JP2019206024A - Indirect spot welding method and control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an indirect spot welding method capable of stably forming a nugget having a desired size and shape regardless of a disturbance such as the presence or absence of a plate gap. SOLUTION: In a first step S1, a welding electrode 10 applies a first current value C1 between both electrodes 10 and 20 while pressurizing a joining portion P with a first pressing force F1. In the second step S2, while the pressure applied by the welding electrode 10 is reduced from the first pressure F1 to the second pressure F2 lower than the first pressure F1, the first current value C1 is applied between the electrodes 10 and 20. A second current value C2 lower than the above is applied. In the third step S3, the welding electrode 10 pressurizes the joining scheduled portion P with the second pressing force F2, and the third current value C3 higher than the first current value C1 is applied between the electrodes 10 and 20. Energize. In the fourth step S4, a fourth current value C4 higher than the third current value C3 is applied between the electrodes 10 and 20 while the welding electrode 10 pressurizes the planned joining portion P with the second pressing force F2. Energize. [Selection diagram] Fig. 3

Description

  The present invention relates to an indirect spot welding method.

  In an automobile assembly process, a vehicle body is assembled by joining a plurality of parts made of metal plates by spot welding. As spot welding, direct spot welding in which a plurality of metal plates are sandwiched between a pair of electrodes and energized is often used. However, depending on the shape of the part, a plurality of metal plates cannot be sandwiched between a pair of electrodes, and direct spot welding may not be applied. In this case, series spot welding in which two portions are simultaneously welded by pressing a pair of electrodes against a plurality of metal plates from one side, or a portion to be joined of a plurality of metal plates is pressurized with a welding electrode from one side. In addition, indirect spot welding is applied in which welding is performed by energizing both electrodes in a state where the ground electrode is in contact with a portion different from the portion to be joined.

  Although series spot welding is actually used in the assembly process of the vehicle body, it is necessary to strike two welding points at the same time. In series spot welding, the current (reactive current) that does not contribute to welding that flows only through the metal plate with both electrodes in contact tends to increase. Value) is difficult to set. For example, there is a means for reducing a reactive current by providing a slit in a metal plate. In this case, however, the productivity is lowered and the cost is increased.

  On the other hand, in direct spot welding, since the welding electrode and the ground electrode are brought into contact with different metal plates, it seems that the current is more likely to flow through the portion to be joined than series spot welding. However, in direct spot welding, the welding electrode and the ground electrode are often arranged apart from each other, and reactive currents that flow through pre-welded points (pre-welded points) are likely to occur. The non-defective product range becomes narrower than welding, making it difficult to set welding conditions.

  For example, Patent Document 1 below discloses an indirect spot welding method performed while controlling the applied pressure and the current value. Specifically, as shown in FIG. 5, the energization time is divided into two time zones t1 and t2, and in the first time zone t1, the current is energized with the current value C1 while being pressurized with the pressurizing force F1, and the next time zone. At t2, energization is performed with a current value C2 higher than C1, while pressurizing with a pressure F2 lower than F1. In this way, by setting the high pressure F1 and the low current value C1 in the first time zone t1, the contact area between the electrode and the metal plate is secured, the current density is suppressed, and the metal plate surface is melted and scattered. Can be prevented. In addition, by setting the pressure force F2 and the high current value C2 in the next time zone t2, sinking of the electrode tip into the metal plate is suppressed. Thereby, since the current density can be sufficiently increased, heat generation sufficient for growing the nugget can be obtained, and the nugget can be stably obtained.

JP 2010-194609 A

  However, it cannot be said that the nugget can be stably formed even if indirect spot welding is performed by the method shown in Patent Document 1 above. In particular, in the assembly process of the vehicle body, a minute gap (plate gap) is often formed between the metal plates to be joined. In this case, indirect spot welding can stably form the nugget. There is a need for a method.

  Therefore, an object of the present invention is to provide an indirect spot welding method capable of stably forming a nugget having a desired size and shape regardless of disturbance such as the presence or absence of a gap.

