JP7540972B2 - Arc welding device and arc welding method - Google Patents

Description

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

One of the welding defects that can occur in arc welding is the blowhole. A blowhole is a defect in which a spherical cavity is formed in the weld metal when the molten metal solidifies while low-boiling-point gas vapor is entrained in the molten metal.

JP 2020-192587 A

In gas metal arc (GMA) welding, blowholes, which are welding defects, may be easily generated depending on the shielding gas used and the welding conditions. For example, the present inventors have found that in a consumable electrode arc welding method using a shielding gas containing argon, when the welding current is set to 350 A to 600 A, argon gas is entrained in the weld metal, causing a large number of blowholes.
Therefore, the inventors of the present application have devised a technology that uses current amplitude control to periodically vary the welding current to stir the molten metal, promote the discharge of bubbles caught in the molten metal, and suppress the occurrence of blowholes.

However, when current amplitude control is used, although there is a central set current and central set voltage that are the center of fluctuation, the welding conditions on the high current side and the welding conditions on the low current side are simply repeated alternately, and the average output of the welding power source does not necessarily correspond to the output when current amplitude control is not performed. Even when current amplitude control is performed, it is desirable to control the average output of the welding power source so that it is approximately the same as the output when current amplitude control is not performed.

The object of the present invention is to provide an arc welding device and method for consumable electrode arc welding using a shielding gas containing argon, capable of controlling current amplitude to suppress the occurrence of blowholes, matching the average output current to the central set current, and maintaining a constant arc length (buried depth in the case of buried arc welding).

In addition, Patent Document 1 discloses a technique for matching the output current to the set current and maintaining the arc length (buried depth in the case of buried arc welding) constant when the current amplitude control is not used. However, the current amplitude control is a control in which high current side conditions and low current side conditions are set based on the center set current, and these conditions are repeatedly switched, and the actual center output current when the current amplitude control is performed appears as a value obtained by further averaging the average output current in each period of the high current side condition and the low current side condition. For this reason, the technique disclosed in Patent Document 1 cannot be applied to the center set current itself.
When applying the technology according to Patent Document 3, the high current side condition and the low current side condition are applied independently. In the current amplitude control, the high current side condition and the low current side condition are repeatedly changed at a frequency of, for example, 0.5 Hz to 3 Hz, so that the duration of each condition is short, about 1 second or less. Therefore, in order to make the output current sufficiently follow the set current each time for each condition period, it is necessary to change the output current at high speed, but in that case, the behavior of the arc changes unnaturally and the weldability deteriorates. In addition, since the average output is expressed as a result of the output including a transient response during switching between the high current side condition and the low current side condition, even if the output current is made to follow the set current each time for each condition period of the high current side and the low current side, the average output does not necessarily match the center set current.

The arc welding device is a consumable electrode type arc welding device that uses a shielding gas containing argon, and is equipped with a power supply circuit that outputs a welding current to the welding wire, a setting circuit that periodically switches between a first welding condition in which a first welding current smaller than a central set current is output to the welding wire and a second welding condition in which a second welding current larger than the central set current is output to the welding wire, a feed speed control circuit that controls the feeding of the welding wire at a feed speed according to the first welding condition and the second welding condition set by the setting circuit, a current detection unit that detects the welding current output from the power supply circuit when welding is performed by periodically switching between the first welding condition and the second welding condition, and a correction unit that corrects the feeding speed of the welding wire and the set voltage related to the first welding condition and the second welding condition based on the difference between the average output current when welding is performed by periodically switching between the first welding condition and the second welding condition.

The arc welding method is a consumable electrode type arc welding method using a welding power source and a shielding gas containing argon, and periodically switches between a first welding condition in which a first welding current smaller than a center set current is output from the welding power source to the welding wire, and a second welding condition in which a second welding current larger than the center set current is output from the welding power source to the welding wire, detects the welding current output from the welding power source when welding is performed by periodically switching between the first welding condition and the second welding condition, and corrects the welding wire feed speed and the set voltage related to the first welding condition and the second welding condition based on the difference between the average output current when welding is performed by periodically switching between the first welding condition and the second welding condition and the center set current.

In this embodiment, in consumable electrode arc welding using a shielding gas containing argon, the first welding condition and the second welding condition are periodically changed to stir the molten metal, promote the discharge of bubbles caught in the molten metal, and suppress the occurrence of blowholes. In particular, changing the welding current in this manner is effective in applying vibration to the molten metal (see FIG. 10).
Furthermore, by correcting the welding wire feed speed and the set voltage for the first welding condition and the second welding condition based on the difference between the average output current in the current amplitude control and the central set current, it is possible to make the average output current match the central set current and maintain a constant arc length.
By correcting the wire feed speed, the average output current can be made to match the center set current. Furthermore, by correcting the set voltage, the arc length can be kept constant. In the case of buried arc welding, which will be described later, by correcting the set voltage, the buried depth can be kept constant.

It is preferable to provide a table or function that associates the difference, the amount of correction for the feed speed, and the amount of correction for the set voltage, and the correction unit determines the amount of correction for the feed speed and the amount of correction for the set voltage by referring to the table or function using the difference based on the welding current detected by the current detection unit.

In this embodiment, the correction amount for the welding wire feed speed and the correction amount for the set voltage can be determined using a table with a simple configuration.

