ARC WELDING METHOD AND ARC WELDING DEVICE

Abstract

A second member has a larger heat capacity than a first member. Welding is conducted while moving a welding torch in a weaving motion so that the welding torch crosses a boundary position between the first member and the second member. During the weaving motion, the first member is subjected to first welding and the second member is subjected to second welding. The first welding includes at least the short-circuit welding. The second welding includes at least the pulse welding.

Description

BACKGROUND

The present invention relates to an arc welding method and an arc welding device.

PCT International Publication No. WO 2016/059805 relates to consumable electrode-type arc welding in which pulse welding and short-circuit welding are alternately repeated, and discloses setting a welding current as of immediately before the shift from the pulse welding to the short-circuit welding to be lower than a base current in a pulse.

SUMMARY

In a case of arc welding two members with different heat capacities due to differences in the plate thickness or differences in the material, conducting pulse welding, whose heat input is high, on a member with a smaller plate thickness, for example, may result in burnt through of the member and cause a joining failure.

It is therefore an object of the present invention to improve the quality of joining members with different heat capacities.

A first aspect is directed to an arc welding method of welding by feeding, toward a welding target, a welding wire that is a consumable electrode, and generating an arc between the welding wire and the welding target, the welding target including a first member and a second member having a heat capacity larger than a heat capacity of the first member, the method including: conducting welding while moving a welding torch in a weaving motion so that the welding torch crosses a boundary position between the first member and the second member alternately multiple times; and switching a welding motion so that, during the weaving motion, the first member is subjected to first welding and the second member is subjected to second welding, the first welding including at least short-circuit welding, the second welding including at least pulse welding.

According to the first aspect, the second member has the larger heat capacity than the first member. The welding is conducted while moving the welding torch in the weaving motion so that the welding torch crosses the boundary position between the first member and the second member alternately multiple times. During the weaving motion, the first member is subjected to the first welding and the second member is subjected to the second welding. The first welding includes at least the short-circuit welding. The second welding includes at least the pulse welding.

This procedure can improve the quality of joining members with different heat capacities. Specifically, the short-circuit welding whose heat input is low is conducted on the first member with the smaller heat capacity, thereby making it possible to reduce burn-through of the first member. Further, the pulse welding whose heat input is high is conducted on the second member with the larger heat capacity, thereby making it possible to reduce insufficient penetration.

In this manner, by switching the welding mode in synchronization with the weaving motion of the welding torch, a proper heat can be input in welding a welding target having different plate thicknesses or a welding target in a complicated shape. As a result, it is possible to achieve a desired penetration depth without causing burn-through.

In DC welding, a pulsed welding current alternating between the peak current and the base current is applied to a welding wire and a welding target. Accordingly, unlike AC welding, DC welding does not require an additional AC unit and can reduce the overall costs for the device.

A second aspect is an embodiment of the arc welding method according to the first aspect. In the second aspect, at least one of the first welding or the second welding includes third welding in which a short-circuit welding period for the short-circuit welding and a pulse welding period for the pulse welding are switched from one to the other multiple times.

According to the second aspect, at least one of the first welding or the second welding includes the third welding. The third welding has characteristics in the middle of those of the short-circuit welding and the pulse welding, with a higher heat input compared to the short-circuit welding and lower heat input compared to the pulse welding. The third welding can reduce a rapid change in the heat input at the time when the welding current is changed.

A third aspect is an embodiment of the arc welding method according to the second aspect. In the third aspect, the method further includes: if the third welding is conducted in the first welding, setting a ratio of the short-circuit welding period for the short-circuit welding in the third welding to be higher than a ratio of the pulse welding period for the pulse welding; and if the third welding is conducted in the second welding, setting the ratio of the pulse welding period for the pulse welding in the third welding to be higher than the ratio of the short-circuit welding period for the short-circuit welding.

According to the third aspect, the method includes the short-circuit welding period for the short-circuit welding and the pulse welding period for the pulse welding. When the first member with a smaller heat capacity is welded by the third welding, the ratio of the short-circuit welding period for the short-circuit welding whose heat input is low as compared to the pulse welding is set to be higher. When the second member with a larger heat capacity is welded by the third welding, the ratio of the pulse welding period for the pulse welding whose heat input is high is set to be higher. This makes it possible to conduct the third welding under proper conditions.

A fourth aspect is an embodiment of the arc welding method according to the second or third aspect. In the fourth aspect, the method further includes: switching welding in order of the pulse welding, the third welding, and the short-circuit welding before the welding torch crosses the boundary position from the second member toward the first member in the second welding.

According to the fourth aspect, the welding gradually shifts to the short-circuit welding before the welding torch is moved from the second member with the larger heat capacity toward the first member with the smaller heat capacity. Accordingly, the pulse welding, the third welding, and the short-circuit welding are performed in coordination with each other, making it possible to reduce a rapid change in the heat input.

A fifth aspect is an embodiment of the arc welding method according to any one of the second to fourth aspects. In the fifth aspect, the method further includes: gradually changing, in the third welding, at least one of the number of pulses in the pulse welding or the number of short circuits in the short-circuit welding.

According to the fifth aspect, the gradual change in at least one of the number of pulses during the pulse welding or the number of short circuits during the short-circuit welding can reduce a rapid change in the heat input.

A sixth aspect is an embodiment of the arc welding method according to any one of the first to fifth aspects. In the sixth aspect, a welding current applied when the welding torch crosses the boundary position from the first member toward the second member is larger than a welding current before the welding torch crosses the boundary position.

According to the sixth aspect, the welding current applied when the welding torch crosses the boundary position is an average welding current which is an average current as the moving average of the welding current. The average welding current applied to the welding wire when the welding torch crosses the boundary position is increased, thereby making it possible to increase the amount of feeding of the welding wire at the boundary position and secure a sufficient thickness of beads. It is thus possible to fill the step height at the boundary between the thinner plate and the thicker plate.

A seventh aspect is an embodiment of the arc welding method according to any one of the second to sixth aspects. In the seventh aspect, a ratio of the number of short circuits of the short-circuit welding in the third welding when the welding torch crosses the boundary position from the second member toward the first member is higher than the ratio of the number of short circuits of the short-circuit welding in the third welding before the welding torch crosses the boundary position.

According to the seventh aspect, the ratio of the number of short circuits at the time when the welding torch crosses the boundary position is set to be larger than the ratio of the number of short circuits before the welding torch crosses the boundary position, so that the ratio of the number of short circuits is increased from before and when the welding torch crosses the boundary position. This makes it possible to secure a sufficient thickness of the beads at the boundary position in the state of low heat input. It is thus possible to fill the step height at the boundary between the thinner plate and the thicker plate.

