Arc-welding method

Abstract

To provide an arc-welding method capable of realizing deep penetration, widening the bead width of a weld bead, and suppressing an increase in spattering.SOLUTION: In an ark-welding method, a welding wire 21 is fed toward a base material 25 at a constant average feeding speed, a pulse current varying in cycles Tp is made to flow in the welding wire 21 on the basis of a first set voltage Vo, and an arc 24 is generated between the welding wire and the base material 25 during a first period To. During a second period Tb, a pulse current is made to flow in the welding wire 21 on the basis of a second set voltage Vb to generate an arc 24 between the wire and the base material 25. The cycle Tp includes a peak current period T2 and a base current period T1. The first period To and the second period Tb respectively include one or more Tp's. The first set voltage Vo is larger than the second set voltage Tb.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to arc welding methods, and more particularly to consumable electrode arc welding methods. [Background technology]

[0002] In buried arc welding, the tip of the welding wire is ignited while submerged in a molten pool formed in the base metal. This technique achieves deeper penetration than conventional welding. Furthermore, by applying a high current, the amount of melted welding wire is increased, enabling high deposition. Furthermore, because the tip of the welding wire is submerged in the molten pool, even if spatter is generated at the tip during welding, it is captured within the molten pool and does not scatter to the surrounding area. This reduces the amount of spatter adhering to the surface and surrounding area of ​​the weld bead after welding, thereby reducing the labor required for post-weld maintenance. Furthermore, in buried arc welding, an arc is ignited on the side of a buried space formed inside the base metal, and molten droplets formed at the tip of the welding wire migrate to the molten pool formed on the side of the buried space. Furthermore, the molten pool formed on the side is supported by arc pressure, stabilizing the buried space (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6777969 Summary of the Invention [Problem to be solved by the invention]

[0004] Arc welding is a technique widely used in the manufacture of steel structures. In particular, semi-automatic carbon dioxide gas arc welding (CO2 welding), which uses carbon dioxide (CO2) as a shielding gas, is used in a variety of fields from the perspectives of cost and construction efficiency.

[0005] Thick plate materials are often used in large steel structures. In these cases, deep penetration and high deposition rates are required through high current welding to improve weld joint quality and construction efficiency. By using buried arc welding in the CO2 welding described above, deep penetration and increased deposition rates can be expected through high current welding. On the other hand, while deep penetration can be achieved with buried arc welding, it is difficult to widen the weld bead, and depending on the structure of the base material, it can be difficult to form a weld bead of the desired shape.

[0006] Furthermore, during high-current welding, the amount of wire melting increases with increasing welding current, lengthening the arc length and making it more likely to become an open arc. When an open arc occurs, the droplets that grow at the tip of the welding wire detach in a drop-transfer mode. This causes a large amount of spatter to scatter around the welded area. This requires maintenance work to remove spatter that has adhered to the surface and surrounding areas of the weld bead after welding, which reduces welding efficiency.

[0007] The present disclosure has been made in consideration of the above points, and its purpose is to provide an arc welding method that can widen the bead width of the weld bead while achieving deep penetration by switching the arc ignition state between an open arc state and a buried arc state at regular intervals, and that can suppress an increase in spatter. [Means for solving the problem]

[0008] In order to achieve the above object, an arc welding method according to the present disclosure includes at least the steps of: feeding a welding wire toward a base metal, which is an object to be welded, at a constant average feed rate during a first period To, and causing a pulse current that varies with a predetermined period Tp to flow through the welding wire based on a first set voltage Vo, thereby generating an arc between the welding wire and the base metal; and feeding the welding wire toward the base metal at the average feed rate during a second period Tb following the first period To, and causing the pulse current to flow through the welding wire based on a second set voltage Vb, thereby generating the arc between the welding wire and the base metal, wherein the period Tp includes a peak current period T2 during which a peak current flows through the welding wire and a base current period T1 during which a base current having a current value lower than the peak current flows through the welding wire, the first period To and the second period Tb each include the period Tp one or more times, and the first set voltage Vo is greater than the second set voltage Vb. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to widen the bead width of the weld bead while achieving deep penetration, and also to suppress an increase in spatter. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram of an arc welding device according to an embodiment; [Figure 2] 4 is a time chart of a welding current waveform and a welding voltage waveform during arc welding according to an embodiment. [Figure 3A] FIG. 3 is a cross-sectional schematic view taken along the welding direction of the base material in a first period. [Figure 3B] FIG. 4 is a cross-sectional schematic view of the base material in the bead width direction in a first period. [Figure 4A] FIG. 10 is another cross-sectional schematic view taken along the welding direction of the base material in the first period. [Figure 4B] FIG. 10 is a cross-sectional view schematically illustrating yet another example of the base material in the welding direction during the first period. [Figure 5A]FIG. 10 is a cross-sectional schematic view taken along the welding direction of the base material in a second period. [Figure 5B] FIG. 10 is a cross-sectional schematic view of the base material in the bead width direction in a second period. [Figure 6A] FIG. 10 is another cross-sectional schematic view taken along the welding direction of the base material in the second period. [Figure 6B] FIG. 10 is a cross-sectional schematic view taken along the welding direction of the base material in a second period. [Figure 7A] FIG. 2 is a cross-sectional schematic view of the base material in a boundary state along the welding direction. [Figure 7B] FIG. 10 is another cross-sectional schematic view along the welding direction of the base material in a boundary state. [Figure 8] FIG. 1 is a cross-sectional schematic diagram of a groove butt joint. [Figure 9A] 9 is a cross-sectional schematic view of a weld bead formed in the joint shown in FIG. 8 by buried arc welding. [Figure 9B] 9 is a cross-sectional schematic view of a weld bead formed in the joint shown in FIG. 8 by arc welding according to the embodiment. [Figure 10A] FIG. 2 is a schematic view showing the appearance of a weld bead formed by buried arc welding. [Figure 10B] 1 is a schematic view showing the appearance of a weld bead formed by arc welding according to an embodiment. FIG. [Figure 10C] FIG. 2 is a schematic view showing the appearance of a weld bead formed by arc welding performed in an open arc state. [Figure 11] This is a diagram summarizing the differences in effects due to differences in welding methods. [Figure 12A] FIG. 1 is a cross-sectional schematic diagram of a weld bead formed in a T-shaped fillet joint by buried arc welding. [Figure 12B] 3 is a cross-sectional schematic view of a weld bead formed in a T-shaped fillet joint by arc welding according to an embodiment. FIG. [Figure 13] 1 shows the evaluation results of the welding state for the first set voltage and the second set voltage in Examples 1 to 25. [Figure 14] 1 shows the evaluation results of the welding state for the first and second periods in Examples 1 to 25. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses.

