Resistance Spot Welding Equipment

Abstract

To improve estimation accuracy of a nugget diameter obtained through major energization under the condition that contact area between metal plates as materials to be welded or contact area between the metal plate and an electrode is increased.SOLUTION: A control device 100 comprises: an acquisition part 111 which acquires respective measurement results of welding-voltage, welding-current, and applied pressure at the time of preliminary energization and calculation result of energizing resistance; a storage part 112 in which expansion amount by an expansion amount measurement part 205 and contraction amount from a peak of the expansion amount are measured at the time of major energization to store respective measured value of the expansion amount and the contraction amount; a determination part 113 which determines whether the energizing resistance value calculated by a resistance calculation part 106 at the time of the preliminary energization is a prescribed threshold value or less; a correction part 114 which corrects, when affirmative determination is given by the determination part 113, the measured value of the expansion amount stored in the storage part 112 to remove noise component thereof; and an estimation part 115 which estimates nugget diameter obtained by the major energization based on the corrected expansion amount by the correction part 114.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a resistance spot welding device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, resistance spot welding is performed when overlapping and joining a plurality of metal plates as welded materials, for example, in a manufacturing process for a vehicle body frame or the like.

[0003] In resistance spot welding, the workpieces are clamped between upper and lower electrodes while an electric current is passed through them, and the metal plates are melted and joined together using Joule heat generated by the electrical resistance of the workpieces themselves.

[0004] In order to increase the joining strength of the fusion zone (also called nugget) between the metal plates, it is necessary to ensure a sufficient nugget diameter, and therefore a method for estimating whether or not a sufficient nugget diameter has been ensured is required.

[0005] Patent Document 1 discloses a resistance spot welding device that, when performing actual welding under the welding conditions of a preset master pattern, estimates the nugget diameter obtained in actual welding based on the deviation between the measurement values ​​and electrical resistance values ​​when performing a preliminary energization (also called master welding or test welding) that registers the master pattern and the measurement values ​​and electrical resistance values ​​during actual welding. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-171942 A Summary of the Invention [Problem to be solved by the invention]

[0007] During the resistance spot welding process, various disturbances may occur, which may increase the contact area between the metal plates or between the metal plates and the electrodes.

[0008] The situation where a disturbance is occurring refers to a situation where the upper electrode and the lower electrode are not in proper, or ideal, contact with the upper and lower metal plates.

[0009] Examples of situations in which this disturbance occurs include a situation in which a gap exists between the upper and lower metal plates and the areas sandwiched by the upper and lower electrodes are in contact, a situation in which the lower electrode is pushing up the upper and lower metal plates, a situation in which the upper electrode is pushing down the upper and lower metal plates, and a situation in which the upper and lower electrodes are tilted and pressing against the upper and lower metal plates.

[0010] In a situation where such a disturbance occurs, when current is passed between the upper and lower metal plates in performing the main welding, the contact area between the metal plates or between the metal plates and the electrode increases and the resistance to current decreases, compared to a situation where the disturbance does not occur (a situation where the contact area between the metal plates or between the metal plates and the electrode is appropriate), and the diameter of the nugget formed by resistance heating becomes smaller.

[0011] For these reasons, there is a concern that the nugget diameter estimation method disclosed in the above Patent Document 1 may result in a decrease in the accuracy of nugget diameter estimation in a situation where a disturbance is occurring.

[0012] The present invention aims to provide a resistance spot welding device that can improve the estimation accuracy of the nugget diameter obtained by performing this current flow even in situations where the contact area between the metal plates to be welded or between the metal plates and the electrode increases due to the occurrence of a disturbance. [Means for solving the problem]

