JPH0580309B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an arc welding power source having an output waveform suitable for high-speed welding of thin plates using a consumable electrode.

[Prior art] In short-circuit arc welding using a consumable electrode,
If the peak value of the output current of the welding power source is lowered and the base value is increased, the occurrence of spatter will be reduced and the bead appearance will be improved.
As shown in the figure, when the arc length is suddenly shortened, the short circuit is not released due to the low peak value of the current, resulting in a long short circuit, during which the heated welding wire explosively fuses and the arc breaks. This has been a problem especially when welding thin plates at high speeds. Conventionally, as a countermeasure against this problem, a method has been proposed in which, as shown in FIG. 3, when the short circuit time T exceeds a predetermined time, this is detected and the output current is suddenly raised.

[Problems to be Solved by the Invention] The above conventional system has the following problems.

(1) In order to rapidly increase the output current, it is necessary to control the output using a high-frequency inverter with a short control cycle, and as explained later, it is difficult to distinguish between a short circuit state and an arc state with an inverter-controlled arc welding power source. .

(2) It is good to open a short circuit by passing a large current, but
Since no consideration is given to promoting the next short circuit, the arc time after the short circuit is opened is longer, and it takes time for the arc to stabilize. That is,
The penetration of the welding wire into the base metal is affected by short circuits and arc cycles, which tends to cause arc disturbances.

An object of the present invention is to provide an arc welding power source that can prevent arc breakage due to welding wire protrusion without distinguishing between short circuit and arc, and can also avoid arc disturbance.

[Means for solving the problem] The above object is achieved by providing a means for detecting the rate of change of the output current of the welding power source, and amplifying the detection signal of the current rate of change and feeding it negative feedback to the control input of the output control section. A current change rate control circuit that controls the rate of change of the output current, a means for detecting the output current value of the welding power source, and a current value determination circuit that determines whether the detected output current value is equal to or higher than a predetermined value are provided. This is achieved by changing the amplification degree of the current change rate control circuit according to the judgment output of this current value judgment circuit, and when the output current value is equal to or higher than a predetermined value, the change rate of the output current is made larger than usual. .

[Function] As shown in Figure 4, if a long short circuit occurs, the output current also increases. Therefore, the detected output current value is judged, and if the output current value is equal to or higher than a predetermined value (a in the figure), the output current increases. If there is, the rate of change of the output current is controlled to be larger than normal by changing the amplification degree for the feedback signal of the current change rate control circuit, and the output current value is suddenly increased to open the short circuit and eliminate the short circuit. Even after opening, the output current value is rapidly reduced until the output current value becomes equal to or less than the predetermined value. This not only opens the short circuit quickly and prevents the arc from breaking, but also promotes the transition from an arc state to the next short circuit, thereby making it possible to avoid arc disturbances. In addition, this method uses the output current value to determine whether a long short circuit has occurred.
Does not require arc discrimination.

[Example] FIG. 1 shows an example of the present invention. In the figure, 1 is an AC input terminal, 2 is an input rectifier circuit that converts AC input at a commercial frequency into DC, 3 is a smoothing capacitor, and 4 is a smoothed DC input terminal that converts the smoothed DC input to a frequency higher than the commercial frequency (for example, 20kHz). This is an inverter circuit that converts AC into AC, and corresponds to the output control section of this welding power source. The AC output of the inverter circuit 4 is stepped down to a voltage suitable for welding by a transformer 5, then converted to DC by an output side rectifier circuit 6, passed through a DC reactor 7, a shunt resistor 8 for current detection, and an output terminal 9. It is supplied to the arc load 12 between the torch 10 and the base material 11. 13 is a welding wire which is a consumable electrode; 14
is the wire feed motor.

A secondary winding 7a provided in the DC reactor 7 as current change rate detection means generates a voltage proportional to the change rate (di/dt) of the welding power source output current. This voltage is amplified by the current change rate control circuit 17 to become a feedback signal, and the signal obtained by adding this and the reference input signal from the output voltage setting device 15 by an adder 16 determines the output pulse width of the inverter circuit 4. By using the control input as shown in FIG. 4, the output of the welding power source is controlled so that the external output characteristic of the welding power source becomes a constant voltage characteristic and an output current waveform as shown in FIG. 4 is obtained. The current change rate control circuit 17 has a variable amplification degree by changing the resistor inserted into the feedback circuit of the operational amplifier using a selection switch, for example, and by changing the amplification degree, the current change rate in the output current waveform can be changed. is controlled in two stages, large and small.