  In order to solve the above-described problems, the present invention pressurizes a planned joining portion of a component made of a plurality of metal plates with a welding electrode, and causes a ground electrode to abut a portion of the component different from the planned joining portion. In the indirect spot welding method of welding the planned joining portion by energizing between both electrodes in a state where the welding is performed, the welding joint is pressed between the two electrodes while pressing the planned joining portion with a first pressure F1. The first step of energizing the first current value C1, and the pressure applied by the welding electrode from the first pressure F1 to the second pressure F2 that is lower than the first pressure F1, A second step of energizing a second current value C2 lower than the current value C1 of 1 and a first joint between both electrodes while pressurizing the planned joining portion with a second applied pressure F2 by the welding electrode. Higher than current value C1 A third step of energizing the third current value C3, and a pressure higher than the third current value C3 between the electrodes while pressing the planned joining portion with the second pressurizing force F2 by the welding electrode. And an indirect spot welding method comprising a fourth step of energizing a current value C4 of 4.

  In the first step, the contact area between the welding electrode and the metal plate and the contact area between the metal plates can be ensured by pressurizing the planned joining portion with the high pressure F1. In this state, by energizing the low current value C1, the contact area between the welding electrode and the metal plate and the contact area between the metal plates are increased while suppressing the current density and preventing the molten scattering of the metal plate surface. Can be made.

  In the second step, while reducing the applied pressure from F1 to F2, by suppressing the current value, the time until the applied pressure decreases to F2 and stabilizes is secured, and the electrode and the metal plate are appropriately adjusted. Then, the heat balance (balance between heat generation of the metal plate due to the energization resistance and heat dissipation from the electrode and the metal plate surface) is adjusted by cooling or keeping the temperature. Thereby, it can transfer to the 3rd step after that smoothly.

  In the third step, the metal plate is softened by energizing with a current value C3 lower than the current value for forming the nugget while being pressurized with the low pressurizing force F2, and the contact area between the metal plates is increased. Can be prevented. Thus, the nugget can be reliably formed by increasing the current value C4 of the main energization in the fourth step in a state where the contact area between the metal plates is ensured.

  As described above, between the first step of energizing the low current value C1 while pressurizing with the high pressurizing force F1, and the fourth step of energizing the high current value C4 while pressurizing with the low pressurizing force F2. By providing the second step and the third step for adjusting the current value in accordance with the change in the applied pressure (transition period), even if there is a gap between the metal plates, burning or spattering can be performed. A nugget having a desired size and shape can be stably formed without being generated.

  In the above indirect spot welding method, if the current value in the fourth step is increased or the energization time is lengthened, the nugget can be expanded, but the input heat is too much, and cracking of the upper plate or electrode There is a risk of problems such as welding. Therefore, in the fourth step, the nugget seed is firmly formed, and in the subsequent fifth step, the pressure is increased by the welding electrode with the second applied pressure F2, and between the electrodes, the fourth current value C4 is exceeded. It is preferable to energize with a low fifth current value C5. In the fifth step, the nugget formation can be stabilized using the preheating of the fourth step while suppressing the input heat amount.

  As described above, according to the indirect spot welding method of the present invention, a nugget having a desired size and shape can be stably formed regardless of disturbances such as the presence or absence of a plate gap.

It is sectional drawing which shows a mode that indirect spot welding is performed with respect to the components which consist of a some metal plate. It is a side view of a welding electrode. It is a graph which shows the pressurization electricity supply pattern of the indirect spot welding method which concerns on embodiment of this invention. (A)-(E) is sectional drawing of the joining plan part periphery in the time shown by A to E of FIG. 3, respectively. It is a graph which shows the pressurization electricity supply pattern of the conventional indirect spot welding method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In the present embodiment, an indirect spot welding method performed in an assembly process of an automobile body is shown. Specifically, for example, a case where a skeleton component 100 of a vehicle body as shown in FIG. 1 is welded is shown. This skeletal component 100 is a frame-shaped component extending in the direction perpendicular to the plane of FIG. The skeleton component 100 includes a first metal plate 1 having a substantially flat plate shape, a second metal plate 2 having a hat shape in cross section, and a first metal plate 1 and a second metal plate 2. And a third metal plate 3 having a cross-sectional hat shape disposed in the hollow portion. As the metal plates 1 to 3, for example, steel plates are used, and specifically, mild steel plates, high-tensile steel plates (tensile strength of 490 MPa or more), ultra-high-tensile steel plates (tensile strength of 980 MPa or more), and the like are used.

  The flange part 2a of the 1st metal plate 1 and the 2nd metal plate 2 is joined via the welding point Q1 welded beforehand by direct spot welding. The bottom portion 2b of the second metal plate 2 and the flange portion 3a of the third metal plate 3 are welded in advance by direct spot welding and joined via an already welded point Q2.

