JPH0751942A - Piercing detecting method and piercing detecting device for machined hole - Google Patents

Abstract

PURPOSE:To detect piercing of a machined hole of a work piece in electric discharge drilling with high accuracy. CONSTITUTION:In the case of drilling a through hole in a hon-conductive material using electrolytic discharge, a piercing detecting electrode 6 connected to an auxiliary electrode 7 through a resistance is provided under a work piece 4, whereby piercing of a drilled hole of the work piece can be electrically detected from the change in voltage between a tool electrode 5 and the piercing detecting electrode 6 caused by very small current flowing between the piercing detecting electrode 6 and the tool electrode 5 through the drilled hole when the drilled hole pierces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting penetration of a machined hole when a non-conductive hard material part is machined by electric discharge machining in an electrolytic solution.
INDUSTRIAL APPLICABILITY The present invention is used in the field of processing small holes in non-conductive hard material parts such as ceramics and Pyrex glass used in microelectronic devices such as sensors.

[0002]

2. Description of the Related Art Recently, with the demand for miniaturization of electronic parts, sensors, etc., micro parts have been often manufactured by utilizing a so-called silicon process developed from semiconductor integrated circuit technology. However, it is often difficult to use a silicon process, for example, it is often necessary to form fine holes in Pyrex glass or the like. A machining method using electric discharge in an electrolytic solution seems to be promising and is being studied for the machining of minute holes such as Pyrex glass and non-conductive ceramics. However, one of the problems with this method is to detect the penetration of the machined hole. If machining is continued after the machining hole has penetrated,
It may be larger than the expected hole diameter, or a taper opposite to the inlet side may be formed on the outlet side of the hole. In the latter case, metal cannot be vapor-deposited on the reverse taper portion in the subsequent vapor deposition step, which causes trouble such as conduction failure. On the contrary, if the processing is stopped in an incomplete penetration state, the hole shape becomes incomplete or burr remains. Detecting that the machined hole has penetrated the workpiece to obtain the desired hole diameter and cross-sectional shape on the outlet side by stopping the machining immediately after the machined hole penetrates the workpiece or after a certain period of time has passed. It is necessary.

As a conventional technique for detecting the penetration of such a machined hole into a workpiece, there is a method of detecting the penetration of a small hole in machining a small hole of a non-conductive hard material such as glass or ruby. That is, in this conventional processing apparatus, a tool electrode immersed in electrolysis and an auxiliary electrode are provided, and the penetration detection electrode is arranged facing the tool electrode across the workpiece and connected to the penetration detection electrode. When a current flows through the ammeter described above, it is determined that a through hole is formed in the workpiece by the tool electrode (Electrical Processing Handbook (published on October 25, 1970, first edition), page 80).

[0004]

In this method, since the tool electrode and the penetration detecting electrode are at the same potential, and the penetration detecting current flows between the penetration detecting electrode and the auxiliary electrode far away, the detection sensitivity is low and the sensitivity is low. In order to raise it, it is necessary to use a large area penetration detection electrode, and when processing a large number of minute holes side by side, arrange a plurality of penetration detection electrodes to detect the penetration of each hole individually. It is subject to area restrictions. In addition, since the absolute value of the detection current is large, the amount of gas generated in the penetration detection electrode is large, and the problem that bubbles block the through holes is likely to occur.

The present invention has been made in view of the above circumstances, and it is possible to detect the penetration of a machined hole of a workpiece with high accuracy and to detect the penetration of a machined hole capable of downsizing the device. It is an object of the present invention to provide a method and a penetration detection device.

[0006]

To solve this problem, the method of detecting a through hole of a machined hole according to the present invention provides a workpiece for machining a through hole in a non-conductive material by utilizing discharge in an electrolytic solution. A penetration detection electrode connected to the auxiliary electrode via a resistor is installed underneath, and the voltage between the tool electrode and the penetration detection electrode caused by the minute current flowing between the penetration detection electrode and the tool electrode through the hole when the machining hole is penetrated. It is characterized by electrically detecting that the machined hole has penetrated the workpiece by the change. Further, the processing hole penetration detecting device of the present invention is a processing hole penetration detecting device for detecting penetration of a through hole when a through hole is processed by utilizing discharge in an electrolytic solution to a non-conductive material, Equipped with a tool electrode and an auxiliary electrode immersed in a liquid, a penetration detection electrode is arranged facing the tool electrode across the workpiece, and the auxiliary electrode and the penetration detection electrode are connected via a resistor. It is characterized by becoming.

