JPH09239622A - Aerial electric dischage machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accelerate machining speed without wearing electrodes by injecting pressure gas containing gas chemically reacting with workpieces as machining medium in the gap between the electrode and the workpiece so that it is forcibly made to flow in an approximately cross direction. SOLUTION: The pressure gas sent from a chuck section or the like into an electrode cylinder is injected so that it is forcibly made flow in the cross direction of the face to be machined which has a thin wall thickness of approximately 0.05 to 3mm from the gap between the face to be machined in the machining area of the workpiece, and discharges the fused machining chips produced due to electrical discharge and chemically reacts with the machining chips and in addition, cools the area to be machined while pulsed voltage is not applied. The workpiece 9 can be given translation motion or vibration motion whose radius is the same as the wall thickness of the electrode 1 or less in addition to the rotation relative to the electrode 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric discharge machining method and a device therefor which are useful as a die machining method and the like.

[0002]

2. Description of the Related Art EDM differs from ordinary machining in which mechanical force is directly applied to a workpiece to perform machining, and a dwell time is provided in a gap between the workpiece and a machining electrode in which a machining fluid intervenes. It is known as a non-contact processing method that applies a voltage pulse placed and uses the discharge phenomenon that occurs at that time, and as the processing method and device, there is a hole or die using a rod-shaped or formed electrode as the processing electrode. So-called ram-type electric discharge machining that performs engraving, wire-electric discharge machining that performs wire saw-shaped cutting using wire electrodes that are continuously renewed and fed in the axial direction as the machining electrodes, and recently, the ram-type electric discharge machining described above. A rod-shaped electrode having a relatively simple shape is used as the machining electrode for the machining, and the machining is performed by relatively moving the machining electrode in a direction perpendicular to the facing direction over the desired machining area to machine the cavity of the surface and the desired shape. Processing method and the like are well known.

In each of the above-described machining processes, a working fluid such as a mineral oil-based working fluid or a water-based working fluid is usually used as a discharge medium in the discharge gap which is always formed with a fine gap between the machining electrode and the workpiece. As an intervening or distribution intervening. The role of the machining fluid in electrical discharge machining is to cool the discharge column from the surroundings and suppress expansion, increasing the discharge energy density, increasing the explosive impact force generated, and scattering the molten material at each discharge point of the electrode and the workpiece. And increase the dispersion of metal vapor and metal melt. In addition, the machining liquid rapidly cools and solidifies machining scraps generated and scattered from the electrode and the workpiece by electric discharge,
The particles are prevented from adhering to the electrode / workpiece, the movement of the machining waste is facilitated, the discharge is generated, the movement of the discharge point is promoted, and the discharge gap length is increased. In addition, depending on the cooling action and the combination of the working fluid used, the electrode, and the work piece, pyrographite produced by decomposition of the working fluid is attached to the working surface of the electrode to prevent or reduce the consumption of the electrode.
Then, mainly during the discharge pause period between voltage pulses, the liquid flow discharges some or more of processing dust, tar, gas, etc., caused by processing and decomposition, to the outside of the discharge gap, and based on the application of the next voltage pulse. The discharge generated in the gap is made normal, and the intended machining action is continued.

Therefore, the inventors of the present invention have been invited to the 1992 Precision Engineering Society Spring Conference Academic Lecture Meeting (1992).
March 25, 2013, See P281
Under the heading "Effect of machining fluid flow between H21 electrodes on EDM characteristics and electric discharge column", the positive polarity of steel to steel It was reported that low consumption machining can be performed by machining, and the present inventor then announced that the Electrical Processing Society of Japan National Convention (1994) (1994
(Refer to P. 35 of the lecture papers on May 18th, referred to as Reference 2 below)
Under the heading "[11] Observation of dispersion of machining chips in single-shot discharge", re-attachment of work chips to the workpiece in the air in single-shot discharge, pulse width of 100 μS
The volume of machining waste generated for (microseconds) or more does not differ much from the case of in-liquid discharge, so even in air machining, as long as the machining waste is discharged outside the discharge gap, normal liquid machining It has been reported that there is a possibility that processing can be performed in the same manner as in the above, and the 1995 Japan Society for Precision Engineering Spring Conference Academic Lecture (1993).
In the collection of lecture papers, P957, March 28, 2013, referred to as Reference 3 below), under the heading "G62: Difference in electrical discharge machining characteristics in air and liquid," The wear of the tool electrode is not seen regardless of the pulse width in the flexible machining, the machining amount increases as the thickness of the electrode is thinner, and the short circuit is more frequent than the submerged machining, and it prevents the short circuit. Reported that it is effective to add rotation and oscillation to the electrode.

The results of the research and development as described in Documents 1 to 3 above are the results of the air discharge machining as referred to in those documents.
In order to replace it with a part of the conventional submerged electrical discharge machining and to introduce it as technology and products that can be industrially used,
There were still various problems.

[0006] Thus, the conventional air discharge machining is disclosed in Japanese Patent Publication Nos. 46-43, 760 and 47-.
Processing stainless steel spinneret orifices, such as those described in US Pat. No. 3,078, was conducted by continuously directing a gas stream containing at least 21%, preferably at least 35% of available oxygen into the area of the spark discharge. Machined by wire electrical discharge machining in gas, by a direct current power supply with positive polarity connection, or by an alternating current power supply of 700 Hz or less to discharge between a tungsten wire electrode and a base, or Japanese Patent Publication No. 52-11,0
No. 73, No. 57-4,451, etc., in which an electrode and a workpiece are opposed to each other in an atmosphere depressurized to atmospheric pressure or less, and pulse discharge is performed between the electrodes, or Further, wire electric discharge machining is performed in a machining liquid spray airflow (Japanese Patent Publication No. 57-4,451), and electric discharge machining is performed while gas is allowed to flow through a discharge gap immersed in the machining liquid (Japanese Patent Publication No. 39-39-39). No. 1,494, No. 40-27,425), and a method in which electric discharge machining is performed while a machining fluid in which gas is mixed in a bubble state is circulated through an electric discharge gap (Japanese Patent Publication No. 39-29,615). However, none of them seems to be in practical use today.

