JP2019076929A - Arc-welding device and arc-welding method - Google Patents

Abstract

To provide an arc welding device that is able to effectively hinder occurrence of magnetic blow and interruption of arc in buried arc welding.SOLUTION: An arc-welding device comprises: a power source circuit 11 that supplies a welding current by applying a welding voltage between a welding wire 5 and a base material 4; and a control unit 12 that periodically changes a voltage set for the power source circuit 11 relating to the welding voltage. The arc welding device generates an ark between a leading end part of the welding wire 5 and the base material 4 by supplying the welding current, causes the leading end part to enter a space surrounded by a recessed welded portion formed in the base material 4 by the arc, and thereby welds the base material 4. The arc welding device comprises a voltage detection unit 13 that detects a welding voltage and a current detection unit 14 that detects a welding current. On the basis of the detected welding voltage and welding current, the control unit 12 controls supply of the welding current so as to obtain a constant voltage characteristic. When the welding current decreases, the control unit temporarily permits deviation from the constant voltage characteristic, thereby maintaining the welding current with a predetermined lower limit current value or above.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an arc welding apparatus and an arc welding method.

  One of the welding methods is consumable electrode type arc welding. The consumable electrode type arc welding method is a method of generating an arc between a welding wire fed to a welding portion of a base material and the base material and welding the base material by the heat of the arc. When the base material is a magnetic material, it is known that a magnetic field generated in the base material causes an arc deflection phenomenon or an arc breakage phenomenon called magnetic blowing to cause instability of welding and a defect in welding.

  In particular, in arc welding in which the welding current is periodically varied during welding, arc breakage due to magnetic blow is likely to occur when the welding current decreases. When magnetic blowing occurs, the arc is largely deflected by magnetism, and as a result, the arc length is extended, so the resistance of the arc is increased, the welding current tends to be reduced, and the arc voltage tends to be increased.

  In the conventional pulse arc welding technology, the occurrence of magnetic blow is detected from the decrease of welding current or the tendency of arc voltage to increase, the welding current is kept high, the rigidity of the arc is strengthened, and the wire feeding speed is controlled. Magnetic blowing is prevented by shortening the arc length (for example, Patent Documents 1-4).

  On the other hand, compared to the general gas shield arc welding method, the technology to realize one pass welding of thick plate of 9 to 30 mm is studied by feeding welding wire at high speed and supplying large current. ing. Specifically, one-pass welding of a thick plate can be realized by feeding the welding wire at about 5 to 100 m / min and supplying a large current of 300 A or more. When high-speed delivery and large current supply of the welding wire are performed, the heat of the arc forms a concave melting portion in the base material, and the tip of the welding wire enters the space surrounded by the melting portion. When the front end of the welding wire penetrates deeper than the surface of the base material, the melted portion penetrates to the back side in the thickness direction of the base material, and one-pass welding becomes possible. Hereinafter, the space surrounded by the concave melting portion is referred to as a buried space, and the arc generated between the tip of the welding wire entering the buried space and the base material or the molten portion is appropriately referred to as a buried arc.

JP, 2015-147245, A JP, 2015-157298, A JP, 2016-2564, A JP, 2016-13573, A

  However, in the conventional method, it takes time to detect the magnetic blowing, so a delay may occur before the arc breakage prevention control works after the magnetic blowing occurs, and the magnetic blowing may not be effectively prevented. In addition, in large current welding of 400 A or more, the magnetic field produced by the welding current itself is large, and magnetic blow is more likely to occur than in the case of less than 400 A, and conventional current control can not sufficiently maintain the rigidity of the arc. There is. In particular, in the case of buried arc welding, it is difficult to shorten the arc length because a space is formed in the molten metal by the arc force. Also, even if the arc voltage is excessively lowered and the arc length is forcibly shortened, the arc is buried very deeply, and welding stability can not be ensured, and in some cases, a short circuit occurs and the arc is extremely unstable. Turn Therefore, the conventional method can not effectively suppress the magnetic blowing.

  The object of the present invention is to effectively suppress the occurrence of magnetic blow and arc breakage in buried arc welding by performing welding control so that the welding current does not fall below a predetermined lower limit current value in buried arc welding with constant voltage characteristics. An arc welding apparatus and an arc welding method that can be performed.

  The arc welding apparatus according to the present invention comprises a power supply circuit for supplying a welding current by applying a welding voltage between a welding wire and a base material, and a control unit for periodically changing a set voltage of the power supply circuit related to the welding voltage. And generating an arc between the tip of the welding wire and the base material by supplying a welding current, and advancing the tip into a space surrounded by a concave melting portion formed in the base material by the arc. A consumable electrode type arc welding apparatus for welding the base material, a voltage detection unit for detecting a welding voltage applied by the power supply circuit, and a current for detecting a welding current supplied from the power supply circuit A control unit that controls supply of a welding current so as to obtain a constant voltage characteristic based on the welding voltage and the welding current detected by the voltage detection unit and the current detection unit; At the time of reduction in the contact current to maintain a predetermined lower limit current value or more of the welding current by temporarily permit deviations from the constant voltage characteristic.

