JPH079153A - Method for controlling plasma cutting device - Google Patents

Abstract

PURPOSE:To obtain the satisfactory cutting quality by automatically changing over at least either one of plasma gas or a plasma current value according to each stage of plasma cutting. CONSTITUTION:In the plasma cutting device 1, a plasma arc is generated between an electrode in a plasma torch 10 and material 3 to be cut to cut the material 3 to be cut. In the cutting stage, the stage of pre-flow is first carried out. A pilot arc is then generated between the electrode and a nozzle. A main arc is started to generate between the electrode and the material 3 to be cut. The main arc is continuously generated between the electrode and the material 3 to be cut to perform cutting. The generation of the main arc is completed. The stage of after-flow is then carried out. At least either of the plasma gas or the plasma current value is then changed over by a controller 60 according to each stage. Consequently, an effective service life of the nozzle can be extended.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of controlling a plasma cutting device, and more particularly to a long life of a nozzle of a plasma cutting device used for cutting and improvement of cutting quality.

[0002]

2. Description of the Related Art Conventionally, a plasma torch of a plasma cutting apparatus for cutting a material to be cut by generating a plasma arc between an electrode and the material to be cut has an electrode for emitting the plasma arc and a plasma arc jet at the tip. It consists of a nozzle with an outlet. The plasma arc reaches the material to be cut from the plasma arc discharge portion of the electrode through the plasma arc ejection port of the nozzle, and cuts the material to be cut. In general, an oxidizing gas (mainly oxygen gas) is often used as the plasma gas for the purpose of improving cutting quality. However, during cutting, when the pilot arc is generated between the electrode and the nozzle, thermal shock is applied to the plasma arc discharge part of the electrode and further oxidation causes the electrode wear to progress abnormally. The effective life of is shortened. The feet of the pilot arc present in the nozzle damage the nozzle in an oxidizing atmosphere. An abnormal arc (hereinafter referred to as a double arc) is likely to occur during the transitional period during the transition from the pilot arc to the main arc, resulting in great damage to the nozzle in an oxidizing atmosphere. There is a problem.

To solve these problems, as a conventional technique,
A method of generating a non-oxidizing gas until the plasma arc transfers to the main arc and an oxidizing gas between the electrode and the nozzle after the transfer of the main arc is disclosed in JP-A-3-258464.
It is disclosed in the publication. FIG. 9 shows a time chart of the gas flow (FIG. 9a) and the arc current (FIG. 9b) of this conventional example. When the time chart of plasma cutting is divided by the switching timing of plasma gas and the generation of arc current, the flow of plasma gas is a flow t1 at the stage of creating a pilot arc between the electrode and the nozzle (hereinafter referred to as preceding flow t1). And the flow t2 at the stage of main arc generation
(Hereinafter referred to as main arc generation t2) and flow t3 at a stage after completion of cutting (before start) (hereinafter referred to as trailing flow t3). At this time, as the gas, a non-oxidizing gas is used in the stages of the leading flow t1 and the trailing flow t3, and an oxidizing gas is used as the plasma gas in the stage of the main arc generation t2. At this time, the non-oxidizing gas is stopped at the same time as shifting from the pilot arc to the main arc, the oxidizing gas is used as the plasma gas, and after the cutting is completed, the main arc is stopped and the plasma gas is changed from the oxidizing gas to the non-oxidizing gas. Switching to gas. In the embodiments of the prior art, nitrogen is used as the non-oxidizing gas and oxygen is used as the oxidizing gas. Further, in the prior art, by using the above sequence, it is attempted to prevent the electrode from being consumed and damaging the nozzle at the stage of generating the pilot arc between the electrode and the nozzle, and to achieve a long life of the electrode and the nozzle. There is. At the same time that the main arc is generated, the plasma gas is switched to the oxidizing gas to improve the cutting performance at the same time.

