CN114147323A - Welding power supply system - Google Patents

Abstract

The invention provides a welding power supply system capable of automating the operation at the start of welding of submerged arc welding and inhibiting impurities from mixing into a welded bead after welding. A welding system (A1) for submerged arc welding is provided with: a welding power supply device (2) having an inverter circuit (25) and supplying power; a wire feeding device (5) for feeding a welding wire; and a control device (1) for controlling the welding power supply device (2) and the wire feeding device (5). A control device (1) causes a wire feeding device (5) to feed a welding wire in a forward direction at the start of welding, causes a welding power supply device (2) to output a start current when the tip of the welding wire comes into contact with an object (W) to be welded, and sets a start current period for feeding the welding wire in the forward direction at a 2 nd speed slower than the 1 st speed from the contact of the welding wire to the start of feeding the welding wire in the forward direction at the 1 st speed for welding.

Description

Welding power supply system

Technical Field

The present invention relates to a welding power supply system for submerged arc welding.

Background

Submerged arc welding has been known. Submerged arc welding spreads granular flux on an object to be welded, feeds a welding wire into the flux, and generates an arc between a tip end of the welding wire and the object to be welded to perform welding. In submerged arc welding, a large current is passed through a large-diameter welding wire, whereby a thick plate can be efficiently welded.

When submerged arc welding is started, an operator inserts steel wool between a welding wire and a workpiece and ignites the steel wool by applying a current, thereby generating an arc between the welding wire and the workpiece. However, in this case, since steel wool needs to be inserted every time welding is performed, an operation by an operator is required. In order to automate this operation, patent document 1 discloses a method of spreading metal powder before spreading flux instead of inserting steel wool.

Documents of the prior art

Patent document

Patent document 1: JP-A-64-34581

According to the method disclosed in patent document 1, since the insertion work of the steel wool by the operator is not required, the welding start work can be automated. However, since metal powder which is not necessary for welding is consumed every time welding is performed, unnecessary cost is incurred. In addition, metal powder is mixed as impurities into the welded bead. These problems are similar to those in the case of steel wool.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a welding power supply system capable of automating the operation at the start of welding in submerged arc welding and capable of suppressing impurities from being mixed into a weld bead after welding.

The welding power supply system according to the present invention is a welding system for performing submerged arc welding, comprising: a welding power supply device having an inverter circuit and supplying power; a wire feeding device for feeding a welding wire; and a control device for controlling the welding power supply device and the wire feeding device, wherein the control device causes the wire feeding device to feed the welding wire in the forward direction at the start of welding, causes the welding power supply device to output a start current when the tip of the welding wire is in contact with an object to be welded, and sets a start current period for feeding the welding wire in the forward direction at a 2 nd speed lower than the 1 st speed from the contact of the welding wire to the start of feeding the welding wire in the forward direction at the 1 st speed for welding.

In a preferred embodiment of the present invention, the 2 nd speed is a speed at which the welding wire is stopped.

In a preferred embodiment of the present invention, the start current period is a period until a preset 1 st time elapses.

In a preferred embodiment of the present invention, the welding power supply system further includes: and a voltage sensor that detects a voltage applied between a tip of the welding wire and the work piece, wherein the start current period is a period until a detection voltage detected by the voltage sensor becomes equal to or greater than a preset voltage threshold.

In a preferred embodiment of the present invention, the start current period is a longer period among a period until the detection voltage becomes equal to or greater than the voltage threshold and a period until a predetermined 2 nd time elapses.

In a preferred embodiment of the present invention, the controller causes the welding wire to be fed in the forward direction at a 3 rd speed at the start of welding, causes the welding wire to be fed in the reverse direction for a predetermined length when the tip of the welding wire comes into contact with the object to be welded, and then causes the welding wire to be fed in the forward direction at a 4 th speed which is slower than the 3 rd speed until the tip of the welding wire comes into contact with the object to be welded again.

