Welding method of submerged arc welding, and submerged arc welding system

Abstract

To provide a welding method of submerged arc welding and a submerged arc welding system which enable satisfactory arc start by a simpler method.SOLUTION: A welding method, which performs submerged arc welding in a submerged arc welding system A1 including a welding power supply device 2, and a wire supply device 5 for supplying a welding wire, includes a cutting step of cutting a welding wire so as to be inclined to an orthogonal surface 9 orthogonal in a direction at which a tip surface 8a extends to the welding wire, before welding start.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a welding method for submerged arc welding and a submerged arc welding system. [Background technology]

[0002] Submerged arc welding has been known for some time. In submerged arc welding, granular flux is dispersed on the workpiece, a welding wire is fed into the flux, and an arc is generated between the tip of the welding wire and the workpiece. In submerged arc welding, a large current is passed through a large-diameter welding wire, allowing for high-efficiency welding of thick plates.

[0003] Patent Document 1 discloses a welding power supply system that automates the work at the start of submerged arc welding and can prevent impurities from being mixed into the welded bead. This welding power supply system provides a start current period, flows a start current during that period, and slows down the welding wire feed speed, thereby achieving good starting performance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-45136 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 requires a process of detecting the contact state between the tip of the welding wire and the workpiece and then passing a start current. Because this process requires a welding power supply and control device with special functions, this method cannot be applied to existing welding power supplies.

[0006] The present invention has been devised in light of the above circumstances, and an object of the present invention is to provide a submerged arc welding method and a submerged arc welding system that enable a good arc start in a simpler manner. [Means for solving the problem]

[0007] A welding method provided by a first aspect of the present invention is a welding method for performing submerged arc welding in a submerged arc welding system including a welding power supply and a wire feeder that feeds a welding wire, and includes a cutting step of cutting the welding wire before starting welding so that a tip end surface of the welding wire is inclined with respect to an orthogonal plane that is orthogonal to a direction in which the welding wire extends.

[0008] In a preferred embodiment of the present invention, the angle of inclination formed between the tip surface and the orthogonal surface is not less than 30° and not more than 60°.

[0009] In a preferred embodiment of the present invention, the submerged arc welding system further includes a carriage on which the wire feeder is mounted and which moves along the welding line, and the tip surface faces in a direction opposite to the direction of travel of the carriage.

[0010] In a preferred embodiment of the present invention, the welding power supply applies a DC voltage between the welding wire and the workpiece while the wire feeder feeds the welding wire at an initial feed speed, and the method further includes a short-circuit detection step of detecting contact between the welding wire and the workpiece, and a spray start step of starting spraying of flux, the spray start step being performed before the short-circuit detection step.

[0011] A submerged arc welding system provided by a second aspect of the present invention is a submerged arc welding system for performing submerged arc welding, comprising a welding power supply device that supplies power, a welding wire, and a wire feeder that feeds the welding wire, wherein a tip surface of the welding wire is inclined with respect to an orthogonal plane that is perpendicular to the direction in which the welding wire extends. [Effects of the Invention]

[0012] The welding method according to the present invention includes a cutting step of cutting the welding wire before the start of welding so that the tip end surface is inclined with respect to a plane perpendicular to the direction of extension of the welding wire. Therefore, when the tip end of the welding wire contacts the workpiece as an electrode at the start of welding, the area of ​​the contact portion is smaller than when the tip end surface is not inclined with respect to the plane perpendicular to the direction of extension of the welding wire. This increases the resistance of the contact portion and reduces the heat capacity of the tip end of the welding wire, so that the tip end melts and transfers preferentially, achieving a smooth arc start. In other words, a good arc start can be achieved by a simple method of simply cutting the welding wire so that the tip end surface is inclined with respect to the plane perpendicular to the direction of extension of the welding wire, which is also performed in a conventional welding method. [Brief explanation of the drawings]

