JPH06210449A - Direct current tig arc welding machine - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent the electrode tip from adhering to the base material even if a bounce occurs when the electrode is short-circuited to the base material and the short circuit is opened to start an arc. [Arrangement] A low current is controlled by an arc start start current setting means 14 for short-circuiting the electrode to the base material, and a steady current is controlled by a steady current setting means 15 when the electrode is released from the base material. Further, when the electrode and the base material are short-circuited / opened and then short-circuited (bounced) again at the time of arc start, the set signal increasing means 16 gradually increases the output current together with the signal from the start current setting means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC TIG arc welder which is feedback-controlled to a constant current output.

[0002]

2. Description of the Related Art Conventionally, a DC TIG arc welding machine has used a tungsten electrode of a high melting point material and supplies a welding current of a constant current to the welding load of the electrode and the base material by the welding machine. , Melt the base material and weld.

By the way, when the tungsten electrode is brought into contact with the base material at the time of arc start and is started with a large constant current, the tungsten electrode is melted into the base material and a welding failure occurs.

Therefore, conventionally, at the time of arc start, the electrodes,
A void is provided between the base materials, and a high frequency (2 to 3 MH is set in this void.
z), a high voltage (2000 to 3000 V) is applied to generate an arc to prevent the above-mentioned welding failure. When an arc is started by providing a gap between the electrode and the base material as described above, it is necessary to remove the light-shielding protector, check the start position, and then reattach the light-shielding protector to start the arc. In addition, it is not easy to set the start position to the correct position without deviation, and there is a problem that it requires skill in workability. Also, when a high frequency high voltage is applied to start an arc, a high frequency high voltage noise is generated, and this noise adversely affects nearby electrical equipment and control equipment. Especially, it is easy to digitize and have a low operating voltage. There is a problem that malfunctions.

Therefore, conventionally, the output current setting signal is held at the start current setting signal at the time of arc start in which the tungsten electrode of the welding load and the base material are short-circuited to start the load power feeding, and the output current is controlled to be lower than the steady value. The start current setting means and the steady current setting means for switching the output current setting signal to the steady current setting signal after the tungsten electrode is separated from the base material and released from the short circuit and shifting the output current to the steady value are provided. A DC TIG welder that starts an arc by output has been proposed.

That is, FIG. 3 is a connection diagram of the proposed DC TIG arc welder. In FIG. 3, 1a to 1c
Is a three-phase input terminal of the welding machine, 2 is an input rectification side rectifier, 3 is a smoothing capacitor, and 4 is an inverter for converting direct current into high frequency alternating current. Like known inverters, output control of transistors, MOSFETs, IGBTs, etc. It is formed by a bridge circuit of the element Q. 5 is an output transformer for converting high frequency alternating current into a voltage required for welding, 6 is an output side rectifier for rectifying the secondary side output of the transformer 5, 7 is a smoothing reactor, 8p and 8n are positive and negative of the welding machine. Output terminal, 9 is a tungsten electrode, 10 is a base material, and the electrode 9 and the base material 10
The welding load 11 is constituted by.

Reference numeral 12 is a current detector for detecting an output current (welding current), 13 is a current / voltage converter for converting a current detection signal of the detector 12 into a negative voltage signal, and 14 is an output current at the time of arc start. A variable resistance arc start current setter for setting a low current start current, a variable resistance steady current setter 15 for setting a steady-state output current to a large capacity steady value, and 17 an operational amplifier. The non-inverting input terminal (+) is grounded, and the inverting input terminal (-) is connected through the input resistors 18, 19, 20 to the converter 13, the setters 14, 1.
5, the negative detection signal of the converter 13 and the setter 14
Error amplification is performed on the positive start current setting signal and the positive steady current setting signal of the setter 15. 21 is a resistor for amplification, 2
Reference numerals 2 and 23 are resistors and capacitors for frequency correction, and 24 is an inverter drive circuit controlled by the output signal (error signal) of the operational amplifier 17, and controls the switching of the control element Q of the inverter 4 so that the output current is a constant current. Feedback control.