In a preferred embodiment of the present invention, the control device sets an end current period from when the wire feeding device stops feeding of the welding wire to when the welding power supply device stops the end current at the end of welding.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the control device brings the tip of the welding wire into contact with the object to be welded at the start of welding, and outputs the start current between the start current periods. By the energization of the start current, the welding wire is ignited, and an arc is generated. The feeding speed of the wire during the start current is 2 nd speed slower than 1 st speed at the time of welding. Therefore, the sticking phenomenon that the tip of the welding wire is pressed against the object to be welded and is closely attached without generating an arc is suppressed. Further, since other materials such as metal powder and steel wool are not used, the operation at the start of welding can be automated, and the mixing of impurities into the weld bead after welding can be suppressed.

Drawings

Fig. 1 is a diagram for explaining a welding system according to embodiment 1, where (a) is a block diagram showing an overall configuration of the welding system, and (b) is a block diagram showing an internal configuration of a welding power supply device.

Fig. 2 (a) is an example of a flowchart showing a start control process, and (b) is an example of a flowchart showing an end control process.

Fig. 3 is a timing chart showing each state during welding in the welding system according to embodiment 1.

Fig. 4 is a timing chart showing each state during welding in a modification of the welding system according to embodiment 1.

Description of reference numerals

A1: welding system, 1: control device, 2: welding power supply device, 25: inverter circuit, 27: voltage sensor, 5: wire feeding device, 7: dispensing device

Detailed Description

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[ 1 st embodiment ]

Fig. 1 is a diagram for explaining a welding system according to embodiment 1. Fig. a is a block diagram showing the overall configuration of the welding system. Fig. b is a block diagram showing an internal configuration of the welding power supply apparatus.

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 carriage 4, a wire feeder 5, a welding tray 6, a spreading device 7, and an electrode 8. The welding system a1 moves the carriage 4 along the welding line of the object W to be welded, and at the same time, disperses the granular flux stored in the hopper of the dispersing device 7, and causes the wire feeding device 5 to feed the wire into the flux. The welding wire is supplied from the welding disc 6. The welding power supply device 2 converts ac power supplied from a commercial power supply P into power suitable for welding and outputs the power, and generates an arc between an electrode 8, which is a tip portion of a welding wire, and an object W to be welded inside a flux. The welding is performed by the heat of the arc. Thereby welding along the weld line of the object W to be welded. Instead of using the carriage 4, the workpiece W may be moved or rotated.

The control device 1 performs various controls of the welding system a 1. The control device 1 may be a control device in which a program for performing various controls of the welding system a1 is installed on a general-purpose computer, or may be a dedicated device for controlling the welding system a 1. The control device 1 moves the carriage 4 at a predetermined moving speed. The moving speed is set according to the material, thickness, and the like of the work W. The control device 1 instructs the spreading device 7 on the spreading of the flux. The control device 1 instructs the wire feeding device 5 to start and stop the feeding of the welding wire. In addition, the wire feed speed is also indicated. The feed speed is set in accordance with the set welding current or the like. The control device 1 instructs the welding power supply device 2 to output electric power. The control performed by the control device 1 at the start of welding and at the end of welding will be described in detail later.

The welding power supply device 2 converts ac power supplied from the commercial power supply P into ac power of a desired frequency and outputs the ac power. Instead of welding power supply device 2, a configuration may be used in which a plurality of welding power supply devices 2 are connected in parallel with each other (specifically, output terminals a of welding power supply devices 2 are connected to each other and to workpiece W, and output terminals b are connected to each other and to the welding wire).

As shown in fig. 1 (b), the welding power supply apparatus 2 includes a rectifying/smoothing circuit 21, an inverter circuit 22, a transformer 23, a rectifying/smoothing circuit 24, an inverter circuit 25, a current sensor 26, a voltage sensor 27, and a control circuit 28.

The rectifying/smoothing circuit 21 converts ac power input from the commercial power supply P into dc power and outputs the dc power. The rectifying/smoothing circuit 21 includes a rectifying circuit for rectifying an ac current and a smoothing capacitor for smoothing. The structure of the rectifying/smoothing circuit 21 is not limited.

