JP2005319486A - Method for series spot welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for series spot welding capable of reliably welding even a narrow part and preventing the appearance of a welded part from being damaged. <P>SOLUTION: A recessed part 30a of a metal plate Wa is formed in a spherical shape fitted to a spherical shape of tip parts 26a, 27a of electrode tips 26, 27. Thus, when the tip parts 26a, 27a of the electrode tips 26, 27 are fitted in the recessed parts 30a formed at weld parts 30 of the metal plate Wa, the tip parts 26a, 27a can be tightly attached to the recessed parts 30a of the metal plate Wa without any space. As a result, a sufficient contact area of the tip parts 26a, 27a with the recessed parts 30a can be ensured, and the contact resistance between the electrode tips 26, 27 and the metal plate Wa can be reduced. Reliable welding can be performed by allowing a large welding current to run from the electrode tips 26, 27 to the metal plate Wa. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a series spot welding method.

  Conventionally, a direct spot welding method and a series spot welding method are known as welding methods for metal plates.

  The direct spot welding method uses the resistance heating of the metal plate that is generated by applying a welding current in the plate thickness direction by pressing the two stacked metal plates directly between the upper and lower electrodes, and using a point-like shape. The weld is obtained. That is, when a welding current is passed, a melted portion of the metal plate (generally referred to as “weld nugget”) is generated at the contact point between the two metal plates, and the two metal plates are welded in a spot shape by the weld nugget.

In the series spot welding method, a point-like welded portion is obtained by flowing a welding current between two electrodes while applying pressure from one direction by a pair of electrodes that separate two stacked metal plates. This series spot welding method includes a type using a back electrode and a type not using it.
In the type using the back electrode, the back electrode is arranged on the back side of the metal plate located on the opposite side to the pressure side of the electrode, one electrode → superposed metal plate → back electrode → superposed metal plate → the other By forming a current path called an electrode and flowing a welding current through the current path, welding is performed in a spot shape on the two metal plates that are overlapped.

  On the other hand, in the type that does not use the back electrode, a current path of one electrode → superimposed metal plate → the other electrode is formed, and a welding current is passed through the current path. Weld in a spot shape. Therefore, it is used when another member or the like assembled in the pre-welding process covers the back side of the metal plate to form a closed cross-section and the back electrode cannot be arranged on the back side of the metal plate.

However, the series spot welding method that does not use a back electrode has a drawback that it is difficult to form a sufficient nugget and a blow hole is formed, so that a sufficient welding strength cannot be obtained. It was.
Therefore, the applicant of the present invention presses and contacts a pair of spaced apart electrodes on one surface of two superimposed metal plates and causes a welding current to flow between the two electrodes, and welds the two metal plates. A series spot welding method, wherein the electrode of the one metal plate is press-contacted with a part of the seat surface that is partially higher than the general part, and the electrode has a spherical tip. A series spot welding method has been developed in which the electrode is welded to the seating surface under pressure contact so as to crush the seating surface (see Patent Document 1).
JP 2002-239742 A (pages 2 to 6, FIGS. 1 to 4)

  In the technique of Patent Document 1, since the spherical tip of the electrode is pressed and contacted so as to crush the seating surface, a dent along the shape of the electrode is generated on the seating surface, and the welding position of the workpiece is higher by one step. There was a problem that the crater-like weld dent with the bearing surface crushed remained and the appearance of the weld dent was poor and the aesthetic appearance was impaired.

For example, the body of an automobile is composed of an underbody that is the bottom of the automobile and an upper body that covers the underbody.
Since the underbody is under the automobile and is not visible to the user, even if the crater-like welding dent is left using the technique of Patent Document 1, the aesthetic appearance is not impaired. The technique of Patent Document 1 can be applied.
However, since the upper body is visible to the user, if the crater-like welding dent is left using the technique of Patent Document 1, the aesthetic appearance is drastically impaired. Therefore, the technique of Patent Document 1 cannot be applied to the welding of the upper body. .

  In the tacking process, the end of the workpiece is often spot-welded. However, when a plane having an area sufficient to form the seating surface of Patent Document 1 cannot be taken at the welded portion of the workpiece end. There is a problem that the technique of Patent Document 1 cannot be applied.

