Arc welding method and arc welding device

Abstract

To provide an arc-welding method capable of improving the stability of buried arc welding even when a droplet transfer mode in a large current period does not become a rotating transfer in a buried arc-welding which stabilizes a molten weld pool by changing a welding current periodically.SOLUTION: An arc-welding method is a consumable electrode type method for welding a base material by generating an arc by supply of a welding current of average 300 A or more to a welding wire and by making a tip of the welding wire approach the space surrounded by a recessed welding portion formed to the base material by the generated arc. A current decrease period decreasing the welding current and a current increase period increasing the welding current are repeated periodically and further, a pulse large current is additionally supplied at the time of change from the current decrease period to the current increase period.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a consumable electrode arc welding method and an arc welding apparatus. [Background technology]

[0002] In recent years, buried arc welding has come into practical use. Buried arc welding is achieved by feeding the welding wire at about 5 to 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, the concave space is 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 is referred to as the buried arc, as appropriate.

[0003] In buried arc welding, the shape of the buried space is easily changed, which causes the molten pool to oscillate and the welding to become unstable. In particular, when the opening of the buried space shrinks, the welding wire and the molten pool may come into contact with each other and the molten pool may oscillate due to the spatial expansion caused by the pressure increase inside the buried space, which is a major cause of welding instability.

[0004] As a technique 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 during the high current period when a large current is supplied a rotating transfer, thereby supporting the opening of the buried space approaching the welding wire with the arc and suppressing the narrowing of the opening. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 105548 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when a large diameter welding wire is used or when the average welding current is small, the droplet transfer mode is unlikely to be a rotating transfer, and the droplet transfer mode transition as described above may not occur, i.e., the opening of the buried space approaching the welding wire may not be supported by the arc.

[0007] The object of the present invention is to provide an arc welding method and an arc welding apparatus that can improve the stability of buried arc welding, in which the welding pool is stabilized by periodically changing the welding current, even when the droplet transfer mode does not become a rotating transfer during a period of high current. [Means for solving the problem]

[0008] The arc welding method according to the present embodiment is 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 of an average current of 300 A or more to a welding wire, and a 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, in which 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 further, when changing from the current reduction period to the current increase period, a pulsed large current is additionally supplied.

[0009] 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.

[0010] In the arc welding method according to this aspect, the value of the additionally supplied pulsed large current is preferably 0.7 to 3 times the set current value.

[0011] 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 arc pushes back the approaching part 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 high 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 high current. If the value of the pulsed high current is set to more than three times the set current value, the large arc force caused by the high 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.

[0012] In the arc welding method according to this aspect, the time period during which the large pulsed current is additionally supplied is preferably 5% to 20% of the change cycle of the current increase period and the current decrease period.

[0013] 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 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 additional supply time of the pulsed large current is less than 5% of the welding current change cycle, the arc does not sufficiently expand and the arc is unlikely to be directed toward the part of the opening of the buried space approaching the welding wire, making it impossible to prevent the welding from becoming unstable. In addition, by setting the additional supply time of high pulse 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 high current. If the additional supply time of high pulse current is set to more than 20% of the welding current change period, the large arc force caused by the high 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.

[0014] The arc welding method according to the present aspect is preferably configured to additionally supply the large pulsed current when the diameter of the welding wire is equal to or greater than a predetermined value, and to not additionally supply the large pulsed current when the diameter of the welding wire is less than the predetermined value.

[0015] According to this aspect, it is possible to prevent the buried arc from becoming unstable due to an unnecessary additional supply of a large current pulse even though the buried arc is already in a stable state.

[0016] In the arc welding method according to this aspect, it is preferable that the large pulse current is additionally supplied when the welding wire has a diameter of 1.4 mm or more.

[0017] According to this aspect, it is possible to prevent the buried arc from becoming unstable due to an unnecessary additional supply of a large current pulse even though the buried arc is already in a stable state.

[0018] The arc welding apparatus according to the present embodiment is a consumable electrode type arc welding apparatus including a power supply unit that generates an arc between the welding wire and a base metal by supplying a welding current of an average current of 300A or more to the welding wire, and causes a tip of the welding wire to enter a space surrounded by a concave molten portion formed in the base metal by the generated arc to weld the base metal, 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 the current reduction period changes to the current increase period, a pulse high current of 0.7 to 3 times the set current is additionally supplied.

[0019] According to this aspect, by additionally supplying a large pulsed current, the arc can be directed toward the portion approaching the opening of the buried space, based on the same principle as in the above-described arc welding method, thereby improving the stability of buried arc welding. Effect of the Invention

[0020] According to the present invention, in buried arc welding, in which the molten pool is stabilized 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. [Brief description of the drawings]

[0021] [Figure 1] 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. [Diagram 2] 3 is a flowchart showing the procedure of the arc welding method according to the first embodiment. [Diagram 3] FIG. 2 is a side cross-sectional view showing the base material to be welded. [Figure 4] FIG. 2 is a schematic diagram showing droplet transfer caused by periodically varying a welding current. [Diagram 5] 4 is a flowchart showing a procedure for welding current variation control. [Figure 6] 4 is a graph showing a waveform of a large pulse current. [Figure 7] 4 is a graph showing a waveform of a welding current when a large pulse current is not applied. [Figure 8] 4 is a graph showing a waveform of a welding current to which a pulse current is applied. [Figure 9] FIG. 11 is a schematic diagram showing one configuration of an arc welding device according to a second embodiment of the present invention. [Figure 10] 6 is a flowchart showing the procedure of an arc welding method according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] An arc welding method and an arc welding apparatus according to an embodiment 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 indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In addition, at least some of the embodiments described below may be arbitrarily combined.

