JPH0641036B2 - Plasma arc cutting device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transfer type plasma arc cutting device for generating a plasma arc using a pilot arc.

Conventional technology Plasma cutting method is already known as a method of cutting by concentrating the energy of the plasma arc on the cutting local part of the material to be cut, and as a principle of the method, after the pilot arc is blown between the electrode and the nozzle, There is one using a so-called pilot arc, which obtains a plasma arc by transferring an arc between materials to be cut.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention is to further improve a conventionally known transfer type plasma cutting device that generates a plasma arc using a pilot arc, and particularly facilitates starting of the plasma arc,
It was developed as a technical problem to be solved to further stabilize the generated plasma arc.

Means for Solving the Problems In the method of the present invention, the above-mentioned technical problem is solved by controlling the arc current in the following procedure.

1) After the pilot arc is generated, the presence / absence of a cutting current is detected, and when it is confirmed that the cutting current has flowed, the control set value of the arc current is switched to a value larger than the reference value during constant current control. 2) After the plasma arc is generated, wait until the cutting current rises to a value at which the plasma arc is stabilized, and when the cutting current reaches a predetermined stable value, use the arc current control set value as a reference value. Switching and constant current control is performed, and in such a control method, a plasma arc cutting device is configured by combining the following components.

1) A high-frequency generator that generates high-frequency discharge is provided between the electrode and the nozzle when the pilot arc is started. 2) Arc current detection means is provided so that the combined value of the pilot current and the cutting current can be detected. 3) A means for detecting a cutting current flowing when a plasma arc is generated is provided, 4) A constant current control circuit for feedback controlling the arc current to a predetermined control set value is provided, 5) An arc Providing switching means for receiving the current detection signal from the current detection means and the detection signal from the disconnection current detection means to change the control set value of the constant current control circuit, and the operation and effect of the present invention. For example, after the pilot arc is generated, the control set value of the arc current can be switched to a value larger than the reference set value for constant current control. The transition to the cut material can Motas minute rising plasma arc can be smoothly.

Further, after the plasma arc is generated, the arc current is held at a constant value by the constant current control, so that the plasma arc can be stably maintained even when the power supply voltage changes, and smooth plasma arc cutting can be performed.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a configuration example of the plasma arc cutting device of the present invention with a system diagram. In the figure, 1 is a DC power supply device serving as an energy supply source of plasma arc, 2 is a plasma torch, 3 is its electrode, 4 is a nozzle, 5 is a working gas shield cup, 6 is a material to be cut, and 7 is a pilot arc. A high frequency generator that is driven at the time of start-up to guide high-frequency discharge between the electrode 3 and the nozzle 4 to facilitate starting of the pilot arc, 8 is a plasma arc generated during cutting work, and 9 is provided in a pilot arc generating electric path. A current limiting resistor, 10 a contact means for opening and closing the pilot arc generating circuit, 11 a constant current control circuit, 12 a control setting value switching means, 13 an arc current detecting means, 1
Reference numeral 4 denotes a cutting current detecting means.

Here, the arc current detecting means 13 determines the pilot current I
The combined value of the cutting current Ic flowing through p and the plasma arc is detected as the arc current Ia, and the cutting current detection means 1
Reference numeral 4 detects a cutting current Ic generated when a plasma arc is generated.

FIG. 2 shows a system diagram of the constant current control circuit, in which the arc current Ia detected by the arc current detecting means 13 is shown.
Is amplified by the amplifier 15 and then input to the error amplifier 16, and the error amplifier 16 controls the control set value switching means 12
It is compared with the standard value set by.

Here, the control set value switching means 12 includes comparators 120 and 121, and each of the comparators determines whether or not the cutting current Ic has reached Ico and Icl.

Then, when the cutting current Ic reaches the detection level Ico, the electromagnetic contactor 19 is driven to switch the contact 19 to set the reference value input to the error amplifier 16 to Ip (RE
Switching from F) to Ia (REF1) and cutting current I
When c reaches Ic1, the electromagnetic contactor 20 is driven to set the reference value input to the error amplifier 16 to Ia (REF
Switching from 1) to Ic (REF2).

Here, Ip (REF) indicates the reference value of the pilot current Ip during constant current control, and Ia (REF1).
Is selected as a control set value of the arc current Ia that has a sufficient rise in the cutting current Ic, and Ic (REF
2) is selected as the reference value of the arc current Ia which is controlled by constant current during the cutting work.

