JP2003071569A - Spot welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot welding method capable of obtaining a predetermined welding strength even if the ratio of the total plate thickness to a thin plate thickness is large in the case where, on at least one of welding members of superposed two thick plates, a welding member of a thin plate is further superposed so as to spot welding these welding members. SOLUTION: At the initial period of the welding, a bearing face of the projecting part 30 formed on the welding place of the thin plate Wa is crushed, the bearing face is deformed into a spherical shape so as to bring the bearing face into contact with the thick plate Wb in a state of point abutting, thereby between the both parts, a current path contracted in a point state is formed, by which the current density of the welding current flowing in the current carrying path is enhanced, and between these, a nugget can be formed. Thereafter, a pressure force higher than the pressure force having crushed the bearing face is applied to squeeze the gap between the thick plates Wb, Wc and by forming a current carrying path on them, the nugget can be formed between them. Accordingly, three or more steel plates superposed with furthermore a thin plate Wa on the superposed two thick plates Wb, Wc can be spot-welded.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method in which a thin plate member to be welded is further stacked on at least one of the two thick plate members to be welded, and these members are sandwiched by a pair of electrodes and energized under pressure. The present invention relates to a spot welding method for spot welding these members to be welded.

[0002]

2. Description of the Related Art Generally, spot welding is used to weld superposed steel sheets. This welding method utilizes resistance heating of the steel sheets generated by directly sandwiching two superposed steel sheets with upper and lower electrode tips and applying a welding current in the sheet thickness direction while applying pressure. I have a part. That is, when an electric current is applied, a molten portion of both steel sheets called a welding nugget (hereinafter referred to as "nugget") is formed at a contact portion of both steel sheets, and the two steel sheets are welded in a dot shape by this nugget.

By the way, even when welding three or more steel plates, there is a demand for utilizing the above-mentioned spot welding method. For example, as shown in FIG. 8 (A), steel sheets such as a floor panel 91, a member 92, and a reinforcement 93 that form a vehicle floor are welded by sandwiching the reinforcement 93 between the floor panel 91 and the member 92. This is the case when you want to do so.

However, as shown in FIG. 8B, for example, when the member 92 and the reinforcement 93 having a large plate thickness are overlapped with each other, a gap is apt to occur between the steel plates. Especially, when the shapes of the steel sheets are complicated, the gap tends to be large.

FIG. 8C shows the case where two thick plates, which are apt to generate a gap when they are overlapped with each other, and three steel plates, which are thin plates such as the floor panel 91, are welded by spot welding. As shown, by increasing the pressure applied to the electrode tips 26 and 27 to deform the three steel plates and to close the gap S between the thick plates, a current path is formed at a portion where the steel plates are in contact with each other, and the steel plates are connected to each other. The method of welding is generally adopted.

[0006]

However, as shown in FIG. 9, the ratio of the total thickness a of the floor panel 91, the member 92 and the reinforcement 93 to the thickness b of the floor panel 91 is 4.5 times or less. In this case, spot welding that achieves a predetermined strength is possible even with the method described above, but if the plate thickness ratio exceeds 4.5 times, spot welding that achieves a predetermined welding strength will be achieved by the method described above. There is a problem that you can not.

Therefore, in such a case, as shown in FIG. 10, for example, both side portions 93a of the reinforcement 93 sandwiched between the floor panel 91 and the member 92 are formed to be expanded, and the enlarged both side portions are formed. After welding the reinforcement 93 having the 93a and the member 92, the side portions 93a of the welded reinforcement 93 and the floor panel 91 are welded to separate the welded portions of the steel plates from each other to form the welded portion Pa. , Pb are used for welding.

However, according to such a method for separating the welded portions, since both side portions 93a of the reinforcement 93 have to be formed to be expanded, there is a new problem that the weight is increased, and the welded portions are The increase in cost also raises the problem of higher costs.