  By the way, when welding a large to-be-welded object (for example, an automobile body) with a complicated three-dimensional shape, first, spot welding is performed by spot welding with two workpieces to be welded fixed with a jig. The two workpieces are temporarily attached so that they cannot be separated, then the jig is removed, and finally, spot welding is additionally performed.

In the additional punching process, since the two workpieces are tacked in the tacking step, the workpiece has sufficient rigidity. Therefore, in the additional punching process, even if the workpiece is pressed from one direction with a pair of electrodes by a series spot welding method that does not use the back electrode including the technique of Patent Document 1, the workpiece is not deformed and normal welding is performed. Can do.
However, in the tacking process, the workpiece is not sufficiently rigid although it is fixed with a jig. Therefore, in the tacking process, when the workpiece is pressed from one direction with a pair of electrodes by a series spot welding method that does not use the back electrode including the technique of Patent Document 1, the workpiece is bent and deformed to perform normal welding. There was a problem that could not.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a series spot welding method that can be reliably welded even in a narrow spot and does not impair the aesthetic appearance of the weld spot.

  According to the first aspect of the present invention, a pair of spaced apart electrodes are brought into pressure contact with one surface of two superimposed metal plates, and a welding current is passed between the two electrodes. A series spot welding method for welding a metal plate, wherein a concave portion having a recessed shape is formed at a portion where the electrode of the one metal plate is pressed and contacted, and the tip of the electrode is pressed and contacted with the concave portion. It is a technical feature that each metal plate is welded.

  According to a second aspect of the present invention, in the series spot welding method according to the first aspect, the tip of the electrode is formed in a spherical shape, and the concave portion of the metal plate is formed in a spherical shape matching the shape of the tip of the electrode. This is a technical feature.

  A third aspect of the present invention is the series spot welding method according to the first or second aspect, wherein the other metal plate superimposed on the one metal plate is opposed to the pressing direction of the electrode. It is a technical feature that a supporting member is provided.

(Claim 1)
According to the first aspect of the present invention, only the recess is formed at the welded portion of the one metal plate even after the two metal plates are welded, and the appearance of the recess is not so bad.
Therefore, according to the first aspect of the present invention, compared to the technique of Patent Document 1 in which a crater-like welding dent in which a stepped higher seating surface is crushed remains in the welding location, a concave welding dent remains in the welding location. Therefore, the aesthetic appearance of the welded part is not impaired.
Therefore, the invention of claim 1 can be applied not only to a workpiece to which aesthetics are not important (for example, an underbody of an automobile) but also to an article to be welded (for example, an upper body of an automobile) where aesthetics are important. Applicable.

Further, in the tacking process by spot welding, the end of the metal plate is often spot-welded, but the area of the welded portion arranged at the end of the one metal plate is small, and the seating surface of Patent Document 1 is used. In some cases, a plane having a sufficient area to form the weld cannot be formed at the welded portion.
However, in the first aspect of the present invention, it is only necessary to form a recess in the welded portion of the one metal plate. Therefore, if the recess is formed small, it is required for the welded portion compared to the technique of Patent Document 1. The plane area can be small, and welding can be reliably performed even in narrow places.

(Claim 2)
In the invention of claim 2, the concave portion of the one metal plate is formed in a spherical shape matching the spherical tip shape of the electrode. Therefore, when the tip of the electrode is fitted in the recess of the one metal plate, the tip can be brought into close contact with the recess without any gap.
As a result, according to the invention of claim 2, it becomes possible to take a sufficient contact area between the tip of the electrode and the concave portion of the one metal plate, and the contact resistance between the electrode and the one metal plate is small. Therefore, a reliable welding can be performed by flowing a large welding current from the electrode to the one metal plate.

Further, since the concave portion of the one metal plate is formed in a spherical shape, the spherical top portion on the back side of the concave portion can be brought into point contact with the other metal plate.
As a result, it is possible to form an energization path with a large contact resistance that is constricted in a point shape by the point contact portion of each metal plate, and the current density of the welding current is higher than the energization path by surface contact. Can be reliably welded.

