WO2025215961A1 - Arc welding control method - Google Patents

Abstract

The present invention is an arc welding control method related to buried arc welding. In the present invention, the waveform of a welding current Aw flowing in a welding wire 21 is changed into a rectangular shape or a trapezoidal shape with respect to time. A pulse period Tw which is a variation period of the welding current Aw is the sum of a peak current period Tp in which a peak current Ip flows in the welding wire 21 and a base current period Tb in which a base current Ib flows. The welding current Aw is controlled so that the ratio of the peak current period Tp to the pulse period Tw is 30-70% and the average current is 250A or more. During n (n is a positive integer) pulse periods Tw, a droplet 21a formed at the tip of the welding wire 21 is separated once and transferred to the base material 25.

Description

Arc welding control method

This disclosure relates to an arc welding control method, particularly an arc welding control method for buried arc welding.

In consumable electrode arc welding, a welding current is passed through the welding wire, which is the consumable electrode, generating an arc between the welding wire and the base material to be welded. This heats the base material and melts the welding wire, causing droplets to grow at its tip. The droplets detach from the welding wire and transfer to the molten molten pool where the base material is melted. After this, the molten pool and droplets cool and solidify, welding the base material.

There are several types of droplet transfer patterns. For example, Patent Document 1 discloses an arc welding control method in which the welding voltage is controlled to a constant voltage state to transfer droplets to the base material by spraying. This arc welding control method includes two steps. In the first step, the arc welding device is controlled so that the welding current flowing through the welding wire alternates between a peak current when the droplets detach from the welding wire and a melting current that curves and continuously changes to have a concave minimum value when melting of the welding wire begins and accelerates. In the second step, the arc welding device is controlled so that the peak current is greater than the average value of the welding current by a value between 25% and 45% of the average value. The arc welding device is further controlled so that the minimum value of the melting current is less than the average value of the welding current by a value between 25% and 45% of the average value of the welding current.

International Publication No. 2016/163073

When arc welding thick base metal plates, the welding current must also be increased. In this case, the arc force also becomes stronger, so the molten pool formed in the base metal is excavated by the arc, and arc welding is performed with the tip of the welding wire entering the space excavated by the molten pool (hereinafter referred to as the buried space), a process known as buried arc welding. In this case, the tip of the welding wire is surrounded by the side walls of the buried space. Furthermore, because the surface of the buried space is covered by the molten pool, the molten pool vibrates in a wavy manner depending on the ignition and irradiation conditions of the arc.

However, when the welding current is high, as disclosed in Patent Document 1, if an attempt is made to spray-transfer droplets to the base metal by controlling the welding voltage to a constant voltage, the side wall of the buried space covered by the molten pool (hereinafter referred to as the molten wall) will become wavy, causing disruptions to the welding voltage. Furthermore, disruptions to the welding voltage will also affect the welding current, causing the arc to randomly irradiate the bottom of the buried space and the molten wall. When this happens, droplets will detach irregularly from the welding wire and the arc state will become unstable. As a result, there is a risk of increased spatter generation. Furthermore, penetration into the base metal will also become unstable, which could lead to a deterioration in the shape of the welded area and, in extreme cases, poor welding.

The present disclosure has been made in light of these points, and its purpose is to provide an arc welding control method that suppresses undulation of the molten metal wall during buried arc welding, achieves a stable, deep penetration depth, and suppresses the generation of spatter.

In order to achieve the above-mentioned object, the arc welding control method disclosed herein generates an arc between a welding wire, which is a consumable electrode, and a base metal, and welds the base metal in a buried arc state. The method controls the welding current so that the time waveform of the welding current flowing through the welding wire changes to a rectangular or trapezoidal shape. The pulse period, which is the fluctuation cycle of the welding current, is the sum of a peak current period in which a peak current flows through the welding wire and a base current period, which follows the peak current period and in which a base current with a current value lower than the peak current flows through the welding wire. The welding current is controlled so that the ratio of the peak current period to the pulse period is 30% or more and 70% or less, and so that the average current, which is the moving average of the welding current over a predetermined period, is 250 A or more. By controlling the welding current so that n pulse periods (n is a positive integer) are repeated, a droplet formed at the tip of the welding wire is detached once and transferred to the base metal.

According to the present disclosure, it is possible to suppress undulations in the molten wall formed by buried arc welding. It also achieves a stable, deep penetration depth and suppresses the occurrence of spatter.

FIG. 1 is a schematic diagram of an arc welding apparatus according to a first embodiment. FIG. 2 is a schematic configuration diagram of another arc welding device according to the first embodiment. FIG. 3 is a time chart of various output waveforms during arc welding. FIG. 4A is a diagram showing the change over time in the state of an arc when the time waveform of the welding current is a trapezoidal wave. FIG. 4B is a diagram showing the change over time in the state of the arc when the time waveform of the welding current is a triangular wave. FIG. 5 is a time chart of various output waveforms during arc welding according to the second embodiment. FIG. 6 is a diagram showing appropriate ranges of the ratio between the peak current period and the base current period and the current amplitude according to the embodiment. FIG. 7 is a diagram for explaining a welding state that occurs when the ratio of the peak current period to the base current period or the current amplitude is outside the appropriate range.

