JPH0138596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency pulsed arc welding circuit that stabilizes the pulsed arc current.

First, the operating principle of this type of high frequency pulsed arc welding circuit will be explained based on FIG. This first
In the high frequency pulsed arc welding circuit shown in the figure,
1 is a DC voltage source with an output voltage of E, 2 is a bridge circuit, and this bridge circuit 2 is connected in series with thyristors 3 and 4 (first and second current control elements), The connected thyristors 5 and 6 (third and fourth current control elements) are connected in parallel in the same current direction, and the thyristors 3,
A capacitor 7 (capacitance C) is inserted between the connection point of thyristor 4 and the connection point of thyristors 5 and 6. In addition, 8 is an induction coil (or wiring inductance) with inductance L, 9 is a welded object 10
and an electrode 11, and 12 indicates an arc.

In this configuration, when the thyristors 3 and 6 are ignited, a series resonant circuit is formed by the DC voltage source 1, the thyristor 3, the capacitor 7, the thyristor 6, the induction coil 8, and the welded part 9, and the capacitor 7 A half-sine current i ₁ flows according to the frequency determined by the capacitance C and the inductance L. This current i ₁
When the current i becomes zero, the thyristors 3 and 6 are turned off, and this current _i1 charges the capacitor ₇ , so when the current i1 becomes zero, the voltage across the capacitor 7 decreases.
Vc becomes maximum in the positive direction. Next, thyristor 4,
5 is ignited, a series resonant circuit is constructed by the DC voltage source 1, thyristor 5, capacitor 7, thyristor 4, induction coil 8, and welding part 9,
A half-sine current i ₂ flows through the capacitor 7 in the opposite direction to the above-described current i ₁ . When this current i ₂ becomes zero,
Thyristors 4 and 5 are turned off, and at this time the voltage Vc
is maximum in the negative direction.

The above operation can be repeated at high frequency using the ignition current Ig ₃₆ for thyristors 3 and 6 shown in Figure 2A and the ignition current Ig ₄₅ for thyristors 4 and 5 shown in Figure 2B. For example, it is possible to supply the welding portion 9 with a high-frequency sinusoidal half-wave pulsed arc current i as shown in FIG.

By the way, when using this type of high-frequency pulsed arc welding circuit, in order to weld the workpiece well, it is necessary to maintain the average value of the pulsed arc current at a predetermined constant value. It is extremely important to uniformly dissolve the However, in an arc load such as the welded part 9 shown in Fig. 1, the arc voltage generated between both ends of the welded part 9 is
The voltage iR generated by the constant voltage component Vo and the dynamic resistance R to the pulsed arc current i, such that Va is Va=Vo+iR
This dynamic resistance R varies greatly depending on the welding conditions (for example, the length of the arc 12). For example, when this dynamic resistance R increases, Q in the series resonant circuit including the capacitance C and inductance L described above decreases, so the amplitude of the voltage Vc across the capacitor 7 decreases, which causes the pulse arc current to decrease. When the peak value of i decreases and the unidirectional resistance R decreases, the amplitude of the voltage Vc increases because the Q increases, thereby increasing the peak value of the pulsed arc current i. C and D in Figure 2 are voltages associated with fluctuations in this dynamic resistance R.
It shows the changes in Vc and pulse arc current i. In this figure, period T ₁ is a constant value of dynamic resistance R ₀ , and period T ₂ is a constant value of dynamic resistance R greater than resistance value R ₀ . If the value R is ₁ , then the period T _{is 3}
correspond to the case where the dynamic resistance R is zero.

In this way, in the high-frequency pulsed arc welding circuit shown in Figure 1, the amplitude of the voltage Vc changes greatly in response to changes in the dynamic resistance R, and this also causes the average value of the pulsed arc current i to change greatly. I had a problem with it.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-frequency pulsed arc welding circuit that can maintain a constant average value of pulsed arc current.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram showing the configuration of an embodiment of the present invention, and in this figure, parts corresponding to those in FIG. 1 are given the same reference numerals. In FIG. 3, reference numeral 1 denotes a variable DC voltage source, which includes a rectifier circuit 1a that rectifies an AC input (not shown) using a thyristor whose conduction angle is controlled, and a chiyoke coil 1b that smoothes the rectified output of the rectifier circuit 1a. and a smoothing capacitor 1c. A saturable reactor 13 having a predetermined magnetic flux saturation characteristic is inserted in series with the capacitor 7 in the bridge circuit 2, and a primary winding 14a of a transformer 14 with a winding ratio of n:1 is inserted in parallel. ing. 15 is a full-wave rectifier circuit in which diodes 16, 17, 18, and 19 are bridge-connected;
The secondary winding 14b of the transformer 14 is inserted between 5a and 15b, and its positive DC output terminal 15c is connected to the positive output terminal 1d of the DC voltage source 1, and the negative DC output terminal 15c is connected to the positive output terminal 1d of the DC voltage source 1. Output end 15d is DC voltage source 1
It is connected to the negative side output terminal 1e of.

Next, the operation of this embodiment with the above configuration will be explained with reference to the time chart shown in FIG.

