Plasma Arc System

Abstract

To provide a plasma arc system which can suppress torch burning due to pilot arc.SOLUTION: A plasma arc welding system B1 comprises: a torch 12 having a nonconsumable electrode 121 and a plasma nozzle 122 which surrounds the nonconsumable electrode 121; a pilot arc power supply circuit 31 which causes pilot arc current Ip to flow between the nonconsumable electrode 121 and the plasma nozzle 122; and a pilot arc voltage detection circuit 36 which detects a voltage value of pilot arc voltage Vp between the nonconsumable electrode 121 and the plasma nozzle 122. The pilot arc power supply circuit 31 detects arc abnormality when the voltage value is a threshold V0 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a plasma arc system. [Background technology]

[0002] Plasma arc welding systems have been known for some time. In plasma arc welding systems, a pilot arc is generated between an electrode and a plasma nozzle, and while plasma gas is ionized and released by the pilot arc, air breakdown occurs between the electrode and the base metal, igniting a main arc (see FIG. 2(a) described later). Then, while the main arc is generated, the base metal is welded. Plasma arc welding systems are disclosed, for example, in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-62912 Summary of the Invention [Problem to be solved by the invention]

[0004] However, if the insulation performance inside the torch deteriorates due to contamination or other factors, the pilot arc may ignite in an unintended location. For example, an insulator is interposed between the electrode and the conductor inside the torch to prevent current flow between the electrode and the insulator. However, if a deteriorated portion of the insulator breaks down, the pilot arc may ignite between the electrode and the conductor inside the torch (see Figure 2(b) below). Also, the pilot arc may ignite between the electrode and the conductor inside the torch through a hole that allows plasma gas to pass through inside the plasma nozzle. In these cases, not only is the main arc unable to ignite, but the inside of the torch may also be burned. The above-mentioned problems occur not only in plasma arc welding systems but also in other plasma arc systems, such as plasma arc cutting systems.

[0005] The present invention was conceived in light of the above circumstances, and has as its object to provide a plasma arc system that can suppress torch burnout due to the pilot arc. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides the following technical means.

[0007] A plasma arc system provided by a first aspect of the present invention comprises a torch having a non-consumable electrode and a plasma nozzle surrounding the non-consumable electrode, a pilot arc power supply circuit that flows a pilot arc current between the non-consumable electrode and the plasma nozzle, and a pilot arc voltage detection circuit that detects a voltage value of a pilot arc voltage between the non-consumable electrode and the plasma nozzle, wherein the pilot arc power supply circuit detects an arc abnormality when the voltage value is equal to or greater than a threshold value.

[0008] In a preferred embodiment of the present invention, the pilot arc power supply circuit flows the pilot arc current controlled to an initial current value smaller than a steady-state current value, and when no arc abnormality is detected, flows the pilot arc current controlled to the steady-state current value.

[0009] In a preferred embodiment of the present invention, the initial current value is 10% or less of the steady-state current value and is 1 A or less.

[0010] In a preferred embodiment of the present invention, the pilot arc power supply circuit stops output of the pilot arc current when an arc abnormality is detected.

[0011] In a preferred embodiment of the present invention, the threshold value is a value that is greater than the voltage value of the pilot arc voltage when a normal pilot arc has occurred and is smaller than a possible value of the pilot arc voltage when a pilot arc has occurred at an unintended location. [Effects of the Invention]

[0012] According to the present invention, the pilot arc power supply circuit passes a pilot arc current between the non-consumable electrode and the plasma nozzle, and the pilot arc voltage detection circuit detects the value of the pilot arc voltage between the non-consumable electrode and the plasma nozzle. The longer the generated pilot arc, the larger the value of the pilot arc voltage. When the value of the pilot arc voltage is equal to or greater than a threshold, the pilot arc power supply circuit determines that an arc longer than the intended pilot arc has occurred and detects an arc abnormality. This makes it possible to detect the occurrence of an arc abnormality and prevent the torch from burning out due to the pilot arc.