Embodiments of the present disclosure will now be described with reference to the drawings. Note that the following description of the preferred embodiment is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses.

(Embodiment 1)
[Configuration of Arc Welding Device]
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.

As shown in FIG. 1, the arc welding device 30 comprises a primary rectifier unit 2, a switching unit 3, a transformer 4, a secondary rectifier unit 5 and a DCL 6, a drive unit 7, a welding voltage detection unit 8, a welding current detection unit 9, a short circuit/arc detection unit 10, a short circuit control unit 11, an arc control unit 12, and a wire feed speed control unit 13. Here, the primary rectifier unit 2 rectifies the power input from the input power source 1. The switching unit 3 converts the output of the primary rectifier unit 2 to AC. The transformer 4 transforms the output of the switching unit 3. The secondary rectifier unit 5 and the DCL 6 rectify the output of the transformer 4. The drive unit 7 controls the switching unit 3. The welding voltage detection unit 8 detects the welding voltage. The welding current detection unit 9 detects the welding current. The short circuit/arc detection unit 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 detection unit 8 and the output of the welding current detection unit 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.

Furthermore, welding wire 21, 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 attached to welding torch 26. An arc 24 is then generated between welding wire 21 and base material 25, which is the workpiece to be welded, to perform welding. Note that welding torch 26 is attached to and moved by manipulator 18, which constitutes an industrial robot, for example.

In addition to the general components arranged in the welding power supply 14, the arc welding device 30 also includes a manipulator 18 that constitutes an industrial robot, and a robot control device 16 that controls the manipulator 18. The wire feed speed corresponding to the set current from the welding condition setting unit 15 within the robot control device 16 is sent as a speed signal from the wire feed speed control unit 13 to the 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 the short circuit control unit 11 or 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 the set current and set voltage.

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 the release of the short circuit. Furthermore, the arc control unit 12 outputs a high current immediately after the short circuit is released in order to form a molten droplet at the tip of the welding wire 21 while maintaining the arc length, and then controls the current and voltage to transition to a lower current to facilitate the formation of a short circuit.

Note that each component of the arc welding device 30 shown in Figure 1 may be configured independently, or multiple components may be combined to form a single device.

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

Furthermore, as shown in Figure 2, the welding power supply 14 may be configured to be installed within the robot control device 17. With this configuration, the arc welding device can be made even more compact.

[Outline of arc welding control method]
FIG. 3 shows a time chart of various output waveforms during arc welding according to the first embodiment. Specifically, it shows the time changes of the feed rate WF, welding current Aw, and welding voltage Vw during arc welding. FIG. 3 also shows the time changes of the arc 24 and the state of the droplet 21a formed at the tip of the welding wire 21 (hereinafter referred to as the arc state). In this embodiment, the base metal 25 is mild steel, and the welding wire 21 is also mild steel. The thickness of the base metal 25 is 6 mm. The shielding gas sprayed onto the base metal 25 during welding is _CO2 . However, the materials of the base metal 25 and the welding wire 21, and the type of shielding gas, are not particularly limited thereto.

When the switch (not shown) of the welding torch 26 is turned on, as described above, the wire feed motor 22 operates in response to a command from the wire feed speed control unit 13, and the feeding operation of the welding wire 21 begins. At the same time, the arc control unit 12 begins controlling the welding output. In the following description, the feed speed of the welding wire 21 is referred to as the feed speed WF. In this embodiment, the welding wire 21 is fed forward toward the base material 25 at the feed speed WF.

The arc control unit 12 controls the welding output based on the set current so that the welding current Aw fluctuates periodically. Specifically, as shown in Figure 3, the waveform of the welding current Aw changes trapezoidally over time. The fluctuation period of the welding current Aw during welding is constant. In the following explanation, this fluctuation period is referred to as the pulse period Tw. The pulse period Tw is composed of a peak current period Tp and a base current period Tb that follows the peak current period Tp. In other words, the pulse period Tw is the sum of the peak current period Tp and the base current period Tb.

During the peak current period Tp, the welding current Aw increases over time and is then maintained at a constant value Ip. During the base current period Tb, the welding current Aw decreases over time from the constant value Ip and is then maintained at a constant value Ib. In the following explanation, the welding current when the current value is Ip will be referred to as the peak current Ip, and the welding current when the current value is Ib will be referred to as the base current Ib. As is clear from Figure 3, the relationship between the respective current values satisfies the relationship shown in equation (1).

Ip>Ib>0...(1)
The difference between the current value Ip and the current value Ib is called the current amplitude Ia. The current amplitude Ia satisfies the relationship shown in equation (2).