[0004]

However, even if the plasma gas (plasma gas circuit) is switched at the same time when the main arc is transferred, it is not immediately replaced with the oxidizing gas, and the non-oxidizing gas is left for a while after the start of cutting. The cutting performance deteriorates because it mixes with gas, and since non-oxidizing gas is used as the plasma gas during piercing, the piercing capacity is reduced, and the double-arc is generated by the blow-up from the material to be cut attached to the nozzle. Induce,
The life of the nozzle is reduced. Further, after cutting, when the melted material of the plasma arc discharge portion of the electrode is re-solidified in the oxidizing gas atmosphere, oxide is generated in the plasma arc discharge portion of the electrode, and it is cooled rapidly, A crack occurs in that part. This crack causes a decrease in thermal conductivity, and at the next stage of creating a pilot arc between the electrode and nozzle, it scatters and adheres to the inner wall of the nozzle to induce a double arc, thereby increasing the effective life of the nozzle. There is a problem of shortening.

The present invention focuses on the above-mentioned conventional problems, and relates to a control method of a plasma cutting apparatus, and more particularly to a long life of a nozzle of a plasma cutting apparatus used for cutting and improvement of cutting quality.

[0006]

To achieve the above object, in the first invention of the plasma cutting apparatus and the cutting method of the present invention, a plasma arc is generated between the electrode and the material to be cut, and the material to be cut is In the plasma cutting apparatus for cutting the, the cutting step, the preflow step, the step of generating a pilot arc between the electrode and the nozzle, the step of starting to generate a main arc between the electrode and the material to be cut, Continuously, a step of generating a main arc between the electrode and the material to be cut and cutting the material to be cut, a step of ending the generation of the main arc between the electrode and the material to be cut, and an after flow It is characterized in that it consists of gradual steps, and at least either plasma gas or plasma current value is automatically switched according to each step.

In the second invention mainly based on the first invention, the preflow step, the step of generating a pilot arc between the electrode and the nozzle, and the generation of the main arc between the electrode and the material to be cut are completed. And the after-flow process, a non-oxidizing gas is started in the process of starting the main arc between the electrode and the material to be cut, and the main arc is continuously generated between the electrode and the material to be cut. Is generated and an oxidizing gas is used as a plasma gas in the step of cutting the material to be cut.

In the third invention mainly based on the first invention, the preflow step, the step of generating a pilot arc between the electrode and the nozzle, and the generation of the main arc between the electrode and the material to be cut are completed. A non-oxidizing gas is used in the step and the after-flow step, an oxidizing gas having a pressure higher than a predetermined pressure suitable for cutting is used in the step of starting the generation of the main arc between the electrode and the material to be cut, and In the step of continuously generating a main arc between the electrode and the material to be cut and cutting the material to be cut, an oxidizing gas having a predetermined pressure suitable for cutting is used as a plasma gas.

In the fourth invention mainly consisting of the second invention or the third invention, as the non-oxidizing gas, nitrogen, argon,
Alternatively, either carbon dioxide or oxygen or air is used as the oxidizing gas.

In the fifth invention, which is mainly based on any one of the first to fourth inventions, the current command value I for the step of generating a pilot arc is used as the current command value for the plasma power source.
p, the current command value Im at the step of starting the generation of the main arc, and the current command value Ie when the arc is extinguished after the step of ending the generation of the main arc between the electrode and the material to be cut is completed. And are set to automatically switch the current value according to each step, and the current command value Ip to the current command value Im and the current command value Im to the current command value I.
When switching to e, switching is performed at a predetermined change rate.

According to the sixth aspect of the invention, which is mainly based on the fifth aspect, the current command value Ip to the power source is set at the same time when the process moves to the step of generating a pilot arc between the electrode and the nozzle, and the value is set between the electrode and the material to be cut. The process moves to the step of starting the generation of the main arc, switches to the current command value Im at the same time as the main arc detection signal, and moves to the step of ending the generation of the main arc between the electrode and the material to be cut, and at the same time the current command value Ie
The current command value Ip is switched to the current command value Im, and the current command value Im is switched to the current command value Ie.

In the seventh invention, which is mainly composed of any one of the first to sixth inventions, the oxidizing gas is ejected from the assist gas ejection port provided outside the plasma torch.

In the eighth invention, which is mainly based on the seventh invention,
Either oxygen or air is used as the oxidizing gas.

In a ninth aspect of the present invention, in the plasma cutting apparatus that cuts the material to be cut by generating a plasma arc between the electrode and the material to be cut, the cutting step has a cutting start point (A).
From a) to the cutting start point (Ba) on the outer periphery of the workpiece 3a, the pilot arc is generated and the main arc is continuously performed, and at the time of the pilot arc generation, the non-oxidizing gas is generated and the main arc is generated or the main arc is continuously generated. It is characterized in that an oxidizing gas is used for and the arc is extinguished by switching from the oxidizing gas to the non-oxidizing gas between the outer peripheral cutting end point (Bb) and the cutting end point (Cb).