[0013] Other features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing the overall configuration of a plasma arc welding system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a simplified enlarged cross-sectional view showing a torch in the plasma arc welding system of FIG. 1. [Figure 3] 2 is a timing chart of each signal in the pilot arc circuit at the start of the plasma arc welding system of FIG. 1. [Figure 4] 10 is a timing chart of signals in a pilot arc circuit at the start of a modified example of the plasma arc welding system of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be specifically described with reference to the drawings, taking as an example a case where the plasma arc system according to the present invention is used as a plasma arc welding system.

[0016] [First embodiment] Fig. 1 is a block diagram showing the overall configuration of a plasma arc welding system B1 according to a first embodiment of the present invention. Fig. 2 is a simplified enlarged cross-sectional view showing a torch 12 in the plasma arc welding system B1. Fig. 2(a) shows a state in which a main arc Ma is generated by a normal pilot arc Pa. Fig. 2(b) shows a state in which an unintended pilot arc Pa is generated.

[0017] As shown in FIG. 1, the plasma arc welding system B1 includes a welding robot 1, an operation control circuit 2, a pilot arc circuit 3, a main arc circuit 4, a plasma gas supply device 81, a shielding gas supply device 82, and a control device 5.

[0018] The welding robot 1 automatically performs plasma arc welding on a base material W. The welding robot 1 includes a manipulator 11 and a torch 12. The manipulator 11 is, for example, an articulated robot. The torch 12 can be driven by the manipulator 11 to move freely up and down, front and back, and left and right.

[0019] As shown in FIG. 2, the torch 12 includes a non-consumable electrode 121 , a plasma nozzle 122 , and a shielding gas nozzle 123 .

[0020] Non-consumable electrode 121 is a metal rod made of, for example, tungsten. Plasma nozzle 122 is a cylindrical member. Plasma nozzle 122 surrounds non-consumable electrode 121. A nozzle opening of plasma nozzle 122 is arranged on the tip side of non-consumable electrode 121.

[0021] Plasma gas PG flows through the plasma nozzle 122. As shown in FIG. 2(a), a pilot arc Pa is generated between the plasma nozzle 122 and the non-consumable electrode 121 using the plasma gas PG as a medium. When the pilot arc Pa is generated, a pilot arc current Ip flows between the plasma nozzle 122 and the non-consumable electrode 121. Unless otherwise specified, the current value of the pilot arc current Ip refers to the time average value of the absolute value of the current value of the pilot arc current Ip. The plasma nozzle 122 is appropriately cooled by a cooling means (not shown).

[0022] A main arc Ma is generated between the non-consumable electrode 121 and the base metal W. The main arc Ma is confined by the nozzle opening of the plasma nozzle 122. When the main arc Ma is generated, a main arc current Im flows between the non-consumable electrode 121 and the base metal W. Either DC or AC is selected as the main arc current Im depending on the material of the base metal W. The main arc current Im may be a DC pulse current or an AC pulse current. Unless otherwise specified, the current value of the main arc current Im refers to the time average value of the absolute value of the current value of the main arc current Im. When the main arc Ma is generated, a main arc voltage Vm is applied between the non-consumable electrode 121 and the base metal W.

[0023] The shield gas nozzle 123 is a cylindrical member. The shield gas nozzle 123 surrounds the plasma nozzle 122. A shield gas SG flows between the shield gas nozzle 123 and the plasma nozzle 122. Unlike this embodiment, the torch 12 does not necessarily have to include the shield gas nozzle 123.

[0024] The operation control circuit 2 has a microcomputer and a memory (both not shown). This memory stores an operation program in which various operations of the welding robot 1 are set. The operation control circuit 2 sends an operation control signal Ms to the welding robot 1 in accordance with the operation program. The welding robot 1 receives the operation control signal Ms and drives the manipulator 11 to move the torch 12 over the base material W. The operation control circuit 2 starts the operation of the welding robot 1 based on a command from the control device 5.

