Arc welding method and arc welding device

Abstract

The present application provides an arc welding method and an arc welding device, in submerged arc welding in which a molten pool is stabilized by periodically changing a welding current, even in a case where a droplet transfer mode cannot be a rotating jet transfer during a high current period, the stability of the submerged arc welding is improved. An arc is generated by supplying a welding current of 300 A or more to a welding wire, and a tip of the welding wire is welded to a base material in a space surrounded by a molten portion formed in the base material by the generated arc, in the arc welding method of the consumable electrode type, 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, a pulse high current is additionally supplied when the current reduction period changes to the current increase period.

Description

Technical Field

[0001] This invention relates to a consumable electrode type arc welding method and an arc welding apparatus. Background Technology

[0002] In recent years, the practical application of submerged arc welding has been promoted. Submerged arc welding is achieved by feeding the welding wire at a speed of approximately 5–100 m / min and supplying a high current of 300 A or more. After the high-speed feeding of the welding wire and the supply of high current, a concave molten pool (molten part) is formed in the base metal. The tip of the welding wire enters the concave space formed in the molten pool (the space surrounded by the concave molten part). Hereinafter, this concave space is referred to as the submerged space, and the arc generated between the tip of the welding wire entering the submerged space and the base metal or molten part is appropriately called the submerged arc.

[0003] In submerged arc welding, the shape of the submerged space is prone to change, resulting in molten pool wobbling and thus welding instability. Especially when the opening of the submerged space narrows, wobbling of the molten pool caused by short circuits between the welding wire and the molten pool, accompanied by spatial expansion due to increased pressure inside the submerged space, becomes a major cause of welding instability.

[0004] As a technique for stabilizing the submerged arc, control of periodic variations in the magnitude of the welding current has been developed (e.g., Patent Document 1). Several current variation modes are proposed, which are controls primarily aimed at achieving the following objectives: by making the droplet transition mode during the high-current supply period a rotating jet transition, the arc supports the opening of the submerged space approaching the welding wire, thereby suppressing the shrinkage of the opening.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2018 / 105548

[0008] However, when using thicker welding wire or when the average welding current is low, the droplet transfer pattern is difficult to achieve as a rotating jet transfer, and there are cases where the droplet transfer pattern described above does not occur. That is, sometimes the arc cannot be used to support the opening of the buried space close to the welding wire. Summary of the Invention

[0009] The purpose of this invention is to provide an arc welding method and an arc welding apparatus that can improve the stability of submerged arc welding, even when the droplet transfer morphology cannot become a rotating jet transfer during high current periods, by stabilizing the molten pool through periodic changes in the welding current.

[0010] The arc welding method involved in this method is a consumable electrode arc welding method. An arc is generated between the welding wire and the base material by supplying a welding current with an average current of 300A or more to the welding wire. The tip of the welding wire enters the space surrounded by the concave molten portion formed in the base material to weld the base material. The welding current is periodically reduced during the current reduction period and increased during the current increase period. Furthermore, when the current changes from the current reduction period to the current increase period, a pulsed high current is supplied.

[0011] In this method, submerged arc welding can be stabilized by periodically varying the welding current. During periods of high average welding current, the droplet transfer pattern becomes a rotating jet transfer, and the arc supports the opening of the submerged space approaching the welding wire, thus suppressing the shrinkage of the opening.

[0012] However, when using a large-diameter welding wire, or when the average welding current is low, even during high current periods, the droplet transfer pattern is difficult to achieve a rotating jet transfer, and sometimes the arc cannot support the opening of the buried space. Therefore, in this method, a pulsed high current, larger than the welding current supplied during high current periods, is added. The arc direction moves continuously in the high conductivity region where the arc plasma has already formed, towards the direction where the distance between the tip of the welding wire and the surface of the molten pool forming the buried space is minimized, thus supporting the molten pool through arc pressure. Since the arc expansion increases with the supply of a pulsed high current, the arc direction can vary over a wider range. That is, the arc easily moves towards the portion of the buried space closer to the tip of the welding wire, making it easier to support the opening of the buried space with the arc and stabilizing the weld.

[0013] Furthermore, as the current changes from a decreasing period to a rising period, an additional pulsed current can be supplied to provide the large pulsed current required for the arc to expand.

[0014] The preferred structure of the arc welding method involved in this method is as follows: the value of the additionally supplied pulsed high current is more than 0.7 times and less than 3 times the set current value.