[0012] (Embodiment) [Configuration of arc welding equipment] 1 is a schematic diagram of an arc welding apparatus according to an embodiment. As shown in FIG. 1, an arc welding apparatus 30 includes a welding power source 16, a manipulator 19, a robot control device 20, and a welding torch 22.

[0013] The welding power source 16 includes a main transformer 2, a primary side rectifier element 3, a switching element 4, a reactor 5, a secondary side rectifier element 6, a welding current detection unit 8, a welding voltage detection unit 9, a short circuit / arc detection unit 10, an output control unit 11, an input unit 12, a wire feed speed control unit 13, a timing unit 14, and a welding condition setting unit 15.

[0014] Welding power source 16 is a power source with a so-called constant voltage characteristic, which controls the welding current output so that the change in welding voltage Vw in response to the change in welding current Aw flowing through welding wire 21 falls within a predetermined range determined by a set voltage. In this embodiment, the set voltage is the moving average value of welding voltage Vw in a pulse period Tp (see FIG. 2), which will be described later. In other words, the set voltage is a target value for feedback control based on the average voltage of welding voltage Vw in the pulse period Tp. Similarly, the set current is the moving average value of welding current Aw in the pulse period Tp. The pulse frequency is the reciprocal of the pulse period Tp. In the following description, pulse period Tp may be simply referred to as period Tp.

[0015] Primary side rectifier element 3 rectifies the output of input power source 1 and outputs it. Switching element 4 controls the welding current output by converting the DC output from primary side rectifier element 3 to AC. Main transformer 2 converts the AC output of switching element 4. The output of main transformer 2 is output as a welding current output via secondary side rectifier element 6, which rectifies the secondary side output of main transformer 2, and reactor 5. Welding voltage detection unit 9 detects the welding voltage, and welding current detection unit 8 detects the welding current.

[0016] Based on a signal from welding voltage detection unit 9, short circuit / arc detection unit 10 determines whether the welding state is a short circuit state in which welding wire 21 and base material 25 are in contact with each other and a short circuit has occurred, or an arc state in which the short circuit has been released and an arc has occurred. Output control unit 11 controls switching element 4 based on an output command from welding condition setting unit 15 to control the welding current output.

[0017] The input unit 12 is a device for inputting conditions necessary for performing arc welding, such as a set voltage, a set current, a pulse frequency, etc. For example, the input unit 12 is composed of an input device such as a touch panel or a keyboard, and a display device such as a liquid crystal display.

[0018] Wire feed speed control unit 13 controls wire feed motor 17 based on an output command from welding condition setting unit 15 to control the feed speed of welding wire 21. Time measuring unit 14 measures the time since welding started.

[0019] Welding condition setting unit 15 has a memory unit (not shown), sets welding conditions based on various numerical values ​​input from input unit 12, and transmits the corresponding conditions as output commands to output control unit 11 and wire feed speed control unit 13. Alternatively, welding condition setting unit 15 reads out a welding program stored in the memory unit, and transmits corresponding conditions from among the welding conditions described in the welding program as output commands to output control unit 11 and wire feed speed control unit 13.

[0020] Welding torch 22 is attached to and moved by manipulator 19, which constitutes an industrial robot. Robot control device 20 is connected to welding condition setting unit 15, and controls the operation of manipulator 19 based on the conditions input from welding condition setting unit 15.

[0021] Welding wire 21, a consumable electrode stored in wire storage unit 18, is fed by wire feed motor 17. One output terminal 16a of two output terminals 16a, 16b of welding power source 16 is connected to welding torch 22 that holds welding wire 21, and power is supplied to welding wire 21 via tip 23 provided on welding torch 22. The other output terminal 16b is connected to base metal 25, which is the workpiece to be welded. An arc 24 is generated between the tip of welding wire 21 and base metal 25, and welding is performed.

[0022] 1, input unit 12 is provided outside welding power source 16, but input unit 12 may be integrated with welding power source 16. Also, robot control device 20 may be incorporated into welding power source 16.

[0023] [Outline of arc welding method] 2 is a time chart of the welding current waveform and welding voltage waveform during arc welding according to this embodiment. Specifically, it shows the changes over time in the welding current Aw and welding voltage Vw during arc welding. In this embodiment, the base metal 25 is mild steel, and the material of the welding wire 21 is also mild steel. The shielding gas sprayed onto the base metal 25 during welding is CO2. However, the materials of the base metal 25 and the welding wire 21, and the type of the shielding gas are not particularly limited to these.

[0024] When the input unit 12 or a torch switch (not shown) is operated to turn on the switch of the welding torch 22, based on the output command from the welding condition setting unit 15, the wire feeding speed control unit 13 transmits a control signal to the wire feeding motor 17 to start the feeding operation of the welding wire 21. Although not shown, the welding wire 21 is fed toward the base material 25 at a constant average speed. That is, the welding wire 21 is fed forward at a constant average feeding speed. At the same time, based on the output command from the welding condition setting unit 15, the control of the welding current output by the output control unit 11 is started. Specifically, the welding current Aw is controlled by the output control unit 11 according to the voltage value and pulse frequency of the set voltage output from the welding condition setting unit 15.

[0025] As shown in FIG. 2, during welding, the welding current Aw and the welding voltage Vw are controlled such that the first period To and the second period Tb occur alternately. In this embodiment, the set voltage in the first period To is Vo, the set voltage in the second period Tb is Vb, and the relationship 0 < Vb < Vo is satisfied. In the following description, the set voltage Vo may be referred to as the first set voltage Vo, and the set voltage Vb may be referred to as the first set voltage Vb. Also, the first period To may be referred to as the open arc period To, and the second period Tb may be referred to as the buried arc period Tb. The open arc state and the buried arc state will be described later. In this embodiment, the first period To and the second period Tb are set to be the same time, but it is not particularly limited thereto, and the first period To may be longer than the second period Tb. Alternatively, the first period To may be shorter than the second period Tb.

[0026] In each of the first period To and the second period Tb, the welding current Aw and the welding voltage Vw fluctuate periodically at the same pulse frequency. As shown in FIG. 2 , the period Tp, which is the reciprocal of the pulse frequency, includes a base current period T1 and a peak current period T2. The value of the welding current Aw flowing through the welding wire 21 in the peak current period T2 is controlled to be larger than the value of the welding current Aw in the base current period T1. The current value Ip1 of the welding current Aw in the peak current period T2 of the first period To is controlled to be larger than the current value Ip2 of the welding current Aw in the peak current period T2 of the second period Tb. The current value Ib of the welding current Aw in the base current period T1 of the first period To and the second period Tb is controlled to be the same. Note that the current value of the welding current Aw may be different between the base current period T1 of the first period To and the base current period T1 of the second period Tb.

