JPH08243740A - Direct current tig arc welding machine - Google Patents

Abstract

PURPOSE: To improve the arc start of a direct current TIG arc welding machine controlled to be feed-back to the constant current output, and to miniaturize the machine. CONSTITUTION: By controlling a control element Q for controlling an output with an error signal between a detecting signal of a direct current to be fed to a welding load 9 and a signal for setting the output current, the output current is controlled to feed-back the output current in this direct current TIG arc welding machine. An auxiliary direct current source 21 to impress a voltage less than an arc current through a current limiting element 22 to a welding load at the time of starting the feed of the load current by subjecting an electrode 7 of the welding load and a base material 8 to short-circuit, and a voltage detecting unit 23 to output a command signal to switch the output current setting signal at the arc starting time and an arc stationary time by detecting the voltage to be impressed to the welding load are installed.

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 welding machine which is feedback-controlled to a constant current output.

[0002]

2. Description of the Related Art In DC TIG arc welding, a DC current feedback-controlled to a constant current is supplied from a welding power source to a tungsten electrode of a high melting point material and a welding load of a base metal,
The base material is melted and welded.

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,
Tungsten electrode melts into the base material and causes welding failure.

Therefore, conventionally, at the time of arc start, a gap is provided between the electrode and the base material, and a high frequency (2 to 3 MH) is provided in this gap.
z), a high voltage (2 to 3000 V) is applied to generate an arc to prevent the above welding failure.

As described above, when an arc is started by providing a gap between the electrode and the base material, it is necessary to remove the light-shielding protector, check the start position, and then reattach the light-shielding protector to start the arc. However, the workability is poor, and it is not easy to accurately set the start position without deviation, and there is a problem that the workability requires skill.

Further, when an arc is started by applying a high frequency and a high voltage, a high frequency and a high voltage noise is generated, and this noise adversely affects nearby electric equipment and control equipment.
In particular, a digitalized device having a low operating voltage has a problem of malfunction.

Therefore, the present applicant has filed Japanese Patent Application No. 4-2184.
No. 2 (Japanese Patent Laid-Open No. 5-185225) proposes a DC TIG welder that can perform an arc start by using only a DC output by an easy work and without causing welding defects. That is, the output current setting signal is held as a 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 load power feeding, and the output current is controlled to be lower than a steady value. And a start current setting means for switching the output current setting signal to a steady current setting signal after the tungsten electrode is separated from the base material and released from the short circuit, and a steady current setting for shifting the output current to the steady value. And a DC TIG arc welder equipped with means for starting an arc by a DC output.

[0008]

However, at the start,
In order to make the current low, the output current is set to a small current and a DC reactor is provided to control the short circuit current. Since a current at the time of welding flows through this DC reactor, it becomes large in size and the welding machine cannot be downsized.

[0009]

In order to solve the above problems, the present invention provides a control for output control by an error signal between a detection signal of a DC output current supplied to a welding load and an output current setting signal. In a DC TIG arc welder that controls elements and feedback-controls the output current, a voltage lower than the arc voltage is applied to the welding load at the time of arc start in which the electrode of the welding load and the base metal are short-circuited to start the load power supply. Equipped with an auxiliary DC power supply that applies a current through a current limiting element, and a voltage detector that detects the voltage applied to the welding load and outputs a command signal that switches the output current setting signal at arc start and arc steady time. It was

The feedback control system is a feedback control system in which the output current at the time of arc start is gradually increased.

[0011]

[Operation] At the time of arc start, a small current is supplied to the welding load from the low-voltage auxiliary DC power supply, and the welding load is arc started from the short circuit. At the start, the output current is switched to a small current for control, and when the arc is steady, it is controlled at a predetermined output current.

Further, feedback control is performed so that the output current at the time of arc start gradually increases.

[0013]

EXAMPLE One example will be described with reference to FIGS. In FIG. 1, 1 is an input terminal of a welding machine, 2 is an input side rectifier having a diode bridge structure, 3 is a smoothing capacitor, 4 is an inverter for converting a direct current formed by smoothing by the capacitor 3 into a high frequency, Transistors, MOSFETs, IGBTs as well as well-known inverters
Is formed by a bridge circuit of a control element Q for output control such as. 5 is an output transformer for converting high-frequency alternating current into a voltage required for welding, 6 is an output side rectifier of a diode bridge configuration for rectifying the secondary side output of the transformer 5, 7 is a tungsten electrode, 8 is a base material, The electrode 7 and the base material 8 constitute a welding load 9.

Reference numeral 11 is a current detector for detecting an output current (welding current), and 13 is a current setting device for setting an output current at arc start to a low current start current and a steady output current to a large capacity steady value. The power source, 14 is an operational amplifier,
The error between the detection signal of the current detector 11 and the setting signal of the current setting power supply 13 is amplified. Reference numeral 12 is an input resistor, 15 is a feedback resistor, and 16 is a feedback capacitor for frequency correction. Reference numeral 17 denotes an inverter drive circuit controlled by the error amplification signal of the operational amplifier 14, which controls switching of the control element Q of the inverter 4 and feedback-controls the output current to a constant current.

