JP7620481B2 - Arc welding method and arc welding device - Google Patents

Description

The present invention relates to a consumable electrode arc welding method and arc welding device.

In recent years, buried arc welding has come into practical use. Buried arc welding is achieved by feeding the welding wire at approximately 5-100 m/min and supplying a large current of 300 A or more. When the welding wire is fed at high speed and a large current is supplied, a concave molten pool (molten portion) is formed in the base material, and the tip of the welding wire enters a concave space (space surrounded by the concave molten portion) formed in the molten pool. Hereinafter, this concave space will be referred to as the buried space, and the arc generated between the tip of the welding wire that has entered the buried space and the base material or the molten portion will be referred to as the buried arc, as appropriate.

In buried arc welding, the shape of the buried space is prone to change, which can cause the molten pool to oscillate and destabilize the weld. In particular, when the opening of the buried space shrinks, this can cause short-circuiting between the welding wire and the molten pool, or the molten pool to oscillate due to spatial expansion caused by an increase in pressure inside the buried space, which is a major cause of weld instability.

As a technology for stabilizing the buried arc, a control that periodically changes the magnitude of the welding current has been developed (for example, Patent Document 1). Several current change patterns have been proposed, but the main aim of these controls is to make the droplet transfer form a rotating transfer during the high current period when a large current is supplied, so that the arc supports the opening of the buried space approaching the welding wire, thereby suppressing the narrowing of the opening.

International Publication No. WO 2018/105548

However, when a thick welding wire is used or when the average welding current is small, the droplet transfer mode is less likely to be a rotating transfer, and the droplet transfer mode transition described above may not occur. In other words, the arc may not be able to support the opening of the buried space approaching the welding wire.

The object of the present invention is to provide an arc welding method and an arc welding device that can improve the stability of buried arc welding, which stabilizes the molten pool by periodically changing the welding current, even when the droplet transfer mode does not become a rotating transfer during the high current period.

The arc welding method according to this embodiment is a consumable electrode type arc welding method in which an arc is generated between the welding wire and the base metal by supplying a welding current of an average current of 300 A or more to the welding wire, and the tip of the welding wire is inserted into a space surrounded by a concave molten portion formed in the base metal to weld the base metal, and a current reduction period in which the welding current is reduced and a current increase period in which the welding current is increased are periodically repeated, and when the current reduction period changes to the current increase period, a pulsed large current is additionally supplied.

In this embodiment, buried arc welding can be stabilized by periodically varying the welding current. During a high current period in which the average value of the welding current is high, the droplet transfer mode becomes a rotating transfer, and the opening of the buried space approaching the welding wire is supported by the arc, thereby suppressing the reduction of the opening.
However, when a large diameter welding wire is used or the average welding current is small, the droplet transfer mode is unlikely to be a rotating transfer even during the high current period, and the opening of the buried space may not be supported by the arc. Therefore, in this embodiment, a pulsed high current larger than the welding current supplied during the high current period is additionally supplied. The direction of the arc moves continuously in the direction in which the distance between the tip of the welding wire and the molten pool surface forming the buried space is minimized in the high electrical conductivity region where the arc plasma has already been formed, and the molten pool is supported by the arc pressure. When a pulsed high current is supplied, the arc spreads more, so that the direction of the arc can be changed over a wider range. In other words, the arc is more likely to be directed toward the portion of the buried space opening close to the tip of the welding wire, and the opening of the buried space is more likely to be supported by the arc, resulting in stable welding.
Furthermore, by additionally supplying a large pulse current when the current decreases and increases, it is possible to apply a large pulse current necessary to expand the arc.

In the arc welding method according to this embodiment, it is preferable that the value of the additionally supplied pulsed large current is 0.7 to 3 times the set current value.

According to this aspect, by setting the value of the pulsed large current to 0.7 times or more the set current value, the arc is sufficiently expanded, and when the opening of the buried space approaches the welding wire, the approaching part is pushed back by the arc before the welding becomes unstable, thereby preventing the welding from becoming unstable. If the value of the pulsed large current is less than 0.7 times the set current value, the arc does not sufficiently expand, and it becomes difficult for the arc to be directed toward the part of the opening of the buried space that is approaching the welding wire, making it impossible to prevent the welding from becoming unstable.
In addition, by setting the value of the pulsed large current to three times or less the set current value, it is possible to prevent the molten pool from fluctuating due to the arc force caused by the large current. If the value of the pulsed large current is set to more than three times the set current value, the large arc force caused by the large current acts on the molten pool for a long period of time, causing the molten pool to fluctuate and the buried arc to become unstable.

