Resistance spot welding method

Abstract

The present invention provides a technique capable of growing nuggets to a desired size in a short time while suppressing the occurrence of sputtering. The resistance spot welding method includes: a pre-energizing step of energizing until an alloy layer diameter, which is the diameter of an alloy layer formed on the outer periphery of a nugget in a welding portion and composed of a constituent material of a plating layer in a metal plate to be welded and a base material of the metal plate, becomes a predetermined target diameter; and a main energization step in which energization is performed after the pre-energization step. The pre-energization step includes a pulse energization in which a high current energization is performed at a current higher than a predetermined threshold current and a low current energization is performed at a current equal to or lower than the threshold current repeatedly at an interval of less than 10 ms. The pulse energization comprises more than two times of high-current energization.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority based on Japanese patent application No. 2022-147720 filed on September 16, 2022, the entire disclosure of which is incorporated into this application by reference. Technical Field

[0003] The present disclosure relates to a method of resistance spot welding. Background Art

[0004] In resistance spot welding, there is a known technique for dividing energization into main energization and pre-energization before the main energization. International Publication No. 2015 / 083381 describes a technique for performing pre-energization (initial energization) in multiple stages, including high current energization with high current and low current energization with low current.

[0005] When a high current is applied for a long time, the nugget may grow rapidly and cause sputtering, but if only a low current is applied, it may take too much time to grow the nugget to a desired size. Therefore, a technology is needed that can suppress the generation of sputtering and grow the nugget to a desired size in a short time. Summary of the invention

[0006] The present disclosure has been made to solve the above-mentioned problems and can be implemented as the following aspects.

[0007] (1) According to one embodiment of the present disclosure, a resistance spot welding method is provided. The resistance spot welding method includes: a preliminary energization step, in which energization is performed until the diameter of an alloy layer formed on the periphery of a weld nugget and composed of a constituent material of a plating layer in a metal plate to be welded and a base material of the metal plate, that is, an alloy layer diameter, which reaches a predetermined target diameter; and a formal energization step, in which energization is performed after the preliminary energization step. The preliminary energization step includes pulse energization of repeatedly performing high current energization with a current higher than a predetermined threshold current and low current energization with a current lower than the threshold current at intervals of less than 10 ms. The pulse energization includes performing the high current energization more than twice.

[0008] According to the resistance spot welding method of this aspect, in the preliminary current application step, high current application and low current application are repeated at short time intervals of less than 10 ms, so that the occurrence of spatter can be suppressed and a nugget of a desired size can be generated in a short time.

[0009] (2) In the resistance spot welding method of the above aspect, the main energizing step may include: ramp energizing in which energizing is performed while increasing the current over time; and constant current energizing in which energizing is performed with a constant current.

[0010] According to the resistance spot welding of this aspect, compared with the case where only ramp current is applied or only constant current is applied, a rapid temperature rise of the molten portion of the workpiece can be suppressed and the nugget can be grown in a short time.

[0011] (3) In the resistance spot welding method of the aspect described above, in the main current-applying step, current may be applied until the diameter of the nugget, i.e., the nugget diameter, reaches a predetermined target nugget diameter, the target diameter being 1.2 times or more of the target nugget diameter.

[0012] According to the resistance spot welding of this aspect, the generation of spatter can be suppressed.

[0013] (4) In the resistance spot welding method of the aspect described above, the current in the low current conduction may be not less than 1 / 3 times and not more than 2 / 3 times the current in the high current conduction.

[0014] According to the resistance spot welding of this aspect, it is possible to suppress a situation in which the current does not fully rise to a high current after the current is passed at a low current, and a situation in which the alloy layer is not formed.

[0015] (5) In the resistance spot welding method of the above aspect, the main current-passing step may include constant current passing of current at a constant current that is less than a current in the high current passing and greater than a current in the low current passing.

[0016] According to the resistance spot welding of this aspect, the occurrence of spatter can be suppressed and a nugget of a desired size can be generated in a short time.

[0017] (6) In the resistance spot welding method of the aspect described above, in the main energizing step, energizing may be performed while increasing the current to a predetermined first current in the ramp energizing, and then the constant current energizing may be performed at a current greater than the first current.

[0018] According to the resistance spot welding of this aspect, the occurrence of spatter can be suppressed and a nugget of a desired size can be generated in a short time.