(Claim 3)
According to a third aspect of the present invention, there is provided a support member that supports the other metal plate in a direction opposite to the pressing direction of the electrode. Therefore, when the electrode is brought into pressure contact with the concave portion of the one metal plate and the back side of the concave portion is brought into pressure contact with the other metal plate, the other metal plate is supported by a support member. Even when the other metal plate does not have sufficient rigidity, the metal plate is not bent and deformed.
As a result, according to the invention of claim 3, the concave portion of the one metal plate can be reliably brought into contact with the other metal plate, so that each metal plate can be normally welded.

[Configuration of the embodiment]
FIG. 1 is a perspective view showing a schematic configuration of a welding apparatus 20 for series spot welding according to an embodiment of the present invention.
The welding device 20 includes a six-axis robot arm 22, air cylinders 24 and 25, electrode tips 26 and 27, a control device 40, and the like.

  The electrode tip 26 is attached to the piston tip protruding from the air cylinder 24, and the electrode tip 27 is attached to the piston tip protruding from the air cylinder 25. The air cylinders 24 and 25 arranged in parallel are attached to the wrist portion 22 a of the 6-axis robot arm 22. The air cylinders 24 and 25 are supplied with compressed air from an air pump (not shown).

  The six-axis robot arm 22 has the electrode chips 26 and 27 supported by the air cylinders 24 and 25 at predetermined positions on two metal plates Wa and Wb (for example, steel plates and aluminum alloy plates, for example). Move. Each of the air cylinders 24 and 25 expands and contracts the piston by the air pressure of the compressed air supplied from the air pump, thereby moving the electrode tips 26 and 27 attached to the tip of the piston forward and backward. The tip portions 26a and 27a of 26 and 27 are brought into pressure contact with the metal plate Wa.

In the metal plate Wa, a recessed portion 30a that is recessed from the general portion 35 is formed at a portion (welding location) 30 where the tip portions 26a, 27a of the electrode tips 26, 27 are in pressure contact.
The other metal plate Wb located below the recess 30 a of the welded portion 30 formed on one metal plate Wa is placed on the support member 50.

The support member 50 includes a cradle 52, an insulating material 54, and a receiving member 56.
The cradle 52 is erected on the floor of a factory where the welding apparatus 20 is installed, and a cradle member 56 is fixedly mounted on the cradle 52 via an insulating material 54. The upper surface of the receiving member 56 is formed flat so that the metal plate Wb can be stably supported.
The cradle 52 and the receiving member 56 have sufficient strength so that the metal plates Wa and Wb do not bend and deform even when the tip portions 26a and 27a of the electrode chips 26 and 27 pressurize the metal plates Wa and Wb. It is formed of a metal material (for example, iron material).

  FIG. 2A is a side view of the tip portions 26a, 27a of the electrode tips 26, 27. FIG. FIG. 2B is a plan view of the recess 30a of the welded portion 30 formed on the metal plate Wa. FIG. 2 (C) is a side view of the recess 30a shown in FIG. 2 (B).

The tip portions 26a, 27a of the electrode tips 26, 27 are formed in a spherical shape.
The concave portion 30a of the metal plate Wa is formed in a spherical shape that matches the spherical shape of the tip portions 26a, 27a of the electrode tips 26, 27.
For this reason, the tip portions 26a, 27a of the electrode tips 26, 27 can be brought into close contact with the concave portion 30a of the metal plate Wa without any gap.

  For example, the plate thickness of the metal plate Wa is set to 0.65 mm, and the plate thickness of the metal plate Wb is set to 0.8 mm or 2 mm. The diameters D0 of the tip portions 26a and 27a of the electrode tips 26 and 27 are formed to 16 mm, and the distance between the tip portions 26a and 27a is set to about 35 mm. And the diameter D1 of the recessed part 30a of the metal plate Wa is set to about 6.6-8 mm.

  FIG. 3 is a circuit diagram showing an electrical configuration of the control device 40 that controls the welding current supplied to the electrode tips 26 and 27 of the welding device 20.