[0013] The present invention provides a resistance spot welding apparatus comprising a pair of electrodes for clamping a workpiece made of a plurality of overlapping metal plates, a current adjusting device for adjusting a value of a welding current flowing between the electrodes, a voltage measuring unit for measuring a welding voltage, a current measuring unit for measuring a welding current, a pressing force measuring unit for measuring a pressing force for clamping the workpiece with the electrodes, a resistance calculating unit for calculating a current resistance of the workpiece based on the measured values ​​of the welding voltage and the welding current, and a control device for controlling a process of welding a region of the workpiece clamped by the electrodes, the control device further comprising an expansion amount measuring unit for measuring an expansion amount of the region of the workpiece clamped by the electrodes and an expansion amount from a peak of the expansion amount, and the control device controls a main current passing between the electrodes in a master pattern for obtaining a target nugget diameter (diameter of an appropriate molten portion) during welding, and a control device for controlling a main current passing through the electrodes in a master pattern for obtaining a target nugget diameter (diameter of an appropriate molten portion) during welding. and a pre-energization in which an electric current is passed between the electrodes with a welding current having a value lower than the value of the welding current set for the main energization before the welding current is passed between the electrodes. The present invention is characterized in that the present invention includes an acquisition unit that acquires the measurement results of the welding voltage, the welding current, and the welding force and the calculation result of the electric current resistance during the pre-energization, a storage unit that measures the expansion amount and the contraction amount from the peak of the expansion amount by the expansion amount measurement unit during the main energization and stores the measurement values ​​of the expansion amount and the contraction amount, a determination unit that determines whether the value of the electric current resistance calculated by the resistance calculation unit during the pre-energization is equal to or lower than a predetermined threshold value, a correction unit that corrects the measurement value of the expansion amount stored in the storage unit to remove noise components when the determination unit makes a positive determination.

[0014] In addition, when the value of the current resistance calculated during the pre-current application becomes equal to or lower than a predetermined threshold value, this indicates a situation in which the contact area between the multiple metal plates that are the workpieces to be welded or between the metal plates and the electrodes has increased due to the occurrence of a disturbance.

[0015] The expansion amount measured by the expansion amount measuring unit is the expansion amount in the overlapping direction of the multiple metal sheets, and is the sum of the expansion amount of the nugget, the expansion amount of the upper metal sheet, and the expansion amount of the lower metal sheet. Since the expansion amounts of the upper metal sheet and the lower metal sheet are noise components, they can be said to be unnecessary for estimating the diameter of the nugget.

[0016] For this reason, in the above configuration, when it is recognized that the contact area between the metal plates, which are the materials to be welded, or between the metal plates and the electrodes has increased due to the occurrence of the disturbance, the expansion amount measured by the expansion amount measuring unit during main current application is corrected, and the corrected expansion amount is used to estimate the diameter of the nugget obtained by performing main current application. In other words, the nugget diameter is estimated by correcting the expansion amount measured by the expansion amount measuring unit so as to remove noise components.

[0017] Therefore, it is possible to improve the estimation accuracy of the nugget diameter obtained by performing the main current supply.

[0018] As a result, the nugget diameter obtained by performing main current application approaches the target nugget diameter, which contributes to improving the joining strength of the welded region between the metal plates.

[0019] In the above-mentioned resistance spot welding apparatus, the control device The welding apparatus performs test welding (also called master welding or preliminary current application) on the workpiece, and further includes a registration unit which acquires a master pattern of welding conditions for ensuring the target nugget diameter during welding when the test welding is performed, and registers this master pattern. Effect of the Invention

[0020] In the present invention, it is possible to improve the estimation accuracy of the nugget diameter obtained by performing this current flow even in situations where the contact area between the metal plates to be welded or between the metal plates and the electrode is increased (situations where disturbances are occurring). [Brief description of the drawings]

[0021] [Figure 1] 1 is a schematic configuration diagram showing a spot welding gun of a resistance spot welding device according to an embodiment; [Diagram 2] FIG. 2 is a block diagram showing a schematic configuration of a control device. [Diagram 3] FIG. 4 is a diagram showing an example of changes in welding current during pre-energization and main energization. [Figure 4] FIG. 11 shows an example of the change in current flow resistance during pre-current flow and main current flow, where (a) shows data when no disturbance occurs and data when a disturbance occurs, (b) shows only the data when no disturbance occurs, and (c) shows only the data when a disturbance occurs. [Diagram 5] FIG. 11 is a diagram showing an example of a change in the amount of expansion during the process of growing a nugget as a result of performing main current application. [Figure 6] 4 is a cross-sectional view for explaining the expansion amount measured by the expansion amount measuring section. FIG. [Figure 7] 1 is a graph showing the relationship between the estimated and measured nugget diameters when the upper and lower electrodes are in proper, or ideal, contact with the upper and lower metal plates with no gap between them. [Figure 8] 1 is a graph showing the relationship between the estimated and measured nugget diameters when a predetermined gap is provided between two metal plates and the areas sandwiched by the upper and lower electrodes are in contact with each other. [Figure 9] 13 is a graph showing the relationship between the estimated and measured nugget diameters when the lower electrode is pushing up the upper and lower metal plates. [Figure 10] 1 is a graph showing the relationship between the estimated and measured nugget diameters when the upper electrode is pressing down on the upper and lower metal plates. [Figure 11] 1 is a graph showing the relationship between the estimated and measured nugget diameters in a situation where the upper and lower electrodes are inclined and press the upper and lower metal plates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to Figures 1 to 11. A resistance spot welding device of this embodiment includes a spot welding gun G.

