JPS6222706B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a DC arc welding apparatus using consumable electrodes.

The power source of conventional consumable electrode type welding equipment has a high welding current.
It was a so-called constant voltage power supply with an output voltage drop of about 2 to 4 V for an increase of 100 A.

Such a constant voltage power supply has the drawback that the output voltage changes with the welding current, and the output voltage changes with changes in the input power supply voltage.

That is, the output of the welding power source is, for example,
The current and voltage conditions are 130A 20V, 200A 25V, and 300A 30V. When the output voltage of this welding power source changes depending on the output current, it is necessary to adjust the voltage setting device (variable resistor knob, etc.) so that the voltage value is suitable for welding. This caused trouble for the workers as it interrupted the welding work. moreover,
If the input voltage changes, for example, by 10%, the output voltage of the welding power source will also change by 10%, which may disrupt the welding conditions and sometimes make welding impossible.

It also detects the output voltage of the power supply and transfers this detected output voltage to an output control element (for example, a transistor,
By providing feedback to the control terminal of a thyristor, etc.), a constant voltage power source can prevent fluctuations in the welding output voltage due to fluctuations in the welding load or fluctuations in the input power supply voltage. The output voltage (hereinafter referred to as no-load voltage) before the welding arc (hereinafter simply referred to as the arc) that is applied between the electrode and the workpiece is sufficiently higher than the output voltage after the arc occurs (hereinafter referred to as the arc voltage). arc is more likely to occur. However, with the constant voltage power supply mentioned above, the no-load voltage is as low as the arc voltage (specifically, a predetermined voltage value), so the no-load voltage is too low to generate an arc. The arc was difficult to start, and it took a long time for the arc to stabilize.

Furthermore, if the no-load voltage is higher than necessary compared to the appropriate arc voltage determined by the welding conditions such as the plate thickness of the workpiece, the current at the time of arc generation will be large and the welding heat input will be excessive, resulting in spatter. This phenomenon was particularly noticeable when welding thin plates.

The present invention eliminates the above-mentioned conventional drawbacks and stabilizes the arc start by detecting the output voltage of an arc welding machine, switching the detected output voltage's partial pressure ratio according to the welding current, and converting the divided voltage to the welding current. and,
This is a DC arc welding machine that compares a preset reference voltage and outputs a voltage adjusted according to the difference between the two voltages.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of a DC arc welding machine according to the present invention.

In the figure, 1 is an input device constituted by a welding transformer, and 2 is an output device using output control elements such as transistors and thyristors, which are connected to the input device 1. The following description will be made regarding an example in which a thyristor is used as the input device 2.

3 is a current detector inserted between the output device 2 and the arc load 4.

5 is an arc voltage detector, and as shown in FIG. 2, it is a voltage dividing circuit consisting of series resistors 6, 7, and 8, a capacitor 9 connected in parallel to these resistors 7 and 8, and a resistor 10 connected in parallel to resistor 8. and a switch 11 inserted in series with a resistor 10. Reference numeral 11 denotes a switch that is opened and closed by the current detector 3. When an arc current flows, the switch 11 is opened and connected to the voltage dividing circuit 5 so that the output of the arc voltage detector 5 increases.
A switching circuit is configured to switch the voltage division ratio. 12 is a constant voltage power supply serving as a reference.

13 is a comparator circuit, one of which has two input terminals connected to the output terminal of the output voltage detector 5 and the reference power supply 12, respectively.
The other output terminal is connected to an output control circuit 14, which will be described later, through an amplifier (not shown). Reference numeral 14 denotes an output control circuit, the output end of which is connected to the gate of a thyristor constituting the output device 2. Reference numeral 15 denotes a no-load voltage supply circuit including a high resistance, which is connected in parallel with the output device 2 and directly supplies the output voltage (no-load voltage) of the input device 1 to the arc load 4.

Next, the operation will be explained according to Fig. 3. Fig. 3 is a waveform diagram for explaining the operation of one embodiment of the present invention, and in the figure, a indicates that the arc voltages e ₁ and E ₁ a are low. , and b indicates the case where the arc voltages e ₁ and E ₁ b are high.

First, when welding with a low arc voltage E ₁ a, the reference voltage e ₃ is set to a correspondingly low voltage E ₃ a. The high no-load voltage E output from the input device 1 is supplied to the output device 2 and also to the arc load 4 through the supply circuit 15. Since the high no-load voltage E supplied to the arc load 4 is supplied through the high resistance of the supply circuit 15, when the arc load 4 is ignited, the supply circuit 1
Due to the voltage drop of 5, the output voltage of output device 2
E′ (arc voltage E′ ₁ a and E′ ₁ b are collectively referred to as E′). Before the arc-suit, no arc current flows, so there is no output from current detector 3, so switch 11
is closed. Since resistors 8 and 10 are connected in parallel by this switch 11, the output e ₂ of the arc voltage detector 5 is a low voltage obtained by dividing the no-load voltage E by resistors 6 and 7 and resistors 8 and 10 with a small voltage division ratio. E′ ₂ .