The control device 40 includes a welding transformer 42, a voltage detector 44, a control circuit 46, an AC power supply 48, thyristors SCR1 and SCR2, and the like. A device including the voltage detector 44, the control circuit 46, and the thyristors SCR1 and SCR2 is referred to as a “timer contactor”.
The electrode tips 26 and 27 are electrically connected to the secondary winding of the welding transformer 42. An AC power supply 48 is electrically connected to the primary winding of the welding transformer 42 via the thyristors SCR1 and SCR2.

The voltage detector 44 detects the voltage between the electrode tips 26 and 27 (secondary voltage of the welding transformer 42) and outputs the voltage value (voltage data) to the control circuit 46.
The gate terminals of the thyristors SCR 1 and SCR 2 that are connected in parallel in opposite directions are connected to the control circuit 46.
The control circuit 46 outputs a trigger signal to the gate terminals of the thyristors SCR1 and SCR2 based on the voltage between the electrode chips 26 and 27 detected by the voltage detector 44, thereby controlling the welding from the AC power supply 48. Switching between energization / interruption of the welding current supplied to the primary side of the transformer 42 and phase control are performed.

[Spot welding process]
FIG. 4 is a perspective view of a main part for explaining a tacking process by spot welding of the metal plates Wa and Wb by the electrode tips 26 and 27 of the welding apparatus 20.

A support member 50 and a plurality of (four in the illustrated example) fastening jigs (clamps) KR are erected on the floor G of the factory where the welding apparatus 20 is installed.
Each metal plate Wa, Wb constitutes an automobile body (upper body or underbody), and the overall shape of each metal plate Wa, Wb is a complicated three-dimensional shape and large. Therefore, the metal plates Wa and Wb are temporarily attached so that they cannot be separated by spot welding using the welding apparatus 20 in a state where the metal plates Wa and Wb are fastened and fixed by the respective fastening jigs KR. .

  FIG. 5 is a partial cross-sectional view for explaining a tacking process by spot welding of the metal plates Wa and Wb by the electrode tips 26 and 27 of the welding apparatus 20.

  First, as shown in FIG. 5 (A), the tip portions 26a, 27a of the electrode tips 26, 27 are positioned above the welded portion 30 of the steel plate Wa with respect to the two overlapped metal plates Wa, Wb. As described above, the electrode tips 26 and 27 are moved and positioned by the six-axis robot arm 22.

  Next, as shown in FIG. 5 (B), by extending the pistons of the air cylinders 24 and 25, the electrode tips 26 and 27 attached to the tips of the pistons are moved, and the electrode tips 26 are moved. , 27 are fitted into a recess 30a formed in the welded portion 30 of the metal plate Wa.

  Even after the tip portions 26a, 27a of the electrode tips 26, 27 are fitted in the recesses 30a of the metal plate Wa, the pistons of the air cylinders 24, 25 are extended to be pressurized by the electrode tips 26, 27. The spherical top on the back side of the recess 30a of the metal plate Wa is brought into contact with the metal plate Wb by bringing the back side of the recess 30a of the metal plate Wa into pressure contact with the metal plate Wb with a predetermined pressure (for example, about 50 kgf). Make point contact.

  Subsequently, as shown in FIG. 5C, the control circuit 46 controls the thyristors SCR1 and SCR2 to energize the welding current from the AC power supply 48 to the primary side of the welding transformer 42. A welding current is passed between the electrode tips 26 and 27 from the next side.

Then, the point resistance of each metal plate Wa, Wb (the contact portion between the spherical top on the back side of the recess 30a of the metal plate Wa and the metal plate Wb) 30b has a large contact resistance. An energization path (solid line with an arrow in the figure) is formed, and the welding current flowing through the energization path has a higher current density than the energization path by surface contact.
The resistance heating value is increased by the welding current, and the metal plates Wa and Wb in the point contact portion 30b are melted to generate a weld nugget Na, and both the metal plates Wa and Wb are welded in a spot shape by the weld nugget Na. The

  Then, by continuing the pressurization and energization by the electrode tips 26 and 27, the metal plate Wa sinks so as to sink into the metal plate Wb at the point contact portion 30b, and the spherical back side of the recess 30a of the metal plate Wa. The weld nugget Na is sequentially formed so as to be directed in the surface direction along the line, and the spot welding is completed.

