JPS6342550B2 - - Google Patents

Description

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

Conventionally, this type of DC arc welding machine includes a DC reactor in the secondary DC circuit of the welding machine in order to reduce ripples in the rectified waveform and to suppress the short-circuit current value during short-circuit transition welding. It's normal.

However, in such a DC arc welding machine, the optimum inductance of the DC reactor is different during startup and during steady arc. In other words, in order to obtain a welding current with a steep rise, it is preferable not to have a DC reactor 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. However, in the globil region, the ripples are large 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 number of short circuits is reduced due to insufficient pinch force for arc regeneration, making it difficult to obtain a uniform bead. is no longer possible and therefore requires appropriate inductance 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. 1 to 10.

FIG. 1 shows a block circuit of a DC arc welding machine according to the present invention. In the figure, 1 is a first DC power source including a transformer and a rectifier, 2 is a DC reactor, and 3 is between a wire and a base material 4. 5 is a second DC power source including a transformer and a rectifier, and 6 is a switching element that is opened after the arc occurs.

Further, FIG. 2 shows a timing chart of the current i ₁ flowing from the first DC power supply 1 and the current i ₂ flowing from the second DC power supply 5. That is, after the arc starting signal T _S turns ON, the switching element 6 turns ON, and after an instantaneous start with the power of i ₂ with a steep rise without any delay element, the switching element 6 turns on for t ₂ seconds after the arc occurs. Turn off later. The circuit is configured such that the activation signal of the first DC power supply 1 is generated within t ₁ second, and the time t ₃ from when i ₂ flows until i ₁ flows is within 0 seconds to t ₂ seconds. There is.

An embodiment of the present invention is shown in FIG. 3, where 7a and 7b are the primary winding and secondary winding of the transformer. 8a-8f are main thyristors, 6a-6c
1 is an auxiliary thyristor corresponding to the switching element 6 in FIG. 1, and 9 is a current limiting resistor that determines the maximum output current of the second DC power supply 5 in FIG.

21 is an arc voltage detector that detects the arc voltage between the wire and the base material 4, and 22 is an auxiliary thyristor 6a when an output signal is input when the arc voltage detector 21 detects that an arc has occurred.
This is a drive circuit that cuts off and turns off the supply of gate signals to ~6c.

In the circuit shown in FIG. 3, when a gate signal is simultaneously applied to the main thyristors 8a to 8f and the auxiliary thyristors 6a to 6c by the activation signal, _i2 which does not pass through the DC reactor 2 flows, and then i which passes through the DC reactor 2. ₁ flows. When i ₂ flows and an arc occurs in the welding load, the arc voltage detector 21 detects the occurrence of an arc, and the arc voltage detector 2 at this time
1 output signal is input to the drive circuit 22, the drive circuit cuts off the supply of gate signals to the auxiliary thyristors 6a to 6c, and the auxiliary thyristors 6a to 6c are turned off. In other words, i ₂ is cut off. This start signal and i ₂ and
The time chart for i ₁ is shown in Figure 2.

By the way, with the starting method described above (hereinafter referred to as the bypass starting method), it is still not possible to obtain a reliable arc start. In other words, even with such a bypass starting method, if the wire tip ball is large at the time of arc starting, for example, 150A
There are disadvantages in that a large current is required and a large capacity power source is required, and the larger the welding current, the larger the ball at the tip of the wire becomes, reducing the success rate of the next arc start.

Therefore, in the present invention, in addition to such a bypass starting method, control (hereinafter referred to as
It is configured to perform ball-less control).

Figure 4 shows the output voltage waveform and the shape of the wire tip when the arc is extinguished when this ballless control is not performed, and Figure 5 is the output voltage waveform when the arc is extinguished when the ballless control is performed. and wire tip shape. When ballless control is performed as in the present invention, the wire tip ball becomes smaller, which reduces the amount of melting heat at the wire tip, resulting in a smaller welding current. This makes it easier to start the arc the next time.

Also, the smaller the current i ₂ that flows from the second DC power supply 5 when starting the arc, the cheaper the price for constructing the second DC power supply 5, so it is better to make i ₂ as small as possible. If ₂ is made small, the arc start success rate will decrease.

