JPS6363329B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new electric discharge machining method for machining a narrow and deep hole by vibrating a cylindrical long electrode in contact with a workpiece under light pressure.

Conventionally, when performing drilling or other processing on an insulating workpiece such as glass, an electrode is brought into vibrating contact with the workpiece, a conductive working fluid such as an electrolyte is supplied, and a pulse discharge is performed. Methods of processing are known. The discharge voltage in this case is a high voltage, and machining is mainly performed using an arc, resulting in poor machined surface roughness and accuracy.

In addition, the machining of small holes with a large shape ratio L (depth)/Dφ (hole diameter) of around 1 mmφ or less by electric discharge machining can be performed using, for example, drawing dies, diesel engine fuel injection nozzles, synthetic fiber nozzles, or wire cut electric discharge machining. Although it is widely used in a wide variety of applications such as preparing holes in workpieces, it is one of the so-called difficult processes in electrical discharge machining (for example, Yoshihiro Iizuka's ``Small hole machining by electrical discharge machining'' Electric discharge machining technology Vol4No.1
(1961), a pipe-shaped material such as a copper pipe or a syringe needle is used as an electrode, and the machining liquid is jetted from the electrode side (in some cases, it is sucked).Also, it is possible to drill a smaller diameter hole into the electrode workpiece. (Since it is difficult to perform jet flow or suction from the lower hole on the side of the workpiece.), the machining speed increases significantly, and a machining speed of 3 to 5 times can be obtained. (For example, "Electrical Discharge Machining Technology Handbook" edited by the Electrical Discharge Machining Technology Study Group, p. 323, Nikkan Kogyo Shimbun, December 20, 1963).
There is no doubt that it is a difficult process that requires various measures depending on the situation, and that it is always a problem that the process takes too much time compared to the scale of the process.

Therefore, the machining fluid in this type of electrical discharge machining is used to maintain insulation in the discharge gap, generate and extinguish the discharge, cool the electrode, workpiece, and gap, and reduce the explosive force in the discharge gap. It is necessary to maintain the generation of kerosene and to discharge machining debris and gas from the discharge gap.In the area of drilling and die-sinking, mineral oil-based oils, mainly so-called kerosene (white kerosene) , Class 4, Class 3 petroleum), but in wire cut electrical discharge machining, water or an aqueous system containing water as the main component is used, and in electrical discharge cutting machining, water glass or water with an inorganic electrolyte added is usually used. Conventionally, ^{electrolytic solutions such} as As wire-cut electrical discharge machines that use water-based machining fluids mainly composed of water (such as additives may be present) have become popular, the drilling and die-sinking fields have also become more environmentally friendly. From the viewpoint of hygiene and disaster prevention, there is a need for a processing machine that uses the above-mentioned water-based liquid as a processing liquid.

For this reason, various proposals have been made regarding water-based machining fluids, such as the
- Items other than Publication No. 16480, related to the setting of pulsed power supply and power supply conditions for machining (for example, 2 Kimoto et al., "Study of underwater electrode low consumption electrical discharge machining": Journal of the Society of Electrical Machining Engineers,
Vol1.No.2P43-50, etc.), but it has not yet appeared as a general-purpose practical machine.

On the other hand, there are various methods for supplying machining fluid in the above-mentioned drilling and die-sinking type electrical discharge machines, such as jet flow, suction, reciprocating movement of electrodes, or a combination of these. The hydraulic pressure of the machining fluid newly supplied to the discharge gap for removal and renewal of the machining fluid is usually around several kg/cm ² or less at most (for example, the pressure of the machining fluid newly supplied to the discharge gap for removal and renewal of the machining fluid, etc. 362 pages, “Theory and Technology of Electrical Discharge Machining”, edited by the Kansai Branch of the Japan Society of Electrical Machining Engineers, No. 131
~132 pages, Yokendo Co., Ltd., November 15, 1971)
This was in good contrast to the high-pressure machining fluid jet method used in electrolytic die engraving in the field of electrical machining technology.

