JPS6249143B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AC arc welding machine that superimposes a high frequency voltage on a welding voltage, and provides an AC arc stabilizing device that has good arc start characteristics and can reduce radio interference.

In an AC arc welding machine, the output current drops to zero every half cycle, and the arc repeats extinction and ignition. Therefore, problems such as arc instability and arc breakage due to restriking failure are likely to occur. Therefore, AC TIG welding machines have conventionally used a spark electrode oscillation method as shown in Figure 1 to superimpose a high frequency voltage on the output voltage of the welding machine to facilitate restriking and stabilize the arc. ing.

In Figure 1, 1 is a torch, 2 is an arc, and 3 is a torch.
is a base material, 4 is a welding machine transformer, 5 is a high frequency transformer, 6 is an oscillation capacitor, 7 is a spark electrode, 8 is a coupling coil, 9 is a high frequency generator, 10
is a high frequency bypass capacitor.

As the secondary voltage of the high frequency transformer 5 increases,
The voltage across the oscillation capacitor 6 also rises, and when the voltage exceeds the discharge starting voltage of the spark electrode 7, the charge charged in the oscillation capacitor 6 is discharged through the primary winding of the coupling coil 8, and at that time, the secondary side The voltage induced in the welding machine is superimposed on the output voltage of the welding machine. The oscillation center frequency at that time is = 1/2π√
It can be expressed as

(L is the inductance seen from the primary side of the coupling coil, C is the capacitance of the oscillation capacitor 6) Figure 2 a is the welding current waveform, b is the high frequency generation situation by a commonly used high frequency generator, and c is the high frequency. FIG. 3 is a diagram showing the generation phase of a high frequency wave in which a high frequency wave is generated only at the time of restriking to reduce noise. When the high frequency wave shown in FIG. 2b is generated, it causes radio wave interference. Measures to reduce interference caused by radio waves, televisions, etc. include reducing the frequency of high-frequency waves as shown in Figure 2c, narrowing the spark gap, and reducing the capacitance of the oscillation capacitor 6 as shown in the above equation. It has been considered to increase the oscillation center frequency and lower the oscillation center frequency, but if this method were used with the same input as before, the oscillation voltage would be lower than the high frequency voltage required for arc starting, making arc starting extremely difficult.

The present invention eliminates the above conventional drawbacks, provides good arc start characteristics even with the same input as the conventional one, lowers the spark oscillation frequency after detecting the welding current, and lowers its high frequency voltage. The aim is to reduce radio wave interference caused by radio waves.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 3, 11 is an oscillation capacitor, and 12 is a high-voltage switch (for example, a vacuum switch generally used to open and close a transformer for a microwave oven), which is turned on when welding current is detected. Further, 7' is a spark gap at two points connected in series. In Figure 3, at the time of arc start, both the welding electrode (tungsten electrode) and the base metal are in a cold state and do not have thermionic emission ability.
A high radio frequency voltage is required to start the discharge. Therefore, in the present invention, the high withstand voltage switch 12 is turned OFF at the time of arc start, and the electric charge charged in the oscillation capacitor 6 is discharged through the two spark gaps and the primary winding of the coupling coil, so that the electric charge sufficient for arc start is discharged. This ensures that a high frequency voltage can be obtained.

On the other hand, after transitioning to arc discharge, the electrode is hot, so
The high-frequency voltage required for restriking is only a fraction of the high-frequency voltage required for arc starting, and in the present invention, after detecting the welding current, short-circuiting one spark gap reduces the high-frequency output voltage, and Since capacitors 6 and 11 are connected in parallel,
The oscillation frequency is also lowered. FIG. 4 shows how the high frequency oscillation center frequency and the high frequency output voltage change at that time.

The present invention has the above configuration and has the advantage of having good arc start characteristics and being able to reduce radio wave interference during arc generation.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit diagram of a conventional AC arc stabilizing device, Fig. 2 a to c are waveform diagrams of various parts of the same device, and Fig. 3 is a main part of an AC arc stabilizing device according to an embodiment of the present invention. FIG. 4 is a diagram showing changes in high frequency voltage and frequency before and after welding current detection by the device of the present invention. 1... Torch, 2... Arc, 3... Base metal, 4... Welding transformer, 5... High frequency transformer, 6... Oscillation capacitor, 7'... Spark gap, 8... Coupling coil, 9... High frequency generator, 10... High frequency Bypass capacitor, 11...Oscillation capacitor, 12
...High pressure switch.

Claims (1)

[Claims] 1. In an AC arc stabilizing device for an AC arc welding machine that superimposes a high frequency voltage generated by a high frequency generator onto a welding voltage, a first oscillation capacitor is connected in parallel to the secondary side of a high frequency transformer that constitutes the high frequency generator. At the same time, the first and second spark gaps and the primary winding of the coupling coil are connected in series between the terminals of the first oscillation capacitor, and the connection point of the first and second spark gaps is connected in series. and one end of the first capacitor, and a switching means is provided in parallel with the first spark gap, and after arc starting, the first spark gap is switched to the switching means. An alternating current arc stabilizing device characterized by short-circuiting by means.