  In the present invention, the welding voltage and the welding current periodically fluctuate in buried arc welding of constant voltage characteristics. When the welding current is reduced due to the periodic fluctuation, arc breakage due to magnetic blowing is likely to occur. Therefore, the control unit controls the supply of the welding current so as to obtain the constant voltage characteristic, and temporarily allows the deviation from the constant voltage characteristic when the welding current is reduced, so that the predetermined lower limit current value or more can be obtained. Maintain welding current. By securing a constant welding current, the rigidity of the arc can be maintained, and the occurrence of magnetic blow and arc breakage in buried arc welding can be effectively suppressed. In addition, the operation time for detecting the occurrence of magnetic blowing is unnecessary, and the occurrence of magnetic blowing and arc breakage can be effectively suppressed without delay.

  In the arc welding apparatus according to the present invention, the control unit calculates a current value of the welding current that can obtain a constant voltage characteristic, and controls the supply of the welding current based on the calculated current value. Unit, a comparison unit that compares the current value of the welding current detected by the current detection unit with the threshold, and the constant voltage control unit controls the detected current value if it is less than the threshold And a limiting unit configured to limit the current value of the welding current to the lower limit current value or more.

In the present invention, when the current value of the welding current detected by the current detection unit is equal to or more than the threshold value, the control unit controls the supply of the welding current so as to obtain the constant voltage characteristic. If the current value is less than the threshold value, it is considered that magnetic blow is likely to occur, and the current value of the welding current is limited to a predetermined lower limit current value or more.
Therefore, it is possible to cope with the sign of magnetic blow without delay and effectively suppress the occurrence of magnetic blow and arc breakage in buried arc welding.

  In the arc welding apparatus according to the present invention, the control unit calculates a current value of the welding current that can obtain a constant voltage characteristic, and controls the supply of the welding current based on the calculated current value. Welding current controlled by the constant voltage control unit when the current value calculated by the constant voltage control unit is smaller than the threshold, and a comparison unit that compares the current value calculated by the constant voltage control unit with the threshold value; And a limiting unit configured to limit the current value of the lower limit current value to the lower limit current value or more.

In the present invention, the control unit calculates the current value of the welding current that can obtain a constant voltage characteristic, and controls the supply of the welding current based on the calculated current value. And a control part controls supply of a welding current so that a constant voltage characteristic may be acquired, when a computed current value is more than a threshold, and when the said current value is less than a threshold, it is easy to generate magnetic blow. It is regarded as a state, and the current value of welding current is limited to a predetermined lower limit current value or more.
Therefore, the sign of magnetic blow can be detected earlier, and the occurrence of magnetic blow and arc breakage in buried arc welding can be more effectively suppressed.

  The arc welding apparatus according to the present invention comprises: a clocking unit for measuring a time during which the current value is limited by the limiting unit; and a lower limit current setting unit for setting the lower limit current value to the limiting unit. The lower limit current setting unit increases the lower limit current value when the time during which the current value is limited is a predetermined time or more.

  In the present invention, if the time during which the current value of the welding current is limited continues for a predetermined time or more, it is considered that magnetic blow is likely to occur, so the lower limit current setting unit increases the lower limit current value. Let By increasing the lower limit current value, the rigidity of the arc can be made stronger, and the occurrence of magnetic blow and arc breakage in buried arc welding can be suppressed more effectively.

  In the arc welding apparatus according to the present invention, the average value of the welding current is 400 A or more, and the lower limit current value is 1⁄4 or more of the average value.

In the present invention, since the average value of the welding current is a large current of 400 A or more, the magnetic field generated by the welding current itself becomes large, and magnetic blow is likely to occur as compared with the case of less than 400 A. Therefore, the control unit controls the welding current so as not to fall below a quarter of the average value of the welding current.
By setting the lower limit current value of the welding current in this manner, it is possible to more effectively suppress the occurrence of magnetic blowing and arc breakage in buried arc welding.

  In the arc welding method according to the present invention, a set voltage of a power supply circuit for supplying a welding current is periodically varied by applying a welding voltage between a welding wire and a base material to thereby change the tip portion of the welding wire and the base material. A consumable electrode type arc welding method for welding the base material by causing the tip to generate an arc and causing the tip portion to enter a space surrounded by the concave melting portion formed in the base material by the arc; The welding voltage and welding current applied and supplied in the power supply circuit are detected, and based on the detected welding voltage and welding current, welding current supply is controlled to obtain constant voltage characteristics, and welding current is reduced. In some cases, welding current of a predetermined lower limit current value or more is maintained by temporarily permitting deviation from the constant voltage characteristic.