[0023] As shown in FIG. 1, the spot welding gun G is configured with an upper electrode 2, a lower electrode 3, an upper electrode lifting device (hereinafter simply referred to as the electrode lifting device) 4, and a current adjusting device 5 as main components.

[0024] The workpieces W are two metal plates W1 and W2 as shown in Fig. 1. The metal plates W1 and W2 are made of an aluminum alloy.

[0025] 1, the gun body 1 is held by a robot arm RA. The upper electrode 2 is attached to the upper part 1a of the gun body 1. The lower electrode 3 is provided on the upper surface of the lower part 1b of the gun body 1.

[0026] The electrode lifting device 4 holds and lifts the upper electrode 2, and is attached to the tip of the upper part 1a of the gun body 1. The electrode lifting device 4 is electrically operated and includes a servo motor 41 and a lifting member 42.

[0027] The servo motor 41 is attached to the tip of the upper part 1a of the gun body 1. The lifting member 42 is connected to a drive shaft (not shown) of the servo motor 41. The upper electrode 2 is attached to the lower end 42a of the lifting member 42.

[0028] This electrode lifting device 4 operates a servo motor 41 in accordance with a command signal from a control device 100 described later, thereby raising and lowering a lifting member 42, thereby clamping the workpiece W between the upper electrode 2 and the lower electrode 3.

[0029] The current adjusting device 5 adjusts the value of the current (welding current value) flowing between the upper electrode 2 and the lower electrode 3 in response to a current command signal transmitted from the control device 100.

[0030] As the current adjusting device 5, for example, a configuration including a variable resistor or a well-known configuration including a converter is adopted.

[0031] In this embodiment, as shown in FIG. 3, pre-energization (also called initial energization) is performed for a predetermined period of time, and then main energization is performed.

[0032] The main current is for melting and joining the metal plates W1, W2, and is applied between the upper electrode 2 and the lower electrode 3 in a master pattern for obtaining a target nugget diameter.

[0033] The pre-energization is performed to remove or reduce the size of an oxide film (a film with high electrical resistance) present on the surfaces of the metal sheets W1 and W2, thereby making it easier to melt the metal sheets W1 and W2 in the main energization. The welding current value in the pre-energization is set lower than the welding current value in the main energization.

[0034] In addition, before performing the welding, a test welding (also called master welding or preliminary current application) is performed on the workpiece W to obtain a master pattern with welding conditions that ensure an appropriate molten part (target nugget diameter), and this master pattern is registered.

[0035] The welding for registering this master pattern is called "test welding", and in order to clearly distinguish it from the previous welding, the previous welding is called "main welding".

[0036] Next, the control device 100 will be described in detail.

[0037] The control device 100 is configured with a central processing unit (CPU) (not shown) at its core, as well as read only memory (ROM), random access memory (RAM), an input / output interface, and the like.

[0038] The control device 100 is connected to a welded material information database WDB and a welding condition database TDB.

[0039] The welded material information database WDB stores information on a plurality of types of welded materials W inputted from an input device 6 operated by a worker. The information on the welded materials W includes combinations of the material, plate thickness, number of overlaps (plate assembly), etc. of the welded materials W. Information on all types of weld materials W that may flow on the line is input in advance from the input device 6 to the weld material information database WDB, and this information is stored in the weld material information database WDB.

[0040] The welding condition database TDB stores a plurality of welding conditions according to the type of workpiece W. Examples of the welding conditions include a welding current value according to the type of workpiece W and a lowering position of the upper electrode 2 by the lifting member 42. Specifically, a welding current value that can ensure a predetermined nugget diameter without causing splashing (spattering of molten metal) during welding is experimentally determined according to the type of workpiece W, and the relationship between the type of workpiece W and the welding current value is stored in advance in the welding condition database TDB. As a result, welding conditions (information such as welding current value) according to all types of workpiece W that may flow on the vehicle body production line are stored in advance in the welding condition database TDB.