An eighth aspect is an embodiment of the arc welding method according to any one of the first to seventh aspects. In the eighth aspect, the weaving motion is a spiral weaving motion moving along a spiral trajectory, and a distance from a center position of the spiral trajectory to a rear end of the spiral trajectory in a direction of welding on the boundary position is shorter than a distance to a front end of the spiral trajectory in the direction of welding.

According to the eighth aspect, the distance from the center position of the spiral trajectory to the rear end of the spiral trajectory in the direction of welding on the boundary position is set shorter than the distance to the front end of the spiral trajectory in the direction of welding, which reduces the penetration and can secure a sufficient thickness of the beads.

A ninth aspect is an embodiment of the arc welding method according to any one of the first to eighth aspects. In the ninth aspect, in at least one of the first welding or the second welding, the welding wire is fed at a constant speed.

According to the ninth aspect, the welding wire is fed at the constant speed.

A tenth aspect is an embodiment of the arc welding method according to any one of the first to eighth aspects. In the tenth aspect, in at least one of the first welding or the second welding, the welding wire is fed while a forward movement and a backward movement of the welding wire are alternately repeated periodically.

According to the tenth aspect, the forward movement and the backward movement of the welding wire are alternately repeated periodically to feed the welding wire.

This feeding can reduce the heat input to the welding target. Specifically, when the welding wire is short-circuited to the welding target, the welding voltage becomes close to 0 V, and the heat input amount, which is the amount of heat per unit time, becomes extremely small.

To address this, in moving the welding wire forward and backward, the welding wire is moved forward, and then when the welding wire is short-circuited to the welding target, the welding wire is moved backward. When an arc occurs between the welding wire and the welding target, the welding wire is accelerated to move forward. This dramatically increases the number of short circuits as compared to constant feeding of the welding wire toward the welding target. It is thus possible to obtain the advantage of cooling the welding target periodically.

The forward and backward movements of the welding wire at the time of short circuit can reduce spatter and improve the quality of welding.

An eleventh aspect is an embodiment of the arc welding method according to any one of the second to tenth aspects. In the eleventh aspect, the weaving motion is a spiral weaving motion moving along a spiral trajectory, and the third welding of switching between the short-circuit welding period for the short-circuit welding and the pulse welding period for the pulse welding multiple times is performed in the spiral weaving motion, and a ratio of the pulse welding period is set to be higher on a side forward of the center position of the spiral trajectory in the direction of welding, while a ratio of the short-circuit welding period is set to be higher on a side rearward in the direction of welding.

According to the eleventh aspect, since the heat input of the pulse welding is higher than the heat input of the short-circuit welding, a weld pool is formed by increasing, at the front in the direction of welding, the ratio of the pulse welding period for the pulse welding whose heat input is high; and the weld pool is cooled by increasing, at the rear in the direction of welding in the spiral weaving motion, the ratio of the short-circuit welding period for the short-circuit welding whose heat input is lower than that of the pulse welding. It is thus possible to reduce burn-through of the welding target and make the scaly wave pattern of the beads clear.

A twelfth aspect is directed to an arc welding device for welding by feeding, toward a welding target, a welding wire that is a consumable electrode, and generating an arc between the welding wire and the welding target, the welding target including a first member and a second member having a heat capacity larger than a heat capacity of the first member, the device including: a welding unit configured to conduct welding while moving a welding torch in a weaving motion so that the welding torch crosses a boundary position between the first member and the second member alternately multiple times; and a controller configured to control an operation of the welding unit, the controller being configured to control the operation of the welding unit so that, during the weaving motion, the first member is subjected to first welding and the second member is subjected to second welding, the first welding including at least short-circuit welding, the second welding including at least pulse welding.

According to the twelfth aspect, since the heat input of the short-circuit welding is lower than the heat input of the pulse welding, the short-circuit welding whose heat input is low is conducted on the first member with the smaller heat capacity, thereby making it possible to reduce burn-through of the first member. Further, the pulse welding whose heat input is high is conducted on the second member with the larger heat capacity, thereby making it possible to reduce insufficient penetration.

According to the aspects of the present disclosure, it is possible to improve the quality of joining members with different heat capacities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic configuration of an arc welding device according to an embodiment.

FIG. 2 is a diagram illustrating a welding current, a welding voltage, a waveform of the feeding speed of a welding wire, and a droplet transfer state in short-circuit welding.

FIG. 3 is a diagram illustrating a welding current, a welding voltage, a waveform of the feeding speed of a welding wire, and a droplet transfer state in pulse welding.

FIG. 4 is a diagram illustrating a welding current, a welding voltage, and a waveform of the feeding speed of a welding wire in pulse mix welding.

FIG. 5 is a side sectional view illustrating a state of performing arc welding in spiral weaving motion.

FIG. 6 is a perspective view illustrating the state of performing arc welding in spiral weaving motion.

FIG. 7 is a perspective view for explanation of the timing of switching among short-circuit welding, pulse welding, and pulse mix welding.

FIG. 8 is a diagram for explanation of a relationship between the welding speed and the appearance of beads in pulse mix welding without spiral weaving motion.

FIG. 9 is a diagram showing a relationship between the welding speed and the appearance of beads in pulse mix welding during spiral weaving motion.

FIG. 10 is a diagram illustrating a trajectory of spiral weaving motion according to a variation of the embodiment.

DETAILED DESCRIPTION

An embodiment of the present invention will be described in detail with reference to the drawings. The following description of the embodiment is merely an example in nature, and is not intended to limit the scope, applications, or use of the present invention.

As shown in FIG. 1, an arc welding device 1 welds a welding target W by generating an arc 16 between a welding wire 15, which is a consumable electrode, and the welding target W.

The arc welding device 1 includes a welding unit 10 and a controller 30. The welding unit 10 includes a welding torch 11, a feeding motor 12, a robot 13, and a power converter 20. The feeding motor 12 feeds the welding wire 15 to the welding torch 11 at a predetermined feeding speed.

The robot 13 includes a plurality of joints. The welding torch 11 is attached to the distal end portion of the robot 13. The robot 13 moves the position of the welding torch 11 with respect to the welding target W. As will be described in detail later, the robot 13 causes the welding torch 11 to move in spiral weaving motion along a spiral trajectory.

The power converter 20 includes a primary rectifier 21, a switching element 22, a main transformer 23, a secondary rectifier 24, a reactor 25, a voltage detector 26, and a current detector 27.

The primary rectifier 21 rectifies the output from an input power supply 5 and outputs the resultant. The switching element 22 converts the DC output from the primary rectifier 21 into an AC. The switching element 22 controls a welding output consisting of a welding current and a welding voltage.

