JPH03124375A - Tig welding power source for ac/dc - Google Patents

Abstract

PURPOSE:To improve arc start performance by connecting capacitors respectively between the rod minus side output wires and between rod plus side output wires of an output side rectifying circuit and providing high-voltage superposing circuits between the terminals of the two capacitors. CONSTITUTION:The high-voltage superposing circuits 19, 20 connected respectively between the terminals of the capacitors 7, 8 charge the capacitors 7, 8 to the high voltage above the arc refiring voltage by turning on a switching element by the signal from a controller. These circuits make contribution to the stabilization of the refiring of the arc by alternately operating at every polarity inversion of the current at the time of AC welding. The high-voltage superposing circuit 19 operates at the time of arc starting to make contribution to the improvement in the arc start performance at the time of DC welding.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter-controlled AC/DC dual TIG welding power source.

[Conventional technology]

In AC TIG welding, arc breakage is likely to occur when the current polarity is reversed, especially when the current polarity is reversed from negative to positive. For this reason, when the current polarity is reversed in the shell, a high frequency high voltage is applied between the electrode and the base metal to help re-ignite the arc. In addition, the arc restriking voltage in normal argon atmosphere is relatively low at around 200V, and the high-frequency superimposition method is prone to radio interference, so inverter-controlled AC/DC dual-use TIG welding power sources are Some devices employ a method in which a voltage (approximately 200 V) from a capacitor previously charged from a high voltage superimposition circuit is applied between the electrode and the base material immediately after the switching element on the positive side of the rod is turned on.

[Problem to be solved by the invention]

However, in AC TIG welding, electrodes made of various materials other than tungsten with 2% thorium (such as pure tungsten) are used, or when the arc length is extremely long, or when helium gas, which has a higher arc voltage than argon gas, is used as a shielding gas. When used, arc breakage may also occur when the current polarity is reversed from positive to negative. In such cases, conventional inverter-controlled TIG welding power sources for intersection surfaces cannot cope with the problem.

In addition, in DC TIG welding, arc start performance improves as the secondary no-load voltage of the welding transformer increases; however, when the secondary no-load voltage is increased, the turns ratio (- As the winding/secondary winding) becomes smaller, the current flowing to the negative side increases, and accordingly, it is necessary to increase the wire size of the transformer-secondary winding, the element capacity of the input side inverter, etc. . In reality, in order to reduce the size and cost of welding power sources, the secondary no-load voltage cannot be set high enough. Therefore, if electrodes made of various materials other than 2% thorium-containing tungsten are used, if the arc length is extremely long, or if helium gas is used as a shielding gas, the arc starting performance will deteriorate and the high frequency and high voltage applied to the electrode will deteriorate. , the arc may fail to start even if it is applied between the base materials.

The purpose of the present invention is to provide stability when the current polarity is reversed in AC TIG welding, even when electrodes made of various materials other than tungsten containing 2% thorium are used, the arc length is extremely long, or helium gas is used as a shielding gas. To provide an AC/DC TIG welding power source which can re-ignite the arc that has been used and which has good arc start performance during DC TIG welding and AC TIG welding.

(Means for Solving Problem 11) In order to achieve the above object, the present invention provides a rectifier circuit having a neutral point on the output side of a welding transformer whose output is controlled by an inverter provided on the input side, The positive and negative output terminals of the output side rectifier circuit are connected to one welding output terminal 4-blade terminal through a switching element for switching current polarity, and the neutral point is connected to the other welding output terminal, respectively, In an AC/DC dual-use TIG welding power source in which a coupling coil that applies a high frequency high voltage for arc starting is connected in series to the neutral point side output line, the output side of the rectifier circuit on the output side is between the bar negative side output line and the bar positive side output. A capacitor is connected between each line, and a high voltage superimposition circuit is connected between the terminals of both capacitors, and these high voltage superposition circuits allow for the It is characterized in that the capacitor connected between the output lines on the side that is intended to supply current to the load is charged in advance to a high voltage higher than the arc restriking voltage.