[0015] According to this method, by making the pulsed high current value at least 0.7 times the set current value, the arc is sufficiently expanded. When the welding wire approaches the opening of the buried space, the approaching portion is pushed back by the arc before welding instability occurs, thus suppressing welding instability. If the pulsed high current value is less than 0.7 times the set current value, the arc is not sufficiently expanded, and the arc is difficult to move towards the opening of the buried space relative to the approaching portion of the welding wire, thus failing to suppress welding instability.

[0016] Furthermore, by setting the pulsed high current value to less than three times the set current value, the molten pool can be prevented from shaking due to the arc force caused by the high current. If the pulsed high current value is greater than three times the set current value, the large arc force caused by the high current will act on the molten pool for a long time, causing the molten pool to shake and the submerged arc to become unstable.

[0017] The preferred structure of the arc welding method involved in this method is as follows: the time for additionally supplying the pulsed high current is more than 5% and less than 20% of the variation period during the current rise and the current decrease.

[0018] According to this method, by ensuring that the additional supply time of the pulsed high current is more than 5% of the welding current variation cycle, the arc is sufficiently extended. When the opening of the buried space is close to the welding wire, the arc pushes the approaching portion back before welding instability occurs, thus suppressing welding instability. If the additional supply time of the pulsed high current is less than 5% of the welding current variation cycle, the arc is not sufficiently extended, and the arc is difficult to move towards the opening of the buried space relative to the welding wire, thus failing to suppress welding instability.

[0019] Furthermore, by limiting the additional supply time of the pulsed high current to less than 20% of the welding current variation cycle, it is possible to avoid molten pool shaking due to the arc force caused by the high current. If the additional supply time of the pulsed high current is greater than 20% of the welding current variation cycle, the large arc force caused by the high current will act on the molten pool for a long time, causing the molten pool to shake and the submerged arc to become unstable.

[0020] The preferred structure of the arc welding method involved in this method is as follows: when the diameter of the welding wire is above a given value, an additional pulsed high current is supplied; when the diameter of the welding wire is below the given value, the additional pulsed high current is not supplied.

[0021] According to this method, it is possible to avoid arc instability caused by unnecessarily supplying large current pulses even when the system is already in a stable state.

[0022] The preferred structure of the arc welding method involved in this method is as follows: when the diameter of the welding wire is 1.4 mm or more, an additional pulsed high current is supplied.

[0023] According to this method, it is possible to avoid unnecessary additional supply of large current pulses even when the system is already in a stable state, which could lead to arc instability.

[0024] The arc welding apparatus involved in this method is a consumable electrode type arc welding apparatus. It includes a power supply unit that generates an arc between the welding wire and the base material by supplying a welding current with an average current of 300A or more to the welding wire. The welding wire is positioned so that its tip enters a space surrounded by a concave molten portion of the base material formed by the generated arc, thereby welding the base material. The power supply unit periodically repeats a current-decreasing period (reducing the welding current) and a current-increasing period (increasing the welding current), ensuring that the welding current's time average corresponds to a set current. Specifically, the period from the latter half of the current-decreasing period to the first half of the current-increasing period can be called a low-current period, and the period from the latter half of the current-increasing period to the first half of the current-decreasing period can be called a high-current period. Furthermore, when the current changes from the current-decreasing period to the current-increasing period, a pulsed high current of 0.7 to 3 times the set current is supplied.

[0025] According to this method, by adding a pulsed high current, the arc can be directed toward the portion approaching the opening of the submerged space using the same principle as the above-mentioned arc welding method, thereby improving the stability of submerged arc welding.

[0026] The effects of the invention

[0027] According to the present invention, in submerged arc welding where the weld pool is stabilized by periodically varying the welding current, the stability of submerged arc welding can be improved even when the droplet transfer mode cannot become a rotating jet transfer during high current. Attached Figure Description

[0028] Figure 1 This is a schematic diagram showing a structure of the consumable electrode type arc welding apparatus according to Embodiment 1.

[0029] Figure 2 This is a flowchart illustrating the steps of the arc welding method according to Embodiment 1.

[0030] Figure 3 It is a side cross-sectional view of the base material of the object to be welded.

[0031] Figure 4 This is a schematic diagram illustrating the droplet transfer caused by periodic variations in welding current.

[0032] Figure 5 This is a flowchart illustrating the steps involved in controlling variations in welding current.

[0033] Figure 6 It is a diagram showing the waveform of a large pulse current.

