JP7155903B2 - Electrode for resistance spot welding and method for manufacturing resistance spot welding joint - Google Patents

Description

The present invention relates to an electrode for resistance spot welding and a method of manufacturing a resistance spot welded joint.

In resistance spot welding using metal plates such as galvanized steel sheets, welding electrodes made of metal with high thermal conductivity and configured so that cooling water circulates inside from the point of continuous welding. is used. By using such an electrode, the temperature rise of the metal plate and the electrode during welding is suppressed.

Further, among such electrodes, from the viewpoint of efficiently cooling the electrode and the object to be welded, there is known an electrode configured so that cooling water can be supplied to the surface of the electrode.
For example, Patent Literature 1 discloses a spot welding apparatus configured to supply a small amount of cooling water to the tip surface by providing a water flow hole opening in the tip surface of the electrode tip. According to the spot welding apparatus disclosed in Patent Document 1, the electrode tip is efficiently cooled, and the heat of fusion can be efficiently removed from the object to be welded. It is said that it can be done.

Japanese Utility Model Laid-Open No. 2-138081

However, as in the spot welding apparatus disclosed in this Patent Document 1, if the holes are only formed at the tip of the electrode, the holes are blocked when a plurality of metal plates are sandwiched between the pair of electrodes. Furthermore, since the cooling water in the vicinity of the metal plate evaporates due to the heat generated by the energization, the water vapor cannot escape to the outside and may stay in the above-mentioned holes or flow back through the holes.
In this way, if the cooling water or water vapor generated from the cooling water stays in the hole or flows backward in the hole, the cooling water becomes less likely to come into contact with the metal plate being welded. It becomes difficult to obtain the desired effect.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a resistance spot welding electrode capable of sufficiently cooling a metal plate being welded, and a method of manufacturing a resistance spot welded joint using the same.

One aspect (aspect 1) of the present invention is a resistance spot welding electrode used for welding a plurality of overlapping metal plates,
a through-hole for supplying cooling water to the tip surface of the electrode; and discharge means consisting of a groove or a hole for discharging the cooling water or steam generated from the cooling water from the tip surface of the electrode to the outside. Further, it is the electrode for resistance spot welding.

The electrode for resistance spot welding of this aspect 1 is provided with the above discharge means, so that cooling water supplied to the electrode tip surface during welding or water vapor generated from the cooling water is discharged from the electrode tip surface to the outside. can be made easier.
As a result, the electrode for resistance spot welding of this aspect 1 is less likely to cause cooling water or water vapor to remain in the through-hole during welding, or to flow backward in the through-hole, and the metal plate being welded. Since fresh cooling water can always be continuously supplied to the metal plate being welded, the metal plate can be sufficiently cooled.
When the metal plate being welded is sufficiently cooled in this way, it is difficult for the martensitic structure to form on the metal plate surface, and hardening is difficult, so the metal plate tends to deform when the joint is processed after welding. Also, there is an advantage that surface cracks of the metal plate are less likely to occur.

In another aspect (aspect 2) of the present invention, in the resistance spot welding electrode of aspect 1, the resistance spot welding electrode has one or more through-holes, and the breakage of the through-holes is The total area is 0.2 mm ² or more.

In still another aspect (aspect 3) of the present invention, in the resistance spot welding electrode according to aspect 1 or 2, the shape of the contact portion with the metal plate of the electrode tip surface surrounds the through hole and is zero. It is an annular shape with a width of 0.2 mm to 2.5 mm.

In still another aspect (aspect 4) of the present invention, in the resistance spot welding electrode according to any one of aspects 1 to 3, the discharge means comprises the groove having a depth of 0.5 mm or more or the groove having a depth of 0.5 mm or more. said hole having a diameter of .

In still another aspect (aspect 5) of the present invention, in the resistance spot welding electrode according to any one of aspects 1 to 4, the discharge means consists of two or more of the grooves or two or more of the holes. .

In still another aspect (aspect 6) of the present invention, in the resistance spot welding electrode of aspect 5, the two or more grooves or the two or more holes are symmetrical about the through hole. are placed in different positions.

In still another aspect (aspect 7) of the present invention, in the resistance spot welding electrode according to any one of aspects 1 to 6, the resistance spot welding electrode extends outward from the opening peripheral edge of the through hole. and a recess in communication with said discharge means.

In still another aspect (aspect 8) of the present invention, in the resistance spot welding electrode according to aspect 7, the opening area of the recess on the electrode tip side is 50% or more of the area of the electrode tip surface.