The inverter circuit 22 is, for example, a unidirectional full-bridge PWM-controlled inverter, and includes 4 switching elements. The inverter circuit 22 switches the switching element in accordance with the output control drive signal input from the control circuit 28, thereby converting the dc power input from the rectifying/smoothing circuit 21 into high-frequency power and outputting the high-frequency power. The inverter circuit 22 may be a circuit that converts dc power into high-frequency power, and may be, for example, a half-bridge type inverter circuit or an inverter circuit having another configuration.

The transformer 23 transforms the high-frequency voltage output from the inverter circuit 22 and outputs the voltage to the rectifying/smoothing circuit 24. The transformer 23 includes a primary winding 23a and a secondary winding 23 b. Each input terminal of the primary winding 23a is connected to each output terminal of the inverter circuit 22. The respective output terminals of the secondary winding 23b are connected to the respective input terminals of the rectifying/smoothing circuit 24. The output voltage of the inverter circuit 22 is transformed in accordance with the turn ratio of the primary winding 23a and the secondary winding 23b, and is input to the rectifying/smoothing circuit 24. The secondary winding 23b is insulated from the primary winding 23a, and therefore, a current input from the commercial power supply P can be prevented from flowing to the secondary circuit. Since transformer 23 transforms the high-frequency voltage output from inverter circuit 22, it is smaller and lighter than a transformer that transforms the ac voltage of commercial power supply P.

The rectifying/smoothing circuit 24 converts the high-frequency power input from the transformer 23 into dc power and outputs the dc power. The rectifying/smoothing circuit 24 includes a rectifying circuit for rectifying a high-frequency current and a dc reactor for smoothing. The structure of the rectifying/smoothing circuit 24 is not limited.

The inverter circuit 25 is, for example, a unidirectional full-bridge PWM-controlled inverter, and includes 4 switching elements. The inverter circuit 25 converts the dc power input from the rectifying/smoothing circuit 24 into ac power by switching the switching element in accordance with the switching drive signal input from the control circuit 28, and outputs the ac power. The inverter circuit 25 switches between a positive polarity, which is a state in which the potential of the output terminal a (connected to the work W) is higher than the potential of the output terminal b (connected to the welding wire), and a reverse polarity, which is a state in which the potential of the output terminal a is lower than the potential of the output terminal b. The inverter circuit 25 may be any circuit as long as it can convert dc power into ac power, and may be, for example, a half-bridge type inverter circuit or an inverter circuit having another configuration.

The current sensor 26 detects the output current of the welding power supply apparatus 2, and in the present 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 apparatus 2 detected by the current sensor 26 is substantially equal to the current flowing through the electrode 8. The current sensor 26 outputs a current value signal corresponding to the detected instantaneous value of the current to the control circuit 28 and the control device 1. The current sensor 26 is not limited in structure as long as it detects an output current from a connection line. The location of the current sensor 26 is not limited. For example, the current sensor 26 may be disposed on a connection line connecting the other output terminal of the inverter circuit 25 and the output terminal b. Further, the current sensor 26 is disposed outside the welding power supply device 2.

The voltage sensor 27 detects the output voltage of the welding power supply device 2, and in the present embodiment, detects the inter-terminal voltage between the output terminal a and the output terminal b. This voltage is substantially equal to the voltage applied between the work W and the tip of the electrode 8. The voltage sensor 27 outputs a voltage value signal corresponding to the detected instantaneous value of the voltage to the control circuit 28 and the control device 1. The voltage sensor 27 is not limited in structure, and may be any device as long as it detects the voltage between the output terminals a and b. The location of the voltage sensor 27 is not limited. For example, the voltage sensor 27 may be disposed outside the welding power supply apparatus 2.

The control circuit 28 is a circuit for controlling the welding power supply device 2, and is implemented by a microcomputer, for example. The control circuit 28 receives a current value signal from the current sensor 26, a voltage value signal from the voltage sensor 27, and various command signals from the control device 1. Then, the control circuit 28 outputs a drive signal to each of the inverter circuit 22 and the inverter circuit 25.

