JP6748556B2 - Arc welding method and arc welding apparatus - Google Patents

Description

The present invention relates to a consumable electrode type arc welding method and an arc welding apparatus.

One of welding methods is a consumable electrode type gas shield arc welding method. The gas shield arc welding method is a method in which an arc is generated between the welding wire fed to the welded part of the base material and the base material, and the base material is welded by the heat of the arc. In order to prevent the base metal from being oxidized, welding is performed while injecting an inert gas around the weld. If it is a thin plate of about 5 mm, the butt joint of the base materials can be welded in one pass.

In addition, there is a technique that realizes one-pass welding of a thick plate of 9 to 30 mm by feeding a welding wire at a higher speed and supplying a large current as compared with a general gas shield arc welding method. Specifically, by feeding the welding wire at about 5 to 100 m/min and supplying a large current of 300 A or more, one-pass welding of the thick plate can be realized. When the welding wire is fed at high speed and supplied with a large current, a concave molten portion is formed in the base material by the heat of the arc, and the tip of the welding wire enters the space surrounded by the molten portion. When the tip portion of the welding wire enters deeper than the surface of the base material, the molten portion penetrates to the back surface side in the thickness direction of the base material, enabling one-pass welding. Hereinafter, the space surrounded by the concave molten portion is referred to as a buried space, and the arc generated between the tip portion of the welding wire entering the buried space and the base material or the molten portion is appropriately referred to as a buried arc.

Furthermore, in gas shielded arc welding, the inductance and external characteristics of the welding power source influence the stability of the welding state, and a technology that achieves the optimum inductance and external characteristics by electronic control according to the welding method etc. (For example, Patent Document 1).

Japanese Patent No. 5186227

On the other hand, the inventors of the present application have found that in the buried arc welding, the buried space can be stably maintained by periodically varying the welding current. The welding current can be changed, for example, by periodically changing the set voltage of the constant voltage characteristic power supply. Usually, the base material melted by the heat of the arc and the molten metal of the welding wire flow in the direction in which the buried space is closed and the tip of the welding wire is buried. When the tip of the welding wire comes into contact with the closed melted portion and short-circuits, the welding becomes significantly unstable. However, if the welding current is changed periodically, the position of the tip of the welding wire that has entered the buried space moves up and down within one cycle of current change. When the position of the wire tip is high, the arc is applied to the side portion of the melted portion, and the closing of the melted portion is suppressed by the force of the arc. As described above, the buried space can be stably maintained by periodically changing the welding current.

However, in the above method, the state transition is repeated between the state where the wire tip position in the buried space is low and the state where it is high, but the external characteristics suitable for stabilizing each state or state transition also vary, With welding control using constant external characteristics, even if the buried space can be maintained, the welding state may not always be stable.

The present invention has been made in view of the above circumstances, and an object thereof is to perform welding in a buried arc welding by varying the welding current while periodically maintaining the buried space by periodically varying the welding current. An object of the present invention is to provide an arc welding method and an arc welding apparatus capable of suppressing the destabilization of the state.

The arc welding method according to the present invention supplies a welding wire to a welded portion of a base material and supplies a welding current to the welding wire from a welding power source so that the tip portion of the welding wire and the welded portion are welded to each other. A consumable electrode for welding the base material by causing an arc to occur and causing the tip to enter the space surrounded by the concave molten portion formed in the base material by the arc generated between the tip and the welded portion. In the arc welding method of the formula, by varying the welding current, a first state in which the tip portion of the welding wire deeply enters the space and a second state in which the tip part shallowly enters the space are periodically performed. And the external characteristics relating to the welding current and voltage of the welding power source are varied in synchronization with the variation of the welding current.

In the present invention, the tip of the welding wire enters the buried space surrounded by the concave molten portion, and a buried arc is generated. Specifically, the tip of the welding wire is surrounded by the melted portion, and by periodically varying the welding current, the wire tip position in the buried space can be raised or lowered. An arc occurs between the bottom and the sides of the.
In the first state, the distal end of the welding wire deeply penetrates into the buried space, and a deep penetration is obtained by the arc radiated to the bottom of the molten portion.
The base metal melted by the heat of the arc and the molten metal of the welding wire tend to flow in the direction in which the buried space is closed and the tip of the welding wire is buried, but in the second state, the tip of the welding wire is closed. Enters the buried space shallowly, and the melted portion is supported by the force of the arc irradiated to the side of the melted portion, so that the buried space is maintained in a stable state.
Further, the external characteristic of the welding power source is periodically changed in synchronization with the change of the welding current. The external characteristic can be expressed as a variation amount of the welding voltage with respect to a unit variation amount of the welding current output from the welding power source having the constant voltage characteristic. The amount of change is called the external characteristic slope. Generally, the smaller the external characteristic gradient, the stronger the self-control action of the arc length, and the larger the fluctuation of the welding current with respect to the change of the arc length due to the disturbance. On the contrary, the larger the external characteristic gradient, the smaller the fluctuation of the welding current with respect to the change of the arc length due to the disturbance, and the smaller the self-control action of the arc length.
By setting the external characteristic of the welding power source to a value suitable for the first state and the second state, or the transition state between the states, the welding state can be more effectively stabilized.

The arc welding method according to the present invention increases the gradient of the external characteristic when increasing the welding current, and decreases the gradient of the external characteristic when decreasing the welding current.

