JP6104013B2 - Spot welding method and spot welding apparatus - Google Patents

Description

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

  For example, 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 is used for an automobile mohawk roof, stiffener, side panel inner, side panel outer, etc. Are known. The laminated plate is formed by spot welding a workpiece in which the two thick plates and the two thin plates are overlapped. In the spot welding, the workpiece is pressed and sandwiched between a first electrode facing the outermost plate and a second electrode facing the outermost plate and having the same contact area as the first electrode. Then, it is performed by energizing both electrodes.

  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, a spot using a second electrode having a contact area smaller than the contact area of the first electrode instead of the second electrode having the same contact area as the first electrode. Welding methods are known.

  According to the spot welding method, since the contact area of the second electrode is smaller than that of the first electrode, the current density in the energization path between the first electrode and the second electrode Increases from the outermost plate side facing the first electrode toward the outermost plate side facing the second electrode. As a result, the amount of heat generation can be increased even on the outermost sheet side of the energization path, and a nugget can be formed also on the outermost sheet side of the workpiece. And with the energization, 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).

Japanese Patent No. 3894544

  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.

  The inventor has intensively studied the cause of the occurrence of sputtering from between the thin plate and the adjacent metal plate. Along with the growth of the nugget formed on the thin plate side of the outermost surface of the workpiece, a gap is generated between the thin plate and the adjacent metal plate in a region where the pressure by the first electrode and the second electrode is small. In other words, it was found that the nugget protrudes from a corona bond formed between the thin plate and the adjacent metal plate. As a result of further investigation based on the above knowledge, the inventor has exposed the nugget from between the thin plate and the adjacent metal plate due to the generation of the gap and the protrusion of the nugget, and spatter is generated. I found out.

The present invention has been accomplished on the basis of the findings, in order to achieve the above object, two metal plates of at least the outermost surface of the thick mutually together to superimpose three or more metal plates When spot welding a workpiece composed of different thick plates and thin plates, the first electrode facing the outermost thick plate and the contact area facing the outermost thin plate and smaller than the contact area of the first electrode In a spot welding method in which the first electrode and the second electrode are energized in a state where the workpiece is pressed and clamped with a second electrode comprising:
After the energization is started and before the size of the nugget generated by the energization exceeds the size at which the slag or metal particles start to scatter, the nugget is provided on the outer periphery of the second electrode while maintaining the energization, The method includes a step of pressing the workpiece with a pressing member capable of pressing the workpiece on the outer peripheral side of a nugget having a size in which slag or metal particles start to scatter.

  In the spot welding method of the present invention, first, in a state where the workpiece is pressed and clamped between the first electrode facing the outermost thick plate and the second electrode facing the outermost thin plate, the first electrode The electrode and the second electrode are energized.

  At this time, since the contact area of the second electrode is smaller than that of the first electrode, the current density in the energization path between the first electrode and the second electrode is the first electrode. The thickness increases from the outermost thick plate facing the second electrode toward the outermost thin plate facing the second electrode. As a result, the amount of heat generation can be increased even on the outermost sheet side of the energization path, and a nugget can be formed also on the outermost sheet side of the workpiece.

  And with the energization, 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, and the workpiece is welded. Can be integrated.

  However, as the nugget formed on the thin plate side of the outermost surface of the workpiece grows, there is a gap between the thin plate and the adjacent metal plate in a region where the pressure by the first electrode and the second electrode is small. Or the nugget may protrude from a corona bond formed between the thin plate and the adjacent metal plate. As a result, the nugget is exposed from between the thin plate and the adjacent metal plate, and sputtering occurs.

  Therefore, in the spot welding method of the present invention, the second energization is performed in a state where the energization is maintained before the size of the nugget formed on the thin plate side of the outermost surface of the workpiece exceeds the size at which spattering starts to occur. The workpiece is pressed by the pressing member provided on the outer periphery of the electrode. The pressing member is provided on the outer periphery of the second electrode, and can press the workpiece on the outer peripheral side of the nugget having a size at which spatter starts to be generated. Therefore, the pressing generates the gap and the nugget protrudes. Can be prevented. Thereby, it is possible to prevent the nugget from being exposed between the thin plate and the adjacent metal plate, and to suppress the occurrence of spatter, thereby obtaining excellent welding quality.

  When the pressing member cannot press the workpiece on the outer peripheral side of the nugget having a size at which spattering starts to occur, the pressing becomes insufficient, and the generation of the gap and the protrusion of the nugget cannot be prevented.

