JP2014184461A - Spot welding method and spot welding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot welding method and a spot welding device in which generation of sputtering can be suppressed.SOLUTION: Under a condition that a first electrode 5 facing a thick plate Pof the outermost surface and a second electrode 8 and auxiliary electrodes 12, 13 facing a thin plate Pof the outermost surface are pressed to a workpiece W so that the pressing force F1 of the first main electrode 5 is equal to the summation of pressing forces F, F, Fof the second main electrode 8 and the auxiliary electrodes 12, 13, each of the main electrodes 5, 8 is electrified and the second main electrode 8 and the auxiliary electrodes 12, 13 are electrified. Before sputtering is generated, both electrifications are maintained, and, under the condition that the pressing force Fof the first main electrode 5 and the summation of pressing forces F, F, Fof the second main electrode 8 and the auxiliary electrodes 12, 13 are maintained as equal, the pressing forces F, Fof the auxiliary electrodes 12, 13 are weakened from the initial pressing forces and the pressing force Fof the second main electrode 8 is strengthened from the initial pressing force.

Description

  The present invention relates to a spot welding method and a spot welding apparatus.

  For example, it is known to use a laminated plate in which two thick plates made of high-tensile steel and two thin plates made of mild steel are overlapped and integrated for a mohawk roof portion of an automobile or the like. The laminated plate is formed by spot welding a workpiece in which the two thick plates and the two thin plates are overlapped. The spot welding is performed by energizing both electrodes while the workpiece is sandwiched and pressed between the first electrode for the outermost thick plate and the second electrode for the outermost thin plate.

  However, since the thick plate has a larger electrical resistance than the thin plate, the amount of heat generated by the energization is larger than that of the thin plate. For this reason, the nugget formed by melting the metal by the energization grows unevenly on the thick plate side of the workpiece. And when the growth of the nugget does not reach the outermost thin plate, there is a problem that the outermost thin plate cannot be welded.

  Therefore, in order to solve the problem, in a state where the work is sandwiched and pressed between the first main electrode for the outermost plate and the second main electrode and the auxiliary electrode for the outermost plate, There has been proposed a spot welding method in which the first main electrode and the second main electrode are energized and the second main electrode and the auxiliary electrode are energized.

  According to the spot welding method, first, the work is sandwiched between the first main electrode, the second main electrode, and the auxiliary electrode, and the work is pressed. The pressing is performed so that the pressing force of the first main electrode is equal to the total pressing force of the second main electrode and the auxiliary electrode. And in the state which maintained the said press, it produces the main electric current which flows through the said workpiece | work by supplying with electricity to said 1st main electrode and said 2nd main electrode, This 2nd main electrode and said auxiliary electrode, Is caused to generate a branching current that flows on the side of the workpiece close to the second main electrode.

  At this time, since the pressing force of the second main electrode against the workpiece is smaller than the pressing force of the first main electrode, the thin plate side of the outermost surface of the workpiece close to the second main electrode The amount of heat generated by the main current can be increased. In addition, since the branch current flows on the thin plate side of the outermost surface of the workpiece, the amount of heat generated on the thin plate side of the outermost surface can be further increased.

  In this way, a nugget can be formed by heat generation by the main current and heat generation by the branch current also on the thin plate side of the outermost surface of the workpiece.

  Then, with both energizations, the nugget formed on the thin plate side of the outermost surface of the workpiece and the other nugget formed on the thick plate side of the outermost surface are combined to grow into a large nugget. As described above, it is possible to prevent the nugget from growing toward the thick plate on the outermost surface of the work, and to weld and integrate the work (for example, see Patent Document 1).

JP 2012-76125 A

  However, the spot welding method has a disadvantage that slag or metal particles may scatter from between the thin plate and the adjacent metal plate. In the present application, “scattering of slag or metal particles” is sometimes referred to as “sputtering”.

  Accordingly, an object of the present invention is to provide a spot welding method and a spot welding apparatus that can eliminate such inconvenience and suppress the occurrence of spatter.

