JPS632707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an arc welding machine having an arc welding power source with superimposed pulses. For joints with different amounts of heat input, such as welded joints of plates with different thicknesses or uranami welding, etc., or welding that requires a large amount of heat input and for which heat input control is difficult, it is necessary to adjust the welding current at a constant cycle. The base metal is melted during period A when the pulse current is high, the amount of heat input is reduced during period B when the base current is low, and the molten pool is cooled and solidified to perform welding to avoid burn-through. It is. Conventionally, in order to obtain such a welding current waveform, the current adjustment bias of the DC power source was changed synchronously in the case of DC welding for welding mild stainless steel or the like. In addition, in the case of AC welding for welding aluminum, etc., the output from a DC power source 1 is converted to rectangular wave AC via an inverter 2 and supplied to a welding load 3, as shown in Fig. 1. It was 4 is a base pulse current switching signal generation circuit. Pulse-like changes in the welding current are achieved by periodically changing the pulse time A and base time B on the DC power supply 1 side, and converting this into alternating current by an inverter. The welding current waveform at this time is as shown in FIG. Figure 2a shows the current waveform during DC welding, and Figure 2b shows the current waveform during AC welding. In the above-mentioned welding apparatus, especially when obtaining AC pulses, a DC power source 1 and an inverter 2 are required, resulting in a large welding apparatus and a complicated and expensive power supply circuit.

The present invention eliminates the above-mentioned conventional drawbacks, and maintains a controlled rectifier circuit so that the direction of the current flowing through the reactor in series with the AC power source and the welding load is always the same, thereby changing the welding current waveform or the like. The approximated arc welding machine is characterized in that the output waveform is changed at a cycle longer than the alternating cycle of the alternating current power source.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3 is a circuit diagram showing an embodiment of the power supply section of the arc welding machine according to the present invention. In the figure, 5 is a transformer, SCR is a controlled rectifier circuit,
A bridge rectifier circuit of thyristors SCR1 to SCR4 is formed. 6 is a reactor connected in series to the DC output terminal of the bridge rectifier circuit. Even when a welding load (not shown) is connected to the AC output terminals 8 and 9, the direction of the current flowing through the reactor 6 is always the same. And reactor 6 is SCR
It is already known that a substantially rectangular wave current is output between the output terminals 8 and 9 by being inserted between the anode of SCR 2 and the cathode of SCR 1, as described in JP-A-51-136544. It is a fact. 7
is a current detection section inserted between the secondary winding of the transformer and the output terminal 9. FIG. 4 shows an embodiment of a control device for controlling the power supply section shown in FIG. In the figure, 17 corresponds to a transformer, 18 corresponds to a control rectifier circuit SCR, 19 a current detection section, and 20 a welding load. 11 is a reference power source for setting a pulse current (high level), and 12 is a reference power source for setting a base current (low level). Reference numeral 13 denotes a reference voltage switching circuit which receives the reference power supplies 11 and 12 for pulse and base current setting as input, and is composed of transistors, relays, etc., and is driven by other inputs, that is, the pulse and base current switching signal generation circuit 21 described later. be done. The pulse/base switching signal generation circuit 21 is constituted by an oscillator (not shown), etc., and generates a switching signal synchronized with the output of this oscillator. 14 is an error amplifier that amplifies the difference voltage between the reference voltage selected by the reference voltage switching circuit 13 and the output of the amplifier 22 that amplifies the signal of the current detection unit 19; Changing phase control circuit, 16
is a thyristor gate signal amplification circuit. This circuit maintains the reference voltage switching circuit 13 even if the load 20 changes.
The differential voltage between the reference voltage selected by the amplifier 22 and the voltage from the current detection section 19 obtained via the amplifier 22 is always constant, and a constant current characteristic is obtained.
Therefore, it can be changed periodically in synchronization with the base current and pulse current selected by the reference voltage switching circuit 13. The output current waveform at this time is shown in Figure 2b, and the pulse current period A is
longer than 0.02sec, and the base current period B is
Practically effective welding can be performed by making the welding time longer than 0.03 sec. According to the results of the experiment, periods A and B
It is preferable that the length of the period A and B be determined according to the heat input control conditions for the workpiece, and the lengths and ratios of the periods A and B can be set in any manner. Figure 5 shows another embodiment of the power supply section of a welding machine for both AC and DC.
0 is an AC/DC changeover switch. Similar to the first embodiment shown in FIG. 3, the output current can be controlled by the control circuit shown in FIG. By switching the AC/DC changeover switch 10 between the AC side and the DC side, AC and DC pulse current waveforms can be generated. In the first and second embodiments described above, the combination of thyristors in the controlled rectifier circuit 18 has been described as having a bridge type circuit configuration, but the combination is not limited to this, and as shown in FIG. The same operation and effect can be obtained by the configuration. In the figure, SCR ₁ and SCR ₂ are thyristors, D ₁ and D ₂ are rectifiers, and 23 is a reactor with a center tap.

As described above, the present invention creates a rectangular welding current waveform by connecting a reactor in series with an AC power source and a welding load, and a controlled rectifier circuit so that the direction of the magnetic flux generated by the current flowing through the reactor is always the same. Alternatively, in an arc welding machine with a waveform similar to this, the output waveform is changed at a cycle longer than the alternating cycle of the AC power source, so it is possible to use a low-frequency pulse welding current with a simple configuration. can occur. In addition, this welding machine can adjust the pulse width arbitrarily, so when welding multiple base materials with different thicknesses, or when welding Uranami welding, it is possible to avoid burn-through due to excessive heat input or penetration due to insufficient heat input. Stable welding can be performed without welding defects such as insufficient welding.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a conventional arc welding machine, Fig. 2a is a welding current waveform diagram of DC arc welding, and b is a welding current waveform diagram when a low frequency pulse is superimposed on AC arc welding. FIG. 4 is a circuit diagram showing one embodiment of a welding power supply circuit used in the present invention. FIG. 4 is a block diagram showing one embodiment of the present invention. FIGS. 5 and 6 are circuit diagrams showing other embodiments of the welding power supply circuit used in the present invention. 10...AC/DC changeover switch, 11...Pulse current reference voltage circuit, 12...Base current reference voltage circuit, 1
3... Reference voltage switching circuit, 15... Phase control circuit,
5, 17...Transformer, 18...Control rectifier circuit, 1
9... Current detection unit, 20... Welding load, 21... Pulse, base current switching signal generation circuit.

Claims (1)

[Claims] 1 By connecting a reactor in series with the AC power source and welding load and a controlled rectifier circuit so that the direction of the magnetic flux generated by the current flowing through this reactor is always the same, the welding current waveform can be made into a rectangular waveform or a shape similar to this. A high-level current setting device and a low-level current setting device for the welding current having the above-mentioned rectangular waveform or an approximate waveform in an arc welding machine with a waveform, and a standard for alternately and synchronously switching the set values from the two current setting devices. a voltage switching circuit; a current detection section that detects the welding current supplied to the welding load; and an error amplifier that outputs a difference signal between a switching signal from the reference voltage switching circuit and a detection signal from the current detection section. and a phase control circuit that controls the phase of the control rectifier circuit using the difference signal from the error amplifier.