Submerged arc welding system and submerged arc welding method

Abstract

To provide a submerged arc welding system that can achieve both penetration depth and arc stability, in submerged arc welding.SOLUTION: A welding system A1 for performing submerged arc welding includes: a welding power supply device 2 for supplying power; and a scattering device 7 for scattering flux 79 on a workpiece W. The welding power supply device 2 periodically switches between: a first period T1 during which a first AC current fluctuating at a first frequency f1 is outputted; and a second period T2 during which a second AC current fluctuating at a second frequency f2 lower than the first frequency f1 is outputted.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Submerged arc welding has been known for some time. In submerged arc welding, granular flux is spread 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 to perform welding. In submerged arc welding, a large current is passed through a large diameter welding wire, thereby enabling high efficiency welding of thick plates.

[0003] In submerged arc welding, a technique for adjusting the penetration depth by adjusting the current waveform of the welding current has been disclosed. For example, Non-Patent Document 1 describes that when an AC welding current is output, the frequency of the current waveform is adjusted to adjust the penetration depth. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Takafumi Miyata, Submerged Arc Welding Power Source with Waveform Control Function, Journal of the Japan Welding Society, Japan, 2008, Vol. 77, No. 7, pp. 635-639 Summary of the Invention [Problem to be solved by the invention]

[0005] When adjusting the frequency of the current waveform, the lower the frequency of the current waveform, the greater the penetration depth but the less stable the arc will be, whereas the higher the frequency of the current waveform, the greater the stability of the arc but the smaller the penetration depth.

[0006] The present invention has been devised in light of the above circumstances, and has an object to provide a submerged arc welding system that can achieve both penetration depth and arc stability in submerged arc welding. [Means for solving the problem]

[0007] A submerged arc welding system provided by a first aspect of the present invention is a submerged arc welding system for performing submerged arc welding, comprising a welding power supply that supplies power and a sprayer that sprays flux onto a workpiece, wherein the welding power supply periodically switches between a first period during which a first waveform current that fluctuates at a first frequency is output and a second period during which a second waveform current that fluctuates at a second frequency lower than the first frequency is output.

[0008] In a preferred embodiment of the present invention, the first frequency and the second frequency are not less than 10 Hz and not more than 100 Hz, and a third frequency for switching between the first period and the second period is not less than 1 Hz and not more than 20 Hz.

[0009] In a preferred embodiment of the present invention, the first waveform current and the second waveform current are square wave AC currents, and a first duty ratio of the first waveform current and a second duty ratio of the second waveform current are individually adjustable.

[0010] In a preferred embodiment of the present invention, the first waveform current and the second waveform current are direct currents that change in a rectangular wave shape, and a first reference value that is a reference for the first waveform current and a second reference value that is a reference for the second waveform current are individually adjustable.

[0011] A submerged arc welding method provided by a second aspect of the present invention is a submerged arc welding method for performing submerged arc welding in a submerged arc welding system including a welding power supply and a spraying device that sprays flux onto a workpiece, the method including a first step in which the welding power supply outputs a first waveform current that fluctuates at a first frequency, and a second step in which the welding power supply outputs a second waveform current that fluctuates at a second frequency that is lower than the first frequency, and periodically switching between the first step and the second step. Effect of the Invention

[0012] According to the present invention, the welding power supply periodically switches between a first period and a second period. In the second period, a second waveform current that fluctuates at a second frequency lower than the first frequency is output, so that the penetration depth is relatively large. In addition, in the first period, a first waveform current that fluctuates at a first frequency higher than the second frequency is output, so that the stability of the arc is relatively improved. Therefore, the submerged arc welding system according to the present invention can achieve both penetration depth and arc stability. [Brief description of the drawings]

[0013] [Figure 1] 1A and 1B are diagrams for explaining a welding system according to a first embodiment, where 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. [Diagram 2] FIG. 4 is a waveform diagram showing an example of a welding current output by a welding power supply. [Diagram 3] 13 is an example of a flowchart illustrating a frequency switching process performed by a frequency switching unit. [Figure 4] 10A and 10B are diagrams for explaining a welding system according to a second embodiment, in which FIG. 10A is a block diagram showing the internal configuration of a control circuit of a welding power supply, and FIG. 10B is a waveform diagram showing an example of a welding current output by the welding power supply. [Diagram 5]11A and 11B are diagrams for explaining a welding system according to a third embodiment, in which (a) is a block diagram showing the internal configuration of a control circuit of a welding power supply, and (b) is a waveform diagram showing an example of a welding current output by the welding power supply. [Figure 6] 10A and 10B are diagrams for explaining a welding system according to a fourth embodiment, in which FIG. 10A is a block diagram showing the internal configuration of a control circuit of a welding power supply, and FIG. 10B is a waveform diagram showing an example of a welding current output by the welding power supply. [Figure 7] 13A and 13B are diagrams for explaining a welding system according to a fifth embodiment, in which (a) is a block diagram showing the internal configuration of a control circuit of a welding power supply, and (b) is a waveform diagram showing an example of a welding current output by the welding power supply. [Figure 8] 13A and 13B are diagrams for explaining a welding system according to a sixth embodiment, in which (a) is a block diagram showing the internal configuration of a control circuit of a welding power supply, and (b) is a waveform diagram showing an example of a welding current output by the welding power supply. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0015] [First embodiment] Fig. 1 is a diagram for explaining a welding system A1 according to a first embodiment. Fig. 1(a) is a block diagram showing the overall configuration of the welding system A1. Fig. 1(b) is a block diagram showing the internal configuration of a welding power supply 2.

