JPS61235079A - Output control device for welding power source - Google Patents

Abstract

PURPOSE:To enable a stabilized welding immediately after the actuation by controlling specifically a high frequency invertor in the welding power source to impress between a welding wire and welding base metal via a DC reactor after the DC conversion the output of the high frequency invertor. CONSTITUTION:An electric power is impressed between output terminals via a high frequency invertor 4 and DC reactor 7. A welding current I and the voltage V between terminals are detected by detectors 12, 11 and compared with the set short circuit current I0 of setters 13, 15 and a set arc voltage V0 by respectively error amplifiers 14, 16. The threshold value voltage E of a mode identifying voltage generator 17 is compared by the output mode discriminator 18 of the detector 11 and the discriminator 18 generates the output of H, L level to show an arc mode and short circuit mode respectively in case of the former being smaller, larger than the latter. This output closes switch 19a, 19b in case of its H level. A comparator 22 makes a continuity width controlling signal Y by comparing the error signal of the amplifiers 16, 14 with the reference signal of the generator 21 respectively via switches 19a, 19b. The circuit 23 gives a base driving signal to the invertor 4 to control the continuity width.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the output of a welding power source used in consumable electrode arc welding while feeding a welding wire.

[Conventional technology]

Conventional welding power sources of this type convert commercial alternating current to direct current, then convert it to high-frequency power using a high-frequency inverter.
There is a method in which the high-frequency power is full-wave rectified and then supplied between the welding wire and the welding base material via a DC reactor.

In this type of welding power source, as mentioned above, a DC reactor is inserted into the output circuit so that when the welding wire and the welding base metal are short-circuited, the molten metal is smoothly absorbed into the molten pool so that the current changes rapidly. For this reason, when the set voltage of the welding power source is Vo, the resistance of the output circuit is Rs, and the inductance of the DC reactor is L, the current Is at the time of the short circuit is directed toward V/Rs. Time constant L/R
s, it increases exponentially as shown in FIG.

The energy stored in the DC reactor during this short circuit is gradually released after the arc occurs, but if Ra is the resistance proportional to the arc length, the current 1a will increase exponentially towards ■/Ra with a very long time constant L/Ra. During this period, molten metal is formed at the tip of the welding wire by the arc force, and a molten pool is formed in the weld base metal. Normally, when the molten pool is stable, the above phenomenon is repeated and very stable welding can be performed.

[Problem that the invention seeks to solve]

However, due to the presence of the DC reactor, the current change rate of the current 1a during the arc period (conventionally, the rate of change of the current 1a is approximately 60~
130 (A/ms)) becomes small, so immediately after startup when the arc length fluctuates rapidly, the current change cannot follow the change in arc length, and the voltage fluctuates greatly as shown in Figure 9, and the number of short circuits also decreases to the above-mentioned steady state. The number of short circuits has decreased to approximately 1/2 of that during welding, and it takes several seconds to recover to the number of short circuits during steady welding, so the bead shape during that time is shown in Figure 10 (a).
As shown in Figs. and fb), the width is wider and the excess welding becomes larger than during steady welding.

For this reason, when the welding length is short, there is a problem in that welding ends without obtaining the desired bead shape.

In addition, when performing high-speed welding, the molten pool is always in an unstable state, and the voltage waveform is always in a disordered state, so the conventional welding power source described above is There was a problem in that it was difficult to perform stable high-speed welding.

[Purpose of the invention]

The present invention was made to solve the above-mentioned conventional problems, and it is possible to suppress the sudden rise of welding current during short circuit, and to increase the rate of current change during arcing, so that it is possible to stabilize the welding current immediately after starting. The object of the present invention is to obtain an output control device for a welding power source that enables welding.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a mode discriminator that distinguishes between short circuit mode and arc mode, and when in arc mode, compares the arc voltage with a set value and controls the high frequency inverter so that the set voltage is reached. In the event of a short circuit, the welding current is compared with a set value and the high frequency inverter is controlled so that the welding current reaches the set value.

〔Example〕

FIG. 1 shows a block diagram of an embodiment of the present invention. In the figure, 1 is a three-phase commercial AC power supply, 2 is a diode full-wave rectifier, 3 is a smoothing circuit, 4 is a high-frequency inverter, 5 is a transformer, 6 is a diode full-wave rectifier, 7 is a DC reactor, 1 ~7 constitute a welding power source. High frequency inverter (transistor inverter)
4 converts the rectified output smoothed by the smoothing circuit 3 into high frequency power (1
, 5kHz or higher), and the political and commercial frequency power is converted to transformer 5.
After being transformed to a predetermined voltage by the diode full-wave rectifier 6
The DC power is converted into DC power and output via the DC reactor 7. 8 is a power supply tip, 9 is a welding wire, and 10 is a welding base material.