[For production]

The present invention connects a capacitor and a high voltage superimposition circuit not only between the positive side output lines of the output side rectifier circuit as described above, but also between the negative side output lines, and in AC TIG welding, from the negative side to the negative side output line of the output rectifier circuit. When reversing the polarity of the current to the positive rod and from the positive rod to the negative rod, the voltage of the capacitor charged from the high voltage superimposition circuit just before the reversal is applied between the electrode and the base material via the switching element. By doing so, a discharge is generated during that time to stabilize the re-ignition of the arc, and in DC TIG welding, when the arc is started, the capacitor connected between the output wire on the negative side of the rod is charged from the high voltage superimposition circuit. By applying a high-frequency high voltage for arc starting, a discharge occurs between the electrode and the base material, and at the same time, the electric charge of the capacitor is discharged between the electrode and the base material, thereby improving arc starting performance. It is.

〔Example〕 An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a commercial frequency three-phase AC voltage applied to an input terminal 1 is converted into DC by an input side rectifier circuit 2. In FIG.

Reference numeral 3 denotes an input-side inverter that converts the DC output of the rectifier circuit 2 into AC at a frequency higher than the commercial frequency (for example, 20 kHz) and applies it to the welding transformer 4. Reference numeral 5 denotes an output side rectifier circuit having a neutral point N, which rectifies the alternating current voltage stepped down by the welding transformer 4 and outputs positive and negative direct current voltages to the neutral point N. 6 is an output current smoothing reactor,
7.8 is a capacitor connected between the negative side output line and the positive side output line of the output side rectifier circuit 5, respectively; 9
, 10 are switching elements (transistors in the figure) constituting the output side inverter for current polarity switching, and connect the positive and negative output terminals of the output side rectifier circuit 5 to one of the welding output terminals via switching elements 9 and 10, respectively. Connect to 11,
By connecting the neutral point N to the other welding output terminal 12, the circuit configuration of the output side inverter is simplified.

Diodes 13 and 14 are connected in antiparallel to the switching elements 9 and 10, and serve to absorb the transient voltage generated in the load cable when the switching elements 9 and 10 are turned off into the capacitor 7.8.

In the above configuration, when the switching element 9 is turned on and the switching element 10 is turned off, the positive output terminal of the output rectifier circuit 5 is connected to the switching element 9, the output terminal 11, the load (not shown), the output terminal 12, and the reactor 6. A DC current with a negative polarity flows to the neutral point N through , and when switching element 9 is turned off and switching element 10 is turned on, the current flows from the neutral point N to the reactor 6, the output terminal 12, and the load (not shown). , the positive polarity DC current flows through the output terminal 11 and the switching element 10 to the negative output terminal of the output rectifier circuit 5. Furthermore, by alternately turning on and off the switching elements 9 and 10, alternating current can be supplied to the load through the above path. At this time, an arbitrary AC output waveform can be obtained by selecting the on/off time ratio and period.

In this way, the switching elements 9 and 10 are turned on.

The drive circuit 18 controls the off state, and the output current value is controlled by comparing the detected current value of the alternator 15 with the set value of the current setter 17, and then using the pulse width control circuit 16 to make sure that the two match. This is done by controlling the output pulse width of the inverter 3.

19 and 20 are high voltage superimposition circuits connected between the terminals of capacitors 7 and 8, which operate alternately each time the polarity of the current is reversed during AC welding, and contribute to repointing the arc and stabilizing the arc; High voltage superimposition circuit 1 during DC welding
9 operates at the time of arc start and contributes to improvement of arc start performance. High voltage superimposition circuit 19.

20 is composed of, for example, a DC power supply 24, a switching element (transistor) 25, a current limiting resistor 26, etc. as shown in FIG. , the capacitors 7 and 8 are charged to a high voltage higher than the arc restriking voltage. The DC power source 24 may be one in which AC voltage from a commercial power source is converted to DC via a transformer and a rectifier circuit, or one in which the tertiary winding voltage of the welding transformer 4 is converted to DC via a rectifier circuit. used.

In addition, in FIG. 1, a high frequency high voltage generation circuit 21, a coupling coil 22, a high frequency bypass capacitor 23
In DC TIG welding and AC TIG welding, a high frequency high voltage is applied between the electrode and the base metal at the time of arc start to ignite the arc, and the coupling coil 22 is connected in series to the neutral point side output line. It is connected to the.

