JPS6254578A - Highly efficient submerged arc welding method - Google Patents

Abstract

PURPOSE:To prevent a undercut and to increase a welding efficiency by approaching one unit of welding power source and plural electrode wires from a feeding mechanism to a base metal in high current density and at high speed and by changing a main arc between electrode wires. CONSTITUTION:Plural electrode wires 11, 12 are connected to the one unit of welding electric source 10 having dropping characteristic to feed the wires 11, 12 simultaneously by one unit of a driving source. The wire 11, 12 are approached for a base metal 14 with a wire feeding mechanism 13 and a big current is passed from the power source 10 as well, then, a main arc is generated on the near electrode wire 11 of one part first, the welding current is concentrated on the wire 11 and a pool 16 is formed. The main arc is moved to the wire 12 with the wire 11 becoming short, thereafter the movement of the main arc is repeated. The welding efficiency is increased and undercut can be prevented because of the arc length becoming short and current density being raised.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an improvement in the submerged arc welding method, in which a current is passed at a high current density from one welding power source to multiple electrode wires A7, and the voltage is lowered. Therefore, welding is performed with high efficiency by placing the weld close to the base metal and alternating the arc.

[Conventional technology]

In the submerged arc welding method, a coiled IK wire fed from a wire reel is sequentially plunged onto the joint into powder particles V (flux) supplied from a hopper, and in which the coiled IK wire is inserted into the base metal and the flux. Weld by generating an arc between J-
The arc is invisible. In addition, this welding method concentrates heat and increases the melting speed of the wire.
It has the advantage of being able to perform high-speed and high-efficiency welding and can increase the penetration of the material.

Therefore, it is also used to construct large storage tanks, such as oil tanks and low-temperature tanks for LPG, and automatic circumferential welding is performed.

In constructing this large J: eel storage tank, circumferential welding of the side walls occupies a very large proportion of the process, and improving welding efficiency has become a major issue, such as shortening the construction period and reducing construction costs.

In the commonly used submerged arc welding method, a single electrode wire is connected to a single welding machine, and a power supply with drooping characteristics automatically controls the wire feeding speed to maintain a constant arc voltage. method is adopted.

When performing submerged arc welding using a power source with such drooping characteristics, if you try to increase the welding speed,
It is necessary to increase the current density, but because the arc length becomes longer, it is not possible to form a good bead of 1q, and there is an upper limit, and once the diameter of the electrode wire is determined, the current density is also determined. .

For example, for a wire with a diameter of 2.41 mm used to construct a large storage tank, the current density (welding current/cross-sectional area of the wire) is 90 mm.
A mp/mm2, and the welding speed is 80 (1
/min culm degree.

On the other hand, a multi-electrode welding method in which two or more electrode wires are simultaneously welded using one or more welding machines has been put into practical use, with the aim of improving welding efficiency.

Currently, in the multi-electrode method using submerged arc welding, which is the most efficient method used to construct large storage tanks, two electrode wires are connected to one power supply with constant voltage characteristics.

However, there is a method that performs high-speed welding while keeping the wire feeding speed constant. For example, even when using two wires (1.6 mm in diameter), the welding current is about 800 Amps, and the Increase the current density to 200Amp/mm2,
The overall welding speed is increased to about 195 (]/min.

[Problem that the invention seeks to solve]

However, although this multi-electrode welding method allows for more efficient welding than when welding by connecting a single wire to a power source with drooping characteristics, it is possible to perform welding with higher efficiency than when welding by connecting a single wire to a power source that has drooping characteristics. When the welding is in a horizontal position, a constant voltage characteristic is used as a power source, so if the welding current is increased as the current density increases, the welding voltage will also rise, and undercuts are likely to occur, resulting in a good condition. Even now it is difficult to obtain beads.

In particular, it is difficult to further increase the current density, and the current method is to use high-temperature sintered flux to prevent undercuts, but it is more expensive than normal molten flux, and Large storage tanks with many locations have problems such as increased construction costs.

The present invention has been made in view of such prior art, and is intended to provide a highly efficient submerged arc welding method that can produce a good bead by 1:7 even when performing highly efficient welding.

