Plasma cutting machine, and method for controlling a plasma cutting machine

Abstract

To avoid the damage of plasma torch at a piercing step in a plasma cutter, and to suppress the wasting of power supply.SOLUTION: A controller moves a plasma torch to a piercing position. The controller generates a plasma arc on the plasma torch to start a piercing step at the piercing position. The controller determines whether or not the piercing step is completed on the basis of arc voltage. The controller holds the plasma torch in a horizontal direction at the piercing position since the start of the piercing step to the completion of the piercing step. The controller moves the plasma torch at least in a predetermined direction including the horizontal direction.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a plasma cutting machine and a method for controlling the plasma cutting machine.

Background Art

[0002] When cutting a material such as a steel plate using a plasma cutting machine, first, a process of making a hole in the material by a plasma arc (hereinafter referred to as a piercing process) is performed. For example, as shown in Patent Document 1, in the piercing process, the plasma cutting machine moves the plasma torch above the cutting start position and ignites a plasma arc in the plasma torch above the cutting start position. When the plasma arc penetrates the material, the piercing process is completed. After the completion of the piercing process, the plasma cutting machine proceeds to the cutting process. In the cutting process, the plasma cutting machine cuts the material by moving the plasma torch along a pre-programmed shape.

[0003] As described above, the cutting process starts after a through hole is formed in the material by the piercing process. The reason is that before the through hole is formed in the material, the molten metal (spatter) melted by the plasma arc blows upward. When the spatter collides with the plasma torch, the plasma torch is damaged and the cutting performance deteriorates. Therefore, in order to avoid spatter, during the piercing process, the plasma torch is retracted to a high position. After a through hole is formed in the material, the plasma cutting machine lowers the plasma torch to a height suitable for cutting and then proceeds to the cutting process.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] A plasma arc is generated by an arc discharge between the electrode of the plasma torch and the material. A current for maintaining the arc discharge (hereinafter referred to as the arc current) is supplied from the plasma power supply to the plasma torch. The plasma power supply adjusts a voltage for maintaining the arc (hereinafter referred to as the "arc voltage") so that the arc current as commanded is supplied to the plasma torch.

[0006] In the piercing process, after the plasma arc penetrates the material, the plasma arc is stretched, so that the arc voltage rises. Also, after the plasma arc penetrates the material, if the plasma torch stays in place, the through hole is enlarged by the plasma arc. Thereby, the distance between the plasma arc and the material widens, and the length of the plasma arc extends, so that the arc voltage further rises. At this time, if the arc voltage rises beyond the outputtable voltage of the plasma power supply, the plasma arc disappears. When the plasma arc disappears, the plasma cutting machine cannot shift to the cutting process, and the processing process may be interrupted. Therefore, in order to prevent the disappearance of the plasma arc, the plasma power supply has an output capacity with some margin.

[0007] The rise in the arc voltage at the completion of the piercing process as described above occurs only for a very short time compared to the cutting stroke. In order to prepare for the rise in the arc voltage in such a short time, a plasma power supply having a sufficiently large output capacity with margin is used, resulting in waste of the power supply capacity.

[0008] An object of the present disclosure is to avoid damage to the plasma torch during the piercing process and suppress waste of the power supply capacity in a plasma cutting machine.

Means for Solving the Problem

[0009] One aspect of the present disclosure is a plasma cutting machine, comprising a table, a plasma torch, a plasma power supply, an actuator, a voltage sensor, and a controller. The table supports the material, and the plasma torch includes an electrode. The plasma power supply is connected to the plasma torch. The actuator supports the plasma torch so as to be movable in horizontal and vertical directions with respect to the table. The voltage sensor detects the arc voltage applied from the plasma power supply to the plasma torch. The controller communicates with the plasma power supply, the actuator, and the voltage sensor.

[0010] The controller is configured to execute the following processes. The controller moves the plasma torch to the piercing position. The controller generates a plasma arc in the plasma torch to start the piercing process at the piercing position. The controller determines whether the piercing process is completed based on the arc voltage. The controller holds the plasma torch at the piercing position in the horizontal direction from the start to the completion of the piercing process. After the completion of the piercing process, the controller moves the plasma torch in a predetermined direction including at least the horizontal direction.