Reference numeral 25 is an arc start switch, 26 is a voltage detector for detecting an output voltage, 27 and 28 are voltage dividing resistors for dividing a reference voltage signal for detecting arc generation, and 29 is a comparator which is an input resistor 30. The voltage detection signal of the detector 26 via the input resistor 31 and the positive reference voltage signal via the input resistor 31 are compared. Reference numeral 32 denotes an opening / closing unit commanding device such as a relay for current setting switching controlled by the output of the comparator 29 or an electronic switch of an analog electronic switch, and its b contact or the opening / closing unit 32a of the analog switch serves as the setting unit 14. When it is inserted between the input resistor 19 and the a-contact or an opening / closing part 32b such as an analog switch is inserted between the setter 15 and the input resistor 20, and the voltage detection signal of the detector 26 is larger than the reference voltage signal. The opening / closing part 32a is opened and the opening / closing part 32b is closed. Reference numeral 33 is a diode for surge absorption provided in parallel in the switching unit command device 32, and + B is a power supply terminal. The resistor 14a, the setting device 14, the comparator 29,
A start current setting means is formed by the opening / closing unit command device 32 and the like, and includes a setting device 15, a comparator 29, and an opening / closing unit command device 32.
The steady current setting means is formed by the above. Further, since the arc start current is usually set smaller than the steady current, the resistor 14a is provided in series with the setter 14. 3 more
Reference numeral 4 is a backflow prevention diode.

When welding, the three-phase input terminals 1a to 1a are first opened with the arc start switch 25 open.
AC power is applied to 1c, and this AC power is applied to the rectifier 2,
Rectified and smoothed by the capacitor 3 and converted to DC,
This direct current is supplied to the inverter 4. At this time, when the switch 25 is opened, the operational amplifier 17 has its inverting input terminal (-) set to zero by the setting signals of the setters 14 and 15.
Output voltage is held at zero. Then, the operational amplifier 17
Drive circuit 24 control element Q is not driven by the output of 0 of
Since the inverter 4 does not operate, both the output current and the output voltage are held at 0. Since the output voltage is 0,
The voltage detection signal of the detector 26 also becomes 0, the transistor of the output stage of the comparator 29 is turned off, the opening / closing unit command device 32 is not energized, the opening / closing unit 32a is closed, and the opening / closing unit 32b is opened. .

Next, in order to start an arc, after the electrode 9 is brought into contact with the base material 10 to short-circuit them, the arc start switch 25 is turned on to close the operational amplifier 1.
The start current setting signal of the setting device 14 is applied to the inverting input terminal (-) of the operational amplifier 1 based on this setting signal.
The output signal of 7 becomes positive, and the drive circuit 24 drives the control element Q of the inverter 4 for switching. And
The high frequency alternating current of the inverter 4 passes through the transformer 5 and the rectifier 6
Is rectified and smoothed by the rectifier 6 and the reactor 7, and is converted into a direct current.
The welding load 11 in the short-circuited state is supplied from 8n.

At this time, the output current is detected by the detector 12, and is proportional to the output current from the converter 13 connected to the detector 12 to the inverting input terminal (-) of the operational amplifier 17 via the input resistor 18. A negative current detection signal is provided.

When the output current is Ix and the arc start current based on the start current setting signal is I1, the output signal of the operational amplifier 17 changes according to I1-Ix,
The drive circuit 24 drives and controls the control element Q so that the output signal becomes zero. By this drive control, the output current at the arc start is feedback-controlled to the arc start current I1 and held.

By the way, when the steady current based on the steady current setting signal is I2 and this current I2 is 350 A, for example, the arc start current I1 prevents the electrode 9 from melting into the base material 10 at the time of arc start. It is set to, for example, 5 to 15 A so as to be I2.

Next, in order to generate an arc, when the electrode 9 is pulled up to separate the electrode 9 from the base material 10 to open the short circuit, the output voltage rises from 0, and the static characteristics of the output current and the output voltage are shown in FIG. From point A to point B along the solid line a. Then, when the point B is reached and an arc is generated between the electrode 9 and the base material 10, the voltage detection signal of the detector 26 becomes larger than the reference voltage signal, the transistor of the output stage of the comparator 29 is turned on, and the switching unit command is issued. The device 32 is energized, and the opening / closing part 32
a is opened and the opening / closing part 32b is closed.

Therefore, instead of the start current setting signal of the setter 14, the steady current setting signal of the voltage V2 (> V1) of the setter 15 is applied to the inverting input terminal (-) of the operational amplifier 17, and based on this signal. The output current shifts to the large-capacity steady-state current I2 by the feedback control. At this time, the characteristics of the output current and the output voltage shift from point B to point C on the solid line B, for example. After that, the output current is the steady current I2.
The TIG welding is performed while being held at.

At the time of arc start, the DC output current is sufficiently lower than the steady current I2, and the arc start current I
Since it becomes 1, by a simple operation of pulling up the electrode 9 in contact with the base material 10, penetration of the electrode 9 into the base material 10 is prevented and an arc is generated by DC output, so that the electrode 9,
It is possible to perform welding without providing a high frequency and a high voltage by providing a gap between the base materials 10.

