JPH0635059B2 - Output control device for welding power source - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling the output of a welding power source used in consumable electrode type arc welding performed while feeding a welding wire.

[Conventional technology]

As a conventional welding power source of this type, after converting commercial alternating current into direct current, it is converted into high frequency power with a high frequency inverter,
There is one 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, a direct current reactor is inserted in the output circuit as described above, and when the welding wire and the welding base metal are short-circuited, the molten metal is rapidly changed so that the molten metal is smoothly absorbed in the molten pool. Therefore, when the setting 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 to V / Rs. Time constant L / Rs
Then, it rises exponentially as shown in FIG. The energy accumulated in the DC reactor at the time of this short circuit is gradually released after the arc is generated, but the resistance proportional to the arc length is R
a, the current Ia exponentially decays toward V / Ra with a very long time constant L / Ra, during which the molten metal is formed at the tip of the welding wire by the arc force and the welding base metal A molten pool is formed. Normally, when the molten pool is stable, the above-mentioned phenomenon is repeated, and extremely stable welding can be performed.

[Problems to be solved by the invention]

However, due to the presence of the DC reactor, the current change rate of the current Ia during the arc period (conventionally, about 60 to
Since 130 [A / ms]) becomes small, the current change cannot keep up with the arc length change immediately after the start when the arc length fluctuates drastically, and the voltage fluctuates greatly as shown in FIG. Since it is reduced to about 1/2 of that during welding, and it takes several seconds to recover the number of short circuits during steady welding, the bead shape during that time is steady as shown in Fig. 10 (a) and (b). The width is wider and the excess is larger than when welding.

Therefore, when the welding length is short, there is a problem that the welding ends without obtaining a desired bead shape.

In addition, when performing high-speed welding, not only immediately after the arc start, but also because the molten pool etc. are always in an unstable state and the voltage waveform is always disturbed, the conventional welding power source described above is stable. However, there is a problem that it is difficult to perform high-speed welding.

[Object of the Invention]

The present invention has been made to solve the above-mentioned conventional problems, and suppresses a sharp rise of the welding current at the time of a short circuit, and can increase the current change rate at the time of arcing, which is stable immediately after startup. An object is to obtain an output control device of a welding power source that enables welding.

[Means for solving problems]

In order to achieve the above object, the present invention is provided with a mode discriminator that distinguishes between a short circuit mode and an arc mode, and controls the high frequency inverter so that the arc voltage becomes a set arc voltage by comparing the arc voltage with the set arc voltage in the arc mode, In the short-circuit mode, the welding current is compared with the set short-circuit current to control the high-frequency inverter so that the set short-circuit current is obtained. In the arc mode, the current change rate is 200 A / ms to 3000 A / ms.
Of the high current change rate.

〔Example〕

FIG. 1 is a block diagram showing 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, and 7 is a DC reactor. A welding power source is constituted by ~ 7. High frequency inverter (transistor inverter)
4 converts the rectified output smoothed by the smoothing circuit 3 into high frequency power (1.5 kHz or more), and the high frequency power is supplied to the transformer 5
After being transformed into a predetermined voltage by the diode full wave rectifier 6
Is converted into DC power by and is output via the DC reactor 7. Reference numeral 8 is a feeding chip, 9 is a welding wire, and 10 is a welding base material.

Reference numeral 11 is a voltage detector, which is a welding wire 9 and a welding base material 1.
The voltage between 0 is detected. A current detector 12 detects the welding current. Reference numeral 13 denotes a short-circuit current setting device. The set short-circuit current value Io set here and the welding current I detected by the current detector 12 are compared by the error amplifier 14. 1
Reference numeral 5 denotes an arc voltage setting device. The set arc voltage Vo set here and the voltage V detected by the voltage detector 11 are compared by the error amplifier 16. Reference numeral 17 denotes a mode discriminating threshold voltage setter. The threshold voltage E (Vo>E> voltage at the time of short circuit) set here is the output of the voltage detector 11 and the mode discriminator (comparator). 18, the mode discriminator generates an H level output indicating the arc mode when the former is smaller than the latter, and an L level output indicating the short circuit mode when the former is smaller than the latter. . The output of the mode discriminator 18 is directly output from the switch 19a.
Further, it is also supplied as an opening / closing signal to the switch 19b via the inverter 20. The switches 19a and 19b are closed when the supplied opening / closing signal is at H level. Reference numeral 21 is a reference signal generator for generating a triangular wave signal, 22 is a comparator, 2
Reference numeral 3 is a base drive circuit for the high frequency 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 compares the conduction width control signal (average voltage control signal). ) Y, the error signal sent from the error amplifier 14 is received through the switch 19b, and this is compared with the triangular wave signal to create a conduction width control signal (average voltage control signal) Y. Upon receiving the conduction width control signal Y, the base driving circuit 23 supplies a base driving signal to the transistors forming the high frequency inverter 4 to control the conduction width.

