JPH0531586A - Resistance welding method for steel sheets - Google Patents

Abstract

PURPOSE:To furnish the resistance welding method capable of improving remarkably an electrode service life when steel sheets including a coated steel sheet coated with a coating material made of metal baser than a steel sheet in electric potential on one side or both sides are subjected to resistance welding or when such resistance welding and resistance welding of bare steel sheets without being coated are performed alternately or in combination by using the same welding machine. CONSTITUTION:In performing resistance welding as mentioned above, foil-like inclusions made of metal having the higher melting point than the electrodes or the coating material and having an energizing property are interposed between electrodes and the coating materials of the coated steel sheets to press the electrodes and pressurization and energizing are carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated steel sheet in which one or both of the steel sheets to be welded are coated with a coating material made of a metal whose potential is lower than that of the steel sheet by plating, laminating rolling, spraying or the like. The present invention relates to a resistance welding method for a steel plate suitable for a certain case, and a case where the welding of such steel plates and the welding of bare steel plates which are not covered are alternately or mixed and resistance welding is performed.

[0002]

2. Description of the Related Art Recently, in order to improve corrosion resistance, a steel sheet such as an automobile body sheet material is plated with a film of a metal which is less base than the steel sheet, such as Zn, Sn and alloys thereof, in order to improve corrosion resistance. Coated steel sheets coated by other means tend to be used frequently. Resistance welding is very efficient and suitable for mass production, and once the proper welding conditions are set, even unskilled people and robots can easily perform welding.
Since it is possible to stably form a weld nugget and obtain a joining strength, joining of steel sheets to each other in the case of including a coated steel sheet as described above is almost always by electric resistance welding.

In the conventional resistance welding of coated steel sheets, for example, as shown in FIG.
20. Metallic films 11, 12, 21, 22, which are base potential lower than 20
The coated parts of coated steel plates 1 and 2 each coated with plating are overlapped, and the tip of each is dressed (cutting into a predetermined shape or polishing to a predetermined surface roughness to adjust the tip ) The upper and lower electrodes 3 and 4 are pressed (for example, a pressing force of 1960 N), and the electrodes 3 and 4 are energized (for example, a welding current of 8000 A). Due to this pressurization and energization, the nugget 13 is formed in the pressurizing portion between the coated steel plates 1 and 2,
The coated steel plates 1 and 2 are joined.

The materials for the electrodes 3 and 4 are JIS
Z 3234 ^-1977 Type 1 or Type 2 of "copper electrode material for resistance welding" according to JIS C 9304 ^-1986
It is common to use a shape defined by “shape and size of spot welding electrode”. The reason why these materials are used for the electrodes is that they have higher thermal conductivity and electrical conductivity than the material to be welded, and it is difficult to join the electrode and the material to be welded at the welded portion, so that they are suitable for continuous welding.

Although it is not a resistance welding method of a steel plate or a coated steel plate in which the surface of the steel plate is coated with a metal that is more base potential than the steel plate, as shown in FIG. 8 (disclosed in Japanese Patent Laid-Open No. 61-159288). In the resistance welding of the materials a and b to be welded made of Al or an Al alloy plate, there is a higher electrical conductivity than the electrodes 3 and 4 between the electrodes 3 and 4 and the materials a and b to be welded. A method has been proposed in which pressurization and energization are performed with the insert materials c and d interposed therebetween. In this resistance welding method, due to the presence of the insert materials c and d having higher electric conductivity than the electrodes 3 and 4, the temperature of the contact portion between the insert materials c and d and the welded materials a and b is increased. Even if the heat input from the electrodes 3 and 4 is excessive, the materials a and b to be welded do not melt in the plate thickness direction to the surface, and the material a to be welded a does not cause surface cracking. , B can be welded to each other.

[0006]

By the way, the number of continuous welding points at which the tip of an electrode is dressed once and then a spot weld having a predetermined required performance is continuously obtained is called the electrode life of the electrode. The determination of the electrode life is based on the following number of continuous dots. The first is the nugget diameter,
Or, it is due to the number of continuous dots until the tensile shear strength of the welded portion becomes equal to or less than a specified value.The second is a pickup (an alloy layer between the electrode and the material to be welded is formed at the tip of the electrode. Is the number of continuous dots until the start of the phenomenon that the appearance is damaged by being transferred to the weld) and the third is the number of continuous dots until the electrode is welded to the welded material and cannot be removed. is there. Generally, the first and third continuous dot numbers are often used, so that the electrode life in this specification depends on the first and third continuous dot numbers.

