JP2509546B2 - Welding power supply - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a welding power source used when performing short-circuit transfer arc welding using a consumable electrode, and in particular, the occurrence of spatter that significantly impairs the welding workability is significantly reduced. It relates to a welding power source to be reduced.

[Prior Art] First, FIGS. 7A to 7F show a general droplet transfer process in short-circuit transfer arc welding in which welding is performed while repeating short circuit and arc generation between a welding wire and a base material. ). In FIG. 7, 11 is a welding wire, 12 is a base metal, 13 is a droplet, (a) is an arc generation state immediately before a short circuit, (b) is an initial state of a short circuit in which the droplet contacts the molten pool (c) Indicates the contact between the droplet and the molten pool and the droplet is migrating, and the droplet is migrating. (D) is the latter half of the short circuit in which the droplet migrates to the molten pool side, causing a constriction between the welding wire and the droplet. The state (e) is the moment when the short circuit is broken and the welding arc is generated, and the state (f) shows the arc generation state in which the welding wire is melted and the droplets grow, and the steps (a) to (f) are repeated.

In such a process, the sputter breaks the short circuit,
It has been clarified that a large amount is generated at the moment when the welding arc is regenerated, that is, in FIG. 7 (e), and the spatter generation amount increases as the welding current at the time of regenerating the welding arc increases.

In view of the above-mentioned cause of spatter generation, control of the welding current as shown in FIG. 8 has been proposed in order to reduce the amount of spatter generation. That is, the welding current is reduced from the short-circuit current I _SP to the arc re-generation current I _RA at the moment of transfer of the droplets to the molten pool (immediately before the arc is generated), and the energy at the completion of the melting transfer is the minimum required for arc re-generation. This is to limit the generation of spatter.

Japanese Patent Laid-Open No. 59-2061 discloses a conventional welding power source in which the generation of spatter is reduced by using such current control.
Some are disclosed in Japanese Patent No. 59. With this welding power source,
The welding current during the period from short circuit to arc reoccurrence is controlled as follows. First, when the applied welding current at the time of short circuit is kept at a predetermined value (I _SP ), and it is detected by the change in applied voltage (see FIG. 8) that the latter half of the short circuit at which constriction occurs is detected, the purpose is to reduce the generation of spatter. The low welding current (I _RA ) is also reduced.

In order to carry out the above-mentioned current control, the conventional welding power source described in the above publication is provided between the DC power source and the welding step-down transformer to output the welding current (between the welding wire and the base metal). The first switch means composed of a switching element for controlling the applied current), the second switch means interposed in the welding current supply path (welding current attenuation path), and the second switch means And an impedance element arranged in parallel with each other, the first and second switch means are turned off when the occurrence of the constriction is detected from the increase change in the arc voltage between the torch and the base metal. Drive control to the state. As a result, the welding current flows through the impedance element and is assisted by the attenuation by the impedance element,
A fast current decay characteristic can be obtained.

[Problems to be Solved by the Invention] By the way, the rise change of the arc voltage is used to judge and detect the constriction. At this time, if the arc voltage can be detected at the position closest to the arc occurrence, the constriction is appropriate. Detection can be performed.

For this purpose, arc voltage detection points are provided on the torch barrel at the same potential as the consumable electrode in the welding torch and the workpiece itself to be welded as the base material, and the voltage between these torch barrel and the workpiece itself is detected. are doing. However, at present, the welding power source and the welding location are separated, and the length of the arc voltage detection wiring and its wiring state cannot be constant, and as a result,
The detected arc voltage fluctuates due to noise and the like, and the constriction cannot be accurately detected, so that it cannot be put to practical use.

Therefore, the threshold voltage value set to detect the occurrence of the necking (the reference voltage value for judging that the necking has occurred when the arc voltage exceeds that value) is set to a higher value to reduce noise. It is desirable to set the value so that it can be determined that the constriction has occurred without being affected. However, in this case, it is necessary to reduce the welding current to a low welding current for the purpose of reducing spatter generation within an extremely short time after the constriction has occurred, but with the conventional welding power source described above, it is sufficiently effective. We cannot attenuate the welding current,
After all, reduction of spatter cannot be realized and it cannot be put to practical use.