Here, when the inventors of the present invention analyzed the case where the plate thickness ratio exceeds 4.5 times, it was found that the following phenomenon occurred. That is, FIG. 8 (C)
As shown in, when the gap (S) between the member (thick plate) 92 and the reinforcement (thick plate) 93 is filled by pressure and welded, the steel plate (the floor panel 91, the member 92 and the reinforcement 93) is applied with a high pressure. When is deformed, as shown in FIG. 11 (A), the contact area between the upper electrode tip 26 and the floor panel (thin plate) 91 superimposed on the reinforcement (thick plate) 93 increases. Therefore, since the current paths (α in the ellipse in the figure) of the welding current flowing from the upper electrode tip 26 to the floor panel (thin plate) 91 are dispersed, the current density is reduced, so that the floor panel (thin plate) 91 is reduced. The heat generated between this and the reinforcement (thick plate) 93 located inside the floor panel (thin plate) 91 is reduced, and a nugget is not formed.

On the other hand, the member (thick plate) 92 and the reinforcement (thick plate) 93 are in point contact with each other due to the deformation of the steel plate due to the high pressure applied to close the gap S. As a result, the current paths are narrowed down and concentrated (β in the ellipse in the figure), and the current density is increased, so that heat generation between the member (thick plate) 92 and the reinforcement (thick plate) 93 is increased, and the nugget is increased. N is formed.

That is, first, the nugget N is formed between the member (thick plate) 92 and the reinforcement (thick plate) 93. The nugget N expands as the energizing time elapses, but when it grows to a certain size, the molten metal becomes spatter D, as shown in FIG. 11 (B), and the steel sheet (member 92, reinforcement). 93) It jumps out from the gap S between them. Therefore, since the growth of the nugget N is hindered, the nugget N does not spread to the floor panel (thin plate) 91 and the floor panel (thin plate) 91 is not spread.
It has been found that the reinforcement and the thick plate 93 cannot be welded.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a thin plate member to be welded on at least one of two superposed plate members to be welded. It is another object of the present invention to provide a spot welding method capable of obtaining a predetermined welding strength even if the ratio of the total plate thickness to the plate thickness of a thin plate is large when these members to be welded are overlapped and spot welded.

[0013]

In order to achieve the above-mentioned object, in the spot welding method according to the first aspect of the present invention, a thin plate is formed on at least one of two superposed thick plate members to be welded. Is a spot welding method of spot-welding these members to be welded by further superposing the members to be welded, sandwiching them with a pair of electrodes and energizing them with pressure, and welding to the members to be welded of the thin plate. In the part, a seating surface that is one step higher than the general part is formed, and among the pair of electrodes, the electrode facing the member to be welded of the thin plate has a tip formed into a spherical surface, and at the initial stage of welding, the thin plate is applied with a low pressing force. The welded member of the thin plate and the welded member of the thick plate adjacent thereto are welded so as to crush the seat surface of the welded member of No. 2, and then the two welded members of the two thick plates are subjected to high pressure. The technology of welding And it features.

According to the first aspect of the present invention, the thin plate member to be welded, which is superposed on at least one of the two plate members to be welded, is provided with a seat surface partially higher than the general portion at a portion to be welded. Of the pair of electrodes, the electrode facing the thin plate member to be welded has a tip formed into a spherical surface. Then, in the initial stage of welding, the seat surface of the thin plate welded member is crushed with a low pressurizing force, and the thin plate welded member and the adjacent thick plate welded member are welded, and then the high pressurizing force is applied. Two
Weld members to be welded of a single thick plate. As a result, at the initial stage of welding, the seat surface of the thin plate is crushed with a low pressure to deform the seat surface formed one step higher than the general portion into a spherical shape. It is possible to make point-to-point contact with the member to be welded. Therefore, between the thin plate welded member and the adjacent thick plate welded member, a current path narrowed in a dot shape is formed by the spherically deformed seat surface. The current density of the flowing welding current can be increased, and the welding current flowing through such an energizing path causes a melt between the thin plate welded member and the adjacent thick plate welded member, that is, a nugget is formed. be able to. After that, by applying a pressing force (high pressing force) higher than the pressing force of crushing the seat surface, the gap between the members to be welded of the two thick plates is closed and the members to be welded of the two thick plates are closed. An energization path can be formed between them. As a result, a nugget can be formed between the members to be welded, which are two thick plates, by the welding current flowing in such an energization path. Therefore, in the case where a thin plate member to be welded is further overlapped on at least one of the two thick plate members to be welded and spot welding is performed on these members to be welded,
Even if the ratio of the thin plate to the thick plate is large, a predetermined welding strength can be secured.