On the basis of the above-mentioned continuous number of dots, the electrode life in resistance welding of an assembly line for bare steel plates used for automobile bodies is about 10,000 points. On the other hand, the electrode life of the galvanized coated steel sheet in the conventional resistance welding method is about 3000 to 45.
It is 00 points, and the electrode life in the case where the resistance welding of the bare steel plates and the resistance welding of the galvanized coated steel plates are performed alternately or in a mixed manner is almost the same as that of the resistance welding of the galvanized coated steel plates. Less than half. Various methods have been considered in order to improve the problem of shortening the life of the electrode, but the current situation is that they have not achieved sufficient results. Therefore, resistance welding of a coated steel sheet such as a galvanized steel sheet is more costly than resistance welding of a bare steel sheet that is not coated, which has been a serious problem particularly in the field of automobile body manufacturing.

When the resistance welding method disclosed in Japanese Patent Laid-Open No. 61-159288 is adopted for welding steel plates including coated steel plates, for example, when chromium copper is used for the electrodes, pure copper is used as an insert material. Since an expensive material such as Ag or Ag must be used, it cannot contribute to the reduction of production cost and the life of the electrode cannot be extended.

The present invention is proposed in order to improve the above-mentioned problems, and an object of the present invention is to provide a steel sheet including a so-called coated steel sheet in which the surface of the steel sheet is coated with a metal whose potential is lower than that of the steel sheet. An object of the present invention is to provide a resistance welding method that can improve the electrode life in the case of resistance welding and can perform welding at a lower cost.

[0010]

In order to achieve the above-mentioned object, the resistance welding method according to the present invention is a coated steel sheet in which one or both of the steel sheets are coated with a coating material made of a metal that is less base than the steel sheet. In resistance welding the steel sheets to each other, between the electrode and the coating material of the coated steel sheet pressing the electrode,
A configuration is adopted in which a foil-like inclusion made of a metal having a higher melting point than that of the electrode or the coating material and having electrical conductivity is sandwiched to apply pressure and current.

That is, according to the method of the present invention, when the above-mentioned coating material of the steel sheet appears on one side or both sides of the welded portions of the steel sheets, the above-described coating material and the electrode are used. It is characterized in that a foil-like inclusion is sandwiched between the members to energize under pressure. Therefore, the method of the present invention, when welding the coated steel sheets coated with the coating material on both sides, the coated steel sheets coated with the coating material on one side, when the coating material is welded on one side or both sides of the welded portion It is applied when welding a double-sided coated steel sheet and a bare steel sheet, and when welding a single-sided coated steel sheet and a bare steel sheet in a state where the coating material of the single-sided coated steel sheet appears on one surface of the welded portion. Among such cases, in the case where the coating material does not appear on one surface of the welded parts of the steel sheets, the foil-like inclusion as described above should be used on the one surface. Does not need

Another one of the resistance welding methods according to the present invention is resistance welding between bare steel plates which are not covered with each other, and one or both of the steel plates is covered with a covering material made of a metal which is lower in electric potential than the steel plates. When performing resistance welding of steel sheets which are coated steel sheets to each other alternately or by mixing using the same welding machine,
To pressurize and energize by sandwiching a foil-like inclusion made of metal having a higher melting point and electrical conductivity than the electrode or the coating material between the electrode and the coating material of the coated steel plate that presses the electrode. Is characterized by.

In the method of the present invention, the foil-like inclusions sandwiched between the electrode and the covering material have a higher melting point than the electrode or the covering material, that is, at least the melting point of the electrode or the covering material is lower. The material is not limited as long as it is a metal having a melting point higher than that of one and having conductivity. Although there are exceptions, the melting point of the covering material is lower than that of the electrode in most cases, so in many cases, a conductive metal having a higher melting point than the covering material may be selected. For example, when welding steel sheets including coated steel sheets coated with Zn or Sn, foil-like inclusions include foils of copper, silver, iron, stainless steel, titanium, nickel and the like, alloys thereof and laminer thereof. It is possible to preferably use a torch material.

[0014]

According to the resistance welding method of the present invention, when the welding current is set in a range in which the heat input amounts to such an extent that the steel sheets are mutually melted by electric resistance and the foil-like inclusions are not melted, the foil-like inclusions are The welding current from the electrodes on the sandwiched side flows to the steel sheet through the foil-like inclusions and the covering material having conductivity, and the welding current from the electrodes on the side not sandwiched the foil-like inclusions directly flows to the steel sheet. Only the steel plates of No. 3 are heated and melted due to mutual resistance, a nugget is formed at a contact portion between the steel plates, and the steel plates are joined to each other. The foil inclusions are removed after welding.
The foil-like inclusions should be cut in advance to an appropriate size and placed at the planned welding location, or formed into a long tape and wound so that it can be continuously supplied to the planned welding location. Constitute. By repeating the above steps, the diameters and indentation surfaces of all nuggets are sound, and spot welded portions that meet the required strength are continuously obtained.

