JP2003251469A - Spot welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spot welding method by which the welding strength of piled works by using a plate material having the lowest rigidity in three plate materials at one side. <P>SOLUTION: In the spot welding method by interposing the work W1 piling the thin plate 32 having low rigidity on the thick plates 30, 31 having high rigidity with one pair of electrode chips 5, 8, the electric power is supplied to between the electrodes 5, 8 by making the pressurized force FU of the electrode chip 8 abutting on the thin plate 32 having the lowest rigidity to smaller than the pressurized force FL of the electrode chip 5 abutted on the thick plate 30. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a spot welding method for spot welding a work in which plates having different rigidities are overlapped. 2. Description of the Related Art A large current is applied to a portion where contact resistance is locally reduced by sandwiching and pressing a work in which metal plates are superposed between a pair of electrodes. Spot welding in which a nugget (weld-like welded portion) is formed on a surface and welding is performed is widely used. Conventionally, the pressing force of the two electrode tips on the work is made substantially equal. Here, as shown in FIG. 5A, when a work W10 in which a thin plate 52 having a low rigidity is superimposed on two thick plates 50 and 51 having a high rigidity is spot-welded, each electrode is formed. When the pressing force F of the chips 55 and 56 to the work W10 is equalized, as shown in FIG. 5B, the thin plate 52 and the thick plate 51 are bent upward and deformed. 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 becomes 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 becomes large. Smaller than. Therefore, in this state, the electrode tips 55,
When a current flows between the thin plates 52 and the thick plates 51 having a small contact resistance, the heat value between the thick plates 50 and 50 having a large contact resistance is obtained.
It becomes smaller than the heat value between 51. As a result, as shown in FIG. 6A, the nugget N10 formed from the thin plate 52 to the thick plate 50 is biased to the thick plate 50 side, and scatter occurs between the thick plates 50 and 51, and furthermore, Nugget N1
0 reaches the surface of the thick plate 50 to cause spread and chip welding. When the amount of current is reduced to prevent scattering and chip welding, the formed nugget N11 becomes smaller as shown in FIG.
There is a disadvantage that it is difficult to secure the welding strength between the steel plate and the thick plate 51. SUMMARY OF THE INVENTION [0007] The present invention solves the above-mentioned disadvantages and improves the welding strength of a work in which three plates are stacked with the plate having the lowest rigidity on one side. It is intended to provide a welding method. SUMMARY OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and a work in which three plate members are overlapped with the plate member having the lowest rigidity on one side, is used as a pair of electrodes. In the method of spot welding by sandwiching between chips, a pressing force of one electrode chip located on the side of the plate material having the lowest rigidity to the work is made smaller than a pressing force of the other electrode chip to the work. According to the present invention, spot welding is performed such that the pressing force of one electrode tip on the workpiece on the side of the plate material having the lowest rigidity is smaller than the pressing force of the other electrode tip. In this case, as will be described in detail later, the contact resistance between the plate material having the lowest pressing force of the electrode tip and the lowest rigidity and the other plate material is increased, and the rigidity being the side where the pressing force of the electrode tip is large is high. 2
The contact resistance between the sheet materials is reduced. Therefore, when electricity is supplied between the electrode chips, the amount of heat generated at the contact portion between the plate having the lowest rigidity and another plate can be increased, thereby increasing the welding strength of the plate having the lowest rigidity. Can be. [0010] Here, rigidity is a property that an object does not change its shape in response to an external force, and in the case of a plate material, it changes depending on the thickness and steel type. For example, if the steel type is the same, the rigidity of the plate material increases as the plate thickness increases. If the plate thickness is the same, the higher the steel grade (the higher the tensile strength, the higher the rank), the higher the rigidity of the plate. 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 a welding state of a workpiece by the spot welding method of the present invention, and FIG. FIG. Referring to FIG. 1, R is a welding robot, and a spot welding gun G is mounted on a wrist 1 at an operating end of the welding robot R. And the welding robot R
Moves the spot welding gun G to each hitting position of the work W1 supported by the clamper C, and performs spot welding of the work W1. The spot welding gun G has a gun body 3 supported by a gun support bracket 2 attached to the wrist 1 so as to be vertically movable. A downwardly extending C-shaped yoke 4 is attached to the gun body 3, and a lower tip 5 which is a fixed electrode tip is attached to a lower end of the C-shaped yoke 4. At the upper end of the gun body 3, a pressing unit 6 driven by a servomotor is mounted.