In the arc welding method according to this aspect, it is preferable that the time for which the pulsed large current is additionally supplied is 5% to 20% of the change cycle of the current increase period and the current decrease period.

According to this aspect, by setting the additional supply time of the pulsed large current to 5% or more of the welding current change cycle, the arc can be sufficiently spread, and when the opening of the buried space approaches the welding wire, the approaching part can be pushed back by the arc before the welding becomes unstable, thereby preventing the welding from becoming unstable. If the additional supply time of the pulsed large current is less than 5% of the welding current change cycle, the arc does not sufficiently spread and the arc is unlikely to be directed toward the part of the opening of the buried space that is approaching the welding wire, making it impossible to prevent the welding from becoming unstable.
In addition, by setting the additional supply time of the large pulsed current to 20% or less of the welding current change period, it is possible to prevent the molten pool from fluctuating due to the arc force caused by the large current. If the additional supply time of the large pulsed current is set to more than 20% of the welding current change period, the large arc force caused by the large current acts on the molten pool for a long period of time, causing the molten pool to fluctuate and the buried arc to become unstable.

The arc welding method according to this aspect is preferably configured to supply the large pulse current additionally when the diameter of the welding wire is equal to or greater than a predetermined value, and not supply the large pulse current additionally when the diameter of the welding wire is less than the predetermined value.

According to this aspect, it is possible to avoid destabilizing the buried arc by unnecessarily supplying additional high current pulses when the buried arc is already in a stable state.

In the arc welding method according to this aspect, if the diameter of the welding wire is 1.4 mm or more, it is preferable to additionally supply the pulsed large current.

According to this aspect, it is possible to avoid destabilizing the buried arc by unnecessarily supplying additional high current pulses when the buried arc is already in a stable state.

The arc welding device according to this embodiment is a consumable electrode type arc welding device that includes a power supply unit that generates an arc between the welding wire and the base material by supplying a welding current of an average current of 300A or more to the welding wire, and that welds the base material by inserting the tip of the welding wire into a space surrounded by a concave molten portion formed in the base material by the generated arc, and the power supply unit periodically repeats a current reduction period in which the welding current is reduced and a current increase period in which the welding current is increased, and makes the time average of the welding current correspond to a set current. In other words, the period from the latter half of the current reduction period to the first half of the current increase period can be called a low current period, and the period from the latter half of the current increase period to the first half of the current reduction period can be called a high current period. Furthermore, when changing from the current reduction period to the current increase period, a pulse high current of 0.7 to 3 times the set current is additionally supplied.

According to this embodiment, by additionally supplying a large pulsed current, the arc can be directed toward the area approaching the opening of the buried space, using the same principle as the above-mentioned arc welding method, improving the stability of buried arc welding.

According to the present invention, in buried arc welding, which stabilizes the molten pool by periodically changing the welding current, the stability of buried arc welding can be improved even when the droplet transfer mode does not become a rotating transfer during the high current period.

1 is a schematic diagram showing one configuration of a consumable electrode type arc welding device according to a first embodiment of the present invention; 3 is a flowchart showing the procedure of an arc welding method according to the first embodiment. FIG. 2 is a side cross-sectional view showing the base material to be welded. FIG. 2 is a schematic diagram showing droplet transfer caused by periodically varying a welding current. 4 is a flowchart showing a procedure for welding current variation control. 4 is a graph showing a waveform of a large pulse current. 4 is a graph showing a waveform of a welding current when a large pulse current is not applied. 4 is a graph showing a waveform of a welding current to which a pulse current is applied. FIG. 6 is a schematic diagram showing one configuration of an arc welding device according to a second embodiment of the present invention. 10 is a flowchart showing the procedure of an arc welding method according to a second embodiment of the present invention.