When welding is performed without interposing the foil-like inclusions as described above between the coating material of the steel plate and the electrode, the number of continuous dots after one dressing of the electrode increases (depending on welding conditions, 3000 to 4500 points), the coating material in contact with the electrode melts and its structure begins to diffuse, and the tip of the electrode begins to melt, alloying both structures, and the required strength of welding cannot be achieved. . However, according to the method of the present invention, the foil-like inclusions prevent melting and alloying of the coating material and the electrode,
The number of continuous hit points of the electrode, that is, the life of the electrode is dramatically improved. Therefore, the cost of resistance welding of steel sheets is also reduced.

[0016]

[Embodiment 1] FIG. 1 is a partial sectional view of an apparatus in which coated steel sheets are resistance-welded to each other according to an embodiment of the present invention. The welded portions of the coated steel sheets 1 and 2 plated with pure zinc coating materials 11, 12 and 21, 22 are overlaid on both sides of the rolled steel sheets 10 and 20, and the coating materials 11 and 21 are placed on the welded portions. Electrodes 3 and 4 whose tips are dressed via foil-like inclusions 13 and 23 made of a metal having a higher melting point than
The cooling water pipes 30, 40 to the introduction pipe 31,
While supplying cooling water to the cooling holes (9 mm diameter) 32, 42 of the electrodes 3, 4 via 41, the electrodes 3, 4 are energized while pressure is applied to the coated steel plates 1, 2. By applying the pressure and current in this manner, the nugget 5 is formed in the pressure contact portion between the coated steel sheets 1 and 2, and the coated steel sheets 1 and 2 are welded.

All of them conform to the conditions of the method of the present invention.
Various types of foil inclusions (see Table 1) 13 and 23 were prepared, and resistance welding of the coated steel plates 1 and 2 was performed using the welding apparatus of FIG. 1 under the following specifications and conditions. [Coated steel plates 1 and 2] 45 mm pure zinc is applied to a rolled steel plate with a thickness of 1 mm.
The g / m ² plated product was cut into pieces with a width of 30 mm and a length of 200 mm as they were received, and many test pieces were created. [Electrodes 3, 4] Chromium-copper alloy corresponding to JIS Z 3234 type 2, outer diameter 16 mm, tip R = 150 m
m. The tip was dressed with # 1000 Emily paper. [Electrode cooling water] 20 ° C., 4 [l] / min. [Welding machine] Single-phase AC welding machine. [Welding conditions] Welding current 8000A, electrode pressure 1960
N, energizing time 10 cycles. [Welding procedure] Continuous 12000 point welding is performed on each test piece in a manner of welding 5 points for 2 seconds / 1 point at 30 mm pitch. The portions of the foil-shaped inclusions 13 and 23 sandwiched between the electrodes 3 and 4 and the coated steel plates 1 and 2 are updated for each spot. [Limited Nugget Diameter of Electrode Life] The minimum nugget diameter of Class A of JIS Z 3140 (4 mm). [Measurement of Nugget Diameter] After welding, one coated steel plate 1 is peeled off from the other coated steel plate 2 by a peel test jig 6 as shown in FIG. 6, and the diameter of the nugget 5 ([long diameter + short form] / 2). Was measured.

As a comparative example, a similar test piece of coated steel sheet was used, and Z was used in place of the foil-like inclusions 13 and 23 of the above-mentioned example.
The inclusions made of n, Pb, and Sn foils were used for welding under the same specifications and conditions as in the above-mentioned embodiment, and the same test piece of coated steel sheet was used as the conventional method.
No. 3, 23 was not used, and welding was performed under the same specifications and conditions as those of the above-mentioned embodiment, and these comparative examples and conventional examples and the above-mentioned Example 1 were used.
When compared with the resistance welding example by the method of Table 1, the results are shown in Table 1.

