JPH03238171A - Method for controlling output of welding power source - Google Patents

Abstract

PURPOSE:To improve the working rate of a production line by supplying a welding current to a welding wire at a point of time when the specified time elapses after detecting a short circuit when the short circuit is detected and shutting off the current when an unshort circuit is detected. CONSTITUTION:Welding is performed while a flux-cored wire 1 being fed by a wire feed motor 13. The short circuit between the welding wire 1 and base metals 2 is then monitored for a period of time till the wire feed motor 13 stops completely after feeding to the motor 13 stops. During this time, when a short circuit detector 18 detects the short circuit, the welding current is supplied to the welding wire 1 at a point of time when the specified time elapses after detecting the short circuit. When an omen of the unshort circuit or short circuit rupture is detected, the current supplied to the welding wire 1 is shut off. Consequently, the failure of an arc start and wire sensing can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for controlling the output of a welding power source used in a consumable electrode type arc welding method in which an arc is generated between a consumable electrode and a base metal to perform welding. In particular, the present invention relates to a method for controlling the output of a welding power source at the end of welding.

[Prior Art] In consumable electrode arc welding, when welding is completed, if the power supply to the wire feed motor that feeds the welding wire toward the base metal is stopped and the welding current is cut off at the same time, the wire Since the feed motor continues to rotate due to inertia, the welding wire plunges into the molten pool and the tip of the welding wire becomes stuck to the base metal.

In order to avoid this, conventionally, a timer is set for the time from when the power supply to the wire feed motor is stopped until the rotation of the feed motor completely stops, and even after the power supply to the wire feed motor is stopped, welding The welding current was continued to be supplied to the wire, and the welding current was cut off when the timer completed timing.

In the conventional method described above, it is possible to avoid sticking of the welding wire and the base metal, but since the welding current is supplied even after the welding wire feeding has stopped, the bond between the welding wire and the base metal can be avoided. The arc continues to occur, and large droplets are formed at the tip of the welding wire. Then, the tip of the welding wire solidifies with oxides and the like adhering to the surface of the droplets, so arc starting may not be possible the next time welding is started. Therefore, in the conventional method,
After welding is completed, it is necessary for the operator to cut the tip of the welding wire with a tool or the like, which is complicated and also causes a reduction in the operating rate of the production line.

In order to eliminate this drawback, the inventors of the present application proposed a method for controlling the output of the welding power source at the end of welding (Japanese Patent Laid-Open No. 80-18
No. 0868). It monitors the short circuit between the welding wire and the base metal after stopping the power supply to the wire feed motor,
When a short circuit is detected, the current supplied to the welding wire is immediately increased, and when a short circuit rupture or a sign of a short circuit rupture is detected, the power supply to the welding wire is immediately stopped. This prevents formation of large droplets at the tip of the welding wire at the end of welding, and allows the tip of the welding wire to be in a state where the next welding can be easily started.

[Problems to be Solved by the Invention] However, in the conventional output control method of the welding power source described above, although there is a remarkable effect when a sled wire is used as the welding wire, the welding wire is a flux-cored wire (flux-cored wire). In the case of welding wire (corrugated welding wire), there is a problem in that droplets cannot be removed at the end of welding.

FIG. 2 is a schematic cross-sectional view showing the state of the welding wire and base metal at the end of welding.

In order to remove the droplets, after stopping the power supply to the wire feeding motor, when welding wire 1 and base metal 2 are short-circuited, a high current is applied to welding wire 1 as a short-circuit current to It is necessary to transfer the droplet 7 at the tip to the base material 2 side. However, in the case of black scored wire, the surface of the crater 3 and droplet 7 at the end of the bead 4 is the slag 5,
6, the slags 5 and 6 are in contact with each other immediately after a short circuit between the welding wire 1 and the base metal 2 (bead 4). If a short circuit current is immediately supplied in this state, the slags 5 and 6 that were in contact will only break.
The droplet 7 formed at the tip of the wire 1 does not migrate to the base material 2 side. Therefore, the droplet 7 cannot be removed. Therefore, when the wire feed motor stops rotating and ends output control, large droplets 7 remain at the tip of the welding wire 1, which may cause arc start to fail when the next welding starts. Alternatively, in the case of automatic welding equipment such as RoboSoto, problems may occur such as the wire sensing operation performed to find the arc start point not being performed properly. As a result, the operating rate of the welding line decreases, and it becomes necessary to cut off the tip of the wire.