  In the present invention, the rigidity of the arc can be maintained while securing a constant welding current, and the occurrence of magnetic blowing and arc breakage in buried arc welding can be effectively suppressed.

  According to the present invention, by performing welding control so that the welding current does not fall below a predetermined lower limit current value in buried arc welding with constant voltage characteristics, the occurrence of magnetic blowing and arc breakage in buried arc welding can be effectively suppressed. can do.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows one structure of the arc welding apparatus which concerns on this Embodiment 1. FIG. It is a flowchart which shows the procedure of the arc welding method which concerns on this Embodiment 1. FIG. It is a schematic diagram which shows the arc welding method which concerns on this Embodiment 1. FIG. It is explanatory drawing which shows the arc breakage | shortage prevention effect by limiting a welding current. It is a bar graph which shows that the frequency | count of arc breakage generation | occurrence | production reduced by restrict | limiting welding current. It is a schematic diagram which shows one structure of the arc welding apparatus which concerns on this Embodiment 2. FIG. It is a schematic diagram which shows one structure of the arc welding apparatus which concerns on this Embodiment 3. FIG.

Hereinafter, the present invention will be described in detail based on the drawings showing the embodiments.
(Embodiment 1)
FIG. 1 is a schematic view showing one configuration of the arc welding apparatus according to the first embodiment. The arc welding apparatus according to the first embodiment is a consumable electrode type gas shielded arc welding machine that performs buried arc welding, and includes a welding power source 1, a torch 2 and a wire feeding unit 3.

  The torch 2 is made of a conductive material such as copper alloy and has a cylindrical shape for guiding the welding wire 5 to the welding portion of the base material 4 and supplying the welding current I necessary for generating the arc 7 (see FIG. 3). Have a contact tip of The contact tip is in contact with the welding wire 5 passing therethrough and supplies a welding current I to the welding wire 5. Further, the torch 2 has a hollow cylindrical shape surrounding the contact tip, and has a nozzle for injecting a shield gas to a portion to be welded. The shielding gas is for preventing the oxidation of the base material 4 and the welding wire 5 melted by the arc 7. The shield gas is, for example, a mixed gas of carbon dioxide gas, carbon dioxide gas and argon gas, an inert gas such as argon, or the like.

  The welding wire 5 is, for example, a solid wire, and the diameter thereof is 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 pack wire housed in a pale pack in a helically wound state, or a reel wire wound on a wire reel. The material of the welding wire 5 may be a solid wire such as YGW11, YGW12, YGW15, YGW17, YGW18, YGW19 or the like. However, flux cored wire, metal cored wire, or any other novel wire may be applied as the welding wire 5.

  The wire feeding unit 3 has a feeding roller for feeding the welding wire 5 to the torch 2 and a motor for rotating the feeding roller. The wire feeding unit 3 pulls the welding wire 5 out of the pale pack or the wire reel by rotating the feeding roller, and feeds the drawn welding wire 5 to the torch 2 at a constant speed. The feeding speed of the welding wire 5 is, for example, about 5 to 100 m / min. In addition, the delivery system of this welding wire 5 is an example, and is not specifically limited.

  The welding power source 1 is a power source with a constant voltage characteristic, and includes a power source circuit 11 connected to the contact tip of the torch 2 and the base material 4 via a feeding cable. The power supply circuit 11 is a circuit that outputs a PWM-controlled direct current, and supplies a welding current I by applying a welding voltage V between the welding wire 5 and the base material 4. Welding power source 1 also includes control unit 12 that controls the supply of welding current I, voltage detection unit 13 and current detection unit 14, and feed speed control unit 15 that controls the feed speed of welding wire 5.

  The voltage detection unit 13 detects the welding voltage V applied between the welding wire 5 and the base material 4 by the power supply circuit 11, and outputs the detected voltage value Vd to the control unit 12.

  The current detection unit 14 is supplied to the welding wire 5 from the welding power supply 1 via the torch 2, detects the welding current I flowing through the arc 7, and outputs the detected current value Id to the control unit 12.

  The control unit 12 includes an output voltage setting unit 12a, a constant voltage control unit 12b, a difference amplification unit 12c, a lower limit current setting unit 12d, a comparison unit 12e, and a restriction unit 12f. Each component constituting the control unit 12 may be configured by hardware or may be configured as a functional unit of software. Further, it goes without saying that part may be configured by hardware and the other part may be configured as software and software. The control unit 12 will be described below as a computer having a CPU, a ROM, a RAM, an input / output unit, etc., and realizing each component as software by arithmetic processing of a CPU that executes a control program.