  In order to achieve the above-mentioned object, when two or more metal plates are overlapped and at least the outermost two metal plates are spot-welded with a workpiece composed of a thick plate and a thin plate having different thicknesses, The first main electrode with respect to the thick plate on the surface and the second main electrode and auxiliary electrode with respect to the thin plate on the outermost surface are divided by the pressing force of the first main electrode and the pressing force of the second main electrode and auxiliary electrode. By energizing the first main electrode and the second main electrode and energizing the second main electrode and the auxiliary electrode in a state where the work is pressed so that the total becomes equal, In the spot welding method of spot welding the workpiece, before the slag or metal particles start to scatter, both energizations are maintained and the pressing force of the first main electrode and the pressing force of the second main electrode and auxiliary electrode are maintained. In a state where the sum of The pressing force of the main electrode of the second with the pressing force of the electrodes weakens than the initial pressing force, characterized in that the strengthening than the initial pressing force.

  In the spot welding method of the present invention, first, the first main electrode with respect to the thick plate on the outermost surface of the workpiece and the second main electrode and auxiliary electrode with respect to the thin plate on the outermost surface are pressed against the workpiece, The first main electrode and the second main electrode are energized, and the second main electrode and the auxiliary electrode are energized. The pressing is performed so that the pressing force of the first main electrode is equal to the total pressing force of the second main electrode and the auxiliary electrode.

  In this case, a main current flowing through the workpiece is generated by energization of the first main electrode and the second main electrode, and the energization of the second main electrode and the auxiliary electrode generates the first current of the workpiece. A branch current that flows on the side close to the main electrode 2 is generated.

  As a result, a nugget is formed on the thin plate side of the outermost surface of the workpiece, and another nugget is also formed on the thick plate side of the outermost surface, and both nuggets are combined to grow into a large nugget. As described above, it is possible to prevent the nugget from growing unevenly on the thick plate side of the outermost surface of the workpiece, and to weld and integrate the workpiece.

  However, as the nugget formed on the thin plate side of the outermost surface of the workpiece grows, spatter may occur from between the thin plate and the adjacent metal plate.

  Therefore, in the spot welding method of the present invention, before the slag or metal particles begin to scatter, both energizations are maintained and the pressing force of the first main electrode and the pressing force of the second main electrode and auxiliary electrode are maintained. In a state where the total is kept equal, the pressing force of the auxiliary electrode is made weaker than the initial pressing force and the pressing force of the second main electrode is made stronger than the initial pressing force.

  As a result, the thin plate and the adjacent metal plate can be brought into close contact with each other compared to the initial stage. Therefore, it is possible to suppress spatter from occurring between the thin plate and the adjacent metal plate, thereby obtaining excellent welding quality.

  Further, the spot welding method of the present invention is used when two or more metal plates are overlapped and at least when a workpiece composed of a thick plate and a thin plate having at least two outermost metal plates having different thicknesses is spot-welded. A first main electrode that presses the outermost plate, a second main electrode and an auxiliary electrode that press the outermost plate, the first main electrode, the second main electrode, and the auxiliary electrode Pressing means against the workpiece so that the pressing force of the first main electrode is equal to the total pressing force of the second main electrode and the auxiliary electrode, the first main electrode, Energizing means for energizing the second main electrode and energizing the second main electrode and the auxiliary electrode, and the first main electrode, the second main electrode, and the auxiliary electrode While being pressed against the work, the first main electrode and the second main electrode are energized and the second main electrode and the auxiliary main electrode are energized. In a spot welding apparatus for spot welding the workpiece by energizing the electrode, both energization is maintained and the pressing force of the first main electrode and the second before the slag or metal particles start to scatter. In a state where the total pressing force of the main electrode and the auxiliary electrode is kept equal, the pressing force of the auxiliary electrode is made weaker than the initial pressing force and the pressing force of the second main electrode is made stronger than the initial pressing force. It can be advantageously implemented by a spot welding device characterized by comprising control means for controlling.

The side view which shows the spot welding apparatus used for implementation of the spot welding method of this invention. The principal part enlarged front view of the spot welding apparatus of FIG. Explanatory sectional drawing which shows the initial state of the spot welding method of this invention. Explanatory drawing which shows the welding state of the workpiece | work by the spot welding method of this invention.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

  The spot welding apparatus of the present embodiment is a welding robot R shown in FIG. 1, and a spot welding gun G is mounted on the wrist 1 at the operating end thereof. The welding robot R moves the spot welding gun G to each spot position of the workpiece W supported by the clamper C, and performs spot welding of the workpiece W on which a plurality of metal plates are superimposed.

  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.

  The gun body 3 is supported by a linear guide 6 fixed to the gun support bracket 2 so as to be slidable in the vertical direction. Is done.

