Manufacturing method of the joint

Abstract

The present invention provides a method for manufacturing a joined body that can suppress the generation of spatter when welding high-strength steel plates, specifically during the main energization phase when the welding current is applied. [Solution] Multiple metal workpieces, including high-strength steel plates, are sandwiched between a first electrode and a second electrode, and a welding current is passed between the electrodes, the current value of which changes over time according to a preset current waveform, to weld the multiple metal workpieces. The current waveform of the welding current includes a high-current period in which a high current higher than the main current required for welding is passed at the beginning of energization to blow away impurities from the metal workpieces, and a main current period in which the main current is passed after the high-current period to perform welding. During the high-current period, the current value of the high-current gradually decreases from the maximum current immediately after the start of energization to the main current during the main current period, and during the main current period, the current value of the main current is set to gradually decrease more slowly than during the high-current period.

Description

Technical Field

[0001] The present disclosure relates to a manufacturing method for manufacturing a joined body by resistance welding.

Background Art

[0002] In Patent Document 1, as a method for manufacturing a resistance welded member, after energizing a first current between electrodes for welding to form a nugget, post-energization is performed by gradually decreasing the energization current from the first current at a constant rate of change. According to this manufacturing method, by performing post-energization after the main energization for welding, it is possible to suppress the occurrence of fusion metal brittle cracks such as internal cracks in the nugget.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above manufacturing method, in the main energization, since the first current value is only passed between the electrodes for a certain period of about 400 ms in order to melt the weld material and form a nugget, there is a problem that spatter is likely to occur during the main energization.

[0005] Note that spatter is generated when the molten metal scatters around due to impurities in the weld material or irregularities on the surface of the weld material. Further, spatter is likely to occur when the weld material is a high-strength steel plate such as a hot stamping material or a high-tensile steel plate.

[0006] One aspect of the present disclosure aims to provide a manufacturing method for a joined body that can suppress the occurrence of spatter during the main energization when flowing a welding current for welding a high-strength steel plate.

Means for Solving the Problems

[0007] In a method for manufacturing a joined body according to one aspect of the present disclosure, a plurality of metal workpieces, including a high-strength steel plate, are sandwiched between a first electrode and a second electrode, and a welding current is passed between the electrodes of the first electrode and the second electrode, the current value of which changes over time according to a preset current waveform, to weld the plurality of metal workpieces.

[0008] Furthermore, the current waveform of the welding current that flows between electrodes during welding includes a high-current period in which a high current higher than the main current required for welding is applied at the beginning of energization to blow away impurities from the metal workpiece, and a main current period in which the main current is applied after the high-current period to perform welding. In the high-current period, the current value of the high-current gradually decreases from the maximum current immediately after the start of energization to the main current in the main current period, and in the main current period, the current value of the main current is set to gradually decrease more slowly than in the high-current period.

[0009] Thus, in the method for manufacturing a joined body according to the present disclosure, when welding multiple metal workpieces, including a high-strength steel plate, by passing an electric current between the first electrode and the second electrode, a high current higher than the main current required for welding is passed through during the high-current period at the beginning of the current application to blow away impurities from the metal workpieces.

[0010] Therefore, when the main current is applied during the main current phase following the high current phase, spatter caused by impurities can be suppressed. In addition, during the high current phase, applying a high current can flatten the surface of the high-strength steel plate to be welded, which also suppresses spatter generation.

[0011] Furthermore, during high-current periods, applying a high current creates gaps between multiple metal workpieces around the welding area. As a result, the welding current can be concentrated at the welding area, reducing current loss caused by current flowing between multiple metal workpieces around the welding area.

[0012] Therefore, according to the method for manufacturing a jointed body of this disclosure, spatter generated during welding of multiple metal workpieces can be suppressed, thereby improving welding quality, and the power consumed during welding can be reduced, allowing for more efficient welding.

[0013] Here, the current waveform of the welding current may be set to change over time in the same way as the resistance value between electrodes measured when multiple measuring metal workpieces, in the same combination as the multiple metal workpieces to be welded, are sandwiched between the first and second electrodes and a constant current is passed between the electrodes.

[0014] In other words, by measuring the resistance between electrodes while applying a constant current in this manner, the rate of heat generation of multiple metal workpieces, the timing of initial heat generation, the timing of the peak resistance at the start of heat generation, and the degree of subsequent current loss (shutting) can be measured as changes in resistance (waveforms).

[0015] Therefore, by setting the welding current value (current waveform) so that the welding current changes in response to the time-dependent change in the measured resistance value, it becomes possible to achieve constant resistance welding, in which the resistance value between electrodes during welding remains almost constant.

