JPH0641026B2 - Welding power output control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling an output of a welding power source in a consumable electrode type arc welding method in which short circuit and arc generation are repeated.

2. Description of the Related Art In a consumable electrode type arc welding method in which short-circuiting and arc generation are repeated, a welding current output waveform of a DC power source having a constant voltage characteristic that is often used conventionally is as shown in FIG.

That is, in the conventional constant voltage DC power supply, from the moment when the droplet formed at the tip of the consumable electrode (hereinafter referred to as the welding wire) contacts the molten pool and short-circuits, the welding current is unique to the inductance and resistance of the electric path. It keeps increasing until the arc re-occurs at an increasing rate determined by the time constant. After the arc is regenerated, the welding current decreases at a decreasing rate determined by the time constant until the short circuit occurs again.

By the way, spatter often occurs at the moment when the droplet grows large at the tip of the welding wire and tries to short-circuit with the molten pool, and at the moment when the droplet is cut and separated from the tip of the welding wire by the electromagnetic drop pinch force. It is reported to be observed.

Especially in the latter case, it is the first in the conventional constant voltage DC power supply.
As shown in the figure, the welding current reaches its maximum at the moment of arc re-occurrence, and the energy at this time seems to blow off some of the droplets at the tip of the welding wire to generate spatter.

In this way, the conventional constant voltage DC power supply generates a large amount of spatter, which leads to a decrease in welding efficiency and a reduction in the efficiency of welding work such as the work to remove spatter scattered and adhered to the welded steel sheet. It adheres and accumulates inside the torch shield nozzle, which obstructs the flow of the shield gas, and causes nitrogen in the atmosphere to mix into the weld metal, causing deterioration of the mechanical performance of the weld, or attempts to prevent it. There is a problem that welding is often forced to be interrupted in order to remove spatter in the nozzle.

Considering the above-mentioned cause of spatter generation, an attempt has been made to control the welding current output as shown in FIG. 2 in order to reduce the spatter generation amount. That is, short-circuit peak welding current at the moment of subsequent to the molten pool of droplet (arc recurrence just before) the current I _SP
To reduce the arc regeneration current I _RA (at the time point in the figure) to minimize the energy required to complete the transfer of droplets to suppress the generation of spatter.
This control method had some effect in reducing spatter as compared with the conventional constant voltage DC power supply. However, depending on the state of the welding cable, which is the current path from the welding power source that supplies the current to the welding location, the reduction rate of spatter or even the welding itself was unstable. That is, the short-circuit peak current I _SP is output to detect the constriction of the droplet, which is a precursor of welding, as a voltage change ΔV, and the welding current is reduced in response to the signal, but the welding cable condition Causes its internal inductance to fluctuate, and thus the current reduction rate. If the iddactance is large and the current reduction rate is small, the current gradually drops and the arc re-generation current I _RA becomes a relatively high level, which is not as great as when a power source having the characteristics shown in Fig. 1 is used. Is generated in a considerable amount. On the contrary, if the inductance is small and the current reduction rate is large, the current drops sharply, the arc re-generation current I _RA becomes extremely constant level, the constriction of the droplet does not proceed, and it reaches the unmelted part of the welding wire. May enter the molten pool and arc may not be regenerated. In particular, when the extension cable is used because the welding part is far from the welding power source, it is impossible to maintain the inductance properly.

Object The present invention has been made in view of the above circumstances, and an object thereof is to correct the fluctuation of the arc regenerating current due to the influence of the internal inductance of the welding cable and to hold the arc regenerating current at an appropriate value. An object of the present invention is to provide a welding power source output control method for reducing spatter.

Outline In the consumable electrode arc welding method in which short circuit and arc generation are repeated alternately, the welding current is reduced immediately after the short circuit, and then the welding current is increased to the short circuit peak current, which is a precursor of the end of short circuit (reoccurrence of arc). constriction detects the lower the welding current in response to the signal, then, an output limiting method for a welding power source which allowed to reach arc recurrence, next by the current value I _RA during arc recurrence in the low-level Determine the signal level to detect the process's drop waist.

Example One example of the present invention will be described below.

In the present embodiment, the welding wire is fed to the base metal through the nozzle at a predetermined feeding speed, while the shield gas is jetted from the nozzle while the arc portion is generated between the welding wire and the base metal. In a consumable electrode type arc welding method in which a short circuit and arc generation are repeated between the welding wire and the base metal while surrounding the welding, the welding power source is configured to output the welding current waveform shown in FIG. To control.

FIG. 3 is an enlarged view of the current-voltage waveform in the process from the constriction of the droplet when the short circuit shown in FIG. 2 is transferred to the arc generation to the arc generation.

The constriction of the droplet is detected by the change in the welding voltage, and the welding current is reduced to a current value that is optimal for suppressing the generation of spatter when the arc is regenerated. When the internal inductance of the droplet cable is appropriate, at time t ₂ when the voltage change ΔV ₀ due to the constriction of the droplet is detected, the welding current is appropriate arc regeneration current I _RA0 as shown by the solid line a.
To lower.

The internal inductance fluctuates depending on the state of the welding cable, and as described above, the current reduction rate also fluctuates. If the internal inductance is large and the current reduction rate is small, the current gradually drops as shown by the broken line b, and if the current is decreased at time t ₂ , the level at arc reoccurrence is higher than the proper value I _RA0. Become I _RA1 . Therefore, the energy of the arc becomes large and spatter is generated. If the internal inductance is small and the current reduction rate is large, the current drops sharply as shown by the broken line c, and if the current is decreased at time t ₂ , the level at arc reoccurrence is lower than the proper value I _RA0. It becomes I _RA2 . Therefore, an arc may not occur.

