JPH08168887A - Spot welding method and equipment therefor - Google Patents

Abstract

PURPOSE: To remove a discoloring caused by the burning of a spot welding, to prevent discoloring in a time of executing spot welding, to unnecessitate the discoloring remove work and to improve the productivity when using the raw material with untreated surface like in the case of stainless vehicle where coating is not performed. CONSTITUTION: A nozzle 2 is installed at an electrode tip of a spot welding, a shield gas and a cooling liquid are jetted from the nozzle 2 onto the weld- heating part of an object to be welded. The equipment is constituted of a control part capable of controlling the required amounts of inert gas (shield gas) and the cooling liquid, and a supply time. Therefore, the discoloring remove work becomes unnecessary, and the effects of shortening of the working process, reducing of man-hours and the space saving of the working place, etc., are realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding method and apparatus for products such as stainless steel vehicles that are used without coating.

[0002]

2. Description of the Related Art When stainless steel is spot-welded, it is burned by the heating of the welding, oxidized, and turned black. When it is used without painting, the discolored part is decolorized to improve the appearance, in terms of appearance.

At present, the discoloration due to burning of spot welding is
It is carried out by a method of removing by a cleaning system of electrolytic polishing type. (Welding technology January and April 1994 issues)

[0004]

Although the discoloration can be removed by the above method, in the case of spot welding, since the number of welding points is large, it takes a long time to remove the discoloration.

An object of the present invention is to prevent the occurrence of discoloration during spot welding, to make discoloration removal work unnecessary, and to improve the production efficiency of products.

[0006]

The above object can be achieved by supplying an inert gas and a cooling liquid in the vicinity of the spot welded portion in spot welding.

[0007]

Operation: The discoloration of the spot-welded portion of stainless steel generally means a portion where the indentation portion of the welding of the workpiece is changed from light brown to black. The cause of discoloration is 250 due to welding heat input.
This is because the metal heated to 300 ° C. or higher reacts with oxygen in the air to oxidize. In order to prevent the generation, it is only necessary to remove air and perform welding.

Shielding with an inert gas must be continued until the surface temperature of the object to be welded is cooled below the discoloration generation temperature. In order to shorten this shield time, start welding current or supply cooling liquid to the welding heating section during energization to forcibly cool the temperature, suppress temperature rise, and increase the cooling rate to shorten the welding cycle. Improve efficiency.

According to the above method, during spot welding, an inert gas is supplied to the welding heating portion of the object to be welded to shut off the atmosphere, and the welding heating portion is cooled by the cooling liquid. Since the cooling liquid increases the cooling rate as compared with the case of using only the inert gas, discoloration can be prevented. Moreover, since the amount of the cooling liquid used is smaller than that in the case of only the case of cooling, the inconvenience associated with the use of the cooling liquid (for example, water) can be reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In FIG. 1, the nozzle 2 is installed concentrically on the outer periphery of the electrode tip 1. The inert shielding gas is
The gas pressure is adjusted by the gas pressure adjuster 11 so that an appropriate flow rate can be obtained from the gas tank 13, and the gas opening / closing valve 9,
It is supplied to the nozzle 2 via the pipe 7. Similarly, the cooling liquid is also supplied from the cooling liquid tank 15 by the pump 14, the flow rate is adjusted by the pressure adjusting valve 12, and is supplied to the nozzle 2 through the cooling liquid opening / closing valve 10 and the pipe 8. The inert gas and the cooling liquid are mixed by the nozzle 2 and jetted from the periphery of the electrode tip 1 to the welded portion. The inert gas and the cooling liquid are supplied by the opening / closing valves 9 and 10 at a necessary time. FIG. 2 is a time chart of welding work.

In FIG. 2, the electrode tip 1 is inserted and fixed in the tapered hole of the electrode holder 3. Nozzle 2
Is attached by screwing it into a male screw at the tip of the electrode holder 3. This thread is sealed. A mixing chamber 17 is provided on the tip end side of the screw from the threaded portion of the nozzle 2, and the connection port 6 of the pipe 7 and the connection port of the pipe 8 are opened. A thin copper wire at the exit of the mixing chamber 12 with a clearance of 0.005 to 0.01 m
A baffle 4 made of m wire mesh is provided so that the cooling liquid and the inert gas are mixed and ejected from the tip of the nozzle 2 in the form of mist. Even if only an inert gas is used, it will be ejected uniformly from the nozzle.