FIG. 3 is an explanatory diagram of the operation of the restriking function in AC TIG welding. The output current waveform is shown in (a).

The upper part of the figure is the current that flows to the load when the switching element 9 is turned on, and the lower part is the current that flows to the load when the switching element 10 is turned on.

(b) and (C) show charging waveforms of capacitors 7 and 8.

The charging period of the capacitor 7 is the EP (positive) period when the switching element 10 is on, and the capacitor 8
During the charging period of EN, the switching element 9 is on.
(bar minus) period. In AC TIG welding, arc breakage tends to occur when the polarity of the current reverses from EN to EP, but immediately after this reversal, a high voltage (approximately 200 V) charged in the capacitor 8 is applied between the electrode and the base metal. This ensures stable restriking. However, when using electrodes made of various materials other than tungsten containing 2% thorium, when the arc length is extremely long, or when helium gas is used as a shielding gas, when the polarity of the current is reversed from EP to EN. The arc may also run out. At that time, the high voltage charged in the capacitor 7
It is applied between the base metals and works effectively to re-ignite the arc. (d),
(e) shows the discharge waveform of capacitor 7.8.

FIG. 4 is an explanatory diagram of the operation at arc start of DC TIG welding. The output current waveform is shown in (g).

The operating period of the high-frequency high-voltage generating circuit 21 is the period from when the torch switch is operated to when the arc star is activated (there is a slight delay), and this period is at least several milliseconds. On the other hand, the operating period of the high voltage superimposing circuit 19 that charges the capacitor 7 is also set to be the same as the operating period of the high frequency high voltage generating circuit 21, and the charging time constant is set to 1 ms or less. Thereby, the electric charge of the capacitor 7 charged to a high voltage at the start of discharge between the electrode and the base material can be discharged between the electrode and the base material, thereby facilitating arc starting. (i) shows the charging waveform of the conductor 7, and (j) shows the discharging waveform.

Similarly, when starting an arc in AC TIG welding, the high voltage charged in the capacitor 7 (or 8) can be used to improve the arc starting performance.

〔Effect of the invention〕

According to the present invention, in an inverter-controlled AC/DC dual-use TIG welding power source, when electrodes made of various materials other than 2% thorium-containing tungsten are used, when the arc length is extremely long, or when using helium as a shielding gas with a high arc voltage. Even when using gas, it stably re-ignites the arc and prevents arc breakage when the current polarity is reversed from negative to positive rod in AC TIG welding, and from positive to positive rod. This has the effect of improving the arc start performance during both DC TIG welding and AC TIG welding.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a detailed circuit diagram of the high voltage superimposition circuit shown in Fig. 1, and Figs. 3 and 4 are time charts for explaining the operation of the embodiment. It is. 3... Input side inverter, 4... Welding transformer, 5
...output side rectifier circuit, N...neutral point, 7, 8...
Capacitor II-2 Sensor, 9, 10... Switching element, 11.12.
...Output terminal for welding, 19.20...High voltage superimposition circuit, 21...High frequency high voltage generation circuit, 22...Coupling coil, 23...High frequency bypass capacitor.

Claims (1)

[Claims] 1. A rectifier circuit with a neutral point is installed on the output side of the welding transformer whose output is controlled by an inverter installed on the input side,
The positive and negative output terminals of the output rectifier circuit are connected to one welding output terminal through a switching element for switching current polarity, and the neutral point is connected to the other welding output terminal, and the neutral point is connected to the other welding output terminal. In an AC/DC dual-use TIG welding power source in which a coupling coil that applies a high-frequency high voltage for arc starting is connected in series to the side output line, there is a In addition to connecting the capacitors, we will also provide high voltage superimposition circuits connected between the terminals of both capacitors, and use these high voltage superimposition circuits to supply current to the load at the time of arc start and current polarity reversal during AC welding. A TIG welding power source for both AC and DC use, characterized in that a capacitor connected between the output lines on the output side is charged in advance to a high voltage higher than the arc restriking voltage.