JP2000218442A - Electric discharge machine and method of flushing in electric discharge machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently discharge molten impurities from electric discharge liquid during electric discharge machining. SOLUTION: A machining tool 12 is arranged in the vicinity of a workpiece 10, and is applied with a voltage within electric discharge liquid so as to effect electric discharge for machining the workpiece 10. A spindle 16 is moved in a thrust direction by magnetic actuators 18, 20 so as adjust the gap between the workpiece 10 and the machining tool 12 while the spindle 19 is ultrasonically vibrated by in response to signals from an ultrasonic wave carrier generating circuit 26 so as to effect ultrasonic cavitations in the electric discharge liquid in order to expel molten impurities. The ultrasonic vibration is effected, for example, during such a period that no voltage pulses for electric discharge is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to flushing of swarf generated during electric discharge machining.

[0002]

2. Description of the Related Art Conventionally, a conductive machining tool is disposed in the vicinity of a conductive workpiece (work) in a discharge liquid space of an electrically poor conductor, and a voltage is applied between the two to discharge the workpiece. Electric discharge machining for machining is widely performed. Among electric discharge machines, those that make small holes in a work, in particular, are equipped with a high-precision rotary specification spindle, unlike wire electric discharge machines and die sinking electric discharge machines. By performing electric discharge machining while rotating the machining tool with the spindle, a hole with high roundness can be formed in the workpiece.

On the other hand, in electric discharge machining, melting chips of a work are generated. When the hole is shallow, the dissolved debris is automatically discharged by natural or forced circulation of the discharge liquid,
When the hole diameter is small and the hole becomes deep, it becomes difficult to discharge the dissolved debris only by circulation of the discharge liquid. The forced circulation of the discharge liquid is performed, for example, by forming the processing tool into a hollow pipe shape and pressurizing the discharge liquid using the pipe.

Therefore, conventionally, every time a workpiece is machined to a certain depth, the machining tool is released from the cutting direction together with the spindle holding the machining tool in rotation, and the machining tool is removed from the hole formed in the object to be machined. The discharge liquid was swept out of the hole by reciprocating in the hole, and the molten debris was discharged together with the discharge liquid.

FIG. 3 shows the relationship between the discharge voltage and the displacement of the spindle in the thrust direction with respect to the time at this time. Discharge voltage is 50-100V, pulse interval is 5-50
Generally, the pulse width is 0 μs and the pulse width is 2 to 50 μs. As an example of the processing, the voltage pulse is continuously applied for about 10 seconds, during which the spindle gradually cuts in the cutting direction (downward in FIG. 3). Thereafter, the spindle is once pulled up and released, and is again positioned at the same position as immediately before the lifting. This escape period is about 2 seconds. Thereafter, the process of applying the voltage pulse again and continuing the processing is repeated. The molten debris is discharged from the hole together with the discharge liquid by a pumping action or a stirring action by the reciprocating movement of the spindle during the escape period.

[0006]

However, in the above-mentioned conventional flushing method, there are many cases where the discharge liquid leaks from the gap between the processing tool and the hole and flows backward. In particular, it is difficult to discharge the molten debris existing at the bottom of the hole. There was a problem.

In addition, during flushing, since the entire spindle is moved by the piston along with the table, there is a problem that the movement is slow and gap leakage is likely to occur.

Further, since the flushing is performed by temporarily suspending the electric discharge machining, there is a problem that if the flushing is frequently performed to compensate for the low efficiency of the discharge, the machining efficiency of the work is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to ensure that even when a hole formed in a workpiece is deep, the melting dust can be reliably removed without unnecessarily reducing the machining efficiency of electric discharge machining. And a flushing method for electric discharge machining.

[0010]

In order to achieve the above object, a first invention is directed to a conductive working tool, a spindle for rotating the working tool, a working tool, and the working tool. A voltage application means for applying a voltage pulse having a predetermined time width at predetermined time intervals to a conductive workpiece to be disposed close to the discharge liquid space and discharging the voltage, and the spindle being driven in a thrust direction at an acoustic or ultrasonic vibration frequency. And a reciprocating drive means for reciprocatingly driving, and generating ultrasonic cavitation between the processing tool and the workpiece. Due to the ultrasonic cavitation generated by reciprocating drive in the thrust direction, it is possible to reliably discharge the molten chips present in the machining holes together with the discharge liquid. More specifically, dissolved debris is discharged by the movement of bubbles generated by ultrasonic waves or the cleaning effect due to the breakage of the bubbles.