[0025] The pilot arc circuit 3 passes a pilot arc current Ip between the non-consumable electrode 121 and the plasma nozzle 122. In this embodiment, the pilot arc circuit 3 controls the current value of the pilot arc current Ip to a set value. In other words, the pilot arc circuit 3 performs constant current control. The pilot arc circuit 3 includes a pilot arc power supply circuit 31, a pilot arc current detection circuit 33, and a pilot arc voltage detection circuit 36.

[0026] The pilot arc power supply circuit 31 includes a circuit in which a commercial power supply, such as 200 V, is rectified and a resistor is inserted in series. As a result, the pilot arc power supply circuit 31 causes a pilot arc current Ip to flow between the non-consumable electrode 121 and the plasma nozzle 122. The pilot arc power supply circuit 31 controls the current value of the pilot arc current Ip to be a set value. Further details of the pilot arc power supply circuit 31 will be described after the descriptions of the pilot arc current detection circuit 33 and the pilot arc voltage detection circuit 36.

[0027] The pilot arc current detection circuit 33 detects the current value of the pilot arc current Ip that flows between the non-consumable electrode 121 and the plasma nozzle 122. The pilot arc current detection circuit 33 sends a pilot arc current detection signal Idp that corresponds to the current value of the pilot arc current Ip. The pilot arc current detection signal Idp is sent to the pilot arc power supply circuit 31.

[0028] The pilot arc voltage detection circuit 36 ​​detects the voltage value of the pilot arc voltage Vp between the non-consumable electrode 121 and the plasma nozzle 122. The pilot arc voltage detection circuit 36 ​​sends a pilot arc voltage detection signal Vdp corresponding to the voltage value of the pilot arc voltage Vp. The pilot arc voltage detection signal Vdp is sent to the pilot arc power supply circuit 31.

[0029] The pilot arc power supply circuit 31 outputs a pilot arc current Ip according to a set current value. The pilot arc power supply circuit 31 performs feedback control so that the current value of the pilot arc current Ip detected by the pilot arc current detection circuit 33 becomes the set current value. In this embodiment, a steady-state current value and an initial current value are set as the set current values ​​in the pilot arc power supply circuit 31. The steady-state current value is a set current value for ionizing the plasma gas PG by the pilot arc Pa. The initial current value is smaller than the steady-state current value, and is preferably 10% or less of the steady-state current value and 1 A or less. In this embodiment, the steady-state current value is 10 to 20 A, and the initial current value is 0.1 to 0.5 A. The steady-state current value and the initial current value are not limited. The initial current value may be any current value that can generate a pilot arc Pa. The initial current value is set appropriately based on experiments or simulations depending on the steady-state current value, the configuration of the torch 12, and the like.

[0030] The pilot arc power supply circuit 31 also compares the voltage value of the pilot arc voltage Vp detected by the pilot arc voltage detection circuit 36 ​​with a threshold value, and detects an arc abnormality if the voltage value of the pilot arc voltage Vp is equal to or greater than the threshold value. An arc abnormality is an abnormality in which a pilot arc Pa occurs in an unintended location (see FIG. 2(b)). In the example of FIG. 2(b), a deteriorated portion of the insulator 124 breaks down, causing a pilot arc Pa to occur between the non-consumable electrode 121 and a conductor 125 inside the torch. When an arc abnormality occurs, the length of the pilot arc Pa becomes longer than that of a normal pilot arc Pa. The longer the generated pilot arc Pa becomes, the larger the voltage value of the pilot arc voltage Vp becomes. The voltage value of the pilot arc voltage Vp when a normal pilot arc Pa is generated (see FIG. 2(a)) can be determined in advance from the configuration of the torch 12 (e.g., the distance between the non-consumable electrode 121 and the plasma nozzle 122, etc.). The voltage value of the pilot arc voltage Vp when an arc abnormality occurs (see FIG. 2(b)) can also be predicted in advance from the configuration of the torch 12, etc. The threshold value is set to a value that is greater than the voltage value of the pilot arc voltage Vp when a normal pilot arc Pa is generated and smaller than the possible value of the pilot arc voltage Vp when an arc abnormality occurs. For example, if the voltage value of the pilot arc voltage Vp when a normal pilot arc Pa is generated is approximately 5 to 6 V, and the voltage value of the pilot arc voltage Vp when an arc abnormality occurs is approximately 9 to 10 V, the threshold value is set to approximately 9 V. The threshold value is not limited. A fixed value that covers all torches 12 that can be connected may be set as the threshold value, or a value that corresponds to the connected torch 12 may be set. The connected torch 12 may be identified based on the torch model number entered by the operator, or the pilot arc power supply circuit 31 may automatically recognize it.