[0019] Furthermore, the present disclosure can be implemented in various forms, for example, it can be implemented in the form of a resistance spot welding device or the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above-mentioned object and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings.

[0021] Figure 1 It is a figure which shows the structure of a resistance spot welding device.

[0022] Figure 2 This is a flow chart showing an example of resistance spot welding.

[0023] Figure 3 This is a diagram showing the results of an experiment conducted to confirm the relationship between the ratio of the alloy layer diameter to the nugget diameter and the presence or absence of sputtering.

[0024] Figure 4 This is a graph showing an example of changes in current.

[0025] Figure 5 This is a graph showing an example of changes in current in the second embodiment.

[0026] Figure 6 This is a graph showing an example of changes in current in the third embodiment. DETAILED DESCRIPTION

[0027] A. First Implementation Method:

[0028] Figure 1 Schematic diagram showing the structure of the resistance spot welding device 100 in this embodiment. Figure 1 As shown, the up-down direction is a direction parallel to the lifting direction of the upper electrode contact 21 as a movable electrode described later. The resistance spot welding device 100 joins the joined member W formed by overlapping two or more metal plates by resistance spot welding. The resistance spot welding device 100 includes a welding gun 10, a power supply device 30, a current sensor 53, a voltage sensor 54, and a control unit 80.

[0029] The joined member W is a steel plate, for example, a steel plate having a coating composed of hot-dip galvanizing, alloyed hot-dip galvanizing, zinc oxide film, or aluminum / silicon alloy on the surface. In this embodiment, as the joined member W, a case where a first metal plate W1 and a second metal plate W2 as two or more metal plates overlap is exemplified.

[0030] The welding gun 10 is mounted on the top of a robot arm (not shown). The gun body 11 is moved to the target welding point of the joined member W by the robot arm. The welding gun 10 has a gun body 11, a moving mechanism 20, a pair of opposing electrode contacts 21 and 22, and a pressurizing device 40. The upper electrode contact 21 is a movable electrode, which is mounted on the upper part of the gun body 11. The lower electrode contact 22 is a fixed electrode, which is mounted on the lower part of the gun body 11 and at a position opposite to the upper electrode contact 21. In addition, the upper electrode contact 21 may be a fixed electrode, and the lower electrode contact 22 may be a movable electrode.

[0031] The moving mechanism 20 moves the upper electrode contact 21 up and down. The moving mechanism 20 includes a servo motor (not shown), converts the rotational force of the servo motor into a linear moving force in the lifting direction, and transmits the converted linear moving force to the upper electrode contact 21, thereby moving the upper electrode contact 21 up and down. The power supply device 30 supplies a welding current of a target current value between the pair of electrode contacts 21 and 22. The pressurizing device 40 includes an air cylinder (not shown), and pressurizes the electrode contacts 21 and 22 by pressing them against the member to be joined W.

[0032] The current sensor 53 detects the current value of the welding current supplied from the power supply device 30, and sends a signal indicating the current value to the control unit 80 at predetermined intervals. The current sensor 53 is implemented using, for example, a toroidal coil. The voltage sensor 54 detects the voltage value between the upper electrode contact 21 and the lower electrode contact 22 at predetermined intervals, and sends a signal indicating the voltage value to the control unit 80.

[0033] The control unit 80 includes a central processing unit (CPU), a microcomputer composed of RAM and ROM, etc. The control unit 80 controls the operation of the resistance spot welding device 100 by executing a pre-installed program by the microcomputer. More specifically, the current value, the energization time, the pressure of the electrode, the energization timing, the pressure timing, etc. are comprehensively controlled. However, part or all of the functions can also be realized by a hardware circuit.

[0034] Figure 2 1 is a flowchart showing an example of resistance spot welding. In step S100, the resistance spot welding device 100 performs welding based on pre-energization. This process is also referred to as a pre-energization process. In the present embodiment, pre-energization refers to energization performed until the diameter of the alloy layer formed on the joined member W, that is, the alloy layer diameter, reaches a predetermined target diameter. More specifically, pre-energization is energization performed at a time and current obtained in advance through experimental experience until the alloy layer diameter reaches the target diameter.