According to the present invention, in the first state where the welding current is small, the inclination of the external characteristics is small and the self-control action of the arc length is strong. Therefore, the position of the tip of the welding wire can be accurately controlled. Therefore, it is possible to prevent the welding state from becoming unstable due to the tip portion of the welding wire coming into contact with the molten portion.
On the other hand, in the second state where the welding current is large, the gradient of the external characteristic is large, and the fluctuation of the welding current due to disturbance can be suppressed. Therefore, by suppressing the disturbance of the welding current due to the disturbance, it is possible to suppress the waving of the molten pool due to the disturbance and avoid the instability of the welding state.
In this way, it is possible to effectively suppress instability due to fluctuations in the welding current.

In the arc welding method according to the present invention, a speed at which the welding wire is fed is constant, the welding power source has a constant voltage characteristic, and the welding is performed by periodically changing a set voltage of the welding power source. When the set voltage of the welding power source is set to the first voltage by periodically varying the current, the slope of the external characteristic is set to the first predetermined value, and the set voltage of the welding power source is set higher than the first voltage. When setting to the second voltage, the slope of the external characteristic is set to a second predetermined value larger than the first predetermined value.

In the present invention, the welding wire is fed at a constant speed, and the setting voltage of the welding power source having a constant voltage characteristic is changed, thereby changing the welding current and raising or lowering the wire tip position in the buried space. it can.
When a low first voltage is set as the setting voltage of the welding power source, the inclination of the external characteristic is set to a small first predetermined value, and when a high second voltage is set as the setting voltage of the welding power source, the inclination of the external characteristic is large. The second predetermined value. In this way, the simple control of switching the setting voltage of the welding power source and the inclination of the external characteristic can increase the self-control action of the arc length in the first state and reduce the disturbance of the welding current in the second state. ..

The arc welding method according to the present invention electronically varies the external characteristic by controlling the welding current supplied by the welding power source.

According to the present invention, even when the welding current is a large current and fluctuates at a high frequency, the external characteristics of the welding power source can be electronically varied in synchronization with the variation of the welding current.

In the arc welding method according to the present invention, the welding current is changed so that the frequency of the welding current is 10 Hz or more and 1000 Hz or less and the average current is 300 A or more.

In the present invention, a welding current having an average current of 300 A or more is supplied to the welding wire, and a buried arc is generated. The concave molten metal formed on the base material by the buried arc may be corrugated and the welding state may become unstable. However, in the present invention, by varying the welding current at a frequency of 10 Hz or more and 1000 Hz or less, the molten metal can be slightly vibrated at a frequency higher than the large undulation cycle of the molten metal, and the undulation can be suppressed. Therefore, the welding state can be stabilized more effectively.

An arc welding apparatus according to the present invention includes a power supply unit that supplies a welding current to a welding wire fed to a welded portion of a base material, and by supplying the welding current to the welding wire, the tip of the welding wire. An arc between the welded portion and the welded portion, and the tip portion is advanced into a space surrounded by a concave molten portion formed in the base metal by the arc generated between the tip portion and the welded portion. A consumable electrode type arc welding apparatus for welding a material, wherein the first state in which the tip portion of the welding wire deeply enters the space and the first state in which the welding wire shallowly enters by changing the welding current. A state changing unit that periodically changes the two states, and an external characteristic changing unit that changes the external characteristics related to the welding current and voltage of the power supply unit in synchronization with the changes in the welding current.

According to the present invention, as described above, by periodically varying the welding current, a deep penetration can be obtained while maintaining the buried space in a stable state, and the welding state becomes unstable due to the variation of the welding current. Can be suppressed.

According to the present invention, in buried arc welding, arc welding capable of suppressing the destabilization of the welding state due to the fluctuation of the welding current while stably maintaining the buried space by periodically changing the welding current. A method and an arc welding apparatus are provided.

It is a schematic diagram which shows one structure of the arc welding apparatus which concerns on this Embodiment 1. 3 is a flowchart showing the procedure of the arc welding method according to the first embodiment. It is a sectional side view which shows the base material of a welding target. It is a graph which shows the change of an external characteristic inclination setting signal and welding current. It is a schematic diagram which shows the arc welding method which concerns on this embodiment. 6 is a graph showing changes in a set voltage and an external characteristic slope set value. It is a graph which shows the increase/decrease aspect of welding current by variation of external characteristic inclination set value. It is a graph which shows the conditions of welding current and voltage which realize a buried arc. It is a conceptual diagram which shows the relationship between the wire diameter and wire protrusion length, and the conditions of the welding current and voltage which implement|achieve a buried arc. It is a graph which shows an example of the conditions of the welding current and voltage which implement|achieve a buried arc in the case where a wire diameter is 1.6 mm and the projection length of a welding wire is 25 mm. It is a chart which shows the experimental result of buried arc welding with a photograph. It is a chart which shows the experimental result of buried arc welding by a schematic diagram.

Hereinafter, the present invention will be described in detail with reference to the drawings showing an embodiment thereof.
FIG. 1 is a schematic diagram showing a configuration of an arc welding device according to the present embodiment. The arc welding apparatus according to the present embodiment is a consumable electrode type gas shield arc welder capable of butt-welding a base material 4 having a plate thickness of 9 to 30 mm in one pass, and includes a welding power source 1, a torch 2, and a torch 2. The wire feeding unit 3 is provided.

The torch 2 is made of a conductive material such as a copper alloy and has a cylindrical shape that guides the welding wire 5 to the welded portion of the base material 4 and supplies the welding current I necessary for generating the arc 7 (see FIG. 5). It has a contact tip. The contact tip comes into contact with the welding wire 5 passing through the inside thereof and supplies the 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 the welded portion. The shield gas is for preventing the base material 4 and the welding wire 5 melted by the arc 7 from being oxidized. The shield gas is, for example, carbon dioxide gas, a mixed gas of 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, has 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 pack wire housed in a pail pack in a spirally wound state, or a reel wire wound on a wire reel.

