JP6666098B2 - High current pulse arc welding method and flux cored welding wire - Google Patents

Description

  The present invention relates to a high current pulse arc welding method, and more particularly, to a high efficiency and high quality when one layer or multi-layer welding is performed downward in a fillet or a groove in a field of a transport machine, a construction machine and the like. The present invention relates to a novel high-current pulse arc welding method which can be welded by a welding method and can prevent pore defects. The present invention also relates to a novel flux-cored welding wire used in the high current pulse arc welding method.

  In the welding of medium-thick plates applied in the fields of transport and construction equipment, consumable electrode type gas shielded arc welding is often used to weld one or more layers in fillets and grooves. High quality and high efficiency are always required issues.

  For high efficiency, it is common to use a high current to increase the melting speed of the welding wire, but with the increase in current, a large amount of spatter is generated, which impairs the appearance of the weld, Quality is also reduced. As a result, the time and labor required for the sputter removal step increase, and the production efficiency decreases.

Conventionally, a solid wire is generally used as a consumable electrode (hereinafter sometimes referred to as a "welding wire"). However, when a method of increasing the melting rate of the welding wire with a high current to improve the efficiency is adopted, the solid wire exhibits a droplet transfer form called rotating transfer at the time of high current welding of 400 A or more.
In this transition mode, Joule heat is excessively generated at the protruding portion of the solid wire from the power supply tip to the arc generation point, and the softened and melted solid wire is melted at the tip of the wire due to the electromagnetic force generated in the arc. It moves while rotating with an arc. At this time, most of the separated droplets are scattered to the surroundings, and the amount of spatter generated is remarkable.

Further, in the case of welding performed at a high current, in addition to generation of spatter, problems relating to pore defects and abrasion of the contact tip occur. In the case of high current welding, the temperature of the molten pool increases, and the time until solidification increases. For this reason, solidification is not completed within the gas shielded range, and nitrogen in the atmosphere is caught in the molten pool, so that it becomes easy to form a solid solution. The solid-dissolved nitrogen turns into gas as nitrogen molecules during cooling, and is generated as bubbles in the molten metal.
When the bubbles in the molten metal solidify as they are, they become pore defects called blow holes. In addition, pore defects that solidify while leaving the atmosphere and remain as holes on the bead surface are called pits. Thus, in high current welding, pore defects are more likely to occur as the current value increases.

  In addition, high current welding has a problem in that the temperature around the contact tip becomes high, and the wear of the contact surface of the contact tip that energizes the welding wire (hereinafter, sometimes referred to as “tip wear”) increases. When the tip wear increases, the displacement and the replacement of the tip become frequent, and the work efficiency is reduced.

The following techniques are available for improving the efficiency of consumable electrode type gas shielded arc welding having these problems.
In Patent Document 1, a solid wire is used as an electrode wire and contains 40 to 70% by volume of argon, 25 to 60% by volume of helium, 3 to 10% by volume of carbon dioxide, and 0.1 to 1% by volume of oxygen. A welding method for obtaining a high welding amount by using a seed mixed gas as a shielding gas has been proposed.
In Patent Literature 2, a slag-based flux-cored wire is used as an electrode wire, carbon dioxide gas is used as a shielding gas, and welding is performed at a current density of 300 A / mm ² or more, thereby obtaining a high welding amount and bead smoothing by slag. A welding method that can also obtain an effect has been proposed.

Patent Literatures 3 and 4 propose a welding method that achieves high efficiency and low spatter by using multiple electrodes of two or more electrodes.
Patent Literature 5 proposes a welding method in which a flux-cored wire is used as a consumable electrode to suppress rotation transfer even at a high current density, thereby achieving high efficiency and low spatter.

JP-A-59-45084 JP-A-03-169485 JP 2008-55509 A JP 2010-264487 A JP 2011-218437 A

  The aim of the welding method of Patent Document 1 is to stabilize the spray transfer, but it does not improve the rotation transfer when the current is further increased, and generates a large amount of spatter. Further, in the welding method of Patent Document 2, since carbon dioxide gas is used as a shielding gas and welding is performed by direct current, the transfer form of droplets is a globular transfer, and a large amount of large spatters are generated.

In Patent Documents 3 and 4, high efficiency is achieved by using multiple electrodes. However, since the equipment is excessively large with multiple electrodes, operability is not excellent, and spatter may increase due to arc interference. Further, in Patent Literature 5, the use of flux-cored wires prevents rotation transition at a single torch and a high current density. However, since the pulse arc has a high current density, the arc length fluctuation is large, and the arc is not generated. Since it is easy to be stable, the quality may be deteriorated due to fine spatter or poor bead appearance.
Further, none of Patent Documents 1 to 5 mentions prevention of pore defects and chip wear which may be problems of high current welding.

  In view of the above circumstances, in the present invention, in high current pulse arc welding of a single electrode having excellent operability, it is possible to realize the suppression of pore defects and chip wear while obtaining an effect of reducing high welding and spatter. Provided are a high current pulse arc welding method and a flux-cored welding wire used in the welding method.

  As a result of intensive studies, the present inventor has found that the above problems can be solved by making high-current welding conditions appropriate in a specific flux-cored welding wire composition, and completed the present invention. Was.