Ia=Ip-Ib...(2)
The welding voltage Vw also fluctuates periodically in response to fluctuations in the welding current Aw. During the peak current period Tp, the increase in the welding current Aw increases the amount of burning of the welding wire 21, lengthening the arc length of the arc 24, and thus the welding voltage Vw increases. During the base current period Tb, the decrease in the welding current Aw shortens the arc length of the arc 24, and thus the welding voltage Vw decreases.

On the other hand, in this embodiment, the feed speed WF is maintained at a constant positive value WF1. Therefore, during welding, the welding wire 21 is fed in the positive direction toward the base material 25 at a constant speed WF1.

The welding state of the base material 25 changes as shown in arc states a to d in Figure 3. As shown in arc state a, a buried space 25a is formed in the base material 25. As described above, buried space 25a is a space formed when the molten pool (not shown) is excavated by the arc 24. The tip of the welding wire 21 enters buried space 25a. In other words, the tip of the welding wire 21 enters deeper into the base material 25 than the welding surface of the base material 25. In other words, the arc welding shown in this embodiment is buried arc welding. Note that in the following description, the state in which the welding wire 21 enters buried space 25a and the arc 24 is generated may be referred to as a buried arc state.

Arc state a occurs during peak current period Tp, and the current value of welding current Aw is Ip. In this case, because welding current Aw is high, an arc 24 is ignited between welding wire 21 and molten wall 25b, which is the side wall of buried space 25a, due to the rotating phenomenon. Furthermore, arc 24 is irradiated onto molten wall 25b while rotating. Furthermore, as welding wire 21 melts, a molten droplet 21a is formed at the tip of welding wire 21.

Over time, arc state a transitions to arc state b. Arc state b occurs during base current period Tb, and the current value of welding current Aw is Ib. In this case, because the welding current Aw has decreased, the rotating phenomenon does not occur, and arc 24 is ignited between the bottom of buried space 25a and the tip of welding wire 21. Arc 24 does not rotate, but is irradiated onto the bottom of buried space 25a. Furthermore, droplet 21a formed at the tip of welding wire 21 grows and increases in size. However, at this point, droplet 21a does not detach from welding wire 21.

In the peak current period Tp of the next pulse period Tw, the arc state changes to c. In this case, the welding current Aw rises again, and the arc 24 ignited between the molten wall 25b and the welding wire 21 rotates due to the rotating phenomenon, and is again irradiated onto the molten wall 25b. Furthermore, as the welding wire 21 melts, the droplet 21a grows further.

After some time has passed, arc state c transitions to arc state d. Arc state d occurs during base current period Tb, and the current value of welding current Aw is Ib. In this case, because the welding current Aw has decreased, the rotating phenomenon does not occur, and arc 24 is irradiated to the bottom of buried space 25a. Furthermore, fully grown droplet 21a detaches from the tip of welding wire 21 and transfers to base material 25.

Furthermore, as is clear from Figure 3, while the feed rate WF is the same value WF1 in arc states a to d, the amount of burning up of the welding wire 21 is greater in arc states a and c than in arc states b and d. As a result, the distance between the droplet 21a and the bottom of the buried space 25a is longer in arc states a and c than in arc states b and d.

In the example shown in Figure 3, the droplet 21a transfers once toward the base material 25 after every two pulse periods Tw. However, the timing of the transfer of the droplet 21a is not particularly limited to this. The welding current Aw and feed speed WF may be controlled so that the droplet 21a transfers once toward the base material 25 after every n pulse periods Tw (n is a positive integer). In this case, too, the welding current Aw and feed speed WF are controlled so that the droplet 21a transfers toward the base material 25 during the base current period Tb or immediately after the end of the base current period Tb. In other words, the droplet 21a transfers away when the distance between the droplet 21a and the bottom of the buried space 25a is short, thereby suppressing the occurrence of spatter.

[About setting welding conditions]
As a result of various studies conducted by the inventors of the present application, it was found that in order to stabilize the behavior of the molten pool including the molten wall 25b during welding and to suppress the occurrence of spatter, it is necessary to appropriately set several welding conditions.

First, during the pulse period Tw, the ratio of the peak current period Tp to the base current period Tb must be 3:7 or greater and 7:3 or less. In other words, the ratio of the peak current period Tp to the pulse period Tw must be 30% or greater and 70% or less. If the ratio of the peak current period Tp to the base current period Tb is less than 3:7, for example, 2:8, the peak current period Tp becomes too short, making it difficult for the welding wire 21 to melt. Therefore, the arc 24 becomes a buried arc, but it ignites while being excessively buried in the molten pool. Therefore, during the peak current period Tp, the arc 24 is not ignited between the welding wire 21 and the molten wall 25b, and the arc force cannot press the molten wall 25b. In other words, the force pressing the molten wall 25b by the arc force is insufficient. As a result, undulation of the molten wall 25b cannot be suppressed, the welding state becomes unstable, and the penetration depth of the base material 25 is unstable.

