JP2000246448A - Main arc stopping method of ac plasma device and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate misarc of a pilot arc at the time of stopping a main plasma arc in an AC plasma device using a water cooling electrode. SOLUTION: Between a water cooling electrode 1 and a top end tip 2 encircling its surrounding side face, a pilot arc current is supplied between both as relatively by taking a top end tip 2 for a positive electrode + and the water cooling electrode for a negative electrode -, a main plasma arc of an AC plasma device to supply an AC main plasma arc current between the electrode 1 and an object 3 to be worked facing thereto is stopped, the main current is shut off when the object 3 is relatively in a positive electrode arc time of the positive electrode for the electrode 1. Between the object 3 and the electrode 1, the AC-DC switch means R0-R2, 11, which impress a DC for positive arc corresponding to switching from ON to OFF of a main arc switch PB1, and the time limit means T1, R1, which shut off a main current as the time limit action is started corresponding to switching and a set time dT is measured, are arranged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an AC plasma apparatus, and more particularly to an AC plasma apparatus using a water-cooled electrode so as to withstand a large current.

[0002]

2. Description of the Related Art An AC plasma apparatus is suitable for welding, cutting, fusing, and the like (hereinafter simply referred to as plasma processing) of a metal such as aluminum, which easily forms an oxide film on the surface.

For example, when aluminum welding is to be performed at a high speed with a main arc current of 250 A, it is preferable that the electrode be cooled with water and the tip tip be cooled with water, because the electrode may be heated and melted.

[0004]

The tip is a positive electrode and the water-cooled electrode is a negative electrode, and a pilot arc is located between the water-cooled electrode and the tip surrounding the side surface thereof.
To maintain the pilot arc continuously by supplying
When the main arc switch is turned on, an AC main arc current is supplied between the material to be processed and the water-cooled electrode, and cut off when the main arc switch is turned off. Often disappears. When the pilot arc disappears, it is necessary to stop the gas supply, return the plasma apparatus to an unused state, and to start the plasma apparatus from the stopped state, which is troublesome. In the case of automatic machining, it is not possible to proceed to the next machining operation according to the set sequence.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the extinction (arc loss) of the pilot arc when the main arc is stopped in an AC plasma apparatus using a water-cooled electrode.

[0006]

SUMMARY OF THE INVENTION The present inventor has studied the cause of the disappearance (arc loss) of the pilot arc when the main arc is stopped in an AC plasma apparatus, and the object to be processed is a negative electrode and the water-cooled electrode is not. The pilot arc often disappears when the main arc is shut off when the positive electrode is used. Conversely, the pilot arc does not disappear when the main arc is shut off when the workpiece is the positive electrode and the water-cooled electrode is the negative electrode. Was confirmed by monitoring the AC polarity when the main arc was stopped. The reason is considered as follows.

That is, during a period in which the material to be processed is the negative electrode and the water-cooled electrode is the positive electrode (reverse pole arc period), a pilot arc current between the tip tip and the material to be processed is supplied by a pilot arc power supply and an alternating current. Since the direction of the main arc current by the main arc power supply is the same (same polarity), and since the water-cooled electrode has a low temperature and the resistance between the tip / water-cooled electrode is large, the pilot current supplied by the pilot arc power supply is low. ,
Rather than flowing from the tip, which is a normal pilot arc passage, to the water-cooled electrode, a bypass loop that flows from the tip, which is an abnormal passage, to the workpiece and returns to the pilot arc power supply through the AC main arc power supply. Normal pilot arc generated between the water-cooled electrode and the tip.
Current greatly attenuates. At this time, if the main arc current is cut off, the resistance between the tip and the water cooling electrode is large, so that the pilot current does not recover (restore), and the main arc current stops and the pilot current also cuts off. In particular, when the electrode tip is not heated to a high temperature, such as a water-cooled electrode, electron emission is poor, and when the pilot current is cut off, the re-ignition property of the pilot arc is very poor even when voltage is applied, and the pilot arc is poor. -Easy to cut.

On the other hand, during the period in which the material to be processed is the positive electrode and the water-cooled electrode is the negative electrode (positive electrode arc period), the tip / tip is not used.
Since the direction of the pilot arc current between the material to be processed, which is to be divided into the material to be processed by the pilot arc power supply and the AC main arc power supply, and the direction of the main arc current by the AC main arc power supply are opposite to each other. Since the pilot arc current does not shunt to the AC main arc power supply, but flows between the tip and the water-cooled electrode and maintains the pilot plasma, even if the main arc current stops here, the pilot arc current remains can not cut. (1) Therefore, in the present invention, the tip (2) is positive (+) and the water-cooled electrode is negative (-) between the water-cooled electrode (1) and the tip (2) surrounding the side surface thereof. ), A main arc of an AC plasma apparatus that supplies a pilot arc current between the two and supplies an AC main arc current between the water-cooled electrode (1) and the workpiece (3) opposed thereto. When stopping, the main arc current is interrupted when the material to be processed (3) is relatively positive (positive arc period) with respect to the water-cooled electrode (1).