That is, the present invention relates to the following [1] to [ 8 ].
[1] A pulse arc welding method of using a welding system including a welding power source, a welding torch, and a feeder to feed a consumable electrode from the feeder through the welding torch, and perform welding while flowing a shielding gas. And
The consumable electrode is a flux-cored welding wire filled with flux in the outer shell,
In the flux-cored welding wire, C is 0.30% by mass or less, Si is 0.30 to 1.60% by mass, Mn is 1.00 to 2.80% by mass, P is 0.050% by mass or less, S 0.050% by mass or less, and at least one element selected from the group consisting of Al, Ti, Zr and Mg in a total amount of 0.05 to 1.50% by mass ,
Al contained in the prior SL flux-cored welding wire, Ti, the ratio of the total mass% of the total mass% of Si and Mn and Zr and Mg, 0.11 ≦ (Al + Ti + Zr + Mg) / (Si + Mn) ≦ 0.60 relation The filling,
The flux-cored welding wire contains at least one oxide selected from the group consisting of Al oxide, Ti oxide, Zr oxide and Mg oxide, Al oxide is converted to Al ₂ O ₃ , Ti oxide is TiO ₂ conversion, Zr oxide conversion as ZrO ₂ conversion, and Mg oxide conversion as MgO conversion, the sum of the oxides is 0.20 mass% ≦ (Al ₂ O ₃ + TiO ₂ + ZrO ₂ + MgO) ≦ 1.50% by mass,
A high current pulse arc welding method, wherein a pulse peak current during welding is 550 to 950 A, a pulse base current is 550 A or less, and a difference between the pulse peak current and the pulse base current is 200 to 600 A.
[2] The flux-cored welding wire is selected from the group consisting of Al powder, Ti powder, Zr powder, Mg powder, and an alloy powder containing at least one element selected from the group consisting of Al, Ti, Zr and Mg. The high current pulse arc welding method according to the above [1], wherein at least one powder is included, and 30% by mass or more of the powder is a powder having a particle size of 100 μm or less.
[ 3 ] The high current pulse arc welding method according to [1] or [2] , wherein a pulse frequency during the welding is set to 50 to 200 Hz.
[ 4 ] The ratio of the pulse frequency at the time of welding to the feed rate at which the consumable electrode is fed is 1.50 (mm / 1 pulse) ≦ [feed rate (mm / sec) / pulse frequency (pulse) The number of times / sec)] ≦ 9.00 (mm / 1 pulse). The high-current pulse arc welding method according to any one of [1] to [ 3 ], wherein the method satisfies the following relationship:
[ 5 ] The height according to any one of [1] to [ 4 ], wherein the inclination of the external characteristic of the welding power source is −14.0 to −4.0 (V / 100 A). Current pulse arc welding method.
[ 7 ] The shield gas is an Ar gas containing Ar and impurities, or an Ar-containing mixed gas containing 0 to 40% by volume of CO ₂ and 0 to 10% by volume of O ₂ with the balance being Ar and impurities. The high current pulse arc welding method according to any one of the above [1] to [ 5 ], wherein:
[ 7 ] A flux-cored welding wire for high-current pulse arc welding, which has an outer shell and contains a flux in the outer shell,
The average current during welding is 400A or more,
C is 0.30% by mass or less, Si is 0.30 to 1.60% by mass, Mn is 1.00 to 2.80% by mass, P is 0.050% by mass or less, and S is 0.050% by mass or less. And at least one element selected from the group consisting of Al, Ti, Zr and Mg in a total amount of 0.05 to 1.50% by mass,
The ratio of the total mass% of Al, Ti, Zr, and Mg contained in the flux-cored welding wire to the total mass% of Si and Mn is 0.11 ≦ (Al + Ti + Zr + Mg) / (Si + Mn) ≦ 0.60. It meets,
It contains at least one oxide selected from the group consisting of Al oxide, Ti oxide, Zr oxide and Mg oxide, where Al oxide is converted into Al ₂ O ₃ , Ti oxide is converted into TiO ₂ , and Zr oxide is converted. In terms of ZrO ₂ and Mg oxide in terms of MgO, the sum of the oxides is 0.20% by mass ≦ (Al ₂ O ₃ + TiO ₂ + ZrO ₂ + MgO) based on the total mass of the flux-cored welding wire. flux-cored welding wire, characterized in Succoth meet ≦ 1.50% by weight of the relationship.
[ 8 ] Al powder, Ti powder, Zr powder, Mg powder, and at least one powder selected from the group consisting of an alloy powder containing at least one element selected from the group consisting of Al, Ti, Zr and Mg. The flux-cored welding wire according to [ 8 ], wherein 30% by mass or more of the powder is a powder having a particle size of 100 µm or less .

According to the present invention, the pulse peak current, the pulse base current, and the composition of the flux-cored welding wire in the pulse arc welding are made to have a specific combination, so that the droplet transfer and the arc can be compared with the conventional high current welding method. Is stable, and effects such as a pore defect resistance effect, low spatter, and chip wear resistance can be obtained.
In other words, in high current welding of a single electrode with excellent operability, it is possible to realize higher efficiency welding than ever before, and by reducing spatter and stomata resistance, the labor of the reworking process can be reduced, and the work efficiency of the welding process is improved. improves. Further, since pore defects and chip wear can be suppressed, improvement in work efficiency and low cost can be realized.

FIG. 1 is an overall configuration diagram showing an example of an apparatus used for the welding method according to the present invention. FIG. 2 is a graph showing an example of a pulse waveform used in the welding method according to the present invention. FIG. 3 is an explanatory diagram showing the self-control of the arc length in the welding method according to the present invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.
The high current pulse arc welding method according to the present invention uses a welding system including a welding power source, a welding torch and a feeder, and feeds a consumable electrode by the feeder through the welding torch and flows a shielding gas. Weld while doing
The consumable electrode is a flux-cored welding wire filled with flux in the outer shell,
In the flux-cored welding wire, C is 0.30% by mass or less, Si is 0.30 to 1.60% by mass, Mn is 1.00 to 2.80% by mass, P is 0.050% by mass or less, S 0.050% by mass or less, and at least one element selected from the group consisting of Al, Ti, Zr and Mg in a total amount of 0.05 to 1.50% by mass, and the pulse peak current at the time of welding is 550. 950 A, a pulse base current of 550 A or less, and a difference between the pulse peak current and the pulse base current of 200 to 600 A.

Further, the flux-cored welding wire according to the present invention has a shell, a flux-cored welding wire for high-current pulse arc welding containing a flux in the shell,
The average current during welding is 400A or more,
C is 0.30% by mass or less, Si is 0.30 to 1.60% by mass, Mn is 1.00 to 2.80% by mass, P is 0.050% by mass or less, and S is 0.050% by mass or less. And at least one element selected from the group consisting of Al, Ti, Zr and Mg in a total amount of 0.05 to 1.50 mass%.

[Welding equipment]
First, a welding device that can be used in the high current pulse arc welding method according to the present invention will be described. The welding apparatus is not particularly limited as long as it performs high current pulse arc welding, and a conventionally used welding apparatus can be used.

