JPH0448549B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an arc welding power source suitable for automatic arc welding using consumable electrodes, particularly for CO ₂ arc welding with short-circuit transfer.

[Background of the invention]

The welding power source used for CO ₂ arc welding has a relatively large capacity on the output side in order to suppress the sudden increase in short-circuit current under normal welding conditions and smooth the short-circuit transition, and to reduce ripples in the output current waveform. Usually, a DC reactor is inserted. On the other hand, in order to facilitate the arc start by instantly melting the wire tip due to a contact short circuit between the welding wire and the base metal at the time of arc start, the current must rise rapidly.

For this reason, with conventional CO ₂ arc welding power supplies,
By short-circuiting the DC reactor only at the time of arc start, the rate of increase in output current is increased and arc start performance is improved.

FIG. 3 shows an example. In the figure, 1 is a welding transformer, 2 is a thyristor that controls the output by controlling the firing angle, 3 is a welding wire used as a consumable electrode, 4 is a wire feed roller, 5 is an arc load,
6 is a base material, and although not shown, the arc is gas-shielded with CO ₂ gas or the like. Reference numeral 7 denotes a DC reactor, which is inserted to suppress a sudden increase in short-circuit current under normal welding conditions and to reduce ripples in the current waveform. 8 is a thyristor connected in parallel with the DC reactor 7 to improve arc starting performance, and 9 is a current detector which outputs a signal when an output current flows. A delay circuit 10 receives this current detection signal and outputs an off signal to the thyristor 8 after a predetermined time.

At the time of arc start, the thyristor 8 is in an on state, and when the welding wire 3 comes into contact with the base metal 6, a short circuit current flows through the thyristor 8, so that the tip of the wire is instantly fused and an arc is generated. During this time, the signal from the current detector 9 enters the delay circuit 10 and turns off the thyristor 8 after a predetermined time delay, so that current flows through the DC reactor 7 and transitions to a normal welding state.

Although this arrangement improves the arc starting performance, it requires a large current thyristor 8 to short-circuit the DC reactor 7, which, together with the use of a large capacity DC reactor 7, increases the size of the device. In addition, it is sufficient if the short circuit is released in a short time at the time of arc start, but depending on the shape of the wire tip or the surface condition of the base material, the short circuit may continue for an abnormally long time. Since the current is a large current, if the short circuit current continues to flow in the DC reactor 7 even after the thyristor 8 is turned off, electromagnetic energy will be accumulated in the DC reactor 7, and when the short circuit is broken and an arc is generated,
The release of the stored energy in the DC reactor 7 increases the arc length, causing a burnback phenomenon in which the wire is welded to the current-carrying tip of the welding torch, impeding work efficiency.

[Purpose of the invention]

An object of the present invention is to provide a power source for arc welding that can ensure the power characteristics necessary for short-circuit transition type arc welding and can perform arc starting well without using a large DC reactor or short-circuit thyristor. It's about doing.

[Summary of the invention]

The present invention provides a consumable electrode type arc welding power source in which the output is controlled by a high-speed switching element such as a power transistor. an output current control means that changes the on/off time ratio of the high-speed switching element so as to suppress changes in the output current under normal welding conditions by amplifying a signal corresponding to the output control signal and adding it to the output control signal; The arc start control means reduces the level of the signal added to the output control signal by the output current control means and increases the rate of increase in the output current. The function of an inductance that controls changes in the output current is realized by a small electronic circuit, and at the time of arc start, the function of suppressing the current change is reduced, thereby improving arc starting performance.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 is a block diagram showing the circuit configuration.
9 and 10 are parts corresponding to those in FIG.

This figure shows an AC input from a commercial frequency power supply that is converted into DC by a rectifier circuit 11, and then converted into high-frequency AC by an inverter circuit 12 using a high-speed switching element 13 such as a power transistor or MOSFET. An example is shown in which the voltage is stepped down by the transformer 14, converted to DC again by the output side rectifier circuit 15, smoothed by the DC reactor 16, and configured as an inverter control power source that supplies DC output to the arc load 5. The output is controlled by controlling the pulse width of the high-speed switching element 13 that constitutes the circuit. This method allows the transformer 14 to be downsized by employing a high frequency inverter. Also, DC reactor 1
Reference numeral 6 is a small device that only smooths the output current waveform. For example, when the switching frequency of the inverter circuit 12 is 20kHz, an inductance of about several tens of μH is sufficient to smooth the output current waveform.

In this example, a secondary winding 17 is provided in the DC reactor 16 as current change rate detection means, and this secondary winding 1
7 (-Mdi/dt, where M is the mutual inductance) is used as a signal corresponding to the rate of change of the output current I.