[0027] [Open arc state, buried arc state, and boundary state] FIG. 3A is a schematic cross-sectional view taken along the welding direction of the base metal in a first period. FIG. 3B is a schematic cross-sectional view taken along the bead width direction of the base metal in a first period. FIG. 4A is another schematic cross-sectional view taken along the welding direction of the base metal in a first period. FIG. 4B is yet another schematic cross-sectional view taken along the welding direction of the base metal in a first period. FIG. 5A is a schematic cross-sectional view taken along the welding direction of the base metal in a second period. FIG. 5B is a schematic cross-sectional view taken along the bead width direction of the base metal in a second period. FIG. 6A is another schematic cross-sectional view taken along the welding direction of the base metal in a second period. FIG. 6B is yet another schematic cross-sectional view taken along the welding direction of the base metal in a second period. FIG. 7A is a schematic cross-sectional view taken along the welding direction of the base metal in a boundary state. FIG. 7B is another schematic cross-sectional view taken along the welding direction of the base metal in a boundary state.

[0028] 3A to 7B, the thickness direction of base material 25 is referred to as the Z direction, the welding direction (extension direction of weld bead 29 (see FIGS. 10A to 10C)) is referred to as the Y direction, and the direction perpendicular to each of the Z direction and the Y direction is referred to as the X direction. Also, the side of base material 25 on which the formation surface of weld bead 29 is provided is referred to as the top or upper side, and the side on which the surface opposite to the formation surface in the thickness direction is provided is referred to as the bottom or lower side.

[0029] In this specification, being perpendicular or parallel means being perpendicular or parallel, taking into account the processing tolerance and assembly tolerance of the base material 25. It does not mean that the objects to be compared are perpendicular or parallel in the strict sense.

[0030] 3A and 3B, during a first period (open arc period) To, an arc 24 (arc length La1) is generated between the tip of welding wire 21 and base metal 25, forming a molten pool 26 from the upper surface to the interior of base metal 25. Furthermore, due to the arc pressure, the irradiated portion of molten pool 26 with arc 24 is pushed downward and recessed. Note that arc length La1 is the average value of the arc length during first period To; in reality, the arc length fluctuates within cycle Tp. The arc length during base current period T1 is shorter than the arc length during peak current period T2.

[0031] During the first period To, the welding wire 21 melts during the peak current period T2 of the cycle Tp, and droplets 21A are formed at the tip 21B of the welding wire 21, and the droplets 21A continue to grow. During the base current period T1, the arc pressure is weaker than during the peak current period T2, so the droplets 21A fall downward and transfer to the weld pool 26. In this way, during the first period To, by using a pulse current that periodically fluctuates with the cycle Tp, the droplets 21A can be transferred regularly toward the weld pool 26. This allows the shape of the weld bead 29 to be uniform along the longitudinal direction (welding direction).

[0032] During the first period To, the tip 21B of the welding wire 21 is not buried in the molten pool 26, and this state is referred to herein as an open-arc state. More specifically, the open-arc state is determined by the position of the tip 21B of the welding wire 21.

[0033] As shown in FIGS. 4A and 4B, in an open arc state, with respect to position h0 of the lower surface (placement surface) of base metal 25 as a reference, the tip position h3 of tip end 21B of welding wire 21 is higher in the Z direction than position h1 of the upper surface (surface) of base metal 25 or position h2 of the upper surface (surface) of weld pool 26. In the example shown in FIG. 4A, position h2 of the upper surface of weld pool 26 is higher than position h1 of the upper surface of base metal 25. Furthermore, tip position h3 of welding wire 21 is higher than position h2 of the upper surface of weld pool 26. In the example shown in FIG. 4B, position h1 of the upper surface of base metal 25 is higher than position h2 of the upper surface of weld pool 26. Furthermore, tip position h3 of welding wire 21 is higher than position h1 of the upper surface of base metal 25. When position h0 is taken as a reference position, positions h1 to h3 are heights in the Z direction from position h0.

[0034] In an open arc state, arc 24 is not surrounded by molten pool 26 or base metal 25, so arc 24 tends to spread in a direction parallel to the top surface of base metal 25. As a result, the width of weld bead 29 in the X direction (hereinafter referred to as bead width) can be increased. On the other hand, because the concentration of arc 24 is weakened, it becomes difficult to form penetration in the thickness direction, and the penetration depth decreases. In addition, spatter 28 (see FIGS. 10A to 10C) tends to scatter around arc 24, increasing the amount of spatter 28 that adheres to the surface and periphery of weld bead 29.

[0035] As shown in FIGS. 5A and 5B, in the second period (submerged arc period) Tb that follows the first period To, similar to the first period To, a molten pool 26 is formed from the upper surface to the interior of the base material 25 by irradiating an arc 24 (arc length La2 < La1). Also, due to the arc pressure, the irradiation location of the arc 24 in the molten pool 26 is pushed downward and is concave. Note that the arc length La2 is the average value of the arc length in the second period Tb. Actually, the arc length fluctuates within the period Tp. The arc length in the base current period T1 is shorter than the arc length in the peak current period T2.

[0036] In the second period Tb, the tip 21B of the welding wire 21 is in a state of being submerged inside the molten pool 26. In the present specification, this state is referred to as a submerged arc state.

[0037] In the submerged arc state, the tip 21B of the welding wire 21 enters the inside of the submerged space 27 formed by the molten pool 26 being pushed downward by the arc pressure. In this case, particularly in the peak current period T2, due to the rotation phenomenon, an arc 24 arcs between the molten pool 26 covering the side surface of the submerged space 27 and the tip 21B of the welding wire 21. Due to the arc pressure, the molten pool 26 on the side surface of the submerged space 27 is pushed, thereby suppressing the undulation of the molten pool 26 and stabilizing its behavior. As a result, the penetration depth into the base material 25 can be stabilized.

[0038] Also, similar to the first period To, in the second period Tb, by making the welding current Aw a pulsed current that periodically fluctuates with the period Tp, the droplets 21A can be regularly transferred toward the molten pool 26. As a result, the shape of the weld bead 29 can be made uniform over the longitudinal direction.

