JPS6064774A - Method for controlling current of welding accompanying short-circuit transfer - Google Patents

Abstract

PURPOSE:To enable continuous operation for long time and to improve working efficiency by increasing the current of a consumable electrode wire to the current larger than a short-circuit current when the contraction of a droplet is not detected upon lapse of specified time after start of a short-circuit period. CONSTITUTION:The contraction of the droplet of a consumable electrode wire is detected at the end period of a short-circuit and the short-circuit current is decreased to decrease generation of spatter in welding accompanying short-circuit transfer. The short-circuit current is increased to prevent the consumable electrode wire from sticking to the base material when the contraction of the droplet is not detected for the specified time or longer in the short-circuit period. The failure of arc generation is thus prohibited during repetition of the short- circuit and the arc and the arc is smoothly started.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for controlling a power source used in welding involving short-circuit transition such as short arc welding and globule welding, and particularly to a method for controlling a welding wire current.

Welding with short circuit transition is characterized by repeated short circuits and arcing between the consumable electrode wire and the weld base metal.

FIG. 1 shows the positional relationship between the consumable electrode wire 10 and the base material 11, as well as the voltage waveform and current waveform of the consumable electrode wire during short-circuit transition welding, and in each figure, a, b , c, d, and e indicate the respective welding states.

That is, the arc length gradually becomes shorter from 3 during arc generation,
This will lead to a short circuit.

At this time, the current is increased and held at a certain constant value. After the point C when the droplets are most firmly bonded to the base materials 10 and 11, the tip of the consumable electrode wire 1o begins to constrict d
After this point, the welding current is rapidly lowered, and at a point e when the current has sufficiently decreased, arc regeneration begins.

According to the conventional welding power supply used in this type of welding, as shown in FIG.
, C", d", and e".

It is known that spatter occurs at time e when this short circuit is broken and an arc occurs, and it has also been revealed that the higher the current at time C, the more spatter is generated. This not only results in waste of welding wire and requires a great deal of time to remove the spatter, but also causes the spatter to get inside the torch nozzle and ultimately clog it.

As a method of reducing spatter without affecting the operating characteristics, a method of lowering the short-circuit current immediately before arc regeneration has been proposed. According to this control, the instant of droplet transfer is at a low current level, which is insufficient for the electromagnetic force effect to complete the droplet transfer, and instead surface tension and gravity contribute greatly to droplet transfer. It turns out. Although this method was effective to some extent in reducing spatter,
Sudden changes in the distance between the welding torch and the base metal, wire feeding speed, welding speed, etc. were not sufficiently considered, and the process was unstable if these changed. That is, in FIG. 2, d',
In the process from the late stage of the short circuit when the droplet at d'' becomes constricted to the arc generation at e and e'', the above-mentioned disturbance affects the molten part at the tip of the consumable electrode wire, or even the unmelted part of the consumable electrode wire. There are also disadvantages in that the consumable electrode wire may get into the molten pool, and the consumable electrode wire may become welded to the base metal, preventing arc regeneration and forcing the welding to be interrupted.

Purpose of the Invention The present invention was made in order to eliminate the various drawbacks mentioned above, and it is possible to reliably reduce the occurrence of spatter in welding involving short-circuit transition, prevent arc regeneration failure, and reduce the number of welding interruptions. It is an object of the present invention to provide a control method for a welding power source that can reduce the

SUMMARY OF THE INVENTION The present invention detects droplet constriction, which is a precursor to arc regeneration, particularly at d', d'' in FIG. When constriction does not occur after a certain period of time after entering the short circuit period,
Increase short circuit current. This increased short circuit current may be a constant value or may increase over time.

Example An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, 101 is a welding power source, 1o3 is a consumable electrode wire, and this consumable electrode wire 103 is fed to the base material 106 through a welding torch 104 while being controlled at a predetermined speed by a motor (not shown). be done. As is well known, a shielding gas flows out from the tip of the torch 104, and the protruding portion of the consumable electrode wire 103 is surrounded by this shielding gas and forms an arc 10 between it and the base material 106.
'5 is generated and consumed, and welding is performed.