The arc welding method and arc welding apparatus according to the embodiments of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is intended to include all modifications within the scope of the claims and meaning equivalent to the claims. In addition, at least some of the embodiments described below may be combined in any combination.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
(Embodiment 1)
1 is a schematic diagram showing one configuration of a consumable electrode type arc welding device according to the present embodiment 1. The arc welding device according to the present embodiment 1 includes a welding power source 1, a torch 2, and a wire feeder 3. In buried arc welding in which the welding current Iw is periodically changed to stabilize the molten pool, the arc welding device according to the present embodiment 1 makes it possible to improve the stability of buried arc welding by additionally supplying a large pulsed current when the current decrease period changes to the current increase period, even if the droplet transfer mode does not become a rotating transfer during the large current period.

The torch 2 is made of a conductive material such as a copper alloy, and has a cylindrical contact tip that guides the welding wire 5 to the part to be welded of the base material 4 and supplies the welding current Iw required to generate the arc 7 (see FIG. 4). The contact tip comes into contact with the welding wire 5 that passes through it, and supplies the welding current Iw to the welding wire 5. The torch 2 also has a hollow cylindrical nozzle surrounding the contact tip that sprays shielding gas to the part to be welded. The shielding gas is intended to prevent oxidation of the base material 4 and welding wire 5 that have been melted by the arc 7. The shielding gas is, for example, carbon dioxide gas, a mixture of carbon dioxide gas and argon gas, an inert gas such as argon, etc.

The welding wire 5 is, for example, a solid wire with a diameter of 0.9 mm to 1.6 mm, and functions as a consumable electrode. The welding wire 5 is, for example, a packed wire wound in a spiral shape and stored in a pail pack, or a reel wire wound on a wire reel.

The wire feeder 3 has a feed roller that feeds the welding wire 5 to the torch 2, and a motor that rotates the feed roller. The wire feeder 3 pulls out the welding wire 5 from the wire reel by rotating the feed roller, and supplies the pulled out welding wire 5 to the torch 2. Note that this method of feeding the welding wire 5 is one example, and is not particularly limited.

The welding power source 1 is connected to the contact tip of the torch 2 and the base material 4 via a power supply cable, and includes a power source unit 11 that supplies the welding current Iw, and a feed speed control unit 12 that controls the feed speed of the welding wire 5. The power source unit 11 and the feed speed control unit 12 may be configured separately. The power source unit 11 includes a power source circuit 11a that outputs a PWM-controlled direct current, an output voltage setting circuit 11b, an average voltage setting circuit 11c, an average current setting circuit 11d, a frequency setting circuit 11e, an amplitude setting circuit 11f, a voltage detection unit 11g, a current detection unit 11h, and a comparison circuit 11i.

The voltage detection unit 11g detects the welding voltage Vw and outputs a voltage value signal Ed indicating the detected voltage value to the comparison circuit 11i.

The current detection unit 11h detects the welding current Iw that is supplied, for example, from the welding power source 1 through the torch 2 to the welding wire 5 and flows through the arc 7, and outputs a current value signal Id indicating the detected current value to the output voltage setting circuit 11b.

The average voltage setting circuit 11c outputs an average voltage setting signal to the output voltage setting circuit 11b to set the average voltage of the periodically fluctuating welding voltage Vw.

The average current setting circuit 11d outputs an average current setting signal for setting the average current of the periodically fluctuating welding current Iw to the output voltage setting circuit 11b and the feed speed control unit 12. When implementing the arc welding method according to the first embodiment, the average current setting circuit 11d outputs an average current setting signal indicating an average current of 300 A or more, preferably an average current of 300 A or more and 1000 A or less, more preferably an average current of 500 A or more and 800 A or less.

The frequency setting circuit 11e outputs a frequency setting signal to the output voltage setting circuit 11b to set a frequency that periodically changes the welding voltage Vw and welding current Iw between the base material 4 and the welding wire 5. When implementing the arc welding method according to the first embodiment, the frequency setting circuit 11e outputs a frequency setting signal indicating a frequency of 10 Hz or more and 1000 Hz or less, preferably a frequency of 50 Hz or more and 300 Hz or less, and more preferably a frequency of 80 Hz or more and 200 Hz or less.

The amplitude setting circuit 11f outputs an amplitude setting signal to the output voltage setting circuit 11b for setting the amplitude of the periodically varying welding voltage Vw or welding current Iw. The amplitude is the voltage difference between the minimum and maximum set voltage values of the varying welding voltage Vw, or the current difference between the minimum and maximum current values of the varying welding current Iw.
When performing the arc welding method according to the first embodiment, in order to set the current amplitude, the amplitude setting circuit 11f outputs an amplitude setting signal indicating a current amplitude of 50 A or more, preferably a current amplitude of 100 A or more and 500 A or less, and more preferably a current amplitude of 200 A or more and 400 A or less.