[0034] Figure 7 This is a diagram showing the waveform of welding current without a pulsed high current.

[0035] Figure 8 It is a diagram showing the waveform of the welding current to which a pulsed current is applied.

[0036] Figure 9 This is a schematic diagram showing one structure of the arc welding apparatus according to Embodiment 2.

[0037] Figure 10 This is a flowchart illustrating the steps of the arc welding method according to Embodiment 2.

[0038] Explanation of reference numerals in the attached figures

[0039] 1. Welding power source

[0040] 5. Welding wire

[0041] 6. Melted portion

[0042] 6a Buried Space

[0043] 7. Electric arc,

[0044] 11 Power Supply Department

[0045] 11a power supply circuit

[0046] 12 Feed rate control unit Detailed Implementation

[0047] The following description, with reference to the accompanying drawings, illustrates the arc welding method and arc welding apparatus according to embodiments of the present disclosure. Furthermore, this disclosure is not limited to these illustrations, but is shown in the claims and is intended to include all modifications of the same meaning and scope as the claims. In addition, at least a portion of the embodiments described below can be combined in any manner.

[0048] The present invention will now be described in detail with reference to the accompanying drawings illustrating its embodiments.

[0049] (Implementation Method 1)

[0050] Figure 1 This is a schematic diagram showing a structure of the consumable electrode type arc welding apparatus according to Embodiment 1. The arc welding apparatus according to Embodiment 1 includes a welding power source 1, a welding torch 2, and a wire feed section 3. In submerged arc welding, where the weld pool is stabilized by periodically varying the welding current Iw, the arc welding apparatus according to Embodiment 1 can improve the stability of submerged arc welding even when the droplet transfer pattern cannot become a rotating jet transfer during the high current period by supplying a pulsed high current during the current decrease period to the current increase period.

[0051] The welding torch 2 has a cylindrical conductive tip made of a conductive material such as a copper alloy, which guides the welding wire 5 to the part of the base material 4 to be welded and supplies an electric arc 7 (see reference). Figure 4 The welding current Iw required to generate the arc 7 is supplied to the welding wire 5 inserted inside the contact tip. Furthermore, the welding torch 2 is formed in a hollow cylindrical shape surrounding the contact tip and has a nozzle for injecting shielding gas into the part to be welded. The shielding gas is used to prevent oxidation of the base material 4 molten by the arc 7 and the welding wire 5. Shielding gases may include, for example, carbon dioxide gas, a mixture of carbon dioxide and argon, or inert gases such as argon.

[0052] The welding wire 5 is, for example, a solid welding wire with a diameter of 0.9 mm or more and 1.6 mm or less, and functions as a consumable electrode. The welding wire 5 is, for example, a drum welding wire that is contained in a packaging drum in a spiral wound state, or a coil welding wire wound on a welding wire spool.

[0053] The wire feeding unit 3 includes: a feed roller for feeding the welding wire 5 to the welding torch 2; and an electric motor for rotating the feed roller. The wire feeding unit 3 pulls the welding wire 5 from the wire spool by rotating the feed roller and supplies the pulled-out welding wire 5 to the welding torch 2. In addition, the feeding method of the welding wire 5 is just one example and is not particularly limited.

[0054] The welding power source 1 includes: a power supply unit 11 that is connected to the contact tip of the welding torch 2 and the base material 4 via a power supply cable and supplies welding current Iw; and a feed speed control unit 12 that controls the feed speed of the welding wire 5. Alternatively, the power supply unit 11 and the feed speed control unit 12 can be configured as separate units. The power supply unit 11 includes a power supply circuit 11a that outputs a DC current controlled by PWM, 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.

[0055] The voltage detection unit 11g detects the welding voltage Vw and outputs a voltage value signal Ed, representing the detected voltage value, to the comparison circuit 11i.

[0056] For example, the current detection unit 11h detects the welding current Iw supplied from the welding power source 1 to the welding wire 5 via the welding torch 2 and flowing through the arc 7, and outputs a current value signal Id, which indicates the detected current value, to the output voltage setting circuit 11b.

[0057] The average voltage setting circuit 11c sends an average voltage setting signal, which is used to set the average voltage of the periodically varying welding voltage Vw, to the output voltage setting circuit 11b.

[0058] The average current setting circuit 11d outputs an average current setting signal, used to set the periodically varying 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 Embodiment 1, the average current setting circuit 11d outputs an average current setting signal that represents an average current of 300A or more, preferably an average current of 300A or more but less than 1000A, and more preferably an average current of 500A or more but less than 800A.