Most importantly, according to research on high-speed electrical discharge machining, especially "Improvement of machining speed in electrical discharge machining using high-speed liquid flow" (Suda Soto, Journal of the Society of Electrical Machining Vol. 4, No. 7, pages 1 to 10), the machining fluid is made of conductive powder. (#400 Graphite) 2g/
The machining power source is a no-load voltage of 43V, which is full-wave rectification of single-phase commercial AC, using a water-based machining fluid consisting of mixed tap water.
The average machining current is 130 to 400 A (current density approximately 10 to 32 A/cm ² ), which is a special case where the electrode machining feed is manual, but the discharge gap flow velocity of the machining fluid is approximately 5 to 20 m. /sec (approximately 5 to 25/min), and after that, ``Prototype of high-speed electrical discharge machining machine'' with automatic electrode feed without mixing the above-mentioned conductor powder (2 people outside Suda, 1971 Spring Conference of Japan Precision Machinery Society) Academic Lecture Preprint, pp. 357-358), such high-speed rough machining is useful for machining small holes with an electrode diameter of approximately 1 mmφ or less, and also for shape ratios L/D≒ It is not yet clear whether it can be applied to processing pores of around 10 or more.

In addition, the dimensions and shape of the electrode, the size of the discharge gap, and the flow rate of the machining fluid described in these documents,
According to the flow rate, the fluid pressure at the inlet of the discharge gap of the machining fluid (tap water x 10 ³ Ωcm order) sent by the pump is lower than 10 Kg/cm ² , and the pump pressure is approximately
Estimated to be 10Kg/ ^cm2 .

Furthermore, as a method of high-speed electrical discharge machining, electrolytic discharge machining methods in which electrical discharge machining is performed at the same time are being researched. It is described in the academic lecture preprint, pp. 437-438, "High-speed drilling of steel by electrolytic discharge machining," 1972 Japan Society of Precision Machinery Spring Conference academic lecture preprint, pp. 415-416, and approximately 10 mm/min. High-speed machining of 40mm/min to 40mm/min is carried out using a machining fluid with a high pressure of approximately 10Kg/ ^cm2.The machining fluid is approximately 20% salt water, and the power source is approximately 50V, which is half-wave rectified commercial alternating current. The voltage and current density are approximately 300 to 800 A/cm ² , and it is not yet clear whether such high-speed rough machining methods can be applied to fine machining.

Therefore, in Japanese Patent Application No. 54-144117 (Japanese Unexamined Patent Publication No. 56-69033), the applicant of the present invention has developed a technique for machining the electric discharge machining gap formed by opposing a rod or cylindrical electrode and a workpiece. Intermittent voltage pulses are applied between the two with a liquid jet intervening, machining is performed by the generated electrical discharge, and a feed that corresponds to the progress of machining or a constant speed feed is applied relatively between the two to generate an electrical discharge. In the object to be processed, the electrode has a thin rod shape with a diameter of around 1 mmφ or less, and a pore with a shape ratio L/D (L: depth of the processed hole, D: diameter of the processed hole) of at least 5. During machining, an aqueous machining fluid containing water as a main component is used as the machining fluid, and the electrical discharge machining is performed in a state in which the aqueous machining fluid is supplied and ejected into the machining gap at a high pressure of at least 20 kg/cm ² or more. A method of electrical discharge machining is presented.

The present invention was made as a method for processing small holes with an L/D of 5 or more, which is extremely difficult to process, and was made for the purpose of improving processing speed, processing accuracy, etc. .

Conventionally, when performing electric discharge machining on conductive workpieces,
Since a constant discharge gap between the electrode and the workpiece with a highly insulating machining fluid interposed therebetween was used to repeatedly generate pulse discharges between the two, the voltage pulses supplied from the machining power source were applied to the opposing gap. The electric discharge is activated by dielectric breakdown of the intervening insulation processing fluid,
In addition, in order to maintain the discharge for a predetermined period of voltage pulse width, a high voltage of about 100V or more was required. For this reason, even if the width of the voltage pulse is controlled, there is little improvement in the machined surface roughness, a large amount of energy is consumed to start the discharge, and the discharge is often obstructed by the influence of machining debris, etc., so it is necessary to increase the machining speed. I couldn't do it.