[0009] To facilitate understanding, symbols or corresponding items of the corresponding elements of the embodiment shown in the drawings and described later are additionally provided in the parentheses for reference. The same applies to the following.

According to this, as described above, the tip chip
(2) Pilot arc current between the workpiece (3) and the pilot arc power supply (4) and AC main arc power supply
Since the direction of the main arc current due to (5) is reversed, the pilot arc current does not shunt to the AC main arc power supply (5) but flows between the tip (2) and the water-cooled electrode (1). Since the pilot plasma is maintained, even if the main arc current stops here, the pilot arc current does not stop. (2) The tip (2) is a positive electrode and the water-cooled electrode (1) is a negative electrode between the water-cooled electrode (1) and the tip (2) surrounding the side surface of the water-cooled electrode (1). When the main arc of an AC plasma apparatus for supplying an AC current and supplying an AC main arc current between the water-cooled electrode (1) and the workpiece (3) opposed thereto is stopped, the workpiece ( 3) is fixed to the positive electrode relatively to the water-cooled electrode (1), and then the main arc current is cut off.

According to this, since the main arc current is interrupted after the main arc is forcibly determined to be the positive arc, the timing for shutting off the main arc current can be easily set, and the pilot arc can be easily set. -The reliability of the control for shutting off the main arc without erasing the arc current is high. (3) The tip (2) is a positive electrode, and the water-cooled electrode (1) is a negative electrode, and a pilot arc is provided between the water-cooled electrode (1) and the tip (2) surrounding the side surface thereof. When the main arc of an AC plasma apparatus for supplying an AC current and supplying an AC main arc current between the water-cooled electrode (1) and the workpiece (3) opposed thereto is stopped, the workpiece ( 3) is switched to the direct current of the positive electrode relatively to the water-cooled electrode (1), and the main arc current is cut off after a lapse of one cycle or more (dT) of the alternating current from this switching.

[0012] According to this, the main arc is switched to direct current and the main arc becomes a positive arc, and the main arc current is cut off after one or more cycles of the preceding alternating current have elapsed.
The main arc current cutoff timing can be easily set, and the reliability of the control for cutting off the main arc without erasing the pilot arc current is high. (4) The tip (2) is a positive electrode and the water-cooled electrode (1) is a negative electrode, and a pilot arc is provided between the water-cooled electrode (1) and the distal tip (2) surrounding the side surface thereof. The main arc switch (PB1) of the AC plasma device, which supplies the AC current and supplies the AC main arc current between the water-cooled electrode (1) and the workpiece (3) facing it, from ON to OFF of the main arc switch (PB1) Between the workpiece (3) / water-cooled electrode (1) in accordance with the switching of the AC / DC switching means (R0 to R2,11) for switching and applying a direct current with the workpiece (3) as a positive electrode; and A main arc stopping device for an AC plasma device, comprising: timed means (T1, R1) for starting a timed operation in response to switching and for measuring a set time dT to cut off a main arc current.

According to this, the main arc is switched to DC and the main arc becomes the positive arc, and the main arc current is cut off after the set time dT has elapsed, so that the pilot arc current is turned off. There is no main arc shut off, the reliability is high.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0015]

FIG. 1 shows a main part of an apparatus for carrying out the present invention. The plasma torch TCH is for cooling a top-type water-cooled electrode 1 whose length is short with respect to its thickness by water-cooling from the back thereof. A cooling water channel is also formed in the tip 2 surrounding the side peripheral surface of the water-cooled electrode 1, and the tip 2 is also forcibly cooled by the cooling water. A pilot gas is supplied between the outer peripheral surface of the water-cooled electrode 1 and the inner wall surface of the tip 2. A cover sleeve is provided outside the tip 2, and a shield gas is supplied between the tip 2 and the cover sleeve.