[0019]

[Table 1]

1 by the resistance welding method of the above-described embodiment of the present invention
After 2000 points of welding, the state of the electrode tip was examined using pressure sensitive paper. The tip of the electrode was almost the same as before welding, and as shown in Table 1, the resistance of the embodiment of the present invention using the foil-like inclusions. According to the welding method, the electrode life is 12000 in any case.
It was above the point, and all the nugget diameters were 4 mm or more, and all the indented surfaces were sound. In this example, since the spot welding was stopped up to 12000 points, it was not possible to confirm to what extent the electrode life reached the maximum, but in the state of the electrode tip after welding, at least several thousand points exceeded 12000 points. It is expected that the value can be achieved.

On the other hand, in the welding by the conventional resistance welding method which does not use the foil-like inclusions as described above, the electrode life is 4470 points as shown in Table 1, and the electrode tip shape becomes 250 points after 250 points. The center portion began to be recessed (diffusion of the structure of the coating material and alloying with the structure of the electrode), and the tip diameter of the electrode increased as the number of hit points increased, and the nugget diameter became 4 mm or less. Further, in the case of the comparative example in which a substance having a melting point lower than that of chromium copper (electrodes 3 and 4) and pure zinc (coating material) is used as the inclusions, the electrode life is 55 to 64 points and Soon after, it began to be welded to the coating material and became impossible to weld.

[0022]

[Embodiment 2] FIGS. 2 and 3 are partial sectional views of an apparatus according to another embodiment of the present invention in which steel plates are resistance-welded to each other. As shown in FIG. 2, Zn-Fe alloy coating materials 11, 12 and 21, 21 are formed on both surfaces of the rolled steel plates 10, 20.
The welded portions of the coated steel sheets 1 and 2 plated with 2 are overlapped, and the tips are dressed on the welded portions via foil-like inclusions 13 and 23 made of a metal having a higher melting point than the coating materials 11 and 21. While the electrodes 3 and 4 are brought into contact with each other and the cooling water is supplied to the cooling holes (9 mm diameter) 32 and 42 of the electrodes 3 and 4 from the cooling water pipes 30 and 40 through the introduction pipes 31 and 41, The coated steel sheets 1 and 2 are energized under pressure to form a nugget 5 in the pressure contact portion between the coated steel sheets 1 and 2, and the coated steel sheets 1 and 2 are spot-welded. In the same manner, the coated steel sheets 1 and 2 are welded at 20 points at a predetermined pitch.

Then, as shown in FIG. 3, the same electrodes 3 and 4 as those used in FIG. 2 are used, and the welded portions of the bare steel plates 10 and 20 not covered with the covering material are overlapped. Then, the electrodes 3 and 4 are brought into contact with each other through the foil-shaped inclusions 13 and 23, and the steel plates 10 and 20 are connected at a predetermined pitch by 20 in the same manner.
Do spot welding. In this way, the resistance welding described in FIG. 2 and the resistance welding described in FIG. 3 are alternately repeated. Since the foil-like inclusions 13 and 23 of this embodiment are long and wound in a tape shape so as to be successively fed out to the welding position, from the welding of the coated steel plates 1 and 2 of FIG. 2 to that of FIG. Bare steel plate 1
Foil-shaped inclusions 13 and 2 are also present when the process is switched to welding 0 and 20.
3 is played as it is.

All of them meet the conditions of the method of the present invention.
Prepare various kinds of foil-like inclusions (see Table 2) 13 and 23, and use the same welding machine, the following specifications and conditions
Resistance welding of 2 and bare steel plates 10 and 20 was performed alternately. [Coated steel plates 1 and 2] Zn-15 on a rolled steel plate having a thickness of 1 mm
What was 60 g / m ² electroplating wt% Fe alloy,
A large number of test pieces cut into a width of 30 mm and a length of 200 mm are prepared as they are in the state of arrival, and these test pieces are stacked and used. [Bare steel plates 10 and 11] SPCC steel plate with a thickness of 1 mm has a width of 3
A large number of test pieces cut to 0 mm and 200 mm in length were created, and these test pieces were used in layers. [Electrodes 3, 4] Made of chromium-zirconium-copper alloy corresponding to JIS Z 3232 type 2, outer diameter 16 mm, tip shape dome shape, and tip of # 1000 emily paper I dressed. [Electrode cooling water] 20 ° C., 4 [l] / min. [Welder] Single-phase rectification resistance welder. [Welding conditions] Welding current 8000A, electrode pressure 1960
N, energizing time 10 cycles. [Welding procedure] 2 seconds / 1 point for test pieces with coated steel sheets, 3
20 points continuous, 4 points welding at 0mm pitch → 4
0 second pause → 2 seconds / 1 point for a test piece with bare steel sheets stacked, 30
20 points continuous → 40 points as if welding 5 points at mm pitch
One second cycle consists of one second pause, and this cycle is repeated for a total of 12000 spot welds. [Limited Nugget Diameter of Electrode Life] The minimum nugget diameter of Class A of JIS Z 3140 (4 mm). [Measurement of Nugget Diameter] After welding, one coated steel plate 1 was peeled from the other coated steel plate 2 with a peel test jig, and the diameter of the nugget 5 ([long diameter + short form] / 2) was measured. Steel plate 10, 20
The nugget diameter was measured in the same manner.