[0039] Similarly to the open arc state, the buried arc state is also determined by the position of the tip end 21B of the welding wire 21. As shown in FIGS. 6A and 6B, in the buried arc state, the tip position h3 of the tip end 21B of the welding wire 21 is located lower in the Z direction than either the upper surface of the base metal 25 (the surface of the base metal 25) or the upper surface of the molten pool 26 (the surface of the molten pool 26), whichever is higher, based on the position h0 of the lower surface (the installation surface) of the base metal 25. In the example shown in FIG. 6A, the position h2 of the upper surface of the molten pool 26 is located higher than the position h1 of the upper surface of the base metal 25. Furthermore, the tip position h3 of the welding wire 21 is lower than the position h2 of the upper surface of the molten pool 26 and higher than the position h1 of the upper surface of the base metal 25. Note that, as shown in FIG. 5A, the tip position h3 of the welding wire 21 may be located higher than both the position h2 of the upper surface of the molten pool 26 and the position h1 of the upper surface of the base metal 25. 6B, the position h1 of the upper surface of the base material 25 is higher than the position h2 of the upper surface of the molten pool 26. Furthermore, the position h3 of the tip of the welding wire 21 is lower than the position h1 of the upper surface of the base material 25 and higher than the position h2 of the upper surface of the molten pool 26.

[0040] In the buried arc state, the arc 24 is surrounded by the molten pool 26 or base metal 25 that covers the inner wall of the buried space 27. Furthermore, because the arc length La2 is shorter than the arc length La1 in the open arc state, the arc 24 extends less in the buried arc state in a direction parallel to the upper surface of the base metal 25 than in the open arc state. Therefore, the bead width of the weld bead 29 formed on the base metal 25 is narrower than in the open arc state. On the other hand, the arc 24 is more concentrated than in the open arc state, which facilitates penetration in the depth direction and increases the penetration depth. Additionally, because spatter 28 adheres to the molten pool 26 or base metal 25 around the arc 24 (see FIG. 5B), scattering around the weld bead 29 is suppressed, and the amount of spatter 28 adhering to the surface and periphery of the weld bead 29 is reduced compared to the open arc state.

[0041] As described above, during welding of base metal 25, an open arc state or a buried arc state is distinguished depending on the position along the Z direction of tip end 21B of welding wire 21. In this case, the position of tip end 21 of welding wire 21 depending on the boundary state between the open arc state and the buried arc state (hereinafter simply referred to as the boundary state) is uniquely determined as follows: In other words, in the boundary state, with position h0 of the bottom surface of base metal 25 as the reference, the top surface as the surface of base metal 25 or the top surface as the surface of molten pool 26, whichever is higher, and tip end 21B of welding wire 21 are located at the same height.

[0042] The tip portion 21B of the welding wire 21 is treated as the tip portion 21B of the welding wire 21 in either a state where the molten droplet 21A is formed at the tip portion of the welding wire 21, or a state where the tip of the welding wire 21 is exposed before the molten droplet 21A is formed or after the molten droplet 21A has transferred to the molten pool 26, for example.

[0043] The threshold voltage Vth is defined as the set voltage when the tip 21B of the welding wire 21 is at a position determined by the boundary state. The threshold voltage Vth is set by performing arc welding at multiple set voltages and visually checking phenomena occurring during welding. This is because the threshold voltage Vth must be set according to changes in various welding conditions. For example, as the wire diameter of the welding wire 21 decreases, the melting rate of the welding wire 21 increases with changes in the welding current Aw, and the amount of melting also increases. In this case, the threshold voltage Vth needs to be lowered to maintain the position h3 of the tip 21B of the welding wire 21.

[0044] Furthermore, when the welding speed, which is the speed at which the wire moves in the welding direction to form a weld bead, is reduced, the molten pool 26 becomes more likely to flow below the welding wire 21 in the base material 25, so the threshold voltage Vth must be increased. On the other hand, when the welding speed is increased, the molten pool 26 becomes less likely to flow below the welding wire 21, so the threshold voltage Vth must be reduced.

[0045] [Relationship between the first and second set voltages and the threshold voltage] If first set voltage Vo is set lower than threshold voltage Vth, the arc length becomes shorter during first period To, and position h3 of tip end 21B of welding wire 21 becomes lower than position h1 of the upper surface of base metal 25 and position h2 of the upper surface of molten pool 26, resulting in a buried arc state. In this case, the spread of arc 24 becomes smaller, making it difficult to increase the bead width of weld bead 29.

[0046] On the other hand, by setting first set voltage Vo to be equal to or higher than threshold voltage Vth, the arc length can be maintained long during first period To, achieving the open arc state described above. Furthermore, the expansion of arc 24 increases, making it possible to widen the bead width of weld bead 29. However, if first set voltage Vo is set higher than a predetermined value, the arc length becomes too long, increasing the amount of spatter 28 generated and resulting in insufficient penetration of base material 25. As is clear from the above, first set voltage Vo satisfies the relationship shown in equation (1).

[0047] Vth≦Vo≦Vo_max (1) Here, Vo_max is the allowable upper limit of the first set voltage Vo.

[0048] If the second set voltage Vb is set higher than the threshold voltage Vth, the arc length becomes longer during the second period Tb, and the position h3 of the tip of the welding wire 21 becomes higher than the position h1 of the upper surface of the base metal 25 and the position h2 of the upper surface of the molten pool 26, resulting in an open arc state. In this case, the amount of spatter 28 generated increases. Also, the penetration depth becomes shallow.

[0049] On the other hand, by setting the second set voltage Vb to a value equal to or lower than the threshold voltage Vth, the arc length can be kept short during the second period Tb, achieving the buried arc state described above. Furthermore, the narrowing of the arc 24 ensures a sufficient penetration depth and reduces the amount of spatter 28. However, if the second set voltage Vb is lower than a predetermined value, the arc length becomes too short, preventing the bead width of the weld bead 29 from widening. Sticking occurs, making stable welding impossible. Sticking is a phenomenon in which the tip 21B of the welding wire 21 comes into contact with the bottom of the molten pool 26, resulting in unstable welding. As is clear from the above, the second set voltage Vb satisfies the relationship shown in Equation (2).

[0050] Vb_min≦Vb≦Vth (2) Here, Vb_min is the allowable lower limit of the second set voltage Vb.

[0051] As is clear from equations (1) and (2), both Vo_max and Vb_min take different values ​​in response to changes in various welding conditions, similar to the threshold voltage Vth.

[0052] For example, when the wire diameter of the welding wire 21 is reduced, the melting rate of the welding wire 21 increases with respect to changes in the welding current Aw, and the melting amount also increases. In this case, Vo_max and Vb_min need to be reduced. When the wire diameter is increased, the melting rate of the welding wire 21 decreases with respect to changes in the welding current Aw, and the melting amount also decreases. In this case, Vo_max and Vb_min need to be increased.