[0011] A method according to another aspect of the present disclosure is a method for controlling a plasma cutting machine, comprising the following processes. The first process is to move the plasma torch to the piercing position. The second process is to generate a plasma arc in the plasma torch to start the piercing process at the piercing position. The third process is to acquire the arc voltage applied to the plasma torch. The fourth process is to determine whether the piercing process is completed based on the arc voltage. The fifth process is to hold the plasma torch at the piercing position in the horizontal direction from the start to the completion of the piercing process. The sixth process is to move the plasma torch in a predetermined direction including at least the horizontal direction after the completion of the piercing process. Note that the names of the above-described processes are given for convenience of explanation and do not limit the order in which each process is executed.

Effect of the Invention

[0012] According to the present disclosure, in a plasma cutting machine, damage to the plasma torch during the piercing process is avoided, and waste of the power supply capacity is suppressed.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. FIG. 1 is a perspective view of a plasma cutting machine 1 according to an embodiment. The plasma cutting machine 1 includes a table 2, a plasma torch 3, an actuator 4, and an input device 5. A material 100 such as a steel plate is placed on the table 2. The table 2 supports the material 100 to be cut. The plasma torch 3 is disposed above the table 2. The plasma torch 3 ejects a plasma arc.

[0015] FIG. 2 is a cross-sectional view showing a part of the plasma torch 3. As shown in FIG. 2, the plasma torch 3 includes an electrode 11, a nozzle 12, and a shield cap 13. The tip of the electrode 11 is disposed within the nozzle 12. The nozzle 12 includes an ejection hole 14. The ejection hole 14 of the nozzle 12 faces the tip of the electrode 11. The shield cap 13 covers the nozzle 12. The shield cap 13 includes an ejection hole 15 facing the ejection hole 14 of the nozzle 12. The plasma torch 3 generates a plasma arc by an arc discharge between the electrode 11 and the material 100.

[0016] The actuator 4 supports the plasma torch 3 so as to be movable in the horizontal and vertical directions with respect to the table 2. As shown in FIG. 1, the actuator 4 includes a first linear guide 21, a first carriage 22, a second linear guide 23, and a second carriage 24. The first linear guide 21 is disposed on the side of the table 2. The first linear guide 21 extends in the X-axis direction. The second linear guide 23 is disposed above the table 2. The second linear guide 23 extends in the Y-axis direction. In the present embodiment, the X-axis and the Y-axis are coordinates along the upper surface of the table 2. The X-axis and the Y-axis are orthogonal to each other and extend in the horizontal direction. The Z-axis is orthogonal to the upper surface of the table 2 and extends in the vertical direction.

[0017] The first carriage 22 is movable in the X-axis direction along the first linear guide 21. The second linear guide 23 is supported by the first carriage 22. The second carriage 24 is movable in the Y-axis direction along the second linear guide 23. The plasma torch 3 is attached to the second carriage 24. The second carriage 24 supports the plasma torch 3 so as to be movable in the Z-axis direction.

[0018] Figure 3 is a block diagram showing the control system of the plasma cutting machine 1. As shown in Figure 3, the plasma cutting machine 1 includes a first motor 25, a second motor 26, and a third motor 27. The first motor 25 moves the first carriage 22 along the first linear guide 21. The second motor 26 moves the second carriage 24 along the second linear guide 23. The third motor 27 moves the plasma torch 3 vertically with respect to the second carriage 24. By driving the first to third motors 25 - 27, the actuator 4 moves the plasma torch 3 to an arbitrary position in the horizontal direction (X, Y-axis directions) and the vertical direction (Z-axis direction) with respect to the material 100 on the table 2.

[0019] As shown in Figure 3, the plasma cutting machine 1 includes a plasma power supply 28 and a voltage sensor 29. The plasma power supply 28 is electrically connected to the plasma torch 3. The plasma power supply 28 supplies power for generating a plasma arc to the plasma torch 3. The plasma power supply 28 includes, for example, a rectifier, an inverter, and a transformer. The voltage sensor 29 detects the arc voltage applied from the plasma power supply 28 to the plasma torch 3. The voltage sensor 29 outputs a signal indicating the arc voltage. The input device 5 includes, for example, a plurality of input keys and a display. The operator inputs data such as processing conditions using the input device 5. The input device 5 outputs a signal indicating the input data.

