JPS6320167A - Arc welding power source - Google Patents

Abstract

PURPOSE:To prevent an arc from running out by connecting the inverter side with the load side by a transformer to allow a welding current to flow to a bypass part with 3rd and 4th unidirectional switches as ON at the time of the low welding current and superimposing a high-frequency pulse current upon the welding current. CONSTITUTION:A control circuit 18 compares the welding current IW detected by a current detector 15 with a lower side reference current set value to turn the switch S8 on in case the welding current IW is lower than the set value. In case both of the switches S8 and S7 are ON, the welding current IW flows back via the switch S8 and a diode D12 and a part of the welding current excites the secondary side of the transformer 6. This exciting current is regenerated to a power source 1 via a primary side of the transformer 6 and diodes D2 and D3 and the welding current IW in the course of this time is made almost the same as the lower side reference current set values. Accordingly, the high-frequency pulse current can be superimposed upon the welding current and the arc is prevented from running out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an arc welding power source suitable for use in, for example, TIG (tungsten inert gas) welding.

[Prior Art] FIG. 4 is a circuit diagram showing the configuration of a walk-in arc welding power source. In the figure, l is a DC power source such as a battery (voltage is E), DI, D2, D3. D4 are diodes connected in series in opposite directions to both ends of the power source E, respectively. Each diode DI, D2. A switching element S1. is connected between the anode and cathode of D3 and D4. S2. S3. S4 is inserted in each case. In this case, the diodes D1 to D4 and the switching elements 5l-34 cause the inverter INV to
is configured. A smoothing reactor (including stray inductance in wiring) L1 arc starter AS1 electrode T1 arc A base material W is inserted in series between the output ends of this inverter INV. Then, a control section (not shown) detects the welding current 1w and appropriately controls the on/off of each switching element 5l-84 so that the average value of the welding current 1w matches the target value. .

FIG. 5 shows switching elements 81 to S in the above circuit.
4 general on/off control timing and welding current 1w
FIG. In this figure, a section 'ra is a section in which the welding current 1w flows in the direction of the arrow shown in FIG. 4, and a section Tb is a section in which the welding current 1w flows in the opposite direction (negative direction) to the above-mentioned arrow. Also, while the switching element S2 is turned on in the interval Ta, energy is stored in the reactor, and similarly, while the switching element S4 is turned on in the interval Tb, the energy is stored in the accelerator I in the opposite direction. Energy is stored. And sections T1, T
,...This is the section where the energy stored in the accelerator is circulated through the switch S3 and the diode DI, and the section T! , T, . . . The energy stored in the beams is transferred to the switching element S1. Diode D
This is the section where the water circulates through 3.

As can be seen from Figure 5 (Po), if the switch control described above is performed, the ripple of the welding current 1W will be reduced due to the smoothing effect of the reactor L, and the welding current 1W will remain at a constant level.
flows alternately in forward and reverse directions.

[Problems to be Solved by the Invention] By the way, in DC TIG welding, it is known that when a high frequency pulse current is superimposed on the welding current, the electromagnetic pinge effect increases and the stability of the arc is improved.

The electromagnetic pinch effect is a property in which the magnetic field generated by the arc current does not exert any force in the direction of reducing the diameter of the arc, and is a desirable property for stabilizing the arc. Therefore, the method of superimposing high-frequency pulsed currents is effective for welding thin plates that require low current welding and tend to have unstable arcs.

On the other hand, in the case of materials that are easily oxidized, such as aluminum, reverse polarity welding or AC welding, which has a cleaning effect to remove the oxide film, is often applied.

However, in the case of an AC welding power source, when welding thin materials, the average value of the welding current must be lowered, which has the disadvantage that the arc becomes unstable. Therefore,
It is conceivable to superimpose high-frequency pulses in the same way as in the case of a DC welding power source, but in the conventional AC welding power source shown in FIG. 4, it is difficult to superimpose the pulses as described below.

That is, in the circuit shown in FIG. 4, since there is a smoothing glue handle L, the ripple component is removed from the welding current as shown in FIG. 5, and therefore, high-frequency pulses cannot be superimposed. Therefore, if the reactor L is removed or set to a small value, as shown by the solid line in Figure 6,
di/dL can be set to a large value. in this case,
Due to the influence of reactor L and wiring stray inductance,
Although the waveform of the welding current 1W cannot be a perfect rectangular wave and becomes a triangular wave as shown in the figure, if the value of di/dt is large, a predetermined effect can be achieved. However, if the reactor L is set to a small value in this way, the smoothing effect disappears, so when the average value of the welding current 1w is small, the welding current fw becomes 0 as shown by the dashed line in FIG.
A problem has arisen in which a section where the arc is broken may occur.