It is preferable to provide a table or function that associates the difference, the central set current, the correction amount of the feed speed, and the correction amount of the set voltage, and the correction unit determines the correction amount of the feed speed and the correction amount of the set voltage by referring to the table or function using the difference and the central set current based on the welding current detected by the current detection unit.

It is preferable that the welding device is provided with a first table or a first function that associates the difference, the center set current, and the correction amount of the feed speed, and a second table or a second function that associates the center set current, the correction amount of the feed speed, and the correction amount of the set voltage, and the correction unit determines the correction amount of the feed speed by referring to the first table or the first function using the difference and the center set current based on the welding current detected by the current detection unit, and determines the correction amount of the set voltage by referring to the second table or the second function using the determined correction amount of the feed speed and the center set current.

In this embodiment, the arc length can be maintained more accurately than in the previous embodiment.

The first and second welding conditions are welding conditions in which the center setting current is 350 A or more and the current fluctuation range is 50 A or more and 150 A or less, and it is preferable that the first and second welding conditions are configured to be switched at a cycle of 1 Hz or more and 5 Hz or less.

In this embodiment, in a welding process where blowholes are likely to occur due to a center current of 350 A or more, the occurrence of blowholes can be effectively suppressed by setting the current fluctuation range to 50 A or more and 150 A or less, and the fluctuation period to 1 Hz or more and 5 Hz or less.

It is preferable that the first welding condition or the second welding condition is a welding condition in which the tip of the welding wire (including the molten area; hereafter, this will be omitted in similar expressions) or the arc generation point in the liquid column formed at the tip enters the space surrounded by the concave molten portion formed in the base metal by the arc.

In this embodiment, the tip of the welding wire, or the arc generation point in the liquid column formed at the tip, enters the space surrounded by the concave molten portion formed in the base metal (see Figs. 5B and 5C). Hereinafter, the space surrounded by the concave molten portion is referred to as the buried space, and the arc generated between the tip of the welding wire that has entered the buried space, or the arc generation point in the liquid column formed at the tip, and the base metal or the molten portion is referred to as the buried arc, as appropriate. Welding performed with a buried arc is referred to as buried arc welding. Buried arc welding is achieved, for example, by feeding the welding wire at about 5 to 100 m/min and supplying a high current of 300 A or more.
On the other hand, an arc in which no concave molten portion is formed, or a normal arc in which the tip of the welding wire and the arc emission point do not penetrate into the concave molten portion, is called a non-buried arc.
In buried arc welding, a deep molten pool is formed, so that argon in the shielding gas remains in the molten metal, and blowholes are likely to occur. In the arc welding method according to the present embodiment, deep penetration can be obtained by buried arc welding, and the occurrence of blowholes can be suppressed.
In addition, by correcting the welding wire feed speed and the set voltage, the average output current can be made to match the center set current, and the embedment depth can be controlled to a constant value.

According to the present invention, in consumable electrode arc welding using a shielding gas containing argon, the occurrence of blowholes can be suppressed by controlling the current amplitude, and the average output current can be matched to the center set current and the arc length (buried depth in the case of buried arc welding) can be maintained constant.

1 is a schematic diagram showing one configuration of an arc welding device according to a first embodiment of the present invention; 3 is a flowchart showing the procedure of an arc welding method according to the first embodiment. FIG. 2 is a cross-sectional side view showing the base material to be welded. 10 is a flowchart showing a procedure for current amplitude control. FIG. 13 is an explanatory diagram of a buried arc state. 4 is a timing chart showing a method of switching welding conditions according to the first embodiment. 10 is a flowchart showing a procedure for a second output correction process. FIG. 2 is a cross-sectional view showing a schematic diagram of a welded joint. 11 is an image showing the results of a radiographic test of a welded joint when the current amplitude control according to the first embodiment was not performed. 11 is an image showing the results of a radiographic test of a welded joint when current amplitude control according to the first embodiment is performed. FIG. 11 is a conceptual diagram showing a table according to the second embodiment. FIG. 13 is a conceptual diagram showing a table according to the third embodiment. 13 is a timing chart showing a method of switching welding conditions according to the fourth embodiment.

Specific examples of arc welding apparatus and methods according to embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments thereof.
(Embodiment 1)
<Arc welding equipment>
1 is a schematic diagram showing one configuration of an arc welding device according to the present embodiment. The arc welding device according to the present embodiment is a consumable electrode type gas-shielded arc welder that uses a shielding gas containing argon, and includes a welding power source 1, a torch 2, and a wire feeder 3. The arc welding device according to the present embodiment can perform both buried arc welding and non-buried arc welding.

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

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

The wire feed unit 3 has a feed roller that feeds the welding wire 5 to the torch 2, and a motor that rotates the feed roller. The wire feed unit 3 pulls out the welding wire 5 from a pail pack or wire reel by rotating the feed roller, and supplies the pulled out welding wire 5 to the torch 2 at a predetermined speed. In the case of buried arc welding, the feed speed of the welding wire 5 is, for example, about 5 to 100 m/min. In the case of non-buried arc welding, the feed speed of the welding wire 5 is, for example, about 1 to 22 m/min. Note that this method of feeding the welding wire 5 is one example, and is not particularly limited.