[0020] As shown in Figure 3, the plasma cutting machine 1 includes a controller 31. The controller 31 is programmed to control the plasma cutting machine 1 based on the acquired data. The controller 31 includes a storage device 32 and a processor 33. The storage device 32 includes a non-volatile memory such as a ROM and a volatile memory such as a RAM. The storage device 32 may include an auxiliary storage device such as a hard disk or an SSD (Solid State Drive). The storage device 32 is an example of a non-transitory computer-readable recording medium. The storage device 32 stores computer instructions and data for controlling the plasma cutting machine 1.

[0021] The processor 33 is, for example, a CPU (central processing unit). The processor 33 executes processes for controlling the plasma cutter 1 according to a program. The controller 31 communicates with the first to third motors 25 - 27, the plasma power supply 28, and the voltage sensor 29. The controller 31 moves the plasma torch 3 by controlling the first to third motors 25 - 27. The controller 31 generates a plasma arc in the plasma torch 3 by controlling the plasma power supply 28. The controller 31 cuts the material 100 by moving the plasma torch 3 while maintaining the plasma arc in the plasma torch 3.

[0022] Next, the processing of the plasma cutter 1 executed by the controller 31 will be described. In the processing by the plasma cutter 1, first, a pierce hole is formed in the material 100 by a piercing process. Then, a product is cut out from the material 100 by a cutting process. FIG. 4 is a flowchart showing the control processing of the plasma cutter 1.

[0023] As shown in FIG. 4, when the processing by the plasma cutter 1 is started, in step S101, the controller 31 moves the plasma torch 3 to the pierce position. The pierce position is a horizontal position on the table 2 and is indicated by XY coordinates. FIG. 5 is a schematic diagram showing the position of the plasma torch 3. As shown in FIG. 5(a), the controller 31 arranges the plasma torch 3 at the first height H1 at the pierce position.

[0024] In step S102, the controller 31 ignites a plasma arc in the plasma torch 3. Thereby, the controller 31 starts the piercing process. FIG. 6 is a diagram showing an example of changes in the arc current and arc voltage and a change in the height of the plasma torch 3. In FIG. 6, the solid line A1 indicates the change in the height of the plasma torch 3, the dashed line I1 indicates the arc current, and the solid line V1 indicates the arc voltage. As shown in FIG. 6, at time T1, the controller 31 applies a high voltage to the electrode 11 of the plasma torch 3. Thereby, a plasma arc is generated in the plasma torch 3. When the plasma arc is generated, the arc voltage decreases at time T2.

[0025] Next, in step S103, the controller 31 raises the plasma torch 3. As shown in FIG. 5, the controller 31 raises the plasma torch 3 to the second height H2 at the piercing position. The second height H2 is located above the first height H1. As shown in FIG. 6, from time T1 to T3, the controller 31 raises the plasma torch 3. Thereby, the arc voltage increases.

[0026] In step S104, the controller 31 holds the plasma torch 3 at the second height H2 at the piercing position. Thereby, as shown in FIG. 5(b), a piercing hole is formed in the material 100 by the plasma arc. At this time, spatter scatters from the material 100, but since the plasma torch 3 is located at the second height H2, collision of the spatter with the plasma torch 3 is avoided. In FIG. 6, from time T3 to T4, the piercing hole 200 is formed in the material 100. At this time, as the piercing hole 200 extends, the arc voltage increases.

[0027] In step S105, the controller 31 determines whether the piercing process is completed. The controller 31 determines whether the piercing process is completed based on the arc voltage. Specifically, the controller 31 obtains the rising rate of the arc voltage per unit time. The controller 31 calculates the rising rate of the arc voltage per unit time from the detected value of the voltage sensor 29. The controller 31 determines that the piercing process is completed when the rising rate is equal to or higher than the threshold value. As shown in FIG. 5(c), the piercing process is completed when the piercing hole 200 penetrates the material 100. When the piercing hole 200 penetrates the material 100, the plasma arc is stretched. Thereby, at times T4 to T5 in FIG. 6, the arc voltage rises rapidly. The controller 31 determines the completion of the piercing process by detecting this rapid rise in the arc voltage.