Now, at time t ₁ , the ignition current shown in A of Figure 4
When the thyristors 3 and 6 are made conductive by Ig ₃₆ and a pulsed arc current i flows as shown in D in the same figure,
The voltage Vc increases as shown in C of the figure. Then, when the voltage Vc becomes 0, the arc current i reaches its maximum value. (Current i flowing through capacitor 7
is 90° ahead of the voltage at both ends Vc. ) then
Voltage Vc further increases and current i decreases.
On the other hand, when the voltage Vc changes as described above, a voltage V ₂ is generated in the secondary winding of the transformer 14. Here, since the turns ratio of the transformer 14 is n:1, the voltage V ₂ becomes V ₂ =Vc/n. Next, when the voltage Vc further increases and reaches a constant voltage nE (E: output voltage of the DC voltage source ₁ ) at time t2, the voltage _V2 becomes _V2 =nE/n=E. That is, it becomes equal to the output voltage of the DC voltage source 1. As a result, the diodes 16, 19 (or 17, 18) become conductive, and the secondary side of the transformer 14 becomes substantially short-circuited via the diodes 16, 19, 17, 18 and the DC voltage source 1. (however,
The forward voltage drop of the diodes 16 and 19 is assumed to be approximately 0. ) As a result, the pulse arc current i after time _t2 starts to flow through the primary winding 14a of the transformer 14, and the current i _c1 flowing through the capacitor 7 becomes zero, so the voltage Vc becomes "nE". ” will no longer rise above that level. In this case, the power generated by the current flowing through the primary winding 14a of the transformer 14 (the shaded area D in FIG. 4) is supplied to the DC voltage source 1 via the transformer 14 and the rectifier circuit 15. be regenerated. In this case, the pulse arc current i after time _t2 does not follow the half-sine waveform shown by the dotted line, but decreases linearly, as shown in FIG. 4D.
Next, at time _t3 , when the thyristors 4 and 5 are made conductive by the ignition current Ig ₄₅ shown in FIG. is started. Then, when the voltage Vc reaches "-nE" at time _t4 , the pulse arc current i flows from then on through the primary winding 14a of the transformer 14 without going through the capacitor 7, in the same manner as in the above case. and the voltage Vc “−
It will no longer fall below nE. Also in this case,
Similar to the operation described above, the power generated by the current flowing through the primary winding of the transformer 14 is regenerated to the DC voltage source 1.

Thus, according to this embodiment, the arc 12
The dynamic resistance R at and the capacitance C of the capacitor 7,
The Q of the series resonant circuit determined by the inductance L of the induction coil 8 (Q of the series resonant circuit represents the increase ratio of the power supply voltage E as is well known) is the voltage
In the range where Vc is large enough to reach "nE" or "-nE", it is possible to clamp the voltage Vc to "nE" and "-nE", respectively, no matter how the dynamic resistance R changes. , that is, the amplitude of voltage Vc is "2nE"
As a result, the average value of the pulse arc current i can be held substantially constant.

Note that if you want to increase or decrease the average value of the pulse arc current i, change the conduction angle of the thyristor in the rectifier circuit 1a to increase or decrease the output voltage E of the DC voltage source 1.
This increases or decreases the amplitude of the voltage Vc by 2nE.
All you have to do is increase or decrease. Another method of increasing or decreasing the average value of the pulsed arc current i is to fix the output voltage E of the DC voltage source 1 and increase or decrease the ignition currents Ig 36 and ₄ of the thyristors 3 and 6 and the thyristors 4 and 5, respectively.
It is also possible to increase or decrease the period of Ig ₄₅ .

Further, in this embodiment, a saturable reactor 13 is inserted in series with the capacitor 7 in consideration of the case where this high frequency pulsed arc welding circuit is used for TIG welding or the like. This saturable reactor 13 reduces di/dt when the thyristors 3 to 6 are turned on and turned off, thereby preventing the pulse arc current i from entering the reverse polarity region. The arc 12 is further stabilized by this action.

As explained above, the high frequency pulsed arc welding circuit according to the present invention includes a direct current voltage source, a bridge circuit including first to fourth thyristors and a capacitor, and an induction coil connected in series. A transformer is connected in parallel to the capacitor, and the output of this transformer is full-wave rectified and regenerated to the DC voltage source. Therefore, the voltage across the capacitor in the bridge circuit can be adjusted to any arbitrary value using a simple circuit configuration. It is possible to clamp the pulse arc current to a constant value, which makes it possible to keep the pulse arc current constant regardless of the welding conditions, and because the fundamental characteristics of the pulse arc welding method are fully utilized, welding unevenness can be reduced. It is possible to perform extremely good welding without any blemishes. Further, according to the present invention, it is also possible to protect the circuit when the arc load is short-circuited. In addition, since a saturable reactor is inserted in series with the capacitor in the bridge circuit, the arc current will not enter the reverse polarity region, resulting in extremely stable TIG
It also becomes possible to perform welding, etc.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a conventional high-frequency pulse arc welding circuit, FIG. 2 is a time chart for explaining the operation of the circuit, FIG. 3 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG. The figure is a time chart for explaining the operation of the same embodiment. 1... DC voltage source, 2... Bridge circuit, 3...
...Thyristor (first current control element), 4...Thyristor (second current control element), 5...Thyristor (third current control element), 6...Thyristor (fourth current control element), 7... Capacitor, 8...
...Induction coil, 9...Welding section, 13...Saturable reactor, 14...Transformer, 15...Full wave rectifier circuit.

Claims (1)

[Claims] 1. A DC voltage source, first and second current control elements sequentially connected in series, and third and fourth current control elements sequentially connected in series in parallel in the same current direction. a bridge circuit in which a capacitor is inserted between a connection point of the first and second current control elements and a connection point of the third and fourth current control elements; and a wiring inductance or an induction coil. , are connected in series to form a resonant circuit, and the first and fourth current control elements and the second and third current control elements are alternately connected and inserted in series in the resonant circuit. In a high-frequency pulsed arc welding circuit that supplies a pulsed arc current to a part of the transformer, the transformer has a primary winding inserted in parallel to the capacitor, and
A high-frequency pulsed arc welding circuit comprising: a full-wave rectifier circuit connected to the next winding and having a DC output end connected in parallel to the DC voltage source. 2. The high frequency pulse arc welding circuit according to claim 1, wherein a saturable reactor is inserted in series with the capacitor.