The present invention is intended to solve such a problem, and it is possible to obtain a current attenuation characteristic having a linear and steep falling slope so that an arc voltage of an arc voltage can be accurately detected in order to accurately detect the occurrence of a constriction. Provides a welding power source that reliably prevents spatter generation by attenuating the welding current in a short time to the minimum current value required for arc reoccurrence even if the threshold voltage value is set high. The purpose is to do.

[Means for Solving Problems] Therefore, the welding power source of the present invention is inserted in the welding current attenuation path (welding current supply path) and the detection means for detecting the transition state of the droplets of the consumable electrode. A predetermined DC voltage is applied to both ends of the switch means that is turned off when the detection value of the detection means reaches a predetermined value (constriction detection threshold voltage value) and a capacitor connected in parallel to the switch means. Is provided.

[Operation] In the above-described welding power source of the present invention, when the detection means detects the symptom of occurrence of arc re-occurrence (occurrence of necking), and the switch means is turned off in response to this, the welding current decay path is generated. Welding current flows into the capacitor in the power supply circuit and absorbs the energy so that a predetermined DC voltage is applied across the capacitor in the power supply circuit PO, in relation to the welding current in the welding current decay path. Since the attenuation rate of the linear expression of the attenuation current equivalently given can be made constant, the current attenuation characteristic having a linear and steep falling slope can be obtained.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a welding power source as a first embodiment of the present invention. 1 is a torch, 2 is a welding wire (consumable electrode), 3 is a base material (work itself), and welding wire 2 is It is fed from a feeding device (not shown). In addition, L is a reactor, D1 and D2 are rectifying diodes, E1 is a commercial AC power supply, and DB1 is
Is a diode bridge that rectifies the AC voltage from the AC power supply E1 into a DC voltage, C1 is a smoothing capacitor, and the DC power supply is configured by the AC power supply E1, the diode bridge DB1, and the capacitor C1. Further, SW1 to SW4 are switching elements, and T1 is a transformer.

Reference numeral 5 denotes a driver that turns on / off the switching elements SW1 to SW4 based on a predetermined signal from a circuit (not shown). Here, the switching elements SW1, SW4, and SW
2 and SW3 are paired and alternately driven on / off to control the welding current I to a set current value. 6 is an arc voltage detection circuit including an amplifier that detects and amplifies the arc voltage between the torch 1 and the base metal 3, and 7 is a constriction detection circuit, which receives the detection signal from the amplifier 6 and short-circuits the detection signal. After the start [see FIG. 7 (b)], a constriction [indication of arc reoccurrence; see FIG. 7 (d)] is detected when the preset threshold voltage value for detection of constriction (predetermined value) is reached. Therefore, it outputs a high level signal. Although not shown in FIG. 1, the welding wire 2
There is provided a short circuit detection circuit that detects the time point when the droplet of No. 1 starts to contact the molten pool of the base material 3 (time point when the short circuit starts) from the output of the arc voltage detection circuit 6.

SWD is a switching element (switch means) inserted in the welding current supply path (welding current attenuation path) between the diode D1 (D2) and the welding cable 4, and 8 is for turning on / off this switching element SWD. It is a driver for controlling, and when the signal from the constriction detection circuit 7 rises from low level to high level, the output signal is set to low level to turn off the switching element SWD.
The driver 8 is configured to turn on the switching element SWD again when the welding current I drops to a predetermined current value. In addition, the driver 5 is the driver 8
When receiving the low level signal from
~ All SW4 are turned off.

On the other hand, PO is a constant voltage power supply (power supply circuit) and is a commercial AC power supply.
It is composed of E2, transformer T2, diode bridge DB2, resistor R1, switching element SW5 and capacitor C2. Capacitor C2, through the backflow prevention diode D3,
It is connected in parallel to the switching element SWD.
Further, the AC voltage from the AC power supply E2 is rectified by the diode bridge DB2 into a DC voltage via the transformer T2 and applied to the capacitor C2. The resistor R1 and the switching element SW5 are provided in parallel with the capacitor C2, and the switching element SW5 is turned on / off by a control circuit (not shown) so that the capacitor C2
The increase in the DC voltage due to the energy absorbed in the capacitor is consumed by the resistor R1
A constant DC voltage V ₀ is applied across C2. The resistor R1 and the switching element SW5 constitute an adjustment circuit that maintains a voltage applied across the capacitor C2 and a predetermined value.

