JPH01215464A - Ignition device for electrical discharge machine - Google Patents

Abstract

PURPOSE:To simplify starting operation of the title electric discharge machine by controlling a switching means to control the voltage impression between two auxiliary electrodes for generating trigger plasma according to the output voltage of a power source to impress the voltage among a main electrode and a main nozzle of a torch and base metal. CONSTITUTION:Ar gases are supplied to the torch 1 and a plasma injection device 30 respectively and the voltage is impressed between the main electrode 1 and the base metal 6 from the power source PWtig. In addition, the DC voltage is impressed between the auxiliary electrode 8 and a nozzle member 7 from DC power units 21 and 22 to convert the commercial AC electric power of an ignition control circuit 20 into DC. By this method, the arc discharge is generated between the electrode 1 and the base metal 6. The output voltage Vtig of the power source PWtig is ten detected by a voltage discrimination circuit 23 and when this voltage is more than a prescribed value, the switching means S1 to control the voltage impression between the auxiliary electrode 8 and the member 7 is turned on and when it is not so, the switching means S1 is turned off. By this method, the need for complicated operation to cut off a power source of a trigger device after confirming the starting timing of the trigger device and the presence or absence of the ignition of the arc discharge is eliminated and the ignition control of the arc discharge can be automated completely.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electrical discharge machine that performs TIG welding, MIG welding, plasma welding, cutting, thermal spraying, and the like.

In particular, it relates to startup control including ignition of discharge.

[Prior Art] For example, in a welding torch, plasma torch, etc., a discharge is generated between at least one main discharge electrode and a workpiece or another electrode (for example, a nozzle electrode), and heat generation or BACKGROUND ART In a processing torch that welds, cuts, thermal sprays, or heats a material to be processed using plasma, it is necessary to ignite an arc discharge. Therefore,
Conventionally, a high frequency ignition method has been used in which a high frequency high voltage is applied between the main electrode for discharge and the workpiece or another electrode to generate a trigger discharge between them, or the main electrode for discharge is used as the workpiece. Arc discharge is generally triggered by a contact ignition method, in which the main electrode for discharge is brought into contact with a material to generate a contact spark, and then the main electrode for discharge is separated from the material to be processed, thereby converting the contact spark discharge into arc discharge.

However, with conventional high-frequency ignition methods, the high-frequency voltage required to start the arc is large, which generates high-energy electromagnetic noise, which can cause malfunctions in microcomputers built into various automatic devices that perform welding processes, etc. There is. Furthermore, since the measuring equipment connected to the arc power supply circuit is damaged during high-frequency ignition, there is a problem that the measuring equipment cannot be easily connected to the power supply line common to the welding electric circuit. In particular, in AC welding, it is necessary to start arc discharge for restriking every half wave of AC, and a large amount of electromagnetic noise is generated.

In addition, with conventional contact ignition methods, there is a high possibility that arc discharge will fail to start depending on the shape of the tip of the discharge electrode, and with AC welding, arc loss may occur when switching between AC half waves, resulting in loss of arc stability. There are things that happen.

Therefore, for example, in the technique disclosed in Japanese Patent Application Laid-open No. 107869/1983, arc discharge is started at a relatively low voltage by generating trigger plasma, thereby reducing the generation of noise accompanying the start of discharge.

[Problems to be Solved by the Invention] However, in the method of starting arc discharge using trigger plasma, the starting operation is complicated and requires skill for one operator. That is, in this type of startup operation, a predetermined voltage is applied to the main mti of the torch, gas is supplied into the torch, and in this state, a voltage is applied to the secondary electrode for generating trigger plasma, and the After supplying gas to the part and visually confirming that arc discharge has occurred between the main electrode and the main nozzle (or workpiece), stop applying voltage to the sub-electrode and stop supplying gas to that part. There is a need to.

In this case, if the generation of triggered plasma continues even after the arc discharge has started, the life of the sub-electrode will be shortened. In particular, in devices that have a filament in the sub-electrode and generate plasma while heating the sub-electrode, a large current is passed through the filament, so if the current is continued for a long time, the filament will break immediately, resulting in repeated Cannot be used.

Therefore, the operator must ensure that the arc discharge is ignited before stopping the energization to the sub-electrode. Further, even if the arc discharge does not ignite for a long time due to a special failure (for example, gas supply abnormality), if the auxiliary electrode is continued to be energized even though it is not ignited, the life of the auxiliary electrode will be shortened. Therefore, the operator is forced to perform troublesome operations.

An object of the present invention is to simplify the starting operation of an electrical discharge machine.

[Means for solving problems] In order to achieve the above object, in the present invention.