As a result, a rod 7 that moves up and down via a ball screw mechanism (not shown) in the gun body 3 projects below the gun body 3, and a lower end of the rod 7 is opposed to the lower chip 5 so as to be an upper chip 8 that is a movable electrode. Is installed. Note that the upper chip 8 and the lower chip 5 constitute a pair of electrode chips of the present invention. The gun body 3 is slidably supported in a vertical direction by a linear guide 11 fixed to the gun support bracket 2. 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 connected to a nut 12 fixed to the gun body 3.
Into the ball screw mechanism, and the servo motor 10
The gun body 3 is moved up and down by the rotation of. The operations of the pressurizing section 6 and the servomotor 10 are controlled by the gun controller 20. When the spot welding gun G reaches each of the hit points of the workpiece W1 by the position control of the robot R, the gun controller 20 operates. The pressure unit 6 and the servomotor 10 are operated to press the work W1 between the lower chip 5 and the upper chip 8 and pressurize the work. Then, in this pressurized state, the gun controller 20 energizes between the lower chip 5 and the upper chip 8 to spot-weld the work W1. Here, as shown in FIG. 2, two steel plates (hereinafter, referred to as "thick plates") 30, 31 having a large thickness and a high rigidity.
Steel plate with low thickness and low rigidity (hereinafter referred to as thin plate)
When spot welding is performed on the workpiece W1 on which the upper chip 32 is overlapped, the pressing force FU of the upper chip 8 located on the thin plate 32 side with respect to the workpiece W1 is applied to the workpiece W1 of the lower chip 5 in accordance with the teaching data stored in advance in the gun controller 20. The pressure is made smaller than FL (FU <
FL). In order to satisfy FU <FL, the gun controller 20 first moves the gun body 3 up by the servo motor 10 to bring the lower chip 5 into contact with the lower surface of the work W1 and pressurize the gun. The upper chip 8 is lowered by 6 to make contact with the upper surface of the work W1. In this case, the pressing force of the pressure source 6 acts equally on the lower chip 5 via the upper chip 8 and the gun body 3, and then the gun body 3 is pushed up by the servomotor 10. At this time, the pressure source 6 is connected to the upper chip 8
When the position of the lower tip 5 is controlled so that the relative position of the lower tip 5 with respect to the gun body 3 does not change, the lower tip 5
Is increased by the amount by which the gun body 3 is pushed up.
Therefore, FU <FL. The pressurizing source 6 is connected to the pressing force FU of the upper chip 8.
When the torque control is performed so that the pressure becomes constant, the pressing force FU of the upper chip 8 does not change even if the gun body 3 is pushed up, but the pressing force FL of the lower chip 5 increases by the pushing force of the gun body 3. Therefore, also in this case, FU <FL
It becomes. When FU <FL, the deflection reaction force becomes FU and F
The work W1 bends downward so as to be equal to the difference L.
The contact pressure between the thin plate 32 and the thick plate 31 is
Since the contact pressure becomes smaller than the contact pressure between the thick plates 30, the contact resistance between the thin plates 32 and the thick plates 31 increases, and the contact resistance between the thick plates 30, 31 decreases. As a result, when a current is applied between the electrode chips 5 and 8 through the current path x1, the calorific value at the contact point between the thin plate 32 and the thick plate 31 is relative to the calorific value at the contact point between the thick plates 30 and 31. Increase. Therefore, as shown in FIG. 2 (b), a good nugget N1 is formed from the thin plate 32 to the thick plate 30 without any bias, and the welding strength of the thin plate 32 can be ensured. Spreading and chip welding on the lower surface can be prevented. FIG. 2 shows an example in which plate materials having different thicknesses are overlapped. However, the present invention is also applicable to a case where a work in which plate materials having the same thickness and different rigid types are overlapped is spot-welded. The effect of the welding method can be obtained. Referring to FIG. 3 (a), a plate material W in which three plate materials 45a to 45c of the same steel type and having the same thickness are stacked.