[0059] The frequency setting circuit 11e outputs a frequency setting signal to the output voltage setting circuit 11b, which is used to set the frequency at which the welding voltage Vw and the welding current Iw between the base material 4 and the welding wire 5 change periodically. When implementing the arc welding method according to Embodiment 1, the frequency setting circuit 11e outputs a frequency setting signal that represents 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.

[0060] The amplitude setting circuit 11f outputs an amplitude setting signal, used to set the amplitude of the periodically varying welding voltage Vw or welding current Iw, to the output voltage setting circuit 11b. 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.

[0061] When implementing the arc welding method according to Embodiment 1, when the amplitude of the current is set, the amplitude setting circuit 11f outputs an amplitude setting signal, which represents a current amplitude of 50A or more, preferably a current amplitude of 100A or more and 500A or less, and more preferably a current amplitude of 200A or more and 400A or less.

[0062] The output voltage setting circuit 11b generates, for example, an output voltage setting signal Ecr representing a rectangular wave target voltage 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 average voltage and average current, frequency, voltage amplitude, or current amplitude set as the target, and outputs the generated output voltage setting signal Ecr to the comparator circuit 11i.

[0063] 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 the differential signal Ev, which represents their difference, to the power supply circuit 11a.

[0064] The power supply circuit 11a includes an AC-DC converter that performs AC-DC conversion on commercial AC, an inverter circuit that converts the AC-DC converted DC to the required AC via a switch, and a rectifier circuit that rectifies the converted AC. The power supply circuit 11a performs PWM control on the inverter according to the differential signal Ev output from the comparator circuit 11i and outputs voltage to the welding wire 5. As a result, a periodically varying welding voltage Vw is applied between the base material 4 and the welding wire 5, and the welding current Iw is switched on, also varying periodically. Furthermore, the power supply unit 11 is configured to input and output an indication signal to the welding power source 1 via a control communication line (not shown). The power supply unit 11 is triggered by the output indication signal to start supplying the welding current Iw to the power supply circuit 11a. The output indication signal is output from the welding robot to the welding power source 1, for example. In the case of a manual welding machine, the output indication signal is output from the welding torch 2 side to the welding power source 1 when the manual operation switch located on the welding torch 2 side is operated.

[0065] Figure 2 This is a flowchart illustrating the steps of the arc welding method according to Embodiment 1. Figure 3 This is a side cross-sectional view showing the base material 4 to be welded. First, the pair of base materials 4 to be welded are positioned in the arc welding apparatus, and various settings of the welding power source 1 are performed (step S11). Specifically, as follows... Figure 3 As shown, plate-shaped first base material 41 and second base material 42 are prepared, and their end faces 41a and 42a, respectively, are joined together as the parts to be welded, and positioned at the given welding operation location. The first and second base materials 41 and 42 are, for example, steel plates made of mild steel, carbon steel for mechanical structures, alloy steel for mechanical structures, etc. The thickness of the first and second base materials 41 and 42 is, for example, 9 mm or more and 30 mm or less. Furthermore, a bevel may be provided on either the first or second base material 41 as needed. Additionally, a backing plate made of the same metal as the base material, such as copper plate or ceramic, may be used as needed.

[0066] Then, the welding power source 1 sets the welding conditions of welding current Iw within the range of frequency above 10Hz and below 1000Hz, average current above 300A, and current amplitude above 50A.

[0067] Furthermore, the setting of the welding current Iw can be entirely performed by the welding operator, or the welding power source 1 can be configured so that its operating unit receives the welding method described in Embodiment 1 and automatically sets all the conditions. Alternatively, the welding power source 1 can be configured so that its operating unit receives a portion of the welding conditions, such as the average current, and determines the remaining welding conditions that are suitable for the received portion of the welding conditions, and performs the condition setting semi-automatically.

[0068] After performing various settings, the welding power supply 1 determines whether the output start condition for welding current Iw is met (step S12). Specifically, the welding power supply 1 determines whether a welding output indication signal has been input. If it is determined that no output indication signal has been input and the output start condition for welding current Iw is not met (step S12 "No"), the welding power supply 1 goes into standby mode in the output indication signal input waiting state.