Therefore, the present inventor further researched and developed, and as a result, the National Convention of Electrical Processing (1995) (November 1995)
(Refer to P129 on the 1st of the month, P129, referred to as Reference 4 below)
Under the heading "[22] Study on improvement of machining speed in air electric discharge machining", in air electric discharge machining as reported in the above-mentioned reference 3, "i) supply air pressure If the supply air pressure is too high, the air volume between the poles will be too large and the machining speed will be reduced due to the arc column sliding on the work piece, and if the supply air pressure is too low, , It becomes difficult to discharge the machining waste, the short-circuit rate increases, and the machining speed decreases because the ratio of the machining waste adhering to the workpiece increases. Ii) The application of high (electric) pressure weight causes a wide gap between the electrodes. Machining becomes possible, effective discharge frequency increases, and it is effective in improving machining speed.iii) Even in mid-air machining, by devising the tool path, 3
It is possible to perform the three-dimensional shape creation processing without (electrode) consumption. In addition, the 1995 Japan Society for Precision Engineering Autumn Meeting Academic Lecture Meeting (1995
September 29, 2013, See P311, Proceedings, below 5
Under the heading "K02 Mechanism of electrode wear-out in air electric discharge machining", "Results of investigating factors of tool electrode wear-out in air by experiments and heat conduction analysis ... i) Copper of the tool electrode material is machined to 2 μm immediately after the electric discharge, and the machining does not proceed. Steel of the workpiece material adheres to the tool electrode immediately after machining, and the adhesion layer thickness is about 8.5 μm within 1 minute. Ii) The influence of the adhesion of steel on the molten state of the copper tool electrode is large, and if the adhesion is 3 μm or more, the copper part of the tool electrode is not removed at all thereafter. Iii) Workpiece adhered to the tool electrode When the time-varying simulation of the adhesion layer thickness was performed, it was qualitatively consistent with the experimental result. "

[0008]

As a result of continuing research and development after that, the present inventor has almost completed one method and apparatus for air electric discharge machining which seems to be practical. The present invention has been proposed. That is, the electrode consumption and machining speed problem mainly in the finishing machining area of the ram type electric discharge machine which uses the mineral oil type machining fluid as the current machining fluid, and the fire decree of this kind of electric discharge machine and the government ordinance and rules concerning dangerous materials. The problem is to solve.

[0009] In electrical discharge machining (hereinafter, unless otherwise specified, "electrical discharge machining" refers to a ram type electrical discharge machine for drilling and die cutting using a mineral oil-based machining liquid. ) When machining in a machining area where the discharge energy per discharge pulse is small and the machining surface roughness is small, so-called positive polarity machining in which the machining electrode is the negative electrode is often used in terms of machining performance. However, there is a problem in that the shape is difficult to obtain even if a complicated and time-consuming machining operation such as translational (or swinging) machining is adopted with a single machining electrode. Also, there is a section that the processing speed in the processing area of the finishing processing conditions is slow and it takes a long time, but there is no need to compare with other processing methods, etc., and the processing speed can be improved. It was what was desired.

Regarding the current electric discharge machine (both the ram type and the wire type), as already mentioned,
The apparatus is generally composed of an electric discharge machine main body, a machining power supply device and a control device, and a machining liquid circulating treatment supply device. Of these three parts, a machining liquid-related device is the cheapest. The use of the working fluid has caused various problems and problems in the installation and use of the electric discharge machine. As is well known, the processing liquid circulation processing supply device is a processing liquid storage tank such as a cleaning tank or a pollution tank, a filtering device for removing processing waste, one or more circulation, pumps such as pumping, a temperature of the processing liquid such as a cooler. Control device, piping and switching, control valve, detection and fire extinguishing device for disaster prevention when the working liquid is mineral oil, ion exchange and control device and supply and treatment of added organic matter when water-based working liquid It is a high-priced product that is made up of devices and the like and requires a considerable amount of floor space, and requires a considerable amount of labor for maintenance and management. Therefore, although the supply of the working fluid during operation, in which it is circulated and supplied to the processing tank by purification or the like, and is circulated through while maintaining an appropriate processing waste concentration in the processing gap of the processing portion, is usually mineral oil. Lamb-type electric discharge machines that use a system-based machining fluid are subject to installation areas and regulations for installation and handling in accordance with the Fire Service Act and governmental regulations and regulations regarding dangerous materials, depending on the amount of machining fluid used and the amount of storage. It tends to be strengthened.

[0011]

SUMMARY OF THE INVENTION The above-mentioned object of the present invention is as follows.
(1) The machining electrode and the object to be machined are opposed to each other with a minute machining gap therebetween, and the machining feed and the feed positioning can be controlled so that the machining gap is relatively close in the opposing direction, and the machining medium is circulated in the machining gap. Intermittent voltage pulses are repeatedly applied between the electrodes and the object to be processed by turning on and off the electronic switch element by controlling the DC voltage source between the electrodes, and the intermittent voltage pulse is repeatedly applied to generate a discharge by the generated discharge. In an electric discharge machining method for machining a machined body, a machining surface of the machining electrode facing the body to be machined has a thin wall width of approximately 0.05 to 3 mm and a length greater than the width in a direction intersecting with the width direction. A machining surface that extends over the entire length of the machining electrode, or a machining surface that can oppose a part of the machining surface of the machining area of the machining object. Almost uniform with the work surface With the above-described fine machining gap formed, a pressurized gas containing a gas that chemically reacts with the workpiece material is injected into the machining gap as a machining medium so that it is forcedly circulated in the width direction. And intervene, and the relative rotation between the electrode and the work piece about the axis in the substantially opposite direction and the relative translation of the fine stroke in a direction substantially perpendicular to the axis in the opposite direction. Both or any one of the movements is applied, and the punching is performed by the machining feed in the facing direction while the discharge is performed by the applied voltage pulse, or the workpiece at a predetermined cut amount position in the facing direction. In the air-electric discharge machining method according to (2), the work piece is processed by providing an air-electric discharge machining method in which the facing portion of the electrode machining surface with respect to the machining area is sequentially moved for machining. Chemical reaction with wood By using oxygen as the gas, or (3) in the method of the electric discharge machining in the above (1), the pressurized gas containing the gas that chemically reacts with the workpiece is compressed air, preferably compressed air. Is compressed gas that is richer in oxygen than air, or compressed oxygen.
(4) In the air-electric discharge machining method described in (1), (2), or (3), the pressurized gas is applied to the machining gap at a pressure of at least 0.05 MPa and 1.0 MPa or less. By supplying the pressurized gas, in the air discharge machining method according to (5), (1), (2), (3), or (4), 20 in the processing gap
m / s to 250 m / s, preferably 50 m / s to 2
In addition, by making the medium flow through at a flow velocity of 00 m / s, (6) above (1), (2), (3), (4),
Alternatively, in the air-electric discharge machining method according to (5), the gas that chemically reacts with the workpiece material is heated and melted by the average discharge power under the set machining conditions, and further melted and scattered. By controlling the supply amount according to the amount of the work material, (7) the above (1), (2), (3),
In the air-electric discharge machining method according to (4), (5), or (6), the workpiece is an iron-based alloy containing iron as a main component,
The processing electrode is a copper-based or copper-based alloy electrode containing copper as a main component, and is a combination processing of workpiece materials,
(8) The above (1), (2), (3), (4), (5),
In the air electric discharge machining method according to (6) or (7),
By making the processing electrode a rod-shaped electrode having a thin wall thickness or a cylindrical body or a cylindrical body, (9) the above (1),
In the air electric discharge machining method according to (2), (3), (4), (5), (6), (7), or (8), a pause between the machining electrode and the workpiece. The intermittent pressurizing voltage pulse applied at a certain time is configured so as to perform the electric discharge machining as the positive polarity with the working electrode as the negative electrode.
0) The above (1), (2), (3), (4), (5),
In the air electric discharge machining method described in (6), (7), (8), or (9), the electric discharge power supplied with a pause between the machining electrode and the workpiece is Load voltage is 100V
By providing the main processing pulse power source having a low front and rear voltage and a large discharge current and at least one auxiliary pulse power source having a high no-load voltage of 200 V or more and a small current capacity, the power is supplied in parallel. , Better achieved.

