JPH0796367A - Arc welder - Google Patents

Abstract

(57) [Abstract] [Purpose] While maintaining high ignition recovery performance, the wiring inductance absorbs excessive transient voltage generated in the low-frequency AC converter to the auxiliary current power supply side, and the auxiliary voltage due to this absorption is absorbed. Provided is an arc welder that suppresses a rise. A low-frequency AC converter that converts a main DC voltage into a low-frequency rectangular-wave AC voltage, applies this to a welding load (31, 32), and generates a positive polarity period and a reverse polarity period of the welding load. 20 and an auxiliary DC power source (37, 38, 39) for generating an ignition recovery auxiliary DC voltage higher than the main DC voltage,
Re-ignition recovery promoting means (40, 41, 42, 4) for supplying the auxiliary DC voltage to the converter to superimpose it on the main DC voltage.
3, 44, 45) are provided, and the re-ignition recovery promoting means supplies the auxiliary DC voltage within a predetermined time after the positive polarity of the welding load is changed to the reverse polarity and within a predetermined value of the auxiliary DC voltage. It has a timing means to do.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc welder used for AC arc welding.

[0002]

2. Description of the Related Art Generally, in AC arc welding, the current flowing through a welding load is publicly proclaimed, and the load alternates between positive polarity and reverse polarity every half cycle, during which the welding current is zero-crossed at each polarity transition. Then, since the arc is interrupted, it is necessary to re-ignite the arc each time.

When a metal that is easily oxidized, for example, aluminum is used as the base material for the welding load, if a sinusoidal alternating current is supplied to the welding load, the base material will not have a half cycle of the reverse characteristic in which the negative electrode becomes positive. Although the oxide film on the surface of the base material is removed by the cleaning action, the energy immediately after the polarity transition is insufficient, the electron discharge is not good, and the arc re-ignition becomes difficult. Therefore, in the conventional arc welder used for this type of AC arc welding, the sine wave of the welding current is changed to a rectangular wave to improve the re-ignition characteristic of the arc.

In such a rectangular wave type arc welder,
For example, as shown in FIG. 5, the AC power supplied to the power input terminal 1 is the input rectifier 2 of the diode bridge configuration.
After being rectified and smoothed by the smoothing capacitor 3, it is applied to the high frequency AC converter 4. This conversion device 4
It is composed of full bridge inverters of switching elements 5 to 8 such as IGBT and MOSFET, and is controlled by the high frequency inverter controller 9 to convert the input DC current into a high frequency AC current. The high frequency AC output of the converter 4 is supplied to the primary winding of the main transformer 10, and the high frequency AC output of the secondary winding 10b thereof is rectified by the main rectifier 11 having a diode bridge configuration. The DC output of the rectifier 11 is smoothed by the DC reactor 12 and supplied to the low frequency output converter 20. This conversion device 20
Switching elements 21 to 24 such as GBT and MOSFET
Of full-bridge inverter, which is controlled by the low-frequency inverter controller 25 to reduce the input DC current to 1
It is converted into a low-frequency rectangular-wave alternating current of 0 Hz to several 100 Hz, and this is supplied to the electrode 31 and the base material 32 that form the welding load. Diodes 26 to 29 for preventing reverse voltage are connected in antiparallel to the switching elements 21 to 24, respectively.

The welding current becomes an alternating current of a rectangular wave, has a large energy when the polarity is changed, and the re-ignition characteristic is improved. However, when the welding current is a small current, the energy stored in the DC reactor 12 is insufficient. Therefore, the base material 32 is positive and the electrode 31 is negative, so that the base material 32 is negative and the electrode 31 is positive. Hard to re-ignite when moving to the opposite polarity.

To compensate for this drawback, an auxiliary DC power supply is provided. That is, this auxiliary DC power supply is the main transformer 10
By rectifying and smoothing the AC output of the third winding 10C by the auxiliary rectifier 38 and the capacitor 37, an auxiliary voltage for ignition recovery higher than the main DC voltage is generated. This auxiliary voltage is passed through the current limiting resistor 54 to the low frequency AC converter 20.
Is supplied to the input side of and is superimposed on the main DC voltage. This auxiliary voltage enhances the no-load voltage during the transition of the welding load polarity, accelerates the recovery of the ignition state and eliminates the above-mentioned drawbacks.

The diode 36 connected in parallel with the current limiting resistor 54 is for absorbing the transient voltage and is used for the low frequency AC converter 20.
It works to prevent the transient rise of the input voltage of. That is, when the cable from the output end of the converter 20 to the load is long and its inductance 35 cannot be ignored,
Due to the switching operation of the switching elements 21 to 24, excessive transient voltage due to the inductance 35 thereof tends to be generated on the input side of the conversion device 20 via the diodes 26 to 29. However, at this time, the diode 36 conducts, the transient voltage is absorbed by the capacitor 37, and the rise of the voltage on the input side of the conversion device 20 is controlled.

However, in recent years, in order to increase the concentration of the arc, a high frequency may be supplied to the welding load, and it is required that the distance from the output end of the welding machine to the welding load be very long. Moreover, expansion of current capacity is required.

