JP2001321953A - Spot welding method and spot welding equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot welding method by which the decrease in the fatigue strength of a welding zone of the spot welding is easily and excellently prevented only by using a spot welding equipment without using a special device such as a press. SOLUTION: The method comprises a first process (S1) where the spot welding zone is electrified by the spot welding equipment while being pressurized, a second process (S2) where the temperature of the welding zone is decreased while the spot welded zone is not pressurized and not electrified after the first process, and a third process (S3) where the spot welding zone is pressurized but not electrified by the spot welding equipment after the second process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding method for performing spot welding using a spot welding apparatus having a function of energizing while applying pressure to a spot welding portion, and a spot welding apparatus used for implementing the spot welding method. .

[0002]

2. Description of the Related Art In recent years, for example, high-strength steel sheets have tended to be frequently used for automobile bodies and the like, and a reduction in fatigue strength of a welded portion due to spot welding has become apparent. As a cause of this, it is considered that tensile residual stress is generated in the vicinity of the welded portion due to spot welding.

Conventionally, in order to prevent a decrease in fatigue strength of a welded portion due to spot welding, a method of converting a tensile residual stress into a compressive residual stress by pressing the vicinity of the welded portion by using a press after a spot welding. Has been proposed.

On the other hand, as another method, in order to prevent a decrease in the fatigue strength of the welded portion due to the spot welding, a current smaller than that at the time of welding is applied to the spot welded portion after the spot welding to burn the spot welded portion. A method of smoothing has been proposed (see JP-A-62-57782).

[0005]

However, in the above-described method of performing a press, a press machine is used separately from the spot welding apparatus. Therefore, it is necessary to incorporate a press working process by the press machine into a production line. There was a problem that a space had to be secured and productivity was reduced.

Further, in the above-described method of normalizing, it is difficult to control the temperature for normalizing, and there is a problem that it is not expected that appropriate normalizing is performed at the spot welding spot.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been conceived in view of the above-mentioned circumstances, and it is possible to easily and satisfactorily perform spot welding simply by using a spot welding device without using a special device such as a press machine. It is an object of the present invention to provide a spot welding method and a spot welding apparatus used for preventing a decrease in fatigue strength of a welded portion due to the above.

In order to solve the above problems, the present invention provides:
The following technical measures have been taken:

According to a first aspect of the present invention, there is provided a spot welding method for performing spot welding using a spot welding apparatus having a function of pressing a spot weld and a function of energizing the spot weld, A first step of energizing the spot welding portion in a pressurized state by the spot welding device, and a second step of reducing the temperature by setting the spot welding portion to a non-pressurized and non-energized state after the first step; After the second step, a third step of applying a pressure without energizing the spot welding portion by using a spot welding device.

According to a second aspect of the present invention, there is provided a first gun portion which has an electrode portion in contact with a spot weld portion, and which is energized while pressing the spot weld portion by the electrode portion, and in contact with the spot weld portion. A spot welding device, comprising: a pressurizing unit; and a second gun unit configured to press the spot welding unit with the pressing unit with a force greater than the pressing force of the first gun unit. .

According to the present invention, after spot welding is performed using the spot welding apparatus, the spot welding portion is pressurized using the spot welding apparatus. Therefore, the spot welding is performed without using a special device such as a press machine. Only by using a welding device, it is possible to easily and satisfactorily prevent a decrease in fatigue strength of a welded portion due to spot welding.

[0012] Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is a schematic side view of a main part of a spot welding apparatus used in the spot welding method according to the present invention. The spot welding apparatus 1 includes a base 2, a cylinder device 3, and a movable rod 4. And

The base 2 has a substantially rectangular base 5, an upright portion 6 extending upward from one side edge of the base 5, and a substantially central portion of the upright portion 6 extending parallel to the base 5 and in the opposite direction. It has a fixed rod 7 and a bracket 8 extending upward from the other side edge of the base 5.

The cylinder device 3 has a pressure of at least 2
It can be changed in steps and is relatively rotatably connected to the bracket 8 of the base 2 via the pin 12. The piston rod 13 of the cylinder device 3 has a bracket 14 attached to a tip end thereof.
Is connected to one end of the movable rod 4 so as to be relatively rotatable.

A predetermined portion of the movable rod 4 at one end side from the center in the length direction is rotatably connected to the tip of the upright portion 6 of the base 2 via a pin 16. A hemispherical electrode 17 is attached to the other end of the movable rod 4 on the surface facing the fixed rod 7.

A hemispherical electrode 18 is attached to the end of the fixed rod 7 of the base 2 on the surface facing the movable rod 4.