In such cases, as shown in Figure 6, hot start control is used to set the output voltage to a high value before arc start and then switch to a steady voltage after arc start, and as shown in Figure 7, output voltage is set high before arc start. If wire slowdown control is performed in which the wire feed speed is slowed down and returned to a steady speed after arc start, a good arc start can be achieved even if the current i ₂ is made small.

In this way, the present invention employs the bypass starting method explained above when starting the arc, and performs the ballless control explained above when extinguishing the arc. In addition to this, by combining the above-mentioned hot start control and wire slowdown control, the configuration cost of the DC power supply can be reduced, and the arc start It is possible to maintain a high success rate.

FIG. 8 is a diagram comparing the arc start performance of the DC arc welding machine according to the embodiment of the present invention with the arc start performance of a conventional machine, and shows the relationship between welding current and arc start success rate in each case. It shows. In the embodiment of the present invention (broken line 10) in which a bypass start-up method and ballless control are performed, and these are further combined with hot-start control and slow-down control, the configuration cost of the second DC power supply 5 can be reduced. As shown in the figure, extremely good characteristics are obtained, with an arc start success rate of 80 to 90% regardless of the magnitude of the welding current. In addition, in the comparison machine (broken line 11) that uses the bypass starting method but does not perform bead-free control, the welding current is
An extremely high arc start success rate of 90% was obtained up to 150A, but as the welding current was increased above 150A, the arc start success rate rapidly decreased.

This means that if ball-free control is not performed, the larger the welding current is, especially when the welding current is 150A or more,
This is thought to be because the wire tip ball becomes larger and the amount of heat required to melt the wire for the next arc start increases, making the next arc start difficult. In addition, conventional machine A (broken line 12) uses only hot start control, slowdown control, and ballless control without using the bypass starting method, and hot start control and slow speed control without using the bypass starting method or ballless control. Only down control is used. Conventional machine B (broken line 13)
60, regardless of the magnitude of the welding current.
It can be seen that only a low arc start success rate of less than % was obtained.

Note that the second DC power supply 5 according to the present invention shown in FIG.
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 must be capable of supplying power of 12,000 VA to 75,000 VA.

Figure 9 shows the results of the experiment, in which the consumable wire was 1.1 mm, the welding current was 120 A, and the welding voltage was
This is the probability of instantaneous arc start at 19V. 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 12,000VA, it will not be possible to supply enough power for arc start, and arc breakage will occur when starting the arc, as shown in Figure 10a, but if it is 12,000VA or more, it will be sufficient for instant start. Figure 10b
As shown in the figure, the arc 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.

As is clear from the above description, according to the present invention, arc starting characteristics are dramatically improved, and this contributes to improved welding quality and welding work efficiency, especially during arc spot welding and 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 DC arc welding machine according to the present invention, FIG. 2 is a timing chart showing the operation of the block circuit of FIG. 1, and FIG. 3 is an electric circuit diagram showing an embodiment of the present invention. Figures 4 and 5 are diagrams for explaining ballless control, Figure 6 is a diagram for explaining hot start control, Figure 7 is a diagram for explaining slowdown control, and Figure 8 is a diagram for explaining the main control. A diagram comparing the performance of a DC arc welding machine according to an embodiment of the invention and a conventional machine. Figure 9 is an experiment to investigate the relationship between the capacity of the second DC power supply shown in Figure 1 and the instantaneous arc start success rate. The results are shown in Figures 10a and 10b for the results shown in Figure 9 when the capacity of the second DC power supply is less than 12,000 VA and when the capacity is 12,000 VA.
It is a figure which shows the welding current waveform at the time of arc start in the above case. DESCRIPTION OF SYMBOLS 1... First DC power supply, 2... DC reactor, 3... Arc, 5... Second DC power supply, 6...
...Switching element.

Claims (1)

[Claims] 1. A first DC power supply that has constant voltage characteristics or quasi-constant voltage characteristics and whose output voltage gradually decreases or decreases to a constant voltage when stopped, and the output of this first DC power source is connected to a wire via a DC reactor. In a DC arc welding machine that performs welding by applying a welding load to a base material, a second DC power source is connected to both ends of the welding load without going through the DC reactor, and the second DC power source and the welding load, a means is connected between the welding load and the welding load.