[0023] 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 apparatus according to the present embodiment 1. The arc welding apparatus 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 apparatus according to the present embodiment 1 makes it possible to improve the stability of buried arc welding by additionally supplying a pulsed large 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 high current period.

[0024] Torch 2 is made of a conductive material such as a copper alloy, and has a cylindrical contact tip that guides welding wire 5 to the part to be welded of base material 4 and supplies welding current Iw required to generate arc 7 (see FIG. 4). The contact tip comes into contact with welding wire 5 passing through it and supplies welding current Iw to welding wire 5. 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 base material 4 and welding wire 5 melted by 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, or the like.

[0025] The welding wire 5 is, for example, a solid wire having 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 around a wire reel.

[0026] 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 rotates the feed roller to pull out the welding wire 5 from the wire reel and supply 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.

[0027] 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 a 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 supply 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.

[0028] 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.

[0029] The current detection unit 11h detects, for example, the welding current Iw that is supplied from the welding power source 1 via 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.

[0030] The average voltage setting circuit 11c outputs an average voltage setting signal for setting the average voltage of the periodically varying welding voltage Vw to the output voltage setting circuit 11b.

[0031] The average current setting circuit 11d outputs an average current setting signal for setting the average current of the periodically varying welding current Iw to the output voltage setting circuit 11b and the feed speed control unit 12. When performing 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, and more preferably an average current of 500 A or more and 800 A or less.

[0032] The frequency setting circuit 11e outputs to the output voltage setting circuit 11b a frequency setting signal for setting a frequency that periodically changes the welding voltage Vw and the welding current Iw between the base material 4 and the welding wire 5. When performing 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.

[0033] The amplitude setting circuit 11f outputs an amplitude setting signal to the output voltage setting circuit 11b to set 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 fluctuating welding voltage Vw, or the current difference between the minimum and maximum current values ​​of the fluctuating welding current Iw. When carrying out the arc welding method according to the first embodiment, in setting 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.

[0034] The output voltage setting circuit 11b generates an output voltage setting signal Ecr indicating, for example, a rectangular wave target voltage so that the welding voltage Vw and welding current Iw become the target average voltage, average current, frequency, voltage amplitude or current amplitude 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 section, and outputs the generated output voltage setting signal Ecr to the comparison circuit 11i.

[0035] The comparison circuit 11i compares the voltage value signal Ed output from the voltage detection section 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.

[0036] 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 a 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 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.

[0037] 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 joined by welding is placed on 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 materials, or ceramics 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.

[0038] All of the conditions for the welding current Iw may be set by a welding operator, or the welding power source 1 may be configured to automatically set all of the conditions by accepting an instruction to carry out the welding method according to the present embodiment 1 at an operation unit. Also, the welding power source 1 may be configured to semi-automatically set the conditions by accepting some of the welding conditions, such as the average current, at an operation unit and determining the remaining welding conditions that are compatible with the accepted part of the welding conditions.

[0039] After various settings are made, the welding power source 1 determines whether or not the output start condition of the welding current Iw is satisfied (step S12). Specifically, the welding power source 1 determines whether or not a welding output instruction signal has been input. If it is determined that the output instruction signal has not been input and the output start condition of the welding current Iw is not satisfied (step S12: NO), the welding power source 1 waits for the input of an output instruction signal.

[0040] When it is determined that the output start condition of the welding current Iw is satisfied (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 wire feed speed may be directly set by a welding operator.

[0041] 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).

[0042] 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 or not 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 the output of the welding current Iw.

[0043] When 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.

[0044] Below, an overview of the periodic variation of the welding current Iw and the droplet transfer will be given. 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.

[0045] Fig. 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 made of the molten metal of the welding wire 5 is formed in the base material 4. 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 Fig. 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.

[0046] 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 when the average value of the welding current Iw is small, and the second state occurs during a large current period when 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 stabilizes in a concave state. Note that in the right diagram of Fig. 4, the tip 5a of the welding wire 5 has become shorter as a result of the transfer of droplets from the tip 5a of the welding wire 5 melted by the large current. By varying such first state and second state at a frequency not less than 80 Hz and not more than 200 Hz, the buried space 6a can be stabilized, and the stability of buried arc welding can be improved.

[0047] 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 rotating transfer even in the second state, and the transition of the droplet transfer mode as described above may not occur.

[0048] However, even in the above case where a thick-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 forming the buried space 6a is the smallest in the high electrical conductivity region where the arc plasma is already formed. Therefore, when the arc 7 spreads more, the arc 7 tends 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 easily supported by the arc 7, so that the welding is stabilized. 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.