[Means for solving problems]

As a result of research and experiments conducted by the inventor of this invention in order to solve the above-mentioned problems, it was found that in conventional power supplies with drooping characteristics that use a single electrode wire, the welding phenomenon occurs as shown in Figure 4. It can be seen that the arc length is long and granular migration is occurring, and if the current density is increased as it is, the arc length will become even longer, problems with beat formation and problems with followability of the power supply will occur, and there is a limit. I understand.

In addition, since the multi-electrode welding method uses a power source with constant voltage characteristics, the arc length is longer (about 30% of the arc voltage), as shown in Figure 5, and the welding voltage was found to be high, indicating that spray migration occurs;
It was considered that these welding phenomena, especially the long arc length, tend to cause undercuts.

Therefore, in order to shorten the arc length and increase the current density without lowering the upper limit of the welding voltage to JO, we conducted various experiments and research. As a result, we used a power source with drooping characteristics, and Electrode wires are used, but instead of generating arcs from multiple electrode wires at the same time, multiple electrode wires are brought close to the base metal, and the arc is generated from the wire closest to the base metal, and the arc generation is alternated in sequence. It was found that welding was extremely effective, and this invention was achieved.

That is, the high-efficiency submerged arc welding method of the present invention involves welding while generating an arc between the electrode wire fed into flux and the base metal. Using a welding power source with drooping characteristics, multiple electrode wires are fed at high speed and high current density to bring the distance to the base metal closer, and the arc is connected to the multiple electrode wires 17R■ This feature is characterized in that the welding is performed by alternating between the two.

(Function) A power supply with drooping characteristics prevents the welding voltage from rising as the welding current increases, and by bringing multiple wires close to the base H, the arc length can be shortened and at the same time The current density is increased by causing most of the current to flow through the wire.

〔Example〕

The high efficiency submerged arc welding method of the present invention will be specifically explained below with reference to the drawings.

As shown in FIG. 1, the high-efficiency submerged arc welding method according to the present invention employs a welding power source 10 with a plurality of electrode wires 11 (two in the illustrated example).
, 12, and the electrode wire 11 is inserted into the flux 15 supplied onto the base material 14 by a wire feeding mechanism 13 that simultaneously drives two feed rollers with one drive source.
．． 12 is about to be sent. Then, this wire feeder (t13 automatically controls the feeding speed to keep the arc voltage constant by adjusting the feeding speed, fsl fl
The distance between +/l and electrode W'c711,12 is small,
For example, what used to be about 10 to 20 mm is now 5 to 8 mm.
They are brought close to each other to within a millimeter, and this state is maintained.

If a large current is applied in this state, an arc will occur in the electrode wire 11 that is even slightly closer to the base metal 14, and the welding current will concentrate on one electrode wire 11, causing small particles to be sprayed and transferred. One boule (molten pool) 16 is formed.

Then, when the electrode wire 11 melts to a certain extent, the electrode wires 11 and 12 are fed by the wire feeding mechanism 13 during this time, so that the other electrode wire 12 gradually approaches the base material 14 from the same length. I will do it.

As a result, the welding current flows through the electrode wire 12 having a low resistance, an arc is generated, and spray transfer occurs. In this case, both electrodes 11 and 12 are close to each other (10 to 2
0 mm), the pool is the same as the electrode wire 11. Also, check the electrode wire A7 of the side where the arc has changed.
Since a small amount of current also flows toward point 11, a small droplet transfer occurs.

When the electrode wire 12 through which the current was mainly flowing becomes shorter due to melting, the electrode wire 12 becomes shorter again.
Current mainly flows through. In this way, arcs are repeatedly generated alternately from the electrode wire r that is closer to the base material 14.

In this case, the current ratio of 2 degrees is different from the case where arcs are generated from two electrode wires 11 and 12 at the same time, and about 70% of the welding current flows through one, so it is about twice that.
An increase in welding rate is achieved.

In this way, the electrode wire is brought close to the base metal and the arc is replaced. Even in high-efficiency submerged arc welding, a good bead can be produced depending on the diameter of the electrode wire used.
There are seven ranges of welding conditions, for example as shown in Table 1. In addition, in the same table, if the number of electrodes (NO) is 1,
These welding conditions correspond to the conventional method.

Table 1 Also, Fig. 2 shows the range of this welding condition in the drawing, and the symbols a to -C, A to C in Table 1 are replaced by the symbols a to C, A to A in Fig. 2. It corresponds to C.