If such requirements are pursued, the inductance of the cable increases, the charging voltage of the capacitor 37 increases due to the transient voltage, and the allowable voltage of the capacitors 37 and the switching elements 21 to 24 of the low frequency AC converter 20 is exceeded. May be damaged. Therefore, the voltage detector provided in parallel with the capacitor 37 detects the voltage, and when the voltage reaches a predetermined value, the charge of the capacitor 37 is discharged. That is, a series circuit of a switching element 51 and a discharge resistor 52 is provided in parallel with the capacitor 37, the switching element 51 controls the discharge switch control device 53 by the output signal of the voltage detector 40, and the voltage across the capacitor 37 is set to a predetermined value. When the value is reached, the electric charge of the capacitor 37 is discharged through the switching element 51 and the resistor 52, and when the voltage across the capacitor 37 drops to the second predetermined value,
The switching element 51 is turned off to stop the discharge.

[0010]

However, the electrodes 31,
It has been experimentally confirmed that the no-load voltage between the base materials 32 needs to be at least 200V to recover the ignition state, and 250V to ensure stable ignition recovery performance. Has been done. The current flowing through the discharge resistor 52 is determined by the voltage at the time of charging the capacitor 37, the voltage at the time of discharging, and the discharge time constant. Under general welding conditions, the current flowing through the discharge resistor 52 is 35 A at the time of discharging. If the difference between the voltage of 1 and the voltage at the time of stopping during discharge is 50V, the power loss reaches 50V × 35A = 1750W. Therefore, the discharge resistor 52 needs to have a large capacity and a large capacity, which hinders the plan for reducing the size and weight of the welding machine.

It is an object of the present invention to absorb an excessive transient voltage generated in a low frequency AC converter into the auxiliary DC power source side while maintaining a high ignition recovery characteristic, and to control the upper limit of the auxiliary voltage associated with this absorption. To do.

[0012]

According to the present invention, a main DC power supply means for generating a main DC voltage for welding, and the main DC voltage is converted into a low frequency rectangular wave AC voltage, which is used as a welding load. A converter means for applying a positive polarity period and a reverse polarity period of this welding load, an auxiliary DC power source means for generating an auxiliary DC voltage for ignition recovery higher than the main DC voltage, and the auxiliary DC voltage. Re-ignition recovery facilitating means for supplying to the converter means for superimposing on the main DC voltage is provided.
Further, the re-ignition recovery promoting means supplies the auxiliary DC voltage within a predetermined re-ignition recovery time after conversion of the welding load from the positive polarity to the reverse polarity and a predetermined value of the auxiliary DC voltage. A timing means is provided.

Further, the timing means is ON / OFF controlled by a signal from the converter means, and the auxiliary DC voltage has a switching element which is turned on at a first predetermined voltage and turned off at a second predetermined voltage. is there.

[0014]

The main DC power supply means generates the main DC voltage for welding. This main DC voltage is converted into a low frequency rectangular wave voltage by the converter means and applied to the welding load. On the other hand, the auxiliary DC power supply means generates an ignition recovery auxiliary DC voltage higher than the main DC voltage. This auxiliary DC voltage is supplied to the converter means by the re-ignition recovery promoting means and superposed on the main DC voltage. The timing circuit of the re-ignition recovery promoting means supplies the auxiliary DC voltage to the welding load within a predetermined period and within a predetermined value after the positive polarity of the welding load is changed to the opposite polarity.

Further, the switching circuit of the timing means is on-controlled by the signal of the converter means, the auxiliary DC voltage is turned on at the first predetermined voltage and turned off at the second predetermined voltage, and the auxiliary DC voltage and the main DC voltage are supplied. Superimposes on DC voltage.

[0016]

FIG. 1 shows a first embodiment of the present invention. In this embodiment, the arc welder shown in FIG.
2 and the discharge switching control device 53 are removed, and instead a re-ignition recovery promoting means is provided. The other parts have the same structure as that shown in FIG.

This re-ignition circuit promoting means is provided between the capacitor 37 of the auxiliary DC power supply means and the low frequency AC converter 20 of the converter means, and is composed of IGBT, MOSFET,
A timing means for the switching element 41 such as a bipolar transistor, a timing conduction controller 42 for controlling the on / off of the switching element 41, a reactor 43 for smoothing the output of the switching element 41, a flywheel diode 45, and a current limiting resistor 44. Has been done.

When the base material 32 shown in FIG. 2A is positive and the electrode 31 is negative and the base material 32 is negative and the electrode 32 is positive and reverse polarity, the low frequency inverter controller 25 is shown. 2 sends a command signal to the timing continuity controller 42.
The drive signal shown in (b) is input to the switching element 41. As a result, the capacitor 37 charged with the auxiliary DC voltage for ignition recovery higher than the main DC voltage is superposed on the main DC voltage via the switching element 41, the reactor 43, and the current limiting resistor 44, and the positive polarity changes to the reverse polarity. It makes the transition easier.