The output voltage setting circuit 11b generates an output voltage setting signal Ecr indicating a target voltage, for example a rectangular wave, based on the current value signal Id, average voltage setting signal, average current setting signal, frequency setting signal, and amplitude setting signal output from each part so that the welding voltage Vw and welding current Iw become the target average voltage and average current, frequency, voltage amplitude, or current amplitude, and outputs the generated output voltage setting signal Ecr to the comparison circuit 11i.

The comparison circuit 11i compares the voltage value signal Ed output from the voltage detection unit 11g with the output voltage setting signal Ecr output from the output voltage setting circuit 11b, and outputs a difference signal Ev indicating the difference to the power supply circuit 11a.

The power supply circuit 11a includes an AC-DC converter that converts commercial AC to DC, an inverter circuit that converts the converted DC to the required AC by switching, and a rectifier circuit that rectifies the converted AC. The power supply circuit 11a PWM controls the inverter according to the difference signal Ev output from the comparison circuit 11i, and outputs a voltage to the welding wire 5. As a result, a periodically changing welding voltage Vw is applied between the base material 4 and the welding wire 5, a welding current Iw flows, and the welding current Iw also changes periodically. The welding power supply 1 is configured to receive an output instruction signal from the outside via a control communication line (not shown), and the power supply unit 11 uses the output instruction signal as a trigger to start supplying the welding current Iw to the power supply circuit 11a. The output instruction signal is output from, for example, a welding robot to the welding power supply 1. In addition, in the case of a manual welding machine, the output instruction signal is output from the torch 2 to the welding power supply 1 when a hand-operated switch provided on the torch 2 is operated.

FIG. 2 is a flow chart showing the procedure of the arc welding method according to the first embodiment, and FIG. 3 is a side cross-sectional view showing the base material 4 to be welded. First, a pair of base materials 4 to be welded is placed in an arc welding device, and various settings of the welding power source 1 are performed (step S11). Specifically, as shown in FIG. 3, a plate-shaped first base material 41 and a second base material 42 are prepared, and the end faces 41a and 42a, which are the parts to be welded, are butted together and placed at a predetermined welding work position. The first and second base materials 41 and 42 are, for example, steel plates such as mild steel, carbon steel for mechanical construction, and alloy steel for mechanical construction. The thickness of the first and second base materials 41 and 42 is, for example, 9 mm or more and 30 mm or less. If necessary, a groove may be provided in the first base material 41 or the second base material. If necessary, a backing such as a metal or copper plate of the same type as the base material, or ceramic, may be used.
The welding power source 1 sets the welding conditions of the welding current Iw within the ranges of a frequency of 10 Hz or more and 1000 Hz or less, an average current of 300 A or more, and a current amplitude of 50 A or more.

The welding current Iw condition settings may be performed entirely by the welding operator, or the welding power source 1 may be configured to receive instructions to carry out the welding method according to the first embodiment at an operation unit and automatically set all conditions. The welding power source 1 may also be configured to receive some welding conditions, such as the average current, at an operation unit, determine the remaining welding conditions that match the received welding conditions, and semi-automatically set conditions.

After various settings have been made, the welding power source 1 determines whether the output start condition for the welding current Iw is met (step S12). Specifically, the welding power source 1 determines whether an output instruction signal for welding has been input. If it is determined that the output instruction signal has not been input and the output start condition for the welding current Iw is not met (step S12: NO), the welding power source 1 waits for the input of an output instruction signal.

If it is determined that the condition for starting the output of the welding current Iw is met (step S12: YES), the feed speed control unit 12 of the welding power source 1 outputs a feed instruction signal to the wire feed unit 3 to instruct the wire feed unit 3 to feed the welding wire 5 at a predetermined speed (step S13). The feed speed of the welding wire 5 is set, for example, within a range of about 5 to 100 m/min. The feed speed control unit 12 determines the feed speed according to the average current setting signal output from the average current setting circuit 11d. The feed speed of the welding wire 5 may be constant or may be varied periodically. Alternatively, the welding operator may directly set the wire feed speed.