Furthermore, the relationship between hot stone speed and welding current is also shown in Figure 'l The diameter J: varies depending on the welding conditions, but it can be used within the range shown.

For example, when two electrode wires with a diameter of 4.6 mm are used, the welding current is 740 Amps, and the welding speed is 1100 CP, the welding speed is 220 g/min.
Using two electrode wires with a diameter of 2.4 mm, the welding current was 85
0 Aml) and the welding speed was 900 PM, the welding speed was 195 g/min.

Furthermore, when two electrode wires with a diameter of 3.2 mm were used, the welding current was 10008 mp, and the welding speed was 90 CPM, the welding speed was 215+J/min. In each case, a good bead was formed and no undercut occurred.

Note that the power supply with constant voltage characteristics explained as the conventional method has 2
When welding by connecting two electrode wires and generating two arcs with a good arc length, welding using a 16 mm diameter electrode wire, a welding current of 750 Amp, and a welding speed of 850 PM. The speed is 190g/m i
It was n. That is, it can be seen that according to the method of this invention, an increase of about 16% is achieved since the welding speed is 220 o/min under almost the same conditions.

[13. In the high-efficiency submerged arc welding method of the present invention, the welding current is mainly concentrated on one of the two electrode wires, and the welding is performed close to the base metal, so penetration is reduced. It is necessary to prevent the burn-through phenomenon to a large extent, and this can be done by using a banking material, for example.

Further, as a specific welding device, for example, it can be constructed by modifying a conventional submerged arc welding machine that uses a single f wire.

In other words, the welding-like power source has drooping characteristics, and the electrode wire V
If the maximum capacity 2 is 800 Δmp so that the diameter of the electrode wire can be changed, the method of the present invention can be used when two 24 mm diameter electrode wires are used (see Table 1).

Therefore, the necessary modification is to enable power to be supplied to the two electrode wires, to enable the two electrode wires to be fed at a wire feed rate m tM, and to be able to feed at high speed.

For this reason, the number of feed rollers is reduced to two and replaced with one of a larger diameter so as to be able to cope with a predetermined welding speed.

Therefore, when welding, conventionally, when one electrode wire with a diameter of 2.41 was used, the welding current was 380 AIn.
p and the welding speed was 480 PM, but if these were set to 850 Amp and 90 CPM, respectively, the welding speed could be increased from 809/min to 195 (+/min).

In this way, if the power source of the conventional welding example is used and the wire feeding mechanism is replaced by replacing the feed roller, the high efficiency 1f Bumage arc welding method A~ shown in Figures 2 and 3 can be achieved with one welding machine. C and normal submerged arc welding method a-C
It can also be used with, expanding the welding range.

In the above embodiment, the number of electrode wires has been explained as two, but the number is not limited to this, and it is also possible to use three or more.

〔Effect of the invention〕

As specifically explained above in conjunction with the embodiments, according to the present invention, multiple electrode wires can be moved at high speed and high current density using one electrode wire feeding mechanism and one welding power source with drooping characteristics. Submerged arc welding is performed by bringing the distance to the base metal closer while feeding and alternating the arc between multiple electrode wires, so even if the current density is increased, the voltage remains the same as in the case of constant voltage characteristics. Since the arc does not rise and the arc length is short, there is no undercut even when welding in a horizontal position, making it possible to weld with high efficiency.