Since the welding power source as the first embodiment of the present invention is configured as described above, it operates as follows.

First, the AC power supply E1 is rectified by the diode bridge DB1, smoothed by the capacitor C1 and converted into a DC power supply. Then, the driver 5 causes the switching element SW
The high-frequency alternating current whose output is controlled by turning ON / OFF 1 to SW4 is stepped down via the transformer T1. Since the switching element SWD is normally on, the diode D1,
The welding current I rectified by D2 is torch 1 → welding wire 2 →
The arc voltage is supplied to the base material 3 and is applied between the welding wire 2 and the base material 3 to perform short-circuit transfer arc welding.

The droplet transfer process in this short-circuit transfer work welding is as described in FIGS. 7 (a) to 7 (f).
After contact with the molten pool of the base material 3 [at the start of a short circuit; see FIG. 7 (b)], the droplets migrate to the molten pool side and a constriction is formed between the welding wire 2 and the droplets. It begins to occur [see FIG. 7 (d)]. At this point, the arc voltage between the torch 1 and the base metal 3 detected by the arc voltage detection circuit 6 becomes large. When the arc voltage reaches the threshold voltage value for detecting the squeeze, the squeeze detection circuit 7 determines that a squeeze has occurred, and outputs a high level signal to the driver 8. Along with this, the driver 8 operates and the switching elements SW1 to SW4 and SWD are controlled to be turned off.

As a result, the welding current I flows in the order of the welding wire 2, the base metal 3, the transformer T1, the diode D1 (D2), the diode D3, the capacitor C2, the reactor L, the torch 1, and the welding wire 2, and is attenuated. During this current decay, in the present embodiment, the welding current flows into the capacitor C2 and its energy is absorbed, and the voltage across the capacitor C2 increases somewhat. However, the switching element SW5 should be turned on / off by the control circuit (not shown). Then, the energy stored in the capacitor C2 is consumed by the resistor R1. Therefore, the voltage across the capacitor C2 is always maintained at a constant value V ₀ .

Here, if the welding current at the time of turning off the switching elements SW1 to SW4 and SWD is I ₀ , the damping current I
Is equivalently expressed by the following equation.

I = I ₀ − (V ₀ / L) · t where I ₀ << V ₀ / R _A , I> 0, R _A is the resistance of the welding wire 2, t is time, and the switching element SW5 and resistance R
With the adjustment circuit consisting of 1, the voltage V ₀ across the capacitor C2
Is kept constant, the current attenuation rate V ₀ / L is constant. In addition, various circuit constants are I ₀ = 400A, L = 50μH, V ₀
= 400V, _RA = 20mΩ, the attenuation current I based on the above formula
Has an attenuation characteristic as shown by the symbol a in FIG. According to this, it is clear that a current attenuation characteristic having a steep falling slope is obtained linearly,
The decay time up to is 40 μsec.

Reference numeral b in FIG. 2 indicates a switching means (switching element SW of this embodiment) in the conventional welding power source.
It is a curve showing a current attenuation characteristic when a resistance of 1Ω is provided as an impedance element in parallel with D). Comparing curves a and b, in the present embodiment, the attenuation time from 400A to 80A is about It can be seen that it is reduced to 1/2 in a short time.

Further, FIG. 3 shows the relationship between the voltage V _SWD applied to the switching element SWD and the time required for the welding current to decrease from 400 A to 80 A, and the symbol c is according to this embodiment. , Symbol d indicates a conventional welding power source (when a resistor R is provided as an impedance element). As is clear from comparison between these curves c and d, in the present embodiment, if the voltage applied to the switching element SWD is the same, the decay time is about 1/2 of the short time. On the contrary, in order to obtain the same decay time, it is understood that in this embodiment, the switching element SWD having a withstand voltage of about 1/2 that of the conventional one may be used.

As described above, when the welding current I decreases to a predetermined current value, the driver 8 again causes the switching element SWD to operate.
Is turned on and the switching elements SW1 to SW4
Is also turned on / off as usual by the driver 5.
After that, the above-described operation is repeated.

