JP2000197976A - Spot welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve weldability by blowing a shield gas. SOLUTION: In a method that by using a bar shaped electrode 102 consisting of the plate shaped 101 acting as one of electrodes at any place on a surface and the welding tip which moves on the plate shaped electrode and acting as the other electrode, by clamping the metal plate 100 of materials to be welded stacked between these electrodes and energizing, by resistance heat generated to stacked joining faces, the joining faces are locally fused to be welded, a shield gas 105 is blown toward the metal plate 100 of the material from the surrounding of the bar shaped electrode 102 during energizing or prior to energizing in this welding, by covering the outer periphery of the bar shaped 102 tip with the shield gas and by energizing between the bar shaped electrode 102 and the plate shaped electrode 101, the joining faces of the metal plate 100 to be welded are locally fused/welded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot resistance welding method, and more particularly, to a welding method in which a fixed plate-like electrode and a rod-like electrode movable on the plate-like electrode are used and these electrodes are overlapped with each other. The present invention relates to a method in which a material is pinched and energized to locally melt and weld a joint surface by resistance heat generated in a superposed joint surface.

[0002] This welding method is suitable for welding thin plates such as stainless steel plates. However, even a low carbon steel plate is suitable for welding thin plates.

[0003]

2. Description of the Related Art In general, a resistance welding method of overlapping and welding is used in joining a thin metal plate or the like. In this welding method, the metal plates to be welded are superimposed and directly energized, utilizing the contact resistance of the superposed metal plates to generate resistance heat at the bonding surfaces,
In this method, the joining surfaces of the metal plates are locally heated and melted using the resistance heat as a heat source to join the metal plates.

[0004] In this resistance welding, the heat source used for heating and melting the metal plate is resistance heat generated based on the contact resistance of the joint surface of the metal plate. Therefore, the temperature of the heat source depends on the welding current and the resistance of the joint surface. It depends on factors such as value and pressure, and this is also said to be a problem of resistance welding. However, resistance welding does not require a welding rod or flux unlike arc welding, spot resistance welding has limited heating, and the base material of the workpiece and the metal plate itself are not used. It is not suitable for welding thin steel plates and stainless steel plates among metal plates, and is widely used for mass production.
That is, spot welding, which joins the joining surfaces of superposed metal plates, is a welding method of forming and welding a weld metal called a nugget, in which a large current is applied in a short time by sandwiching the metal plate with a pair of electrodes. The joining surfaces are melted and joined. Such a welding method of heating and melting in a very short time can be applied to easily oxidizable steel types such as stainless steel sheets and aluminum steel sheets, and is an indispensable welding method for manufacturing automobiles and the like.

[0005] That is, resistance welding, particularly spot resistance welding, has been conventionally used for joining metal plates called thin plates such as automobile frames, steel furniture, and home electric appliances.

In such a spot resistance welding machine having a variety of uses, a pair of electrodes, which are electrically heated by sandwiching a superposed metal plate, are provided with a pressing force by a pressing portion. Is constituted by a structure in which a welding current is supplied to a pair of electrodes by a welding power source. The electrodes exposed to a high temperature during welding are cooled by cooling water, and the cooling water is sent by a water-cooled cable. It is supposed to be.

[0007] Among such spot resistance welding machines,
What is used for joining processing such as automobile frames is
This is a so-called stationary spot welding machine. However, according to the stationary spot welding machine, since a pair of electrodes is fixed, a metal plate is moved to the pair of electrodes during welding, and welding is performed. Stationary spot welding machines are not suitable for housings that are difficult to move, such as housings and large products.

[0008] Therefore, such a welded article is called an article different from an automobile frame or the like. Therefore, at least one electrode and a pressurizing portion for pressing the electrode are integrally formed. A portable spot welder configured to move the gun is used.

In the portable spot welding machine, the welding gun is configured to be portable by separating from a power source such as a welding transformer.
The connection is made by a flexible current-carrying cable. With this type of welding machine, even for large parts and structures, the welding gun itself with the electrode at the tip can move freely, so welding can be performed without moving the structure of the work to be welded. It is.

