JPS62124076A - Ac tig (tungsten inert gas) welding machine - Google Patents

Abstract

PURPOSE:To conduct the opposite polarity current of a small ratio by constituting the titled welding machine so that a current for circulating from the second constant current power source to the first constant-current power source side is limited by a DC reactor provided on the output side circuit of the first constant current power source. CONSTITUTION:When a transistor 16 is in an off-state, when an electric conduction is being executed from the first constant current power source 1 to an arc load 25, the transistor 16 is set to an on-state for a prescribed time by a signal 18 from a control circuit 17. Also, a pulsative opposite polarity current being larger than a straight polarity conducting until that time is conducted from the second constant-current power source 2, and the opposite polarity current is conducted to the arc load 25 by a short time being shorter than an electric conduction time of the straight polarity current. In this way, a current waveform conducting to the arc load 25 becomes an AC waveform, and the ratio of the opposite polarity current flowing to the arc load 25 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an AC TIG welding machine that can make the ratio of reverse polarity current much smaller than the ratio of positive polarity current.

[Background of the Invention] Conventionally, the reverse polarity current applied to obtain a cleaning effect in AC TIG welding is sufficient to be about 10% of the overall average current value, and it is better to suppress the ratio of reverse polarity current to this level. Although it is known that this is preferable in terms of consumption and weldability, in order to realize this, a welding machine would have to be extremely large and expensive, and there was no one that could be put to practical use.

That is, in the conventional example shown in FIG.
2 through transistors Q and Q2 to the arc load R, and by increasing the current flowing from one power source E2 in a pulsed manner, a positive polarity current is generated as shown in FIG. The reverse polarity current IRP is made to flow through the arc load R for a short period of time, which is shorter than the energizing time of the ISP, but since the current is controlled using a series regulator method, the losses in the transistors Q□ and Q2 are large. The elements used are large and are not practical.

The conventional example shown in FIG. 6 was proposed by the present inventor in Japanese Patent Application No. 57-189185, and a positive polarity current is supplied to the arc load R from two power supplies E1 and E2 through chopper-controlled transistors Q1 and Q2. ISP and reverse polarity current rRp are passed alternately, and when commutation from positive polarity current to reverse polarity current, transistors Q, Q2 are turned off and transistors Q3, Q
4 is turned on, flywheel current is passed through diodes D and D2 and the DC reactor for current smoothing, and diode D is also turned on when commutating from reverse polarity current to positive polarity current.
By passing a flywheel current through the transistors Q and D2 and the DC reactor L, a spike voltage that would destroy the transistors Q and Q2 is prevented from being generated in the DC reactor L during commutation. In this conventional example, since the transistors are operated in a switching mode, the loss is small, but four transistors are required to turn on and off large currents, and the device becomes large.

[Object of the Invention] An object of the present invention is to solve the problems of the prior art described above, and to flow a reverse polarity current at a much smaller ratio than the positive polarity current as described above, with a smaller, lighter, and cheaper structure. Our goal is to provide an AC TIG welding machine that can.

[Summary of the Invention] In order to achieve the above object, the present invention provides a first constant current power supply that supplies a positive polarity current to an arc load;
A second constant current power supply is provided that supplies reverse polarity current to the arc load, at least the first constant current power supply has a DC reactor in its output side circuit, and the second constant current power supply further has a DC reactor in its output side circuit. The switching element is turned on for a predetermined period of time by a signal from the control circuit while the arc load is being energized from a first constant current power source that has a switching element that turns on and off, and does not have a switching element in the output side circuit. Then, by passing a pulsed current larger than the current that had been flowing from the second constant current power source, the reverse polarity current was made to flow through the arc load for a short period of time, which was shorter than the current flow time of the positive polarity current. It is something.

[Embodiment of the Invention] An embodiment of the present invention is shown in FIG.