[0035] The alloy layer is a layer formed by melting the first metal plate W1 and the second metal plate W2 to form an alloy. More specifically, the alloy layer is a layer formed at the periphery of the nugget at the weld portion and is composed of the constituent materials of the plating layers in the first metal plate W1 and the second metal plate W2 to be welded and the base materials of the first metal plate W1 and the second metal plate W2. The alloy layer diameter is obtained by measuring a portion determined to be an alloy layer by observation using a scanning electron microscope (SEM), for example.

[0036] The alloy layer is formed as the temperature of the boundary portion of the first metal plate W1 and the second metal plate W2 rises by energizing. For example, the alloy layer is formed when the temperature of the joined member W is above 1200 degrees and below 1500 degrees. By continuously energizing, the alloy layer grows and the diameter of the alloy layer increases. Moreover, by continuously energizing, as the temperature of the molten portion of the first metal plate W1 and the second metal plate W2 rises, a nugget is formed in the central portion of the alloy layer.

[0037] In the present embodiment, the target diameter is 1.2 times the diameter of the desired nugget formed in the formal energization process described later, that is, the target nugget diameter. The target diameter is preferably 1.2 times or more and 1.5 times or less of the target nugget diameter. The nugget diameter can be estimated, for example, using the amount of expansion of the joined member W in the perpendicular direction relative to the surface direction and the resistance value between the pair of electrode contacts 21 and the electrode contacts 22.

[0038] Figure 3 This is a graph showing the results of an experiment conducted to confirm the relationship between the ratio of the alloy layer diameter to the nugget diameter and the presence or absence of sputtering. Figure 3 In the figure, the × mark indicates that sputtering occurs, and the ○ mark indicates that sputtering does not occur. Figure 3 As shown in the figure, regardless of the time of power-on, when the ratio of the alloy layer diameter to the nugget diameter is less than 1.2, the frequency of sputtering is high. In addition, regardless of the time of power-on, when the ratio of the alloy layer diameter to the nugget diameter exceeds 1.2, the generation of sputtering is suppressed. That is, it is confirmed through experiments that when the alloy layer diameter is more than 1.2 times the target nugget diameter, the generation of sputtering is suppressed compared with the case where the alloy layer diameter is less than 1.2 times the target nugget diameter.

[0039] In this embodiment, the pre-energization step repeats pulse energization of high current energization with a current higher than a predetermined threshold current and low current energization with a current lower than the threshold current at intervals of less than 10 ms. The threshold current can be determined in advance by experiment or experience.

[0040] In step S110 (refer to Figure 2 ), the resistance spot welding device 100 performs welding based on formal energization. This process is also referred to as a formal energization process. In the present embodiment, the formal energization process is a process of energizing until the diameter of the nugget reaches a predetermined target nugget diameter. In addition, in the present embodiment, the formal energization process performs constant current energization in which energization is performed with a constant current. The current in the constant current energization can be determined in advance by experiments or experience.

[0041] Figure 4 This is a graph showing an example of the change in current during resistance spot welding. Figure 4 In the graph, the vertical axis represents current and the horizontal axis represents time. In the present embodiment, the resistance spot welding device 100 performs a 30 ms pre-energization process and then performs a 200 ms main energization process.

[0042] In this embodiment, pulse power-on includes three high current power-ons and two low current power-ons. More specifically, after 6ms of high current power-on, 6ms of low current power-on is performed, after 6ms of high current power-on again, 6ms of low current power-on is performed, and finally 6ms of high current power-on is performed. Any high current power-on is performed with the same high current I1, and any low current power-on is performed with the same low current I2.

[0043] The high current I1 is preferably 8kA or more and 15kA or less. The power-on time t1 under the high current I1 is preferably 4ms or more and 8ms or less. The low current I2 is preferably 1 / 3 or more of the high current I1 and 2 / 3 or less of the high current I1. When the difference between the high current I1 and the low current I2 is too large, after the power is applied with the low current I2, the current cannot rise completely to the high current I1, and welding may not be possible. In addition, when the difference between the high current I1 and the low current I2 is too small, it is possible to form a nugget without forming an alloy layer by applying power under the low current I2. Therefore, the difference between the high current I1 and the low current I2 is preferably about 5kA. The power-on time t2 under the low current I2 is preferably 4ms or more and 8ms or less. The pulse power-on preferably includes 2 or more and 5 or less high current power-ons. The comprehensive power-on time t3 in the pulse power-on is preferably 20ms or more and 40ms or less.