[0069] If the condition for starting the output of 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 indicating the feed of the welding wire to the welding wire feed unit 3, and feeds the welding wire 5 at a given speed (step S13). The feed speed of the welding wire 5 is set, for example, in the 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. In addition, the feed speed of the welding wire 5 can be a fixed speed or it can be periodically varied. Furthermore, it can also be configured so that the welding operator can directly set the feed speed of the welding wire.

[0070] Next, the power supply unit 11 of the welding power supply 1 uses the voltage detection unit 11g and the current detection unit 11h to detect the welding voltage Vw and the welding current Iw (step S14), and performs PWM control so that the detected welding voltage Vw and welding current Iw values, frequency and amplitude are consistent with the set welding conditions, and the welding current Iw changes periodically (step S15).

[0071] Next, the power supply unit 11 of the welding power supply 1 determines whether to stop the output of the welding current Iw (step S16). Specifically, the welding power supply 1 determines whether the input of the output indication signal continues. If it is determined that the input of the output indication signal continues and the output of the welding current Iw is not stopped (step S16 "No"), the power supply unit 11 returns the process to step S13 and continues the output of the welding current Iw.

[0072] If it is determined that the output of welding current Iw should be stopped (step S16 "Yes"), the power supply unit 11 returns the process to step S12.

[0073] The following is a summary of the periodic variations in welding current Iw and droplet transfer.

[0074] In the arc welding method according to Embodiment 1, the power supply unit 11 controls the welding current Iw such that the frequency of the welding current Iw is 10Hz or more and 1000Hz or less, the average current is 300A or more, and the current amplitude is 50A or more.

[0075] Preferably, the power supply unit 11 controls the welding current Iw such that the frequency of the welding current Iw is 50Hz or higher and 300Hz or lower, the average current is 300A or higher and 1000A or lower, and the current amplitude is 100A or higher and 500A or lower.

[0076] Figure 4 This is a schematic diagram illustrating the droplet transfer caused by periodic variations in the welding current Iw. Under the aforementioned welding conditions, if the welding current Iw is periodically varied, a concave molten portion 6 is formed in the base material 4, consisting of the molten base material 4 and the molten metal of the welding wire 5, which are formed by the thermal fusion of the base material 4 and the arc 7 generated between the tip 5a of the welding wire 5 and the part to be welded. Furthermore, when the arc 7 is photographed using a high-speed camera, as shown... Figure 4 As shown in the left figure, it is confirmed that the first state in which an arc 7 is generated between the front end 5a of the welding wire 5 and the bottom 61 of the molten portion 6 and the second state in which an arc 7 is generated between the front end 5a and the side 62 of the molten portion 6 alternate periodically.

[0077] Specifically, the process repeats the first state where the arc 7 sputters from the tip 5a of the welding wire 5 towards the bottom 61 of the molten portion 6, and the second state where the arc 7 sputters from the tip 5a of the welding wire 5 towards the side 62 of the molten portion 6. The first state occurs during a low-current period when the average value of the welding current Iw is small, and the second state occurs during a high-current period when the average value of the welding current Iw is large. The first state is characterized by a coarse droplet transfer pattern of the welding wire 5. The second state is characterized, for example, by a rotating jet transfer pattern or a pendulum transfer pattern of the welding wire 5.

[0078] Coarse droplet transfer is an example of a droplet transfer from the tip 5a of the welding wire 5 to the bottom 61 of the molten portion 6. Rotating jet transfer is an example of a droplet transfer from the tip 5a of the welding wire 5 to the side 62 of the molten portion 6. In addition, pendulum transfer is a characteristic droplet transfer pattern in which the liquid column formed at the tip 5a of the welding wire 5 and the arc 7 swing in a pendulum-like manner on the same plane, and the plane is continuously rotated bit by bit around the protruding direction of the welding wire 5 as the central axis.

[0079] The buried space 6a is closed, and the molten metal flows towards the front end 5a of the buried welding wire 5. However, in the second state, the arc 7 splashes towards the side 62 of the molten portion 6, and the molten metal of the molten portion 6 is pushed back in a direction away from the welding wire 5, stabilizing the buried space 6a in a concave state. Additionally, in Figure 4 In the right figure, as a result of the transition through the molten droplets at the tip 5a of the welding wire 5, which is molten by a high current, the tip 5a of the welding wire 5 becomes shorter.

[0080] By varying the first and second states at frequencies above 80 Hz and below 200 Hz, the buried space 6a can be stabilized, thereby improving the stability of submerged arc welding.

