JPS6365429B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding power source output control device, and its purpose is to control the output power in the event of a short circuit in an output control device for consumable electrode arc welding devices such as CO ₂ welding and MIG welding. The object of the present invention is to provide a device that can easily select an appropriate welding operation state by electrically controlling the welding operation and improve the operation efficiency. As a power source for consumable electrode arc welding, a power source with constant voltage characteristics is usually used, and recently a control rectifier element (hereinafter referred to as a thyristor) is often used for output control. Further, as the output control method, there are a case where the output signal voltage is feedback-controlled to obtain a constant voltage characteristic, and a case where the output voltage value is simply specified and controlled. However, in the case of arc welding, short-circuiting and arcing are repeated in the load state, so short-circuit characteristics such as the rise of load current during short-circuiting have a large effect on welding workability. For this reason, workability is usually improved by providing an inductance in the welding output circuit to adjust the short circuit characteristics. However, during actual welding, the optimal amount of inductance varies depending on the welding current, welding speed, welding posture, etc., but the inductance amount is determined according to the average usage conditions. This is because it is not easy to adjust the amount of inductance, and because it is heavy and expensive, it is practically impossible to adjust the amount of inductance.

FIG. 1 shows an example of the overall configuration of a general welding power supply device. T ₁ is a main transformer having a primary winding and a secondary winding, and the secondary side has a double star connection, and an interphase reactor L ₁ is arranged between each star connection. SCR ₁ to _{SCR 6} are controlled rectifying elements (thyristors), G ₁ to _{G 6} are each thyristor SCR ₁
~ Gate of SCR ₆ , K ₁ ~ _{K 6} is thyristor SCR ₁ ~
The cathode of SCR ₆ , L ₁ is an interphase reactor, L ₂ is a reactor, 1 is a consumable electrode, 2 is a base material to be welded, and 3 is an arc. Currently, welding power supplies using thyristors usually input 200V three-phase AC, and the DC output circuit via the main transformer _T1 has a power supply that is connected to Reactor _L2 is installed to set an appropriate current rise. In Figure 1, the gate circuit of the thyristor is K ₁ - G ₁ and K ₄ - G ₄ , K ₂ - G ₂ and K ₅ - G ₅ , K ₃
-G ₃ and K ₆ -G ₆ are required as a set of three types with different phases.

In a conventional thyristor power supply like this,
The gate circuit configuration includes open-loop control in which each thyristor operates in constant phase to control the average output, and feedback control in which the output voltage during welding is fed back to obtain the set average output. However, this type of control usually shortens the control response time to ensure system stability.
It was impossible to reduce the time to 6 msec or less. However, the short circuit time during welding is approximately 3~
Since 15 msec is appropriate, a reactor that is difficult to adjust was required on the DC side to suppress the current rise in the event of a short circuit. In other words, in this method of adjusting the rise of the welding current in the event of a short circuit using a reactor, it is extremely difficult to adjust the welding current to the optimum value depending on the welding current, welding speed, welding posture, etc., as described above. .

The present invention distinguishes whether the output state is a short circuit or an arc, and electrically controls the output appropriately for the short circuit and arc occurrence, which have an important effect on welding work, thereby improving short circuit characteristics. This is an attempt to easily obtain an appropriate welding working condition through adjustment, and its configuration will be explained below with reference to the drawings shown as examples. Figure 2 shows an example of the control circuit of a welding power source output control device, where SCR is a group of thyristors arranged in the main circuit, 1 is a consumable electrode, 2 is the base material to be welded, 3 is an arc, 4 5 is an average output control circuit, 6 is a short circuit and arc characteristic improvement circuit, 7 is a gate circuit that sends a control signal to the thyristor, 8 is a consumable electrode 1 This is an arc voltage detection circuit that generates a voltage signal proportional to the voltage between the current-carrying part and the welding base material 2. In the above configuration, the detection circuit 4 detects whether the output state is an arc or a short circuit, and the result is input to the short circuit and arc characteristic improvement circuit 6. Further, the arc voltage detection circuit 6 detects the voltage between the current-carrying part of the consumable electrode 1 and the welding base material, and the result is input to the characteristic improvement circuit 6. The characteristic improvement circuit 6 determines the amount of output reduction in response to the signal input from the arc voltage detection circuit 8 when it is detected by the signal input from the detection circuit 4 that the output state has shifted from an arc state to a short circuit state. The conduction period α of the thyristor is determined, and this α is controlled and outputted so as to become smaller as time passes. The gate circuit 7 controls the thyristor SCR according to the output of the characteristic improvement circuit 6 and the output of the average output control circuit 5. In addition, the characteristic improvement circuit 6 increases the output in response to the signal input from the arc voltage detection circuit 4 when it is detected by the signal input from the detection circuit 4 that the output state has shifted to short-circuit or arcing. The conduction period β of the thyristor that determines the amount of electricity is determined, and this β is controlled and outputted so as to become smaller as time passes. That is, the detection circuit 4 detects whether the output state is a short circuit or an arc, and in the case of a short circuit, the output is immediately lowered than the set average output (welding voltage suitable for the welding current) after the short circuit. This amount of output reduction is the conduction period α of the thyristor. Thereafter, control is performed to gradually increase the output toward the average set output during the short-circuit period. That is, the output current at the time of a short circuit is appropriately controlled based on the amount of output reduction during the short circuit, the conduction period α, and the degree of increase in output thereafter.