Further, as one type of portable spot welding machine, the one electrode is not formed in the shape of a circular contact at the tip end as in a so-called R type, but is formed as a plate having good conductivity such as a copper plate. There has been proposed a welding machine which can be constructed and welded anywhere on which a metal plate is placed. In this welding machine, one electrode is formed in a plate shape, while the other electrode is formed in a so-called R shape or the like, and the pressurizing portion to which this electrode is attached has a rod shape, also called a spot gun. It is configured as a rod-shaped electrode. When welding with this welding machine, an operator presses a rod-shaped electrode against a metal plate placed on a plate-shaped electrode, conducts electric current, and performs resistance welding. According to this method, the worker can freely move the rod-shaped electrode on the plate-shaped electrode, but the pressing force at the time of welding depends on the force of the worker pressing the rod-shaped electrode downward, which becomes heavy labor. Therefore, it is not suitable for welding of mass products.

In order to eliminate such a drawback of wasting of labor, the present inventor has previously proposed a spot gun disclosed in Japanese Patent Publication No. 3-56147.

That is, in this spot gun, as shown in FIG. 6, a plate electrode 11 made of a conductive material is provided, and the surface of the plate electrode 11 functions as a lower electrode over the entire surface. Welding can also be performed with the metal material 12 to be placed. A support column 1 is provided on the side of the plate electrode 11.
A support arm 15 is rotatably supported by a support column 14, and the support arm 15 moves on the work surface 11 in a plane. At the free end of the support arm 15, the support 1
7 is attached so as to be able to move up and down. The rod-shaped arm 36 is supported at the lower end of the support 17 at a pivot point 41, and the rod-shaped arm 36 pivots about the pivot point 41. Bar-shaped arc
A welding tip 32 is attached to a tip of the arm 36, and the welding tip 32 forms an upper electrode.

When the welding gun as the upper electrode is constructed as described above, when the rear end of the rod-shaped arm 36 rotatably supported by the tip of the support 17 is pulled by the cylinder 35, the rod-shaped arm is pulled. 36 rotates around a pivot point 41,
The pulling force from the cylinder 35 is doubled by the lever mechanism and applied to the welding tip 32 at the tip, and the welding tip 32 is pressed downward by the doubled pressing force.

In such a spot welding machine, the surface of the plate-like electrode 11 can be used freely as a lower electrode, and in the case of a rod-like electrode composed of a rod-like arm 36, etc., the welding tip is large due to the leverage mechanism. Since the pressing force is applied, there is no muscular labor of the operator, and this is a suitable welding method for sheet metal processing such as a steel plate.

However, when welding a stainless steel plate or the like instead of a low carbon steel plate, stainless steel has a lower thermal conductivity and a larger thermal expansion coefficient than mild steel.
In the weld zone, the heat-affected zone formed around the nugget increases, and carbides such as Cr precipitate in the heat-affected zone. Also,
Since a stainless steel plate or the like is oxidized when a nugget is formed during welding and at least the heat-affected zone is discolored, it is extremely troublesome to remove this discoloration as a post-treatment after welding.

Further, the tip of the welding tip serving as the upper electrode is formed in an R shape or the like so as to make an arc contact. However, one of the electrodes is formed as a plate-like electrode so as to function as the lower electrode over the entire surface. The diameter of the nugget cannot be controlled accurately, and the contact area of the welding tip of the upper electrode is determined by the shape of the tip, but the contact area of the plate-like electrode of the lower electrode depends on the pressing force and expands. The shunt increases, and this shunt may be ineffective, which is not preferable. In addition, the shunt current flows to the adjacent welding point, which reheats the heat-affected zone at the welding point, which undesirably deteriorates the strength of the welded part.

[0017]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks. More specifically, the present invention aims to solve the problem by sandwiching a metal plate between a plate-like electrode constituting a lower electrode and a rod-like electrode constituting an upper electrode. We propose a spot resistance welding method that can prevent discoloration due to oxidation of the surface of the nugget formed at the time of welding and can also remove defects due to shunting.