Further, still another aspect (aspect 9) of the present invention is a method for manufacturing a resistance spot welded joint, comprising a step of sandwiching a plurality of superimposed metal plates between a pair of electrodes and energizing the joint,
The manufacturing method, wherein the electrode for resistance spot welding according to any one of aspects 1 to 8 is used as at least one of the pair of electrodes.

Still another aspect (aspect 10) of the present invention is the manufacturing method according to aspect 9, wherein the plurality of metal plates includes at least one plated steel plate,
The at least one electrode is arranged so as to be in contact with the plated steel sheet when the plurality of metal sheets are energized.

In still another aspect (aspect 11) of the present invention, in the production method of aspect 9 or 10, the flow rate of the cooling water is 3 L/min or more.

ADVANTAGE OF THE INVENTION According to this invention, the metal plate during welding can be fully cooled.

FIG. 1 is a cross-sectional view for explaining how a resistance spot welding electrode 1 according to one embodiment of the present invention is used. FIG. 2 is a perspective view of the resistance spot welding electrode 1 shown in FIG. FIG. 3 is a top view of the resistance spot welding electrode 1 shown in FIG. 2 as viewed from the tip side. FIG. 4 is a front view of the resistance spot welding electrode 1 viewed in the direction of arrow IV shown in FIG. FIG. 5 is a front view of a resistance spot welding electrode 10 according to another embodiment of the invention. FIG. 6 is a front view of a resistance spot welding electrode 1' according to yet another embodiment of the present invention. FIG. 7 is a front view of a resistance spot welding electrode 1'' used in an embodiment of the present invention. FIG. 8(a) is a view showing measurement positions of hardness distribution of a resistance spot welded joint obtained in an example of the present invention, and FIGS. 8(b) and (c) are examples of the present invention. 2 is a hardness distribution diagram in the horizontal direction and plate thickness direction of the resistance spot welded joint obtained in .

BEST MODE FOR CARRYING OUT THE INVENTION A preferred embodiment of a resistance spot welding electrode and a method for manufacturing a resistance spot welded joint of the present invention will be described in detail below with reference to the drawings.

<Electrodes for resistance spot welding>
A resistance spot welding electrode 1 according to one embodiment of the present invention, as shown in FIG. used as an electrode for In addition, in the present embodiment shown in FIG. 1, an ordinary resistance spot welding electrode 2 is used as the upper electrode.

As shown in FIGS. ₁ to 4, the resistance spot welding electrode ₁ of the present embodiment communicates with the electrode tip surface S1 from the inside of the electrode for supplying cooling water _CW to the electrode tip surface S1. and _four grooves ₁₂ formed in the electrode tip surface S1 for discharging the cooling water _CW or water vapor generated from the cooling water _CW to the outside from the electrode tip surface S1, and a discharge means 14 whose end communicates with the through-hole 11; a recessed portion 15 extending outward from the peripheral edge of the opening of the through-hole ₁₁ in the electrode tip surface S1 and communicating with the discharge means 14; It has

Since the electrode 1 for resistance spot welding of this embodiment has a specific structure provided with the through hole 11 and the discharge means 14, the discharge means ₁₄ supplies the electrode tip surface S1 during welding. _The cooled water _CW or water vapor generated from the cooled water _CW can be easily discharged to the outside from the electrode tip surface S1.
As a result, the resistance spot welding electrode 1 prevents the cooling water _CW and water vapor from staying in the through-hole 11 or flowing back in the through-hole 11 during welding. Since fresh cooling water _CW can always be supplied to the plate, the metal plate being welded can be sufficiently cooled.

The electrode 1 for resistance spot welding of this embodiment, as shown in FIGS. It has the same structure as the electrode.
Further, in the present invention, the structure of the resistance spot welding electrode is not limited to such an embodiment, and may be provided with a through hole and discharge means as described later. It may or may not have it.

Hereinafter, a specific structure of the resistance spot welding electrode of the present invention will be described in detail using the resistance spot welding electrode 1 of the above-described embodiment.

[Through hole]
In the above-described embodiment, as shown in FIGS. 1 and 4, the through-hole 11 extends _linearly along the central axis CL of the electrode 1 inside the resistance spot welding electrode ₁ , and extends along the electrode tip surface S1. It is formed so as to open on the side.
The through hole 11 functions as a flow path for discharging cooling water _CW supplied from an arbitrary cooling water supply device from _an opening on the electrode tip surface S1 _side and supplying it onto the electrode tip surface S1. When the cooling water supplied onto the electrode tip surface S1 through the through hole ₁₁ contacts the surface of the metal plate 3 being welded (specifically, the lower metal plate 31), , the metal plate 3 can be efficiently cooled.

