JPS6145978Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is a welding method suitable for an inert gas arc welding machine that is configured to detect the arc start of a non-consumable electrode inert gas arc welding machine using an AC power source by the flow of a positive current. It concerns an arc initiation detector.

Conventionally, in an inert gas arc welding machine using a non-consumable electrode such as tungsten, a high-frequency voltage is applied at the start of welding, but the welding arc does not necessarily start at the same time as the application of the high-frequency voltage. For this reason, the high-frequency voltage is attenuated or the electrode movement is started after the welding current actually starts to flow,
It is necessary to start the program control of the welding conditions. Conventionally, a relay was operated by combining a magnetic amplifier or a current transformer with a rectifier circuit, or in the case of a welding machine in which an auxiliary power circuit with a high no-load voltage is connected in parallel to the main power circuit of the welding current to stabilize the arc, a relay was directly connected across the current limiting resistor in the auxiliary power circuit and the start of the welding arc was detected by operating the relay. These conventional methods have the disadvantage that when light metals such as aluminum are welded with a non-consumable electrode using an AC welding power source, the true start of the welding arc cannot be detected. That is, when light metals are welded with a tungsten electrode, it is well known that there is a polarity effect in which a large amount of current flows in the positive polarity direction, where the electrode side becomes negative potential due to the difference in thermionic emission capacity, during welding, but conversely, when welding starts, only a current flows in the reverse polarity direction for a short time. The reason for this is that at the start of welding, the temperature of the electrode is low and it acts as a cold cathode, and the melting point of the tungsten electrode is higher than that of the workpiece, making it difficult to generate metal vapor, preventing the generation of a cathode spot, and as a result, the welding arc does not ignite when the tungsten electrode is the cathode and in positive polarity. The period during which this reverse polarity current flows lasts for several cycles or more, and since the power supplied from the power source during this period is reverse polarity, most of it is consumed to heat the electrode, so it does not contribute much to melting the workpiece, and during this period the arc is prone to extinction and is an unstable period. Therefore, the above-mentioned conventional device, which considers the welding arc to have been established simply because the welding current has flowed, generates a signal as if the welding arc had been started immediately at the beginning of this unstable period, and is therefore inaccurate in that it does not detect the true start of the welding arc.

The present invention focuses on the above, and is configured to start the welding arc when a positive current flows in AC arc welding.

FIG. 1 shows an example of a welding machine using the welding arc initiation detector of the present invention. In the figure, A and B are power supply terminals, to which AC power of 200V to 400V is usually supplied. 1 is a switch that was closed during welding, and 2 is a welding transformer. The output of the welding transformer 2 is supplied to the welding electrode 4 and the workpiece 5 via the welding arc starting detector 3. In the case of the figure, the welding arc starting detector 3 is composed of a current transformer 301 serving as a current detector, a load resistor 302, and a diode 303 forming a half-wave rectifier circuit. A high frequency voltage that helps start the welding arc is superimposed on the secondary circuit of the welding transformer 2 through which welding current flows by a high frequency generating circuit 6 and coupling coils C, C. C1 and C2 are bypass capacitors that prevent high frequency voltage from entering the welding transformer. When the switch 1 is closed at the start of welding, the output voltage of the welding transformer 2 is applied to the electrode 4 and the workpiece 5, and at the same time, the output of the high frequency generation circuit 6 is applied through the coupling coils C and C. , a spark discharge is generated between the electrode 4 and the workpiece 5 to induce a main welding arc. When this welding arc is started, as described above, a current flows only in the direction of the reverse polarity, that is, from the electrode 4 to the workpiece 5, and after the electrode 4 is heated by this current, a true current including a current in the positive polarity direction flows. Welding arc occurs. As shown in the figure, the rectifier 303 that constitutes the welding arc starting detector 3 switches the current transformer 30 when a positive current flows.
Since they are connected in the direction of conduction depending on the terminal voltage of the load resistor 302 of No. 1, an output is generated from the moment a positive current flows to the output terminals a and b, and this signal can be transmitted directly or through an arc. A signal that is delayed for a certain period of time until it stabilizes is used as a starting signal for the welding arc to move the electrode, attenuate the high-frequency voltage, start a welding condition program, etc.

As described above, in the present invention, the conduction of positive polarity current is detected and used as a starting signal for the welding arc.
Operation becomes reliable without confusing the unstable period at the start of welding.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an example of a welding machine using the welding arc initiation detector of the present invention. 2... Welding transformer, 3... Welding arc starting detector, 301... Current transformer, 302... Load resistor,
303...Diode.

Claims (1)

[Scope of utility model registration request] In a non-consumable electrode inert gas arc welding machine that uses an AC power source, there is a current detector that detects the output current of the welding transformer, and a half-wave rectifier that extracts only the signal corresponding to the positive polarity current from the output signal of the current detector. A welding arc initiation detector comprising a circuit.