When receiving a command signal instructing the start of power output from the control device 1, the control circuit 28 starts output of the drive signal to each of the inverter circuit 22 and the inverter circuit 25, thereby starting output of power. When receiving a command signal instructing the stop of the power output from the control device 1, the control circuit 28 stops the output of the drive signal to stop the power output.

The control circuit 28 calculates an effective current value from the current value signal input from the current sensor 26. Then, the control circuit 28 generates an output control drive signal for controlling the switching element of the inverter circuit 22 based on the effective current value and the current command value input from the control device 1, and outputs the output control drive signal to the inverter circuit 22. That is, the control circuit 28 performs feedback control so that the current effective value matches the current command value. The control circuit 28 can also generate an output control drive signal based on the voltage value signal and the voltage command value input from the voltage sensor 27.

The control circuit 28 generates a switching drive signal for controlling the switching element of the inverter circuit 25 based on the current value signal input from the current sensor 26 and the waveform command signal generated therein, and outputs the switching drive signal to the inverter circuit 25. That is, the control circuit 28 performs feedback control so that the waveform of the output current matches the waveform instructed by the waveform instruction signal. In the present embodiment, the waveform command signal is a sine wave signal. The control circuit 28 generates a switching drive signal based on the waveform command signal and outputs the switching drive signal to the inverter circuit 25, whereby the inverter circuit 25 outputs a sinusoidal alternating current corresponding to the waveform command signal. The control circuit 28 may generate the switching drive signal based on only the waveform command signal without using the instantaneous value of the output current.

When a command signal for dc output is input from the control device 1, the control circuit 28 sets the switching drive signal to be output to the inverter circuit 25 to a signal for setting a given switching element in an on (on) state and setting the other switching elements in an off (off) state. For example, if the state of each switching element is fixed so that the output terminal a on the positive side of the rectifying/smoothing circuit 24 is connected to the output terminal a and the output terminal b on the negative side of the rectifying/smoothing circuit 24 is connected to the output terminal b, the welding power supply device 2 outputs dc power with the output terminal a being the positive electrode and the output terminal b being the negative electrode. That is, welding system a1 is a dual-purpose welding system that can output not only ac power but also dc power. Further, the welding power supply apparatus 2 can control the output current based on the current command value input from the control apparatus 1. Therefore, the welding system a1 can properly control the output current.

Next, a control process performed by the control device 1 at the start and end of welding will be described. Fig. 2 is a flowchart for explaining a control process performed by the control device 1.

Fig. 2 (a) is an example of a flowchart showing a start control process at the start of welding. The start control process is started when, for example, an operation button for starting welding is pressed.

The feeding of the welding wire is first started (S1). Specifically, the control device 1 instructs the wire feeding device 5 to start feeding of the welding wire. At this time, the control device 1 gives an instruction to feed the welding wire in the forward direction (direction from the welding tray 6 to the carriage 4) at a predetermined micro-motion speed (not limited, but, for example, about 5 m/min). The inching speed corresponds to "speed 3" of the present invention. Next, a dc voltage (not limited, but, for example, about 15V) is applied between the work W and the electrode 8 (S2). Specifically, the control device 1 instructs the welding power supply device 2 to output a dc voltage. In the present embodiment, the welding power supply apparatus 2 causes the inverter circuit 25 to output a dc voltage under the control of the control circuit 28. The welding power supply apparatus 2 may further include a dc power supply connected in parallel to the output terminals a and b, and a dc voltage applied between the workpiece W and the electrode 8 may be output from the dc power supply.

Next, it is determined whether or not the electrode 8 is in contact with the work W and short-circuited (S3). Specifically, the control device 1 performs determination based on the voltage value signal input from the voltage sensor 27. When the electrode 8 and the work W are short-circuited, the voltage between the electrode 8 and the work W decreases rapidly and approaches "0". The control device 1 determines that a short circuit occurs when the voltage detected by the voltage sensor 27 (hereinafter referred to as "detection voltage") is equal to or less than a short circuit detection threshold. The method of determining the short circuit is not limited, and the control device 1 may determine the short circuit based on a current value signal input from the current sensor 26, for example. If the short is not detected (no in S3), 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.