The spot welding method according to claim 2 is the spot welding method according to claim 1, wherein the seat surface is circular and the diameter thereof is 1 to 3 times the diameter of the electrode. Characterize.

According to the second aspect of the present invention, the seating surface partially formed higher than the general portion is circular, and its diameter is 1 to 3 times the diameter of the electrode. As a result, since the seat surface is circular, it is possible to easily form spherical deformation by the tip spherical surface of the electrode. Further, since the diameter of the seat surface is set to be 1 times the diameter of the electrode at a minimum, even if the positions of the electrode and the seat surface are slightly varied, the seat surface can be deformed into a spherical shape by the tip spherical surface of the electrode. Further, since the diameter of the seat surface is set to three times the diameter of the electrode at the maximum, the seat surface can be partially deformed into a spherical shape without the entire seat surface being gently bent.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the spot welding method of the present invention will be described below with reference to the drawings. FIG. 1 shows a welding apparatus 20 to which the spot welding method according to the present invention is applied and thin plates Wa, thick plates Wb, Wc which are members to be welded.
Is shown. First, the configuration of the welding device 20 will be described with reference to FIG.

The welding device 20 includes a pair of electrodes, electrode tips 26 and 27, a cylinder 24 that supports one electrode tip 26 and that can pressurize a member to be welded by the electrode tips 26 and 27. The pressure switch device 25 that can switch the pressure by adjusting the pressure of the air supplied to the cinder 24, the welding transformer T that can supply the welding current to the electrode tips 26, 27, and the electrode tips 26, 27 are supplied. Welding current controller CONT that can arbitrarily control welding current
It consists of

The pair of electrode tips 26 and 27 are positioned so as to face each other with a predetermined space therebetween, one electrode tip 26 is movably supported by the cylinder 24, and the other electrode tip 27 is fixed. Has been done. The tip portions 26a and 27a of the electrode tips 26 and 27 are formed into spherical surfaces (see FIG. 2A).

The cylinder 24 has a movable portion that can be moved in the direction of the other electrode tip 27 by the pressurized air, and one electrode tip 26 can be supported by this movable portion. As a result, when the movable portion is moved by the pressurized air supplied from the air source, the electrode tip 26 is moved to the electrode tip 27.
Can be moved in any direction. In the present embodiment, the pressurized air of, for example, about 3500 N is supplied to the cylinder 24 from the air source via the pressing force switching device 25.
6 and 27, a thin plate Wa and a thick plate W positioned between them.
b and Wc can be pressurized.

The pressurizing force switching device 25 is interposed between the air source and the cylinder 24, and is configured to switch the pressurized air supplied from the air source to, for example, a predetermined pressure in two stages. In the present embodiment, at the initial stage of welding, control is performed so that pressurized air with a low pressure is applied to the cylinder 24, and thereafter,
Control is performed so that pressurized air with a high pressure is applied. As a result, the cylinder 24 is thin plate W with a low pressure in the initial stage of welding.
a, the thick plates Wb, Wc can be pressed, and thereafter, the thin plates Wa, thick plates Wb, Wc can be pressed with a high pressure.

The welding current control device CONT is interposed between the welding power source and the welding transformer T, and, for example, in synchronization with a change in the pressing force of the pressing force switching device 25, the pair of electrode tips 26 and 27 are connected to each other. It is configured so that the value of the welding current supplied can be controlled. In the present embodiment, at the initial stage of welding, a low welding current of 9 kA, for example, is applied to the electrode tips 26, 27.
And a high welding current of, for example, 12 kA is controlled to be supplied to the electrode tips 26 and 27 during high pressure thereafter.

