JPS63281777A - Power unit for ac arc welding machine - Google Patents

Abstract

PURPOSE:To improve the directivity and stabilization of an arc by turning on and off the operation of a high-frequency conversion part with higher frequency than changeover frequency of the smooth output to make the smooth output pulsative when the smooth output is the straight polarity. CONSTITUTION:When a switching transistor control part 22 turns a transistor 36 on and selects the smooth output of the straight polarity, an operating signal is outputted to a low-frequency pulse generation circuit 40. When the low-frequency pulse generation circuit 40 receives said signal, it starts the monostable operation and outputs a low-frequency pulse to a high-frequency converter circuit control part 14. Then, the high-frequency converter circuit control part 14 controls an output current with the low-frequency pulse as a reference value. Accordingly, the output current is made to a waveform of said low-frequency pulse. By this method, the width of the arc becomes short and its directivity is improved and besides, it is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a power supply device for an AC arc welding machine that performs arc welding on aluminum or the like 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 has been put into practical use, which once converts a commercial power source into a high frequency wave, and then transforms the voltage and shapes the wave into a rectangular wave.

A circuit diagram of this power supply device for an arc welding machine is shown in FIG.

In this power supply device for an arc welding machine, as shown in the figure, a three-phase AC power source 7o is connected to a rectifier circuit 71 and a smoothing capacitor 7.
After rectification and smoothing in step 2, switching transistor 73.
74 and an output control circuit 75 perform high frequency switching to convert to high frequency (usually 2 to 20 KH2). Furthermore, the high frequency output is transformed to several tens to hundreds of tens of times with a transformer 76, and then a rectifier? 7.78, the smoothing reactor 79 and the smoothing capacitor 80 convert it back into direct current. After this, switching transistors 81, 82, 83, 84 and low frequency $1
A reverse switching operation is performed by the 1 t1 circuit 85 to obtain a highly accurate rectangular wave (usually 50 to 10 QHz) welding current. 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 frequency, the transformer and the accelerator 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 current detector 89. The current control of the control circuit 75 can be performed accurately with a fast response speed. Furthermore, AC arc welding can be performed by the inverse switching operation of the switching transistors by the low frequency control circuit 85, and DC arc welding can be performed by keeping either one of the switching transistors 81, 84 or 82, 83 on.

(C) Problems to be solved by the invention However, in the above power supply device for an AC arc welding machine,
When operating the arc in a small current range, the directionality and stability of the arc is poor, and the welding finish is poor, especially when welding aluminum, where welding is performed when the polarity is positive and cleaning is performed when the polarity is negative. there were.

In view of the above drawbacks, an object of the present invention is to turn on and off the operation of a high frequency converter at a frequency higher than the switching frequency of the smoothed output when the smoothed output is of positive polarity, thereby making the smoothed output pulse-like. An object of the present invention is to provide a power supply device for an AC arc welding machine that can improve arc directionality and stability.

(d) Means for Solving the Problems The power supply device for an arc welding machine of the present invention includes a first rectifier circuit that once converts an AC power source into a DC voltage, and a switching element that converts the DC voltage into a high frequency. , a high frequency conversion circuit that compares the reference value and the power supply output value and controls the on/off frequency or duty of the switching element based on the magnitude of the error; a first smoothing circuit that smoothes the positive rectified output; a second smoothing circuit for smoothing the rectified output of the first smoothing circuit;
and an opening/closing circuit that switches the smoothed output of the second smoothing circuit at low frequency and applies it to the welding electrode and the base material with positive polarity or negative polarity, and the opening/closing circuit selects the smoothed output with positive polarity. In some cases, the present invention is characterized in that a low-frequency pulse generation circuit is provided that sets the reference value to a low-frequency pulse having a higher frequency than the frequency at which the smoothed output is switched.

(e) Function In the power supply device for an arc welding machine according to the present invention, AC power is once rectified into DC power by the first rectifier circuit, and then converted into high frequency power by the switching element. At this time, the on/off frequency or duty of the switching element is set based on the comparison result (error) between the power supply output value and the reference value. Furthermore, the high frequency voltage is transformed by a transformer, and positive and negative rectified voltages are taken out by a rectifier circuit. These two rectified outputs are smoothed by a first smoothing circuit and a second smoothing circuit, respectively, and are applied to the welding electrode and the base material with positive or reverse polarity. At this time, positive polarity and negative polarity are alternately switched in the switching circuit to perform AC arc welding.

On the other hand, when the switching circuit selects positive polarity smoothed output, the low frequency pulse generation circuit sets the reference value in the high frequency conversion circuit control section to a low frequency pulse with a higher frequency than the frequency at which the smoothed output is switched. do. Therefore, the switching element of the high frequency conversion circuit section is modulated by the low frequency pulse, and the smoothed output becomes a pulse of the low frequency. When the smoothed output has negative polarity, the low frequency pulse generation circuit does not operate. At this time, the smoothed output is not pulse modulated.