[0018]

That is, the method of the present invention comprises a rod-shaped electrode consisting of a plate-like electrode serving as one electrode at any point on the surface and a welding tip moving on the plate-like electrode and serving as the other electrode. In this method, the welded material overlapped between these electrodes is sandwiched and energized, and the welding surface is locally melted and welded by the resistance heat generated on the overlapped joining surface. Before or during energization, a shield gas is blown from the periphery of the rod-shaped electrode toward the material to be welded, the outer periphery of the tip of the rod-shaped electrode is covered with the shield gas, and welding is performed by energization between the rod-shaped electrode and the plate-shaped electrode. The joint surface of the material is locally melted and welded.

Also, while at least the outer periphery of the tip of the rod-shaped electrode is surrounded by a spaced cover, the tip of the cover is separated from the plate-shaped electrode to form a shield gas exhaust passage. Then, while the shield gas is exhausted over the entire circumference, the joining surface is locally melted and welded.

The configuration of these means will be described in more detail with reference to the drawings as follows.

FIG. 1 is an explanatory view showing one embodiment of the method of the present invention.

FIG. 2 is a perspective view showing a cross section of a part of a welding tip portion forming an upper electrode in FIG.

FIG. 3 is a plan view of a nugget welded in a conventional example.

FIG. 4 is a plan view of an example of a nugget welded by the method of the present invention.

FIG. 5 is a flow chart showing an example of the pressure, the current and the flow rate of the shield gas in the method of the present invention.

FIG. 6 is a layout diagram of a conventional spot welding machine.

In FIGS. 1 and 2, reference numeral 101 denotes a plate-like electrode. The plate-like electrode 101 is made of a conductive material such as copper or an alloy thereof while being fixed, and functions as a lower electrode over the entire surface. A welding tip 102 is arranged as a rod-shaped electrode on the plate-shaped electrode 101, the welding tip 102 functions as an upper electrode, and the tip shape is configured to make an arc-shaped contact with a metal plate 100 such as a normal R-shaped or the like. . That is, the rod-shaped electrode is composed of a welding tip 102, and the welding tip 102 is attached to the tip of a rod-shaped arm 103, as shown in FIG. Apply pressure. Also, the welding tip 102 is usually mounted via a shank 104, and the bar-shaped arm 103 is arranged horizontally as in the conventional example shown in FIG. To be able to The tip of the welding tip 102 has a rod shape, and the tip has a spherical shape or the like, but may have any shape such as an inverted conical shape.

In welding, a metal plate 100 to be welded is sandwiched between a plate-shaped electrode 101 and a welding tip 102 composed of a rod-shaped electrode, and the welding tip 102 composed of a rod-shaped electrode is pressed downward and energized for a short time. And perform resistance welding using the contact resistance of the superposed joint surfaces,
The joining surfaces of the two metal plates are fusion-bonded.

In performing spot resistance welding as described above, prior to applying a voltage between the welding tip 102 made of a rod-shaped electrode and the plate-shaped electrode 101 and energizing the same, the welding tip 102 is turned downward from the periphery of the welding tip 102 made of a rod-shaped electrode. Then, the shield gas 105 is blown out. This blowing is continued during the energization, and is continued for a predetermined time even after the energization is stopped.

The shield gas 105 is made of argon, helium or a mixed gas thereof, and is blown downward at a flow rate of 0.8 to 6.0 L / min. When the gas is blown out in this manner, the welded portion of the metal plate 100 is covered with the shield gas, and the surrounding gas is circulated around the welded portion. .

By cooling in this way, even if the metal plate to be welded is a stainless steel plate, the periphery of the nugget is appropriately cooled in the welded portion, and the heat-affected zone generated as a so-called corona bond is reduced. Sex is enhanced.