  The top plate portion 3b of the third metal plate 3 and the first metal plate 1 are joined by the indirect spot welding method according to one embodiment of the present invention. Specifically, the joint portion P between the first metal plate 1 and the top plate portion 3b of the third metal plate 3 is pressurized with the welding electrode 10 from one side in the thickness direction (upper side in the figure), The joint portion P is welded by energizing the electrodes 10 and 20 with the ground electrode 20 in contact with a portion different from the joint portion P of the skeleton component 100. In the illustrated example, the ground electrode 20 is brought into contact with the bottom 2b of the second metal plate 2 from below.

  This indirect spot welding method is connected to the above-described indirect spot welding apparatus having the welding electrode 10 and the ground electrode 20 and the indirect spot welding apparatus. It is carried out by equipment equipped with a control device for controlling the value. The indirect spot welding apparatus includes a pressurizing unit that pressurizes the metal plate by driving the welding electrode 10 in the axial direction. As the pressurizing means, an air cylinder or an electric cylinder can be used. In the present embodiment, an air cylinder is used.

  As shown in FIG. 2, the welding electrode 10 has a flat surface 11 and a tapered surface 12 provided continuously on the outer peripheral side of the flat surface 11. The shape of the tip of the welding electrode 10 is not limited to this. For example, a welding electrode having a spherical tip may be used.

  In the present embodiment, welding is performed according to a pressurization energization pattern shown in FIG. 3 according to a command from the control device. Hereinafter, this pressurization energization pattern will be described in detail.

[First Step S1]
In 1st step S1, the joining plan part P is pressurized with the relatively high 1st pressurizing force F1 with the welding electrode 10. FIG. Accordingly, the gaps between the metal plates 1 and 3 are filled so that the two metal plates 1 and 3 are brought into contact with each other, the contact area between the welding electrode 10 and the first metal plate 1, and the first metal plate 1. And a contact area between the third metal plate 3 can be secured. In this state, by passing a relatively low first current value C1 between the electrodes 10 and 20, the current density is suppressed and the metal plates 1 and 3 are prevented from being melted and scattered on the surfaces of the metal plates 1 and 20. By softening, the contact area between the welding electrode 10 and the first metal plate 1 and the contact area between the first metal plate 1 and the third metal plate 3 can be expanded {FIG. 4 (A). reference}. In addition, the area | region shown with a dot in FIG. 4 is a heat affected zone.

[Second Step S2]
In the second step S2, first, a command to reduce the applied pressure is issued to the pressurizing means that applies applied pressure to the welding electrode 10 (see FIG. 3). At this time, due to the structure of the pressurizing means, a transition period is inevitably provided in which the actual pressurizing force does not drop instantaneously from F1 to F2 at the same time as the command is received, but gradually decreases from F1 to F2. In particular, when an air cylinder is used as a pressurizing means for the welding electrode 10 as in this embodiment, for example, the response to the change in the applied pressure is worse than when an electric cylinder is used, and it takes time to decrease the applied pressure. And the value of the applied pressure becomes unstable. When a high current value is applied in such a state where the applied pressure is unstable, the energized state (current density) becomes unstable, and the welding state may vary.

  Therefore, in the second step S2, energization is performed with a current value C2 that is lower than the current value C1 of the first step while the applied pressure is decreased from F1 to F2. Thus, by suppressing the input heat amount in the state where the applied pressure is unstable, the welding electrode 10 and the metal plates 1 and 3 can be appropriately cooled or kept warm to adjust the heat balance. At this time, it is preferable to suppress the current value (set to C2) during the entire period in which the applied pressure is reduced. In the illustrated example, the period in which the applied pressure is reduced coincides with the period in which the current value C2 is energized. ing. In the second step S2, the state around the joint portion P of the metal plates 1 and 3 hardly changes {see FIG. 4 (B)}.

[Third Step S3]
Thereafter, when a pressure detection unit (not shown) for detecting the pressure of the pressurizing means detects that the pressure has dropped to F2, the current value is increased. In the present embodiment, the applied pressure is reduced to F2 and the current value is increased at the same time (see FIG. 3). At this time, if the current value is increased from the low current value C2 in the second step S2 to the current value of the main energization that forms the nugget (current value C4 in the next fourth step S4), sputtering may occur. Therefore, in the third step S3, while pressurizing with the low pressurizing force F2, first, the metal plates 1 and 3 are softened by energizing with the current value C3 lower than the current value C4 of the main energization, and these contact areas Can be enlarged {see FIG. 4C}.