[0012]

According to the air-electric discharge machining method of the first aspect of the present invention, a machining fluid and its circulation are required, though a control and supply device for a pressurized gas containing a gas that chemically reacts with a workpiece is required. Air-electric discharge machining that does not require a processing and feeding device can be performed in a stable state at a machining speed of a certain level or more over a certain width of rough, medium, and finishing machining areas.
It becomes possible to continue the processing, and it becomes possible to reliably and repeatedly perform the surface processing and the desired cavity processing on the object to be processed, and the boring processing to a certain depth. According to the air electric discharge machining method of the second aspect of the present invention, the machining speed of the air electric discharge machining according to the first aspect can be remarkably improved. According to the air-electric discharge machining method of the third aspect of the present invention, the machining speed of the air-electric discharge machining according to the first aspect can be reliably improved and the machining can be reliably continued.
According to the air-electric discharge machining method of the invention of claim 4,
In this way, the electric discharge machining according to claim 3 can be reliably performed under suitable machining conditions. According to the aerial electric discharge machining method of the fifth aspect of the present invention, the aerial electric discharge machining according to the fourth aspect can be performed under better machining conditions. According to the air electric discharge machining method of the sixth aspect of the present invention, the air electric discharge machining according to the fifth aspect can be performed in a better machining state. According to the air electric discharge machining method according to the invention of claim 7, the air electric discharge machining according to claim 6 is put into practical use as machining of an iron material mold or the like using a machining electrode made of copper or a copper alloy. You will be able to serve. According to the air electric discharge machining method according to the invention of claim 8, the air electric discharge machining according to claim 7 is applied to punching of a workpiece, and desired cavity machining such as surface machining or progressive scanning generation machining. Can be reliably processed as continuous processing. According to the air-discharge processing method according to the invention of claim 9, the air-discharge processing according to claim 8 can be performed without electrode wear or low wear even in the processing conditions of finishing. You will definitely be able to do it. According to the air electric discharge machining method according to the invention of claim 10, the air electric discharge machining according to claim 9 is performed in a more stable state by widening the machining gap, reducing short circuit discharge, and generating effective discharge. The processing can be performed, and the processing can be surely completed as intended.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of the overall configuration of an embodiment for carrying out the air discharge machining method of the present invention, in which 1 is a cylindrical machining electrode, 2 is an electrode chuck, and 3 is a spindle main shaft. Rotating device for rotating the electrode 1 around a central axis or a desired bias axis, 4 is a machining head, 5 is a feed screw, 6 is a DC or AC servomotor for machining feed and positioning of the machining head, and 7 is the servomotor. 6, a feed position (current position) of the tip of the electrode 1 is detected, and a detection signal is supplied to a CNC control device which will be described later. A rotation speed detecting device such as a finger speed generator or an encoder for detecting and supplying a detection signal to the CNC control device, 9 is a workpiece, 10
Is a machining table on which the workpiece 9 is installed, 11 is an xy cross table on which the machining table is placed, and 12 and 13 are positions for feeding and positioning the machining table 10 through the cross table 11 in the xy axial directions. Machining feed and positioning servomotors for xy axes (not shown) of the detection and rotation speed detection device, 14 is a drive device for each of the servomotors 6, 12 and 13, and 15 is a CNC control device for electric discharge machining. Reference numeral 15A is a computer, 15B is an input device such as a keyboard, 15C is an external storage device such as a paper tape, a magnetic tape, a floppy disk, or a compact disk for electric discharge machining data and programs.
5D is a numerical controller, 16 is a pulse power source for electric discharge machining which supplies intermittent voltage pulses between the machining electrode 1 and the workpiece 9, 17 is a DC voltage source, 18 is an ON / OFF electronic switch element such as FET. , 19 are connected in series with the switching element 18 and the voltage source 17, and are used to detect the current amplitude of the discharge pulse by the FET.
A current limiting resistor that is switched and set with the number of parallel connections of
Is a voltage pulse condition setting device for selectively switching the ON time τON and the OFF time τOFF of the electronic switch element 18 with a signal from the CNC controller 15, 21 is a reverse voltage prevention diode, 22 is the electrode 1 / workpiece 9 A device for detecting an electric discharge machining state of a machining gap between them, 23 is an air compressor or a compressed or liquefied gas cylinder or a combination thereof, and a compressed gas supply device containing a gas that chemically reacts with a workpiece material, and 24 is required. An air dryer for removing water vapor, which is provided accordingly, 25 is a decompression adjusting valve for the compressed compressed gas.

FIG. 2 is an enlarged side view of the electric discharge machine section shown in FIG. 1, and is similar to that shown in FIG.
6, a processing waste processing nozzle 28 that scatters or removes the processing waste of the processed part 9 of the workpiece, and an xy cross table 1
1 is a diagram in which a base 27 for installing 1 and the like are additionally illustrated.

3A to 3I are front views of electrode tips showing examples of tubular shapes of the tubular machining electrode 1, wherein A is a cylindrical electrode.
B is a polygonal electrode, C is a rectangular electrode, D is a triangular electrode, E is a flat rectangular electrode, and one side portion 1A is made of an insulator. Ribs that intersect in the radial direction may be provided.
Further, F is a cylindrical electrode in the case where a portion having a predetermined arc length at predetermined arc intervals is made of an insulator, and the like, the rotation around the central axis and the translation (swing) movement of a small radius in both directions or Although it can be applied to the surface processing or the sequential scanning generation processing of the object to be processed in the state where either one of them is given, in the case of drilling or digging, the cylindrical electrode except for the cylindrical electrode E is processed. Since the unprocessed core of the processed body may be present and it may be difficult to continue the processing, in the case of processing such as perforation, for example, a flat rectangular shape G, a semicircular shape H, and an oblong shape I are used. Such a cylindrical electrode may be used and rotated about the x mark in the figure. The processing surface of the axial tip of the processing electrode 1 is
The work piece 9 has an outer shape and a shape that can face each other in a normal part of the work area 9 and rarely in most of the work area, and the work surface has a thin thickness width when viewed locally. The machined surface is formed so as to extend over a length that is several times the width or more in the direction intersecting the width direction, and is fed into the electrode cylinder from the chuck portion 3 or the like as shown in the drawing. The pressurized gas is approximately the above-mentioned processing surface from the gap between the processing surface of a part of the processing region of the processing object 9 and the electrode processing surface whose placement is controlled so as to form a substantially uniform fine gap as a whole. In the above-mentioned width direction, the molten machining scraps that are jetted so as to be forced to flow in the width direction and discharged and discharged are discharged and cleaned, and also chemically react with the external machining scraps and the melted portion. The area will be cooled.