By constructing the welding device 20 in this way, a steel plate (a thin plate W) is formed between the pair of electrode tips 26, 27.
a, thick plates Wb, Wc) can be sandwiched between them for energization under pressure, so that a welding current can flow between both electrode tips 26, 27.

Next, the construction of the thin plate Wa which is further superposed on one of the two superposed thick plate members to be welded will be described with reference to FIG. As shown in FIG. 2, the thin plate Wa pressed by the electrode tip 26 is partially formed with a convex portion 30 having a seating surface 30 a that is one step higher than the general portion 35, and the configuration of the convex portion 30. Is shown in Fig. 2 (B) and Fig. 2
It is shown in (C). As shown in FIG. 2 (B) and FIG. 2 (C), the convex portion 30 formed on the thin plate Wa is formed in a hollow truncated cone shape, and has a circular seat surface 30a at the top thereof. .

That is, the convex portion 30 is the general portion 35 of the thin plate Wa.
It is configured to have a seating surface 30a formed as a circular flat surface at the top through a tapered portion 30b formed so as to rise while decreasing its diameter. Since the seat surface 30a located at the top is thus formed in a circular shape, the seat surface 30a can be easily deformed into a spherical shape by the tip portion 26a of the electrode tip 26, as described later.

Specifically, the convex portion 30 is formed by pressing the thin plate Wa, for example, the seat surface 30a.
When the seat surface diameter D1 which is the diameter of the seat is set to 22 mm, the projection diameter D2 which is the diameter of the projection 30 is set to 28 mm, and the seat surface height H which is the height from the general portion 35 to the seat surface 30a is set. Is set to 1 mm.

Further, the seat surface diameter D1 of the seat surface 30a as described above.
Is set in a range of 1 to 3 times the tip diameter D0 of the electrode tip 26 (electrode tip 27) described above.

That is, in the case of this embodiment, the tip diameter D0 is 1
Since the length is 6 mm, the seat surface diameter D1 is set between 16 mm, which is one time the value, and 48 mm, which is three times the value. As a result, the seat surface diameter D1 is at least the tip diameter D of the electrode tip 26.
Since it is set to 0 and 1 times, that is, the same, the seat surface 30a can be deformed into a spherical shape by the spherical surface of the tip end portion 26a of the electrode tip 26 even if the positions of the electrode tip 26 and the seat surface 30a are slightly varied. . Further, since the seat surface diameter D1 is set to be three times as large as the tip diameter D0 of the electrode tip 26 at the maximum, the seat surface 30a does not flex gently as a whole.
Can be partially deformed into a spherical shape.

Next, each step of spot welding performed by this spot welding method will be described with reference to FIGS. Here, FIG. 3 shows the welding of the thin plate Wa and the thick plate Wb, FIG. 4 shows the state of the thin plate Wa, the thick plates Wb and Wc at the initial stage of welding, and FIG. 5 shows the thin plate Wa and the thick plate after the initial stage of welding. Wb, W
The state of c is shown. Further, FIG. 6 shows a pressurization pattern and an energization pattern by the welding device 20, and FIG. 7 shows an example of a floor portion of a vehicle welded by the spot welding method. First, with reference to FIG. 3, welding of the thin plate Wa and the thick plate Wb adjacent thereto will be described.

As shown in FIG. 3A, the convex portion 3 of the thin plate Wa is
The electrode tips 26 and 27 are moved and positioned so that they are located above 0. Next, as shown in FIG. 6 (A),
During the five cycles from the start of energization, the pressurizing force switching device 25 supplies the cylinder 24 with pressurized air having a low pressurizing force of about 490N. As a result, the electrode tip 26 is pushed down in the direction of the seat surface 30a of the convex portion 30, and the electrode tip 26
As a result, the seat surface 30a is crushed in the direction of the thick plate Wb (see FIG. 3 (B)). After that, the seat surface 30a is thick plate W
At the same time as contacting b, as shown in FIG. 6 (B), 9 kA
Welding current is supplied between the electrode tips 26 and 27. Here, one cycle refers to the reciprocal of the frequency of the commercial AC power, specifically, 1/60 second or 1/50 second.

