JP2023064324A - plasma arc system - Google Patents

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

The present invention relates to plasma arc systems.

Plasma arc welding systems have been known for some time. In a plasma arc welding system, a pilot arc is generated between an electrode and a plasma nozzle, and plasma gas is ionized and emitted by the pilot arc. is ignited (see FIG. 2(a), which will be described later). Then, while the main arc is being generated, the base material is welded. A plasma arc welding system is disclosed, for example, in Patent Document 1 and the like.

JP 2015-62912 A

However, if the insulation performance deteriorates due to contamination inside the torch, the pilot arc may be ignited in an unintended location. For example, an insulator is interposed between the conductor inside the torch and the electrode in order to prevent current flow with the electrode. The pilot arc may be ignited in between (see FIG. 2(b), which will be described later). Also, a pilot arc may be ignited between the electrode and the conductor inside the torch through the hole for passing the plasma gas inside the plasma nozzle. In these cases, the main arc cannot be ignited, and the inside of the torch may burn out. The problems described above occur not only in plasma arc welding systems, but also in other plasma arc systems, such as plasma arc cutting systems.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plasma arc system capable of suppressing burning of a torch due to a pilot arc.

In order to solve the above problems, the present invention takes the following technical measures.

A plasma arc system provided by a first aspect of the present invention includes a torch having a non-consumable electrode and a plasma nozzle surrounding the non-consumable electrode, and a pilot arc current passing between the non-consumable electrode and the plasma nozzle. a pilot arc power supply circuit; and 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, wherein the pilot arc power supply circuit detects a voltage value equal to or higher than a threshold value. detect an arc fault.

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

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

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

In a preferred embodiment of the present invention, the threshold value is greater than the voltage value of the pilot arc voltage when a normal pilot arc occurs, and the voltage of the pilot arc voltage when the pilot arc occurs in an unintended location. The value is smaller than the possible values.

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 voltage value of the pilot arc voltage between the non-consumable electrode and the plasma nozzle. to detect The longer the generated pilot arc, the greater the voltage value of the pilot arc voltage. When the voltage value of the pilot arc voltage is equal to or higher than the threshold value, the pilot arc power supply circuit determines that an arc longer than the intended pilot arc has occurred, and detects an arc abnormality. As a result, the occurrence of an arc abnormality can be detected, and burnout of the torch due to the pilot arc can be suppressed.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

1 is a block diagram showing the overall configuration of a plasma arc welding system according to a first embodiment of the present invention; FIG. 2 is a simplified enlarged cross-sectional view showing a torch in the plasma arc welding system of FIG. 1; FIG. FIG. 2 is a timing chart of each signal of the pilot arc circuit when the plasma arc welding system of FIG. 1 is started; FIG. FIG. 2 is a timing chart of each signal of the pilot arc circuit at startup of the modification of the plasma arc welding system of FIG. 1; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, taking as an example the case where the plasma arc system according to the present invention is used as a plasma arc welding system.

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

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, and a shield gas supply device. 82 and the control device 5 .

The welding robot 1 performs plasma arc welding on the base material W automatically. Welding robot 1 includes a manipulator 11 and a torch 12 . Manipulator 11 is, for example, an articulated robot. The torch 12 is driven by the manipulator 11 so as to freely move up, down, forward, backward, left and right.

As best seen in FIG. 2, the torch 12 has a non-consumable electrode 121, a plasma nozzle 122, and a shield gas nozzle 123. As shown in FIG.

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

A plasma gas PG flows through the plasma nozzle 122 . As shown in FIG. 2A, 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. A pilot arc current Ip flows between the plasma nozzle 122 and the non-consumable electrode 121 when the pilot arc Pa is generated. The current value of the pilot arc current Ip means the time average value of the absolute values of the pilot arc current Ip unless otherwise specified. The plasma nozzle 122 is appropriately cooled by cooling means (not shown).

A main arc Ma is generated between the non-consumable electrode 121 and the base material W. As shown in FIG. Main arc Ma is constrained by the nozzle opening of plasma nozzle 122 . A main arc current Im flows between the non-consumable electrode 121 and the base material W when the main arc Ma is generated. Either direct current or alternating current is selected as the main arc current Im according to the material of the base material W. The main arc current Im may be a direct current pulse current or an alternating current pulse current. The current value of the main arc current Im means the time average value of the absolute values of the main arc current Im, unless otherwise specified. A main arc voltage Vm is applied between the non-consumable electrode 121 and the base material W when the main arc Ma is generated.

The shield gas nozzle 123 is a cylindrical member. A 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 may not include the shield gas nozzle 123 .