That is, in spot resistance welding, usually,
Each opposing end of the upper and lower electrodes has a rounded spherical shape, such as a so-called R type, and the contact with the metal plate is a point contact. Under this condition, a pressing force is applied. When a direct current is applied by a DC power supply or the like which is controlled by the current, a current flows only during the point contact, and a nugget is formed at a contact portion where the current flows.

On the other hand, even if one end is a welding tip 102 formed of a rod-shaped electrode, the other end of the plate-shaped electrode 101 whose contact portion or area is not determined by the pressing force or the like is determined by the metal plate 100 to be welded. On the other hand, the welding tip 102 of the rod-shaped electrode is a point contact, and the contact portion of the plate-shaped electrode 101 is not limited to the area pressed by the welding tip 102 but inevitably expands to the periphery.

For this reason, the current flowing downward in the thickness direction of the metal plate 100 increases its width and the current distribution becomes wide. Therefore, in such welding, the shape of the nugget becomes uneven, and the width of the heat affected zone around the nugget becomes large and wide.

On the other hand, components such as Cr are more easily oxidized in stainless steel plates than in mild steels. However, the spot resistance welding method itself is essentially a welding method in which a large current is applied by short-time energization and pressurized, and is melted only during energization to form a nugget. It is even said that there is no need to cover with shield gas.

However, among the thin plates, the stainless steel plate has a lower thermal conductivity and a higher thermal expansion coefficient than the low carbon steel plate. Due to this, a defect occurs in the welded portion, and even when the appearance of the welded portion is viewed, the periphery of the nugget is discolored, such as yellow, and the product value is impaired, and even the welding strength is impaired depending on welding conditions.

That is, in resistance welding, Joule heat is generated at the joint surface of the metal plate 100 by energization, and a part of the Joule heat is a water-cooled rod-shaped electrode welding tip 102.
The heat is dissipated by dissipating heat to the other part of the metal plate 100 and the heat balance between the heat dissipation and the Joule heat causes the joining surface of the metal material to melt to form a nugget and join.

However, the thermal conductivity of a stainless steel plate is low. From this point, the welding tip 102 of the rod-shaped electrode
Dissipation of heat into the metal plate 100 or the like is lower than that of the low carbon steel plate, the heat balance is lost, and the heat-affected zone called a corona bond increases. The formation of hard carbide such as Cr is apt to occur in the heat-affected zone, and the heat-affected zone in which the carbide is precipitated does not crimp even when a pressing force is applied, so that the strength of the welded portion also decreases.

This is also referred to as weld decay, and in welding stainless steel plates, the energization time is reduced as much as possible and the current density is reduced to remove obstacles such as weld decay due to the heat affected zone.

The stainless steel sheet has a larger thermal expansion coefficient than the low carbon steel sheet. This tends to cause distortion during welding.

In order to eliminate such obstacles, nuggets that are as small as possible are continuously formed, thereby ensuring welding strength.

However, in the method of the present invention, one of the electrodes is constituted by a plate-like electrode which functions as a lower electrode at any point on the surface because of easiness of processing a metal plate or the like.
The current distribution in the thickness direction of the metal plate 100 expands downward,
It is impossible to reduce the diameter of the nugget to be generated or the diameter of the heat affected zone around the nugget to control their shapes and dimensions.

More specifically, when welding is performed by point contact between a pair of electrodes, a small nugget is continuously formed by changing the shape and dimensions of an electrode tip to be used, and the area of the nugget is reduced. Or by reducing the heat-affected zone created in the surroundings, thus eliminating obstacles such as weld decay.

From the above, according to the method of the present invention,
A metal plate is placed on a plate-shaped electrode that has a large contact area and serves as an electrode at any part of the surface, and the metal plate is pressed and welded by a rod-shaped electrode welding tip. From shield gas 10
5 is sprayed downward and sprayed on the surface of the metal plate 100 as shown in FIG.

The sprayed shield gas 105 flows in a cylindrical shape around the welding tip 102 forming a rod-shaped electrode,
Thereby, the metal plate 100 on the plate-shaped electrode 101, particularly, the heat-affected zone of the metal plate is covered and cooled, and the nugget 10 is cooled.
The generation of the heat-affected zone around 6 is kept low.