2 is spot welded, the pressing force F of the upper tip 44 is
If U and the pressure FL of the lower chip 43 are made equal (FL =
FU), since the plate members 45a to 45c have the same rigidity,
The contact resistance between the plate members 45a and 45b is equal to the plate members 45b and 45c.
It becomes equal to the contact resistance between them. Therefore, the electrode tip 4
When electricity is supplied between the plate members 45 and 45c, the heat value at the contact point between the plate members 45a and 45b is equal to the heat value at the contact point between the plate members 45b and 45c.
A good nugget N2 without bias is formed over 5c. However, in general, the higher the rigidity of the rigid type used, the higher the electrical resistance of the plate material. Therefore, FIG.
As shown in (b), plate members (hereinafter, referred to as high-strength steel plates) 47a and 47b formed of rigid types having high rigidity are combined with plate members (hereinafter, referred to as soft plates) 46 formed of rigid types having low rigidity. When the overlapped works W3 are sandwiched between the upper chip 44 with the pressing force FU of the upper chip 44 equal to the pressing force FL of the lower chip 43 (FU = FL), the soft plate 46 and the high-strength steel plate 47a having a small rigidity and a large contact area are sandwiched. The contact resistance therebetween is smaller than the contact resistance between the high-tensile steel plates 47a and 47b having high rigidity and a small contact area. Therefore, when current is applied between the electrode tips 43 and 44 and the current density in the current path x3 is uniform, the calorific value between the soft plate 46 having a low contact resistance and the high-tensile steel plate 47a is larger than the contact heat. High tensile strength steel plate 47 with high resistance
The amount of heat generated between a and 47b is smaller. As a result, the formed nugget N3 is biased toward the high-tensile steel plate 47b, and the welding strength of the soft plate 46 becomes insufficient. Tends to occur. Therefore, as shown in FIG. 3C, the pressing force FU of the upper chip 44 is made smaller than the pressing force FL of the lower chip 43 (FU <FL), so that the soft plate 46 and the high-strength steel plate 4
By setting the contact pressure between the high-strength steel plates 47a and 47b higher than the contact pressure between the high-strength steel plates 47a and 47b, the contact resistance between the soft plate 46 and the high-tensile steel plates 47a can be increased. Then, the electrodes 43, 44 are kept in a state where the contact resistance between the soft plate 46 and the high-tensile steel plate 47a is increased.
By applying a current between the soft plate 46 and the high-tensile steel plate 47,
a, the heat generated between the soft plate 46 and the high-strength steel plate 47b is increased.
Shift to the side. Therefore, the welding strength of the soft plate 46 can be improved, and at the same time, it is possible to prevent the high-strength steel plate 47b from being spread or chipped. In this embodiment, the DR type electrode tip shown in FIG. 4A having a spherical tip is used, but the spherical shape shown in FIG. 4B is further flattened. An R-type electrode tip or a CF-type electrode tip having a conical shape with a flattened tip as shown in FIG. 4C may be used. D
The R-type and CF-type electrode tips are advantageous in terms of electrode life because the contact area change during 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 performing 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 work by the spot welding method of the present invention. FIG. 4 is an explanatory diagram of a shape of an electrode tip. FIG. 5 is an explanatory view of a welding state of a work according to a conventional method. FIG. 6 is an explanatory view of a welding state of a work according to a conventional method. [Explanation of symbols] W1 ... Work, G ... Spot welding gun, C ... Clamper,
5, 8: electrode tip, N1: nugget, x1: energizing path, 30, 31: thick plate, 32: thin plate

Claims (1)

Claims: 1. A method for spot welding a work in which three plate members are laminated with one plate having the lowest rigidity on one side, and sandwiched by a pair of electrode tips, wherein the plate member has the lowest rigidity. A spot welding method characterized in that a pressure applied to a work of one electrode tip is smaller than a pressure applied to a work of another electrode tip.