In the present invention, the structure and arrangement of the through-holes are not limited to the structure and arrangement of the above-described embodiments as long as cooling water can be supplied to the tip surface of the electrode. It may extend linearly along the central axis, or may extend in a spiral or wavy form.

Moreover, the cross-sectional shape of the through-hole may have a circular cross-sectional shape as in the above-described embodiment, or may have a geometric shape such as a square shape. However, from the point of view of the cooling efficiency of the electrode, etc., the through-hole preferably has a circular cross-sectional shape.

Furthermore, the cross-sectional dimension of the through-hole is preferably such that the cross-sectional area of the through-hole is 0.2 mm ² or more from the viewpoint of the cooling efficiency of the electrode and the metal plate.
In addition, since the electrode for resistance spot welding of the present invention can have one or more through-holes, when the electrode has a plurality of through-holes, the total cross-sectional area of the plurality of through-holes is preferably 0.2 mm ² or more. In addition, the upper limit of the total cross-sectional area of the through-holes can be a predetermined value in consideration of the desired cooling efficiency and productivity. .
Here, the fact that the total cross-sectional area of the through-holes is 0.2 mm ² or more means that all cut points in the direction in which the electrodes extend (the cut points are cut in a direction perpendicular to the direction in which the electrodes extend) means that the total cross-sectional area of the through-holes is 0.2 mm ² or more.

Moreover, the upper limit of the diameter of one through-hole can adopt a predetermined value in consideration of the diameter of the tip of the electrode, current supply conditions, etc. For example, the diameter is ⅓ of the diameter of the tip of the electrode.
In this specification, the diameter of a through-hole means the diameter of a cross-sectional shape perpendicular to the direction in which the through-hole extends. When the cross-sectional shape of the through-hole is non-circular such as square, it means the diameter of a circle having an area equal to the cross-sectional area of the shape.

When two or more through-holes are provided, it is preferable to provide the through-holes at symmetrical positions with respect to the central axis of the electrode from the viewpoint of cooling efficiency.

[Ejection means]
In the above-described embodiment, as shown in FIGS. 2 to 4, the discharge means 14 are arranged at symmetrical positions with respect to the through hole 11 on the electrode tip surface S1 of the resistance spot welding electrode ₁ , and , four grooves 12 extending radially outward from the through hole 11 side. The four grooves 12 are arranged so as to communicate with the through holes 11 via the recesses 15 .

The discharging means 14 discharges the cooling water _CW supplied onto the electrode tip surface S1 through the through _- hole 11 during welding or the water vapor generated from the cooling water _CW through the recess 15 to the electrode tip surface. It functions as _a channel for discharging from S1 to the outside.
As described above, the resistance spot welding electrode 1 of the present embodiment is provided with such a discharge means 14, so that the cooling water _CW and water vapor remain in the through hole 11 during welding, and the through hole Since it is difficult for reverse flow to occur in 11 and fresh cooling water _CW can be continuously supplied to the metal plate being welded, the metal plate can be sufficiently cooled.

In the present invention, the discharge means for the resistance spot welding electrode is not limited to the groove portion as in the above-described embodiment, and may be formed by a hole portion as described later.

In the case where the discharge means consists of grooves, the structure and arrangement of the grooves are the same as those of the above-described embodiments as long as the cooling water and water vapor supplied to the electrode tip surface can be discharged to the outside from the electrode tip surface. The form is not limited. For example, the groove may extend outward from the through-hole side in a straight line or in a curved line, and the cross-sectional shape orthogonal to the extending direction of the groove may be quadrangular. However, it may be V-shaped (triangular) or U-shaped.

In addition, in the above-described embodiment, the four grooves 12 are arranged so as to indirectly communicate with the through holes 11 via the recesses 15, but the present invention is limited to such an aspect. Instead, for example, as in an embodiment to be described later, the discharge means may directly communicate with the through hole without providing a recess.
If cooling water or water vapor is likely to be discharged outside from the tip surface of the electrode depending on conditions such as the striking angle, the discharge means does not necessarily have to communicate with the through hole. Here, the striking angle means the angle between the central axis of the electrode and the plate surface of the metal plate when the electrode contacts the metal plate. Welding can also be done at other angles.

