JP2018167288A - Plasma arc cutting device and plasma arc cutting method - Google Patents

Abstract

To extend a service life of an electrode of a plasma torch.SOLUTION: A plasma arc cutting device 1 comprises: a plasma torch 10 having an electrode 11; a power supply unit 20 which supplies DC current between the electrode 11 and a cut material W in order to generate plasma arc P between the electrode 11 and the cut material W, and can overlap AC current on DC current; and a controller 30 for controlling the power supply unit 20. The controller 30 so controls the power supply unit 20 that when cutting the cut material W having a plate thickness of 6 mm or more, AC current whose difference between a maximum value and a minimum value is not less than 25% and not more than 40% of DC current is overlapped on DC current.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a plasma cutting apparatus and a plasma cutting method.

  Conventionally, a material to be cut such as a steel plate is cut by plasma cutting. In plasma cutting, a direct current voltage is applied between the electrode in the plasma torch and the material to be cut, and a plasma arc is generated by flowing a working gas such as oxygen gas to relatively move the electrode and the material to be cut. The material to be cut is cut by moving it.

  In oxygen plasma cutting using oxygen gas as a working gas, the electrode is exposed to an oxidizing atmosphere with high-purity oxygen gas and a high temperature of the plasma arc acts. In order to withstand such severe use conditions, hafnium having a high melting point and a low work function has been used as an electrode material. This extends the life of the electrode to a usable level.

  Further, as a method for further extending the life of the electrode, Patent Document 1 superimposes an alternating current having a predetermined frequency and amplitude on a direct current supplied to generate a plasma arc between the electrode and the material to be cut. Thus, a technique for extending the life of the electrode as compared with the case of supplying only a direct current is disclosed.

Japanese Patent No. 2819393

  In recent years, the demand for cutting a material having a relatively large thickness by plasma cutting has been increasing. The material to be cut is, for example, a steel plate. In order to meet this demand, a large current having a current value exceeding 200 A is used as a direct current for plasma cutting.

  On the other hand, the technique described in Patent Document 1 is based only on the experimental result under the condition that the average value of the supply current supplied between the electrode and the material to be cut is 70A. In plasma cutting, a current of 70 A is mainly used when cutting thin plates (thickness of less than 6 mm), medium thick plates (thickness of 6 mm or more and less than 16 mm) and thick plates (thickness of 16 mm or more). ) Is not used for cutting. For this reason, when the current value of the direct current exceeds 200 A, it is considered that the technique described in Patent Document 1 cannot be applied. Actually, the inventors tried to apply the technique described in Patent Document 1 under the condition that the current value of the direct current exceeds 200 A, but a sufficient effect for extending the life of the electrode was not obtained.

  The present invention has been made in view of the above circumstances, and provides a plasma cutting apparatus and a plasma cutting method capable of extending the life of an electrode when cutting a workpiece having a large plate thickness. Objective.

  The plasma cutting device according to the first aspect of the present invention includes a plasma torch having an electrode and a direct current between the electrode and the workpiece to generate a plasma arc between the electrode and the workpiece. A power supply unit capable of supplying a current and superimposing an alternating current on the direct current; and a control unit for controlling the power supply unit. When the control unit cuts the material to be cut having a thickness of 6 mm or more, the difference between the maximum value and the minimum value of the alternating current is 25% to 40% of the direct current. The power supply unit is controlled to superimpose the alternating current on the direct current.

  In the plasma cutting apparatus, the control unit may control the power supply unit such that the frequency of the alternating current is 50 Hz or more and 300 Hz or less.

  In the plasma cutting apparatus, the control unit may control the power supply unit so that the magnitude of the direct current is 250 A or more and 350 A or less.

  The plasma cutting method according to the second aspect of the present invention is a plasma cutting method for cutting the material to be cut by a plasma arc generated between the electrode of the plasma torch and the material to be cut, and has a plate thickness of 6 mm or more. When the material to be cut is cut, the direct current supplied between the electrode and the material to be cut to generate the plasma arc has a difference between the maximum value and the minimum value of the alternating current. The alternating current having a magnitude of 25% to 40% is superimposed on the direct current.