[0031] The pilot arc power supply circuit 31 starts and stops outputting the pilot arc current Ip based on a command from the control device 5. In this embodiment, when the control device 5 inputs a command to start outputting the pilot arc current Ip, the pilot arc power supply circuit 31 first outputs the pilot arc current Ip controlled to an initial current value. Then, if the pilot arc power supply circuit 31 does not detect an arc abnormality, it outputs the pilot arc current Ip controlled to a steady current value. Even while outputting the pilot arc current Ip controlled to the steady current value, the pilot arc power supply circuit 31 continues to determine whether or not there is an arc abnormality by comparing the voltage value of the pilot arc voltage Vp detected by the pilot arc voltage detection circuit 36 ​​with a threshold value. Note that, if an arc abnormality occurs, the arc abnormality is usually detected while the pilot arc current Ip is flowing at the initial current value. Therefore, the pilot arc power supply circuit 31 does not need to continue determining whether or not there is an arc abnormality while outputting the pilot arc current Ip at the steady current value.

[0032] On the other hand, if the pilot arc power supply circuit 31 detects an arc abnormality, it stops the output of the pilot arc current Ip. In this case, the pilot arc power supply circuit 31 outputs an abnormality detection signal to the control device 5 to notify the operator that an arc abnormality has been detected. Note that, if the pilot arc power supply circuit 31 detects an arc abnormality, it may notify the operator of the abnormality using a notifying means (such as a buzzer, a warning light, or a warning display) (not shown). Also, if the pilot arc power supply circuit 31 detects an arc abnormality, it may output an abnormality detection signal to the control device 5 or notify the operator of the abnormality without stopping the output of the pilot arc current Ip.

[0033] 3A and 3B are timing charts of the signals in the pilot arc circuit 3 when the plasma arc welding system B1 is started. (a) shows the change in the current value of the pilot arc current Ip. (b) shows the change in the voltage value of the pilot arc voltage Vp.

[0034] When the control device 5 issues a command to start outputting the pilot arc current Ip, the pilot arc power supply circuit 31 outputs the pilot arc current Ip controlled to an initial current value I1. As shown in FIG. 3(a), from time t1 to time t3, the pilot arc current Ip is at the initial current value I1. The time from time t1 to time t3, i.e., the time during which the pilot arc current Ip controlled to the initial current value I1 is output, is not limited, but is, for example, approximately 50 to 100 milliseconds. At time t2 during this period, the pilot arc power supply circuit 31 starts acquiring the pilot arc voltage Vp detected by the pilot arc voltage detection circuit 36. In this embodiment, the acquisition of the pilot arc voltage Vp begins at time t2, which is after time t1 when the pilot arc current Ip stabilizes at the initial current value I1, so as not to detect fluctuations in the pilot arc voltage Vp at the start of outputting the pilot arc current Ip. Note that the pilot arc power supply circuit 31 may start acquiring the pilot arc voltage Vp from the beginning of outputting the pilot arc current Ip.

[0035] As shown by the solid line in Figure 3(b), between time t2 and time t3, the pilot arc voltage Vp does not become equal to or greater than the threshold value V0, and the pilot arc power supply circuit 31 does not detect an arc abnormality, so the pilot arc current Ip is increased from the initial current value I1 to a steady-state current value I2. As shown in Figure 3(a), after time t4, the pilot arc current Ip becomes the steady-state current value I2. As shown in Figure 3(b), as the pilot arc current Ip is increased, the pilot arc voltage Vp also increases. However, because the pilot arc voltage Vp does not become equal to or greater than the threshold value V0, no arc abnormality is detected.

