JPH0236016A - Power source for micro process - Google Patents

Abstract

PURPOSE:To perform micro process with minimum effect by floating volume by connecting high impedance dc high voltage source parallel to dc low voltage source, and making discharge between an electrode and a material to be processed preceded at low voltage for detection, and by applying high voltage in the procedure. CONSTITUTION:Voltage for detection of low voltage source 12 is at first applied to a degree that discharge is generated for a condition in a gap between an electrode 7 and a material to be processed 8 to be detected, and a discharge point where the discharge is started is detected. Only when the discharge point is detected, the current of the pulse width designated by the discharge point is made from the high impedance dc high voltage source 11, and the floating volume of the gap is to be charged at low voltage for detection as the discharge current flows concentrating in the discharge point. In this way, the effect from the energy accumulated to the floating voltage is reduced, and as the process at a certain level of discharge current is possible, a homogeneous micro engraving process can be performed.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is a power supply for micromachining, particularly a power source with a surface roughness of 3 μm RM.
The present invention relates to a power supply for micromachining that is capable of micromachining smaller than ax and is suitable for mold discharge machining in which a relatively large stray capacitance exists.

[Conventional technology]

Micromachining in electric discharge machining is 1 to 1 in terms of normal surface roughness.
This refers to a range of 3 μm RMax or less, and in this range, a pulse having a small and accurate discharge current peak value and pulse width is required.

However, in general, the peak current that actually flows during processing varies depending on the voltage applied to one gap and circuit constants such as impedance stray capacitance in the conductor circuit leading to the gap. Therefore, the machined surface roughness is a collection of machining craters (marks on the metal surface blown away by electrical discharge) of different sizes.

Therefore, considering the desired surface roughness, it is necessary to remove electrical machining conditions and electrical connections that would undesirably increase the surface roughness, and specifically, to improve the machining voltage. By suppressing the discharge current to a low value, the above-mentioned uniform micromachining can be performed. However, machining cannot actually be performed with this method, because in order to start an electric discharge, a relatively small power source impedance is required to continue supplying electrons at least until an electron avalanche occurs within the gap. However, in reality, the wiring leading to the gap is inevitably long due to machine strokes, etc., and the impedance must be high. There wasn't.

However, if the power source impedance can be reduced for a short period of time at the start of discharge, processing can be performed. It's a method. That is, this is a method as shown in FIG. 2, in which capacitors are connected in parallel across gaps as shown in the figure.

In FIG. 2, numeral 1 is a main power supply, 2 is a capacitor, 3 is a resistor, and 4 is a FETl-transistor.

5 is a diode, 6 is an inductance, and 57 is an electrode.

8 represents a workpiece, and 9 represents a capacitor.

In the case shown in Fig. 2, the voltage of the main electrode Al is selected to a predetermined value, and the capacitor 9 is
The capacitance of FET1 is determined and the FET is turned on and off by a constant periodic pulse applied to the gate of transistor 4.
) A capacitor 9 is charged from the main power supply 1 via a transistor 4, and the discharge energy of the capacitor 9 is used to perform processing.

(Problems to be Solved by the Invention) The machined surface roughness is determined by the discharge energy stored in the capacitor 9, but determining the repetition of machining depends on the charging speed, that is, the magnitude of the power source impedance.

Therefore, in order to increase the machining speed, machining is performed by reducing the power supply impedance, but if you try to increase the machining speed while performing micromachining, the 8th problem will occur, resulting in a practical failure, and it will be difficult to reproduce the machining. There was a problem that reliability and reliability could not be obtained.

Various papers have been published in the past regarding the triggers for the initiation of electrical discharge, but microdischarges are caused by rapid generation of Joule heat due to current concentration at microscopic contacts, melting and evaporation of metal, evaporation of machining fluid, and This can be considered to be due to the generation of local pressure and a series of subsequent processes.

Therefore, the energy applied at that time melts the contact point,
Whether or not it can be dispersed is thought to be determined by the size of the contact point and the number of contact points at the same time. If the contact point is large or there are many contact points.

The current density per piece is so small that it cannot be melted and scattered.

In other words, the chance of normal discharge is greatly reduced. In practice, short circuits occur frequently, resulting in instability. For this reason, it is necessary to accurately control the gap and to avoid increasing the number of contact points unnecessarily.
It is recalled that great care must be taken in chip evacuation.

However, in the conventional configuration shown in FIG.