  According to such a plasma cutting apparatus and plasma cutting method, the alternating current is superimposed on the direct current by superimposing the alternating current of the above-described magnitude on the direct current supplied between the electrode and the material to be cut. The life of the electrode can be extended compared with the case where there is no electrode.

  According to the plasma cutting apparatus and the plasma cutting method described above, the life of the electrode can be extended when a material to be cut having a large thickness is cut.

It is a figure showing the whole plasma cutting device composition concerning one embodiment of the present invention. It is a figure which shows the waveform of the electric current supplied between an electrode and a to-be-cut material.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a diagram showing an overall configuration of a plasma cutting apparatus 1 according to an embodiment of the present invention. As shown in FIG. 1, the plasma cutting apparatus 1 includes a plasma torch 10 having an electrode 11, a power supply unit 20, and a control unit 30 that controls the power supply unit 20.

  The plasma torch 10 has a nozzle portion 12 having a space inside. The nozzle portion 12 has an outer diameter formed of a cylindrical body having a conical shape on the distal end side and a cylindrical shape on the proximal end side. The electrode 11 is disposed inside the nozzle portion 12. A working gas flow path 13 through which working gas flows is formed between the electrode 11 and the nozzle portion 12. A nozzle hole 12 a communicating with the distal end side of the working gas flow path 13 is formed at the distal end of the nozzle portion 12.

  The electrode 11 has a cylindrical outer shape having a bottom on the tip side. An electrode material 14 made of, for example, hafnium is provided at the tip of the electrode 11. The electrode 11 can be cooled by circulating cooling water in the internal space of the electrode 11. The electrode 11 is made of a metal having a relatively high conductivity, such as copper.

  The proximal end side of the working gas channel 13 is connected to the working gas supply source 15 via a hose or the like. The working gas supply source 15 can supply a working gas such as oxygen gas to the working gas flow path 13. The working gas supplied from the working gas supply source 15 to the proximal end side of the working gas flow path 13 is ejected from the nozzle hole 12 a through the distal end side of the working gas flow path 13.

  The power supply unit 20 supplies a direct current between the electrode 11 and the workpiece W in order to generate a plasma arc P between the electrode 11 of the plasma torch 10 and the workpiece W. The power supply unit 20 is configured to be able to superimpose an alternating current on a direct current. The power supply unit 20 is electrically connected to each of the electrode 11 and the workpiece W. The power supply unit 20 is also electrically connected to the nozzle unit 12 of the plasma torch 10. The power supply unit 20 can generate a plasma arc P by applying a predetermined voltage between the electrode 11 and the material to be cut W using electric power supplied from a commercial power supply. In the power supply unit 20, the supply of the direct current and the superposition of the alternating current on the direct current are performed based on an instruction from the control unit 30.

  The control unit 30 is electrically connected to the power supply unit 20 and configured to be able to transmit and receive signals to and from the power supply unit 20. In the present embodiment, the control unit 30 controls the power supply unit 20 so that a predetermined alternating current is superimposed on the direct current supplied by the power supply unit 20 when cutting the workpiece W having a large plate thickness. More specifically, when the control unit 30 cuts the workpiece W having a thickness of 6 mm or more, the difference between the maximum value and the minimum value of the alternating current is 25% or more and 40% or less with respect to the direct current. The power supply unit 20 is controlled so as to superimpose an alternating current of a magnitude on the direct current.

  Further, the control unit 30 controls the magnitude of the direct current supplied by the power supply unit 20 and the frequency of the alternating current superimposed on the direct current. Specifically, the control unit 30 can control the power supply unit 20 so that the magnitude of the direct current is 250 A or more and 350 A or less. Moreover, the control part 30 can control the power supply part 20 so that the frequency of an alternating current may be 50 Hz or more and 300 Hz or less.

