Arc welding control method

Abstract

In a first step of an arc welding control method according to the present disclosure, a welding current Aw is passed through a welding wire 21 in an arc start period Ts, and the welding wire 21 and a base material 25 are short-circuited while alternately repeating forward feeding and reverse feeding of the welding wire 21, so that a molten droplet formed at the tip of the welding wire 21 is short-circuit transferred to the base material 25. In a second step, in a main welding period Th after the arc start period Ts, the welding current Aw is varied at a period Tf between a peak current Ip and a base current Ib while alternately repeating the forward feeding and reverse feeding of the welding wire 21, so that the molten droplet is separated from the tip of the welding wire 21 and transferred to the base material 25.

Description

Arc welding control method

[0001] The present disclosure relates to a method for controlling arc welding.

[0002] In consumable electrode arc welding, an arc is generated between a welding wire, which is a consumable electrode, and a base metal, which is a workpiece, to weld the base metal. In this case, a molten pool is not formed on the base metal until a predetermined period (also called the arc start period) has elapsed since the arc was generated, which makes spatter more likely to occur. The spatter adheres to the base metal, damaging the appearance of the welded area and causing welding defects, resulting in reduced welding quality and yield. In particular, in pulse welding, which transfers molten droplets, a high peak current flows through the welding wire during the peak period, which strengthens the arc force and increases the amount of melted welding wire, resulting in significant generation of large spatter during the arc start period.

[0003] Therefore, Patent Document 1 proposes a method in which, during the arc start period, the welding wire is fed forward and backward cyclically to control the wire feed speed, thereby causing droplets formed at the tip of the welding wire to short-circuit and transfer to the base metal, and then causing the droplets to drop-transfer to the base metal. By doing so, during the arc start period, it is possible to forcibly release the short circuit without relying on an electromagnetic pinch force, and it is possible to reduce not only large spatter but also the amount of spatter generated.

[0004] Furthermore, Patent Document 2 discloses a configuration in which a detachment detection unit is provided to detect droplets detaching from the tip of a welding wire in pulse welding in which a peak current and a base current having a lower current value are periodically passed through the welding wire. In this case, if the detachment detection unit does not detect droplets detaching during the reverse feeding of the welding wire, the welding wire is fed forward at a constant speed after the end of the reverse feeding period. Also, if the detachment detection unit detects droplets detaching while the welding wire is fed forward at a constant speed, forward and reverse feeding of the welding wire is periodically repeated.

[0005] Alternatively, if the detachment detection unit detects the detachment of a droplet during the forward feeding period of the welding wire between the time when the command value for the welding wire feed speed becomes maximum and the time when the period switches to the reverse feeding period, the welding wire is fed forward at a constant speed at the time when the reverse feeding is switched to the forward feeding. Also, if the detachment detection unit detects the detachment of a droplet while the welding wire is being fed forward at a constant speed, the forward feeding and reverse feeding of the welding wire are cyclically repeated.

[0006] This prevents droplets from dropping onto the base material at undesired times during welding, thereby preventing spatter from occurring.

[0007] Patent No. 4807479 Patent No. 7041034

[0008] In pulse welding, a peak current and a base current lower than the peak current are alternately and periodically applied to a welding wire, and the welding wire feed speed and pulse frequency can be synchronized with the generation and detachment of droplets, enabling smooth droplet transfer. Generally, pulse welding is widely used in consumable electrode arc welding such as MIG welding (Metal Inert Gas Welding) and MAG welding (Metal Active Gas Welding).

[0009] On the other hand, in consumable electrode arc welding, a method is generally used in which a shielding gas that has low reactivity with molten metal is sprayed onto the welding point of the base material to prevent the molten base material or welding wire from reacting with the air around the base material. ２ (carbon dioxide gas) is often used. ２ is available at a lower cost than inert gases such as argon. ２ By using this, the arc tends to concentrate, which allows for deeper penetration into the base material.

[0010] However, CO as a shielding gas ２ When using CO , the arc reaction force becomes large and droplet transfer becomes difficult. Therefore, when performing pulse welding in which the welding wire is fed at a constant speed in MIG welding or MAG welding, ２ The method of using as a shielding gas has not been adopted.

[0011] The present disclosure has been made in consideration of the above points, and its purpose is to provide an arc welding control method that can reduce spatter during the arc start period and stabilize droplet detachment during the main welding period.

[0012] In order to achieve the above object, an arc welding control method according to the present disclosure is an arc welding control method for performing welding by generating an arc between a welding wire that is a consumable electrode and a base metal, the method including: a first step of, during an arc start period, flowing a welding current through the welding wire and alternately feeding the welding wire forward and backward to short-circuit the welding wire and the base metal, thereby short-circuiting a molten metal formed at the tip of the welding wire to the base metal; and a main welding period provided after the arc start period, alternately feeding the welding wire forward and backward to vary the welding current flowing through the welding wire at a predetermined cycle, thereby transferring a molten metal from the tip of the welding wire to the base metal. and a second step of detaching the droplet from the welding wire or transferring the droplet by short-circuiting from the welding wire to the base metal, wherein the arc start period is a period from an initial short-circuit detection point in time at which an initial short circuit between the welding wire and the base metal is detected to a point in time at which the main welding period starts, the cycle includes a peak current period in which a peak current flows through the welding wire and a base current period subsequent to the peak current period in which a base current flows through the welding wire, a current value of the base current being lower than the current value of the peak current, and an average feed speed of the welding wire during the main welding period being equal to or higher than the average feed speed at an end of the arc start period.

[0013] According to the present disclosure, a molten pool can be stably formed on the base material during the arc start period, thereby reducing spatter. Also, during the main welding period, droplets can be stably detached from the welding wire at a constant cycle, thereby reducing spatter and stabilizing the shape of the weld bead.

[0014] Fig. 1 is a schematic diagram of an arc welding apparatus according to embodiment 1. Fig. 2 is a schematic diagram of another arc welding apparatus according to embodiment 1. Fig. 3 is a diagram showing waveforms of a welding current, a welding voltage, and a wire feed speed. Fig. 4 is a diagram showing waveforms of a welding current, a welding voltage, and a wire feed speed according to embodiment 2. Fig. 5 is a diagram showing waveforms of a welding current, a welding voltage, and a wire feed speed according to embodiment 3. Fig. 6 is a diagram showing waveforms of a welding current according to embodiment 4. Fig. 7 is a diagram showing waveforms of a welding current according to embodiment 5. Fig. 8 is a diagram showing waveforms of a welding current, a welding voltage, and a wire feed speed according to embodiment 6.