[0015]

In general, the relationship between the plasma current and the plasma gas flow rate when performing plasma cutting with the plasma gas pressure kept constant is as shown in FIG. That is, when the plasma gas pressure is constant, the plasma current and the plasma gas flow rate are in inverse proportion. Therefore, according to the above configuration, in the main arc generation start T3 step,
Simultaneously with the detection signal of the main arc generation, the plasma gas circuit is connected to the oxidizing gas circuit, and in parallel with this, the current command value to the plasma power supply is gradually increased at a predetermined rate and the current command when the main arc occurs. The value is changed to Im and the non-oxidizing gas remaining in the circuit is rapidly expelled while gradually increasing at a predetermined change rate. As a result, there is almost no time delay with respect to the main arc transfer, and the plasma gas can be replaced with only the oxidizing gas.

On the contrary, when the plasma power supply start command is turned off and the process of the main arc generation is completed, the circuit of plasma gas is connected to the circuit of non-oxidizing gas again, and in parallel with this. Then, the current command value to the plasma power source is changed at a predetermined change rate to the current command value Ie for extinguishing the main arc to quickly expel the oxidizing gas remaining in the circuit to remove the plasma gas. Only the oxidizing gas is substituted. At this time, as the current command value Ie decreases, the gas flow rate is in inverse proportion to the current as shown in FIG. 8, and therefore the gas is further accelerated to replace the gas. As a result, the re-solidification of the melt in the plasma arc discharge portion of the electrode is carried out in the non-oxidizing gas, so that the generation of oxide in the plasma arc discharge portion of the electrode is prevented and cracking does not occur. As a result, it is possible to prevent a double arc that is caused by the scattering of the plasma arc discharge portion adhering to the inner wall of the nozzle and inducing it. In addition, these current commands also provide the effect of mitigating thermal shock to the electrode due to arc ignition and the effect of preventing rapid cooling of the electrode when the arc is extinguished. At the stage of generating a pilot arc between the electrode and the nozzle, the inside of the plasma gas circuit is filled with a non-oxidizing gas to prevent the electrode from being oxidized. Further, it is possible to prevent the blow-up of the material to be cut from adhering to the nozzle due to the ejection of the assist gas performed in parallel with the sequence, so that the life of the nozzle can be extended.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a control method for a plasma cutting apparatus according to the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a schematic view for explaining an example of an embodiment of a plasma cutting apparatus of the present invention. In FIG. 1, the plasma cutting device 1 includes a plasma torch 10, a plasma gas supply device 30, an assist gas supply device 40, a plasma power supply 50, and a control device 60. Further, the material 3 to be cut is disposed below the plasma torch 10,
The material 3 to be cut is placed on the support 5.

FIG. 2 shows a sectional view of the plasma torch and the plasma power source 50 and the like. The plasma torch 10 has an electrode 11 at the center, and a gas 12 is provided outside the electrode 11.
Plasma gas passage 13 is provided, and the nozzle 1 is provided so as to cover the electrode 11 with the plasma gas passage 13 interposed therebetween.
5 are arranged. A protective cap 17 is provided outside the nozzle 15, and an assist gas passage 19 is provided between the nozzle 15 and the protective cap 17. Further, hafnium, zirconium, tungsten, and alloys thereof are buried in the lower center part of the electrode 11, and a cooling hole is provided in the center part thereof.

The plasma gas passage 13 is connected to a plasma gas supply device 30 via a plasma gas pipe 13a. In FIG. 1, the plasma gas supply device 30 includes a non-oxidizing gas source 31, an oxidizing gas source 32, and a non-oxidizing gas flow rate adjusting valve 33 (hereinafter, non-oxidizing gas flow rate) connected to the non-oxidizing gas source 31. Adjusting valve 33), an oxidizing gas flow rate adjusting valve 34 (hereinafter referred to as oxidizing flow rate adjusting valve 34) connected to the oxidizing gas source 32, and one of them is a non-oxidizing flow rate adjusting valve 33 and an oxidizing flow rate adjusting valve. And a plasma gas switching valve 35 connected to the plasma gas pipe 13a.

