JPH09271941A - Power source for arc welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the welding speed by reducing the amplification ratio for the prescribed period when the voltage to make the current rate-of-change of a current rate-of-change control circuit to be positive is not less than the prescribed value, and reducing the amplification ratio for the prescribed period after the prescribed delay time when the voltage to make the current rate-of-change to be negative is not less than the prescribed value to stabilize the arc. SOLUTION: Just after the load is changed from the short circuit to the arc (when the current rate-of-change is positive), the welding power source output current is rapidly reduced for the prescribed period to promote the short circuit. Immediately after the load is changed from the line arc to the short circuit (the current rate-of- change is negative), the incomplete short circuit is prevented by preventing the current increase, and stabilization from the short circuit to the open condition is realized and the regular welding can be achieved by increasing the current after the prescribed period for the prescribed period. As a result, the welding with little incomplete short circuit becomes possible, generation of large spatters can be prevented, the stable arc condition can be obtained even with the low arc voltage, and the welding speed can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an arc welding power source suitable for high speed welding of thin plates using consumable electrodes.

[0002]

2. Description of the Related Art FIG. 3 is a connection diagram of an arc welding power source using a conventional consumable electrode, which is a simplified diagram of the one disclosed in Japanese Patent Publication No. 4-53619. Reference numeral 1 is an arc welding power source, which converts an input from a commercial AC power source 2 into a direct current by an input side rectifier circuit 3 and smoothes it by a smoothing capacitor 4 and then a high frequency alternating current (for example, 20%) by an inverter circuit 5.
kHz), and the voltage is reduced to a voltage suitable for welding by the transformer 6, converted again to direct current by the output side rectifier circuit 7, smoothed by the direct current reactor 8, and the direct current output to the arc load 12 is output. Supply. 10 is a welding wire which is a consumable electrode, 11 is a wire feeding motor, and 13 is a base material. A secondary winding 8a is provided in the DC reactor 8 as a current change rate detecting means, and the voltage induced in the secondary winding 8a is
Of the output current I supplied to the load 12 (di / d
It is used as a signal corresponding to t). Since the voltage includes an inverter component, it is passed through the filter circuit 15 and inverted and amplified by the current change rate control circuit 16 to be a feedback signal. Then, the feedback signal and the output voltage setting device 1
A signal obtained by adding the reference input signal from 7 to the adder 18 is used as a control input for determining the output pulse width of the inverter circuit 5 to suppress the current change. The signals of the filter circuit 15, the current change rate control circuit 16, the output voltage setting unit 17, and the adder 18 relating to the output current I are as shown in FIG.
A to D of FIG. And Tokuhei 4-
No. 53619 realizes reduction of spatter and prevention of arc breakage with a simple configuration by strengthening suppression of change in output current when a short-circuit state for a long time and an arc state for a long time continue.

[0003]

When a thin plate is welded at high speed by using a consumable electrode, it is necessary to regularly generate short circuits. However, in the above-mentioned conventional technique, when the current change rate at the time of short-circuiting and at the time of arcing is made small, the short-circuiting time shown by the section of a and b when the welding current waveform of FIG.
The arc generation time shown in section (2) becomes long, the number of short circuits is greatly reduced, and the bead appearance is deteriorated. Further, when the arc length is suddenly shortened, the short circuit is not opened, and a long short circuit shown in the section c occurs, during which the overheated welding wire explosively melts and breaks the arc. , The welding speed cannot be increased. On the other hand, if the current change rate at the time of a short circuit and at the time of an arc is increased to increase the number of short circuits,
As shown in the welding current waveform of (b), the number of short circuits increases. However, a short circuit for a very short time as shown in the section of d (hereinafter referred to as an incomplete short circuit. Note that the incomplete short circuit causes the droplet to form on the base metal due to the electromagnetic pinch force due to the rapid rise of the current at the initial stage of the short circuit. It occurs when the short circuit is opened before the transition) occurs frequently. During this time, the droplets at the tip of the welding wire hardly migrate to the base metal, and the same result as the number of short circuits is reduced, resulting in large droplet growth. Then, a large short-circuit current may flow at the time of the next short-circuit indicated by the section e, and a large amount of spatter may occur or the arc may be broken. The object of the present invention is to solve the above-mentioned problems, prevent the occurrence of incomplete short circuits when the number of short circuits is increased, and short circuits occur regularly even if welding is performed at high speed,
An object of the present invention is to provide an arc welding power source that can stabilize the arc.

[0004]

The inventor has found that the output of the power supply change rate control circuit 16 shifts from a short circuit to an arc as shown in C of FIG. It was noted that the point where the transition from −h to a short circuit was the maximum of −.
As a result, the problems described above include output current change rate detection means for detecting the change rate of the output current, and current for controlling the change rate of the output current by inputting the detection signal of the output current change rate to the output control unit. A constant rate characteristic circuit for generating an arc between the consumable electrode and the base material.
In the welding power source, a voltage that makes the current change rate positive among the output voltages of the current change rate control circuit is detected, and if the detected voltage is a predetermined value or more, the amplification factor of the current change rate control circuit is set to a predetermined value. Of the output voltage of the current change rate control circuit and a circuit for decreasing the current change rate are detected, and if the detected voltage is equal to or higher than a predetermined value, a predetermined delay time is passed and a predetermined delay time is passed. And a circuit that reduces the amplification factor of the current change rate control circuit for a time. Then, the power supply change rate control circuit is an inverting amplifier, a capacitor and a resistor are connected in series between the input and output of the inverting amplifier, and a forward direction occurs when a voltage for making the power supply change rate positive is generated in parallel with the resistance. A switching element in which a plurality of diodes connected in series are connected and a plurality of diodes are connected in series in a forward direction when a voltage that negatively changes the power supply is generated in parallel with the above resistance Is connected in series, and the switching element is ON-delayed by the negative voltage.