[0016] The welding system A1 is a welding system for performing submerged arc welding. As shown in FIG. 1(a), the welding system A1 includes a control device 1, a welding power supply device 2, a welding torch 3, a carriage 4, a wire feeder 5, a wire reel 6, a spreader 7, and an electrode 8. The welding system A1 causes the spreader 7 to spread granular flux 79 and the wire feeder 5 to feed the welding wire into the flux 79 while moving the carriage 4 along the welding line of the workpiece W. The welding wire is supplied from the wire reel 6. The welding power supply device 2 converts AC power supplied from a commercial power source P into power suitable for welding and outputs it, and generates an arc between the electrode 8, which is the tip of the welding wire, and the workpiece W inside the flux 79. Welding is performed by the heat of the arc. As a result, welding is performed along the welding line of the workpiece W. Instead of using the carriage 4, the workpiece W may be moved or rotated.

[0017] Welding torch 3 guides the welding wire fed by wire feeder 5 to the welding point. The tip of the welding wire becomes electrode 8 protruding from the tip of welding torch 3. Welding torch 3 has a contact tip (not shown) that is disposed at the tip and is conductive to welding power supply 2. Welding power supply 2 passes a welding current through the welding wire in contact with the contact tip. Welding torch 3 is fixed to cart 4, and moves as cart 4 moves. Note that welding torch 3 may be directly fixed to cart 4, or may be indirectly fixed via an arm or the like.

[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 therein for performing various controls of the welding system A1, or may be a dedicated device for controlling the welding system A1. The control device 1 moves the carriage 4 at a predetermined moving speed. The moving speed is set according to the material and thickness of the workpiece W. The control device 1 instructs the spraying device 7 to start and end spraying of the flux 79. The spraying device 7 may start and stop spraying the flux 79 manually. The control device 1 instructs the wire feeder 5 to start and stop feeding the welding wire and the feeding speed of the welding wire. The feeding speed is set according to the welding current to be set. The control device 1 instructs the welding power source 2 to output power.

[0019] Welding power supply 2 converts AC power supplied from commercial power supply P into desired power and outputs it. As shown in Fig. 1(b), welding power supply 2 includes a rectifying and smoothing circuit 21, an inverter circuit 22, a transformer 23, a rectifying and smoothing circuit 24, an inverter circuit 25, a current sensor 26, a voltage sensor 27, and a 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 according 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.

[0021] The rectifying and smoothing circuit 24 converts the high frequency power input from the transformer 23 into DC power and outputs it. The inverter circuit 25 converts the DC power input from the rectifying and smoothing circuit 24 into AC power and outputs it by switching the switching elements according to a switching drive signal input from the control circuit 28. The inverter circuit 25 switches between a positive polarity in which the potential of the output terminal a (connected to the workpiece W) is higher than the potential of the output terminal b (connected to the welding wire), and a reverse polarity in which the potential of the output terminal a is lower than the potential of the output terminal b.

[0022] The current sensor 26 detects the output current of the welding power supply 2, and in this embodiment, is disposed on a connection line connecting one output terminal of the inverter circuit 25 and the output terminal a. The output current of the welding power supply 2 detected by the current sensor 26 is approximately equal to the current flowing through the electrode 8. The current sensor 26 outputs a current value signal corresponding to the detected current instantaneous value to the control circuit 28 and the control device 1. The position where the current sensor 26 is disposed is not limited. The voltage sensor 27 detects the output voltage of the welding power supply 2, and in this embodiment, detects the inter-terminal voltage between the output terminal a and the output terminal b. The voltage is approximately equal to the voltage applied between the workpiece W and the tip of the electrode 8. The voltage sensor 27 outputs a voltage value signal corresponding to the detected voltage instantaneous value to the control circuit 28 and the control device 1. The voltage sensor 27 may detect the voltage between the lead wire attached to the welding torch 3 and the lead wire attached to the workpiece W.

[0023] 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 set values ​​from control device 1. Control circuit 28 then outputs drive signals to inverter circuit 22 and inverter circuit 25, respectively.

[0024] When the control circuit 28 receives a command signal from the control device 1 to start the power output, the control circuit 28 starts outputting drive signals to the inverter circuits 22 and 25, respectively, to start the power output. When the control circuit 28 receives a command signal from the control device 1 to stop the power output, the control circuit 28 stops outputting the drive signals to stop the power output. The control circuit 28 includes a drive signal generating unit 281, a first frequency setting unit 282, a second frequency setting unit 283, a switching frequency setting unit 284, a frequency switching unit 285, and a drive signal generating unit 286.