The present invention was proposed in view of these points, and uses a low-insulating machining fluid mainly composed of water, and pressurizes the machining feed while applying high-frequency vibration to the electrode. The lightly pressurized contact state between the electrode and the workpiece is oscillatedly separated by the applied high-frequency vibration, and a voltage pulse whose no-load voltage is sufficiently lower than 100 V is applied between the electrode and the workpiece to discharge the object. It is something to be processed.

The present invention will be explained below with reference to the drawings. Reference numeral 1 denotes a pipe electrode for machining small and deep holes, and is fixed to a chuck 4 at the tip of a horn 3 at the tip of a vibrator 2. 5
6 is a cylinder that supports the horn 3; 6 is a piston inserted into the cylinder; 7 is a motor that feeds the piston 6; 8 is a pressure spring inserted between the piston 6 and the cylinder 5; 9 is a workpiece. 10 is a pump that pressurizes and jets machining fluid into the machining gap via the pipe electrode 1; 11 stores machining fluid mainly consisting of water, such as distilled water or water treated with ion exchange resin; 12 is a processing power source that supplies a processing voltage pulse with a no-load voltage sufficiently lower than 100 V between the electrode 1 and the workpiece 9, and 13 is a high frequency power source that excites the vibrator 2.

The vibration by the vibrator 2 is 5KHz to 100KHz, and is propagated to the electrode 1 via the horn 3.
Further, by controlling the feed of the piston 6 by the motor 7, the pressure of the spring 8 acts on the horn 3 through the cylinder 5 and is applied to the electrode 1, so that the electrode 1 is moved to the workpiece 9.
On the other hand, even if the machining liquid jetting the electrode cannot directly push it up, it can act as a pushing force to a considerable extent, for example, with an outer diameter of 1 mmφ and an inner diameter of 0.8 mmφ.
When machining fluid is supplied between the 120 mm long electrode 1 and the workpiece 9 at a pump pressure of 40 Kg/cm ² , it is approximately 50 gf.
In this contact state, high-frequency vibration is applied by the vibrator 2, and the tip of the electrode 1 causes contact/separation vibration with respect to the workpiece 9.
That is, contact and separation will be repeated. A pressurized jet of a low-insulating machining fluid mainly composed of water is supplied from a pump 10 to the machining section of the electrode 1 and the workpiece 9 that vibrate when contacting and separating, and a no-load voltage of 100 V is applied thereto from a machining power source 12. A machining voltage pulse sufficiently lower than that is supplied, and intermittent pulsed discharge is performed. Discharge mainly occurs when the electrodes 1 contact and then separate due to high-frequency vibrations, and of course can also occur when they approach each other, and since the vibrations are high-frequency and have minute amplitudes, the discharge may be interrupted even when they separate. Therefore, the discharge with a predetermined pulse width is stably performed. Since high-frequency vibration is applied to the electrode 1, the movement of the discharge point is extremely good even when pressurized feed is applied to maintain a light pressurized contact between the electrode 1 and the workpiece 9.
Furthermore, since the no-load voltage of the machining voltage pulse is low due to the low insulation resistance of the machining fluid, machining can be stably continued in a transient arc discharge state. The no-load voltage of the voltage pulse is usually around 5V, but in some cases, the no-load voltage of the voltage pulse is about 5V, because it does not require a voltage to start the discharge in the gap and maintain the discharge during that time, as in conventional electrical discharge machining using a machining fluid with high insulation resistance. can be made at a low voltage of about 15 to 20V, and because it is processed at such a low voltage, short circuits do not cause large currents to flow.
The machined surface does not become rough and can be machined with high precision. Unlike conventional electrical discharge machining, it is not necessary to maintain a constant gap, and there is no interference with electrical discharge due to machining debris, etc., so machining progresses stably and Speed increases significantly.
Machining chips can be easily washed away by the disturbance effect caused by electrode vibration and by the jet of machining fluid from the pump 10, allowing machining to proceed at high speed. The motor 7 is driven to follow the progress of machining,
By feeding the piston 6, the pressure of the spring 8 can be kept constant, and a constant light contact pressure state can be maintained between the electrode 1 and the workpiece 9. Therefore, the electrode 1 penetrates deeply into the workpiece 9 as the machining progresses, and the electrode 1 is machined by pulsed discharge while repeating moderate contact and separation due to the interaction of constant pressure and vibration. Holes can be easily drilled through the hole in a short time.