The assist gas passage 19 is connected to an assist gas supply device 40 via an assist gas pipe 19a. The assist gas supply device 40 includes an oxidizing gas source 41.
And an assist gas flow rate adjusting valve 42 connected to the oxidizing gas source 41 (hereinafter referred to as assist flow rate adjusting valve 42).
And an assist gas switching valve 43 connected to the assist gas pipe 19a. In the present embodiment, the oxidizing gas source 32 and the oxidizing gas source 41 use the same gas source in the same container, and therefore, the oxidizing gas source 32 will be used in the following description.

In FIG. 2, the cathode 5 of the plasma power source 50
1a is connected to the electrode 11 and the anode 51b of the power supply 50
Is connected to the nozzle 15 via a resistor and a switch 52 (not shown). The anode 51b of the power source 51 is connected to the material 3 to be cut via a switch 53 and a main arc current detector 54 (hereinafter referred to as the main current detector 54). Between the electrode 11 and the nozzle 15, a pilot arc current detector 55 (hereinafter, pilot current detector 55
Is said to be provided. Pilot current detector 55
The main current detector 54 is connected to the control device 60 described later. This is performed by narrowing a high temperature plasma gas stream 7 generated by an arc discharge generated between the electrode 11 and the material 3 to be cut through the holes 15a of the nozzle 15 and injecting it into the material 3 to be cut.

The control device 60 comprises a controller and the like,
The control device 60 includes a plasma gas switching valve 35, an assist gas switching valve 43, a non-oxidizing flow rate adjusting valve 33, an oxidizing flow rate adjusting valve 34, an assist flow rate adjusting valve 42, a switch 52, a switch 53, a pilot current detector 55, and , And is connected to the main current detector 54. In addition, the control device 60
An input device 61 for inputting a current command value to the plasma power source 50 and an input key 62 for a locus of a cut shape and the like are attached to the. The control device 60 detects the pilot current detector 55, the main current detector 54, the position sensor, the time, and the like according to the current command value from the input device 61 to the plasma power supply 50, and the plasma gas switching valve 3 is detected.
5, assist gas switching valve 43, non-oxidizing flow rate adjusting valve 33,
Oxidation flow rate adjustment valve 34 or assist flow rate adjustment valve 4
The command is output to 2.

Next, the operation of the above structure will be described with reference to the time charts of FIGS. 3 and 4 or an example of the cutting locus of FIG. First, in FIG. 3, for the gas flows of the oxidizing gas of the assist gas, the oxidizing gas of the plasma gas, and the non-oxidizing gas of the plasma gas, the vertical axis indicates ON (flow) and OFF (stop). The gas flow is plotted along the horizontal axis, preflow T1, pilot arc T2,
The main arc generation start T3, the main arc continuation T4, the main arc generation end T5, and the afterflow T6 will be described separately. The stage of preflow T1 is provided to fill the inside of the plasma gas circuit with a non-oxidizing gas in order to prevent thermal shock and the like at the time of pilot arc generation, and to stabilize the plasma gas flow rate. The gas circuit 13, 13a is a control device 60
A non-oxidizing flow rate adjusting valve 33 and a plasma gas switching valve 35 are operated by a command from the above to be connected to the non-oxidizing gas source 31. Next, the operation moves to pilot arc T2.

The stage of the pilot arc T2 is the electrode 11
And in the stage of generating a pilot arc in the nozzle 15, the current command value to the plasma power source 50 is automatically switched to the current command value Ip (shown in FIG. 4) when a predetermined pilot arc is input from the input device 61. . At this time,
The plasma gas circuits 13, 13a are continuously connected to the non-oxidizing gas source 31.

The step of starting T3 of the main arc is provided in order to fill the plasma gas circuit 13 and 13a with the oxidizing gas because the cutting quality is deteriorated when cutting is performed by using the non-oxidizing gas as the plasma gas 12. At this stage, the plasma gas circuit is connected to the oxidizing gas source 32 by operating the oxidizing flow rate adjusting valve 34 and the plasma gas switching valve 35 in response to a command from the control device 60. In parallel with this, the current command value to the plasma power source is gradually changed at a predetermined change rate to the current command value Im (shown in FIG. 4) when the main arc occurs. At this time, by providing a slope (shown in (a) of FIG. 4) to the current command value for the plasma power source 50, the non-oxidizing gas remaining in the plasma gas circuit 13 and 13a is expelled quickly between these slopes. Since it can be filled with oxidizing gas, the transition to good quality cutting becomes smooth. When the current command value reaches Im after a lapse of a certain time (hereinafter referred to as up-slope time Tu), the main arc continuation T4 is entered.