In such a structure, when spot welding is started, the electrode pressing force is exerted, and the electrode tip 1 causes the workpiece 1 to be welded.
Pressurize 6. Simultaneously with the start of electrode pressure, the gas on-off valve 9 is opened, an inert gas (argon gas, shield gas) is supplied to the nozzle 2 and ejected from the nozzle 2, and the electrode tip 1
The workpiece 16 at the tip of is shielded with gas. After that, welding current is applied to perform welding heating. The time difference between the start of the supply of the inert gas and the start of the welding energization is for the purpose of discharging the air flowing into the nozzle 2 while the supply of the gas is stopped and increasing the purity of the shield gas during welding. When the welding current is started, the cooling liquid opening / closing valve 12 is opened to supply the cooling liquid (water). The inert gas and the cooling liquid are mixed and ejected from the tip of the nozzle 2 to cool the work 16 to be welded. After the welding current is stopped, the inert gas and the cooling liquid are supplied for a predetermined time.

When the welding current starts to flow, the workpiece 16 is welded.
Generates heat around the mating surfaces of the objects to be welded, melts and welds. The position where the surface temperature of the work piece 16 is maximized is often slightly outside the outer periphery where the electrode tip 1 is in contact with the work piece. Generally, the temperature of this part is 400 to 70.
0 ° C. In order to prevent discoloration, the shield must be held for a long time until the temperature rising part cools below the discoloration limit temperature. Therefore, the amount of gas is large and the welding time is substantially lengthened by using only the inert gas. On the other hand, if only the cooling liquid (water) is supplied, the amount of the cooling liquid becomes large, so that the rusting of the object to be welded is promoted, and the cooling liquid is accumulated in the welding work place, so that the working environment is deteriorated. With a mixture of the two, the respective drawbacks can be improved, the amounts of the inert gas and the cooling liquid used can be reduced, and the welding time can be shortened.

FIG. 4 shows a material SUS301L having a plate thickness of 1.5 m.
Welding current of 8,300 A, energizing time of 20 Hz,
It is the result of investigating the elapsed time after the start of energization and the surface temperature of the object to be welded at a position at a distance of 4 mm from the center of the electrode tip when welding was performed under the welding conditions of electrode pressure of 9,300 N. The time to cool to 250 ° C. was 2.9 seconds when the cooling liquid was not ejected. However, when water as a cooling liquid was ejected from the nozzle at a flow rate of 100 cc / min and an argon gas of 10 l / min and welded, the welding time was shortened to 1.8 seconds.

When the flow rate of the cooling liquid is increased, the cooling effect is increased, but since it has a harmful effect of adhering to the object to be welded or accumulating in the work place, the flow rate is kept to the minimum necessary.
Determine the timing of coolant supply.

The shield gas may be nitrogen gas other than an inert gas such as argon gas. In addition, the use of water as the cooling liquid has a large latent heat of vaporization and thus has a large cooling effect. However, when it is used for steel materials, there is a risk of causing rust. Alcohol has a low evaporation temperature and has many advantages in terms of cooling, but you must be careful about fire. These are selected according to the work piece and work environment.

[0017]

According to the present invention, discoloration removal work after welding is unnecessary, and there are effects such as shortening of work steps, reduction of man-hours, and reduction of work space.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a spot welding apparatus according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of the electrode portion of FIG.

FIG. 3 is an electrode pressure force of the welding apparatus of FIG. 1, a shield gas,
3 is a time chart of welding current and cooling liquid.

FIG. 4 is a diagram showing the relationship between the elapsed time after the start of energization and the surface temperature of the workpiece.

[Explanation of symbols]

1 ... Electrode tip, 2 ... Nozzle, 3 ... Electrode holder, 4 ...
Baffle, 5 ... Water cooling pipe, 6 ... Hose fastener, 7 ... Gas hose, 8 ... Cooling liquid hose, 9 ... Gas on-off valve, 10
... cooling liquid opening / closing valve, 11 ... gas pressure regulator, 12 ... cooling liquid pressure regulating valve, 13 ... gas tank, 14 ... pump, 15 ...
Coolant tank, 16 ... Objects to be welded, 17 ... Mixing chamber.

Claims (5)

[Claims] 1. A spot welding method, comprising supplying an inert gas and a cooling liquid in the vicinity of a spot welded portion in spot welding. 2. The spot welding method according to claim 1, wherein the supply position of the inert gas and the cooling liquid is the outer peripheral portion of the spot welding portion. 3. The spot welding method according to claim 1, wherein the inert gas and the cooling liquid are mixed and supplied to a spot welding portion. 4. The spot welding method according to claim 1, wherein the cooling liquid is water. 5. A nozzle provided concentrically with the electrode, a mixing chamber provided around the electrode on the upstream side of the nozzle, a baffle provided between the mixing chamber and the nozzle, and A spot welding electrode device comprising a gas and liquid supply port connected to a mixing chamber.