JPH0435006Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field This invention relates to a power supply device for an arc welding machine that performs arc welding using a switching transistor.

(b) Prior Art As a conventional power supply device for an AC arc welding machine, a power supply device for an arc welding machine that first converts a commercial power source into a high frequency wave, then transforms it and shapes it into a rectangular wave has been put into practical use.

A circuit diagram of this power supply device for an arc welding machine is shown in FIG. As shown in the figure, in this power supply device for an arc welding machine, a three-phase AC power source 70 is rectified and smoothed by a rectifier circuit 71 and a smoothing capacitor 72, and then high-frequency switching is performed by switching transistors 73, 74 and an output control circuit 75. Convert to high frequency (usually 2-20KHz). Furthermore, the high frequency output is transformed to several tens to hundreds of volts by a transformer 76, and then converted back to direct current by rectifiers 77, 78, a smoothing reactor 79, and a smoothing capacitor 80. After that, the switching transistors 81, 82, 83, 84 and the low frequency control circuit 85 perform an inversion switching operation to generate a highly accurate rectangular wave (usually 50 to 100 Hz).
I am trying to obtain a welding current of . In the figure,
86 is a high frequency oscillator for facilitating arc ignition at the start of operation when performing TIG welding or the like.
Further, 89 is a current detector, and its detected value is fed back to the output control circuit 75 to perform constant current control of the output.

In the above power supply device for an arc welding machine, since voltage transformation and rectification can be performed at high frequencies, the transformer and reactor can be configured for high frequency use, making it possible to achieve miniaturization and low cost, as well as output based on the detected value of the current detector 89. The current control of the control circuit 75 can be performed accurately with a fast response speed. Also, the low frequency control circuit 85
Accordingly, AC arc welding can be performed by the reverse switching operation of the switching transistors, and DC arc welding can be performed by keeping either one of the switching transistors 81, 84 or 82, 83 in the ON state.

By the way, when AC arc welding is performed using the above-mentioned apparatus, the switching transistor is operated by the low frequency control circuit 85.
This switching operation was performed from the time the power supply device was started.

(c) Problems that the invention aims to solve However, with conventional power supplies, when performing AC arc welding, the output was always switched at a low frequency from the beginning of startup, which caused severe electrode wear depending on the type of electrode. In some cases, the arc start did not work properly. For example, when using a normal electrode made of tungsten, the electrode wears out extremely rapidly, and with an electrode made by mixing tungsten with thorium to increase the hardness of the electrode, electrode wear is relatively less likely to occur. There was a problem with poor arc start performance.

The purpose of this invention is to provide a power supply device for an arc welding machine that can prevent electrode wear and provide optimal arc starting performance regardless of the type of electrode.

(d) Means for Solving Problems This invention consists of a first rectifier circuit connected to an AC power source and once converting the AC power source into DC; and a first rectifier circuit connected to the output side of the first rectifier circuit. , a high frequency conversion circuit that converts a DC voltage into high frequency; a transformer that is connected to the output side of the high frequency conversion circuit and converts the high frequency voltage; and a transformer that is connected to the output side of the transformer and that converts the high frequency voltage. a second rectifier circuit that rectifies the output of the second rectifier into positive and negative; a smoothing circuit that is connected to the output side of the second rectifier circuit and includes a smoothing reactor and a smoothing capacitor that smooth the rectified output;
an opening/closing circuit connected to the output side of the smoothing circuit and having a switching element and switching the smoothing output of the smoothing circuit to apply positive or negative polarity to the welding electrode and the base material; and a switching circuit for smoothing output polarity of the opening/closing circuit. a low frequency control circuit connected to the control terminal and controlling the switching cycle at low frequency; a timer that measures a certain period of time from when the start switch is operated; and a timer connected to the timer and configured to output a smoothed positive polarity output. A start-up mode including mode selection terminals for a first mode in which a smoothed output of negative polarity is applied, a second mode in which a smoothed output of negative polarity is applied, and a third mode in which a smoothed output of positive polarity and negative polarity is alternately switched and applied. a selection switch, and the low frequency control circuit applies only a positive smoothed output to the welding electrode and the base material until the timer times out when the first mode is selected by the startup mode selection switch. a circuit that outputs a predetermined control signal to the opening/closing circuit so that the operation is performed, and a circuit that outputs a predetermined control signal to the opening/closing circuit so that when the second mode is selected, only a smooth output of negative polarity is applied to the welding electrode and the base material until the timer times out. a circuit that outputs a predetermined control signal to the opening/closing circuit; and when a third mode is selected, a smooth output of positive polarity and negative polarity is alternately switched and applied to the welding electrode and the base material regardless of the timer. A switching control signal is output to the switching circuit.