[0015] 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.

[0016] First Embodiment [Configuration of Arc Welding Apparatus] FIG. 1 is a schematic diagram of an arc welding apparatus according to a first embodiment, and FIG. 2 is a schematic diagram of another arc welding apparatus according to the first embodiment.

[0017] As shown in FIG. 1 , the arc welding device 30 includes a primary rectifier 2, a switching unit 3, a transformer 4, a secondary rectifier 5 and a DCL 6, a driver 7, a welding voltage detector 8, a welding current detector 9, a short circuit / arc detector 10, a short circuit controller 11, an arc controller 12, and a wire feed speed controller 13. The primary rectifier 2 rectifies the power input from the input power source 1. The switching unit 3 converts the output of the primary rectifier 2 into AC. The transformer 4 transforms the output of the switching unit 3. The secondary rectifier 5 and the DCL 6 rectify the output of the transformer 4. The driver 7 controls the switching unit 3. The welding voltage detector 8 detects the welding voltage. The welding current detector 9 detects the welding current. The short circuit / arc detector 10 detects whether the welding state is a short circuit state or an arc state based on at least one of the output of the welding voltage detector 8 and the output of the welding current detector 9. The short circuit control unit 11 controls the welding output when a short circuit occurs. The arc control unit 12 controls the welding output when an arc occurs. The wire feed speed control unit 13 controls the wire feed speed according to the set current.

[0018] Welding wire 21, which is a consumable electrode stored in wire storage unit 20, is fed by wire feed motor 22. Electric power is supplied to welding wire 21 via tip 23 provided on welding torch 26. An arc 24 is generated between welding wire 21 and base metal 25, which is the workpiece to be welded, to perform welding. Welding torch 26 is attached to and moved by manipulator 18, which constitutes, for example, an industrial robot.

[0019] In addition to the general components arranged in the welding power supply 14, the arc welding apparatus 30 also includes a manipulator 18 that constitutes an industrial robot, and a robot control device 16 that controls the manipulator 18. A wire feed speed corresponding to a set current from a welding condition setting unit 15 in the robot control device 16 is sent as a speed signal from a wire feed speed control unit 13 to a wire feed motor 22. The wire feed speed output from the wire feed speed control unit 13 is also sent as a speed signal to a short circuit control unit 11 or an arc control unit 12, thereby controlling the welding output in a short circuit state or an arc state. The welding condition setting unit 15 is used to set welding conditions such as a set current and a set voltage.

[0020] The short circuit control unit 11 outputs a short circuit current upon receiving a short circuit determination signal from the short circuit / arc detection unit 10, and performs control to melt the tip of the welding wire 21 and promote release of the short circuit. The arc control unit 12 outputs a high current immediately after release of the short circuit in order to form a molten droplet at the tip of the welding wire 21 while ensuring the arc length, and then controls the current and voltage to transition to a low current so that a short circuit can easily occur.

[0021] Each of the components constituting the arc welding device 30 shown in FIG. 1 may be configured independently, or a plurality of components may be combined to form a single device.

[0022] Arc welding apparatus 30 further includes an industrial robot including manipulator 18 and robot controller 16 that controls the operation of manipulator 18, and welding power supply 14. The industrial robot includes welding condition setting unit 15. Welding power supply 14 may also include switching unit 3, drive unit 7, welding current detection unit 9, welding voltage detection unit 8, short circuit / arc detection unit 10, short circuit control unit 11, arc control unit 12, and wire feed speed control unit 13.

[0023] 2, the welding power supply 14 may be provided within the robot control device 17. With this configuration, the arc welding device can be made even more compact.

[0024] [Outline of Arc Welding Control Method] Fig. 3 is a diagram showing waveforms of the welding current, welding voltage, and wire feed speed. In this embodiment, the base material 25 is mild steel, and the material of the welding wire 21 is also mild steel. The shielding gas sprayed onto the base material 25 during welding is CO ２ 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.

[0025] As shown in Fig. 3 , the feeding operation of welding wire 21 starts at time P1 when a switch (not shown) of welding torch 26 is turned on. In the following description, the feeding speed of welding wire 21 will be referred to as wire feed speed Wf. When wire feed speed Wf has a positive value, welding wire 21 is fed forward, and the tip of welding wire 21 moves toward base material 25. When wire feed speed Wf has a negative value, welding wire 21 is fed backward, and the tip of welding wire 21 moves in a direction away from base material 25.

[0026] In response to a command from wire feed speed control unit 13, wire feed motor 22 feeds welding wire 21 in the forward direction at a constant feed speed Wfa from time P1, thereby moving the tip of welding wire 21 toward base metal 25. Until time P2, welding voltage Vw is a constant no-load voltage, and welding current Aw remains zero. At time P2, the tip of welding wire 21 contacts base metal 25, causing a short circuit, and welding voltage Vw becomes zero. Short circuit / arc detection unit 10 detects a short circuit between welding wire 21 and base metal 25, and welding wire 21 begins to be fed backward. In response to a command from arc control unit 12, welding current Aw begins to flow through welding wire 21. The period from time P1 to time P2 is referred to as slow-down period Ta, and the aforementioned feed speed Wfa is referred to as slow-down speed Wfa. By providing slow-down period Ta and appropriately setting slow-down speed Wfa, welding wire 21 can be reliably brought into contact with base metal 25. In addition, by passing the welding current Aw through the welding wire 21 in this state and feeding the welding wire 21 in the reverse direction, it is possible to reliably generate an arc 24 between the tip of the welding wire 21 and the base material 25. Note that the time point P2 may also be referred to as the initial short circuit detection time point P2.

[0027] From time P2, the welding wire 21 is periodically fed back and forth a plurality of times, thereby being short-circuited with the base metal 25 and repeatedly released from the base metal 25 at regular intervals. As the welding current Aw flows and the welding wire 21 is heated, a droplet (not shown) is formed at the tip of the welding wire 21, and the droplet is transferred to the base metal 25 when the welding wire 21 is short-circuited with the base metal 25. Furthermore, during the period from the release of the short circuit to the next short circuit, an arc 24 is generated between the welding wire 21 and the base metal 25. When the welding wire 21 and the base metal 25 are short-circuited, the welding current Aw increases. When the welding wire 21 and the base metal 25 are separated from each other and the arc 24 begins to be generated, the welding current Aw decreases. Furthermore, the welding voltage Vw increases in response to the generation of the arc 24. When the welding wire 21 and the base metal 25 are short-circuited, the welding voltage Vw decreases to zero or near zero. The welding current Aw and welding voltage Vw periodically repeat the above-described changes in response to the feeding operation of welding wire 21. In addition, arc control unit 12 controls welding current Aw, and in conjunction with this, wire feed speed control unit 13 controls wire feed speed Wf.

[0028] The average wire feed rate, which is the time average of the wire feed rate Wf, increases over time and reaches a constant value (=Wfh) at time P3. The period from time P2 to time P3 is referred to as the arc start period Ts. In this embodiment, during the arc start period Ts, the welding wire 21 and the base metal 25 are periodically short-circuited and released, forming a molten pool (not shown) in the base metal 25. The arc start period Ts is typically approximately 0.1 seconds to 2 seconds. Because the welding wire 21 and the base metal 25 are periodically short-circuited and released multiple times during this short period, the molten pool reliably grows and expands near the welding start point, forming a molten pool sufficient to suppress spatter. This suppresses spatter generation.

[0029] In this embodiment, in order to suppress the generation of spatter, the short circuit / arc detection unit 10 predicts the release of the short circuit based on a signal from the welding voltage detection unit 8, and performs so-called neck detection control (necking detection control), in which the welding current Aw is sharply reduced just before the short circuit is released. The welding current Aw just before the short circuit is released is called the neck current. In this embodiment, the neck current just before the transition to the main welding period Th is called the neck current In.

[0030] The periodically varying average feed speed of the welding wire 21 is referred to as the average feed speed Wfs. The maximum value of the forward feed speed during one period of the arc start period Ts, i.e., the period from when the welding wire 21 and the base material 25 are short-circuited to when the next short circuit occurs, is referred to as the first forward feed speed Wff, and the maximum value of the reverse feed speed is referred to as the first reverse feed speed Wfg. This period corresponds to a wire feed cycle in which the welding wire 21 repeatedly moves forward and backward. In the following description, the maximum reverse feed speed refers to the case where the absolute value of the reverse feed speed is maximum. In other words, it is the value at which the welding wire 21 is reversely fed at the fastest speed. In the following description, the reverse feed speeds are compared in absolute value.

[0031] Note that time point P3 is not limited to the time point when the average feed speed Wfs reaches a constant value Wfh, but may be, for example, the time point when the wire feed speed Wf becomes zero before or after the average feed speed Wfs reaches a constant value Wfh.

[0032] During the arc start period Ts, the first forward feed speed Wff increases with the number of cycle repetitions, while the first reverse feed speed Wfg is approximately constant. Therefore, as described above, the average feed speed Wfs increases with time. Note that the wire feed speed Wf is determined in accordance with the welding current Aw. That is, during the arc start period Ts, the time average value of the welding current Aw also increases with time. However, the first reverse feed speed Wfg does not necessarily have to be constant. The first reverse feed speed Wfg may also increase as the average feed speed Wfs increases.

[0033] After time P3, welding wire 21 continues to periodically alternate between forward and reverse feeding. However, the average feed rate is maintained at a constant value Wfh. Specifically, at or just before time P3, arc 24 is generated, and welding voltage Vw increases. From the time point at which welding voltage Vw exceeds arc determination level voltage Va (also referred to as voltage threshold Va), welding wire 21 periodically alternates between forward and reverse feeding multiple times. The period after time P3 is referred to as main welding period Th. Main welding period Th is the period during which a welded portion (not shown), such as a weld bead, is substantially formed on base material 25.

[0034] As shown in FIG. 3 , during the main welding period Th, the welding current Aw fluctuates periodically. Specifically, after the base current Ib flows through the welding wire 21, a peak current Ip having a current value higher than the base current Ib flows through the welding wire 21. The period during which the peak current Ip flows through the welding wire 21 is called the peak current period Tp, and the period during which the base current Ib flows through the welding wire 21 is called the base current period Tb. The sum of the peak current period Tp and the subsequent base current period Tb corresponds to the fluctuation period Tf of the welding current Aw (hereinafter simply referred to as the period Tf). The reciprocal of the period Tf corresponds to the fluctuation frequency Fa of the welding current Aw. The fluctuation of the welding current Aw is controlled by the arc control unit 12.

[0035] Specifically, a peak current period Tp during which a peak current Ip flows and a base current period Tb during which a base current Ib flows are alternately repeated. In this embodiment, a droplet formed at the tip of the welding wire 21 is detached by inertial force and transferred to the base material 25 immediately after the peak current period Tp or the peak current period Tp.

[0036] The period Tf corresponds to the wire feeding period described above during the main welding period Th. The wire feeding period during the main welding period Th is set independently of the wire feeding period during the arc start period Ts. The wire feeding periods during both periods may be different or the same.

[0037] Also, immediately before time point P3, the short circuit between the welding wire 21 and the base material 25 is released, and after the neck current In flows through the welding wire 21, the welding current Aw is increased to the base current Ib. Note that in the example shown in Fig. 3, the welding current Aw increases in a single step from the neck current In to the base current Ib, but this is not particularly limited. For example, if the difference in current value between the neck current In and the base current Ib is large, the increase from the neck current In to the base current Ib may be increased in two or three or more steps.

[0038] Furthermore, although it depends on the diameter (also referred to as wire diameter) of the welding wire 21 and the set current, it is preferable that the current value of the base current Ib during the main welding period Th be set in the range of 50 A or more and 200 A or less. This suppresses excessive melting of the welding wire 21 during the base current period Tb and prevents the arc 24 from disappearing, which is known as arc interruption. The set current is a moving average value of the welding current Aw with respect to time that is preset for each period of arc welding when performing arc welding. Therefore, the average feed rate Wfs is determined corresponding to the set current.

[0039] The maximum value of the forward feed speed in the cycle Tf during the main welding period Th is referred to as a second forward feed speed Wff2, and the maximum value of the reverse feed speed is referred to as a second reverse feed speed Wfg2.

[0040] During main welding period Th, wire feed speed Wf is controlled by wire feed speed control unit 13 so that second reverse feed speed Wfg2 is greater than first reverse feed speed Wfg during arc start period Ts. Also, wire feed speed control unit 13 controls wire feed speed Wf so that second forward feed speed Wff2 is greater than first forward feed speed Wff during arc start period Ts. Therefore, wire feed speed Wf is controlled so that average feed speed Wfh during main welding period Th is higher than average feed speed Wfs during arc start period Ts excluding the time immediately before the end.