[0013] [Figure 1] 1A and 1B are diagrams for explaining a welding system according to a first embodiment, in which FIG. 1A is a block diagram showing the overall configuration of the welding system, and FIG. 1B is a block diagram showing the internal configuration of a welding power supply. [Figure 2] FIG. 4 is a diagram showing an example of a characteristic line of an external characteristic set by a control circuit. [Figure 3] FIG. 2 is a simplified diagram for explaining a tip surface of an electrode. [Figure 4] 4 is an example of a flowchart showing a start control process performed by the control device according to the first embodiment. [Figure 5] FIG. 2 is a simplified diagram for explaining a tip surface of an electrode. [Figure 6] 10 is an example of a flowchart illustrating a start control process performed by a control device according to a second embodiment. [Figure 7] FIG. 10 is a simplified diagram for explaining the movement of an electrode. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0015] [First embodiment] 1A and 1B are diagrams for explaining a welding system A1 according to a first embodiment. Fig. 1A is a block diagram showing the overall configuration of the welding system A1. Fig. 1B is a block diagram showing the internal configuration of a welding power supply 2.

[0016] Welding system A1 is a welding system for performing submerged arc welding. As shown in FIG. 1(a), welding system A1 includes control device 1, welding power supply 2, carriage 4, wire feeder 5, wire reel 6, sprayer 7, and electrode 8. Wire feeder 5, wire reel 6, sprayer 7, and electrode 8 are mounted on carriage 4. Welding system A1 moves carriage 4 along a weld line of workpieces W, spraying granular flux stored in a hopper of sprayer 7 and causing wire feeder 5 to feed welding wire into the flux. The welding wire is supplied from wire reel 6. Welding power supply 2 converts AC power supplied from commercial power source P into power suitable for welding and outputs it. An arc is generated within the flux between electrode 8, which is the tip of the welding wire, and workpiece W. The heat of the arc causes welding. This results in welding along the weld line of workpieces W. Instead of using the carriage 4, the workpieces W may be moved or rotated.

[0017] The control device 1 performs various controls of the welding system A1. The control device 1 may be a general-purpose computer with a program installed that performs various controls of the welding system A1, or it may be a dedicated device for controlling the welding system A1. The control device 1 moves the carriage 4 at a predetermined speed. The speed is set depending on the material and thickness of the workpiece W. The control device 1 instructs the sprayer 7 to start and stop spraying flux. Note that the sprayer 7 may start and stop spraying flux manually. The control device 1 instructs the wire feeder 5 to start and stop feeding the welding wire and the welding wire feed speed. The welding feed speed for welding is set depending on the set welding current, etc. The control device 1 instructs the welding power supply 2 to start and stop power output. Details of the control performed by the control device 1 when starting welding will be described later.

[0018] Welding power supply 2 converts AC power supplied from commercial power supply P into desired power and outputs it. Note that a plurality of welding power supplies 2 connected in parallel (specifically, output terminals a of welding power supplies 2 are connected to each other and connected to workpieces W, and output terminals b of welding power supplies 2 are connected to each other and connected to welding wire) may be used in place of welding power supply 2.

[0019] As shown in FIG. 1(b), welding power supply 2 includes rectifying and smoothing circuit 21, inverter circuit 22, transformer 23, rectifying and smoothing circuit 24, inverter circuit 25, current sensor 26, voltage sensor 27, and control circuit 28.

[0020] The rectifying and smoothing circuit 21 converts AC power input from the commercial power source P into DC power and outputs it. The inverter circuit 22 converts the DC power input from the rectifying and smoothing circuit 21 into high-frequency power and outputs it by switching the switching elements in response to an output control drive signal input from the control circuit 28. The transformer 23 transforms the high-frequency voltage output by the inverter circuit 22 and outputs it to the rectifying and smoothing circuit 24. The rectifying and smoothing circuit 24 converts the high-frequency power input from the transformer 23 into DC power and outputs it.

[0021] Inverter circuit 25 converts the DC power input from rectifying and smoothing circuit 24 into AC power and outputs it by switching the switching element in response to a switching drive signal input from control circuit 28. Inverter circuit 25 switches between a positive polarity in which the potential of output terminal a (connected to workpiece W) is higher than the potential of output terminal b (connected to the welding wire), and a reverse polarity in which the potential of output terminal a is lower than the potential of output terminal b.

