JPS5868474A - Power source for pulse arc welding - Google Patents

Abstract

PURPOSE:To ensure regeneration of an arc by detecting occurrence of short- circuit using a short-circuit detecting circuit, and in case of occurrence of short- circuit, eliminating the short-circuit by supplying large current corresponding to pulse current with priority to and regardless of set pulse frequency and time width. CONSTITUTION:When an arc is generated normally without causing short-circuit between an electrode 1 and an object 2 or 3 to be welded during welding, pulse current value of pulse peak value and pulse time width determined by a signal synthesized by a signal synthesizing circuit 13 is supplied at a specified period overlapping with the output of DC power source 8 for base current. In case of occurrence of short-circuit, output of a short-circuit detecting circuit 9 is supplied to a gate circuit 14 and output of the circuit 13 is cut off. At the same time, an output signal of a pulse peak current setting device 10 is supplied directly to a driving circuit 6 and an output current controlling element 5 is made to conduct to output large current corresponding to pulse peak current continuously. By this way, it is possible to regenerate the arc easily by melting and scattering the tip of the electrode 1 by rapid heating.

Description

[Detailed description of the invention] This paper relates to the improvement of power supplies suitable for

In pulsed arc welding using a consumable electrode, power is supplied from a direct current source that outputs a pulse current period of a large current and a base current period of a small current periodically (repeatedly).
This is done by forcibly spraying droplets from the consumable electrode onto the workpiece. In this way, arc welding methods that use direct current are susceptible to the effects of the magnetic fields that exist around the welding arc (if these magnetic fields are unbalanced, the direction of the arc will be distorted and it will deviate from its designated position). Arc blow phenomenon is likely to occur.

Particularly in pulsed arc welding, during the pulse current period of a large current, the electromagnetic pinch force acting on the arc column is strong, so the force that causes the arc to move in a straight line, that is, the rigidity of the arc, is obtained, so the arc blow phenomenon is prevented. In the base current period, where the current value is small, the arc is less rigid and arc blowing is more likely to occur even with a small external magnetic field.

Furthermore, when fillet welding magnetic materials, this tendency becomes more severe, and in severe cases, arc breakage may occur. In other words, in fillet welding, much of the magnetic flux generated by the welding current passes through the vertical member on the side closer to the torch.
This creates an extreme magnetic field imbalance around the torch. Particularly in ferromagnetic materials such as mild steel, there is a residual magnetic phenomenon, so when performing pulse arc welding, high current and small current are alternated (resulting in the strong magnetic field generated during high current). A residual magnetic field is generated in the workpiece, and during the next small current period, this residual magnetic field acts strongly and thickens (deflects) the arc.Figure 1 shows the magnetic flux generated when performing horizontal fillet welding. This is a schematic diagram illustrating the situation, and since welding is normally performed with the electrode l tilted toward the vertical member 3 side of the workpiece than the horizontal member 2, the magnetic flux along the Ik of the electrode 1 on the vertical member 3 side becomes high; Therefore, the residual magnetic field also becomes stronger.As a result, the arc is blown in a direction perpendicular to the plane of the figure.

Figure 2 shows how arc blow occurs due to the external magnet n1 in pulsed arc welding, where (λ) shows the change in welding current, and (1)) shows the change in the welding current (a).
) The appearance of the arc when the current changes is shown on electrode 1.
and the surface of the workpiece, and the same figure (C
) shows the changes in the output voltage of the welding power source corresponding to (a) and (bl) above. However, when the base current is low (%X7AE), the arc is weak and tends to spread, and the residual magnetic field gradually becomes stronger (becomes stronger) due to the large magnetic field generated during pulse current. Arc blow occurs. If this tendency becomes strong (as shown in (a) in the figure), the arc length becomes extremely long (eventually, the arc breaks and the no-load voltage of the power supply output is applied between the electrode and the workpiece. Even if arc breakage occurs, the electrode l continues to be fed at a nearly constant speed, so the tip of the electrode gradually approaches the surface of the workpiece, and eventually the two come together as shown in (b). Short circuit.This results in
A short-circuit current flows through the electrode, and the tip of the electrode is locally heated and fused, and an arc is generated again as shown in (2). Whether or not the arc can be smoothly regenerated after this short circuit occurs is an important factor in welding stability. If a short circuit occurs during the base current period as shown in Figure 2 (b), the short circuit current is small and the cause of arc breakage is the low current period as described above. Because the arc blow was so large, the tip of the electrode was cooled to a considerably low temperature, so it did not reach the point of overheating and melting the tip of the electrode. This base current period is followed by the next pulse current period (in this case, sufficient current will flow for overheating, but by that time the electrode is already being fed continuously and firmly attached to the workpiece). Since they are in contact, only the tip of the electrode generates a small amount of heat, but in the middle of the electrode, the heating due to the specific resistance progresses, softens it, and causes it to melt.If the electrode breaks by +8 in the middle, the arc The arc will be generated at a high position, and the arc will immediately flare up and the arc length will grow rapidly, leading to arc breakage again.Once arc breakage occurs due to arc blow, welding becomes extremely unstable. Not only does it take a considerable amount of time to stabilize the welding process, but also it is impossible to obtain a good welding result because these parts have to be replaced.