Reference numeral 11 is a voltage detector, which detects the welding wire 9 and the welding base material 1.
Detects voltage between 0 and 0. 12 is a current detector that detects welding current. Reference numeral 13 denotes a short-circuit current setting device, and an error amplifier 14 compares the set short-circuit current value io set here with the welding current I detected by the current detector 12. 1
Reference numeral 5 denotes an arc voltage setter, and an error amplifier 16 compares the set arc voltage Vo set here with the voltage (2) detected by the voltage detector 11. 17 is a threshold voltage setting device for mode discrimination, and the threshold voltage E set here (Vo'>E>voltage at the time of short circuit) is determined by the output of the voltage detector 11 and the mode discriminator (comparator). ) 18, and when the former is smaller than the latter, the mode discriminator generates an output of level I (indicating arc mode), and in the opposite case, outputs level L (indicating short circuit mode). The output of this mode discriminator 18 is directly sent to the switch 19.
a, and is also supplied as an open/close signal to the switch 19b via the inverter 20. The switches 19a and 19b are closed when the supplied open/close signal is at H level. 21
2 is a reference signal generator that generates a triangular wave signal, 22 is a comparator, and 23 is a base drive circuit for the station inverter 4. The comparator 22 receives the error signal output from the error amplifier 16 via the switch 19a, compares it with the triangular wave signal X of FIG. 2 output from the reference signal generator 21, and generates a conduction small control signal (average voltage control signal ) Y and also the error amplifier 14
receives the error signal sent out by the switch 19b, and compares it with the triangular wave signal to create a small conduction control signal (average voltage control signal) Y. The base drive circuit 23 receives the small conduction control signal Y and supplies a base drive signal to the transistors constituting the high frequency inverter 4 to control their conduction.

In this configuration, during the arc period when an arc is generated between the welding wire 9 and the welding base metal 10, the mode discriminator 18 determines that it is the arc mode and sends out an H level output. , switch 19a is closed,
An error signal ε=Va−Vo between the arc voltage Va taken out via the voltage detector 11 and the set arc voltage 0 is input to the comparator 22. Since the comparator 22 sends out a small conduction control signal Y that increases or decreases in proportion to the magnitude of the error signal ε while the high frequency inverter 4 is conductive, the arc voltage is maintained at the set arc voltage vO.

Furthermore, when the welding wire 9 and the welding base metal 10 come into contact and short-circuit, the mode discriminator 18 determines that the short-circuit mode is present and generates an L-level output, so the switch 19b is closed this time. An error signal εi between the short circuit current 1 s detected by the current detector 12 and the set short circuit current 0 is input to the comparator 22. Since the comparator 22 sends out a small conduction control signal that increases or decreases in proportion to the magnitude of the error signal ε1=Is-Io while the high-frequency inverter 4 is conductive, the short-circuit current is equal to the set short-circuit current as in the case of the arc described above. maintained. Note that the short circuit period is normally 3ms to 1Qms, and in order to stably control this period without destroying the elements even if the DC reactor is made small, the switching frequency of the high frequency inverter must be set to 1.5 kHz. It is desirable to set the above.

In this way, in this embodiment, the magnitude of the short-circuit current can be controlled at a constant current to the set short-circuit current value, so it is possible to set the DC reactor flux value low and increase the current change rate during the arc period. becomes.

In addition, in this device, if the no-load voltage is 60 volts and the set arc voltage 0 is 40 volts, by setting the DC reactor value to 100 micro-henries, the current change will be approximately 200 amperes/millisecond. Got the rate.

Next, the effects of the apparatus of implementation series A will be specifically explained based on experimental results.

The present inventors observed numerous voltage waveforms from immediately after arc start until transition to a steady state, and found that as the voltage waveform during the arc period stabilized, the number of short circuits increased and reached a steady state. It was found that the results converged.

Therefore, we set the voltage Va during the arc period as shown by the line in Figure 4, and varied the current rate of change to find out how much the number of short circuits in one second immediately after arc start compared to the number of short circuits during steady welding. We conducted experiments and measurements on the following welding devices: Welding wire diameter: 1.2mm, Welding base material plate thickness: 2.3mm, Welding speed: 1.5m/min Power source: 320 amperes , 26-volt overlap fillet welding The results shown in FIG. 3 were obtained.

From this figure, the number of short circuits in 1 second immediately after arc start is:
It can be seen that when the current change rate is 200 A/ms, it reaches about 90% of that during steady welding, and at 300 A/ms or more, the number of short circuits is almost the same as that during steady welding immediately after arc start.