[0041] The forward feed speed (Wf) during forward feed, the reverse feed speed (Wf) during reverse feed, the wire feed cycle (Wf) during alternate forward and reverse feed, and the frequency (its reciprocal) are set independently for the arc start period Ts and the main welding period Th. The ratio of the forward feed amount to the reverse feed amount of the welding wire 21 during forward feed and the speed ratio are also set independently for the arc start period Ts and the main welding period Th. The speed ratio during the arc start period Ts is the absolute value of the ratio of the first forward feed speed Wff to the first reverse feed speed Wfg, based on the average feed speed Wfs. The speed ratio during the main welding period Th is the absolute value of the ratio of the second forward feed speed Wff2 to the second reverse feed speed Wfg2, based on the average feed speed Wfh.

[0042] During the arc start period Ts, these values ​​are optimized to stabilize the repetition cycle in which the welding wire 21 is short-circuited with the base metal 25 and then an arc 24 is generated between the base metal 25 and the tip of the welding wire 21. On the other hand, during the main welding period Th, these values ​​are optimized to detach a droplet formed at the tip of the welding wire 21 by inertial force and transfer it to the base metal 25.

[0043] In the arc start period Ts, the speed ratio is set to 1, that is, the absolute value of the first reverse feed speed Wfg is set to be equal to the first forward feed speed Wff with respect to the average feed speed Wfs. Similarly, in the main welding period Th, the absolute value of the second reverse feed speed Wfg2 is set to be equal to the second forward feed speed Wff2 with respect to the average feed speed Wfh. However, this is not particularly limited. Taking into consideration the burning of the welding wire 21, etc., the speed ratio may be set in the range of 1 to 4 for each period. For example, in the main welding period Th, the ratio of the absolute value of the second reverse feed speed Wfg2 to the second forward feed speed Wff2 with respect to the average feed speed Wfh may be set to be 1:4.

[0044] In the present embodiment, the welding wire 21 is periodically fed and reversed at a constant frequency and speed amplitude set for each of the arc start period Ts and the main welding period Th. However, this is not limiting. The welding wire 21 may be non-periodic. For example, the welding wire 21 may be fed forward during the arc start period Ts, and then switched to reverse feeding when the short circuit / arc detection unit 10 detects a short circuit between the welding wire 21 and the base material 25. In this case, the forward feeding operation may be switched to after a predetermined time has elapsed since the start of the reverse feeding. Furthermore, during the main welding period Th, the short circuit / arc detection unit 10 may cause a peak current Ip to flow through the welding wire 21 when the welding voltage Vw exceeds the voltage threshold Va, and then cause a base current Ib to flow after a predetermined time has elapsed. While the base current Ib is flowing, the peak current Ip may be caused to flow through the welding wire 21 for a predetermined time when the welding voltage Vw drops to the voltage threshold Va.

[0045] [Effects, etc.] As described above, the arc welding control method according to the present embodiment is a method for controlling arc welding in which arc 24 is generated between welding wire 21, which is a consumable electrode, and base material 25 to perform welding, and includes at least a first step and a second step described below.

[0046] In the first step, during the arc start period Ts, a welding current Aw is passed through the welding wire 21, and the welding wire 21 is alternately fed forward and backward, thereby short-circuiting the welding wire 21 and the base material 25, thereby short-circuiting the droplet formed at the tip of the welding wire 21 and transferring it to the base material 25.

[0047] In the second step, during the main welding period Th provided after the arc start period Ts, the welding wire 21 is alternately fed forward and backward while the welding current Aw is varied at a predetermined period Tf, so that droplets are detached from the tip of the welding wire 21 and transferred to the base material 25.

[0048] Arc start period Ts is the period from initial short circuit detection time P2, when the first short circuit between welding wire 21 and base metal 25 is detected, to time P3, when the main welding period starts.

[0049] The period Tf includes a peak current period Tp during which a peak current Ip flows through the welding wire 21, and a base current period Tb following the peak current period Tp during which a base current Ib flows through the welding wire 21. The current value of the base current Ib is lower than the current value of the peak current Ip.

[0050] The average feed speed Wfh during the main welding period Th is the same as the average feed speed Wfs at the end of the arc start period Ts.

[0051] According to this embodiment, a molten pool can be reliably formed on the base material 25 at the beginning of welding, and subsequent detachment of droplets from the welding wire 21 can be stabilized. Specifically, at the beginning of arc welding, an arc start period Ts is provided, and the wire feed speed Wf is controlled so that the welding wire 21 alternates between forward and reverse feed at a predetermined frequency and speed amplitude. This allows for forcible opening of the short circuit without relying on electromagnetic pinch force, and prevents large spatter, i.e., spatter of a size similar to that of droplets, from adhering around the welded area, damaging the appearance, or causing poor welding. Furthermore, not only the generation of large spatter but also the amount of spatter itself can be reduced.

[0052] Furthermore, according to this embodiment, a main welding period Th is provided following the arc start period Ts, and so-called pulse welding is performed in which a peak current Ip and a base current Ib are alternately passed through the welding wire 21. In addition, by alternately feeding the welding wire 21 forward and backward at a predetermined frequency and speed amplitude, it is possible to smoothly detach a droplet formed at the tip of the welding wire 21. The frequency during the main welding period Th is the reciprocal of a cycle Tf, which is the sum of the peak current period Tp and the base current period Tb.

[0053] According to this embodiment, during the main welding period Th, the welding wire 21 is alternately fed forward and backward, so that the droplets grown at the tip of the welding wire 21 are subjected to vibration in the direction of gravity, causing the droplets to fall. ２By using this, even when droplets are difficult to detach due to the arc reaction force, the weld can be reliably transferred to the base material 25 as a drop (detachment transfer) for each cycle Tf. This allows, for example, the width and height of the weld bead formed on the base material 25 to be constant along its length.

[0054] The first reverse feed speed Wfg during the arc start period Ts is controlled to be constant. The first forward feed speed Wff during the arc start period Ts is controlled to increase as the number of repetitions of forward and reverse feed of the welding wire 21 increases. The second reverse feed speed Wfg2 during the main welding period Th is controlled to be greater than the first reverse feed speed Wfg during the arc start period Ts. The second forward feed speed Wff2 during the main welding period Th is controlled to be greater than the first forward feed speed Wff during the arc start period Ts.