As comparative examples, the same coated steel plate and bare steel plate test pieces were used, and instead of the foil-like inclusions 13 and 23 of the above-mentioned examples, inclusions made of Zn, Pb and Sn foils were used.
Welding under the same specifications and conditions as in the above example, using the same coated steel plate and bare steel plate test pieces as the conventional method, and using the foil-shaped inclusions 13 and 23, the same specifications and When the resistance welding was carried out under the conditions and the comparative example and the conventional example were compared with the resistance welding example by the method of the above-mentioned embodiment, the results are shown in Table 2.

[0026]

[Table 2]

After 12000 spot welding by the resistance welding method of Example 2, the state of the electrode tip was examined in the same manner as in Example 1. The electrode tip was almost the same as before welding, and as shown in Table 2, According to the resistance welding method of Example 2 of the present invention using the foil-like inclusion, the electrode life was 12,000 points or more in any case, all the nugget diameters were 4 mm or more, and all the indentation surfaces were sound. Also in this example, as in the case of Example 1, the spot welding was stopped up to 12000 points, so it was not possible to confirm to what extent the electrode life reached the maximum, but in the state of the electrode tip after welding, 12000
It is expected that at least thousands of points will be achieved.

On the other hand, in the welding by the conventional resistance welding method which does not use the foil-like inclusions as described above, the electrode life is 1260 points as shown in Table 2, and when the welding point exceeds 150 points, the tip shape of the electrode becomes The center portion began to dent, and the tip diameter of the electrode increased as the number of hit points increased, and the nugget diameter became 4 mm or less. Also, chromium as an inclusion
In the case of the comparative example using a substance having a lower melting point than the zirconium-copper alloys (electrodes 3 and 4) and the Zn-15 wt% Fe alloy (coating material), the electrode life was 15 to 33 points, and the inclusions were Shortly after the start of welding, welding began to occur with the coating material and welding became impossible.

[0029]

[Embodiment 3] FIG. 4 is a partial cross-sectional view of an apparatus in which coated steel sheets are resistance-welded to each other according to another embodiment of the present invention. The welded portions of the coated steel sheets 1 and 2 obtained by plating the coated steel sheets 11 and 21 of Zn-10 wt% Ni alloy on one surface of the rolled steel sheets 10 and 20 are respectively covered with the coating materials 11 and 21.
1 in such a manner that it appears on the surface, and a foil-like inclusion 1 made of a metal having a higher melting point than the covering materials 11 and 21 is placed on the welded portion.
The electrodes 3 and 4 whose tips are dressed are brought into contact with each other through the cooling pipes 3 and 23, and the cooling water pipes 30 and 40 are introduced into the introducing pipes 31 and 4.
While supplying cooling water to the cooling holes (9 mm diameter) 32, 42 of the electrodes 3, 4 via the electrode 1, the coated steel plates 1, 2 by the electrodes 3, 4
By energizing the coated steel sheets 1 and 2 while applying pressure, the nugget 5 is formed in the pressure contact portion between the coated steel sheets 1 and 2, and the coated steel sheets 1 and 2 are welded.

All of them meet the conditions of the method of the present invention.
Foil-like inclusions (see Table 3) 13 and 23 of various types were prepared, and the resistance welding of the coated steel sheets 1 and 2 was performed under the following specifications and conditions by the resistance welding method described in FIG. [Coated steel sheets 1 and 2] Zn-on one side of a rolled steel sheet having a thickness of 1 mm
Width 30mm, length 200mm with the surface condition of 10g% Ni alloy electroplated at 20g / m ² as received.
Cut into a number of test pieces and stack them. [Electrodes 3, 4] A chromium-copper alloy corresponding to the second type of JIS Z 3234, having an outer diameter of 16 mm and a truncated cone-shaped tip. The tip was dressed with # 1000 Emily paper. [Electrode cooling water] 20 ° C., 4 [l] / min. [Welding machine] Single-phase AC welding machine. [Welding conditions] Welding current 8000A, electrode pressure 1960
N, energizing time 10 cycles. [Welding procedure] Continuous 12000 point welding is performed on each test piece in a manner of welding 5 points for 2 seconds / 1 point at 30 mm pitch. The portions of the foil-shaped inclusions 13 and 23 sandwiched between the electrodes 3 and 4 and the coating materials 11 and 21 are updated for each spot. [Limited Nugget Diameter of Electrode Life] The minimum nugget diameter of Class A of JIS Z 3140 (4 mm). [Measurement of Nugget Diameter] After welding, one coated steel plate 1 was peeled off from the other coated steel plate 2 with a peel test jig in the same manner as in Example 1, and the diameter of the nugget 5 ([long diameter + short form] / 2). Was measured.

