JPS6230072B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to pulsed arc welding for use in pulsed arc welding of a gas shield using a consumable electrode in an inert gas such as argon gas or a gas mixture of oxygen, carbon dioxide, etc. with an inert gas. It is related to power supply.

Generally, in pulsed arc welding, a low-output base current is passed between an electrode and a base metal, and a pulsed current is supplied at an arbitrary period to be superimposed on the base current to perform welding. When the welding current is a pulsed current, the molten metal at the tip of the fed wire becomes spray-like small particles due to the pinch force when the current is large and separates from the tip at high speed, resulting in spatter. It has the advantage of having less

A conventional pulse arc welding power source is shown in FIG. In the figure, 1 is a three-phase transformer, 2 is a rectifier that rectifies the output of three-phase transformer 1, 3 and 4 are current-limiting resistors that limit the current flowing from the rectified output to the load, and 5 is a base current. It is a switching device that switches three-phase transformer 1, rectifier 2, current limiting resistors 3, 4,
The switch 5 constitutes a base current supply power source that supplies base current to the load. 6 is a single-phase transformer, and 7 is a controlled rectifier having a control element such as a thyristor.The single-phase transformer 6 and controlled rectifier 7 constitute a pulse current supply power supply that supplies pulses to the load, and serves as a base current supply power supply. Current is supplied to the load in parallel. Note that 8 is a consumable electrode, 9 is a base material, and 10 is a reactor that limits excessive current when the electrode 8 is short-circuited to the base material 9.

However, the pulsed arc welding power source shown in Figure 1 generates pulses by controlling the phase of a power source using a commercial frequency, so the peak value of the pulse current changes greatly depending on the control angle, and the spray effect is reduced. Because of this, uniform welding results cannot be obtained. For example, if the pulse current is less than the critical current value for spray welding, the pulse width will be narrow and the droplets will become a large lump larger than the wire diameter and transfer irregularly. On the other hand, if the pulse current exceeds the critical current, the droplets will become finer and a relatively stable spray transfer will be possible, but if the pulse current becomes even larger, the pulse width will become wider and too much heat will be input into the base material, causing the droplets to become finer. If it is a thin plate, melting may occur. Therefore, in order to perform optimal welding, it was necessary to vary the base current as well as the pulse current. In addition, when welding a narrow gap, if high arc welding is performed, the arc will spread too much, the molten metal will not transfer smoothly to the base metal, and the state of shielding by the shielding gas will deteriorate. Welding defects were likely to occur. Furthermore, since a single phase is used to supply the pulse current and a three-phase is used to supply the base current, an imbalance occurs in the input current, causing other equipment connected to the input power supply to malfunction. There were negative effects such as

The present invention eliminates the above-mentioned drawbacks of the prior art and balances the three-phase input current to provide an optimal welding current that provides a high-quality weld with smooth welding transition and a stable welding arc. The purpose is to provide a pulsed arc welding power source that outputs pulsed arc welding power.

FIG. 2 is a circuit diagram showing one embodiment of the present invention. In FIG. 2, the same reference numerals as in FIG. 1 indicate the same functions in the same figure. 11 is a welding transformer whose secondary side is star-connected; 12 is a rectifier that performs full-wave rectification or controlled rectification of the output of the welding transformer 11; 13 is a capacitor that smoothes the output of the rectifier 12; and 14 is a A chopper supplies smoothed DC voltage to an on-off welding load by a control element such as a transistor or a thyristor, 15 is a control device for controlling the switching operation period of the chopper 14, and 16 is a secondary side connection of the welding transformer 11. is the first current limiter that is connected to the neutral point of the star-shaped connection and supplies the base current, 17 is a diode that prevents the base current from flowing back into the first current limiter, and 18 is the output of the rectifier 12 and the load. A second current limiter is provided between the welding load and the welding load and supplies a superimposed current to the welding load.

Now, when the input power is applied to the welding transformer 11, the welding transformer 11 transforms it to the required voltage,
The voltage is rectified by a rectifier 12 and smoothed by a capacitor 13. The smoothed DC voltage is
A superimposed current having a high no-load voltage and a large droop flows, which is applied between the electrode 8 and the base material 9 via the second current limiter 18, as shown in FIG. 3a. In addition, a three-phase half-wave rectifier circuit constituted by diodes D ₁ , D ₂ , and D ₃ of the rectifier 12 is applied between the electrode 8 and the base material 9 via the first current limiter 16, as shown in FIG. It has a low no-load voltage indicated by b, and a base current with small droop flows. Then, the control device 15 sets the continuity of the chopper 14 to a desired point in the optimum range for pulsed arc welding, that is, the range A in FIG. 4, for example, the pulse width is 0.5 msec, and the pulse current is set to 600 A.
Between the pulse currents, a diode 17, a first current limiter 16, an electrode 8, a base material 9,
A base current of three-phase half-wave current flows through the diodes of the rectifier 12. When the chopper 14 conducts from this base current and a pulse current flows, the diode 17 is reverse biased and the base current is cut off. When the base current is interrupted, reactor 1
0, the rise of the pulse current is delayed and the pulse current tries to break off, but since a small current flows to the load via the second current limiter 18, the arc continues and the pulse current flows to reach the optimum level. Pulsed arc welding is performed.

In addition, Fig. 4 shows the results of photographing the arc phenomenon using a high-speed camera and finding the optimal value of the pulse arc, where range A is the optimal range and range B is the optimal value.
Range C is the region where the droplet does not transfer reliably due to insufficient energy, and the droplet may become larger than the wire diameter. Range C is the region where the heat input to the base material is excessive and the base material is a thin plate. Melting occurs.

In the above embodiment, the diode of the rectifier 12 is used to generate a three-phase half-wave current of the base current, but the diode may be replaced by a thyristor, and the thyristor may be made fully conductive. When changing the desired value in range A, the control device 15 changes the pulse width of the chopper, controls the control element of the rectifier 12, varies the output of the rectifier 12, and adjusts the pulse current to match the pulse width. Bye.

As described above, the pulsed arc welding power source of the present invention obtains the pulse current and pulse width necessary for pulsed arc welding using the rectifier and chopper, and uses the welding transformer, rectifier, and first current limiter to obtain the base current and pulse width necessary for pulsed arc welding. and the second voltage is applied to the load from the output of the rectifier.
Since a current limiter is installed to obtain a superimposed current, the optimal pulse for pulsed arc can be obtained, resulting in high-quality welding. Furthermore, since a common power source is used for the pulse current and the base current, unbalance in the input current is unlikely to occur, and adverse effects such as malfunction of other devices can be avoided.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional pulsed arc welding power source, Figure 2 is a circuit diagram of an embodiment of the pulsed arc welding power source of the present invention, and Figure 3 is an output characteristic diagram of the base current and superimposed current in Figure 2. , FIG. 4 is a characteristic diagram of the pulse width and pulse current of the pulsed arc welding power source of FIG. 2. 11... Welding transformer, 12... Rectifier, 14... Chopper, 15... Control device, 16, 18... Current limiter,
17...Daio.

Claims (1)

[Claims] 1. A welding transformer in which the secondary winding is star-connected,
A rectifier that rectifies the output of this welding transformer, a chopper that turns on and off the output of this rectifier and supplies pulsed current to the welding load, and a chopper that is provided between the neutral point of the welding transformer and the welding load. A pulse arc welding machine comprising a first current limiting element and a second current limiting element provided between the output of the rectifier and the welding load.