By the way, the inventor of the present invention has set the thickness of 1.5 mm to 1 mm.
8-8 austenitic stainless steel was welded. At this time, argon gas was used as the shield gas 105,
This argon gas was sprayed and welded as shown in FIG. 2, and was welded without using a shield gas for comparison.
This result is shown in FIG.
The nugget without spraying is shown in Fig. 3.
It was as follows.

Each of the nuggets 106 in FIGS. 3 and 4 is enlarged at the same magnification. By comparison, both have a diameter of 5
The nugget 106 was formed by pressing with a rod-shaped electrode welding tip 102 on which a nugget 106 mm could be formed, and its area was almost the same. However, looking at the surrounding heat-affected zone 107, the width thereof was reduced to about 1/3 in FIG. 4 as compared with FIG. 3, and reduced to 1/5 or less in terms of area.

When cooling as described above, the shield gas 105 does not necessarily need to be cooled, and ordinary temperature is sufficient. The flow rate is preferably in the range of 0.8 to 6 L / min. 0.8
If the rate is not more than L / min, the cooling effect cannot be achieved even if the shield effect can be achieved. Also, even if it exceeds 6 L / min, the cooling effect is not so improved.

As shown in FIG. 5, the shield gas 105 is supplied with a pressing force (Kgf), a current (A),
It is preferable to control the gas flow rate (L / min) and blow out.

That is, as shown in FIG. 5, the shielding gas 105 is blown out at the same time as pressing downward by the welding tip 102 forming a rod-shaped electrode to apply a pressing force to the surface of the metal plate. When you energize after taking a squeeze like this,
The periphery and the joint surface of the metal plate 100 are shielded and do not oxidize, and the periphery of the metal plate 100 is sufficiently cooled.

Next, after the squeeze is taken out and blown out, the energization is started. The Joule heat generated during the welding is not only scattered toward the water-cooled rod-shaped electrode welding tip 102, but also the shield gas 1 flowing downward.
Also, heat is removed by the heat treatment part 05, and the heat-affected zone can be made as small as possible.

Next, even after the nugget is formed by this energization, the shield gas 105 continues to be blown downward, and is pressed by the welding tip 102 composed of a rod-shaped electrode to hold the metal plate.

More specifically, surface defects such as oxidation of the nugget and discoloration of the surrounding heat-affected zone are known as one of the defects of the welded portion. This surface defect is caused by residual heat after the end of the current supply, and oxidation is suppressed by promoting the removal of the residual heat.

When the shield gas 105 is blown out and welded along the entire periphery of the welding tip 102 composed of a rod-shaped electrode, a component easily oxidized such as a metal plate other than a stainless steel plate, for example, an aluminum material is contained. Even if the material is used, the surface oxidation during welding is sufficiently suppressed, so that it is not necessary to clean the nugget surface and the like by a chemical treatment after welding even with such a material.

Further, since the method of the present invention is a resistance welding method utilizing the fact that the contact portion on which the metal plate is placed functions as one electrode regardless of the surface of the plate-like electrode 101, Metal plate 100 placed on electrode 101
Each time the rod is pressed by the welding tip 102 of the rod-shaped electrode, the contact area and the contact resistance with the plate-shaped electrode 101 change, and a shunting phenomenon inevitably occurs. Such a welding method is a welding method that takes into consideration the fact that a shunting phenomenon occurs essentially. In this case, a low carbon steel sheet does not appear so much, but a stainless steel sheet clearly appears.

That is, when the branching phenomenon occurs, the current density decreases, and sufficient penetration cannot be obtained. In the case of stainless steel sheet, the adjacent welded point, especially the heat affected zone around it, is heated by shunting and further raised.
The precipitation of carbides such as r is promoted, and the brittle portions appear, and further, re-oxidation occurs on the surface of the already welded spot, which may cause discoloration.