The welding power source 1 is connected to the contact tip of the torch 2 and the base material 4 via a power supply cable, and includes a power source unit 11 that supplies the welding current I, and a feed speed control circuit 12 that controls the feed speed of the welding wire 5. The power source unit 11 and the feed speed control circuit 12 may be configured separately. The power source unit 11 is a power source with constant voltage characteristics, and includes a power source circuit 11a that outputs a PWM-controlled direct current, a control circuit 11b, a setting circuit 11c, a voltage detection unit 11d, a current detection unit 11e, a correction unit 11f, and a table 13.

The setting circuit 11c is a circuit that periodically switches between a first welding condition of a low current (first welding current) and a second welding condition of a high current (second welding current) for buried arc welding based on a center set current. The center set current is a current value set by an operator, and the welding power source 1 receives the center set current through an operation unit (not shown).
The first and second welding conditions are welding conditions in which at least the central set current of the welding current I is 350 A or more and the current fluctuation range is 50 A or more and 150 A or less. The central set current of the welding current I is more preferably 400 A or more.
For example, the first welding condition is a condition in which the welding current I is 350 A, and the second welding condition is a condition in which the welding current I is 450 A (400 A±50 A).
Also, the first welding condition may be a welding current I of 300 A, and the second welding condition may be a welding current I of 500 A (400 A±100 A).
Furthermore, the first welding condition may be a condition in which the welding current I is 250 A, and the second welding condition may be a condition in which the welding current I is 550 A (400 A±150 A).
The setting circuit 11c switches between the first and second welding conditions at a cycle of 1 Hz to 5 Hz, and more preferably, the setting circuit 11c is configured to switch between the first and second welding conditions at a cycle of 2 Hz to 3 Hz.

When the first welding condition is set, the setting circuit 11c outputs a current setting signal Ir indicating a low current value lower than the central set current to the control circuit 11b, and outputs a feed speed signal F indicating the feed speed of the welding wire 5 corresponding to the low current value to the feed speed control circuit 12.
The setting circuit 11c also stores a set voltage (also referred to as a unitary voltage) recommended for a set current in a steady welding state in a recommended environment, and the setting circuit 11c determines the recommended set voltage based on the set current. Specifically, when the first welding condition is set, the setting circuit 11c determines a set voltage (unitary voltage) based on the set current of the first welding condition, and outputs an output voltage setting signal Vr indicating the determined set voltage to the control circuit 11b. However, the feed speed of the welding wire 5 and the set voltage under the first welding condition are appropriately corrected by a correction unit 11f described later.

Similarly, when the second welding condition is set, the setting circuit 11c outputs a current setting signal Ir indicating a high current value higher than the central set current to the control circuit 11b, and outputs a feed speed signal F indicating the feed speed of the welding wire 5 corresponding to the high current value to the feed speed control circuit 12. When the second welding condition is set, the setting circuit 11c determines a set voltage (unified voltage) based on the set current of the second welding condition, and outputs an output voltage setting signal Vr indicating the determined set voltage to the control circuit 11b. However, the feed speed and set voltage of the welding wire 5 under the second welding condition are appropriately corrected by the correction unit 11f described below.

The feed speed control circuit 12 acquires the feed speed signal F output from the setting circuit 11c, and controls the feeding of the welding wire 5 by the wire feed unit 3 based on the acquired feed speed signal F. When the feed speed control circuit 12 acquires the feed speed signal F related to the first welding condition, it outputs a feed instruction signal indicating a low feed speed value to the wire feed unit 3 to rotate the feed roller, and when the feed speed control circuit 12 acquires the feed speed signal F related to the second welding condition, it outputs a feed instruction signal indicating a high feed speed value to the wire feed unit 3 to rotate the feed roller.

The voltage detection unit 11d detects the arc voltage V and outputs a voltage value signal Vd indicating the detected voltage value to the control circuit 11b.

The current detection unit 11e detects the welding current I that is supplied, for example, from the welding power source 1 through the torch 2 to the welding wire 5 and flows through the arcs 7a and 7b, and outputs a current value signal Id indicating the detected current value to the control circuit 11b and the correction unit 11f.

The welding power supply 1 according to the first embodiment behaves as a power supply having constant voltage characteristics. For example, the welding power supply 1 stores external characteristics that cause the arc voltage V to drop by 2 V or more and 20 V or less in response to an increase in the welding current I of 100 A. The external characteristics may be different for each combination of the set current and set voltage, or may be common.

The control circuit 11b is a circuit that controls the operation of the power supply circuit 11a so that the power supply circuit 11a operates with constant voltage characteristics and outputs a voltage corresponding to the current setting signal Ir and the output voltage setting signal Vr. The control circuit 11b electronically controls the electric resistance R and the reactor L present in the current path of the welding power supply 1 to realize the constant voltage characteristics.
The control circuit 11b calculates a difference signal Ei based on the voltage value signal Vd output from the voltage detection unit 11d, the current value signal Id output from the current detection unit 11e, and the current setting signal Ir and output voltage setting signal Vr output from the setting circuit 11c, and outputs the calculated difference signal Ei to the power supply circuit 11a. The difference signal Ei is a signal indicating the difference between the detected current value and the current value to be output from the power supply circuit 11a.