[0041] Furthermore, the control device 100 is connected to a pressure measuring unit 201, an electrode displacement measuring unit 202, a voltage measuring unit 203, a current measuring unit 204, an expansion amount measuring unit 205, and the like.

[0042] The pressure measuring unit 201 measures the pressure applied by the electrodes 2, 3 to the workpiece W, and is composed of, for example, a load cell accommodated inside the electrode lifting device 4.

[0043] When the metal plates W1, W2 expand as they melt when the main current is applied, a reaction force against the pressure applied by the electrodes 2, 3 is generated in the metal plates W1, W2, and the pressure measured by the pressure measuring unit 201 becomes large. Therefore, based on the change in the pressure measured by the pressure measuring unit 201, it can be determined whether the metal plates W1, W2 have melted to a predetermined amount (target melting amount).

[0044] The electrode displacement measuring unit 202 is housed inside the electrode lifting device 4 and is configured by an encoder that detects the rotation angle position of the output shaft of the servo motor 41 to measure the lifting position of the upper electrode 2 .

[0045] In the case where the power transmission system is provided with a ball screw or the like, when the metal plates W1, W2 expand as they melt as described above, a reaction force against the pressing forces of the electrodes 2, 3 is generated in the metal plates W1, W2.

[0046] This reaction force acts as a force to move the upper electrode 2 upward, so by detecting the rotational angle position of the output shaft of the servo motor 41, it is also possible to determine whether the metal plates W1, W2 have melted to a predetermined amount (target melting amount) based on the rotational angle position.

[0047] The voltage measuring unit 203 detects the voltage (potential difference) between the electrodes 2 and 3. Furthermore, the current measuring unit 204 detects the actual welding current value between the electrodes 2 and 3. The configurations of the voltage measuring unit 203 and the current measuring unit 204 are well known, and therefore a description thereof will be omitted here.

[0048] The expansion amount measuring unit 205 measures the amount of expansion of the region of the workpiece W that is clamped between the upper electrode 2 and the lower electrode 3, as well as the amount of contraction from the peak of the expansion amount, and stores the measured values ​​of the expansion amount and the contraction amount in the memory unit 112.

[0049] The expansion amount and contraction amount are expressed as dimensions along the overlapping direction (plate thickness direction) of the metal plates W1 and W2 of the workpiece W. The expansion amount measuring unit 205 detects the amount of push-back from the metal plates W1 and W2 to the upper electrode 2 and the lower electrode 3 as the expansion amount.

[0050] Furthermore, as shown in FIG. 2, the control device 100 includes a workpiece information acquisition unit 101, a welding condition It includes a selection unit 102, an electrode position adjustment unit 103, a welding current adjustment unit 104, a registration unit 105, a resistance calculation unit 106, a welding current correction amount calculation unit 107, a comparison unit 108, and the like.

[0051] The weld material information acquisition unit 101 acquires information on a specific weld material W from a weld material information database WDB.

[0052] The weldable material information acquisition unit 101 recognizes the weldable material W that has flowed along the vehicle body production line (for example, by reading information on a tag or the like attached to the weldable material W), and acquires (extracts) information on the weldable material W that matches the recognized weldable material W from the weldable material information database WDB.

[0053] The welding condition selection unit 102 acquires specific welding conditions from this welding condition database TDB.

[0054] The welding condition selection unit 102 acquires (extracts) welding conditions corresponding to the type of the workpiece W, which is the information transmitted from the workpiece information acquisition unit 101, from the welding condition database TDB.

[0055] The electrode position adjustment unit 103 transmits an electrode position command signal according to the welding conditions (electrode position conditions) selected by the welding condition selection unit 102 to the electrode lifting device 4 during test welding or main welding.

[0056] The welding current adjusting unit 104 transmits a current command signal to the current adjusting device 5 in accordance with the welding conditions (welding current value conditions) selected by the welding condition selecting unit 102 during test welding.

[0057] During main welding, the welding current adjusting unit 104 transmits to the current adjusting device 5 a current command signal instructing a welding current value corrected based on various parameters.