[0049] 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 FIG. 6) instantaneously. On the contrary, if the high current condition continues for a long time, the large arc force acts on the molten pool for a long time, which causes the molten pool to become unstable.

[0050] Therefore, in this embodiment, in addition to the welding current variation control shown in FIG. 4, a large pulse current is additionally supplied as an additional arc stabilization control.

[0051] FIG. 5 is a flowchart showing a procedure of the welding current variation control. The welding power source 1 performs PWM control so that the welding current Iw varies 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.

[0052] Next, the welding power source 1 determines whether or not 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 the welding current variation control.

[0053] 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 or not 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 or not the welding wire 5 is a large-diameter wire. The operator can set the diameter of the welding wire 5 used in the welding power source 1, and the welding power source 1 can determine whether or not the welding wire 5 is large-diameter by reading out the set diameter. A large-diameter welding wire 5 is, for example, a wire having a diameter of 1.4 mm or 1.6 mm or more.

[0054] If it is determined that the welding wire 5 is not thick (step S33: NO), the welding power source 1 continues the welding current variation control without additionally applying a large pulse current. If the welding wire 5 is not thick, the control for applying a large pulse current is not performed because the buried arc 7 can be stabilized by only periodically changing the welding current Iw shown in FIG.

[0055] 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). That is, 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.

[0056] Fig. 6 is a graph showing the waveform of a large pulse current, Fig. 7 is a graph showing the waveform of a welding current Iw when no large pulse current is applied, and Fig. 8 is a graph showing the waveform of a welding current Iw when a pulse current is applied. In Figs. 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 Fig. 6 in order to stabilize buried space 6a.

[0057] However, in order to apply 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.

[0058] Therefore, the application of a large pulsed current is used as additional arc stabilization control in combination with the welding current control shown in Figures 4 and 7. In other words, a large pulsed current is additionally supplied as additional arc stabilization control in the welding current control shown in Figures 4 and 7.

[0059] Normally, as shown in Fig. 7, the welding current Iw is limited so as not to 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-time pulsed 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 a pulsed large current is additionally supplied when the welding current Iw rises, as shown in Fig. 8, it becomes easier to change the current suddenly in accordance 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.

[0060] The rise and fall behavior of the welding current Iw at 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.

[0061] 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.

[0062] If the pulsed large 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 pulsed large current or supply time increases, the buried arc stabilization effect due to the arc expansion becomes greater, and when the pulsed large 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.

[0063] On the other hand, if the pulsed high current is more than twice the set current value or the supply time is more 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 the supply time is more than 20% of the current change period, the buried arc becomes more unstable than when voltage amplitude control that periodically changes the set voltage is not used.

[0064] (Example) An example of welding conditions that can improve the stability of buried arc welding by using 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 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 (cycle 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.

[0065] According to the arc welding method and arc welding apparatus of embodiment 2 configured as described above, in buried arc welding, in which the molten 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.

[0066] Furthermore, by setting the target value of the additionally supplied pulsed large current to be 0.7 to 3 times the set current value and setting the supply time so that the current change period is 5% to 20%, the arc 7 is expanded and made easier to direct toward the approaching portion of 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.

[0067] Furthermore, by determining whether the welding wire 5 has a large diameter and configuring the system to supply a large pulsed current only when there is a risk of the buried arc welding becoming unstable, it is possible to suppress the additional supply of unnecessary large pulsed current. Since supplying a large pulsed current when the buried arc is already stable may cause unexpected adverse effects, by controlling in this way, the buried arc can be more effectively stabilized.

[0068] (Embodiment 2) The arc welding method and 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 this difference will be mainly described below. 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 description will be omitted.

[0069] Fig. 9 is a schematic diagram showing one configuration of an arc welding device according to embodiment 2. For convenience of drawing, the average voltage setting circuit 11c, the average current setting circuit 11d, the frequency setting circuit 11e, the amplitude setting circuit 11f, and the voltage detection unit 11g shown in Fig. 1 are omitted in Fig. 9.

[0070] 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 the 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 (for example, 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 (for example, 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, and one end of the cutoff switch SW2 is connected to the cathode of the rectifier DR, and the other end of the cutoff switch SW2 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 is controlled by the power supply unit 11.

[0071] 10 is a flowchart showing the procedure 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).

[0072] Next, the welding power source 1 performs control to add a large pulse current (steps S235 to S237) as in the first embodiment. Furthermore, the welding power source 1 opens the cutoff switch SW2 to discharge the capacitor C (step S238). By discharging the charged capacitor C, a large pulse current can be additionally supplied more effectively, and the buried arc can be stabilized. Note that steps S237 and S238 may be executed in the reverse order.

[0073] According to the arc welding method and arc welding apparatus of embodiment 2 configured as described above, in addition to controlling the welding current, a large pulsed current can be effectively supplied using capacitor C, thereby improving the stability of buried arc welding. [Explanation of symbols]

[0074] 1 welding power source, 5 welding wire, 6 molten part, 6a buried space, 7 arc, 11 power source unit, 11a power source circuit, 12 feed speed control unit

Claims

1. 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.

2. 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.

3. 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.

4. 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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