JPH03248773A - Ac arc welding power source - Google Patents

Abstract

PURPOSE:To stabilize the arc regeneration at the time of changing over the polarity by connecting an AC reactor in series to an AC output circuit with the AC arc welding power source to change over the DC power source output by switching elements and obtain the AC output. CONSTITUTION:The AC reactor 2 showing a high inductance value at the time of a low current and a low inductance value at the time of a high current is connected in series to the AC output circuit with the AC arc welding power source to change over the DC power source 1 output by the switching elements 3a-3b and obtain the AC output. Consequently, the necessary and sufficient voltage for arc restrike at the time of changing over the polarity is charged to a capacitor and the safety and certainty of arc restrike can be improved regardless of size of a current value and length of a cable used.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to improvement of an arc welding power source,
In particular, the present invention relates to an arc welding power source that alternately switches between positive and reverse polarity to supply power to a welding part.

<Prior art> A power source used for arc welding that switches between positive polarity, where the electrode side is at a negative potential, and reverse polarity, where the electrode side is at a positive potential, is a combination of a DC power source and a switching element for polarity switching. It is proposed that it can be obtained by

(For example, Japanese Patent Application Laid-open No. 18275/1983). FIG. 5 is a connection diagram showing an example of this type of conventional device. In the figure, 1 is a known DC power supply, and 2 is a reactor for smoothing the output of the DC power supply 1. 3a to 3d are bridge-connected switching elements, and 4a to 4d are diodes connected antiparallel to the switching elements 3a to 3d, respectively. Further, 5 is an electrode, 6 is an object to be welded, 7 is a switching element, and a switching element drive circuit for driving 3a to 3d. 8 is a relatively large capacitor for smoothing the output of the DC power supply 1 and absorbing surge voltage generated in the circuit.

FIG. 6 is a diagram for explaining the operation of the conventional device shown in FIG.
The relationship between s2 and output voltage Eo is shown over time. In FIG. 5, when drive signals sl and s2 are output alternately from the switching element drive circuit 6, the switching elements 3a and 3b or the switching elements 3C and 3d simultaneously repeat conduction and disconnection, and the electrode 4 and the electrode 4 are connected to each other. A rectangular wave voltage in which the output voltage of the DC power supply 1 is switched between positive and reverse is supplied between the workpiece 5 and the workpiece 5 .

<Problems to be Solved by the Invention> In the conventional device described above, the operation when the drive signal sr disappears from the state where it is supplied, the drive signal S2 is supplied, and the current switches from the positive polarity to the reverse polarity is explained. Let's explain with an example. Due to the disappearance of the signal s1, the switching elements 3b, 3
When d changes from ON to OFF, the power supply from the DC power source 1 is cut off, but due to the inductance included in the output circuit cable, a current flows from the workpiece 6 to the electrode 5 (positive current). continues to flow through the diodes 4c, 4a, which can quickly become zero, and the capacitor 8 is charged by this current. The energy that charges the capacitor 8 is the electromagnetic energy stored in the inductance of the cable during the positive polarity period, and this charging voltage becomes higher than the output voltage of the DC power supply 1, and then the signal s2 is supplied. When the switching elements 3a and 3c are brought into conduction, the voltage is applied between the electrode 5 and the workpiece 6, and serves to ignite the reverse polarity arc (re-ignition of the welding arc).

Therefore, it is necessary that the charging voltage of this capacitor generated at the time of polarity switching has a value sufficient to re-ignite the arc, and at the same time, be below the withstand voltage of the switching elements 3a to 3d.

However, this voltage V is determined by the inductance Lc of the output circuit such as a cable and the welding current 1 g, and if the capacitance of the capacitor 8 is C, then it becomes V-Iafr77-. For this reason, when the welding current is small, if a capacitor with a large capacity is used to prevent the generated charging voltage from exceeding the withstand voltage of the switching element, assuming that the cable is long and the inductance Lc is large, and the welding current is large. If a short cable is used, the charging voltage will be insufficient and the arc will fail to re-ignite. On the other hand, if a small capacitance capacitor is used when a small current or a short cable is used, the charging voltage will become excessive when a large current or a long cable is used, and the switching element will be destroyed.

Furthermore, if the current changes suddenly when changing the polarity, a loud arcing noise will be generated, which will worsen the working environment.

Means for Solving the Problems> The present invention provides an AC arc welding power source that obtains an AC output by switching the output of a DC power source using a switching element, in which an inductance with a large inductance value is connected in series with the AC output circuit when the current is small. By connecting an AC reactor that exhibits a relatively small inductance value at high currents, the capacitor generates the necessary and sufficient voltage to re-ignite the arc when switching polarity regardless of the magnitude of the current value used or the length or shortness of the cable. It was designed so that it would be charged.

<Example> FIG. 1 shows an example of the present invention. In the same figure, the same reference numerals 1 to 8 denote the same functions as those of the embodiment shown in FIG. Reference numeral 9 denotes an AC reactor, which constitutes a main part of the present invention. FIG. 2 shows an example of the characteristics of the AC reactor used in the present invention.

In the figure, the horizontal axis shows the welding current Ia flowing through the AC reactor, and the vertical axis shows how the inductance value La changes with respect to this current. In the figure, the current value I a at which the inductance suddenly decreases.