The air discharge machining method of the present invention will be described with reference to FIGS. 1 to 3 as described above. As shown in FIG. 3, the machined surface has a thin and thick width, and preferably, a pressurized gas is used as a machining medium. In order to discharge the products such as processing chips that are melted and scattered by the discharge pulse to the outside of the processing gap,
And a gas that chemically reacts with the workpiece material that is contained in the pressurized gas at a predetermined ratio in part or more by chemically reacting the discharge melting part of the workpiece and the processing dust that is melted and scattered, such as nitriding or nitriding. To increase the processing amount and reduce the re-welding of processing scraps to the electrode / workpiece, it is composed of a normal cylindrical body through which a pressurized gas as the processing medium is passed at a predetermined high speed in the width direction. The machining electrode 1 is attached to a machining head 4 which is gripped by a chuck 2 and is servo-mechanically fed by a Z-axis servomotor 6 or is positionally fed by a rotary drive device 3 so as to be rotated as necessary. The workpiece 9 attached to the table 10 is opposed to the workpiece 9. On the other hand, if necessary, the workpiece 9
Alternatively, the machining of the electrode 1 is configured so that a translational movement or a swinging movement whose radius is equal to or less than the wall thickness of the electrode 1 can be given by the drive control of the x and y axis servomotors 12 and 13 along with the rotation with respect to the machining electrode 1. As for the surface, the compressed gas supply device 23 is configured such that each part maintains a state in which a substantially uniform fine gap is formed and maintained between the surface and the work surface of the work body 9.
The pressurizing gas supplied from the above is set in a state in which it can be flown and jetted uniformly from each part of the fine processing gap, and the processing control feed is performed by the servo motor 6 in the Z-axis direction for drilling, or in this state. Is a servo motor 12, which is a portion of the electrode processing surface facing the processing area of the workpiece 9 in the xy plane direction,
13 In-air electrical discharge machining is performed by electric discharge generated based on intermittent voltage pulses applied between the machining electrode 1 and the workpiece 9 while maintaining the state regardless of sequential movement such as scanning by control drive. It is a thing. The machining pulse power supply 16 used in the air-electric discharge machining of the present invention may preferably be provided with one or more auxiliary power supplies of a certain type as described later, but is basically not provided. The reverse voltage prevention diode 21, the current limiting resistor 19 and the on / off electronic switch element 18 are connected to the DC voltage source 17 whose load voltage is about 60 to 120 V, that is, about 100 V, and which can be set to switch the voltage as required. With a normal machining pulse power supply, which is configured so that any desired number of series circuits can be connected in parallel and connected in series via a machining gap, the voltage pulse ON time or discharge pulse duration τON The voltage pulse condition setting device 20 for setting the voltage pulse pause time τ OFF and the current limiting resistance switching device 19 for setting the discharge current amplitude Ip are connected to the input device 15B in the CNC control device 15.
The computer 15 calculated based on the input machining command and machining information from the computer and various read data for machining performance, machining conditions and machining program creation from the storage device 15C.
Set by the processing condition setting command output of A, and NC
The control device 15D is provided with an operation control command such as the size and shape of a hole to be machined in the workpiece 9, the locus of scanning, the Z-axis position of the electrode 1, and the feed.

Hereinafter, the air discharge machining method of the present invention will be described with reference to experimental examples. The following experimental conditions and evaluation items are defined as described below unless otherwise noted. Machining Electrode Material: Copper Shape, Dimension: Outer Diameter φ8.61 mm, Inner Diameter φ8.0 mm Workpiece Material: Steel S45C Machining Amount = Pre-machining Workpiece Weight-Post-working Object Weight (g) Machining Electrode Consumption ＝ Machining electrode weight before machining-Machining electrode weight after machining (g) Machining speed = Machining amount / Machining time (g / sec) Machining electrode consumption rate = Machining electrode consumption amount / Machining amount x 100 (%) Machining amount per discharge = Machining amount / effective discharge number (g / shot) Effective discharge frequency = Effective discharge number / Processing time (1 / sec) Short circuit rate = (Total discharge number-Effective discharge number) / Total discharge number x 100 (%) Effective discharge The number is a short-circuit detection circuit that takes the logical product of the presence or absence of the current sensor output signal of the discharge circuit and whether the detected discharge voltage is above a certain threshold value. The effective discharge was counted by the counter. As a processing mode, the above-mentioned cylindrical processing electrode is
Rotation (180 rpm) with respect to the work electrode in the axial direction opposite to the work piece, and translational motion or rocking motion in the xy plane direction with respect to the work piece with respect to the work electrode (radius: about 10% of pipe electrode wall thickness) While giving both or either of
With the Z-axis position of the machining electrode fixed, the workpiece is moved back and forth while performing the desired stroke length in the y-axis direction and servo control in the x- and y-axis directions, and at both ends of the y-axis stroke. Then, the processing electrode is fixed in proximity to the surface of the object to be processed by a predetermined cut amount in the opposite Z-axis direction. In such electrical discharge machining in the air, the discharge start gap length of the machining gap in which the pressurized gas circulates at a fairly high speed (gs: first when the machining electrode is fed close to the surface of the workpiece) Is about 5 μm / 100V or less, and there is a rest time, for example, a duty factor of about 70% and a voltage pulse of a set machining condition is applied to the air discharge. The average machining gap length (gm) during machining differs depending on the set machining conditions, but seems to be considerably larger than the above-mentioned discharge start gap length, but the generated machining debris restrains movement in the machining medium in the machining gap. It seems that it is considerably smaller than the average machining gap length of machining in the machining liquid which is suspended and floats and intervenes in the machining gap together with the machining medium. Thus, the above-mentioned depth of cut means that the machining electrode is fed to the surface of the work piece in the proximity of the work piece, and the machining surface of the electrode tip is roughly fed to the surface position of the work piece before the work piece is fed. When the electric discharge is continued for a certain amount, the z-axis is reached when reaching the other y-axis end and folding back, with the aim of the machining depth of the electric discharge machining under the set machining conditions or a length shorter than the machining depth. The depth of cut is set.