This invention was made in view of the above-mentioned circumstances, and it is possible to superimpose a high-frequency pulse current on the welding current in an AC welding power source, and even when the average value of the welding current is set to a small value, arc breakage occurs. The purpose is to provide a welding power source that does not require any damage.

Means for Solving Problem E] This invention was made to solve the above-mentioned problem, and includes a transformer to which the output of an inverter is supplied to the primary side, and a transformer provided on the secondary side of this transformer. a first unidirectional switch that supplies current to the load from the forward direction; a second unidirectional switch that supplies current from the reverse direction; a third unidirectional switch that circulates the load current through a path different from that of the first unidirectional switch; and a third unidirectional switch that circulates the load current in the reverse direction through a path different from that of the secondary side and the second unidirectional switch. and a fourth unidirectional switch for circulating current, and the third and fourth unidirectional switches are turned on when the welding current falls below a predetermined value.

[Function] Since the inverter side and the load (arc side) are connected by a transformer, the load current is regenerated to the power supply via the transformer, which increases the di/dt of the arc current. 3. Since the fourth unidirectional switch is turned on, the welding current flows through a bypass path that does not go through a transformer, thereby reducing di/dt.
This prevents the welding current from becoming zero.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention. In the figure, parts corresponding to those in FIG. 4 described above are given the same reference numerals, and their explanations will be omitted.

In FIG. 1, 6 is a high frequency transformer whose primary coil is connected to the output end of the inverter INV, the cathode of the diode 13 is connected to one end of the secondary coil, and the anode of the diode 11 is connected to the switching element S7. connected via. The anode of the diode 13 is connected to the base material W via the switching element 9 and the current detector 15 in order, and the cathode of the diode II is connected to the cathode of the diode I2 and the current detector 15, respectively, and the switching element It is connected to the anode of the diode 14 via SIO. The other end of the secondary coil of the transformer 6 is connected to the anode of the diode 12 via the switching element S8, and is also connected to the electrode T via the secondary coil of the high frequency transformer 16, and is also connected to the cathode of the diode 14. has been done. 18 is a control circuit that performs on/off control of the switching elements 81 to S4 and switching elements S7 to SIO, and drive control of the arc starter +7, and the welding current 1w detected by the current detector 15 is set by the setting unit 22. On/off control is performed based on the peak current setting value 1p%, which is obtained by integrating the deviation between the average current setting value and the current feedback, and the lower reference current setting value ib. Also,
An oscillator is provided in the control circuit 18, and the switching elements are switched on/off based on the period of the output signal (frequency is 15 kHz or more) of the oscillator.

Next, the operation of this embodiment with the above configuration will be explained.

First, an average current setting value of 1 wa is input from the setting section 22.

Peak current setting value ipx and lower reference current setting value ib
is supplied to the control circuit 18. Then, the control circuit 18
Arc starter +7 is driven to generate arc 8, and during period T1 shown in FIG. 2, switching elements Sl and S4 are turned on and switching element S7 is turned off (all other switching elements are turned off). . As a result, on the secondary side of the transformer 6, a current flows along a path of switching element 7 -> diode Dll -> current detector 15 - base material W - electrode T. Here, the inductance of the secondary side wiring of the transformer 6 is L2, the primary coil of the transformer 6, 2
If the number of turns of the secondary coil is N+, Nt, and the voltage between the electrode and the base material is Va, the welding current IW is expressed by the following formula.

Iw= (EX (Nt/N1) Va)/L2...
(Then, the control circuit 18 integrates the deviation between the average value of the welding current 1W detected by the current detector 15 and a predetermined set value, and multiplies this integration result by a predetermined constant to obtain (96). (hereinafter referred to as integral deviation) is compared with the instantaneous value of welding current 1w.When welding current Iw exceeds the integral deviation, switching element Sl.

Turn off S4. When the switching elements Sl and S2 are turned off, the energy stored in the secondary side of the transformer 6 causes the current to turn to current 1 in the same path as in the period T11, and the welding current! W decreases rapidly. That is, period T5. to go into. The welding current rw during this period T1 is expressed by the following equation.

Iw-iipl (EX(Nu/N+)+Va)/L
t...(2) Next, the control circuit 18 is a current detector! 5 compares the welding current 1w detected by the lower reference current setting value ib, and when the welding current 1w falls below the lower reference current setting value ib, the switching element S8 is turned on.

At this time, the switching element S7 may remain on or may be switched off. And switching element S7
．． When both S8 are on, the welding current 1w circulates through the switching element S8 and the diode D12, and part of it excites the secondary side of the transformer 6. This exciting current flows through the primary side of the transformer 6 and the diode D2. It is regenerated to the power supply 1 via D3. On the other hand, when the switching element S7 is off and the switching element 68 is on, the welding current 1w circulates through the switching element S8 and the diode D12. That is, if the switching element S8 is on, all or part of the welding current 1w flows through the switching element S8 and the diode 12, which are the bypass path, in order.