[0036] On the other hand, as shown by the dashed line in FIG. 3(b), after time t2, when the pilot arc voltage Vp becomes equal to or greater than the threshold value V0, the pilot arc power supply circuit 31 detects an arc abnormality and stops outputting the pilot arc current Ip.

[0037] The main arc circuit 4 passes a main arc current Im between the non-consumable electrode 121 and the base metal W. In this embodiment, the main arc circuit 4 controls the current value of the main arc current Im to a set value. In other words, the main arc circuit 4 performs constant current control. The main arc circuit 4 includes a main arc power supply circuit 41. In reality, the main arc circuit 4 includes a configuration for detecting the main arc current Im and the main arc voltage Vm, but this will not be described or explained here.

[0038] The main arc power supply circuit 41 receives input from a commercial power supply such as three-phase 200V, and performs output control such as inverter control and thyristor phase control. As a result, the main arc power supply circuit 41 causes a main arc current Im to flow between the non-consumable electrode 121 and the base metal W. The main arc power supply circuit 41 controls the current value of the main arc current Im or the voltage value of the main arc voltage Vm to be a set value. The main arc power supply circuit 41 starts and stops the output of the main arc current Im based on commands from the control device 5.

[0039] The plasma gas supply device 81 is for supplying plasma gas PG into the plasma nozzle 122. The plasma gas supply device 81 controls the flow rate based on a command from the control device 5 to supply the plasma gas PG. The shielding gas supply device 82 is for supplying shielding gas SG between the plasma nozzle 122 and the shielding gas nozzle 123. The shielding gas supply device 82 controls the flow rate based on a command from the control device 5 to supply the shielding gas SG.

[0040] The control device 5 controls the plasma arc welding system B1. When starting welding using the plasma arc welding system B1, the control device 5 first causes the plasma gas supply device 81 to start supplying the plasma gas PG and causes the shielding gas supply device 82 to start supplying the shielding gas SG. Next, the control device 5 causes the pilot arc power supply circuit 31 to start outputting the pilot arc current Ip. Then, if no abnormality detection signal is input from the pilot arc power supply circuit 31, the control device 5 causes the main arc power supply circuit 41 to start outputting the main arc current Im. After the main arc Ma stabilizes, the control device 5 may cause the pilot arc power supply circuit 31 to stop outputting the pilot arc current Ip, or may cause the pilot arc power supply circuit 31 to continue outputting the pilot arc current Ip. Then, the control device 5 causes the operation control circuit 2 to start operation of the welding robot 1. On the other hand, if the control device 5 receives an abnormality detection signal from the pilot arc power supply circuit 31, the control device 5 stops the plasma gas supply device 81 and the shielding gas supply device 82 without causing the main arc power supply circuit 41 to output the main arc current Im. In this case, the control device 5 may notify the operator of the abnormality by a notifying means (not shown) (by a buzzer, a warning light, a warning display, or the like).

[0041] Next, the effects of the plasma arc welding system B1 will be described.

[0042] According to this embodiment, the pilot arc power supply circuit 31 passes a pilot arc current Ip between the non-consumable electrode 121 and the plasma nozzle 122. The pilot arc voltage detection circuit 36 ​​detects the voltage value of the pilot arc voltage Vp between the non-consumable electrode 121 and the plasma nozzle 122. The longer the generated pilot arc Pa, the greater the voltage value of the pilot arc voltage Vp. The pilot arc power supply circuit 31 detects an arc abnormality when the voltage value of the pilot arc voltage Vp is equal to or greater than a threshold value. When the pilot arc power supply circuit 31 detects an arc abnormality, it stops outputting the pilot arc current Ip. This makes it possible to prevent the torch 12 from being burned by the pilot arc Pa.

[0043] Furthermore, according to this embodiment, before outputting the pilot arc current Ip controlled to the steady-state current value, the pilot arc power supply circuit 31 outputs the pilot arc current Ip controlled to an initial current value smaller than the steady-state current value. This prevents the torch 12 from burning out due to the pilot arc current Ip controlled to the steady-state current value flowing when an arc abnormality occurs. Furthermore, in this embodiment, the initial current value is 10% or less of the steady-state current value and 1 A or less. Therefore, even when an arc abnormality occurs, the torch 12 is prevented from burning out due to the pilot arc current Ip controlled to the initial current value flowing.