The power supply circuit 11a includes an AC-DC converter that converts commercial AC to DC, an inverter circuit that converts the converted DC to a required AC by switching, a rectifier circuit that rectifies the converted AC, etc. The power supply circuit 11a PWM controls the inverter in accordance with a difference signal Ei output from the control circuit 11b so that the difference signal Ei becomes small, and outputs a welding current and voltage to the welding wire 5. As a result, a predetermined arc voltage V is applied between the base material 4 and the welding wire 5, and a welding current I flows.
The welding power supply 1 is configured to receive an output instruction signal from the outside via a control communication line (not shown), and the power supply unit 11 uses the output instruction signal as a trigger to start supplying the welding current I to the power supply circuit 11a. The output instruction signal is a signal that is output from the torch 2 to the welding power supply 1 when, for example, a hand-operated switch provided on the torch 2 is operated.

Furthermore, the setting circuit 11c includes a correction unit 11f and a table 13. The table 13 stores information necessary for matching the average output current with the central set current and for maintaining a constant arc length (buried depth in the case of buried arc welding). Specifically, the table 13 stores a difference ΔI between the average output current output from the welding power source 1 or the power supply circuit 11a and the central set current, a correction amount ΔF for the feed speed of the welding wire 5, and a correction amount ΔV for the set voltage, in association with each other.
The correction unit 11f determines a correction amount ΔF for the feed speed of the welding wire 5 and a correction amount ΔV for the set voltage by referring to the table 13 using the difference ΔI between the average output current output from the welding power source 1 when the current amplitude control is performed and the central set current as a key. The correction amount ΔF is a correction amount for the feed speed for matching the average output current with the central set current. The correction amount ΔV is a correction amount for the feed speed and the set voltage for maintaining constant the arc length during non-buried arc welding or the buried depth during buried arc welding.
The setting circuit 11c outputs the current setting signal Ir and the feed speed signal F, which have been appropriately corrected by the correction section 11f, to the control circuit 11b and the feed speed control circuit 12.

Here, the table 13 is illustrated as an example of information correlating the difference ΔI between the average output current and the central set current, the correction amount ΔF for the feed speed of the welding wire 5, and the correction amount ΔV for the set voltage, but a function correlating the difference ΔI, the correction amount ΔF, and the correction amount ΔV may be used. Also, although one table 13 in which the difference ΔI, the correction amount ΔF, and the correction amount ΔV correspond to each other has been described, the table 13 may be composed of a plurality of tables or a plurality of functions. For example, one table or function correlating the difference ΔI with the correction amount ΔF, and one table or function correlating the difference ΔI with the correction amount ΔV may be provided.
Furthermore, the correction table 13 for buried arc welding and the correction table 13 for non-buried arc welding may be configured as separate tables. In the case of non-buried arc welding, the average output current can be made to match the central set current with greater precision, and the arc length can be maintained constant, while in the case of a non-buried arc, the average output current can be made to match the central set current, and the burial depth can be maintained constant.

2 is a flow chart showing the procedure of the arc welding method according to this embodiment, and FIG. 3 is a side cross-sectional view showing the base material 4 to be welded. First, a pair of base materials 4 to be joined by welding are placed on an arc welding device, and various settings such as the welding mode and whether or not to use current amplitude control are performed (step S111). Specifically, as shown in FIG. 3, a plate-shaped first base material 41 and a second base material 42 are prepared, and the end faces 41a and 42a, which are the parts to be welded, are butted together and placed at a predetermined welding work position. The first base material 41 and the second base material 42 are, for example, stainless steel. Note that, if necessary, the first base material 41 and the second base material 42 may be provided with a groove of any shape, such as a Y-shape or a L-shape. The first and second base materials 41 and 42 may also be steel plates, such as mild steel, carbon steel for mechanical construction, and alloy steel for mechanical construction. Note that the above is an example of a butt welded joint, but is not limited by the type of welded joint, including fillet welded joints and T-joints.

After various settings have been made, the welding power source 1 determines whether the output start condition for the welding current I is met (step S112). Specifically, the welding power source 1 determines whether an output instruction signal for welding has been input. If it is determined that an output instruction signal has not been input and the output start condition for the welding current I is not met (step S112: NO), the welding power source 1 waits for the input of an output instruction signal.

When it is determined that the output start condition of the welding current I is satisfied (step S112: YES),
The welding power source 1 determines whether or not to execute the current amplitude control (step S113). The operator can select whether or not to use the current amplitude control, and the welding power source 1 accepts the setting of whether or not to use the current amplitude control via an operation unit (not shown).

When it is determined that the current amplitude control is not to be performed (step S113: NO), the welding power source 1 performs welding control without using the current amplitude control (step S114). The welding power source 1 also corrects the feed speed of the welding wire 5 and the set voltage required to match the output current with the set current and to maintain the arc length or the buried depth constant (step S115). Hereinafter, the correction in step S115 is referred to as the first output correction. In the first output correction, when the welding current I detected by the current detection unit 11e becomes smaller than the set current value, the correction unit 11f performs a correction to increase the feed speed of the welding wire 5 according to the difference between the detected welding current I and the set current value. The correction unit 11f also performs a correction to increase not only the feed speed of the welding wire 5 but also the set voltage at the same time.
When the welding current I detected by the current detection unit 11e becomes larger than a set current value, the correction unit 11f performs a correction to reduce the feed speed of the welding wire 5 according to the difference between the detected welding current I and the set current value. Moreover, the correction unit 11f performs a correction to reduce not only the feed speed of the welding wire 5 but also the set voltage at the same time.

In this way, by reflecting the above correction amount in the feed speed Fset and the set voltage Vset when current amplitude control is not performed, and setting the feed speed to Fset+ΔF and the set voltage to Vset+ΔV, it is possible to obtain the set output while maintaining a constant arc length or burial depth.