Due to the above effects, the power output becomes a pulse with a frequency higher than the frequency that switches between positive and negative polarity when the polarity is positive, the width of the arc is shortened, the directivity is improved, and the stability is also increased. . Further, when performing aluminum welding, a cleaning effect is performed when the polarity is negative, but since low frequency pulse modulation is not performed when the polarity is negative, the cleaning effect is not bad.

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

In the figure, the first rectifier circuit 2 is composed of a full-wave rectifier circuit 10. The full-wave rectifier circuit 10 includes a three-phase AC power supply 1
It is connected to the. Furthermore, a series circuit of smoothing capacitors lla and llb is connected in parallel to the full-wave rectifier circuit 10. The smoothed DC voltage is supplied to the high frequency conversion circuit 3.

The high-frequency conversion circuit 3 includes series-connected transistors 12.13, which are switching elements connected to the transformer 4, and a high-frequency conversion circuit control section 14 that turns these transistors 12.13 on and off alternately. The high frequency conversion circuit control unit 14 compares the magnitude of the output current (power supply output) from the current detector 23 (described later) with a reference value, and determines the on/off duty or on/off frequency of the transistors 12 and 13 based on the error. Control. The reference value is set by a low frequency pulse generation circuit 40, which will be described later.

The primary winding of the transformer 4 is arranged between the connection point of the transistor 12.13 and the connection point of the capacitors lla, llb,
Transistor 12.13, smoothing capacitor 113.11
b and the primary winding of the transformer 4 constitute a half-bridge circuit.

The secondary output of the transformer 4 is rectified and smoothed, and selectively guided to the welding electrode 8 and the base metal by a switching circuit 7, which will be described later.

Diodes 31, 32, and 33 are connected to both terminals of the secondary winding.
．． A rectifier circuit 5 composed of 34 is connected. In the rectifier circuit 5, the rectified outputs of the diodes 30, 31, and 32 become positive with respect to the center tap, and the rectified outputs of the diodes 33, 34, and
The rectified output becomes negative with respect to the intermediate tap. This positive rectified output is guided to the smoothing axle 6a, and the negative rectified output is guided to the smoothing reactor 6b. A smoothing capacitor 6C is connected to the output side of the smoothing reactor 6a, and a smoothing capacitor 6d is connected to the output side of the smoothing reactor 6b.

Positive and negative smoothed outputs of the smoothing circuit including the smoothing reactor 6a and the smoothing circuit including the smoothing reactor 6b are led to the switching circuit 7. The switching circuit 7 is a transistor 36.37
and a switching transistor control section 22 that performs on/off control of these transistors.

In the switching circuit 7, during arc welding operation, the switching transistor control section 22 turns on the transistors 36 and 37 alternately to apply positive and negative smoothed outputs to the base material. As a result, a low frequency rectangular wave current is passed between the welding electrode 8 and the base material 9 to perform AC arc welding. The switching frequency at this time is a low frequency of about 50 to 100H2.

A high frequency oscillator 24 is connected to the welding electrode 8. This high frequency oscillator 24 is driven at startup to facilitate arc starting.

The output of the current detector 23 is transmitted to the high frequency conversion circuit control section 14.
and is compared with the reference value output from the low frequency pulse generation circuit as described above. High frequency conversion circuit control section 14
Then, those errors are eliminated (transistor 12.
13, the output current (power supply output) is eventually controlled to a magnitude corresponding to the reference value. Therefore, when the reference value is a constant value, the output current is subjected to constant current control during that time.

A low frequency pulse generation circuit 40 is connected to the switching transistor control section 22, and when the switching transistor control section 22 selects a positive smoothed output,
That is, when the transistor 36 is turned on, an operating signal is output to the low frequency pulse generation circuit 40.

When the low frequency pulse generation circuit 40 receives the operation signal, it oscillates a low frequency pulse to generate a high frequency conversion control unit 14.
Output for. When not receiving an operation signal, that is, when the switching transistor control section 22 turns on the transistor 37 and selects negative polarity, it outputs a signal at a predetermined level.

FIG. 2 is a circuit diagram of the low frequency pulse generation circuit 40.

This low frequency pulse generation circuit 40 includes an astable multi-by-break 51 and a monostable multi-by-break 52.

The astable multi-by-break 51 starts oscillating when it receives an operation signal from the switching transistor control section 22 . The output clock of this astable multivibrator is led to the input terminal of the monostable multipipe rake 52 to perform monostable operation. The monostable time setting is performed by the pulse frequency setter 43. A pulse current setter 41 is connected to the output Q of the monostable multi-bi break 52 and Q. A base current setter 42 is connected to each. The pulse current setting device 41 determines the height of the “H” pulse, and the base current setting device 42
determines the “L” height of the pulse. Pulse current setting device 4
1. The output of the base current setter 42 is the OR gate 54.5
5 to form a low frequency pulse, which is output to the high frequency conversion circuit control section 14 as a reference value.