[0044] In the first embodiment, the pilot arc power supply circuit 31 first outputs the pilot arc current Ip at an initial current value and then outputs the pilot arc current Ip at a steady current value, but this is not limiting. The pilot arc power supply circuit 31 may output the pilot arc current Ip at a steady current value from the beginning, without outputting the pilot arc current Ip at an initial current value.

[0045] FIG. 4 is a timing chart of each signal in the pilot arc circuit 3 at startup in this modified example. Similar to FIG. 3, FIG. 4(a) shows the change in the current value of the pilot arc current Ip, and FIG. 4(b) shows the change in the voltage value of the pilot arc voltage Vp. When the control device 5 issues a command to start outputting the pilot arc current Ip, the pilot arc power supply circuit 31 outputs the pilot arc current Ip controlled to a steady-state current value I2. As shown in FIG. 4(a), at time t1, the pilot arc current Ip reaches the steady-state current value I2. At time t2, which follows time t1, the pilot arc power supply circuit 31 begins acquiring the pilot arc voltage Vp detected by the pilot arc voltage detection circuit 36. As shown by the solid line in FIG. 4(b), if the pilot arc voltage Vp does not become equal to or greater than the threshold value V0 after time t2, the pilot arc power supply circuit 31 does not detect an arc abnormality and therefore continues to output the pilot arc current Ip at the steady-state current value I2. 4(b), if the pilot arc voltage Vp becomes equal to or greater than the threshold value V0 after time t2, the pilot arc power supply circuit 31 detects an arc abnormality and stops the output of the pilot arc current Ip. In this modification as well, the pilot arc power supply circuit 31 detects an arc abnormality and stops the output of the pilot arc current Ip when the voltage value of the pilot arc voltage Vp is equal to or greater than the threshold value, thereby preventing the torch 12 from being burned by the pilot arc Pa.

[0046] In the first embodiment, the plasma arc welding system B1 is described as including the welding robot 1 in which the manipulator 11 moves the torch 12, but the present invention is not limited to this. The plasma arc welding system B1 may be configured such that the torch 12 is attached to a carriage and the carriage is moved, or such that the worker holds and moves the torch 12.

[0047] In the first embodiment, the present invention is described as being applied to a plasma arc welding system, but the present invention is not limited to this and can also be applied to other plasma arc systems such as a plasma arc cutting system.

[0048] The plasma arc system according to the present invention is not limited to the above-described embodiment, and the specific configuration of each part of the plasma arc system according to the present invention can be freely designed and modified in various ways. [Explanation of symbols]

[0049] B1: plasma arc welding system, 12: torch, 121: non-consumable electrode, 122: plasma nozzle, 31: pilot arc power supply circuit, 36: pilot arc voltage detection circuit

Claims

1. a torch having a non-consumable electrode and a plasma nozzle surrounding the non-consumable electrode; a pilot arc power supply circuit that supplies a pilot arc current for generating a pilot arc between the non-consumable electrode and the plasma nozzle; a pilot arc voltage detection circuit for detecting a voltage value of a pilot arc voltage between the non-consumable electrode and the plasma nozzle; Equipped with the pilot arc power supply circuit causes the pilot arc current controlled to an initial current value smaller than a steady-state current value to flow, detects an arc abnormality when the voltage value when the pilot arc is generated is equal to or greater than a threshold value, and causes the pilot arc current controlled to flow at the steady-state current value when no arc abnormality is detected. Plasma Arc System.

2. The initial current value is 10% or less of the steady-state current value and is 1 A or less.

10. The plasma arc system of claim 1.

3. the threshold value is a value that is greater than a voltage value of the pilot arc voltage when a normal pilot arc has occurred and is smaller than a possible value of the pilot arc voltage when a pilot arc has occurred at an unintended location.

3. The plasma arc system of claim 1 or 2.

Images