The wire feeding unit 3 has a feeding roller that feeds the welding wire 5 to the torch 2, and a motor that rotates the feeding roller. The wire feeding unit 3 draws the welding wire 5 from the pail 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. The method of feeding the welding wire 5 is an example and is not particularly limited.

The welding power source 1 is connected to the contact tip of the torch 2 and the base material 4 via the power feeding cable, and the power source unit 11 for supplying the welding current I and the feeding speed control unit for controlling the feeding speed of the welding wire 5. 12 and. The power supply unit 11 and the feeding speed control unit 12 may be separately configured. The power supply unit 11 is a power supply having a constant voltage characteristic and outputs a PWM-controlled DC current, a current setting change amount calculation circuit 11b, a current setting integration circuit 11c, a difference amplification circuit 11d, and an output voltage setting circuit 11e. An inductance setting circuit 11f, an external characteristic setting circuit 11g, a frequency setting circuit 11h, a current amplitude setting circuit 11i, an average current setting circuit 11j, a current detection unit 11k, and a voltage detection unit 11l.

The voltage detection unit 11l detects the welding voltage V and outputs a voltage value signal Vd indicating the detected voltage value to the current setting change amount calculation circuit 11b.

The current detection unit 11k detects, for example, the welding current I supplied from the welding power source 1 to the welding wire 5 through the torch 2 and flowing through the arc 7, and outputs the current value signal Id indicating the detected current value as the current setting change amount. It outputs to the calculation circuit 11b and the difference amplifier circuit 11d.

The frequency setting circuit 11h outputs to the output voltage setting circuit 11e a frequency setting signal for setting a frequency for periodically varying the welding voltage V and the welding current I between the base material 4 and the welding wire 5. When carrying out the arc welding method according to the present embodiment, the frequency setting circuit 11h outputs a frequency setting signal indicating a frequency of 10 Hz or more and 1000 Hz or less, preferably a frequency of 50 Hz or more and 300 Hz or less, and more preferably a frequency of 80 Hz or more and 200 Hz or less. Output.

The current amplitude setting circuit 11i outputs an amplitude setting signal for setting the amplitude of the welding current I that fluctuates periodically to the output voltage setting circuit 11e. When performing the arc welding method according to the present embodiment, the current amplitude setting circuit 11i has a current amplitude of 50 A or more, preferably 100 A or more and 500 A or less, and more preferably 200 A or more and 400 A or less. Output the setting signal.

The average current setting circuit 11j outputs to the output voltage setting circuit 11e an average current setting signal for setting the average current of the welding current I that fluctuates periodically. When performing the arc welding method according to the present embodiment, the average current setting circuit 11j, the average current of 300A or more, preferably the average current of 300A or more 1000A or less, more preferably the average current of 500A or more 800A or less. The indicated average current setting signal is output.

The output voltage setting circuit 11e is a circuit that outputs an output voltage setting signal Er indicating the set voltage of the welding power source 1 having a constant voltage characteristic to the current setting change amount calculation circuit 11b. The output voltage setting circuit 11e is for periodically varying the welding current I with a target frequency, current amplitude, and average current based on the frequency setting signal, amplitude setting signal, and average current setting signal output from each unit. The output voltage setting signal Er having an arbitrary waveform is generated, and the generated output voltage setting signal Er is output to the current setting change amount calculation circuit 11b. The output voltage setting signal Er is, for example, a rectangular wave signal.

The inductance setting circuit 11f outputs an inductance setting signal Lr indicating the inductance of the welding power source 1 to the current setting change amount calculation circuit 11b. In the present embodiment, the inductance setting signal Lr is a constant level signal.

The external characteristic setting circuit 11g outputs, to the current setting change amount calculation circuit 11b, an external characteristic inclination setting signal Rr indicating an external characteristic inclination that varies in synchronization with the variation of the output voltage setting signal Er. The external characteristic slope setting signal Rr is, for example, a rectangular wave signal and outputs a signal in phase with the output voltage setting signal Er. That is, when the rectangular-wave output voltage setting signal Er output from the output voltage setting circuit 11e is at a low level, the external characteristic setting circuit 11g outputs a low level external characteristic slope setting signal Rr to output the output voltage setting signal. When Er is at high level, the external characteristic setting circuit 11g outputs a high level external characteristic inclination setting signal Rr (see FIG. 4). The higher the signal level of the external characteristic inclination setting signal Rr, the larger the external characteristic inclination.

The current setting change amount calculation circuit 11b, the current setting integration circuit 11c, and the difference amplification circuit 11d are circuits for electronically varying the external characteristic inclination of the welding power source 1.