  The cutting speed, which is the speed at which the workpiece W is cut, varies depending on the thickness of the workpiece W and the magnitude of the direct current supplied by the power supply unit 20. For example, when the thickness of the material to be cut W is 6 mm and the magnitude of the direct current is 250 A, the cutting speed is 4000 mm / min. When the thickness of the material to be cut W is 6 mm and the magnitude of the direct current is 500 A, the cutting speed is 8000 mm / min. And when the plate | board thickness of the to-be-cut material W is 50 mm and the magnitude | size of a direct current is 500 A, a cutting speed is 800 mm / min.

  Here, the direct current supplied by the power supply unit 20 and the alternating current superimposed on the direct current will be described in detail. FIG. 2 is a diagram illustrating a waveform of a current supplied between the electrode 11 and the workpiece W. FIG. 2A shows a waveform when an alternating current is not superimposed on a direct current. FIG. 2B shows a waveform of the alternating current superimposed on the direct current. FIG. 2C shows a waveform when an alternating current is superimposed on a direct current.

As shown in FIG. 2A, the direct current is a substantially constant current C1 with a predetermined current value I regardless of the passage of time. As shown in FIG. 2B, the alternating current superimposed on the direct current is a current C2 having a predetermined amplitude A and a predetermined frequency F. As shown in FIG. 2C, a current obtained by superimposing an alternating current on a direct current is a current C3 obtained by superimposing an alternating current having a predetermined amplitude A and a predetermined frequency F on a direct current having a current value I. It is. In this case, the average current value of the current C3 becomes the current value I, and the current value of the current C3 changes over time in the range of the amplitude A with the current value I as the center. The amplitude A (also referred to as the magnitude of the alternating current), which is the difference between the maximum value and the minimum value of the alternating current, is the average current value of the current C3, that is, the current value I of the direct current (also referred to as the magnitude of the direct current). (Hereinafter referred to as ripple rate) R. The ripple rate R is expressed by the following equation (1).
R = (A / I) × 100 [%] (1)

  When the alternating current is not superimposed on the direct current, the power supply unit 20 supplies the current C <b> 1 shown in FIG. 2A between the electrode 11 and the workpiece W. In addition, when the alternating current is superimposed on the direct current, the power supply unit 20 supplies the current C3 shown in FIG. 2C between the electrode 11 and the workpiece W.

  Next, a plasma cutting method using the plasma cutting apparatus 1 will be described.

  First, the working gas is supplied from the working gas supply source 15 to the periphery of the electrode 11 of the plasma torch 10 through the working gas flow path 13. At the same time, a voltage is applied between the electrode 11 and the nozzle unit 12 by the power supply unit 20, thereby generating a pilot arc from the electrode 11 in the nozzle unit 12. By continuously supplying the working gas, the working gas that has been made plasma in the nozzle portion 12 by the pilot arc is injected from the nozzle hole 12a, and a voltage is applied between the electrode 11 and the workpiece W by the power source portion 20 to generate plasma. An arc (main arc) P is formed. At the same time, the voltage applied between the electrode 11 and the nozzle portion 12 is stopped to stop the pilot arc. The material to be cut W is melted by the thermal energy of the plasma arc P, and the melt is removed by the jet energy of the plasma arc P. As a result, a groove penetrating in the thickness direction of the workpiece W is formed, and plasma cutting is performed.

  In the present embodiment, in the above-described plasma cutting method, when cutting the workpiece W having a thickness of 6 mm or more, the electrode 11 and the workpiece W are generated in order to generate the plasma arc P by the power supply unit 20. An alternating current is superimposed on a direct current supplied by applying a voltage between the two. The magnitude of the alternating current is set so that the difference between the maximum value and the minimum value of the alternating current is 25% or more and 40% or less with respect to the direct current. By doing in this way, the lifetime of the electrode 11 can be extended compared with the case where an alternating current is not superimposed on a direct current.

  Note that the cutting speed of the workpiece W can be controlled by a known speed control means.

  EXAMPLES Hereinafter, although an Example is given and this invention is further demonstrated, this invention is not limited by these.

  In the present embodiment, the current value of the direct current supplied between the electrode and the material to be cut (the average current value of the current when the alternating current is superimposed on the direct current) I and the alternating current superimposed on the direct current. The effect of extending the life of the electrode was examined by changing the current magnitude (ripple ratio R) and frequency F.

[Comparative Example 1]
In the plasma cutting apparatus, oxygen gas was used as the working gas, and the gas flow rate was 50 NL (normal liters) / min. Hafnium was used for the electrode material. The current value I of the direct current supplied between the electrode and the material to be cut was set to 250A. Note that no alternating current is superimposed on the direct current. Under this condition, the plasma arc was generated for 1 minute, and then the supply of current from the power supply unit was stopped. This operation of generating a plasma arc for 1 minute was repeated, the electrode was consumed, and the life of the electrode was measured. As a result, the lifetime of the electrode was 90 minutes.

[Example 1]
Compared with the conditions of Comparative Example 1, the lifetime of the electrodes was measured under the condition that an alternating current with a ripple rate of 32% and a frequency of 150 Hz was superimposed on the direct current. As a result, the lifetime of the electrode was 150 minutes.

[Example 2]
Compared with the conditions of Comparative Example 1, the lifetime of the electrodes was measured under the condition that an alternating current with a ripple rate of 32% and a frequency of 300 Hz was superimposed on the direct current. As a result, the lifetime of the electrode was 270 minutes.

[Comparative Example 2]
Compared with the conditions of Comparative Example 1, the lifetime of the electrodes was measured under the condition that the current value of the direct current was 300A. As a result, the lifetime of the electrode was 165 minutes.

Example 3
Compared with the conditions of Comparative Example 2, the lifetime of the electrodes was measured under the condition that an alternating current with a ripple rate of 33.3% and a frequency of 50 Hz was superimposed on the direct current. As a result, the lifetime of the electrode was 225 minutes.

Example 4
Compared with the conditions of Comparative Example 2, the lifetime of the electrodes was measured under the condition that an alternating current with a ripple rate of 33.3% and a frequency of 150 Hz was superimposed on the direct current. As a result, the lifetime of the electrode was 240 minutes.

[Comparative Example 3]
Compared with the conditions of Comparative Example 2, the lifetime of the electrodes was measured under the condition that an alternating current with a ripple rate of 13.3% and a frequency of 300 Hz was superimposed on the direct current. As a result, the lifetime of the electrode was 172 minutes.

[Comparative Example 4]
Compared with the conditions of Comparative Example 1, the electrode lifetime was measured under the condition that the current value of the direct current was 350 A. As a result, the lifetime of the electrode was 131 minutes.

Example 5
Compared with the conditions of Comparative Example 4, the life of the electrodes was measured under the condition that an alternating current with a ripple rate of 28.6% and a frequency of 100 Hz was superimposed on the direct current. As a result, the lifetime of the electrode was 212 minutes.

  Tables 1 to 3 show the measurement results in the above-described examples and comparative examples. In Tables 1 to 3, the electrode life ratio is shown in addition to the current value I, the ripple rate R, the frequency F, and the electrode life. The electrode life ratio is a ratio indicating the life when the alternating current is superimposed on the direct current when the life when the alternating current is not superimposed on the direct current at the same current value I is 100.

  As shown in Table 1, an AC current having a ripple rate R of 32% is superimposed on the DC current as compared with Comparative Example 1 in which the current value I of the DC current is 250 A and the AC current is not superimposed on the DC current. In Examples 1 and 2, the electrode life ratios were 167 and 300, respectively. Thereby, in Example 1 and 2, it was confirmed that the lifetime of an electrode extends significantly with respect to the comparative example 1. FIG.

  Further, as shown in Table 2, in contrast to Comparative Example 2 in which the current value I of the direct current is 300 A and the alternating current is not superimposed on the direct current, an alternating current having a ripple rate R of 33.3% is applied to the direct current. In Examples 3 and 4 superimposed on the current, the electrode life ratios were 136 and 145, respectively. As a result, in Examples 3 and 4, it was confirmed that the life of the electrode was significantly increased as compared with Comparative Example 2. In Comparative Example 3 in which an alternating current with a ripple rate R of 13.3% was superimposed on a direct current, the electrode life ratio was 104 compared to Comparative Example 2, and the life of the electrode was slightly increased, but the life was sufficient. The growth of was not obtained.