[0044] In the present embodiment, the main energization is performed by constant current energization in which the energization is performed for 200 ms at a constant current Ie. The current Ie is preferably equal to or less than the high current I1 and equal to or greater than the low current I2.

[0045] According to the resistance spot welding method of the present embodiment described above, in the pre-energization process, high current energization and low current energization are repeatedly performed at short time intervals of less than 10 ms, so that the temperature of the welding point of the joined member W can be raised to the temperature region where the alloy layer can be generated by high current energization, and the generation of sputtering can be suppressed by low current energization. That is, the generation of sputtering can be suppressed, and a nugget of a desired size can be generated in a short time.

[0046] In addition, in the pre-energization process, high current energization is performed last, and then the formal energization process is entered. Therefore, when entering the formal energization process from the pre-energization process, a sharp increase in current can be avoided. As a result, a sharp increase in the temperature of the molten portion of the joined member W can be suppressed in the formal energization process, thereby suppressing the generation of sputtering.

[0047] In addition, the diameter of the alloy layer formed by the preliminary energization is 1.2 times or more the desired nugget diameter formed by the main energization. Therefore, compared with the case where the alloy layer diameter is less than 1.2 times the desired nugget diameter, the generation of sputtering can be suppressed.

[0048] In addition, the low current I2 is 1 / 3 or more and 2 / 3 or less of the high current I1. Therefore, it is possible to prevent the current from completely rising to the high current I1 after the low current I2 is passed, and prevent the alloy layer from being formed.

[0049] In addition, the current Ie in the main energization step is equal to or less than the high current I1 and equal to or greater than the low current I2. Therefore, it is possible to suppress the occurrence of sputtering and to generate a nugget of a desired size in a short time.

[0050] B. Second Implementation Method:

[0051] The spot welding method of the second embodiment is different from the spot welding method of the first embodiment in that the pre-energization step (see Figure 2 Step S100 includes ramp energization in which the current is increased as time passes, and the other steps are the same as those of the first embodiment. The structure of the resistance spot welding device 100 of the second embodiment is the same as that of the resistance spot welding device 100 of the first embodiment, so the description of the structure of the resistance spot welding device 100 is omitted.

[0052] Figure 5 is a graph showing an example of the change in current in the second embodiment. Figure 5 In the graph, the vertical axis represents current and the horizontal axis represents time. In the present embodiment, the resistance spot welding device 100 performs a 200 ms pre-energization process and then performs a 200 ms main energization process.

[0053] In the ramp energization in the second embodiment, energization is performed while increasing the current from a current I3 that is greater than the low current I2 and less than the high current I1 to a current I4 that is greater than the current I3 and less than the high current I1 over time.

[0054] According to the resistance spot welding method of the second embodiment described above, ramp energization is performed after pulse energization, so a larger alloy layer can be generated while maintaining the ratio of the nugget diameter to the alloy layer diameter.

[0055] C: Third embodiment:

[0056] The spot welding method of the third embodiment is different from the spot welding method of the first embodiment in that the main energization step (see Figure 2Step S110 includes ramp energization, and other steps are the same as those of the first embodiment. The structure of the resistance spot welding device 100 of the third embodiment is the same as that of the resistance spot welding device 100 of the first embodiment, so the description of the structure of the resistance spot welding device 100 is omitted.

[0057] Figure 6 is a graph showing an example of the change in current in the third embodiment. Figure 6 In the graph, the vertical axis represents current and the horizontal axis represents time. In the present embodiment, the resistance spot welding device 100 performs a 30 ms pre-energization process and then performs a 200 ms main energization process.

[0058] The formal power-on in the third embodiment is performed after the ramp power-on for 100ms, and then the constant current power-on at the current Ie for 100ms. The ramp power-on is performed while increasing the current from the current Is which is higher than the low current I2 and lower than the current Ie to the current Ie. Preferably, the ramp power-on is performed to increase the current to a level lower than the current in the constant current power-on. That is, the current in the constant current power-on is preferably higher than the current increased in the ramp power-on.

[0059] According to the resistance spot welding method of the third embodiment described above, compared with the case where only ramp current or only constant current is applied during the main current application, a rapid temperature rise of the molten portion of the workpiece can be suppressed and a nugget can be grown in a short time.