When it is determined that current amplitude control is to be performed (step S113: YES), the welding power source 1 performs welding control using current amplitude control (step S116). The welding power source 1 also corrects the feed speed of the welding wire 5 and the set voltage under the first and second welding conditions, which are necessary to match the average output current when current amplitude control is performed with the central set current and to maintain a constant arc length or buried depth (step S117). Hereinafter, the correction in step S117 is referred to as the second output correction. The processing of steps S116 and S117 will be described in detail later.

When the processing of step S115 or step S117 is completed, the power supply unit 11 of the welding power supply 1 determines whether or not to stop the output of the welding current I (step S118). Specifically, the welding power supply 1 determines whether or not the input of the output instruction signal is continuing. If the input of the output instruction signal is continuing and it is determined that the output of the welding current I should not be stopped (step S118: NO), the power supply unit 11 returns the process to step S113 and continues outputting the welding current I. If it is determined that the output of the welding current I should be stopped (step S118: YES), the power supply unit 11 ends the process.

<Current Amplitude Control>
4 is a flow chart showing the procedure of the current amplitude control. The setting circuit 11c of the welding power source 1 judges whether or not the switching period has arrived (step S131). The switching frequency is 1 Hz to 5 Hz, and the setting circuit 11c judges whether or not a time corresponding to the period of the switching frequency has elapsed since the current welding conditions were set. When it is judged that the switching period has arrived (step S131: YES), the setting circuit 11c switches the welding conditions (step S132). When the first welding conditions are set, the setting circuit 11c sets the second welding conditions. When the second welding conditions are set, the setting circuit 11c sets the first welding conditions. It is advisable to set the first welding conditions at the start of welding, for the first time.

When the process of step S132 is completed or when it is determined that the switching period has not arrived (step S131: NO), the welding power source 1 performs welding control by controlling the feeding of the welding wire 5 and the output of the power source unit 11 based on the welding conditions set by the setting circuit 11c (step S133). Specifically, the feed speed control circuit 12 of the welding power source 1 outputs a feed instruction signal for instructing the wire feeding to the wire feeder 3, and feeds the welding wire 5 at a speed corresponding to the feed speed signal F. The power source unit 11 of the welding power source 1 detects the arc voltage V and the welding current I by the voltage detection unit 11d and the current detection unit 11e, and PWM controls the output of the power source unit 11 so that the detected welding current I and arc voltage V are on the external characteristic lines corresponding to the set current and set voltage.
The critical current at which the buried arc state can be achieved varies depending on the type of welding wire 5 and shielding gas. For example, when a stainless steel solid wire is used as the welding wire 5 and a mixed gas of 98% argon + 2% oxygen is used as the shielding gas, the buried arc state is achieved when the first welding condition and the second welding condition are set such that the average current is 350 A or more. At least one of the first welding condition and the second welding condition only needs to satisfy the buried arc condition. In the case of the above welding wire 5 and shielding gas, it is difficult to maintain the buried arc under low current conditions, particularly under 350 A, but if the buried arc is achieved under high current conditions, deep penetration can be obtained. The buried arc includes both the fully buried arc and the semi-buried arc, which will be described later.
The power supply unit 11 is preferably configured to have external characteristics such that the drop in arc voltage V with respect to an increase in welding current I of 100 A is 2 V or more and 20 V or less. By setting the external characteristics of the power supply unit 11 in this manner, it becomes easy to maintain the buried arc state.

5 is an explanatory diagram of a buried arc state. In buried arc welding using a shielding gas containing argon, when a high current of 300 A or more is supplied to the welding wire 5 and the welding wire 5 is fed at about 5 to 100 m/min, a liquid column 8 is formed at the tip 5a of the welding wire 5, which is an elongated molten wire. Also, a concave molten portion 6 made of the base material 4 and the molten metal of the welding wire 5 is formed in the base material 4. An arc 7a with a high brightness is formed between a relatively lower portion of the liquid column 8 and the concave molten portion 6. On the other hand, an arc 7b with a relatively low brightness is formed at a relatively upper portion of the liquid column 8 or between the solid welding wire 5 and the concave molten portion 6.
Fig. 5A shows an arc state in which the generation points of arcs 7a and 7b on the welding wire 5 or liquid column 8 side have not entered the buried space surrounded by the concave molten portion 6. Fig. 5B shows a semi-buried arc state in which only the generation point of arc 7b on the liquid column 8 side has entered the buried space, and Fig. 5C shows a completely buried arc state in which even the generation point of arc 7a on the welding wire 5 or liquid column 8 side has entered the buried space.
In quasi-buried arc welding or buried arc welding, deep penetration is obtained by the arc 7a or 7b irradiated to the bottom 61 of the concave molten portion 6.

6 is a timing chart showing the method of switching welding conditions according to the first embodiment. The horizontal axis represents time, and the vertical axis represents set current. The first and second welding conditions are periodically switched by the processes in steps S131 and S132, and the set values of the first welding current and the second welding current vary periodically, as shown in FIG.
In this way, by switching between the first welding condition and the second welding condition, in which the central setting current of the welding current I is 350 A or more and the current fluctuation range is 50 A or more and 150 A or less, at a period of 1 Hz or more and 5 Hz or less, the molten metal can be vibrated and the occurrence of blowholes can be suppressed.

