Submerged arc welding system

Abstract

To provide a submerged arc welding system which facilitates adjustment of a parameter, without requiring to switch control at the time of welding start by an arc start method.SOLUTION: A submerged arc welding system A1 for performing submerged arc welding includes: a welding power supply device 2 which has an inverter circuit 22 and supplies power; a wire feeding device 5 for feeding a welding wire; a control device 1 for controlling the welding power supply device 2 and the wire feeding device 5; and a voltage sensor 27 for detecting a voltage applied between the tip of the welding wire and an object W to be welded. The control device 1 makes the wire feeding device 5 feed the welding wire at an initial feeding rate, at the time of the welding start, makes the wire feeding device 5 stop feeding when the tip of the welding wire is short-circuited to the object W to be welded, makes the welding power supply device 2 start output of welding current, and makes the wire feeding device 5 start feeding at a welding feeding rate for welding, when a detection voltage Vd detected by the voltage sensor 27 is equal to or more a voltage threshold V0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a submerged arc welding system for performing submerged arc welding. [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 adjustment of three parameters: the starting current, the welding wire feed speed, and the end condition of the starting period. This makes it difficult to adjust the conditions for achieving good starting performance. Furthermore, the welding power supply system requires a process for detecting the contact state between the tip of the welding wire and the workpiece and then applying the starting current at the start of welding, which requires additional time. In submerged arc welding, when starting an arc with the second or subsequent electrode in multiple-electrode welding, a method is sometimes used in which an arc is generated by inserting the welding wire into a molten pool formed by a leading electrode and applying current. For this arc start method with the second or subsequent electrode, the process of detecting and controlling the contact state hinders a smooth arc start. Therefore, it is necessary to switch the control for arc start depending on the arc start method, which reduces workability.

[0006] The present invention was devised in light of the above circumstances, and has an object to provide a submerged arc welding system that does not require switching control at the start of welding depending on the arc start method and that allows easy adjustment of parameters. [Means for solving the problem]

[0007] The submerged arc welding system provided by the present invention is a submerged arc welding system for performing submerged arc welding, and includes a welding power supply having an inverter circuit for supplying power, a wire feeder for feeding welding wire, a control device for controlling the welding power supply and the wire feeder, and a voltage sensor for detecting a voltage applied between a tip of the welding wire and a workpiece, wherein the control device causes the wire feeder to feed the welding wire at an initial feed speed when welding starts, stops feeding when the tip of the welding wire is short-circuited to the workpiece, causes the welding power supply to start outputting a welding current, and when the voltage detected by the voltage sensor becomes equal to or greater than a voltage threshold, causes the wire feeder to start feeding at a welding feed speed for welding.

[0008] In a preferred embodiment of the present invention, the welding power supply has output characteristics according to set external characteristics, and the slope of the characteristic line of the external characteristics is not less than −40 V / 100 A and not more than −0.5 V / 100 A.

[0009] In a preferred embodiment of the present invention, the voltage threshold is 20V or more and 40V or less.

[0010] In a preferred embodiment of the present invention, the control device causes the welding power supply to output a short-circuit release current if the detected voltage is less than a predetermined voltage even after a predetermined time has elapsed since the welding power supply started to output the welding current.

[0011] In a preferred embodiment of the present invention, the tip end surface of the welding wire is inclined with respect to a plane perpendicular to the direction in which the welding wire extends.

[0012] In a preferred embodiment of the present invention, the welding machine further includes a carriage on which the wire feeder is mounted and which moves along the welding line, and the control device controls the movement of the carriage independently of the control of the wire feeder and the welding power supply at the start of welding. [Effects of the Invention]

[0013] According to the present invention, when a control device detects a short circuit at the start of welding, it stops the feeding of the welding wire and starts the output of the welding current without flowing a start current for generating an arc. Then, when the detected voltage reaches or exceeds a voltage threshold, the control device starts feeding at the welding feed speed for welding. Therefore, the operator only needs to set the voltage threshold, and does not need to set the feed speed and start current from the time of short circuit detection until switching to the welding feed speed. This facilitates parameter adjustment. Furthermore, the above-described control at the start of welding can be commonly used for various arc start methods. Therefore, there is no need to switch the control at the start of welding depending on the arc start method. [Brief explanation of the drawings]

[0014] [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] 10 is an example of a flowchart illustrating a start control process. [Figure 4] 4 is a timing chart showing each state when a start control process is executed in the welding system according to the first embodiment. [Figure 5] 10 is a timing chart showing each state when a start control process is executed by employing another arc start method in the welding system according to the first embodiment. [Figure 6] 10 is a timing chart showing each state when a short circuit release process is executed together with a start control process in the welding system according to the first embodiment. [Figure 7] 10 is a simplified diagram for explaining a tip surface of an electrode according to a second embodiment. FIG. [Figure 8] 10 is a simplified diagram for explaining the movement of an electrode according to the third embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0016] [First embodiment] 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.