This output E′ ₂ is converted to reference voltages e ₃ and E ₃ a by the comparator circuit 13.
The differential voltage (E ₃ a - E' ₂ ) is input to the output control circuit 14. The output control circuit 14 applies to the thyristor gate of the output device 2 a gate signal (not shown) whose phase is shifted by an amount corresponding to the differential voltage (E ₃ a−E′ ₂ ). The thyristor is then fired, and the output device 2 obtains an output voltage E'a that has been changed by an amount corresponding to the differential voltage (e ₃ -e ₂ ). Therefore, the voltage applied to the terminals of the arc load 4 changes from the no-load voltage E to the arc voltage E'a after the arc is ignited. Most of the arc current at arc start is supplied by the output device 2.

When the current detector 3 detects the arc current at the time of arc start, the switch 11 is opened and the parallel resistor 10 of the arc voltage detector 5 is removed from the circuit. When the resistor 10 is opened, the voltage division ratio of the arc voltage detector 5 increases, so that the output e ₂ becomes a high voltage E ₂ a. Therefore, _the difference voltage _{(e 3 −
e2} ) becomes smaller. As the differential voltage (e ₃ −e ₂ ) becomes smaller, the phase of the gate signal output from the output control circuit 14 is delayed and applied to the output device 2. From the output device 2, the output voltage (arc voltage) E _{1 a} is changed by an amount corresponding to the decreased differential voltage (e ₃ −e ₂ ).
is output.

Next, when welding with a high arc voltage e ₁ (E ₁ b), the reference voltage e ₃ is set to a correspondingly high voltage E ₃ b. Even if the reference voltage _e3 changes, the no-load voltage E
does not change, so the output _e2 of the arc voltage detector 5 also remains _E'2 . Since the voltage difference (e ₃ -e ₂ ) between this output e ₂ and the reference voltage e ₃ becomes large, the arc voltage E'b becomes higher than the voltage E'a according to this voltage difference. After the arc starts, the arc voltage E ₁ b becomes higher according to the preset reference voltage E ₃ b. Depending on the welding conditions such as the plate thickness of the workpiece, the arc voltage E ₁ (arc voltages E ₁ a and E ₁ b are collectively referred to as E ₁ ) can be set high (E ₁ b) or lower (E ₁ a), by setting the reference voltage e ₃ according to this arc voltage E ₁ , the arc voltage E' immediately after the arc occurs (although the no-load voltage E remains the same) , can be set higher or lower depending on the arc voltage E ₁ . (Arc voltage
E′ collectively refers to arc voltages E′a and E′b. ) The arc is easily generated by the high no-load voltage E, and the generated arc is maintained by the next high arc voltage E' and the arc current supplied from the output device 2, and then the set arc is maintained. Welding at voltage E ₁ .

As a result of implementing the above invention in an arc welding machine, the voltage division ratio of the voltage division resistance, the comparison circuit 13, and the output control circuit 1 are as follows.
By adjusting the gain of 4 to an appropriate value, the change in output current can be reduced to less than 1V per 100A, and even if the input voltage is 10%, the output voltage fluctuation can be reduced to about 5%. I was able to do that.

The purpose of the capacitor 9 of the arc voltage detector 5 is to smooth the arc detection voltage. Due to the action of the resistor 15 connected in parallel, the voltage e ₄ has a small change width even though the voltage change of the arc voltage e ₁ is large. This prevents hunting, which occurs due to delays in the charging and discharging time of the smoothing capacitor (which adversely affects welding).

Further, in the embodiment of the present invention, the no-load voltage supply circuit 15 is connected to the input device 1, but the no-load voltage supply circuit 15 may be supplied not from the input device 1 but from another power source. Furthermore, the same effects as in the above embodiment can be obtained even in a circuit that does not have a no-load voltage supply circuit.

Further, although the present invention has been described only at the time of arc start, effective arc generation (arc start) can be performed even when the arc breaks during welding.

As described above, the present invention detects the output voltage of an arc welding machine, switches the voltage division ratio of the detected output voltage according to the welding current, compares this divided voltage with a preset reference voltage, and Since an output voltage corresponding to the difference between the two voltages is output, arc starting can be performed easily and stably. In addition, if you change the set output voltage (arc voltage), you can also change the output voltage setting at arc start, so you can start the arc in a stable state from low arc voltage to high arc voltage. . Furthermore, after arc starting, the set output voltage can be maintained at a constant level regardless of load fluctuations or input power fluctuations.

Furthermore, the output voltage can be controlled without manipulating the reference voltage, and the configuration is simple.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG.
The figure is a circuit diagram showing an embodiment of an arc voltage detector. FIG. 3 is a waveform diagram for explaining the operation of the present invention. 1... Input device, 2... Output device, 3... Arc current detector, 4... Arc load, 5... Arc voltage detector, 6, 7, 8, 10... Resistor, 11...
...Switch, 12... Constant voltage power supply, 13... Comparison circuit, 14... Output control circuit, 15... No-load voltage supply circuit.

Claims (1)

[Claims] 1. An output device that adjusts the output of the arc welding machine, a current detector that detects the welding current output from the output device, a voltage dividing circuit that divides the arc voltage output from the output device, and the current detector A switching circuit that switches the voltage division ratio of the voltage dividing circuit to a small one at the start of welding and a large one at the time of welding arc generation based on a detection signal from the voltage dividing circuit compares the output voltage of the voltage dividing circuit with a preset reference voltage, A DC arc welding machine comprising: a comparison circuit that outputs a difference signal; and a control circuit that controls the output device according to the difference signal.