Particularly in the case of die-cut electrical discharge machining, the number of contact points increases, making it unstable, but the power source impedance is reduced and the current is branched to each contact point. , it is true that the capacitance of capacitor 9 cannot correspond to various changes in the gap between the two.
It could not be said that it was reproducible or reliable.

In addition, if the chips and gas in the machining gap are properly discharged and machining is being performed (the generated ions are deionized and the insulation is restored during the pause time after discharge), As long as this situation continues, it is okay to lower the power supply impedance, but once the insulation does not recover after a discharge occurs, if the power supply impedance is relatively large because it is small, the charging current will flow directly into the gap between the two. This results in machining that results in rough surface roughness. For this reason, it became difficult to adjust the processing fluid and the power source impedance, and in the end, we had no choice but to prepare for some surface roughness (but we couldn't expect anything more.Furthermore, the capacitor 9
is connected to the gap.

Since the discharge current becomes an oscillating current determined by the discharge circuit constant including the gap, the degree of collision of electrons with the electrode 7 increases, resulting in a disadvantage that the wear of the electrode 7 is doubled.

The present invention aims to solve the above-mentioned drawbacks,
The direction in which the capacitor 9 shown in FIG. 2 is actively arranged is stopped, and the stray capacitance in the gap, which cannot be ignored in the molding process, is charged with a low detection voltage that can discharge it, and a preliminary discharge is caused in the gap. 5. Taking the start of the preceding discharge as a trigger, a high voltage from the main machining power source is applied, and the discharge current due to the high voltage is concentrated at the discharge point where the preceding discharge is occurring, and machining is carried out. It is an object of the present invention to provide an IT source for microfabrication that is designed to reduce the influence of energy generated in the process.

(Means for Solving Problem i1) In order to achieve the above object, the power supply for micromachining of the present invention is a power supply for molding electric discharge machining in which micromachining with a surface roughness of 3 μm RMax or less is performed. a DC low voltage source equipped with a switching element that is turned on and off by pulses, a comparator that detects a gap voltage at the start of discharge that occurs between the electrode and the workpiece due to the applied voltage of the DC low voltage source; A monostable multivibrator that receives a discharge start detection signal and generates a trigger signal, and a switching element that is controlled by the trigger signal of the monostable multivibrator, and a high voltage source connected in parallel to the DC low voltage source. An impedance DC high voltage source is provided, and the low voltage detection voltage of the DC low voltage source is used to advance the discharge between the electrode and the workpiece, and the start of this preliminary discharge is used as a trigger to generate the high voltage of the high impedance DC high voltage source. The present invention is characterized in that it has a configuration that applies , thereby reducing the influence of stray capacitance between the electrode and the workpiece, and allowing micro-machining to be carried out.

[Effect]

In order to detect the state of the gap, a relatively low detection voltage that causes discharge is first applied to the gap, and the discharge point at which the discharge starts is detected based on the voltage change over one gap. Only when this discharge point is detected, a current with a specified pulse width is applied to the discharge point from the relatively high-voltage main machining power source, and the discharge current is concentrated at the discharge point. Since the area of the workpiece is large, the stray capacitance in the gap, which cannot be ignored, is charged with a relatively low detection voltage, and the influence of the energy accumulated in the stray capacitance is reduced, so that it is always uniform. Fine processing becomes possible.

The present invention will be explained below with reference to FIG.

〔Example〕

In FIG. 1, numerals 1.3 to 8 correspond to those in FIG. 11 is a high impedance DC high voltage source;
12 is a DC low voltage a, t3 is a comparator, 14 is a monostable multivibrator, 15 is a stray capacitance, and 16 is an FET)
Ranjista.

1 to 19 are resistors, and 20.21 is a variable resistor.

22 represents a capacitor.

The DC low voltage source 12 connects the high voltage of the main I source 1 to the resistor 17.
A low-voltage detection voltage is generated which is divided by the resistor 18 and the variable resistor 20 and turned on and off by pulses of a constant period applied to the base of the FET transistor 16.

The detection voltage applied from this DC low voltage source 12 to the electrode 7 is set to a voltage low enough to discharge the gap between the electrode 7 and the workpiece 8. The detection voltage is set in the range of 20 to 25 V to 50 V. In order to efficiently detect the occurrence of a discharge point having a high contact resistance in a gap, a relatively high value is selected as the resistance value of the resistor 19 to accurately detect a change in the voltage applied to one gap.