If the current is set to a low value of about several tens of amperes, the AC reactor will be effective only during the period when the current is small during polarity switching. Therefore, as shown in FIG. 3, which shows the change in welding current 1a, the current waveform changes in a slope shape within a range of several tens of amperes or less, where the inductance value of the AC reactor suddenly changes before and after the polarity is switched. In this case, if the capacitor 8 is set to a relatively large capacity, which is necessary when using a large current and a long cable, the inductance of the AC reactor 9 will have little effect at large currents, but the voltage generated by the cable inductance will be almost all. This voltage is suppressed by the capacitor 8 of large capacity to a value necessary for restriking the arc, so that the switching element is not destroyed. Conversely, when welding is performed with a small current, the AC reactor 9 exhibits a relatively large inductance value, which induces a voltage sufficient for arc regeneration and charges the capacitor 8.

Furthermore, in either case, the rise of the welding current becomes gradual when switching the polarity, so the generation of arc noise is reduced.

An AC reactor having the characteristics as shown in FIG. 2 can be easily obtained by reducing the cross-sectional area of the iron core and setting the core so that it is magnetically saturated at approximately several tens of amperes. In particular, if a grain-oriented silicon steel plate having rectangular magnetization characteristics is used as the core material, a more distinct change in inductance can be obtained.

FIG. 4 is a connection diagram showing another embodiment of the present invention. In the figure, a DC power supply 1 connects an AC power supply 101 to a rectifier circuit 10.
2, this DC is converted to AC again by an inverter 103 consisting of a switching transistor, and the obtained AC output is converted to a voltage suitable for arc welding by a transformer 104 having a center tap in the secondary winding. After converting the DC current into positive and negative polarity using rectifiers 105a and 105b, it is smoothed by reactors 106a and 106b and capacitors 107a and 107b to obtain positive, negative and zero DC outputs at output terminals aSb and c. It is. Here, as shown in the figure, the reactors 106a and 106b share an iron core, and the winding direction is determined to have a polarity such that magnetic flux in the same direction is generated in the shared iron core by the current flowing through each reactor. Further, the positive output terminal (a) of this DC power supply is connected to the switching element 4a, and the negative output terminal is connected to the switching element 4b.The other terminal of each switching element 4a'-4b is commonly connected, and one It serves as an AC output terminal and is connected to the electrode 5. The zero output terminal C of the DC power source 1 becomes the other AC output terminal and is connected to the workpiece 6 via an AC reactor 9 having the same characteristics as the embodiment shown in FIG.

In the embodiment of FIG. 4, two switching elements 4a
, 4b are alternately ON-OFF controlled, and this AC output current changes in a slope shape only during the low current period before and after polarity switching due to the action of the AC reactor 9. The waveform will be similar. In addition, by using the AC reactor 9 with current-inductance characteristics as shown in FIG. 2, similar to the embodiment shown in FIG. The voltage for restriking can be obtained safely and reliably.

In addition, in the DC power supply 1 used in FIG. 4, the rectifier 1 is
Since the current flowing through 05a and 105b has a substantially rectangular waveform, a high-quality DC voltage with little ripple in the output voltage can be obtained.

Further, by setting the operating frequency of the inverter circuit 103 to a value sufficiently higher than the commercial frequency, the smoothing reactor can be made extremely small.

<Effects of the Invention> Since the present invention is as described above, upon switching the polarity,
The arc can be regenerated safely and reliably, and the rise of the current during arc regeneration is gradual, which reduces arc noise and improves the working environment.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining the characteristics of an AC reactor used in the present invention,
Fig. 3 is a waveform diagram of welding current obtained by the power source of the present invention, Fig. 4 is a connection diagram showing another embodiment of the invention, Fig. 5 is a connection diagram showing an example of a conventional device, and Fig. 6 5 is a waveform diagram of welding current obtained by the conventional device shown in FIG. 5. FIG. 1...DC power supply, 2...DC reactor, 3a-3
b...Switching element, 4a-4b...Diode, 5...Electrode, 6...Work to be welded, 8...Capacitor, 9...AC reactor, 102
... Rectifier circuit, 103 ... Inverter, 104-.
・Transformer, 105a, 105b・= Rectifier, 106a,
106b...DC reactor, 107a, 107b.
rndensa,

Claims (1)

[Claims] 1. The output of a DC power supply is supplied to the DC input terminals of four switching elements connected in a bridge manner, and two opposing elements of the switching elements are simultaneously connected as a pair and each pair is In an AC arc welding power source that obtains an AC output from an AC output terminal of the switching element by alternately ON-OFF controlling the elements, when a small current is generated between the AC output terminal of the switching element and the arc welding output terminal, An AC arc welding power source that has an AC reactor connected in series that has a high inductance value and a relatively low inductance value at high currents. 2. A DC power supply having three output terminals: positive, zero, and negative;
two sets of switching elements, one terminal of which is connected to the positive output terminal and the negative output terminal of the DC power supply, and the other terminals of which are connected in common and are alternately controlled to turn ON and OFF; and a common connection portion of the switching element; In the AC arc welding power source that obtains an AC output from the zero output terminal of the DC power source, a high current is generated when the current is small between the zero output terminal of the DC power source or the common connection part of the switching element and the welding output terminal. An AC arc welding power source that has an AC reactor connected in series that exhibits an inductance value and exhibits a relatively low inductance value at high currents. 3. The DC power supply has a DC reactor in series with the positive output terminal and the negative output terminal, respectively, and the DC reactors share an iron core, and the current flowing through each reactor winding causes the shared iron core to flow in the same direction. The AC arc welding power source according to claim 2, having a polarity that induces a magnetic flux of.