When the short circuit is detected (yes in S3), feeding of the wire in the reverse direction (the direction from the carriage 4 to the welding disk 6) is started (S4). Specifically, the control device 1 instructs the wire feeding device 5 to start feeding of the welding wire in the reverse direction. As a result, the welding wire moves in the reverse direction, and the electrode 8 in contact with the workpiece W is pulled away and retracted. Next, it is determined whether or not the electrode 8 has been retracted by a predetermined length (not limited, but about 3mm, for example) (S5). Specifically, the control device 1 counts the time from the start of the reverse feeding, and determines whether or not the time required for retracting a given length has elapsed. If the retraction is not completed (no in S5), the process returns to step S5, and the determination in step S5 is repeated. That is, the control device 1 waits until the retraction is completed. When the retraction is completed (yes in S5), the wire is fed forward at the decelerated speed (S6). The deceleration speed is a speed sufficiently lower than the inching speed (for example, 0.1m/min, although not limited thereto). The deceleration speed corresponds to "speed 4" of the present invention.

By the processing in steps S1 to S6, the welding wire is fed at a relatively fast speed until the electrode 8 is once brought into contact with the workpiece W, and is fed at a relatively slow speed after being retracted after the contact. This shortens the time until the electrode 8 comes into contact with the work W, and suppresses the electrode 8 from being pressed against the work W with a strong stress. In addition, steps S3 to S6 may be omitted when pressing the electrode 8 against the workpiece W with a strong stress when the electrode 8 is in contact with the workpiece W is suppressed, for example, when the inching speed is sufficiently low. That is, the feed at the retracting and decelerating speeds may not be performed.

Next, it is determined whether or not the electrode 8 is again in contact with the work W and short-circuited (S7). If the short circuit is not detected (no in S7), the process returns to step S7, and the determination in step S7 is repeated. That is, the control device 1 waits until a short circuit is detected. If a short circuit is detected (yes at S7), the feeding of the wire is stopped (S8). Specifically, the control device 1 instructs the wire feeding device 5 to stop the feeding of the welding wire.

Next, flux is spread at and around the welding start point of the object W to be welded where the wire is in contact (S9). Specifically, the control device 1 instructs the spreading device 7 on the spreading of the flux. The spreading device 7 spreads a predetermined appropriate amount of flux.

Next, the output of the start current is started (S10). Specifically, the control device 1 instructs the welding power supply device 2 to start outputting the current. The starting current is, for example, a dc current of about 1000A. The current value of the starting current is not limited, and may be different depending on the material and diameter of the wire used. The starting current is not limited to a direct current, and may be an alternating current.

Next, the measurement of the elapsed time T for determining the start current period is started (S11). The start current period is a period in which the start current flows in a state in which the feeding of the welding wire is stopped. Next, the standby time T is set to a preset 1 st time T1 (not limited, but about 400ms, for example) (S12), and the 1 st time T1 is a set time for defining a start current period by time. The 1 st time T1 is a time until the electrode 8 is ignited by the start of the current flow, an arc is generated between the tip of the electrode 8 and the work W, and the arc is stabilized, and is set based on experiments and simulations. That is, the start current period is a period for allowing the start current to flow to the electrode 8 from the time when the electrode 8 and the work W are again brought into contact and short-circuited, thereby generating and stabilizing the arc. The 1 st time T1 may be set for each material and diameter of the wire used, or may be set for a single time applicable to all wires usable in the welding system a 1.

In the welding process executed after the start control process is completed, the control device 1 causes the wire feeding device 5 to feed the welding wire in accordance with the welding conditions, causes the welding power supply device 2 to output the welding power, and moves the carriage 4. Further, the control device 1 causes the spreading device 7 to spread the flux in accordance with the movement of the carriage 4. The welding power output by the welding power supply device 2 may be ac power or dc power. Further, a description of specific control of the welding process is omitted.

Fig. 2 (b) is an example of a flowchart showing the end control processing at the end of welding. For example, the termination control process is started when welding is completed to a welding termination point of the object W to be welded, or when an operation button for terminating welding is pressed.