[0055] By doing so, the average feed speed Wfs can be increased over time during the arc start period Ts. As a result, at start point P3 of the main welding period Th, the average feed speed Wfs during the arc start period Ts and the average feed speed Wfh during the main welding period Th can be made the same, allowing for a smooth transition in the feeding operation of the welding wire 21. Furthermore, the second forward feed speed Wff2 during the main welding period Th is made higher than the first forward feed speed Wff during the arc start period Ts, and the second reverse feed speed Wfg2 during the main welding period Th is made higher than the first reverse feed speed Wfg during the arc start period Ts. By doing so, the average feed speed Wfh can be increased to a desired value, and the feed amount of the welding wire 21 corresponding to the welding current Aw can be ensured during the main welding period Th.

[0056] Furthermore, start point P3 of main welding period Th may be the point at which the average wire feed speed Wfs during arc start period Ts reaches a predetermined value Wfh or a point near the point at which the predetermined value Wfh is reached. The point near the point at which the predetermined value Wfh is reached may be, for example, the point at which the wire feed speed Wf becomes zero around the time when the average wire feed speed Wfs reaches the predetermined value Wfh, or may be a point at which a second time has elapsed since the point at which the average wire feed speed Wfs reaches the predetermined value Wfh.

[0057] Immediately before the main welding period Th, during the arc start period Ts, the welding current Aw having the same current value as the base current Ib during the main welding period Th is controlled to flow through the welding wire 21. Furthermore, when the welding voltage Vw between the welding wire 21 and the base material 25 exceeds the voltage threshold value Va, the arc start period Ts is switched to the main welding period Th, and the main welding period Th begins.

[0058] In this way, the arc 24 can be stabilized, and by detecting that the arc 24 is in a stable state, the welding state can be reliably shifted to the main welding period Th.

[0059] Immediately before the main welding period Th, the short circuit between the welding wire 21 and the base material 25 is released, and a neck current In, which is the welding current Aw at the time of release of the short circuit, flows through the welding wire 21. From this state, the welding current Aw is increased in one or more stages to transition to the base current Ib.

[0060] In this way, the arc 24 can be stabilized just before the main welding period Th, and a smooth transition to the main welding period Th can be achieved.

[0061] The current value of the base current Ib during the main welding period Th is preferably equal to or greater than 50 A and equal to or less than 200 A. By setting the current value of the base current Ib in this manner, it is possible to prevent the welding wire 21 from excessively melting and prevent the arc from interrupting.

[0062] In this embodiment, the wire feed speed Wf is controlled so that the time waveform becomes a sine wave during both the arc start period Ts and the main welding period Th, but this is not particularly limited, and the feeding operation of the welding wire 21 may be controlled so that the time waveform becomes a trapezoidal wave. This control can also be applied to Embodiments 2 to 6 described later.

[0063] (Embodiment 2) Fig. 4 is a diagram showing waveforms of the welding current, welding voltage, and wire feed speed according to embodiment 2. For ease of explanation, in Fig. 4 and the following drawings, the same parts as those in embodiment 1 are designated by the same reference numerals, and detailed explanations thereof will be omitted.

[0064] Among the various waveforms shown in Fig. 4, the time waveform of the wire feed speed Wf during the main welding period Th differs from the time waveform of the wire feed speed Wf of the first embodiment shown in Fig. 3. Specifically, as shown in Fig. 4, during the main welding period Th, a third reverse feed speed Wfg3, which is the maximum value of the reverse feed speed when the welding wire 21 first performs a reverse feed operation, is controlled to be larger than the second reverse feed speed Wfg2 in the subsequent reverse feed operations.

[0065] The third reverse feed speed Wfg3 is set to be 5% to 30% greater than the second reverse feed speed Wfg2, or to be 10 m / min to 30 m / min. The value of the third reverse feed speed Wfg3 can be changed appropriately depending on the period Tf, the material and diameter of the welding wire 21, the set current for the main welding period Th, and the like. Note that the third reverse feed speed Wfg3 is in the range of 30 m / min to 100 m / min, depending on the set current.

[0066] In the early stage of the main welding period Th, depending on the growth rate of the droplets and the wire feed cycle, the droplets may not be completely detached from the welding wire 21. On the other hand, according to this embodiment, by setting the maximum value of the reverse feed speed to the third reverse feed speed Wfg3 in the first wire feed cycle immediately after the start of the main welding period Th, the droplets can be shaken off more strongly and reliably detached. In other words, droplet detachment can be stabilized.

[0067] 4, the maximum value of the reverse feed speed is set to the third reverse feed speed Wfg3 only in the first wire feed cycle immediately after the start of the main welding period Th, but this is not particularly limited. For example, the maximum value of the reverse feed speed may be set to the third reverse feed speed Wfg3 in multiple wire feed cycles immediately after the start of the main welding period Th in which the welding wire 21 is periodically fed forward and backward. It is sufficient that droplets are stably detached and transferred to the base material 25 in each cycle Tf at the beginning of the main welding period Th. In other words, if one or more wire feed cycles immediately after the start of the main welding period Th are defined as a first period, the third reverse feed speed Wfg3 in the first period is controlled to be greater than the second reverse feed speed Wfg2, which is the maximum value of the reverse feed speed after the first period has elapsed.

[0068] Furthermore, according to this embodiment, it is possible to achieve the same effects as those achieved by the method described in embodiment 1. That is, by reliably forming a molten pool in the base material 25 during the arc start period Ts at the beginning of welding, it is possible to suppress the generation of spatter and stabilize the detachment of droplets from the welding wire 21 during the subsequent main welding period Th.

[0069] Third Embodiment FIG. 5 is a diagram showing waveforms of a welding current, a welding voltage, and a wire feed speed according to a third embodiment.

[0070] Among the various waveforms shown in Fig. 5, the time waveform of the peak current Ip during the main welding period Th differs from the time waveform of the peak current Ip of the first embodiment shown in Fig. 3. Specifically, as shown in Fig. 5, during the main welding period Th, the second peak current value Ip2, which is the current value of the peak current that first flows through the welding wire 21, is controlled to be higher than the first peak current value Ip, which is the current value of the subsequent peak currents.

[0071] The second peak current value Ip2 is set to be higher than the first peak current value Ip by 5% to 20%, or to be set to be 10 A to 100 A. The second peak current value Ip2 can be changed as appropriate depending on the period Tf, the material and diameter of the welding wire 21, the set current for the main welding period Th, and the like. Note that the second peak current value Ip2 is in the range of 350 A to 600 A, depending on the set current.