  For example, as shown in FIG. 1, in the welding apparatus 1, a welding torch 11 is attached to a distal end, and the welding torch 11 is a work to be welded (hereinafter, also referred to as “work” or “base material”) W. A robot 10 that moves along the welding line, a wire supply unit (not shown) that supplies a welding wire to the welding torch 11, and a current that is supplied to the consumable electrode via the wire supply unit and the consumable electrode and the workpiece And a welding power source unit 30 for generating an arc between the power source and the welding power source. Further, the welding device includes a robot control unit 20 that controls a robot operation for moving the welding torch 11.

<Welding wire with flux>
The consumable electrode in the present invention is a flux-cored welding wire in which the outer shell is filled with flux. That is, the flux-cored welding wire is composed of a cylindrical outer shell and a flux filled inside the outer shell.
The flux-cored welding wire may be either a seamless type having no outer skin or a seam type having a outer seam. Further, the surface of the wire (outside the outer skin) may or may not be plated with copper.

  The flux-cored welding wire contains a predetermined amount of C, Si, Mn, P and S, and further contains a predetermined amount in total of at least one element selected from the group consisting of Al, Ti, Zr and Mg. Al, Ti, Zr and Mg are known as strong deoxidizing elements, but also have a strong denitrifying effect, and are elements that easily react with N to form nitrides.

  Hereinafter, the numerical range of the component amount of the flux-cored welding wire will be described together with the reasons for the limitation. Unless otherwise specified, the amount of components is expressed as the sum of the amounts of components in the outer sheath and the flux, and the mass of each component contained in the flux-cored welding wire (outer skin + flux) is specified as a percentage of the total mass of the wire. I do.

(C: 0.30% by mass or less)
C in the welding wire or the weld metal is effective in increasing the strength of the weld metal. The lower limit is not set because there is no problem even if the content is small, but if it is contained in a large amount exceeding 0.30% by mass, it is combined with oxygen during welding and becomes CO gas to form a droplet surface. Generate bubbles. The generated bubbles are scattered to generate spatter. Therefore, the content of C is specified to be 0.30% by mass or less.
On the other hand, C may not be contained, but is preferably 0.01% by mass or more for securing strength.

(Si: 0.30 to 1.60 mass%)
Si in the welding wire is a deoxidizing element and is an element necessary for securing the strength and toughness of the weld metal. If the addition amount is small, blowholes are generated due to insufficient deoxidation, so the content is 0.30% by mass or more, preferably 0.50% by mass or more.
On the other hand, if contained in a large amount exceeding 1.60% by mass, a large amount of slag that is difficult to peel off during welding is generated and welding defects such as slag winding crowding occur, so the upper limit is 1.6% by mass. 1.30 mass% or less is preferable.

(Mn: 1.00 to 2.80 mass%)
Mn in the welding wire, like Si, exhibits an effect as a deoxidizing agent or a sulfur scavenger, and is necessary for securing the strength and toughness of the weld metal. 1.00 mass% or more is contained to prevent generation of welding defects due to insufficient deoxidation. Preferably, it is at least 1.10% by mass.
On the other hand, if contained in a large amount exceeding 2.80% by mass, a large amount of slag that is difficult to peel off during welding is generated, and welding defects such as slag winding crowding are generated. Further, the strength is excessively increased, and the toughness of the weld metal is significantly reduced. For this reason, the upper limit of the Mn content is 2.80% by mass, and it is preferably 2.30% by mass or less.

(P: 0.050% by mass or less (including 0% by mass))
(S: 0.050% by mass or less (including 0% by mass))
Since both S (sulfur) and P (phosphorus) are impurity elements, and it is preferable to minimize the content, the lower limit is not set. If each of them is present in a large amount exceeding 0.050% by mass, welding defects such as cracks in the weld metal occur. Therefore, in both cases, the upper limit is 0.050% by mass.

(Strong denitrifying element: 0.05-1.50 mass% in total)
Al, Ti, Zr and Mg are elements having a strong denitrifying effect (strong denitrifying elements). The lower limit of the content of at least one strongly denitrifying element selected from the group consisting of Al, Ti, Zr and Mg is set to 0.05% by mass in total. If the content is 0.05% by mass or more, N dissolved in welding during welding and the strongly denitrifying element react with each other to form a nitride. Therefore, pore defects generated when the N is released into the atmosphere as N ₂ (gas). Can be prevented. The lower limit of the total content of the strong denitrifying elements is preferably 0.10% by mass or more, more preferably 0.25% by mass or more.
On the other hand, when the total amount of the strong denitrifying elements exceeds 1.50% by mass, nitrides and oxides generated by the strong denitrifying elements are generated on the surface of the molten pool, and the arc is deflected, resulting in a large amount of spatter. Will occur. Therefore, the upper limit of the total amount of the strong denitrification elements is 1.50% by mass, preferably 1.00% by mass or less, and more preferably 0.80% by mass or less.

(Other elements)
(Mo, Ni, Cr, B)
Mo, Ni, Cr, B may be added to improve the strength or toughness of the weld metal. If these elements are added excessively, cracks are likely to occur. Therefore, Mo is preferably 1.00% by mass or less, Ni is preferably 1.00% by mass or less, Cr is preferably 5.00% by mass or less, and B is 0.0050% by mass. % Is preferable.

(Li, K, Na)
Li, K, and Na may be added to stabilize the arc, reduce the amount of spatter generated, and improve the penetration performance. Each element is preferably contained in an amount of 0.010 to 1.000% by mass.
Examples of compounds of Li, K, and Na contained in the flux-cored welding wire include oxides and carbonates such as LiO ₂ , Li ₂ CO ₃ , K ₂ O, and Na ₂ O, and fluorine compounds such as K ₂ SiF _6. Compounds.

(The rest)
Other elements constituting the flux-cored welding wire include Fe and impurities. Examples of the impurities include Co and W. In the case of having plating, Cu is also included as another element.