At the stage of the main arc continuation T4, stable plasma cutting is performed by the oxidizing gas. At this time, the plasma gas circuits 13 and 13a are continuously connected to the oxidizing gas source 32.

At the stage of the main arc generation end T5, the plasma power source start command is turned off, the melt of the plasma arc discharge part of the electrode is re-solidified in the non-oxidizing gas, and the oxide of the plasma arc discharge part is re-solidified. It is provided in order to prevent the generation and to prevent the generation of cracks. At this stage, the plasma gas circuits 13 and 13a operate the non-oxidizing flow rate adjusting valve 33 and the plasma gas switching valve 35 in response to a command from the control device 60. And is again connected to the non-oxidizing gas source 31. In parallel with this, the current command value to the plasma power supply 50 is gradually changed at a predetermined change rate to the current command value Ie at the time of main arc occurrence. At this time, by providing a slope (shown in (b) of FIG. 4) to the current command value for the plasma power supply, the oxidizing gas remaining in the plasma gas circuit can be quickly expelled and filled with the non-oxidizing gas. Therefore, it is possible to prevent the double arc caused by the scattered matter of the plasma arc discharge portion of the electrode being attached to the inner wall of the nozzle.
When the current command value reaches Ie after a lapse of a certain time (hereinafter referred to as down slope time Td), the main current generation end step is ended, the plasma power supply is stopped, and the flow proceeds to the after flow T6 step. Sequence ends.

At the stage of afterflow T6, the plasma gas circuits 13 and 13a are continuously operated, and the non-oxidizing gas source 31 is used.
It is connected to the. Further, in parallel with the above sequence, in order to prevent the blow-up from the material to be cut 3 from adhering to the nozzle in each of the above steps, an oxidizing gas is supplied from the assist gas jet port 19a outside the plasma torch. Is gushing out. The turning on and off of the assist gas is performed by the assist flow rate adjusting valve 42 and the assist gas switching valve 43 according to a command from the control device 60, and an appropriate amount of assist gas is appropriately supplied. Further, in the above description, the flow of the oxidizing gas of the plasma gas and the gas of the non-oxidizing gas of the plasma gas is indicated as ON (flow), but the gas set to an appropriate amount is appropriately adjusted by the flow rate adjusting valve. It goes without saying that they will be supplied after being supplied. In this embodiment, oxygen and air are used as the oxidizing gas and nitrogen, argon or carbon dioxide is used as the non-oxidizing gas.

Next, switching of the current command value in FIGS. 3 and 4 will be described. The switching timing (horizontal axis) is the same as the gas flow, and the preflow T1, the pilot arc T2, the main arc generation start T3, the main arc continuous T4, the main arc generation end T5, and the afterflow T6 are performed. I will explain separately. In addition, the vertical axis indicates the flow of the current as ON (flow) and OFF (stop) in FIG. 3, and shows the magnitude of the current command value in FIG.

The start-up switch (not shown) is pushed from the control device 60 to output a start-up command to the plasma power source, and at the same time, the stage of preflow T1 starts. Therefore, at the stage of the preflow T1, the current command value is zero and the current flowing through the electrode 11 is also zero. A predetermined time (for example,
After the elapse of (time until the plasma gas circuit is filled with a non-oxidizing gas to prevent thermal shock when the pilot arc is generated and the plasma gas flow rate is stabilized), the pilot arc T2 is entered. To do.

At the pilot arc T2 stage, the switch 52 is turned on and the pilot arc T2 stage is entered, and at the same time, the current command value is automatically switched stepwise from zero to the current command value Ip when the pilot arc is generated. A pilot arc is generated, and further, the pilot arc is transferred to the main arc, and the main arc transfer signal from the plasma power supply 50 is transmitted to the main arc current detector 54.
When it is detected by, the process proceeds to the stage of the main arc generation start T3.