A first sub-electrode and a second sub-electrode used to generate trigger plasma.
a switching means for controlling voltage application between the sub-electrode of the first power supply means; and detecting the output voltage of the first power supply means and controlling the switching means according to the output voltage, when the output voltage is equal to or higher than a predetermined value; Control means is provided for setting the voltage between the first sub-electrode and the second sub-electrode to an energizing level, and setting it to a de-energizing level when the voltage is not likely to be applied.

[Function] The power supply device used in this type of device has a voltage-current characteristic that is a drooping characteristic, and when a current exceeding a predetermined value flows through the output terminal, the voltage suddenly decreases as shown in Figure 3. decreases to In other words, when the arc discharge between the main electrode and the nozzle electrode (or base metal) is not ignited, almost no current flows, so the output voltage of the power supply is high, but when the arc discharge ignites, a large current flows, and the output voltage of the power supply drops rapidly. Therefore, the control means generates a trigger plasma by applying a voltage between the first sub-electrode and the second sub-electrode when the arc discharge is not ignited, and when the arc discharge is ignited, the control means generates the trigger plasma. The voltage application between the first *+ electrode and the second sub-electrode is released. Accordingly, the period during which the first sub-fIt electrode and the second sub-electrode are energized is only the minimum period necessary for ignition of the arc discharge, so the life of the filament etc. is long. Become.

However, under special conditions, such as when an abnormality occurs in the gas supply, the arc discharge may not ignite for a long time even after the trigger plasma is generated. In that case, if the trigger plasma continues to be generated, the filament will quickly break. Therefore, in a preferred embodiment of the present invention to be described later, a time measuring means is provided for measuring the time elapsed since the output voltage of the main power supply reaches a predetermined value or more, and when the measured time exceeds a predetermined value, the switching means is controlled. Protective means are provided for setting the voltage between the first sub-electrode and the second sub-electrode to a de-energizing level.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[Embodiment] FIG. 1 shows one type of arc welding torch 10 and its ignition control circuit 20 for carrying out the present invention.

Specifically, this torch 10 is a DC non-consumable electrode type arc welding torch. In Figure 1, PW
tig is the main power source for arc welding and supplies DC power to the output terminal. In this example, the main power supply PWtig is
It has output characteristics as shown in the figure. That is, when there is no load, the output voltage is about 80V, when a relatively small current flows, the output voltage is about 30 to 40V, and when the rated load current of about 30OA, which causes arcing, flows, the output voltage suddenly decreases. decreases to

A rod-shaped main electrode 1 made of tungsten is arranged in the center of the torch 10, and its tip is located in the center of the shield cap 3.

One end of the pipe 5 opens into the space between the main electrode 1 and the shield cap 3. Argon gas is supplied to this pipe 5 from a cylinder (not shown).

Note that although the gas supplied through the pipe 5 is called a shielding gas, this may not be necessary in some cases.

In this example, the workpiece (
The negative and positive output terminals of the main power source PWtig are connected to the base material) 6 and the main electrode l, respectively.

A plasma injector 30 is arranged in the torch 10 at a position facing the side surface of the main electrode 1 . The plasma injector 30 includes a conductive nozzle member 7 and a sub-electrode 8 disposed inside the nozzle member 7.

The sub-electrode 8 includes a filament for heating it. Moreover, in the inner space of the plasma injector 30,
One end of the pipe 11 is open.

Argon gas is supplied into the plasma injector 30 through this pipe 11 .

This torch IO generates an arc discharge as follows. That is, first, argon gas is supplied into the torch 10 via the pipe 5, and between the main electrode 1 and the workpiece 6,
After applying a predetermined voltage from the power source PWtig, argon gas is supplied into the plasma injector 30 through the pipe 11 to create a space between the filament of the sub-electrode 8 and between the sub-electrode 8 and the nozzle member 7. Apply the specified DC voltage. When the sub-electrode 8 is heated to a high temperature by this, a discharge occurs between the sub-electrode 8 and the nozzle member 7, which ionizes the argon gas and forms plasma gas at the tip of the nozzle member 7. The liquid is ejected from the nozzle 7a toward the main electrode 1 at high speed. Triggered by this plasma gas,
Arc discharge occurs between the main electrode 1 and the workpiece 6.

The ignition control circuit 20 includes two DC power supplies 21 and 2.
It is equipped with 2. The output terminal of one DC power supply device 21 is connected between the filament rains of the sub-electrode 8, and the output terminal of the other DC power supply device 21 is connected to the filament of the sub-electrode 8. ! The output terminal 22 is connected to the sub-electrode 8 on the negative side and to the nozzle member 7 on the positive side.