Next, when an arc occurs, the output is increased from the set average output immediately after the arc occurs. This output increase amount is the conduction period β of the thyristor. Thereafter, control is performed to gradually reduce the output toward the average set output during the arc generation period. That is, the output current at the time of arcing is appropriately controlled by the amount of increase in output at the time of arc occurrence, the conduction period β, and the degree of decrease in output thereafter. The welding voltage signal of the arc voltage detection circuit 8 increases almost proportionally as the distance between the current-carrying part of the consumable electrode 1 and the welding base metal 2 increases, and when the welding conditions are the same and the current-carrying part of the consumable electrode 1 If the distance between the welding base metal 2 and the welding base metal 2 is the same, the consumable electrode 1
The voltage between the current-carrying part of the electrode 1 and the welding base metal 2 is almost the same, and its output is connected to a short-circuit and arc characteristic improvement circuit 6. It is possible to automatically control the amount of subsequent output decrease (thyristor conduction period α) and the output increase amount after arc occurrence (thyristor conduction period β). Is the output state short-circuited?
The state of change in the firing phase of the thyristor, which changes depending on whether an arc is occurring or not, will be explained with reference to FIG.

In FIG. 3, a indicates a short circuit period, b indicates an arc generation period, and θ indicates an ignition phase that provides a reference conduction period T depending on the welding output. Assuming that the short-circuit is initiated for time t ₁ , the firing phase of the thyristor is delayed by the conduction period α to bring the firing phase to θ ₁ , and then during the short-circuit period the firing phase is gradually advanced towards the θ phase (the Figure 3, line A). In this way, the output after a short circuit is reduced and the rise of the welding current is suppressed. Next, at time t ₂ when an arc occurs, the firing phase of the thyristor is advanced by β from the θ phase to θ ₂ , and then the firing phase of the thyristor is gradually changed to θ along line B in Figure 3.
By bringing the welding arc closer to the phase, the output after arc generation is increased and the welding arc is maintained.

In the case of the above-mentioned method of suppressing the amount of increase in output immediately after a short circuit, the short circuit may not be opened satisfactorily, and in extreme cases, repelling may occur.
In addition, cissing means that without transitioning from a short circuit to an arc,
This refers to the wire melting and scattering. This indicates that there is an appropriate value for the amount of output suppression immediately after a short circuit, and this appropriate value changes depending on the distance between the consumable electrode current-carrying part of the welding torch and the weld base metal. According to detailed experimental results, it has been found that as the distance between the consumable electrode current-carrying part and the weld base metal increases, it is preferable in terms of welding characteristics to decrease the value of the suppression amount (i.e., α) at the time of a short circuit. The effect of the distance between the electrode current-carrying part and the base metal is large in so-called semi-automatic welding, where the torch is held in the hand during welding, and the distance changes depending on the movement of the hand. This may occur.

In order to prevent instability of the welding arc due to variations in the distance l between the consumable electrode current-carrying part and the welding base metal, the output suppression amount (conduction period α) immediately after a short circuit is varied in accordance with the distance l, so that a good The change control amount when maintaining a stable welding arc will be explained.

Figure 4 shows the distance l between the current-carrying part of the consumable electrode and the welding base metal.
The relationship between the value of and the appropriate suppression amount (conduction period α) at the time of short circuit is shown. The value of the appropriate suppression amount (conduction period α) at the standard distance l ₁ between the current-carrying part and the base metal corresponding to the welding output current value becomes smaller as the distance l increases. Also, as the appropriate suppression amount during short circuit changes, the appropriate kick amount during arcing (i.e. conduction period β)
It is controlled so that the stiffness amount β is also reduced at the same time as the suppression amount α is reduced.

