JP6785177B2 - Plasma cutting device and plasma cutting method - Google Patents

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 has been cut by plasma cutting. In plasma cutting, a DC voltage is applied between the electrode in the plasma torch and the material to be cut, and a working gas such as oxygen gas is passed to generate a plasma arc, so that the electrode and the material to be cut are relatively separated. The material to be cut is cut by moving it.

In oxygen plasma cutting using oxygen gas as the working gas, the electrodes are exposed to an oxidizing atmosphere by high-purity oxygen gas and the high temperature of the plasma arc acts on them. In order to withstand such harsh usage conditions, hafnium having a high melting point and a small work function has been conventionally used as an electrode material. This extends the life of the electrode to the extent that it can be used.

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

Japanese Patent No. 2819393

In recent years, there has been an increasing demand for cutting a material to be cut having a relatively large plate thickness by plasma cutting. The material to be cut is, for example, a steel plate. In order to meet this demand, a large current having a current value of more than 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 results under the condition that the average value of the supply current supplied between the electrode and the material to be cut is 70 A. In plasma cutting, a current of 70 A is mainly used for cutting thin plates (plate thickness less than 6 mm), and medium-thick plates (plate thickness 6 mm or more and less than 16 mm) and thick plates (plate thickness 16 mm or more). ) Is not used to cut. Therefore, 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. In fact, the inventors have 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 have not obtained a sufficient effect of extending the life of the electrode.

The present invention has been made in view of the above circumstances, and provides a plasma cutting device and a plasma cutting method capable of extending the life of an electrode when cutting a material to be cut having a large plate thickness. The purpose.

The plasma cutting device according to the first aspect of the present invention is a plasma torch having an electrode and 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. It includes a power supply unit capable of supplying a current and superimposing an AC 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 plate 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 is controlled so as to superimpose the alternating current on the direct current.

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

In the above plasma cutting device, 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. The difference between the maximum value and the minimum value of the AC current in the DC current supplied between the electrode and the material to be cut in order to generate the plasma arc is the difference between the maximum value and the minimum value of the AC current when the material to be cut is cut. The AC current having a magnitude of 25% or more and 40% or less is superimposed on the DC current.

According to such a plasma cutting device and a plasma cutting method, the AC current is superimposed on the DC current by superimposing the AC current of the above-mentioned magnitude on the DC current supplied between the electrode and the material to be cut. The life of the electrode can be extended as compared with the case without it.

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

It is a figure which shows the whole structure of the plasma cutting apparatus which concerns on one Embodiment of this invention. It is a figure which shows the waveform of the electric current supplied between an electrode and a material to be cut.

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 device 1 according to an embodiment of the present invention. As shown in FIG. 1, the plasma cutting device 1 includes a plasma torch 10 having an electrode 11, a power supply unit 20, and a control unit 30 for controlling 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 tubular body having a conical tip side and a cylindrical base end side. The electrode 11 is arranged inside the nozzle portion 12. A working gas flow path 13 through which the working gas flows is formed between the electrode 11 and the nozzle portion 12. At the tip of the nozzle portion 12, a nozzle hole 12a communicating with the tip side of the working gas flow path 13 is formed.

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 base end side of the working gas flow path 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 base end side of the working gas flow path 13 passes through the tip end side of the working gas flow path 13 and is ejected from the nozzle hole 12a.

The power supply unit 20 supplies a direct current between the electrode 11 and the material W to be cut in order to generate a plasma arc P between the electrode 11 of the plasma torch 10 and the material W to be cut. Further, the power supply unit 20 is configured so that an alternating current can be superimposed on the direct current. The power supply unit 20 is electrically connected to each of the electrode 11 and the material W to be cut. Further, 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 the plasma arc P by applying a predetermined voltage between the electrode 11 and the material W to be cut by using the electric power supplied from the commercial power source. The power supply unit 20 supplies the direct current and superimposes the alternating current on the direct current based on the instruction from the control unit 30.

The control unit 30 is electrically connected to the power supply unit 20 and is 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 as to superimpose a predetermined alternating current on the direct current supplied by the power supply unit 20 when cutting the material W to be cut having a large plate thickness. More specifically, when the control unit 30 cuts the material W to be cut having a plate 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 having the magnitude of the above 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. Further, the control unit 30 can control the power supply unit 20 so that the frequency of the alternating current is 50 Hz or more and 300 Hz or less.