Therefore, as shown in the period 'I'+s shown in Fig. 2, the value of di/dt becomes extremely small, and the welding current 1w during this period becomes Iw#1ibl - (3), and the lower reference current setting It becomes approximately equal to the value ib. Then, when one cycle (frequency is 15 kHz or more) of the output signal of the oscillator in the control circuit T8 ends, each switching element 5l-94, S7 to SIO is again put into the on/off state as in the case of the period T. . From then on, period T I
l+ T It+ T The same operation as T3 is performed, and after the series of operations from period Tll to T13 has been performed a predetermined number of times, switching cables S3 and S2 are turned on, and the welding current! Switch the direction of W. Then, during the period TII', only the switching cable S9 is turned on, and during the period T
1. In '', switching elements S3 . S2 is turned off and period T1
, ', the switching element S9 is turned on or off to turn on the switching element SIO. In this case, the switching of the switching elements in each section T11'' to T'+s is exactly the same as in the sections T11 to 'r13 described above, only the direction of the welding current IW is different. That is, each section 1l-T1. The value of the welding current 1W at ~T13' is also expressed by the above-mentioned equations (1) to (3). Also, the interval T,1
~T 1. The operation of the control circuit 18 in ' is also the same as in the above case.

In this embodiment, the above-mentioned periods have the following relationship.

T, /(T, +T1t"Tt3)=T++'BaTz"T
＋＊゛+Tta゛)＜(1/2) ・・・・・・(
4) This type of relationship was established for the following reasons. That is, in period 'I'11, E(V
) is applied, and -E (V) is applied to the transformer 6 during the regeneration period of period Tlt+T13. In this case, the regeneration period is the period T3. If it is shorter, biased magnetization will occur in the transformer 6,
Eventually, a situation will occur where the saturation occurs, but during the period T1. If is shorter than the regeneration period, the transformer 6 will be excited in the opposite direction by the same amount as it is excited in the forward direction, so that biased magnetization will not occur and saturation of the transformer 6 will be avoided.

Furthermore, the switching elements S7 and S9 switch only when polarity is changed, and the switching elements S8 . Since SIO switches only at low current,
In either case, the loss is small.

Next, FIG. 3 is a circuit diagram showing the configuration of another embodiment of the present invention. This embodiment includes a transformer 6 shown in FIG.
Instead, a transformer 6' having a secondary coil with a center tap is provided.

The Aiji coil is a switching cable Sl.

Excitation control is performed only in S4, and polarity reversal is not performed. In this case, the direction of the welding current 1w is switched by switching cables S7 and S9 provided on the secondary side. The operation of this circuit is exactly the same as that of the circuit shown in FIG. 1 described above. , In each of the above embodiments, the switching cables 5l-94, S7. S9
Since the switching is performed at a frequency of 15 kH2 or higher, there are no auditory problems during welding operations.

[Effects of the Invention] As explained above, according to the present invention, there is provided a transformer to which the output of the inverter is supplied to the primary side, and a transformer provided to the secondary side of this transformer to supply current to the load from the positive direction. a first unidirectional switch and a second unidirectional switch that supplies current from the opposite direction; and a second unidirectional switch that routes the load current in the forward direction through a route different from the secondary side and the first unidirectional switch. a third unidirectional switch that circulates the load current in the reverse direction, and a fourth unidirectional switch that circulates the load current in the reverse direction through a path different from the secondary side and the second unidirectional switch. Since the third and fourth unidirectional switches are turned on when the welding current falls below a predetermined value, the high-frequency pulse current can be superimposed on the welding current, and the welding current Even if the average value is set small, there is an advantage that arc breakage does not occur.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a waveform diagram showing a welding current of 1 W in the same example.
4 is a circuit diagram showing the configuration of a conventional welding power source, FIG. 5 is a waveform diagram showing a welding current of 1 W in the conventional welding power source, and FIG. 6 is a circuit diagram showing the configuration of another embodiment of the present invention. The figure is a waveform diagram when high-frequency pulse current is superimposed in a conventional welding power source. 11~! 4... Dyed (first to fourth unidirectional switches), S7 to SIO... (first to fourth unidirectional switches), S7 to SIO... (first to fourth unidirectional switches)
fourth unidirectional switch).

Claims (1)

[Claims] a transformer through which the output of the inverter is supplied to the primary side;
A first unidirectional switch that is provided on the secondary side of the transformer and supplies current to the load from the forward direction, a second unidirectional switch that supplies current from the reverse direction, and a load current in the forward direction. a third unidirectional switch that circulates the load current in the reverse direction through a path different from that of the secondary side and the first unidirectional switch; and a fourth unidirectional switch for circulating the welding current through a path different from the unidirectional switch, and the third and fourth unidirectional switches are turned on when the welding current falls below a predetermined value. Characteristic arc welding power source.