The feeding of the welding wire is first stopped (S21). Specifically, the control device 1 instructs the wire feeding device 5 to stop the feeding of the welding wire. Next, the output of the end current is started (S22). Specifically, the control device 1 instructs the welding power supply device 2 to terminate the output of the current. The end current is, for example, a dc current of about 500A. The current value of the end current is not limited, and may be different depending on the material and the length of the wire used. The end current is not limited to a direct current, and may be an alternating current. By applying a finishing current to the electrode 8 in a state where the feeding of the welding wire is stopped, the electrode 8 is ignited. Next, a standby is performed until the detection voltage V detected by the voltage sensor 27 becomes equal to or higher than a preset end-time voltage threshold Ve (not limited to, but about 35V, for example) (S23). The end-time voltage threshold Ve is a threshold for the detection electrode 8 to start burning up so that the detection voltage V starts rising. The electrode 8 burns up and the arc length becomes longer, and the diameter of the tip of the electrode 8 becomes larger as the detection voltage V becomes larger. The end-time voltage threshold Ve is set to a voltage at which the electrode 8 surely starts to ignite and the diameter of the tip of the electrode 8 does not become too large. In step S23, instead of comparing the detected voltage V with the end-time voltage threshold Ve, the amount of change in the detected voltage V from the start of the output of the end current, or the rate of change in the detected voltage V may be compared with the threshold.

Next, the output of the end current is ended (S24). Specifically, the control device 1 instructs the welding power supply device 2 to end the output of the end current. The period from when the feeding of the wire is stopped to when the end current is stopped is the end current period when the end current flows to the electrode 8. Next, the spreading of the flux is completed (S25), and the end control process is completed.

The processing shown in the flowchart of fig. 2 is an example, and the start control processing and the end control processing performed by the control device 1 are not limited to the above.

Fig. 3 is a timing chart showing each state during welding in the welding system a 1. Fig. (a) shows a temporal change in the welding state. Fig. b shows a time change of the detection voltage detected by the voltage sensor 27. Fig. c shows a time change of the detected current detected by the current sensor 26. In this figure, (d) shows a temporal change in the wire feed speed. When the welding wire is fed forward, the feeding speed is a positive value, and when the welding wire is fed backward, the feeding speed is a negative value. Fig. e shows a time change in the flux spreading state. Turned ON when the flux is spread. The vertical axis and the horizontal axis of the timing chart shown in fig. 3 are appropriately enlarged and reduced for easy understanding, and the waveforms shown are also simplified, exaggerated, or emphasized for easy understanding (the same applies to fig. 4).

At time t0, the operation button for starting welding is pressed, the welding state is turned ON (see fig. 3 a), and the control process is started. At this time, the wire feeding in the forward direction in the micro-speed system is started (see (d) of fig. 3), and the output of the dc voltage is started (see (b) of fig. 3). Further, the feeding speed is increased with an inclination by inertia after the instruction of the control device 1. The same applies to the subsequent change of the feed speed.

At time t1, the electrode 8 is in contact with the work W and short-circuited, and the detection voltage abruptly decreases (see fig. 3 (b)). This causes a short circuit to be detected, and the wire starts to be fed in the reverse direction, and the feed speed becomes a negative value (see (d) of fig. 3). By the feeding of the welding wire in the reverse direction, the electrode 8 is pulled away from the work W, the detection voltage returns to the original state, the withdrawal of a predetermined length is completed at time t2, and the feeding of the welding wire in the forward direction at the deceleration speed is started (refer to (d) of fig. 3).

Then, at time t3, the electrode 8 and the workpiece W again contact each other and short-circuit occurs, and the detection voltage rapidly decreases (see (b) of fig. 3), and the detection current rapidly increases (see (c) of fig. 3). This causes a short circuit to be detected, the wire feeding to be stopped, the feeding speed to be "0" (see fig. 3 (d)), and the flux spreading to be started (see fig. 3 (e)). Further, the output of the current starts (see (c) of fig. 3), the electrode 8 burns up to generate an arc between the tip of the electrode 8 and the work W, and the detection voltage becomes a predetermined voltage (see (b) of fig. 3). The start current period continues from time T3 to time T4 after the 1 st time T1 elapses, and the start current is supplied to the electrode 8. As a result, the electrode 8 burns up, the arc length gradually increases, and the detection voltage gradually increases in accordance with the increase (see fig. 3 (b)).