In order to confirm the effectiveness of the air discharge machining using a pressurized gas that chemically reacts with the material to be processed, argon, nitrogen, air, etc. were used as the pressurized gas as the processing medium.
Further, the electric discharge machining was performed under the following conditions in oxygen and the electric discharge machining liquid (kerosene), and the results shown in FIGS. 4 and 5 were obtained. Experimental machining conditions Discharge current amplitude Ip (A) 20 No-load voltage (V) 280 Applied machining voltage polarity PL Positive polarity Discharge pulse width τ ON (μS) 20, 350, and 1000 Duty factor (%) 71 Swing radius (μm) 30 Pressurized gas supply pressure (MPa) 0.3 Depth of cut (μm) 5 (however, τON: 20 μS) 15 (however, τON: 350 and 1000 μS) FIG. 4 shows the type of pressurized gas used and processing conditions. In the comparison chart of the processing speeds due to the difference, there is no processing result when the argon gas is used when the pulse width is 20 μS, because the processing could not be performed under the setting processing conditions of the pulse width. According to the figure, oxygen (O2, air is about 21% oxygen and about 7%) as a gas that chemically reacts with the workpiece material (iron: Fe).
When it is supplied with (8% nitrogen), the processing speed is the highest, and in the region near the finishing processing with a pulse width of 20 μS, it is about 10 times higher than in liquid processing and several times higher than in air. On the other hand, it can be seen that the inert gas (which does not chemically react with the material to be processed) argon can hardly be processed. This is because when the pressurized gas of the processing medium is oxygen and air containing 21% oxygen, the workpiece material melted by the electric discharge explosively burns due to the oxidation reaction, and the reaction heat generated thereby causes the workpiece to be processed. It is considered that the processing speed was increased because the melting region of the body was further expanded. Further, it is considered that the smaller the generated machining waste is, the larger the surface area is with respect to the same machining waste volume, so that the chemical reaction with the supply gas such as oxidation is promoted. It can be useful. On the other hand, in the case of nitrogen, since it has a certain degree of reactivity with iron of the workpiece material, and the nitride has high hardness and wear resistance, it is expected to be used as surface treatment as well. However, it is considered that the chemical reaction between nitrogen and iron, which is the material to be processed, is as vigorous as that of oxygen and does not generate reaction heat, so that the fusion zone does not expand and the processing speed does not increase. Further, in the case of argon, the processing amount is only the processing waste blown away by the argon gas flow to the outside without being reattached to the surface of the object to be processed in the processing gap. It is recognized that there is very little even under the processing conditions of. The above-described tendency and state of the machining speed are in agreement with the result of collation by obtaining the machining amount per discharge from the machining data obtained as described above. The machining mechanism of the method is not only due to the fact that the melted portion of the machining gap is blown away by the discharge shock and the pressurized gas flowing at high speed, but the workpiece material in the discharged portion of the workpiece is more than a part of the supplied pressurized gas. It can be seen that the chemical reaction with is greatly affecting the processing result. Therefore, in the air electric discharge machining method of the present invention, in order to enhance the efficiency of machining, the gas that chemically reacts with the workpiece material is heated and melted by the average machining electric discharge power under the set machining conditions, Furthermore, it seems that it is preferable to adjust the supply amount according to the amount of the work material to be melted and scattered, and as a method for this, the ratio of the gas that chemically reacts with the work material in the supplied pressurized gas Is increased like an oxygen-rich gas, or the gap flow rate or flow velocity of the pressurized gas is increased within a range where the arc column does not slip from the gap due to movement or the like. When the pulse width of the above processing conditions is 350 μS, the discharge current amplitude Ip is 60 A.
However, the increase in processing amount when using argon and nitrogen is 2
~ 3 times, about 20% increase for air, about 60 for oxygen
%, But in the case of in-liquid processing, processing stability is poor and about 1
It decreased to / 8. FIG. 5 is a comparison diagram of the machining electrode wear rate during the above-described machining. According to this data, the electrode wear rate of the machining electrode in the case of air and oxygen is extremely small regardless of the pulse width τON. , And oxygen is less than in the case of air, whereas in nitrogen and argon, the working electrode consumption rate increases as the pulse width increases, and in the case of argon, the rate of increase is high, and the discharge current amplitude is 6
When it was set to 0 A, all the components except nitrogen increased, oxygen was about 40 times, argon was about 16 times, nitrogen was unchanged, air was about 25 times, and liquid was about 19 times. Next, the pulse width τON
When the surface to be machined of the object to be machined at 350 μS and discharge current amplitude Ip of 20 A was observed, a resolidification layer was formed in layers on the surface to be machined in the case of liquid and nitrogen. It was found that a large number of holes were formed in the layer, and that many reattachments involving gas such as melt-processed dust were involved, but in the case of oxygen, formation of a resolidified layer was hardly seen. In any case, according to the air electric discharge machining method of the present invention, there is almost no wear of the machining electrode in the area of the finishing machining with a large pulse width τON, which has a large electrode wear in the conventional ordinary electric discharge machining. It is recognized that there are excellent features to say.

Then, in the report of the above-mentioned reference 1 which is the initial stage of the development of the air discharge machining method of the present invention, steel (S45C) is used for both the positive and negative electrodes and a pressurized air flow is made to flow. It was suggested that the possibility of low-consumption (electrode) low-consumption machining with positive polarity was caused by the discharge of. Then, the present inventor, as reported in the above-mentioned Document 3, has a positive electrode in a liquid and in an air (in a combination of a copper electrode and a steel workpiece, which is a combination of a normal electric discharge machining electrode and a workpiece ( Pressurized air), pulse width is 20
In the machining from μS to 2500μS, the electrode wear rate is a large wear rate with a small pulse width and a small wear rate with a large pulse width, which is conventionally known in the submerged machining, whereas It was confirmed that there was almost no wear of the machining electrode over a range of small to large pulse widths, and that there was no electrode wear or low wear machining due to the positive polarity under the finishing conditions.
Then, at the same time, in the case of air electric discharge machining which is the object of the present invention, the melt or machining waste generated by the electric discharge between the electrode and the workpiece is cooled as compared with the case of submerged machining. Since it is slow, the electrode and the work piece can be easily discharged outside the work gap without reattaching to the facing work gap surface between the electrode and the work piece, and also for the forced discharge action. In order to increase the area of the machined surface of the machined surface of the machined gap formed opposite to each other, that is, to increase the area of the machined surface to a certain extent or more, it is most preferable in the width direction of the machined surface having a thin thickness. Since the value differs to some extent depending on the processing conditions and is within the diameter of the discharge arc column which is larger than that in the liquid, or within several times of the diameter, the processed surface intersects with the width direction within a range where there is no problem in strength. Desired to be several times larger than the width in the direction It is preferable to form it so as to extend over the length, and in order to promptly discharge the processing waste etc. out of the processing gap, a processing medium such as air having a chemical reaction with the object to be processed is processed. Since it is preferable that the machining electrode is circulated in the width direction of the machined surface where the flow passage is shortened in the gap, the machining electrode is a cylindrical body having a thin wall thickness and a fine gap between the machined surface and the machined surface. And pressurizing gas of the processing medium is ejected from the cylindrical electrodes opposed to each other to an annular processing gap such as an annulus of the surface to be processed, and further generated processing waste and the like. In order to prevent the redeposition of
Relative rotation about an axis in a substantially opposite direction between the electrode and the workpiece and / or relative translational movement or oscillating movement of a minute radius or stroke in a direction substantially perpendicular to the opposite direction axis. It is preferable that the electric discharge machining is performed in a state where one of them is applied.