The output voltage setting unit 12a outputs an output voltage setting value Er indicating the output voltage E of the welding power source 1 having constant voltage characteristics to the constant voltage control unit 12b. Output voltage setting unit 12a cycles welding current I at a target frequency, current amplitude and average current based on the average current setting value, frequency setting value and amplitude setting value of welding current I set in welding power source 1 It generates an output voltage set value Er having an arbitrary waveform for fluctuating as needed, and outputs the generated output voltage set value Er to the constant voltage control unit 12b. The output voltage set value Er is, for example, a value that is periodically increased and decreased as represented by a rectangular wave signal.
The average current setting value is a numerical value for setting the average current of the welding current I which fluctuates periodically. When carrying out the arc welding method according to the first embodiment, the average current setting value is an average current of 300 A or more, preferably an average current of 300 A to 1000 A, more preferably 500 A to 800 A. is there.
The frequency setting value is a numerical value for setting a frequency at which the welding voltage V and the welding current I between the base material 4 and the welding wire 5 are periodically varied. When the arc welding method according to the first embodiment is performed, the frequency setting value is a frequency of 10 Hz or more and 1000 Hz or less, preferably 50 Hz or more and 300 Hz or less, more preferably 80 Hz or more and 200 Hz or less.
The above-mentioned amplitude setting value is a numerical value for setting the amplitude of the welding current I which fluctuates periodically. When the arc welding method according to the first embodiment is performed, the amplitude setting value is a current amplitude of 50 A or more, preferably a current amplitude of 100 A to 500 A, and more preferably 200 A to 400 A.

  The constant voltage control unit 12 b electronically varies the inductance of the welding power source 1 to realize a predetermined constant voltage characteristic and control the supply of the welding current I. The constant voltage control unit 12b calculates a welding current control setting value Irc indicating a welding current I which can obtain a predetermined constant voltage characteristic based on the output voltage setting value Er, and the calculated welding current control setting value Irc. Are output to the differential amplification unit 12c via the restriction unit 12f.

Hereinafter, electronic control of the inductance by the constant voltage control unit 12b will be described.
An electrical resistance R and a reactor L exist in the current path of the welding power source 1. The resistance value Rm of the electrical resistance R is an electronically formed resistance including the resistance of the fixed portion caused by the wiring inside the welding power source 1 and the external feeding cable. The inductance value Lm of the reactor L is an electronically formed inductance including an inductance of a fixed amount caused by the winding of the coil and the feeding cable provided inside the welding power source 1. Usually, the resistance value Rm is 0.01 to 0.3 Ω, and the inductance value Lm is 20 to 500 μH.

The welding power source 1 shown in FIG. 1 is equivalent to a circuit in which an electric resistance R, a reactor L, a torch 2 and a base material 4 are connected in series to a power supply circuit 11, and the voltage drop in the torch 2 and the base material 4 is a welding voltage Assuming that V, the output voltage of the power supply circuit 11 satisfies the following equation.
E = Rm.i + Lm.di / dt + v (1)
However,
E: Output voltage Rm of power supply circuit 11: Resistance value Lm of electric resistance R: Inductance value of reactor L i: Value of welding current I v: Value of welding voltage V t: time

If the said Formula (1) is arranged, it will become a following formula (2).
di / dt = (E-v-Rm.i) / Lm (2)

When both sides of the above equation (2) are integrated, the following equation (3) is obtained.
i = ∫ {(E-v-Rm.i) / Lm} .dt (3)

Here, the current value i on the left side of the above equation (3) is set to the welding current control set value (Irc) for controlling the output of the power supply circuit 11, the output voltage E is set to the output voltage set value (Er), The current value i on the right side is set to the current value (Id) of the detected welding current I, the voltage value v is set to the voltage value (Vd) of the detected welding voltage V, and the resistance value (Rm) is set to the external characteristic slope When the value (Rr) and the inductance value (Lm) are respectively replaced with the inductance setting value (Lr), the above equation (3) is expressed by the following equation (4).
Irc = ∫ {(Er−Vd−Rr · Id) / Lr} · dt (4)
However,
Irc: welding current control set value Er: output voltage set value Rr: external characteristic inclination set value Lr: inductance set value Vd: detected value of welding voltage V Id: detected value of welding current I

  The constant voltage control unit 12b sets the current based on the input voltage value Vd, current value Id, and output voltage setting value Er, and the external characteristic inclination setting value Rr and inductance setting value Lr set for the welding power source 1. The amount of change per unit time (Er−Vd−Rr · Id) / Lr of the value is calculated. Then, the constant voltage control unit 12b integrates the amount of change and outputs a welding current control set value Irc obtained by integration to the limiting unit 12f. The set value of welding current I indicated by welding current control set value Irc is represented by the above-mentioned equation (4).