Furthermore, if the moving average value of the welding current Aw over a predetermined period, for example, the pulse period Tw, is taken as the average current, the average current must be 250 A or more. Note that the average current corresponds to the aforementioned set current that determines the welding output.

It is also preferable to control the welding current so that the current amplitude Ia is equal to or greater than a predetermined value and equal to or less than the value of a first straight line that represents the relationship between the peak current period Tp relative to the pulse period Tw and the current amplitude Ia. More specifically, it is preferable to set the current amplitude Ia within an appropriate range of 100 A or greater (see FIGS. 6 and 7). It is also preferable that the first straight line be Ia = -10 x TpR + 200, where TpR is the ratio of the peak current period Tp to the pulse period Tw.
Furthermore, it is preferable to set the pulse period Tw to 0.7 msec or more and 2.5 msec or less. The influence of these conditions on the generation of the molten pool and spatter will be described later.

[Effects, etc.]
As described above, the arc welding control method according to this embodiment is a method for controlling arc welding in which an arc 24 is generated between the welding wire 21 and the base material 25, and the base material 25 is welded in a buried arc state.

The welding current Aw flowing through the welding wire 21 is controlled so that the time waveform of the welding current Aw changes into a trapezoidal shape.

The pulse period Tw, which is the fluctuation period of the welding current Aw, is the sum of the peak current period Tp, during which the peak current Ip flows through the welding wire 21, and the base current period Tb, following the peak current period Tp, during which the base current Ib, which has a lower current value than the peak current Ip, flows through the welding wire 21.

The welding current Aw is controlled so that the ratio of the peak current period Tp to the pulse period Tw is 30% or more and 70% or less, and so that the average current, which is the moving average value of the welding current Aw over a specified period, is 250 A or more. By doing this, during n pulse periods Tw (n is a positive integer), the droplet 21a formed at the tip of the welding wire 21 is detached once and transferred to the base material 25.

According to this embodiment, deep penetration into the base material 25 can be achieved by buried arc welding. Furthermore, undulation of the molten wall 25b, including the molten wall 25b, can be suppressed, stabilizing the behavior of the molten pool. This allows for a stable penetration depth into the base material 25.

For example, if the ratio of the peak current period Tp to the pulse period Tw is less than 30%, the peak current period Tp becomes too short, making it difficult for the welding wire 21 to melt. In this case, a buried arc state can be achieved during welding, but because the rotating phenomenon does not occur, the arc 24 does not ignite between the molten wall 25b and the welding wire 21. As a result, the molten metal on the molten wall 25b cannot be fully supported by the arc force, and the state of the molten pool becomes unstable. As a result, the penetration depth into the base material 25 is unstable, and the shape of the welded area may deteriorate. There is also a risk of a large amount of spatter being generated.

Furthermore, if the ratio of the peak current period Tp to the pulse period Tw exceeds 70%, the peak current period Tp becomes too long. In this case, the arc control unit 12 reduces the current value of the base current Ib so that the average current corresponding to the set current maintains the set value. As a result, the welding wire 21 becomes difficult to melt. In this case, as mentioned above, although a buried arc state can be achieved during welding, the arc 24 does not ignite between the molten wall 25b and the welding wire 21, and therefore the molten metal on the molten wall 25b cannot be supported by the arc force, resulting in an unstable weld pool state. In this case, too, the penetration depth into the base material 25 is unstable, and there is a risk of the shape of the welded area deteriorating. There is also a risk of a large amount of spatter being generated.

On the other hand, according to this embodiment, by setting the ratio of the peak current period Tp to the pulse period Tw within the aforementioned range, it is possible to ignite the arc 24 between the molten wall 25b and the welding wire 21 during the peak current period Tp. Furthermore, because the arc 24 can be rotated due to the rotating phenomenon, it is possible to irradiate the molten wall 25b evenly on average over time. This stabilizes the behavior of the molten pool including the molten wall 25b, making it possible to suppress rippling of the molten wall 25b. As a result, it is possible to stabilize the penetration depth into the base material 25 and suppress the occurrence of spatter.

Furthermore, if the average current decreases, the welding wire 21 becomes less likely to melt, and as mentioned above, the state of the molten pool becomes unstable. For this reason, the average current must be set to a predetermined value or higher. As a result of research by the present inventors, setting the average current to 250 A or higher promotes melting of the welding wire 21, ensuring that the molten droplets 21a grow and are transferred to the base material 25. Furthermore, when the average current is set to 250 A or higher, the molten droplets 21a undergo globular transfer. In other words, the molten droplets 21a grow to a size equal to or larger than the diameter of the welding wire 21 and are transferred to the base material 25. Furthermore, setting the average current to 250 A or higher suppresses rippling of the molten wall 25b and stabilizes the behavior of the molten pool, including the molten wall 25b. This stabilizes the penetration depth into the base material 25 and suppresses the generation of spatter.

Furthermore, as shown in this embodiment, by making the time waveform of the welding current Aw a trapezoidal wave, the state of the arc 24 can be stably made into a buried arc. This will be explained using the drawings.