In addition, it is easy to apply to conventional equipment, and can be achieved by simply modifying the wire feeding mechanism, greatly expanding the weldable range.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the high-efficiency submerged arc welding method of the present invention, and FIG. 1 is an explanatory diagram of the welding principle;
Figure 2 is an explanatory diagram of the usable range of welding current and welding speed, Figure 3
The figure is an explanatory diagram of the change in welding speed with respect to the welding current. Figure 4 is an explanatory diagram of the welding phenomenon when a single electrode wire is used with a power source having drooping characteristics. Figure 5 is an explanatory diagram of the welding phenomenon when a single electrode wire is used with a power source with drooping characteristics. - It is an explanatory diagram of a welding phenomenon when two electrode wires A7 are used. 10... Welding power source, 11... RTI pole work wire 2
... Electrode wire, 13 ... Wie A7 feeding mechanism, 14
...Base material, 15...Flux, 16...Pool. (1 other person) Fig. 4 Fig. 5 Melting;r +sSs ;Yo2wearing (g/m1n) Carving tl):□ Den; June 9th, Giut Agency Department Officer 1, Kushi ``1''
Indication of 1985 Special Revision Application No. 194096 2, Name of the invention High-efficiency rib-merged arc melting 1B method, 311i Relationship with the case Patent applicant (009) Ishikawajima Harima Takahiro Kogyo Co., Ltd. 4th generation Person (zip code 105)] 68 compensation pairs and details i! :'s "Claims" and "Detailed Description of the Invention" columns and Figures 2, J3 and 3 of the drawings.
1j: 4゜7.7 As per Yamamasa's facing attachment, details: 1. Title of the invention: High-efficiency submerged arc welding method 2. Claims: Between the electrode wire fed into the flux and the base material. In the submerged arc welding method, in which welding is performed while generating an arc, multiple electrode wires A7 are welded at high speed and i! A high-efficiency submerged arc welding method characterized in that the main arc is alternated between a plurality of electrodes V7 and welding is performed by bringing the distance #I to the base metal closer while feeding at a current density of 5. 3. Detailed Description of the Invention (Field of Industrial Application) This invention relates to an improvement in the submerged arc welding method using a single welding power source. J2 A current is passed through several electrode wires at a high current density, and in order to lower the voltage, they are brought close to the base metal, and the main arc is intertwined and welded with high efficiency. (Prior art) In the submerged arc welding method, a coiled electrode wire fed from a wire reel is sequentially plunged into a granular flux supplied from a hopper onto a joint. Welding is performed by generating an arc between the base metal and the base metal, and the arc is invisible. In addition, this welding method has the advantage of good heat concentration and a high weld melting rate, allowing for relatively efficient welding and the ability to increase penetration into the base metal. Therefore, it is also used to construct large storage tanks, such as oil tanks and low-temperature tanks for LPG, and automatic circumferential welding is performed. In constructing such a large 4v2 storage tank, circumferential welding of the side walls occupies a very large proportion of the process, and improving welding efficiency has become a major issue, such as shortening the construction period and reducing construction costs. In the commonly used submerged arc welding method, one electrode wire is connected to one welding machine, and a power supply with drooping characteristics automatically controls the wire feeding speed to maintain a constant arc length. A method has been adopted. When performing submerged arc welding using a power source with such drooping characteristics, it is necessary to increase the current density in order to increase the welding speed, but since the arc length becomes longer, it is difficult to obtain a good bead. There is an upper limit, and if the diameter of the electrode wire 7 is determined, the current density is also determined. For example, a diameter of 2.4n+n+ used for constructing a large storage tank.
The area) is 90 A mp/mm2, and the welding speed is about 80 (1/min).On the other hand, multiple welding methods, in which two or more electrode wires are welded simultaneously using one or more welding machines, Electrode welding has been put into practical use, and efforts are being made to improve welding efficiency.Currently, the multi-electrode method using submerged arc welding, which is the most efficient method used to construct large storage tanks, requires only one power supply with constant voltage characteristics. There is a method that connects two electrode wires to perform high-speed welding while keeping the wire feeding speed constant. , the current density per each wire was increased to 200 Amp/ml12, and the overall welding speed was increased to about 195 o/min. (Problems to be Solved by the Invention) However, although this multi-electrode welding method allows for more efficient welding than when welding by connecting a single wire to a power source with drooping characteristics, When welding in a horizontal position, such as when welding the circumference of the side wall of a large storage tank, a power source with constant voltage characteristics is used, so when the welding current is increased as the current density increases, the welding voltage also increases. It is currently known that undercuts are likely to occur, and it is difficult to obtain even better current density.In particular, it is difficult to further increase the current density, and even at present, undercuts occur when using high-temperature sintered flux. This invention is more expensive than ordinary fused flux, and in the case of a large storage tank with a large number of welded parts, the cost will increase the construction cost. The purpose of this invention is to provide a high-efficiency submerged arc welding method that can perform highly efficient welding and obtain a good bead. [Means for solving the problems] The above-mentioned problems As a result of research and experiments conducted by the inventor of the present invention in order to solve the problem, it was found that in the conventional power supply with drooping characteristics using one electrode wire A7, the welding phenomenon is