Electronic control of the inclination of the external characteristic will be described.
An electric resistance R and a reactor L exist in the energization path of the welding power source 1. The resistance value Rm of the electric resistance R is a resistance value that is electronically formed, including a fixed resistance value due to the internal wiring of the welding power source 1, the external power supply cable, and the like. The inductance value Lm of the reactor L is an inductance value that is electronically formed including the fixed inductance value caused by the routing of the coil and the power supply cable provided inside the welding power source 1. Usually, the resistance value Rm is 0.01 to 0.3Ω 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 source circuit 11a, and a drop voltage in the torch 2 and the base material 4 is a welding voltage. When V is set, the output voltage of the power supply circuit 11a satisfies the following formula.
E=Rm·i+Lm·di/dt+v... (1)
However,
E: Output voltage Rm of power supply circuit 11a: 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

When the above equation (1) is arranged, the following equation (2) is obtained.
di/dt=(Ev-Rm·i)/Lm (2)

Integrating both sides of the above equation (2) gives the following equation (3).
i=∫{(Ev-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 11a, 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 replaced with the inductance setting value (Lr), the above equation (3) is represented 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: Welding voltage V detection value Id: Welding current I detection value

The current setting change amount calculation circuit 11b outputs the voltage value signal Vd, the current value signal Id, the output voltage setting signal Er, the external characteristic inclination setting signal Rr, and the inductance setting signal Lr output from the above circuits, A change amount (Er-Vd-Rr·Id)/Lr of the current set value per unit time is calculated, and a current setting change amount signal ΔIr indicating the change amount is output to the current setting integration circuit 11c.

The current setting integration circuit 11c integrates the current setting change amount signal ΔIr output from the current setting change amount calculation circuit 11b, and outputs a welding current control setting signal Irc obtained by integration to the difference amplification circuit 11d. .. The set value of the welding current I indicated by the welding current control setting signal Irc is represented by the above equation (4).
As described above, the current setting change amount calculation circuit 11b and the current setting integration circuit 11c correspond to the circuit that calculates the above equation (4).

The difference amplifier circuit 11d amplifies the difference between the current value signal Id output from the current detection unit 11k and the welding current control setting signal Irc output from the current setting integration circuit 11c, and the amplified difference indicating the difference. The signal Ei is output to the power supply circuit 11a.

The power supply circuit 11a includes an AC-DC converter that performs AC-DC conversion of commercial AC, an inverter circuit that converts the AC-DC converted DC into a desired AC by switching, a rectifier circuit that rectifies the converted AC, and the like. The power supply circuit 11a PWM-controls the inverter so that the difference signal Ei becomes smaller in accordance with the difference signal Ei output from the difference amplifier circuit 11d, and outputs a voltage to the welding wire 5. As a result, a welding voltage V that changes periodically is applied between the base material 4 and the welding wire 5, and a welding current I is applied. The power supply circuit 11a controls the output according to the difference signal Ei so that the above expression (4) is satisfied, and therefore the inductance setting value and the external characteristic inclination setting value of the welding power supply 1 can be electronically generated.
The welding power source 1 is configured such that an output instruction signal is input from the outside via a control communication line (not shown), and the power source unit 11 uses the output instruction signal as a trigger to weld the power source circuit 11a. The supply of the current I is started. The output instruction signal is output from the welding robot to the welding power source 1, for example. Further, 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 this embodiment, and FIG. 3 is a side sectional view showing the base material 4 to be welded. First, the pair of base materials 4 to be joined by welding are arranged in the arc welding apparatus, and various settings of the welding power source 1 are performed (step S11). Specifically, as shown in FIG. 3, a plate-shaped first base material 41 and a second base material 42 are prepared, and end surfaces 41a, 42a which are welded portions are butted against each other and placed at a predetermined welding work position. .. It should be noted that the first base material 41 and the second base material 42 may be provided with a groove having an arbitrary shape such as a Y shape or a rectangular shape, if necessary. The first and second base materials 41, 42 are 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.
Then, the welding power source 1 sets the welding condition of the welding current I within a range of a frequency of 10 Hz or more and 1000 Hz or less, an average current of 300 A or more, and a current amplitude of 50 A or more.

The welding operator may set all the conditions of the welding current I, or the welding power source 1 receives the execution of the welding method according to the present embodiment at the operation unit and automatically sets all the conditions. It may be configured to do so. Further, the welding power source 1 accepts some welding conditions such as the average current at the operation unit, determines the remaining welding conditions that match the accepted some welding conditions, and sets the conditions semi-automatically. It may be configured.

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

When it is determined that the output start condition of the welding current I is satisfied (step S12: YES), the feeding speed control unit 12 of the welding power source 1 sends a feeding instruction signal instructing the feeding of the wire to the wire feeding unit 3 And the welding wire 5 is fed at a predetermined speed (step S13). The feeding speed of the welding wire 5 is a constant speed, and is set within a range of, for example, about 5 to 100 m/min. The feed rate control unit 12 may determine the feed rate in accordance with the average current setting signal output from the average current setting circuit 11j, or the welding operator may directly set the wire feed rate. It may be configured to.

Next, the power source unit 11 of the welding power source 1 detects the welding voltage V and the welding current I by the voltage detection unit 11l and the current detection unit 11k (step S14), and the frequency, current amplitude and average of the detected welding current I. The output voltage setting signal Er and the external characteristic inclination setting signal Rr are periodically changed so that the current and the external characteristics and inductance of the welding power source 1 match the set welding conditions, and the output is PWM-controlled (step S15). .. That is, the welding power source 1 periodically fluctuates the output voltage setting signal Er in the constant voltage characteristic so that the welding current I 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. To control the output. Further, the external characteristic inclination setting signal Rr is periodically changed so as to be synchronized with the periodic variation of the output voltage setting signal Er in phase, and the external characteristic inclination of the welding power source 1 is electronically changed.

Next, the power supply unit 11 of the welding power supply 1 determines whether to stop the output of the welding current I (step S16). Specifically, the welding power source 1 determines whether the input of the output instruction signal is continuing. When the input of the output instruction signal is continued and it is determined that the output of the welding current I is not stopped (step S16: NO), the power supply unit 11 returns the process to step S13 and continues to output the welding current I.