Reference numeral 21 is an auxiliary DC power source having a voltage lower than the arc voltage, for example, a low voltage of about 10 V, which is limited to a small current of 10 mA or less by the current limiting resistor 22 and the welding load 9
Supply a direct current to. Reference numeral 23 is a voltage detector that is connected to the output of the welding machine and detects the voltage of the welding load, and issues a command to start and switch the detection signal current setting power supply 13. Reference numeral 24 is a backflow prevention diode.

A DC voltage is applied to the electrode 7 and the base material 8 from the auxiliary DC power source through the resistor 22. At this time, since the output voltage of the voltage detector 23 is not short-circuited, the output of the voltage detector 23 is 0, whereby the analog switches 13a and 13b are turned off, and the output current setting power supply 13 outputs the current for setting the output current. The signal becomes 0, and the error amplification signal output from the operational amplifier 14 becomes 0. As a result, the output current of the inverter controlled via the inverter drive circuit 17 is 0 as shown in FIG. 2 (c).

Then, at time t1, when the electrode 7 and the base material 8 are short-circuited, the voltage detector 23 detects a short circuit of the output and turns on the analog switch 13b of the current setting power source 13 to start the current setting power source. Setting power supply 13a
The command signal for setting the current of the small current is input to the operational amplifier 14. On the other hand, the load current is detected by the current detector 11, and the error between the detected detection signal and the command signal is amplified by the operational amplifier 14. The command signal for setting the current charges the feedback capacitor 16, and the output voltage of the operational amplifier 14 gradually rises. As the output of the operational amplifier 14 rises, the output current of the inverter 4 is controlled as shown in FIG.
It gradually rises as shown in (c).

At time t2, when the electrode 7 is separated from the base metal 8, an arc is generated between the electrode 7 and the base metal 8, and the voltage of the welding load 9 becomes higher than the output voltage of the auxiliary DC power supply 21.
The voltage of the welding load 9 is detected by the voltage detector 23,
Input to the power supply 13 for current setting, analog switch 13b
Is turned off and the analog switch 13d is turned on, and the command signal of the steady current setting power supply 13c of the current setting power supply 13 is input to the operational amplifier 14. On the other hand, the error between the detection signal detected by the current detector 11 and the command signal of the steady current setting power supply 13c is amplified by the operational amplifier 14. Depending on the output of the operational amplifier 14, FIG.
As shown in (c), the output current of the inverter 4 is feedback-controlled and becomes a steady-state current.

With this, a small current is supplied to the welding load by the low-voltage auxiliary DC power source, the current flowing when the welding load is short-circuited is detected, and the inverter 4 can be started. Further, when the welding load is short-circuited, the current flowing through the welding load gradually rises softly, and the electrode is not melted into the base material by setting a small current value. Further, when the electrode is pulled up from the base material, an arc is generated, and it is possible to shift to the set current in the steady state.

In the above embodiment, no smoothing reactor is provided at the output of the output side rectifier 6, but when a smoothing reactor is added, a small capacity reactor may be used.

[0021]

According to the present invention, at the time of arc start, a small current can be supplied to the welding load from the auxiliary DC power supply of low voltage to start the welding load from a short circuit. Also, the current output from the inverter is gradually increased in a soft manner at the start, and the start set current is controlled to a small current so that the electrodes do not melt into the base metal and welding defects due to short-circuit current occur. Nor. Since the current is small, it is easy to separate the short-circuited electrode from the base material, and the arc current can be shifted to the set arc current in the steady state. Further, the welding machine can be started without providing a smooth reactor, and the welding machine can be made compact and inexpensive.

Further, unlike the conventional case, it is not necessary to provide a suitable gap between the electrode and the base material and to apply high frequency and high voltage.
The worker does not need to repeatedly attach and detach the light-shielding protector to check the start position, workability is significantly improved, and a circuit that generates high frequency and high voltage can be omitted, and the cost of the welding machine can be reduced.

[Brief description of drawings]

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

FIG. 2 is a time chart diagram of each part of FIG.

[Explanation of symbols]

 2 Input side rectifier 3 Smoothing capacitor 4 Inverter 5 Output transformer 6 Output side rectifier 7 Electrode 8 Base material 9 Welding load 11 Current detector 13 Current setting power supply 14 Operational amplifier 16 Feedback capacitor 17 Inverter drive circuit 21 Auxiliary DC power supply 22 Limit Current element (resistance for current limiting) 23 Voltage detector

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

Claims (2)

[Claims] 1. A DC TIG having a feedback control system for controlling the output current by controlling a control element for output control by an error signal between a detection signal of a DC output current supplied to a welding load and an output current setting signal. In an arc welder,
At the time of an arc start to short-circuit the electrode of the welding load and the base metal to start the load power supply, an auxiliary DC power supply for applying a voltage lower than the arc voltage to the welding load through a current limiting element, and a voltage applied to the welding load. And a voltage detector that outputs a command signal for switching the output current setting signal at the time of arc start and arc steady state, and a DC TIG arc welding machine. 2. The DC TIG arc welder according to claim 1, wherein the feedback control system is a feedback control system that gradually increases an output current at arc start.