Figure 4A shows the change in the arc state over time when the welding current time waveform is a trapezoidal wave. Figure 4B shows the change in the arc state over time when the welding current time waveform is a triangular wave.

As shown in Figures 4A and 4B, during the peak current period Tp, due to the rotation phenomenon, the arc 24 rotates around the longitudinal direction of the welding wire 21 as its centerline. Therefore, during the peak current period Tp, the arc 24 is ignited between the molten wall 25b and the welding wire 21. On the other hand, as shown in Figure 4B, if the time waveform of the welding current Aw is a triangular wave, the period during which the current value of the welding current Aw is maintained at Ip becomes shorter than in the case shown in Figure 4A.

As shown in Figure 4A, when the time waveform of the welding current is a trapezoidal wave, by ensuring that the period during which the current value of the welding current Aw is maintained at Ip is longer than a predetermined period, the period during which the arc 24 rotates and irradiates the molten wall 25b is also longer. This stabilizes the behavior of the molten pool including the molten wall 25b, and suppresses undulation of the molten wall 25b. As a result, the penetration depth into the base material 25 can be stabilized and spatter generation can be suppressed.

On the other hand, as shown in Figure 4B, when the time waveform of the welding current is a triangular wave, the period during which the current value of the welding current Aw is maintained at Ip becomes shorter, which makes it difficult to completely suppress the undulations of the molten wall 25b and stabilize the behavior of the molten pool including the molten wall 25b. As a result, the state of the arc 24 cannot be made into a stable buried arc, and it becomes difficult to stabilize the penetration depth into the base material 25. It also becomes difficult to suppress the generation of spatter.

In addition, from the perspective of ensuring that the current value of the welding current Aw is maintained at Ip for a period of time longer than a predetermined period, the time waveform of the welding current Aw is not limited to a trapezoidal wave, and may be, for example, a rectangular wave.

It is also preferable to set the current amplitude Ia within an appropriate range of 100 A or more (see FIGS. 6 and 7).
By doing so, even if the ratio of the peak current period Tp to the pulse period Tw changes within the aforementioned range, the current value Ip of the peak current Ip can be prevented from becoming too small, thereby preventing the molten wall 25b from waviness, stabilizing the behavior of the molten pool including the molten wall 25b, and stabilizing the penetration depth into the base material 25.

Furthermore, the current value Ib of the base current Ib can be prevented from becoming too large. This prevents the welding wire 21 from melting excessively during the base current period Tb, and the arc length from becoming longer than a predetermined length. If the arc length becomes too long, the arc 24 will ignite without being buried in the molten pool, resulting in the generation of a large amount of spatter. In other words, by keeping the current amplitude Ia within the appropriate range of 100 A or more (see Figures 6 and 7), the generation of spatter can be reliably suppressed.

Furthermore, according to this embodiment, during n pulse periods Tw, the droplets 21a detach from the welding wire 21 once and transfer to the base material 25. In other words, the periodic detachment and transfer of the droplets 21a stabilizes the state of the arc 24 during welding, making it possible to stabilize the penetration depth into the base material 25 and suppress the occurrence of spatter. It also makes it possible to suppress irregular changes in the shape of the welded area.

Furthermore, it is preferable to control the welding current Aw so that the pulse period Tw is 1.43 msec or more and 3.33 msec or less. If waving occurs in the molten pool formed on the base material 25, the waving period will often be in the range of more than 3.33 msec and less than 20 msec due to the influence of the viscosity of the molten pool, etc.

In this embodiment, by defining the pulse period Tw as described above, it is possible to vibrate the molten pool at a higher frequency than the frequency corresponding to the waviness period. By shortening this period, it is possible to stabilize the behavior of the molten pool, including the molten wall 25b, and suppress waviness of the molten wall 25b. As a result, it is possible to stabilize the penetration depth into the base material 25 and suppress the generation of spatter.

In this embodiment, the thickness of the base material 25 is 6 mm, but this is not particularly limited. The arc welding control method of this embodiment is useful when the thickness of the base material 25 is 6 mm or more, and even more specifically, when the thickness is 10 mm or more. In other words, it is possible to suppress the waviness of the molten wall 25b formed by buried arc welding, achieve deep penetration into the base material 25, and obtain a stable penetration depth. It is also possible to reduce the amount of spatter generated during welding. For example, the arc welding control method shown in this embodiment is useful when butt welding thick plates.

Furthermore, according to this embodiment, stable, deep penetration can be achieved, so when performing multi-layer V-groove welding, for example, the number of welds, i.e., the number of welding passes, can be reduced. This shortens welding time and reduces welding costs.

(Embodiment 2)
Fig. 5 is a time chart of various output waveforms during arc welding according to embodiment 2. For ease of explanation, in Fig. 5 and the following drawings, the same parts as those in embodiment 1 are denoted by the same reference numerals, and detailed explanations thereof will be omitted.