The cutting speed, which is the speed at which the material W to be cut is cut, varies depending on the thickness of the material W to be cut and the magnitude of the direct current supplied by the power supply unit 20. For example, when the plate thickness of the material W to be cut is 6 mm and the magnitude of the direct current is 250 A, the cutting speed is 4000 mm / min. Further, when the plate thickness of the material W to be cut is 6 mm and the magnitude of the direct current is 500 A, the cutting speed is 8000 mm / min. When the plate thickness of the material W to be cut is 50 mm and the magnitude of the direct current is 500 A, the 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 showing a waveform of a current supplied between the electrode 11 and the material W to be cut. FIG. 2A shows a waveform when an alternating current is not superimposed on the direct current. FIG. 2B shows a waveform of an alternating current superimposed on a 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 current C1 whose current value is 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. Then, as shown in FIG. 2C, the current in which the AC current is superimposed on the DC current is the current C3 in which the AC current having a predetermined amplitude A and a predetermined frequency F is superimposed on the DC current of the current value I. 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 with the passage of time in the range of the amplitude A centering on the current value I. 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 DC current (also referred to as the magnitude of the DC current). The ratio to the ratio (hereinafter referred to as the ripple ratio) is expressed by R. The ripple rate R is expressed by the following equation (1).
R = (A / I) x 100 [%] ... (1)

When the alternating current is not superimposed on the direct current, the power supply unit 20 supplies the current C1 shown in FIG. 2A between the electrode 11 and the material W to be cut. When an 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 material W to be cut.

Next, a plasma cutting method using the plasma cutting device 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 via the working gas flow path 13. At the same time, the power supply unit 20 applies a voltage between the electrode 11 and the nozzle unit 12, so that a pilot arc is generated from the electrode 11 in the nozzle unit 12. By continuously supplying the working gas, the working gas turned into plasma in the nozzle portion 12 by the pilot arc is injected from the nozzle hole 12a, and the power supply portion 20 applies a voltage between the electrode 11 and the material W to be cut to generate plasma. The 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 W to be cut is melted by the thermal energy of the plasma arc P, and the melt is removed by the injection energy of the plasma arc P. As a result, a groove penetrating in the thickness direction of the material W to be cut is formed, and plasma cutting is performed.

In the present embodiment, in the above-mentioned plasma cutting method, when cutting the material W to be cut having a plate thickness of 6 mm or more, the electrode 11 and the material W to be cut are used in order to generate the plasma arc P by the power supply unit 20. The alternating current is superimposed on the 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 so, the life of the electrode 11 can be extended as compared with the case where the alternating current is not superposed on the direct current.

The cutting speed of the material W to be cut can be controlled by a known speed control means.

Hereinafter, the present invention will be further described with reference to examples, but the present invention is not limited thereto.

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

[Comparative Example 1]
In the plasma cutting device, oxygen gas was used as the working gas, and the gas flow rate was set to 50 NL (normal liter) / min. Hafnium was used as the electrode material of the electrode. The current value I of the direct current supplied between the electrode and the material to be cut was set to 250 A. The alternating current is not superimposed on the direct current. Under this condition, after generating a plasma arc for 1 minute, the supply of current from the power supply unit was stopped. The operation of generating the plasma arc for 1 minute was repeated to wear the electrodes, and the life of the electrodes was measured. As a result, the life of the electrode was 90 minutes.

[Example 1]
Compared with the condition of Comparative Example 1, the life of the electrode was measured under the condition that the AC current having a ripple ratio of 32% and the frequency of 150 Hz was superimposed on the DC current. As a result, the life of the electrode was 150 minutes.

[Example 2]
Compared with the condition of Comparative Example 1, the life of the electrode was measured under the condition that the AC current having a ripple ratio of 32% and the frequency of 300 Hz was superimposed on the DC current. As a result, the life of the electrode was 270 minutes.

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

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

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

[Comparative Example 3]
Compared with the condition of Comparative Example 2, the life of the electrode was measured under the condition that the AC current having a ripple ratio of 13.3% and the frequency of 300 Hz was superimposed on the DC current. As a result, the life of the electrode was 172 minutes.