By limiting the lower limit of welding current I, lower limit current setting unit 12 d outputs, to limiting unit 12 f, a lower limit current value Imin for preventing arc breakage due to magnetic blowing. The lower limit current value Imin is a set value for limiting the welding current I to a predetermined lower limit current value Imin or more. The lower limit current value Imin is desirably set to 1/4 or more of the average current of the welding current I, preferably to 1/3 of the average current, and more preferably to 1/2 of the average current.
For example, when the average current of welding current I is 600A and the amplitude is 300A, the lower limit current value Imin may be set to 300A.

The comparison unit 12 e is a component for determining whether or not the welding current I should be limited, and compares the current value Id of the welding current I detected by the current detection unit 14 with a predetermined threshold value, The comparison value indicating the comparison result is output to the limiting unit 12 f. Specifically, when the current value Id of the welding current I is less than the threshold, the comparison unit 12e outputs a comparison value of a negative value to the limiting unit 12f, and when the current value Id is equal to or more than the threshold, “0 The above value is output to the limiting unit 12 f.
The threshold is a value at least equal to or less than the lower limit current value Imin.

  The limiting unit 12 f is a component for limiting the lower limit of the welding current I, and receives the welding current control set value Irc, the lower limit current value Imin, and the comparison value. Limiting portion 12 f selects welding current control set value Irc output from constant voltage control portion 12 b when a comparison value of “0” or more is input, and differential amplification of selected welding current control set value Irc is performed. Output to unit 12c. If the comparison value is a negative value, the lower limit current value Imin output from the lower limit current setting unit 12d is selected, and the selected lower limit current value Imin is output to the difference amplification unit 12c.

  Differential amplification unit 12c amplifies the difference between current value Id output from current detection unit 14 and welding current control set value Irc or lower limit current value Imin output from limitation unit 12f, and amplifies the difference to indicate the difference. The difference value ΔI is output to the power supply circuit 11. That is, when the current value Id of the welding current I is equal to or more than the threshold value, the difference amplification unit 12c outputs a difference value ΔI obtained by subtracting the current value Id from the welding current control set value Irc to the power supply circuit 11. When the current value Id of the welding current I is less than the threshold value, the difference amplification unit 12 c outputs the difference value ΔI obtained by subtracting the current value Id from the lower limit current value Imin to the power supply circuit 11.

  The power supply circuit 11 includes an AC-DC converter that AC-DC converts commercial AC, an inverter circuit that converts AC-DC converted direct current into required AC by switching, a rectifier circuit that rectifies converted AC. The power supply circuit 11 performs PWM control of the inverter so that the difference value ΔI is reduced according to the difference value ΔI output from the difference amplification unit 12 c, and outputs a DC voltage to the welding wire 5. As a result, a periodically varying welding voltage V is applied between the base material 4 and the welding wire 5, and the welding current I is conducted. The power supply circuit 11 can generate the inductance setting value Lr of the welding power supply 1 and the external characteristic inclination setting value Rr electronically in order to control the output such that the above equation (4) is satisfied according to the difference value ΔI. . That is, the power supply circuit 11 basically operates as a power supply having a constant voltage characteristic, and when welding current I decreases, the welding from the constant voltage characteristic is temporarily permitted to perform welding at a predetermined lower limit current value Imin or more. The welding current I can be supplied to the welding wire 5 such that the current I is maintained.

  The welding power source 1 is configured to receive an output instruction signal from the outside through a control communication line (not shown), and the control unit 12 uses the output instruction signal as a trigger to weld to the power supply circuit 11. Start the supply of current I. The output instruction signal is output from, for example, a welding robot (not shown) to the welding power source 1. In the case of a manual welding machine, the output instruction signal is output from the torch 2 side to the welding power source 1 when the hand operation switch provided on the torch 2 side is operated.

FIG. 2 is a flowchart showing the procedure of the arc welding method according to the first embodiment, and FIG. 3 is a schematic view showing the arc welding method according to the first embodiment. First, the pair of base materials 4 to be joined by welding is disposed in the arc welding apparatus, and various settings of the welding power source 1 are performed (step S11). Specifically, as shown in FIG. 3, the plate-shaped first base material 41 and the second base material 42 are prepared, and the end faces 41a and 42a which are to-be-welded parts are butted and arranged at a predetermined welding operation position . If necessary, the first base material 41 and the second base material 42 may be provided with a groove having an arbitrary shape such as Y-shape, re-shape, or I-groove. The first and second base materials 41 and 42 are, for example, steel plates such as mild steel, carbon steel for machine structure, alloy steel for machine structure, etc., and have a thickness of 9 mm or more and 30 mm or less.
And welding power supply 1 sets up welding conditions of welding current I within the range of frequency 10Hz or more and 1000Hz or less, average current 300A or more, and current amplitude 50A or more.

  In addition, the condition setting of the welding current I may be entirely performed by the welding operator, and the welding power source 1 receives execution of the welding method according to the first embodiment at the operation unit, and all the condition settings are automatically performed. It may be configured to In addition, welding power source 1 receives a part of welding conditions such as average current at the operation unit, determines the remaining welding conditions that conform to the received part of welding conditions, and performs the condition setting semi-automatically You may configure.