The time chart shown in Figure 5 differs from the time chart of embodiment 1 shown in Figure 3 in that the feed speed WF fluctuates periodically. Specifically, the feed speed WF fluctuates with the same period as the welding current Aw, i.e., the pulse period Tw, and during the peak current period Tp, the feed speed WF increases from WF3 to WF2 and is maintained at WF2 for a certain period. The period during which the feed speed WF is maintained at WF2 is the same as the period during which the current value of the welding current Aw is maintained at Ip. During the base current period Tb, the feed speed WF decreases from WF2 to WF3 and is maintained at WF3 for a certain period. The period during which the feed speed WF is maintained at WF3 is the same as the period during which the current value of the welding current Aw is maintained at Ib. Note that both WF2 and WF3 are positive values. When the moving average value of the feed speed WF during the pulse period Tw is taken as the average feed speed, the average feed speed in this embodiment is the same as WF1 in the first embodiment described above, and is maintained at a constant value during welding. However, the value of the average feed speed is not particularly limited to this, and may be different from WF1. It can be changed as appropriate depending on the current value of the average current described above. Furthermore, each value of the feed speed WF satisfies the relationship shown in equation (3).

WF2>WF1>WF3>0...(3)
According to this embodiment, by increasing or decreasing the feed rate WF in response to an increase or decrease in the welding current Aw, the distance between the droplet 21a and the bottom of the buried space 25a can be kept constant during both the peak current period Tp and the base current period Tb. This more reliably stabilizes the state of the arc 24 during welding. As a result, the penetration depth into the base material 25 can be stabilized and spatter generation can be suppressed.

The arc welding control methods shown in the first and second embodiments are useful when the shielding gas is _CO . The shielding gas may be a mixed gas mainly containing _CO , for example, a mixed gas containing 50% or more of _CO and argon.

As is well known, when the shielding gas is _CO2 or a mixed gas mainly containing _CO2 , the arc reaction force is large, making it difficult to stabilize the state of the arc 24 inside the buried space 25a. According to the arc welding control method shown in Embodiments 1 and 2, even when the arc reaction force is large, the state of the arc 24 during welding can be stabilized, thereby suppressing undulation of the molten wall 25b. As a result, deep penetration into the base material 25 can be achieved, and a stable penetration depth can be obtained. Furthermore, the amount of spatter generated during welding can be reduced.

The technology disclosed herein will be explained in more detail below using examples. Note that the examples shown below do not in any way limit the technology disclosed herein.

[Common welding conditions]

Table 1 shows the common conditions for arc welding in the examples. As a method for evaluating welding, arc welding of base material 25 was performed under the common conditions shown in Table 1, with the ratio of peak current period Tp to base current period Tb changed, and the welding condition was evaluated under each condition. After welding, the penetration depth of the welded area and the number of spatters generated were evaluated, and the results were reflected in the evaluation results of the welding condition. Other methods, such as taking images of the state of the welded area during welding with a camera, may also be reflected in the evaluation results of the welding condition.

Note that the welding speed in Table 1 refers to the speed in the welding direction at which the tip of the welding wire 21 moves along the surface of the base material 25, and corresponds to the speed at which the weld is formed along a weld line (not shown).

Furthermore, when the ratio of the peak current period Tp to the base current period Tb was changed, the welding current Aw was controlled so that the average current maintained the value shown in Table 1. In general, when the average current is set high, the ratio of the peak current period Tp to the pulse period Tw increases, and the current amplitude Ia decreases. Furthermore, when the average current is set low, the ratio of the peak current period Tp to the pulse period Tw decreases, and the current amplitude Ia increases.

[Welding Condition Evaluation Results]

Table 2 shows the evaluation results of the welding condition for the ratio of the peak current period Tp to the base current period Tb and the current amplitude. In Table 2, the evaluation results are indicated by ○ (OK) or × (NG). An × evaluation result includes two types of evaluation results, _X1 and _X2 (see FIG. 7 ). Evaluation result _X1 corresponds to a state in which the arc 24 is buried, the behavior of the weld pool is unstable, and the welding is unstable. In other words, this corresponds to a state in which the arc 24 is ignited while buried in the weld pool, but the behavior of the weld pool is unstable during welding, resulting in unstable welding. In this case, the penetration depth of the weld varies. Evaluation result _X2 corresponds to a state in which the arc 24 is not buried, that is, the arc 24 is ignited without being buried in the weld pool, and a large amount of spatter is generated. An evaluation result of ○ corresponds to a state in which the arc 24 is buried, the welding is stable, and the amount of spatter generated is below a predetermined threshold.

As shown in Table 2, Examples 1 to 8 received evaluation results of ◯, while Comparative Examples 1 to 16 received evaluation results of ×. These results demonstrate that there is an appropriate range for the ratio of the peak current period Tp to the base current period Tb, in other words, the ratio of the peak current period Tp to the pulse period Tw, and the current amplitude Ia.