This embodiment is an example in which both the first constant current power supply 1 and the second constant current power supply 2 are of a switching regulator type whose current is controlled by a high frequency inverter, and the AC input voltage of the commercial frequency from the AC power supply 3 is three. The phase full-wave rectifier circuit 4 and smoothing capacitor 5 convert the current into direct current. 6.7 is a high frequency inverter, which is driven by drive circuits 8 and 9, converts the DC voltage smoothed by the smoothing capacitor 5 into high frequency AC (for example, 20 kl (z)) and applies it to the primary side of the welding transformers 1o and 11. 12.13 is welding transformer 10.1
1 is an output side rectifier diode that converts the secondary voltage of 1 into DC again, 14.15 is a DC reactor that smoothes the output current, and 14.15 is a DC reactor that smoothes the output current. The relationship between the inductance value LRP of the DC reactor 15 on the constant current power supply 2 side is LsP>LR
It is set to P. 16 is the second constant current 71iit2
A transistor shown as an example of a switching element that turns on and off the output side circuit of the control circuit 17.
controlled by The first constant current power supply 1 does not have such a switching element in its output side circuit. 19 is a shunt resistor for detecting the positive polarity current ISP, 20 is a shunt resistor for detecting the reverse polarity current IRP, 21 is a bang generator for ISP setting, 22 is a bang generator for IRP setting, and the control circuit 17 The ISP setting signal and IRP setting signal generated from these bang generators 21 and 22 are synchronized. Reference numerals 23 and 24 are comparison amplifiers, and in the first constant current power supply 1, the ISP setting signal from the bang generator 21 and the xsp detection signal from the shunt resistor 19 are compared and amplified and a signal is applied to the drive circuit 8 to generate a high frequency signal. The conduction width of the inverter 6 is controlled to perform constant current control, and the second constant current power supply 2 drives a signal obtained by comparing and amplifying the IRP setting signal from the baton generator 22 and the IRP detection signal from the shunt resistor 20. By adding it to the circuit 9, the conduction width of the high frequency inverter 7 is controlled to perform constant current control.

Reference numeral 25 denotes an arc load, which is connected so that the current from the first constant current power source 1 and the current from the second constant current power source 2 flow in opposite directions.

Next, the flow of current during welding will be explained with reference to FIGS. 2 and 3.

The waveforms of the ISP setting signal and IRP setting signal generated from the button generators 21 and 22 are as shown in Fig.
The P setting signal has a continuous waveform, and the IRP setting signal has a pulse waveform.

During welding, a current with a waveform shown by ISP in FIG. 3 flows through the output side circuit of the first constant current power source 1, and a current with a waveform shown by IRP in FIG. 3 flows through the output side circuit of the second constant current power source 2. current flows.

When the transistor 16 is in the off state, all the ISP current from the first constant current power source 1 is flowing through the arc load 25, and while the first constant current power source 1 is energizing the arc load 25, , the transistor 16 is turned on for a predetermined period of time by the signal 18 from the control circuit 17, and a pulse-like IRP that is larger than the ISP current flowing up to that point is generated.
By flowing current from the second constant current power supply 2, the ISP
The IRP current is passed through the arc load 25 for a short time shorter than the current application time.

By doing this, the current waveform flowing through the arc load 25 becomes an AC waveform as shown by IOU↑ in Fig. 3, and the ratio of the IRP current flowing through the arc load 25 can be set to about 10% of the overall average current value. can.

In this case, as shown in FIG. 3, if the current is controlled so that the ISP current flowing from the first constant current power supply 1 during the IRP period is reduced in a pulsed manner, the IR required for the cleaning action can be reduced.
Since the P current is passed through the arc load, less current is required from the second constant current power source 2, and the power source capacity can be reduced.

In addition, in Figure 3, there are ISP and IR in the IRP section.
The reason why the P current increases as indicated by the diagonal line is due to the loop current flowing from the second constant current power supply 2 to the first constant current power supply 1 side.

Generally, when flowing ISP current and IRP current from two power supplies to an arc load, there are two problems: the current flows from one power supply to the other power supply circuit, and the spike voltage generated by the inductance of the power supply circuit during commutation. However, in this embodiment, these problems are solved as follows.

