JP2549514Y2 - DC arc welding machine - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an arc welding machine for performing welding using a DC power supply, and particularly to an arc starter at the start of welding.

[0002]

2. Description of the Related Art Arc welding of DC arc welding using consumable electrodes.
At the start, a small arc is generated at the same time when the consumable electrode comes into contact with the workpiece, and grows and shifts to a steady welding arc, or when the consumable electrode completely short-circuits with the workpiece. In some cases, a large short-circuit current flows, and the short-circuit current melts the work to be transferred to an arc. The arc start is performed more smoothly in the former case. For this purpose, it is necessary to make the rising speed of the current at the time of the arc start sufficiently high and to flow a larger current for a certain period of time at the time of contact. There is.

[0003] Conventionally, for the above purpose, Arc Star
In such a case, a capacitor is connected between the output terminals so that a large current can be output only when the consumable electrode contacts the workpiece. ing. (For example, Japanese Utility Model Laid-Open No.
No. 874, No. 2-144267, etc.)

FIG. 1 is a circuit diagram showing a basic configuration of a conventional DC arc welding machine. In the figure, 1 is a commercial AC power supply, 2 is a DC power supply for rectifying the power from the AC power supply 1 and converting it to DC suitable for arc welding, 3 is a DC reactor, 4 is a welding torch, 5 is a welding torch 4 The consumable electrode which is fed toward the work 6 to be welded
A series circuit comprising discharging diode 72., 8 Ri charging circuit der for charging the capacitor of the series circuit 7 before starting welding, thyristors and the switching transistor
Alternatively, a relay contact that closes temporarily at the start of welding is used.
You. When a welding start command is given, first, the no-load voltage of the DC power supply 2 that converts the output of the AC power supply 1 to a DC output starts charging according to the welding start command . In this case, the charging circuit 8
When the thyristor is used, the capacitor 71 starts to be charged by the conduction of the thyristor, and when the charging current becomes lower than the holding current of the thyristor of the charging circuit 8, the thyristor becomes non-conductive and the charging is completed. .

Next, together with the welding start command described above,
When the consumable electrode 5 starts to be fed at a low speed and the tip of the electrode 5 comes into contact with the workpiece 6, the consumable electrode 5 is superimposed on the main current supplied from the DC power supply 2 through the DC reactor 3 and has been charged up to that time. The electric charge of the capacitor 71 is discharged through the diode 72, and a peak current having a large peak value flows.
As a result, the contact portion of the consumable electrode 5 is rapidly heated and melted and scattered to generate a small arc. If the output current supplied from the DC power supply 2 via the DC reactor 3 rises while the small arc continues, the operation shifts to the steady state arc.

FIG. 2 is a diagram showing a change over time of the output current in the conventional apparatus of FIG. 1. The time when the tip of the electrode 5 contacts the workpiece 6 is time 0, and from this time to time t1. A current Ic having a high peak value mainly due to discharge from the capacitor 71 flows. On the other hand, since the output current Ia from the DC power supply 2 is suppressed from rising by the DC reactor 3, the low current gradually increases as shown by the broken line in the figure. FIG. 3 is a connection diagram showing an example of a conventional device in which the capacitor 71 is discharged from an intermediate tap provided in the DC reactor 3. In FIG.
Diode 72 constituting a circuit for discharging one charge
Is connected to the intermediate tap of the DC reactor 3, and the same reference numerals are given to those having the same functions as those in the embodiment of FIG. In the apparatus shown in the figure, since the charge of the capacitor 71 is discharged to the welding load through a part of the DC reactor 3, the change of the output current at the time of starting the arc is caused by the current Ic due to the discharge of the capacitor 9 as shown in FIG.
Has a relatively low peak value and its duration (from t = 0 to t =
t1) becomes longer. During this time, the current Ia flowing from the DC power supply 2 via the DC reactor 3 is large, so that the transition from the initial arc to the steady arc becomes relatively easy.