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

[Example 5]
Compared with the condition of Comparative Example 4, the life of the electrode was measured under the condition that the ripple rate was 28.6% and the AC current having a frequency of 100 Hz was superimposed on the DC current. As a result, the life of the electrode was 212 minutes.

The measurement results in each of the above-mentioned Examples and Comparative Examples are shown in Tables 1 to 3. In addition, 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 superposed on the direct current when the life when the alternating current is not superposed on the direct current is 100 at the same current value I.

As shown in Table 1, an alternating current having a ripple ratio R of 32% is superimposed on the direct current, as opposed to Comparative Example 1 in which the current value I of the direct current is 250A and the alternating current is not superimposed on the direct current. In Examples 1 and 2, the electrode life ratios were 167 and 300, respectively. As a result, it was confirmed that in Examples 1 and 2, the life of the electrode was significantly extended as compared with Comparative Example 1.

Further, as shown in Table 2, an AC current having a ripple ratio R of 33.3% is applied to DC as compared with Comparative Example 2 under the condition that the current value I of the DC current is 300 A and the AC current is not superimposed on the DC current. In Examples 3 and 4 superposed on the current, the electrode life ratios were 136 and 145, respectively. As a result, it was confirmed that in Examples 3 and 4, the life of the electrode was significantly extended as compared with Comparative Example 2. In Comparative Example 3 in which an AC current having a ripple ratio R of 13.3% was superimposed on a DC current, the electrode life ratio was 104 as compared with Comparative Example 2, and the life of the electrodes was slightly extended, but a sufficient life was obtained. No growth was obtained.

Further, as shown in Table 3, an AC current having a ripple ratio R of 28.6% is applied to DC as compared with Comparative Example 4 under the condition that the DC current current value I is 350A and the AC current is not superimposed on the DC current. In Example 5 superposed on the electric current, the electrode life ratio was 162. As a result, it was confirmed that in Example 5, the life of the electrode was significantly extended as compared with Comparative Example 4.

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

The plasma cutting device 1 according to the present embodiment is between the plasma torch 10 having the electrode 11 and the electrode 11 and the material W to be cut in order to generate a plasma arc P between the electrode 11 and the material W to be cut. It includes a power supply unit 20 capable of supplying a direct current and superimposing an alternating current on the direct current, and a control unit 30 for controlling the power supply unit 20. When the control unit 30 cuts the material W to be cut having a plate 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 of the direct current. The power supply unit 20 is controlled so that the current is superimposed on the direct current.

Further, the plasma cutting method according to the present embodiment is a plasma cutting method for cutting the material W to be cut by the plasma arc P generated between the electrode 11 of the plasma torch 10 and the material W to be cut, and is 6 mm or more. The difference between the maximum value and the minimum value of the AC current in the DC current supplied between the electrode 11 and the material W to be cut in order to generate the plasma arc P when cutting the material W to be cut having a plate thickness. Superimposes an AC current having a magnitude of 25% or more and 40% or less with respect to the DC current.

According to the plasma cutting device 1 and the plasma cutting method described above, the AC current is superimposed on the DC current by superimposing the AC current of the above magnitude on the DC current supplied between the electrode 11 and the material W to be cut. The life of the electrode 11 can be extended as compared with the case where the electrode 11 is not used.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to this embodiment. Configurations can be added, omitted, replaced, and other changes can be made without departing from the spirit of the present invention.

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 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 and
A power supply unit 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 that controls the power supply unit and
With
When the control unit cuts the material to be cut having a plate 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. A plasma cutting device that controls the power supply unit so as to superimpose the alternating current on the direct current. The plasma cutting apparatus according to claim 1.
The control unit is a plasma cutting device that controls the power supply unit so that the frequency of the alternating current is 50 Hz or more and 300 Hz or less. The plasma cutting apparatus according to claim 1 or 2.
The control unit is a plasma cutting device that controls the power supply unit so that the magnitude of the direct current is 250 A or more and 350 A or less. 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.
When cutting the material to be cut having a plate thickness of 6 mm or more, the maximum and minimum values of alternating current are added 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 with respect to the direct current is superimposed.

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