[0072] As described above, in the early stage of the main welding period Th, depending on the degree of droplet growth and the wire feeding cycle, the droplets may not be completely detached from the welding wire 21. On the other hand, according to this embodiment, by passing a second peak current Ip2 higher than the first peak current Ip through the welding wire 21 in the cycle Tf immediately after the start of the main welding period Th, the growth of the droplets is promoted and the droplets can be reliably detached. In other words, droplet detachment can be stabilized.

[0073] 5, the current value of the peak current is set to the second peak current value Ip2 only in the first cycle Tf immediately after the start of the main welding period Th, but this is not particularly limited. For example, the current value of the peak current may be set to the second peak current value Ip2 in multiple cycles Tf immediately after the start of the main welding period Th. It is sufficient that droplets are stably detached and transferred to the base material 25 for each cycle Tf in the early stage of the main welding period Th. In other words, if one or multiple cycles Tf immediately after the start of the main welding period Th are defined as the second period, the current value of the peak current in the second period, that is, the second peak current value Ip2, is controlled to be higher than the first peak current value Ip, that is, the current value of the peak current after the second period has elapsed.

[0074] Furthermore, according to this embodiment, it is possible to achieve the same effects as those achieved by the method described in embodiment 1. That is, by reliably forming a molten pool in the base material 25 during the arc start period Ts at the beginning of welding, it is possible to suppress the generation of spatter and stabilize the detachment of droplets from the welding wire 21 during the subsequent main welding period Th.

[0075] (Fourth embodiment) Fig. 6 is a diagram showing a waveform of a welding current according to a fourth embodiment.

[0076] The welding current Aw shown in Fig. 6 has a peak current period Tp in the main welding period Th that is different from the peak current period Tp of the first embodiment shown in Fig. 3. Specifically, as shown in Fig. 6, during the main welding period Th, the welding current Aw is controlled so that a second peak current period Tp2, which is the peak current period of the peak current Ip that first flows through the welding wire 21, is longer than a first peak current period Tp, which is the peak current period of the subsequent peak current Ip.

[0077] The second peak current period Tp2 is set to be longer than the first peak current period Tp by 5% to 30%, or to be set to be 20 μsec to 500 μsec. The second peak current period Tp2 can be changed as appropriate depending on the period Tf, the material and diameter of the welding wire 21, the set current for the main welding period Th, and the like.

[0078] As described above, in the early stage of the main welding period Th, depending on the degree of droplet growth and the wire feeding cycle, the droplets may not completely detach from the welding wire 21. On the other hand, according to this embodiment, the peak current period (second peak current period Tp2) in the cycle Tf immediately after the start of the main welding period Th is set to the first time period that is longer than the first peak current period Tp, thereby promoting the growth of the droplets and ensuring that the droplets are detached. In other words, droplet detachment can be stabilized.

[0079] In FIG. 6 , the peak current period is set to the second peak current period Tp2 only in the first cycle Tf immediately after the start of the main welding period Th, but this is not limited to this. For example, the peak current period may be set to the second peak current period Tp2, which is longer than the first peak current period Tp, in multiple cycles Tf immediately after the start of the main welding period Th. It is sufficient that droplets are stably detached and transferred to the base metal 25 in each cycle Tf at the beginning of the main welding period Th. In other words, if one or multiple cycles Tf immediately after the start of the main welding period Th are defined as the third period, the second peak current period Tp2, which is the peak current period in the third period, is controlled to be longer than the first peak current period Tp, which is the peak current period after the third period. The first period, the second period, and / or the third period may be the same or different periods.

[0080] Furthermore, according to this embodiment, it is possible to achieve the same effects as those achieved by the method described in embodiment 1. That is, by reliably forming a molten pool in the base material 25 during the arc start period Ts at the beginning of welding, it is possible to suppress the generation of spatter and stabilize the detachment of droplets from the welding wire 21 during the subsequent main welding period Th.

[0081] Fifth Embodiment FIG. 7 is a diagram showing a waveform of a welding current according to a fifth embodiment.

[0082] The welding current Aw shown in Figure 7 differs from the time waveform of the welding current Aw of the first embodiment shown in Figure 3 in that the welding current Aw increases from the neck current In, which is the current obtained by steeply reducing the welding current Aw immediately before the short circuit is released, to a peak current Ip around start point P3 of the main welding period Th. In other words, the difference in Figure 3 is that the welding current Aw increases from the current value of the base current Ib immediately before the main welding period Th to the peak current Ip around start point P3 of the main welding period Th. Note that in Figure 7, the current value of the base current Ib' immediately before the main welding period Th is the same as the current value of the neck current In, which is the welding current Aw when the short circuit between the welding wire 21 and the base material 25 is released immediately before the main welding period Th.

[0083] When the current difference between the neck current In and the base current Ib is small, as shown in this embodiment, the current value of the base current Ib immediately before the main welding period Th may be controlled to be the same as the current value of the neck current In. In this case as well, excessive melting of the welding wire 21 can be suppressed before and after the start of the main welding period Th, and interruption of the arc can be prevented.

[0084] Furthermore, according to this embodiment, it is possible to achieve the same effects as those achieved by the method described in embodiment 1. That is, by reliably forming a molten pool in the base material 25 during the arc start period Ts at the beginning of welding, it is possible to suppress the generation of spatter and stabilize the detachment of droplets from the welding wire 21 during the subsequent main welding period Th.

[0085] Sixth Embodiment The arc start period Ts is not limited to the period described in the first embodiment, i.e., from the time point P2 when the initial short circuit is detected to the time point P3 when the average feed rate Wfs reaches a predetermined value Wfh, but may be variously modified. For example, the arc start period Ts may be a predetermined time from the time point P2 when the initial short circuit is detected, e.g., a first time that is longer than the first peak current period Tp, which is the peak current period in one or more cycles Tf immediately after the start of the main welding period Th, until the first time point has elapsed. Alternatively, the arc start period Ts may be a period from the time point P2 when the initial short circuit is detected to the time point when the forward and reverse feed of the welding wire 21 has been repeated a predetermined number of times. Alternatively, as shown in FIG. 8 , the arc start period Ts may be a period from the time point P2 when the initial short circuit is detected to the time point P4 when the average feed rate Wfs reaches a predetermined speed threshold value Ws.

[0086] If the arc start period Ts is the period from the time P2 when the first short circuit is detected to the time P4 when the average feed speed Wfs reaches the speed threshold value Ws, it is preferable to set a second arc start period Ts2 between the arc start period Ts and the main welding period Th.