[0007]

In the conventional apparatus shown in FIG. 1, the discharge of the capacitor 71 ends in a short period of time, so that the start of the arc may fail. That is, in order to stabilize the arc in the steady state, the inductance of the DC reactor 3 is relatively large. Therefore, the rising speed of the welding current Ia at the time of the arc start is slow, and t1 immediately before the discharge of the capacitor 71 is completed. However, as shown in FIG. 2, the main current Ia does not sufficiently rise, and as a result, the small arc generated may disappear.

In order to solve this problem, a capacitor 7 is required.
A method of increasing the time required for discharge by increasing the capacity of the discharge current Ic is also conceivable, but the peak of the discharge current Ic shown in FIG.
Since the arc value is increased, arcing occurs between the consumable electrode 5 and the power supply portion of the welding torch 5 so that a smooth arc start is not performed. However, there is a disadvantage in that the cost is increased due to the increase in the capacity. Also,
At the time of the arc start, an excessive current flows through the series diode 72, and there is a possibility that the diode is destroyed.
Has to be increased, resulting in a disadvantage that it becomes uneconomical.

Further, in the conventional device shown in FIG. 3, although the above-mentioned problem can be solved, the peak value decreases due to the position where the intermediate tap of the DC reactor 3 is drawn out, that is, the inductance between the intermediate tap and the output terminal. This makes it difficult to start the first arc, and the peak value and the discharge continuation time have a front and back relationship. Moreover, since these appropriate values change depending on the material and thickness of the consumable electrode used, it was not easy to find the optimum position of the tap. Furthermore, if the inductance after the intermediate tap is increased in order to lengthen the discharge time, the rising speed of the discharge current Ic of the capacitor is slowed down, which makes it difficult to generate a small arc to be generated by the discharge current Ic. was there.

[0010]

According to the present invention, two sets of capacitors for assisting the arc start are provided, one set discharges directly from an output terminal to a welding load, and the other set includes a DC reactor. The discharge to the welding load is performed through the IGBT to obtain an initial current change waveform optimum for arc start.

[0011]

FIG. 5 is a connection diagram showing an embodiment of the present invention .
This corresponds to the invention corresponding to claim 1 of the invention. In the figure, reference numeral 9 denotes a first series circuit including a capacitor 91 and a diode 92, which is connected between an intermediate tap of the DC reactor 3 and an output terminal (b). Reference numeral 10 denotes a second series circuit including a capacitor 101 and a diode 102, which is connected to the output terminal side of the DC reactor 3, that is, between the output terminal (a) and the other output terminal (b). The charging circuit 8 for charging the capacitors 91 and 101 of the first and second series circuits at the time of starting the welding is shown in FIG.
Thyristor similar to conventional equipment and temporary conduction at the start of welding
Element 81 composed of a switching transistor or a relay contact and a backflow prevention diode 8
The capacitors 91 and 92 are charged to the peak value of the output voltage of the DC power supply 2. Reference numeral 11 denotes an auxiliary discharge circuit for discharging the residual charges of the capacitors 91 and 101 after the completion of welding, and a voltage appears between the terminals (a) and (b) even during non-welding due to the residual charges, so that the worker receives an electric shock. Provided to prevent danger. The auxiliary discharge circuit includes an inverter 111 for inverting a start signal from the welding start command circuit 12, a transistor 112 turned on by the output of the inverter 111, and a current limiting resistor 11
Consists of three.

In FIG. 5, components having the same functions as those of the conventional device shown in FIGS. 1 and 3 are denoted by the same reference numerals, and description thereof is omitted. FIG. 6 is a waveform diagram showing a change in current flowing at the start of welding in the embodiment of FIG.