  Further, as shown in Table 3, in comparison with Comparative Example 4 in which the current value I of the direct current is 350 A and the alternating current is not superimposed on the direct current, an alternating current having a ripple rate R of 28.6% is applied to the direct current. In Example 5 superimposed on the current, the electrode life ratio was 162. Thereby, in Example 5, it was confirmed that the lifetime of an electrode extends significantly with respect to the comparative example 4. FIG.

  From the above, when the current value I of the direct current is in the range of 250A to 350A, only the direct current is supplied by superimposing the alternating current with the ripple rate R of 25% to 40% and the frequency F of 50 Hz to 300 Hz on the direct current. It was confirmed that the life of the electrode was extended as compared with the case of doing so.

  The plasma cutting device 1 according to this embodiment includes a plasma torch 10 having an electrode 11 and a gap between the electrode 11 and the workpiece W in order to generate a plasma arc P between the electrode 11 and the workpiece W. A power supply unit 20 capable of supplying a direct current and superimposing the alternating current on the direct current and a control unit 30 for controlling the power supply unit 20 are provided. When the control unit 30 cuts the workpiece W having a thickness of 6 mm or more, the difference between the maximum value and the minimum value of the AC current is 25% or more and 40% or less of the AC current. The power supply unit 20 is controlled so that the current is superimposed on the direct current.

  In addition, the plasma cutting method according to the present embodiment is a plasma cutting method for cutting the material to be cut W by a plasma arc P generated between the electrode 11 of the plasma torch 10 and the material to be cut W, and is 6 mm or more. The difference between the maximum value and the minimum value of the alternating current in the direct current supplied between the electrode 11 and the material to be cut W in order to generate the plasma arc P when the material W to be cut is cut. However, an alternating current having a magnitude of 25% to 40% is superimposed on the direct current.

  According to the plasma cutting apparatus 1 and the plasma cutting method described above, the alternating current is superimposed on the direct current by superimposing the alternating current having the above-described magnitude on the direct current supplied between the electrode 11 and the workpiece W. The life of the electrode 11 can be extended compared with the case where it is not made.

  Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this embodiment. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Plasma cutting device 10 Plasma torch 11 Electrode 12 Nozzle part 12a Nozzle hole 13 Working gas flow path 14 Electrode material 15 Working gas supply source 20 Power supply part 30 Control part A Amplitude C1, C2, C3 Current F Frequency I Current value P Plasma arc R Ripple rate W Material to be cut

Claims (4)

A plasma torch with electrodes;
A power source capable of supplying a direct current between the electrode and the material to be cut in order to generate a plasma arc between the electrode and the material to be cut, and superimposing an alternating current on the direct current; ,
A control unit for controlling the power supply unit;
With
When the control unit cuts the material to be cut having a thickness of 6 mm or more, the difference between the maximum value and the minimum value of the alternating current is 25% to 40% of the direct current. A plasma cutting device that controls the power supply unit so that the AC current is superimposed on the DC current. The plasma cutting device according to claim 1,
The said control part controls the said power supply part so that the frequency of the said alternating current may be 50 Hz or more and 300 Hz or less. The plasma cutting device. The plasma cutting device according to claim 1 or 2,
The said control part controls the said power supply part so that the magnitude | size of the said direct current may be 250A or more and 350A or less. The plasma cutting device. A plasma cutting method of cutting the workpiece by a plasma arc generated between an electrode of the plasma torch and the workpiece,
When cutting the material to be cut having a thickness of 6 mm or more, the maximum value and the minimum value of the alternating current are applied to the direct current supplied between the electrode and the material to be cut in order to generate the plasma arc. A plasma cutting method in which the alternating current having a difference of 25% or more and 40% or less is superimposed on the direct current.

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