  A second servo motor 10 is provided at the upper end of the gun body 3 for displacing the holder 9 that supports the upper chip 8 in the vertical direction. A substantially flat bracket 11 is attached to the body of the upper chip 8. As shown in FIG. 2, the bracket 11 is provided with actuators 14 and 15 for displacing the first auxiliary electrode 12 and the second auxiliary electrode 13 extending downward in the vertical direction. The operations of the second servo motor 10 and the actuators 14 and 15 are controlled by an electrically connected gun controller 16.

  The lower chip 5, the upper chip 8, and the auxiliary electrodes 12 and 13 are energized with the workpiece W sandwiched therebetween, and their energization is controlled by the electrically connected gun controller 16. In the present embodiment, the case where the upper chip 8 is a positive electrode and the lower chip 5 and the auxiliary electrodes 12 and 13 are negative electrodes will be described. However, the upper chip 8 is a negative electrode, and the lower chip 5 and the auxiliary electrodes 12 and 13 are positive electrodes. Also good.

As shown in FIG. 3, the workpiece W is, for example, 0.6 to 0.7 mm thick on _two thick plates P ₁ and P ₂ made of high-tensile steel having a thickness of 0.8 to 1.8 mm, for example. Two thin plates P ₃ and P ₄ made of mild steel are superposed, and a thick plate P ₁ and a thin plate P ₄ are arranged on the outermost surface. Spot welding of the workpiece W by welding robot R, a lower chip 5 with made to face the plank P ₁ of the outermost surface of the workpiece W, the upper chip 8 and the auxiliary electrodes 12, 13 in thin plate P ₄ of the outermost surface of the workpiece W Make it face each other.

  Next, with reference to FIG.3 and FIG.4, the spot welding method of the workpiece | work W by the welding robot R is demonstrated.

First, the servo motors 7 and 10 and the actuators 14 and 15 are actuated by the gun controller 16 to bring the lower chip 5 into contact with the thick plate P ₁ on the outermost surface of the workpiece W as shown in FIG. 8 and the auxiliary electrodes 12, 13 into contact with the sheet _{P 4} of the outermost surface. Next, the lower chip 5, the upper chip 8, and the auxiliary electrodes 12 and 13 are pressed against the work W. At this time, the pressing force F ₁ of the lower chip 5, the pressing force F ₂ of the upper chip _8, is equal to the sum of the pressing force F ₄ of the first pressing force of the auxiliary electrode 12 in F ₃ and the second auxiliary electrode 13 The operation of the second servo motor 10 and the actuators 14 and 15 is controlled by the gun controller 16 as (F ₁ = F ₂ + F ₃ + F ₄ ).

Next, the main current I ₁ flowing through the workpiece W is generated by energizing the lower chip 5 and the upper chip 8 while maintaining the pressing, and the upper chip 8 and the auxiliary electrodes 12 and 13 are energized. As a result, a branch current I ₂ flowing on the thin plate P ₄ side on the outermost surface of the workpiece W is generated.

Here, since the thick plates P ₁ and P ₂ have a larger electric resistance than the thin plates P ₃ and P ₄ , the nugget N ₁ is formed on the thick plates P ₁ and P ₂ side by the energization.

At this time, since the pressing force F ₂ of the upper chip 8 against the workpiece W is smaller than the pressing force F ₁ of the lower chip 5 (F ₂ <F ₁ ), the outermost thin plate pressed by the upper chip 8 The amount of heat generated by the main current I ₁ can be increased at the contact surface between P ₄ and the adjacent thin plate P ₃ . Further, since the sheet P ₄ side outermost surface of the workpiece W has a branch current I ₂ flows, it is possible to further increase the amount of heat generated at the thin plate P ₄ side of the outermost surface.

In this way, the nugget N ₂ can also be formed on the thin plate P ₄ side of the outermost surface of the workpiece W by the heat generated by the main current I ₁ and the heat generated by the branch current I ₂ .

However, if the energization is continued as it is, spatter is generated from between the thin plates P ₃ and P ₂ adjacent to the thin plates P ₄ and P _{3 as} the nugget N ₂ grows.

