JPH11333569A - Method and device for series spot welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for the series spot welding, by which defective welding does not occur. SOLUTION: The applied current of initial welding is made two times a steady state current and the pressurizing forces of electrode tips 30A and 30B to plates 40 and 44 are made 1.25 times steady state pressurizing forces. That is, by increasing the pressurizing forces in the initial welding, the contact resistance of the plates 40 and 44 is decreased. Simultaneously with that, by making a high current to flow, the current is made to flow through the plate 44 on the opposite side of the electrode tips, and weld nuggets are produced at contact points of the plates 40 and 44. And, after the weld nuggets is produced once, the steady state current is made to flow, and by decreasing the pressurizing forces, the weld nuggets are grown up, and both plates 40 and 44 are welded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a series spot welding method and a series spot welding apparatus in which metal plates are overlapped and current is applied to a pair of electrodes from one side of the metal plate to perform welding.

[0002]

2. Description of the Related Art Direct spot welding is widely used for welding steel sheets. This welding method is shown in FIG.
Are pressed directly while sandwiching the steel plates 40, 42 which are superimposed as shown in, between the upper and lower electrode tips 30A, 30B,
An electric current flows in the thickness direction, and a spot-like weld is obtained by utilizing the resistance heating of the steel sheet. That is, when an electric current is applied, a molten portion of both steel plates called a welding nugget indicated by N in the figure is formed at a contact portion between the both steel plates 40 and 42, and the two steel plates are welded in a dotted shape by this welding nugget.

On the other hand, series spot welding is currently used together with the direct spot welding. In this series spot welding, the steel plates 40 and 42 overlapped as shown in FIG.
At B, pressure is applied from one direction, and a current is applied to obtain a point-like welded portion. In the direct spot welding described above, the steel plate is sandwiched between the electrode tips, so it is necessary to perform welding for each point. On the other hand, in series spot welding, multiple points can be welded simultaneously with multiple electrode tips. Since it is possible to increase the speed of welding, it is currently used for welding automobile bodies and the like.

[0004]

However, the series spot welding has a higher probability of occurrence of poor welding than the direct spot welding. That is, in the series spot welding, as shown by the solid line J in FIG. 4 (B), the upper steel plate 40 penetrates through the upper steel plate 40 from one electrode tip 30A, passes through the lower steel plate 42, and again. When a current flows through the electrode tip 30B through the other electrode tip 30B, a welding nugget N is generated at a contact point between the steel plate 40 and the steel plate 42 (a point pressed by the electrode tips 30A and 30B), and welding is performed. Done. However, in practice, FIG.
As indicated by the broken line B in (B), most of the current flows as a shunt from one electrode tip 30A to the other electrode tip 30B through the upper steel plate 40, and forms a welding nugget N shown in the figure. Is useless. For this reason, poor welding may occur as described above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a series spot welding method and a series spot welding apparatus which do not cause welding defects.

[0006]

According to a first aspect of the present invention, at least two metal plates are overlapped with each other, and a current is applied to a pair of electrodes separated from one side of the metal plate. In the series spot welding method to be welded,
It is a technical feature that the applied current at the initial stage of welding is applied to 1.5 times or more of the subsequent steady current.

According to a second aspect of the present invention, there is provided a series spot welding method in which at least two metal plates are overlapped with each other and a current is applied to a pair of electrodes separated from one side surface of the metal plate to perform welding. Is applied 1.5 times or more of the subsequent steady-state current, and the welding force of the electrode to the metal plate at the initial stage of welding is set to 1.1 times or more of the subsequent steady-state pressure. I do.

A third aspect of the present invention is characterized in that, in the second aspect, after the applied current in the initial stage of the welding is set to a steady current, the applied pressure of the electrode to the metal plate is set to a steady applied pressure.

According to a fourth aspect of the present invention, there is provided a series spot welding apparatus comprising: a pair of electrodes that press at least two superposed metal plates from one side surface in the same direction; and a current control device that applies a current to the electrodes. It is a technical feature that the current control device applies the applied current at the initial stage of welding at least 1.5 times the subsequent steady-state current.

