JP3894544B2 - 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.
[0003]
Then, as shown in FIG. 5A, when spot welding a workpiece W10 in which a thin plate 52 having low rigidity is superimposed on two thick plates 50, 51 having high rigidity, the thick plates 50, 51 and In the state where the thin plate 52 is in close contact with no gap, when the power source 57 energizes the work W2 with the pair of electrode chips 55 and 56 having the same shape, the current density in the energization path x10 between the electrode chips 55 and 56 is substantially uniform. It becomes. Therefore, as shown in FIG. 5B, a good nugget N10 is formed from the thin plate 52 to the thick plate 50, and the necessary welding strength can be obtained.
[0004]
However, actually, when the workpiece W10 is pressed by the electrode tips 55 and 56, the thin plate 52 and the thick plate 51 are bent upward in the drawing as shown in FIG. There may be a gap between 51 and the thin plate 52 and between the thick plate 50 and the thick plate 51. In this case, the contact area between the electrode chip 55 and the thin plate 52 is increased by the bending of the thin plate 52, whereas the contact area between the thin plate 52 and the thick plate 51 and between the thick plate 51 and the thick plate 50 is a gap. Becomes smaller.
[0005]
Therefore, the current density in the energization path x11 between the electrode tips 55 and 56 is higher in the lower side in the figure, and the local heat generation is greater between the thick plates 50 and 51 than between the thin plate 52 and the thick plate 51. Will increase. As a result, as shown in FIG. 6B, there is a disadvantage that the nugget N11 that is biased downward in the drawing is formed, and the welding strength between the thin plate 52 and the thick plate 51 is reduced.
[0006]
[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.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for spot welding a work in which three plate materials are stacked with a plate material having the lowest rigidity on one side, sandwiched between a pair of electrode tips, on the plate material side having the lowest rigidity. The contact area between the one electrode tip positioned and the workpiece is made smaller than the contact area between the other electrode tip and the workpiece, and from one electrode tip positioned on the plate material side having the lowest rigidity when energized to the other The welding is performed by gradually reducing the current density toward the electrode tip .
[0008]
According to the present invention, spot welding is performed such that the contact area between the workpiece and one electrode tip on the plate material side having the lowest rigidity is smaller than the contact area between the other electrode tip and the workpiece. . In this case, as will be described in detail later, the current density in the current-carrying path between the pair of electrodes is changed from the plate material side having the smallest contact area with the electrode tip to the opposite plate member having the largest contact area with the electrode tip. It becomes smaller gradually. Therefore, a large current locally flows through the contact portion between the plate member having the lowest rigidity and another plate member, and the amount of heat generated in the contact portion increases, thereby increasing the welding strength of the plate member having the lowest rigidity. .
[0009]
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.
[0010]
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.
[0011]
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.
[0012]
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.
[0013]
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.
[0014]
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.
[0015]
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.
[0016]
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 on which the tops are stacked, spot welding is performed using a pair of electrode tips in which the tip diameter of the upper tip 8 is smaller than the tip diameter of the lower tip 5.
[0017]
In this case, the thin plate 32 having low rigidity is bent upward when pressed against the upper chip 8, so that a gap is generated between the thin plate 32 and the thick plate 31. The thick plate 31 also bends upward, but since the rigidity of the thick plate 31 is higher than that of the thin plate 32, the bending degree is smaller than that of the thin plate 32, and the gap generated between the thick plates 30 and 31 is the same as that of the thin plate 32 and the thick plate. 31 is smaller than the gap. Therefore, the contact area between the thin plate 32 and the thick plate 31 is smaller than the contact area between the thick plate 31 and the thick plate 30.
[0018]
In addition, since the tip diameter of the upper chip 8 is smaller than the tip diameter of the lower chip 5, the contact area between the lower chip 5 and the thick plate 30 is larger than the contact area between the upper chip 8 and the thin plate 32. Therefore, the current density in the energization path x 1 between the upper chip 8 and the lower chip 5 gradually decreases from the upper chip 8 toward the lower chip 5.