However, the shield gas 1 blown downwardly
05 is discharged along the plate electrode 101,
The shield gas 105 is discharged radially along the entire circumference, whereby the adjacent formed nugget and the heat-affected zone around it are covered and cooled. For this reason, the branch flow phenomenon itself cannot be suppressed, but the influence of the branch flow on the heat-affected zone of the welded point can be suppressed.

As described above, in the method of the present invention, it is preferable to spray as shown in FIGS. 1 and 2 when covering the entire periphery of the welding tip 102 formed of a rod-shaped electrode with the shield gas 105.

That is, as shown in FIGS. 1 and 2, a metal plate 100 is superimposed on a plate-like electrode 101, and a welding tip 102 forming a rod-like electrode is pressed from above on the metal plate 100, and current is welded. Welding tip 1 forming this rod-shaped electrode
02 is covered by a cover 108, and the lower end of the cover 108 is separated from the surface of the metal plate 100 to be welded, and the separation forms an annular passage 109 over the entire circumference. Is emitted radially over the entire circumference.

That is, as shown in FIGS. 1 and 2, the sheath 108 is provided so as to surround the periphery of the welding tip 102 forming a rod-shaped electrode. Like this 10
8, the inner wall surface 108a of the canopy 108
An annular passage 109 is formed between the electrode and the outer periphery of the welding tip 102 forming a rod-shaped electrode. The seal is formed by the annular passage 109.
The flowing gas 105 is caused to flow downward. Annular passage 109
A supply passage 110 is connected to a part of the supply passage 110, a supply duct 111 is connected to the supply passage 110, and an end of the supply duct 111 is connected to a shield gas supply source (not shown).

With such a configuration, the shear from the supply source is
Gas 105 is connected to the communication duct 111 and the supply passage 1.
10, the gas is supplied to the annular passage 109, and the shield gas 105 is blown downward. The canopy 108 is attached to a part of the welding tip 102 forming a rod-shaped electrode,
Since 08 is attached to the tip of the rod-shaped arm 103 which forms a lever together with the welding tip 102, it is necessary to be lightweight and made of a heat-resistant synthetic resin such as Teflon.

That is, the sheath 108 is usually formed in a cylindrical shape, and the welding tip 102 forming a rod-like electrode is slightly projected from the tip thereof. With this configuration, when welding tip 102 is brought into contact with and pressed against the surface of metal plate 100 during welding, the lower end of annular passage 109 is separated from the surface of metal plate 100 over the entire circumference. , An annular exhaust passage 112 is formed.

The exhaust passage 112 is formed at the lower end of the cover 108 over the entire circumference as follows.

The inventor of the present invention focused on the fact that it is effective to blow out a shield gas and cool it in spot resistance welding of such a stainless steel plate.
The manner of blowing the shield gas was examined, and as one of them, a longitudinal groove was provided in the axial direction of the shank 104 holding the tip 102 forming a rod-shaped electrode, and a supply passage of the shield gas was formed by the longitudinal groove. Shield gas was supplied through this. However, since it is a vertically elongated groove, the number thereof cannot be increased around the shank 104, so that the blowing of the shield gas is inevitably partially biased. It was non-uniform, and almost no improvement in welding strength was observed.

On the other hand, as shown in FIGS. 1 and 2, an annular passage 109 is provided to spray the shield gas 105 over the entire circumference, and this is uniformly distributed from an annular exhaust passage 112 formed over the entire circumference. Upon discharge, the objective was fully achieved.

[0066]

Next, an embodiment will be described.

A hollow metal box made of a 18-8 austenitic stainless steel plate having a thickness of 1.5 mm is placed on the plate-like electrode 101 as a workpiece, and the overlapped portion of the workpiece is shown in FIG. Thus, the welding tip 102 of the rod-shaped electrode
(R-shaped electrode) was pressed and resistance-welded.

The plate electrode is made of a copper alloy plate.
The welding gun for pressurizing the welding tip formed of the rod-shaped electrode applies a large pressing force to the welding tip 102 at the tip by levering the rod-shaped arm 103 to weld the overlapped portion inside the metal box. .