When performing arc welding using a flux-cored wire, the slag prevents the molten metal from dripping, so this flux-cored wire is suitable for fillet welding in a vertical position, and also reduces the appearance of the bead. It has the advantage of being beautifully finished. Therefore, even when a flux-cored wire is used, there is a need for the development of a method for controlling the output of a welding power source that does not form droplets at the tip of the wire at the end of welding.

The present invention has been made in view of such problems, and includes:
Even when a flux-cored wire is used, large droplets are not formed at the end of welding (we provide a method for controlling the output of a welding power source that allows the tip of the wire to be in a state where the next operation can be easily started). The purpose is to

[Means for Solving the Problems] A welding power source output control method according to the present invention is a welding power source used in a consumable electrode type arc welding method in which welding is performed while feeding a flux-cored welding wire by a wire feeding motor. In the output control method, a short circuit between the welding wire and the base metal is monitored from the time when the power supply to the wire feed motor is stopped until the wire feed motor is completely stopped.)
If a short circuit is detected during this period, the welding current is supplied to the welding wire after a predetermined period of time has passed after the detection of the short circuit, and if a non-short circuit or a sign of short circuit breakage is detected, the current supplied to the welding wire is cut off. Features.

[Operation 5-6- In the present invention, after stopping power supply to the wire feed motor, a short circuit between the welding wire and the base metal is monitored. If a short circuit is detected between the welding wire and the base metal,
After detecting a short circuit, the device waits for a predetermined period of time without applying welding current immediately. Immediately after a short circuit is detected, only the slag on the crater and the slag at the tip of the wire are in contact, but
By waiting for a predetermined time, the tip of the welding wire advances due to inertia and slightly enters the base metal side. This ensures reliable contact between the welding wire and the base metal. At this point, a predetermined welding current is supplied to the welding wire.

Then, the droplet at the tip of the wire moves to the base metal side.

Then, there is no short circuit between the welding wire and the base metal, resulting in a non-short circuit state.

When this non-short circuit state is detected, the current supplied to the welding wire is cut off. Alternatively, in order to reliably avoid the occurrence of spatter due to arc recurrence, a sign of short-circuit breakage is detected by fluctuations in the welding voltage or welding current, and upon detection of this sign of short-circuit breakage, the current supplied to the welding wire is cut off or May be reduced.

When the current supplied to the wire is cut off or reduced due to a sign of short-circuit breakage, the droplet interposed between the wire and the base material becomes constricted due to surface tension and breaks.

This operation is repeated until the wire feed motor completely stops. Therefore, when the wire feed motor is completely stopped, the welding wire and the base metal are not short-circuited, and no droplets remain at the tip of the welding wire. Therefore, the next sequence of welding can be easily started.

The welding current is the current applied to smoothly transfer the droplet when the droplet at the tip of the wire is completely short-circuited to the molten pool, and the value of this welding current depends on the diameter of the welding wire used and the shield. Determined by gas components etc.

[Embodiments] Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a welding power source used in the embodiment method of the present invention.

The wire feed motor 13 is driven and controlled by the motor drive circuit 12 and feeds the welding wire 1 toward the base material 2. The motor drive circuit 12 is connected to the stop signal generator 11, and when a stop signal is input from the stop signal generator 11,
The motor drive circuit 12 stops power supply to the wire feed motor 13 and performs dynamic braking on the wire feed motor 13.

The wire 1 and the base material 2 are each connected to two power terminals of a welding power source 15, and welding current is supplied from the welding power source 15. The current value of this welding current is set by the output setting device 14.

A voltage detector 16 is interposed between two power terminals of the welding power source 15. This voltage detector 1e detects the voltage between the power supply terminals and outputs the result to the short circuit detector 18. The short circuit detector 18 is configured to receive the output of the voltage detector 16 as well as a stop signal output from the stop signal generator 11. When a stop signal is input from the stop signal generator 11, this short circuit detector 18 enters the subsequent control operation state, and generates a short circuit signal or Outputs a non-short circuit signal. The output signal of this short circuit detector 18 is input to a timer 21.

A switch 17 is provided between the output setting device 14 and the welding power source 15.
is interposed. This switch 17 is the output stop circuit 2
It is turned on and off by 0.

This output stop circuit 20 is connected to a timer 19 and a timer 21. The timer 19 receives a stop signal from the stop signal generator 11, and when this stop signal is input, the timer 19 maintains the output stop circuit 20 in the operating state for a preset time in the timer 19. do.

The timer 19 is set with at least the time until the wire feeding motor 13 stops rotating due to inertia.

