JPS6350077Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a DC arc welding machine having a welding power source using a smoothing capacitor on the output side.

Conventionally, in order to stabilize the welding arc, a smoothing circuit B consisting of a current limiting reactor 5 and a capacitor 6 connected in series was connected in parallel to the output side of a DC arc welding power source A as shown in Fig. 1. A DC reactor 8 is connected in series to a welding load consisting of an electrode 10, a base material 11, and an arc 12. A DC arc welding power source A (hereinafter simply referred to as power source A) consists of an AC power source 1 connected to the primary side of a welding transformer 3, a contact 2 of a switch (not shown), and four diodes connected to the secondary side. Rectifier circuit 4
The power supply is turned on and off by opening and closing contacts 2. DC reactor 8
Use a large reactance value of about 400μH, and the reactance value of current-limiting reactor 5 is several
Use a small one of about 10 μH. For capacitor 6, use one with a large capacity of about 50,000 μF. The current limiting reactor 5 suppresses rapid changes in the charging current and discharging current of the capacitor 6, reduces ripple, and prevents deterioration of the capacitor 6 due to rush current when the power is turned on. A contact 9 of a switch (also not shown) and a resistor 7 connected in series are connected to the capacitor 6 in parallel. Contact 9
is open during welding and is closed when welding is completed, so that the electric charge stored in capacitor 6 during welding is discharged via resistor 7 when welding is completed. The smoothing capacitor 6 used in the welding machine needs to have a large capacity. Therefore, if the current carrying capacity of the contact 9 of the switch is made large, the switch will need to be large, which is not preferable. In addition, in order to reduce the current carrying capacity of the contact 9, the resistance value of the resistor 7 must be increased, which increases the discharge time constant and causes the electrode 10 to come into contact with the base metal 11 after welding, causing a spark arc. Misoperation or
If a worker touches the electrode 10 or the base material 11, he or she will receive an electric shock, which is dangerous. In addition, the no-load voltage of the DC arc welding machine with the capacitor 6 connected to the output side of the power source A becomes high, so when the arc is interrupted,
There have been cases where the consumable electrode burns up rapidly and the diameter of the tip of the wire increases greatly after welding is completed, making it difficult to start the next weld.

Further, the arc characteristics in a DC arc welding machine using a consumable wire electrode are largely influenced by the DC reactor 8 connected in series with the power source A. In the small current range where the molten metal undergoes short-circuit transition, the smaller the inductance value of this DC reactor 8, the smoother the transition, and the arc 1
2 is stable. In a large current range where molten metal transfers by spraying, the arc 12 is more stable when the inductance of the DC reactor 8 is larger because there are fewer spatters.

However, in a DC reactor with an iron core, due to the magnetization characteristics of the iron core, when the DC current is small, the inductance is large, and when the DC current is large, the inductance is small, so the above-mentioned appropriate inductance value and welding current The relationship is the opposite. Therefore, it has been difficult to stably perform welding from a large current range to a small current range using a single DC reactor.

The present invention eliminates the above-mentioned conventional drawbacks, and includes a DC reactor connected in series to a DC arc welding power source and a load, a smoothing circuit including a capacitor connected in parallel to the power source, and a smoothing circuit connected in parallel to this smoothing circuit. This is a DC arc welding machine that is provided with an impedance circuit that does not include a capacitor, and the impedance circuit is further comprised of a control winding of a DC reactor connected in series to a power source and a resistor.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a circuit diagram showing an embodiment of the DC arc welding machine according to the present invention. In this figure, the same parts as in FIG. 1 are given the same reference numerals. 8' is an iron core of the DC reactor 8, and 13 is a control winding wound around the iron core 8', which is connected in series with a resistor 14. This series circuit C is connected between the output terminals of power supply A, and is configured to be excited by the output current of power supply A. The winding direction of the control winding 13 is such that the direction in which the iron core 8' is excited by the output voltage of the DC power supply A is opposite to the direction in which the iron core 8' is excited by the welding machine output current flowing in the main winding of the DC reactor 8. It is wound so that

Next, the operation of one embodiment of the present invention will be described. First, an operator holds a welding torch (not shown) in his hand and operates a torch switch attached to the torch to close contact 2, and AC power 1 is supplied to welding transformer 3. The AC output of the welding transformer 3 is rectified by the rectifier circuit 4 to become DC,
Furthermore, it is applied to the welding electrode 10 via the main winding of the DC reactor 8 . The welding electrode 10 is, for example, a consumable wire electrode, and is fed toward the base material 12 by a wire feeding device (not shown). The fed wire 10 contacts the base material 11 and an arc 12 is generated. During welding, the smoothing capacitor 6 is repeatedly charged and discharged. The charge accumulated in the capacitor 6 after welding is completed by operating the torch switch is discharged through the resistor 14 as shown in FIG. In the figure, _T1 indicates the discharge time. FIG. 4 shows the external characteristics of the DC arc welding machine according to the present invention, that is, the output voltage (vertical axis, indicated as secondary voltage in the figure) at the + terminal and - terminal to which the welding electrode 10 and base material 11 are connected. The relationship between the output current (horizontal axis, indicated as secondary current in the figure) is shown. In the figure, the solid lines indicate the output voltage and current characteristics of a conventional DC arc welding machine.
The broken line shows the output voltage and current characteristics of a DC arc welding machine to which the present invention is applied. The external characteristics of the conventional DC arc welding machine shown by the solid line are approximately constant voltage characteristics (the output voltage tends to decrease slightly as the output current increases), but when the output current reaches zero, The output voltage (including no-load voltage) exhibits a characteristic that increases suddenly when approaching the target. The increase in the output voltage (including the no-load voltage) in the low output current range is due to the effect of the smoothing circuit B, and is caused by the fact that the degree of ripple reduction in the output voltage is greater where the output current is small than where the output current is large.
However, an increase in the output voltage (including no-load voltage) in this low output current range is not favorable for arc welding, and causes the wire electrode to bulge when the arc is interrupted. As for the external characteristics of the DC arc welding machine according to the present invention, the increase in output voltage (including no-load voltage) especially in the low output current range is limited (improved) as shown by the broken line. The reason for this is that the current flowing through the main winding of the DC reactor 8 causes the iron core 8'
This is because the direction of the magnetic flux induced in the iron core 8' by the current flowing through the control winding 13 is opposite to that of the magnetic flux induced in the iron core 8'. According to the present invention, welding arc 1
Even if 2 is off, the control winding 13 and resistor 14 are always connected.
Since a predetermined load current flows through the welding electrode 10 and the base metal 11, the no-load voltage generated between the welding electrode 10 and the base material 11 is low. Since the output voltage at the end of welding can be lowered, burning up of the wire electrode 10 can also be eliminated. Also, open contact 2 of the welding machine,
When the power is turned off to the load side of the welding transformer 3, the charge stored in the capacitor 6 is transferred to the impedance circuit C.
discharge through.

