JP3894545B2 - Spot welding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spot welding method for spot welding a workpiece in which plate materials having different rigidity are overlapped.
[0002]
[Prior art]
A large current is applied to the part where the contact resistance is locally reduced by pressing a workpiece with a metal plate overlapped between a pair of electrodes, and a nugget (meteorite-like welding is applied to the contact surface between the metal plates. Spot welding is generally used, in which a part is welded. Conventionally, the pressure applied to the workpiece by both electrode tips has been made substantially uniform.
[0003]
Here, as shown in FIG. 5A, when spot welding a workpiece W10 in which a thin plate 52 having a low rigidity is superimposed on two thick plates 50, 51 having a high rigidity, each electrode tip 55, When the pressure F applied to the workpiece W10 of 56 is made uniform, the thin plate 52 and the thick plate 51 are bent upward and deformed as shown in FIG. In this case, since the rigidity of the thin plate 52 is smaller than that of the thick plates 51 and 50, the thin plate 52 is more easily deformed.
[0004]
Therefore, the contact area between the thin plate 52 and the thick plate 51 is larger than the contact area between the thick plates 50 and 51, and the contact resistance between the thin plate 52 and the thick plate 51 is smaller than the contact resistance between the thick plates 50 and 51. Become.
[0005]
Accordingly, when the electrode chips 55 and 56 are energized in this state, the amount of heat generated between the thin plate 52 and the thick plate 51 having a small contact resistance is smaller than the amount of heat generated between the thick plates 50 and 51 having a large contact resistance. As a result, as shown in FIG. 6 (a), the nugget N10 formed from the thin plate 52 to the thick plate 50 is biased toward the thick plate 50, causing scattering between the thick plates 50 and 51, The nugget N10 reaches the surface of the thick plate 50 and causes surface scattering and chip welding.
[0006]
Therefore, if the amount of energization is reduced to prevent scattering and chip welding, the nugget N11 to be formed is reduced as shown in FIG. 6B, and the welding strength between the thin plate 52 and the thick plate 51 is ensured. There was an inconvenience that it was difficult to do.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a spot welding method capable of solving the above inconvenience and improving the welding strength of a workpiece obtained by superimposing three plate materials with the plate member having the lowest rigidity on one side.
[0008]
[Means for Solving the Problems]
The present invention has been made to achieve the above object, and the first high-tensile steel plate is more rigid than the second high-tensile steel plate , the first high-tensile steel plate, and the second high-tensile steel plate. In a method of spot welding by sandwiching a work sandwiched between a low soft plate and a pair of electrode tips, the pressure applied to the work of one electrode tip located on the soft plate side is set to the second high-tensile steel plate side. It is characterized by being made smaller than the pressure applied to the workpiece of the other electrode tip located at the position .
[0009]
According to the present invention, spot welding is performed such that the pressing force of one electrode tip against the workpiece on the plate material side having the lowest rigidity is smaller than the pressing force of the other electrode tip. In this case, although details will be described later, the contact resistance between the plate material having the lowest rigidity on the side where the pressure force of the electrode tip is low and the other plate material is increased, and the rigidity on the side where the pressure force of the electrode tip is large is high. The contact resistance between the two sheets is reduced. Therefore, when electricity is applied between the electrode tips, the amount of heat generated at the contact portion between the plate with the lowest rigidity and the other plate can be increased, thereby increasing the welding strength of the plate with the lowest rigidity. Can do.
[0010]
Here, the rigidity is a property that the object does not change its shape with respect to an external force. In the case of a plate material, the rigidity changes depending on the thickness and the steel type. For example, if the steel type is the same, the greater the plate thickness, the higher the rigidity of the plate material. Further, if the plate thickness is the same, the higher the rank of the steel type (the higher the tensile strength, the higher the rank), the higher the rigidity of the plate material.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
An example of an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of a spot welding gun used for carrying out the spot welding method of the present invention, FIGS. 2 and 3 are explanatory views of the welding situation of a workpiece by the spot welding method of the present invention, and FIG. It is explanatory drawing.
[0012]
Referring to FIG. 1, R is a welding robot, and a spot welding gun G is mounted on the wrist 1 at the operating end of the welding robot R. Then, the welding robot R moves the spot welding gun G to each spot position of the workpiece W1 supported by the clamper C, and performs spot welding of the workpiece W1.
[0013]
The spot welding gun G includes a gun body 3 that is supported by a gun support bracket 2 attached to the wrist 1 so as to be movable up and down. A C-shaped yoke 4 that extends downward is attached to the gun body 3, and a lower tip 5 that is a fixed electrode tip is attached to the tip of the lower portion of the C-shaped yoke 4.