[0053] Furthermore, when the welding speed is reduced, it becomes easier for the molten pool 26 to flow below the welding wire 21, so it is necessary to increase Vo_max and Vb_min. On the other hand, when the welding speed is increased, it becomes more difficult for the molten pool 26 to flow below the welding wire 21, so it is necessary to decrease Vo_max and Vb_min.

[0054] [Regarding the first and second periods] As described above, during first period To in the open arc state, the bead width of weld bead 29 can be increased, but the penetration depth becomes shallower and the amount of spatter 28 increases. Moreover, during second period Tb in the buried arc state, the penetration can be increased and the amount of spatter 28 can be suppressed, but the bead width of weld bead 29 cannot be increased beyond a predetermined value.

[0055] Furthermore, if the difference between first period To and second period Tb becomes greater than a predetermined value, the bead width and penetration depth of weld bead 29 will vary greatly along the longitudinal direction (welding direction) of weld bead 29, which may result in a decrease in welding quality. In view of the above, it is preferable that first period To and second period Tb satisfy the relationship shown in formula (3), and it is more preferable that they satisfy the relationship shown in formula (4).

[0056] T_min≦(Tо, Tb)≦T_max ···(3) T_min≦Tо=Tb≦T_max ···(4) Here, T_min is the allowable lower limit value of the first period To and the second period Tb, and T_max is the allowable upper limit value. Both T_min and T_max take different values ​​depending on the changes in various welding conditions.

[0057] For example, when the wire diameter of the welding wire 21 is reduced, the melting rate of the welding wire 21 increases with respect to changes in the welding current Aw, and the melting amount also increases. In this case, T_min and T_max need to be shortened. When the wire diameter is increased, the melting rate of the welding wire 21 decreases with respect to changes in the welding current Aw, and the melting amount also decreases. In this case, T_min and T_max need to be lengthened.

[0058] Furthermore, when the welding speed is reduced, it becomes easier for the molten pool 26 to flow below the welding wire 21, so it is necessary to increase T_min and T_max. On the other hand, when the welding speed is increased, it becomes more difficult for the molten pool 26 to flow below the welding wire 21, so it is necessary to decrease T_min and T_max.

[0059] [Effects, etc.] As described above, the arc welding method according to this embodiment includes at least the following two steps: First, during a first period (open arc period) To, welding wire 21 is fed toward base metal 25, which is the workpiece, at a constant average feed rate, and a pulse current that varies with a predetermined pulse period Tp (period Tp) is applied to welding wire 21 based on a first set voltage Vo, thereby generating arc 24 between welding wire 21 and base metal 25.

[0060] In a second period (buried arc period) Tb following the first period To, the welding wire 21 is fed toward the base material 25 at a constant average feed rate, and a pulse current is passed through the welding wire 21 based on the second set voltage Vb to generate an arc 24 between the welding wire 21 and the base material 25.

[0061] Here, the constant average feed speed at which welding wire 21 is fed toward base material 25 may be a constant feed speed of welding wire 21, or a feed speed that periodically switches between high and low speed states in a pulsed manner. Furthermore, the feed speed may be the same or different in first period To and second period Tb.

[0062] The period Tp includes a peak current period T2 during which a peak current flows through the welding wire 21, and a base current period T1 during which a base current having a current value lower than the peak current flows through the welding wire 21. Each of the first period To and the second period Tb includes one or more periods Tp. The first set voltage Vo has a voltage value different from that of the second set voltage Vb. More specifically, the first set voltage Vo is set to be higher than the second set voltage Vb.

[0063] In addition, during the first period To, the tip of the welding wire 21 is in an open arc state where it is not buried inside the molten pool 26 formed in the base material 25, and during the second period Tb, the tip is in a buried arc state where it is buried inside the molten pool 26.

[0064] According to this embodiment, arc welding of the base material 25 is performed by switching from a first period To, in which the welding current Aw is controlled based on a first set voltage Vo, to a second period Tb, in which the welding current Aw is controlled based on a second set voltage Vb, which is a voltage value equal to or lower than the first set voltage Vo. Furthermore, arc welding is performed by alternately switching between the first period To and the second period Tb as necessary.

[0065] In this way, by arc welding base material 25 while switching between the open arc state and the buried arc state at predetermined time intervals, it is possible to achieve a deep penetration equivalent to that of buried arc welding while increasing the bead width of weld bead 29. In addition, the amount of spatter 28 generated can be reduced compared to when arc welding is performed in a constantly open arc state. These points will be explained further.

[0066] Fig. 8 is a cross-sectional schematic view of a groove butt joint. Fig. 9A is a cross-sectional schematic view of a weld bead formed by buried arc welding on the joint shown in Fig. 8. Fig. 9B is a cross-sectional schematic view of a weld bead formed by arc welding according to an embodiment.

[0067] Fig. 10A is a schematic view of the appearance of a weld bead formed by buried arc welding, Fig. 10B is a schematic view of the appearance of a weld bead formed by arc welding according to an embodiment, and Fig. 10C is a schematic view of the appearance of a weld bead formed by arc welding performed in an open arc state.

[0068] 8 is a groove butt joint in which a first plate material 25A and a second plate material 25B are butted together at their groove faces. When arc welding is performed along the groove face of this base material 25 to form a weld bead 29 on base material 25, the shape of weld bead 29 varies depending on the welding method.

[0069] 8 is welded by buried arc welding, a weld bead 29 can be formed on the groove face even if the first plate material 25A and the second plate material 25B are both thick plates. Note that a thick plate refers to a plate material with a thickness of 6 mm or more.

[0070] However, when continuous buried arc welding is performed, melting of the groove surface may be insufficient, resulting in unmelted material and undercutting, as shown in Fig. 9A. Furthermore, the contact angle α0 between the top surface of base material 25 and the edge of weld bead 29 may become large. In this case, residual stress may be concentrated in and around weld bead 29, potentially reducing the fatigue strength of the joint, including weld bead 29.

[0071] On the other hand, according to this embodiment, the bead width of weld bead 29 can be made wider than in the case shown in Fig. 9A. As a result, the entire groove face is sufficiently melted, as shown in Fig. 9B, which suppresses the occurrence of unmelted material and, ultimately, undercuts. Furthermore, since the contact angle α1 between the upper surface of base material 25 and the edge of weld bead 29 can be made smaller than the aforementioned α0, the concentration of residual stress in and around weld bead 29 can be suppressed, improving the fatigue strength of the joint.

[0072] Furthermore, according to this embodiment, as shown in FIG. 10B, the amount of spatter 28 generated can be reduced compared to when the base metal 25 is welded in a constantly open arc state, as shown in FIG. 10C. With the arc welding method of this embodiment, the amount of spatter 28 generated can be reduced to the same level as when the base metal 25 is arc welded in a constantly buried arc state, or slightly more. Note that FIG. 10A is a schematic diagram of the appearance of a weld bead formed by constantly buried arc welding. This reduces the maintenance time after welding and improves the efficiency of the welding process, including subsequent processes.