[0019]
Therefore, at the contact portion between the thin plate 32 and the thick plate 31 on the upper chip 8 side, a large current flows locally and the resistance heat generation amount increases, while the contact between the thick plate 31 and the thick plate 30 on the lower chip 5 side. In the part, since the current is dispersed, the resistance heat generation amount is reduced. As a result, as shown in FIG. 2B, a good nugget N1 having no deviation from the thin plate 32 to the thick plate 30 can be formed. And thereby, the welding strength between the thin plate 32 and the thick plate 31 can be improved.
[0020]
Further, as shown in FIG. 3 (a), the workpiece W2 in which the plate materials 40, 40 and 42 having the same steel type are overlapped is regulated so as not to generate a gap, and the lower tip having the same diameter at the front end portion is formed. When spot welding is performed between the upper tip 44 and the upper tip 44, the current density in the energization path x2 between the upper tip 44 and the lower tip 43 becomes uniform, so that the nugget N2 is formed around the contact portion of the plate material.
[0021]
However, generally, the higher the rigidity of the steel type, the higher the electrical resistance of the plate material. Therefore, as shown in FIG. 3 (b), plate materials (hereinafter referred to as soft plates) formed of steel materials having low rigidity on plate materials (hereinafter referred to as high-tensile steel plates) 46 and 47 formed of steel types having high rigidity. When spot welding is performed on the workpiece W3 on which the 45 is overlapped, even if the current density in the energization path x3 is uniform, the amount of heat generated in the high-tensile steel plates 46 and 47 having higher electric resistance is higher in the soft plate 45 having lower electric resistance. More than the amount.
[0022]
Therefore, the formed nugget N3 is biased toward the high-tensile steel plates 46 and 47, and the welding strength between the soft plate 45 and the high-tensile steel plate 46 is reduced. Therefore, in this case as well, as shown in FIG. 3C, by using a pair of electrode tips in which the tip diameter of the upper tip 49 is smaller than the tip diameter of the lower tip 48, the gap between the upper tip 49 and the lower tip 48 is used. The current density in the current path x4 can be gradually decreased from the upper chip 49 toward the lower chip 48.
[0023]
As a result, a large current locally flows through the soft plate 45, the amount of heat generated at the contact portion between the soft plate 45 and the high-tensile steel plate 46 increases, and the formed nugget N4 shifts toward the soft plate 45. The welding strength of the plate 45 can be improved.
[0024]
3B and 3C show the workpiece W3 in which the soft plates 45 and the high-tensile steel plates 46 and 47 having different thicknesses are overlapped, the thicknesses of the plate materials 45, 46 and 47 are the same. Even in this case, as shown in FIG. 3C, the electrical resistance of the soft plate 45 and the high-tensile steel plates 46 and 47 is reduced by making the tip diameter of the upper tip 49 smaller than the tip diameter of the lower tip 48. Thus, good spot welding can be performed while suppressing the bias of the nugget caused by the difference.
[0025]
Further, in the present embodiment, the DR type electrode tip having a spherical shape at the tip shown in FIG. 4A is used. However, the R type 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.
[0026]
Further, in the present embodiment, as shown in FIG. 2A, by making the tip diameter of the upper tip 8 smaller than the tip diameter of the lower tip 48, the contact area of the electrode tip on the soft plate 32 side is increased. Although the contact area of the electrode tip on the high-tensile steel plate 30 side is made smaller, the tip diameters of the upper tip 8 and the lower tip 5 are made the same, and the flatness of the tip portion of the upper tip 8 is made smaller than that of the lower tip 5. By doing so, the contact area of the electrode tip on the soft plate 32 side may be made smaller than the contact area of the electrode tip on the high-tensile steel plate 30 side.
[0027]
Further, by making the upper chip 8 and the lower chip 5 have a similar shape with the lower chip 5 being larger, the contact area of the electrode chip on the soft plate 32 side is smaller than the contact area of the electrode chip on the high-tensile steel plate 30 side. It may be made to become.
[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 an explanatory diagram of the shape of an electrode tip.
FIG. 5 is an explanatory diagram 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)

In the method of spot welding by sandwiching a work piece in which three plate materials are laminated with the plate material having the lowest rigidity as one side between a pair of electrode tips,
The contact area between one electrode chip located on the plate material side having the lowest rigidity and the workpiece is made smaller than the contact area between the other electrode chip and the workpiece, and located on the plate material side having the lowest rigidity when energized. A spot welding method, wherein welding is performed by gradually decreasing the current density from one electrode tip to the other electrode tip .

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