Figure 6 is a diagram showing the appropriate ranges for the ratio of the peak current period to the base current period and the current amplitude in an embodiment. Figure 7 is a diagram illustrating the welding state that occurs when the ratio of the peak current period to the base current period or the current amplitude falls outside the appropriate range.

In Examples 1 to 8, the ratio of the peak current period Tp to the base current period Tb was in the range of 3:7 to 7:3. In other words, the ratio of the peak current period Tp to the pulse period Tw was 30% or more and 70% or less. Furthermore, the current amplitude Ia was 100A or more and 170A or less. In other words, the range in which the ratio of the peak current period Tp to the base current period Tb and the current amplitude Ia each satisfy the aforementioned ranges corresponds to the appropriate range.

As shown in Figures 6 and 7, the appropriate range for the ratio of the peak current period Tp to the base current period Tb is preferably between 3:7 and 7:3. In other words, the ratio of the peak current period Tp to the pulse period Tw is preferably 30% or more and 70% or less. Furthermore, the appropriate range for the current amplitude Ia, which is the difference between the current value Ip of the peak current Ip and the current value Ib of the base current Ib, is preferably 100 A or more, and the welding current Aw is preferably controlled so that the current amplitude Ia is less than or equal to the value of the first straight line, which represents the relationship between the peak current period Tp and the current amplitude Ia relative to the pulse period Tw. More specifically, it is preferable to set the current amplitude Ia to 100 A or more. Furthermore, the first straight line is preferably Ia = -10 x TpR + 200, where TpR is the ratio of the peak current period Tp to the pulse period Tw.

When the ratio of the peak current period Tp to the base current period Tb and the current amplitude Ia each satisfy the appropriate range, the arc 24 becomes a buried arc and the number of spatters generated falls below a predetermined threshold. In other words, it is confirmed that the arc 24 has ignited between the molten wall 25b and the welding wire 21, and the behavior of the molten pool during welding has stabilized, which is thought to have stabilized the penetration depth into the base material 25. Furthermore, it is thought that the generation of spatters has been suppressed because the arc 24 ignited while buried in the molten pool.

On the other hand, in the cases shown in Comparative Examples 1 to 4, the ratio of the peak current period Tp to the base current period Tb was within the appropriate range, but the current amplitude Ia was outside the appropriate range. Among these, as shown in Figure 7, under the conditions shown in Comparative Examples 1 and 9, the ratio of the peak current period Tp to the base current period Tb was 3:7, which was within the appropriate range, but the current amplitude Ia was larger than the appropriate range. In this case, the current value Ip of the peak current Ip increases to maintain the average current at a constant value. This is thought to have promoted melting of the welding wire 21, lengthening the arc length and preventing the arc 24 from being buried in the molten pool. This is thought to have resulted in an increase in the number of spatters (X ₂ in the upper left corner of Figure 7).

Furthermore, under the conditions shown in Comparative Examples 2 and 10 to 12, the ratio of the peak current period Tp to the base current period Tb was 3:7, which was within the appropriate range, but the current amplitude Ia was smaller than the appropriate range. In this case, the current value Ib of the base current Ib increases to maintain the average current at a constant value. This is thought to have promoted melting of the welding wire 21, lengthening the arc length and preventing the arc 24 from being buried in the molten pool. This is thought to have resulted in an increase in the number of spatters (X ₂ in the lower left of Figure 7).

Furthermore, under the conditions shown in Comparative Examples 3 and 13, the ratio of the peak current period Tp to the base current period Tb was 7:3, which was within the appropriate range, but the current amplitude Ia was smaller than the appropriate range. In this case, the average current was maintained at a constant value, so the peak current Ip decreased, making it difficult for the welding wire 21 to melt. In this case, the arc 24 became a buried arc, but it ignited while excessively buried in the molten pool. Therefore, during the peak current period Tp, the arc 24 was not ignited between the welding wire 21 and the molten wall 25b, and the arc force was unable to press the molten wall 25b. In other words, the arc force was insufficient to press the molten wall 25b. As a result, it was not possible to suppress the undulation of the molten wall 25b, resulting in an unstable welding state and an unstable penetration depth of the base metal 25 ( _X1 in the lower right corner of Figure 7).

Furthermore, under the conditions shown in Comparative Examples 4 and 14 to 16, the ratio of the peak current period Tp to the base current period Tb was 7:3, which was within the appropriate range, but the current amplitude Ia was greater than the appropriate range. In this case, the average current was maintained at a constant value, so the base current Ib decreased in value, making it difficult for the welding wire 21 to melt. In this case, the arc 24 was also buried, but it ignited while excessively buried in the molten pool. Therefore, during the peak current period Tp, the arc 24 was not ignited between the welding wire 21 and the molten wall 25b, and the arc force was unable to press the molten wall 25b. As a result, it was not possible to suppress the undulation of the molten wall 25b, resulting in an unstable welding state and an unstable penetration depth into the base metal 25 ( _X1 in the upper right corner of Figure 7).