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

FIG. 4 is a graph showing changes in the external characteristic inclination setting signal Rr and the welding current I. The horizontal axis of each graph shown in FIG. 4 represents time, and the vertical axis of each graph shown in FIGS. 4A to 4D respectively represents the output voltage setting signal Er of the welding power source 1, the external characteristic inclination setting signal Rr, the base material 4, and A welding voltage V and a welding current I between the welding wires 5 are shown.

In the arc welding method according to the present embodiment, the power supply unit 11 having the constant voltage characteristic periodically changes the output voltage setting signal Er as shown in FIG. 4A and also sets the external characteristic inclination setting as shown in FIG. 4B. The signal Rr is periodically changed in phase. When the output voltage setting signal Er is thus periodically changed, the welding voltage V and the welding current I are periodically changed as shown in FIGS. 4C and 4D.

FIG. 5 is a schematic diagram showing the arc welding method according to the present embodiment. When the welding current I is periodically changed under such welding conditions, the concave shape formed by the molten metal of the base material 4 and the welding wire 5 melted by the heat of the arc 7 generated between the tip portion 5a of the welding wire 5 and the welded portion. The molten portion 6 of is welded to the base material 4, and the tip portion 5a of the welding wire 5 is buried and enters the space 6a. Then, when the state of the arc 7 was photographed by a high-speed camera, as shown in the left diagram of FIG. 5, the welding wire 5 deeply penetrated into the space 6a, and the tip portion 5a of the welding wire 5 and the bottom portion 61 of the fusion portion 6 were formed. Periodically, a first state in which an arc 7 is generated and a second state in which the welding wire 5 enters the buried space 6a shallowly and the arc 7 is generated between the tip portion 5a and the side portion 62 of the melting portion 6 are periodically performed. It was confirmed to fluctuate.

In this way, the tip portion 5a of the welding wire 5 enters the buried space 6a and is surrounded by the molten portion 6, and the welding current I is periodically changed to change the tip portion 5a of the buried space 6a. The position can be moved up and down.
In the first state, the distal end portion 5a of the welding wire 5 deeply penetrates into the buried space 6a, and the arc 7 with which the bottom portion 61 of the molten portion 6 is irradiated provides deep penetration.
In the second state, the tip portion 5a of the welding wire 5 shallowly enters the buried space 6a, and the melting portion 6 is supported by the force of the arc 7 with which the side portion 62 of the melting portion 6 is irradiated. Maintained in a stable condition.
Therefore, the buried space 6a can be stably maintained by periodically changing the welding current I.

FIG. 6 is a graph showing changes in the set voltage and the set value of the external characteristic slope. In FIG. 6, the horizontal axis represents the welding current I and the vertical axis represents the welding voltage V. FIG. 6A shows a state in which the welding power source 1 is set to a low first voltage ErL. At this time, the first state shown in FIG. 5 is obtained.
In FIG. 6A, the solid straight line EC1 indicates the external characteristics of the welding power source 1 when the first voltage ErL is set as the set voltage, and the curve L1 indicates the arc characteristic, and the intersection A of the straight lines EC1 and L1 is stable. This is the operating point.
In FIG. 6B, the solid straight line EC2 is the external characteristic of the welding power source 1 when the second voltage ErH is set as the set voltage. The second voltage ErH is higher than the first voltage ErL, and the slope of the external characteristic is larger than that when the first voltage ErL is set as the set voltage.

When the set voltage changes from the first voltage ErL to the second voltage ErH, the intersection B of the straight line EC2 and the curve L1 becomes a high current, and the welding current I increases. Since the feeding speed of the welding wire 5 is constant, when the welding current I becomes large, the droplet transfer of the welding wire 5 is promoted and the arc length becomes long, and the tip portion 5a of the welding wire 5 becomes larger than the buried space 6a. Move from bottom to top. That is, the first state shown in the left diagram of FIG. 5 transits to the second state shown in the right diagram of FIG.
When the set voltage changes from the second voltage ErH to the first voltage ErL, the intersection A of the straight line EC1 and the curve L2 has a low current, and the welding current I decreases. Since the feeding speed of the welding wire 5 is constant, when the welding current I is small, the droplet transfer of the welding wire 5 is suppressed and the arc length is shortened, and the tip portion 5a of the welding wire 5 becomes less than the buried space 6a. Move from top to bottom. That is, the second state shown in the right diagram of FIG. 5 transits to the first state shown in the left diagram of FIG.

FIG. 7 is a graph showing the manner in which the welding current I is increased/decreased due to fluctuations in the external characteristic inclination set value. When the set voltage is switched from the first voltage ErL to the second voltage ErH, a large second predetermined value RrH is set as the external characteristic gradient set value, so that the welding current I fluctuates due to disturbance as shown in FIG. Is suppressed.
Conversely, when the set voltage is switched from the second voltage ErH to the first voltage ErL, a small first predetermined value RrL is set as the external characteristic gradient set value. In this case, as shown in FIG. 7, the fluctuation of the welding current I due to the disturbance becomes large, but the self-control action of the arc length becomes strong, and the positions of the tip portion 5a of the welding wire 5 and the molten portion 6 become stronger. The relationship is controlled with good precision.