Therefore, before the spatter is generated, both energizations are maintained by the gun controller 16 and the pressing force F ₁ of the lower tip 5 and the pressing forces F ₂ , F ₃ and F _{4 of the} upper tip 8 and the auxiliary electrodes 12 and 13 are maintained. The pressures F ₃ and F ₄ of the first auxiliary electrode 12 and the second auxiliary electrode 13 are made weaker than the initial energization state while keeping the total of Specifically, the energization time at which sputtering starts to occur is measured in advance, and before the energization time is exceeded, the auxiliary electrodes 12 and 13 are slightly raised by the actuators 14 and 15 as shown in FIG. The pressing forces F ₃ and F ₄ of the auxiliary electrodes 12 and 13 against the workpiece W are made smaller than the initial energization. Thus, the pressing force F ₁ of the lower chip 5 and the total of the pressing forces F ₂ , F ₃ and F ₄ of the upper chip 8 and the auxiliary electrodes 12 and 13 are maintained to be equal. pressing force F ₂ is enhanced from an initial energizing.

As a result, the thin plate P _{4 on} the outermost surface of the workpiece W and the adjacent thin plate P ₃ can be brought into closer contact compared to the initial stage. Therefore, it is possible to obtain excellent welding quality by suppressing spattering from between the thin plates P ₃ and P ₂ adjacent to the thin plates P ₄ and P ₃ .

By continuing both energizations, the nugget N ₁ formed on the thick plates P ₁ and P ₂ side and the nugget N ₂ formed on the outermost thin plate P ₄ side are combined to form a large nugget N ₃ . The workpiece W can be grown and integrated by welding.

Therefore, according to the spot welding method of the present embodiment, it is possible to obtain the excellent welding quality by suppressing the generation of spatter, and the nugget N ₃ is the thick plate P ₁ side of the outermost surface of the workpiece W and the outermost surface. in any without being biased also the sheet P ₄ side, it is possible to perform good spot welding.

In the present embodiment, the method of spot welding a workpiece W in which two thin plates P ₃ and P ₄ made of mild steel are superposed on _two thick plates P ₁ and P _{2 made} of high-tensile steel has been described. In the spot welding method of the present embodiment, when two or more metal plates are overlapped and at least the outermost two metal plates are workpieces composed of a thick plate and a thin plate having different thicknesses, the metal plate It is applicable regardless of the number of sheets.

5 ... first electrode, 10 ... pressing means (the second servo motor), 8 ... second electrode, 12, 13 ... auxiliary electrode 16 ... conductive member, the control means (gun controller), N 2 _... nugget, P ₁ ... Metal plate, outermost thick plate, P ₂ ... Metal plate, thick plate, P ₃ ... Metal plate, thin plate, P ₄ ... Metal plate, outermost thin plate, R ... Spot welding device, W ... Workpiece.

Claims (2)

When two or more metal plates are superposed and at least two outermost metal plates are spot-welded with a workpiece consisting of a thick plate and a thin plate having different thicknesses, the first surface with respect to the outermost thick plate The main electrode and the second main electrode and auxiliary electrode with respect to the thinnest outermost plate are arranged such that the pressing force of the first main electrode and the total pressing force of the second main electrode and auxiliary electrode are equal. Spot welding for spot welding the workpiece by energizing the first main electrode and the second main electrode and energizing the second main electrode and the auxiliary electrode while being pressed against the workpiece. In the method
Before the slag or metal particles begin to scatter, the two energizations are maintained and the pressing force of the first main electrode and the total pressing force of the second main electrode and the auxiliary electrode are maintained to be equal. A spot welding method characterized in that the pressing force of the auxiliary electrode is made weaker than the initial pressing force and the pressing force of the second main electrode is made stronger than the initial pressing force. When the two or more metal plates are superposed and at least the two outermost metal plates are spot welded with a thick plate and a thin plate having different thicknesses, the outermost thick plate is pressed. 1 main electrode, the second main electrode and auxiliary electrode for pressing the outermost thin plate, and the first main electrode, the second main electrode and the auxiliary electrode are pressed against the first main electrode. Energizing the first main electrode and the second main electrode, pressing means for pressing the work so that the pressure and the total pressing force of the second main electrode and the auxiliary electrode are equal; The first main electrode, the second main electrode, and the auxiliary electrode are pressed against the work in a state where the first main electrode, the second main electrode, and the auxiliary electrode are pressed against the work. By energizing the main electrode and the second main electrode, and energizing the second main electrode and the auxiliary electrode, In the spot welding apparatus for spot welding a click,
Before the slag or metal particles begin to scatter, the two energizations are maintained and the pressing force of the first main electrode and the total pressing force of the second main electrode and the auxiliary electrode are maintained to be equal. A spot welding apparatus comprising control means for controlling the pressing force of the auxiliary electrode to be weaker than the initial pressing force and controlling the pressing force of the second main electrode to be stronger than the initial pressing force.

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