[0005]

FIG. 1 shows an embodiment of the present invention. The same parts as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted. Reference numeral 20 denotes a capacitor, one of which is connected to the input terminal A of the current change rate control circuit 16 and the other of which is connected to the connection point S. Reference numeral 21 is a discharging resistor, one of which is connected to the output terminal K of the current change rate control circuit 16 and the other of which is connected to a connection point S. 22 to 25 are diodes connected in series, the anode of the diode 22 is connected to the output terminal K, and the cathode of the diode 25 is connected to the input terminal A. 26
-30 are diodes, which are connected in series,
The anode of the diode 30 is connected to the connection point S, and the diode 2
The cathode of 6 is connected to the collector C of the transistor 31. 31 is a transistor, collector C is a diode
The cathode of the diode 26, the emitter E is connected to the output terminal K, and the base B is connected to the cathode of the diode 33. 32 is a resistor, one of which is connected to the input end A and the other of which is connected to the connection point T. 33 is a diode whose anode is a connection point T
In addition, the cathode is connected to the base B of the transistor 31. 34 is a capacitor, one of which is connected to the connection point T and the other of which is connected to the output terminal K. Reference numeral 35 is a diode having an anode connected to the output terminal K and a cathode connected to the connection point T.

The operation will be described below with reference to FIG. 2 corresponding to FIG. In addition, what is shown by a dotted line in the same figure is what is shown in FIG. Immediately after the load changes from short circuit to arc (when the current change rate is positive), the current change rate control circuit 1
The input-output voltage of 6 becomes the point f in FIG.
Since the voltage is higher than the forward voltage of 2, 23, 24 and 25, a current flows from the output terminal K through the capacitor 20 and the amplification factor of the current change rate control circuit 16 is reduced, so that the output current sharply decreases. As a result, the burning of the arc is prevented and the short circuit is promoted. The time t ₁ when the output current sharply decreases is determined by the charging time of the capacitor 20. Immediately after the load is short-circuited from the arc (when the power supply change rate is negative), the voltage between the input and output of the current change rate control circuit 16 is as shown in FIG.
It becomes the g point of and the diode 26, 27, 28, 29, 3
Since it is higher than the forward voltage of 0, a current flows from the input terminal A through the capacitor 20 from the point h after the ON delay time t _{2 of the} transistor 31, and this current reduces the amplification factor of the current change rate control circuit 16. Therefore, the output current is rapidly increased for a predetermined time. As a result, it is possible to prevent an incomplete short circuit by preventing an abrupt current increase at the point g, and to stabilize the opening from a short circuit due to the abrupt current increase from the point h, and to reduce the number of short circuits. Welding with a large number and less incomplete short circuits can be performed. The time t ₃ when the output current rapidly increases is determined by the charging time of the capacitor 20. In the diode 33, the transistor 31 is turned on.
This is for determining the threshold value for N, and the diode 35 is for keeping the ON delay time constant by preventing the capacitor 33 from being charged in the reverse direction.
The power supply change rate control circuit 16 may be an inverting amplifier. Further, although the predetermined voltage is generated by connecting a plurality of diodes in series, other means may be used.

[0007]

As described above, according to the present invention,
Immediately after the load changes from a short circuit to an arc (when the power supply change rate is positive), the welding power supply output current is sharply reduced for a specified period of time to prevent the arc from burning and to accelerate the short circuit. Immediately after a short circuit from the arc (when the power supply change rate is negative), an incomplete short circuit is prevented by preventing a rapid current increase, and after a predetermined time, it is increased rapidly for a predetermined time. Therefore, it is possible to stabilize the opening from the short circuit, and the short circuit can perform regular welding. As a result, the number of short circuits becomes large and regular, welding with few incomplete short circuits can be performed, and the generation of large-sized spatters can be prevented. Further, a stable arc state can be obtained even at a low arc voltage, and the welding speed can be improved. Furthermore, excessive growth of droplets is suppressed, workability is improved, and a uniform bead appearance is obtained. This has the effect.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram of each part in the present invention.

FIG. 3 is a conventional connection diagram.

FIG. 4 is a waveform diagram of each conventional unit.

FIG. 5 is a conventional welding waveform diagram.

[Explanation of symbols]

 8a Secondary winding 11 Base material 13 Welding wire 16 Current change rate control circuit 20,34 Capacitor 21 Discharge resistance 22-30, 33,35 Diode 31 Transistor 31 32 Resistance

Claims (2)

[Claims] 1. An output current change rate detecting means for detecting a change rate of an output current, and a current change rate control for controlling a change rate of an output current by inputting a detection signal of the output current change rate to an output control section. And an arc welding power source having a constant voltage characteristic for generating an arc between the consumable electrode and the base material, the current change rate of the output voltage of the current change rate control circuit is made positive. A voltage is detected, and if the detected voltage is equal to or higher than a predetermined value, a circuit that reduces the amplification factor of the current change rate control circuit for a predetermined time and a current change rate of the output voltage of the current change rate control circuit A circuit that detects a voltage to be negative and reduces the amplification factor of the current change rate control circuit for a predetermined time after a predetermined delay time when the detected voltage is a predetermined value or more Arc welding power source. 2. A current change rate control circuit is an inverting amplifier, a capacitor and a resistor are connected in series between the input and output of the inverting amplifier, and when a voltage that makes the power supply change rate positive is generated in parallel with the resistance, Connected in series with a plurality of diodes in the same direction, and connected in series with a plurality of diodes in the forward direction when a voltage that negatively changes the power supply is generated in parallel with the above resistance And a switching element connected in series,
The arc welding power source according to claim 1, wherein the switching element is ON-delayed by the negative voltage.