Next, the power supply unit 11 of the welding power supply 1 detects the welding voltage Vw and the welding current Iw using the voltage detection unit 11g and the current detection unit 11h (step S14), and performs PWM control so that the values, frequency, and amplitude of the detected welding voltage Vw and welding current Iw match the set welding conditions and the welding current Iw fluctuates periodically (step S15).

Next, the power supply unit 11 of the welding power supply 1 determines whether or not to stop the output of the welding current Iw (step S16). Specifically, the welding power supply 1 determines whether the input of the output instruction signal is continuing. If the input of the output instruction signal is continuing and it is determined that the output of the welding current Iw should not be stopped (step S16: NO), the power supply unit 11 returns the process to step S13 and continues outputting the welding current Iw.

If it is determined that the output of the welding current Iw should be stopped (step S16: YES), the power supply unit 11 returns the process to step S12.

The periodic variation of the welding current Iw and the droplet transfer will be outlined below.
In the arc welding method according to the first embodiment, the power supply unit 11 controls the welding current Iw so that the frequency of the welding current Iw is 10 Hz or more and 1000 Hz or less, the average current is 300 A or more, and the current amplitude is 50 A or more.
Preferably, power supply unit 11 controls welding current Iw so that the frequency of welding current Iw is 50 Hz or more and 300 Hz or less, the average current is 300 A or more and 1000 A or less, and the current amplitude is 100 A or more and 500 A or less.

Figure 4 is a schematic diagram showing droplet transfer caused by periodically varying the welding current Iw. When the welding current Iw is periodically varied under the above welding conditions, the base material 4 is melted by the heat of the arc 7 generated between the tip 5a of the welding wire 5 and the welded part, and a concave molten portion 6 consisting of the molten metal of the welding wire 5 and the base material 4 is formed. When the state of the arc 7 was photographed with a high-speed camera, it was confirmed that, as shown in the left diagram of Figure 4, a first state in which the arc 7 is generated between the tip 5a of the welding wire 5 and the bottom 61 of the molten portion 6 and a second state in which the arc 7 is generated between the tip 5a and the side 62 of the molten portion 6 periodically fluctuate.

Specifically, a first state in which the arc 7 jumps from the tip 5a of the welding wire 5 to the bottom 61 of the molten portion 6 and a second state in which the arc 7 jumps from the tip 5a of the welding wire 5 to the side 62 of the molten portion 6 are repeated. The first state occurs during a small current period in which the average value of the welding current Iw is small, and the second state occurs during a large current period in which the average value of the welding current Iw is large. The first state is a state in which the droplet transfer mode of the welding wire 5 is drop transfer. The second state is a state in which the droplet transfer mode of the welding wire 5 is, for example, rotating transfer or pendulum transfer.
Drop transfer is an example of a form of droplet transfer from the tip 5a of the welding wire 5 to the bottom 61 of the molten portion 6, and rotating transfer is an example of a form of droplet transfer from the tip 5a of the welding wire 5 to the side 62 of the molten portion 6. Pendulum transfer is a characteristic droplet transfer form in which the liquid column and arc 7 formed at the tip 5a of the welding wire 5 swing like a pendulum on the same plane, while the plane as a whole rotates little by little with the protruding direction of the welding wire 5 as the central axis.
The molten metal tries to flow in a direction in which the buried space 6a closes and the tip 5a of the welding wire 5 is buried, but in the second state, the arc 7 jumps to the side 62 of the molten portion 6, the molten metal in the molten portion 6 is pushed back in a direction away from the welding wire 5, and the buried space 6a is stabilized in a concave state. In the right diagram of Figure 4, the tip 5a of the welding wire 5 is shortened as a result of the transfer of the droplets from the tip 5a of the welding wire 5 melted by the large current.
By varying the first and second states in the range of 80 Hz to 200 Hz, the buried space 6a can be stabilized, and the stability of buried arc welding can be improved.

However, when a large diameter welding wire 5, for example a welding wire 5 having a diameter of 1.4 mm or more, is used, or when the average welding current is small, the droplet transfer mode is unlikely to become a rotating transfer even in the second state, and the droplet transfer mode transition described above may not occur.