The main transformer 23 converts the AC voltage output from the switching element 22 The output of the main transformer 23 is output as a welding output via the secondary rectifier 24 and the reactor 25. The secondary rectifier 24 rectifies the secondary output of the main transformer 23. The voltage detector 26 detects a welding voltage V. The current detector 27 detects a welding current I.

The controller 30 includes a driver 31, a short-circuit welding controller 33 for controlling first welding including short-circuit welding, a pulse welding controller 32 for controlling second welding including pulse welding, a pulse mix welding controller 34 for controlling third welding, which will be described later, a welding condition setting unit 35, a storage 36, a feeding speed controller 37, a first switcher 38, a second switcher 39, and a robot controller 40.

The driver 31 controls the switching element 22. The pulse welding controller 32 performs the control for the pulse welding. The short-circuit welding controller 33 performs the control for the short-circuit welding. The pulse mix welding controller 34 performs the control for the third welding.

The third welding is a welding mode in which the short-circuit welding and the pulse welding are alternately repeated multiple times, each at given number of times. In this embodiment, the third welding is defined as “pulse mix welding,” which will be used in the following description.

In the pulse mix welding, it is preferable that the feeding of the welding wire 15 is basically the forward and backward movements of the welding wire 15 in the case of the short-circuit welding, and is basically constant feeding of the welding wire 15 in the case of the pulse welding. However, the feeding is not limited thereto. For example, as will be described later with reference to FIG. 3, the feeding speed of the welding wire 15 may be changed during the pulse welding. Alternatively, the welding wire 15 may be fed at a constant speed during the short-circuit welding.

In the pulse mix welding, the number of pulses during the pulse welding and/or the number of short circuits during the short-circuit welding may be gradually changed. The gradual change in at least one of the number of pulses during the pulse welding or the number of short circuits during the short-circuit welding can reduce a rapid change in the heat input. For example, in FIG. 4 which will be described later, the six times of pulses and three times of short circuits is repeated, but the times may be changed to three times of pulses and six times of short circuits, which is repeated multiple times. The number of pulses and the number of short circuits are merely examples and are not limited thereto.

The number of pulses and the number of short circuits may be gradually changed, for example, at each predetermined welding distance, each predetermined welding time, or each preset teaching point.

The welding condition setting unit 35 sets welding conditions including a welding current and a welding voltage. Specifically, the welding condition setting unit 35 sets the welding current set for welding, the welding voltage set for welding, the feeding speed of the welding wire 15, the kind of shielding gas, the material of the welding wire 15, the diameter of the welding wire 15, the period for the pulse welding and the number of pulse outputs, the period for the short-circuit welding and the number of short-circuit outputs, and other conditions.

The shielding gas is selected depending on the material of the welding wire and the purpose. For example, argon gas (Ar) is used in welding an aluminum alloy. MIG gas (98% of Ar and 2% of O2) is used in welding stainless steel. MAG gas (80% of Ar and 20% of CO2) is used in welding mild steel. When emphasis is placed on cost reduction in welding mild steel, carbon dioxide (CO2) is used. The kind of the shielding gas is merely an example.

The storage 36 stores predetermined thresholds. The thresholds stored in the storage 36 are thresholds of welding parameters related to the heat input given to the welding target W, such as the welding current, the welding voltage, and the feeding speed. The storage 36 outputs the welding motion, proper control values, the feeding speed of the welding wire 15, and other paraments stored in advance, based on the output from the welding condition setting unit 35.

The feeding speed controller 37 controls the feeding speed of the welding wire 15 in accordance with the set current for the welding current set by the welding condition setting unit 35. Here, the feeding speed and the welding current are correlated with each other. More specifically, there is a correlation between the average welding speed (also referred to as the amount of feeding) as a moving average and the average welding current (also referred to as a set current) that is an average current as a moving average.

The first switcher 38 outputs a signal for welding output of any of the pulse welding controller 32, the short-circuit welding controller 33, and the pulse mix welding controller 34 in accordance with the output of the storage 36.

The second switcher 39 selects the output of the feeding speed of any one of the pulse welding controller 32, the short-circuit welding controller 33, and the pulse mix welding controller 34 in accordance with the output of the storage 36.

The robot controller 40 controls the operation of the robot 13. The robot controller 40 gives a current command to a motor (not shown) of each axis of the robot 13 so as to move the welding torch 11 in the direction of welding of the welding target W.

<Method of Controlling Arc Welding Device>

Next, an operation of the arc welding device 1 will be described. The arc welding device 1 applies a current between the welding wire 15 and the welding target W, while shielding the welding point of the welding target W from the outside air by supplying the shielding gas through a gas supply port (not shown).

Accordingly, an arc 16 occurs between the welding wire 15 and the welding target W. The heat of the arc 16 melts a tip end portion of the welding wire 15 and part of the welding target W. The melted welding wire 15 turns into a droplet, which drops onto the welding target W and forms a weld pool together with the part of the welding target W melted by the heat of the arc 16.

The welding torch 11 moves in the direction of welding in the spiral weaving motion on the welding target W. Beads are formed on the welding target W along with the movement of the welding torch 11, and the welding target W is welded.

The arc welding device 1 welds the welding target W, while switching among the short-circuit welding, the pulse welding, and the pulse mix welding.

FIG. 2 is a diagram illustrating the welding current, the welding voltage, the waveform of the feeding speed of the welding wire, and a droplet transfer state in the short-circuit welding. In FIG. 2, the vertical axis represents the welding current I, the welding voltage V, and the feeding speed WF, while the horizontal axis represents time.

In the short-circuit welding, the welding current I is controlled so that a short-circuit period and an arc period alternate. The short-circuit period is a short-circuit state in which the welding wire 15 and the welding target W are in contact with each other and short-circuited. The arc period is an arc state in which the arc 16 occurs between the welding wire 15 and the welding target W. In the short-circuit period, the welding wire 15 and the welding target W are short-circuited. In the arc period, the arc 16 occurs between the welding wire 15 and the welding target W. In the short-circuit welding, a welding current of 100 A, for example, is applied to the welding wire 15.

In FIG. 2, P1 indicates the point of time when the short circuit is started. In the short-circuit period from P1 to P2, the initial short-circuit current is output for a predetermined time from the time point P1, and the short-circuit current is gradually increased thereafter.

P2 indicates the time point when the short-circuit state ends and an arc state occurs. In the arc period from P2 to P3, a first welding current, which is a peak current, is output immediately after the occurrence of the arc, and the current then shifts to a second welding current which is lower than the first welding current. The period from P2 to P3 is the arc period that is an arc state in which the arc 16 occurs between the welding wire 15 and the welding target W. In the arc period, the arc 16 occurs between the welding wire 15 and the welding target W, and a droplet is formed at the tip end portion of the welding wire 15 by the heat of the arc 16, which also melts part of the welding target W.