The operation control circuit 2 has a microcomputer and memory (both not shown). This memory stores a work program in which various operations of the welding robot 1 are set. The motion control circuit 2 sends a motion control signal Ms to the welding robot 1 according to the work 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 motion control circuit 2 starts the motion of the welding robot 1 based on a command from the control device 5 .

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. That is, 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 .

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. Thereby, the pilot arc power supply circuit 31 causes the 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 a set value. Other descriptions of the pilot arc power supply circuit 31 will be given after the descriptions of the pilot arc current detection circuit 33 and the pilot arc voltage detection circuit 36 .

The pilot arc current detection circuit 33 is for detecting the current value of the pilot arc current Ip flowing between the non-consumable electrode 121 and the plasma nozzle 122 . A pilot arc current detection circuit 33 sends a pilot arc current detection signal Idp corresponding to the current value of the pilot arc current Ip. A pilot arc current detection signal Idp is sent to the pilot arc power supply circuit 31 .

A pilot arc voltage detection circuit 36 is for detecting 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 delivers a pilot arc voltage detection signal Vdp corresponding to the voltage value of the pilot arc voltage Vp. A pilot arc voltage detection signal Vdp is sent to the pilot arc power supply circuit 31 .

The pilot arc power supply circuit 31 outputs a pilot arc current Ip according to the 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 current value and an initial current value are set as the set current value 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, preferably 10% or less of the steady-state current value, and 1 A or less. In this embodiment, the steady-state current value is 10-20A, and the initial current value is 0.1-0.5A. Note that 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 the pilot arc Pa. The initial current value is appropriately set based on experiments and simulations according to the steady-state current value, the configuration of the torch 12, and the like.

In addition, the pilot arc power supply circuit 31 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 when the voltage value of the pilot arc voltage Vp is equal to or higher than the threshold value. do. Arc anomaly is an anomaly that occurs where the pilot arc Pa is not intended (see FIG. 2(b)). In the example of FIG. 2(b), the deteriorated portion of the insulator 124 is destroyed and a pilot arc Pa is generated between the non-consumable electrode 121 and the conductor 125 inside the torch. When an arc abnormality occurs, the length of pilot arc Pa becomes longer than that of normal pilot arc Pa. As the length of the generated pilot arc Pa increases, the voltage value of the pilot arc voltage Vp increases. The voltage value of the pilot arc voltage Vp when a normal pilot arc Pa is generated (see FIG. 2(a)) is known in advance from the configuration of the torch 12 (for example, the distance between the non-consumable electrode 121 and the plasma nozzle 122). can. Also, the voltage value of the pilot arc voltage Vp when an arc abnormality occurs (see FIG. 2(b)) can be assumed in advance from the configuration of the torch 12 and the like. The threshold value is set to a value that is greater than the voltage value of the pilot arc voltage Vp when the normal pilot arc Pa occurs and less than the value that the pilot arc voltage Vp can take when an arc abnormality occurs. For example, when the voltage value of the pilot arc voltage Vp when the normal pilot arc Pa occurs is about 5 to 6 V, when the arc abnormality occurs, the voltage value of the pilot arc voltage Vp is about 9 to 10 V. , the threshold is set to about 9V. Note that the threshold is not limited. Further, the threshold value may be set to a fixed value that can cover all the torches 12 that can be connected, or may be set to a value that corresponds to the connected torch 12 . The connected torch 12 may be specified based on the model number of the torch input by the operator, or may be automatically recognized by the pilot arc power supply circuit 31 .

The pilot arc power supply circuit 31 starts and stops outputting the pilot arc current Ip based on commands from the control device 5 . In this embodiment, when a command to start outputting the pilot arc current Ip is input from the control device 5, the pilot arc power supply circuit 31 first outputs the pilot arc current Ip controlled to the initial current value. Then, when no arc abnormality is detected, the pilot arc power supply circuit 31 outputs the pilot arc current Ip controlled to the steady-state current value. The pilot arc power supply circuit 31 compares the voltage value of the pilot arc voltage Vp detected by the pilot arc voltage detection circuit 36 with the threshold value even while outputting the pilot arc current Ip controlled to the steady-state current value to detect an arc abnormality. continue the judgment. When an arc abnormality occurs, the arc abnormality is normally detected while the pilot arc current Ip of the initial current value is flowing. Therefore, the pilot arc power supply circuit 31 does not have to continue the determination of the arc abnormality while the pilot arc current Ip of the steady current value is being output.