In FIG. 3, the output signal of a voltage detector 110 that detects the voltage between the welding torch 104 and the base metal 106 is applied to the differential circuit 113, and the detected voltage is applied to the differential circuit 1.
In step 13, the voltage differential value is compared with the set value set by the differential setter 115 with respect to time, and when the voltage differential value becomes larger than the set value, it is determined that a constriction has occurred in the consumable electrode wire,
The comparator 114 applies a control signal to the welding power source 101 and switches the switch 120 to the low current setting device 121 to reduce the output current of the welding power source 101 and thus the current in the consumable electrode wire 103.

The setting value of the setting device 115 is determined corresponding to the differential value of the voltage value between the consumable electrode wire and the base metal when the welding wire is creased.

Note that instead of using the voltage differential value ■, the consumable electrode wire 10
The constriction of the consumable electrode wire may be detected by the time differential dR (2) of the resistance R between the consumable electrode wire 3 and the base material 106.

Note that 122 is a current setting device during welding, and the welding power source 101 operates according to the deviation between the set value applied from the current setting device 122 to the error amplifier 101a and the consumable electrode wire current detected by the current detector 112. Power control circuit 101b
The output current of the current setting device 122 is controlled to be the value set by the current setting device 122.

Reference numeral 123 denotes a timer that starts counting from the time when the short circuit between the consumable electrode wire and the base metal is detected by the current detector 112, and if the arc is not regenerated after a certain period of time Tl, the switch 120 is switched to the setting device 124. to supply a short circuit current increased to the desired value to the consumable electrode wire.

This short circuit current melts the consumable electrode wire end, creating a constriction and regenerating the arc.

The above-mentioned setting time and the short circuit current to be increased will be explained in more detail.

In this type of welding, the short-circuit time is not uniform, and it is generally said that 90-95% is distributed within 1-5 m5ec, but in any case, the short-circuit time is The reference setting time T1 from the start of the short-circuit period until the short-circuit current starts to increase can be arbitrarily set to a time that does not lead to an abnormal situation such as welding of the consumable electrode wire to the base material. Further, the measurement start point of the short circuit period T may be any point at which the voltage or current applied to the consumable electrode wire changes. For example, in FIG.
to the switching point p1 to the current IsP. In the following embodiments, the measurement start point for this short circuit period is the time point P2 when the short circuit current becomes the lowest.

Note that when using the time point PO, the timing at which the current reaches the lowest level may not be determined depending on the state of adhesion of the droplet to the base material, and it is necessary to take this minimum level time into consideration.

During welding, if the short circuit and arc regeneration are performed normally, the timer 23 starts operating immediately after the short circuit between the consumable electrode wire and the base metal and at the same time as the application of the short circuit current starts. When the constriction of the consumable electrode wire is detected from the soil during the reference setting time T1 of the timer 23, the current to the consumable electrode wire decreases according to the value set by the setting device 21, and after that, when an arc is normally generated, Timer 23 is reset and the next arc cycle begins. The operations during this time are shown in steps 81 to S6 in FIG. 5, and the above-mentioned operations are repeated during normal operation.

In the above-described operation, if for some reason the constriction of the droplet does not occur, or even if it does occur, if - is small, the timer 23 reaches the reference setting time T1. If the constriction of the droplet is not detected in step S6, the process proceeds to step S7, where the timer 23 is reset, and the switch 2o is switched to the setting device 124, so that the current of the consumable electrode wire is lowered from the short circuit current "SP". is also set to a large ISP ten α1t. Here, α□ is a constant, [ is time, and the consumable electrode wire current increases with time. Instead of α□t, a constant value α□ is added to the short circuit current 'SP. Anything is fine.

Furthermore, another timer (not shown) is operated at the same time as the current of the consumable electrode wire increases, and the reference setting increase time L1
If a constriction of the droplet is detected during this period, the process returns to step S1 to generate a normal arc.

On the other hand, if no constriction is detected during the reference setting increase time t1, the original short circuit current IsP is set in step Sll, the process returns to step S5, the timer 23 is restarted, and the above-described operation is repeated.