[0025] The drive signal generating unit 281 is configured to generate an output control drive signal to be output to the inverter circuit 22. The drive signal generating unit 281 calculates an effective current value from a current value signal input from the current sensor 26. Then, the drive signal generating unit 281 generates an output control drive signal for controlling the switching elements of the inverter circuit 22 based on the effective current value and a current command value input from the control device 1, and outputs the output control drive signal to the inverter circuit 22. That is, the drive signal generating unit 281 performs feedback control so that the effective current value coincides with the current command value (constant current control). The drive signal generating unit 281 can also generate an output control drive signal based on a voltage value signal and a voltage command value input from the voltage sensor 27, and perform feedback control so that the effective voltage value coincides with the voltage command value (constant voltage control).

[0026] In submerged arc welding, poor penetration is often a problem, especially in one-pass welding or the first layer of multi-layer welding. In particular, when performing back-bead welding using a backing material, poor penetration such as no back bead or insufficient melting width of the back bead is likely to occur. In order to suppress poor penetration, it is effective to deepen the penetration, and for that, it is effective to increase the current command value of the welding current or to decrease the voltage command value of the welding voltage. If the voltage command value is decreased, the arc length becomes shorter and deep penetration can be obtained. However, the current command value and the voltage command value are often set in the range by the construction guidelines or standards, and cannot necessarily be adjusted freely. In addition, when the current command value and the voltage command value are manipulated, the wire feed speed changes, so it is necessary to manage the change in the amount of weld metal that accompanies the current command value and the voltage command value. In particular, when the current command value is increased, the heat input by welding increases, which impairs the mechanical performance of the welded part. For the above reasons, a method for suppressing poor penetration without changing the current command value and the voltage command value is desired. In order to suppress poor penetration, there is a method of lowering the frequency of the current waveform of the AC welding current. However, lowering the frequency increases the penetration depth but impairs the stability of the arc. The welding power supply 2 according to this embodiment periodically switches between a period in which an AC current that fluctuates at a relatively high frequency is output and a period in which an AC current that fluctuates at a relatively low frequency is output.

[0027] Fig. 2 is a waveform diagram showing an example of a welding current output by welding power supply 2. The horizontal axis indicates time, and the vertical axis indicates the welding current. As shown in Fig. 2, welding power supply 2 periodically switches between a first period T1 during which a first AC current fluctuating at a relatively high first frequency f1 is output, and a second period T2 during which a second AC current fluctuating at a relatively low second frequency f2 is output. In this embodiment, the waveforms of the first AC current and the second AC current are square waves.

[0028] The first frequency setting unit 282, the second frequency setting unit 283, the switching frequency setting unit 284, the frequency switching unit 285, and the drive signal generating unit 286 are configured to generate a switching drive signal to be output to the inverter circuit 25.

[0029] The first frequency setting unit 282 is configured to set the first frequency f1. The first frequency f1 can be set, for example, to a value between 10 Hz and 100 Hz. The first frequency setting unit 282 sets the first frequency f1 in response to an operation of an operation unit (not shown) of the welding power supply 2 or the control device 1 by an operator. The first frequency setting unit 282 may set a fixed first frequency f1.

[0030] The second frequency setting unit 283 is configured to set the second frequency f2. The second frequency f2 can be set to, for example, a frequency lower than the first frequency f1, in the range of 10 Hz to 100 Hz. The second frequency setting unit 283 sets the second frequency f2 in response to an operation of the operation unit by an operator. Note that the second frequency setting unit 283 may set a fixed second frequency f2.

[0031] The first frequency f1 is set to, for example, 100 Hz. The second frequency f2 is set to, for example, 50 Hz. The first frequency f1 and the second frequency f2 are not limited. The first frequency f1 and the second frequency f2 may be adjusted to optimal values ​​by an operator trying out welding. The settable ranges of the first frequency f1 and the second frequency f2 are not limited to those described above.

[0032] The switching frequency setting unit 284 is configured to set a third frequency f3, which is a frequency of a switching cycle between the first period T1 and the second period T2. The third frequency f3 can be set to a frequency lower than the second frequency f2, for example, between 1 Hz and 20 Hz. If the third frequency f3 is lower than 1 Hz, the duration of the first period T1 and the second period T2 becomes too long, and a discontinuous back wave is formed. In addition, the welding becomes more unstable due to the long duration of the second period T2. Conversely, if the third frequency f3 is higher than 20 Hz, the duration of the first period T1 and the second period T2 becomes too short, and the back wave formation effect is difficult to obtain. It is more preferable that the third frequency f3 is between 3 Hz and 10 Hz. If the third frequency f3 is 3 Hz or more, the duration of the second period T2 becomes sufficiently short, and there is no influence on the instability of the welding. In addition, when the third frequency f3 is 10 Hz or less, the duration of the first period T1 and the second period T2 is not too short, and the effect of forming a back wave is easily obtained. Note that the desirable range of the third frequency f3 changes depending on the first frequency f1 and the second frequency f2.