Moreover, as for the depth of the groove, a predetermined depth can be adopted in consideration of the efficiency of discharging cooling water and water vapor.
However, since the tip surface of the electrode enters the metal plate when the electrode presses the metal plate, the groove formed in the tip surface of the electrode should have a depth of 0.5 mm or more so as not to block the groove. It is preferable to have The upper limit of the depth of the groove can adopt a predetermined value in consideration of the shape of the tip of the electrode, the energization conditions, etc., and is, for example, 5 mm deep.
In this specification, the depth of the groove means the depth of the deepest part of the groove.

Furthermore, as for the width of the groove, a predetermined width (for example, a width of 0.5 mm or more) can be adopted in consideration of the efficiency of discharging cooling water and water vapor. In this specification, the width of the groove means the maximum length in the direction orthogonal to the extending direction of the groove and the extending direction of the electrode.

Regarding the number and arrangement position of the grooves, a predetermined number and arrangement position can be adopted in consideration of the discharge efficiency of the cooling water and water vapor. It is preferable to provide two or more grooves for one resistance spot welding electrode, and in order to make it more difficult for cooling water and water vapor to stagnate, the two or more grooves are symmetrical about the through hole. It is particularly preferable that each be arranged at a position where

As described above, in the present invention, the discharge means for the resistance spot welding electrode is not limited to grooves, and may be formed by holes.
Here, FIG. 5 is a front view of a resistance spot welding electrode 10 according to another embodiment of the present invention.

In this alternative embodiment, the resistance spot welding electrode 10 is similar to the resistance spot welding embodiment described above, except that the evacuation means are formed by four holes 13, as shown in FIG. It has the same configuration as the electrode 1 .
That is, the four holes 13 in the resistance spot welding electrode 10 are arranged at symmetrical positions with respect to the through hole ₁₁ on the electrode tip surface S1 in the same manner as the groove 12 described above, and the through hole It is provided so as to radially extend from the 11 side toward the outer side.

This hole portion 13 also allows the cooling water _CW supplied onto the electrode tip surface S1 through the through hole ₁₁ or water vapor generated from the cooling water _CW to pass through the recessed portion 15 during welding. It functions as _a flow path for discharging from the tip surface S1 to the outside.
Since the electrode 10 for resistance spot welding is provided with the discharge means composed of such a hole portion 13, it is possible to achieve the same effect as the discharge means 14 composed of the groove portion 12 described above. Even if the tip surface of the electrode enters the metal plate when pressurizing , the holes 13 are unlikely to be blocked, and there is an advantage that the function as the discharging means can be exhibited more reliably.

Even when the discharge means is formed of a hole, if the structure and arrangement of the hole can discharge the cooling water and water vapor supplied to the electrode tip surface to the outside from the electrode tip surface, the above embodiment can be applied. is not limited to the structure or arrangement of For example, similarly to the grooves described above, the holes may extend linearly or curvedly outward from the through-hole side. The orthogonal cross-sectional shape may be circular or polygonal.

Regarding the cross-sectional dimension of the hole, it is possible to adopt a predetermined cross-sectional dimension in consideration of the discharge efficiency of cooling water and water vapor. It preferably has a diameter of 5 mm or more. The upper limit of the diameter of the hole can adopt a predetermined value in consideration of the diameter of the tip of the electrode, current supply conditions, etc. For example, the diameter is ⅓ of the diameter of the tip of the electrode.
In this specification, the diameter of the hole means the diameter of the cross-sectional shape perpendicular to the extending direction of the hole. For example, when the cross-sectional shape of the hole is circular, the diameter of the circle is When the cross-sectional shape of the hole is non-circular such as square, it means the diameter of a circle having an area equal to the cross-sectional area of the shape.

Furthermore, with respect to the number and arrangement positions of the holes, it is possible to adopt a predetermined number and arrangement position in consideration of the discharge efficiency of the cooling water and water vapor. , It is preferable that two or more holes are provided for one resistance spot welding electrode, and in order to make it more difficult for cooling water and steam to stagnate, two or more holes form a through hole. It is particularly preferable that they are arranged at symmetrical positions about the center.