That is, as shown in FIG. 3 (B), the presence of the projection 30 causes the cylinder 24 to add the space K formed between the thin plate Wa and the thick plate Wb. The pressed electrode tip 26 crushes the seat surface 30a of the convex portion 30. At this time, the tip portion 26a of the electrode tip 26
Has a spherical surface as described above, the seat surface 30
a is deformed into a spherical shape similar to that of the tip portion 26a,
It is crushed toward the thick plate Wb side. As a result, a recess having a spherical recess is formed on the seat surface 30a, and thus a contact surface 30c that projects spherically toward the thick plate Wb is formed on the back side of the seat surface 30a.

Then, as pressure is further applied by the cylinder 24, as shown in FIG. 3 (C), the top of the spherical contact surface 30c formed on the back side of the seat surface 30a becomes the thick plate Wb. Contact. That is, the most protruding portion of the contact surface 30c is earlier than the other portion of the thick plate Wb.
Contact in a dotted manner.

In such a state, as shown in FIG. 4 (A), the welding current applied between the thin plate Wa and the thick plates Wb, Wc is applied between the electrode tip 26 and the thin plate Wa and the thick plate Wb. It flows to the thick plate Wb through a certain point contact portion 30d. However, since there is a gap S between the thick plate Wb and the thick plate Wc,
As shown by the arrow in FIG. 4 (A), such a welding current largely diverges in the surface directions of the thick plate Wb and the thick plate Wc, flows from the thick plate Wb to the thick plate Wc, and the electrode tip 2
To 7.

Since the gap S exists between the thick plates Wb and Wc in this manner, it is not possible to form a current-carrying path for increasing the current density at the shortest distance in the plate thickness direction between the thick plates Wb and Wc. A nugget cannot be formed between these thick plates Wb and Wc. On the other hand, as shown in FIG. 4 (B), between the thin plate Wa and the thick plate Wb, an energization path that is narrowed in a point manner in the point contact portion 30d, that is, an energization path with a large contact resistance is formed. Therefore, since the current density can be increased by such a narrowed energizing path, the resistance heating value is increased by the welding current flowing through the energizing path, and the nugget Na is formed between the thin plate Wa and the thick plate Wb. can do.

As described above, after welding the thin plate Wa and the thick plate Wb adjacent thereto (shown in FIG. 6 (A), after 5 cycles from the start of energization), as shown in FIG. 5 (A). , The thin plate Wa and the thick plates Wb and Wc are pressurized with a high pressure of about 3430 N by further increasing the pressure applied by the cylinder 24, and a welding current of 12 kA is applied in synchronization with the increase of the pressure (FIG. 6). (See (B)). Thereby, the thick plate Wb,
Since the gap S between Wc is filled with the electrode chips 26 and 27, the thick plate Wb and the thick plate Wc are in point contact with each other. The arrow shown in FIG. 5 (A) indicates the electrode tip 26,
27 shows the pressing direction by 27.

That is, as shown in FIG. 5 (B), the thin plate Wa and the thick plates Wb, Wc are pressed by a high pressing force to sufficiently close the gap S generated between the thick plates Wb, Wc. As a result, an energization path having a large contact resistance is formed in the pressurizing section. Therefore, the nugget Nb can be formed between the thick plates Wb and Wc by the welding current flowing through the energization path.

As described above, by forming the nugget Na between the thin plate Wa and the thick plate Wb, and subsequently forming the nugget Nb between the thick plates Wb and Wc, the two superposed thicknesses are formed. The spot welding of the three steel plates in which the thin plate Wa is further laid on one of the plates Wb and Wc is completed.