First, the current loop from the first constant current power supply 1 to the second constant current power supply 2 side is
A transistor 16 provided in the output side circuit of the constant current power supply 2
This can be prevented by turning off the

Furthermore, when the transistor 16 is turned on, the fRp'R flow is pulsed and flows for a short time compared to the ISP current, with respect to the loop current flowing from the second constant current power supply 2 to the first constant current power supply 1 side. , as mentioned above, LSP>L
Since it is an RP, there is no need to provide a switching element on the first constant current power supply 1 side to turn on and off the output side circuit.
The DC reactor 14 having a large inductance limits the current flowing from the second constant current power source 2 to the first constant current power source 1 side, so that the necessary IRP current can flow through the arc load 25.

On the other hand, the inductance of the DC reactor 15 is small, and especially when the first and second constant current power supplies are both of the switching regulator type in which the current is controlled by a high frequency inverter as in this embodiment, the second constant current power supply The inductance of the DC reactor 15 required for smoothing the output current of step 2 is several tenths of that of thyristor control, so the spike voltage generated when the transistor 16 is turned off can be kept below the withstand voltage of the transistor 16. can be suppressed to a low value.

Since the second constant current power supply 2 has a small ratio of IRP current, current control may be performed using a series regulator method, and in this case, the DC reactor 15 is not required.

Furthermore, when the transistor 16 is turned off, even if a spike voltage is generated in the DC reactor 14 due to the sneak current from the second constant current power supply 2 that was flowing until then, the IRP
Since this is the time of commutation from the current to the ISP current, the generated spike voltage is applied to the arc load 25 and commutation is easily performed, generating a high voltage that can destroy switching elements such as the transistor 16. Never.

[Effects of the Invention] As described above, in the present invention, a switching element that turns on and off the output side circuit is provided only in the second constant current power supply that supplies reverse polarity current, and a pulsed current flows to the arc load, and the positive electrode Because the structure is configured to limit the sneak current from the second constant current power source to the first constant current power source side by a DC reactor installed in the output side circuit of the first constant current power source that supplies constant current, the output side circuit There is only one switching element that turns on and off, and the reverse polarity current flowing through this switching element is about 10% of the overall average current value. The spike voltage applied to the switching element during current and commutation can also be sufficiently suppressed, ensuring operational reliability.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of a current setting signal in this embodiment, FIG. 3 is an output current waveform diagram thereof, and FIG. 4 is a circuit diagram of a conventional example. FIG. 5 is an output current waveform diagram, and FIG. 6 is a circuit diagram of another conventional example. 1... First constant current power supply 2... Second constant current power supply 6.7... High frequency inverter 10.11... Welding transformer 14.15... DC reactor 16... Switching element 17... Control circuit 18... Control signal

Claims (3)

[Claims] (1) A first constant current power supply that supplies a positive polarity current to the arc load and a second constant current power supply that supplies a reverse polarity current to the arc load, of which at least the first constant current power supply is on the output side The second constant current power supply, which has a DC reactor in its circuit, further has a switching element for turning on and off the output circuit, and the first constant current power supply, which does not have a switching element in the output circuit, is connected to the arc load. During energization, the switching element is turned on for a predetermined period of time by a signal from the control circuit, and a pulsed current larger than the current flowing until then is caused to flow from the second constant current power supply, thereby causing a positive current to flow. An AC TIG welding machine characterized by passing a reverse polarity current through an arc load for a short period of time shorter than the energization time. (2) The first and second constant current power supplies control the output current using high frequency inverters, and both have DC reactors in their output circuits, and the inductance of the DC reactor of the first constant current power supply is The AC TIG welding machine according to claim 1, wherein the inductance value is larger than the inductance value of the DC reactor included in the second constant current power source. (3) When current is supplied from the second constant current power source to the arc load, the current is controlled so as to reduce the current flowing from the first constant current power source to the arc load; The AC TIG welding machine described in (2).