JPH0696194B2 - Waveform control method for short-circuit arc welding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a waveform control method for short-circuit arc welding suitable for high-speed welding of thin plates using consumable electrodes.

[Prior Art] Conventionally, it has not been generally performed to control the waveform of short-circuit arc welding, in particular, to control the rise of the current at the initial stage of the short-circuit. I was letting you. Further, as related art, there is JP-A-61-108179, which monitors the arc voltage or current during short-circuit arc welding, detects the arc state immediately before the short-circuit, and limits the output current of the welding power source. It was a thing.

[Problems to be Solved by the Invention] Generally, in short-circuit arc welding using consumable electrodes,
When the current change rate during short circuit and during arcing is small, when welding is performed at high speed, as shown in the welding current waveform diagram of FIG. 2, the short circuit time shown in section a and the arc generation time shown in section b Longer, the number of short circuits is greatly reduced and the bead appearance is deteriorated.When the arc length is suddenly shortened, the short circuit is not opened and a long short circuit occurs, during which the heated welding wire is explosive. It may melt and cause arc breakage, and the welding speed cannot be increased.

Further, if the current change rate during short circuit and during arc is increased to increase the number of short circuits, the number of short circuits increases as shown in the welding current waveform diagram of FIG. The short-circuiting for a short time (hereinafter referred to as incomplete short-circuiting) frequently occurs during this time. During this period, the droplets at the tip of the welding wire did not transfer to the base metal, and the number of short-circuits actually decreased. And the droplet grows large, d
At the time of the next short circuit shown in the section (2), a large short circuit current may flow, large spatter may be generated, or the arc may be broken. The incomplete short circuit here is an electromagnetic pinch force due to a rapid rise of current at the initial stage of the short circuit, and is a phenomenon in which the short circuit is broken before the droplet migrates to the base material due to surface tension.

In Japanese Patent Laid-Open No. Sho 61-108179, the incomplete short circuit is prevented by limiting the current at the initial stage of the short circuit, but it is necessary to extend the lead wire to the tip of the torch and detect the arc state immediately before the short circuit. The torch structure is special, and the waveform of the detection signal is blunted by the inductance of the conductor, which is a problem in practical use.

An object of the present invention is to prevent the occurrence of an incomplete short circuit when the number of short circuits is increased, to stably generate an arc even when welding is performed at high speed, and to be easily applied to actual work. It is to provide a waveform control method for short-circuit arc welding.

[Means for Solving Problems] The above object is to detect the output current value of welding and its change rate during short-circuit arc welding, and the detected output current value causes a short circuit between the droplet and the base metal. It is determined whether or not it is in the current region of a predetermined value or less, and when the output current value is in the current region of the predetermined value or less, the change rate of the detected output current value is higher than that in the other current regions. It is achieved by increasing the amplification degree of the output current and controlling it so that the rate of change of the output current value is reduced based on the difference between the rate of change of the amplified output current value and the preset setting value. It

[Operation] When the current value determination circuit determines that the welding power supply output current value is in a current region of a predetermined value or less at which a short circuit occurs between the droplet and the base metal, the present invention is more effective than other times. The rate of change of the output current is reduced, that is, as shown in the welding current waveform diagram of FIG. 4, the rate of change of the output current is set to a region where the output current is small (I ₂₁ or less) where an incomplete short circuit is likely to occur. In the initial stage of the short circuit shown in the section e of FIG. 4, by making the current smaller than usual and making it larger than usual in other current regions so that the macroscopic current change rate becomes larger than usual. The current rise is made gentle to prevent the occurrence of incomplete short circuits, and the number of short circuits is increased so that stable welding with good bead appearance can be performed even at high speed welding.

The waveform control of such short-circuit arc welding uses a high frequency inverter in the output control unit of the welding power source, and the current change rate control circuit that negatively feeds back the current change rate detection signal to the output control unit by the determination output of the current value determination circuit. This can be easily realized by changing the amplification degree and controlling the output pulse width or output frequency of the inverter.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 4.

FIG. 1 shows the circuit configuration of the welding power source. In the figure, 1 is an AC input terminal, 2 is an input side rectifier circuit for converting an AC input of a commercial frequency into DC, 3 is a smoothing capacitor, 4 is a smoothed DC input with a frequency higher than the commercial frequency (for example, 20ak H).
z) An inverter circuit that converts into alternating current, and corresponds to the output control section of the main welding power source. The AC output of the inverter circuit 4 is stepped down to a voltage suitable for welding by the transformer 5, converted into DC by the output side rectification circuit 6, passes through the DC reactor 7, the shunt resistor 8 for current detection, and passes through the output terminal 9 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, and 14 is a wire feeding motor.