It was also observed that when the number of short circuits in one second immediately after arc start reached approximately 90% or more of that during steady welding, the appearance of the bead was almost the same as that during steady welding.

Figure 5 shows the voltage and current waveforms during the arc period measured in the above experiment, and Figure (a) shows the waveforms when the current change rate is 800 A/m s using the device of the above example. These are voltage and current waveforms, and this figure shows that even in a very short period of time, from just after an arc occurs until the next short circuit occurs, the voltage waveform is stable and arc length fluctuations are absorbed by a fast current change rate. I understand. Figure (b) shows the voltage and current waveforms in the case of the conventional current change rate mentioned above,
Arc length fluctuations are not absorbed and the arc voltage is unstable.

Further, FIG. 6 shows voltage and current waveforms immediately after startup when the device of the above embodiment is used and the current change rate is 800 A/ms. Comparing this voltage/current waveform with the conventional voltage/current waveform immediately after startup shown in FIG. 9, it can be seen that most arc length fluctuations are absorbed and the voltage is stable.

In addition, Fig. 7(a) shows the state of the welded part when the current change rate is 800 A/ms in high-speed welding, and Fig. 7(b) shows the state of the welded part when the current change rate is 300 A/ms in the same high-speed welding.
The state of the welded part is shown at 000 A/ms. The welding specifications are as follows.

Wire diameter: l, 2mm Solid welding base material plate thickness: 2.3mm Welding speed: 3. Om/mm CO2 gas shield voltage, current: 360 amperes, 26 ports According to the above measurements, when the current change rate exceeds 3000 A/m s, large droplets are formed at the tip of the welding wire and are blown off as spatter. In the case of high-speed welding, the phenomenon of undercuts and humping beads occurring due to an insufficient amount of welding to the weld base metal appears strongly, and as the current rate of change is further increased, the number of welding defects increases rapidly.

From the above experimental results, as the current change rate during the arc period,
It is clear that stable and good welding can be achieved by providing a high current change rate of 200 A/ms to 3000 A/ms, and according to the apparatus of the example, the time constant of the welding current at the time of short circuit can be adjusted to the desired value. The above-mentioned high current change rate can be easily provided by setting the value of .

〔Effect of the invention〕

As explained above, the present invention makes it possible to significantly increase the rate of change in current during the arcing period by reducing the value of the DC reactor compared to the conventional one, making it possible to perform stable welding immediately after startup, and also to achieve stable, high-speed welding. There are advantages to realizing welding.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a waveform diagram of each part in the above embodiment, Fig. 3 is a measurement diagram showing the relationship between the current change rate and the number of short circuits, and Fig. 4 is the above Characteristic diagram of the arc voltage used in the measurement. Figure 5(a) is a voltage/current waveform diagram according to the above embodiment. Figure 5(b) is a voltage/current waveform diagram using a conventional device. Figure 6 is a diagram of the voltage/current waveform according to the above embodiment. Figure 7 (a) and (b) are photographs of the welded area according to the above embodiment, and Figure 8 is a diagram of the voltage and current waveforms during steady welding to explain the problems of the conventional method. Current waveform diagram, Figure 9 is a voltage/current waveform diagram immediately after startup to explain conventional problems, and Figures 10 (a) and (b) show bead shapes to explain conventional problems. They are a top view and a side view. 4-High frequency inverter, 7-DC reactor, 13-Short circuit current setting device, 14.16-Error amplifier, 15--Arc voltage setting device, 17-Mode identification voltage generator, IEL
-----[--Do discriminator, 19a, 19b-switch,
21--Reference signal generator, 22-Comparator, 23-Base drive circuit.

Claims (1)

[Claims] In a consumable electrode type welding power source that converts the output of a high frequency inverter into DC power and then applies it between the welding wire inserted between the output terminals via a DC reactor and the welding base metal,
A first error amplifier receives the voltage between the output terminals and compares it with the set arc voltage; a second error amplifier receives the welding current flowing through the output terminal and compares it with the set short-circuit current; and the output terminal A mode discriminator receives a voltage between the two and compares it with a set voltage for mode discrimination to discriminate between short circuit mode and arc mode, and when the mode discriminator discriminates the arc mode, the circuit is closed to generate an error signal of the first error amplifier. a switch that inputs the error signal of the second error amplifier to the comparator when the mode discriminator determines the short circuit mode, and a switch that inputs the error signal of the second error amplifier to the comparator; Output control of a welding power source, characterized in that the signal is compared with a reference signal, a frequency control signal that increases or decreases in response to an increase or decrease in the error signal is created, and the frequency control signal is supplied to a drive circuit of the high frequency inverter. Device.