In this configuration, when the arc period in which the arc is generated between the welding wire 9 and the welding base metal 10 is reached, the mode discriminator 18 discriminates that the arc mode is set and outputs the H level output. , Switch 19a is closed,
An error signal ε = Va−Vo between the arc voltage Va extracted via the voltage detector 11 and the set arc voltage Vo is input to the comparator 22. Since the comparator 22 outputs the conduction width control signal Y that increases or decreases the conduction width of the high frequency inverter 4 in proportion to the magnitude of the error signal ε, the arc voltage is maintained at the set arc voltage Vo.

Further, when the welding wire 9 and the welding base material 10 come into contact with each other and short-circuit, the mode discriminator 18 discriminates that the mode is the short-circuit mode and generates an L level output, so that the switch 19b is closed this time. An error signal εi between the short circuit current Is detected by the current detector 12 and the set short circuit current Io is input to the comparator 22. Since the conduction width control signal for increasing / decreasing the conduction width of the high frequency inverter 4 of the comparator 22 in proportion to the magnitude of the error signal εi = Is-Io is sent, the short-circuit current becomes the set short-circuit current as in the case of the arc. Maintained.
The short-circuit period is usually 3 ms to 10 ms, and the switching frequency of the high-frequency inverter should be 1.5 kHz or more in order to control this period stably without damaging the element even if the DC reactor is reduced. It is desirable to do.

As described above, in this embodiment, the magnitude of the short-circuit current can be constant-current-controlled to the set short-circuit current value, so that the reactor value of the DC reactor can be set low to increase the current change rate in the arc period. Becomes

In addition, in this device, when the no-load voltage is 60 V and the set arc voltage Vo is 40 V, by setting the value of the DC reactor to 100 μHenry, a current change rate of about 200 amperes / millisecond can be obtained. Obtained.

Next, the effect of the apparatus of the embodiment will be specifically described based on the experimental result.

The inventors of the present invention observed many voltage waveforms from immediately after the arc start until the steady state transition, and as the voltage waveform during the arc period became stable, the number of short circuits increased and the number of steady short circuits increased. I found that it converged.

Therefore, the voltage Va during the arc period is set as shown by the line in FIG. 4 and the current change rate is variously changed so that the number of short circuits within one second immediately after the arc start is higher than the number of short circuits during steady welding. The following welding tests were conducted and measured to see if the welding conditions were met. Welding wire diameter: 1.2 mm, welding base metal plate thickness: 2.3 mm, welding speed: 1.5 m / min Power supply: 320 amps, 26-volt lap fillet welding The results shown in Fig. 3 were obtained.

From this figure, the number of short circuits per second immediately after the arc start is
When the current change rate is 200 A / ms, it is about 9 during steady welding.
It can be seen that the number of short circuits, which is almost the same as that during steady welding, can be obtained immediately after arc start at 0%, and at 300 A / ms or more. It was also observed that the appearance of the bead was almost the same as that during steady welding when the number of short circuits per second immediately after the arc start reached about 90% or more of that during steady welding.

FIG. 5 shows the voltage / current waveforms during the arc period measured in the above experiment. FIG. 5 (a) shows the voltage when the current change rate is 800 A / ms using the apparatus of the above embodiment.・ It is a current waveform, and it can be seen from this figure that the voltage waveform is stable and the arc length fluctuation is absorbed at a fast current change rate even during a very short period from immediately after the arc to the next short circuit. . FIG. 6B shows the voltage / current waveform in the case of the above-mentioned conventional current change rate, in which the fluctuation of the arc length is not absorbed and the arc voltage is unstable.