The operation of the embodiment of FIG. 5 will be described with reference to the waveform diagram of FIG. In FIG. 5, until the welding start signal is output from the start instruction circuit 12, the output signal of the start instruction circuit 12 is at a low level, the DC power supply 2 does not generate an output, and the switching element 81 of the charging circuit 8 Also remain non-conductive, the capacitors 91 and 101 are not charged. On the other hand, at this time, since the inverter 111 outputs a high-level signal obtained by inverting the low-level output, the transistor 112 of the auxiliary discharge circuit 11 is conducting, whereby the capacitors 91 and 101 are discharged through the resistor 113 and the residual charge is discharged. Is gone. When a start switch attached to the torch 4 is pressed by a command from an operator or the like, the start command circuit 12 outputs a high-level signal, whereby the DC power supply 2 generates a predetermined output.
At the same time, the output of the start command circuit 12 causes the switching element 81 of the charging circuit 8 to conduct, and the auxiliary discharging circuit 11
Transistor 112 is turned off. As a result, the capacitors 91 and 101 are rapidly charged, and their terminal voltages reach the peak value of the no-load output voltage of the DC power supply 2.
When the terminal voltages of the capacitors 91 and 101 rise, the switch
The charging is completed by shutting off the chin element 81. Of this charge
Completion is when using a relay contact for the switching element
By limiting the closing time to a certain time.
When using a thyristor, the terminal voltage of the capacitor
When the pressure rises, the
Complete. In this state, the electrode 5 is fed toward the workpiece 6 by an electrode feeding mechanism (not shown) and its control device. The electrode is fed and the tip is
When the contact is made, the charged charges of the capacitors 91 and 101 are discharged through the diode 92, the intermediate tap of the DC reactor and the diode 102, respectively, and at the same time, the power from the DC power supply 2 starts flowing through all the windings of the DC reactor 3. . At this time, capacitor 1
Discharge current Ic from 01 rises and wave height is high duration is short as shown in since there is nothing to limit the current to other than the welding load consisting of the electrodes and the object to be welded FIGS. 6 (a) to the discharge circuit It becomes a current.

The discharge current from the capacitor 91 flows through a part of the DC reactor 3, so that the rising speed and
The waveform has a low peak value and a long duration, as shown in FIG. 6B. The output current from the DC power supply 2 increases according to a time constant determined by the DC reactor 3 as shown in FIG. As a result, a current having a waveform shown by a solid line in FIG. 6 flows through the electrode 5 and the workpiece 6. As a result, the first small current arc is activated by the steeply rising current of (a), and the current (b) following this is supplied by the DC power supply 2 having a slow rising.
In this case, the arc generated by flowing the output current (c) during the period until the current sufficiently increases is maintained.

[0015] Figure 7 is Ri <br/> Oh connection diagram showing another embodiment of the present invention, corresponding to devise the present invention of claim 2. In the figure, the DC reactor 3 is divided into two DC reactors 3a, 3a.
b, these are connected in series, and one end of the capacitor 91 is connected to the connection point. The other ends of the capacitors 91 and 101 are commonly connected to the diode 13. Further, the auxiliary discharge circuit 11 includes capacitors 91 and 10
1 and a common connection point and an output terminal (b). 7 is the same as the embodiment shown in FIG.
It is the same as the conventional device of FIG.

In the embodiment shown in FIG.
Constitutes a first series circuit together with the capacitor 91, and constitutes a second series circuit together with the capacitor 101. In FIG. 7, the diode 13 is a capacitor.
Electrodes for discharging the charge of the sensors 91 and 101 to the welding load.
In the same figure, a capacitor is provided.
It is shared by 91 and 101. This diode is
The capacitor 91 and the capacitor 101 are independent of each other.
And a switching element serving as a charging circuit.
The capacitor 8 is similarly separated into the capacitor 91 and the capacitor 101.
Of course, it may be provided.

FIG. 8 is a connection diagram showing still another embodiment.
This corresponds to claim 3 of the present invention . In this figure, only the DC reactor 3 are connected in <br/> series with the output current circuit from the direct current power source 2, a straight flow reactor 14 that will be connected in series with the first capacitor 91 discharges the capacitor 91 It is connected in series only to the circuit. Also diode 13
Are shared by the first and second series circuits as in the embodiment of FIG. Further, in the embodiment of FIG. 8, a DC power supply 84 is separately provided as a power supply for charging the capacitors 91 and 101, and charging is performed via the switching element 81 which is temporarily closed at the start of welding. And a supplement for discharging residual charge is connected in parallel with the capacitor 101.
A resistor 114 having a relatively high resistance value is connected as an auxiliary discharge circuit . In the embodiments of FIGS. 7 and 8, similarly to the embodiment of FIG. 5, a current having a waveform as shown in FIG. 6 flows.