[0017] 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. In welding system A1, carriage 4 moves along a weld line on 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 the power. An arc is generated within the flux between electrode 8, which is the tip of the welding wire, and workpieces W. Heat from the arc causes welding. This results in welding along the weld line on workpieces W. Instead of using carriage 4, workpieces W may be moved or rotated.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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)

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The internal configuration of control circuit 28 is not limited to that described above. Control circuit 28 may control the output current and output voltage so that the output characteristics of welding power supply 2 match the set external characteristics.

[0037] 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.

[0038] Next, we will explain the control process at the start of welding that is performed by the control device 1. Figure 3 is an example of a flowchart showing the start control process at the start of welding that is performed by the control device 1. The start control process is started, for example, when an operation button that starts welding is pressed.

[0039] First, flux begins to be sprayed onto the welding start point of the workpiece W and its surrounding area (S1). Specifically, control device 1 instructs sprayer 7 to spray flux. Sprayer 7 sprays a preset appropriate amount of flux. Next, feeding of the welding wire begins (S2). 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 feed speed. The initial feed speed is a so-called slowdown speed, which is sufficiently slower than the welding feed speed for welding (for example, but not limited to, about 0.5 m / min).

[0040] Next, application of a DC voltage (no-load voltage) begins between the workpiece W and electrode 8 (S3). 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.

[0041] Next, it is determined whether or not the electrode 8 has come into contact with the workpieces W and caused a short circuit (S4). 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 lower 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 (S4: 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 (S4: YES), the feeding of the welding wire is stopped (S5). Specifically, the control device 1 instructs the wire feeder 5 to stop feeding the welding wire.

[0042] Next, the output of the welding current begins (S6). Specifically, control device 1 instructs welding power supply 2 to output a welding current according to the welding conditions to be output when actually welding. 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 determined by equation (1) above.

[0043] 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.

[0044] In this embodiment, the start period is the period from when the electrode 8 is short-circuited to the workpiece W until the detected voltage Vd reaches the voltage threshold V0 (until the generated arc stabilizes). The purpose of the start period is to ensure a desired arc length regardless of the arc start method, various conditions, or environment. Furthermore, the arc length correlates with the voltage. Therefore, the end condition of the start period is when the detected voltage Vd reaches or exceeds the voltage threshold V0.

[0045] 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. Next, the movement of the carriage 4 is started, and the start control process is terminated. After the start control process is terminated, 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 is continued. In addition, the spraying of flux by the sprayer 7 and the movement of the carriage 4 are also continued.

[0046] The process shown in the flowchart of FIG. 3 is an example, and the start control process performed by the control device 1 is not limited to the above.

[0047] FIG. 4 is a timing chart showing each state when the start control process is executed in welding system A1. (a) in FIG. 4 shows the change over time of the welding start signal. (b) in FIG. 4 shows the change over time of the detected voltage Vd detected by voltage sensor 27. (c) in FIG. 4 shows the change over time of the detected current detected by current sensor 26. (d) in FIG. 4 shows the change over time of the welding wire feed speed. When the welding wire is fed in the forward direction, the feed speed is a positive value, and when the welding wire is fed in the reverse direction, the feed speed is a negative value. Note that the vertical and horizontal axes of the timing chart shown in FIG. 4 have been appropriately enlarged or reduced for ease of understanding, and the waveforms shown have also been simplified, exaggerated, or emphasized for ease of understanding (the same applies to FIGS. 5 and 6).

[0048] At time t0, the operation button to start welding is pressed, turning on the start signal (see FIG. 4(a)), and the start control process begins. At this time, forward feeding of the welding wire begins at the initial feeding speed (slow-down speed) (see FIG. 4(d)), DC voltage output begins, and the detected voltage Vd becomes the no-load voltage (see FIG. 4(b)). Note that flux has been sprayed in advance at the welding start point and its surrounding area.