Although it is possible to use an insulating oil such as kerosene as the machining fluid supplied from the pump 10, the use of a machining fluid that is mainly water, such as water treated with ion exchange resin, can reduce the risk of fire. In addition, there is no electrolytic action, and the processing speed is further improved.

Next, to provide an example, when drilling a hole in WC-CO carbide material using a Cu pipe with a diameter of 0.5 mmφ as an electrode, the tip of the electrode is brought into contact with the workpiece under light pressure. Vibrates at 28KHz and 20W. Water with a specific resistance of 10 ⁴ to ^{10 5} Ωcm is used as the machining fluid.
A jet is generated from the electrode pipe by a pump.
A low voltage pulse with a no-load voltage of 35V was used as the machining power source, and electrical discharge machining was performed at an average machining current of 4A. At this time, extremely high-speed processing with an electrode penetration speed of about 8 mm/min was achieved. The electrode consumption ratio was about 3%.

Note that there is no need to synchronize the vibration of the electrode and the supply of machining voltage pulses, but if the contact-release vibrating electrode contacts the workpiece, it can be switched on and machining pulses are applied, and each pulse will generate the discharge starting voltage. Since stable discharge can be performed at a low voltage without the need for a machining power supply, a lower no-load voltage is better.

Furthermore, in the above embodiments, the high-frequency vibration is applied directly to the electrode, but it is also possible to apply vibration to the supplied machining fluid and apply vibration to the electrode. For example, if high-frequency vibration is applied to the pressurized machining liquid jetted from the electrode pipe at a supply part such as a pump discharge part, the jetted liquid will vibrate the lightly pressurized electrode from the contact area between the tip of the electrode pipe and the workpiece. The liquid is ejected in a pushing-up manner, and the action of pushing up the electrode pipe becomes vibratory, so that the electrode vibrates as a result, and the tip of the electrode comes into contact with and separates from the workpiece.

As described above, the present invention is a contact electrical discharge machining method that uses a water-based, low-insulating machining fluid that is completely different from conventional electrical discharge machining. By vibrating contact and separation with the workpiece, the discharge caused by each applied voltage pulse is easily activated, and the no-load voltage and discharge sustaining voltage of the voltage pulse can be extremely low, allowing machining to be performed with less interference from machining debris etc. It stabilizes the pores and enables high-speed, high-efficiency electrical discharge machining. Furthermore, by pressurized jetting or suctioning the machining liquid from the jet hole provided in the electrode or the workpiece, machining debris is washed away and removed, allowing for highly efficient through-hole machining, such as when machining narrow and deep holes. be able to.

[Brief explanation of drawings]

The drawing is an explanatory diagram of an embodiment of the processing method of the present invention. 1... Electrode, 2... Vibrator, 3... Horn, 7
... Feed motor, 8 ... Pressure spring, 9 ... Workpiece, 10 ... Pump, 12 ... Processing power supply.

Claims (1)

[Claims] 1 A voltage pulse is applied intermittently between the elongated cylindrical electrode and the conductive workpiece, with a jet of machining fluid interposed in the discharge machining gap formed by facing each other, and machining is performed by the generated discharge. In electrical discharge machining of small and deep holes by relatively applying feed according to the progress of machining, a low insulating machining fluid mainly composed of water is used as the machining fluid, and a high frequency is applied to the electrode. In a state where vibration is applied, the lightly pressurized contact state between the electrode and the workpiece caused by pressurizing the machining feed is vibrationally separated by the applied high-frequency vibration, and a gap is created between the electrode and the workpiece. A method for electric discharge machining of a small hole, characterized in that electric discharge machining is performed by applying the voltage pulse with a no-load voltage sufficiently lower than 100V.