As described above, according to the welding power source of the present embodiment, when the sign of arc reoccurrence (occurrence of necking) is detected as an increase in arc voltage, the switch element SWD is turned off in response to this, and welding is performed. The welding current I in the current attenuation path flows into the capacitor C2 in the power supply circuit PO, absorbs the energy, is consumed by the resistor R1, and a predetermined DC voltage V ₀ is applied to the capacitor C2 in the power supply circuit PO, Attenuation rate of linear expression [I = I ₀ − (V ₀ / L) · t] of damping current I ₀ given equivalently in relation to welding current I in the above welding current damping path
Since V ₀ / L can be kept constant, it is possible to obtain a current attenuation characteristic (see FIG. 2) having a linear and steep falling slope. Therefore, even if the threshold voltage value for necking detection is set high, the welding current I can be effectively attenuated to a low welding current within an extremely short time after the necking occurs. As a result, the occurrence of constriction can be accurately detected without being affected by noise and the like, and the occurrence of spatter can be reliably prevented.

In the present embodiment, as an example of the detection means for detecting the droplet transfer state of the consumable electrode, the means for detecting the droplet transfer state of the consumable electrode by the arc voltage is described. Any means for detecting a constriction, which is a precursor of arc regeneration of a consumable electrode, such as a change in welding current or welding current, may be used.

Further, according to the present embodiment, as described with reference to FIG. 3, there is an effect that the withstand voltage of the switching element SWD can be lowered as compared with the conventional welding power source.

In the present embodiment, if the welding current is sharply reduced immediately after the short circuit as well as when the constriction occurs, it is possible to prevent the spatter caused by the current increase immediately after the short circuit. Further, when the welding current is lower than a predetermined low welding current, the switching element SWD is turned on to prevent the welding current I from falling too much, thereby preventing arc breakage during arc regeneration. .

Further, in the present embodiment, when the occurrence of the constriction is detected, the current attenuation characteristics when all the switching elements SW1 to SW4 and SWD are in the OFF state have been described, but according to the welding power source of the present invention, Even if only the switching element SWD is turned off and the switching elements SW1 to SW4 are not all turned off, the same effect as described above can be obtained.
That is, when only the switching element SWD is turned off, if the no-load voltage of the welding power source is V _P , the damping current Ia
Is represented by Ia = I ₀ − (V ₀ −V _P ) · t / L, and although the slope of the damping (damping rate) is slightly reduced, there is no change in that a linear slope is obtained. Even if the target value is a low current, the damping can be performed quickly and in a short time. For example, when only the switching element SWD is turned off, the time t required to attenuate the welding current I from 400 A to 80 A is V _P = 70 V, and t = L · (I ₀ −Ia) / (V ₀ −V _P ) = 50 · (400−80) / (400−70) ≈ 48 μsec.

Further, in the present embodiment, the adjusting circuit is composed of the resistor R1 and the switching element SW5, but instead of this,
Zener diodes may be used.

Next, a welding power source as a second embodiment of the present invention will be described. FIG. 4 is a circuit diagram thereof. Note that, in FIG. 4, the same reference numerals as those used above indicate the same parts, and the description thereof will be omitted. In addition, in FIG. 4, the arc voltage detection circuit 6, shown in FIG. The constriction detection circuit 7 and the drivers 5 and 8 are not shown.

As shown in FIG. 4, the second embodiment is constructed almost similarly to the first embodiment. However, the constant voltage power supply PO1 (power supply circuit) in the second embodiment has a constant voltage of the first embodiment. Voltage power supply P
Flywheel diode D instead of resistor R1 at O
An energy regeneration circuit composed of 4, a transformer T3 and a diode D5 is provided.

This energy regeneration circuit uses a capacitor C2 during current decay.
The energy stored in the capacitor C1 is regenerated in the capacitor C1 by the on / off operation of the switching element SW5. That is, the voltage applied to both ends of the capacitor C2, which exceeds the predetermined value V ₀ , is regenerated to the welding power source primary side DC voltage to maintain the voltage across the capacitor C2 at a constant value V ₀ . is there.