(Content ratio of strong denitrification element)
Al, Ti, Zr and Mg are denitrifying elements and also act as deoxidizing elements. Therefore, by adding deoxidizing elements Si and Mn, pore defects due to oxygen are prevented by Si and Mn, and Al, Ti, Zr and Mg exhibit more effects as denitrifying elements than as deoxidizing elements. To promote the reaction with N. Therefore, the ratio (Al + Ti + Zr + Mg) / (Si + Mn) of the total mass% of Al, Ti, Zr and Mg contained in the flux-cored welding wire to the total mass% of Si and Mn is preferably 0.03 or more, More preferably, it is 0.08 or more.
In addition, since oxides of Al, Ti, Zr and Mg have excellent thermionic electron emission ability, if an appropriate amount is present on the molten pool, it contributes to arc stability. Therefore, from the viewpoint that the arc stability is increased by the optimum cathode spot forming effect and the slag removability is further improved, (Al + Ti + Zr + Mg) / (Si + Mn) is preferably 0.60 or less, and 0.40 or less. Is more preferable.

(Metal powder)
When Al, Ti, Zr and Mg contained in the flux-cored welding wire are powders or alloy powders, that is, from the group consisting of Al powder, Ti powder, Zr powder, Mg powder, and Al, Ti, Zr and Mg When at least one powder selected from the group consisting of alloy powders containing at least one selected element is included, it is preferable that 30% by mass or more of the total of the powders is a powder having a particle size of 100 μm or less.
This is because the finer the particle size, the easier it is to dissolve uniformly in the molten pool, so that the reaction with N is promoted, and the more excellent the pore resistance is. Further, since the smaller the particle size of the powder, the more preferable, the content of the powder having a particle size of 100 μm or less is more preferably 50% by mass or more, while there is no upper limit and the content may be 100% by mass.
Incidentally, examples of the alloy powder include Fe-Al (ferroaluminum) and Fe-Ti (ferrotitanium).

  The content of the powder having a particle size of 100 μm or less is sieved by sieving Al powder, Ti powder, Zr powder, Mg powder, and alloy powder thereof through a 100 μm mesh based on JIS Z8801-1: 2006. Can be measured.

(High melting point oxide)
Further, the flux-cored welding wire contains at least one oxide selected from the group consisting of Al oxide, Ti oxide, Zr oxide and Mg oxide, converts Al oxide to Al ₂ O _{3, and} converts Ti oxide to Ti oxide. The sum of the oxides in terms of TiO ₂ , Zr oxide in terms of ZrO ₂ , and Mg oxide in terms of MgO is 0.05% by mass ≦ (Al ₂ (O ₃ + TiO ₂ + ZrO ₂ + MgO) ≦ 1.50 mass% is preferably satisfied.

Al oxide, Ti oxide, Zr oxide and Mg oxide are all high melting point oxides of 1800 ° C. or higher. The inclusion of the high-melting-point oxide is preferable because the flux column can remain in the high-temperature arc, and stable droplet transfer can be realized.
If the content of the high melting point oxide with respect to the flux-cored welding wire is less than 0.20% by mass, the flux columns may be dissolved. Therefore, the content of the high melting point oxide is preferably 0.20% by mass or more, and more preferably 0.25% by mass or more.
On the other hand, if it exceeds 1.50% by mass, a large amount of slag is generated, and welding defects such as slag entrainment may occur. Therefore, the amount is preferably 1.50% by mass or less, more preferably 1.00% by mass or less.

If the average particle size of the high-melting oxide composed of Al oxide, Ti oxide, Zr oxide, and Mg oxide is too large, the oxide may bite into the flux at the time of wire forming, and may break. Therefore, the average particle size of the Al oxide, Ti oxide, Zr oxide, and Mg oxide is preferably 350 μm or less, more preferably 300 μm or less. As the average particle size is smaller, the disconnection is more difficult, and the components in the flux are mixed so as to be evenly distributed.
The particle size of the oxide can be measured through a sieve with openings of 75, 100, 150, 200, 250, 300, 355, and 425 μm according to JIS Z 8801-1: 2006.

(Flux filling rate)
The flux filling rate in the flux-cored welding wire is preferably 10 to 25% by mass. If the flux filling ratio is less than 10% by mass, the arc stabilizing effect of the flux column may be lost. On the other hand, if it exceeds 25% by mass, there is a possibility that breakage during feeding or arc pressure immediately below the wire becomes small and penetration does not occur. The flux filling rate is more preferably 12% by mass or more, and more preferably 22% by mass or less.
In addition, this flux filling rate is defined as the mass of the flux filled in the outer skin as a ratio to the total mass of the wire (the outer skin + flux).

  The final product diameter of the flux-cored welding wire does not matter, but it is preferably 1.2 to 1.6 mm as a generally used range.

<Method of manufacturing flux-cored welding wire>
The manufacturing method of the flux-cored welding wire is not particularly limited, and may be manufactured by a general manufacturing process. For example, it is manufactured by molding a mild steel or stainless steel hoop into a U-shape, filling a U-shaped molded hoop with a flux, molding the flux into a cylindrical mold filled with the flux, and drawing to a target diameter. I just need.

  The material of the outer skin can be used without any particular limitation, such as mild steel and stainless steel, and the element composition in the total weight of the flux-cored welding wire may be within the above range.

  The particle size of the flux can be determined by sieving. According to JIS Z 8801-1: 2006, a sieve having an opening of 75, 100, 150, 200, 250, 300, 355, or 425 μm can be used.

<Shield gas>
The shielding gas used in the high current pulse arc welding method according to the present invention is not particularly limited, and Ar gas, carbon dioxide gas (carbon dioxide, CO ₂ ), oxygen gas (O ₂ ), a mixed gas thereof, or the like may be used. Can be. These may contain oxygen, nitrogen, hydrogen and the like as inevitable impurities.
Even with welding using 100% CO ₂ as a shielding gas, the gas shielded arc welding method according to the present invention can obtain the effects of suppressing entrapment in the atmosphere and preventing an oxidation reaction. However, by using Ar gas or an Ar-containing mixed gas as the shielding gas, it becomes possible to further reduce the oxidation reaction of the molten metal. Therefore, it is preferable to use an Ar gas (100% Ar) composed of Ar and unavoidable impurities or an Ar-containing mixed gas as the shield gas.

In the case of an Ar-containing mixed gas, it is preferable to contain Ar, at least one of CO ₂ and O ₂ , and an unavoidable impurity, and the CO ₂ content is 0 to 40% by volume and the O ₂ content is 0 to 10% by volume. Is more preferable. More preferably, it contains 80% by volume or more of Ar, and the balance is at least one of carbon dioxide and oxygen and unavoidable impurities.