[0058] The registration unit 105 creates and registers a master pattern during the process of performing the test welding.

[0059] The master pattern is an ideal current pattern (welding current change pattern) for obtaining the target nugget diameter during actual current application, and also includes the pressure, electrode displacement, welding voltage, current resistance, etc. measured or calculated during pre-current application.

[0060] In addition, the target nugget diameter is a value that enables sufficient enhancement of the joint strength of the welded region between the metal plates W1, W2, and is determined in advance through experiments, etc., depending on the plate thicknesses and number of overlapping metal plates W1, W2.

[0061] The voltage value measured by the voltage measuring unit 203 and the welding current value measured by the current measuring unit 204 are input to the resistance calculation unit 106, which calculates the current flow resistance by dividing these voltage values ​​by the welding current value.

[0062] A welding current correction amount calculation unit 107 calculates a correction amount for the welding current based on the deviation amount calculated by the comparison unit 108 so as to bring the actual nugget diameter obtained in the main welding closer to the target nugget diameter.

[0063] The welding current correction amount calculated by the welding current correction amount calculation unit 107 is such that the smaller the actual nugget diameter in the actual welding is estimated to be relative to the target nugget diameter, the larger the correction amount calculated in the direction of increasing the welding current.

[0064] The comparison unit 108 calculates the amount of deviation between at least one of the measured values ​​measured by the measuring units 201, 202, 203 during execution of test welding and at least one of the measured values ​​measured by the measuring units 201, 202, 203 during execution of main welding (the same as the parameter measured during execution of test welding). In this embodiment, the applied pressure measured by the applied pressure measuring unit 201 is used as the main parameter for calculating the amount of deviation.

[0065] When calculating this deviation amount, the selection of which measurement value to use (the applied pressure, the electrode displacement, or the voltage) is made appropriately depending on the material of the workpiece W, etc. (details will be described later).

[0066] The comparison unit 108 further calculates the amount of deviation between the value of the electrical resistance calculated by the resistance calculation unit 106 when test welding is performed and the value of the electrical resistance calculated by the resistance calculation unit 106 when main welding is performed.

[0067] Next, the control device 100 is further configured to include an acquisition unit 111, a memory unit 112, a judgment unit 113, a correction unit 114, an estimation unit 115, etc., for the purpose of improving the estimation accuracy of the nugget diameter obtained by executing this current flow in a situation where the contact area between the metal plates W1, W2, which are the workpieces W, or between the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3 increases due to the occurrence of an external disturbance (a situation where the current flow resistance is below a predetermined threshold value).

[0068] The acquisition unit 111 acquires the measurement results of the welding voltage, welding current, and welding pressure during pre-energization, and the calculation results of the energization resistance (value of electrical resistance).

[0069] During current flow, the memory unit 112 measures the expansion amount of the area of ​​the workpiece W that is clamped between the pair of electrodes 2, 3 and the contraction amount from the peak of the expansion amount using the expansion amount measuring unit 205, and stores the measured values ​​of the expansion amount and the contraction amount.

[0070] The determination unit 113 determines whether the value of the current flow resistance calculated during pre-current flow is equal to or less than a predetermined threshold value. Here, it is determined whether the contact areas between the metal plates W1, W2, which are the materials to be welded W, and between the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3 are increasing due to the occurrence of a disturbance.

[0071] When the judgment unit 113 makes a positive judgment, that is, when the contact area between the metal plates W1, W2, which are the welded materials, or between the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3 is increasing (when the electrical resistance is below a predetermined threshold), the correction unit 114 corrects the measured value of the expansion amount stored in the memory unit 112 to remove noise components.

[0072] The expansion amount is corrected by the following formula:

[0073] Corrected expansion amount = [Measured expansion amount] - [Correction coefficient] x ([Average current resistance during pre-current application in test welding] - [Average current resistance during pre-current application in actual welding]) The correction coefficient is empirically determined from data obtained through experiments, simulations, and the like.

[0074] The estimation unit 115 estimates the nugget diameter obtained by performing the main current application based on the expansion amount stored in the storage unit 112.

[0075] The nugget diameter is estimated by the following formula.

[0076] Estimated nugget diameter = ([corrected expansion amount] x [expansion coefficient]) + ([shrinkage amount from peak of corrected expansion amount] x [shrinkage coefficient]) + [constant]) The expansion coefficient, contraction coefficient, and constants are empirically determined from data obtained by experiments, simulations, and the like.