[0016] Therefore, as described in Japanese Patent Publication No. 06-198453, for example, it is not necessary to measure the resistance value between electrodes during welding and control the welding current so that the resistance value does not change significantly in order to suppress spatter generation. Thus, welding conditions such as the current waveform of the welding current can be easily set. Furthermore, the processing load of the control during welding can also be reduced.

[0017] Next, the constant current supplied between the electrodes when measuring resistance may be set to a current value that does not cause welding spatter. In this way, the resistance value used to set the welding current is measured in such a way that spatter does not occur when current is passed between the electrodes. As a result, the welding current is also set in a way that does not produce spatter, thereby improving the welding quality of multiple metal workpieces being welded.

[0018] In addition, for welding a plurality of metal workpieces to be welded, a welding apparatus capable of controlling the welding current with a time resolution in milliseconds may be used. By doing so, when welding a plurality of metal workpieces, since the welding current can be controlled with a time resolution in milliseconds, the welding current flowing during welding can be accurately changed corresponding to the change in the resistance value measured before welding. Therefore, constant-resistance welding can be realized better.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic diagram showing the configuration of the welding apparatus of the embodiment. [Figure 2] It is an explanatory diagram showing the current waveform of the welding current energized during welding. [Figure 3] It is an explanatory diagram showing the measurement result of the resistance value measured to set the welding current. [Figure 4] It is a flowchart showing the resistance measurement process performed during the measurement of the resistance value. [Figure 5] It is an explanatory diagram showing the state of the workpiece during welding.

Mode for Carrying Out the Invention

[0020] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. [Configuration] The welding apparatus 1 shown in FIG. 1 is configured to weld a workpiece W in which a plurality of metal workpieces P1 and P2 are overlapped by resistance spot welding. That is, the welding apparatus 1 is used to manufacture a joined body of a plurality of metal workpieces P1 and P2 by welding the workpiece W.

[0021] At least one of the plurality of metal workpieces P1 and P2 is a high-tensile steel sheet with a tensile strength of 590 MPa (megapascal) or more, such as a hot press material or a high-tensile material. For example, the first metal workpiece P1 may be a hot-dip galvanized steel sheet with a tensile strength of 590 MPa or higher. Alternatively, the first metal workpiece P1 may be a high-tensile steel sheet with a tensile strength of 980 MPa or higher, a so-called ultra-high-tensile steel material.

[0022] Furthermore, the second metal workpiece P2, like the first metal workpiece P1, may be, for example, a hot-dip galvanized steel sheet, but is not limited to a high-tensile steel sheet. In other words, the second metal workpiece P2 may be a steel sheet with a lower tensile strength than the high-tensile steel sheet, or it may be a high-tensile steel sheet or ultra-high-tensile steel material similar to the first metal workpiece P1.

[0023] In this embodiment, at least one of the metal workpieces P1 and P2 to be welded is made of high-tensile steel plate because the higher the tensile strength of the metal workpieces P1 and P2, the greater the electrical resistance (hereinafter simply referred to as resistance) at the overlapping portion before welding.

[0024] In other words, the welding apparatus 1 of this embodiment is suitable for welding high-tensile steel plates, which have high resistance at the overlapping portion. Therefore, at least one of the metal workpieces P1 and P2 to be welded is a high-tensile steel plate.

[0025] However, the welding apparatus 1 of this embodiment can also be used to weld steel plates with lower tensile strength than high-tensile steel plates. Furthermore, although this embodiment describes welding two metal workpieces P1 and P2, the welding apparatus 1 can also be used to weld three or more metal workpieces stacked on top of each other.

[0026] The welding apparatus 1 includes a resistance welding machine 20. The resistance welding machine 20 welds multiple metal workpieces P1 and P2, arranged as workpieces W, in the stacking direction by resistance spot welding. The stacking direction is the direction in which the multiple metal workpieces P1 and P2 are aligned by overlapping, and corresponds to the direction normal to the surface of the metal workpieces P1 and P2, in other words, the thickness direction of the metal workpieces P1 and P2.

[0027] The resistance welding machine 20 includes a first electrode 21 and a second electrode 22. The first electrode 21 is positioned below the workpiece W. The second electrode 22 is positioned above the workpiece W, together with the first electrode 21, so as to sandwich the workpiece W in the stacking direction. The first electrode 21 is movable in the vertical direction relative to the second electrode 22.

[0028] The first electrode 21 and the second electrode 22 each contact the workpiece W during welding. The first electrode 21 contacts a metal workpiece P2 located below the workpiece W. The second electrode 22 contacts a metal workpiece P1 located above the workpiece W. The first electrode 21 and the second electrode 22 clamp the workpiece W by applying pressure to both sides in the stacking direction.