[0033] The switching frequency setting unit 284 sets the third frequency f3 in response to the operation of the operation unit by the operator. The switching frequency setting unit 284 may set a fixed third frequency f3. The third frequency f3 is set to, for example, 5 Hz. The third frequency f3 is not limited. The third frequency f3 may be adjusted to an optimal value by the operator trying out welding. The settable range of the third frequency f3 is not limited to the above.

[0034] The frequency switching unit 285 switches between the first frequency f1 input from the first frequency setting unit 282 and the second frequency f2 input from the second frequency setting unit 283, using the third frequency f3 input from the switching frequency setting unit 284, and outputs the switched frequency to the drive signal generating unit 286. In this embodiment, the first period T1 during which the first frequency f1 is output is equal to the second period T2 during which the second frequency f2 is output.

[0035] 3 is an example of a flowchart showing a frequency switching process performed by the frequency switching unit 285. The frequency switching process is started, for example, when the control circuit 28 receives a command signal from the control device 1 instructing the start of power output. Also, the frequency switching process is stopped, for example, when the control circuit 28 receives a command signal from the control device 1 instructing the stop of power output.

[0036] First, the first frequency f1 input from the first frequency setting unit 282 is output (S1). Next, it is determined whether or not the first period T1 has elapsed since the start of output of the first frequency f1 (S2). The first period T1 is calculated based on the third frequency f3 input from the switching frequency setting unit 284. For example, when the third frequency f3 is 5 Hz, T1 (= T2) = (1 / 2) · (1 / f3) = 0.1 seconds. If the first period T1 has not elapsed (S2: NO), the process returns to step S2, and the determination of step S2 is repeated. That is, the output of the first frequency f1 is continued during the first period T1. On the other hand, if the first period T1 has elapsed (S2: YES), the second frequency f2 input from the second frequency setting unit 283 is output (S3).

[0037] Next, it is determined whether or not the second period T2 has elapsed since the start of output of the second frequency f2 (S4). The second period T2 is also calculated based on the third frequency f3 as described above. If the second period T2 has not elapsed (S4: NO), the process returns to step S4, and the determination of step S4 is repeated. That is, the output of the second frequency f2 is continued during the second period T2. On the other hand, if the second period T2 has elapsed (S4: YES), the process returns to step S1, and steps S1 to S4 are repeated. Note that the process shown in the flowchart of FIG. 3 is an example, and the frequency switching process performed by the frequency switching unit 285 is not limited to the one described above.

[0038] The drive signal generating unit 286 generates and outputs a switching drive signal based on the frequency input from the frequency switching unit 285. The drive signal generating unit 286 generates a first square wave signal having a frequency of the first frequency f1 during a first period T1 in which the first frequency f1 is input from the frequency switching unit 285. In this embodiment, the duty ratio of the first square wave signal is 50%. In addition, the drive signal generating unit 286 generates a second square wave signal having a frequency of the second frequency f2 during a second period T2 in which the second frequency f2 is input from the frequency switching unit 285. In this embodiment, the duty ratio of the second square wave signal is 50%. Therefore, the drive signal generating unit 286 outputs a signal in which the first square wave signal and the second square wave signal are switched at a third frequency f3 to the inverter circuit 25 as a switching drive signal.

[0039] The inverter circuit 25 switches between positive polarity (a state in which the potential of the output terminal a is higher than the potential of the output terminal b) and negative polarity (a state in which the potential of the output terminal a is lower than the potential of the output terminal b) in response to the switching drive signal. As a result, the welding current output by the inverter circuit 25 becomes a first AC current that fluctuates at a first frequency f1 in a first period T1, and becomes a second AC current that fluctuates at a second frequency f2 in a second period T2, as shown in Fig. 2, and the first period T1 and the second period T2 are periodically switched at a third frequency f3.

[0040] The welding system A1 pushes down the molten metal with a strong arc force during the second period T2, and also applies high heat input to the deep part of the molten metal or the workpiece W to achieve deep penetration. In particular, when backing material is used to perform backing welding, a significant backing formation effect can be obtained. The submerged arc welding method according to this embodiment is preferably applied to one-pass welding or the first layer in multi-layer welding. Note that in the second and subsequent layers of multi-layer welding, penetration depth is rarely required, so that the application of this control often does not provide a significant effect, but there is no problem if it is applied. More preferably, the submerged arc welding method according to this embodiment is applied to a pass in which backing material such as flux 79, copper plate, or ceramic backing is used to perform backing welding.

[0041] Next, the operation and effects of the welding system A1 according to this embodiment will be described.