P3 indicates the time point when the next short circuit after the one at P1 has occurred. The state at P3 is the same as the state at the time point P1. When a short circuit occurs between the welding wire 15 and the welding target W that have been brought into contact with each other, the droplet formed at the tip end portion of the welding wire 15 in the arc period is short-circuited and transferred to the welding target W, which forms a weld pool and causes the short-circuit welding.

In this manner, in the short-circuit welding, the short-circuit period from P1 (P3) to P2 and the short-circuit period from P2 to P3 are alternately repeated periodically.

In the example shown in FIG. 2, feeding of the welding wire is controlled such that the forward movement and the backward movement are alternately repeated periodically multiple times in accordance with the shape of a sine wave having a predetermined frequency and a predetermined speed amplitude as a basic waveform. At a peak of the forward movement, a short circuit occurs around the time point P1. At a peak of the backward movement, an arc occurs around the time point P2. At a peak of the forward movement after the time point P2, the next short circuit occurs around the time point P3.

As described above, the period from P1 to P3 is defined as one cycle of the control, and this cycle is repeated to perform welding.

FIG. 3 is a diagram illustrating the welding current, the welding voltage, the waveform of the feeding speed of the welding wire, and a droplet transfer state in pulse welding. In FIG. 3, the vertical axis represents the welding current I, the welding voltage V, and the feeding speed WF, while the horizontal axis represents time. The pulse welding is welding in which a peak current IP and a base current IB are alternately repeated. In the pulse welding, a welding current of 200 A, for example, is applied to the welding wire 15.

As shown in FIG. 3, the arc welding device 1 applies the welding current I and the welding voltage V to the welding wire 15. The pulse waveform of the welding current I includes a pulse rising period IPRT, a peak current period IPT, a pulse falling period IPFT, and a base current period IBT. In the pulse rising period IPRT, the welding current I shifts from the base current IB to the peak current IP. In the peak current period IPT, the welding current I is the peak current IP. In the pulse falling period IPFT, the welding current I shifts from the peak current IP to the base current IB. In the base current period IBT, the welding current I is the base current IB.

The pulse rising period IPRT, the peak current period IPT, the pulse falling period IPFT, and the base current period IBT are periodically repeated in this order at the pulse frequency PHz, which can provide a periodic droplet transfer state.

In the pulse rising period IPRT and the peak current period IPT, the feeding speed WF of the welding wire 15 is set to a first feeding speed WF1. In the pulse falling period IPFT, the feeding speed WF of the welding wire 15 is changed from the first feeding speed WF1 to a second feeding speed WF2.

The arc welding device 1 generates an arc 16 between the welding wire 15 and the welding target W, thereby forming a droplet at the tip end portion of the welding wire 15 by the heat of the arc 16, which also melts part of the welding target W.

The droplet formed at the tip end portion of the welding wire 15 is transferred from the tip end of the welding wire 15 and adheres to the welding target W by the droplet transfer, thereby forming a weld pool in the welding target W. In the pulse welding in which the peak current IP and the base current IB are alternately repeated, one-pulse one-drop welding is performed in which a pulse cycle 1/PHz including one peak current IP and one base current IB is defined as one pulse unit, and one droplet is transferred to the welding target W in each pulse cycle, in other words, each pulse with one peak current. The arc welding device 1 changes the arc length H of the arc 16 with respect to the reference arc length H1 in a droplet separation state in which a droplet has been transferred. Specifically, the arc welding device 1 accelerates and decelerates the welding wire 15 during the pulse welding.

In the example shown in FIG. 3, at the start of the pulse falling period IPFT, the feeding speed WF of the welding wire 15 is changed from the first feeding speed WF1 to the second feeding speed WF2, that is, the welding wire 15 is accelerated. At the time point TP, a short circuit between the welding wire 15 and the welding target W is detected. In the period from the time point TP to the time point NP, the welding current is increased to the current IS.

At the time point NP, the feeding speed WF of the welding wire 15 is changed from the second feeding speed WF2 to a third feeding speed WF3, that is, the welding wire 15 is decelerated.

On detection, at time point NP, of a constriction in a droplet formed between the welding wire 15 and the welding target W, the welding current I drops sharply from the current IS at the time point NP toward the current IN, which is lower than the current IS.

In the period from the time point NP to the time point AP, the welding current I is maintained at the second current IN.

On detection of the opening of the short circuit between the welding wire 15 and the welding target W at the time point AP, the third feeding speed WF3 of the welding wire 15 is changed to the first feeding speed WF1.

Although an example in which the feeding speed WF of the welding wire 15 is changed in the pulse welding period is illustrated in FIG. 3, normal one-pulse one-drop pulse welding may be performed at a constant feeding speed WF of the welding wire 15. In this case, the arc 16 continuously occurs at the peak current and the base current without a short circuit between the welding wire 15 and the welding target W, and a droplet formed on the tip end of the welding wire 15 is separated in the air from the tip end of the welding wire 15 and transferred to the welding target W so that one-pulse one-drop occurs in which one droplet is transferred to the welding target W in each pulse with one peak current.

FIG. 4 is a diagram illustrating the welding current, the welding voltage, and the waveform of the feeding speed of the welding wire in the pulse mix welding. The pulse mix welding is a welding mode in which a pulse welding period Tp for pulse welding and a short-circuit welding period Ts for short-circuit welding are alternately repeated multiple times. Pulse mix welding as DC welding, which is a combination of DC short-circuit welding and DC pulse welding, will be described herein. In FIG. 4, the vertical axis represents the welding current I, the welding voltage V, and the feeding speed WF, while the horizontal axis represents time.

In the pulse welding period Tp for the pulse welding, a welding current I is controlled so that the welding current I flowing through the welding wire 15 forms a plurality of pulses in which a peak current Ip and a base current Ib are alternately repeated.

In the short-circuit welding period Ts for the short-circuit welding, the welding current I is controlled so that at least one short-circuit period S for causing a short circuit between the welding wire 15 and the welding target W and at least one arc period A for generating an arc 16 between the welding wire 15 and the welding target W alternately appear.

The pulse welding period Tp and the short-circuit welding period Ts are alternately repeated so that a pulse welding period Tp follows a short-circuit welding period Ts and another short-circuit welding period Ts follows the pulse welding period Tp.

The pulse welding period Tp can be detected by detecting, for example, a change in the welding current I from a value larger than a preset threshold Is to a value smaller than the threshold Is. The short-circuit welding period Ts can be detected by detecting, for example, a change in the welding voltage V from a value larger than a preset threshold Vs to a value smaller than the threshold Vs.