  Generally, the flow rate of the shielding gas may be 35 L / min or less. Accordingly, it is possible to prevent the shield gas flow velocity from being excessively increased, and to suppress the air from being drawn into the shield atmosphere due to the high-speed gas flow.

<Welding power supply>
The welding power source is not particularly limited, and a power source conventionally used for pulse arc welding can be used.

<Welding torch>
The welding torch is not particularly limited, and a torch similar to a conventional one can be used.
An example of a welding torch is shown below. A torch clamp is mounted on the welding torch. The current-carrying bracket is used to pass a weak current used for detecting contact between the nozzle and the work to the nozzle. The torch clamp fixes the welding torch to the robot.

  The torch barrel is supported by a torch clamp and has a mechanism for supporting a nozzle and a tip body. The torch barrel can supply the supplied welding wire to the tip of the tip body (the rear end of the contact tip) via the inner tube with the tip body mounted. In addition, the torch barrel supplies a welding current to the tip body and further supplies a shielding gas to a space formed between the inner tube and the tip body. The tip body includes an orifice, an orifice support nut, and a mechanism for supporting the contact tip. Note that the chip body is formed of a conductive material such as a metal.

  The orifice has a mechanism for rectifying the shield gas. That is, the orifice usually has a cylindrical shape, and is mounted by being inserted from the front end side of the outer periphery of the tip body. The contact tip is provided with a mechanism for feeding a welding current to the welding wire and guiding the welding wire to a work to be welded. Note that, like the chip body, the contact chip is also formed of a conductive material such as metal.

The posture of the welding torch may be vertical or inclined with respect to the base material.
When the welding torch is inclined toward the opposite side of the welding progress direction, the angle between the perpendicular to the base material and the torch is referred to as the advance angle, and when inclined toward the welding progress direction, the perpendicular to the base material And the torch are referred to as a sweep angle.

By providing the welding torch with an advancing angle, it is possible to more effectively enhance the shielding property during arc welding. In addition, since the rear of the bead can be shielded by providing the receding angle to the electrode, the oxidation reaction of the bead immediately after welding can be suppressed.
In order to obtain a proper penetration and a good bead shape on the welding line, the range of the advancing angle is -15 to 40 °, that is, the upper limit of the advancing angle is 40 °, and the upper limit of the receding angle is 15 °. More preferably, the electrodes are tilted.

(nozzle)
The nozzle has a mechanism for ejecting a shielding gas supplied from a gas supply device (not shown) to a base metal to be welded. The nozzle is formed in a cylindrical shape having an internal space in which the tip body, the orifice, and the contact tip in an assembled state can be housed. Further, the nozzle has a female screw portion on the inner surface at the rear end, into which a male screw portion formed at the tip of the torch barrel is screwed. With this configuration, the nozzle can shield the weld from the atmosphere using the shield gas rectified by the orifice.
In the welding method according to the present invention, it is preferable to use a torch that is water-cooled to the vicinity of the nozzle from the viewpoint of chip wear.

<Feeder>
The feeder is not particularly limited, and a conventionally used feeder can be used.

<Pulse arc welding conditions>
The pulse defined by the present invention is a current waveform that repeats a rectangular or trapezoidal shape. FIG. 2 shows an example of the current waveform. The time at the upper bottom of a rectangular or trapezoidal shape is a pulse peak current period (pulse peak period) Tp, and the time at the lower bottom is a pulse base current period (pulse base period) Tb. The current in the pulse peak period Tp is defined as a pulse peak current Ip, and the current in the pulse base period Tb is defined as a pulse base current Ib. Then, the time integration of the welding current over time is averaged to obtain an average current Ia. That is, in the case of a rectangular wave, it is represented by Ia = (Ip.Tp + Ib.Tb) / (Tp + Tb). The number of pulses per second (the number of times one wavelength repeats) is defined as the pulse frequency.

The pulse current waveform is a method in which droplets generated in the low-current pulse base period Tb and the high-current pulse peak period Tp are separated by the electromagnetic force of the pulse peak current Ip. If the separation timing is incorrect, the spatter may increase, the arc may be deflected, and the bead appearance may be poor.
For example, if the pulse peak current Ip is too low, arc rigidity cannot be obtained, and the arc may be deflected. On the other hand, if the pulse base current Ib is too high, the droplet may be detached at the time of the rise of the peak current, and the droplet may be scattered by the arc pressure of the peak current to increase spatter. In particular, in the case of high-current pulse arc welding, the transition to the rotation is likely to occur, so that it is difficult to obtain appropriate pulse conditions.
In the high current pulse arc welding method according to the present invention, the flux-cored welding wire to be used is limited to a specific composition, and the optimum conditions of the pulse arc welding in which a synergistic effect appears when the welding wire is used are defined below.

(Pulse peak current Ip: 550-950A)
The pulse peak current at the time of welding is 550A or more and 950A or less. If it is less than 550A, the arc will be insufficiently rigid, and the arc will be easily pulled to the cathode spot based on the oxide generated from Al, Ti, Zr, and Mg in the welding wire for high current. As a result, arc deflection occurs, and spatter tends to increase. On the other hand, when the current exceeds 950 A, the current becomes excessively high and the temperature becomes high, so that the flux column of the flux-cored welding wire does not remain, the arc stability is deteriorated, and the amount of spatter generated tends to increase.

(Pulse base current Ib: 550 A or less)
The pulse base current at the time of welding is 550 A or less. If the pulse base current exceeds 550 A, the arc pressure applied to the droplet during the pulse base period Tb becomes excessive, thereby promoting arc instability and increasing the amount of spatter generated.

(Difference between pulse peak current Ip and pulse base current Ib: 200 to 600 A)
The difference between the pulse peak current Ip and the pulse base current Ib during welding is 200 A or more and 600 A or less. When the current difference is less than 200 A, the balance of droplet transfer is lost, the possibility of droplet detachment at the peak current increases, and spatter tends to increase. On the other hand, if the current difference exceeds 600 A, the fluctuation in the arc length at the time of the peak current becomes large, so that nitrogen is easily involved and pore defects are liable to occur.