As described above, by performing welding using the spot welding method of the present invention, for example, as shown in FIG. 7, a floor panel 71 constituting a floor portion of a vehicle,
Even in the case of spot welding three steel plates such as the member 72 and the reinforcement 73, it is possible to secure a predetermined welding strength in the welded portion P. As a result, unlike the conventional spot welding method as shown in FIG. 10, it is not necessary to expand both side portions 93a of the reinforcement 93 to separate the welding portion into two welding portions Pa and Pb. Can be welded at one place. Therefore,
Since it is not necessary to enlarge both side portions 73a of the reinforcement 73, it is possible to suppress an increase in weight and also to prevent an increase in cost due to an increase in welding points.

As described above, according to the spot welding method according to the present embodiment, the thin plate Wa superposed on one of the two thick plates Wb and Wc has a part to be welded rather than a general part. While forming a raised seat surface 30a,
Of the pair of electrode tips 26, 27, the electrode tip 26 facing the thin plate Wa has a tip 26a formed into a spherical surface. Then, in the initial stage of welding, the seat surface 30a of the thin plate Wa is crushed with a low pressure so that the thin plate Wa and the thick plate W adjacent thereto are crushed.
Welded with b, and then two thick plates Wb, W with high pressure.
Weld c together.

As a result, in the initial stage of welding, the thin plate W
By crushing the seat surface 30a of a with low pressure, the general portion 3
Since the seat surface 30a formed one step higher than 5 is deformed into a spherical shape, the seat surface 30a deformed into this spherical shape is formed into a thin plate Wa.
It is possible to make point-to-point contact with the adjacent thick plate Wb. Therefore, the thin plate Wa and the thick plate W adjacent to the thin plate Wa
A current path narrowed in a dot shape is formed by the seat surface 30a that is deformed into a spherical shape, and the current density of the welding current flowing through this current path can be increased. The welding current flowing through the path allows the thin plate Wa and the adjacent thick plate Wb to be melted, that is, to form the nugget Na. After that,
By applying a pressing force (high pressing force) higher than the pressing force that crushes the seat surface 30a, it is possible to close the gap S between the two thick plates Wb, Wc, and thus the two thick plates Wb, W
An energization path can be formed between c. As a result, the welding current flowing through such an energization path causes
A nugget Nb can be formed between the two thick plates Wb and Wc. Therefore, the thin plate Wa is further stacked on one of the two stacked thick plates Wb and Wc.
It is possible to spot-weld one steel plate.

Specifically, for example, when the ratio of the total plate thickness a of the three steel plates to the plate thickness b of the thin plate Wa exceeds 4.5 times, the energization time is 5 cycles from the start of energization. By crushing the seat surface 30a of the thin plate Wa with a low pressure of 490 N and passing a welding current of 9 kA, a nugget Na can be formed between the thin plate Wa and the thick plate Wb adjacent thereto. After the energization time has passed 5 cycles from the start of energization, a high pressing force of 3430 N is applied and a welding current of 12 kA is caused to flow in synchronism with this pressing force, so that between the two thick plates Wb and Wc. Nugget N
b can be formed. Therefore, even if the plate thickness ratio exceeds 4.5 times, spot welding of three steel plates in which a thin plate Wa is further stacked on one of the two stacked thick plates Wb and Wc can be performed. it can.

Further, according to the spot welding method according to the present embodiment, the seat surface 30a has a circular shape, and the seat surface diameter D1 thereof.
Is 1 to 3 times the tip diameter D0 of the electrode tip 26. Accordingly, since the seat surface 30a is circular, it is possible to easily form a spherical deformation of the tip end portion 26a of the electrode tip 26 due to the spherical surface. Further, since the seat surface diameter D1 is set to be at least one time the tip diameter D0 of the electrode tip 26 at a minimum,
Even if the positions of the electrode tip 26 and the seat surface 30a vary to some extent, the spherical surface of the tip portion 26a of the electrode tip 26 causes the seat surface 30a.
Can be deformed into a spherical shape, and since the seat surface diameter D1 is set to be three times the tip diameter D0 of the electrode tip 26 at the maximum, the seat surface 30a does not flex gently as a whole.
0a can be partially deformed into a spherical shape.