In each of the embodiments shown in FIGS. 5 and 7, a relatively high resistance value (for example, 100
When a resistor of .OMEGA. To several k.OMEGA. Is connected, the residual discharge of the capacitor is discharged by this resistor during non-welding, so that the auxiliary discharge circuit 11 shown in each embodiment can be replaced with this.

[0019]

[Effects of the Invention] In the present invention, a capacitor which is charged at the start of welding and which is discharged when the electrode and the workpiece come into contact is connected so as to be directly discharged to the output terminal;
Two systems, one connected so as to discharge via a DC reactor, are provided, so the small current arc generated when the electrode comes into contact with the workpiece to the main arc by the DC power source for welding. This ensures that the arc start does not fail.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an example of a conventional device.

FIG. 2 is a diagram showing a change in current flowing at the time of arc start by the apparatus of FIG. 1;

FIG. 3 is a connection diagram showing an example of another conventional device.

FIG. 4 is a diagram showing a change in current flowing at the time of arc start by the apparatus of FIG. 3;

FIG. 5 is a connection diagram showing an embodiment of the DC arc welding machine of the present invention.

FIG. 6 is a diagram showing a change in current flowing at the time of arc start in the DC arc welding machine of the present invention.

FIG. 7 is a connection diagram showing another embodiment of the present invention.

FIG. 8 is a connection diagram showing still another embodiment of the present invention.

[Explanation of symbols]

 2 DC power supply 3, 3a, 3b, 14 DC reactor 4 Welding torch 5 Consumable electrode 6 Work piece 8 Charging circuit 9 First series circuit 10 Second series circuit 11 Auxiliary discharge circuit 12 Start command circuit 13, 72 , 82, 83, 92, 102 Diode 81 Switching element 84 DC power supply for charging 91, 101 Capacitor 112 Transistor

Claims (4)

(57) [Scope of request for utility model registration] And 1. A DC reactor equipped with an intermediate tap that is connected to one output terminal of the DC power source, a first connected between the other output terminal of said DC power supply and the intermediate tap of the DC reactor A first series circuit including a capacitor and a diode having a polarity for discharging the electric charge of the first capacitor to an arc welding load; and a first series circuit connected between an output terminal side of the DC reactor and the other terminal of the DC power supply. A second series circuit comprising a second capacitor and a diode having a polarity for discharging the electric charge of the second capacitor to an arc welding load; and charging the first and second capacitors respectively before starting the welding arc. ; and a charging circuit for a DC arc welding machine and the other terminal of the DC power supply and the output terminal of said DC reactor was output terminal for the arc welding load . 2. A first DC reactor connected to one output terminal of a DC power supply , and a first DC reactor connected to the first DC reactor .
A second DC reactor connected in series with the first DC reactor ;
Connection point of the DC power supply and the second DC reactor and the DC power supply
First capacitor connected between the other output terminal of
And discharge the electric charge of the first capacitor to an arc welding load.
A first series circuit composed of the polarity of the diode, before
The output terminal side of the second DC reactor and the DC power supply
A second capacitor connected between the other terminal and the other terminal;
A second series circuit comprising a diode having a polarity for discharging a charge of a second capacitor to an arc welding load;
And a charging circuit for charging the second capacitor before the start of the welding arc, respectively, and arc welding the output terminal of the second DC reactor and the other terminal of the DC power supply. DC arc welding machine used as output terminal for load. 3. A power supply connected to one output terminal of a DC power supply.
A first DC reactor and a first DC reactor ;
Connect between the output terminal and the other output terminal of the DC power supply.
Connected first capacitor and the power of the first capacitor.
From a diode with a polarity to discharge the load to the arc welding load
And a first series circuit connected in parallel with the first series circuit.
Connected second capacitor and second DC reactor and
The second capacitor discharges the polarity of the diode and
A second series circuit, and the first and second capacitors.
Charge each time before starting the welding arc
And an output end of the first DC reactor.
And the other terminal of the DC power supply to the arc welding load.
Arc welding machine with output terminal 4. The method according to claim 1, wherein the first and second capacitors have a melting point.
An auxiliary discharge circuit that discharges residual charge when connection is stopped
3. The direct current arc welding machine according to claim 1 or 2.