  After various settings are performed, the welding power source 1 determines whether the output start condition of the welding current I is satisfied (step S12). Specifically, welding power source 1 determines whether or not a welding output instruction signal has been input. When it is determined that the output designating signal is not input and the output start condition of the welding current I is not satisfied (step S12: NO), the welding power source 1 stands by in an input waiting state of the output designating signal.

  When it is determined that the output start condition of the welding current I is satisfied (step S12: YES), the feed speed control unit 15 of the welding power source 1 transmits a wire feed command signal instructing wire feed to the wire feed unit 3 And the welding wire 5 is fed at a predetermined speed (step S13). The feed speed of the welding wire 5 is a constant speed, and is set, for example, in the range of about 5 to 100 m / min. The feed rate may be determined by the feed rate control unit 15 in accordance with the welding current control set value Irc output from the constant voltage control unit 12b, or the welder may feed the wire. The feed rate may be set directly.

Next, control unit 12 of welding power source 1 detects welding voltage V and welding current I by voltage detection unit 13 and current detection unit 14 (step S14), and calculates welding current control setting value Irc (step S15). .
Then, the control unit 12 determines whether the current value Id of the welding current I detected by the current detection unit 14 is less than a threshold (step S16). If it is determined that welding current I is less than the threshold (step S16: YES), control unit 12 limits welding current control set value Irc not to fall below predetermined lower limit current value Imin (step S17). When the process of step S17 is finished, or when it is determined that the detected welding current I is equal to or more than the threshold (step S16: NO), the control unit 12 sets the welding current control set value Irc or the lower limit current value Imin, The difference value ΔI of the current value Id of the welding current I is output to the power supply circuit 11, and the supply of the welding current I is controlled (step S18). The power supply circuit 11 performs PWM control of the output of the welding power supply 1 so that the welding current I matches the welding current control set value Irc or the lower limit current value Imin according to the difference value ΔI output from the control unit 12. That is, welding power source 1 periodically fluctuates at a frequency of 10 Hz or more and less than 1000 Hz, an average current of 300 A or more, and a current amplitude of 50 A or more while maintaining welding current I at the lower limit current value Imin or more. The output is controlled by periodically changing the output voltage set value Er.

  Next, the control unit 12 of the welding power source 1 determines whether to stop the output of the welding current I (step S19). Specifically, welding power source 1 determines whether or not the input of the output instruction signal is continuing. If it is determined that the output of the welding current I is not stopped (step S19: NO), the control unit 12 returns the process to step S13 and continues the output of the welding current I. If it is determined that the output of welding current I is to be stopped (step S19: YES), control unit 12 returns the process to step S12.

  When the welding current I is periodically varied according to the above-described welding conditions and procedure, as shown in FIG. 3, the tip portion 5a of the welding wire 5 and the portion to be welded in a stable state where magnetic blowing and arc breakage do not occur. Concave molten portion 6 consisting of molten metal of base metal 4 and welding wire 5 is formed in base metal 4 by heat of arc 7 generated in the meantime, and tip portion 5a of welding wire 5 is buried and enters space 6a. . When the state of the arc 7 is photographed with a high-speed camera, as shown in the left view of FIG. 3, the welding wire 5 deeply penetrates into the embedded space 6 a and the tip portion 5 a of the welding wire 5 and the bottom portion 61 of the melting portion 6 The first state in which the arc 7 is generated and the second state in which the welding wire 5 shallowly enters the embedded space 6a and the arc 7 is generated between the tip portion 5a and the side portion 62 of the melting portion 6 periodically It has been confirmed that it fluctuates.

Thus, the tip 5 a of the welding wire 5 enters the embedded space 6 a and is surrounded by the molten portion 6, and by periodically changing the welding current I, the tip 5 a of the embedded space 6 a is You can move the position up and down.
In the first state, the distal end 5 a of the welding wire 5 deeply penetrates into the buried space 6 a, and a deep penetration is obtained by the arc 7 irradiated to the bottom 61 of the melting portion 6.
In the second state, the tip portion 5a of the welding wire 5 shallowly enters the buried space 6a, and the molten portion 6 is supported by the force of the arc 7 irradiated to the side portion 62 of the molten portion 6, so the buried space 6a It is maintained in a stable state.
Therefore, the buried space 6a can be stably maintained by periodically changing the welding current I.