These DC power supplies 21 and 22 convert commercial AC power applied between their input terminals a and b into predetermined DC power. Therefore, when no AC power is applied between their input terminals a and b, no voltage appears at their output terminals. Input terminal (a) of DC power supply 21.22
, b) are electrical contacts S2. It is connected to a commercial AC power line via a fuse 29 and a power switch SW.

On the other hand, the output voltage of the main power supply PWtig is 1 ignition control circuit 2
The voltage is applied between the input terminals a and b of the voltage identification circuit 23 via the resistor 25 and the diode bridge 24 provided at the voltage discriminator circuit 23 . Specifically, this circuit 23 includes an analog voltage comparator, a relay driver, and a relay, and binary-identifies the voltage between its input terminals a and b to turn on/off the relay.
Control off.

The threshold voltage of this analog voltage comparator is the main power supply PW
If it is converted to the output voltage Vt1g of tig.

It is about 30V. SL is the electrical contact of the relay.

Therefore, as shown in FIG. 3, when the voltage Vt1g is 30V or more, the electric contact S1 is turned on (closed state), and otherwise, the electric contact S1 is turned off. Note that the terminal c of the voltage identification circuit 23
, d is its own power input terminal.

27 is a timer relay, and S3 is an electrical contact of the timer relay 27. Further, 28 is a relay, and S2 is its electrical contact. The series circuit of electric contact s3 and relay 28 and timer relay 27 are connected in parallel, and one end of the parallel circuit is connected to electric contact s1 through power switch SW, and the other end is connected to electric contact s1. It is connected to a commercial power line via a fuse 29 and a power switch SW. In addition, the electrical contact S
3 and 5 are normally closed, and are switched to open when a predetermined voltage is applied to the timer relay 27 and a predetermined time Tco elapses.

A solenoid valve 26 is arranged in the middle of the pipe 11. This electromagnetic valve 26 blocks the fluid passage when no voltage is applied to its solenoid, and allows passage of fluid when voltage is applied to the solenoid. The solenoid terminal of the solenoid valve 26 is
It is connected to the power line in parallel with the input terminal of the DC power supply device 21.

Therefore, when electrical contact S2 is closed, argon gas is supplied to plasma injector 30, but when S2 is opened, the supply of gas is stopped.

Figures 2a and 2b show the operating timing of the device in Figure 1. Figure 2a shows the case when the arc discharge is ignited normally, and Figure 2b shows the timing when the arc discharge is ignited normally. This is in case of failure. Normally, it operates as shown in Figure 2a.

First, the operation in that case will be explained with reference to FIG. 2a.

When the power switch SW is turned on and the main power supply PWtig is turned on, a voltage of about 80V appears at its output terminal. At this time, in the voltage identification circuit 23, since the input voltage is higher than the threshold level, the relay is turned on and the electrical contact S1
turns on. Therefore, at the same time that a predetermined voltage is applied between the terminals of the timer relay 27, the electrical contact SL is closed,
A predetermined power supply voltage is applied between the terminals of the relay 28 via S3. This switches the electrical contact S2 of the relay 28 to the closed state.

Therefore, the solenoid valve 26 is turned on, and the DC power supply devices 21 and 2
Power is supplied to 2. After a while, the temperature of the filament of the sub-electrode 8 becomes high, and a discharge occurs between the sub-electrode 8 and the nozzle member 7. As a result, the argon gas in the plasma injector 30 turns into a plasma state, and flows from the nozzle 7a to the main electrode. Spouts on the 1st side. This plasma gas injection is used as a trigger.

Arc discharge occurs between the main electrode l and the workpiece 6.

When the ignition of the arc discharge is completed, a large current of about 300A flows from the main power supply PWtig.

As shown in FIG. 3, the voltage V tig drops rapidly.

As a result, the voltage applied to the voltage identification circuit 23 becomes below its threshold voltage, the internal relay is turned off, and the electrical contact S1 is switched to the open state. When sl opens, the voltage applied to timer relay 27 and relay 28 is cut off. Therefore, the electrical contact s2 is switched to the open state. Therefore, the solenoid valve 26 is closed and the supply of argon gas into the plasma injector 30 is stopped, and at the same time, the DC power supply 21.
22 is cut off, the energization of the filament of the sub-electrode 8 is stopped, and the voltage application between the sub-electrode 8 and the nozzle member 7 is also terminated. Therefore, the generation of plasma from the plasma injector 30 is stopped, and only the plasma arc discharge between the main electrode 1 and the workpiece 6 continues.

Next, the case of FIG. 2b will be explained. When the power switch SW is turned on and the main power supply PWtig is turned on, a voltage of about 80V appears at its output terminal.