As described above, when the cable to the welding load is long, the excessive transient voltage generated on the input side of the conversion device 20 due to its inductance is absorbed by the capacitor 37 via the diode 36 and the capacitor 37. , The auxiliary voltage rises as shown in FIG. 2 (c). This increase in the auxiliary voltage is advantageous for re-ignition, but it causes a disadvantage that a too high voltage is required for the capacitor 37 and the switching elements 21 to 24 of the conversion device 20. The voltage detector 40 provided in parallel with the capacitor 37 monitors the voltage of the capacitor 37, and when the value reaches the first predetermined value (the voltage H shown by the chain double-dashed line in FIG. 2C), A signal is sent to the timing continuity controller 42. The timing continuity controller 42 responds to this signal in accordance with FIG.
Generating a drive signal as shown in FIG.
Turn on. As a result, the charge of the capacitor 37 is discharged to the conversion device 20 via the switching element 41, the reactor 43, and the resistor 44, and the voltage of the capacitor 37 gradually drops. When this voltage reaches a voltage L having a predetermined value shown by the one-dot chain line in FIG. 2C, the voltage detector 40 sends a signal to the conduction controller 42 to stop the drive signal from the conduction controller 42.

Next, FIG. 3 shows another embodiment. The difference from the arc welder of FIG. 1 is that the reactor 43 and the rough wheel diode 45 are removed, and the drive signal output from the conduction controller 42 is the capacitor 3 as shown in FIG.
When the voltage of 7 reaches the first predetermined value H, a drive signal for continuously turning on the switching element 41 is output, and other operations are the same as those of the arc welder of FIG. 1.
Therefore, the reactor 43 and the diode 45 are removed and the arc welder is downsized. The waveform of each part shown in FIG. 4 corresponds to the waveform of each part of FIG.

In the above embodiment, the auxiliary DC power supply voltage is obtained by rectifying the voltage generated in the tertiary winding of the converter 10. However, it is obtained by receiving the input AC power supply and transforming it. You can also In the above embodiment, a method of rectifying a three-phase commercial AC voltage, converting the obtained DC voltage into a high frequency AC voltage, rectifying this AC voltage, and then converting it into a low frequency AC voltage for welding. Although the transformer 10 is made smaller and lighter by using the commercial power source, the commercial power source can be directly input to the transformer, and the commercial power source is directly rectified by the rectifier 11 to change the output voltage of the conversion device 20 to a desired value. You can also do it.

[0022]

According to the present invention, by superimposing the auxiliary DC voltage for ignition recovery higher than the main DC voltage on the main DC voltage, the re-ignition characteristic of the arc is restored when the positive polarity is changed to the reverse polarity. The ignitability is improved. Further, when the cable to the welding load is long, the auxiliary DC voltage for ignition can be kept within a predetermined value by being regenerated to the welding load through the re-ignition recovery promoting means and the converter means. The voltage applied to the capacitor of the DC power supply and the switching element of the converter can be controlled. Furthermore, the discharge resistance required in the past is no longer necessary, and the size and weight of the welding machine can be reduced.

[Brief description of drawings]

FIG. 1 is a block connection diagram showing an embodiment of an arc welding machine of the present invention.

FIG. 2 is a time chart diagram showing waveforms of respective parts of the arc welding machine of FIG.

FIG. 3 is a block connection diagram showing another embodiment of the arc welding machine of the present invention.

FIG. 4 is a time chart showing waveforms at various parts of the arc welding machine shown in FIG.

FIG. 5 is a block connection diagram of a conventional arc welder.

[Explanation of symbols]

 2 input rectifier 4 high frequency AC converter 9 high frequency inverter controller 10 transformer 11 main rectifier 20 low frequency AC converter (converter means) 21-24 switching element 25 low frequency inverter controller 31 electrode 32 base material 35 inductance 36 diode 37 condenser 38 auxiliary rectifier 40 voltage detector 41, 46 timing means (switching element) 42, 47 timing conduction controller 43 reactor 44 current limiting resistance H first predetermined value L second predetermined value

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenzo Dangami 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture Sansha Electric Manufacturing Co., Ltd. (72) Atsushi Kinoshita 2-chome, Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture No.14-3 Sansha Electric Manufacturing Co., Ltd.

Claims (2)

[Claims] 1. A main DC power supply means for generating a main DC power supply for welding, and the main DC voltage is converted into a low frequency rectangular wave AC voltage, which is applied to a welding load, and the positive electrode of the welding load. A converter means for generating a charge period and a reverse polarity period, an auxiliary DC power supply means for generating an auxiliary DC voltage for ignition recovery higher than the main DC voltage, and the auxiliary DC voltage for supplying to the converter means. Re-ignition recovery promoting means for superimposing on the main DC voltage is provided, and the re-ignition recovery promoting means further supplies the auxiliary DC voltage after the conversion of the positive polarity of the welding load to the reverse polarity. An arc welding machine having a predetermined re-ignition recovery time and a timing means for performing within a predetermined value of the auxiliary DC voltage. 2. The timing means has a switching element which is turned on / off by a signal from the converter means, and the auxiliary DC voltage is turned on at a first predetermined voltage and turned off at a second predetermined voltage. The arc welder according to Item 1.