As is clear from the above explanation, if the constriction of the droplet occurs during the standard set increase time E1 during the short circuit period as shown in Figure 4+2), then the arc period will begin, and as shown in Figure 4 As shown in (b), the reference setting increase time t
If no droplet fins occur even after 1 elapses, the short circuit current returns to 'sp'.

Furthermore, if no constriction of the droplet occurs, step S
Returning to step 5, the timer 23 is set, and thereafter, in step S8, the current of the consumable electrode wire returns to the point X in FIG. Repeat the above operation until.

Here, to touch on the short circuit current IsP, IS
P itself has no direct effect on sputtering, and the lower the re-arc current 'RA, the less spatter will be generated.) However, the current falls below the ISP with a time constant determined by the inductance and resistance in the welding current path, so if we consider that the time from waist detection to arc generation is almost constant, the lower the IsP, the lower the IRA, and as a result, It is known that the lower the ISP, the less spatter occurs. However, in the method of the present invention, especially in FIG.
), the constriction of the droplet is detected in the process of IsP+α, and re-arc occurs at transport λ(>”RA), but such cases are only occasional and have a severe effect on spatter. In other words, instead of increasing the short-circuit current only when an abnormality occurs occasionally, 'SP in the normal case can be set as low as possible, and the occurrence of spatter can be further suppressed.

According to the present invention, the current applied to the consumable electrode wire after a short circuit does not need to be constant, and may vary over time.

Effects of the Invention As detailed above, the present invention detects the constriction of the droplet of the consumable electrode wire at the end of the short circuit in welding involving short circuit transition and reduces the short circuit current, thereby effectively reducing the occurrence of spatter. At the same time, during the short circuit period, if droplet fins are not detected for a certain period of time, the short circuit current is increased, which prevents the consumable electrode wire from being welded to the base metal, thereby reducing the risk of short circuits and arcs. This effectively prevents arc regeneration failure during repetition, and also makes arc start smoother. Furthermore, as a result, continuous welding for a long period of time becomes possible, which improves welding work efficiency and contributes to unmanned welding robot work.

[Brief explanation of drawings]

Figure 1 shows the process of short-circuit transfer welding, (a) shows the droplet transfer process, (b) shows the voltage waveform, and (c) shows the current waveform.
Fig. 2 is a diagram showing voltage and current waveforms showing the process of short-circuit transition welding that reduces the current immediately before arc regeneration, Fig. 3 is a block diagram showing an example of a circuit applied to the control method of the present invention, and Fig. 4 Figures (a) and (b) are voltage and current waveform diagrams of an embodiment of the control method of the present invention, and Fig. 5 is a flowchart showing the control method of the present invention. 101... Welding power source 103... Consumable electrode wire 106... Base material 1i0... Voltage detector 112... Current detector 114... Comparison circuit 123... Timer 124... Setting device Patent applicant: Kobe Steel, Ltd. (1 person) Patent attorney: Aoyama and Sogai (2 persons) Figure 1 Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) Regarding welding with short circuit transition in which short circuit and arc generation occur alternately between the consumable electrode wire and the base metal, a predetermined short circuit current sp is supplied to the electrode wire at the time of short circuit, and the current occurs at the end of the short circuit. In a control method that detects the constriction of a droplet of a consumable electrode wire and reduces the current of the consumable electrode wire in response to the constriction detection, if the constriction is not detected after a certain period of time after entering the short circuit period, the consumable electrode wire A current control method for welding with short circuit transition, characterized in that the current is increased to a current larger than the short circuit current IsP. (2) The current control method for welding with short-circuit transition according to claim 1, wherein the current flowing through the consumable electrode wire increases with time when no fining is detected. (3) The scope of the claim is that the increased current is supplied after the lapse of the above-mentioned certain period of time, and if no constriction is detected after the lapse of the certain period of time, the current supplied to the consumable electrode is returned to the short-circuit current generator sP. 2. The method of controlling a welding current with short-circuit transition according to item 1.