As described above, by periodically changing the external characteristics of the welding power source 1 in the same phase as the set voltage of the output voltage E, the self-control action of the arc length and the action of suppressing the disturbance of the welding current I due to the disturbance. You can switch.
Therefore, when the welding current I is small and the tip portion 5a of the welding wire 5 is deeply entering the buried space 6a, the position of the tip portion 5a of the welding wire 5 is accurately controlled, and the welding state becomes unclear due to a short circuit or the like. You can prevent it from becoming stable.
On the other hand, when the welding current I is large and the disturbance of the welding current I due to disturbance may cause the waving of the molten pool, the disturbance of the welding current I due to disturbance can be suppressed so that the welding state does not become unstable. ..

<Welding conditions for buried arc>
The welding conditions for realizing the buried arc will be supplemented below.
In arc welding, generally, the position of the tip portion 5a of the welding wire 5 is located above the base material 4, and in that state, an arc 7 is generated between the tip portion 5a of the welding wire 5 and the base material 4. The arc 7 generated in this state is called a non-buried arc. In the non-buried arc, the distance between the tip 5a of the welding wire 5 and the surface of the molten metal formed on the surface of the base material 4 is called the arc length. This arc length decreases as the welding voltage V decreases. It is known to shorten. In normal arc welding, when the welding voltage V is lowered and the arc length is shortened, the distance between the molten metal and the position of the tip portion 5a of the welding wire 5 becomes shorter, and finally the arc length becomes 0 and the welding wire 5 becomes shorter. And the base material 4 are short-circuited, and it becomes difficult to maintain the arc 7.

However, in high current welding, the molten metal is pushed away by the arc pressure, so that a short circuit is less likely to occur even if the voltage is lowered. As a result, even if the tip 5a of the welding wire 5 is located at a position deeper than the base material 4 or the surface of the molten metal, the presence of the buried space 6a, that is, the space formed by the molten metal being pushed away by the arc pressure. The short circuit does not occur and the arc 7 can be maintained. This is the buried arc phenomenon.

That is, the buried arc 7 can be realized by generating the arc 7 under a low voltage condition in the high current region where the arc pressure becomes strong. Specifically, the welding current I is required to be 300 A or more (for example, Satoshi Asai, "Higher efficiency of factory welding-case of heavy electric equipment welding"), Japan Welding Association Welding Information Center, WE-COM. Magazine No. 16, April 2015). The voltage value capable of realizing the buried arc varies depending on the welding current I, the wire diameter, and the protruding length of the welding wire 5, but as described above, the position of the tip portion 5a of the welding wire 5 is set to the base material 4 or A buried arc can be realized by setting the voltage so low that it can be lowered to a position lower than the surface of the molten metal.

FIG. 8 is a graph showing the conditions of welding current I and voltage for realizing the buried arc. The horizontal axis represents the welding current I, and the vertical axis represents the welding voltage V. The white part shows the welding current I and voltage that can realize the buried arc. As shown in FIG. 8, when the welding voltage V is high with respect to the welding current I, normal arc welding, that is, non-buried arc welding is performed. Conversely, when the welding voltage V is too low, the output is insufficient and the arc 7 is maintained. Will be difficult. In the intermediate region, there is a range in which the arc 7 is generated in the buried space 6a and becomes a buried arc.

Further, the range of welding conditions for realizing the buried arc is affected by the wire diameter and the protruding length of the welding wire 5 as described above.

FIG. 9 is a conceptual diagram showing the relationship between the wire diameter and the wire protrusion length, and the conditions of the welding current I and the voltage for realizing the buried arc. As shown in FIG. 9, the larger the wire diameter or the shorter the protruding length of the welding wire 5, the range of welding current I and voltage at which a buried arc can be realized is as shown by the symbols Arc3, Arc2, and Arc1, In this order, the same current shifts to the lower voltage region side.

FIG. 10 is a graph showing an example of conditions of welding current I and voltage for realizing a buried arc when the wire diameter is 1.6 mm and the protruding length of the welding wire 5 is 25 mm. In FIG. 10, the horizontal axis represents the welding current I and the vertical axis represents the welding voltage V. The black circle plot shows the boundary between the non-buried arc and the buried arc. In FIG. 10, the black circle plot on the upper polygonal line becomes a non-buried arc when the welding voltage V is increased at the welding current I indicated by the black circle plot, and becomes a buried arc when the welding voltage V is decreased. Further, the black circle plot on the lower polygonal line becomes a buried arc when the welding voltage V is increased at the welding current I indicated by the black circle plot, and becomes a non-buried arc when the welding voltage V is decreased. In short, when the welding voltage V is high with respect to the welding current I, normal arc welding, that is, non-buried arc welding is performed, and conversely, when the welding voltage V is too low, the output is insufficient and it becomes difficult to maintain the arc 7. In the intermediate region, there is a range in which the arc 7 is generated in the buried space 6a and becomes a buried arc.

As described above, the welding current I for realizing the buried arc is 300 A or more, and when the tip 5a of the welding wire 5 approaches the molten metal, it is possible to generate the arc pressure that pushes away the molten metal. It is a current value. Further, the welding voltage V for realizing the buried arc is a voltage value capable of lowering the position of the tip 5a of the welding wire 5 to a position lower than the base material 4 or the surface of the molten metal.
Regarding the specific welding current I and voltage, the welding current I and voltage may be appropriately determined in consideration of the trends shown in FIGS. 8 and 9 while using the range of the welding current I and voltage shown in FIG. 10 as a reference.

As described above, according to the arc welding method and the arc welding apparatus according to the present embodiment, in the buried arc welding, the welding current I is cyclically varied to stably maintain the buried space 6a and the welding current I. By changing the external characteristic of the welding power source 1 in accordance with the change of the welding current I, it is possible to suppress the instability of the welding state due to the change of the welding current I.