Further, when the astable multi-by-break 51 does not receive an operation signal from the switching transistor control section 22, it does not perform astable operation. In other words, monostable operation is not allowed. At this time, a monostable multi-pipe break is used in which the output Q of the monostable multi-bi break becomes 'H.' Therefore, the high-frequency conversion circuit control section 2
The reference value outputted to 2 becomes the reference value of the level set by the pulse current setting device 41.

The frequency of the output pulse of the monostable multipipe rake 52 can be varied by the pulse frequency setter 42, but the range of frequencies that can be varied is a low frequency of about 10 to 12). However, the frequency is higher than the switching frequency by the switching transistor control section 22.

Next, the operation will be explained.

When the power is turned on, the commercial power supply voltage is converted into a high frequency by the transistors 12 and 13, which are switching elements. At this time, the high frequency conversion circuit side? The reference value outputted to B14 is the level set by the pulse current setting device 41. The switching frequency is set such that the magnitude of the current output is equal to this reference value. The voltage converted to a high frequency is transformed and smoothed, and the smoothed output is supplied to a load while being alternately switched between positive polarity and negative polarity at a low frequency by transistors 36 and 37. At startup, the high frequency oscillator 24 is driven by another circuit. This makes it easy to start an arc. When an arc starts and the output current begins to flow, the current flows through the current detector 23.
The result is sent to the high frequency conversion circuit control section 14 and compared with the reference value. The switching frequency and on/off duty of the transistors 12 and 13 are controlled so that the output current becomes equal to the reference value (.

During the above operation, when the switching transistor control section 22 turns on the transistor 36 and selects the positive smoothed output, the low frequency pulse generation circuit 40
Outputs an operation signal to. Low frequency pulse generation circuit 4
0 starts monostable operation upon receiving this signal, and outputs a low frequency pulse to the high frequency conversion circuit control section 14. Then, the high frequency conversion circuit control section 14 controls the output current using the low frequency pulse as a reference value. Therefore, the output current has the waveform of this low frequency pulse.

Since the output current is in the form of a low-frequency pulse, the width of the arc becomes shorter, the directivity becomes better, and it becomes more stable.

This effect is extremely large, especially when the current is small. In addition,
When negative polarity smoothed output is selected, the above reference value is set by the pulse current setting device 41 in order to prevent monostable operation.
The output current is at the level set by , and the output current does not change in a pulsed manner. Therefore, when aluminum is TUG welded, the effectiveness of the cleaning action performed with negative polarity is not reduced.

FIG. 3 shows a waveform diagram of the power supply device.

(a) to (e) in the figure are waveforms at positions (a) to (e) in FIG. 1. The period 3tliT1 in (e) is set by the pulse frequency setter 43, IF is set by the pulse current setter 41, and Is is set by the base current setter 42.

Note that the reason why the base current is set by the base current setting device 42 is to ensure stability of the arc.

Figure 4 shows the output current of positive polarity at a certain period (0.5~20H).
An example of creating a difference in height with z) is shown below. This can be achieved by providing another multi-by-break in the low-frequency pulse generation circuit 40 and using this oscillation output to reduce or not reduce the output of the monostable multi-by-break 52 by a certain level. By doing this, it is possible to control the penetration depth. Furthermore, when welding a vibrator or the like, it is possible to weld with a large current and cool it with a small current. In this case, the welded part will not sag (and good welding will be possible).

(g) Effects of the Invention As described above, in the power supply device for an AC arc welding machine according to the present invention, when the positive polarity is selected, the low frequency pulsed current becomes the welding current. In some cases, the width of the arc becomes smaller and the directivity becomes better, which has the effect of sustaining a more stable arc.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a power supply device for an AC arc welding machine which is an embodiment of the present invention. Fig. 2 is a circuit diagram of a low frequency pulse generation circuit, Fig. 3 is a waveform diagram during operation, Fig. 4 is an output current waveform diagram of another embodiment, and Fig. 5 is a conventional power supply device for an AC arc welding machine. FIG. 1-AC power supply, 2-first rectifier circuit, 3-high frequency conversion circuit, 4-transformer, 5-rectifier circuit, 7-switching circuit, 8-welding electrode, 9-base material, 40-low frequency pulse generation circuit.

Claims (1)

[Claims] (1) a first rectifier circuit that once converts an AC power source into DC;
A switching element that converts DC voltage into high frequency, and a high frequency conversion circuit control section that compares the reference value and the power output value and controls the on/off frequency or duty of the switching element based on the magnitude of the error. a transformer that transforms high-frequency voltage; a second rectifier circuit that rectifies the output of the transformer into positive and negative; a first smoothing circuit that smoothes the positive rectified output; and a first smoothing circuit that smooths the negative rectified output. and a switching circuit that switches the smoothed outputs of the first and second smoothing circuits at a low frequency and applies the smoothed outputs of positive or negative polarity to the welding electrode and the base material, the switching circuit A low-frequency pulse generation circuit is provided that sets the reference value to a low-frequency pulse having a higher frequency than the frequency at which the smoothed output is switched when the smoothed output of positive polarity is selected. Power supply device for AC arc welding machine.