However, even in the above case where a large diameter welding wire 5 is used, a phenomenon that can contribute to the stabilization of buried arc welding has been confirmed. This is because the arc 7 spreads more when a large current is applied. The arc 7 faces the direction in which the distance between the tip 5a of the welding wire 5 and the molten pool surface that forms the buried space 6a is the smallest in the high electrical conductivity region where the arc plasma has already been formed. Therefore, when the arc 7 spreads more, the arc 7 is more likely to face the approaching part of the opening of the buried space 6a to the welding wire 5 over a wider range, and the approaching part is more easily supported by the arc 7, stabilizing the welding. As the opening of the buried space 6a is pushed back, the direction of the arc 7 changes continuously, and finally returns to the steady state of downward.

In the above-mentioned buried arc stabilization method by arc expansion, the high current state does not necessarily have to continue for a long time. Once the arc 7 is directed toward the approaching part of the opening of the buried space 6a relative to the welding wire 5, the direction of the arc 7 is maintained regardless of the magnitude of the welding current Iw until the approaching part is pushed back. Therefore, it is sufficient to apply a pulsed high current (see Figure 6) momentarily. Rather, if the high current condition continues for a long time, the large arc force acts on the molten pool for a long time, causing the molten pool to become unstable.

Therefore, in this embodiment, in addition to the welding current fluctuation control shown in Figure 4, a large pulse current is additionally supplied as an additional arc stabilization control.

Figure 5 is a flowchart showing the procedure of the welding current variation control. The welding power source 1 performs PWM control so that the welding current Iw changes periodically (step S31). In other words, the welding power source 1 periodically repeats a current reduction period in which the welding current Iw is reduced and a current increase period in which the welding current Iw is increased. For example, the welding power source 1 can vary the welding current Iw by periodically repeating a period in which a voltage higher than the average voltage is set and a period in which a lower set voltage is set. That is, in the period in which a voltage higher than the average voltage is set, the welding current Iw increases, resulting in the current increase period. In the period in which a voltage lower than the average voltage is set, the welding current Iw decreases, resulting in the current reduction period. In other words, the period from the latter half of the current reduction period to the first half of the current increase period can be called a small current period, and the period from the latter half of the current increase period to the first half of the current reduction period can be called a large current period.

Next, the welding power source 1 determines whether it is time to switch from the current decrease period to the current increase period (step S32). If it is determined that it is not time to switch to the current increase period (step S32: NO), the welding power source 1 does not apply additional large pulse current and continues welding current variation control.

When it is determined that it is time to switch from the current decrease period to the current increase period (step S32: YES), the welding power source 1 determines whether the diameter of the welding wire 5 is equal to or greater than a predetermined value (step S33). That is, the welding power source 1 determines whether the welding wire 5 is a large-diameter wire. The operator can set the diameter of the welding wire 5 to be used with the welding power source 1, and the welding power source 1 can determine whether the welding wire 5 is large-diameter by reading the set diameter. A large-diameter welding wire 5 is, for example, a wire with a diameter of 1.4 mm or 1.6 mm or more.

If it is determined that the welding wire 5 is not thick (step S33: NO), the welding power source 1 does not apply additional pulsed large current and continues welding current variation control. If the welding wire 5 is not thick, the buried arc 7 can be stabilized by only periodically changing the welding current Iw shown in FIG. 4, so control to apply a pulsed large current is not performed.

If it is determined that the welding wire 5 has a large diameter (step S33: YES), the welding power source 1 additionally supplies a large pulse current when switching from the current decrease period to the current increase period (step S34). In other words, the welding power source 1 additionally supplies a large pulse current in accordance with the timing at which the welding current Iw starts to increase.

Figure 6 is a graph showing the waveform of a large pulse current, Figure 7 is a graph showing the waveform of the welding current Iw when no large pulse current is applied, and Figure 8 is a graph showing the waveform of the welding current Iw when a pulse current is applied. In Figures 6 to 8, the horizontal axis shows time, and the vertical axis shows the welding current Iw. In buried arc welding using a large diameter welding wire 5, the welding power source 1 additionally supplies a large pulse current as shown in Figure 6 to stabilize the buried space 6a.

However, to provide an instantaneous large pulse current, the welding current Iw needs to be increased and decreased sharply, but the achievable rate of change depends on the secondary resistance or inductance of the arc welding device. If the secondary resistance or inductance is large, such as when the secondary power cable is long or wound, the welding current Iw cannot be changed sharply, a sufficiently high current cannot be output, and the buried arc 7 cannot be stabilized.