[0049] At time t1, the electrode 8 comes into contact with the workpiece W and shorts out, causing a sudden drop in the detected voltage Vd (see FIG. 4(b)) and a sudden increase in the detected current (see FIG. 4(c)). When the detected voltage Vd falls below the short-circuit detection threshold, a short circuit is detected and the start period begins. At this time, the feeding of the welding wire stops and the feed speed becomes "0" (see FIG. 4(d)). The output of the welding current also begins (see FIG. 4(c)), causing the electrode 8 to burn, generating an arc between the tip of the electrode 8 and the workpiece W. The arc length gradually increases, and the detected voltage Vd correspondingly gradually increases (see FIG. 4(b)). At time t2, the detected voltage Vd becomes equal to or greater than the voltage threshold V0, ending the start period and restarting the feeding of the welding wire at the welding feed speed.

[0050] The above describes a case where the start control process is used for an arc start method in which the electrode 8 is brought into contact with the workpiece W in welding system A1 (with one electrode 8). The start control process can also be used for an arc start method for the second or subsequent electrode in multiple-electrode submerged arc welding. For the second or subsequent electrode, when the electrode 8 reaches the welding start position, the start signal is turned ON, and the start control process is initiated. With the no-load voltage applied, the welding wire is fed at an initial feed rate. The start period begins when the electrode 8 is inserted into and short-circuits the molten pool formed by the leading electrode. In other words, the feeding of the welding wire is stopped, and the output of the welding current is initiated. Then, an arc is generated between the tip of the electrode 8 and the workpiece W, and when the detected voltage Vd becomes equal to or greater than the voltage threshold V0, the start period ends, the feeding of the welding wire is resumed at the welding feed rate, and the start control process ends.

[0051] The start control process can also be used for an arc start method using steel wool. In this case, steel wool is interposed between the electrode 8 and the workpiece W. Therefore, as shown in FIG. 5, immediately (within 1 ms) after the activation signal is turned ON and the start control process is started, the electrode 8 conducts electricity to the workpiece W, a short circuit is detected, the start period begins, the feeding of the welding wire is stopped, and the output of the welding current is started. Therefore, the welding wire is hardly fed. Then, an arc is generated between the tip of the electrode 8 and the workpiece W, and when the detected voltage Vd becomes equal to or greater than the voltage threshold V0, the start period ends, the feeding of the welding wire is resumed at the welding feed speed, and the start control process ends.

[0052] The start control process can also be used for an arc start method when the tip of the electrode 8 is already in contact with the workpiece W. In this case, since the electrode 8 and the workpiece W are in contact, as shown in FIG. 5, immediately (within 1 ms) after the activation signal is turned ON and the start control process is started, the electrode 8 is electrically connected to the workpiece W, a short circuit is detected, the start period begins, the feeding of the welding wire is stopped, and the output of the welding current is started. Therefore, the welding wire is hardly fed. Then, an arc is generated between the tip of the electrode 8 and the workpiece W, and when the detected voltage Vd becomes equal to or greater than the voltage threshold V0, the start period ends, the feeding of the welding wire is resumed at the welding feed speed, and the start control process ends. In this way, the start control process can be commonly used for various arc start methods.

[0053] Next, the operation and effects of the welding system A1 according to this embodiment will be described.

[0054] According to this embodiment, when a short circuit is detected at the start of welding, the control device 1 stops the feeding of the welding wire and starts the output of the welding current without flowing a start current for generating an arc. Then, when the detected voltage Vd becomes equal to or greater than the voltage threshold V0, the control device 1 starts feeding at the welding feed speed for welding. Therefore, the operator only needs to set the voltage threshold V0, and does not need to set the feed speed and start current from the time of short circuit detection until switching to the welding feed speed. This facilitates parameter adjustment. Furthermore, the start control process at the start of welding can be used in common with various arc start methods. Therefore, there is no need to switch the control at the start of welding depending on the arc start method.

[0055] Furthermore, according to this embodiment, the control device 1 stops the feeding of the welding wire during the start period. For example, if the welding wire is fed in the forward direction during the start period, the short circuit may be prevented from being released or the tip of the electrode 8 may be pressed against the workpiece W, resulting in a stick phenomenon. On the other hand, if the welding wire is fed in the reverse direction during the start period, the short circuit may be released more quickly and the arc length may be more easily secured. However, the welding wire may not be fed in the forward direction without delay at the end of the start period, causing the arc length to temporarily exceed the intended length. In this embodiment, the feeding of the welding wire is stopped during the start period, which prevents the short circuit from being released and prevents the stick phenomenon from occurring, and also makes it easier to adjust the arc length to the desired length.