[0022] Current sensor 26 detects the output current of welding power supply 2 and, in this embodiment, is disposed on the connecting line connecting one output terminal of inverter circuit 25 and output terminal a. The output current of welding power supply 2 detected by current sensor 26 is substantially equal to the current flowing through electrode 8. Current sensor 26 outputs a current value signal corresponding to the detected instantaneous current value to control circuit 28 and control device 1. The configuration of current sensor 26 is not limited as long as it detects the output current from the connecting line. The location of current sensor 26 is also not limited. For example, current sensor 26 may be disposed on the connecting line connecting the other output terminal of inverter circuit 25 and output terminal b. Current sensor 26 may also be disposed external to welding power supply 2.

[0023] Voltage sensor 27 detects the output voltage of welding power supply 2, and in this embodiment, detects the voltage between output terminal a and output terminal b. This voltage is approximately equal to the voltage applied between workpiece W and the tip of electrode 8. Voltage sensor 27 outputs a voltage value signal corresponding to the detected instantaneous voltage value to control circuit 28 and control device 1. The configuration of voltage sensor 27 is not limited. Furthermore, the location where voltage sensor 27 is disposed is not limited. For example, voltage sensor 27 may detect the voltage between a lead wire attached to a welding torch that guides the welding wire to the welding point and a lead wire attached to workpiece W. Furthermore, voltage sensor 27 may be disposed external to welding power supply 2.

[0024] Control circuit 28 is a circuit for controlling welding power supply 2, and is realized by, for example, a microcomputer. Control circuit 28 receives a current value signal from current sensor 26, a voltage value signal from voltage sensor 27, and various command signals and various setting values ​​from control device 1. Control circuit 28 then outputs drive signals to inverter circuit 22 and inverter circuit 25, respectively.

[0025] When control circuit 28 receives a command signal from control device 1 instructing it to start power output, it starts outputting drive signals to inverter circuit 22 and inverter circuit 25, respectively, to start power output. When control circuit 28 receives a command signal from control device 1 instructing it to stop power output, it stops outputting drive signals to stop power output.

[0026] Control circuit 28 controls the output current and output voltage so that the output characteristics of welding power supply 2 become the set external characteristics. The external characteristics are characteristics that show the relationship between the welding current and the welding voltage, and are generally expressed by a characteristic line that shows the characteristics. Control circuit 28 sets the external characteristics by setting an arithmetic expression that simplifies the characteristic line. Control circuit 28 sets, as the external characteristics, so-called constant voltage characteristics, in which the welding voltage does not change much even when the welding current changes.

[0027] Fig. 2 is a diagram showing an example of a characteristic line of the external characteristic set by control circuit 28. The horizontal axis of the diagram indicates the current value I, and the vertical axis indicates the voltage value V. In Fig. 2, the characteristic line X of the external characteristic is a straight line with a slope of Kr, in which the voltage value V becomes the reference voltage value Vr when the current value I becomes the reference current value Ir. The function representing the external characteristic is given by the following equation (1). V=Kr (I-Ir)+Vr (1)

[0028] The slope Kr is not limited. However, it is important to quickly obtain an appropriate arc length at the start of the arc. The arc length correlates with the welding voltage. The closer the external characteristic is to a completely constant voltage characteristic (Kr = 0), the more quickly the welding voltage can approach the desired voltage. However, if the slope Kr is greater than -0.5 / 100 A, the welding voltage is more susceptible to voltage changes due to voltage noise, etc. Furthermore, if the slope Kr is less than -40 V / 100 A, the current change relative to the voltage change is too small, making it difficult to change the wire melting amount of a large-diameter welding wire. Therefore, in this embodiment, the slope Kr is set to be greater than -40 V / 100 A and less than -0.5 V / 100 A. In other words, the external characteristic set by the control circuit 28 is such that the voltage drop relative to a 100 A current increase is 0.5 V or more and 40 V or less. It is more desirable that the slope Kr be greater than -15 V / 100 A and less than -1.5 V / 100 A.

[0029] The control circuit 28 includes a target current setting section 281, a current control section 282, and a drive signal generating section 285 as functional components.

[0030] Target current setting unit 281 is a functional component for setting a target current, which is a target value of the output current of welding power supply 2. Target current setting unit 281 sets a function (the above-mentioned formula (1)) indicating the external characteristics based on a preset slope Kr, a reference voltage value Vr, and a reference current value Ir.