As a comparative example, the same coated steel plate test piece was used, and instead of the foil-like inclusions 13 and 23 of the above-mentioned examples, Zn, which has a lower melting point than chromium-copper alloy and Zn-Ni alloy,
The inclusions made of Pb and Sn foils were used for welding under the same specifications and conditions as in the above-mentioned embodiment, and the same coated steel plate test piece was used as the conventional method.
No. 3 was used, welding was performed under the same specifications and conditions as in Example 3, and the comparative examples and the conventional example were compared with the resistance welding example by the method of Example 3, and the results are shown in Table 3. .

[0032]

[Table 3]

After continuous 12000 spot welding by the resistance welding method of the third embodiment of the present invention, the state of the electrode tip was examined in the same manner as in the case of the first embodiment. The tip of the electrode was almost the same as before the welding. According to the resistance welding method of the third embodiment of the present invention using a foil-like inclusion as in No. 3, the electrode life is 12000 points or more in any case, and the nugget diameters are all 4 mm.
As a result, all the indented surfaces were sound. This Example 3
However, since spot welding was stopped up to 12000 points, it was not possible to confirm to what extent the electrode life would reach the maximum, but in the state of the electrode tip after welding, it is possible to reach a value exceeding 12000 points by at least several thousand points. Expected.

On the other hand, in the welding by the conventional resistance welding method which does not use the foil-like inclusion as described above, the electrode life is 4683 points as shown in Table 3, and when the number of welding points exceeds 200, the tip shape of the electrode is The center portion began to dent, and the tip diameter of the electrode increased as the number of hit points increased, and the nugget diameter became 4 mm or less. Further, in the case of the comparative example in which a material having a lower melting point than chromium copper and a Zn-Ni alloy is used as an inclusion, the electrode life is 48 to 65 points, and the inclusion begins to be welded to the coating material shortly after the start of welding. It became impossible to weld.

[0035]

Example 4 Ten kinds of foil-like inclusions (see Table 4) were prepared, and resistance welding between coated steel sheets was performed under the following specifications and conditions. [Coated steel plate] A rolled steel plate having a thickness of 1 mm, coated with 100 μm of Zn (coating material) by an arc spraying method on the surface as received, width 30 mm, length 200 mm
Cut into multiple pieces to create a number of test pieces, and stack these test pieces so that the coating material appears on both sides. [Electrode] Chromium-copper alloy corresponding to JIS Z 3234 type 2 with an outer diameter of 16 mm and a domed tip as shown in FIG. The tip was dressed with # 1000 Emily paper. [Electrode cooling water] 20 ° C., 4 [l] / min. [Welder] Single-phase rectification resistance welder. [Welding conditions] Welding current 8000A, electrode pressure 1960
N, energizing time 10 cycles. [Welding procedure] Continuous 12000 point welding is performed on each test piece in a manner of welding 5 points for 2 seconds / 1 point at 30 mm pitch. The part sandwiched between the foil-like inclusion electrode and the covering material is updated for each spot. [Limited Nugget Diameter of Electrode Life] The minimum nugget diameter of Class A of JIS Z 3140 (4 mm). [Measurement of Nugget Diameter] After welding, one coated steel sheet was peeled off from the other coated steel sheet by a peel test jig in the same manner as in Example 1,
The nugget diameter ([long diameter + short shape] / 2) was measured.

As a comparative example, the same coated steel plate test piece was used, and instead of the foil-like inclusion, an inclusion made of a chromium-copper alloy and a foil of Zn, Pb, Sn having a lower melting point than Zn was used. While welding under the same specifications and conditions as the above example, using a similar coated steel plate test piece as a conventional method,
Welding was performed under the same specifications and conditions as in Example 4 without using the foil-like inclusions, and these Comparative Examples and Conventional Example were compared with the resistance welding example by the method of Example 4, and Table 4
It was a sword.