[Hollow part]
The electrode for resistance spot welding according to the present invention may have a recess extending outward from the peripheral edge of the opening of the through hole and communicating with the discharge means, as in each of the above-described embodiments.
For example, in the embodiments shown in FIGS. 1 to 4, the resistance spot welding electrode 1 extends outward from the opening peripheral edge of the through hole 11 on the electrode tip side while expanding in a substantially V shape. In addition, it has recesses 15 that communicate with the four grooves 12 that are the discharge means 14 .
The recessed portion 15 discharges the cooling water _CW supplied to the electrode tip surface S ₁ or water vapor generated from the cooling water _CW by the discharge means 14 to the outside, and a certain amount or more of the cooling water CW is always discharged in the electrode tip surface S ₁ . It functions as a liquid reservoir for securing cooling water. _The recessed portion 15 also has a function of adjusting the shape of the contact portion S2 with the metal plate _on the electrode tip surface S1.

In the present invention, it is not an essential feature that the resistance spot welding electrode extends outwardly from the opening peripheral edge of such a through hole and has a recess communicating with the discharge means, but the resistance spot welding electrode Welding electrodes preferably have such recesses.
When the electrode for resistance spot welding has such a recessed portion, cooling water and water vapor supplied to the electrode tip surface during welding are discharged to the outside by the discharge means, and a constant amount is always discharged on the electrode tip surface. Since it is possible to secure the above amount of cooling water, it is more difficult for the cooling water and water vapor to stay in the through-holes or flow back through the through-holes. There is an advantage that a wider contact area can be ensured and the surface of the metal plate at the welded portion can be cooled more efficiently.

In addition, when the electrode for resistance spot welding does not have such a recessed portion, the above-mentioned through-hole is opened at the tip surface of the electrode and communicates with the discharging means.
Here, FIG. 6 is a front view of a resistance spot welding electrode 1' according to still another embodiment of the present invention. In the embodiment shown in FIG. 6, since the resistance spot welding electrode ₁ ' does not have a recessed portion, the through hole ₁₁ is opened at the electrode tip surface S1 and formed in the electrode tip surface S1. It is configured to be in direct communication with an ejection means 14 consisting of four grooves 12 formed in a groove.

Also in such a resistance spot welding electrode ₁ ', the cooling water _CW and water vapor supplied to the electrode tip surface S1 during welding are removed by providing the discharge means 14 consisting of the four grooves 12. , it is possible to facilitate discharge to the outside from the electrode tip surface _S1 .
From the viewpoint of cooling efficiency, it is preferable that the diameter of the through-hole of the electrode not having such a recessed portion is larger than that of the electrode having the above-described recessed portion.

Moreover, in the present invention, the structure of the above-described recess is not limited to the structure of each of the above-described embodiments, as long as it does not hinder the effects of the present invention. For example, even if the recessed portion has a structure that extends outward from the opening peripheral portion of the through hole while expanding in a substantially V shape, the concave portion may be curved like an arc from the opening peripheral portion of the through hole. It may have a structure extending outward while expanding in diameter.
In addition, in the recessed portion, the structure of the portion that expands in diameter from the opening peripheral portion of the through-hole can adopt a structure that forms an angle of 90° or more and less than 180° with the central axis of the electrode. Here, the angle formed by the portion expanding from the opening peripheral portion of the through hole and the central axis of the electrode means the angle on the side opposite to the tip side of the electrode among the angles formed by these portions.

Further, in the present invention, it is preferable that the opening area of the recess on the electrode tip side is 50% or more of the area of the electrode tip surface. When the recessed portion is formed in this manner, the surface of the metal plate at the welded portion can be cooled more efficiently. The upper limit of the opening area of the recess on the tip side of the electrode can be a predetermined value in consideration of the shape of the tip of the electrode.
Furthermore, it is preferable that the recess has a structure capable of securing a water volume (mm ³ ) equal to the area of the electrode tip surface (mm ² )×1 (mm) within a depth of 5 mm from the tip of the electrode. When the recess has such a structure, the cooling water can be more stably secured on the electrode tip surface, so that the effects of the recess can be obtained more reliably.

[Electrode tip surface]
In this specification, the electrode tip surface of the resistance spot welding electrode is the surface that contacts the surface of the metal plate to be welded during welding, and the range defined by the outer edge of the portion that contacts the surface of the metal plate. means the inner surface.
Therefore, as in the embodiments shown in FIGS. 1 to 4, when the electrode tip surface is formed with grooves, depressions, or the like, the electrode tip surface has a portion that contacts the surface of the metal plate during welding, It has a portion that does not come into contact with the surface of the metal plate (that is, a portion in which grooves, depressions, etc. are formed).