[0029] In this state, the resistance welding machine 20 supplies a welding current between the first electrode 21 and the second electrode 22. The workpiece W is welded by the resistance heating generated by the welding current supplied from the resistance welding machine 20.

[0030] Furthermore, the resistance welding machine 20 is configured to control the welding current with a time resolution of milliseconds. This is so that the welding control unit 50 described below can control the welding current according to a preset current waveform.

[0031] The welding apparatus 1 includes a resistance measuring unit 30, a current waveform generation unit 40, and a welding control unit 50 as a welding current control system. Of these, the welding control unit 50 is configured to control the welding current flowing between the first electrode 21 and the second electrode 22 when the workpiece W is welded by the resistance welding machine 20. That is, as illustrated in Figure 2, the welding control unit 50 controls the welding current by changing the current value of the welding current over time in accordance with a preset current waveform.

[0032] The current waveform of the welding current controlled by the welding control unit 50 is divided into two phases: the initial high-current phase TA, when current is supplied to the workpiece W via each electrode 21, 22, and the main current phase TB, which is performed after the high-current phase by supplying the main current for welding.

[0033] The high-current period TA is the period during which a high current, higher than the main current required for welding the workpiece W, is applied to blow away impurities from the metal workpieces P1 and P2. The main current period TB is the period after the high-current period during which the main current is applied and welding is performed.

[0034] During the high-current period TA, the current supplied to the workpiece W gradually decreases from the maximum current immediately after the start of energization to the main current during the main current period TB. During the main current period TB, the current value of the main current is set to decrease more slowly compared to the high-current period TA.

[0035] Specifically, in the initial high-current phase TA, the welding current is started at a maximum current of 10kA or more within a time of, for example, 10ms to 15ms, and then gradually decreased in a curved manner over a predetermined time (for example, 50 to 60ms) to the current of the main current phase (for example, 6 to 7kA). In the main current phase TB, for example, the main current is gradually decreased from, for example, 6 to 7kA to about 5kA until a predetermined time (for example, 300ms to 400ms) has elapsed after the start of welding. Note that the times and current values ​​for the high-current phase TA and the main current phase TB are examples and should be set appropriately depending on the number, thickness, material, and other combinations of metal workpieces P1 and P2 to be welded.

[0036] Next, the current waveform generation unit 40 is configured to set the current waveform of the welding current controlled by the welding control unit 50. The resistance measurement unit 30 is configured to measure the resistance value between the first electrode 21 and the second electrode 22 by performing the resistance measurement process shown in Figure 4, and to measure waveform data that the current waveform generation unit 40 uses to set the current waveform of the welding current.

[0037] The resistance measurement unit 30 and the current waveform generation unit 40 described above are for setting the current waveform of the welding current controlled by the welding control unit 50. This welding current waveform only needs to be set by the time the resistance welding machine 20 performs welding on the workpiece W to be welded under the control of the welding control unit 50 and production of the joined body begins.

[0038] Therefore, the resistance measurement unit 30 and the current waveform generation unit 40 may be provided together with the welding control unit 50 as a function of one welding apparatus 1, as shown in Figure 1, or they may be provided as a function of a second welding apparatus configured separately from welding apparatus 1. The second welding apparatus shall be equipped with a resistance welding machine 20, a first electrode 21, and a second electrode 22, similar to welding apparatus 1 shown in Figure 1.

[0039] In this case, the second welding apparatus may be installed together with welding apparatus 1 in a production plant that welds workpieces W to manufacture a jointed body, or it may be installed in a production plant separate from welding apparatus 1. Furthermore, the second welding apparatus may be installed in a control facility that manages the welding conditions of multiple welding apparatuses 1 installed in one or more production plants.

[0040] Next, the functions of the resistance measurement unit 30 and the current waveform generation unit 40 are realized by performing the resistance measurement process shown in Figure 4 in the welding apparatus 1 or the second welding apparatus. This resistance measurement process is performed with multiple metal workpieces P1 and P2 of the same combination as the workpiece W to be welded, sandwiched between the first electrode 21 and the second electrode 22 as the measurement targets.

[0041] As shown in Figure 4, in the resistance measurement process, at S110 (where S represents a step), current control is initiated to supply a preset constant current for measurement between the first electrode 21 and the second electrode 22 via the resistance welding machine 20. The constant current for measurement is set to a current value that does not generate spatter when a constant current is supplied to the workpiece W.