On the other hand, when the output of the short-circuit detector 18 is a short-circuit signal, the timer 21 delays the short-circuit signal by a time set in advance in this timer 21, and then sends this short-circuit signal to the output stop circuit 20 to prevent the short-circuit from occurring. When the output of the detector 18 is a non-short circuit signal, a non-short circuit signal 10- is immediately sent to the output stop circuit 20.

In the output control method of the welding power source according to the present embodiment, the switch 17 is closed when the welding is in a steady state in which welding progresses. Then, the welding current set by the output setting device 14 is supplied from the welding power source 15 to the wire 1, an arc is generated between the tip of the wire 1 and the base metal 2, and welding is performed.

When welding is to be stopped, a stop signal is output from the stop signal generator 11 in response to an operator's operation.

This stop signal is input to the motor drive circuit 12, and the motor drive circuit 12 cuts off the power supply to the wire feed motor 13 and performs dynamic braking on the wire feed motor 13. However, even if the power supply to the wire feed motor 13 is stopped and dynamic braking is performed, the wire feed motor 13
Since the welding wire 1 continues to rotate due to inertia without stopping instantaneously, the welding wire 1 is still fed out toward the base material 2, although the feeding speed gradually decreases.

On the other hand, the stop signal from the stop signal generator 11 is also input to the short circuit detector 18 and the timer 19.
8 and timer 19 start operating. The short circuit detector 18 detects the voltage between the terminals of the welding power source 15 detected by the voltage detector 16,
That is, based on the voltage between the welding wire 1 and the base material 2, a short circuit or non-short circuit state between the wire 1 and the base material 2 is detected. Further, the timer 19 defines the duration of control to be performed thereafter, and starts timing upon input of a stop signal from the stop signal generator 11.

After the stop signal generator 11 outputs the stop signal, if the welding wire 1 and the base metal 2 are not short-circuited, the voltage detected by the voltage detector 16 is the welding voltage value in the arc generation state. , the short circuit detector 18 detects a non-short circuit state and outputs a non-short circuit signal to the timer 21. This non-short circuit signal is immediately input to the output stop circuit 20 via the timer 21. When the output stop circuit 20 receives the non-short circuit signal, it turns off the switch 17 and cuts off the output of the welding power source 15.

Then, the voltage detector 16 outputs O[V]. Based on this signal, the short circuit detector 18 determines that there is a short circuit, and outputs a short circuit signal. This short circuit signal is input to the timer 21, delayed by the time set in the timer 21, and output to the output stop circuit 20. When the output stop circuit 20 receives this short circuit signal, it turns on the switch 17, and the welding power source 15 generates an output voltage again. However, since no true short circuit has occurred at this point, no arc is generated between the wire 1 and the base material 2, so the voltage detector 16 detects a no-load voltage (non-short circuit state). Then, the short circuit detector 18 outputs a non-short circuit signal, and this non-short circuit signal causes the output stop circuit 20 to turn off the switch 17. Thereafter, by repeatedly opening and closing the switch 17 until a true short circuit occurs, the short circuit or non-short circuit state is sampled.

On the other hand, when the slag 6 covering the droplet 7 at the tip of the welding wire 1 comes into contact with the slag 5 covering the bead 4 on the base metal 2 (see FIG. 2), a voltage is detected by the voltage detector 16. If the value changes from the predetermined welding voltage value, the short circuit detector 18
detects a short circuit caused by contact 13- between the slugs.

In this manner, when a true short circuit is detected, the short circuit signal from the short circuit detector 18 is input to the output stop circuit 20 after being delayed by the timer 21 for a predetermined period of time. During this delay time, the wire 1 advances further toward the base material 2, breaks the slag, and brings the wire 1 and the base material 2 into direct contact, resulting in a short circuit. When the short circuit signal delayed for a predetermined time by the timer 21 is input to the output stop circuit 20, the output stop circuit 20 turns on the switch 17, and the welding power source 15 supplies welding current to the welding wire 1. Then, the droplet at the tip of the welding wire 1 transfers to the base material 2. Then, this droplet becomes the base material 2
When moving to the side, the short circuit between the welding wire 1 and the base metal 2 is broken. As a result, the short circuit detector 18 detects a non-short circuit, and the output stop circuit 20 immediately turns off the switch 17. Then, the welding power source 15 continues to output intermittently until a short circuit occurs again.