At that time, in the voltage identification circuit 23, since the input voltage is greater than the threshold level, the internal relay is turned on and its electrical contact Sl is turned on. Therefore, at the same time as a predetermined voltage is applied between the terminals of timer relay 27, a predetermined power supply voltage is applied between the terminals of relay 28 via closed electrical contacts Sl and S3.

This switches the electrical contact S2 of the relay 28 to the closed state.

Therefore, the solenoid valve 26 is turned on, and the DC power supply devices 21 and 2
2 is supplied with power and an arc discharge is normally ignited between the main electrode l and the workpiece 6 after a relatively short time, as in the case of FIG. 2a described above. However, if the arc discharge does not ignite for some reason, the following will occur.

That is, unless arc discharge occurs, the voltage Vt1g remains at a high level, so the input voltage of the voltage identification circuit 23 is higher than the threshold level, and the electrical contact S1 remains closed. However, since the timer relay 27 continues counting time while the electrical contact S1 is in the closed state, if arc discharge does not occur, when the timer relay 27 has counted the predetermined time Tco, the electrical contact S3 will be in the open state. Switch. This cuts off the voltage applied to relay 28 and opens electrical contact S2. Therefore, the electromagnetic valve 26 is closed and the supply of argon gas into the plasma injector 30 is stopped, and at the same time, the input power of the DC power supply device 21, 22 is cut off, so that the energization of the filament of the sub-electrode 8 is stopped. At the same time,
The voltage application between the sub-electrode 8 and the nozzle member 7 is also cut off. Therefore, the filament energization time is limited to within the time Tco. When ignition of the arc discharge fails in this way, the next ignition operation will not be performed until the electrical contact S3 is switched to closed, that is, until the main power source PWtig is turned off, so the abnormality will continue to occur. One-point firing operation is not repeated.

In the above embodiment, the nozzle member 7 was used as the second sub-electrode, but a special electrode may be provided near the sub-electrode (first sub-electrode) 8 to replace the electrode of the nozzle member 7. good.

[Effects] As described above, according to the present invention, the troublesome operation of shutting off the power to the trigger device after checking the activation timing of the trigger device and the ignition of arc discharge is unnecessary, and the point of arc discharge Arc control can be fully automated. Furthermore, if a circuit is provided to limit the activation time of the trigger device as shown in the above embodiment, even if one firing failure occurs, damage to the filament etc. can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of one type of arc welding torch lO and its ignition control circuit 20 for carrying out the present invention. 2a and 2b are time charts showing an example of the operation of the ignition control circuit 20 of FIG. 1, respectively. FIG. 3 is a graph showing the correlation between the output current I jig of the main power supply PWtig and the output voltages Vt and ig. 1: Main electrode 3: Shield cap 5, 11: Pipe 6: Processing target material (base material) 7: Nozzle member (sub nozzle, second sub electrode) 8: Sub electrode (first sub electrode) lO: Torch 20: Ignition control circuit 21.2
2: DC power supply device (second power supply means) 23: Voltage identification circuit (control means) 24: Diode bridge 25: Resistor II 26: Solenoid valve 27: Timer relay (time measurement means) 28: Relay 29: Fuse 30: Plasma injector PWt
ig: Main power supply (first power supply means) Sl: Electrical contact (switching means) S2: Electrical contact S3: Electrical contact (protective means) SW: Power switch

Claims (3)

[Claims] (1) A main electrode provided on the torch, a first power supply means connected to at least one of the main nozzle and the base material and the main electrode and applying a voltage between them, disposed opposite to the main electrode. a sub-nozzle, a first sub-electrode placed opposite to the sub-nozzle, and a second sub-electrode placed near the first sub-electrode.
In an ignition device for an electrical discharge machine, comprising: a sub-electrode; and a second power supply means for applying a voltage between the first sub-electrode and the second sub-electrode: a switching means for controlling voltage application between the second sub-electrode; and a switching means for detecting the output voltage of the first power supply means and controlling the switching means according to the output voltage; control means for setting the voltage between the first sub-electrode and the second sub-electrode to an energizing level when the output voltage is less than a predetermined value; Machine ignition device. (2) The first sub-electrode includes a filament, and the second power supply means includes heater energizing power supply means for supplying a predetermined power between terminals of the filament. The ignition device for the electrical discharge machine described in Section 1. (3) The control means includes a time measurement means for measuring the time after the output voltage of the first power supply means reaches a predetermined value or more, and when the measured time reaches a predetermined value or more, controls the switching means to The ignition device for an electrical discharge machine according to claim 1, further comprising a protection means for setting the voltage between the first sub-electrode and the second sub-electrode to a de-energizing level.