When the piston rod 13 of the cylinder device 3 is extended, the movable rod 4 rotates about the pin 16,
The electrode 17 is close to the electrode 18. Therefore, the electrode 17
If a plurality of metal plates to be spot-welded are positioned between the electrode 17 and the electrode 18, the metal plate is sandwiched between the electrodes 17 and 18, and spot-welded in a pressurized state.

Although not shown, the spot welding apparatus 1 is provided with an energization control device for controlling an energization current for spot welding, a fluid control device for controlling the operation of the cylinder device 3 and the pressing force, and the like. I have.

Next, the procedure of the spot welding method according to the present invention will be described.

FIG. 2 is a flowchart for explaining the procedure of the spot welding method according to the present invention. In the spot welding method according to the present invention, the spot welding unit 1 is energized in a pressurized state using the spot welding apparatus 1. (S1), then the spot weld is depressurized and de-energized to solidify the molten portion, that is, the nugget (S2). Then, the spot weld is depressurized and de-energized, and the tensile residual stress of the nugget is set. Is changed to a compressive residual stress (S3).

That is, using the spot welding apparatus 1 described above, for example, two metal plates 21 and 2 as shown in FIG.
When spot welding 2 is performed, first, the metal plates 21 and 22 are overlapped, and the position to be spot-welded and the electrode 18 are aligned. And the piston rod 1 of the cylinder device 3
Extend 3 As a result, the movable rod 4 rotates about the pin 16, and the metal plates 21 and 22 are connected to the electrode 18 and the electrode 1.
7 and are sandwiched. In a state where a predetermined pressure is applied to the metal plates 21 and 22 via the electrodes 17 and 18 by the cylinder device 3, the metal plates 21 and 22 are
Electric power is supplied to the spot welding portion 23 of FIG. The pressure at this time is, for example, 3.5 kN. This pressing force may be at least the minimum force required at the time of energization, and may be appropriately determined according to various design conditions.

Thereafter, the power supply to the spot welding portion 23 is stopped, and the pressure applied to the metal plates 21 and 22 by the cylinder device 3 is released.

In a state where the temperature of the spot welds 23 of the metal plates 21 and 22 is lowered and the nuggets 24 are solidified by spot welding, the nuggets 2
4 and a region outside thereof are in a balanced stress state as indicated by arrows in FIG. That is, a tensile residual stress acts on the nugget 24.

After the nugget 24 is solidified, the cylinder device 3 applies a pressing force to the spot welds 23 of the metal plates 21 and 22 via the electrodes 17 and 18. At this time, no current is passed through the electrodes 17 and 18. This pressure is
By using the variable pressure function of the cylinder device 3, the operation is performed with a sufficiently larger force than at the time of energization. For example, 10
The pressure is set to about 25 to 35 kN, which is about twice as large. Needless to say, the pressure should be equal to or greater than the minimum force capable of converting the tensile stress of the nugget 24 into the compressive stress.
What is necessary is just to determine appropriately considering the strength of 7, 18 and the spot welding part 23.

After pressurizing for a predetermined time, the piston rod 13 of the cylinder device 3 is retracted, and the pressing force applied to the metal plates 21 and 22 is released. Spot weld after pressurization 2
3 is in a stress state opposite to that before pressurization as indicated by an arrow in FIG. That is, the tensile residual stress of the nugget 24 is
It is converted into compressive residual stress by the pressing force.

By converting the tensile residual stress of the nugget 24 into a compressive residual stress, the fatigue strength of the spot welded portion 23 is improved satisfactorily. This significantly accelerates the growth rate of the crack in the state where the tensile residual stress is acting on the nugget 24, but suppresses or stops the growth rate of the crack in the state where the compressive residual stress is acting on the nugget 24. It is thought that it is.

FIG. 5 is a view for explaining the change in residual stress depending on the presence or absence of pressurization after solidification of the nugget. The residual stress of the nugget 24 when no pressurization is performed is indicated by an X mark. The residual stress of the nugget 24 when
This is indicated by a mark. A positive value of the residual stress is a tensile residual stress, and a negative value is a compressive residual stress. results of the experiment,
As is clear from FIG. 5, when no pressure was applied,
Although a tensile residual stress of about 50 to 180 MPa acts on the nugget 24, when the nugget 24 is pressurized, the nugget 2
It was confirmed that no residual tensile stress acted on No. 4 or a residual compressive stress of about 60 MPa acted on No. 4.