Then, at time t4, the start current period ends, the start control process ends, and the welding process starts according to the welding conditions. Thereby, the welding current corresponding to the current command value is output (see (c) of fig. 3), and the feeding of the welding wire is started (see (d) of fig. 3).

At time t5, the operation button for terminating welding is pressed, whereby the welding state is turned OFF (see fig. 3 (a)), and the termination control process is started. At this time, the feeding of the wire is finished (see (d) of fig. 3), and the output of the finishing current is started (see (c) of fig. 3). By terminating the current supply, the electrode 8 is gently ignited, and the detection voltage starts to rise (see fig. 3 (b)). When the detection voltage is equal to or higher than the end-time voltage threshold Ve at time t6, the end current period is ended, the output of the end current is ended (see fig. 3 c), the flux spreading is ended (see fig. 3 e), and the end control process is ended. In addition, even if the control device 1 instructs the wire feeding device 5 to stop the feeding, the feeding of the welding wire is not immediately stopped due to inertia. When the actual welding wire is detected by a signal from an encoder, not shown, of wire feeding device 5, control device 1 may start the output of the end current and start the end current period.

Next, the operation and effect of the welding system a1 according to the present embodiment will be described.

According to the present embodiment, the control device 1 brings the tip of the welding wire into contact with the object W to be welded at the start of welding, and causes the wire feeding device 5 to output the start current while stopping the feeding of the welding wire during the start current period. The electrode is ignited by the energization of the 1 st time T1 of the start current, and an arc is generated between the tip of the electrode 8 and the work W, and the arc is in a stable state. Meanwhile, since the welding wire is not fed, the sticking phenomenon that the tip of the electrode 8 is pressed against the object W to be welded is suppressed. Further, since it is not necessary to use other materials such as metal powder and steel wool for generating an arc, the operation at the start of welding can be automated, and contamination of impurities in the weld bead after welding can be suppressed. When metal powder or steel wool is inserted to start welding, the distance between the welding wire and the workpiece at the time of arc starting and the amount of metal powder or steel wool vary depending on the operator, and therefore the success rate of arc starting and the welding result at the start portion may be affected. However, according to the present embodiment, since the operation at the start of welding can be automated, a welding result with high reproducibility can be obtained without causing variation by the operator.

Further, according to the present embodiment, the control device 1 feeds the welding wire at the inching speed at the start of welding, retracts the welding wire by a predetermined length after bringing the tip into contact with the workpiece W, and then feeds the welding wire at the deceleration speed. This shortens the time until the electrode 8 comes into contact with the work W, and prevents the electrode 8 from being pressed against the work W by a strong stress.

Further, according to the present embodiment, control device 1 causes wire feeding device 5 to stop feeding of the welding wire at the end of welding, and causes welding power supply device 2 to output the end current until detection voltage V becomes equal to or greater than end voltage threshold Ve. When the electrode 8 is energized to stop the current in a state where the feeding of the welding wire is stopped, the electrode 8 is ignited, and the current is stopped immediately when the ignition is started. Therefore, the tip diameter of the electrode 8 is not so large, and a sharp state is obtained. Consequently, the contact area between the tip of the electrode 8 and the workpiece W is reduced and the current density can be increased during the subsequent welding, thereby suppressing the failure of the arc generation. Further, it is not necessary to cut the electrode 8 with a pincer or the like so that the tip end is sharp.

In the present embodiment, the case where the feeding of the welding wire is stopped during the current start period is described, but the present invention is not limited to this. The welding wire may be fed forward at a 2 nd speed sufficiently slower than the 1 st speed which is the feeding speed at the time of welding during the start current. In this case, the sticking phenomenon caused by the tip of the electrode 8 being pressed against the work W is also suppressed. The stop of the feeding of the welding wire is a case where the 2 nd speed is "0" which is a speed for stopping the welding wire. In addition, the 2 nd speed is desirably slower, and it is more desirable to stop the feeding (the 2 nd speed is "0").