[0010] The series spot welding method according to claim 1 comprises:
The applied current at the initial stage of welding is applied to 1.5 times or more of the steady current. That is, even if a steady current flows in the initial stage of welding, the resistance (contact resistance) between the metal plate on the electrode side and the metal plate on the opposite side (rear side) is large. Flows through. Therefore, by supplying a large current in the initial stage of welding, a current is also supplied to the metal plate on the opposite side of the electrode, and a welding nugget is created at a contact point between the metal plate on the electrode side and the metal plate on the opposite side of the electrode. Then, once the welding nugget is created, a steady current is applied to grow the welding nugget and weld both metal plates.

The series spot welding method according to claim 2 is
The current applied at the initial stage of welding is applied to 1.5 times or more of the steady current, and the pressure applied to the metal plate by the electrode is set to 1.1 times or more of the steady pressure. That is, even if a steady current flows in the initial stage of welding, the resistance (contact resistance) between the metal plate on the electrode side and the metal plate on the opposite side (rear side) is large. Flows through. Therefore, by increasing the pressing force in the early stage of welding, the contact resistance between the two metal plates is reduced,
By supplying a large current, a current is also supplied to the metal plate on the opposite side of the electrode, and a welding nugget is created at a contact point between the metal plate on the electrode side and the metal plate on the opposite side of the electrode. Then, once the welding nugget has been created, a steady current is applied and the pressing force is reduced to grow the welding nugget and weld both metal plates.
Here, the reason why the pressing force is reduced when the welding nugget is grown is that even if the welding nugget becomes large, if the pressing force is high, the welding nugget portion is depressed and poor welding occurs.

In the series spot welding method according to the third aspect, after the applied current in the initial stage of welding is set to a steady current, the pressure applied to the metal plate of the electrode is set to the steady pressure. That is, first,
A large current is applied in the early stage of welding to create a welding nugget at the contact point between the metal plate on the electrode side and the metal plate on the opposite side of the electrode. And
Once a welding nugget is created, a steady current is applied to grow the welding nugget. Then, before the welding nugget grows and the welding nugget portion collapses, the pressing force is reduced to a steady pressing force, thereby preventing the occurrence of poor welding.

According to the fourth aspect of the present invention, the current control device applies the applied current at the initial stage of welding to 1.5 times or more of the steady current. That is, even if a steady current is applied at the initial stage of welding, the resistance (contact resistance) between the metal plate on the electrode side and the metal plate on the opposite side (rear side) is large.
Flows through the metal plate on the electrode side. Therefore, by supplying a large current in the initial stage of welding, a current is also supplied to the metal plate on the opposite side of the electrode, and a welding nugget is created at a contact point between the metal plate on the electrode side and the metal plate on the opposite side of the electrode. Then, once the welding nugget is created, a steady current is applied thereafter to grow the welding nugget and weld both metal plates.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a series spot welding method and a series spot welding apparatus according to one embodiment of the present invention will be described with reference to the drawings. FIG. 1A shows a configuration of a series spot welding apparatus using a series spot welding method according to one embodiment. The series spot welding device includes an electrode tip 30A, 30B and a pressing device 2 for pressing the electrode tip 30A, 30B to a welding position.
0 and a current control device 10 for controlling a current applied to the electrode chips 30A and 30B. The series spot welding apparatus welds a flat steel plate 40 (0.8 mm in thickness) to a steel plate 44 (0.8 mm in thickness) on which a reinforcing member M is formed.

FIG. 1B is a plan view of a steel plate 40 showing a welding spot by the series spot welding apparatus, that is, FIG.
(A) It is a B arrow view of the steel plate 40 in a middle. The series spot welding apparatus includes a plurality of sets of electrode tips 30A and 30B and simultaneously welds a plurality of welding points P along a reinforcing member M (multipoint welding). Here, since the reinforcing member M is formed on the steel plate 44 side, welding is performed without using a jig. However, when welding flat steel plates, it is preferable to support the steel plate on the opposite side of the electrode tips 30A and 30B with a jig.

In the series spot welding apparatus of this embodiment, the occurrence of poor welding is prevented by applying a large current at the initial stage of welding and increasing the pressure applied to the steel plates 40 and 44 by the electrode tips 30A and 30B. This current / pressure control will be described in more detail with reference to FIGS.