[0031] Target current setting unit 281 sets a target current based on a function indicating the set external characteristic and a voltage value V (e.g., effective voltage value) corresponding to a voltage value signal input from voltage sensor 27. That is, target current setting unit 281 substitutes voltage value V, which is the output voltage of welding power supply 2 detected by voltage sensor 27, into equation (1) above to calculate current value I, and sets calculated current value I as the target current. Target current setting unit 281 outputs the set target current to current control unit 282.

[0032] Current control unit 282 is a functional component for controlling the output current of welding power supply 2. Current control unit 282 performs feedback control so that the output current of welding power supply 2 becomes a target current. Specifically, current control unit 282 calculates the deviation between the current value signal input from current sensor 26 and the target current input from target current setting unit 281. Then, current control unit 282 performs calculations using, for example, PI control on the calculated deviation, and outputs the calculated value to drive signal generation unit 285.

[0033] The drive signal generation unit 285 is a functional component for generating an output control drive signal to be output to the inverter circuit 22. The drive signal generation unit 285 generates an output control drive signal for PWM control by, for example, a triangular wave comparison method, based on the calculated value input from the current control unit 282. The drive signal generation unit 285 outputs the generated output control drive signal to the inverter circuit 22.

[0034] Inverter circuit 22 converts the DC power input from rectifying and smoothing circuit 21 into high-frequency power and outputs it by switching the switching elements in response to the output control drive signal input from drive signal generation unit 285. The high-frequency power is converted into DC power via transformer 23 and rectifying and smoothing circuit 24, and then converted into AC power by inverter circuit 25 and output from welding power supply 2. The output current of welding power supply 2 is controlled to the target current set by target current setting unit 281.

[0035] The internal configuration of control circuit 28 is not limited to that described above. Control circuit 28 only needs to control the output current and output voltage so that the output characteristics of welding power supply 2 match the set external characteristics.

[0036] Furthermore, when a DC output command signal is input from the control device 1, the control circuit 28 outputs a switching drive signal to the inverter circuit 25 to fix certain switching elements to the ON state and fix the other switching elements to the OFF state. For example, when the states of the switching elements are fixed so that the positive output terminal of the rectifying and smoothing circuit 24 is connected to the output terminal a and the negative output terminal of the rectifying and smoothing circuit 24 is connected to the output terminal b, the welding power supply 2 outputs DC power with the output terminal a as the positive electrode and the output terminal b as the negative electrode. In other words, the welding system A1 is an AC / DC dual-purpose welding system that can output not only AC power but also DC power. Furthermore, the welding power supply 2 can control the output current based on the current command value input from the control device 1. Therefore, the welding system A1 can appropriately control the output current.

[0037] 3, in this embodiment, a tip surface 8a of the electrode 8 (welding wire) is inclined with respect to an orthogonal plane 9 that is perpendicular to the direction in which the electrode 8 extends. The inclination angle α formed between the tip surface 8a and the orthogonal plane 9 is not limited, but is 45° in this embodiment.

[0038] Typically, in submerged arc welding, the welding wire is cut perpendicular to its extension. In other words, the inclination angle α is 0°. In this case, when the tip surface 8a is smooth and in complete contact with the workpiece W, the electrical resistance near the tip surface 8a is approximately equal to the electrical resistance of the rest of the welding wire. Therefore, when the welding current flows, the welding wire is uniformly heated throughout by resistance heating and melts near the center between the power contact tip and the workpiece W. In this case, the large-diameter welding wire melts rapidly, significantly destabilizing the arc start. Furthermore, there is a risk that the tip of the melted welding wire may protrude from the dispersed flux or that the arc may become too long, resulting in arc interruption. However, in reality, the tip surface 8a is not completely smooth and cannot be in complete contact with the workpiece W. Therefore, the portion of the tip surface 8a in contact with the workpiece W has a locally high electrical resistance and melts preferentially due to resistance heating. However, as the inclination angle α approaches 0°, the local resistance increase becomes smaller, and as described above, the welding wire becomes more likely to melt. On the other hand, as the inclination angle α approaches 90°, the contact area between the welding wire and the workpiece W becomes smaller, resulting in increased local resistance. Furthermore, the heat capacity of the tip of the welding wire becomes smaller. Therefore, the tip melts and transfers preferentially, achieving a smooth arc start. However, as the inclination angle α approaches 90°, the cross-sectional area of ​​the portion to be cut increases, making cutting the welding wire more difficult. For these reasons, it is desirable that the inclination angle α between the tip surface 8a and the orthogonal surface 9 be between 30° and 60°. If the inclination angle α is less than 30°, the welding wire becomes more likely to melt, making it difficult to achieve a smooth arc start. On the other hand, if the inclination angle α is greater than 60°, a very large force is required to cut the welding wire, making cutting difficult.