(e) Effect In the power supply device for an arc welding machine according to this invention,
The starting mode is switched to one of the first to third modes depending on the material of the electrode and the magnitude of the current at starting. For example, when the current at startup is relatively large, the third mode is selected and the arc start is quickly performed. Also, when the current at startup is small, the first or second
Select one of the modes. For example, if the electrode is made of tungsten, which tends to wear out the electrode if the positive polarity continues until the arc starts, the second mode is selected. Further, when an electrode made of a material in which tungsten and thorium are mixed is used, the first mode is selected. In this first mode, since the electrode is negative, electrons continue to be emitted from the electrode, but since a tungsten electrode mixed with thorium is used as the electrode, it is possible to prevent the electrode from being worn out. Furthermore, in the second mode, since the base material is negative, no electrons are emitted from the electrode. Therefore, electrode consumption can be prevented.

(f) Embodiment FIG. 1 is a circuit diagram of a power supply device for an AC arc welding machine which is an embodiment of this invention.

In the figure, the first rectifier circuit 2 is constructed of a full-wave rectifier circuit. The first rectifier circuit 2 is connected to the three-phase AC power supply 1 . Further, a series circuit of smoothing capacitors 11a and 11b is connected in parallel to the first rectifier circuit 2. The smoothed DC voltage is supplied to the high frequency conversion circuit 3.

The high frequency conversion circuit 3 includes series-connected transistors 12 and 13 connected to the transformer 4, and a high frequency conversion circuit control section 14 that turns these transistors 12 and 13 on and off alternately. The primary winding of the transformer 4 is arranged between the connection point of the transistors 12 and 13 and the connection point of the capacitors 11a and 11b, and forms a half bridge between the transistors 12 and 13, the smoothing capacitors 11a and 11b, and the primary winding of the transformer 4. The circuit is configured.

The secondary output of the transformer 4 is rectified and smoothed, and selectively connected to the welding electrode 9 and the base material 1 by a switching circuit 8, which will be described later.
It leads to 0.

The secondary winding includes diodes 31, 32, 3.
A rectifier circuit 5 composed of 3 and 34 is connected. This rectified output is guided to a smoothing reactor 6 and a smoothing capacitor 7. The switching circuit 8 connected to the rectifying and smoothing circuit is a switching transistor 41
-44. A low frequency control circuit 16 connected to the bases of each of the switching transistors 41 to 44 is a circuit that performs an inverted switching operation on each switching transistor. A mode selection switch 17 is connected. The contact 19 of this switch 17 is the first
mode, contact 20 selects the second mode, and contact 21 selects the third mode.

FIG. 2 shows a block diagram of the low frequency control circuit. A starting switch 50 interlocked with a power switch (not shown) operates a clock pulse generating circuit 51 and a timer 58 when turned on.
The clock pulse generation circuit 51 is a transistor 41
Generate ~44 switching pulses. Further, the timer 58 sets the smoothed output to positive or negative polarity for a certain period of time when the first mode or the second mode is selected at startup. The output of the clock pulse generation circuit 51 is connected to diodes 54, 5.
5 to flip-flops 52 and 53, where it is inverted and connected to transistors 41 and 53, respectively.
44 and the bases of transistors 42 and 43. Flip-flops 52, 53 are interconnected such that both outputs are always of opposite polarity. Transistors 56 and 57 for shorting the input side of the flip-flop are connected to the cathodes of the diodes 54 and 55, the base of the transistor 56 is connected to the contact 19 of the startup mode selection switch 17, and the base of the transistor 57 is connected to the contact 20. has been done.