[0073] Figure 11 is a diagram summarizing the differences in effect due to different welding methods. Each item shown in Figure 11 is set to 100% when the base material 25 is welded using only a buried arc, that is, when the base material 25 is welded in a constantly buried arc state.

[0074] 11, according to this embodiment, the penetration depth was able to be made equal to that when the base metal 25 was welded using only the buried arc. On the other hand, when the base metal 25 was welded using only the open arc, that is, when the base metal 25 was welded in a constantly open arc state, the penetration depth was less than 90% of that when the base metal 25 was welded using only the buried arc.

[0075] Furthermore, according to this embodiment, the bead width of the weld bead 29 could be increased to 120% to 165% compared to when the base material 25 was welded using only a buried arc. Also, the amount of spatter 28 generated could be reduced to 100% to 150% compared to when the base material 25 was welded using only a buried arc. On the other hand, when the base material 25 was welded using only an open arc, the amount of spatter 28 generated exceeded 150% compared to when the base material 25 was welded using only a buried arc.

[0076] Furthermore, according to this embodiment, the bead width can be increased while ensuring the penetration depth, so that, for example, in fillet welding, the leg length can be increased.

[0077] 12A and 12B are cross-sectional schematic views of a weld bead formed in a T-shaped fillet joint by buried arc welding according to an embodiment.

[0078] 12A and 12B has a so-called T-shaped fillet joint structure in which the side of a third plate 25C is butted against the top surface of a fourth plate 25D. When fillet welding was performed on this base plate 25 using only buried arc, a weld bead 29 with a leg length L0 was formed, as shown in Fig. 12A. On the other hand, when fillet welding was performed using the arc welding method shown in this embodiment, a weld bead 29 with a leg length L1 (>L0) was formed, as shown in Fig. 12B.

[0079] As described above, according to this embodiment, the leg length of the fillet weld can be increased, thereby ensuring the strength of the welded portion and improving the welding quality.

[0080] Furthermore, according to this embodiment, it is possible to achieve deeper penetration than when the base material 25 is welded only by open arc. As a result, when arc welding the thick base material 25, the number of welding passes in the multi-layer welding process can be reduced, and the man-hours and takt time during welding can be shortened.

[0081] Furthermore, according to this embodiment, by setting the welding current Aw to a pulse current that periodically fluctuates with the cycle Tp during each of the first period To and the second period Tb, it is possible to regularly transfer the droplets 21A toward the molten pool 26 at regular time intervals. This allows the shape of the weld bead 29 to be uniform along the longitudinal direction.

[0082] As described above, according to this embodiment, it is possible to improve the welding quality during welding of large steel structures, and also improve the welding efficiency.

[0083] The direction along the thickness direction of base material 25 is defined as the Z direction, and the installation surface of base material 25, which in the examples shown in Figures 3A to 7B is the lower surface of base material 25, is defined as the reference position h0 in the Z direction. Furthermore, relative to the reference position h0, the position along the Z direction on the surface of molten pool 26 is defined as position h2, and the position along the Z direction on the surface of the base material irradiated by arc 24, which in the examples shown in Figures 3A to 7B is the lower surface of base material 25, is defined as position h1.

[0084] In the open arc state, an arc 24 is generated between the welding wire 21 and the base material 25, with position h3, which is the position along the Z direction of the tip of the welding wire 21, higher than the higher of positions h1 and h2, and the base material 25 is arc-welded.

[0085] In the buried arc state, arc 24 is generated between welding wire 21 and base metal 25 with position h3 lower than whichever of positions h1 and h2 is higher, and base metal 25 is arc-welded.

[0086] By doing so, in the open arc state, the arc length La1 can be ensured and the bead width can be widened. Also, in the buried arc state, the tip end 21B of the welding wire 21 can be reliably positioned inside the buried space 27. As a result, the arc 24 is irradiated onto the side surface of the buried space 27 covered by the molten pool 26, and the arc pressure can suppress rippling of the molten pool 26. Also, because the spatter 28 is mainly absorbed by the molten pool 26 in the buried space 27, the amount of spatter 28 generated on the surface of the weld bead 29 and its periphery can be reduced.

[0087] Furthermore, the state in which the higher of positions h1 and h2 is at the same height as position h3 is defined as the boundary state between the open arc state and the buried arc state, and the set voltage corresponding to the boundary state is defined as the threshold voltage Vth. The first set voltage Vo satisfies the relationship shown in equation (1), and the second set voltage Vb satisfies the relationship shown in equation (2).

[0088] Vth≦Vo≦Vо_max (1) Vb_min≦Vb≦Vth (2) By setting the threshold voltage Vth in this way, it is possible to reliably create an open arc state and a buried arc state during welding.

[0089] Furthermore, first period To is preferably equal to second period Tb. This makes it possible to suppress variations in the bead width and penetration depth of weld bead 29 along the longitudinal direction of weld bead 29, thereby improving the welding quality.

[0090] Furthermore, the materials of base material 25 and welding wire 21 are not limited to the above-mentioned mild steel. For example, base material 25 and welding wire 21 may each be made of a steel material such as stainless steel or high-tensile steel.

[0091] In addition, in the case of CO2 welding in which the shielding gas is CO2, the arc reaction force makes it difficult for the droplets 21A to detach toward the base material 25, but according to this embodiment, the detachment of the droplets 21A is promoted by passing a pulse current through the welding wire 21 in each of the first period To and the second period Tb. Furthermore, by using CO2 welding, the arc 24 contracts due to the thermal pinch effect, thereby obtaining deep penetration and improving both the welding speed and work efficiency. [Example]

[0092] The technology of the present disclosure will be described in more detail below with reference to examples. Note that the examples shown below do not limit the technology described in the present disclosure in any way.

[0093] [Table 1]

[0094] Table 1 shows common conditions for arc welding in Examples 1 to 25. Note that bead-on-plate is a structure in which linear weld bead 29 is formed on base metal 25, which is a plate material. The welding speed is the speed at which tip end 21B of welding wire 21 moves in the welding direction along the surface of base metal 25, and corresponds to the speed at which weld bead 29 is formed along a weld line (not shown).

[0095] As a result of preliminary investigation under the common conditions shown in Table 1, the threshold voltage Vth was found to be 40 V. Based on the obtained threshold voltage Vth (= 40 V), the first set voltage Vo, the second set voltage Vb, the first period To, and the second period Tb were each changed, and the base material 25 was arc-welded, and the welding quality was evaluated based on each evaluation item shown in Table 2.

[0096] [Table 2]

[0097] Table 2 shows the evaluation items and the evaluation criteria for the welding of the present invention. In this study, evaluation was carried out for the evaluation items (evaluation items I to VII) shown in Table 2. Furthermore, for each evaluation item, a ○ (OK) or × (NG) was judged based on the judgment criteria shown in Table 2. Details of each item will be explained below.

[0098] First, evaluation item I is the arc ignition state in the first period To. If the open arc state was only in the first period To, it was judged as ○, and if the open arc state was not in the first period To or if the open arc state was in a period other than the first period To, it was judged as ×.

[0099] Evaluation item II is the arc ignition state in the second period Tb. If the buried arc state was present only in the second period Tb, it was judged as ○, and if the buried arc state was not present only in the second period Tb or if the buried arc state was present in periods other than the second period Tb, it was judged as ×.

[0100] Evaluation item III is the amount of spatter 28. When the amount of spatter 28 generated was less than, equal to, or 150% or less than that generated when welding was performed in a constantly buried arc state, it was judged as ◯, and when the amount of spatter 28 generated was more than 150% than that generated when welding was performed in a constantly buried arc state, it was judged as ×.

[0101] Evaluation item IV is welding stability. When no sticking occurred during welding, it was judged as ◯, and when sticking occurred, it was judged as ×.

[0102] Evaluation item V is bead width. When the bead width increased by 20% or more compared to when welding was performed in a constantly buried arc state, it was judged as ○, and when the increase was less than 20%, it was judged as ×.

[0103] Evaluation item VI is penetration depth. When the penetration depth was reduced by less than 10% (in other words, the penetration depth was 90% or more) compared to when welding was performed in a constantly buried arc state, it was judged as good, and when the reduction was 10% or more (in other words, the penetration depth was less than 90%) it was judged as bad.

[0104] Evaluation item VII is the fluctuation range of penetration depth. When the fluctuation range of penetration depth along the longitudinal direction (welding direction) of weld bead 29 was less than 1 mm, it was judged as ○, and when the fluctuation range was 1 mm or more, it was judged as X. The evaluation results will be explained below.

[0105] [Table 3]

[0106] Table 3 shows the overall evaluation results of the welding state for Examples 1 to 25. Fig. 13 shows the evaluation results of the welding state for the first set voltage and the second set voltage for Examples 1 to 25. Fig. 14 shows the evaluation results of the welding state for the first period and the second period for Examples 1 to 25. The reference conditions shown in Table 3 are for welding performed in a constantly buried arc state, and the reference conditions for the set voltages (first set voltage Vo, second set voltage Vb) at this time were 37 V. In Examples 1 to 25, the number entered in evaluation item V is the actual measured value of the bead width, and the number entered in evaluation item VI is the actual measured value of the penetration depth. In Figs. 13 and 14, the numbers assigned in the figures are Example numbers.

[0107] In Table 3 and Figures 13 and 14, the results for examples that were judged as ○ for all of the evaluation items I to VII were judged as ○ overall, and the results for examples that were judged as × for any one of the evaluation items I to VII were judged as × overall.

[0108] As shown in Table 3, the overall evaluation was ○ for Examples 1 to 6 and Examples 17 to 20. That is, it was found that in these Examples, the first set voltage Vo, the second set voltage Vb, the first period To, and the second period Tb were set to conditions suitable for actual welding. On the other hand, the overall evaluation was X for Examples 7 to 16 and Examples 21 to 25. That is, it was found that in these Examples, at least one of the first set voltage Vo, the second set voltage Vb, the first period To, and the second period Tb was not set to a condition suitable for actual welding. Furthermore, as shown in FIG. 13, in this study, the aforementioned Vo_max was 48 V and Vb_min was 32 V.

[0109] In Example 7, the first set voltage Vo (=39 V) was set lower than the threshold voltage Vth (=40 V), and as a result, evaluation items I, II, and V were judged as ×. This was thought to be because the ignition state of the arc 24 was a buried arc state in both the first period To and the second period Tb, which resulted in an increase in the bead width of less than 20%.

[0110] In Example 8, the second set voltage Vb (= 31 V) was set lower than Vb_min (= 32 V), and as a result, evaluation items I, II, IV, and V were judged as ×. This was thought to be because the ignition state of the arc 24 was a buried arc state in both the first period To and the second period Tb, the increase in bead width was less than 20%, and sticking occurred.

[0111] In Example 9, the first set voltage Vo (=39 V) was set lower than the threshold voltage Vth (=40 V), and the second set voltage Vb (=31 V) was set lower than Vb_min (=32 V), resulting in a rating of × for evaluation items I to V. This is thought to be because the ignition state of arc 24 was a buried arc state in both the first period To and the second period Tb, the increase in bead width was less than 20%, sticking occurred, and the amount of spatter 28 generated also increased.

[0112] In Example 10, the first set voltage Vo (=49 V) was set higher than Vo_max (=48 V), and as a result, evaluation items III and VI were judged as X. This was thought to be because the arc length became too long during the first period To, which increased the amount of spatter 28 generated and the decrease in penetration depth.

[0113] In Example 11, the second set voltage Vb (=31 V) was set lower than Vb_min (=32 V), and as a result, evaluation item IV was judged as ×. In other words, it was thought that the arc 24 was buried too much, causing sticking.

[0114] In Example 12, the first set voltage Vo (=49 V) was set higher than Vo_max (=48 V) and the second set voltage Vb (=31 V) was set lower than Vb_min (=32 V), resulting in a rating of X for evaluation items III and IV. This was thought to be because, during the first period To, the arc length became too long, increasing the amount of spatter 28 generated, while, during the second period Tb, the arc 24 was too buried, causing sticking.

[0115] In Example 13, the first set voltage Vo (=49 V) was set higher than Vo_max (=48 V), and as a result, evaluation items I to III and VI were judged as ×. This is thought to be because the ignition state of arc 24 was an open arc state in both the first period To and the second period Tb, and the amount of spatter 28 generated and the decrease in penetration depth increased.

[0116] In Example 14, the second set voltage Vb (=42 V) was set higher than the threshold voltage Vth (=40 V), and as a result, evaluation items I to III were judged as ×. This was thought to be because the ignition state of arc 24 did not become a buried arc state in either the first period To or the second period Tb, and the amount of spatter 28 generated increased.

[0117] In Example 15, the first set voltage Vo (=49 V) was set higher than Vo_max (=48 V), and the second set voltage Vb (=42 V) was set higher than the threshold voltage Vth (=40 V), resulting in a rating of × for evaluation items I to III and VI. This is thought to be because the ignition state of the arc 24 was an open arc state in both the first period To and the second period Tb, which increased the amount of spatter 28 generated and the decrease in penetration depth.