[0039] In this embodiment, as shown in FIG. 3, the tip surface 8a of the electrode 8 (welding wire) faces in the direction opposite to the traveling direction of the carriage 4 (the direction of the arrow in the figure). Note that the direction in which the tip surface 8a faces is not limited to this. The tip surface 8a is formed when an operator cuts the welding wire with pliers or the like when the previous welding process is completed. Note that the welding wire may also be cut just before the start of the welding process. In other words, it is sufficient that the electrode 8 (welding wire) is cut before the welding process is started to form the tip surface 8a. Furthermore, the cutting of the welding wire does not have to be done manually by an operator and may be automated.

[0040] Next, a description will be given of the control process at the start of welding performed by the control device 1. Fig. 4 is an example of a flowchart showing the start control process at the start of welding performed by the control device 1. The start control process is started, for example, when an operation button for starting welding is pressed.

[0041] Before the start control process, a cutting process is performed (S0) to cut the tip of the electrode 8 (welding wire). In the cutting process, an operator cuts the electrode 8 (welding wire) using pliers or the like. At this time, the operator performs the cutting so that the tip surface 8a is inclined with respect to the orthogonal plane 9 at an inclination angle α of 45°. Note that the inclination angle α is not limited, but is preferably 30° or more and 60° or less. The cutting process may be performed when the previous welding process is completed or may be performed immediately before the start control process. Although the cutting process is not included in the start control process performed by the control device 1, for convenience it is shown in the flowchart of FIG. 4 as a process related to the start control process. Note that the cutting process may not be performed by an operator, but may be performed automatically in response to an instruction from the control device 1.

[0042] In the start control process, first, a short circuit detection step (S1 to S3) is performed. In the short circuit detection step, first, feeding of the welding wire is started (S1). Specifically, control device 1 instructs wire feeder 5 to start feeding the welding wire. At this time, control device 1 instructs wire feeder 5 to feed the welding wire in the forward direction (from wire reel 6 toward carriage 4) at an initial feeding speed. The initial feeding speed is a so-called slowdown speed, which is sufficiently slower than the welding feeding speed for welding (for example, but not limited to, about 0.5 m / min).

[0043] Next, application of a DC voltage (no-load voltage) begins between the workpiece W and electrode 8 (S2). Specifically, control device 1 instructs welding power supply 2 to output a DC voltage. In this embodiment, welding power supply 2 is controlled by control circuit 28, and inverter circuit 25 outputs the DC voltage. Note that welding power supply 2 may also be provided with a separate DC power supply connected in parallel to output terminals a and b, and the DC voltage to be applied between the workpiece W and electrode 8 may be output from this DC power supply. The no-load voltage is not limited to, but is, for example, about 100 V.

[0044] Next, it is determined whether or not the electrode 8 has come into contact with the workpieces W and caused a short circuit (S3). Specifically, the control device 1 makes this determination based on a voltage value signal input from the voltage sensor 27. If the electrode 8 has been short-circuited to the workpieces W, the voltage between the electrode 8 and the workpieces W drops sharply and approaches "0." The control device 1 determines that a short circuit has occurred when the voltage detected by the voltage sensor 27 (hereinafter referred to as "detected voltage") becomes equal to or less than the short-circuit detection threshold. Note that the method for determining a short circuit is not limited. For example, the control device 1 may determine that a short circuit has occurred based on a current value signal input from the current sensor 26. If a short circuit is not detected (S3: NO), the process returns to step S3, and the determination in step S3 is repeated. That is, the control device 1 waits until a short circuit is detected. If a short circuit is detected (S3: YES), the feeding of the welding wire is stopped (S4). Specifically, the control device 1 instructs the wire feeder 5 to stop feeding the welding wire.