In the embodiment, the control set value of the error amplifier 16 is selected by a pilot current regulator 21, an arc current regulator 22, which is configured by providing three variable resistors in parallel with the reference power source Eo.
23 is performed by opening and closing the contacts formed by making a and b contacts of the electromagnetic contactors 19, 20 as one set.

Next, the control operation of the method of the present invention will be described.

Until a pilot arc is generated, an electromagnetic contactor 19,
Since the contacts 19 and 20 of 20 are as shown in the figure, the reference value of the error amplifier 16 is the pilot current regulator 2
The voltage level is defined by 1.

Therefore, the high frequency generator 7 is driven to drive the electrode 3 and the nozzle 4.
When a high frequency discharge is led in the meantime to generate a pilot arc (see FIG. 4 to), the cutting current Ic does not flow in this state, so the arc current detection means 13 detects the pilot current Ip and the pilot current Ip is detected. Current Ip
(Ip = Ia) is constant current controlled by the control set value Ip (REF).

Next, in this state, the plasma torch 2 is brought close to the material 6 to be cut to generate the plasma arc 8 (t2 in FIG. 4).
), The cutting current Ic flows out with the generation of the plasma arc 8, and the cutting current detection means 14 detects this.

Then, when the detected cutting current Ic reaches the level of Ico, the output of the comparator 120 is inverted and the electromagnetic contactor 19 is driven to switch the contact 19. Thus, the contact a of the contact 19 is closed, the contact b is opened, and the arc current regulator 22 is selected as the reference value of the error amplifier 16,
The arc current Ia (Ia = Ip + Ic) is Ia (REF
It will be controlled in 1).

Here, Ia (REF1) is sufficiently higher than the reference value Ia (REF2) at the time of constant current control of the arc current Ia in order to allow the cutting current Ic to have a sufficient rise and facilitate the transfer of the plasma arc. Since the cutting current Ic is selected as the level, the cutting current Ic rises at a steep rise due to the arc current Ia (t2 in FIG. 4).
See t3. ) Then, when the cutting current Ic reaches a level at which the plasma arc can be stably maintained, that is, Ic1 (see t3 in FIG. 4), subsequently, the output of the comparator 121 is inverted,
The electromagnetic contactor 20 is driven.

Then, the a contact of the contact 20 is closed and the b contact is opened, the arc current regulator 23 is selected as the reference value of the error amplifier 16, and the arc current Ia is constant-current controlled with Ia (REF2) as the reference value. .

To facilitate understanding of the above control operation, FIG. 3 shows a control flow in the method of the present invention, and FIG. 4 shows current waveform diagrams during control.

As a result, in the method of the present invention, when it is detected that the DC power supply device 1 is turned on, the harmonic generator 7 is driven to generate the pilot arc, and the cutting current Ic flows, the arc current of the arc current is detected. The control set value is switched to a value Ia (REF1) larger than the reference set value during constant current control to smooth the transition to arc plasma and further stabilize the plasma arc generated by the cutting current Ic (Ic1). ) Is reached, the control set value of the arc current Ia is switched to Ia (REF2), and the arc current Ia
Can be constant.

As a result, the generated plasma arc is stably maintained and the material to be cut can be smoothly cut.

In the above examples, the method of the present invention only shows the case of the positive polarity, but it goes without saying that the method of the present invention can also be carried out in the case of the opposite polarity.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a plasma arc cutting device of the present invention, FIG. 2 is a system diagram showing a configuration of a constant current control circuit, and FIG.
FIG. 4 is a diagram showing a control flow of the method of the present invention, and FIG. 4 is a diagram showing waveforms of respective currents during control operation. (Explanation of reference numerals) In the figure, 1 is a DC power supply device, 2 is a plasma torch,
3 is an electrode, 4 is a nozzle, 5 is a shield cup, 6 is a material to be cut, 7 is a high-frequency generator, 8 is a plasma arc generated during cutting work, 9 is a current limiting resistor, 10 is its contact means, and 11 is a constant means. A current control circuit, 12 is a control set value switching means, 13 is an arc current detecting means, 14 is a cutting current detecting means, Ia is an arc current, Ic is a cutting current, and Ip is a pilot current.

Claims (1)

[Claims] 1. A plasma arc cutting device for cutting a material to be cut by generating a plasma arc between the electrode and the material to be cut after a pilot arc is blown between the electrode and the nozzle. High-frequency generator that generates high-frequency discharge between the electrode and the nozzle when starting, arc current detection means,
A plasma arc cutting device comprising: a cutting current detection means, a constant current control circuit for feedback controlling an arc current, and a switching means for changing a control set value of the constant current control circuit.