Furthermore, when a true short circuit occurs, the output stop circuit 20 turns on the switch 14-17 after the delay time set in the timer 21 has elapsed. As a result, the droplet at the tip of the welding wire 1 transfers to the base material 2. In this way, the operation of detecting short circuits and non-short circuits is repeated. Then, the timer 19 finishes counting the preset time in line with the complete stop of the motor 13, and the timer 1
9 makes the output stop circuit 20 inactive. This completes the welding process.

As described above, the control method according to the present embodiment monitors the short circuit between the wire 1 and the base material 2 after stopping the power supply to the wire feeding motor 13, and - once the short circuit is broken, The state between welding wire 1 and base metal 2 is detected at regular intervals while waiting for the next short circuit. When a short circuit actually occurs, timer 2 is activated until welding wire 1 and base metal 2 are in direct contact.
The welding current is then supplied to the welding wire 1 to melt the tip of the welding wire 1, transfer the droplet to the base metal, and then break the short circuit. As the output control of the welding power source 15 is repeated in this way, the rotation of the wire feeding motor 13 due to inertia stops, the depression (crater) in the molten pool disappears, and the timing of the timer 19 is completed when no short circuit occurs. However, the output circuit 20 turns off the switch 17 and the welding is completed.

In this embodiment, the welding power source is controlled at the end of welding as described above, so even when a flux-cored wire is used, welding can be completed with the tip of the wire in good condition.

Note that instead of ending the output control of the welding power source when the timer 19 completes timing, a tacho generator is connected to the wire feed motor 18, and when the signal from the tacho generator reaches approximately zero value, the output stop circuit is activated. The control may be terminated by making the controller 20 inactive. Similarly, the back electromotive voltage of the wire feeding motor 13 is detected, and when the value of the back electromotive voltage reaches approximately zero, the output stop circuit 20 is put into a non-operating state and the control is terminated. You can do it like this. Thereby, effects similar to those of the above embodiment can be obtained.

Furthermore, when the signal from the tachogenerator connected to the wire supply motor 13 or the back electromotive force of the motor 13 reaches a specific value, and the rotational speed of the motor 13 drops to a specific value, the timer 19 starts timing. When the timer 19 completes timing, the output stop circuit 20 may be rendered inactive and the control may be terminated. The amount of wire fed during welding varies depending on the welding conditions, but by using this control method, the welding power source can be maintained even more reliably until the motor 13 completely stops, regardless of the amount of wire fed during welding. The output can be controlled.

[Effects of the Invention] As explained above, according to the present invention, when finishing welding, after stopping the power supply to the wire feed motor that feeds the welding wire toward the base metal, the welding wire and the base metal are If the slag covering the droplet at the tip of the welding wire comes into contact with the slag covering the surface of the base metal and a short circuit is detected, the welding wire will be in direct contact with the base metal. After the required predetermined time has elapsed, welding current is supplied to the welding wire to transfer the droplet at the tip of the welding wire to the base metal, and the melt 17
- If the droplets move to the base metal side and a non-short circuit occurs, the current supplied to the welding wire will be cut off, so even if you use a flax-cored wire, when you finish controlling the output of the welding power source, the wire tip will The state immediately after the droplet transfer is maintained, the formation of large droplets is avoided, and the next welding process can be easily started. Therefore, failures in arc starting and wire sensing are prevented, and there is no need for an operator to cut the tip of the wire using a tool or the like, and the operating rate of the production line can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a welding power source used in the embodiment method of the present invention, and FIG. 2 is a schematic cross-sectional view showing the state of the welding wire and base metal at the end of welding. 1: welding wire, 2: base metal, 3: crater, 4: bead, 5, 6; slag, 7: droplet, 11: stop signal generator,
12; Motor drive circuit, 13; Wire feeding motor, 14
; Output setting device, 15: Welding 18- Power supply, 16: Voltage detector, 17; Switch, 8; Short circuit detector, 19° 21: Timer, 20; Output stop circuit 19-

Claims (1)

[Claims] (1) In a method for controlling the output of a welding power source used in a consumable electrode arc welding method in which welding is performed while feeding a flux-cored welding wire by a wire feeding motor, the power supply to the wire feeding motor is stopped. The welding wire is monitored for short circuits between the welding wire and the base metal until the wire feeding motor completely stops, and if a short circuit is detected during this period, welding is performed on the welding wire at a predetermined time after the detection of the short circuit. A method for controlling the output of a welding power source, comprising supplying a current, and cutting off the current supplied to the welding wire when a non-short circuit or a sign of short circuit breakage is detected.