It can be seen that the migration of particles as shown in the figure is occurring, and if the current density is increased as it is, problems such as bead formation such as a longer arc length and problems with the followability of the power source will occur.
It turns out there are limits. In addition, since the multi-electrode welding method uses a power source with constant voltage characteristics, the arc length is long (about 30% of the arc voltage) as shown in Fig.
It was found that spray transfer occurs when the voltage is high, and these phenomena, especially when the arc IQ is 1, make it easy for undercutting to occur. ; It was noticed. (・, Shorten the arc length, and increase the welding voltage by V
? As a result of various experiments and research in order to cover the increase in current density by 1 without incurring It has been found that it is extremely effective to generate main arcs from wires that are close to each other and weld while alternating the generation of main arcs in a short period of time.
This invention was achieved. 71 However, the high-efficiency "bumerge arc welding method" of the present invention requires a single welding machine to perform welding while generating an arc between the electrode wire fed into the flux and the base metal. The electrode wire A7 feeding structure and the drooping characteristics of one unit are used to feed multiple electrode wires at high speed and high current density using a welding power source, and how close the base metal is to approach the main arc. The special feature is that the electrode wires are alternately used for welding. to prevent multiple wires A7
By bringing the wire closer to the base H, the arc length is shortened, and at the same time, most of the current (main current) is passed through the wire closest to the wire to alternate the main arc, thereby increasing the current sound intensity. ing. (Example) The high efficiency submerged arc welding method of the present invention will be specifically explained below with reference to the drawings.The welding principle of the high efficiency submerged arc welding method of the present invention is as shown in FIG. A single welding power source 10 with a plurality of (two in the illustrated example) electrode wires 1711
．． 12 is connected to the flux 15 supplied onto the base material 14 by the side 13 of the one-twir feeder, which simultaneously drives two feed rollers or one feed roller with two wheels with one drive source. Insert the electrode wire 11. '
+2 is now sent. The wire feeding mechanism 13 automatically adjusts the feeding speed to keep the arc length constant, but the distance between the base material 14 and the wire 1711. 7-1
1mmPi! If was 4-7IIIm
It is designed to maintain this state by bringing them close to each other. If a large current is not passed in this state, the following situation will occur in a very short time. First, a main arc occurs in the electrode wire 11 that is even slightly closer to the base metal 14, and the welding current increases to 1.
Spray transfer of small particles occurs in a concentrated manner on the main electrode wire A711, and one pool (molten pool) 16 is formed (
(See state 1.2 in Figure 1). Then, when the electrode wire 1711 melts to some extent, the electrode wires 11 and 12 are fed by the wire feeding mechanism 13 during this time as well, so the other wire 7111i 11 wire 12 gradually approaches the base material 14 from the same length. This will happen. Then, as in the third state in FIG. 1, the welding current will flow through the electrode wire 12 with low resistance, a main arc will occur, and spray transfer will occur. In this case as well, since both electrodes 11 and 12 are arranged close to each other (10 to 20 ml), they form the same pool as the electrode wire 11. In addition, since a current of only <2 flows to the electrode wire 11 on which the arc has changed, a slight transfer of droplets occurs due to the nub arc. When the electrode wire V12 through which the current was mainly flowing becomes shorter due to melting, the current mainly flows through the first electrode wire 11 again. Thus 1! ] The main arc is repeatedly generated from the electrode wire that is closer to the material 14. The current density in this case is about 7% of the welding current, unlike the case where arcs are generated from two electrode wires V11°12 at the same time.