[0037]

[Table 4]

After continuous 12,000 spot welding by the resistance welding method of the fourth embodiment of the present invention described above, the state of the electrode tip was examined in the same manner as in the case of the first embodiment. According to the resistance welding method of the third embodiment of the present invention using a foil-like inclusion as in No. 4, the electrode life is 12000 points or more in any case, and the nugget diameters are all 4 mm.
As a result, all the indented surfaces were sound. This Example 4
However, since spot welding was stopped up to 12000 points, it was not possible to confirm to what extent the electrode life would reach the maximum, but in the state of the electrode tip after welding, it is possible to reach a value exceeding 12000 points by at least several thousand points. Expected.

On the other hand, in the welding by the conventional resistance welding method which does not use the foil-like inclusions as described above, the electrode life is 3533 points as shown in Table 4, and when the number of welding points exceeds 250, the tip shape of the electrode is changed. The center portion began to dent, and the tip diameter of the electrode increased as the number of hit points increased, and the nugget diameter became 4 mm or less. Also, chromium as an inclusion
In the case of the comparative example using a material having a melting point lower than that of copper alloy and Zn, the electrode life was 43 to 58 points, and inclusions began to be welded to the coating material shortly after the start of welding, and welding became impossible.

[0040]

[Embodiment 5] FIG. 5 is a partial cross-sectional view of an apparatus according to still another embodiment of the present invention, in which coated steel sheets are resistance-welded to each other. On one side of the rolled steel plates 10 and 20, Zn-
The welded portions of the coated steel sheets 1 and 2 plated with the coating materials 11 and 22 of 15 wt% Fe alloy, respectively, are overlapped so that only the coating material 11 of one coated steel sheet 1 appears on the surface, and the welded portions are The electrode 3 after dressing is brought into contact with the coated steel plate 1 side through a foil-like inclusion 13 made of a metal having a higher melting point than the coating material 11, and the electrode 4 after dressing is directly contacted with the coated steel plate 2 side. Contact, cooling water piping 30,
While supplying cooling water from 40 to the cooling holes (9 mm diameter) 32, 42 of the electrodes 3, 4 via the introduction pipes 31, 41, the electrodes 3, 4 are energized while pressure is applied to the coated steel plates 1, 2. By doing so, the nugget 5 is formed in the pressure contact portion between the coated steel sheets 1 and 2, and the coated steel sheets 1 and 2 are welded.

All of them meet the conditions of the method of the present invention.
Various kinds of foil-like inclusions (see Table 5) 13 were prepared, and resistance welding of the coated steel sheets 1 and 2 was performed under the following specifications and conditions by the resistance welding method described in FIG. [Coated steel sheets 1 and 2] Zn-on one side of a rolled steel sheet having a thickness of 1 mm
Width 30mm, length 200mm with the surface condition of 15g% Fe alloy electroplated at 60g / m ²
Cut into many pieces to make test pieces, and
It is used by stacking like. [Electrodes 3, 4] A chromium-copper alloy corresponding to the second type of JIS Z 3234, having an outer diameter of 16 mm and a dome-shaped tip. The tip was dressed with # 1000 Emily paper. [Electrode cooling water] 20 ° C., 4 [l] / min. [Welder] Single-phase rectification resistance welder. [Welding conditions] Welding current 8000A, electrode pressure 1960
N, energizing time 10 cycles. [Welding procedure] Continuous 12000 point welding is performed on each test piece in a manner of welding 5 points for 2 seconds / 1 point at 30 mm pitch. The portion of the foil inclusion 13 sandwiched between the electrode 3 and the covering material 11 is
Updated for each spot. [Limited Nugget Diameter of Electrode Life] The minimum nugget diameter of Class A of JIS Z 3140 (4 mm). [Measurement of Nugget Diameter] After welding, one coated steel sheet 1 was peeled off from the other coated steel sheet 2 by a peel test jig as in Example 1, and the nugget diameter was measured.

As a comparative example, a similar test piece of coated steel sheet was used, and instead of the foil-like inclusions 13 in the above-mentioned example, chromium-
Zn, Pb, which has a lower melting point than copper alloys and Zn-Fe alloys
Using an inclusion made of Sn foil, welding under the same specifications and conditions as in the above-mentioned example, using a similar test piece of a coated steel sheet as the conventional method, and using no foil-like inclusion 13 Welding under the same specifications and conditions as in Example 5 and comparing these comparative examples and conventional examples with the resistance welding example according to Example 5, the results are shown in Table 5.