[0087] FIG. 8 is a diagram showing waveforms of the welding current, welding voltage, and wire feed speed according to the sixth embodiment. FIG. 8 differs from the various waveforms of the first embodiment shown in FIG. 3 in that a second arc start period Ts2 is provided between the arc start period Ts and the main welding period Th. In the example shown in FIG. 8 , the arc start period Ts is the period from time P2 when the initial short circuit is detected to time P4 when the average feed speed Wfs reaches the speed threshold value Ws, and the second arc start period Ts2 is the period from time P4 to the aforementioned time P3. Note that the speed threshold value Ws is a value lower than the average feed speed Wfh during the main welding period Th. In this case, the average feed speed Wfh during the main welding period Th is higher than the average feed speed Wfs at the end of the arc start period Ts (time P4).

[0088] The time waveforms of the wire feed speed Wf, the welding voltage Vw, and the welding current Aw are similar between the second arc start period Ts2 and the main welding period Th. In other words, during the second arc start period Ts2, the welding current Aw flowing through the welding wire 21 may be varied in the cycle Tf while the welding wire 21 is alternately fed forward and backward, thereby causing droplets to detach from the tip of the welding wire 21 and transfer to the base material 25.

[0089] The average feed rate in second arc start period Ts2 is controlled to be higher than the average feed rate Wfs in arc start period Ts and lower than the average feed rate Wfh in main welding period Th. In other words, the set current as a moving average in second arc start period Ts2 is controlled to be higher than the set current as a moving average in arc start period Ts and lower than the set current as a moving average in main welding period Th.

[0090] When the difference between the set current during the arc start period Ts and the set current during the main welding period Th is large, the set current during the arc start period Ts needs to be increased, and the average feed rate Wfs is set correspondingly high. However, if the average feed rate Wfs is set too high during the arc start period Ts where the short-circuit transition occurs, the welding wire 21 may plunge into the base material 25 during forward feed, or the welding wire 21 may suddenly break off after contacting the base material 25 during reverse feed. When this happens, spatter is more likely to occur.

[0091] Therefore, as shown in this embodiment, a second arc start period Ts2 is provided between the arc start period Ts and the main welding period Th, and the set current and average feed rate during the second arc start period Ts2 are appropriately set. By doing so, even if there is a large difference between the set current during the arc start period Ts and the set current during the main welding period Th, the generation of spatter during the arc start period Ts can be suppressed.

[0092] 8, it is preferable that the peak current and base current during second arc start period Ts2 increase stepwise to approach the respective current values ​​of peak current Ip and base current Ib during main welding period Th. This allows the amount of heat input to base metal 25 during second arc start period Ts2 to be increased stepwise, thereby preventing the appearance and shape of the weld from becoming non-uniform. Furthermore, arc 24 can be stabilized during second arc start period Ts2 and the transition period from second arc start period Ts2 to main welding period Th.

[0093] The stepwise increase rates of the peak current, base current, average feed speed Wfs, etc. in the second arc start period Ts2 may be the same as or different from those in the arc start period Ts.

[0094] For example, by making the rate of increase in the second arc start period Ts2 lower than the rate of increase in the arc start period Ts, the increase in the amount of heat input to the base material 25 during the main welding period Th can be more mitigated, and the arc 24 can be further stabilized during the second arc start period Ts2 and the transition period from the second arc start period Ts2 to the main welding period Th.

[0095] Furthermore, according to this embodiment, it is possible to achieve the same effects as those achieved by the method described in embodiment 1. That is, by reliably forming a molten pool in the base material 25 during the arc start period Ts at the beginning of welding, it is possible to suppress the generation of spatter and stabilize the detachment of droplets from the welding wire 21 during the subsequent main welding period Th.

[0096] Other Embodiments In the present specification, CO ２ However, the type of shielding gas used in the arc welding of the present disclosure is not particularly limited to this. ２ The shielding gas may be a mixed gas of CO ２When the gas is mainly composed of CO, the arc reaction force is large, and as described above, droplets are difficult to detach in normal pulse welding. On the other hand, according to the arc welding control method disclosed herein, even when a shielding gas with a high arc reaction force is used, droplets can be stably detached from the welding wire 21 during the main welding period Th. ２ When the mixing ratio is 25% or more, the effects of the method of the present disclosure can be particularly exhibited.

[0097] However, the CO of the shielding gas ２ The mixing ratio of CO is not particularly limited to this. ２ The amount of argon gas may be increased. ２ The welding wire 21 and the base material 25 may be made of any gas that does not contain argon, helium, or other inert gas. The materials of the welding wire 21 and the base material 25 are not limited to mild steel.

[0098] CO ２ Even when a shielding gas with a high arc reaction force such as that described above is not used, by reliably forming a molten pool on the base material 25 during the arc start period Ts at the beginning of welding, it is possible to suppress the generation of spatter and stabilize the detachment of droplets from the welding wire 21 during the subsequent main welding period Th, as described above. In particular, during the main welding period Th, by alternately feeding the welding wire 21 forward and backward, a force that shakes off the droplets, in addition to gravity, is applied to the droplets, and the droplets can be stably transferred to the base material 25 for each cycle Tf. Furthermore, since droplets can be detached even when the current value of the peak current Ip is low, it is possible to suppress the generation of spatter during the main welding period Th.

[0099] When the droplets are shaken off, there is no problem if they are transferred by short-circuiting rather than by drop transfer.

[0100] The arc welding control method disclosed herein is useful because it can reliably form a molten pool in the base material at the beginning of welding, thereby suppressing the occurrence of spatter and stabilizing the detachment of droplets from the welding wire during the subsequent main welding period.

[0101] REFERENCE SIGNS LIST 1 Input power supply 2 Primary rectifier 3 Switching unit 4 Transformer 5 Secondary rectifier 6 DCL 7 Drive unit 8 Welding voltage detector 9 Welding current detector 10 Short circuit / arc detector 11 Short circuit controller 12 Arc controller 13 Wire feed speed controller 14 Welding power supply 15 Welding condition setting unit 16 Robot controller 17 Robot controller 18 Manipulator 20 Wire storage unit 21 Welding wire 22 Wire feed motor 23 Tip 24 Arc 25 Base metal 26 Welding torch 30 Arc welding device Ip Peak current Ip2 Second peak current Ib Base current In Neck current Ta Slow-down period Ts Arc start period Ts2 Second arc start period Th Main welding period Tp Peak current period Tp2 Second peak current period Tb Base current period Tf Cycle Va Arc determination level voltage (voltage threshold) Wfa Slow-down speed Wfs Average feed speed during arc start period Wfh Average feed speed during main welding period Wff First forward feed speed Wff2 Second forward feed speed Wfg First reverse feed speed Wfg2 Second reverse feed speed Wfg3 Third reverse feed speed