  That is, by using the flux-cored welding wire of the present invention and setting the pulse peak current, the pulse base current and the difference between these currents to the above ranges, the droplet transfer and the arc are more stable compared to the conventional high current welding method. In addition, excellent effects such as a pore defect resistance effect, low spatter, and chip wear resistance can be obtained.

(Average current Ia)
Average current Ia is obtained by temporally averaging the time integral of the welding current during welding. That is, in the case of a rectangular wave, the average current can be defined by Ia = (Ip.Tp + Ib.Tb) / (Tp + Tb).

(Pulse frequency Fp)
When the pulse frequency at the time of welding is in a low frequency range of 50 to 200 Hz, it is preferable that a longer pulse base period can be ensured, a sudden change in arc length can be suppressed, and arc deflection can be suppressed. Further, within the pulse base period, since the arc pressure of the droplet is small, the movement of the droplet which has increased during the pulse peak period can be suppressed, and as a result, the rotation transition can be suppressed, which is preferable. . Further, with respect to chip wear, the pulse frequency is low, and a chip cooling effect can be expected during the pulse base period, so that chip wear is preferably reduced.

(Feed speed / Pulse frequency)
In pulse arc welding, spatter increases when the timing of detachment of droplets is incorrect. Therefore, it is preferable to determine the feed rate of the consumable electrode (flux-cored welding wire) in addition to the pulse frequency to transfer the droplets and obtain further low spatter and arc stability. However, since the appropriate feed speed changes depending on the pulse frequency, the ratio of the feed speed to the pulse frequency [feed speed (mm / sec) / pulse frequency (number of pulses / sec = Hz)] per wavelength Is specified (mm / 1 pulse).

The feed rate per wavelength represented by [feed rate (mm / sec) / pulse frequency (number of pulses / sec = Hz)] is from 1.50 (mm / 1 pulse) to 9.00 (mm / 1). Pulse) or less.
If it is less than 1.50 (mm / 1 pulse), the welding amount is insufficient at the time of peak current, and the arc tends to crawl, so that arc instability such as arc length variation and arc deflection may occur. If it exceeds 9.00 (mm / 1 pulse), the wire may plunge into the molten pool at the time of the base current, and the wire may be short-circuited, which may increase spatter.

  The pulse peak current, pulse base current, pulse peak period, pulse base period, and pulse frequency can all be adjusted by setting the welding power source.

  “High current” in the high current pulse arc welding method according to the present invention indicates that the value of the average current Ia is 400 A or more.

(External characteristics)
In the case of high-current pulse arc welding, a pulse peak current having a large current difference and a pulse base current are switched at high speed, so that the arc length fluctuation becomes large. In order to suppress the variation in the arc length, the variation in the arc length can be suppressed by making the current change insensitive. On the other hand, if the change in current is made too insensitive, the self-control of the arc length is lost. Therefore, high current pulse arc welding has an appropriate range of the inclination of external characteristics.

As shown in FIG. 3, if the arc length is shortened from _{l O} to _{l S,} current increases to _{I S} from _{I O.} Therefore, the melting rate of the welding wire increases act to increase the arc length, arc length is pulled back to the original length l _O. If the arc length on the opposite is long from _{l O} to _{l L,} current decreases from _{I O} to _{I L.} Therefore, the melting rate of the welding wire is reduced acts to shorten the arc length, arc length is also pulled back to its original length l _O. Such a phenomenon that the arc length is controlled so as to be automatically returned to the original length is called an arc length self-control operation. The effect of the self-control action appears as the slope of the current-voltage curve becomes gentler. The slope of the current-voltage curve is the slope of the external characteristic of the welding power source.

In the present invention, the slope of the external characteristic is preferably -14.0 (V / 100A) or more and -4.0 (V / 100A) or less.
By setting it to −4.0 (V / 100 A) or less, it is possible to suppress a large current change at the time of high current pulse arc welding and to suppress an arc length variation. Therefore, welding with lower spatter can be realized, and chip wear is further suppressed. On the other hand, if the value is lower than -14.0 (V / 100A), the self-control action of the arc is lost, so that the effect of suppressing the fluctuation of the arc length may not appear.

<Material to be welded (workpiece, base material)>
A conventionally known material can be used as the material to be welded. For example, a rolled steel material for a welding structure belonging to JIS G 3106: 2015, a rolled steel sheet for a general structure belonging to JIS G 3101: 2015, and the like can be given.

<Weldment>
Although the welding method according to the present invention is performed at a high current, the welded article welded by the welding method is welding of a medium-thick plate in the field of a transport machine, a construction machine, and the like. It is particularly preferably used in the case of layer or multi-layer welding.

(Spatter amount)
The amount of spatter can be quantified by, for example, installing a box on both sides of the welded portion and performing welding, collecting all generated spatter from the inside of the box (inside the box), and measuring the mass. The smaller the value of the spatter amount of the obtained welded product, the better, but the preferred value varies depending on the wire composition used.

(Bead appearance)
As the bead appearance, it is preferable that there is no meandering on the bead surface. Note that the bead surface means a weld metal (a part of a weld portion, which is melt-solidified during welding) formed by one pass, and conforms to the definition in JIS Z 3001-1: 2013.

(Weld defect)
It is preferable that the welded article does not have any pore defects caused by nitrogen such as pits and blow holes, slag entrapment, and welding defects such as welding cracks. The welding defect can be evaluated by visual observation of the bead surface or macro observation of the cross section of the bead.

(Arc stability)
The arc stability at the time of welding can be determined by visual observation using a light-shielding surface and a current waveform, based on a change in arc length. In the current waveform, it is preferable that the ratio (fluctuation rate) of a high current equal to or higher than the set peak current value or a low current equal to or lower than the set base current value flows.

(Tip wear)
The smaller the value of contact tip wear (tip wear) after welding, the better. For example, by measuring the tip wear area after welding, the tip wear amount per unit time can be evaluated.

  Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these Examples, and the present invention is implemented with modifications within a range that can be adapted to the gist of the present invention. And they are all included in the technical scope of the present invention. Further, the welding conditions described here are examples, and the present embodiment is not limited to the following welding conditions.

<Evaluation method>
(Particle size of strong denitrification element powder)
The proportion of the powder having a particle size of 100 μm or less in the total content of the single metal powder and the alloy powder of the strong denitrifying element composed of Al, Ti, Zr and Mg contained in the flux-cored welding wire is JIS Z8801-1: 2006. Was measured using a sieve having an opening of 100 μm.