FIG. 2A is a graph showing the pattern of the flowing current. The current is plotted on the vertical axis and the elapsed time is plotted on the horizontal axis. FIG. 2B is a graph showing the pattern of the pressing force, in which the horizontal axis represents the pressing force and the horizontal axis represents the elapsed time.
Here, the series spot welding equipment is 0.2-0.3
Finish the welding in seconds. Here, a steel plate 4 having a thickness of 0.8 mm is used.
The welding of 0 and 44 is performed in about 0.25 seconds. In the present embodiment, the current control device 10 shown in FIG. 1 supplies 9 KA as a steady current, and the pressurizing device 20 applies 200 kg to the electrode tips 30A and 30B as a steady pressing force. Then, at the beginning of welding (0.05 seconds), the current controller applies a current of 18 KA, twice the steady current, and then reduces the current to a steady current (9 KA). Similarly,
The pressurizing device 20 applies a pressing force of 250 kg, which is 1.25 times the steady pressing force, at the beginning of welding (0.06 seconds), and then reduces the pressure to the steady pressing force (200 kg) to perform pressurization.

The formation of the welding nugget in the steel plates 40 and 44 in the initial state and the steady state is shown in FIG.
This will be described in more detail with reference to FIG.
FIG. 3A is an explanatory diagram of a welding nugget formed at an early stage of welding. Even if a steady current is applied in the initial stage of welding, the resistance (contact resistance) between the steel plate 40 on the electrode tip 30A, 30B side and the steel plate 44 on the opposite side (rear side) of the electrode tip, that is, the electrode tip 30A, 30B. Since the resistance of the pressurized portion is large, the current flows through the steel plate 40 on the electrode tip side as described above with reference to FIG. Therefore, in the present embodiment, by increasing the pressing force in the initial stage of welding, both steel plates 4 are increased.
The contact resistance is reduced by increasing the contact area of the electrodes 0 and 44, and at the same time, a large current is caused to flow, so that a current also flows to the steel plate 44 on the opposite side of the electrode chip, that is, as shown by the solid line J, the electrode tip 30A. -Steel plate 40-Steel plate 44-Steel plate 40-
A current is caused to flow through the electrode tip 30B. When the current flows in this manner, a welding nugget N is created at a contact point between the steel plate 40 and the steel plate 44.

FIG. 3B is an explanatory view showing a welding nugget formed at the end of welding, that is, a growing nugget when a steady current is flowing. Once the welding nugget N has been created as described above with reference to FIG.
When a current flows through the welding nugget N, the steel plate 4
0, the contact resistance between the steel plate 44 and the steel plate 44 decreases, and even if a large current does not flow, as shown by the solid line J, the electrode tip 30A-the steel plate 40-the weld nugget N-the steel plate 44-the weld nugget N-
A current flows through a path between the steel plate 40 and the electrode tip 30B. For this purpose, a steady current (9 KA) is applied to grow the welding nugget N and weld the two steel plates 40 and 44.

In the series spot welding apparatus according to the present embodiment, once the welding nugget N is once created (after 0.05 seconds) as described above with reference to FIG. 3A, the current is reduced to a steady current. At the same time, the applied pressure is set to a steady value (200
Kg). This is because if the pressing force is not reduced even if the welding nugget N is increased to a certain extent, the electrode tips 30A and 30B cause the steel plate 40 to sink as shown in FIG. is there.

In the series spot welding apparatus of the present embodiment, the current is reduced to a steady current (after 0.05 seconds), and then the pressure applied by the electrode tips 30A and 30B is reduced to the steady pressure (0. At the end of 06 seconds). This is because once the welding nugget N has been created as described above with reference to FIG. 3A (after 0.05 seconds), a steady current is applied and a high pressing force is applied thereafter. Grow welding nuggets. Before the welding nugget grows and the welding nugget portion described above with reference to FIG. 3 (C) collapses, the pressing force is set to a steady pressing force, thereby efficiently welding while preventing the occurrence of poor welding. I do.

In this embodiment, the steady-state current is 9
At the beginning of welding (0.05 seconds), a current of 18 KA, twice the steady state current, was applied. Here, according to an experiment performed by the inventor, it has been found that the occurrence rate of defective welding can be significantly reduced by flowing a current 1.5 times the steady state current in the initial stage of welding. Further, in the series spot welding apparatus of the present embodiment, the electrode tips 30A, 3
200 kg was added to OB, and a pressure of 250 kg, which was 1.25 times the steady pressure, was applied at the beginning of welding.
Here, according to the experiment, it was found that the incidence of defective welding can be reduced by increasing the initial pressing force to about 1.1 times.