[0028] Note that the controller 31 invalidates the determination of the completion of the piercing process during a predetermined time from the start time of the generation of the plasma arc. Thereby, for example, it is possible to prevent the completion of the piercing process from being erroneously determined due to the voltage rise at the time of generation of the plasma arc between times T1 to T3 in FIG. 6.

[0029] In step S105, when the controller 31 determines that the piercing process is not completed, the process proceeds to step S106. In step S106, the controller 31 determines whether a predetermined time has elapsed since the start of the piercing process. The predetermined time may be set for each cutting condition. Alternatively, the predetermined time may be a constant value. When the predetermined time has not elapsed since the start of the piercing process, the process returns to step S104. That is, the controller 31 holds the plasma torch 3 at the second height H2 at the piercing position until the completion of the piercing process or until a predetermined time has elapsed since the start of the piercing process. In step S105, when the controller 31 determines that the piercing process is completed, or in step S106, when the controller 31 determines that a predetermined time has elapsed since the start of the piercing process, the process proceeds to step S107.

[0030] In step S107, the controller 31 starts the cutting process while lowering the plasma torch 3. As shown in FIG. 5(d), the controller 31 moves the plasma torch 3 horizontally along the target trajectory while lowering the plasma torch 3 to the third height H3. The third height H3 is located below the second height H2. The third height H3 is located below the first height H1. After the plasma torch 3 reaches the third height H3, as shown in FIG. 5(e), the controller 31 moves the plasma torch 3 horizontally along the target trajectory while holding the height of the plasma torch 3 at the third height H3. The target trajectory is determined by the controller 31 according to the preset target shape of the product. By moving the plasma torch 3 along the target trajectory, the product is cut out from the material 100. Note that the piercing position, the first to third heights H3, and the target shape of the product described above are stored in the storage device 32.

[0031] In the plasma cutting machine 1 according to the present embodiment described above, the controller 31 determines the completion of the piercing process based on the arc voltage. Therefore, the completion of the piercing process can be determined with higher accuracy compared to the case where the completion of the piercing process is determined based on the estimated time until the completion of the piercing process. Thereby, by shortening the time of the piercing process, an increase in the arc voltage due to the expansion of the piercing hole 200 can be suppressed.

[0032] Also, in the plasma cutting machine 1 according to the embodiment, after the piercing process is completed, the controller 31 quickly moves the plasma torch 3 horizontally while lowering it. Therefore, compared with the case where the plasma torch 3 descends while being held at the piercing position after the completion of the piercing process, the expansion of the piercing hole 200 can be suppressed. Thereby, the increase in the arc voltage can be suppressed. In FIG. 6, although the voltage rises rapidly at time T1, since the current is small, it does not cause an increase in the power supply capacity. As described above, in the plasma cutting machine 1 according to the present embodiment, the power supply capacity of the plasma power supply 28 for preparing for the increase in the arc voltage due to the piercing process can be suppressed to be small. Alternatively, if the power supply capacity is the same, since the arc voltage can be suppressed, the arc current can be increased. Thereby, the cutting performance of the plasma cutting machine 1 can be improved while suppressing the increase in the power supply capacity.

[0033] In FIG. 6, the two-dot chain line A2 indicates the change in the height of the plasma torch 3 according to the comparative example, and the two-dot chain line V2 indicates the arc voltage according to the comparative example. In the comparative example, the controller lowers the plasma torch straight down after a predetermined time from the start of the piercing process. Then, the controller stops the descent of the plasma torch at a predetermined height position, and then moves the plasma torch horizontally. In the comparative example, the predicted time from the start to the completion of the piercing process is set as the predetermined time. Since the predicted time is estimated with a margin, as shown in FIG. 6, in the comparative example, the plasma torch starts to descend at a time T5' later than the time T5 described above. Also, in the comparative example, the plasma torch descends straight down and then moves horizontally. Therefore, as shown by V2 in FIG. 6, the maximum voltage of the arc voltage becomes large. On the other hand, in an example according to the present embodiment, as shown by V1 in FIG. 6, the maximum voltage of the arc voltage is suppressed to be low. Thereby, the cutting performance of the plasma cutting machine 1 can be improved while suppressing the increase in the power supply capacity.

