining step, wherein a test material corresponding to the material to be welded is prepared using predetermined welding conditions in order to obtain a nugget with a target nugget diameter in the main joining step. A preparation step of performing preliminary energization to prepare 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, as a master pattern in the main joining step; , and
The main bonding step includes
Using the correction value, which 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 correction section after the determination section, the A resistance correction step of correcting the main resistance value in the main bonding step;
An estimating step of estimating a nugget diameter in the corrected section using a difference between the corrected resistance value, which is the main resistance value corrected by the resistance correcting 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 section. The resistance spot welding method according to claim 1 or 2,
The resistance spot welding method, wherein 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 pre-energization section and the energization section in the main joining step are, respectively, a pre-energization section for performing pretreatment on the material to be welded and a main energization section after the pre-energization section. and a main energization section for melting the material to be welded and promoting nugget growth,
A resistance spot welding method that satisfies the following formula (1) when 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 resistance spot welding method, wherein the main joining step further includes a current adjusting step of adjusting the welding current value so that the nugget diameter estimated in the estimating step approaches the target nugget diameter. A resistance spot welding device,
a pair of electrodes for sandwiching a material to be welded in which a plurality of metal plates are superimposed on each other;
a voltage measuring unit that measures a welding voltage value;
a current measuring unit that measures a welding current value;
and a control device that controls the operation of the resistance spot welding device,
The control device is
a resistance calculation unit that calculates electrical resistance during welding using the measured welding voltage value and the measured welding current value;
The value of the electrical resistance calculated by the resistance calculation unit when preliminary energization was performed on the test material corresponding to the material to be welded using predetermined welding conditions to obtain the target nugget diameter. a storage device that stores a certain master resistance value as a master pattern for welding the materials to be welded;
Using the correction value, which 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 weld material, in a predetermined determination interval, the correction value after the determination interval a resistance correction unit that corrects the main resistance value in the correction section;
A resistance spot welding apparatus comprising: an estimating unit 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 unit, and the master resistance value. .

Images