Specifically, by periodically changing the external characteristic inclination of the welding power source 1 in phase with the set voltage of the output voltage E, when the welding current I is small, the self-control action of the arc length is increased, When the current I is large, the disturbance of the welding current I due to disturbance is reduced. By controlling the external characteristic inclination and the welding current I in this way, it is possible to effectively suppress the instability of the welding state when the welding current I increases or decreases.

Further, the self-control action of the arc length in the first state is increased by the simple control of switching the setting voltage of the welding power source 1 having the constant voltage characteristic and the value of the external characteristic slope, and the welding current I in the second state Disturbance can be reduced.

Further, since the external characteristic inclination of the welding power source 1 is electronically changed, even if the welding current I changes with a large current and at a high frequency, the welding power source 1 is synchronized with the welding current I. It is possible to electronically change the external characteristic inclination of.

Furthermore, even when performing gas shielded arc welding using a large current of 300 A or more, it is possible to suppress waving of the molten metal by varying the welding current I at a high frequency of 10 Hz or more, and the bead is disturbed. It is possible to prevent the occurrence of dripping.
Further, in order to suppress the waviness of the molten metal more effectively, it is necessary to keep the arc length constant. In the case of general constant current pulse welding, since the self-control action of the arc length cannot be obtained, it is necessary to perform some control for ensuring a constant arc length. The arc welding device according to the present embodiment has a constant voltage characteristic and can obtain the self-control action of the arc length, so that the arc length is kept constant and the corrugation of the molten metal can be suppressed more effectively.

FIG. 11 is a diagram showing the experimental results of the buried arc welding with a photograph, and FIG. 12 is a diagram showing the experimental results of the buried arc welding with a schematic diagram. The frequency and amplitude of the welding current I under the welding conditions of a wire diameter of 1.4 mm, a protruding length of the welding wire 5 of 18 mm, a feeding speed of the welding wire 5 of 17.5 m/min, and an average welding current of 530 A. Was changed and buried arc welding of thick plates was performed.
11 and 12 show the experimental results when the frequency of the welding current I is 0 Hz and the amplitude thereof is 0 A, that is, the appearance and shape of the bead when welding is performed without vibrating the welding current I. There is. The middle figure of FIG. 11 and FIG. 12 shows the bead shape when welding is performed under the condition that the frequency of the welding current I is 10 Hz and the amplitude thereof is 50 A. The lower diagrams of FIGS. 11 and 12 show the frequency of the welding current I of 50 Hz. , Shows the appearance and shape of the bead when welding is performed under the condition that the amplitude is 100A.

As can be seen from the experimental results shown in FIGS. 11 and 12, by vibrating the welding current I under the welding conditions of the frequency of 10 Hz or more and the current amplitude of 50 A or more, a better bead shape can be obtained as compared with the case of the frequency of 0 Hz. I understand. Such a good bead shape indicates that the buried space 6a is stabilized by vibrating the welding current I at a frequency of 10 Hz, and the occurrence of a short circuit is suppressed.
Further, by vibrating the molten metal at a high frequency, the operation principle of suppressing the corrugation of the molten metal makes it possible to suppress the corrugation of the molten metal and stabilize the buried space 6a even if the frequency of the welding current I is 10 Hz or more. It is expected that it can be made into. Further, since the waving of the molten metal can be sufficiently suppressed with the current amplitude of 50 A, it is expected that the waving of the molten metal can be suppressed even with the current amplitude of 50 A or more. In fact, when welding was performed under the welding conditions of a melting current frequency of 50 Hz and a welding current of 100 A or more, a better bead shape was obtained as shown in FIGS. 11 and 12. The wire diameter, the protruding length of the welding wire 5, the feed rate, and the average current are not particularly limited as long as the buried arc described below can be realized, and the frequency of the welding current I is 10 Hz. Under the above conditions and the current amplitude of 50 A, a good bead shape is similarly obtained. Particularly, if the frequency is 50 Hz and the current amplitude is 100 A or more, a better bead shape can be obtained.

The welding conditions described in the embodiment are examples, and the material of the welding wire 5, the wire system, the protruding length, the feeding speed of the welding wire 5, the range of the welding current I, and the numerical range described above. It is not limited to.

As the material of the welding wire 5, solid wires such as YGW11, YGW15, YGW17, YGW18, and YGW19 can be used in addition to YGW12. However, a flux cored wire, a metal cored wire, or another new wire may be applied as the welding wire 5.

Furthermore, the protruding length of the welding wire 5 is preferably 10 mm or more and 35 mm or less. The longer the protrusion length, the shallower the penetration, so it is better to keep it at 35 mm at the longest. On the other hand, when the protruding length is shortened, the tip end approaches the molten pool, and chip consumption becomes severe. Since this is a large current welding, this tendency is particularly remarkable, and if it is less than 10 mm, frequent tip replacement is required. Furthermore, the protruding length of the welding wire 5 influences the transition current of the transition form. Also from the viewpoint of the balance, there is an appropriate range for the protruding length, and an appropriate range is about 10 to 35 mm.

The wire diameter is preferably 0.9 mm or more and 1.6 mm or less, for example. The wire diameter can be basically adapted to any wire diameter by appropriately changing the welding conditions and is not particularly limited, but in consideration of general distribution, it is 0.9 mm. About 1.6 mm is realistic. Also, the wire diameter affects the transition current in the droplet transfer form. Also from this viewpoint, when the extremely thick welding wire 5 or the thin welding wire 5 is used, the transition region of the droplet transfer form is greatly expanded, and it becomes difficult to use an arbitrary droplet transfer form. Therefore, about 0.9 to 1.6 mm is appropriate.