(Spatter amount)
Welding was performed for 1 minute in a state where a box made of a copper plate was installed on both side surfaces of the welded portion. All spatters generated during the welding were collected from the box (inside the box), and the total mass of the collected spatter was measured. The mass at this time was defined as the amount of sputtering (g / min).

(Bead appearance)
The presence or absence of meandering on the bead surface of the obtained welded product was visually confirmed, and the quality of the bead appearance was determined.

(Weld defect)
As welding defects, the presence or absence of pore defects, slag entrapment, and welding cracks were evaluated by visual observation of the bead surface and macro observation of the cross section of the bead. In the macro observation of the cross section of the bead, macro observation was performed on any five places in the cross section of the bead to determine the presence or absence of a welding defect.

(Tip wear)
A large plate having a size of 25 mm (t) x 650 mm (w) x 650 mm (l) is welded with a bead-on-plate for 1 hour, and the chip wear area when the welded chip is viewed from the front with an optical microscope is shown. It was measured by the area converted from the number of pixels of the electronic data.

(Arc stability)
The arc stability at the time of welding was determined based on a change in arc length by visual observation using a light-shielding surface and a current waveform. In the current waveform, when welding is performed for 60 seconds, the current exceeds +50 A with respect to the set peak current value, and the current falls below -50 A with respect to the set base current value. Each was counted, and the total value of the counts at that time was defined as a fluctuation value.

<Test Examples 1 to 55>
High current pulse arc welding was performed using a steel wire of JIS G3101: 2015 SS400 as a base material and a flux-cored welding wire. The wire diameter of the welding material was 1.4 mm, and a mixed gas of Ar: CO ₂ in a volume ratio of 80:20 was used as the shielding gas.
When evaluating the bead appearance, two fillets (size 12 mm (t) x 50 mm (w) x 500 mm (l)) are T-shaped, and downward fillet welding is performed. Perpendicular to. When performing other evaluations, downward welding of the bead-on-plate was performed.

Table 1 shows the composition of the flux-cored welding wire used in each test example.
The pulse arc welding conditions are as follows, and specific welding conditions of each test example are shown in Table 2.
-Pulse peak current: 550-1000A
・ Pulse base current: 100 to 600A
・ Pulse peak period: 1.5 to 7.5 msec
・ Pulse frequency: 30 to 300 Hz
・ Average current: 450 to 620A
-Feeding speed: 16.0-26.0m / min
・ Arc voltage: appropriate voltage (30-50V)
・ External characteristics: -16.0 to -1.0 (V / 100A)

  In Table 1, a chemical composition of "-" indicates that the chemical composition is an unavoidable impurity and is not actively added. In addition, wire no. Are the flux-cored welding wires satisfying the condition of the flux-cored welding wire in the present invention, and the flux-cored welding wires W24 to W34 are wires that do not satisfy the condition. The flux-cored welding wire of W34 is a conventional welding wire, and is a welding wire to which Al, Ti, Zr and Mg are not added.

  In Table 2, "f.rate" represents a feeding speed at which a consumable electrode (flux-cored welding wire) is fed. “No.” represents the test example number, and “No.” (Test Example) 1-No. No. 39 is an embodiment satisfying the conditions of the welding method according to the present invention. 40-No. No. 44 is a comparative example which does not satisfy the pulse arc welding conditions in the present invention. 45-No. 55 is a comparative example which does not satisfy the composition of the flux-cored welding wire in the present invention.

No. 1 to No. Table 3 shows the results regarding the spatter, bead appearance, welding defects, chip wear and arc stability of the welded product obtained in No. 55.
In Table 3, the evaluation of “sputtering” indicates that ◎ indicates that the value was 0.80 (g / min) or less, and ○ indicates that the evaluation exceeded 0.80 (g / min) and 1.60 (g / min) or less. X indicates that it is more than 1.60 (g / min).
In "Evaluation of bead appearance", "O" indicates a normal bead, and "X" indicates that a bead appearance defect exists.
In the “welding defect evaluation”, ○ indicates a state in which none of pore defects, slag entrapment, and welding cracks exist, and X indicates a state in which any one or more of them exist. In addition, when it was x, the defect seen in parentheses was also described.
In the evaluation of “tip wear”, “○” indicates that the wear area was less than 0.65 mm ² , and that even if a pulse was applied, the wear resistance was equal to or higher than that of conventional constant current welding. Indicates that the area is 0.65 mm ² or more.
The evaluation of “Arc stability” indicates that the variation value is less than 250, ○ indicates that the variation value is 250 or more and less than 500, x indicates that the variation value is 500 or more, and This indicates that the variation in arc length is large enough to confirm arc instability by visual observation using a light-shielding surface.

  No. 1 to No. In Example 39, the welding wire and the pulse peak current and the pulse base current had the optimum composition, so that no pore defects were generated and the arc was stable. In particular, no. 1 to No. 27 is a welding wire having a more preferable composition, a pulse frequency, external characteristics, and the like, and the arc stability and the low spattering property are further improved.

On the other hand, the comparative example No. Reference numeral 40 denotes a case where the pulse peak current is excessively large, the temperature of the wire tip becomes high, and the flux column does not remain. As a result, arc deflection occurred and the arc became unstable, resulting in increased spatter and meandering of the beads. No. Reference numeral 41 denotes a case where the pulse peak current is too small, and an appropriate arc stiffness cannot be obtained during the pulse peak period, and is affected by a cathode spot formed by Al or Ti oxide. As a result, arc deflection occurred and the arc became unstable, resulting in increased spatter and meandering of the beads.
No. Reference numeral 42 indicates a case where the difference between the pulse peak current and the pulse base current is excessively large. The arc became unstable, and the occurrence of pore defects was confirmed. No. Reference numeral 43 indicates a case where the difference between the pulse peak current and the pulse base current is too small. The advantage of the pulse was reduced, and an increase in spatter was confirmed.
No. Reference numeral 44 denotes a case where the pulse base current was excessively large, and the arc pressure during the pulse base period during which the droplet was separated increased, so that the spatter increased.