[Fourth Step S4]
In a state where the contact area between the metal plates 1 and 3 is secured in this way, the current is increased to the current value C4 of the main energization in the subsequent fourth step S4 (see FIG. 3). Thus, seeds of nuggets (nuggets that do not reach a desired size) can be reliably formed without causing sputtering (see FIG. 4D). In the illustrated example, an annular nugget N is formed in the planned joining portion P of both metal plates 1 and 3 in the fourth step S4.

[Fifth Step S5]
After forming the nugget seed in the above step S4, the fourth current value C4 is applied between the electrodes 10 and 20 while being pressurized with the second applied pressure F2 by the welding electrode 10 in the fifth step S5. Is applied with a lower fifth current value C5 (see FIG. 3). In the illustrated example, the fifth current value C5 is lower than the third current value C3, and further lower than the first current value C1. The fifth current value C5 is higher than the second current value C2. The fifth step S5 can stabilize the nugget state by using the preheating of the metal plates 1 and 3 heated in the fourth step S4 while suppressing the amount of heat input to the metal plates 1 and 3. Yes {see FIG. 4 (E)}. In the illustrated example, the annular nugget N formed in the fourth step S4 grows on the inner diameter side in the fifth step S5, and the hollow portion is filled into a substantially disk shape.

  Thus, the nugget N having a desired size and shape (particularly, the amount of penetration in the thickness direction into the metal plate 3) is formed in the portion P to be joined between the metal plate 1 and the top plate portion 3b of the metal plate 3. Then, both the metal plates 1 and 3 are joined via the nugget N.

  The present invention is not limited to the above embodiment. For example, when the nugget N having a desired size and shape is formed in the fourth step S4, the fifth step S5 may be omitted.

1-3 Metal plate 10 Welding electrode 20 Ground electrode 100 Skeletal part N Nugget P Planned joint part Q1, Q2 Pre-welded point

Claims (3)

By pressurizing the part to be joined of a part made of a plurality of metal plates with a welding electrode and energizing between both electrodes in a state where the ground electrode is in contact with a part different from the part to be joined among the parts, In the indirect spot welding method of welding the joint planned portion,
A first step of energizing a first current value C1 between both electrodes while pressurizing the joint-scheduled portion with a first pressure F1 by the welding electrode;
While lowering the pressure applied by the welding electrode from the first pressure F1 to the second pressure F2 lower than the first pressure F1, a second current value C2 lower than the first current value C1 is set between both electrodes. A second step of energizing;
A third step of energizing a third current value C3 higher than the first current value C1 between the electrodes while pressurizing the joining portion with the second applied pressure F2 by the welding electrode;
A fourth step of energizing a fourth current value C4 higher than the third current value C3 between the electrodes while pressurizing the portion to be joined with the second applied pressure F2 by the welding electrode. Indirect spot welding method.   After the fourth step, while pressurizing the joint portion with the second applied pressure F2 by the welding electrode, a fifth current value C5 lower than the fourth current value C4 is provided between both electrodes. The indirect spot welding method according to claim 1, further comprising a fifth step of energizing. By pressurizing the part to be joined of a part made of a plurality of metal plates with a welding electrode and energizing between both electrodes in a state where the ground electrode is in contact with a part different from the part to be joined among the parts, A control device connected to an indirect spot welding device for welding the joint part to be welded, for controlling the pressure of the welding electrode and the current value between the electrodes,
A first step of energizing a first current value C1 between both electrodes while pressurizing the joint-scheduled portion with a first pressure F1 by the welding electrode;
While lowering the pressure applied by the welding electrode from the first pressure F1 to the second pressure F2 lower than the first pressure F1, a second current value C2 lower than the first current value C1 is set between both electrodes. A second step of energizing;
A third step of energizing a third current value C3 higher than the first current value C1 between the electrodes while pressurizing the joining portion with the second applied pressure F2 by the welding electrode;
A fourth step of energizing a fourth current value C4 higher than the third current value C3 between the two electrodes while pressing the planned joining portion with the second applied pressure F2 by the welding electrode; The control device that controls the applied pressure and the current value so that

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