Since the feeding speed of the welding wire 5 correlates with the welding current I, it may be appropriately determined according to the welding current I so that the buried space 6a is formed.

Further, the output voltage setting signal Er and the external characteristic inclination setting signal Rr are exemplified by rectangular wave signals, but the waveform of each setting signal is not particularly limited and may be a triangular wave or any other waveform. When the output voltage setting signal Er is a triangular wave, the external characteristic inclination setting signal Rr is increased when the output voltage setting signal Er is equal to or more than the threshold value, and when the output voltage setting signal Er is less than the threshold value, the external characteristic inclination setting signal is Control may be performed so as to reduce Rr.

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

1 Welding power source 2 Torch 3 Wire feeding part 4 Base material 5 Welding wire 5a Tip part 6 Melting part 6a Buried space 61 Bottom part 62 Side part 7 Arc 11 Power supply part 11a Power supply circuit 11b Current setting change calculation circuit 11c Current setting integration circuit 11d Differential amplifier circuit 11e Output voltage setting circuit 11f Inductance setting circuit 11g External characteristic setting circuit 11h Frequency setting circuit 11i Current amplitude setting circuit 11j Average current setting circuit 11k Current detection unit 11l Voltage detection unit 12 Feed rate control unit 41 First mother Material 42 Second base material R Electric resistance L Reactor V Welding voltage I Welding current Er Output voltage setting signal Lr Inductance setting signal Rr External characteristic inclination setting signal Vd Voltage value signal Id Current value signal ΔIr Current setting change signal Irc Welding current control Setting signal Ei Differential amplification signal

Claims (7)

The welding wire is fed to the welded portion of the base material, and a welding current is supplied from the welding power source to the welding wire to generate an arc between the tip portion and the welded portion of the welding wire. And a consumable electrode type arc welding method for welding the base metal by causing the tip to enter the space surrounded by the concave molten portion formed in the base metal by the arc generated between the welded parts,
By varying the welding current, the first state in which the tip portion of the welding wire deeply enters the space and the second state in which the distal end shallowly enters the space are periodically varied,
When increasing the welding current in synchronism with the fluctuation of the welding current, the inclination of the external characteristic relating to the welding current and voltage of the welding power source is increased, and when decreasing the welding current, the inclination of the external characteristic is changed. Arc welding method to reduce . The welding wire is fed to the welded portion of the base material, and a welding current is supplied from the welding power source to the welding wire to generate an arc between the tip portion and the welded portion of the welding wire. And a consumable electrode type arc welding method for welding the base metal by causing the tip to enter the space surrounded by the concave molten portion formed in the base metal by the arc generated between the welded parts,
By changing the welding current so that the frequency is 10 Hz or more and 1000 Hz or less and the average current is 300 A or more, the first state in which the distal end portion of the welding wire deeply enters the space and shallowly enters the space. Cyclically fluctuating the second state,
The inclination of the external characteristic relating to the welding current and voltage of the welding power source is changed in synchronization with the change of the welding current.
Arc welding method. The arc welding method according to claim 2 , wherein when increasing the welding current, the inclination of the external characteristic is increased, and when decreasing the welding current, the inclination of the external characteristic is decreased. The speed of feeding the welding wire is constant,
The welding power source has a constant voltage characteristic, by periodically varying the set voltage of the welding power source, to periodically vary the welding current,
When the set voltage of the welding power source is set to a first voltage, the inclination of the external characteristic is set to a first predetermined value, and the set voltage of the welding power source is set to a second voltage higher than the first voltage, The slope of the external characteristic is set to a second predetermined value that is larger than the first predetermined value.
The arc welding method according to claim 1 or claim 3 . The arc welding method according to any one of claims 1 to 4 , wherein the inclination of the external characteristic is electronically varied by controlling the welding current supplied by the welding power source. The welding wire sent to the welded part of the base material is provided with a power supply part for supplying a welding current, and by supplying the welding current to the welding wire, an arc is formed between the tip part of the welding wire and the welded part. A consumable electrode type arc that is generated and welds the base metal by causing the tip to enter the space surrounded by the concave molten portion formed in the base metal by the arc generated between the tip and the welded portion. A welding device,
A state changing unit that periodically changes the welding current by changing the first state in which the tip portion of the welding wire deeply enters the space and the second state in which the distal end of the welding wire shallowly enters the space;
When increasing the welding current in synchronism with the fluctuation of the welding current, the inclination of the external characteristic relating to the welding current and voltage of the power supply unit is increased, and when decreasing the welding current, the inclination of the external characteristic is changed. An arc welding device having a reduced external characteristic variation part. The welding wire sent to the welded part of the base material is provided with a power supply part for supplying a welding current, and by supplying the welding current to the welding wire, an arc is formed between the tip part of the welding wire and the welded part. A consumable electrode type arc that is generated and welds the base metal by causing the tip to enter the space surrounded by the concave molten portion formed in the base metal by the arc generated between the tip and the welded portion. A welding device,
By changing the welding current so that the frequency is 10 Hz or more and 1000 Hz or less and the average current is 300 A or more, the first state in which the distal end portion of the welding wire deeply enters the space and shallowly enters the space. A state changing unit that periodically changes the second state,
An external characteristic variation unit that varies the inclination of the external characteristic relating to the welding current and voltage of the power source unit in synchronization with the variation of the welding current;
Arc welding equipment equipped with.