Therefore, in the present invention, when the current I _RA at the time of arc reoccurrence is monitored and the state of the broken line b, that is, the inductance of the welding cable is large and the voltage change ΔV ₀ is detected, the current is reduced. When the current at the time of arc re-occurrence becomes I _RA1 , which is higher than the appropriate value I _RA0 , the detection level of the welding voltage when the droplet is constricted is set to ΔV ₁ which is lower than ΔV ₀ . Then, in the process of constriction in the next droplet and arc generation, when the welding current is decreased as indicated by the solid line d at time t ₁ when the voltage change ΔV ₁ is detected, the current at the time of arc reoccurrence Becomes the proper current value I _RA0 . On the other hand, when the current is lowered when the state of the broken line c, that is, the inductance of the welding cable is small and the voltage change ΔV ₀ is detected, the current at seek reoccurrence is at a level lower than the proper value I _{RA0.
When RA2} is reached, the detection level of the welding voltage when the droplet is constricted is set to ΔV ₂ which is higher than ΔV ₀ . Then, in the process in which the next droplet is constricted and the arc is generated, the welding current is changed to the solid line e at the time t ₃ when the voltage change ΔV ₂ is detected.
When the arc is regenerated, the current becomes a proper current value I _RA0 when the arc is regenerated.

The arc regenerated current I _RA for suppressing the generation of spatter and for continuing the welding stably is 30 to 150 A.
However, it is found that the time from the detection of the constriction of the droplet to the arc re-generation is 100 to 500 μsec.
I _RA current value I _RA0 , droplet constriction voltage detection level ΔV ₀
Is appropriately determined in consideration of the above points.

The current-voltage waveforms shown in FIGS. 2 and 3 are merely schematic representations, and the current and voltage levels and the time level do not show ratios.

FIG. 4 shows the configuration of the control device for performing the above-mentioned control, and the voltage detector 1 detects the welding voltage between the welding wire 3 and the welding base metal 4 fed via the welding torch 2. .
The comparator 5 compares the welding voltage from the voltage detector 1 with the constriction detection level from the constriction detection level setting device 6, and when the welding voltage becomes higher than the constriction detection level, the welding current is arced to the current switching circuit 7. A signal for reducing the regenerated current is output. The welding power source 10 is controlled by the output signal of the current switching circuit 7, and the welding current is controlled.
The current detector 8 detects the welding current, and the minimum value memory 9 indicates the minimum value of the welding current in the process of constriction of the droplet and subsequent rupture of the droplet leading to arc generation, that is, the arc recurrent current at this time. Remember.

In the squeezing detection level setting device 6, the setting value of the squeezing detection level is changed according to the signal representing the arc re-generated current from the minimum value storage 9. That is, the minimum value storage 9
If the output signal of is large, the internal inductance of the welding cable is large and the current reduction rate is small. Therefore, if the set value of the constriction detection level is low, and if the output signal of the minimum value storage unit 9 is small, the internal inductance is small. Since the current decrease rate is large, the constriction detection level setting value is increased. The changed neck detection level setting value is given to the comparator 5, and the comparator 5 compares the changed neck detection level setting value with the welding voltage. As a result, the comparator 5 supplies a signal to the current switching circuit 7 when the welding voltage reaches the changed necking detection level set value in the process from the necking of the droplet of the magnetic field to the arc generation. Then, the welding current is reduced so that the arc reoccurrence current I _RA0 becomes appropriate at the time of arc reoccurrence.

The above process is repeated while welding is in progress. Therefore, even if the internal inductance changes depending on the condition of the welding cable, stable welding with less spatter can be performed.

In the above example, the constriction of the droplet was detected by the change of the welding voltage, but the constriction of the droplet can be detected by other methods such as the change of the resistance between the welding wire and the base metal, and according to it. Needless to say, the type of setting value of the waist detection level is different.

Effect As described above, in the present invention, the signal level, which is the reference value for detecting the droplet constriction in the next process, is determined according to the welding current at the time of arc reoccurrence at the low level, so that the welding is performed. The welding current at the time of arc reoccurrence and an appropriate value can be maintained against variations in the internal inductance due to the cable, and the amount of spatter generated can be reduced and welding with good workability can be performed.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing a welding current output waveform of a conventional welding power source, FIG. 2 is a waveform diagram showing welding current and welding voltage output waveforms of a welding power source to which the present invention is applied, and FIG. FIG. 4 is a partial enlarged view of FIG. 4 and is a block diagram showing an embodiment of a control device for a welding power source to which the present invention is applied. 1 ... Voltage detector, 3 ... Welding wire, 4 ... Welding base metal, 5 ... Comparator, 6 ... Constriction detection level setting device, 7
... current switching circuit, 8 current detector, 9 minimum value memory, 10 welding power source.

Claims (1)

[Claims] 1. A welding electrode which feeds a consumable electrode to a base material at a predetermined feed rate, and at the same time, sprays a shield gas from a nozzle to surround an arc portion generated between the consumable electrode and the base material and weld the same. In the consumable electrode type arc welding method in which short circuit and arc generation are repeated between the consumable electrode and the base material,
Immediately after a short circuit, the welding current is reduced and then raised to a predetermined short-circuit peak current, the constriction of droplets that is a precursor of arc reoccurrence is detected, and the welding current is set to a low level value I _RA in response to the signal. reduced, then the arc the output control method of a welding power source which allowed to reach recurrence, the reference level for detecting the constriction of a droplet of the next process in accordance with the welding current value I _RA during arc recurrence at that low level A method for controlling the output of a welding power source, characterized in that