As described above, it is possible to easily and satisfactorily prevent a decrease in fatigue strength of a welded portion due to spot welding by using only one spot welding device 1 without using a special device such as a press machine. Therefore, the purchase cost and installation space for a special device such as a press machine can be reduced, and the productivity can be improved because a processing step using a special device is not required. Furthermore, there is no problem of difficulty in temperature control such as normalization, and the tensile residual stress of the nugget 24 can be easily and reliably converted into the compressive residual stress, so that a decrease in fatigue strength can be prevented.

Also, as in the present embodiment, the electrodes 17, 1
If the metal plate 8 is made hemispherical, a large proof stress can be obtained when the metal plates 21 and 22 are pressed, and the electrodes 17 and 1 can be used for a long time.
8 can be avoided as much as possible.

FIG. 6 is a schematic plan view of a main part of a spot welding apparatus according to another embodiment. The spot welding apparatus 31 includes a first gun 32 for energization and a second gun 32 for pressurization.
The gun part 33 is provided side by side. That is, the first gun unit 3
The two movable rods 4a are moved by pins 16a
And a spot welded portion is sandwiched between the hemispherical electrode 17a attached to the tip of the movable rod 4a and the hemispherical electrode on the fixed side (not shown in FIG. 6). Apply current while applying pressure. The movable rod 4b of the second gun part 33 is rotated about the pin 16b by the cylinder device 3b, and the hemispherical pressurizing part 17b attached to the distal end of the movable rod 4b and the hemispherical pressing part on the fixed side. The spot welding portion is sandwiched between the pressing portion (not shown in FIG. 6) and the spot welding portion is pressed with a force larger than the pressing force of the first gun portion 32.

The spot welding device 31 includes a first gun portion 32 for energizing the spot welding portion while pressurizing the spot welding portion,
A second gun portion 33 for pressurizing the spot welding portion with a large force after energization is provided independently of each other. The other configuration is the same as that of the spot welding device 1 shown in FIG.

As described above, if the first gun portion 32 and the second gun portion 33 are provided independently of each other, the material of the electrode 17a and the material of the pressurizing portion 17b can be made different.
It is possible to select a material having a small resistivity suitable for energization as the material of a and a high-strength material suitable for pressurization as the material of the pressurizing portion 17b. Therefore, the electrodes 17a
The electrode 17a is not deteriorated and damaged.
Replacement frequency can be reduced.

The spot welding apparatus used for carrying out the spot welding method according to the present invention is not limited to the specific configuration as in the spot welding apparatuses 1 and 31 described above. A device can be employed.

The spot welding method and the spot welding apparatus according to the present invention can be used for spot welding by an operator or spot welding by a welding robot.
Any of them can be adopted.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a main part of a spot welding apparatus used in a spot welding method according to the present invention.

FIG. 2 is a flowchart illustrating a procedure of a spot welding method according to the present invention.

FIG. 3 is an explanatory diagram for explaining a stress distribution state of a spot weld before pressurization in a state where a nugget is solidified.

FIG. 4 is an explanatory diagram illustrating a stress distribution state of a spot weld after pressurization in a state where a nugget is solidified.

FIG. 5 is an explanatory diagram illustrating a change in residual stress depending on whether or not pressure is applied after solidification of a nugget.

FIG. 6 is a schematic plan view of a main part of a spot welding apparatus according to another embodiment.

[Explanation of symbols]

 1,31 Spot welding device 2 Base 3,3a, 3b Cylinder device 4,4a, 4b Movable rod 5 Base 6,6a, 6b Standing portion 7 Fixed rod portion 8 Bracket portion 12 Pin 13 Piston rod 14,14a, 14b Bracket 15 , 15a, 15b Pin 16, 16a, 16b Pin 17, 17a Electrode 17b Pressing part 18 Electrode 21 Metal plate 22 Metal plate 23 Spot welded part 24 Nugget 32 First gun part 33 Second gun part

Claims (2)

[Claims] 1. A spot welding method for performing spot welding using a spot welding apparatus having a function of pressing a spot welding part and a function of energizing the spot welding part. A first step of energizing the welded part in a pressurized state; a second step of reducing the temperature by setting the spot welded part to a non-pressurized and non-energized state after the first step; and the second step And a third step in which the spot welding device is pressed by the spot welding device without applying power. 2. A first gun portion having an electrode portion abutting on the spot weld portion and energizing while applying pressure to the spot weld portion by the electrode portion, and a pressurizing portion abutting on the spot weld portion. A second gun portion for pressing the spot welding portion by the pressing portion with a force larger than the pressing force of the first gun portion.