The feeding speed controller 37 gives a control output to the feeding motor 12 so that the feeding speed WF of the welding wire 15 be a preset feeding speed in the pulse welding period Tp and the short-circuit welding period Ts. Accordingly, the welding wire 15 is fed at the constant third feeding speed WF3 in the pulse welding period Tp.

On the other hand, in the short-circuit welding period Ts, the feeding speed WF of the welding wire 15 is changed in accordance with a periodic waveform having a predetermined amplitude and a predetermined period. The feeding speed WF shown in FIG. 4 changes in accordance with a sine wave as a periodic waveform.

At a pulse start time point Tps at which the number of short circuits has reached the count preset by the welding condition setting unit 35, the short circuit is opened. The pulse start time point Tps may also be a time point at which time preset by the welding condition setting unit 35 has elapsed. At the pulse start time point Tps, the pulse welding period Tp for the pulse welding starts.

The pulse mix welding controller 34 starts the pulse welding period Tp and generates the first pulse of the plurality of pulses.

Even after the pulse start time point Tps, the feeding speed WF continues to change in accordance with the periodic waveform of the short-circuit welding period Ts toward the third feeding speed WF3 of the welding wire 15 of the pulse welding period Tp preset by the welding condition setting unit 35. Once the feeding speed WF reaches the third feeding speed WF3 in the pulse welding period Tp, a feeder 14 feeds the welding wire 15 at the third feeding speed WF3.

After that, when the number of pulses has reached the count preset by the welding condition setting unit 35 in the pulse welding period Tp, or when the time preset by the welding condition setting unit 35 has elapsed in the pulse welding period Tp, the pulse mix welding controller 34 changes the welding current I to a current I3 different from the base current Ib in the pulses, after the formation of the last pulse.

The time point at which the welding current I changes to the current I3 after the formation of the last pulse is used as a trigger, and the feeding speed WF is changed from the third feeding speed WF3 of the pulse welding period Tp to a speed in accordance with the above-described periodic waveform, at a feed switching time point Tvs, at which the welding current I is the current I3, thereby starting the feed of the welding wire 15 in the forward direction and the backward direction.

In this manner, the welding is performed while alternately repeating the pulse welding period Tp and the short-circuit welding period Ts under the set conditions and feeding the welding wire 15 at the most suitable feeding speed WF in each mode at that time.

In this embodiment, the welding mode is switched among the short-circuit welding, the pulse welding, and the pulse mix welding in accordance with the heat capacity of the welding target W.

Specifically, as shown in FIGS. 5 and 6, the welding target W includes a first member W1 and a second member W2. The second member W2 has a greater plate thickness than the first member W1. The second member W2 thus has a larger heat capacity than the first member W1. The first member W1 and the second member W2 are made of aluminum, for example. The first member W1 and the second member W2 are arranged to abut on each other.

The position where the first member W1 and the second member W2 abut on each other is a boundary position Wb between the first member W1 and the second member W2. The arc welding device 1 conducts welding by moving the welding torch 11 in a spiral weaving motion in which the welding torch 11 crosses the boundary position Wb between the first member W1 and the second member W2 alternately multiple times.

The spiral weaving motion is a motion of the welding torch 11 along a spiral trajectory, in which the welding torch 11 is moved in the direction of welding while making circular trajectories.

In the example shown in FIG. 6, the welding wire 15 fed by the welding torch 11 moves in a circular motion in which the welding wire 15 circles about the center RC of rotation that moves in the direction of welding on the boundary position Wb between the first member W1 and the second member W2, while keeping a distance from the center RC of rotation by a radius r of rotation and at a predetermined rotation frequency. The size of the radius r of rotation shown in FIG. 6 is merely an example and not limited thereto. For example, in FIGS. 5 and 6, the welding torch 11 may be moved to a position where the welding wire 15 can be fed to the upper surface of the second member W2.

The arc welding device 1 changes the welding motion during the spiral weaving motion so that the first member W1 is subjected to the first welding and that the second member W2 is subjected to the second welding. The first welding includes at least the short-circuit welding whose heat input is low. The second welding includes at least the pulse welding whose heat input is high. Third welding is performed in at least one of the first welding or the second welding. The third welding is pulse mix welding in which the short-circuit welding and the pulse welding are alternately repeated multiple times, each at given number of times.

Now, the timing of switching the welding mode among the short-circuit welding, the pulse welding, and the pulse mix welding will be described with reference to FIG. 7.

As shown in FIG. 7, the start position of the arc welding on the boundary position Wb between the first member W1 and the second member W2 is referred to as 0°, and the arc welding is performed in the direction of welding, while rotating the welding torch clockwise about the center RC of rotation.

In FIG. 7, the section between 20° and 160° is referred to as a first section 41, the section between 160° and 190° as a second section 42, the section between 190° and 350° as a third section 43, and the section between 350° and 20° as a fourth section 44. The angle range of each section is merely an example.

In the first section 41, the first switcher 38 selects an output of the short-circuit welding controller 33 suitable for the first member W1 with a smaller heat capacity, thereby performing the short-circuit welding, in the first welding for welding the first member W1.

In the first section 41, the first switcher 38 may select an output of the pulse mix welding controller 34 after the start of the short-circuit welding to perform the pulse mix welding. The pulse mix welding is the third welding in which the pulse welding period Tp for the pulse welding and the short-circuit welding period Ts for the short-circuit welding are alternately repeated multiple times. The pulse mix welding has characteristics in the middle of those of the short-circuit welding and the pulse welding, with a higher heat input compared to the short-circuit welding and lower heat input compared to the pulse welding. The pulse mix welding can reduce a rapid change in the heat input at the time when the welding current is changed.

In performing the pulse mix welding in the first welding, the controller 30 controls the operation of the welding unit 10 so that the ratio of the short-circuit welding period Ts for the short-circuit welding is higher than the ratio of the pulse welding period Tp for the pulse welding in the pulse mix welding. This makes it possible to conduct the pulse mix welding under proper conditions. The first welding may be controlled to perform only the short-circuit welding, but no pulse mix welding. In the pulse mix welding, the number of pulses during the pulse welding and/or the number of short circuits during the short-circuit welding may be gradually changed.

The second section 42 is an area across the first member W1 and the second member W2. In the second section 42, the welding motion is changed so that the first member W1 is subjected to the first welding including at least the short-circuit welding and that the second member W2 is subjected to the second welding including at least the pulse welding.

Specifically, the first switcher 38 selects an output of the pulse mix welding controller 34 to perform pulse mix welding as the third welding in which the pulse welding period Tp for the pulse welding and the short-circuit welding period Ts for the short-circuit welding are alternately repeated multiple times. The pulse mix welding can reduce a rapid change in the heat input at the time when the welding current is changed.