Further, the spot welding method of the present invention is used when spot welding a workpiece in which three or more metal plates are overlapped and at least two outermost metal plates are made of a thick plate and a thin plate having different thicknesses. A first electrode opposed to the outermost thick plate, a second electrode opposed to the outermost thin plate and having a contact area smaller than the contact area of the first electrode, the first electrode, and the A pressurizing unit that sandwiches and pressurizes the workpiece with a second electrode; and an energizing unit that energizes the first electrode and the second electrode. The first electrode and the second electrode In the spot welding apparatus for energizing the first electrode and the second electrode in a state where the workpiece is pressed and clamped, the slag or metal particles provided on the outer periphery of the second electrode start to scatter A pressing member capable of pressing the workpiece on the outer peripheral side of the size nugget, and the energization And a pressing means for causing the pressing member to advance and retreat with respect to the work and to press the work with the pressing member after energizing the first electrode and the second electrode by means. Spot welding equipment.
Can be advantageously implemented.

The block diagram which shows the spot welding apparatus used for implementation of the spot welding method of this invention. 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.

  A pressure unit 6 and a pressing unit 7 each having a servo motor as a drive source are mounted on the upper end of the gun body 3. Below the gun body 3, a first rod 8 that moves up and down via a first ball screw mechanism (not shown) in the gun body 3 by the pressurizing unit 6, and a pressing part 7 inside the gun body 3. And a second rod 9 that moves up and down via a second ball screw mechanism (not shown).

  An upper tip 10 that is a movable electrode is attached to the lower end of the first rod 8 so as to face the lower tip 5. As shown in FIG. 2, each of the lower chip 5 and the upper chip 10 is a DR type in which the tip has a dome-shaped spherical shape and has a flat portion at the apex thereof. In the lower chip 5 and the upper chip 10, the area of the flat portion is a contact area with the workpiece W, and the upper chip 10 has a smaller contact area than the lower chip 5. In addition, since the lower chip 5 and the upper chip 10 are the DR type, they can be used for a long period of time while suppressing changes in the contact area during wear.

  An insulating member 11 is attached to the lower end of the second rod 9 and is provided on the outer periphery of the upper chip 10 and can press the workpiece W on the outer periphery side of a nugget having a size that starts to generate spatter. The insulating member 11 has heat resistance that can withstand the heat generated in the workpiece W by spot welding, and is formed so that the size thereof is larger than the size of the nugget at the start of occurrence of sputtering measured in advance. .

  The gun body 3 is supported by a linear guide 12 fixed to the gun support bracket 2 so as to be slidable in the vertical direction, and is moved up and down by the rotation of a servo motor 13 mounted on the upper end of the gun support bracket 2.

  The operations of the pressurizing unit 6, the pressing unit 7 and the servo motor 13 are controlled by a gun controller 14. When the spot welding gun G reaches each hitting point position of the workpiece W by the position control of the robot R, the gun controller 14 operates the pressurizing unit 6 and the servo motor 13 to cause the lower tip 5, the upper tip 10, The workpiece W is sandwiched between the lower tip 5 and the upper tip 10 in this pressurized sandwiched state, and the workpiece W is spot welded. Further, the gun controller 14 operates the pressing portion 7 and the servo motor 13 as necessary to lower the insulating member 11 and press it against the workpiece W.

As shown in FIG. 2, the workpiece W is, for example, 0.6 to 0.65 mm thick on two thick plates P ₁ and P ₂ made of high-tensile steel having a thickness of 1.0 to 1.4 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. Welding spot welding the workpiece W by the robot R is performed on the chip 10 are opposed to the thin plate P ₄ of the outermost surface of the workpiece W with it is opposed planks P ₁ of the outermost surface of the workpiece W to the lower chip 5.

  Next, with reference to FIG.2 and FIG.3, the spot welding method of the workpiece | work W by the welding robot R is demonstrated.

First, the pressure controller 6 and the servo motor 13 are operated by the gun controller 14, and the workpiece W is pressed and sandwiched between the lower chip 5 and the upper chip 10 as shown in FIG. At this time, the lower chip 5 faces the plank P ₁ of the outermost surface of the workpiece W, the upper chip 10 is opposed to the sheet P ₄ of the outermost surface of the workpiece W.

  Next, in a state where the workpiece W is pressed and clamped between the lower tip 5 and the upper tip 10, the workpiece W is spot welded by energizing between the lower tip 5 and the upper tip 10.