The current value determination circuit 18 compares a signal obtained by amplifying a voltage proportional to the output current value generated in the current detection shunt resistor 8 with an amplifier 19 and a reference signal from an overcurrent setting device 20 using a comparator 21, and outputs the result. This is a circuit that determines whether the current value is greater than or equal to a predetermined value, and in the present invention, the determination output of this current value determination circuit 18 is used as a control signal for a selection switch or the like that changes the amplification degree of the current change rate control circuit 17. By doing so, when the output current value is above a predetermined value, the amplification degree of the current change rate control circuit 17 is reduced until the gain becomes almost zero, and the change rate of the output current is made larger than usual. ing.

In the above configuration, as shown in FIG. 4, if the welding wire 13 plunges into the base metal 11 due to a sudden change in arc length or the like and a long short circuit occurs, the output current value will be changed to the reference signal from the overcurrent setting device 20. When the current value exceeds a predetermined current value (a in the figure) corresponding to , the amplification degree of the current change rate control circuit 17 decreases, so the output current value of the welding power source rapidly increases and opens the short circuit. Even after the short-circuit is opened, the amplification degree of the current change rate control circuit 17 remains reduced in the section where the output current value is equal to or greater than a, so the output current value rapidly decreases to point a. In the current region lower than point a, the current change rate control circuit 17 returns to the normal amplification degree, so
The current changes relatively slowly as shown in the figure.

This sudden drop in current value immediately after the short circuit is released results in a long arc period, as seen in Figure 3 of the conventional example, and the arc remains stable without being disturbed and with almost no effect on the short circuit/arc cycle. It is possible to move to a new arc.

As described above, according to this method, it is possible to prevent arc breakage due to the welding wire protrusion without requiring discrimination between short circuit and arc, and also to avoid arc disturbance.

In particular, in an arc welding power source controlled by an inverter, the inductance value of the DC reactor 7 on the output side is made small due to the need to make the power source smaller and lighter, so the proportion of voltage sharing by the impedance of the welding cable increases, resulting in The difference in the output terminal voltage during a short circuit and an arc is small and varies depending on the cable length, making it very difficult to distinguish between a short circuit and an arc, so the effects of the present invention are significant.

Furthermore, in the above embodiment, when the output current value increases,
The explanation has been made assuming that the output of the comparator 21 is inverted at the same current value both when the current decreases, but by giving the comparator 21 a hysteresis characteristic, as shown in Figure 5, when the current increases, the output current value sharply increases from point a. and when the current decreases after opening the short circuit, a-
By rapidly decreasing the output current value to the value b, the arc period can be further shortened and arc disturbances can be reduced.

As a means for detecting the rate of change of the output current, instead of providing the DC reactor secondary winding 7a shown in FIG. 1, the differential value of the current detection signal by the shunt resistor 8 may be taken.

[Effects of the Invention] According to the present invention, when a long short circuit occurs due to the welding wire thrusting, the short circuit can be quickly opened to prevent arc breakage, and arc breakage can be prevented without distinguishing between a short circuit and an arc. This method is particularly effective when high-speed welding of thin plates is performed using a consumable electrode, since the transition to the next short circuit can be promoted and arc disturbance can be avoided.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention;
Fig. 2 is an output current waveform diagram showing an example where arc breakage occurs due to the welding wire thrusting, and Fig. 3 is an output current waveform diagram showing an example where arc breakage can be prevented by conventional technology but arc disturbance occurs. FIG. 4 is an output current waveform diagram showing that both arc breakage and arc disturbance can be prevented by an embodiment of the present invention.
The figure is an output current waveform diagram of another embodiment of the present invention in which the current value determination circuit has hysteresis characteristics. 4... Output control unit (inverter), 7a... Current change rate detection means (DC reactor secondary winding), 8
...Output current value detection means (shunt resistor), 11
... Base material, 12 ... Arc load, 13 ... Consumable electrode (welding wire), 15 ... Output voltage setting section,
16...Addition unit, 17...Current change rate control circuit,
18...Current value determination circuit.

Claims (1)

[Claims] 1. In an arc welding power source with constant voltage characteristics that generates an arc between a consumable electrode and a base metal, means for detecting a rate of change in a welding power source output current, and a detection signal for the rate of current change. a current change rate control circuit that controls the rate of change of the output current by amplifying the output current and providing negative feedback to the control input of the output control section; a means for detecting the output current value of the welding power source; It has a current value determination circuit that determines whether or not the current value is equal to or greater than a predetermined value, and the amplification degree of the current change rate control circuit is changed based on the determination output of this current value determination circuit, and when the output current value is equal to or greater than a predetermined value, , an arc welding power source characterized in that the rate of change of output current is made larger than usual. 2. The arc welding power source according to claim 1, wherein the current value determination circuit has hysteresis characteristics. 3. Claim 1 or 2, characterized in that the output control section is a high frequency inverter.
Arc welding power source described in section.