[0045] Next, a flux spray start step is performed. That is, spraying of flux starts to the welding start point where the welding wire is in contact with the workpiece W and its surrounding area (S5). Specifically, the control device 1 instructs the spraying device 7 to spray flux. The spraying device 7 sprays a predetermined appropriate amount of flux.

[0046] Next, current output begins (S6). Specifically, control device 1 instructs welding power supply 2 to output a current. The current instructed at this time may be a start current for starting, or a welding current according to the welding conditions that is output when actually welding. In the case of a welding current, control circuit 28 of welding power supply 2 controls the output current and output voltage so as to achieve output characteristics (constant voltage characteristics) according to the set external characteristics. Therefore, the relationship between the welding current and welding voltage output by welding power supply 2 is in accordance with the above equation (1).

[0047] Next, it is determined whether or not the detected voltage Vd detected by voltage sensor 27 is equal to or greater than a predetermined voltage threshold V0 (S7). The voltage threshold V0 is a threshold for detecting that an arc has been generated by the welding current and stabilized, and is set to the voltage at which the generated arc length reaches a desired length. The voltage threshold V0 is not limited, but is preferably between 20 V and 40 V. If the voltage threshold V0 is set to less than 20 V, a sufficient arc length will not be ensured. On the other hand, if the voltage threshold V0 is set to more than 40 V, the arc length will be excessive, making it more likely that the arc will be interrupted. In this embodiment, the voltage threshold V0 is set to 30 V. In this case, it has been confirmed that good starting performance can be obtained under all conditions, at least in a wire diameter range of φ2.4 mm to φ6.4 mm and a welding current range of 300 A to 1500 A, in an environment where the power cable electrically connecting output terminal b of welding power supply 2 and electrode 8 is approximately 40 m long. The appropriate value of the voltage threshold V0 varies depending on the state of the power cable and also on the position where the voltage sensor 27 detects the voltage. Therefore, the actually set voltage threshold V0 can be adjusted by the operator depending on the situation. The control device 1 may also store a table that associates conditions such as the wire diameter, wire material, welding current setting, and power cable length with the optimal voltage threshold V0, and automatically set the voltage threshold V0 to a value corresponding to each condition.

[0048] If the detected voltage Vd is not equal to or greater than the voltage threshold V0 (S7: NO), the process returns to step S7, and the determination in step S7 is repeated. That is, the control device 1 waits until the detected voltage Vd becomes equal to or greater than the voltage threshold V0. If the detected voltage Vd becomes equal to or greater than the voltage threshold V0 (S7: YES), the feeding of the welding wire is resumed (S8). Specifically, the control device 1 instructs the wire feeder 5 to resume feeding of the welding wire. The welding wire feed speed at this time is the welding feed speed for welding set in the welding conditions. Note that if a start current was output in step S6, it is switched to the welding current. Next, the movement of the carriage 4 begins (S9), and the start control process ends. After the start control process ends, the wire feed continues at the welding feed speed set in the welding conditions, and the output of welding power at the welding current and welding voltage according to the welding conditions continues. In addition, the spraying of flux by the sprayer 7 and the movement of the carriage 4 also continue.

[0049] The process shown in the flowchart of FIG. 4 is an example, and the start control process performed by the control device 1 is not limited to the above.

[0050] Next, the operation and effects of the welding method according to this embodiment will be described.

[0051] The welding method according to this embodiment includes a cutting step of cutting the electrode 8 (welding wire) before the start of welding so that the tip surface 8 a is inclined with respect to an orthogonal plane 9 perpendicular to the extension direction of the electrode 8. Therefore, when the tip of the electrode 8 (welding wire) contacts the workpiece W at the start of welding, the area of ​​the contact portion is smaller than when the tip surface 8 a is not inclined with respect to the orthogonal plane 9. This increases the resistance of the contact portion and reduces the heat capacity of the tip portion of the electrode 8, allowing the tip portion to melt and transfer preferentially, achieving a smooth arc start. Generally, in submerged arc welding, to ensure the joint soundness of the arc start portion, the tip portion of the welding wire that has been oxidized due to the heat of the previous welding process is cut off before the start of the next welding process. In other words, a good arc start can be achieved by simply cutting the welding wire so that the tip surface 8 a is inclined with respect to the orthogonal plane 9 in the welding wire cutting step, which is also performed in conventional welding methods.