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, the contact area of the upper chip 10 with the outermost thin plate P ₄ is smaller than the contact area of the lower chip 5 with the outermost thick plate P ₁ . The current density in the energization path X increases gradually from the outermost surface thick plate P ₁ side facing the lower chip 5 toward the outermost surface thin plate P ₄ facing the upper chip 10. As a result, it is possible to increase the amount of heat generated at the thin plate P ₄ side outermost surface of the conduction path X, we can form a nugget N ₂ even in thin P ₄ side outermost surface of the workpiece W.

However, if the energization is continued as it is, as the nugget N ₂ grows, a gap is generated between the thin plate P ₄ and the adjacent metal plate P ₃ in a region where the pressure by the lower chip 5 and the upper chip 10 is small. The nugget N ₂ may protrude from the corona bond formed between the thin plate P ₄ and the adjacent metal plate P ₃ . As a result, the nugget N ₂ is exposed from between the thin plates P ₄ and P ₃ and the adjacent thin plates P ₃ and P ₂ and spattering occurs.

Therefore, before the size of the nugget N ₂ exceeds the size at which spattering starts to occur, the pressing portion 7 and the servo motor 13 are operated by the gun controller 14 while maintaining the energization. As shown, the insulating member 11 is lowered and pressed against the thin plate P _{4 on} the outermost surface of the workpiece W. The timing for operating the pressing unit 7 and the servo motor 13 can be determined, for example, by measuring in advance the energization time until the start of sputtering and the size of the nugget N _{2 at} this time.

Since the insulating member 11 can press the workpiece W on the outer peripheral side of the nugget N _{2 having} a size at which sputtering starts to occur, the generation of the gap and the protrusion of the nugget N ₂ can be prevented by the pressing. As a result, to obtain a weld quality nugget N ₂ is prevented from being exposed, sputtering is superior to suppress the occurrence from between the sheet P ₃ and planks P ₂ adjacent to the sheet P _4, P ₃ Can do.

Then, by continuing the energization while maintaining the pressing the workpiece W by the insulating member 11, which is formed in a thin plate P ₄ side of the plank P _1, P ₂ side formed nuggets N ₁ and the top surface The nugget N ₂ is combined to grow into a large nugget N ₃ , and the workpiece W can be welded and integrated.

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, a method for spot welding a workpiece W in which two thin plates P3 and P4 made of mild steel are superimposed on two thick plates P1 and P2 made of high-tensile steel has been described. According to the spot welding method, if three or more metal plates are superposed and at least two metal plates on the outermost surface are workpieces composed of a thick plate and a thin plate having different thicknesses, the number of metal plates depends on the number. It is applicable.

5 ... first electrode, 6 ... pressing means, 7 ... pressing means, 10 ... second electrode, 11 ... pressing member (insulating member), 14 ... conductive member (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)

Work two metal plates of at least the outermost surface is made of different thicknesses plate and the thin thicknesses to each other during the spot welding with superposed three or more metal plates, the faces the plank top surface In a state where the workpiece is pressed and clamped between the first electrode and the second electrode having a contact area smaller than the contact area of the first electrode and facing the outermost thin plate, the first electrode and the second electrode In the spot welding method of energizing the second electrode,
After the energization is started and before the size of the nugget generated by the energization exceeds the size at which the slag or metal particles start to scatter, the nugget is provided on the outer periphery of the second electrode while maintaining the energization, A spot welding method comprising a step of pressing the workpiece with a pressing member capable of pressing the workpiece on the outer peripheral side of a nugget having a size in which slag or metal particles start to scatter. Work two metal plates of at least the outermost surface is made of different thicknesses plate and the thin thicknesses to each other during the spot welding with superposed three or more metal plates, the faces the plank top surface The workpiece is sandwiched between the first electrode, the second electrode facing the outermost thin plate and having a contact area smaller than the contact area of the first electrode, and the first electrode and the second electrode And a pressurizing means for pressurizing, and an energizing means for energizing the first electrode and the second electrode, and the workpiece is pressed and clamped between the first electrode and the second electrode In the spot welding apparatus for energizing the first electrode and the second electrode,
A pressing member provided on the outer periphery of the second electrode and capable of pressing the workpiece on the outer peripheral side of a nugget having a size in which slag or metal particles begin to scatter;
And a pressing means for causing the pressing member to advance and retreat with respect to the workpiece and to press the workpiece by the pressing member after the first electrode and the second electrode are energized by the energizing means. Spot welding equipment.

Images