[0007]

[Operation] When the machining hole is drilled by the electric discharge from the tool electrode and the machining hole penetrates the workpiece, an electric current flows between the penetration detection electrode and the tool electrode through the hole, which causes the machining hole to penetrate the workpiece. The penetration can be detected.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings showing an embodiment. FIG. 1 shows a conceptual diagram of a machined hole penetration detecting device in a machined hole machining device for a non-conductive material utilizing discharge in an electrolytic solution. The machined hole penetration detection device 1 is filled with the electrolytic solution 3 in the container 2. The electrolytic solution 3 is an aqueous solution of sodium nitrate, sodium hydroxide or the like. A tool electrode 5 and a penetration detection electrode 6 are arranged so as to face each other with the workpiece 4 sandwiched therebetween, and in addition to this, an auxiliary electrode 7 is immersed in the electrolytic solution 3. Both the tool electrode 5 and the penetration detection electrode 6 are connected to the comparator 8.

The workpiece 4 is fixed to a table 11 made of a non-conductive material and immersed in the electrolytic solution 3. Electrolyte 3
A machining power source 12 capable of generating a direct current or a pulsed current is normally connected to the tool electrode 5 and the auxiliary electrode 7 therein so that the tool electrode 5 is the negative pole and the auxiliary electrode 7 is the positive pole, and a voltage is applied. Then, a discharge is generated between the tool electrode 5 having a small surface area and the electrolytic solution 3. Since the tool electrode 5 is placed in contact with the workpiece 4, the workpiece 4 is subjected to the heat of discharge and the chemical action of the electrolytic solution 3, and elution occurs at the portion facing the tip of the tool electrode 5. The holes can be machined by sending the tool electrode 5 in accordance with the machining amount by a method utilizing gravity. The penetration detection electrode 6 is connected to the auxiliary electrode 7 via the resistor 13. Before the processed hole penetrates the workpiece 4, almost no current flows because the workpiece 4 made of a non-conductive material blocks the space between the penetration detection electrode 6 and the tool electrode 5.
Therefore, there is almost no voltage drop due to the resistor 13, and therefore the penetration detection electrode 6 with respect to the tool electrode 5 (ground potential) is
Is almost equal to the voltage of the machining power supply 12.
When the machined hole penetrates the workpiece 4, a current flows through the hole between the penetration detection electrode 6 and the tool electrode 5, a voltage drop occurs due to the current and the resistance 13, and the grounded tool electrode 5
The voltage of the penetrating detection electrode 6 with respect to is dropped. By applying this voltage change to the comparator 8 and making a comparison by comparing it with a preset reference voltage, and by checking the output, the fact that the machined hole has penetrated the workpiece 4 can be taken out as an electrical signal. it can. The resistor 13 also limits the amount of gas generated on the penetration detection electrode 6 by limiting the current flowing at the time of penetration, and prevents troubles and the like due to the generated gas.

(Experimental Example 1) An experiment was conducted under the following conditions using the apparatus shown in FIG. 1 (however, a voltmeter was connected instead of the comparator 8). Workpiece: 0.2 mm thick Pyrex glass Tool electrode: Copper pipe for electrical discharge machining with an outer diameter of 0.2 mm Tool electrode pressing force: 8 g Penetration detection electrode: φ0.3 mm × 3 mm platinum wire Resistance: 10 kΩ, 100 kΩ, 1 MΩ, 10 MΩ Electrolyte: NaNO ₃ aqueous solution with a specific gravity of 1.20 Processing power supply: DC constant voltage of 50V

First, an experiment was conducted for the above-mentioned four types of resistance values inserted between the penetration detecting electrode and the auxiliary electrode while changing the processing time, and attention was paid to the voltage of the penetration detecting electrode with respect to the tool electrode. The time until a sharp voltage drop is observed varies, but if machining is stopped immediately after a voltage drop is seen, the machining hole penetrates and machining is stopped before a voltage drop is seen. Confirmed that the processed hole did not penetrate.

As an example of the voltage change when the resistance value is 1 MΩ, the penetration detection electrode voltage with respect to the tool electrode shows 47 V at the beginning with respect to the machining voltage of 50 V, but 5 V after the start of machining.
It drops sharply to 30V or less in 6s and then fluctuates after that for 15s in 75s.
It dropped to about 10V at V and 90s. It is considered that this is because the current flowing through the machined hole increases as the machined hole becomes larger, resulting in a larger voltage drop due to the resistance. It may be possible to use this to control the size of the processed hole on the outlet side. In addition, the current value flowing in this case is 50 V / 1 MΩ = 50 μA at the maximum, which is very small. When the processing was stopped for 2 min15s and the size of the processed hole was measured, a mortar-shaped through hole with a diameter of 0.8 mm at the inlet and a diameter of 0.3 mm at the outlet was formed.