Therefore, the application of a large pulsed current is used in combination with the welding current control shown in Figures 4 and 7 as additional arc stabilization control. In other words, an additional supply of a large pulsed current is performed as additional arc stabilization control in the welding current control shown in Figures 4 and 7.

Normally, as shown in FIG. 7, the welding current Iw is limited so that it does not change suddenly, and the same waveform of the welding current Iw can be obtained whether the secondary resistance and inductance are large or small. The welding power source 1 applies a short pulse of large current when the welding current Iw controlled in this way rises, that is, when switching from the current decrease period to the current increase period. If an additional pulse of large current is supplied when the welding current Iw rises, as shown in FIG. 8, it becomes easier to change the current suddenly in line with the rise of the welding current Iw, and it becomes possible to output the current required to direct the arc 7 toward the opening of the buried space 6a.

The rise and fall behavior of the welding current Iw in the applied portion depends on the secondary resistance and inductance of the welding environment, but since this is merely an additional stabilization control, the welding will not become unstable even if a high current cannot be output. If a high current can be output, the buried arc 7 becomes more stable.

The target value of the additionally supplied pulsed large current is preferably 0.7 to 3 times the set current value, and the supply time is preferably 5% to 20% of the current change period. More preferably, the pulsed large current is preferably 1 to 2 times the set current value, and the supply time is preferably 8% to 15% of the current change period. The set current value is the average current value of the welding current Iw set in the average current setting circuit 11d.

If the high pulse current is less than 0.7 times the set current value or the supply time is less than 5% of the current change cycle, the arc 7 does not expand sufficiently and the intended buried arc stabilization effect is hardly achieved. As the high pulse current or supply time increases, the buried arc stabilization effect due to the arc expansion becomes greater, and when the high pulse current is 1 time or more the set current value or the supply time is 8% or more of the current change cycle, the buried arc stabilization effect becomes noticeable to the welding operator.

On the other hand, if the pulsed high current is more than twice the set current value, or if the supply time is greater than 15% of the current change period, the strong arc force during the high current period begins to cause the molten pool to fluctuate, i.e., to become unstable. In particular, if the pulsed high current is more than three times the set current value, or if the supply time is greater than 20% of the current change period, the buried arc becomes more unstable than when voltage amplitude control, which periodically changes the set voltage, is not used.

(Example)
An example of welding conditions that can improve the stability of buried arc welding by a pulsed large current will be described. A solid wire with a wire diameter of 1.6 mm is used as the welding wire 5, carbon dioxide gas is used as the shielding gas, and buried arc welding is performed with a welding current of 600 A and an arc voltage of 45 V. The set voltage is changed at ±4 V and 100 Hz (period of 10 ms) to change the welding current Iw and stabilize the buried arc. At this time, the buried arc stability can be improved by applying an output current command of 1000 A in a rectangular shape for 0.5 ms at the rise of the welding current Iw.

According to the arc welding method and arc welding apparatus of embodiment 2 configured in this manner, in buried arc welding, in which the welding pool is stabilized by periodically changing the welding current Iw, the stability of buried arc welding can be improved even if the droplet transfer mode does not become a rotating transfer during the high current period.

Furthermore, by setting the target value of the additionally supplied pulsed large current to 0.7 to 3 times the set current value and setting the supply time to a current change period of 5% to 20%, the arc 7 is expanded and made easier to direct to the portion approaching the opening of the buried space 6a relative to the welding wire 5, thereby suppressing the oscillation of the molten pool and improving the stability of buried arc welding.

Furthermore, by determining whether the welding wire 5 has a large diameter and configuring it so that a large pulsed current is supplied only when there is a risk of the buried arc welding becoming unstable, it is possible to suppress the unnecessary additional supply of a large pulsed current. Since applying a large pulsed current when the buried arc is already stable may cause unforeseen adverse effects, by controlling in this way, it is possible to more effectively stabilize the buried arc.

(Embodiment 2)
The arc welding method and the arc welding apparatus according to the second embodiment differ from the first embodiment in that a capacitor for arc start is used to assist the application of a large pulse current, and therefore, the following mainly describes this difference. The other configurations and effects are the same as those of the first embodiment, so the same reference numerals are used for corresponding parts and detailed descriptions are omitted.