In performing the pulse mix welding in the first welding for the first member W1, the controller 30 controls the operation of the welding unit 10 so that the ratio of the short-circuit welding period Ts for the short-circuit welding is higher than the ratio of the pulse welding period Tp for the pulse welding in the pulse mix welding. In performing the pulse mix welding in the second welding for the second member W2, the controller 30 controls the operation of the welding unit 10 so that the ratio of the short-circuit welding period Ts for the short-circuit welding is lower than the ratio of the pulse welding period Tp for the pulse welding in the pulse mix welding.

In other words, when the pulse mix welding is performed on the first member W1, the ratio of the short-circuit welding period Ts for the short-circuit welding during the pulse mix welding is set to be higher than when the pulse mix welding is performed on the second member W2. On the other hand, when the pulse mix welding is performed on the second member W2, the ratio of the short-circuit welding period Ts for the short-circuit welding during the pulse mix welding is set to be lower than when the pulse mix welding is performed on the first member W1.

That is, in the pulse mix welding, it is possible to increase the ratio of the short-circuit welding period for the short-circuit welding, whose heat input amount is small, when the first member W1 with the smaller heat capacity is the area to be welded; on the other hand, it is possible to increase the ratio of the pulse welding period for the pulse welding, whose heat input amount is large as compared to the short-circuit welding, when the second member W2 with the larger heat capacity than the first member W1 is the area to be welded. Accordingly, the pulse mix welding can be performed under proper conditions.

The first welding may be controlled to perform only the short-circuit welding, but no pulse mix welding. In the pulse mix welding, the number of pulses during the pulse welding and/or the number of short circuits during the short-circuit welding may be gradually changed.

In the second section 42, the controller 30 controls the welding unit 10 to increase the amount of welding current to be applied to the welding wire 15 before the welding torch 11 moving from the first member W1 toward the second member W2 crosses the boundary position Wb. In other words, the welding current applied when the welding torch 11 crosses the boundary position Wb from the first member W1 toward the second member W2 is larger than the welding current applied before the welding torch 11 crosses the boundary position Wb. Specifically, the average welding current (also referred to as a “set current”), which is an average current as the moving average of the welding current applied when the welding torch 11 crosses the boundary position Wb from the first member W1 toward the second member W2 is larger than the average welding current applied before the welding torch 11 crosses the boundary position Wb. Accordingly, in the second section 42, a welding current larger than the welding current applied to the welding wire 15 in the first section 41 is applied to the welding wire 15.

The average welding current and the amount of feeding of the welding wire 15 are correlated with each other. Thus, the second section 42, which is the area of the step height between the first member W1 and the second member W2 including the boundary position Wb, may be welded with an increased amount of feeding of the welding wire 15 as compared to the first section 41 and the third section 43 to secure the amount of welding.

In this manner, it is possible to increase the amount of feeding of the welding wire 15 and secure a sufficient thickness of the beads in the boundary position Wb by increasing the current value of the current to be applied to the welding wire 15 when the welding torch 11 moving from the first member W1 with the smaller heat capacity toward the second member W2 with the larger heat capacity crosses the boundary position Wb. It is thus possible to fill the step height at the boundary between the thinner plate with the smaller heat capacity and the thicker plate with the larger heat capacity.

In the third section 43, the first switcher 38 selects an output of the pulse welding controller 32 suitable for the second member W2 with a larger heat capacity, thereby performing the pulse welding, in the second welding for welding the second member W2.

In the third section 43, after the start of the pulse welding, the first switcher 38 may select an output of the pulse mix welding controller 34 to perform pulse mix welding as the third welding in which the pulse welding period Tp for the pulse welding and the short-circuit welding period Ts for the short-circuit welding are alternately repeated multiple times. The pulse mix welding can reduce a rapid change in the heat input at the time when the welding current is changed.

In performing the pulse mix welding in the second welding for the second member W2, the controller 30 controls the operation of the welding unit 10 so that the ratio of the pulse welding period Tp for the pulse welding is higher than the ratio of the short-circuit welding period Ts for the short-circuit welding in the pulse mix welding. This makes it possible to conduct the pulse mix welding under proper conditions. The second welding may be controlled to perform only the pulse welding, but no pulse mix welding. In the pulse mix welding, the ratio of the pulse welding period Tp for the pulse welding or the number of pulses during the pulse welding, and/or the ratio of the short-circuit welding period Ts for the short-circuit welding or the number of short circuits during the short-circuit welding may be gradually changed.

The fourth section 44 is an area across the first member W1 and the second member W2. In the fourth section 44, the welding motion is changed so that the first member W1 is subjected to the first welding including at least the short-circuit welding and that the second member W2 is subjected to the second welding including at least the pulse welding.

Specifically, the first switcher 38 selects an output of the pulse mix welding controller 34 to perform pulse mix welding as the third welding in which the pulse welding period Tp for the pulse welding and the short-circuit welding period Ts for the short-circuit welding are alternately repeated multiple times. The pulse mix welding can reduce a rapid change in the heat input at the time when the welding current is changed.

In performing the pulse mix welding in the first welding for the first member W1, the controller 30 controls the operation of the welding unit 10 so that the ratio of the short-circuit welding period Ts for the short-circuit welding is higher than the ratio of the pulse welding period Tp for the pulse welding in the pulse mix welding. In performing the pulse mix welding in the second welding for the second member W2, the controller 30 controls the operation of the welding unit 10 so that the ratio of the short-circuit welding period Ts for the short-circuit welding is lower than the ratio of the pulse welding period Tp for the pulse welding in the pulse mix welding.

In other words, when the pulse mix welding is performed on the first member W1, the ratio of the short-circuit welding period Ts for the short-circuit welding during the pulse mix welding is set to be higher than when the pulse mix welding is performed on the second member W2. On the other hand, when the pulse mix welding is performed on the second member W2, the ratio of the short-circuit welding period Ts for the short-circuit welding during the pulse mix welding is set to be lower than when the pulse mix welding is performed on the first member W1.

That is, in the pulse mix welding, it is possible to increase the ratio of the short-circuit welding period for the short-circuit welding, whose heat input amount is small, when the second member W1 with the smaller heat capacity is the area to be welded; on the other hand, it is possible to increase the ratio of the pulse welding period for the pulse welding, whose heat input amount is large as compared to the short-circuit welding, when the second member W2 with the larger heat capacity than the first member W1 is the area to be welded. Accordingly, the pulse mix welding can be performed under proper conditions.

The first welding may be controlled to perform only the short-circuit welding, but no pulse mix welding. In the pulse mix welding, the number of pulses during the pulse welding and/or the number of short circuits during the short-circuit welding may be gradually changed.