The output current control means amplifies the induced voltage of the secondary winding 17 with an amplifier circuit 18, adds it to an output control signal from an output voltage setter (potentiometer) 20 with an adder circuit 19, and sends it to the drive circuit 21. In addition, by driving the high-speed switching element 13 of the inverter circuit 12 with a pulse-width modulated signal, the on-time width of the switching element is narrowed when the output current I is about to increase under normal welding conditions. On the other hand, when the output power supply I is about to decrease, the on-time width of the switching element is widened and the switching element functions as an inductance to suppress the current change. The current reduction rate during the arc generation period is determined by the amplification degree of the amplifier circuit 18.

Fig. 2 is a diagram showing the output current waveform and the signal waveform of each part. By changing the amplification degree according to the magnitude of the welding current by switching the feedback resistor inserted in the amplifier circuit 18, etc., the current that matches the output current value can be adjusted. A waveform is obtained.

The arc start control means can be constituted by, for example, an analog switch 22 connected in parallel with the current detector 9, the delay circuit 10, and the amplifier circuit 18. A high-speed switching element such as a transistor is used for the analog switch 22. At the time of arc start, the analog switch 22 is turned on, and the current that flows due to the contact short circuit between the welding wire 3 and the base metal 6 is detected by the current detector 9. ,
After a predetermined period of time, the delay circuit 10 outputs an off signal to turn off the analog switch 22. The delay time of the delay circuit 10 is normally set to the time required for arc starting.

With this configuration, at arc start, the amplifier circuit 18 is short-circuited by the analog switch 22, and the amplification degree of the input signal from the DC reactor secondary winding 17 becomes 1, so when the short-circuit current increases, the adder circuit At 19, the level of the signal added to the output control signal becomes smaller than in a normal welding state, and the control bias for pulse width control output from the adding circuit 19 to the drive circuit 21 becomes high, suppressing an increase in the output current I. The ability to Therefore, when the welding wire 3 and the base metal 6 contact and short-circuit, the rate of increase in current increases, and the sharp increase in the short-circuit current causes the tip of the welding wire 3 to melt instantly, resulting in a good arc start.

According to this embodiment, even at arc start, the induced voltage in the DC reactor secondary winding 17 is added to the output control signal, thereby functioning to some extent to suppress the current rise, thereby preventing the short circuit current from becoming excessive. The effect of preventing this can be obtained.

As in the above embodiment, the amplifier circuit 18 is switched to the switch 2.
2, it is also possible to reduce the signal amplification degree of the entire system by other means, such as using an attenuator only at the time of arc start to lower the input level of the amplifier circuit 18. The same effect can be obtained. In addition, in order to increase the current increase rate at arc start, in addition to lowering the signal amplification degree as described above, the addition circuit 19 switches the signal added to the output control signal to zero or a constant level close to it. It's okay.

In the above embodiment, the main circuit and the control circuit are isolated by extracting the voltage from the secondary winding 17 of the DC reactor 16, but if insulation is not required,
The voltage may be extracted directly from the DC reactor 16. Alternatively, although the circuit configuration becomes somewhat complicated, the output current I may be converted into a voltage using a current detector, and this may be differentiated to obtain a signal corresponding to the rate of change of the output current.

〔Effect of the invention〕

According to the present invention, the on-off time ratio of the high-speed switching element is changed according to the change rate of the output current by the output current change rate detection means and the output current control means,
It functions as an inductance to suppress changes in output current during normal welding conditions, and
At the time of arc start, the above current change suppression function is lowered by the arc start control means to increase the current increase rate, so a small DC reactor that only smooths the output current waveform is used for short-circuit transition type arc welding. The necessary power characteristics can be obtained,
In addition, a good arc start can be achieved without using a large current thyristor that short-circuits a DC reactor as in the prior art, and the welding power source can be made smaller and lighter.

In addition, because the DC reactor inserted into the power supply circuit is smaller, even if the short circuit continues for an abnormally long time at arc start, less energy is stored in the DC reactor, and the welding wire will be welded to the current-carrying tip when the short circuit is released. It is possible to prevent the burnback phenomenon from occurring.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a diagram showing the output current waveform and signal waveforms of various parts in this embodiment, and FIG. 3 is a block diagram of the conventional example. 13: High-speed switching element, 17: Output current change rate detection means (secondary winding of DC reactor), 1
8, 19: Output current control means (18: amplifier circuit,
19: addition circuit), 9, 10, 22: arc start control means (9: current detector, 10: delay circuit, 22: analog switch).

Claims (1)

[Claims] 1 In a consumable electrode type arc welding power supply device that turns on and off a high-speed switching element such as a power transistor at a switching frequency of 10 kHz or higher and controls the output by changing the on/off time ratio, the inductance connected to the output side circuit is DC reactor with secondary winding at 10μH,
an amplifier circuit that amplifies the voltage induced in the secondary winding; an addition means that adds the amplified signal and the output control signal; and an output current control means that changes the output current based on the addition result of the addition means; A power supply device for arc welding, comprising arc start control means for reducing the level of the amplified signal for a preset time at the time of arc start.