<Output correction>
7 is a flowchart showing the procedure of the second output correction. The welding power source 1 detects the welding current when welding is performed using the current amplitude control by the current detection unit 11e (step S151). The correction unit 11f of the welding power source 1 calculates the average output current based on the welding current detected by the current detection unit 11e (step S152). For example, the correction unit 11f calculates the average value of the welding current I for one cycle in which the welding current fluctuates. The correction unit 11f may also calculate a moving average of the welding current I over multiple cycles as the average output current.

Next, the correction unit 11f calculates the difference ΔI between the central set current and the average output current (step S153), and determines the correction amount ΔF of the feed speed by referring to table 13 using the difference ΔI as a key (step S154). It also calculates the correction amount ΔV of the set voltage based on the difference ΔI (step S155).

Then, the correction unit 11f corrects the feed speed and the set voltage of the welding wire W based on the calculated correction amount ΔF and correction amount ΔV (step S156). The timing of the correction is not particularly limited, but for example, the correction unit 11f may correct the feed speed and the set voltage at the timing of switching from the second welding condition to the first welding condition. Also, the correction unit 11f may be configured to correct the feed speed and the set voltage at the timing of switching between the first welding condition and the second welding condition.

In this way, when current amplitude control is used, the welding conditions are divided into low current side conditions (first welding conditions) and high current side conditions (second welding conditions), and the correction amounts ΔF and ΔV are applied to each period. That is, in the high current side conditions, the high current side feed speed Fset_high and set voltage Vset_high are used to set the feed speed to Fset_high+ΔF and the set voltage to Vset_high+ΔV. Similarly, in the low current side conditions, the low current side feed speed Fset_low and set voltage Vset_low are used to set the feed speed to Fset_low+ΔF and the set voltage to Vset_low+ΔV. With this control method, regardless of switching between high and low current conditions, the feed speed and set voltage are continuously corrected based on the center set current, and even when using current amplitude control, the average output current can be matched to the center set current while maintaining a constant arc length or burial depth.

(Example)
When buried arc welding is performed with a center set current of 400 A, using a φ1.6 mm stainless steel solid wire as the welding wire 5 and 98% argon + 2% oxygen as the shielding gas, and the welding current is varied at an amplitude of ±100 A and 2 Hz, the wire feed speed and set voltage under each of the high current side and low current side conditions can be corrected using the above method to match the average output current to the center set current while maintaining a constant buried depth.

<Effects of current amplitude control>
FIG. 8 is a cross-sectional view showing a welded joint. FIG. 8A is a cross-sectional view of a welded joint obtained by non-buried arc welding, and FIG. 8B is a cross-sectional view of a welded joint obtained by buried arc welding. In buried arc welding, as shown in FIG. 8B, the penetration at the center of the bead 9 is deeper than that of the bead 9 obtained by normal arc welding, and exhibits a so-called finger-shaped penetration. This tendency is more pronounced as the argon content in the shielding gas increases, and it is known that blowholes are more likely to remain at the deepest part. In addition, argon is an inert gas, and if it is caught in the molten metal, it becomes a cause of blowholes. Therefore, blowholes are very likely to occur in buried arc welding using a shielding gas containing argon.

Figure 9 is an image showing the results of a radiographic test of a welded joint when the current amplitude control according to the first embodiment was not performed. For example, when buried arc welding is performed on a stainless steel plate SUS304 using a stainless steel solid wire with a welding current of 400 A and a welding speed of 30 cm/min, many blowholes are generated, as shown in the radiographic test results in Figure 9.

Therefore, in this embodiment 1, the occurrence of blowholes is suppressed by switching and varying the first and second welding conditions, in which the center setting current of the welding current I is 350 A or more and the current fluctuation range is 50 A or more and 150 A or less, at a cycle of 1 Hz or more and 5 Hz or less.

Fig. 10 is an image showing the results of a radiographic test of a welded joint when the current amplitude control according to the present embodiment 1 was performed. In Fig. 10, "A (excellent)" indicates that no blowholes occurred, "B (good)" indicates that the number of blowholes occurred was reduced, and "C (fair)" indicates that the number of blowholes occurred was slightly reduced.
10, for example, when welding is performed using a stainless steel plate SUS304 as the base material 4 and a stainless steel solid wire as the welding wire 5 under conditions of a central set current of 400 A, an arc voltage of 31.5 V, a wire extension length of 20 mm, and a welding speed of 30 cm/min, the occurrence of blowholes can be suppressed by performing welding under a first welding condition in which the welding current I is 300 A and a second welding condition in which the welding current I is 500 A, varying the frequency at 2 Hz or 3 Hz. Note that when the first welding condition and the second welding condition are varied at a frequency of 1 Hz, the effect is inferior to a frequency of 2 Hz or higher, but the amount of blowholes generated can be reduced.
Furthermore, as shown in the upper part of FIG. 10, by performing welding under the same conditions as above, a first welding condition in which the welding current I is 350 A and a second welding condition in which the welding current I is 450 A are varied at a frequency of 1 Hz or more, it is possible to somewhat reduce the occurrence of blowholes.
Furthermore, as shown in the lower part of FIG. 10, by performing welding under the same conditions as above, a first welding condition in which the welding current I is 250 A and a second welding condition in which the welding current I is 550 A are varied at a frequency of 1 Hz, it is possible to suppress the occurrence of blowholes.
From the above results of the radiographic transmission test, it is understood that blowholes can be effectively suppressed by setting the current fluctuation range to 50 A or more, more preferably 100 A or more. It is also understood that blowholes can be effectively suppressed by setting the fluctuation frequency to 1 Hz or more, more preferably 2 Hz or more.