Accordingly, the pulse welding, the pulse mix welding, and the short-circuit welding are performed in coordination with each other, making it possible to reduce a rapid change in the heat input.

Further, in the fourth section 44, the ratio of the short-circuit welding period Ts for the short-circuit welding, whose heat input is low as compared to the pulse welding, is gradually increased in the pulse mix welding, before the welding torch 11 crosses the boundary position Wb between the first member W1 and the second member W2 from the second member W2 with the larger heat capacity toward the first member W1 with the smaller heat capacity. In other words, the ratio of the number of short circuits in the short-circuit welding in the pulse mix welding at the time when the welding torch 11 crosses the boundary position Wb is larger than the ratio of the number of short circuits in the short-circuit welding in the pulse mix welding before the welding torch 11 crosses the boundary position Wb.

In this manner, the ratio of the number of short circuits at the time when the welding torch 11 crosses the boundary position Wb is set to be larger than the ratio of the number of short circuits before the welding torch 11 crosses the boundary position Wb, so that the ratio of the number of short circuits is increased from before and when the welding torch 11 crosses the boundary position Wb. This makes it possible to secure a sufficient thickness of the beads at the boundary position Wb in the state of low heat input. It is thus possible to fill the step height at the boundary between the thinner plate with the smaller heat capacity and the thicker plate with the larger heat capacity.

The heat input is lower in the short-circuit welding than in the pulse welding. In the pulse mix welding in which the short-circuit welding period Ts for the short-circuit welding and the pulse welding period Tp for the pulse welding are alternately repeated multiple times at a predetermined ratio, the short-circuit welding period Ts has a cooling effect since the heat input is low in the short-circuit welding. The heat input to the first member W1 is therefore reduced, which makes it possible to reduce the burn-through. In the pulse welding period Tp, the arc 16 spreads and increases the width of the beads, and the droplets of the welding wire 15 are regularly separated and transferred to the beads formed by the pulse welding with the high heat input. Spatter is thus reduced.

The pulse mix welding during the spiral weaving motion can increase the welding speed without degrading the quality of welding due to burn-through or other causes. The relationship between the welding speed and the appearance of beads will be described below with reference to FIGS. 8 and 9.

FIG. 8 is a comparative example showing a relationship between the welding speed and the appearance of beads in pulse mix welding without the spiral weaving motion. FIG. 8 shows a photograph showing the appearance of the beads and a schematic view obtained by tracing the photograph of the appearance of the beads to facilitate visual understanding.

As shown in FIG. 8, at welding speeds [m/min] of 0.3 m/min and 0.4 m/min, the beads are formed in a continuous scaly pattern and have good appearance. On the other hand, when the welding speed [m/min] is increased to 0.5 m/min, the scaly pattern of the beads becomes uniform, and the beads have deteriorated appearance. For example, as the welding speed increases, the scaly pattern of the beads tend to be gradually widened in the direction of welding, and the boundary lines between the beads tend to become thinner. Thus, the welding speed cannot be increased when only the pulse mix welding is performed without the spiral weaving motion.

FIG. 9 is a diagram showing a relationship between the welding speed and the appearance of beads in pulse mix welding in the spiral weaving motion. FIG. 9 shows a photograph showing the appearance of the beads and a schematic view obtained by tracing the photograph of the appearance of the beads to facilitate visual understanding.

As shown in FIG. 9, at any of the welding speeds [m/min] of 0.7 m/min, 0.8 m/min, 0.9 m/min, and 1.0 m/min, the beads are formed in a continuous scaly pattern, and the weld beads have good appearance. For example, even when the welding speed is increased, the scaly pattern of the beads is not much changed in its shape, and the boundary lines between the beads are clearly visible.

In view of this, it is believed that in the pulse mix welding in the spiral weaving motion, the scaly pattern of the beads are easily formed because the weld pool formed by the pulse welding with a high heat input is cooled by the short-circuit welding with a low heat input in the spiral weaving motion. This can increase the welding speed, while ensuring the quality of welding.

As described above, the arc welding method using the arc welding device 1 according to this embodiment can improve the quality of joining members with different heat capacities. Specifically, it is possible to reduce the burn-through of the first member W1 by performing, on the first member W1 with a smaller heat capacity, at least short-circuit welding and performing mainly the short-circuit welding whose heat input is low as compared to pulse welding, in other words, by increasing the ratio of the short-circuit welding period Ts for the short-circuit welding whose heat input is low. It is also possible to reduce insufficient penetration by performing, on the second member W2 with a larger heat capacity, at least pulse welding and performing mainly the pulse welding whose heat input is high, in other words, by increasing the ratio of the pulse welding period Tp for the pulse welding whose heat input is high.

According to the arc welding method using the arc welding device 1 of the present embodiment, even if the welding target W has a difference in thickness at many welding points, the short-circuit welding, the pulse welding, and the pulse mix welding can be set for the welding target W that consists of a combination of members with different heat capacities, in accordance with the welding parameters (such as the welding current I, the welding voltage V, the feeding speed of the welding wire 15, and the thickness of the welding target W) related to the heat input to the welding target W, by adjusting the welding conditions. This enables welding with high productivity and high quality with less spatter and less burn-through or the like at the welding points of the welding target W.

Variation of Embodiment

As shown in FIG. 10, the arc welding device 1 performs welding, with the welding torch 11 moving in the spiral weaving motion along the direction of welding. In the example shown in FIG. 10, the welding wire 15 fed by the welding torch 11 moves in a circular motion in which the welding wire 15 circles about the center RC of rotation that moves on the boundary position Wb between the first member W1 and the second member W2, while keeping a distance from the center RC of rotation by a radius r of rotation and at a predetermined rotation frequency.

In the example shown in FIG. 10, the welding torch 11 does not move along the circular trajectory. The distance r1 from the center RC of rotation of the spiral trajectory to the rear end of the spiral trajectory in the direction of welding is set to be shorter than the distance r2 to the front end of the spiral trajectory in the direction of welding. This reduces the area where the arc 16 is formed at the rear in the direction of welding, which reduces the penetration and can secure a sufficient thickness of the beads.

In the example shown in FIG. 10, the distance r2 to the front end of the spiral trajectory in the direction of welding is set to be equal to the radius r of rotation, and the distance r1 to the rear end of the spiral trajectory in the direction of welding is set to be shorter than the distance r2. The distances are not limited thereto. For example, the distance r1 may be set to be equal to the radius r of rotation, and the distance r2 may be set to be longer than the distance r1.

Other Embodiments

The embodiment described above may be modified as follows.