[0118] To summarize the above, under the welding conditions in Examples 1 to 26, the first set voltage Vo satisfies the relationship shown in formula (5), and the second set voltage Vb satisfies the relationship shown in formula (6).

[0119] Vth(V)≦Vo(V)≦(Vth+8)(V) (5) (Vth-8)(V)≦Vb(V)≦Vth(V) ···(6) In these cases, the first set voltage Vo is set to a voltage value different from the second set voltage Vb. More specifically, the first set voltage Vo is set to be higher than the second set voltage Vb.

[0120] The inventors of the present invention have found that the threshold voltage Vth falls within the range of 30 to 45 V even when the conditions shown in Table 1 are changed within the ranges shown below.

[0121] The range of variation for each condition is as follows: The wire diameter of the solid welding wire 21 is in the range of 1.2 mm or more and 1.6 mm; the shielding gas is CO2; the average current is in the range of 300 A or more and 700 A or less; and the welding speed is in the range of 15 cm / min or more and 100 cm / min or less.

[0122] The fluctuation range of this threshold voltage Vth is close to the allowable ranges of the first set voltage Vo and the second set voltage Vb shown in Fig. 13. The threshold voltage Vth is a value determined by the positional relationship between the tip of the welding wire 21 and the molten pool 26 during welding, and there is no problem if the threshold voltage Vth is close to the first set voltage Vo and the second set voltage Vb. In addition, even when the threshold voltage Vth fluctuates within the range of 30 to 45 V, it is considered that the first set voltage Vo satisfies the relationship shown in formula (5), and the second set voltage Vb satisfies the relationship shown in formula (6).

[0123] On the other hand, in Examples 16 and 21 to 25, the setting ranges for the first period To and the second period Tb were not appropriate, and therefore the overall evaluation was ×.

[0124] Specifically, in Example 16, both the first period To and the second period Tb were set to 0.1 sec, and as a result, evaluation items I and II were judged to be ×. This was thought to be because both the first period To and the second period Tb were too short, and switching between the open arc state and the buried arc state was not performed well.

[0125] In Examples 21 to 25, both the first period To and the second period Tb were set in the range of 1.6 seconds to 2.0 seconds, and as a result, evaluation item VII was judged to be ×. This was thought to be because both the first period To and the second period Tb were too long, in other words, both the open arc state and the buried arc state were too long, which resulted in a large difference in penetration depth in each period.

[0126] Considering the above, it is considered that the overall evaluation of the welding condition can be made good by setting the aforementioned T_min to 0.2 sec and T_Max to 1.5 sec. In other words, it was found that it is preferable that the first period To and the second period Tb are 0.2 sec or more and 1.5 sec or less, respectively. [Industrial Applicability]

[0127] The arc welding method disclosed herein is useful because it can achieve deep penetration, increase the bead width of the weld bead, and suppress an increase in spatter. [Explanation of symbols]

[0128] 1 Input power 2. Main transformer 3 Primary side rectifier element 4 Switching elements 5 Reactor 6 Secondary side rectifier element 8 Welding current detector 9 Welding voltage detector 10 Short circuit / arc detection section 11 Output control section 12 Input section 13 Wire feed speed control unit 14 Timing section 15 Welding condition setting section 16 Welding power source 17 Wire feed motor 18 Wire storage section 19 Manipulator 20 Robot control device 21 Welding wire 21A droplet 21B Tip 22 Welding torch 23 chips 24 Arc 25 Base material 26 Molten pool 27 Filled Space 28 Spatter 29 Weld Bead 30 Arc welding equipment Ip1, Ip2 peak current Ib Base current T1 Base current period T2 Peak current period Tp period (pulse period) To 1st period (open arc period) Tb Second period (buried arc period) Vо First set voltage Vb Second set voltage Vth threshold voltage

Claims

1. during a first time period To, feeding a welding wire toward a base metal, which is an object to be welded, at a constant average feed rate, and applying a pulse current that fluctuates with a predetermined period Tp to the welding wire based on a first set voltage Vo to generate an arc between the welding wire and the base metal; during a second time period Tb subsequent to the first time period To, feeding the welding wire toward the base metal at the average feed speed, and applying the pulse current to the welding wire based on a second set voltage Vb to generate the arc between the welding wire and the base metal, the period Tp includes a peak current period T2 in which a peak current flows through the welding wire, and a base current period T1 in which a base current having a current value lower than the peak current flows through the welding wire, the first period To and the second period Tb each include the cycle Tp one or more times; The arc welding method according to claim 1, wherein the first set voltage Vo is greater than the second set voltage Vb.

2. The arc welding method according to claim 1, During the first period To, the tip of the welding wire is in an open arc state in which it is not buried in the molten pool formed on the base metal, The arc welding method is characterized in that, during the second period Tb, the tip of the welding wire is in a buried arc state in which it is buried inside the molten pool.

3. The arc welding method according to claim 2, In the open arc state, the arc is generated between the welding wire and the base metal in a state in which the tip of the welding wire is higher than either the surface of the molten pool or the irradiated surface of the arc on the base metal, whichever is higher; In the buried arc state, the arc is generated between the welding wire and the base metal in a state in which the tip of the welding wire is lower than either the surface of the molten pool or the irradiated surface, whichever is higher.

4. The arc welding method according to claim 3, When a state in which the tip of the welding wire is at the same height as the surface of the molten pool or the irradiated surface of the base metal, whichever is higher, is defined as a boundary state between the open arc state and the buried arc state, and a voltage corresponding to the boundary state is defined as a threshold voltage Vth, The first set voltage Vo satisfies the relationship shown in formula (5), and the second set voltage Vb satisfies the relationship shown in formula (6), Vth(V)≦Vo(V)≦(Vth+8)(V)...(5) (Vth-8)(V)≦Vb(V)≦Vth(V)...(6) Furthermore, the arc welding method is characterized in that Vo>Vb is satisfied.

5. The arc welding method according to claim 1, The arc welding method, wherein the first period To is equal to the second period Tb.

6. The arc welding method according to claim 5, The arc welding method is characterized in that the first period To and the second period Tb are 0.2 seconds or more and 1.5 seconds or less, respectively.

7. The arc welding method according to claim 1, 10. An arc welding method, wherein the base material and the welding wire are made of a steel material.

8. The arc welding method according to any one of claims 1 to 7, During welding of the base metal, a shielding gas is sprayed onto the welding portion of the base metal, The shielding gas is CO ２ An arc welding method characterized by:

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