JPH0641035B2 - Plasma arc cutting device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to improvements in plasma arc cutting devices.

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 method of generating a plasma arc by 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 Problems In a plasma arc cutting device that cuts 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 electrode and nozzle when starting arc, arc current detection means, cutting current detection means, constant current control circuit for feedback control of arc current, change control set value of constant current control circuit The cutting current detecting means detects the presence or absence of the cutting current after the pilot arc is generated by the switching means and the opening / closing means for opening / closing the pilot arc generating electric circuit in response to the drive signal from the cutting current detecting means. When it is confirmed that the current has flowed, the control set value of the arc current is changed to the control set value of the above constant current control circuit. The switching operation of the switching means switches to a value larger than the reference value for constant current control during cutting work, and after a plasma arc occurs, wait until the cutting current rises to a stable value for the plasma arc, and the cutting current When a predetermined stable value is reached, the switching means opens the pilot arc generating circuit to cut off the pilot current, and the switching current is set to a predetermined value by switching the switching means to perform constant current control. It is characterized by having done.

According to the present invention, since the control set value of the arc current after the generation of the pilot arc is switched to a value larger than the reference value at the constant current control of the cutting current performed during the cutting work,
The cutting current has a sufficient rise, and the plasma arc can be smoothly transferred to the material to be cut.

Further, after the plasma arc is generated, the pilot current is cut off, and at the same time, the cutting current is controlled to a constant value by the constant current control. Therefore, not only the energy loss due to the current limiting resistance but also the heat generation loss in the nozzle is caused. There is almost no plasma arc, and 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 switching means for changing the control set value, 13 an arc current detecting means, 14 a cutting current Detecting means 24 is an opening / closing 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.

In the error amplifier 16, as a result of such comparison, the error between the input arc current Ia and the reference value is amplified and input to the PWM control circuit 17, and the PWM control circuit 17 responds to the input error amount. A pulse signal having a width is generated and a drive signal is sent to the drive circuit 18.

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 (REF) and cutting current Ic
When Ic1 reaches Ic1, the electromagnetic contactor 20 is driven,
The reference value input to the error amplifier 16 is switched from Ia (REF) to Ic (REF).

Here, Ip (REF) indicates the reference value of the pilot current Ip during constant current control, and Ia (REF)
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)
Is selected as a reference value of the cutting current Ic which is controlled by a constant current during the cutting work.

In the embodiment, the control set value of the error amplifier 16 is selected by the pilot current regulator 21 and the arc current regulator 2 which are configured by providing three variable resistance elements in parallel with the reference power source Eo.
2. The disconnecting current adjuster 23 is opened and closed by opening and closing the contacts constituted by the a and b contacts of the electromagnetic contactors 19 and 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 Ip (REF) 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, the cutting current Ic does not flow in this state, so that the arc current detection means 13 causes the pilot current Ip to flow.
Only this is detected, and the pilot current Ip (Ip = Ia) is subjected to constant current control with the control set value Ip (REF) (see FIG. 4 to t1).

Then, in this state, the plasma torch 2 is brought close to the material 6 to be cut to generate the plasma arc 8 (t1 in FIG. 4).
(See) and the cutting current Ic flows out with the generation of the plasma arc 8, and the cutting current detection means 14 detects this. Then, the detected cutting current Ic is Ico
When it reaches the level of 1, 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 and the contact b of the contact 19 is opened to bring the arc current regulator 22 to the reference value of the error amplifier 16.
Is selected, and the arc current Ia (Ia = Ic + Ip) is Ia
It will be controlled by (REF).

Here, Ia (REF) is the cutting current I during the cutting work.
Since a value larger than the reference value Ic (REF) when c is subjected to constant current control is selected, the cutting current Ic also rises greatly along with the arc current Ia (fourth value).
See FIGS. T2 to t3).

Then, the cutting current Ic reaches a level at which the plasma arc can be stably maintained, that is, Ic1 (see t3 in FIG. 4).
Then, the output of the comparator 121 is inverted and the electromagnetic contactor 20 is driven.

When the electromagnetic contact 20 is driven, the contact a of the contact 20 is closed and the contact b of the contact 20 is opened, and the opening / closing means 24 is driven to open the contact means 10 to open the pilot arc generating electric path to cut off the pilot current Ip. At the same time, the cutting current regulator 23 is selected as the reference value of the error amplifier 16, and the cutting current Ic is subjected to constant current control with Ic (REF) 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, according to 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 is detected. The control set value of is switched to a value Ia (REF) larger than the reference value Ic (REF) that is constant current controlled during the cutting operation of the cutting current Ic, smoothing the transition to arc plasma, and further cutting current Ic After reaching the level (Ic1) for stabilizing the generated plasma arc, the pilot current Ip can be cut off and the control set value can be switched to Ic (REF) to make the cutting current Ic constant.

As a result, the generated plasma arc is maintained stable, and energy loss due to the current limiting resistance and heat loss at the electrodes and nozzles can be effectively prevented by blocking the pilot current Ip.

In the above examples, the present invention only shows an example of the case of the positive polarity, but it goes without saying that the present invention can also be implemented 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 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 setting value switching unit, 13 is an arc current detecting unit, 14 is a cutting current detecting unit, 24 is an opening / closing unit, 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, and starting the pilot arc. A high-frequency generator that sometimes generates high-frequency discharge between the electrode and the nozzle, an arc current detection means, a cutting current detection means, a constant current control circuit that feedback-controls the arc current, a switching means that changes the control set value of the constant current control circuit, And the opening / closing means for opening / closing the pilot arc generating electric circuit in response to the drive signal from the current cutting current detecting means, the presence or absence of the cutting current after the pilot arc is detected by the cutting current detecting means, and the cutting current flows. When it is confirmed that the control setting value of the arc current is changed, the control value of the constant current control circuit is changed. By switching the stage, the value is switched to a value larger than the reference value for constant current control during cutting work, and after a plasma arc is generated, wait until the cutting current rises to a stable value for the plasma arc, and the cutting current is set to a predetermined value. When the stable value is reached, the pilot arc generating electric circuit is opened by the switching means to cut off the pilot current, and the switching current is set to a predetermined value, and the switching means is switched to perform constant current control. A plasma arc cutting device characterized in that