In a second aspect based on the first aspect, the reciprocating drive means includes a feedback control circuit for magnetically levitating the spindle in a non-contact manner and controlling a position in a thrust direction, and a feedback control circuit. A superimposing circuit for superimposing an ultrasonic carrier signal. By superimposing the ultrasonic carrier signal on the feedback control circuit, the spindle can be ultrasonically vibrated with a simple configuration.

In a third aspect based on the second aspect, the feedback control circuit comprises: a magnetic actuator for driving the spindle in a thrust direction; a detection means for detecting a position of the spindle in the thrust direction; And a position control means for supplying a drive signal to the magnetic actuator based on a detection signal from the means.

According to a fourth aspect of the present invention, a conductive processing tool and a conductive processing object are arranged close to each other in a discharge liquid space, and a voltage pulse having a predetermined time width is provided between the processing tool and the processing object. Is applied to the workpiece at predetermined time intervals to discharge the workpiece, thereby processing the object to be processed, wherein the spindle is reciprocated in a thrust direction at an ultrasonic vibration frequency at a predetermined timing of the electrical discharge machining. Thereby, ultrasonic cavitation is generated between the processing tool and the workpiece. Due to the ultrasonic cavitation generated by reciprocating drive in the thrust direction, it is possible to reliably discharge the molten chips present in the machining holes together with the discharge liquid.

In a fifth aspect based on the fourth aspect, the predetermined timing is an entire period of the electric discharge machining. By generating ultrasonic cavitation during the period of electric discharge machining, it is possible to reliably discharge the molten debris and improve the accuracy of electric discharge machining.

In a sixth aspect based on the fourth aspect, the predetermined timing is a non-application period of the voltage pulse. By performing the process during the period in which the voltage pulse is not applied, the molten debris can be discharged without lowering the electric discharge machining efficiency.

In a seventh aspect based on the fourth aspect, the predetermined timing is when a predetermined amount or more of swarf exists in a space between the processing tool and the workpiece. And Processing efficiency can be improved by generating ultrasonic cavitation only when the melting debris is present in a predetermined amount or more.

In an eighth aspect based on the seventh aspect, it is characterized in that whether or not the melting debris is present in a predetermined amount or more is determined by an electric resistance value between the processing tool and the object to be processed. I do. Since the swarf is conductive, the amount of swarf affects the conductivity between the working tool and the workpiece (specifically, the conductivity of the discharge liquid between them),
By measuring the electric resistance between the two, the amount of the melting debris can be easily and accurately measured.

In a ninth aspect based on the eighth aspect, the electric resistance value is set between the processing tool and the workpiece between the voltage pulse non-application period and another voltage pulse. Is detected by a current value caused by the second voltage applied to the first and second electrodes. By detecting the magnitude of the current value between the processing tool and the object to be processed, it is possible to easily and accurately measure the electric resistance value between the two and the amount of melted debris.

In a tenth aspect based on the fourth aspect, at the predetermined timing, the spindle is further reciprocated by superimposing a sound wave vibration frequency in a thrust direction. By generating ultrasonic cavitation at the timing of replacing the discharge liquid in the machining hole of the workpiece by the reciprocating motion of the spindle, it is possible to reliably discharge the molten debris present at the bottom of the machining hole.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an electric discharge machine according to this embodiment. A processing tool 12, such as tungsten or copper tungsten, is arranged near the work 10, and a gap between the work 10 and the processing tool 12 is filled with a discharge liquid, such as water or mineral oil, which is an electrically poor conductor. Processing tool 12
Is mounted on the tip of the spindle 16 in the spindle outer cylinder 14 and is rotated by a motor 22. The spindle 16 is supported by the air flowing from the air inlet receptacle 17.

A magnetic actuator (rotating side) 20 is provided on the spindle 16, and magnetically interacts with a magnetic actuator (fixed side) 18 provided on the spindle outer cylinder 14. Have been. A thrust displacement sensor 24 for detecting the position of the spindle in the thrust direction (direction along the rotation axis) is provided above the spindle outer cylinder 14, and outputs a detected signal.