In such a welding machine, the tip 1
1, a cover 108 made of Teflon is provided around 4 mm from the surface of the plate-like electrode as shown in FIG. 106 was welded so that it could be discharged.

The welding is carried out as shown in the flow chart of FIG. 5, first, supply of argon gas and pressurization by the tip tip 102, and after 15 cycles of squeeze (S), power is supplied. For 20 cycles,
Over the next 15 cycles, the supply of argon gas and pressurization by the tip were continued for 15 cycles to form a unit nugget.

The welding conditions were a welding current of 5000 A, a pressure of 250 kgf, and a flow rate of argon gas of 0.8 to
It was 2 L / min.

The nugget obtained under these conditions is shown in FIG.
For comparison, the nugget when welding was performed under the same welding conditions without flowing argon gas was as shown in FIG.

When comparing FIG. 3 and FIG. 4, the width of the heat-affected zone was completely different, but the area around the nugget in FIG. 4 turned yellow and required chemical treatment.

In the case of the comparative example in which argon gas was not blown out in this welding, when welding was performed adjacent to the welded nugget, the color of the yellowed heat-affected zone around the welded nugget changed. It turned out that the degree became deep, and it was found that it was affected by the diversion.

On the other hand, when the argon gas was blown out as described above, such a phenomenon could hardly be visually recognized.

[0076]

As described above in detail, the method of the present invention uses a plate-like electrode and a welding tip of a rod-like electrode that can move on the plate-like electrode. A method of locally melting and welding the joint surface by resistance heat generated on the overlapped joint surface, and from around the welding tip of the rod-shaped electrode during or before energization at the time of welding in this method. In this method, the shield gas is blown downward and welded.

According to this method, a nugget can be sufficiently developed and welded even with a stainless steel plate or the like, and problems such as shunting caused by the use of a plate-like electrode can be minimized. No surface defects such as yellowing occur.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of the method of the present invention.

FIG. 2 is a perspective view showing a cross section of a part of a welding tip portion forming an upper electrode in FIG. 1;

FIG. 3 is a plan view of a nugget welded in a conventional example.

FIG. 4 is a plan view of an example of a nugget welded by the method of the present invention.

FIG. 5 shows a pressing force, a current and a shear in the method of the present invention.
5 is a flow chart showing an example of a flow rate of a cold gas.

FIG. 6 is a layout view of a conventional spot welding machine.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 metal plate 102 welding tip, rod-shaped electrode 103 rod-shaped arm 104 shank 106 nugget 110 supply passage 111 supply duct 112 exhaust passage

Claims (5)

[Claims] 1. A plate-like electrode serving as one electrode at any point on the surface and a rod-like electrode made of a welding tip moving on the plate-like electrode and serving as the other electrode are superposed between the electrodes. In a method in which the material to be welded is energized, and the welding surface is locally melted and welded by resistance heat generated in the overlapped welding surface, the rod-shaped electrode is electrically connected during welding or prior to the welding. A shield gas is blown out toward the material to be welded from the surroundings, the outer periphery of the tip of the rod-shaped electrode is covered by the shield gas, and the welding surface of the material to be welded is energized between the rod-shaped electrode and the plate-shaped electrode. Spot welding method characterized by locally melting and welding. 2. An exhaust passage for the shield gas is formed by surrounding at least the outer periphery of the tip of the rod-shaped electrode with a spaced cover, and separating the tip of the cover from the plate-shaped electrode. 2. The spot resistance welding method according to claim 1, wherein said joint surface is locally melted and welded while exhausting said shield gas over the entire circumference through an exhaust passage. 3. The spot resistance welding method according to claim 1, wherein the shield gas is blown out while the material to be welded is sandwiched between the electrodes for a predetermined time after the end of energization during welding. . 4. The method according to claim 1, wherein said shield gas is 0.8 to 6.0 L /
4. A blowout at a flow rate of at least one minute.
The spot resistance welding method described. 5. The spot resistance welding method as claimed in claim 1, wherein said shield gas is a mixture of argon, helium, orgon and helium.