[Operations and effects of the embodiment]
As described above in detail, according to this embodiment, the following actions and effects can be obtained.

  [1] The concave portion 30a of the metal plate Wa is formed in a spherical shape that matches the spherical shape of the tip portions 26a, 27a of the electrode tips 26, 27. Therefore, as shown in FIG. 5 (B), when the tip portions 26a, 27a of the electrode tips 26, 27 are fitted into the recesses 30a formed in the welded portions 30 of the metal plate Wa, the tip portions 26a and 27a can be closely attached to the recess 30a of the metal plate Wa without any gap.

  As a result, a sufficient contact area between the tip portions 26a, 27a and the concave portion 30a can be obtained, and the contact resistance between the electrode tips 26, 27 and the metal plate Wa is reduced. Thus, reliable welding can be performed by flowing a large welding current from the metal plate Wa to the metal plate Wa.

The range of the diameter D1 of the recess 30a of the metal plate Wa is set to 20 to 80% of the diameter D0 of the tip portions 26a and 27a of the electrode tips 26 and 27 (or the base portions of the electrode tips 26 and 27). Is preferably 30 to 60%, particularly preferably 40 to 50%.
When the diameter D1 of the concave portion 30a is larger than this range, the shape of the concave portion 30a does not match the shape of the tip portions 26a and 27a of the electrode tips 26 and 27, and the tip portions 26a and 27a can be brought into close contact with the recess 30a without any gap. Since it becomes impossible, the contact area of the front-end | tip parts 26a and 27a and the recessed part 30a decreases, and normal welding becomes difficult.
When the diameter D1 of the recess 30a is smaller than this range, the contact area between the tip portions 26a, 27a of the electrode tips 26, 27 and the recess 30a is reduced, and normal welding becomes difficult.

[2] In the present embodiment, a small concave portion 30a is formed in the welded portion 30 of the metal plate Wa, and the tip portions 26a, 27a of the electrode tips 26, 27 are accurately aligned with the small concave portion 30a. Each electrode tip 26 and 27 is positioned by the six-axis robot arm 22.
That is, in this embodiment, spot welding is performed aiming at the small recessed part 30a of the metal plate Wa. Therefore, if the positioning accuracy of the recess 30a and the electrode tips 26 and 27 is low, welding cannot be performed well.

  However, this embodiment is applied to the tacking process. In the tacking process, spot welding is performed with the metal plates Wa and Wb clamped and fixed by the clamping jig KR. The positions of the tip portions 26a, 27a of the metal plate Wa and the concave portion 30a of the metal plate Wa do not vary, and the positioning accuracy of the concave portion 30a and the electrode tips 26, 27 is high. Accurate spot welding can be performed.

[3] Since the concave portion 30a of the metal plate Wa is formed in a spherical shape, the spherical top on the back side of the concave portion 30a of the metal plate Wa can be brought into point contact with the metal plate Wb.
As a result, it becomes possible to form an energization path having a large contact resistance constricted in a point shape by the point contact portion 30b of each metal plate Wa, Wb, and the current density of the welding current is increased as compared with the energization path by surface contact. The metal plates Wa and Wb can be reliably welded.

[4] In the present embodiment, only the small spherical concave portion 30a is formed in the welded portion 30 of the metal plate Wa even after the metal plates Wa and Wb are welded, and the appearance of the concave portion 30a is not so bad. .
Therefore, according to the present embodiment, compared to the technique of Patent Document 1 in which a crater-like welding dent in which a one-step higher seating surface is crushed remains in the welding location, a small concave-shaped welding dent (recess 30a) is welded. Since it only remains in the location 30, the beauty of the weld location is not impaired.
Therefore, this embodiment can be applied not only to a workpiece to which aesthetics are not important (for example, an underbody of a car) but also to a workpiece to be aesthetically important (for example, an upper body of a car). .