[0081] In cases where a large diameter welding wire 5 is used, such as a welding wire 5 with a diameter of 1.4 mm or more, or when the average welding current is small, the droplet transfer morphology in the second state is also difficult to become a rotating jet transfer, and there are cases where the droplet transfer morphology does not occur as described above.

[0082] However, even when using a larger diameter welding wire 5 as described above, a phenomenon contributing to the stabilization of submerged arc welding was observed. This is due to the increased expansion of the arc 7 under high current. In the high conductivity region where the arc plasma has formed, the arc 7 is oriented in a direction that minimizes the distance between the tip 5a of the welding wire 5 and the surface of the molten pool forming the submerged space 6a. Therefore, as the arc 7 expands, it becomes easier for the arc 7 to approach the opening of the submerged space 6a relative to the portion of the welding wire 5 over a larger range. Since it becomes easier to support the approaching portion with the arc 7, welding is stabilized. Furthermore, as the opening of the submerged space 6a is pushed back, the orientation of the arc 7 continuously changes, eventually returning to a steady state, i.e., downward orientation.

[0083] In the above-described submerged arc stabilization method based on arc expansion, it is not necessary to maintain a high current state for an extended period. If the arc 7 initially points towards the portion of the submerged space 6a that is close to the welding wire 5, then this arc 7 will maintain its orientation until the close portion is pushed back, regardless of the magnitude of the welding current Iw. Therefore, as long as a pulsed high current is applied instantaneously (see reference...), the stabilization can be achieved. Figure 6 That's fine. On the contrary, if a high current condition is maintained for a long time, the large arc force acting on the molten pool for a long time will cause the molten pool to become unstable.

[0084] Therefore, in this embodiment, Figure 4 In the welding current variation control shown, as a further addition to the arc stabilization control, an additional pulsed high current is supplied.

[0085] Figure 5This is a flowchart illustrating the steps of controlling welding current variation. Welding power supply 1 performs PWM control to cause the welding current Iw to change periodically (step S31). In other words, welding power supply 1 periodically repeats a current-decreasing period that reduces the welding current Iw and a current-increasing period that increases the welding current Iw. For example, welding power supply 1 can vary the welding current Iw by periodically repeating a period where a voltage higher than the average voltage is set and a period where a voltage lower than the average voltage is set. That is, during the period where the voltage is set higher than the average voltage, the welding current Iw increases, which is the current-increasing period. During the period where the voltage is set lower than the average voltage, the welding current Iw decreases, which is the current-decreasing period. Furthermore, the period from the latter half of the current-decreasing period to the first half of the current-increasing period can also be considered a low-current period, and the period from the latter half of the current-increasing period to the first half of the current-decreasing period can also be considered a high-current period.

[0086] Next, welding power source 1 determines whether the timing is for switching from the current decrease period to the current increase period (step S32). If it is determined that the timing is not for switching from the current increase period (step S32 "No"), welding power source 1 does not apply additional pulsed high current and continues to control the welding current variation.

[0087] If the timing of the switch from a current decrease period to a current increase period is determined (step S32 "Yes"), the welding power source 1 determines whether the diameter of the welding wire 5 is greater than or equal to a given value (step S33). That is, the welding power source 1 determines whether the welding wire 5 is a coarse-diameter welding 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 the welding wire 5 is coarse-diameter by reading the set diameter. A coarse-diameter welding wire 5 refers, for example, a welding wire with a diameter of 1.4 mm or 1.6 mm or more.

[0088] If it is determined that welding wire 5 is not of the correct diameter (step S33 "No"), welding power source 1 does not apply an additional pulsed high current and continues to control the welding current fluctuation. If welding wire 5 is not of the correct diameter, since it is possible to pass through only... Figure 4 The control of the periodic variation of the welding current Iw shown stabilizes the submerged arc 7, so no control of imparting a large pulsed current is performed.

[0089] If it is determined that the welding wire 5 is of a large diameter (step S33 "Yes"), the welding power source 1 supplies an additional pulsed high current when switching from the current reduction period to the current rise period (step S34). That is, the welding power source 1 supplies an additional pulsed high current in coordination with the timing of the welding current Iw turning up.

[0090] Figure 6 It is a diagram showing the waveform of a large pulse current. Figure 7This is a diagram showing the waveform of the welding current Iw without a large pulsed current. Figure 8 This is a diagram showing the waveform of the welding current Iw, which is given a pulse current. Figure 6 to Figure 8 The horizontal axis represents time, and the vertical axis represents the welding current Iw. The welding power source 1 additionally supplies power to stabilize the submerged space 6a in submerged arc welding using a large-diameter welding wire 5. Figure 6 A pulsed high current as shown.