  No. In No. 45, the amount of C in the welding wire was excessive, and spatter increased. No. In No. 46, the amount of Si was excessive, and slag entrainment occurred. No. 47 and No. In No. 48, the amount of Si or Mn was too small, and a pore defect occurred because the deoxidizing effect was not obtained. No. No. 49 had an excessive amount of Mn, and slag was involved. No. 50 and No. No. 51 had excessive amounts of P and S, respectively, and cracks occurred.

  No. In No. 52, the total content of elements having a strong denitrification effect was excessive, spatter increased, and bead meandering occurred. No. In No. 53, an element having a strong denitrifying effect consisting of Al, Ti, Zr and Mg was not added, and the denitrifying effect was not obtained, and pore defects occurred. No. In No. 54, the total content of the elements of strong denitrification was too small, the denitrification effect was not obtained, and pore defects occurred.

  No. Reference numeral 55 denotes a conventional welding wire with no addition of Al, Ti, Zr, and Mg as the conventional reference for the present invention, which is welded under conventional welding conditions (constant voltage DC) without using a pulse. It is. Since Al, Ti, Zr and Mg were not added, no denitrification effect was obtained, and pore defects were generated by welding under a high current of 550 A average current. In addition, the arc was unstable due to normal DC welding without using a pulse, which is one of the welding methods according to the present invention, and increased spatter and meandering of beads occurred.

  From the above, No. satisfying the welding method according to the present invention. 1 to No. In the case of No. 39, it was proved that in high current welding, pore defects were prevented, and good arc stability, low spatter, bead shape, and chip wear resistance were obtained.

DESCRIPTION OF SYMBOLS 1 Welding apparatus 10 Robot 11 Welding torch 20 Robot control unit 30 Welding power supply unit W Workpiece (workpiece, base metal)

Claims (8)

A pulse arc welding method that uses a welding system including a welding power source, a welding torch and a feeder, supplies consumable electrodes by the feeder through the welding torch, and performs welding while flowing a shield gas. ,
The consumable electrode is a flux-cored welding wire filled with flux in the outer shell,
In the flux-cored welding wire, C is 0.30% by mass or less, Si is 0.30 to 1.60% by mass, Mn is 1.00 to 2.80% by mass, P is 0.050% by mass or less, S 0.050% by mass or less, and at least one element selected from the group consisting of Al, Ti, Zr and Mg in a total amount of 0.05 to 1.50% by mass ,
Al contained in the prior SL flux-cored welding wire, Ti, the ratio of the total mass% of the total mass% of Si and Mn and Zr and Mg, 0.11 ≦ (Al + Ti + Zr + Mg) / (Si + Mn) ≦ 0.60 relation The filling,
The flux-cored welding wire contains at least one oxide selected from the group consisting of Al oxide, Ti oxide, Zr oxide and Mg oxide, Al oxide is converted to Al ₂ O ₃ , Ti oxide is TiO ₂ conversion, Zr oxide conversion as ZrO ₂ conversion, and Mg oxide conversion as MgO conversion, the sum of the oxides is 0.20 mass% ≦ (Al ₂ O ₃ + TiO ₂ + ZrO ₂ + MgO) ≦ 1.50% by mass,
A high current pulse arc welding method, wherein a pulse peak current during welding is 550 to 950 A, a pulse base current is 550 A or less, and a difference between the pulse peak current and the pulse base current is 200 to 600 A.   The flux-cored welding wire is at least one selected from the group consisting of Al powder, Ti powder, Zr powder, Mg powder, and an alloy powder containing at least one element selected from the group consisting of Al, Ti, Zr and Mg. The high current pulse arc welding method according to claim 1, wherein the powder contains powder, and 30% by mass or more of the powder is a powder having a particle size of 100 µm or less. The high current pulse arc welding method according to claim 1 or 2 , wherein a pulse frequency during the welding is set to 50 to 200 Hz. The ratio between the pulse frequency at the time of welding and the feed speed for feeding the consumable electrode is 1.50 (mm / 1 pulse) ≦ [feed speed (mm / sec) / pulse frequency (number of pulses / sec). The high current pulse arc welding method according to any one of claims 1 to 3 , wherein a relationship of ≤ 9.00 (mm / 1 pulse) is satisfied. The high current pulse arc welding method according to any one of claims 1 to 4 , wherein a slope of an external characteristic of the welding power source is -14.0 to -4.0 (V / 100A). . The shielding gas is an Ar gas comprising Ar and impurities, or an Ar-containing mixed gas comprising 0 to 40% by volume of CO ₂ and 0 to 10% by volume of O ₂ , with the balance being Ar and impurities. The high current pulse arc welding method according to any one of claims 1 to 5 , wherein A flux-cored welding wire for high current pulsed arc welding having an outer shell and containing a flux in the outer shell,
The average current during welding is 400A or more,
C is 0.30% by mass or less, Si is 0.30 to 1.60% by mass, Mn is 1.00 to 2.80% by mass, P is 0.050% by mass or less, and S is 0.050% by mass or less. And at least one element selected from the group consisting of Al, Ti, Zr and Mg in a total amount of 0.05 to 1.50% by mass,
The ratio of the total mass% of Al, Ti, Zr, and Mg contained in the flux-cored welding wire to the total mass% of Si and Mn is 0.11 ≦ (Al + Ti + Zr + Mg) / (Si + Mn) ≦ 0.60. It meets,
It contains at least one oxide selected from the group consisting of Al oxide, Ti oxide, Zr oxide and Mg oxide, where Al oxide is converted into Al ₂ O ₃ , Ti oxide is converted into TiO ₂ , and Zr oxide is converted. In terms of ZrO ₂ and Mg oxide in terms of MgO, the sum of the oxides is 0.20% by mass ≦ (Al ₂ O ₃ + TiO ₂ + ZrO ₂ + MgO) based on the total mass of the flux-cored welding wire. flux-cored welding wire, characterized in Succoth meet ≦ 1.50% by weight of the relationship. Al powder, Ti powder, Zr powder, Mg powder, and at least one powder selected from the group consisting of alloy powders containing at least one element selected from the group consisting of Al, Ti, Zr and Mg; The flux-cored welding wire according to claim 7 , wherein 30% by mass or more of the powder is powder having a particle size of 100 µm or less.