Figure 9 is a schematic diagram showing one configuration of an arc welding device according to the second embodiment. For convenience of drawing, the average voltage setting circuit 11c, average current setting circuit 11d, frequency setting circuit 11e, amplitude setting circuit 11f, and voltage detection unit 11g shown in Figure 1 are omitted in Figure 9.

The arc welding device according to the second embodiment includes a capacitor C, a rectifier DR, a charging switch SW1, and a cutoff switch SW2. One end of the capacitor C is connected to ground, and the other end of the capacitor C is connected to the anode of the rectifier DR. The cathode of the rectifier DR is connected to the positive potential of the power supply circuit 11a or the output terminal of the power supply unit 11. The charging switch SW1 is, for example, a thyristor. One end (e.g., an anode) of the charging switch SW1 is connected to the positive potential of the power supply circuit 11a or the output terminal of the power supply unit 11, and the other end (e.g., a cathode) of the charging switch SW1 is connected to the other end of the capacitor C, and opens and closes the connection path between the power supply circuit 11a and the capacitor C. The cutoff switch SW2 is, for example, a power semiconductor switch, one end of which is connected to the cathode of the rectifier DR, and the other end of which is connected to the positive potential of the power supply circuit 11a or the output terminal of the power supply unit 11. The opening and closing of the charging switch SW1 and the cutoff switch SW2 are controlled by the power supply unit 11.

Figure 10 is a flowchart showing the steps of the arc welding method according to the second embodiment. As in the first embodiment, the welding power source 1 performs PWM control so that the welding current Iw changes periodically (step S231). The welding power source 1 determines whether or not it is in a high current period (step S232). If it is in a high current period (step S232: YES), the welding power source 1 closes the charging switch SW1 to charge the capacitor C (step S233). If it is not in a high current period (step S232: NO), the charging switch SW1 and the cutoff switch SW2 are opened to stop charging (step S234).

Then, the welding power source 1 performs control to add a large pulse current, as in the first embodiment (steps S235 to S237). Furthermore, the welding power source 1 opens the cutoff switch SW2 to discharge the capacitor C (step S238). By discharging the charged capacitor C, it is possible to more effectively supply additional large pulse current and stabilize the buried arc. Note that steps S237 and S238 may be executed in the reverse order.

According to the arc welding method and arc welding device of embodiment 2 configured in this manner, in addition to controlling the welding current, a large pulse current can be effectively supplied using capacitor C, thereby improving the stability of buried arc welding.

1 welding power source, 5 welding wire, 6 melting part, 6a buried space, 7 arc, 11 power source unit, 11a power circuit, 12 feed speed control unit

Claims (4)

A consumable electrode arc welding method in which an arc is generated between a welding wire and a base metal by supplying a welding current having an average current of 300 A or more to a welding wire, and a tip end of the welding wire is inserted into a space surrounded by a concave molten portion formed in the base metal to weld the base metal,
a current decreasing period in which the welding current is decreased and a current increasing period in which the welding current is increased are periodically repeated;
Furthermore, when the current decreasing period changes to the current increasing period, a large pulse current is additionally supplied,
The value of the additionally supplied pulsed large current is 0.7 to 3 times the set current value, which is the average value of the welding current,
The time for which the large pulse current is additionally supplied is 5% to 20% of the change cycle of the current increase period and the current decrease period.
Arc welding method. When the diameter of the welding wire is equal to or larger than a predetermined value, the pulsed large current is additionally supplied, and when the diameter of the welding wire is less than the predetermined value, the pulsed large current is not additionally supplied.
The arc welding method according to claim 1 . When the diameter of the welding wire is 1.4 mm or more, the pulse large current is additionally supplied.
The arc welding method according to claim 1 or 2 . A consumable electrode type arc welding device comprising: a power source unit that generates an arc between a welding wire and a base metal by supplying a welding current having an average current of 300 A or more to the welding wire; and a tip end of the welding wire is inserted into a space surrounded by a concave molten portion formed in the base metal by the generated arc to weld the base metal,
The power supply unit includes:
a current decreasing period in which the welding current is decreased and a current increasing period in which the welding current is increased are periodically repeated;
Furthermore, when the current decreasing period changes to the current increasing period, a large pulse current is additionally supplied,
The value of the additionally supplied pulsed large current is 0.7 to 3 times the set current value, which is the average value of the welding current,
The time for which the large pulse current is additionally supplied is 5% to 20% of the change cycle of the current increase period and the current decrease period.
Arc welding equipment.

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