[0077] Next, the technical idea that has led to the configuration for achieving the above object in the control device 100 will be described.

[0078] First, the inventors of the present application discovered that when the metal plates W1, W2 are made of aluminum alloy, in a situation in which the contact area of ​​one of the metal plates W1, W2, which is the workpiece W, or between the metal plates W1, W2 and the upper electrode 2 or lower electrode 3 increases due to the occurrence of an external disturbance, when comparing with the same welding result (nugget diameter), the peak expansion amount of the area of ​​the workpiece W that is clamped between the upper electrode 2 and the lower electrode 3 becomes larger than in a situation in which no external disturbance occurs (a situation in which the contact area is appropriate) (see, for example, Figure 5).

[0079] In addition, the inventors of the present application have found that when the metal plates W1, W2 are made of an aluminum alloy, the welding current during main energization must be set to a large current compared to when the metal plates W1, W2 are made of an iron-based metal. Therefore, during main energization, it is necessary to set the energization resistance calculated in a state where the disturbance does not occur (a state where the contact area is appropriate) and the energization resistance calculated in a state where the contact area between the metal plates W1, W2, which are the welded materials W, or between the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3 increases due to the occurrence of the disturbance. It was found that while the difference between the resistance and the current resistance becomes smaller during pre-energization (energization where the welding current is set to a value lower than the welding current value set for main energization), the difference between the current resistance calculated in a situation where the disturbance does not occur (a situation where the contact area is appropriate) and the current resistance calculated in a situation where the contact area between one of the metal plates W1, W2, which are the workpiece W, or the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3 increases due to the occurrence of the disturbance becomes larger (see Figures 4(a) to (c)).

[0080] Based on these findings, the inventors have arrived at the technical idea that it is possible to recognize, based on the value of the current resistance calculated during pre-current application, whether the occurrence of the disturbance has increased the contact area between the metal plates W1, W2, which are the workpieces W, or between the metal plates W1, W2 and the upper electrode 2 or the lower electrode 3.

[0081] Therefore, when the value of the current resistance calculated during the pre-current application becomes equal to or lower than a predetermined threshold value, it can be recognized that this indicates a situation in which the contact area between the multiple metal plates W1, W2, which are the materials to be welded, and between the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3, is increasing due to the occurrence of a disturbance.

[0082] 6, the expansion amount measured by the expansion amount measuring unit 205 is the expansion amount in the overlapping direction of the multiple metal plates W1, W2, and is the sum of the expansion amount A of the nugget (see reference numeral 10 in FIG. 6), the expansion amount B of the upper metal plate W1, and the expansion amount C of the lower metal plate W2. Since the expansion amount B of the upper metal plate W1 and the expansion amount C of the lower metal plate W2 are noise components, they can be said to be unnecessary for estimating the diameter of the nugget (10).

[0083] From this, the inventors have come up with the technical idea that when it is recognized that the occurrence of the disturbance has increased the contact area between the metal plates W1, W2, which are the materials W to be welded, and between the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3, the measurement value of the expansion amount measured by the expansion amount measuring unit 205 during the main current application and stored in the memory unit 112 is corrected, and the corrected expansion amount and the contraction amount from the peak of the corrected expansion amount are used to estimate the diameter of the nugget (10) obtained by performing the main current application, thereby making it possible to improve the estimation accuracy.

[0084] Next, resistance spot welding using the resistance spot welding apparatus configured as described above will be described.

[0085] First, the weld material information acquisition unit 101 recognizes a weld material W that has been conveyed along the vehicle body production line, and acquires information on a weld material W that matches the recognized weld material W from the weld material information database WDB.

[0086] After acquiring the information on the workpiece W, the welding condition selection unit 102 acquires the welding conditions (such as the welding current value between the upper electrode 2 and the lower electrode 3) corresponding to the type of workpiece W (information transmitted from the workpiece information acquisition unit 101) from the welding condition database TDB.

[0087] Test welding is performed under the acquired welding conditions. Specifically, an electrode position command signal corresponding to the lowered position of the upper electrode 2, which is the selected welding condition, is output from the electrode position adjustment unit 103 to the electrode lifting device 4, and a current command signal corresponding to the welding current value, which is the selected welding condition, is output from the welding current adjustment unit 104 to the current adjustment device 5, thereby performing test welding at this welding current value.