The secondary winding 7a provided in the DC reactor 7 as the current change rate detecting means generates a voltage proportional to the change rate (di / dt) of the welding power source current. This voltage is applied to the current change rate control circuit
Amplified by 17 to make a feedback signal, and this and output voltage setting device
The signal obtained by adding the reference input signal from 15 with the adder 16,
By using the control input for determining the output pulse width of the inverter circuit 4, the external output characteristic of the welding power source becomes a constant voltage characteristic, and the output of the welding power source is output so that the output current waveform as shown in FIG. 4 is obtained. Take control.

The current change rate control circuit 17, for example, has a variable amplification degree by changing the resistance inserted in the feedback circuit of the operational amplifier by a selection switch.By changing the amplification degree, the current change rate in the output current waveform is changed. Is controlled in two steps, large and small.

The current value determination circuit 18 compares a signal obtained by amplifying the voltage proportional to the output current value generated in the current detection shunt resistor 8 with the amplifier 19 and the reference signal from the current level setting device 20 with the comparator 21, and short-circuits the signal. It is a circuit for determining whether the output current value during arc welding is in a current region of a predetermined value or less at which a short circuit occurs between the droplet and the base material, and in the present invention, the determination output of this current value determination circuit 18 Is a control signal such as a selection switch for changing the amplification factor of the current change rate control circuit 17,
When the output current value is in the current region of the predetermined value or less, the amplification degree of the current change rate control circuit 17 is increased and the change rate of the output current is decreased compared to the other cases.

When short-circuit arc welding is performed using the welding power source having the above configuration, as shown in FIG. 4, if the output current value is equal to or less than the predetermined value I ₂₁ set by the current level setter 20, the current change rate ( di / dt) becomes smaller than usual, an incomplete short circuit as shown in the section c of FIG. 3 does not occur, a short circuit with periodicity occurs, and further, in the current region exceeding I ₂₁ If the current change rate (di / dt) is set to be larger than usual, the macroscopic current change rate (di / dt) is larger than the normal welding current waveform shown in Fig. 3, Even in high-speed welding, it is possible to increase the number of short-circuits with an average current value of 100 A, 30 to 40 times / second, and with an average current value of 270 A, 100 times / second or more. Here, the current value I ₂₁ for switching the current change rate is
It goes without saying that it is set according to the average current value during welding.

EFFECTS OF THE INVENTION According to the present invention, it is possible to prevent the occurrence of incomplete short circuits due to the rapid rise of current in the initial stage of short circuits, increase the number of short circuits, and perform stable high-speed welding with good bead appearance. You can

Further, according to the present invention, waveform control is performed by changing the current change rate depending on whether or not the output current value of the welding power source is in a current region below a predetermined value at which a short circuit occurs between the droplet and the base material. Since there is no problem that the torch structure is special because the arc state immediately before the short circuit is detected, it can be applied to both automatic and semi-automatic welding.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a welding power source used in an embodiment of the present invention, FIG. 2 is a welding current waveform diagram when the number of short circuits is abnormally reduced by performing high-speed welding with an ordinary welding power source, and FIG. The figure shows a welding current waveform chart when an incomplete short circuit occurs when high-speed welding is performed by increasing the current change rate of the output current from that of a normal welding power source, and FIG. It is a welding current waveform diagram with many and incomplete short circuits. 4 ... Output control unit (inverter), 7a ... Current change rate detecting means (DC reactor secondary winding), 8 ... Output current value detecting means (shunt resistance), 11 ... Base metal, 12 ... Arc Load, 13 ... consumable electrode (welding wire), 15 ... output voltage setting section, 16 ... adder, 17 ... current change rate control circuit, 18
...... Current value judgment circuit, 20 ...... Current level setter, 21 ……
comparator.

Claims (3)

[Claims] 1. When short-circuit arc welding, the output current value of welding and its rate of change are detected, and whether the detected output current value is in a current region below a predetermined value at which a short circuit occurs between a droplet and a base metal. When the output current value is in the current region of the predetermined value or less, the amplification rate of the change rate of the detected output current value is increased and amplified when the output current value is in the current region other than the predetermined value. A waveform control method for short-circuit arc welding, characterized in that control is performed so as to reduce the change rate of the output current value based on the difference between the change rate of the output current value and the preset set value. 2. When the output current value is in a current region below a predetermined value at which a short circuit occurs between the droplet and the base material, the rate of change of the output current value is made smaller than usual, and the other current regions When it is, the control method is performed such that the rate of change of the output current value is larger than usual, and the waveform control method for short-circuit arc welding according to claim 1. 3. The waveform control method for short-circuit arc welding according to claim 1, wherein the output current value is controlled by an inverter.