The above will be described below with reference to experimental data. Experimental processing conditions No-load voltage (V) 280 Applied voltage polarity In-liquid reverse polarity In-air positive polarity Discharge current amplitude Ip (A) 20 Voltage pulse width τ ON (μS) 20, 60, 210, 350, 1000, 1500, 2000, And 2500 Copper pipe electrode inner diameter (φ mm) 8 Copper pipe electrode wall thickness width (mm) 0.3, 0.5, 1.0, 3.5, and 5.0 Rotation speed (rpm) 52 Translation (swing) Movement diameter (mm) 10% of wall thickness Processing medium Liquid kerosene: No jet flow Pressurized gas Air: 0.5 MPa

FIG. 6 shows the machining amount per discharge pulse (mm ³ ) and the discharge pulse width of each machining in liquid and in air using a copper pipe electrode having a wall thickness width of 0.3 to 5.0 mm. In the compressed air jet (hereinafter referred to as "in the air"), the machining amount is proportional to the discharge pulse width, whereas in the liquid, the discharge pulse width τON ≈ 1000 μS Even with a thick copper pipe electrode, it is proportional to the pulse width τON, but 1
When it exceeds 000 μS, the processing amount of the one having a large thickness width decreases. This is probably because as the wall thickness of the pipe electrode becomes thicker and thicker, the machining gap during electrical discharge increases the proportion of time it is included in the decomposed bubbles of the machining fluid, and the state of the machining gap approaches the state of air discharge. Be done.

FIG. 7 shows the relationship between the wall thickness of the pipe electrode and the machining amount when the discharge pulse width τON is 350 μS. The machining is performed as the wall thickness of the pipe electrode becomes thinner in both air and liquid. Although the amount increases, the rate of change is larger and exponential in the case of air than that of liquid. At a wall thickness of 0.3 mm, the processing amount in air is larger than in liquid. The reason is that the air jet jet oxidizes and further nitrids the melted portion in the air, Becomes almost the same as the diameter of the arc column of the discharge, making it difficult for re-adhesion of molten processing waste to the processing surface etc., and most of the molten portion is blown away and removed by the air jet. On the other hand, it is considered that the removal rate of the melted portion may decrease due to the high cooling rate, partly because there is no jet in the liquid. Further, such a relationship between the wall thickness width of the pipe electrode and the processing amount showed the same tendency in other regions where the discharge pulse width is small and where it is larger.

In FIG. 8, the wall thickness of the pipe electrode is 0.3.
It shows the relationship between the discharge pulse width τON and the electrode wear rate (%) when the value is mm. In the air, there is no wear of the machining electrode over the entire discharge pulse width τON, or there is very low wear. On the other hand, in the submerged processing, the generally known tendency of electrode consumption is in agreement, the pulse width τON is small, and the consumption rate is remarkably increased.
The principle of low electrode consumption in submerged machining is explained by the adhesion of carbon to the electrode machining surface, but in air discharge machining of the present invention,
There is no carbon, and the low or no consumption phenomenon is considered to be due to the adhesion of the workpiece material to the electrode processing surface, as described later.

FIG. 9 shows a wall thickness of the pipe electrode of 3.5 m.
The discharge pulse width τON and the short-circuit rate (%) at m were examined, and the difference was more remarkable in the air than in the liquid, and the smaller the pulse width τON, the more remarkable the difference. This is because in air discharge machining in which machining chips are discharged by a high-speed air jet, the machining gap length often becomes a value close to the discharge start gap length (gs≈5 μm), but there is no jet flow. It is considered that in the submerged machining, the generated machining chips are restricted by the machining liquid, the concentration of the machining chips in the machining gap is high, and the machining gap length is large. Therefore, when the influence of the application of the rotation and the translation (oscillation) motion to the electrode in the aerial working was examined in relation to the above short-circuit rate, it was as shown in FIG. That is, both the rotation and the translational (oscillation) motions are effective in reducing the short-circuit rate, and the effect is high particularly in the region where the pulse width is small,
Also, it is understood that the simultaneous application of both is more effective. From the above, the size of the thickness width of the working electrode of the present invention is
At most about 3 mm or less, preferably 1-2 mm or less,
The optimum value is equal to or smaller than the diameter of the arc discharge column during air discharge (around 200 μm (= 0.2 mm) with a discharge current amplitude of 20 A and a discharge pulse width of 20 μs), although it differs depending on the pulse conditions. It is about 2.0 times, but about 0.05 mm or more, preferably 0.1 mm or more and 1 mm, which does not cause problems in mechanical, thermal strength, discharge power supply, and the like.
It is better to do the following. The jet pressure of the pressurized gas is at least 0.05 MPa or more, preferably 0.08 to 0.
1 MPa or more and 1.0 MPa or less, preferably 0.5 MPa
It is preferable that the pressure is not more than MPa.

Next, in order to clarify the mechanism and the cause of no electrode wear in the method of air discharge machining of the present invention,
Experiments and heat conduction analyzes have been performed, which will be explained. 11A is an explanatory view of the side of the electrode / workpiece part of the experimental method, FIG. 11B is an explanatory view of the production of the measurement sample of the measuring method, and C of FIG. 11 is the removal depth and the adhesion layer in the measuring method. It is a side section explanatory view of thickness. Experimental processing conditions Electrode (copper, mm) 10 × 10 × 20 Workpiece (S45C, mm) Inner diameter φ5, outer diameter φ10 Cylinder No load voltage (V) 280 Voltage pulse width (τON, μS) 20 Duty factor (%) 71 Discharge current amplitude (A) 20 Translational (vibration) radius of motion (mm) 0.5 Under the above conditions, machining with machining time changed from 0 to 400 sec, the copper portion of the electrode (copper) at different machining times When the removal depth and the thickness of the adhered layer of the steel workpiece material on the electrode processing surface were measured, the results shown in FIG. 12 were obtained. This FIG.
According to the above, the copper-worked surface of the electrode (copper) was once machined to a depth of about 2 μm (removal depth from the copper-copper reference surface) within an extremely short time from the start of air discharge processing. After that, the processing does not proceed, while the steel of the workpiece material adheres to the electrode processing surface immediately after the processing is started, and within about 1 minute, the adhesion layer thickness becomes constant at about 8.5 μm, that is, It was found that the peeling and removal of the portion and the re-deposition of the same amount as the removed amount were repeated, and if the thickness of the adhesion layer was about 3 μm, as a result, the processing without electrode consumption was continued. .