[0042] According to this embodiment, the frequency switching unit 285 switches between the first frequency f1 and the second frequency f2 at the third frequency f3 and outputs the switching drive signal to the drive signal generating unit 286. The drive signal generating unit 286 generates and outputs a switching drive signal based on the frequency input from the frequency switching unit 285. The inverter circuit 25 switches between positive and negative polarity according to the switching drive signal. As a result, the welding current output by the inverter circuit 25 is a current in which the first AC current fluctuating at the first frequency f1 and the second AC current fluctuating at the second frequency f2 lower than the first frequency f1 are periodically switched at the third frequency f3. Since the second AC current has a second frequency f2 lower than the first frequency f1, the penetration depth can be relatively increased. Furthermore, since the first AC current has a first frequency f1 higher than the second frequency f2, the stability of the arc can be relatively improved. Therefore, the welding system A1 can achieve both the penetration depth and the stability of the arc.

[0043] Also, according to this embodiment, the first frequency setting unit 282 sets the first frequency f1 to 10 Hz or more and 100 Hz or less. Also, the second frequency setting unit 283 sets the second frequency f2 to 10 Hz or more and 100 Hz or less. Therefore, it is possible to prevent the first frequency f1 and the second frequency f2 from becoming too large and from becoming too small. The switching frequency setting unit 284 sets the third frequency f3 to 1 Hz or more and 20 Hz or less. Therefore, since the duration of the first period T1 and the second period T2 is not too long, it is possible to prevent discontinuous back waves from being formed. Also, it is possible to prevent the duration of the second period T2 from being too long and causing welding to become unstable. Also, since the duration of the first period T1 and the second period T2 is not too short, it is easy to obtain the back wave formation effect.

[0044] Second Embodiment FIG. 4 is a diagram for explaining a welding system A2 according to a second embodiment. FIG. 4(a) is a block diagram showing the internal configuration of a control circuit 28 of welding power supply 2 of welding system A2. FIG. 4(b) is a waveform diagram showing an example of a welding current output by welding power supply 2. In FIG. 4, elements that are the same as or similar to those in the first embodiment are given the same reference numerals as those in the first embodiment. Welding system A2 according to this embodiment differs from welding system A1 according to the first embodiment in that the ratio between the first period T1 and the second period T2 can be changed.

[0045] As shown in FIG. 4(a), the control circuit 28 according to the present embodiment further includes a switching ratio setting unit 287. The switching ratio setting unit 287 is configured to set a ratio R (=T1 / T) of the first period T1 to the total period T (=T1+T2). The ratio R can be set, for example, between 25% and 75% (i.e., T1:T2 is 1:3 to 3:1). FIG. 4(b) shows a waveform of a welding current when the ratio R is 25%. If the ratio R is smaller than 25%, the duration of the first period T1 becomes too short, and welding tends to become unstable. Conversely, if the ratio R is larger than 75%, the duration of the second period T2 becomes too short, and the penetration depth becomes insufficient. Note that the desirable range of the ratio R changes depending on the first frequency f1, the second frequency f2, and the third frequency f3.

[0046] The switching ratio setting unit 287 sets the ratio R in response to the operation of the operation unit by the worker. The switching ratio setting unit 287 may set a fixed ratio R. The ratio R is not limited. The ratio R may be adjusted to an optimal value by the worker trying out welding. The settable range of the ratio R is not limited to the above.

[0047] In this embodiment, the welding current output by inverter circuit 25 is a current obtained by periodically switching between a first AC current that varies at a first frequency f1 and a second AC current that varies at a second frequency f2 lower than the first frequency f1 at a third frequency f3. Therefore, welding system A2 can achieve both a good penetration depth and arc stability. According to this embodiment, welding system A2 has a common configuration with welding system A1, and thus achieves the same effects as welding system A1. Furthermore, according to this embodiment, switching ratio setting unit 287 sets a ratio R of the first period T1 to the total period T. As a result, welding system A2 can change the ratio between the first period T1 and the second period T2, and therefore can more finely adjust the penetration depth and the arc stability.

[0048] Third Embodiment FIG. 5 is a diagram for explaining a welding system A3 according to a third embodiment. FIG. 5(a) is a block diagram showing the internal configuration of a control circuit 28 of welding power supply 2 of welding system A3. FIG. 5(b) is a waveform diagram showing an example of a welding current output by welding power supply 2. In FIG. 5, elements that are the same as or similar to those in the first embodiment are given the same reference numerals as those in the first embodiment. Welding system A3 according to this embodiment differs from welding system A1 according to the first embodiment in that the first duty ratio D1 of the first AC current and the second duty ratio D2 of the second AC current can be changed.

[0049] As shown in FIG. 5( a ), the control circuit 28 according to this embodiment further includes a first duty setting section 288 and a second duty setting section 289 , and includes a switching section 280 instead of the frequency switching section 285 .

[0050] The first duty setting unit 288 is configured to set a first duty ratio D1 of the first AC current. The first duty ratio D1 is set to a duty ratio of one period (=high level period T1) of the first AC current. H + Low level period T1 L ) during the high-level period T1 H The first duty ratio D1 is, for example, 25% or more and 75% or less (i.e., T1H : T1 L The first duty setting unit 288 sets the first duty ratio D1 in accordance with the operation of the operation unit by the operator. The first duty setting unit 288 may set a fixed first duty ratio D1. The first duty ratio D1 is not limited. The first duty ratio D1 may be adjusted to an optimal value by the operator trying out welding. The settable range of the first duty ratio D1 is not limited to the above.