[0088] In this test welding, the welding force is measured by the welding force measuring unit 201, the electrode displacement is measured by the electrode displacement measuring unit 202, the voltage is measured by the voltage measuring unit 203, the welding current is measured by the current measuring unit 204, and the electrical resistance is calculated by the resistance calculation unit 106.Based on the measurement results and calculation results, the registration unit 105 creates and registers a master pattern.

[0089] After this, actual welding is performed. In actual welding, pre-energization and main energization are performed in sequence, and main energization is performed according to the master pattern registered in the above test welding.

[0090] In addition, during the process of performing the main current, a comparison unit 108 calculates the amount of deviation between the value of the electrical resistance of the pre-current calculated by the resistance calculation unit 106 when test welding is performed and the value of the electrical resistance of the pre-current calculated by the resistance calculation unit 106 during the performance of the main welding using the master pattern, and a welding current correction amount calculation unit 107 calculates a correction amount of the welding current based on the amount of deviation so as to bring the nugget diameter obtained in the main welding closer to the target nugget diameter.

[0091] In the main energization, the current welding current value is corrected by the calculated correction amount (corrected welding current value) and set as the control current value.

[0092] During the process of passing current, the expansion amount measuring unit 205 measures the expansion amount of the region of the workpiece W clamped between the pair of electrodes 2, 3 and the contraction amount from the peak of the expansion amount, and stores the measured values ​​of the expansion amount and the contraction amount in the memory unit 112.

[0093] On the other hand, during the execution of the pre-energization, the judgment unit 113 judges whether or not the value of the energization resistance calculated by the resistance calculation unit 106 is equal to or less than a predetermined threshold value. This judgment can be said to be a judgment of whether or not a situation has arisen in which the contact areas of the metal plates W1, W2, which are the materials to be welded W, with each other or between the metal plates W1, W2 and the upper electrode 2 or the lower electrode 3 have increased due to the occurrence of a disturbance.

[0094] If the judgment unit 113 makes a positive judgment, the measurement value of the expansion amount stored in the memory unit 112 is corrected by the correction unit 114 to remove noise components, and the nugget diameter obtained by performing this current flow is estimated by the estimation unit 115 based on the corrected expansion amount and the contraction amount from the peak of the corrected expansion amount.

[0095] In this way, the nugget diameter obtained by performing the main current application is estimated. It is possible to improve the estimation accuracy of the nugget diameter obtained by performing this current flow even in situations where the contact area between the metal plates W1, W2 or between the metal plates W1, W2 and the upper electrode 2 and the lower electrode 3 increases due to the occurrence of external disturbances.

[0096] As a result, the actual nugget diameter obtained by performing main current application approaches the target nugget diameter, which contributes to improving the joint strength of the welded region between the metal plates W1, W2.

[0097] For reference, the following experiment was carried out to confirm the above-mentioned effect, and will be described in detail.

[0098] This experimental example compares the nugget diameter estimated by the above-mentioned nugget diameter estimation method with the nugget diameter actually measured at that time, and verifies whether the estimated nugget diameter matches or is close to the measured value.

[0099] The workpieces W used in this experiment were two metal plates W1 and W2 made of an aluminum alloy.

[0100] FIG. 7 shows the experimental results in a situation where no disturbance occurs, and FIGS. 8 to 11 each show the experimental results in a situation where a disturbance occurs individually.

[0101] Specifically, FIG. 7 shows the relationship between the estimated and measured nugget diameters when the upper and lower electrodes are in proper, or ideal, contact with the upper and lower metal sheets with no gap between them.

[0102] FIG. 8 shows the relationship between the estimated and measured nugget diameters when a gap (e.g., 2 mm) is provided between the upper and lower metal plates W1, W2 and the areas clamped by the upper electrode 2 and the lower electrode 3 are in contact.

[0103] FIG. 9 shows the relationship between the estimated and measured nugget diameters when the lower electrode 3 is pushing up the upper and lower metal sheets W1, W2.

[0104] FIG. 10 shows the relationship between the estimated and measured nugget diameters when the upper electrode 2 is pressing down on the upper and lower metal plates W1, W2.

[0105] FIG. 11 shows the relationship between the estimated and measured nugget diameters when the upper electrode 2 and the lower electrode 3 are tilted and pressing the upper and lower metal plates W1, W2.