[0017]

However, in order to generate an arc, the electrode 9 is pulled up and the electrode 9 is used as a base material 10.
When the short circuit is released by moving away from, the bounce may occur, that is, the manual operation causes the open, the short circuit, and the open in a short time. Alternatively, the arc start is performed by the electrode 9
The base material 10 is short-circuited and opened. However, conversely, the operation may be performed in which the electrode 9 and the base material 10 are first opened and started, and then short-circuited and opened. When the electrode 9 is released from the base material 10 in this manner, the output voltage rises, the detection signal of the detector 26 becomes larger than the reference voltage signal, and the opening / closing unit command device 32 is energized as described above, and the opening / closing unit 32a.
Is opened and the opening / closing part 32b is closed. Then, the steady current setting signal is applied to the inverting input terminal (-) of the amplifier 17, and the steady current flows in the output. By the way, DC TIG
When performing precision welding using an arc welder, the tip of the electrode is sharply polished and when the electrode shorts to the base material and a steady current flows, the contact resistance at the time of contact increases and the electrode tip The Joule heat of the above may increase and the tip may melt and adhere to the base material. Particularly when bounce occurs, the tip is heated by the first short circuit, and the tip of the electrode may adhere to the base material due to the subsequent short circuit.

[0018]

A direct current TIG which controls a control element for output control by an error signal between a detection signal of a direct current output current supplied to a welding load and an output current setting signal to feedback control the output current. An arc welder, in which the output current setting signal is held at a start current setting signal at the time of arc start to short-circuit the electrode of the welding load and the base metal to start load power feeding, and the output current is lower than a steady value. A start current setting means for controlling the output current and the output current setting signal is switched to a steady current setting signal after the electrode is separated from the base material and released from the short circuit, and the steady current is set to shift the output current to the steady value. Setting means,
When the electrode is short-circuited to the base material, a setting signal current increasing means for gradually increasing the arc start current setting signal is provided, and the arc start is performed by the DC output.

[0019]

In the DC TIG arc welding machine of the present invention constructed as described above, the DC output current is controlled to be lower than the steady value by the start current setting means at the time of arc start, and this low current is short-circuited. It is supplied to the electrodes and base material.
Furthermore, when the electrode separates from the base material and an arc occurs, the steady current setting means causes the output current to shift to a steady value. In addition, there is little current flowing through the electrode and the base metal at the time of arc start, and this current prevents the electrode from melting into the base metal.Therefore, a simple operation to separate the short-circuited electrode from the base metal makes it possible to use only DC output for welding failure. You can start the arc without causing.

When the electrode is short-circuited with the base material, the output current is gradually increased together with the arc start current setting signal, and even if bounce occurs, the tip of the electrode is not heated so much that the electrode adheres to the base material. There is nothing to do.

[0021]

EXAMPLE One example will be described with reference to FIGS. In FIG. 1, the same reference numerals as those in FIG. 4 indicate the same or equivalent functions, and the points different from FIG. 4 are the following points (a) and (a). (A) A soft start capacitor 16 is provided between the output of the opening / closing part 32a of the opening / closing part command device 32 and the ground. (A) Open / close unit 32 such as an a contact or an analog switch that is closed when the command device 32 instructed by the open / close unit command device 32 operates in parallel with the soft start capacitor 16
The point where c is provided.

The basic operation of the DC TIG arc welder shown in FIG. 1, that is, the arc start current is set based on the setting signal of the arc start current setting device 14 at the time of arc start, and based on the setting signal of the steady current setting device 15, The operation of setting the steady current is the same as that of the above-described welding machine shown in FIG.

Next, the operation when the electrode 9 is short-circuited to the base material 10 to generate an arc, and then the electrode 9 is pulled up to separate from the base material of the electrode 9 and released from the short circuit, the bounce occurs. . Now, when the arc start switch 25 is turned on as shown in FIG. 2 (a), the capacitor 16 causes the resistor 14a and the arc start current setting device 14 to operate.
Charge the setting signal via. Therefore, the amplifier 17
The arc start current setting signal that is input to the inverting input terminal (-) of rises as the capacitor is charged. Based on this setting signal, the output signal of the amplifier 17 becomes positive, the control element Q of the inverter 4 is switching-controlled by the drive circuit 24, and the output current gradually rises as shown in FIG. 2 (c).

When the electrode 9 is detached from the base material 10, the output voltage rises as shown in FIG. 2B, and the voltage detection signal of the voltage detector 26 becomes larger than the reference voltage signal as described above. The opening / closing unit command device 32 operates to open and close the opening / closing unit 32.
a is opened and the opening / closing parts 32b and 32c are closed.