On the other hand, in conventional welding power sources, both the pulse time width and pulse frequency of the Noculus current period are determined at the time set by the welding power source, regardless of the state of the welding arc. It is unclear whether the time when an arc blow occurs and a short circuit occurs is during the pulse current period or the base current period. Therefore, when a short circuit occurs, arc breakage and arc regeneration are repeated as described above, and the arc becomes extremely unstable, making it impossible to obtain a good welding result.

The present invention provides a short circuit detection circuit that detects the occurrence of a short circuit,
When a short circuit occurs, irrespective of the set pulse frequency and time width, a large current equivalent to the pulse current or a separately determined base current is supplied to ensure arc regeneration. be.

FIG. 3 is a connection diagram showing an embodiment of the pulse arc welding power source of the present invention. In the figure, reference numeral 4 denotes a DC power supply for supplying a large current, and a switching control element is used to obtain DC by rectifying a commercial AC power supply by a known means. 6 is a drive circuit for driving the output current control element 5, 7 is a DC reactor, and 8 is another DC power supply for supplying base current. 9 is a short circuit detection circuit which receives the voltage between output terminals 4 and 81 and determines that there is a short circuit and outputs an output when the input voltage exceeds a certain value.

This short-circuit detection circuit 9 is designed to be sufficiently lower than the lowest voltage at the time of arc generation, and the above-described It is set so that a short circuit is determined when the voltage has a higher value than the voltage drop during short circuit type ML. 10 is a pulse peak current setting device for setting the peak value of the pulse current, 11 is a pulse time width setting device for setting the duration of the pulse current, and 12 is a pulse frequency for setting the repetition frequency of the pulse current. The set value of these setting devices is determined independently or in conjunction with each other as necessary, or in relation to the feeding speed of the electrode 1. Reference numeral 13 denotes a pulse peak current setting device 10.
, pulse time width setting device 11 and pulse frequency setting device 1
14 is a signal synthesis circuit 13 which receives the output signals of 2 and obtains a composite signal of these input signals.
While the short circuit detection circuit 9 is detecting a short circuit by inputting the output of the pulse peak current setting device 10 and the output of the pulse peak current setting device 10 as input, the output of the pulse peak current setting device 10 is transmitted to the drive circuit 6, and the signal is synthesized outside the short circuit detection circuit. This is a gate circuit that transmits the output of the circuit 13 to the drive circuit 6.

By configuring as shown in Fig. 3, the electrode 1 during welding can be
While the arc is normally generated without short-circuiting the workpiece 2 or 3, the pulse peak value and the pulse current with the pulse time width determined by the signal synthesized by the signal synthesis circuit 17 are at a predetermined value. It is supplied superimposed on the output of the base current DC power supply 8 at a period of . When a short circuit occurs, the output of the short circuit detection circuit 9 is supplied to the gate circuit 14, the output of the signal synthesis circuit 13 is cut off, and instead, the output signal of the pulse peak current setting device 10 is directly supplied to the drive circuit 6 for output. The current control element 5 conducts so as to continuously output a large current corresponding to the pulse peak current. As a result, the short-circuited tip of the electrode 1 is rapidly heated, melted and scattered, and the arc is easily regenerated.

As soon as the arc is regenerated, the output of the short circuit detection circuit 9 disappears, so the gate circuit 14 again supplies the output signal of the signal synthesis circuit 13 to the drive circuit 6, and the output current is divided into the pulse current period and the base current period ( It doesn't work and the output becomes normal pulse arc welding output.

