JPS6258824B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC arc stabilizing device for an AC arc welding machine that superimposes a high frequency current on a welding current.
The present invention provides an AC arc stabilizing device with excellent arc stability and starting characteristics.

In an AC arc welding machine, the output current passes through the zero point every half cycle, so the arc is repeatedly extinguished and ignited, resulting in problems such as arc instability and arc breakage due to failed re-ignition. Therefore, in AC TIG welding machines, as shown in Fig. 1, a high frequency voltage has been superimposed on the output voltage of the welding machine to facilitate restriking.

In FIG. 1, 1 is a welding transformer, 2 is a high frequency generator, 3 is a coupling coil, 4 is a torch, 5 is an arc, and 6 is a base material.

FIGS. 2a and 2b show the phase relationship between the high frequency generation phase and the welding current by a high frequency generator that has been commonly used in the past. FIG. 2a shows the welding current, and FIG. 2b shows the high frequency current superimposed on the welding current.

However, in the conventional device described above, high frequency waves are generated several to several dozen times during a half cycle, causing radio wave interference.

Therefore, as a measure to reduce radio wave interference, a method has been attempted in which a high-frequency current is singly superimposed when the welding current is re-ignited, but since the high-frequency current is generated only once every half cycle, if the re-ignition fails, the arc will be lost. This method had the disadvantage of being inferior to conventional methods in terms of arc stability, starting characteristics, etc.

The present invention eliminates the above-mentioned conventional drawbacks, and relates to an AC arc welding machine in which a high-frequency current is singly superimposed when the welding current is re-ignited. It provides a stabilizing device.

FIGS. 3a, 3b, and 3c are diagrams for explaining the operation of the present invention, where a is the no-load voltage waveform of the welding machine, and the shaded area is the high frequency generation phase range. b is a diagram showing an example of a high frequency generation phase, and c is a diagram showing an arc voltage and current at the time of ignition.

When the arc is started, both the welding electrode and the base metal are in a cold state, and a high no-load voltage of the welding machine is required to start the discharge.

However, if the high frequency is generated before the welding machine output voltage reaches a predetermined voltage (for example, 30V), the welding machine no-load voltage does not reach the discharge starting voltage, and the arc does not start.

On the other hand, if the high frequency is generated after the welding machine output voltage reaches its peak voltage, it will take time for the welding electrode to become a hot cathode, resulting in poor arc start characteristics.

The present invention is also characterized in that a single high-frequency current is generated when the welding machine output voltage reaches a predetermined voltage.According to the present invention, the above-mentioned conventional drawbacks are eliminated and good arc starting characteristics are achieved. can be obtained.

On the other hand, the same thing can be said about the stability of the arc as when starting the arc. When welding materials such as aluminum, which form an oxide film with a higher melting point than the base metal, arc breakage is likely to occur immediately after starting the arc or during multilayer welding. In other words, if the torch is fixed until a molten pool is formed even though it has been cleaned at the time of starting the arc, or if the torch is to be welded again in a place that has been welded and cleaned, the cathode must be attached to the base metal. Dots are difficult to form and arc breakage is likely to occur. The output voltage of the welding machine during steady arcing has the voltage waveform shown in Figure 3c, but arc breakage is particularly likely to occur when the polarity changes, and when arcing occurs, the no-load voltage as shown in Figure 3a appears. Therefore, if the high-frequency current is generated at an appropriate time, arc discharge as shown in FIG. 3c can occur instantaneously for the same reason as described at the time of arc start, and arc stability can be maintained.

FIG. 4 is a block diagram showing an embodiment of the present invention;
FIG. 5 is a specific circuit diagram of the main parts of FIG. 4, that is, a welding machine output voltage detector and a high frequency starting signal generator. Moreover, FIGS. 6a to 6f are diagrams showing the operating states of the main parts in FIG. 5.

In FIG. 4, the same parts as in FIG. 1 are given the same numbers.

In FIG. 4, 7 is a high frequency starting signal generator, and 8 is a welding machine output voltage detector that detects that the welding machine output voltage has reached a predetermined voltage (discharge starting voltage) in a half cycle after zero crossing.
The high-frequency starting signal generator 7 is operated by the output of the welding machine output voltage detector 8, and the output of the high-frequency starting signal generator 7 causes the high-frequency generator 2 to output a single high-frequency current. The current is superimposed on the welding machine output current via the coupling coil 3.

In the above configuration, when an arc start is to be performed, the welding machine output voltage is the welding machine no-load voltage shown in Figure 6a, and when this welding machine output voltage reaches a predetermined voltage after zero crossing, it is The welding machine output voltage detector 8 detects this, and the high-frequency starting signal generator 7 operates, and the output of the high-frequency starting signal generator causes the high-frequency generator 2 to generate a single high-frequency current, and this high-frequency current Since it is superimposed on the welding machine output current via the coupling coil 3, arc starting can be performed reliably.

On the other hand, the output voltage of the welding machine in the arc generation state is a rectangular wave shown in FIG. 6d, but when the polarity is reversed, it instantaneously becomes a pulse-like high voltage, and this high voltage exceeds a predetermined voltage. Therefore, when this high voltage reaches a predetermined voltage, the welding machine output voltage detector 8 detects this, which causes the high frequency starting signal generating device 7 to operate.
With the output of can.