The spindle 16, that is, the processing tool 12
A circuit for controlling the position in the thrust direction of the workpiece 10 based on the position detection signal from the thrust displacement sensor 24.
A position control circuit 30 for determining a position in the thrust direction necessary to form a desired hole in the thrust direction and outputting a control signal; an electromagnet driver 32 for driving the magnetic actuator 18 based on the control signal from the position control circuit 30; Carrier signal (2) for reciprocatingly driving the machining tool 16 (or the processing tool 12) in the thrust direction at the ultrasonic vibration frequency.
An ultrasonic carrier generating circuit 26 for generating a sine wave signal of 0 kHz or more) and an adder 28 for superimposing the ultrasonic carrier signal on the position detection signal are provided. Usually, a sine wave is used as the ultrasonic carrier, but a rectangular wave may be used. The thrust displacement sensor 24, the position control circuit 30, the electromagnet driver, and the magnetic actuator 18 constitute a feedback circuit, and adjust the distance between the workpiece 10 and the processing tool 12 by controlling the position of the spindle 16 in the thrust direction to a desired position. And the spindle 1 by the ultrasonic carrier signal
6 is vibrated by a very small amount in the thrust direction at the ultrasonic vibration frequency to generate ultrasonic cavitation in the discharge liquid. That is, the magnetic actuators 18 and 20 control the position of the spindle 16 in the thrust direction, thereby controlling the work 1.
It has a function of adjusting the distance between the tool 0 and the processing tool 12 and a function of vibrating the spindle 16 in the thrust direction at an ultrasonic vibration frequency.

In such a configuration, when the work 10 is machined, the discharge pulse power supply 40 adjusts the position of the machining tool 12 in the thrust direction by a feedback circuit from the discharge pulse power supply 40 to the work 10 and the machining tool 12 for a predetermined time width and a predetermined time. A voltage pulse is applied at time intervals to generate a discharge between the workpiece 10 and the processing tool 12 for processing, and the spindle 16 is ultrasonically vibrated in a thrust direction at a predetermined timing (in a direction indicated by an arrow 100 in the figure). Dissolved debris is discharged from the hole of the workpiece 10 together with the discharge liquid. In addition, the brush 42 is for energizing the spindle 16.

Here, the timing at which the spindle 16 (or the machining tool 12) is ultrasonically oscillated is arbitrary, and the ultrasonic cavitation is always generated by superimposing the ultrasonic carrier signal on the position detection signal during the electric discharge machining. Is also possible.

It is also preferable that the spindle 16 be ultrasonically vibrated during a period in which no discharge voltage is applied to the workpiece 10 and the machining tool 12, that is, a period in which no voltage pulse is applied. Specifically, the work 10 and the processing tool 12
A signal from a known power supply control circuit that controls the driving of a power supply that applies a voltage to the power supply is supplied to the adder 28, and the adder 28 operates only when no voltage pulse is supplied from the power supply during the non-application period The ultrasonic carrier signal from the workpiece 10 is superimposed on the position detection signal, and the hole of the workpiece 10 and the machining tool 1 are
Ultrasonic cavitation is generated in the discharge liquid between the first and second discharge liquids. The non-application period of this voltage pulse corresponds to a relief period in FIG.

When the spindle 16 is ultrasonically oscillated during the non-application period of the voltage pulse, the spindle 16 is not oscillated during the entire non-application period, but only when there is a predetermined amount or more of scum in the discharge liquid. It is also effective to discharge the melting debris by ultrasonic vibration. Further, a voltage pulse may be continuously applied until the amount of the melting waste reaches a predetermined amount, and after the detection of the predetermined amount, the voltage pulse may be stopped to discharge the melting waste.

More specifically, a signal from the power supply control circuit and a signal indicating that a predetermined amount or more of swarf is present are supplied to the adder 28, and based on both signals, the ultrasonic carrier generation circuit 2
6 may be superimposed on the position detection signal. Of course, this may be performed not only during the period during which the voltage pulse is not applied.

Note that the amount of the melting debris can be measured by any method. However, since the melting debris is conductive, the electric resistance value of the discharge liquid between the work 10 and the processing tool 12 must be measured. Can measure the amount of melting debris. In other words, there is a negative phase between the amount of melting debris and the electrical resistance value,
The smaller the electric resistance value, the more molten debris will be present. Therefore, for example, by applying a voltage (DC or AC) lower than the discharge voltage to the workpiece 10 and the processing tool 12, and detecting the current value resulting from the low voltage, the amount of the melting debris can be measured. Whether or not the amount of the melting debris is equal to or more than the predetermined value can be determined based on whether or not the current value caused by the low voltage is equal to or more than the predetermined value.

Here, the voltage value of the low voltage is selected such that the working tool does not wear out, and is usually a DC or AC of about 1 to 2 V. At this time, since the current flowing between the processing tool and the object to be measured is usually about 0.1 amperes, it is easy to determine whether or not the amount of the melting debris has exceeded a certain value.