The electrode model described above is applied to a processed electrode having a high thermal conductivity such as copper, and a workpiece material (steel) having a higher melting point than the electrode.
In the state where a substance with a high melting point is attached to the surface, the unsteady heat conduction analysis of the electrode when a single discharge is generated is performed to investigate the influence of the attachment.
Analysis was performed using the axial symmetry model under the boundary conditions shown in FIG. In FIG. 13, a calculation area of 650 μm in the radial direction and 345 μm in the depth direction is divided into 40 × 60 meshes, and the size of the mesh is 3 from the center in the radial direction.
5 μm up to 0 mesh, 50 μm thereafter, 1 μm from the machined surface to 45 mesh in the depth direction,
After that, the thickness was set to 20 μm. In this analysis, heat of vaporization and heat of fusion were taken into account, and the diameter of the arc column immediately after the dielectric breakdown was single-discharged using the pulse width as a parameter.
The diameter of the generated discharge mark was made equal to the diameter of the arc column, and the change was obtained. The effect of the adhesion of steel is reflected in the analysis by using the value of steel as the thermophysical property value of the mesh corresponding to the adhesion layer of steel, and the thermophysical property value at the boundary between steel and copper is Harmonic mean was used. The following are the conditions for analysis. Thermal conductivity W / (m · K) Copper 398 Steel 53 Specific heat J / (kg · K) Copper 386 Steel 460 Density kg / m ³ Copper 8880 Steel 7870 Fig. 14 shows the analysis results with the discharge pulse on the vertical axis. 2 shows the relationship between the discharge elapsed time and the melting depth from the surface including the adhesion layer of the material steel to be processed on the processed electrode processing surface. As can be seen, when the workpiece material is not attached (C
u-all) is 14 μm at maximum 5 μsec after the start of discharge.
After melting to the depth of 10 μsec
After that, it has not melted. This is because the heat flux input to the surface of the copper electrode decreases as the arc column expands, the surface temperature decreases, and the solidification again occurs. On the other hand, when all the electrodes are made of steel (Fe-all), no peak is seen unlike copper, and there is a tendency for the peak to gradually increase even after 10 μsec. This is because steel has a higher melting point and lower thermal conductivity than copper. Next, paying attention to the case where the workpiece material adheres to the surface of the copper electrode, the thickness of the adhered layer is 1 μm (Fe-al
In l), the effect is not so different from the case of no adhesion, but the effect of adhesion appears when the thickness of the adhesion layer is 3 μm or more. For example, if there is an adhesion layer of 3 μm in the vicinity of 5 μsec immediately after the dielectric breakdown, the copper portion melts at the boundary between the steel adhesion layer and the copper portion because the melting point of copper is low, but the steel adhesion layer melts only 2 μm. No, the remaining 1 μm steel part is the solid phase and the molten copper part is not removed. Therefore, considering that only the melted portion on the surface is removed, there is no adhesion layer (Cu-
In the case of all), 14 μm is removed, but if there is an adhesion layer of 3 μm, the steel is removed by 2 μm from the surface, and the copper portion is not removed. Further, as the thickness of the adhesion layer becomes thicker, the melting depth also becomes deeper, but it is understood that no depth of the adhesion layer is more than the thickness of the adhesion layer. Therefore,
Even if it melts because the melting point of copper is low at the boundary between the steel adhesion layer and the copper part, the copper part will not be consumed, and the adhesion of the workpiece material will have a large effect on the machining electrode wear. It became clear.

By the way, it is assumed that the deposition of steel and the removal of the electrode material (steel or copper) proceed simultaneously in one discharge pulse. In actual continuous discharge, discharge is generated at a certain point on the surface of the machining electrode, and discharge is generated again at all the other surfaces, and then again generated at that point. In the process of repeating such a cycle, the recession of the copper surface and the growth of the steel layer at the point of interest can be simulated. The basic simulation within one discharge pulse was performed as follows. First, the discharge pulse width of 20 μsec is divided into eight steps. Then, within each time step, it is considered that the workpiece material is first attached to the electrode and then removed by the melting depth shown in FIG. The thickness of the adhered workpiece material is considered to be X% of the depth at which the workpiece melts at that time using the result of Fe-all in FIG. By repeating the above with respect to the electric discharge that occurs at the point of interest, the time change of the surface state of the processing electrode during processing can be obtained. FIG. 15 shows the result of calculation of the value of X described above for three ways of 25, 50, and 75. In the figure, the time from the end of the discharge at the point of interest to the discharge at all other points and returning to that point again is omitted,
The time variation of the surface condition of the electrode is shown continuously. As can be seen, the adhesion layer thickness does not exceed a certain value at any X value. On the other hand, looking at the removal depth of the copper part,
When the X value is 75, there is no removal of copper. Although it is removed at 25 and 50, it can be seen that the removal is performed only at the first discharge and not thereafter. The qualitative agreement between the simulation result and the measurement result of FIG. 12 confirms that the cause of no consumption of the machining electrode in air machining is the steel of the workpiece material that adheres to the electrode. As described above, since the machining electrode 9 can be processed without wear, the machining electrode 9 is
As described with reference to FIGS. 1 to 3, it is desirable to use a thin-walled and thick-width tubular body. However, as shown in E and F of FIG. If necessary, a part or more of it is a high resistance body or an insulator 1A made of ceramics or a rigid resin having a certain degree of heat resistance or a composite material.
Even if it is composed of, the electrode 1 is rotated or translated (swing).
By performing machining while moving, air discharge machining can be continued.

As described above, the relationship between the short circuit rate and the discharge pulse width τON in FIG. 9 and the effect of rotation and oscillation on the short circuit rate in FIG. 10 have been pointed out. As a pressurizing gas containing a gas that chemically reacts with the workpiece material instead of the conventionally used machining liquid,
With positive polarity machining, there is no wear or low wear of the machining electrode over the entire range from small to large discharge pulse width τON, especially in the finishing machining condition area where discharge pulse width τON is small, and the machining speed is also high. Although it is faster than submerged machining, not only is the discharge start gap (gs) length smaller than in liquid, but the average machining gap length (gm) during machining is the same as when machining in liquid. It is considered to be considerably small because the amount of dust and the like staying in the machining gap is small, and it is almost in agreement with the experimental data that the short circuit rate is high in the air discharge machining of FIGS. 9 and 10 where the discharge pulse width τON is small. are doing. For this reason, therefore, in the above-mentioned 2-3 experimental examples, the no-load voltage shown in FIG.
The most normal type intermittent main voltage pulse power supply for turning on / off the electronic switching device 18 in which the direct current voltage source 17 of about 0 V is connected via the current limiting resistor 19 and the reverse voltage prevention diode 21 Auxiliary power supply composed of a high voltage (280 V) direct current high voltage source having a small normal current capacity or a high voltage voltage pulse power source having the high voltage source synchronized with the voltage pulse of a normal type main pulse power source or having an appropriate phase difference By using the machine with the above, the average machining voltage is increased to widen the average machining gap length without reducing the discharge repetition frequency between the electrode and the workpiece as much as possible, thereby reducing the short circuit rate and effective discharge. The processing of the present invention is performed by increasing the frequency, and one auxiliary power supply of high voltage as described above according to FIG. 16 and additionally a supplementary power supply of higher voltage are additionally provided. Shows an embodiment of a valid discharge machining pulse power supply with the law. In the figure, reference numeral 16 is a normal main power supply circuit for generating and supplying a voltage pulse for machining a rectangular wave which is the most usual and has a regular rest time, and which is usually a no-load voltage of about 60 to 120 V. In contrast to the provision of the DC voltage source 17, the first auxiliary power source 32 has a DC high voltage source 32A having a voltage capacity of about 280V and a small current capacity, a reverse voltage prevention diode 32B, a current limiting resistor 32C, and an electronic switch element. Open / close switch 3 for 32D series connection circuit
3 is configured to be connectable in parallel to the main power supply circuit 16, and the electronic switch element 32D is synchronized with the switch element 18 of the main power supply circuit 16 by the pulse condition setting control device 20 or has an appropriate phase difference with an appropriate pulse width. A high-voltage small-current voltage pulse is supplied to the machining gap to increase the average machining voltage of the machining gap, thereby making it possible to perform electric discharge machining in the air while maintaining a wide machining gap length. In addition, 30 is a gap parallel resistance, 31 is a polarity switcher, and is set to a positive polarity at the time of the air electric discharge machining of this invention. In the above-mentioned air-electric discharge machining provided with the first auxiliary power supply 32, the short-circuit rate is considerably high as already seen in some experimental examples. Therefore, the second auxiliary power supply 34 of higher voltage is additionally provided. And processed.
That is, a series connection circuit of a direct current high voltage source 34A having a small current capacity of about 500 V with no load voltage, a reverse voltage prevention diode 34B, and a current limiting high resistance 34C is connected in parallel to the machining gap via the open / close switch 35 and is turned on. The off electronic switch element 34D is connected in parallel to the series circuit of the voltage source 34A and the high resistance 34C, and the electronic switch element 34D is connected to the switch element 18 of the main power supply circuit 16 by, for example, an opposite phase by the pulse condition setting control device 20. On / off control is performed to apply a higher voltage pulse to the machining gap to increase the average machining voltage of the machining gap, and a servo control device (not shown) based on detection from the machining gap by the machining state detection device 22. By increasing the detection voltage supplied to the machine, it becomes possible to machine in the state where the machining gap length is expanded, and the machining performance of air discharge machining is improved.