At the stage of the main arc generation start T3, the current command value to the plasma power source 50 is gradually changed at a predetermined change rate to the current command value Im at the time of main arc generation.
When the current command value reaches Im after the up-slope time Tu has passed (or by a signal from the main current detector 54), the main arc continuation T4 is entered.

At the stage of the main arc continuation T4, the switch 52 is turned off, and the switch 53 is turned on to output a predetermined current Im from the plasma power source to cut the plasma.
When the material 3 to be cut is cut by a predetermined amount and the cutting is close to the end position, and the position is detected by a position sensor described later or time, etc., the controller 60 outputs 0FF to the plasma power source and at the same time The process proceeds to the stage of arc generation end T5.

At the stage of the main arc generation end T5, the current command value to the plasma power source is gradually changed to the current command value Ie when the main arc is generated at a predetermined change rate. When the current command value reaches Ie after the down slope time Td elapses, the stage of ending the main current generation ends, and the switch 5
When 3 is cut off, the plasma power supply 50 is stopped and the process proceeds to the stage of afterflow T6.

At the stage of afterflow T6, the current command value is zero and the current flowing through the electrode 11 is also zero.

An example of the cutting trajectory of FIG. 5 is shown. When cutting the circular work piece 3a of the material 3 to be cut along the cutting locus, the cutting start point (Aa), the cutting start point (Ba) and the end point (Bb) on the outer periphery of the work piece 3a (hereinafter, Outer circumference cutting start point (Ba) or outer circumference cutting end point (Bb)), cutting end point (Cb), run-up section (Ea) between cutting start point (Aa) and outer circumference cutting start point (Ba), and , And an arc extinguishing section (Fb) between the outer circumference cutting end point (Bb) and the cutting end point (Cb). Cutting start point (A
In a), at least the preflow T1, the pilot arc T2, and the main arc generation start T3 are performed. Further, at the outer periphery cutting start point (Ba), it is completely in the stage of main arc continuation T4. Furthermore, this state is continued until the cutting end point (Bb) or the arc extinguishing section (Fb) on the outer periphery of the workpiece 3a. In the arc extinguishing section (Fb), a stage of main arc generation end T5 or afterflow T6 is performed. At this time, the preflow T
1, pilot arc T2, main arc generation start T
3, main arc continuous T4, main arc generation end T
5. The switching of the stages of the afterflow T6 is performed by using the plasma torch at the cutting start point (Aa), the outer circumference cutting start point (Ba), or the outer circumference cutting end point (Bb).
Whether it is detected by a position sensor attached to the Y-axis movable device, or the cutting time is set and grasped in time at the time of teaching, or the cutting locus is stored in the XY-axis movable device or a control device such as a robot. Occasionally indicate the position or by doing so.

Next, referring to FIG. 6 and FIG. 7, the second
Examples will be described. The same reference numerals as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In FIG.
The plasma gas passage 13 is connected to the plasma gas supply device 70 via the plasma gas pipe 13a. The plasma gas supply device 70 includes a non-oxidizing gas source 31, a high-pressure oxidizing gas source 72, and an optimum pressure oxidizing gas source 73, one of which is connected to each gas source and the other of which is connected to the plasma gas pipe 13a. And a gas switching valve 75. The assist gas passage 19 is connected to the optimum pressure oxidizing gas source 73 via the assist gas pipe 19 a, the assist gas switching valve 43, and the assist flow rate adjusting valve 42.

In the above structure, the operation of the plasma gas will be described below. However, since the steps of preflow T1 and pilot arc T2 are the same, explanations thereof are omitted, and steps of main arc generation start T3 and main arc are started. The stage of the arc continuation T4 will be described. At the stage of the main arc generation start T3, the plasma gas 1
Since cutting quality is deteriorated when a non-oxidizing gas is used for No. 2, the plasma gas circuit is provided to fill 13 and 13a with the oxidizing gas. At this stage, the plasma gas circuit is provided with the controller 60. The plasma gas switching valve 75 is operated in response to a command from, and the high-pressure oxidizing gas source 72 is connected. By the supply from the high-pressure oxidizing gas source 72, the non-oxidizing gas remaining in the plasma gas circuit 13 and 13a can be quickly expelled and filled with the oxidizing gas, so that the transition to good quality cutting becomes smooth. In addition,
At this time, similarly to the first embodiment, the current command value for the plasma power supply may be gradually changed at a predetermined rate of change to the current command value Im (shown in FIG. 4) when the main arc occurs. When the current command value reaches Im after the lapse of a predetermined time, the main arc continuation T4 is entered.