Claims

1. A method for controlling arc welding in which an arc is generated between a welding wire, which is a consumable electrode, and a base metal to perform welding, comprising at least a first step of, during an arc start period, causing a welding current to flow through the welding wire and alternately feeding the welding wire forward and backward, thereby short-circuiting the welding wire and the base metal, thereby causing a droplet formed at the tip of the welding wire to be short-circuited and transferred to the base metal; and a second step of, during a main welding period provided after the arc start period, causing the welding current flowing through the welding wire to vary at a predetermined cycle while alternately feeding the welding wire forward and backward, thereby causing the droplet to detach from the tip of the welding wire or to be short-circuited and transferred to the base metal, wherein the arc start period is the period from an initial short-circuit detection point in time when a first short circuit between the welding wire and the base metal is detected, to the start of the main welding period, and the cycle includes a peak current period in which a peak current flows through the welding wire, and a base current period following the peak current period in which a base current flows through the welding wire, a current value of the base current being lower than a current value of the peak current; and an average feed speed of the welding wire during the main welding period being equal to or higher than the average feed speed at an end of the arc start period.

2. An arc welding control method according to claim 1, wherein the forward feed speed, which is the feed speed of the welding wire during forward feed, the reverse feed speed, which is the feed speed during reverse feed, the speed ratio, which is the absolute value of the ratio of the maximum value of the forward feed speed to the maximum value of the reverse feed speed, based on the average feed speed, and the frequency, which is the reciprocal of the wire feed cycle that alternately repeats the forward feed and the reverse feed, are set independently of each other during the arc start period and the main welding period.

3. An arc welding control method according to claim 2, wherein the reverse feed speed during the arc start period is controlled so that its maximum value is constant, the maximum value of the forward feed speed during the arc start period is controlled so that it increases with each increase in the number of repetitions of the forward feed and the reverse feed, the maximum value of the reverse feed speed during the main welding period is controlled so that it is greater than the maximum value of the reverse feed speed during the arc start period, and the maximum value of the forward feed speed during the main welding period is controlled so that it is greater than the maximum value of the forward feed speed during the arc start period.

4. An arc welding control method as set forth in claim 2, wherein a third reverse feed speed, which is the maximum value of the reverse feed speed during a first period including one or more wire feed cycles immediately after the start of the main welding period, is controlled to be greater than a second reverse feed speed, which is the maximum value of the reverse feed speed after the first period has elapsed; the third reverse feed speed is controlled to be greater than the second reverse feed speed by 5% or more and 30% or less; and the third reverse feed speed is in the range of 30 m / min to 100 m / min.

5. An arc welding control method as set forth in claim 2, wherein a third reverse feed speed, which is the maximum value of the reverse feed speed during a first period including one or more wire feed cycles immediately after the start of the main welding period, is controlled to be greater than a second reverse feed speed, which is the maximum value of the reverse feed speed after the first period has elapsed, and wherein the third reverse feed speed is controlled to be 10 m / min or more and 30 m / min or less.

6. An arc welding control method according to claim 1, wherein a second peak current value, which is the current value of the peak current during a second period including one or more cycles immediately after the start of the main welding period, is controlled to be higher than a first peak current value, which is the current value of the peak current after the second period has elapsed; the second peak current value is controlled to be higher by 5% or more and 20% or less than the first peak current value; and the second peak current value is in the range of 350 A to 600 A.

7. An arc welding control method according to claim 1, wherein a second peak current value, which is the current value of the peak current during a second period including one or more cycles immediately after the start of the main welding period, is controlled to be higher than a first peak current value, which is the current value of the peak current after the second period has elapsed, and wherein the second peak current value is controlled to be 10 A or more and 100 A or less.

8. An arc welding control method as claimed in claim 1, wherein the second peak current period, which is the peak current period in a third period including one or more cycles immediately after the start of the main welding period, is controlled to be longer than the first peak current period, which is the peak current period after the third period has elapsed, and the second peak current period is controlled to be longer by 5% or more and 30% or less than the first peak current period, or the second peak current period is controlled to be longer by 20 μsec or more and 500 μsec or less.

9. An arc welding control method according to claim 1, wherein the main welding period is started at the point when the average feed rate during the arc start period reaches a predetermined value or at a point close to the point when the predetermined value is reached.

10. An arc welding control method according to claim 9, wherein the vicinity of the time point is the time point at which the welding wire feed speed becomes zero before or after the average feed speed reaches the predetermined value, or the time point after a second time has elapsed from the time point at which the average feed speed reaches the predetermined value.

11. The arc welding control method according to claim 1, wherein the base current is controlled to flow through the welding wire immediately before the main welding period, and the main welding period starts when the welding voltage between the welding wire and the base metal exceeds a predetermined voltage threshold.

12. The arc welding control method according to claim 11, wherein immediately before the main welding period, a short circuit between the welding wire and the base material is released, and the welding current is increased in one or more stages from the neck current, which is the welding current at the time of short circuit release, to the base current.

13. An arc welding control method according to claim 11, wherein the current value of the base current immediately before the main welding period is the same as the current value of the neck current, which is the welding current when the short circuit between the welding wire and the base material is released immediately before the main welding period.

14. The arc welding control method according to claim 1, wherein the current value of the base current during the main welding period is 50 A or more and 200 A or less.

15. An arc welding control method according to claim 1, wherein the arc start period is the period from the time when the first short circuit is detected until a first time has elapsed, or the period from the time when the first short circuit is detected until the welding wire has been fed forward and backward a predetermined number of times, or the period from the time when the first short circuit is detected until the average feed speed reaches a predetermined speed threshold.

16. An arc welding control method as defined in claim 15, wherein, when the arc start period is a time from the time of the initial short circuit detection when the average feed speed reaches the speed threshold, the speed threshold is lower than the average feed speed during the main welding period, a second arc start period is provided between the arc start period and the main welding period, and during the second arc start period, the welding current flowing through the welding wire is varied in the cycle while the welding wire is alternately fed forward and backward, thereby causing the droplet to detach from the tip of the welding wire and transfer to the base material, and the average feed speed during the second arc start period is higher than the average feed speed during the arc start period and lower than the average feed speed during the main welding period.

17. In the method for controlling arc welding according to any one of claims 1 to 16, the shielding gas sprayed onto the base metal during arc welding is CO ２ The arc welding control method is characterized in that the mixture ratio of the above gas is 25% or more.

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