[0042] Then, in S120, the resistance value between the first electrode 21 and the second electrode 22 is repeatedly measured until a predetermined measurement time has elapsed and the measurement is determined to be complete in S130. This resistance value is measured by obtaining the inter-electrode voltage between the first electrode 21 and the second electrode 22 from the resistance welding machine 20, and calculating the resistance value from that inter-electrode voltage and a constant current.

[0043] Next, when it is determined that the measurement is complete in S130, the process moves to S140, where the constant current is stopped, and a current waveform of the welding current is generated based on the time-series data of the resistance values ​​that were repeatedly measured in S120.

[0044] In other words, in S140, as shown in Figure 3, the waveform of resistance change is obtained from the time-series data of resistance measured in S120. Then, the welding current waveform shown in Figure 2 is set so that the welding current changes over time at the same rate as the waveform of resistance change, and this is stored as welding current control data in a storage medium such as flash memory or hard disk.

[0045] The process in S140 functions as a current waveform generation unit 40. After storing the welding current waveform in the storage medium in S140, the resistance measurement process is terminated. The welding current waveform stored in the memory medium in S140 is used by the welding control unit 50 to control the welding current flowing between the first electrode 21 and the second electrode 22 via the resistance welding machine 20. The welding control unit 50 allows the user to appropriately tune the welding current flowing during welding of the workpiece W based on the current waveform set by the resistance measurement process.

[0046] [effect] As described above, in the welding apparatus 1 of this embodiment, the resistance measuring unit 30 measures the resistance value between the electrodes by passing a constant current between the electrodes while the workpiece W to be measured is sandwiched between the first electrode 21 and the second electrode 22.

[0047] This is because, by applying a constant current, the rate of heat generation of the workpiece W, the initial heat generation timing, the peak resistance timing at the heat generation initiation point, and the subsequent degree of current loss (shutting) can be measured as waveforms of changes in resistance value.

[0048] Then, when welding metal workpieces P1 and P2 that are the same combination as the workpiece W whose resistance value was measured by the resistance measurement unit 30, the welding control unit 50 changes the welding current over time at the same rate of change as the waveform of the change in resistance value measured by the resistance measurement unit 30.

[0049] Therefore, according to the welding apparatus 1 of this embodiment, constant resistance welding can be achieved, as shown in Figure 2, in which the resistance value between electrodes during welding is kept almost constant, without monitoring the resistance change of the workpiece W while welding is being performed.

[0050] Furthermore, the welding conditions for this constant-resistance welding can be easily set by resistance measurement processing by the resistance measurement unit 30 and the current waveform generation unit 40, and the processing load on the welding control unit 50 during welding can be reduced.

[0051] Furthermore, since the resistance welding machine 20 is configured to control the welding current with a time resolution of milliseconds, the welding control unit 50 can accurately control the welding current in accordance with the waveform of the change in resistance value measured by the resistance measurement unit 30. As a result, constant resistance welding can be achieved more effectively.

[0052] Furthermore, the constant current that the resistance measuring unit 30 supplies between the electrodes when measuring resistance is set to a current value that does not generate spatter during welding. Therefore, the welding current that the welding control unit 50 supplies between the electrodes during welding is also set to prevent spatter from occurring, thereby improving the welding quality of the workpiece W to be welded.

[0053] Next, the current waveform of the welding current set by the resistance measurement process shown in Figure 4 is divided into a high-current period TA at the beginning of welding and a main current period TB after the high-current period TA, as shown in Figure 2. During the high-current period TA, a high current higher than the main current is applied as the welding current.

[0054] Therefore, impurities can be blown away from the workpiece W to be welded during the high-current period TA, thereby suppressing the generation of spatter caused by impurities during welding with this current. In addition, by applying a high current during the high-current period TA, the surface of the workpiece W to be welded can be flattened, which also suppresses the generation of spatter.

[0055] Furthermore, by passing a large current greater than the main current during the high-current period TA, heat is introduced into the workpiece W, and as shown in Figure 5A, a gap GA is created between the metal workpieces P1 and P2 around the welding point M sandwiched between the first electrode 21 and the second electrode 22. As a result, the welding current can be concentrated at the welding point M, and current loss caused by current flowing between the metal workpieces P1 and P2 around the welding point M can be reduced.

[0056] Furthermore, during the high-current period TA and the main current period TB, the welding current decreases in a curved manner in response to the change in resistance values ​​measured as described above. However, as shown in Figure 5B, this welding current flows through the area around the welding point M where the metal workpieces P1 and P2 are in contact. This is because the resistance increases in the central part of the welding point M due to the melting of the workpiece W.