[0052] Furthermore, according to this embodiment, the inclination angle α formed between the tip end surface 8a and the orthogonal surface 9 is equal to or greater than 30° and equal to or less than 60°. Therefore, the occurrence of melting of the welding wire can be suppressed, and the labor required to cut the welding wire can be reduced.

[0053] Furthermore, if the cutting process is performed when the previous welding process is completed, the start control process can be performed at the start of the welding process without performing the cutting process.

[0054] In this embodiment, the electrode 8 advances in a direction perpendicular to the surface of the workpiece W, but this is not limiting. The electrode 8 may advance in a direction inclined from the direction perpendicular to the surface of the workpiece W. For example, as shown in FIG. 5, when the electrode 8 advances at an angle β with respect to the surface of the workpiece W, the inclination angle α may be set to an angle calculated as α = 45° + (90° - β).

[0055] 6 and 7 are diagrams for explaining a welding system A2 according to a second embodiment. FIG. 6 is an example of a flowchart showing the start control process performed by a control device 1 according to the second embodiment. FIG. 7 is a simplified diagram for explaining the movement of an electrode 8. Note that the block diagram showing the overall configuration of a welding system A2 according to the second embodiment and the block diagram showing the internal configuration of a welding power supply 2 are similar to those of the welding system A1 shown in FIG. 1, and therefore will not be described or explained here. The welding system A2 according to this embodiment differs from the welding system A1 according to the first embodiment in the start control process performed by the control device 1.

[0056] As shown in FIG. 6 , in the start control process according to this embodiment, a flux spray start step (S5) is performed before the short-circuit detection steps (S1 to S3) are performed. That is, in the start control process according to this embodiment, flux is first sprayed (S5), and then welding wire feeding is started at an initial feed rate for short-circuit detection (S1). Therefore, the electrode 8 is inserted from outside the sprayed flux into the flux. When the welding wire is cut in a direction perpendicular to the direction of extension of the welding wire, as in the conventional method, the tip end surface 8 a of the electrode 8 is not inclined (parallel) with respect to the orthogonal plane 9. Therefore, when the electrode 8 is inserted into the flux, the flux, which is an insulator, may be trapped between the tip end surface 8 a of the electrode 8 and the workpiece W. In this case, the short circuit is not detected, and the arc start fails. On the other hand, in this embodiment, the tip end surface 8 a of the electrode 8 is inclined with respect to the orthogonal plane 9. Therefore, as shown in FIG. 7, when the electrode 8 is inserted into the flux 79 (see the broken arrow and the electrode 8 indicated by the broken line), it is possible to prevent the flux from being caught between the front end face 8a and the workpiece W.

[0057] Furthermore, as shown in FIG. 6 , the start control process according to this embodiment does not control the movement of the carriage 4. The movement control of the carriage 4 is executed independently of the start control process. When the start control process controls the start of movement of the carriage 4 as in the first embodiment, the carriage 4 does not start moving unless a short circuit is detected in step S3. On the other hand, in this embodiment, the movement control of the carriage 4 is executed independently of the start control process. Therefore, even if a short circuit is not detected due to flux being trapped between the front end surface 8 a and the workpieces W, the carriage 4 may move. In this case, as the carriage 4 moves as indicated by the solid arrow in FIG. 7 , the electrode 8 also moves relative to the workpieces W along with the carriage 4. This causes the flux trapped between the front end surface 8 a and the workpieces W to separate or break, allowing the electrode 8 to come into contact with the workpieces W.

[0058] The welding method according to this embodiment also includes a cutting step of cutting the electrode 8 (welding wire) at an angle relative to the orthogonal plane 9 before starting welding. Therefore, when the tip of the electrode 8 (welding wire) comes into contact with the workpiece W at the start of welding, the contact area is reduced, so the tip portion melts and transfers preferentially, achieving a smooth arc start. In other words, the welding method according to this embodiment also enables a good arc start with a simple method. Furthermore, this embodiment also achieves the same effects as the first embodiment by using a configuration common to the first embodiment.