[0034] Even if the controller 31 determines that the piercing process is not completed based on the arc voltage, when it determines that a predetermined time has elapsed since the start of the piercing process, it moves the plasma torch 3 horizontally while lowering it. Therefore, depending on the cutting conditions, even when the increase in the arc voltage during piercing penetration is small and the change in the arc voltage as described above cannot be detected, the increase in the arc voltage can be suppressed.

[0035] The controller 31 determines the completion of the piercing process based on the rate of increase in the arc voltage per unit time. Thereby, it is possible to suppress the influence of differences in cutting conditions such as the height of the welding torch or the value of the arc current during the piercing process, and accurately determine the completion of the piercing process.

[0036] As described above, one embodiment of the present invention has been explained. However, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention. For example, the configuration of the plasma torch 3 may be changed. The configuration of the actuator 4 may be changed. The processing by the controller 31 described above may be changed or added. A part of the processing by the controller 31 may be omitted. The execution order of the processing by the controller 31 may be changed.

[0037] The method for determining the completion of the piercing process may be changed. For example, when the arc voltage is equal to or higher than a predetermined threshold value, the completion of the piercing process may be determined. In the above embodiment, after the completion of the piercing process, the controller 31 moves the plasma torch 3 horizontally while lowering it. However, after the completion of the piercing process, the controller 31 may move the plasma torch 3 horizontally.

Industrial Applicability

[0038] According to the present disclosure, in a plasma cutting machine, damage to the plasma torch during the piercing process is avoided, and waste of the power supply capacity is suppressed.

Explanation of Signs

[0039] 2 Table 3 Plasma torch 4 Actuator 28 Plasma power supply 29 Voltage sensor 31 Controller

Claims

1. A plasma cutting machine for cutting materials by a plasma arc, a table for supporting the material, a plasma torch including an electrode, a plasma power source connected to the plasma torch, an actuator for supporting the plasma torch so as to be movable in horizontal and vertical directions with respect to the table, a voltage sensor for detecting an arc voltage applied from the plasma power source to the plasma torch, a controller that communicates with the plasma power source, the actuator, and the voltage sensor, comprising The controller moves the plasma torch to the piercing position, generates a plasma arc in the plasma torch to start a piercing process at the piercing position, determines whether the piercing process is completed based on the arc voltage, holds the plasma torch at the piercing position in the horizontal direction from the start to the completion of the piercing process, after completion of the piercing process, moves the plasma torch in the horizontal direction while lowering it, invalidates the determination of completion of the piercing process based on the arc voltage during a predetermined time from the start of generation of the arc, and validates the determination of completion of the piercing process based on the arc voltage after the predetermined time has elapsed from the start of generation of the arc, Plasma cutting machine.

2. The controller obtains a rising rate of the arc voltage per unit time, and determines that the piercing process is completed when the rising rate is equal to or higher than a threshold value. The plasma cutting machine according to claim 1.

3. Even if the controller determines that the piercing process is not completed based on the arc voltage, when a predetermined time has elapsed after the start of the piercing process, the controller moves the plasma torch in a predetermined direction including at least the horizontal direction. The plasma cutting machine according to claim 1 or 2.

4. A method for controlling a plasma cutting machine including a plasma torch and cutting a material by a plasma arc, comprising: moving the plasma torch to a piercing position; generating a plasma arc in the plasma torch to start a piercing process at the piercing position; obtaining an arc voltage applied to the plasma torch; determining whether the piercing process is completed based on the arc voltage; holding the plasma torch at the piercing position in the horizontal direction from the start to the completion of the piercing process; after the completion of the piercing process, moving the plasma torch in the horizontal direction while lowering it; invalidating the determination of the completion of the piercing process based on the arc voltage during a predetermined time from the start of the generation of the arc; validating the determination of the completion of the piercing process based on the arc voltage after the predetermined time has elapsed from the start of the generation of the arc; A method comprising the above.

5. further comprising obtaining a rising rate of the arc voltage per unit time, and determining that the piercing process is completed when the rising rate is equal to or higher than a threshold value. The method according to claim 4.

6. Even if it is determined that the piercing process is not completed based on the arc voltage, when a predetermined time has elapsed after the start of the piercing process, further comprising moving the plasma torch in a predetermined direction including at least the horizontal direction. The method according to claim 4 or 5.

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