FIG. 2 is a block diagram showing a case where a sound carrier is further superimposed on an ultrasonic carrier.
The sound carrier having a frequency of several kHz output from the sound carrier generation circuit 50 is superimposed on the ultrasonic carrier by the adder 52. In this case, when ultrasonic vibration is applied to the spindle to generate ultrasonic cavitation in the discharge liquid space, the ultrasonic carrier can be further superimposed on the ultrasonic carrier at the ultrasonic vibration frequency. As a result, the spindle vibrates in the thrust direction at the frequency of the acoustic wave and simultaneously generates ultrasonic cavitation. By reciprocating vibration of the processing tool with the frequency of the sound wave, the discharge liquid is exchanged in the processing hole of the workpiece and ultrasonic cavitation is generated at the same time, so that the molten debris existing at the bottom of the processing hole is more efficiently discharged.

The forced circulation of the discharge liquid is performed by making the working tool into a hollow pipe shape and pressurizing the discharge liquid by using this pipe, but it is also possible to generate ultrasonic cavitation simultaneously with the forced circulation.

[0033]

As described above, according to the present invention,
Even when the hole formed in the workpiece is deep, the molten debris can be reliably discharged without unnecessarily lowering the machining efficiency of the electric discharge machining.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a control circuit according to another embodiment of the present invention.

FIG. 3 is a timing chart showing escape of a spindle.

[Explanation of symbols]

10 workpiece, 12 processing tool, 14 spindle outer cylinder, 16 spindle, 17 air inflow receptacle,
Reference Signs List 18 magnetic actuator (fixed side), 20 magnetic actuator (rotating side), 22 motor, 24 thrust displacement sensor, 26 ultrasonic carrier generation circuit, 28 adder, 30 position control circuit, 32 electromagnet driver, 40
Discharge pulse power supply, 42 brush, 50 sound wave carrier generation circuit.

[Procedure amendment]

[Submission date] February 10, 1999 (1999.2.1
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 9

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

In a ninth aspect based on the eighth aspect, the electric resistance value is applied between the processing tool and the workpiece between the voltage pulse and another voltage pulse. It is characterized by being detected by a current value caused by the second voltage. By detecting the magnitude of the current value between the processing tool and the object to be processed, it is possible to easily and accurately measure the electric resistance value between the two and the amount of melted debris.

Claims (10)

[Claims] A conductive processing tool; a spindle for rotating and driving the processing tool; and a predetermined time interval between the processing tool and a conductive workpiece to be disposed close to the processing tool in a discharge liquid space. Voltage applying means for applying and discharging a voltage pulse having a predetermined time interval, and reciprocal driving means for reciprocatingly driving the spindle in a thrust direction at an acoustic or ultrasonic vibration frequency, comprising: An electric discharge machine characterized by generating ultrasonic cavitation between a machining object. 2. The electric discharge machine according to claim 1, wherein the reciprocating drive unit magnetically levitates the spindle in a non-contact manner and controls a position in a thrust direction, and an ultrasonic wave is transmitted to the feedback control circuit. An electric discharge machine, comprising: a superimposing circuit for superimposing a carrier signal. 3. The electric discharge machine according to claim 2, wherein the feedback control circuit includes: a magnetic actuator that drives the spindle in a thrust direction; a detection unit that detects a position of the spindle in the thrust direction; And a position control means for supplying a drive signal to the magnetic actuator based on the detection signal. 4. A conductive processing tool and a conductive workpiece are arranged close to each other in a discharge liquid space, and a voltage pulse having a predetermined time width is applied between the processing tool and the workpiece at predetermined time intervals. A flashing method of electric discharge machining in which the object to be machined is machined by causing an electric discharge by performing a reciprocating vibration of the spindle in a thrust direction at an ultrasonic vibration frequency at a predetermined timing of the electric discharge machining. A flushing method for electrical discharge machining, wherein ultrasonic cavitation is generated between the workpiece and the workpiece. 5. The method according to claim 4, wherein the predetermined timing is the entire period of the electric discharge machining. 6. The flushing method according to claim 4, wherein the predetermined timing is a period during which the voltage pulse is not applied. 7. The electric discharge machining method according to claim 4, wherein the predetermined timing is when there is a predetermined amount or more of swarf present in a space between the processing tool and the workpiece. Flushing method. 8. The method according to claim 7, wherein the determination as to whether or not the melting debris is present in a predetermined amount or more is made based on an electric resistance value between the machining tool and the workpiece. Flushing method. 9. The method according to claim 8, wherein the electric resistance value is applied between the processing tool and the workpiece during a period in which the voltage pulse is not applied and another voltage pulse. A flushing method for electric discharge machining, wherein the method is detected by a current value caused by a second voltage. 10. The flushing method according to claim 4, wherein the spindle is reciprocated at the predetermined timing by further superimposing a sound wave vibration frequency in a thrust direction.