At the stage of the main arc continuation T4, in order to perform stable plasma cutting with the oxidizing gas, the circuit of the plasma gas operates the plasma gas switching valve 75 according to a command from the control device 60, and the optimum pressure oxidizing property is obtained. Connect to gas source 73. By the supply from the optimum pressure oxidizing gas source 73, the optimum pressure gas flows through the plasma nozzle 15, and stable plasma cutting is performed. Since the next main arc generation end T5 and afterflow T6 are the same as those in the first embodiment, the description thereof will be omitted. The assist gas passage 19 is connected to the optimum pressure oxidizing gas source 73, and a predetermined appropriate amount flows from the stage of the preflow T1 through the assist gas switching valve 43 and the assist flow rate adjusting valve 42.

In the second embodiment described above, the high pressure oxidizing gas source 72 and the optimum pressure oxidizing gas source 73 are provided, but as shown in FIG. The oxidizing gas and the optimum pressure oxidizing gas may be adjusted.

[0041]

As described above, according to the present invention,
A control function to switch to the plasma gas circuit is provided, and at the stage of generating a pilot arc between the electrode and the nozzle, the plasma gas circuit is filled with a non-oxidizing gas to prevent oxidation of the electrode, and the main arc is generated. In the step (1), the plasma gas circuit is connected to the oxidizing gas circuit, and the non-oxidizing gas is expelled quickly, so that good cutting quality can be obtained. At the end of main arc generation, the circuit for plasma gas is connected to the circuit for non-oxidizing gas again, and the current command value to the plasma power supply is changed at a predetermined rate to reduce the oxidative gas remaining in the circuit. Since the gas is expelled quickly and the plasma gas is replaced only with the non-oxidizing gas, the re-solidification of the melt at the electrode's plasma arc discharge part is performed in the non-oxidizing gas, so that the electrode's plasma arc discharge part is oxidized. The generation of objects is prevented and cracking can be prevented. Further, it is possible to prevent the blow-up of the material to be cut from adhering to the nozzle due to the ejection of the assist gas performed in parallel with the sequence, so that an excellent effect of extending the effective life of the nozzle is obtained.

[Brief description of drawings]

FIG. 1 shows a schematic view for explaining a first embodiment of a plasma cutting apparatus of the present invention.

FIG. 2 shows a cross-sectional view of a plasma torch of the present invention and a schematic diagram for explaining connection with a plasma power supply and a control device.

FIG. 3 is a time chart diagram of gas flow and current in the first embodiment of the plasma cutting apparatus of the present invention.

FIG. 4 is a time chart diagram of a current command value of the plasma cutting apparatus of the present invention.

FIG. 5 is a diagram illustrating an example of a cutting locus of a material to be cut and types of gas to be cut.

FIG. 6 shows a schematic view for explaining a second embodiment of the plasma cutting apparatus of the present invention.

FIG. 7 is a time chart diagram of gas flow and current in the second embodiment of the plasma cutting apparatus of the present invention.

FIG. 8 is a diagram showing a relationship between a plasma current and a plasma gas flow rate when performing plasma cutting with the plasma gas pressure kept constant.

FIG. 9 is a time chart of gas flow and arc current of a conventional plasma cutting device.

[Explanation of symbols]

1 plasma cutting device, 3 material to be cut, 10
Plasma torch, 11 electrodes, 13 plasma gas passages, 15 nozzles, 19 assist gas passages, 3
0, 70 Plasma gas supply device, 31 Non-oxidizing gas source, 32 Oxidizing gas source, 33 Non-oxidizing gas flow rate adjusting valve, 34 Oxidizing gas flow rate adjusting valve, 35, 75 Plasma gas switching valve, 40 Assist gas supply Device, 4
2 Assist gas flow control valve, 50 plasma power supply,
54 pilot arc current detector, 55 main arc current detector, 60 controller, 72 high pressure oxidizing gas source, 73 optimum pressure oxidizing gas source,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideho Hoshino 1200 Manda, Hiratsuka, Kanagawa Prefecture Komatsu Ltd. (72) Inventor Masahiko Hasegawa 1200, Hiratsuka, Kanagawa Ltd. Komatsu Ltd.