In this embodiment, spot welding of three steel plates in which a thin plate Wa is further stacked on one of the two stacked thick plates Wb and Wc has been described, but the present invention is not limited to this. For example, if a thin plate is superposed on both of the two superposed thick plates, 4
Even spot welding of one steel plate can be applied, and the same effect as described above can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a welding device to which a spot welding method according to an embodiment of the present invention is applied.

FIG. 2 (A) is a side view of the tip of an electrode tip used in the spot welding method of the present embodiment, and FIG. 2 (B) is a seat surface formed on a steel plate used in the spot welding method. A plan view and FIG. 2C are side views of the seat surface shown in FIG. 2B.

FIG. 3 is an explanatory view showing a welding process by the spot welding method of the present embodiment, FIG. 3 (A) is a seat surface before being deformed by pressurization of the electrode tip, and FIG. FIG. 3 (C) shows the bearing surface in the middle of deformation by pressure, and the initial stage of nugget formation by welding current application.

FIG. 4 (A) is an explanatory view showing a welding process (initial welding) by the spot welding method of the present embodiment, and FIG.
4 is an enlarged view of FIG. 4 (A).

5 (A) is an explanatory view showing a welding process by the spot welding method of the present embodiment, and FIG. 5 (B) is an enlarged view of FIG. 5 (A).

FIG. 6 (A) is an explanatory diagram showing a pressure pattern in the spot welding method of the present embodiment, and FIG. 6 (B) shows a welding current conduction pattern in the spot welding method of the present embodiment. FIG.

FIG. 7 is a sectional view of a floor portion of a vehicle welded by the spot welding method according to the present embodiment.

8 (A) is a perspective view of three steel plates before spot welding, FIG. 8 (B) is a cross-sectional view of FIG. 8 (A), and FIG.
[Fig. 4] is an explanatory view showing a welding method for three steel plates by a conventional spot welding method.

FIG. 9 is an explanatory diagram showing a ratio of the total thickness of the floor panel (thin plate), the member (thick plate) and the reinforcement (thick plate) to the plate thickness of the floor panel (thin plate).

FIG. 10 is a cross-sectional view of a floor portion of a vehicle welded by a conventional spot welding method.

FIG. 11 (A) is an explanatory view showing a current path flowing through the steel plates when welding three steel plates by a conventional spot welding method, and FIG. 3] is an explanatory view showing a welding state in FIG.

[Explanation of symbols]

20 Welding equipment 24 cylinders 25 Pressure switching device 26, 27 electrode chip (pair of electrodes) 26a, 27a Tip (tip) 30 convex 30a seat surface 35 General Department 71, 91 floor panel 72, 92 members 73, 93 Reinforce Wa thin plate Wb, Wc thick plate D0 tip diameter (electrode diameter) D1 seat surface diameter (seat surface diameter) D2 convex part diameter H seat height N, Na, Nb Nuggets S gap P Welding site (site to be welded) Pa, Pb Welding point

Claims (2)

[Claims] 1. A thin plate member to be welded is further overlapped on at least one of the two thick plate members to be welded, and these members are sandwiched by a pair of electrodes to be energized under pressure so that these members to be welded are formed. A spot welding method for spot welding, wherein a member to be welded of the thin plate is partially formed with a seat surface that is one step higher than a general portion at a portion to be welded, and the thin plate of the pair of electrodes is to be welded. The electrode facing the member has a spherical tip, and at the initial stage of welding, the seat surface of the thin plate member to be welded is crushed with a low pressure so that the thin plate member to be welded and the adjacent thick plate to be welded A spot welding method, comprising: welding a member to each other, and then welding two thick plate members to be welded together with a high pressure. 2. The spot welding method according to claim 1, wherein the seating surface is circular and the diameter thereof is 1 to 3 times the diameter of the electrode.