On the other hand, when an arc abnormality is detected, the pilot arc power supply circuit 31 stops outputting the pilot arc current Ip. In this case, the pilot arc power supply circuit 31 outputs an abnormality detection signal to the controller 5 to notify that an arc abnormality has been detected. In addition, when the pilot arc power supply circuit 31 detects an arc abnormality, the operator may be notified of the abnormality (buzzer, warning light, warning display, etc.) by a notification means (not shown). Further, when an arc abnormality is detected, the pilot arc power supply circuit 31 may output an abnormality detection signal to the control device 5 without stopping the output of the pilot arc current Ip, or notify the operator of the abnormality. may

FIG. 3 is a timing chart of each signal of the pilot arc circuit 3 when the plasma arc welding system B1 is started. FIG. 4(a) shows the changing state of the current value of the pilot arc current Ip. FIG. 4(b) shows the changing state of the voltage value of the pilot arc voltage Vp.

When instructed to start outputting the pilot arc current Ip from the controller 5, the pilot arc power supply circuit 31 outputs the pilot arc current Ip controlled to the initial current value _I1 . As shown in FIG. 3(a), from time t1 to time t3, the pilot arc current Ip reaches the initial current value _I1 . The time from time t1 to time t3, that is, the time for outputting the pilot arc current Ip controlled to the initial current value _I1 is not limited, but is, for example, about 50 to 100 milliseconds. From the time t2 of 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, in order not to detect fluctuations in the pilot arc voltage Vp at the start of the output of the pilot arc current Ip, the pilot arc is started from the time t2 after the time t1 when the pilot arc current Ip is stabilized at the initial current value _I1 . Acquisition of voltage Vp is started. The pilot arc power supply circuit 31 may start acquiring the pilot arc voltage Vp from the beginning of the output of the pilot arc current Ip.

As indicated by the solid line in FIG. 3(b), the pilot arc voltage Vp did not reach or exceed the threshold value _V0 between time t2 and time t3, and the pilot arc power supply circuit 31 did not detect an arc abnormality. The pilot arc current Ip is raised from the initial current value _I1 to the steady current value _I2 . As shown in FIG. 3(a), after time t4, the pilot arc current Ip reaches the steady-state current value _I2 . As shown in FIG. 3(b), the pilot arc voltage Vp also increases as the pilot arc current Ip increases. However, since the pilot arc voltage Vp does not exceed the threshold value _V0 , no arc abnormality is detected.

On the other hand, as indicated by the dashed line in FIG. 3(b), after time t2, when the pilot arc voltage Vp becomes equal to or higher than the threshold value _V0 , the pilot arc power supply circuit 31 detects an arc abnormality, and the pilot arc current Stop outputting Ip.

The main arc circuit 4 passes a main arc current Im between the non-consumable electrode 121 and the base material W. As shown in FIG. In this embodiment, the main arc circuit 4 controls the current value of the main arc current Im to be a set value. That is, the main arc circuit 4 performs constant current control. The main arc circuit 4 includes a main arc power supply circuit 41 . Actually, the main arc circuit 4 includes a configuration for detecting the main arc current Im and the main arc voltage Vm, but the description and explanation are omitted.

The main arc power supply circuit 41 receives, for example, a three-phase 200 V commercial power supply as input, and performs output control such as inverter control and thyristor phase control. Thereby, the main arc power supply circuit 41 causes the main arc current Im to flow between the non-consumable electrode 121 and the base material W. As shown in FIG. 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 a set value. The main arc power supply circuit 41 starts and stops outputting the main arc current Im based on commands from the control device 5 .

The plasma gas supply device 81 is for supplying the plasma gas PG to the inside of the plasma nozzle 122 . The plasma gas supply device 81 controls the flow rate based on the command from the control device 5 and supplies the plasma gas PG. The shield gas supply device 82 is for supplying the shield gas SG between the plasma nozzle 122 and the shield gas nozzle 123 . The shield gas supply device 82 supplies the shield gas SG by controlling the flow rate based on a command from the control device 5 .

A controller 5 controls the plasma arc welding system B1. When starting welding by 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 shield gas supply device 82 to start supplying the shield gas SG. Next, the pilot arc power supply circuit 31 is caused to start outputting the pilot arc current Ip. When the abnormality detection signal is not input from the pilot arc power supply circuit 31, the main arc power supply circuit 41 is caused to start outputting the main arc current Im. After the main arc Ma is stabilized, the control device 5 may cause the pilot arc power supply circuit 31 to stop outputting the pilot arc current Ip or continue outputting the pilot arc current Ip. Then, the control device 5 causes the motion control circuit 2 to start the motion of the welding robot 1 . On the other hand, when the abnormality detection signal is input from the pilot arc power supply circuit 31, the control device 5 operates the plasma gas supply device 81 and the shield gas supply device 82 without causing the main arc power supply circuit 41 to output the main arc current Im. stop. In this case, the control device 5 may notify the operator of the abnormality (buzzer, warning light, warning display, etc.) by means of notification means (not shown).