In the above embodiment, the flat steel plate 4
Although the example in which the 0 and the steel plate 44 on which the reinforcing member M is formed is welded without using a jig, the series spot welding apparatus of this embodiment welds two flat steel plates using a jig. Alternatively, three or more steel plates can be welded simultaneously.

According to the series spot welding method and the series spot welding apparatus of the present embodiment, since the occurrence rate of defective welding can be reduced, the reliability of series spot welding can be improved. For this reason, the welding time can be shortened by using the series spot welding device capable of simultaneous multiple-point welding instead of the direct spot welding device that welds one point at a time.

[0025]

As described above, according to the series spot welding method of the first aspect, a large current is applied in the initial stage of welding, so that a current is also applied to the metal plate on the opposite side of the electrode, and the metal plate on the electrode side is connected to the electrode plate. Create a welding nugget at the point of contact with the opposite metal plate.
Then, once the welding nugget is created, a steady current is applied to grow the welding nugget and weld both metal plates. That is, since the welding nugget is formed at the initial stage of welding, welding can be performed without generating a defective portion.

[0026] The series spot welding method of claim 2 is
By increasing the pressing force in the early stage of welding, the contact resistance between the two metal plates is lowered, and at the same time, a large current is passed, so that a current also flows to the metal plate on the opposite side of the electrode, and the metal plate on the electrode side and the electrode opposite to each other. Create a welding nugget at the point of contact with the side metal plate. Then, once the welding nugget has been created, a steady current is applied and the pressing force is reduced to grow the welding nugget and weld both metal plates. That is, since the welding nugget is formed at the initial stage of welding, welding can be performed without generating a defective portion.

In the series spot welding method according to the third aspect, a large current is applied at the initial stage of welding to create a welding nugget at a contact point between the metal plate on the electrode side and the metal plate on the opposite side of the electrode. Then, once a welding nugget is created, a steady current is applied to grow the welding nugget. Here, before the welding nugget grows and the welding nugget portion collapses, the pressing force is reduced to a steady pressing force to prevent the occurrence of poor welding.
Therefore, welding can be performed without generating a defective portion.

In the series spot welding apparatus according to the fourth aspect, a large current is applied in the initial stage of welding, so that an electric current also flows to the metal plate on the opposite side of the electrode, and the contact between the metal plate on the electrode side and the metal plate on the opposite side of the electrode. Create a welding nugget at the point. Then, once the welding nugget is created, a steady current is applied thereafter to grow the welding nugget and weld both metal plates. That is, since the welding nugget is formed at the initial stage of welding, welding can be performed without generating a defective portion.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating a configuration of a series spot welding apparatus according to an embodiment of the present invention.
(B) is a top view of the steel plate which shows the welding place by a series spot welding apparatus.

FIG. 2 (A) is a graph showing a pattern of a flowing current, and FIG. 2 (B) is a graph showing a pattern of a pressing force.

FIG. 3A is an explanatory diagram of a welding nugget formed at an early stage of welding, FIG. 3B is an explanatory diagram of a welding nugget formed at an end of welding, and FIG. () Is an explanatory diagram of defective welding.

FIG. 4A is an explanatory diagram of direct spot welding according to the related art, and FIG. 4B is an explanatory diagram of series spot welding according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Current control device 20 Pressurizing device 30A, 30B Electrode tip 40 Steel plate (metal plate) 44 Steel plate (metal plate) N Welding nugget

Claims (4)

[Claims] 1. A series spot welding method in which at least two metal plates are overlapped with each other and a current is applied to a pair of electrodes separated from one side surface of the metal plate to perform welding. A series spot welding method characterized in that the current is applied to 1.5 times or more of the steady current. 2. A series spot welding method in which at least two metal plates are overlapped with each other and a current is applied to a pair of electrodes separated from one side of the metal plate to perform welding. A series spot welding method comprising: applying 1.5 times or more of the steady current to the metal plate at an initial stage of welding, and applying 1.1 times or more of the subsequent steady force to the metal plate. . 3. The series spot welding method according to claim 2, wherein after the applied current at the initial stage of welding is set to a steady current, the pressing force of the electrode on the metal plate is set to a steady pressing force. 4. A series spot welding apparatus comprising: a pair of electrodes that presses at least two superposed metal plates from one side surface in the same direction; and a current control device that applies a current to the electrodes. A series spot welding apparatus, wherein the apparatus applies an applied current at the initial stage of welding at least 1.5 times the subsequent steady current.