[0057] As the welding current flows in this manner, current loss is eliminated, and a weld nugget is formed on the workpiece W. The diameter of the weld nugget can be controlled by shifting the welding current up or down while maintaining the current waveform shown in Figure 2.

[0058] [Differentiation] Although a welding apparatus 1 for realizing the manufacturing method of the joint of the present disclosure has been described above, the manufacturing method of the present disclosure is not limited to the welding apparatus 1 of the above embodiment, and can take various forms. For example, the welding apparatus 1 described above may be used for welding a workpiece W in which three or more metal workpieces are stacked.

[0059] Furthermore, in the above embodiment, the welding current waveform shown in Figure 2 was described as being set based on the waveform of resistance change obtained by passing a constant current through the workpiece W for measurement. However, the welding current waveform does not necessarily have to be set based on the waveform of resistance change measured earlier. For example, the current waveform including the high-current period TA and the main current period TB may be set by experiment or simulation.

[0060] Furthermore, the function of one component in the above embodiment may be distributed among multiple components. The functions of multiple components may be integrated into one component. Some parts of the configuration of the above embodiment may be omitted. At least some parts of the configuration of the above embodiment may be added to or replaced with the configuration of other above embodiments. Any aspect included in the following technical concept constitutes an embodiment of the present disclosure.

[0061] [Technical concepts disclosed in this specification] This specification discloses the following technical concepts: [Item 1] A manufacturing method for producing a joint by resistance welding, Multiple metal workpieces, including high-strength steel plates, are sandwiched between a first electrode and a second electrode, and a welding current is passed between the first electrode and the second electrode, the current value of which changes over time according to a preset current waveform, to weld the multiple metal workpieces. A method for manufacturing a joined body, wherein the current waveform includes a high-current period in which a high current higher than the main current required for welding is applied at the beginning of energization to blow away impurities from the metal workpiece, and a main current period in which the main current is applied after the high-current period to perform welding, wherein during the high-current period, the current value of the high-current gradually decreases from the maximum current immediately after the start of energization towards the main current during the main current period, and during the main current period, the current value of the main current gradually decreases more slowly than during the high-current period.

[0062] [Item 2] A method for manufacturing a joint described in item 1, A method for manufacturing a joined body, wherein the current value of the welding current is set to change over time in the same way as the resistance value between electrodes measured when multiple measuring metal workpieces, which are the same combination as the multiple metal workpieces to be welded, are sandwiched between the first electrode and the second electrode and current is passed between the electrodes.

[0063] [Item 3] A method for manufacturing a joint described in item 2, A method for manufacturing a joined body, wherein the current supplied between the electrodes when measuring the resistance value is set to a current value that does not cause spatter due to welding.

[0064] [Item 4] A method for manufacturing a joint described in any one of items 1 to 3, A method for manufacturing a joined body, wherein a welding apparatus capable of controlling the welding current with a time resolution of milliseconds is used for welding the plurality of metal workpieces. [Explanation of Symbols]

[0065] 20... Resistance welding machine, 21... First electrode, 22... Second electrode, 30... Resistance measurement unit, 50... Welding control unit, P1, P2... Metal workpiece, TA... High current period, TB... Main current period.

Claims

1. A manufacturing method for producing a joint by resistance welding, Multiple metal workpieces, including high-strength steel plates, are sandwiched between a first electrode and a second electrode, and a welding current is passed between the first electrode and the second electrode, the current value of which changes over time according to a preset current waveform, to weld the multiple metal workpieces. A method for manufacturing a joined body, wherein the current waveform includes a high-current period in which a high current higher than the main current required for welding is applied at the beginning of energization to blow away impurities from the metal workpiece, and a main current period in which the main current is applied after the high-current period to perform welding, wherein during the high-current period, the current value of the high-current gradually decreases from the maximum current immediately after the start of energization towards the main current during the main current period, and during the main current period, the current value of the main current gradually decreases more slowly than during the high-current period.

2. A method for manufacturing a joint according to claim 1, A method for manufacturing a joined body, wherein the current value of the welding current is set to change over time in the same way as the resistance value between electrodes measured when multiple measuring metal workpieces, which are the same combination as the multiple metal workpieces to be welded, are sandwiched between the first electrode and the second electrode and current is passed between the electrodes.

3. A method for manufacturing a joint according to claim 2, A method for manufacturing a joined body, wherein the current supplied between the electrodes when measuring the resistance value is set to a current value that does not cause spatter due to welding.

4. A method for manufacturing a joint according to any one of claims 1 to 3, A method for manufacturing a joined body, wherein a welding apparatus capable of controlling the welding current with a time resolution in milliseconds is used for welding the plurality of metal workpieces.

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