By the way, in order to perform arc regeneration well after a short circuit occurs, the current supplied at the time of a short circuit must be set to a value equal to or greater than a certain value, and when the arc is regenerated by this large current, it must be immediately restarted during normal RS welding. An important factor is to restore the current to . This is a case where an element that can control both of these cuts is used. On the other hand, when controlling and rectifying an alternating current power source using a normal thyristor to obtain a specified direct current, a pulse current and a base current are obtained by phase control.
With large currents, only the start of conduction can be controlled and is determined by the power supply voltage phase at the time of cutoff, so the current can be returned to the original output immediately after the short circuit is cleared, and during that half-wave period, the large current is Some instability remains due to the continuous flow. When using a transistor as an output control element,
In addition to being able to immediately return to the original current after the short circuit is resolved, it is now possible to use a switching regulator system that controls the output current itself by switching between ON and OFF so that the average current reaches the set value. In this case, the internal power consumption of the transistor is small, and a low-cost device can be obtained. This method is especially convenient when used to control the pulse peak value because the current to be handled is large. In this case, since the base current has a small current value, it is advantageous from the viewpoint of arc stability at low currents to perform analog control as a separate power supply. Of course, the base current power source 8 can be omitted by providing a separate base current setting circuit and adding this output as an input to the signal synthesis circuit 13. Furthermore, since the pulse current for spray transfer of droplets waiting for normal arc welding is determined by the relationship between its peak value and pulse time width, the pulse peak value is unique even for the same electrode diameter. Although it is not determined, the current required to break the short circuit and regenerate the arc is determined depending on the electrode diameter. For this reason, only the peak value of the current required for arc regeneration is important, so the pulse peak current value set for normal welding may not always be a satisfactory value. Therefore, the third
As shown by the broken line in the figure, more reliable control can be achieved by providing another current setting device 15 that determines the current to be supplied in the event of a successful short circuit and supplying it to the gate circuit 14 instead of the output of the pulse peak current setting device 10. It becomes possible.

As described above, according to the present invention, when a short circuit occurs, a large current is immediately supplied to the welding part to eliminate the short circuit, and after the short circuit is eliminated, the original welding current is immediately restored, so pulse arc welding can be performed extremely stably. Figure 1 is a schematic diagram showing the state of magnetic flux f- in horizontal fillet welding, Figure 2 is an explanatory diagram showing the state when arc blow occurs, and Figure 3 is a diagram showing the pulsed arc welding of the present invention. FIG.

1... Consumable electrode, 2, 3... Work to be welded, 4...
Direct power supply, 5... Output current control element, 6... Drive circuit, 8... DC power supply for base current, 9... Short circuit detection circuit, lO... Pulse peak value setter, 11...・Pulse time width setting device, 12...Pulse frequency setting device, 1
3... Signal synthesis circuit, 14... Gate circuit, 15.
・・Current setting device, agent Patent attorney Hiroshi Nakai Drawing IT letter (no internal changes) Procedural amendment of Figure 1 to Figure 2 (voluntary) Commissioner of the Japan Patent Office 1.8 Jf indication patent 1 + ji5t5-16850 ['15 J2, name of invention 'rli lI'+ for pulsed arc welding≠≠! 3. Relationship with the person making the amendment Patent applicant address 〒532 Yodogawa-ku, Osaka City [Yo 2-J11]
No. 1 No. 11 Name (026) Osakahen 11:,
Ki Co., Ltd. Representative Director and President Keiji Kobayashi Department 4, Deputy Person Il Address 11112-111-11 Yodogawa-ku, Osaka 532 [- Engraving of drawings (Contents include foreign soil) 1 391

Claims (1)

[Scope of Claims] 1. In a pulsed arc welding power source that periodically outputs a pulse current period of a large current and a base current period of a small current, the load connected to the output terminal is in a short-circuited state. a short-circuit detection circuit that detects that the short-circuit detection circuit is present in 2. A power source for pulsed arc welding, comprising a short circuit extra-large current supply circuit. 2. A power source for pulsed arc welding according to claim 1, wherein the current supplied during the short circuit is equal to the current during the pulse current period. 3. 4. A pulsed arc welding power source according to claim 1, wherein the current supplied during the short circuit is set separately from the current during the pulsed current period.4. The pulsed arc welding power source according to any one of claims 1 to 3, wherein the current during the period is controlled by a switching regulator. 5. The pulse current and the base current are output from separate power sources to output terminals. A power source for pulsed arc welding according to any one of claims 1 to 4, which is supplied in a superimposed manner.