[0056] Furthermore, in this embodiment, the control circuit 28 sets the slope Kr of the characteristic line X of the external characteristics to be greater than or equal to −40 V / 100 A and less than or equal to −0.5 V / 100 A, thereby making the device less susceptible to voltage changes due to voltage noise and the like, and also making it possible to appropriately adjust the amount of current change relative to voltage changes.

[0057] In this embodiment, the voltage threshold V0 is set to 20 V or more and 40 V or less. Therefore, welding system A1 can prevent arc interruption while ensuring a sufficient arc length at the start of welding. Furthermore, by setting the voltage threshold V0 to 30 V, welding system A1 can obtain good startability over a wide range of conditions.

[0058] When starting an arc, it is important to release the short circuit as quickly as possible. In the start control process, the output of the welding current is started without flowing the start current during the start period, so that it may be difficult to release the short circuit when the set welding current is small. To prevent this, the control device 1 may use the short circuit release process in combination with the start control process. The short circuit release process is performed when a predetermined time T has elapsed since the start period began. X Even after the detection voltage Vd has passed, the X When the short-circuit release current I XThis is a process that promotes short circuit release by passing a predetermined voltage V X is, for example, 15V, and the short-circuit release current I X is, for example, a direct current of 2000 A. X , a given voltage V X , and the short-circuit release current I X The short-circuit releasing current I X The flow of current causes the electrode 8 to burn more, facilitating the release of the short circuit and making it easier for an arc to occur between the tip of the electrode 8 and the workpiece W.

[0059] 6 is a timing chart showing the states when the welding system A1 executes the start control process and the short circuit release process. The time changes shown in FIG. 6 are the same as those in FIG. 4. As shown in FIG. 6, from time t1 to a predetermined time T X At time t3 after the time has elapsed, the detection voltage Vd reaches the predetermined voltage V X Therefore, the short circuit release current I X (See Figure 6(c)). This causes the detection voltage Vd to rise. Note that the short-circuit release current I X The time for which the detection voltage Vd is applied is not limited, and does not have to be a fixed time. For example, X (or higher voltage), the short-circuit release current I X The short circuit removal process is not limited to the above, and may be any process that promotes short circuit removal by passing a high current when the short circuit is not removed.

[0060] 7 is a diagram for explaining a welding system A2 according to a second embodiment, and is a simplified diagram for explaining the tip surface of an electrode 8 according to the second embodiment. Note that the block diagram showing the overall configuration of the welding system A2 according to the second embodiment and the block diagram showing the internal configuration of the 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 shape of the tip of the electrode 8 (welding wire).

[0061] In this embodiment, the 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.

[0062] 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.

[0063] Furthermore, in this embodiment, the tip surface 8a of the electrode 8 (welding wire) faces in the opposite direction to the traveling direction of the carriage 4 (the direction of the arrow shown in the figure). However, 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. However, 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, but may be automated.

[0064] In this embodiment, too, when a short circuit is detected at the start of welding, the control device 1 stops the feeding of the welding wire and starts the output of the welding current without flowing a start current for generating an arc. Then, when the detected voltage Vd becomes equal to or greater than the voltage threshold V0, the control device 1 starts feeding at the welding feed rate for welding. Therefore, the operator only needs to set the voltage threshold V0, making parameter adjustment easy. Furthermore, the start control process at the start of welding can be used in common with various arc start methods. Therefore, there is no need to switch the control at the start of welding depending on the arc start method. Furthermore, this embodiment also achieves the same effects as the first embodiment by using a configuration common to the first embodiment.

[0065] Furthermore, according to this embodiment, the tip surface 8a of the electrode 8 (welding wire) is inclined with respect to the orthogonal plane 9. Therefore, when the tip of the electrode 8 (welding wire) comes into contact with the workpiece W at the start of welding, the area of ​​the contact portion is smaller than when the tip surface 8a 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, so that the tip portion melts and transfers preferentially, achieving a smooth arc start. Furthermore, according to this embodiment, the inclination angle α formed by the tip surface 8a and the orthogonal plane 9 is 30° or more and 60° or less. Therefore, the occurrence of melting of the welding wire can be suppressed while the labor required to cut the welding wire can be reduced.