[0043]

[Table 5]

After continuous 12000 spot welding by the resistance welding method of the fifth embodiment of the present invention, the state of the electrode tip was examined in the same manner as in the case of the first embodiment. The tip of the electrode was almost the same as before the welding. According to the resistance welding method of Example 5 of the present invention using a foil-like inclusion as in No. 5, the electrode life is 12000 points or more in any case, and the nugget diameters are all 4 mm.
As a result, all the indented surfaces were sound. This Example 5
However, since spot welding was stopped up to 12000 points, it was not possible to confirm to what extent the electrode life would reach the maximum, but in the state of the electrode tip after welding, it is possible to reach a value exceeding 12000 points by at least several thousand points. Expected.

On the other hand, in the welding by the conventional resistance welding method which does not use the foil-like inclusions as described above, the electrode life is 4520 points as shown in Table 5, and the tip shape of the electrode exceeds 150 welding points. The center portion began to dent, and the tip diameter of the electrode increased as the number of hit points increased, and the nugget diameter became 4 mm or less. Also, chromium as an inclusion
In the case of the comparative example using a substance having a lower melting point than the copper alloy and the Zn-Fe alloy, the electrode life is 59 points to 6 points, respectively.
It was 9 points, and the inclusions began to be welded to the covering material shortly after the start of welding and became unusable.

Although the above-mentioned embodiment does not show an example of resistance welding between a coated steel plate and a bare steel plate, such an example has substantially the same effect as that of the fifth embodiment. Further, the resistance welding method of the steel sheet according to the present invention is not limited to the above-mentioned examples, and within the scope of the claims, changes or substitutions of non-main parts or addition of other requirements. It also includes the case of implementation.

[0047]

According to the resistance welding method for steel sheets according to the present invention, resistance welding is performed between steel sheets including a coated steel sheet on one or both sides of which a coating material made of a metal that is less base than the steel sheet is coated. In the case where the resistance welding of and the resistance welding of the bare steel plates are alternately or mixed and performed by the same welding machine,
The electrode life can be dramatically improved and
It is possible to reduce the manufacturing cost of a steel sheet product by such resistance welding.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an apparatus for explaining an embodiment of a resistance welding method according to the present invention.

FIG. 2 is a partial cross-sectional view of an apparatus for explaining one step of the resistance welding method according to another embodiment of the present invention.

FIG. 3 is a partial cross-sectional view of an apparatus for explaining another step of resistance welding which is alternately performed with the step of the resistance welding method of FIG.

FIG. 4 is a partial sectional view of an apparatus for explaining a resistance welding method according to still another embodiment of the present invention.

FIG. 5 is a partial cross-sectional view of an apparatus for explaining a resistance welding method according to still another embodiment of the present invention.

FIG. 6 is a perspective view of a peel test jig for peeling steel plates after welding.

FIG. 7 is a partial sectional view for explaining a conventional resistance welding method for a coated steel sheet.

FIG. 8 is a partial cross-sectional view for explaining a conventional example of the technique of resistance welding an aluminum plate.

[Explanation of symbols]

1,2 coated steel sheet 10,20 steel plate 11,12,21,22 coating material 13,23 Foil-like inclusions 3,4 electrodes 30, 40 Cooling water piping 31,41 Introductory pipe 32, 42 cooling holes 5 Nuggets 6-pole test jig

Claims (4)

[Claims] 1. A coating material for an electrode and a coated steel sheet that presses the electrode when one or both of the steel sheets are resistance-welded to each other, which is a coated steel sheet coated with a coating material made of a metal whose potential is lower than that of the steel sheet. A resistance welding method for a steel sheet, characterized in that a foil-like inclusion made of a metal having a higher melting point than that of the electrode or the coating material and having electrical conductivity is sandwiched between the electrode and the electrode, and pressure and current are applied. 2. The resistance welding method for a steel sheet according to claim 1, wherein one or both of the steel sheets is a coated steel sheet whose both surfaces are coated with a coating material made of a metal that is more base than the steel sheet. 3. The resistance welding method for a steel sheet according to claim 1, wherein one or both of the steel sheets is a coated steel sheet whose one surface is coated with a coating material made of a metal whose potential is lower than that of the steel sheet. 4. Resistance welding between uncoated bare steel plates and resistance welding between steel plates, wherein one or both of the steel plates are coated steel plates coated with a coating material made of a metal that is less base potential than the steel sheets. , Alternately using the same welding machine or mixed, between the electrode and the coating material of the coated steel plate for pressing the electrode, the melting point is higher than the electrode or the coating material, and the electrical conductivity is A resistance welding method for steel plates, which comprises pressing and energizing with a foil-like inclusion made of a metal that is sandwiched therebetween.