In the present invention, the tip shape of the electrode for resistance spot welding is, for example, a dome radius type (DR type), a dome type (D type), a radius type (R type), etc. described in JIS C 9304: 1999. known shape can be adopted.

₁ to ₄ , the shape of the contact portion S2 with the metal plate on the electrode tip surface S1 is intermittently formed by four grooves 12, as shown in FIG. It also has an annular shape surrounding the through hole 11 .
In the present invention, the shape of the contact portion with the metal plate on the electrode tip surface of the resistance spot welding electrode is preferably an annular shape surrounding the through hole as in the above-described embodiment, and further, 0.2 mm to An annular shape with a width of 2.5 mm is particularly preferred. When the shape of the contact portion is an annular shape, the cooling water can be efficiently brought into contact with the surface of the metal plate at the welded portion, and the shape of the contact portion is an annular shape having the above-mentioned specific width. , the surface of the metal plate at the welded portion can be cooled more efficiently.

Note that the annular shape described above is not limited to a circle, and may be a triangle, a square, or more polygonal shape as long as the shape surrounds the through hole.
In addition, in the embodiment shown in FIGS. 1 to 4, since the discharge means 14 is formed by the groove portion ₁₂ , the contact portion S2 has an intermittent annular shape, but in the present invention The contact portion may have a continuous annular shape when the discharge means is formed by the above-described hole without being limited to such an embodiment.

In addition, since the electrode for resistance spot welding in the present invention directly water-cools a metal plate, that is, a direct water-cooled electrode, the material forming the electrode tip surface is not limited to a material with high thermal conductivity such as copper.

[Cooling water]
In the present invention, the cooling water used for resistance spot welding electrodes can be the same as the cooling water used for ordinary resistance spot welding electrodes.
Regarding the temperature and flow rate of the cooling water, the same conditions as those used for ordinary resistance spot welding electrodes can be adopted, but the flow rate of the cooling water must be 3 L/min or more. is preferably a flow rate of When the flow rate of the cooling water is such a flow rate, the surface of the metal plate to be welded can be cooled more stably and more efficiently.
In addition, the flow rate of the cooling water means the flow rate when the cooling water is flowed with the electrodes removed.

<Method for manufacturing resistance spot welded joint>
Next, a method for manufacturing a resistance spot welded joint according to the present invention using the above specific resistance spot welding electrode will be described in detail using the resistance spot welding electrode 1 of the embodiment shown in FIGS. 1 to 4. FIG.

In the method of manufacturing a resistance spot welded joint using the resistance spot welding electrode 1 of the above-described embodiment, as shown in FIG. 1 and a normal resistance spot welding electrode 2 located on the upper side to apply current (hereinafter sometimes referred to as "energization step").
In such an energization step, a pair of electrodes positioned above and below apply a predetermined pressure and current (energized current) to the two metal plates 3, thereby This is the step of melting the neighboring region to form a nugget. Through such steps, it is possible to obtain a resistance spot-welded joint in which the two overlapping metal plates 3 are firmly joined.

In this manufacturing method, since the specific resistance spot welding electrode 1 having the through hole 11 and the discharge means 14 is used as the lower electrode, the discharge means 14 of the resistance spot welding electrode 1 is used. Also, the cooling water _CW supplied to the electrode tip surface S1 during welding or water vapor _{generated from the cooling water CW can} be easily discharged to the outside from the electrode tip surface _S1 .
As a result, the present manufacturing method makes it difficult for the cooling water _CW or water vapor to remain in the through-hole 11 or flow back through the through-hole 11 during welding. Therefore, the metal plate can be sufficiently _cooled .

In addition, in the present invention, the electrode to which the electrode for resistance spot welding provided with the above specific through-hole and discharge means (hereinafter sometimes simply referred to as "specific electrode for resistance spot welding") is used during welding. Such specific resistance spot welding electrodes are not limited to aspects of the above-described embodiments (i.e., the lower electrode) as long as they can sufficiently cool the plurality of metal plates, and such specific resistance spot welding electrodes may include only the upper electrode or the lower electrode. It may be applied to the electrodes only or to both the upper and lower electrodes.
That is, the method for manufacturing a resistance spot welded joint of the present invention includes a mode in which both electrodes of a pair of electrodes used for welding are the above specific resistance spot welding electrodes, or one of the pair of electrodes used for welding. Includes embodiments in which only the electrode consists of the specific resistance spot welding electrode described above and the other electrode consists of a normal resistance spot welding electrode.