In the present embodiment, the case where the start current period is defined by time has been described, but the present invention is not limited to this. The start current period is a period for generating an arc between the electrode 8 and the workpiece W and stabilizing the arc to flow the start current, and therefore, the start current period can be terminated when the stabilization of the arc can be detected. Fig. 4 is a timing chart showing each state during welding in a modification that differs in a predetermined method in the current start period. In this modification, when the detection voltage V detected by the voltage sensor 27 is equal to or greater than a preset start-time voltage threshold value Vs (not limited to, but, for example, about 20V), the start current period is terminated. The start-time voltage threshold Vs is a threshold for detecting arc stability, and is set to a voltage at which the arc length of the generated arc reaches a predetermined length. In the timing chart shown in fig. 4, at time t4, the detection voltage V becomes equal to or higher than the start-time voltage threshold value Vs, and the current start period ends (see (b) of fig. 4), and the start control process ends and the welding process starts in accordance with the welding conditions. According to this modification, since the starting current period is terminated when the arc length is a predetermined length based on the detection voltage V, it is possible to suppress the occurrence of the sticking phenomenon by terminating the starting current period when the arc length is still short, or to suppress the electrode 8 from being excessively ignited and welded by a welding torch not shown.

In addition, when the detection voltage V is equal to or higher than the initial voltage threshold value Vs too soon, the arc may not be stabilized yet. In this case, the welding is started after the start current period ends in a state where the arc is unstable. To prevent this, when the detection voltage V is equal to or higher than the start-time voltage threshold value Vs, the start current period may be continued until a predetermined 2 nd time T2 (not limited, but, for example, about 100 ms) elapses. That is, the start current period may be a longer period among a period until the detection voltage V becomes equal to or greater than the start voltage threshold value Vs and a period until the 2 nd time T2 elapses. The 2 nd time T2 is a time required for the arc to be stabilized at a minimum, and is set in advance depending on the material and diameter of the wire used.

The welding system according to the present invention is not limited to the above-described embodiment. The specific configuration of each part of the welding system according to the present invention can be changed in various ways.

Claims (7)

1. A welding power supply system for performing submerged arc welding, comprising:

a welding power supply device having an inverter circuit and supplying power;

a wire feeding device for feeding a welding wire; and

a control device for controlling the welding power supply device and the wire feeding device,

the control device causes the wire feeding device to feed the welding wire in the forward direction at the start of welding, causes the welding power supply device to output a start current when the tip of the welding wire is in contact with the object to be welded, and sets a start current period for feeding the welding wire in the forward direction at a 2 nd speed that is slower than the 1 st speed from the contact of the welding wire to the start of feeding the welding wire in the forward direction at the 1 st speed for welding.

2. The welding power supply system of claim 1,

the 2 nd speed is a speed at which the welding wire is stopped.

3. Welding power supply system according to claim 1 or 2,

the start current period is a period until a preset 1 st time elapses.

4. Welding power supply system according to claim 1 or 2,

the welding power supply system further includes:

a voltage sensor for detecting a voltage applied between a tip of the welding wire and the work piece,

the start current period is a period until a detection voltage detected by the voltage sensor becomes equal to or greater than a preset voltage threshold.

5. The welding power supply system of claim 4,

the start current period is a longer period among a period until the detection voltage becomes equal to or greater than the voltage threshold and a period until a preset 2 nd time elapses.

6. The welding power supply system according to any one of claims 1 to 5,

the control device causes the welding wire to be fed in the forward direction at a 3 rd speed at the start of welding, and to be fed in the reverse direction by a predetermined length when the tip of the welding wire comes into contact with the object to be welded, and then to be fed in the forward direction at a 4 th speed which is slower than the 3 rd speed until the tip of the welding wire comes into contact with the object to be welded again.

7. The welding power supply system according to any one of claims 1 to 6,

the control device sets, at the end of welding, an end current period from when the wire feeding device stops feeding of the welding wire to when the welding power supply device stops ending the current.

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