[5] FIG. 6 is a main part perspective view showing an example of the welding location 30 arranged at the end EP of the metal plate Wa.
In the tacking process, the end portion EP of the metal plate Wa is often spot-welded. However, as shown in FIG. 6, the area of the welded portion 30 arranged at the end portion EP of the metal plate Wa is narrow. In some cases, a plane having a sufficient area to form the seating surface cannot be formed at the welded portion 30.

  However, according to the present embodiment, it is only necessary to form a small recess 30a in the welded portion 30 of the metal plate Wa, so that the area of the plane required for the welded portion 30 is small compared to the technique of Patent Document 1. In addition, welding can be reliably performed even in a narrow portion (end portion EP).

  [6] As shown in FIGS. 5B and 5C, the back side of the recess 30a of the metal plate Wa is brought into pressure contact with the metal plate Wb, and the spherical top on the back side of the recess 30a of the metal plate Wa is placed on the metal plate. When making point contact with Wb, the back side of metal plate Wb (the side opposite to the front side in contact with metal plate Wa) is placed on receiving member 56 of support member 50.

Here, the upper surface of the receiving member 56 is formed flat so that the metal plate Wb can be stably supported, and the receiving base 52 and the receiving member 56 are formed of a metal material having sufficient strength.
Therefore, the receiving member 56 supports the metal plate Wb in a direction (vertically upward) opposite to the pressurizing direction (vertically downward) of the electrode tips 26 and 27.

  Accordingly, when the back side of the concave portion 30a of the metal plate Wa is brought into pressure contact with the metal plate Wb, the metal plate Wb is supported by the receiving member 56. Therefore, even if the metal plate Wb does not have sufficient rigidity, the metal plate Wb Does not bend and deform. As a result, the concave portion 30a of the metal plate Wa can be reliably brought into point contact with the metal plate Wb, so that the metal plates Wa and Wb can be normally welded.

[7] Since the insulating material 54 is provided between the cradle 52 and the receiving member 56, the cradle 52 and the receiving member 56 are insulated.
That is, in the present embodiment, the cradle 52 and the receiving member 56 are formed of a metal material in order to obtain sufficient strength, and the receiving member 56 does not function as a back electrode.

Therefore, a current path of one of the electrode tips 26 and 27 → the metal plate Wa → the metal plate Wb → the receiving member 56 → the receiving base 52 is not formed, and no current flows through the receiving base 52.
Therefore, the welding current does not leak from the electrode tips 26 and 27 to unnecessary portions via the cradle 52, and the equipment trouble that occurs in the welding apparatus 20 and other equipment in the factory due to the leakage current is prevented. It can be prevented beforehand.

Further, since separate support members 50 are provided for each of the two recesses 30 a formed in the metal plate Wa, no welding current flows between the two support members 50.
Therefore, the welding current flowing between the electrode tips 26 and 27 is not divided between the support members 50, and it is possible to prevent the welded state of the metal plates Wa and Wb from being varied due to the divided flow.

[Another embodiment]
By the way, the present invention is not limited to the above-described embodiment, and may be embodied as follows, and even in that case, operations and effects equivalent to or higher than those of the above-described embodiment can be obtained.

  (1) In the said embodiment, the supporting member 50 is provided for every two recessed part 30a formed in the metal plate Wa. However, as shown in FIG. 7, one support member 50 common to the two recesses 30a may be provided.

(2) In the above embodiment, the receiving member 56 and the receiving base 52 are formed of a metal material, and the insulating material 54 is provided between the receiving member 56 and the receiving base 52.
However, the insulating material 54 may be omitted if at least one of the receiving member 56 and the receiving base 52 is formed of an insulating material having sufficient strength (for example, ceramic).

(3) In the above embodiment, the tip portions 26a, 27a of the electrode tips 26, 27 are formed in a spherical shape.
However, as long as the metal plates Wa and Wb can be reliably welded, the tip portions 26a and 27a of the electrode tips 26 and 27 may be formed in any shape (for example, conical shape, pyramid shape, etc.). .
Even in this case, the concave portion 30a of the metal plate Wa needs to be shaped to match the shape of the tip portions 26a, 27a of the electrode tips 26, 27.