As described above, the arc welding device and method according to the first embodiment can suppress the occurrence of blowholes in consumable electrode arc welding with a center current of 350 A or more using a shielding gas containing argon, and can control the average output when current amplitude control is performed to be the same as the output when current amplitude control is not performed.

In addition, as described above, the occurrence of blowholes can be suppressed by controlling the current amplitude, and by correcting the feed speed of the welding wire 5 and the set voltage, the average output current can be matched to the central set current, and the arc length or, in the case of buried arc welding, the buried depth can be maintained constant.

Furthermore, table 13 associates the difference ΔI between the average output current and the central setting current with the correction amount ΔF and the correction amount ΔV, and table 13 can be easily created and parameters can be easily set.

Furthermore, according to this embodiment 1, deep penetration can be achieved by buried arc welding, and the occurrence of blowholes can be suppressed.

Furthermore, according to this embodiment 1, the occurrence of blowholes can be effectively suppressed in buried arc welding of stainless steel.

In this embodiment 1, an example in which two welding conditions, the first welding condition and the second welding condition, are periodically changed is described, but it may be configured to periodically switch between three or more welding conditions.

In addition, in this embodiment 1, an example of suppressing the occurrence of blowholes in buried arc welding has been described, but the present invention may also be applied to non-buried arc welding.

Furthermore, in this embodiment 1, an example in which the welding current is constantly corrected has been described, but the timing of the correction is not particularly limited. The correction process may be performed when the set current is switched, or at an appropriate timing such as every half cycle or every two cycles.

(Embodiment 2)
The arc welding method and the arc welding apparatus according to the second embodiment differ from those of the first embodiment in the configuration of the table 13 and the processing of the correction unit 11f, and therefore the above differences will be mainly described below. The other configurations and effects are the same as those of the first embodiment, so the same reference numerals are used for the corresponding parts and detailed description will be omitted.

Figure 11 is a conceptual diagram showing a table according to the second embodiment. Table 13 includes, for example, a first table 213a for correcting the feed speed and a second table 213b for correcting the set voltage.

Figure 11A is a conceptual diagram of the first table 213a. The first table 213a stores the average output current output from the welding power source 1 or power source circuit 11a, the difference ΔI between the average output current and the central set current, the central set current, and a correction amount ΔF for the feed speed of the welding wire 5, in association with each other. The correction amount ΔF is a correction amount for the feed speed that is mainly used to match the average output current with the central set current.

Figure 11B is a conceptual diagram of the second table 213b. The second table 213b stores the average output current output from the welding power source 1 or the power circuit 11a, the difference ΔI between the center set current, the center set current, and the correction amount ΔV of the set voltage in association with each other. The correction amount ΔV is the correction amount of the set voltage mainly for maintaining the arc length or burial depth constant.

The correction unit 11f determines a correction amount ΔF for the feed speed of the welding wire 5 by referring to the first table 213a using the difference ΔI between the average output current and the central set current output from the welding power source 1 when current amplitude control is performed, and the central set current as a key. The correction unit 11f also determines a correction amount ΔV for the set voltage by referring to the second table 213b using the difference ΔI and the central set current as a key.

As in the first embodiment, the first table 213a and the second table 213b may be configured as a first function and a second function.

The arc welding apparatus and method according to the second embodiment allow for more precise control of the arc length or buried depth than in the first embodiment.

(Embodiment 3)
The arc welding method and the arc welding apparatus according to the third embodiment differ from those of the first embodiment in the configuration of the table 13 and the processing of the correction unit 11f, and therefore the above differences will be mainly described below. The other configurations and effects are the same as those of the first embodiment, so the same reference numerals are used for the corresponding parts and detailed description will be omitted.

Figure 12 is a conceptual diagram showing a table according to the third embodiment. Table 13 includes, for example, a first table 313a for correcting the feed speed and a second table 313b for correcting the set voltage.

Figure 12A is a conceptual diagram of the first table 313a. The configuration of the first table 313a is similar to that of the first table 213a according to the second embodiment.

Figure 12B is a conceptual diagram of the second table 313b. The second table 313b stores the correction amount ΔF of the welding wire 5, the center set current, and the correction amount ΔV of the set voltage in association with each other. The correction amount ΔV is the correction amount of the set voltage to maintain a constant arc length or burial depth.

The correction unit 11f determines the correction amount ΔF of the feed speed of the welding wire 5 by referring to the first table 313a using the difference ΔI between the average output current and the central set current output from the welding power source 1 when current amplitude control is performed, and the central set current as a key. The correction unit 11f also determines the correction amount ΔV of the set voltage by referring to the second table 313b using the correction amount ΔF of the welding wire 5 and the central set current as a key.

As in the first embodiment, the first table 313a and the second table 313b may be configured as a first function and a second function, respectively.

The arc welding apparatus and method according to the third embodiment allow for more precise control of the arc length or buried depth than in the first embodiment.