In so-called spray arc welding, in which welding is performed with a high output voltage by operating the secondary slider (arrow portion) of the welding transformer 3, the wire electrode 10 and the base metal 11 are almost always short-circuited. Because there is no pulsation in the output welding current, there is almost no pulsation.
That is, from the main winding of the DC reactor 8 to the control winding 1
There is almost no induced voltage to 3, and DC reactor 8
is excited by the output of power supply A. Therefore, in the DC reactor 8, saturation of the iron core 8' becomes less likely to occur by the amount of reverse excitation caused by the control winding 13, and the inductance value equivalently increases, and the reactance of the circuit increases, so that the ripple in the output current is reduced. This decreases the arc, stabilizes it, and reduces spatter.

In so-called short arc welding, in which welding is performed at a low output voltage by operating the secondary side slider (arrow portion) of the welding transformer 3, the wire electrode 10 and the base metal 11 may be short-circuited and arc welded. As this process repeats, the welding current will pulsate greatly depending on short circuits and arcs. Since this pulsating current flows through the DC reactor 8, a voltage is induced in the control winding 13 due to the action of the transformer. Since the main winding of the DC reactor 8 and the control winding 13 are in a reverse excitation relationship, in the event of a short circuit, a high voltage is applied to the impedance circuit C consisting of the control winding 13 and the resistor 14, and a large current flows. Since the reverse induced current in the main winding due to this large current is added to the welding current, the short circuit current increases accordingly and the pinch effect of the consumable wire electrode 6 is accelerated, so that the molten metal is quickly will be migrated.

Next, when the short circuit transitions to an arc state,
An induced current is generated in the DC reactor 8 in a direction that maintains the current flowing through the DC reactor 8 at the time of the short circuit. A voltage generated across the DC reactor 8 due to the generation of this induced current is applied to the welding power source A. Therefore, the output voltage between the + terminal and the - terminal is higher than the voltage of the welding power source A by the terminal voltage of the DC reactor 8, and the arc is stably generated. The above phenomenon equivalently results in a reduction in the inductance value of the DC reactor 8. That is, the inductance of the DC reactor 8 can be made small in the small current range where short arc welding is performed, and the inductance of the DC reactor 8 can be made large in the large current range where spray arc welding is performed.

As described above, the present invention includes a DC reactor connected in series to a DC arc welding power source, a smoothing circuit including a capacitor connected in parallel to the power source, and an impedance circuit not including a capacitor connected in parallel to this smoothing circuit. This is a DC arc welding machine with an impedance circuit consisting of a control winding of a DC reactor connected in series with a power source and a resistor, so the wire electrode 10 and base material 11 are Since the voltage applied between the welds is low, the wire electrode 10 does not flare up when welding is completed, and the ball of the wire electrode does not become large, making it easy to start the arc during the next welding. Furthermore, even if the worker touches the output terminal or the electrode 10 when performing work such as storing the welding machine after cutting off the AC power supply after welding is completed,
Since capacitor 6 has already been discharged, there is no danger of electric shock. Furthermore, compared to a conventional DC arc welding machine, the contact 9 and a sequence circuit for controlling the contact 9 are not required, and the structure can be simplified. Furthermore, during welding, it is a simple configuration to reduce the inductance value of the DC reactor 8 in the small current range for short arc welding, and to increase the inductance value of the DC reactor 8 in the high current range for spray arc welding. realizable. As a result, there is an effect that the welding arc is stable.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional DC arc welding machine. FIG. 2 is a circuit diagram showing an embodiment of the present invention. FIG. 3 is a characteristic diagram showing the discharge state of the capacitor 6 of the smoothing circuit B, and FIG. 4 is an external characteristic diagram showing the relationship between the output voltage and output current of the DC arc welding machine. A...DC arc welding power source, B...Smoothing circuit,
6... Capacitor, 8... DC reactor, 8'
...Iron core, 10...Welding (wire) electrode, 11...
... Base material, 13 ... Control winding, 14 ... Resistor.

Claims (1)

[Scope of utility model registration request] A DC reactor with an iron core connected in series to a DC arc welding power source and a load, a smoothing circuit including a capacitor connected in parallel to the power source, and a DC reactor connected in parallel to the smoothing circuit and connected to the iron core of the DC reactor. A DC arc welding machine characterized by having an impedance circuit consisting of a control winding and a resistor wound in a direction to cancel the magnetic flux generated by the DC arc welding machine.