[0066] 8 is a diagram for explaining a welding system A3 according to a third embodiment, and is a simplified diagram for explaining the movement of an electrode 8 according to the third embodiment. Note that the block diagram showing the overall configuration of the welding system A3 according to the third embodiment and the block diagram showing the internal configuration of the 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 A3 according to this embodiment differs from the welding system A1 according to the first embodiment in the shape of the tip of the electrode 8 (welding wire) and the start control process performed by the control device 1.

[0067] The tip shape of the electrode 8 (welding wire) according to this embodiment is the same as that in the second embodiment. The start control process according to this embodiment is such that step S9 (control of movement of the carriage 4) is not performed in the start control process shown in Fig. 3. The control of movement of the carriage 4 is performed independently from the start control process.

[0068] In the start control process according to this embodiment, flux is first sprayed (S1), and then feeding of the welding wire is started at an initial feed rate for short-circuit detection (S2). 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) 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. 8 , when the electrode 8 is inserted into the flux 79 (see the electrode 8 indicated by the dashed arrow and dashed line), it is possible to prevent the flux from being trapped between the tip end surface 8 a and the workpiece W.

[0069] As in the first embodiment, when the start control process controls the start of movement of the carriage 4, the carriage 4 will not start moving unless a short circuit is detected in step S4. On the other hand, in the present embodiment, the movement control of the carriage 4 is executed independently of the start control process, so that the carriage 4 can move even if a short circuit is not detected due to flux being trapped between the front end surface 8a and the workpieces W. In this case, as the carriage 4 moves as indicated by the solid arrow in FIG. 8, the electrode 8 also moves relative to the workpieces W along with the carriage 4. As a result, the flux trapped between the front end surface 8a and the workpieces W is separated or destroyed, allowing the electrode 8 to come into contact with the workpieces W.

[0070] In this embodiment, too, when a short circuit is detected at the start of welding, the control device 1 stops the feeding of the welding wire and starts the output of the welding current without flowing a start current for generating an arc. Then, when the detected voltage Vd becomes equal to or greater than the voltage threshold V0, the control device 1 starts feeding at the welding feed rate for welding. Therefore, the operator only needs to set the voltage threshold V0, making parameter adjustment easy. Furthermore, the start control process at the start of welding can be used in common with various arc start methods. Therefore, there is no need to switch the control at the start of welding depending on the arc start method. Furthermore, this embodiment also achieves the same effects as the first and second embodiments by using a configuration common to the first and second embodiments.

[0071] Furthermore, in the start control process according to this embodiment, after the flux is sprayed (S1), feeding of the welding wire is started at an initial feed rate for short-circuit detection (S2). Even in this case, because 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 start control process according to this embodiment, the movement control of the carriage 4 is executed independently from 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.

[0072] The submerged arc welding system according to the present invention is not limited to the above-described embodiment, and the specific configuration of each part of the submerged arc welding system according to the present invention can be freely designed and modified in various ways. [Explanation of symbols]

[0073] A1 to A3: welding system, 1: control device, 2: welding power supply device, 25: inverter circuit, 27: voltage sensor, 5: wire feeder, W: workpiece

Claims

1. 1. A submerged arc welding system for performing submerged arc welding, comprising: a welding power supply having an inverter circuit for supplying power; a wire feeder that feeds a welding wire; a control device that controls the welding power supply and the wire feeder; a voltage sensor that detects a voltage applied between the tip of the welding wire and the workpiece; Equipped with The control device causes the wire feeder to feed the welding wire at an initial feed speed at the start of welding, stops feeding when the tip of the welding wire is short-circuited to the workpiece, causes the welding power supply to start outputting a welding current, and causes the wire feeder to start feeding at a welding feed speed for welding when the detected voltage detected by the voltage sensor becomes equal to or higher than a voltage threshold. Submerged arc welding system.

2. the welding power supply has output characteristics according to set external characteristics, The slope of the characteristic line of the external characteristics is −40 V / 100 A or more and −0.5 V / 100 A or less. The submerged arc welding system of claim 1 .

3. The voltage threshold is 20 V or more and 40 V or less. The submerged arc welding system of claim 1 .

4. the control device causes the welding power supply to output a short-circuit release current when the detected voltage is less than a predetermined voltage even after a predetermined time has elapsed since the welding power supply started to output the welding current. The submerged arc welding system of claim 1 .

5. 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; 5. A submerged arc welding system according to claim 1.

6. The wire feeder is mounted on a carriage that moves along the welding line. the control device controls the movement of the carriage independently of the control of the wire feeder and the welding power supply at the start of welding.

6. The submerged arc welding system of claim 5.

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