A current limiting resistor and a pilot arc power supply 4 are connected to an electrode support cup which supports the tip 2 and the water-cooled electrode 1 and is integral with the electrode and has the same potential. Although not shown, the pilot arc power supply 4 includes a high frequency voltage generator for starting the pilot arc, a DC arc power supply for supplying the pilot arc, and a pilot start switch. When the pilot start switch is turned on in a state where the pilot gas is supplied at the flow rate of, the high frequency voltage generator applies the high frequency high voltage to the tip 2 /
Applied between the water-cooled electrodes 1. As a result, when dielectric breakdown (discharge) occurs between the tip 2 and the water-cooled electrode 1, a pilot arc current flows between the tip 2 and the water-cooled electrode 1 from the DC arc power supply until the pilot start switch is turned off.
A pilot arc current continuously flows between the tip 2 and the water-cooled electrode 1.

The flow rate of the pilot gas is controlled by the main plasma arc.
When the main arc switch PB1 is turned on after the flow rate is high and the supply of the shield gas is started, the inverter 5 causes the AC main arc between the water-cooled electrode 1 and the workpiece 3 to be turned on. -Start supplying the electric current, and
Main plasma arc is generated between the workpieces 3. The pilot arc is a kind of fire for generating and maintaining the main plasma arc. Particularly, in an AC plasma arc, a positive pole arc current and a reverse pole arc current having different current directions are alternately repeated, and when the polarity is reversed, the arc current once becomes 0 (A) ( (Arc OFF), and the role of assisting the pilot arc is great when the main arc reignites.

FIG. 2 shows electric signals appearing in various parts of the control system electric circuit shown in FIG. Hereinafter, please refer to FIG. 2 together with FIG. When the main arc switch PB1 of the main arc on / off controller 14 shown in FIG. 1 is turned on, the relay R0 is energized (on), and the normally open contact r01 is closed (on). Relay R1 is energized (ON)
At the same time, the normally closed contact piece r02 of the relay R0 opens (off). When the relay R1 is turned on, the normally open self-holding piece r11 is closed, and even if the relay R0 is turned off and the normally open piece r01 is opened, the relay R1 continues to be turned on (self Retention). When the relay R1 is turned on, the normally open contact r12 is closed, but the normally closed contact r02 of the relay R0 is closed.
Is open when the relay R0 is turned on.
1 and relay R2 are not energized. That is, the turning off is continued.

When the relay R1 is turned on, the normally open contact r between the AC signal generator 8 and the switching driver 7 is turned on.
13, the AC signal Sac generated by the AC signal generator 8 is closed.
Is supplied to the switching driver 7, which continues until the main arc switch PB1 is turned off.

The AC signal generator 8 compares the triangular wave with a set voltage V1 of the variable resistor 9 when the triangular wave level is equal to or higher than V1. Otherwise, a comparator that converts the signal into a low-level L binary signal, and a + Vc level while the binary signal is high,
During L, an output amplifier for generating an AC signal (ternary signal) Sac at -Vc level (the middle is 0: reference level = equipment earth level) is included. This AC signal Sac is supplied to the switching driver 7 only while the normally open contact r13 is closed. The AC signal Sac only while the normally open contact r13 is closed is the switching control signal Scc to the switching driver 7. FIG. 2 shows these signals Sac and Scc.

The + Vc level of the switching control signal Scc instructs the occurrence of a "positive arc", and in response, the switching driver 7 causes the transistor for conducting the positive arc of the transistor H bridge 6 which is a chopper. Tp
1, Tp2 is made conductive. Other transistors Tn1, Tn
n2 is non-conductive. Thus, the + output terminal of the DC power supply 10 is connected to the workpiece 3 through the choke and Tp1, and the − output terminal of the DC power supply 10 is connected to the transistor Tp2.
The main plasma arc current flows from the workpiece 3 (+) to the water-cooled electrode 1 (-) through the connection to the water-cooled electrode 1. In this “positive electrode arc” energizing period, the main plasma arc current flows from the tip 2 to the water-cooled electrode 1.
In this case, even if the main plasma arc current stops there, the pilot arc current does not disappear.

The -Vc level of the switching control signal Scc instructs the occurrence of a "reverse pole arc". In response to this, the switching driver 7 sets the transistor for conducting the reverse pole arc of the transistor H bridge 6. Tn1 and Tn2 are made conductive. The other transistors Tp1 and Tp2 are non-conductive. Thus, the + output terminal of the DC power supply 10 is connected to the water-cooled electrode 1 through the choke and Tn1, and the DC power supply 1
0 is connected to the workpiece 3 through the transistor Tn2, and a main plasma arc current flows from the water-cooled electrode 1 (+) toward the workpiece 3 (-). During the “reverse pole arc” energizing period, the main plasma arc current is in a direction to suppress the energization of the pilot arc current from the tip 2 to the water-cooled electrode 1.
The pilot arc current between the / water-cooled electrode 1 is reduced, and if the main plasma arc current is interrupted there, the pilot arc current between the tip 2 and the water-cooled electrode 1 is easily extinguished (return or re-arcing). Hateful).