[0106] 7 to 11, even in situations where various types of disturbances are occurring, the plotted points that are the measurement results are located on the ideal line shown by the solid line or on the larger (+) side tolerance line (see dashed line) and the smaller (-) side tolerance line (see dashed line) that are lower than the ideal line. Incidentally, the values ​​of the larger and smaller tolerance lines can be set to ±10% of the value shown by the ideal line.

[0107] These results confirmed that the accuracy of the estimated value of the nugget diameter region (plug fracture region) managed under mass production is improved compared to, for example, the case where the expansion amount is not corrected when estimating the nugget diameter (data not shown).

[0108] The present invention is not limited to the above-described embodiment, and all modifications and applications encompassed within the scope of the claims and equivalents thereto are possible.

[0109] (1) In the above embodiment, an example is given of welding two metal plates W1, W2. However, the present invention is not limited to this, and the present invention can also be applied to, for example, the case of welding three or more metal plates.

[0110] (2) In the above embodiment, an example was given in which the two metal plates W1 and W2 were made of an aluminum alloy. However, the present invention is not limited to this, and they may be made of, for example, iron-based metals (steel), magnesium, titanium, copper, etc.

[0111] (3) In the above embodiment, an example is given of a resistance spot welding device equipped with a configuration (welding current correction amount calculation unit 107, comparison unit 108, etc.) that corrects the welding current so that the nugget diameter obtained by performing this welding approaches the target nugget diameter. However, the present invention is not limited to this and can also be applied to a resistance spot welding device that does not have a configuration that corrects the welding current.

[0112] (4) In the above embodiment, an example is given in which not only the corrected expansion amount but also the shrinkage amount from the peak of the corrected expansion amount is used to estimate the nugget diameter, but the present invention is not limited to this, and it is possible to use only the corrected expansion amount to estimate the nugget diameter. [Industrial Applicability]

[0113] The present invention is applicable to resistance spot welding devices. [Explanation of symbols]

[0114] 2 Upper electrode 3. Bottom electrode 5 Current regulator 10. Nugget 100 Control device 104 Welding current adjustment unit 106 Resistance calculation unit 111 Acquisition Department 112 Storage section 113 Judgment section 114 Correction section 115 Estimation Department 201 Pressure measurement unit 202 Electrode displacement measurement unit 203 Voltage measurement section 204 Current measurement section 205 Expansion measurement section W Welding material W1,W2 Metal plate

Claims

[Claim 1] 1. A resistance spot welding apparatus comprising: a pair of electrodes for clamping a workpiece consisting of a plurality of overlapping metal plates; a current adjusting device for adjusting a value of a welding current flowing between the electrodes; a voltage measuring unit for measuring a welding voltage; a current measuring unit for measuring a welding current; a pressing force measuring unit for measuring a pressing force for clamping the workpiece with the electrodes; a resistance calculating unit for calculating an electrical resistance of the workpiece based on the measured values ​​of the welding voltage and the welding current; and a control device for controlling a process of welding an area of ​​the workpiece that is clamped by the electrodes, An expansion amount measuring unit is further provided which measures the expansion amount of the region of the workpiece that is clamped by the electrodes and the contraction amount from the peak of the expansion amount, The control device executes a main current supplying operation in which a current is supplied between the electrodes in a master pattern for obtaining a target nugget diameter (diameter of an appropriate molten portion) during welding, and a pre-current supplying operation in which a current is supplied between the electrodes before the main current supplying operation with a welding current having a value lower than the value of the welding current set in the main current supplying operation, an acquisition unit that acquires the measurement results of the welding voltage, the welding current, and the welding pressure and the calculation result of the energization resistance during the pre-energization; a storage unit that measures the expansion amount and the contraction amount from the peak of the expansion amount by the expansion amount measuring unit during the main energization and stores the measured values ​​of the expansion amount and the contraction amount; a determination unit that determines whether or not the value of the energization resistance calculated by the resistance calculation unit during the pre-energization is equal to or less than a predetermined threshold value; a correction unit that corrects the measured value of the expansion amount stored in the storage unit to remove noise components when the determination unit makes a positive determination; an estimation unit that estimates a nugget diameter obtained by performing the main current application based on the expansion amount corrected by the correction unit.

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