Furthermore, under the conditions shown in Comparative Examples 5 and 6, while the current amplitude Ia was within the appropriate range, the ratio of the peak current period Tp to the base current period Tb was 2:8. In other words, the ratio of the peak current period Tp to the pulse period Tw was smaller than the appropriate range. In this case, the peak current period Tp was too short, making it difficult for the welding wire 21 to melt. Therefore, the arc 24 became a buried arc, but it ignited while excessively buried in the molten pool. Therefore, during the peak current period Tp, the arc 24 was not ignited between the welding wire 21 and the molten wall 25b, and the arc force was unable to press the molten wall 25b. As a result, it was not possible to suppress the undulation of the molten wall 25b, resulting in an unstable welding state and an unstable penetration depth into the base metal 25 ( _X1 on the left in Figure 7).

Furthermore, under the conditions shown in Comparative Examples 7 and 8, while the current amplitude Ia was within the appropriate range, the ratio of the peak current period Tp to the base current period Tb was 8:2. In other words, the ratio of the peak current period Tp to the pulse period Tw was greater than the appropriate range. In this case, the peak current period Tp became too long, resulting in an increase in the average current. If the welding current Aw was controlled to maintain a constant average current, the base current Ib value Ib decreased, making it difficult for the welding wire 21 to melt. Therefore, the arc 24 became a buried arc, but it ignited while excessively buried in the molten pool. Therefore, during the peak current period Tp, the arc 24 was not ignited between the welding wire 21 and the molten wall 25b, and the arc force was unable to press the molten wall 25b. As a result, it was not possible to suppress the undulation of the molten wall 25b, resulting in an unstable welding state and an unstable penetration depth into the base metal 25 ( _X1 on the right side of Figure 7).

The arc welding control method disclosed herein is useful because it can suppress undulations in the molten wall formed by buried arc welding, achieve a stable, deep penetration depth, and suppress the generation of spatter.

1 Input power supply 2 Primary rectifier 3 Switching unit 4 Transformer 5 Secondary rectifier 6 DCL
Reference Signs List 7 Drive unit 8 Welding voltage detection unit 9 Welding current detection unit 10 Short circuit/arc detection unit 11 Short circuit control unit 12 Arc control unit 13 Wire feed speed control unit 14 Welding power supply unit 15 Welding condition setting unit 16 Robot control unit 17 Robot control unit 18 Manipulator 20 Wire storage unit 21 Welding wire 21a Melt droplet 22 Wire feed motor 23 Tip 24 Arc 25 Base material 25a Buried space 25b Melt wall 26 Welding torch 30 Arc welding device Ip Peak current Ib Base current Ia Current amplitude Tp Peak current period Tb Base current period Tw Pulse period

Claims (9)

1. An arc welding control method for generating an arc between a welding wire that is a consumable electrode and a base metal, and welding the base metal in a buried arc state, comprising:
controlling the welding current so that the time waveform of the welding current flowing through the welding wire changes to a rectangular or trapezoidal shape;
a pulse period, which is a fluctuation cycle of the welding current, is the sum of a peak current period in which a peak current flows through the welding wire and a base current period, which follows the peak current period and in which a base current having a current value lower than the peak current flows through the welding wire,
a welding current control unit that controls the welding current so that a ratio of the peak current period to the pulse period is 30% or more and 70% or less, and so that an average current, which is a moving average value of the welding current over a predetermined period, is 250 A or more, thereby causing a droplet formed at the tip of the welding wire to detach once and transfer to the base material during n pulse periods (n is a positive integer). 2. The arc welding control method according to claim 1,
a control circuit for controlling the welding current so that a current amplitude, which is a difference between the current value of the peak current and the current value of the base current, is 100 A or more and is equal to or less than the value of a first straight line that represents the relationship between the peak current period and Ia as the current amplitude relative to the pulse period; 3. The arc welding control method according to claim 2,
The arc welding control method, wherein the first straight line is Ia=-10×TpR+200, and TpR is a ratio of the peak current period to the pulse period. 2. The arc welding control method according to claim 1,
10. An arc welding control method comprising: controlling a feeding operation of the welding wire so that the feeding speed of the welding wire is constant. 2. The arc welding control method according to claim 1,
When the moving average value of the welding wire feed speed during the predetermined period is defined as an average feed speed,
a welding wire feed operation controlled so that the feed rate increases relative to the average feed rate during the peak current period and decreases relative to the average feed rate during the base current period. 2. The arc welding control method according to claim 1,
10. An arc welding control method comprising: controlling the welding current so that the pulse period is 1.43 msec or more and 3.33 msec or less. 2. The arc welding control method according to claim 1,
The arc welding control method is characterized in that the thickness of the base material is 6 mm or more. 8. The arc welding control method according to claim 7,
An arc welding control method, characterized in that the thickness of the base material is 10 mm or more. 2. The arc welding control method according to claim 1,
During welding of the base metal, a shielding gas is sprayed onto the welding portion of the base metal,
10. The arc welding control method, wherein the shielding gas is _CO2 .