Since about 0% flows in one tree, it becomes about twice as much, and an increase in the hot stone speed is achieved. Even in the high-efficiency Bumage arc welding method, in which the electrode wire A7 is brought close to the base metal and the main arc is alternated, there is a range of welding conditions that can produce a good bead depending on the diameter of the electrode wire used. For example, in Table 1. In addition, in the same table, when the number of electrodes (No.) is 1, the welding conditions are equivalent to those of the conventional method. Also, Fig. 2 shows the range of this welding condition in the drawing, and symbols a to c and A-B in Table 1 correspond to symbols a to C1A to B in Fig. 2. 1. Furthermore, the relationship between welding speed and welding current is shown in Figure 3. Both IJ' and J: differ depending on the diameter d5 of electrode wire A7 and welding conditions, but they can be used within the range shown in the figure. . For example, when two electrodes with a diameter of 1.6 mm are used, the welding current is 740 Amp, and the welding speed is 1100 CI), the welding speed is 220 g/min, and
Two electrode wires with a diameter of 2.4 mm were used, and the welding current was 85
The welding speed was 195 r/m1nr when the welding speed was 90 CP M. In all cases, good beads were formed and no undercutting occurred. Note that the constant voltage characteristics explained as the conventional method are applied to two power sources.
1.6 m when connecting two pole wires and welding with a strong arc generated at 2 water volume.
Using an electrode wire with a diameter of m, the welding current was 750AIIIρ.
and the welding speed is 1 when the welding speed is 850PM.
It was 900/min. In other words, it can be seen that according to the method of this invention, an increase of about 16% was achieved since the welding rate was 220 g/min under almost the same conditions. In addition, in the high-efficiency submerged arc welding method of this invention, mainly one electrode 1 No. A of the two electrode wires is used.
Since the welding current is concentrated at 7 and the welding is carried out close to the base metal, it is necessary to prevent the burn-through phenomenon due to large penetration, which can be solved by using a backing material, for example. Further, as a specific welding neck, for example, it can be constructed by modifying a conventional one-piece merged arc welding machine that uses a single electrode wire. In addition, the power supply of the welding machine has a drooping characteristic, and the maximum capacity is 800Amp so that it can be used by changing the diameter of the electrode wire.
If so, it can be used when two electrode wires of 2.4 mm and 1 yen are used according to the method of this invention (see Table 1). Therefore, the necessary modification is to be able to supply power to two electrode wires, to be able to feed two electrode wires using a wire feeder, and to be able to feed them at high speed. For this reason, the feed roller is changed to two or one with two grooves and replaced with a larger diameter one to accommodate a predetermined welding speed. Conventionally, when welding, when one electrode wire with a diameter of 2.4 mm is used, the welding current is 380 Am.
p and the welding method +a was set to 480 PM, but if these were set to 850 Δmp and 90 cP to 1, respectively, the welding speed could be increased from 80 q/min to 195 w/min. If you use the power supply of a conventional welding machine and change the wire feeding mechanism by replacing the feed roller, you can achieve high-efficiency submerging as shown in Figures 2 and 3 with one welding machine. It can also be used with arc welding method A-8 and normal 4-knob merged arc welding method a-C, and the welding range can be expanded. Although the above embodiment has been described using two electrodes, the invention is not limited to this, and it is also possible to use three or more electrodes. [Effects of the Invention] As specifically explained above in conjunction with the embodiments, the present invention enables the production of multiple Submerged arc welding is performed by feeding the electrode wires at high speed and high current density while bringing them closer to the base metal, and by alternating the main arc between multiple electrode wires.
Even when the current density is increased, the voltage does not rise as it does with constant voltage characteristics, and the arc length is short, so even when welding in a horizontal position, there is no undercut, resulting in high efficiency. Can be welded. Furthermore, it is easy to apply to conventional equipment, and can be achieved by simply modifying the wire feeding mechanism, greatly expanding the weldable range. 4. Brief description of the drawings Figures 1 to 3 show an embodiment of the high-efficiency submerged arc welding method of the present invention, and Figure 1 is an explanatory diagram of the welding principle;
Figure 2 is an explanatory diagram of the usable range of welding current and welding speed, Figure 3
The figure is an explanatory diagram of the change in welding speed with respect to the welding current. Figure 4 is an explanatory diagram of the welding phenomenon when a single electrode wire is used by a power supply with drooping characteristics. It is an explanatory view of a welding phenomenon when two electrode wires are used. 10... Welding power source, 11... Electrode wire A7.12.
...electrode wire, 13...wire feeding mechanism, 14...
- Base material, 15...Flux, 16...Pool. Applicant: Ishikawajima-Harima Heavy Industries Co., Ltd. Rakuo Mei (9/m1n) Houkifuma (Amρ,)

Claims (1)

[Claims] In the submerged arc welding method, which involves welding while generating an arc between the electrode wire fed into the flux and the base metal, multiple welds can be welded using one electrode wire feeding mechanism and one welding power source with drooping characteristics. High-efficiency submerged arc welding is characterized in that the electrode wires are fed at high speed and high current density while the distance from the base metal is brought closer to welding by alternating the arc between multiple electrode wires. Law.