In this embodiment, the second member W2 has a greater plate thickness than the first member W1 to have a different heat capacity. For example, the first member W1 and the second member W2 may be made of different materials to have different heat capacities. For example, the first member W1 may be made of aluminum and the second member W2 may be made of a mild steel material, while having the same thickness. As a result, the first member W1 and the second member W2 have different heat capacities: the first member W1 has a smaller heat capacity and the second member W2 has a larger heat capacity. In other words, the second member W2 has a relatively larger heat capacity than the first member W1.

In this embodiment, the arc welding is performed on the first member W1 and the second member W2 abutting on each other. The welding is however not limited thereto. For example, the first member W1 and the second member W2 may be overlapped with each other in the thickness direction, and the edges of the first member W1 and the second member W2 may be arc-welded.

Here, for example, if the first member W1 and the second member W2 have the same plate thicknesses, the overlapping area of the first member W1 and the second member W2 has a larger heat capacity than the non-overlapping area. That is, the overlapping area of the two plate materials is assumed to be the second member, and the non-overlapping area as the first member, and the welding mode may be switched among the short-circuit welding, the pulse welding, and the pulse mix welding as in this embodiment.

In this embodiment, the pulse mix welding is performed in the first welding and the second welding. The welding is not limited thereto. For example, the first welding may be short-circuit welding, and the second welding may be pulse welding. The first welding may be short-circuit welding, and the second welding may be pulse mix welding. The first welding may be pulse mix welding, and the second welding may be pulse welding.

In this embodiment, the welding torch 11 moves in the spiral weaving motion. The motion is however not limited thereto. For example, the welding torch 11 may move in a weaving motion in which the welding torch 11 moves in the advance direction of the welding while swinging periodically side to side with respect to the boundary position Wb between the first member W1 and the second member W2 so as to cross the boundary position Wb alternately multiple times; and the welding torch 11 may move in a zigzag weaving motion. In this case, the weaving motion is preferably a motion in which the welding torch 11 swings periodically side to side with respect to the boundary position Wb with small swings at an acute angle.

In this embodiment, the spiral trajectory in the spiral weaving motion has the same radius r on the first member W1 side and on the second member W2 side, but may have different radii.

In this embodiment, the forward movement and the backward movement of the welding wire 15 are periodically repeated to feed the welding wire 15. The feeding is however not limited thereto. For example, the welding wire 15 may be fed at a constant speed.

During the weaving motion of this embodiment, a ratio of the pulse welding may be set to be higher on the side forward of the center position of the spiral trajectory in the direction of welding, and a ratio of the short-circuit welding may be set to be higher on the side rearward in the direction of welding. In this manner, the weld pool is formed at the front in the direction of welding by increasing the ratio of the pulse welding whose heat input is high, and the weld pool is cooled at the rear in the direction of welding by increasing the ratio of the short-circuit welding whose heat input is low. It is thus possible to reduce burn-through of the welding target W and make the scaly wave pattern of the beads clear.

As described above, the present invention can improve the quality of joining members with different heat capacities, which is very practical and useful and therefore highly applicable in the industry.

Claims

1. An arc welding method of welding by feeding, toward a welding target, a welding wire that is a consumable electrode, and generating an arc between the welding wire and the welding target, the welding target including a first member and a second member having a heat capacity larger than a heat capacity of the first member, the method comprising:conducting welding while moving a welding torch in a weaving motion so that the welding torch crosses a boundary position between the first member and the second member alternately multiple times; andswitching a welding motion so that, during the weaving motion, the first member is subjected to first welding and the second member is subjected to second welding,the first welding including at least short-circuit welding,the second welding including at least pulse welding.

2. The arc welding method of claim 1, wherein at least one of the first welding or the second welding includes third welding in which a short-circuit welding period for the short-circuit welding and a pulse welding period for the pulse welding are switched from one to the other multiple times.

3. The arc welding method of claim 2, further comprising: if the third welding is conducted in the first welding, setting a ratio of the short-circuit welding period for the short-circuit welding in the third welding to be higher than a ratio of the pulse welding period for the pulse welding; andif the third welding is conducted in the second welding, setting the ratio of the pulse welding period for the pulse welding in the third welding to be higher than the ratio of the short-circuit welding period for the short-circuit welding.

4. The arc welding method of claim 2, further comprising: switching welding in order of the pulse welding, the third welding, and the short-circuit welding before the welding torch crosses the boundary position from the second member toward the first member in the second welding.

5. The arc welding method of claim 2, further comprising: gradually changing, in the third welding, at least one of the number of pulses in the pulse welding or the number of short circuits in the short-circuit welding.

6. The arc welding method of claim 1, wherein a welding current applied when the welding torch crosses the boundary position from the first member toward the second member is larger than a welding current before the welding torch crosses the boundary position.

7. The arc welding method of claim 2, wherein a ratio of the number of short circuits of the short-circuit welding in the third welding when the welding torch crosses the boundary position from the second member toward the first member is higher than the ratio of the number of short circuits of the short-circuit welding in the third welding before the welding torch crosses the boundary position.

8. The arc welding method of claim 1, wherein the weaving motion is a spiral weaving motion moving along a spiral trajectory, anda distance from a center position of the spiral trajectory to a rear end of the spiral trajectory in a direction of welding on the boundary position is shorter than a distance to a front end of the spiral trajectory in the direction of welding.

9. The arc welding method of claim 1, wherein in at least one of the first welding or the second welding, the welding wire is fed at a constant speed.

10. The arc welding method of claim 1, wherein in at least one of the first welding or the second welding, the welding wire is fed while a forward movement and a backward movement of the welding wire are alternately repeated periodically.

11. The arc welding method of claim 2, wherein the weaving motion is a spiral weaving motion moving along a spiral trajectory, and the third welding of switching between the short-circuit welding period for the short-circuit welding and the pulse welding period for the pulse welding multiple times is performed in the spiral weaving motion, anda ratio of the pulse welding period is set to be higher on a side forward of the center position of the spiral trajectory in the direction of welding, while a ratio of the short-circuit welding period is set to be higher on a side rearward in the direction of welding.

12. An arc welding device for welding by feeding, toward a welding target, a welding wire that is a consumable electrode, and generating an arc between the welding wire and the welding target, the welding target including a first member and a second member having a heat capacity larger than a heat capacity of the first member, the device comprising:a welding unit configured to conduct welding while moving a welding torch in a weaving motion so that the welding torch crosses a boundary position between the first member and the second member alternately multiple times; anda controller configured to control an operation of the welding unit,the controller being configured to control the operation of the welding unit so that, during the weaving motion, the first member is subjected to first welding and the second member is subjected to second welding,the first welding including at least short-circuit welding,the second welding including at least pulse welding.