FIG. 4 is an explanatory view showing the arc breakage preventing effect by limiting the welding current I. As shown in FIG. The horizontal axis of the graphs shown in FIGS. 4A and 4B represents time, and the vertical axis represents the value of welding current I. FIG. 4A shows the time change of the welding current I when the lower limit of the welding current I is not limited, and FIG. 4B shows the time change of the welding current I when the lower limit of the welding current I is limited There is.
The implementation conditions of buried arc welding for verifying the effect of arc breakage prevention are as follows. The thickness of the base material 4 is 19 mm, the wire diameter of the welding wire 5 is 1.4 mm, the wire feeding speed is 22 m / min, the average value of the welding current I is 600 A, and the output voltage set value Er is 48V. The welding power source 1 periodically fluctuates the welding current I at an amplitude of approximately ± 300 A and a frequency of 140 Hz. The base material 4 is a groove I, has a gap of 4 mm, and uses a water-cooled copper plate as a backing.

Under the above-described welding conditions, the welding current I is entirely reduced as the magnetic blow occurs. As shown in FIG. 4A, when the welding current I is reduced to about 200 A, particularly in a low current region, the rigidity of the arc 7 can not be maintained, which may lead to arc breakage. In the example shown in FIG. 4A, the arc 7 can not be maintained at time = 30 (ms), and the arc 7 is broken.
On the other hand, as shown in FIG. 4B, if the lower limit of the welding current I is limited to 300 A under the same welding conditions, the rigidity of the arc 7 is sufficiently maintained even in the low current region, and arc breakage can be prevented. .

  FIG. 5 is a bar graph showing that limiting the welding current I reduces the number of occurrences of arc breakage. In FIG. 5, the two bars on the left side indicate the number of arc breakage occurrences when the current limit of the welding current I is not applied, and the two bars on the right side indicate the arc break when the current limit of welding current I is applied. Indicates the number of occurrences. The hatched bars and the filled bars respectively show the results obtained by performing the welding experiment twice. As apparent from the bar graph of the experimental results shown in FIG. 5, by limiting the welding current I, the number of occurrences of arc breakage can be dramatically reduced. In the experimental results shown by the hatched bars, the number of arc breaks has been successfully reduced from 89 times to 15 times by performing current limitation.

  According to the arc welding apparatus and the arc welding method according to the first embodiment, in embedded arc welding with constant voltage characteristics, by performing welding control such that welding current I does not fall below predetermined lower limit current value Imin, embedded arc welding is performed. The occurrence of magnetic blowing and arc breakage can be effectively suppressed.

  Further, when the current value Id of the welding current I detected by the current detection unit 14 is less than the threshold value, the control unit 12 according to the first embodiment considers that magnetic blow is likely to occur, and the welding current The control set value Irc is limited to a predetermined lower limit current value Imin or more. Therefore, it is possible to cope with the sign of magnetic blow without delay and effectively suppress the occurrence of magnetic blow and arc breakage in buried arc welding.

Second Embodiment
The arc welding apparatus according to the second embodiment differs from the first embodiment in the configuration relating to the setting of the lower limit current value Imin. Therefore, the difference will be mainly described below. The other configurations and effects are the same as those of the embodiment, and therefore the corresponding portions are denoted by the same reference numerals and the detailed description will be omitted.

  FIG. 6 is a schematic view showing one configuration of the arc welding apparatus according to the second embodiment. The arc welding apparatus according to the second embodiment includes a welding power source 201 similar to that of the first embodiment. The control part 212 which concerns on Embodiment 2 is provided with the time measuring part 12g which time-measures the time which the electric current value of the welding current I is made to limit by the limitation part 12f. The comparison value output from the comparison unit 12e is input to the time counting unit 12g, and the time measurement unit 12g measures the time during which the negative comparison value is input, and counts the lower limit current value Imin when measuring a predetermined time or more. Is outputted to the lower limit current setting unit 12d. When a positive comparison value is input to the timer unit 12g, the timer is reset. When a positive comparison value is input after a negative comparison value is input for a predetermined time or more, the timer unit 12g causes the lower limit current setting unit 12d to change the lower limit current value Imin to a value before the change. Output to

  When the change instruction is output from the timer unit 12g, the lower limit current setting unit 12d increases the lower limit current value Imin and outputs the increased lower limit current value Imin to the limiting unit 12f. In addition, when the release instruction is output from the timer unit 12g, the lower limit current setting unit 12d returns the lower limit current value Imin to the value before the increase and outputs the original lower limit current value Imin to the limiting unit 12f.

  According to the arc welding apparatus and the arc welding method according to the second embodiment, it is considered that magnetic blowing is likely to occur when the state where the current value Id of the welding current I is less than the threshold continues for a predetermined time or more. The lower limit current setting unit 12d increases the lower limit current value Imin. By this control, the rigidity of the arc 7 can be made stronger, and the occurrence of magnetic blow and arc breakage in buried arc welding can be more effectively suppressed.

  In the above embodiment, only the lower limit current value Imin is changed. However, the threshold may be increased or decreased together with the lower limit current value Imin.