[0059] Furthermore, in the welding method according to this embodiment, the flux spray start step (S5) is performed before the short-circuit detection steps (S1 to S3) are performed in the start control process. Even in this case, since the tip surface 8a of the electrode 8 is inclined with respect to the orthogonal plane 9, when the electrode 8 is inserted into the flux 79, it is possible to prevent the flux from being trapped between the tip surface 8a and the workpieces W. Furthermore, in the welding method according to this embodiment, the movement control of the carriage 4 is performed independently of the start control process. Therefore, even if the flux is trapped between the tip surface 8a and the workpieces W, the trapped flux is removed by moving the carriage 4, allowing the electrode 8 to come into contact with the workpieces W. Furthermore, in this embodiment, the tip surface 8a of the electrode 8 faces the opposite direction from the traveling direction of the carriage 4. This makes it possible to more effectively prevent the flux from getting caught between the tip surface 8a and the workpiece W when the electrode 8 is inserted into the flux 79 while the carriage 4 is moving, compared to when the tip surface 8a of the electrode 8 faces the same side as the direction of travel of the carriage 4.

[0060] As shown in the first and second embodiments, the welding method according to the present invention can be employed regardless of the control processing at the start of welding. Furthermore, the welding method according to the present invention can be employed not only in the arc start method in which the electrode 8 and the workpiece W are separated from each other as shown in the first and second embodiments, but also in, for example, an arc start method in which the electrode 8 and the workpiece W are brought into contact with each other in advance. Furthermore, the welding method according to the present invention can be employed, for example, in an arc start method using the second or subsequent electrode in multiple-electrode submerged arc welding, or in an arc start method using steel wool.

[0061] Furthermore, the welding method according to the present invention can be employed regardless of the functions of the welding power supply and the control device. For example, there are no limitations on the output characteristics of the welding power supply. Furthermore, thyristor-controlled or movable-iron-core welding power supplies can also be used. Furthermore, there are no limitations on the configuration of the control device. In other words, the welding method according to the present invention does not require welding power supplies and control devices with special functions, and existing welding power supplies and control devices can be used. Furthermore, the welding method according to the present invention is not limited to cases where the electrode 8 is moved by traveling carriage 4, but can also be employed when the electrode 8 is moved by a robot or when the workpiece W is moved without moving the electrode 8.

[0062] The submerged arc welding method and submerged arc welding system according to the present invention are not limited to the above-described embodiments, and the specific configurations of the components of the submerged arc welding method and submerged arc welding system according to the present invention can be freely designed and modified in various ways. [Explanation of symbols]

[0063] A1, A2: welding system, 2: welding power supply, 4: carriage, 5: wire feeder, 8: electrode, 8a: tip surface, 9: orthogonal surface, W: workpiece

Claims

1. A welding method for performing submerged arc welding in a submerged arc welding system including a welding power supply and a wire feeder that feeds welding wire, comprising: a cutting step of cutting the welding wire before starting welding so that a tip end surface of the welding wire is inclined with respect to a plane perpendicular to an extending direction of the welding wire, Welding method.

2. The inclination angle between the tip surface and the orthogonal surface is 30° or more and 60° or less. The welding method according to claim 1 .

3. the submerged arc welding system further includes a carriage on which the wire feeder is mounted and which moves along the welding line; The tip surface faces the opposite direction to the traveling direction of the carriage. The welding method according to claim 1 .

4. a short circuit detection step of detecting contact between the welding wire and the workpiece by causing the wire feeder to feed the welding wire at an initial feed speed while the welding power supply applies a DC voltage between the welding wire and the workpiece; a spraying start step of starting spraying of flux; Furthermore, The spray start step is performed before the short circuit detection step.

4. The welding method according to claim 1.

5. 1. A submerged arc welding system for performing submerged arc welding, comprising: a welding power supply for supplying power; A welding wire; a wire feeder that feeds the welding wire; Equipped with a tip end surface of the welding wire is inclined with respect to a plane perpendicular to a direction in which the welding wire extends; Submerged arc welding system.

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