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

According to this embodiment, the pilot arc power supply circuit 31 passes the pilot arc current Ip between the non-consumable electrode 121 and the plasma nozzle 122 . Pilot arc voltage detection circuit 36 detects the voltage value of pilot arc voltage Vp between non-consumable electrode 121 and plasma nozzle 122 . As the length of the generated pilot arc Pa increases, the voltage value of the pilot arc voltage Vp increases. The pilot arc power supply circuit 31 detects arc abnormality when the voltage value of the pilot arc voltage Vp is equal to or higher than the threshold. The pilot arc power supply circuit 31 stops outputting the pilot arc current Ip when an arc abnormality is detected. As a result, burnout of the torch 12 due to the pilot arc Pa can be suppressed.

Further, according to the present embodiment, 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 before outputting the pilot arc current Ip controlled to the steady-state current value. do. This prevents the torch 12 from burning out due to the flow of the pilot arc current Ip controlled to the steady-state current value when an arc abnormality occurs. Further, 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 pilot arc current Ip controlled to the initial current value is prevented from flowing and causing the torch 12 to burn out.

In the above-described first embodiment, the pilot arc power supply circuit 31 first outputs the pilot arc current Ip of the initial current value and then outputs the pilot arc current Ip of the steady-state current value. It is not limited to this. The pilot arc power supply circuit 31 may output the pilot arc current Ip of the steady current value from the beginning without outputting the pilot arc current Ip of the initial current value.

FIG. 4 is a timing chart of each signal of the pilot arc circuit 3 at the start of the modification. As in FIG. 3, FIG. 4(a) shows the changing state of the current value of the pilot arc current Ip, and FIG. 4(b) shows the changing state of the voltage value of the pilot arc voltage Vp. When instructed to start outputting the pilot arc current Ip from the controller 5, the pilot arc power supply circuit 31 outputs the pilot arc current Ip controlled to the 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 . From time t2 after time t1, the pilot arc power supply circuit 31 starts acquiring the pilot arc voltage Vp detected by the pilot arc voltage detection circuit . As shown by the solid line in FIG. 4(b), after time t2, when the pilot arc voltage Vp does not reach or exceed the threshold value _V0 , the pilot arc power supply circuit ₃₁ does not detect an arc abnormality. Continue to output the pilot arc current Ip. On the other hand, as indicated by the dashed line in FIG. 4(b), after time t2, when the pilot arc voltage Vp becomes equal to or higher than the threshold value _V0 , the pilot arc power supply circuit 31 detects an arc abnormality, and the pilot arc current Stop outputting Ip. Also in this modification, the pilot arc power supply circuit 31 detects an arc abnormality and stops outputting the pilot arc current Ip when the voltage value of the pilot arc voltage Vp is equal to or higher than the threshold value. burnout can be suppressed.

Moreover, in the said 1st Embodiment, although the plasma arc welding system B1 demonstrated the case where the manipulator 11 was provided with the welding robot 1 which moves the torch 12, it is not restricted to this. The plasma arc welding system B1 may have a configuration in which the torch 12 is attached to a cart and the cart is moved, or a configuration in which the torch 12 is gripped and moved by an operator.

Also, in the first embodiment, the case where the present invention is applied to a plasma arc welding system has been described, but the present invention is not limited to this. The invention is also applicable to other plasma arc systems, such as plasma arc cutting systems.

The plasma arc system according to the invention is not limited to the embodiments described above. The specific configuration of each part of the plasma arc system according to the present invention can be modified in various ways.

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 (4)

a torch having a non-consumable electrode and a plasma nozzle surrounding the non-consumable electrode;
a pilot arc power supply circuit that causes a pilot arc current to flow between the non-consumable electrode and the plasma nozzle;
a pilot arc voltage detection circuit for detecting a voltage value of the pilot arc voltage between the non-consumable electrode and the plasma nozzle;
with
The pilot arc power supply circuit detects an arc abnormality when the voltage value is equal to or greater than a threshold.
plasma arc system. The pilot arc power supply circuit supplies the pilot arc current controlled to an initial current value smaller than the steady current value, and supplies the pilot arc current controlled to the steady current value when no arc abnormality is detected. ,
The plasma arc system of Claim 1. The initial current value is 10% or less of the steady-state current value and 1 A or less,
3. The plasma arc system of Claim 2. The threshold is a value that is greater than the voltage value of the pilot arc voltage when a normal pilot arc occurs and smaller than a value that the voltage value of the pilot arc voltage can take when the pilot arc occurs in an unintended location. ,
A plasma arc system according to any one of claims 1 to 3.

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