(Embodiment 3)
The arc welding apparatus according to the third embodiment is different from that according to the first embodiment in the detection method of the magnetic blow, so the following mainly describes the difference. The other configurations and effects are the same as those of the embodiment, and therefore the corresponding portions are denoted by the same reference numerals and the detailed description will be omitted.

  FIG. 7 is a schematic view showing one configuration of the arc welding apparatus according to the third embodiment. The arc welding apparatus according to the third embodiment includes a welding power source 301 similar to that of the first embodiment. The comparison unit 12e of the control unit 312 according to the third embodiment is not the current value Id of the welding current I detected by the current detection unit 14, but a welding current control setting value Irc output from the constant voltage control unit 12b. The threshold value is compared with a predetermined threshold value, and a comparison value indicating the comparison result is output to the limiting unit 12 f. Specifically, when the welding current control set value Irc is less than the threshold, the comparison unit 12e outputs a comparative value of a negative value to the limiter 12f, and when the welding current control set value Irc is equal to or more than the threshold, A value of “0” or more is output to the limiting unit 12 f.

  According to the arc welding apparatus and the arc welding method of the third embodiment, it is possible to cope with the sign of magnetic blow without delay, and to effectively suppress the occurrence of magnetic blow and arc breakage in buried arc welding. it can.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is indicated not by the meaning described above but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

1,201,301 welding power source 2 torch 3 wire feeding part 4 base metal 5 welding wire 5a tip 6 melting part 6a buried space 61 bottom 62 side 7 arc 11 power circuit 12, 212, 312 control part 12a output voltage setting Section 12b Constant voltage control section 12c Differential amplification section 12d Lower limit current setting section 12e Comparison section 12f Limiting section 12g Time measuring section 13 Voltage detection section 14 Current detection section 15 Feeding speed control section 41 First base material 42 Second base material R Electricity Resistance L Reactor E Setting voltage V Welding voltage I Welding current Vd Welding voltage voltage value Id Welding current current value Er Output voltage setting value Irc Welding current control setting value ΔI Difference value Imin Lower limit current value

Claims (6)

A power supply circuit for supplying a welding current by applying a welding voltage between a welding wire and a base material, and a control unit for periodically changing a set voltage of the power supply circuit related to the welding voltage A consumable electrode for generating an arc between a tip portion of the welding wire and a base material, and advancing the tip portion into a space surrounded by a concave melting portion formed in the base material by the arc to weld the base material Type arc welding apparatus,
A voltage detection unit that detects a welding voltage applied by the power supply circuit;
A current detection unit for detecting a welding current supplied by the power supply circuit;
The control unit
Based on the welding voltage and the welding current detected by the voltage detection unit and the current detection unit, the supply of welding current is controlled so as to obtain a constant voltage characteristic, and when the welding current decreases, the constant voltage characteristic is obtained An arc welding apparatus that maintains welding current above a specified lower limit current value by temporarily permitting deviation of The control unit
A constant voltage control unit that calculates a current value of the welding current that can obtain a constant voltage characteristic and controls supply of the welding current based on the calculated current value;
A comparison unit that compares the current value of the welding current detected by the current detection unit with a threshold value;
The arc welding apparatus according to claim 1, further comprising: a limiting unit configured to limit the current value of the welding current controlled by the constant voltage control unit to the lower limit current value or more when the detected current value is less than a threshold value. . The control unit
A constant voltage control unit that calculates a current value of the welding current that can obtain a constant voltage characteristic and controls supply of the welding current based on the calculated current value;
A comparison unit that compares the current value calculated by the constant voltage control unit with a threshold value;
The arc welding apparatus according to claim 1, further comprising: a limiting unit that limits the current value of the welding current controlled by the constant voltage control unit to the lower limit current value or more when the calculated current value is less than a threshold. . A time measuring unit which measures a time during which the current value is limited by the limiting unit;
A lower limit current setting unit configured to set the lower limit current value in the limiting unit;
The lower limit current setting unit
The arc welding apparatus according to claim 2 or 3, wherein the lower limit current value is increased when the time during which the current value is limited is a predetermined time or more. The average value of welding current is over 400A,
The arc welding apparatus according to any one of claims 1 to 4, wherein the lower limit current value is a quarter or more of the average value. By applying a welding voltage between the welding wire and the base material, the set voltage of the power supply circuit supplying the welding current is periodically varied to generate an arc between the tip of the welding wire and the base material, and the arc is generated by the arc A consumable electrode type arc welding method of welding a base material by causing the tip end to enter a space surrounded by a concave melting portion formed on the base material, and welding the base material,
Detecting welding voltage and welding current applied and supplied by the power supply circuit;
Based on the detected welding voltage and welding current, the supply of welding current is controlled so that constant voltage characteristics can be obtained, and when welding current decreases, temporary deviation from the constant voltage characteristics is permitted. A method of arc welding that maintains the welding current above the lower limit current value.

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