[0051] The second duty setting unit 289 is configured to set a second duty ratio D2 of the second AC current. The second duty ratio D2 is set to a value corresponding to one period (=high level period T2) of the second AC current. H + Low level period T2 L ) during the high-level period T2 H The second duty ratio D2 is, for example, 25% or more and 75% or less (i.e., T2 H : T2 L The second duty setting unit 289 sets the second duty ratio D2 in accordance with the operation of the operation unit by the operator. The second duty setting unit 289 may set a fixed second duty ratio D2. The second duty ratio D2 is not limited. The second duty ratio D2 may be adjusted to an optimal value by the operator trying out welding. The settable range of the second duty ratio D2 is not limited to the above. The first duty ratio D1 and the second duty ratio D2 may be set in conjunction with each other, or may be set independently of each other.

[0052] The switching unit 280 switches between the first frequency f1 and the first duty ratio D1 and the second frequency f2 and the second duty ratio D2 at the third frequency f3 and outputs the switching drive signal to the drive signal generating unit 286. The drive signal generating unit 286 generates and outputs a switching drive signal based on the frequency and duty ratio input from the switching unit 280. The drive signal generating unit 286 generates a first square wave signal with the first frequency f1 and the first duty ratio D1 during the first period T1 in which the first frequency f1 and the first duty ratio D1 are input from the switching unit 280. The drive signal generating unit 286 also generates a second square wave signal with the second frequency f2 and the second duty ratio D2 during the second period T2 in which the second frequency f2 and the second duty ratio D2 are input from the frequency switching unit 285. The drive signal generating unit 286 outputs a signal in which the first square wave signal and the second square wave signal are switched at a third frequency f3 as a switching drive signal to the inverter circuit 25. Fig. 5(b) shows a waveform of the welding current when the first duty ratio D1 and the second duty ratio D2 are both 25%.

[0053] In this embodiment, the welding current output by the inverter circuit 25 is a current obtained by periodically switching between a first AC current that varies at a first frequency f1 and a second AC current that varies at a second frequency f2 lower than the first frequency f1 at a third frequency f3. Therefore, the welding system A3 can achieve both a penetration depth and arc stability. In addition, according to this embodiment, the welding system A3 has a common configuration with the welding system A1, and thus achieves the same effects as the welding system A1. Furthermore, according to this embodiment, the first duty setting unit 288 sets the first duty ratio D1 of the first AC current, and the second duty setting unit 289 sets the second duty ratio D2 of the second AC current. As a result, the welding system A3 can set the duty ratios of the first AC current and the second AC current individually.

[0054] [Fourth embodiment] FIG. 6 is a diagram for explaining a welding system A4 according to a fourth embodiment. FIG. 6(a) is a block diagram showing the internal configuration of a control circuit 28 of welding power supply 2 of welding system A4. FIG. 6(b) is a waveform diagram showing an example of a welding current output by welding power supply 2. In FIG. 6, elements that are the same as or similar to those in the first embodiment are given the same reference numerals as those in the first embodiment. The welding system A4 according to this embodiment differs from the welding system A1 according to the first embodiment in that the waveforms of the first AC current and the second AC current are sine waves.

[0055] As shown in Fig. 6(a), the control circuit 28 according to this embodiment includes a waveform command generating unit 290 instead of the frequency switching unit 285. The waveform command generating unit 290 generates a waveform command signal for commanding the waveform of the welding current. The waveform command generating unit 290 generates a first sine wave signal of a first frequency f1 input from the first frequency setting unit 282 and a second sine wave signal of a second frequency f2 input from the second frequency setting unit 283. Then, the waveform command generating unit 290 switches between the first sine wave signal and the second sine wave signal at a third frequency f3 input from the switching frequency setting unit 284, and outputs the switched signal to the drive signal generating unit 286 as a waveform command signal.

[0056] The drive signal generating unit 286 generates and outputs a switching drive signal based on the difference between the current value signal input from the current sensor 26 and the waveform command signal input from the waveform command generating unit 290. The inverter circuit 25 switches each switching element on and off in response to the switching drive signal. That is, the drive signal generating unit 286 performs feedback control so that the waveform of the welding current matches the waveform command signal. In this embodiment, the waveform command signal generated by the waveform command generating unit 290 is a sine wave signal. The drive signal generating unit 286 generates a switching drive signal based on the waveform command signal and outputs it to the inverter circuit 25, so that the inverter circuit 25 outputs a sine wave welding current in response to the waveform command signal (see FIG. 6(b)). Note that the drive signal generating unit 286 may generate a switching drive signal based only on the waveform command signal without using the current value signal input from the current sensor 26.