[0060] In the ramp energization, the current is increased to a predetermined first current, that is, current Ie, and energization is performed at a constant current Ie. Therefore, it is possible to suppress the occurrence of sputtering and to generate a nugget of a desired size in a short time.

[0061] D. Other implementation methods:

[0062] (D1) In the above-mentioned embodiment, the pulse power-on includes three high current power-ons and two low current power-ons. Without limitation thereto, the pulse power-on only needs to include two or more high current power-ons. More specifically, the pulse power-on only needs to include power-on of a first high current for less than 10 ms with a first high current, power-on of a first low current for less than 10 ms with a low current lower than the first high current, and power-on of a second high current for less than 10 ms with a second high current higher than the low current.

[0063] (D2) In the above-mentioned embodiment, the pulse energization starts with high current energization. However, the present invention is not limited to this, and the pulse energization may start with low current energization.

[0064] (D3) In the above-mentioned embodiment, any high current conduction is conducted with the same high current I1 for the same conduction time t1, and any low current conduction is conducted with the same low current I2 for the same conduction time t2. Without limitation to this, as long as the high current conduction is always conducted with a current higher than the low current conduction, the current and conduction time of each high current conduction in the pulse conduction and the current and conduction time of each low current conduction can be arbitrarily determined.

[0065] (D4) In the second embodiment described above, the pre-energization step is to perform ramp energization after pulse energization. However, the present invention is not limited thereto, and pulse energization may be performed after ramp energization. Alternatively, pulse energization and ramp energization may be performed multiple times.

[0066] (D5) In the third embodiment described above, the formal energization process is to perform constant current energization after ramp energization. Not limited to this, the formal energization process may be to perform ramp energization after constant current energization, or may be to perform only ramp energization. In addition, the formal energization process may be to perform constant current energization and ramp energization multiple times respectively.

[0067] (D4) The energization may be a combination of the second embodiment and the third embodiment described above. More specifically, the pre-energization step may be a ramp energization followed by pulse energization, and the main energization step may be a constant current energization followed by ramp energization.

[0068] The present disclosure is not limited to the above-mentioned embodiments, and can be implemented in various structures without departing from its main purpose. For example, the technical features in the embodiments corresponding to the technical features in each mode recorded in the summary of the invention column can be appropriately replaced or combined in order to solve the above-mentioned problems or to achieve part or all of the above-mentioned effects. In addition, if the technical feature is not described as a necessary feature in this specification, it can be appropriately deleted.

[0069] Description of symbols

[0070] 10… welding gun, 11… gun body, 20… moving mechanism, 21… upper electrode contact, 22… lower electrode contact, 30… power supply device, 40… pressurizing device, 53… current sensor, 54… voltage sensor, 80… control unit, 100… resistance spot welding device, W… member to be joined, W1… first metal plate, W2… second metal plate.

Claims

1. A resistance spot welding method, wherein: include: a pre-energizing step of energizing until the diameter of an alloy layer formed on the periphery of a nugget at a weld portion and composed of a constituent material of a plating layer in a metal plate to be welded and a base material of the metal plate, that is, an alloy layer diameter, reaches a predetermined target diameter; and The formal power-on process is performed after the pre-power-on process. The pre-energization process includes repeatedly performing pulse energization of high current energization with a current higher than a predetermined threshold current and low current energization with a current lower than the threshold current at intervals of less than 10 ms. The pulse energization includes two or more times of the high current energization.

2. The resistance spot welding method according to claim 1, wherein: The main energization process includes ramp energization, which performs energization while increasing the current as time passes, and constant current energization, which performs energization with a constant current.

3. The resistance spot welding method according to claim 1 or 2, wherein: In the main current supplying step, current is supplied until the diameter of the nugget, that is, the nugget diameter, reaches a predetermined target nugget diameter. The target diameter is greater than 1.2 times the target nugget diameter.

4. The resistance spot welding method according to claim 1 or 2, wherein: The current in the low current conduction is not less than 1 / 3 times and not more than 2 / 3 times the current in the high current conduction.

5. The resistance spot welding method according to claim 1 or 2, wherein: The main energization step includes constant current energization of performing energization with a constant current that is less than the current in the high current energization and greater than the current in the low current energization.

6. The resistance spot welding method according to claim 2, wherein: In the main energization step, energization is performed while increasing the current to a predetermined first current in the ramp energization, and thereafter, the constant current energization is performed at a current equal to or higher than the first current.

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