Claims (9)

[Claims] 1. In a plasma cutting apparatus for cutting a material to be cut by generating a plasma arc between an electrode and the material to be cut, a cutting step is a preflow step, and a pilot arc is generated between the electrode and a nozzle. And a step of starting to generate a main arc between the electrode and the material to be cut, and a step of continuously generating a main arc between the electrode and the material to be cut and cutting the material to be cut, It consists of the steps of terminating the generation of the main arc between the electrode and the material to be cut, the after-flow step, and the automatic steps of at least either the plasma gas or the plasma current value depending on each step. A method of controlling a plasma cutting device, characterized by switching. 2. The method of controlling a plasma cutting apparatus according to claim 1, wherein a preflow step, a step of generating a pilot arc between the electrode and the nozzle, and a step of generating a main arc between the electrode and the material to be cut. The non-oxidizing gas is used in the step of terminating and the after-flow step, the step of starting the generation of the main arc between the electrode and the material to be cut, and continuously, between the electrode and the material to be cut. A method of controlling a plasma cutting device, characterized in that an oxidizing gas is used as a plasma gas in a step of generating a main arc and cutting a material to be cut. 3. The method for controlling a plasma cutting apparatus according to claim 1, wherein a preflow step, a step of generating a pilot arc between the electrode and the nozzle, and a step of generating a main arc between the electrode and the material to be cut. The non-oxidizing gas is used in the step of terminating and the after-flow step, and the oxidizing gas of a pressure higher than a predetermined pressure suitable for cutting is used in the step of starting the generation of the main arc between the electrode and the material to be cut. In addition, the main arc is continuously generated between the electrode and the material to be cut, and in the step of cutting the material to be cut, an oxidizing gas having a predetermined pressure suitable for cutting is used as the plasma gas. A method for controlling a plasma cutting device. 4. The method for controlling a plasma cutting device according to claim 2, wherein the non-oxidizing gas is nitrogen,
A method for controlling a plasma cutting device, wherein either argon or carbon dioxide is used as an oxidizing gas, and either oxygen or air is used. 5. The method of controlling a plasma cutting device according to claim 1, wherein a current command value I for a process of generating a pilot arc is used as a current command value for the plasma power source.
p and the current command value I during the process of starting the generation of the main arc
m and the current command value Ie when the process of ending the generation of the main arc between the electrode and the material to be cut is terminated and the arc is extinguished, and the current value corresponding to each process is gradually set. A method for controlling a plasma cutting device, in which the current command value Ip is switched to the current command value Im and the current command value Im is switched to the current command value Ie at a predetermined rate of change. 6. The method for controlling a plasma cutting apparatus according to claim 5, wherein the current command value I to the power source is transferred to the step of generating a pilot arc between the electrode and the nozzle.
p and shift to the step of starting the generation of the main arc between the electrode and the material to be cut, and switch to the current command value Im at the same time as the main arc detection signal to generate the main arc between the electrode and the material to be cut. Simultaneously with the transition to the ending step, the current command value is switched to Ie, the current command value Ip to the current command value Im and the current command value Im to the current command value I
A method of controlling a plasma cutting device, which switches at a predetermined change rate when switching to e. 7. The method of controlling a plasma cutting device according to claim 1, wherein the oxidizing gas is jetted from an assist gas jet port provided outside the plasma torch. 8. The method for controlling a plasma cutting device according to claim 7, wherein either oxygen or air is used as the oxidizing gas. 9. A plasma cutting apparatus for cutting a material to be cut by generating a plasma arc between an electrode and the material to be cut, wherein the cutting step starts cutting the outer periphery of the workpiece 3a from a cutting start point (Aa). By the point (Ba), the pilot arc is generated and the main arc continues, and
A non-oxidizing gas is used when the pilot arc is generated, and an oxidizing gas is used for the main arc generation or the main arc continuation. Further, the oxidizing gas is used between the outer peripheral cutting end point (Bb) and the cutting end point (Cb). A method for controlling a plasma cutting device, which comprises extinguishing an arc by switching from a nonoxidizing gas to a nonoxidizing gas.