[0057] According to this embodiment, the waveform command generating unit 290 generates a first sine wave signal of a first frequency f1 and a second sine wave signal of a second frequency f2, switches between them at a third frequency f3, and outputs the waveform command signal to the driving signal generating unit 286. The driving signal generating unit 286 generates and outputs a switching driving signal based on the difference between the current value signal and the waveform command signal. The inverter circuit 25 switches each switching element on and off in response to the switching driving signal. As a result, the welding current output by the inverter circuit 25 is a current in which a first AC current that fluctuates at the first frequency f1 and a second AC current that fluctuates at a second frequency f2 lower than the first frequency f1 are periodically switched at the third frequency f3. Therefore, the welding system A4 can achieve both a penetration depth and arc stability. Also, according to this embodiment, the welding system A4 has a common configuration with the welding system A1, and thus has the same effects as the welding system A1. Furthermore, according to this embodiment, the welding system A4 can output a welding current having a sine wave shape in response to a waveform command signal.

[0058] In the present embodiment, the welding system A4 outputs a welding current having a sine wave shape, but the present invention is not limited to this. The welding system A4 can output a welding current having a waveform corresponding to the waveform command signal generated by the waveform command generating unit 290, and can therefore output a welding current having another waveform.

[0059] Fifth embodiment FIG. 7 is a diagram for explaining a welding system A5 according to a fifth embodiment. FIG. 7(a) is a block diagram showing the internal configuration of a control circuit 28 of welding power supply 2 of welding system A5. FIG. 7(b) is a waveform diagram showing an example of a welding current output by welding power supply 2. In FIG. 7, elements that are the same as or similar to those in the fourth embodiment are given the same reference symbols as those in the fourth embodiment. The welding system A5 according to this embodiment differs from the welding system A4 according to the fourth embodiment in that it outputs a direct current that changes in a rectangular wave shape and has different reference values ​​in the first period T1 and the second period T2.

[0060] As shown in FIG. 7(a), the control circuit 28 according to the present embodiment further includes a first reference value setting unit 291 and a second reference value setting unit 292. The first reference value setting unit 291 is configured to set a first reference value in the first period T1. The first reference value is a current value that is a reference for the direct current that changes in a rectangular wave shape in the first period T1, and is an average current value in the first period T1. The second reference value setting unit 292 is configured to set a second reference value in the second period T2. The second reference value is a current value that is a reference for the direct current that changes in a rectangular wave shape in the second period T2, and is an average current value in the second period T2. The first reference value setting unit 291 and the second reference value setting unit 292 set the first reference value and the second reference value in response to the operation of the operation unit by the operator. The first reference value and the second reference value may each be set to a fixed value. The first reference value and the second reference value are not limited. The first and second reference values ​​can be adjusted to optimum values ​​by an operator performing trial welding.

[0061] The waveform command generating unit 290 generates a first rectangular wave signal that fluctuates around a first reference value at a first frequency f1 input from a first frequency setting unit 282, and a second rectangular wave signal that fluctuates around a second reference value at a second frequency f2 input from a second frequency setting unit 283. Then, the waveform command generating unit 290 switches between the first rectangular wave signal and the second rectangular wave signal at a third frequency f3 input from a switching frequency setting unit 284, and outputs the signal to the drive signal generating unit 286 as a waveform command signal.

[0062] Drive signal generating unit 286 generates and outputs a switching drive signal based on the difference between the current value signal input from current sensor 26 and the waveform command signal input from waveform command generating unit 290. Inverter circuit 25 switches each switching element on and off in response to the switching drive signal. In this way, inverter circuit 25 outputs a welding current having a waveform in response to the waveform command signal. Fig. 7(b) shows the waveform of the welding current when second reference value I2 is set to a value larger than first reference value I1.

[0063] According to this embodiment, the waveform command generating unit 290 generates a first square wave signal that changes at a first frequency f1 and a second square wave signal that changes at a second frequency f2, switches between them at a third frequency f3, and outputs the waveform command signal to the driving signal generating unit 286. The driving signal generating unit 286 generates and outputs a switching driving signal based on the difference between the current value signal and the waveform command signal. The inverter circuit 25 switches each switching element on and off according to the switching driving signal. As a result, the welding current output by the inverter circuit 25 is a current in which the first square wave DC current that changes at the first frequency f1 and the second square wave DC current that changes at a second frequency f2 lower than the first frequency f1 are periodically switched at the third frequency f3. Therefore, the welding system A5 can achieve both a penetration depth and arc stability. Also, according to this embodiment, the welding system A5 has a common configuration with the welding system A4, and thus has the same effects as the welding system A4. Furthermore, in this embodiment, the first reference value setting unit 291 sets the first reference value, and the second reference value setting unit 292 sets the second reference value. This allows the welding system A5 to individually set the first reference value of the first square-wave DC current and the second reference value of the second square-wave DC current. By setting the second reference value larger than the first reference value, the welding system A5 can increase the penetration depth in the second period T2.

[0064] Sixth Embodiment FIG. 8 is a diagram for explaining a welding system A6 according to a sixth embodiment. FIG. 8(a) is a block diagram showing the internal configuration of a control circuit 28 of welding power supply 2 of welding system A6. FIG. 8(b) is a waveform diagram showing an example of a welding current output by welding power supply 2. In FIG. 8, elements that are the same as or similar to those in the fourth embodiment are given the same reference numerals as those in the fourth embodiment. The welding system A6 according to this embodiment differs from the welding system A4 according to the fourth embodiment in that the waveforms of the first AC current and the second AC current are offset.