[0014]
In addition, a pressurization unit 6 using a servo motor as a drive source is mounted on the upper end of the gun body 3, and the gun body 3 moves up and down via a ball screw mechanism (not shown) in the gun body 3. A rod 7 projects downward from the gun body 3, and an upper tip 8 that is a movable electrode is attached to the lower end of the rod 7 so as to face the lower tip 5. The upper chip 8 and the lower chip 5 constitute a pair of electrode chips of the present invention.
[0015]
The gun body 3 is supported by a linear guide 11 fixed to the gun support bracket 2 so as to be slidable in the vertical direction. A servo motor 10 is mounted on the upper end of the gun support bracket 2, and a ball screw 9 connected to the servo motor 10 is screwed into a nut 12 fixed to the gun body 3 to constitute a ball screw mechanism. The gun body 3 is moved up and down by the rotation of.
[0016]
The operation of the pressurizing unit 6 and the servo motor 10 is controlled by the gun controller 20, and when the spot welding gun G reaches each striking position of the workpiece W1 by the position control of the robot R, the gun controller 20 And the servo motor 10 are operated to pressurize the workpiece W1 between the lower chip 5 and the upper chip 8. Then, in this pressurized state, the gun controller 20 energizes between the lower tip 5 and the upper tip 8 to spot weld the workpiece W1.
[0017]
Here, as shown in FIG. 2, a steel plate (hereinafter referred to as a thin plate) 32 having a small thickness and a low rigidity on two steel plates (hereinafter referred to as thick plates) 30 and 31 having a large thickness and high rigidity. When spot welding is performed on the workpiece W1 overlaid, the pressure FU applied to the workpiece W1 of the upper tip 8 located on the thin plate 32 side is applied to the workpiece W1 of the lower tip 5 in accordance with teaching data stored in advance in the gun controller 20. The pressure is made smaller than the pressure FL (FU <FL).
[0018]
In order to make FU <FL in this way, the gun controller 20 first moves the gun body 3 up by the servo motor 10 to bring the lower tip 5 into contact with the lower surface of the workpiece W1 and also uses the pressure source 6 to move up. The chip 8 is lowered and brought into contact with the upper surface of the workpiece W1. In this case, the pressurizing force of the pressurizing source 6 acts equally on the lower tip 5 via the upper tip 8 and the gun body 3, and then the gun body 3 is pushed up by the servo motor 10. At this time, if the position of the pressurizing source 6 is controlled so that the relative position of the upper tip 8 with respect to the gun body 3 does not change, the pressure FL of the lower tip 5 is increased by the amount pushed up by the gun body 3 by pushing up the gun body 3. To increase. Therefore, FU <FL.
[0019]
When the pressure source 6 is torque controlled so that the pressure FU of the upper tip 8 is constant, the pressure FU of the upper tip 8 does not change even if the gun body 3 is pushed up, but the pressure of the lower tip 5 is not changed. FL increases by the pushing force of the gun body 3. Therefore, also in this case, FU <FL.
[0020]
When FU <FL, the workpiece W1 bends downward so that the bending reaction force becomes equal to the difference between FU and FL. Since the contact pressure between the thin plate 32 and the thick plate 31 is smaller than the contact pressure between the thick plates 31 and 30, when viewed relatively, the contact resistance between the thin plate 32 and the thick plate 31 increases, The contact resistance between the plates 30 and 31 is reduced.
[0021]
As a result, when current is passed between the electrode tips 5 and 8 through the energization path x1, the amount of heat generated at the contact point between the thin plate 32 and the thick plate 31 is relatively increased with respect to the amount of heat generated at the contact point between the thick plates 30 and 31. To do.
[0022]
Therefore, as shown in FIG. 2B, a good nugget N1 having no deviation is formed from the thin plate 32 to the thick plate 30, and the welding strength of the thin plate 32 can be ensured, and the surface of the thick plate 30 is displayed on the lower surface. Scattering and chip welding can be prevented from occurring.
[0023]
In addition, FIG. 2 shows an example in which plate materials having different thicknesses are overlapped, but the spot welding method of the present invention is also applicable to the case of spot welding a workpiece in which plate materials having different thicknesses and different thicknesses are overlapped. An effect can be obtained.