When the main arc switch PB1 is turned off, the relay R0 is turned off, thereby opening the normally open contact r01. However, since the self-holding piece r11 is closed, the relay R1 keeps on. When the relay R0 is turned off, the normally closed contact piece r02 is closed, and the timer T1
And the relay R2 is turned on. When the relay R2 is turned on, the normally open contact r2 closes, whereby the low potential V2 of the variable resistor 11 for setting the positive polarity DC arc is applied to the binarizing comparator of the AC signal generator 8, Add as a threshold. Immediately before that, the high potential V1 was applied, but this high potential V1 is discharged to the low potential V2 by closing r2, and the threshold value becomes V2.
From V1 to V1. Therefore, the control signal Scc is + Vc
And the DC “Positive electrode arc” energized (Tp1, Tp
2 on).

In the timer T1, the time of two cycles of 50 Hz alternating current (40 msec) is set as a time limit value dT.
When that time has elapsed, the normally closed contact piece t1 is opened by time over. As a result, the relay R1 is turned off, the self-holding contact r11 is opened, and the control signal Sac is supplied to the normally open contact r12 for supplying power to the timer T1 and the relay R2 and the switching driver 7. Opening piece r13
Opens. With the opening of r13, the control signal Scc causes the reference potential (0: equipment arc) to instruct the turning off of the main plasma arc.
In response, the switching driver 7 restrains all the transistors Tp1, Tp2, Tn1, and Tn2 to OFF (non-conduction). This allows the main plasma arc
Current is cut off. When the relay R1 is turned off, the main arc on / off controller 14 returns to the standby state shown in FIG. 1 where the switch PB1 is turned on.

As described above, since the main plasma arc is shut off when the "positive electrode arc" is energized, the pilot arc does not disappear and the main arc switch PB1 is repeatedly turned on. For example, in the case where the plasma torch TCH is turned on / off and partially processed while moving the plasma torch TCH to various parts of the processing target material, or in the case where substantially the same processing is performed while replacing the processing target material one after another, The efficiency of the machining operation for turning on / off only the main plasma arc can be maintained at a high level.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main part of a device configuration for implementing the present invention in one aspect.

FIG. 2 is a time chart showing electric signals of a control circuit shown in FIG. 1; 1: water-cooled electrode 2: tip tip 3: material to be processed 4: pilot arc power supply 9, 11: variable resistor R0 to R2: relay r01, r02, r11 to r13, r2: relay piece T1: timer t1: Timer piece

Claims (4)

[Claims] 1. A pilot arc current is supplied between a water-cooled electrode and a distal tip surrounding the side of the water-cooled electrode, using the distal tip as a positive electrode and the water-cooled electrode as a negative electrode, and supplying a pilot arc current between the two. A main arc of an AC plasma apparatus for supplying an AC main arc current to a facing workpiece.
A main arc stopping method for an AC plasma apparatus, wherein the main arc current is cut off when the material to be processed has a positive electrode relative to the water-cooled electrode when the arc is stopped. 2. A pilot arc current is supplied between the water-cooled electrode and the tip that surrounds the side of the water-cooled electrode with the tip being a positive electrode and the water-cooled electrode being a negative electrode. A main arc of an AC plasma apparatus for supplying an AC main arc current to a facing workpiece.
When stopping the arc, the material to be processed is fixed to the positive electrode relative to the water-cooled electrode, and then the main arc current is cut off.
Method for stopping main arc of AC plasma apparatus. 3. A pilot arc current is supplied between the water-cooled electrode and the tip surrounding the side surface thereof, with the tip being a positive electrode and the water-cooled electrode being a negative electrode. A main arc of an AC plasma apparatus for supplying an AC main arc current to a facing workpiece.
When the arc is stopped, the material to be processed is switched to the positive direct current relative to the water-cooled electrode, and the main arc current is cut off after a lapse of one or more cycles of the alternating current from this switching.
Method for stopping main arc of AC plasma apparatus. 4. A pilot arc current is supplied between the water-cooled electrode and the tip surrounding the side surface thereof, with the tip being a positive electrode and the water-cooled electrode being a negative electrode. A main arc of an AC plasma apparatus for supplying an AC main arc current to a facing workpiece.
AC / DC switching means for switching and applying a direct current having the material to be processed as a positive electrode between the material to be processed and the water-cooled electrode in response to switching of the switch from ON to OFF; and starting a timed operation in response to the switching. A main arc stopping device for the AC plasma apparatus, comprising: a time limiter for interrupting the main arc current when the set time dT is measured.