Although the correction amount ΔV of the set voltage per correction amount ΔF of the feed speed is calculated based on a parameter corresponding to the central set current, it may be calculated individually as parameters based on the set current under the high current side condition and the low current side condition, such as ΔV_high and ΔV_low, respectively. For example, a table may be provided in which the correction amount ΔF of the feed speed, the set current for the first welding condition or the second welding condition, and the correction amount ΔV of the set voltage are associated with each other, and correction unit 11f may be configured to determine the correction amount of the set voltage for the first welding condition using the difference ΔI and the set current for the first welding condition as keys, and to determine the correction amount of the set voltage for the second welding condition using the difference ΔI and the set current for the second welding condition as keys.
Alternatively, based on the correction amount ΔV, the correction amount ΔV_high for the high current condition and the correction amount ΔV_low for the low current condition may be divided proportionately according to the current value.

(Embodiment 4)
The arc welding method and arc welding apparatus according to the fourth embodiment further differs from the first embodiment in that the set voltage is varied between 10 Hz and 1000 Hz, and therefore the above difference will be mainly described below. The other configurations and effects are the same as those of the first to third embodiments, so the same reference numerals are used for corresponding parts and detailed description will be omitted.

Figure 13 is a timing chart showing a method of switching welding conditions according to the fourth embodiment. In Figure 13, the horizontal axis represents time, the vertical axis of Figure 13A represents the set current, and the vertical axis of Figure 13B represents the set voltage. However, Figure 13A shows the set values of the first welding current and the second welding current corresponding to the first and second welding conditions, and does not show fluctuations in the set voltage due to high-frequency vibration.

In the current amplitude control, the control circuit 11b according to the fourth embodiment further periodically varies the set voltage at a frequency of 10 Hz to 1000 Hz, preferably 50 Hz to 300 Hz, and more preferably 80 Hz to 200 Hz. Due to the variation in the set voltage, the output welding current I varies, for example, with a current amplitude of 50 A or more.

According to the arc welding device and the arc welding method of the fourth embodiment, the molten pool can be stabilized by micro-vibration, thereby preventing the bead 9 from becoming turbulent and dripping, and the molten pool can be slowly and strongly vibrated at a frequency of 1 Hz or more and 5 Hz or more, thereby suppressing the occurrence of blowholes.

1 welding power source, 2 torch, 3 wire feeder, 4 base material, 5 welding wire, 6 melting part, 11 power source, 11a power circuit, 11b control circuit, 11c setting circuit, 11f correction unit, 12 feed speed control circuit, 13 table

Claims (7)

A consumable electrode type arc welding device using a shielding gas containing argon,
a power supply circuit for outputting a welding current to the welding wire;
a setting circuit that periodically switches between a first welding condition under which a first welding current smaller than a central set current is output to the welding wire and a second welding condition under which a second welding current larger than the central set current is output to the welding wire;
a feed speed control circuit that controls the feeding of the welding wire at a feed speed according to the first welding condition and the second welding condition set by the setting circuit;
a current detection unit that detects a welding current output from the power supply circuit when welding is performed by periodically switching between the first welding condition and the second welding condition;
a correction unit that corrects the welding wire feed speed and set voltages for the first welding condition and the second welding condition based on a difference between an average output current when welding is performed by periodically switching between the first welding condition and the second welding condition and the central set current. a table or function correlating the difference, a correction amount of the feed speed, and a correction amount of the set voltage;
The correction unit is
The arc welding device according to claim 1 , wherein the feed speed correction amount and the set voltage correction amount are determined by referring to the table or function using the difference based on the welding current detected by the current detection unit. a table or function that associates the difference, the central set current, a correction amount of the feed speed, and a correction amount of the set voltage;
The correction unit is
2. The arc welding device according to claim 1, wherein the feed speed correction amount and the set voltage correction amount are determined by referring to the table or function using the difference based on the welding current detected by the current detection unit and the central set current. a first table or a first function that associates the difference, the center setting current, and a correction amount of the feed speed;
a second table or a second function that associates the center set current, the feed speed correction amount, and the set voltage correction amount;
The correction unit is
2. The arc welding device according to claim 1, wherein a correction amount for the feed speed is determined by referring to the first table or the first function using the difference based on the welding current detected by the current detection unit and the central set current, and a correction amount for the set voltage is determined by referring to the second table or the second function using the determined correction amount for the feed speed and the central set current. The first welding condition and the second welding condition are
5. The arc welding device according to claim 1, wherein the welding conditions are such that the center set current is 350 A or more and the current fluctuation range is 50 A or more and 150 A or less, and the first welding condition and the second welding condition are switched at a cycle of 1 Hz or more and 5 Hz or less. The first welding condition or the second welding condition is
6. The arc welding device according to claim 1, wherein the welding conditions are such that the tip of the welding wire, or the arc generation point in the liquid column formed at the tip, enters a space surrounded by a concave molten portion formed in the base metal by the arc. A consumable electrode arc welding method using a welding power source and a shielding gas containing argon, comprising:
a first welding condition under which a first welding current smaller than a center set current is output from the welding power source to the welding wire, and a second welding condition under which a second welding current larger than the center set current is output from the welding power source to the welding wire are periodically switched and set;
detecting a welding current output from the welding power source when welding is performed by periodically switching between the first welding condition and the second welding condition;
and correcting a welding wire feed speed and set voltages for the first welding condition and the second welding condition based on a difference between an average output current when welding is performed by periodically switching between the first welding condition and the second welding condition and the central set current.

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