(4) In the above embodiment, the pressing direction of the metal plate Wa by the electrode tips 26 and 27 is the vertically downward direction, and the receiving member 56 supports the metal plate Wb in the vertically upward direction.
However, the pressing direction of the metal plate Wa by the electrode tips 26 and 27 is not limited to the vertically downward direction, and may have an appropriate inclination angle with respect to the vertically downward direction.
In that case, the receiving member 56 may support the metal plate Wb in a direction opposite to the pressing direction of the electrode tips 26 and 27.

  (5) The said embodiment is applied to the temporary attachment process by spot welding. However, the present invention is also applicable to spot welding additional punching processes.

Generally, in the additional punching process, it is only necessary to provide a minimum work positioning and fixing means, and the metal plates Wa and Wb are tightened without using a tightening jig KR for performing strong fixing as in the temporary mounting process. Since spot welding is performed in a non-fixed state, the positioning accuracy of the welded portions 30 of the metal plates Wa and Wb and the electrode tips 26 and 27 is low.
For this reason, in the technique of Patent Document 1, the diameter of the seating surface is set to 1 to 3 times the diameter of the electrode tip, and even if the positions of the electrode tip and the seating surface vary somewhat, the seating tip is caused by the tip spherical surface of the electrode tip. The surface is deformed into a spherical shape so that reliable welding can be performed.

Therefore, when the above embodiment is applied to a general additional punching process, the positioning accuracy of the concave portion 30a of the metal plate Wa and the electrode tips 26 and 27 is low, so that accurate spot welding is performed on the small concave portion 30a. I can't.
However, when there is no variation in the positions of the welded portions 30 of the metal plates Wa and Wb and the positions of the electrode tips 26 and 27, even when the above embodiment is applied to the additional punching process, the small concave portion 30a of the metal plate Wa. Therefore, accurate spot welding can be performed.

The perspective view which shows schematic structure of the welding apparatus 20 of the series spot welding in one Embodiment which actualized this invention. 2A is a side view of the tip portions 26a and 27a of the electrode tips 26 and 27. FIG. FIG. 2B is a plan view of the recess 30a0 of the welded portion 30 formed on the metal plate Wa. FIG. 2C is a side view of the recess 30a shown in FIG. The circuit diagram which shows the electric constitution of the control apparatus 40 which controls the welding current supplied to each electrode tip 26,27 of the welding apparatus 20. FIG. The principal part perspective view for demonstrating the temporary attachment process by the spot welding of the metal plates Wa and Wb by the electrode tips 26 and 27 of the welding apparatus 20. FIG. The partial cross section figure for demonstrating the spot welding process of the metal plates Wa and Wb by the electrode tips 26 and 27 of the welding apparatus 20. FIG. The principal part perspective view which shows an example of the welding location 30 arrange | positioned at the edge part of the metal plate Wa. Explanatory drawing for demonstrating the structure of the supporting member 50 in another embodiment which actualized this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Welding device 24, 25 ... Air cylinder 26, 27 ... Electrode tip 26a, 27a ... Tip part of electrode tip 30 ... Welding location 30a ... Recess 30b ... Point contact part 35 ... General part 40 ... Control device 42 ... Welding transformer 44 ... Voltage detector 46 ... Control circuit 48 ... AC power supply 50 ... Support member 52 ... Receiving base 54 ... Insulating material 56 ... Receiving member SCR1, SCR2 ... Thyristor Wa, Wb ... Metal plate

Claims (3)

This is a series spot welding method in which a pair of spaced apart electrodes are pressed against one surface of two superimposed metal plates, a welding current is passed between the two electrodes, and the two metal plates are welded. And
A concave portion having a recessed shape is formed at a portion where the electrode of the one metal plate is brought into pressure contact, and the metal plate is welded by bringing the tip of the electrode into pressure contact with the recess. Series spot welding method. In the series spot welding method according to claim 1,
The series spot welding method, wherein the tip of the electrode is formed in a spherical shape, and the concave portion of the metal plate is formed in a spherical shape matching the shape of the tip of the electrode. In the series spot welding method according to claim 1 or 2,
A series spot welding method, comprising: a support member that supports the other metal plate superimposed on the one metal plate in a direction opposite to a pressing direction of the electrode.

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