Next, when the resistance value was changed to 10 kΩ, the voltage was initially 49 V, but a phenomenon in which the voltage suddenly dropped was observed 120 seconds after the start of machining in this case, and dropped to about 40 V. After that, however, the voltage rose and recovered to nearly the original 49V. This is because the electric current (maximum value is 50V / 10kΩ = 5mA) flowing through the penetration detection electrode generates gas (oxygen in this case) due to electrolysis at the penetration detection electrode, which covers the surface of the penetration detection electrode or generates gas. The cause is considered to be blocking the processed hole. In the case of 10 kΩ, it is difficult to see the correlation between the voltage and the size of the hole, but it is possible to detect the penetration of the machined hole. Machining was stopped at 150s, and a hole size of φ0.75mm at the inlet and φ0.25mm at the outlet was obtained.

When separately processed under the same conditions as above,
Penetration of the machined hole was detected at 60s. Machining was stopped in the same 150s as above, and the hole diameter was measured.
m was 0.3 mm at the exit. This is because, even if the processing time is the same, if the processing speeds (time until penetration) differ due to various causes, it is considered that the hole diameter of the outlet will be different because the processing time after penetration will differ. It suggests that it is necessary to detect the penetration of the machined hole to control the hole diameter.

FIG. 2 shows the relationship between the machining time after penetration and the exit hole diameter. However, a needle was used as the tool electrode, and the tool electrode pressing force was 12 g and the resistance was 1 MΩ. The time taken for the machined hole to penetrate varies from 59s to 85s, but a good correlation is obtained as shown in Fig. 2 when arranged by the machining time after penetration.

(Experimental Example 2) Under the same conditions as in Experimental Example 1 above, when a pulsed power source (on time: 50 μs, off time: 5 μs) of the same voltage (peak value: 50 V) was used as the processing power source, the penetration The time is about 25s, and the processing speed is considerably improved. Since the exit hole diameter at the time of penetration is kept almost the same,
Considered to be more advantageous than DC power supply. The exit hole system has a high expansion speed as shown in FIG. 3, reflecting the fact that the processing time after penetration is high. As for the effect of the pulse power source, it is considered that the impact force is generated due to the pulsed gas generation.

[0017]

EFFECTS OF THE INVENTION A conventional machined hole in which a large area penetration detecting electrode is connected to the same polarity as a tool electrode and a relatively large current value flowing between the penetration detecting electrode and a long distance auxiliary electrode is measured. In contrast to the detection device, in the processed hole detection device of the present invention, a penetrating detection electrode having a small area is connected to an auxiliary electrode through a resistor having a high resistance value, and a minute current flowing between the penetrating detection electrode and a tool electrode close to the auxiliary electrode. The change in voltage of the penetrating detection electrode due to the change in is detected. In this way, since the penetration detection current flows between the penetration detection electrode and the tool electrode immediately above it, the detection sensitivity is good, and the detection current value can be suppressed to mA or less, so the amount of gas generated from the penetration detection electrode is extremely small. Can be made smaller. Therefore, it is possible to make the adverse effect of the generated gas extremely small. Further, because of the high sensitivity, the penetrating detection electrodes need only a small area, and the penetrating detection electrodes can be arranged closely when processing a plurality of holes at the same time. Although a non-dissolving material such as platinum must be used as the material of the penetration detecting electrode, since the penetration detecting electrode itself may be small, there is almost no cost problem.

[Brief description of drawings]

FIG. 1 is a structural explanatory view of a machined hole penetration detection device.

FIG. 2 is a graph showing a relationship between a processing time after the processing hole is penetrated and a processing hole diameter.

FIG. 3 is a graph showing the relationship between the processing time after the processing hole is penetrated and the processing hole diameter.

[Simple explanation of symbols]

 1 Processing Hole Penetration Detection Device 2 Container 3 Electrolyte 4 Workpiece 5 Tool Electrode 6 Penetration Detection Electrode 7 Auxiliary Electrode 8 Comparator 11 Table 12 Processing Power Supply 13 Resistance

Claims (2)

[Claims] 1. When machining a through-hole in a non-conductive material by utilizing discharge in an electrolyte, a through-detection electrode connected to an auxiliary electrode via a resistor is provided below the workpiece, It is characterized by electrically detecting that the machined hole has penetrated the workpiece by a voltage change between the tool electrode and the penetration detection electrode caused by a minute current flowing between the penetration detection electrode and the tool electrode through the hole at the time of penetration. Method for detecting penetration of machined holes. 2. A penetration detecting device for a processed hole, which detects penetration of the through hole when a through hole is processed in a non-conductive material by utilizing electric discharge in an electrolyte solution. A tool electrode and an auxiliary electrode are provided, a penetration detection electrode is arranged to face the tool electrode across a workpiece, and the auxiliary electrode and the penetration detection electrode are connected via a resistor. A machined hole penetration detection device.