Note that as the distance l between the current-carrying part of the consumable electrode and the welding base metal increases, the value of the suppression amount α at the time of short circuit is decreased, and the value of the kick amount β at the time of arc generation is accordingly decreased to stabilize the welding arc. Experimental results have confirmed that repellency is less likely to occur.

That is, FIG. 5 shows the values of the suppression amount α as α ₁ , α ₂ , α ₃
(as shown in Fig. 4, α ₁ > α ₂ > α ₃ ), and the values of the stiffness β are set as β ₁ , β ₂ , β ₃ (as shown in Fig. 4, β ₁ > β ₂ >
β ₃ ), and shows the probability of repelling when the distance l between the electrode and the base material is changed. When the distance l is changed from l ₁ to l ₂ , the amount of suppression is α ₁ and the amount of kick is β If it is ₁
Repelling occurred 13 times for 100 changes in the distance between the electrode base materials (repelling probability 13%), and no repelling occurred if the suppression amount α ₂ and the sharpness amount β ₂ were used.

In addition, in the above experiment, l ₁ is 15 mm, l ₂ is 18 mm,
l ₃ is 22mm, α ₁ = 18°, α ₂ = 10°, α ₃ = 2°, β ₁
=
18°, β ₂ = 9°, and β ₂ = 1°. In addition, the experimental conditions are
The welding current was 120 A, the welding voltage was 19 V, a normal solid wire with a diameter of 1.2 mm, and the shielding gas was CO ₂ gas.

Depending on the length of the distance l as described above, the suppression amount after short circuit (conduction period α) and the value of the kick amount after arc generation (conduction period β) are determined by the welding voltage, which has a nearly linear relationship with the distance l. It is automatically controlled by signals and can maintain a stable welding arc.

The present invention has the configuration and operation as described above, and adds control to actively suppress the increase in welding output in the event of a short circuit, while increasing the welding output to maintain the welding arc in the event of an arc, and to control the main thyristor point. By controlling the arc phase and optimizing the dynamic characteristics of the welding power source, the welding characteristics of the welding arc can be significantly improved, and the amount of output decrease after short circuit and the amount of output increase after arc occurrence are smaller than those of the consumable electrode. Control can be performed automatically by changing the distance depending on the distance between the current-carrying part and the base metal to be welded. As a shielding gas
In the COO ₂ welding method using CO ₂ , the consumable electrode melts and transfers to the base metal due to repeated short circuits with the base metal, so-called short-circuit transfer, and the consumable electrode becomes molten and transfers to the base metal. The effect is particularly remarkable in the medium current range where so-called globule migration, which transfers to metal, is unstable, and the edges of the weld bead are greatly improved, resulting in a good weld bead without cold laps or whiskers. and welding spatter is extremely small.
Therefore, it is possible to obtain extremely good welding conditions and to improve work efficiency.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a welding power supply device, FIG. 2 is a block diagram showing an embodiment of a welding power source output control device according to the present invention, and FIG. FIG. 4 shows the value of the distance l between the consumable electrode current-carrying part and the welding base material in the device of the present invention, and
FIG. 5 is a diagram showing the relationship between the amount of suppression at the time of short circuit (conduction period α) and the amount of kick at the time of arc (conduction period β), and FIG. 5 is a characteristic diagram showing the relationship between the distance between the electrode base materials and the repellency probability. DESCRIPTION OF SYMBOLS 1...Consumable electrode, 2...Base material to be welded, 4...Output state detection circuit, 5...Average output control circuit, 6...
...Short circuit and arc characteristic improvement circuit, 8...Arc voltage detection circuit.

Claims (1)

[Claims] 1. In an arc welding device using a consumable electrode and using a plurality of control rectifying elements as an output control means, an output state detection circuit detects whether the welding output state is an arc state or a short circuit state, and the control according to the welding output An average output control circuit that provides a reference conduction period T of a rectifying element; and an average output control circuit that makes the conduction period of the control rectifier element shorter by α than the reference conduction period T immediately after a short circuit occurs, and increases the conduction period as time passes after the short circuit occurs. a short-circuit characteristic improving circuit that gradually approaches the reference conduction period T; and immediately after an arc occurs, the conduction period is made longer than the reference conduction period T by β;
an arc characteristic improvement circuit that gradually brings the conduction period closer to the reference conduction period T with the passage of time after the arc occurs; and the value of α as the voltage value detected by the arc voltage detection circuit increases. A welding power source output control device comprising an appropriate suppression amount control circuit that controls the value of β to a small value and a tight voltage control circuit that controls the value of β to a small value.