In the above configuration, when the switch 18 is connected to the contact 21 and the third mode is selected, the output of the clock pulse generation circuit 51 is directly supplied to the flip-flops 52 and 53 because the transistors 56 and 57 are both off. be done. Therefore, the output current has the waveform shown in FIG. 3C from the time of startup. This third mode is selected when the arc current is set high. When the arc current is set to a small value, it takes a relatively long time to start the arc, so it is necessary to prevent the electrodes from becoming severely worn out during this time. Therefore, when the electrode 9 is made of only tungsten, which tends to wear out the electrode due to long-term thermionic emission, the first mode is selected. When this mode is selected, the activation switch 50
When turned on, the flip-flop 52 outputs "L" because the transistor 56 remains on until the timer 58 times up. Therefore, the flip-flop 53 outputs "H". When timer 58 is up, transistor 5
Since flip-flops 6 and 57 are both off, flip-flops 52 and 53 are alternately turned on and off in response to the output of clock pulse generation circuit 51. Therefore, the smoothed output has the waveform shown in FIG. 3a. In this first mode, thermionic emission occurs from the base material 10 when the timer 58 times up, resulting in a transition to an arc state. The time until the timer 58 times out is set to a length that allows the base material 10 to sufficiently emit thermionic electrons and transition to an arc state.

On the other hand, when a highly hard material such as thorium-doped tungsten is used for the electrode 9, switch 1 is used.
8 selects the second mode. If a material with such high hardness is selected for the electrode 9, electrode wear is less likely to occur, but there is a problem in that arc starting performance deteriorates. Therefore, at this time, the electrode is made negative from the time of startup so that thermionic electrons are continuously emitted from the electrode. That is, in FIG. 2, when the contact 20 of the startup mode selection switch 17 is selected, the transistor 57 is turned on and the flip-flop 53 is turned on.
outputs "L", which causes flip-flop 52 to continue outputting "H". This state continues until the timer 58 times up, so that the smoothed output eventually has the waveform shown in FIG. 3b. Note that timer 5
The time until the time-up of 8 is set to a length that allows sufficient thermionic emission from the electrode 9 during this time and transition to an arc state.

As described above, even when starting an arc with a low current, it is possible to select an appropriate mode depending on the material of the electrode so as not to cause electrode wear and to prevent poor arc starting.

(g) Effects of the invention As described above, according to this invention, electrode wear can be prevented by selecting the mode, and arc start performance can be prevented from deteriorating. Therefore, there is an advantage that the life of the electrode can be extended.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a power supply device for an arc welding machine that is an embodiment of this invention, Figure 2 is a circuit diagram of a low frequency control circuit, Figure 3 is a diagram showing the output current waveform of each mode, and Figure 4. shows a circuit diagram of a conventional power supply device for an arc welding machine. 9... Electrode, 10... Base material, 16... Low frequency control circuit, 17... Starting mode selection switch.

Claims (1)

[Claims for Utility Model Registration] A first rectifier circuit connected to an alternating current power source and converting the alternating current power source into direct current; a high frequency conversion circuit that converts to high frequency; a transformer that is connected to the output side of the high frequency conversion circuit and transforms the high frequency voltage; and a transformer that is connected to the output side of the transformer and converts the output of the transformer into positive and negative. a second rectifier circuit that rectifies; a smoothing circuit that is connected to the output side of the second rectifier circuit and includes a smoothing reactor and a smoothing capacitor that smooths the rectified output; and a smoothing circuit that is connected to the output side of the smoothing circuit and that an opening/closing circuit which has a switching element and which switches the smoothing output of the smoothing circuit and applies positive polarity or negative polarity to the welding electrode and the base material; and a switching circuit that is connected to the smoothing output polarity switching control terminal of the opening/closing circuit and reduces the switching period. a low-frequency control circuit that controls frequency, and has a timer that measures a certain period of time from when the start switch is operated; a first mode that is connected to the timer and applies a positive smoothed output; and a first mode that applies a smoothed output of negative polarity. a startup mode selection switch comprising mode selection terminals for a second mode that applies a smoothed output and a third mode that alternately switches and applies positive and negative smoothed outputs; The circuit is configured to send a predetermined control signal to the opening/closing circuit so that only positive polarity smoothed output is applied to the welding electrode and the base material until the timer times up when the first mode is selected by the startup mode selection switch. and outputting a predetermined control signal to the opening/closing circuit so that only negative polarity smoothed output is applied to the welding electrode and the base material until the timer times up when the second mode is selected. a circuit, and when the third mode is selected, outputting a switching control signal to the opening/closing circuit, which alternately switches between positive and negative smoothed outputs regardless of the timer and is applied to the welding electrode and the base metal; A power supply device for an AC arc welding machine, characterized by comprising: