JPS6320631B2 - - Google Patents

Description

Detailed Description of the Invention The present invention rectifies the secondary AC voltage of a transformer to obtain a DC output with constant voltage characteristics or quasi-constant voltage characteristics, and provides a DC arc that automatically feeds consumable wire to perform welding. It relates to welding machines, and in particular to improving their arc starting characteristics.

Conventionally, in this type of DC arc welding machine, in order to reduce the ripple component of the rectified waveform and to suppress the short-circuit current value during short-circuit transition welding, as shown in Figure 1, the secondary side DC of the welding machine is The circuit usually includes a DC reactor. In FIG. 1, 1 is a DC power source including a transformer, 2 is a DC reactor, 3 is an arc as a welding load, and 4 is a base material.

However, in such a DC arc welding machine, the optimum inductance of the DC reactor 2 is different at startup and during a steady arc. In other words, it is preferable not to have the DC reactor 2 in order to obtain a welding current with a steep rise at startup, but if the inductance is too small during a steady arc, the short circuit current will extend too much in the short circuit transition region, causing a lot of spatter. Also, ripples are large in the globil region and the bead is not clean. On the other hand, if the inductance is too large, the short circuit current is suppressed too much and the pinch force for arc regeneration is insufficient, reducing the number of short circuits and obtaining a uniform bead. I can't do it anymore,
Therefore, appropriate inductance is required during steady arcing.

Conventionally, the necessary inductance during arcing was also present during arc starting, so measures to improve arc starting, such as hot starting and wire slowdown, were taken, but these efforts were not sufficiently effective.

The present invention has been developed in view of the current situation, and changes the inductance of the main circuit between arc starting and steady arc, thereby improving the arc starting characteristics without impairing the arc characteristics during steady arc. This is a dramatic improvement. Hereinafter, the DC arc welding machine of the present invention will be explained using the drawings of FIGS. 2 to 6.

FIG. 2 shows a block circuit of a DC arc welding machine according to the present invention, and in the figure, 1 to 4 are the first
The same parts as 1 to 4 in the figure are shown.

5 is a DC power source including a transformer and a rectifier, and 6 is a switching element that is opened after an arc occurs.

In addition, Fig. 3 shows the DC power supply (first DC power supply) 1
Current flowing from i ₁ and DC power supply (second DC power supply)
5 shows a timing chart of the current i ₂ flowing from 5. That is, after the arc starting signal T _S turns ON, the switching element 6 turns ON, and i ₁ with a steep rise without any delay element flows. After an instantaneous start with the power of _i1 , the switching element 6 is turned off _t2 seconds after the arc occurs. The circuit is configured such that the activation signal for the DC power source 1 is generated within t ₁ seconds, and the time t ₃ from when i ₂ flows until i ₁ flows is within 0 seconds to t ₂ seconds.

In addition, the DC power supply 5 according to the present invention supplies power of 12,000 VA to 75,000 VA as a result of experiments confirming that the product of no-load voltage (maximum output voltage) and output short-circuit current (maximum output current) has an appropriate value. It has to be possible.

Figure 4 shows the results of an experiment, in which the probability of instantaneous arc start was determined using a consumable wire of 1.2 mmφ, a welding current of 120 A, and a welding voltage of 19 V. Through this experiment, they found that it is sufficient to use a DC power source 5 that can supply power of 12,000 VA to 75,000 VA. In other words, if it is less than 12000VA,
It is not possible to supply enough power to start the arc, and as shown in Figure 5a, the arc breaks when starting the arc, but if it is 12,000 VA or more,
Since there is sufficient power for instant start, Fig. 5b
As shown in the figure, the Ata starts with one shot. However, if it exceeds 75,000 VA, the burning of the wire tip becomes large at the time of arc start, and the arc start characteristics deteriorate. Furthermore, it is not economical to increase the capacity of the DC power supply 5 more than necessary.

An embodiment of the present invention is shown in FIG. 6, where 7a and 7b are the primary winding and secondary winding of the transformer. 8a-8f are main thyristors, 6a-6c
The story is an auxiliary thyristor corresponding to the switching element 6 in FIG. 2, and 9 a current-limiting resistor that determines the maximum output current of the DC power supply in FIG.

In the circuit shown in FIG. 6, when gate signals are simultaneously applied to the main thyristors 8a to 8f and the auxiliary thyristors 6a to 6c by the activation signal, as is clear from the timing chart in FIG _.
flows and starts the arc, then at the same time as i ₁ flows
i ₂ is cut off.

As is clear from the above description, according to the present invention, arc starting characteristics are dramatically improved, and arc spot welding in particular contributes to improved welding quality and welding work efficiency during fully automatic welding. It is possible to obtain extremely excellent effects.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a conventional DC arc welding machine, FIG. 2 is a block circuit diagram of a DC arc welding machine according to the present invention, and FIG. 3 is a timing chart showing the operation of the block circuit of FIG. Figure 4 shows the experimental results of investigating the relationship between the capacity of the second DC power supply shown in Figure 2 and the instantaneous arc start success rate, and Figures 5a and b show the results shown in Figure 4, respectively. The capacity of the second DC power supply is 12000VA
FIG. 6 is an electric circuit diagram showing an embodiment of the present invention. 1... DC power supply (first DC power supply), 2... DC reactor, 3... Arc, 5... DC power supply (second DC power supply), 6... Switching element.

Claims (1)

[Claims] 1 The first having constant voltage characteristics or quasi-constant voltage characteristics
In a DC arc welding machine that performs welding by applying the output of a DC power source to a welding load via a DC reactor, a second DC power source capable of supplying power to both ends of the welding load without going through the DC reactor. When the arc starts, power is supplied from the second DC power source to the welding load, and after the arc occurs, power is supplied from the first DC power source to the welding load, and power from the second DC power source is connected. A direct current arc welding machine characterized by being configured to stop supply.