[0024]
Referring to FIG. 3A, when spot welding is performed on a plate material W2 in which three plate materials 45a to 45c having the same steel type and the same thickness are overlapped, the pressure force FU of the upper tip 44 and the pressure of the lower tip 43 are applied. When the pressure FL is equal (FL = FU), the rigidity of the plate members 45a to 45c is the same, so the contact resistance between the plate members 45a and 45b is equal to the contact resistance between the plate members 45b and 45c. Therefore, when the electrode chips 43 and 44 are energized, the amount of heat generated at the contact point of the plate members 45a and 45b is equal to the amount of heat generated at the contact point of the plate members 45b and 45c, and the plate member 45a and the plate member 45c are biased. A good nugget N2 is formed.
[0025]
However, generally, the higher the rigidity of the rigid type used, the higher the electrical resistance of the plate material. Therefore, as shown in FIG. 3 (b), plate materials (hereinafter referred to as soft plates) 47a and 47b formed by a rigid material having low rigidity on plate materials (hereinafter referred to as high-tensile steel plates) 47a and 47b formed by a rigid material having high rigidity. When the workpiece W3 overlaid with 46 is sandwiched with the pressure force FU of the upper tip 44 equal to the pressure force FL of the lower tip 43 (FU = FL), the soft plate 46 having a small rigidity and a large contact area The contact resistance between the high-tensile steel plates 47a is smaller than the contact resistance between the high-tensile steel plates 47a and 47b having high rigidity and a small contact area.
[0026]
Therefore, when energized between electrode tips 43 and 44, if the uniform current density in the current path x 2 is found the calorific value the contact resistance is lower軟板46 between high-tensile steel plate 47a, the contact resistance This is less than the amount of heat generated between the high high-strength steel plates 47a and 47b.
As a result, the formed nugget N3 is biased toward the high-strength steel plate 47b, the welding strength of the soft plate 46 becomes insufficient, and the nugget N3 reaches the surface of the high-strength steel plate 47b, so that surface scattering and chip welding are likely to occur. Become.
[0027]
As a result, the formed nugget N3 is biased toward the high-strength steel plate 47b, the welding strength of the soft plate 46 becomes insufficient, and the nugget N3 reaches the surface of the high-strength steel plate 47b, so that surface scattering and chip welding are likely to occur. Become.
[0028]
Therefore, as shown in FIG. 3C, the pressure FU of the upper tip 44 is made smaller than the pressure FL of the lower tip 43 (FU <FL), and the contact between the soft plate 46 and the high-tensile steel plate 47a. By making the pressure lower than the contact pressure between the high-tensile steel plates 47a and 47b, the contact resistance between the soft plate 46 and the high-tensile steel plate 47a can be increased.
[0029]
In this way, the amount of heat generated between the soft plate 46 and the high-tensile steel plate 47a is increased by energizing the electrodes 43 and 44 with the contact resistance between the soft plate 46 and the high-tensile steel plate 47a being increased, As a result, the nugget N4 formed from the soft plate 46 to the high-tensile steel plate 47b is shifted to the soft plate 46 side. Therefore, it is possible to improve the welding strength of the soft plate 46 and to prevent surface scattering and chip welding from occurring on the high-tensile steel plate 47b side.
[0030]
In the present embodiment, the DR electrode tip having a spherical shape at the tip shown in FIG. 4A is used. However, the R shape of the spherical shape shown in FIG. 4B is further flattened. An electrode tip or a CF-type electrode tip having a conical shape with a flattened tip as shown in FIG. 4C may be used. The DR-type and CF-type electrode tips are advantageous in terms of electrode life because the contact area change at the time of wear is smaller than that of the R-type electrode tips.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a spot welding gun used for carrying out a spot welding method of the present invention.
FIG. 2 is an explanatory view of a welding state of a workpiece by the spot welding method of the present invention.
FIG. 3 is an explanatory view of a welding state of a workpiece by the spot welding method of the present invention.
FIG. 4 is a diagram illustrating the shape of an electrode tip.
FIG. 5 is an explanatory view of a welding state of a workpiece by a conventional method.
FIG. 6 is an explanatory view of a welding state of a workpiece by a conventional method.
[Explanation of symbols]
W1 ... Workpiece, G ... Spot welding gun, C ... Clamper, 5, 8 ... Electrode tip, N1 ... Nugget, x1 ... Current path, 30, 31 ... Thick plate, 32 ... Thin plate

Claims (1)

A work in which a first high-tensile steel plate is sandwiched between a second high-tensile steel plate, the first high-tensile steel plate, and a soft plate having lower rigidity than the second high-tensile steel plate, and a pair of electrodes In the method of spot welding sandwiched between tips,
A spot welding method characterized in that the pressure applied to the workpiece of one electrode tip positioned on the soft plate side is made smaller than the pressure applied to the workpiece of the other electrode tip positioned on the second high-tensile steel plate side .

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