In addition, when the above specific resistance spot welding electrode is applied only to one of the pair of electrodes used for welding, the metal plate that comes into contact with the resistance spot welding electrode during welding, as well as the metal A metal plate adjacent to the plate can also be cooled.
On the other hand, when the specific electrodes for resistance spot welding are applied to both electrodes of the pair of electrodes used for welding, the plurality of metal plates can be cooled more reliably and efficiently from both sides.
When the metal plate being welded is cooled in this way, the martensite structure is less likely to form on the surface of the metal plate, that is, it is less likely to be hardened. There is an advantage that surface cracks of the metal plate are less likely to occur.

In the present invention, various welding conditions (e.g., energizing current, energizing time, electrode pressure, squeezing time, etc.) can adopt predetermined conditions in consideration of desired joint strength, productivity, and the like.

[Ordinary electrode for resistance spot welding]
In the method for manufacturing a resistance spot welded joint of the present invention, at least one of the pair of electrodes used for welding may be the specific electrode for resistance spot welding. A resistance spot welding electrode may be used, or a specific resistance spot welding electrode similar to the one electrode may be used.
In the present specification, ordinary resistance spot welding electrodes are not particularly limited as long as they are known electrodes that can be used for resistance spot welding other than the specific electrodes for resistance spot welding.

<Metal plate>
In the present invention, as the metal plate to be welded, a metal plate suitable for desired joint strength and the like can be used. Examples of such metal sheets include steel sheets having a tensile strength of 270 MPa to 2500 MPa class, and such steel sheets may be steel sheets plated with zinc or the like (that is, plated steel sheets).

When such a plated steel plate is used as the metal plate, it is possible to obtain a welded joint excellent in corrosion resistance and the like. Therefore, in the present invention, the plurality of metal plates preferably includes at least one plated steel plate.
Furthermore, when the plurality of metal plates includes a plated steel plate, the specific electrode for resistance spot welding is arranged so as to be in contact with the plated steel plate when energizing the plurality of metal plates (that is, a plurality of In a sheet of metal plate, it is preferable that the plated steel plate is overlapped so as to be in contact with the specific electrode for resistance spot welding.
In general, in resistance spot welding of multiple metal sheets, including plated steel sheets, during welding, the molten plated metal is affected by the tensile stress due to the pressure of the electrode and the thermal expansion or contraction of the base material. By penetrating into and lowering the grain boundary strength (so-called liquid metal embrittlement (LME)), surface cracks are likely to occur. Also in the resistance spot welding used, the metal plate can be sufficiently cooled, so a particularly advantageous effect can be exhibited.

In the present invention, the plurality of metal plates may be all metal plates of the same type, or only some of the metal plates may be of the same type. Different types of metal plates may be used.

Furthermore, as for the number of metal plates, two or more can be adopted depending on the application of the joint.

Further, in the present invention, as steps other than the above-described energization step, for example, there may be predetermined processing steps before and after the energization step.

The resistance spot welding electrode and the method for manufacturing a resistance spot welded joint of the present invention are not limited to the above-described embodiments and examples described later, and are within the scope of the present invention. , can be appropriately combined, substituted, changed, or the like.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited only to such Examples.

As the upper electrode, a normal resistance spot welding electrode (Cr—Cu DR type electrode, electrode diameter: 16 mm, electrode tip diameter (diameter): 6.0 mm, curvature radius near the electrode shaft: R8, electrode tip curvature Radius: R40), and as the lower electrode, resistance spot welding electrode 1 ″ of the present invention shown in FIG. A stationary spot welder was provided with R8).
The resistance spot welding electrode 1'' used in this example has the same structure as the resistance spot welding electrode 1 of the embodiment shown in FIGS. 1 to 4, except for the dimensions.

Furthermore, as a test material, prepare two galvanized steel sheets (plate thickness 1.6 mm) with a tensile strength of 590 MPa class, and after superimposing the two steel sheets to form a plate set, the plate set is Two steel plates were welded by sandwiching between upper and lower electrodes of a stationary spot welder and energizing them.
Welding conditions are as follows.
Electrode pressure: 1.96 kN
Squeeze time: 1 sec Energizing time: 0.36 sec Pressure holding time after energizing: 0.2 sec Energizing current: 9.5 kA

Regarding the resistance spot welded joint obtained in this way, when the surface of the steel plate in contact with the resistance spot welding electrode 1'' during welding was observed, no surface cracks were confirmed.