Further, FIG. 6 shows voltage / current waveforms immediately after starting when the current change rate is set to 800 A / ms using the apparatus of the above-mentioned embodiment. Comparing the voltage / current waveform with the conventional voltage / current waveform immediately after the start-up shown in FIG. 9, it can be seen that the arc length variation is almost absorbed and the voltage is stable.

Further, FIG. 7 (a) shows the state of the welded portion when the current change rate is 800 A / ms in high speed welding.
In (b), the current change rate is 3000A in the same high-speed welding.
Shows the state of the welded part when / ms is set. The welding specifications are as follows.

Wire diameter: 1.2 mm Solid welding Weld base metal plate thickness: 2.3 mm Welding speed: 3.0 m / mm CO ₂ gas shield Voltage, current: 360 ampere, 26 volts Incidentally, according to the above measurement, the current change rate is 3000 A. If it exceeds / ms, a large droplet will be formed at the tip of the welding wire and blown off as spatter.In the case of high speed welding, the amount of welding to the welding base metal will be insufficient and undercutting or humping beads will occur. It appears strongly and the number of welding defects increases sharply as the current change rate is further increased.

From the above experimental results, as the current change rate during the arc period,
It is clear that stable and good welding can be realized by giving a high current change rate of 200 A / ms to 3000 A / ms. According to the apparatus of the embodiment, the time constant of the welding current at the time of short circuit is desired. It is possible to easily give the above-mentioned high current change rate by setting the value of.

〔The invention's effect〕

As described above, according to the present invention, the value of the DC reactor can be made smaller than that of the conventional one, and the rate of current change in the arc period can be significantly increased. Therefore, stable welding can be performed immediately after starting, and stable and high speed. There is an advantage in realizing welding.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform chart of each part in the above embodiment, and FIG. 3 is a measurement showing the relationship between the current change rate and the number of short circuits. Fig. 4 is a characteristic diagram of the arc voltage used for the above measurement, Fig. 5 (a) is a voltage / current waveform diagram according to the above embodiment, and Fig. 5 (b) is a voltage / current waveform diagram according to a conventional device. FIG. 6 is a voltage / current waveform diagram immediately after starting according to the above embodiment, FIG. 7 is a voltage / current waveform diagram at the time of steady welding for explaining the conventional problems, and FIG. 8 is a conventional problem. And current waveform diagram immediately after startup for
FIGS. (A) and (b) are a plan view and a side view, respectively, showing a bead shape for explaining a conventional problem. 4 ... High frequency inverter, 7 ... DC reactor, 13
...... Short-circuit current setting device, 14, 16 ・ ・ ・ Error amplifier, 15
...... Arc voltage setter, 17 ...... Mode identification voltage generator, 18 ...... Mode discriminator, 19a, 19b ...... Switch, 21 …… Reference signal generator, 22 …… Comparator, 23 ・ ・ ・
… Base drive circuit.

Claims (1)

[Claims] 1. The output of a high-frequency inverter is stepped down to a predetermined voltage via a transformer to be converted into DC power, which is then applied via a DC reactor between a welding wire inserted between output terminals and a welding base metal. In a consumable electrode type welding power source, a first error amplifier that inputs the voltage between the welding wire and the welding base metal and compares it with a set arc voltage, and inputs a welding current flowing through the output terminal and compares it with a set short circuit current. A second error amplifier, a mode discriminator for discriminating short circuit / arc mode by inputting a voltage between the output terminals and comparing it with a mode discriminating set voltage, and being closed at the time of discriminating the arc mode of the mode discriminator. A switch for inputting the error signal of the error amplifier No. 1 to the comparator, and the error signal of the second error amplifier is inputted to the comparator when the mode discriminator is closed when the short circuit mode is judged. The comparator is configured to compare the input error signal with a reference signal to generate a frequency control signal that increases / decreases in response to an increase / decrease in the error signal, and outputs the frequency control signal to the high frequency inverter. It is supplied to the drive circuit, and the no-load voltage of the transformer and the value of the DC reactor are set so that the current change rate at the time of discriminating the arc mode of the mode discriminator is 200 A / ms to 3000 A / ms. Characteristic welding power output control device.