Therefore, the electric charge charged in the capacitor 16 is discharged by the opening / closing section 32c. Also, instead of the start current setting signal, the steady current setting signal is sent to the amplifier 1
It is input to the non-inverting input terminal (-) of 7 and a steady current tries to flow based on the steady current setting signal. However, the electrode 9 and the base material 10 are short-circuited again before the arc is generated between the electrode 9 and the base material 10. Then, as described above, the capacitor 16 is charged again by the setting signal, and the output current gradually rises. When the bounce is performed, the above operation is repeated. Then, when the electrode 9 is completely separated from the base material 10, a steady current flows to the output based on the steady current setting signal.

In the above embodiment, the electrode 9 and the base material 10 were short-circuited to start the arc, but the electrode 9 and the base material 10 were opened to start the arc, and then the electrode 9 and the base material 1 were started.
When 0 is short-circuited and then the electrode 9 and the base material 10 are opened to start an arc, the same operation can be performed.

In the above embodiment, the soft start capacitor 16 is provided between the output of the switching unit command device 32 and the switching unit 32a and the ground. However, an integrator is provided in series with the switching unit 32, and the electrode 9 is Setting signal increasing means for setting the output of the integrator to 0 when the base material 10 is short-circuited and thereafter increasing the output may be provided.

Although the above-mentioned embodiment is applied to the inverter-controlled welding machine, the AC power source is transformed by the transformer and the output thereof is feedback-controlled to a constant current by the phase control of the thyristor as a control element for output control to perform welding. Of course, it can also be applied to a welding machine or the like that supplies a load. And
The arc start current I1, the steady current I2, etc. may be set according to the welding conditions and the like based on the settings of the start current setting signal, the steady current setting signal, and the like.

[0029]

Since the present invention is configured as described above, it has the following effects. At the time of arc start, the DC output current is controlled to be lower than the steady value by the start current setting means, and this low current is supplied to the short-circuited tungsten electrode 9 and the base material 10, and the electrode 9 is separated from the base material 10 to generate an arc. When it occurs, the output current shifts to the steady value by the steady current setting means, so that the current flowing through the electrode 9 and the base material 10 is small at the time of arc start, and when the electrode 9 is short-circuited to the base material 10, the output current gradually increases. It is possible to prevent the electrode 9 from melting into the base material 10 due to this current rise, and to easily start the short-circuited electrode 9 from the base material 10 by using only the DC output to start an arc start without causing a welding failure. it can.

Since it is not necessary to apply a high frequency and a high voltage to the electrode 9 and the base material 10 by providing appropriate gaps as in the conventional case, the worker repeatedly attaches and detaches the light shielding protector to confirm the start position. It is not necessary, the workability is remarkably improved, the circuit for generating high frequency and high voltage is omitted, and the price of the welding machine can be reduced.

[Brief description of drawings]

FIG. 1 is a connection diagram of an embodiment of a DC TIG arc welder of the present invention.

FIG. 2 is a timing chart for explaining the operation of FIG. 1 when an arc is started.

FIG. 3 is a connection diagram of an example of a conventional DC TIG arc welder.

FIG. 4 is a static characteristic diagram of output current and output voltage of the DC TIG arc welding machine.

[Explanation of symbols]

 4 Inverter 9 Tungsten electrode 10 Base metal 11 Welding load 12 Current detector 13 Current / voltage converter 14 Arc start current setting device 15 Steady current setting device 16 Capacitor (setting signal increasing means) 17 Operational amplifier 24 Inverter drive circuit 25 Arc start Switch 26 Voltage detector 29 Comparator 32 Switchgear command device Q Control element

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Atsushi Kinoshita 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture Sansha Electric Co., Ltd.

Claims (1)

[Claims] 1. A direct current TIG arc welding machine for feedback controlling the output current by controlling a control element for output control by an error signal between a detection signal of a direct current output current supplied to a welding load and an output current setting signal. , A start current setting for controlling the output current to be lower than a steady value by holding the output current setting signal at a start current setting signal at the time of arc start in which the electrode of the welding load and the base material are short-circuited to start load power supply Means for switching the output current setting signal to a steady current setting signal after the electrode is separated from the base material and released from the short circuit, and the steady current setting means for shifting the output current to the steady value; When a short circuit occurs in the base material, it is equipped with setting signal increasing means for gradually increasing the arc start current setting signal, and the arc starts by the DC output. DC T characterized by doing so
IG arc welder.