Here, FIG. 8(a) is a diagram showing the measurement positions of the hardness (Vickers hardness: HV) distribution of the resistance spot welded joint obtained in the example of the present invention, and FIG. 8(b) and ( c) are hardness distribution diagrams in the horizontal and through-thickness directions of the resistance spot-welded joint, respectively.
The specific measurement positions of the hardness distribution of the resistance spot welded joint shown in FIG. 8(a) are as follows.
(1) Horizontal hardness measurement position In the horizontal direction at a depth of 0.1 mm from the upper surface of the lower steel plate, each range of 7 mm in the horizontal + direction and 7 mm in the - direction with the center of the nugget as the base point , was measured at a pitch of 0.5 mm.
However, each range of 1 mm on the nugget side and 2 mm on the base material side from the vicinity of the boundary between the nugget and the base material was measured at a pitch of 0.25 mm.
(2) Hardness measurement position in the plate thickness direction In the plate thickness direction passing through the center of the nugget, the base point is a position 0.1 mm deep from the lower surface of the lower steel plate, and the hardness is measured upward at a pitch of 0.2 mm. It was measured.

As shown in FIG. 8(c), the upper steel plate that was in contact with the normal resistance spot welding electrode during welding has a high temperature (a temperature equal to or higher than the A1 transformation point) during welding, and is rapidly cooled after welding. As a result, martensite transformation occurs partially, and the steel becomes as hard as 280HV. On the other hand, the lower steel plate in contact with the resistance spot welding electrode 1'' during welding is sufficiently cooled during welding, and the steel plate temperature does not reach a high temperature exceeding the A1 transformation point. Therefore, the hardness was about 200 HV, which was almost the same as the hardness of the base material steel plate before welding.

According to the present invention, the metal plate being welded can be sufficiently cooled, and the metal plate after welding is less likely to harden. It can be applied to various structural parts that require strength.
Therefore, the electrode for resistance spot welding and the method for manufacturing a resistance spot welded joint of the present invention have high industrial applicability.

REFERENCE SIGNS LIST 1 resistance spot welding electrode 11 through hole 12 groove 13 hole 14 discharge means 15 depression 2 normal resistance spot welding electrode 3 multiple metal plates 31 lower metal plate 32 upper metal plate _CW cooling water S ₁ electrode tip surface S ₂ contact part

Claims (11)

A resistance spot welding electrode used for welding a plurality of overlapping metal plates,
A through hole for supplying cooling water to the electrode tip surface, and a groove for discharging the cooling water supplied to the electrode tip surface during welding or water vapor generated from the cooling water from the electrode tip surface to the outside. or discharge means consisting of a hole. The resistance spot welding electrode according to claim 1, wherein the resistance spot welding electrode has one or more through holes, and the total cross-sectional area of the through holes is 0.2 mm ² or more. 3. The resistance spot according to claim 1 or 2, wherein the electrode tip surface has an annular shape in which the shape of the contact portion with the metal plate surrounds the through hole and has a width of 0.2 mm to 2.5 mm. Welding electrodes. Resistance spot welding electrode according to any one of claims 1 to 3, wherein said discharge means consists of said groove having a depth of 0.5 mm or more or said hole having a diameter of 0.5 mm or more. The electrode for resistance spot welding according to any one of claims 1 to 4, wherein said discharge means consists of two or more of said grooves or two or more of said holes. The electrode for resistance spot welding according to claim 5, wherein the two or more groove portions or the two or more hole portions are arranged at symmetrical positions with respect to the through hole. The resistance spot according to any one of claims 1 to 6, wherein the resistance spot welding electrode has a recess extending outward from the opening peripheral edge of the through hole and communicating with the discharge means. Welding electrodes. 8. The electrode for resistance spot welding according to claim 7, wherein the recessed portion has an opening area on the electrode tip side that is 50% or more of the area of the electrode tip surface. A method for manufacturing a resistance spot welded joint, comprising a step of holding a plurality of overlapping metal plates between a pair of electrodes and energizing them,
The manufacturing method, wherein the electrode for resistance spot welding according to any one of claims 1 to 8 is used as at least one of the pair of electrodes. The plurality of metal plates includes at least one plated steel plate,
10. The manufacturing method according to claim 9, wherein said at least one electrode is arranged so as to come into contact with said plated steel sheet when energizing said plurality of metal sheets. The manufacturing method according to claim 9 or 10, wherein the cooling water has a flow rate of 3 L/min or more.

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