In addition, Fig. 6 d is shown in a large vertical direction for easy understanding, and if the peak value of the no-load voltage shown in Fig. 6 a is approximately 80 V, the voltage shown in Fig. 6 d is The welding machine output voltage when the arc is stable is about 20~
It is about 25V.

Next, referring to FIG. 5, welding machine output voltage detector 8 and high frequency starting signal generator 7 in FIG.
The specific circuit will be explained.

In FIG. 5, 9 is a transformer, 10 to 14 are diodes, 15 is a generating diode for a photothyristor (not shown) that provides a high frequency starting signal,
16-20 are resistors, 21 is a capacitor, 22,2
3 is a transistor. One end of the resistor 20 is connected to the power supply (+B), and the emitter of the transistor 23 is grounded. Figure 6 a shows the output voltage waveform of the welding machine at no load, b and c show the operating states of transistors 22 and 23 at that time, d shows the welding machine output voltage at the time of arc occurrence, and e and f show the transistors at that time. 22 and 23 are diagrams showing operating states.

In FIG. 5, a full-wave rectified waveform of the welding machine output voltage is obtained at a point P on the anode side of the diode 10 and the diode 11, as shown in FIG.
Since one end of the resistor 17 is connected to the power supply (+B), the connection point Q between the resistor 6 and the resistor 17 is connected to the point P.
The voltage shown in FIG. 8 is obtained by shifting the voltage by B·R ₁₆ /R ₁₆ +R ₁₇ . Note that R ₁₆ and R ₁₇ are the resistance values of the resistor 16 and the resistor 17, respectively. Also,
In FIG. 8, there is a portion where the potential at point Q is a negative potential, but even if the magnitude of this negative potential is large, it will not become larger than the forward voltage drop of the diode 12. The transistor 22 is turned on when the voltage at point Q is equal to or higher than the voltage between the base and emitter of the transistor 22, and is turned off when the voltage at the point Q becomes equal to or lower than the voltage between the base and emitter of the transistor 22. Since the capacitor 21 and the resistor 19 constitute a differential circuit, only when the transistor 22 is turned off, the transistor 23 is turned on, the light emitting diode 15 is activated, the photothyristor is fired, and a high frequency can be generated. In other words, the phase when generating the high frequency is determined by the resistance value division ratio of the resistor 16 and the resistor 17. Therefore, by arbitrarily setting the resistance value division ratio of resistor 16 and resistor 17, the phase in which the high frequency is generated can be arbitrarily determined.

Note that the phase for generating the above-mentioned high frequency varies slightly depending on the shape of the electrode, etc., but in order to bring the no-load voltage of the welding machine to the discharge starting voltage and start the arc, the welding machine output voltage must be at a predetermined voltage (discharge starting voltage ), and it is preferable that the phase be before 90°, where it takes time for the welding electrode to become a hot cathode.

In addition, in this embodiment, the high frequency activation signal is generated by detecting the level of the welding machine output voltage, so as mentioned above, the phase for generating the high frequency during no load is changed when the welding machine output voltage reaches a predetermined voltage (for example, 30V). Even if the phase is set to 90 degrees, after an arc occurs, a high frequency wave can be generated instantaneously after the polarity is reversed by a rectangular arc voltage, as shown in d, e, and f in FIG.

As described above, the present invention has the advantage of realizing a single-shot high frequency superimposition type AC arc stabilizing device which has excellent arc stability and starting characteristics.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a welding machine equipped with a conventional AC arc stabilizing device, Figs. Welding machine output voltage waveform diagram under load,
Figure 3b is a high-frequency voltage waveform diagram of the same device, Figure 3c
4 is a block diagram of the device of the present invention, FIG. 5 is an electrical circuit diagram of the main parts of the device of the present invention, and FIGS. 6 a to 6 f are explanations of the operation of the device of the present invention. Figure 7 shows the point P of the electric circuit of the device of the present invention.
FIG. 8 is a voltage waveform diagram at point Q of the same electric circuit. 1...Welding transformer, 2...High frequency generator, 3...Cutplinder coil, 4...Torch,
5... Arc, 6... Base metal, 7... High frequency starting signal generator, 8... Welding machine output voltage detector.

Claims (1)

[Scope of Claims] 1. A welding machine output voltage detector that detects that the output voltage of the welding machine reaches a predetermined voltage in a half cycle after zero crossing, and a start signal that is activated by the output of the welding machine output voltage detector. A generator, a high frequency generator that generates a single high frequency current by the output of this starting signal generator, and a coupling coil that superimposes the single high frequency current generated from this high frequency generator on the output current of the welding machine. AC arc stabilizing device for AC arc welding machine. 2. The welding machine output voltage detector includes a rectifying circuit that rectifies the output voltage of the welding machine, two resistors connected in series that divides the output voltage of this rectifying circuit, and the above-mentioned 2.
A first transistor that receives as input the voltage at the connection point of the two resistors, a differentiating circuit that performs charging and discharging by turning on and off this first transistor, a second transistor that receives the output of this differentiating circuit as input, and this second transistor. An alternating current arc welding machine according to claim 1, characterized in that the starting signal generating device includes a photothyristor that is operated by the light emitted from the light emitting diode. Arc stabilizer.