[0065] As shown in FIG. 8(a), the control circuit 28 according to the present embodiment further includes a first offset setting unit 293 and a second offset setting unit 294. The first offset setting unit 293 is configured to set a first offset value in the first period T1. The first offset value is a value that sets a positive and negative current ratio of the first AC current in the first period T1, and is, for example, a value of (-25)% or more and 25% or less. The second offset setting unit 294 is configured to set a second offset value in the second period T2. The second offset value is a value that sets a positive and negative current ratio of the second AC current in the second period T2, and is, for example, a value of (-25)% or more and 25% or less. The first offset setting unit 293 and the second offset setting unit 294 set the first offset value and the second offset value in response to the operation of the operation unit by the operator. The first offset value and the second offset value may each be set to a fixed value. The first offset value and the second offset value are not limited. The first offset value and the second offset value can be adjusted to optimum values ​​by an operator performing trial welding.

[0066] The waveform command generating unit 290 generates a first square wave AC signal having a first frequency f1 and offset according to the first offset value, and a second square wave AC signal having a second frequency f2 and offset according to the second offset value. Then, the waveform command generating unit 290 switches between the first square wave AC signal and the second square wave AC signal at a third frequency f3 input from the switching frequency setting unit 284, and outputs the switched signal to the drive signal generating unit 286 as a waveform command signal.

[0067] Drive signal generating unit 286 generates and outputs a switching drive signal based on the difference between the current value signal input from current sensor 26 and the waveform command signal input from waveform command generating unit 290. Inverter circuit 25 switches each switching element on and off in response to the switching drive signal. In this way, inverter circuit 25 outputs a welding current having a waveform in response to the waveform command signal. Fig. 8(b) shows the waveform of the welding current when the first offset value is set to (-15)% and the second offset value is set to 15%.

[0068] According to this embodiment, the waveform command generating unit 290 generates a first square wave AC signal that changes at a first frequency f1 and a second square wave AC signal that changes at a second frequency f2, switches between them at a third frequency f3, and outputs the waveform command signal to the driving signal generating unit 286. The driving signal generating unit 286 generates and outputs a switching driving signal based on the difference between the current value signal and the waveform command signal. The inverter circuit 25 switches each switching element on and off according to the switching driving signal. As a result, the welding current output by the inverter circuit 25 is a current in which the first square wave AC current that changes at the first frequency f1 and the second square wave AC current that changes at a second frequency f2 lower than the first frequency f1 are periodically switched at the third frequency f3. Therefore, the welding system A6 can achieve both a penetration depth and arc stability. Also, according to this embodiment, the welding system A6 has a common configuration with the welding system A4, and thus has the same effects as the welding system A4. Furthermore, in this embodiment, the first offset setting unit 293 sets the first offset value, and the second offset setting unit 294 sets the second offset value. This allows the welding system A6 to individually set the first offset value of the first square wave AC current and the second offset value of the second square wave AC current. By setting the second offset value to be larger than the first offset value, the welding system A6 can increase the penetration depth in the second period T2.

[0069] The welding system according to the present invention is not limited to the above-described embodiment, and the specific configuration of each part of the welding system according to the present invention can be freely designed in various ways. [Explanation of symbols]

[0070] A1 to A6: Welding system, 2: Welding power supply, 7: Spraying device

Claims

1. 1. A submerged arc welding system for performing submerged arc welding, comprising: a welding power supply for supplying power; A spraying device for spraying flux onto the workpiece; Equipped with The welding power supply device comprises: a first period during which a first waveform current varying at a first frequency is output and a second period during which a second waveform current varying at a second frequency lower than the first frequency is output; Submerged arc welding system.

2. the first frequency and the second frequency are equal to or higher than 10 Hz and equal to or lower than 100 Hz, a third frequency for switching between the first period and the second period is equal to or higher than 1 Hz and equal to or lower than 20 Hz; 2. The submerged arc welding system of claim 1.

3. the first waveform current and the second waveform current are square wave AC currents; a first duty ratio of the first waveform current and a second duty ratio of the second waveform current are individually adjustable.

3. A submerged arc welding system according to claim 1 or 2.

4. the first waveform current and the second waveform current are direct currents that change in a square wave shape, a first reference value serving as a reference for the first waveform current and a second reference value serving as a reference for the second waveform current are individually adjustable.

3. A submerged arc welding system according to claim 1 or 2.

5. A submerged arc welding method for performing submerged arc welding in a submerged arc welding system including a welding power supply device and a spraying device that sprays flux onto a workpiece, comprising: a first step of outputting a first waveform current fluctuating at a first frequency from the welding power supply; a second step of outputting a second waveform current from the welding power supply, the second waveform current fluctuating at a second frequency lower than the first frequency; Equipped with periodically switching between the first step and the second step; Submerged arc welding method.

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