[0091] In order to deliver a large instantaneous pulse current, the welding current Iw needs to increase or decrease rapidly. However, the rate of change that can be achieved depends on the secondary resistance or inductance of the arc welding device. In cases where the secondary power cable is long or coiled, or where the secondary resistance or inductance is high, the welding current Iw cannot increase or decrease rapidly, and a sufficiently high current cannot be output, thus failing to stabilize the submerged arc.

[0092] Therefore, the application of a large pulsed current is used as an additional arc stabilization control, along with... Figure 4 as well as Figure 7 The welding current is controlled and used as shown. That is, as Figure 4 as well as Figure 7 The welding current control shown in the figure includes additional arc stabilization control, which provides an additional pulsed high current supply.

[0093] Typically, such as Figure 7 As shown, the welding current Iw is limited to prevent abrupt changes, ensuring the same waveform of welding current Iw is obtained regardless of whether the secondary-side resistance and inductance are high or low. Welding power supply 1 provides a short-duration pulse of high current during the rise of the controlled welding current Iw, i.e., during the transition from the current decrease period to the current rise period. If an additional pulse of high current is supplied during the rise of welding current Iw, then as... Figure 8 As shown, the rising edge of the welding current Iw can be easily matched to cause the current to increase or decrease rapidly, and the required current can be output to bring the arc 7 close to the opening of the buried space 6a.

[0094] Furthermore, the rise and fall of the welding current Iw is influenced by the secondary resistance and inductance of the welding environment, and is ultimately only an additional stabilization control. Therefore, even if a high current cannot be output, the welding will not become unstable. When a high current can be output, the submerged arc welding is more stable.

[0095] The target value of the additionally supplied pulsed high current is expected to be at least 0.7 times and less than 3 times the set current value, and the supply time is expected to be at least 5% and less than 20% of the current variation period. More preferably, the pulsed high current is expected to be at least 1 time and less than 2 times the set current value, and the supply time is at least 8% and less than 15% of the current variation period. Furthermore, the set current value is the average current value of the welding current Iw set by the average current setting circuit 11d.

[0096] If the pulsed high current is less than 0.7 times the set current value, or the supply time is less than 5% of the current variation period, the arc will not expand sufficiently, and the expected arc stabilization effect will be almost unattainable. As the pulsed high current or supply time increases, the arc stabilization effect brought about by arc expansion becomes greater. If the pulsed high current is more than 1 times the set current value, or the supply time is more than 8% of the current variation period, the welding operator can actually feel the arc stabilization effect.

[0097] 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 variation period, the strong arc force during the high current period begins to become a factor contributing to the instability of the molten pool, i.e., the arc subsidence. 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 variation period, the arc subsidence becomes unstable compared to the case where voltage amplitude control that causes periodic changes in the set voltage is not used.

[0098] (Example)

[0099] This example illustrates welding conditions under which the stability of submerged arc welding can be improved by using a pulsed high current. Using welding wire 5, a solid wire with a diameter of 1.6mm was employed. Carbon dioxide gas was used as the shielding gas, and submerged arc welding was performed with a welding current of 600A and an arc voltage of 45V. Furthermore, the welding current Iw was varied by changing the set voltage at ±4V, 100Hz (period 10ms), to stabilize the submerged arc. At this point, by applying a 1000A output current command in a rectangular pattern over 0.5ms as the welding current Iw rises, the stability of the submerged arc can be improved.

[0100] According to the arc welding method and arc welding apparatus of Embodiment 2 with such configuration, in submerged arc welding where the molten pool is stabilized by periodically changing the welding current Iw, the stability of submerged arc welding can be improved even when the droplet transfer mode cannot become a rotating jet transfer during high current.

[0101] Furthermore, by setting the target value of the additionally supplied pulsed high current to 0.7 times or more and 3 times or less of the set current value, and setting the supply time to 5% or more and 20% or less of the current change cycle, the arc 7 is extended, thereby making it easier for the arc to approach the opening of the submerged space 6a relative to the portion close to the welding wire 5. This suppresses the shaking of the molten pool and improves the stability of submerged arc welding.