As a result, the same effects as those of the first embodiment can be obtained by the second embodiment, and in the second embodiment, energy loss at the time of current attenuation can be suppressed, and at the same time, the current attenuation rate can be kept constant. You can keep it.

In addition, in the above-mentioned first and second embodiments, the case where the main circuit of the unipolar welding power source by the full bridge type inverter is provided is described, but the forward and reverse polarity switching type welding power source has each polarity. The arc phenomenon is the same for each case. Therefore, by providing the switching element SWD and the constant voltage power supply PO (PO1) in the welding current attenuation path, the present invention can be applied to the forward / reverse polarity switching type welding power supply.
Also, the same application and effects as in the case of the second embodiment can be obtained.

Also, in the half-bridge type inverter and chopper type power source as shown in FIGS. 5 and 6, respectively,
The present invention includes a switching element SWD and a constant voltage power supply PO (P
By providing O1) in the welding current attenuation path, the same application and effect as in the first and second embodiments can be obtained. However, in FIGS. 5 and 6, symbol E indicates a DC power source, SW1A and SW1B indicate switching elements, and T indicates a transformer.

A Zener diode may be used instead of the capacitor in which the switching element SWD of the constant voltage power supply in each of the above-described embodiments is provided in parallel. Further, instead of the diode D3 for backflow prevention, switching means or the like synchronized with the operation of the switching element SWD may be used.

[Effects of the Invention] As described in detail above, according to the welding power source of the present invention, when the sign of arc re-occurrence is detected and the switch means is turned off in response to this, welding in the welding current decay path is performed. A current flows into the capacitor in the power supply circuit and absorbs the energy so that a predetermined DC voltage is applied across the capacitor in the power supply circuit PO, and is equivalent in relation to the welding current in the welding current attenuation path. By making the decay rate of the primary expression of the decay current given to the constant, the current decay characteristic having a linear and steep falling slope is obtained, so that a sign of arc re-generation (for example, (Necking) can be reliably detected, and the current value immediately before arc reoccurrence and arc regeneration can be set to a low value, and spatter can be reliably prevented from occurring. Further, according to the present invention, compared with the conventional welding power source, the withstand voltage of the switch means can be lowered, and unlike the conventional welding power source, without switching all switching elements off,
Even if only the switch means is turned off, by applying a predetermined DC voltage across the capacitor in the power supply circuit in the same manner as described above, a current attenuation characteristic having a linear and steep falling slope can be obtained. Has the effect of.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a welding power source as a first embodiment of the present invention, FIGS. 2 and 3 are graphs for explaining the operation of the first embodiment, and FIG. 4 is a graph showing the operation of the present invention. FIG. 7 is a circuit diagram showing a welding power source as a second embodiment, and FIGS. 5 and 6 are circuit diagrams showing modified examples of the welding power source to which the present invention is applied.
(A)-(f) is a figure which shows the transfer process of the droplet of a consumable electrode, FIG. 8 is a graph for demonstrating the example of control of the welding current (voltage) for reducing the generation amount of spatter. . In the figure, 2 ... Welding wire (consumable electrode), 3 ... Base metal, 5 ... Driver, 6 ... Arc voltage detection circuit, 7 ...
... Constriction detection circuit, 8 ... Driver, PO, PO1 ... Constant voltage power supply (power supply circuit), C2 ... Capacitor, R1 ... Resistance, SW
1 to SW5: Switching element, SWD: Switching element (switch means). In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

(57) [Claims] 1. A welding power source for a consumable electrode, which controls a welding current by controlling the output of a DC voltage by turning on / off one or more switching elements, and a detecting means for detecting a transition state of droplets of the consumable electrode. A switch means which is inserted in the welding current attenuation path and which turns off when the value detected by the detecting means reaches a predetermined value, and a predetermined DC voltage across a capacitor connected in parallel to the switch means. A welding power source, which is provided with a power supply circuit for applying a voltage. 2. The welding power source according to claim 1, wherein the power source circuit has an adjusting circuit for maintaining a voltage applied across the capacitor at a predetermined value. 3. The power supply circuit has a regenerative circuit for regenerating a voltage component, which exceeds a predetermined value, of the voltage applied across the capacitor to a welding power source primary side DC voltage. The welding power source according to claim 1.