When a constant period pulse is applied to the gate of the FET transistor 16, the FET1 transistor 16 is turned on, and the low voltage detection voltage is applied from the DC low voltage source 12 to the electrode 7. When a discharge starts at one point in the gap between the electrode 7 and the workpiece 8, the voltage across the gap drops, and the comparator 13, which detects the voltage change in the gap, detects the gap voltage at the start of the discharge. , monostable multivibrator 1
4 Apply the trigger. The monostable multivibrator 14
Since a constant periodic pulse applied to the gate of the FET transistor 16 is input as a strobe signal, the variable resistor 2 is inputted from the monostable multivibrator 14.
1 and the capacitor 22 (FET in the high impedance DC high voltage source 11)
Output to transistor 4. As a result, the FET transistor 4 is turned on, and a current pulse with a good rise determined by the value of the high-resistance resistor 3 is discharged from the high-impedance DC high-voltage source 11, which is the main processing power source, at the low voltage detection voltage mentioned above. In other words, the pulsed discharge current supplied from the high impedance DC high voltage source 11 flows concentratedly into one discharge point where the preceding discharge started, and the discharge current It will be narrowed down. At this time, the energy stored in the stray capacitance charged with a low voltage will be released via the electrode 7, but the energy stored in the stray capacitance will be charged with the low voltage detection voltage. The energy is low because it is only generated by the high impedance DC high voltage aZ, and it is smaller than the energy from the high impedance DC high voltage aZ, so it is hardly affected by it. Therefore, the energy supplied to the electrode 7 depends on the energy supplied from the high impedance DC high voltage source 11, and the desired surface roughness is obtained for one discharge point where the preliminary discharge is started. It is possible to flow a low discharge current 1 having a peak value sufficient for, for example, ip to about IA, making it possible to perform desired uniform microfabrication.

Note that when the detection voltage of the DC low voltage source 12 does not cause discharge to start in the gap between the electrode 7 and the workpiece 8.

Since no voltage change occurs in the gap, the comparator 13
Since no trigger is applied to the monostable multivibrator 14, the high impedance DC high voltage att is turned off, and the floating capacitor 1115 is not charged with the high voltage of the high impedance DC high voltage source 11. The stray capacitance 15 is charged only by the low DC low voltage source 12, and the energy stored in the stray capacitance 115 is charged by the high impedance DC high voltage source 11 as described above. It has almost no effect during processing.

〔Effect of the invention〕

As explained above, the stray capacitance between the electrode and the workpiece, which cannot be ignored during molding, is charged with a low detection voltage, and this low detection voltage Let the advance discharge occur.

Since the high voltage of the main machining power source is applied at the start of the preceding discharge voltage, it is possible to narrow down the discharge current to one discharge point due to the preceding discharge, and the discharge current is accumulated in the stray capacitance. Since the influence of energy is small, machining can always be performed with a predetermined discharge current, and uniform micromachining becomes possible.

Also, since the energy stored in stray capacitance is small,
The discharge oscillation current is reduced, and the amount of electrode wear is reduced.

[Brief explanation of the drawing]

FIG. 1 shows the configuration of an embodiment of a power supply for microfabrication according to the present invention.
FIG. 2 shows the circuit configuration of a conventional electrical discharge machining power source. In the figure, 1 is the main power supply, 4 is the FET, 7 is the electrode, 8 is the workpiece, and 9 is the capacitor. 11 is a high impedance DC high voltage source, 12 is a DC low voltage source, 13 is a comparator, 14 is a monostable multivibrator, 15 is a stray capacitance, and 16 is a transistor (FET).

Claims (1)

[Claims] A power source for mold electric discharge machining in which micromachining with a surface roughness of 3 μm RMax or less is performed, comprising: a DC low voltage source equipped with a switching element that is turned on and off by pulses of a predetermined cycle; and the DC low voltage source. a comparator for detecting the gap voltage at the start of discharge generated between the electrode and the workpiece by the applied voltage of the source; and receiving a detection signal for the start of discharge detected by the comparator;
A monostable multivibrator that generates a trigger signal, a switching element controlled by the trigger signal of the monostable multivibrator, and a high impedance DC high voltage source connected in parallel to the DC low voltage source, A configuration is used in which a low-voltage detection voltage from a DC low-voltage source is used to advance a discharge between the electrode and the workpiece, and the start of this preliminary discharge is used as a trigger to apply a high voltage from a high-impedance DC high-voltage source. A power supply for micromachining that is characterized by reducing the influence of stray capacitance with the workpiece and performing mold micromachining.