[0102] Furthermore, by determining whether the welding wire 5 is of a large diameter, the system limits the supply of pulsed high current only to situations where submerged arc welding may become unstable, thus suppressing the additional supply of unnecessary pulsed high current. If a pulsed high current is applied when the submerged arc is already stable, unpredictable adverse effects may occur. Therefore, by controlling it in this way, the submerged arc can be stabilized more effectively.

[0103] (Implementation Method 2)

[0104] The arc welding method and arc welding apparatus described in Embodiment 2 use a capacitor for arc initiation to assist in imparting a large pulsed current, which differs from Embodiment 1. Therefore, the following mainly describes this difference. Other structures and effects are the same as in Embodiment 1, so the corresponding parts are labeled with the same reference numerals and detailed descriptions are omitted.

[0105] Figure 9 This is a schematic diagram showing one structure of the arc welding apparatus according to Embodiment 2. Additionally, in Figure 9 For ease of diagramming, the following are omitted: Figure 1 The circuits shown are: average voltage setting circuit 11c, average current setting circuit 11d, frequency setting circuit 11e, amplitude setting circuit 11f, and voltage detection unit 11g.

[0106] The arc welding apparatus according to Embodiment 2 includes a capacitor C, a rectifier DR, a charging switch SW1, and a disconnecting 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 semiconductor thyristor. One end of the charging switch SW1 (e.g., the anode) 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 of the charging switch SW1 (e.g., the cathode) is connected to the other end of the capacitor C, thus opening and closing the connection path between the power supply circuit 11a and the capacitor C. The disconnecting 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 power supply unit 11 controls the opening and closing of the charging switch SW1 and the disconnecting switch SW2.

[0107] Figure 10This is a flowchart illustrating the steps of the arc welding method according to Embodiment 2. The welding power supply 1 is controlled by PWM in the same manner as in Embodiment 1, causing the welding current Iw to change periodically (step S231). The welding power supply 1 determines whether it is in a high-current period (step S232). If it is in a high-current period (step S232 "Yes"), the welding power supply 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"), it opens the charging switch SW1 and the cut-off switch SW2 to stop charging (step S234).

[0108] Next, welding power source 1 performs additional pulsed high current control in the same manner as in Embodiment 1 (steps S235 to S237). Then, welding power source 1 opens the cut-off switch SW2, discharging capacitor C (step S238). By discharging the charged capacitor C, the additional pulsed high current can be supplied more effectively, stabilizing the submerged arc. Furthermore, steps S237 and S238 can be performed in reverse order.

[0109] According to the implementation method 2 with such configuration, the arc welding method and arc welding apparatus can effectively supplement the supply of pulsed large current by using a capacitor C in addition to welding current control, thereby improving the stability of submerged arc welding.

Claims

1. An arc welding method, a consumable electrode type arc welding method, wherein an arc is generated between the welding wire and the base material by supplying a welding current with an average current of 300A or more to the welding wire, and the tip of the welding wire enters a space surrounded by a concave molten portion formed in the base material to weld the base material, characterized in that... The periodic repetition of the current reduction period that causes the welding current to decrease and the current increase period that causes the welding current to increase. Furthermore, during the transition from the current decrease period to the current increase period, an additional pulsed large current is supplied. The value of the additional pulsed high current supplied is more than 0.7 times and less than 3 times the average value of the welding current, i.e., the set current value.

2. The arc welding method according to claim 1, characterized in that, The additional supply of the pulsed high current is for a period of more than 5% and less than 20% of the variation period during the current rise and the current decrease.

3. The arc welding method according to claim 1 or 2, characterized in that, If the diameter of the welding wire is above a given value, an additional pulsed high current is supplied; if the diameter of the welding wire is below the given value, no additional pulsed high current is supplied.

4. The arc welding method according to claim 1 or 2, characterized in that, When the diameter of the welding wire is 1.4 mm or more, an additional pulsed high current is supplied.

5. An arc welding apparatus, a consumable electrode type arc welding apparatus, comprising a power supply section for generating an arc between a welding wire and a base material by supplying a welding current of 300A or more with an average current to the welding wire, wherein the tip of the welding wire is inserted into a space surrounded by a concave molten portion of the base material formed by the generated arc for welding the base material. The arc welding apparatus is characterized in that... The power supply unit periodically repeats the current reduction period that decreases the welding current and the current increase period that increases the welding current. Furthermore, during the transition from the current decrease period to the current increase period, an additional pulsed large current is supplied. The value of the additional pulsed high current supplied is more than 0.7 times and less than 3 times the average value of the welding current, i.e., the set current value.

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