FIG. 17 and FIG. 18 show that in the air-electric discharge machining of the present invention, in order to improve machining performance such as machining speed, the chemical reaction such as heat generation with the workpiece material is not excessive or insufficient, or preferable machining is performed. The amount of gas that causes a state, that is, mainly the flow rate and flow rate, and the amount of electric discharge machining dust that does not redeposit on the machining gap surface of the electrode / workpiece, and also depends on the thickness of the machining electrode. However, in order to know the supply pressure and the flow velocity of the gas that generate a physical and mechanical force preferable for discharging the machining waste to the outside of the machining gap without sliding the discharge column formed in the machining gap to the outside of the machining gap. , About 2 to 15 compressed air
Nl / min, ordinarily 3 to 10 Nl (however, Nl is a standard state, that is, a temperature of 0 ° C., a flow rate in which the pressure is converted to the atmospheric pressure), and the supply pressure is varied to supply and circulate. FIG. 9 is a characteristic curve diagram of the machining speed and the machining amount per discharge pulse with respect to the depth of cut (μm). Experimental processing conditions No-load voltage (V) 280, 500 Discharge current amplitude (A) 20 Discharge pulse width (μS) 350 Duty factor (%) 70 Translation (oscillation) radius of motion (μm) 30 Rotation speed (rpm) 180 Compression Air supply pressure (MPa) 0.1, 0.3, 0.5 In addition, the mode of processing such as electrodes / workpieces and notches is
As described above.

In the aerial processing, it is necessary to promote the removal of the molten portion between the electrodes by supplying compressed air between the electrodes. Therefore, it is considered that the stronger the air pressure supplied between the poles, the higher the processing speed. However, when the air flow velocity is too high, the arc column is caused to flow in the direction of the air flow and slides on the surface of the workpiece, so that the machining speed decreases. Therefore, the influence of the supply pressure was investigated by changing the supply pressure. FIG. 17 shows the result of the processing speed, and FIG. 18 shows the result of the processing amount per discharge. The plot of 0.1 MPa in the figure ends halfway because the machining becomes very unstable with a cutting depth larger than this and no subsequent experiments have been conducted. As can be seen from FIG. 18, the processing amount of 0.3 MPa is the highest, followed by 0.1 MPa, and 0.5 MPa.
Has been minimized. This is because when the supply air pressure is large, the flow rate of air flowing between the poles becomes excessive, the arc column is flown along the air flow, and the arc column slides on the work piece before the work piece melts sufficiently. Because. However, if the supply air pressure is too low, the air flow rate will decrease, and the amount of oxygen to be oxidized in the processing waste and the molten portion will be insufficient to accelerate the processing by the chemical reaction. If it is not removed and remains in the gap between the gaps, or even if it is removed from the gap between the gaps, the rate of redeposition on the upper surface of the work piece in the vicinity of the gap before the solidification of the machining increases. It is considered that the processing amount of is reduced. This is considered to be the reason why the processing amount of 0.1 PMa is smaller than that of 0.3 PMa when the depth of cut is large. From the above, it is considered that there is an optimum value for the air flow rate flowing between the poles, and in the above case,
0.3 MPa seems to correspond to this. Next, looking at the relationship with the depth of cut, it can be imagined that there is an optimum value for the depth of cut even with the supply air pressure. It is considered that this is because when the depth of cut is small, the gap between the electrodes becomes wide, the flow rate of the air flowing between the gaps becomes excessive, and the processing amount becomes small for the reason described above. In addition, it is generally known that the machining amount changes when the gap is widened.
Can be considered as one. Conversely, if the depth of cut increases,
It is conceivable that the air flow rate between the poles decreases due to the narrow gap between the poles, making it difficult to discharge the machining waste, and at the same time increasing the rate of reattachment of the machining waste, reducing the machining amount. FIG. 19 shows the result of the effective discharge frequency. As you can see,
At 0.5 MPa, the discharge frequency decreases as the depth of cut increases, but at 0.1 MPa and 0.3 MPa, there is a depth of cut that maximizes the discharge frequency. If the depth of cut is too large, the gap between the poles will become narrower and the flow rate of the air flowing between the poles will decrease.
It is considered that this is the reason why the discharge frequency decreases when the depth of cut is 20 μm or more. On the contrary, when the depth of cut is small, the gap between the electrodes is wide, and thus the discharge frequency decreases. FIG. 20 shows the results of the short-circuit rate, and it can be seen that the short-circuit rate increases as the depth of cut increases at any supply air pressure. It is considered that this is because the gap between the electrodes becomes narrower as the depth of cut increases.

The above is the first auxiliary power supply 3 in FIG.
FIGS. 21 to 23 show the results when the no-load voltage using 280 is 280 V, and the second auxiliary power source 34 is also used at the same time to set the no-load voltage to 500 V. In FIG. 21, it can be seen that the machining gap has spread the gap between them against the depth of cut. Fig.22 shows the result of machining amount per discharge. When high voltage is superposed, 0.3MP
While the processing amounts of a and 0.5 MPa are reduced to less than half of those before the superimposition, the degree of reduction is small at 0.1 MPa. It is thought that this is because the gap between the electrodes was widened by applying the high voltage in a superimposed manner, and as described in the previous paragraph,
It is considered that the air flow rate becomes excessive and the arc column slides on the work piece. FIG. 23 shows the result of the effective discharge frequency, which shows that the effect of high voltage superimposition appears regardless of the magnitude of the supply air pressure. Moreover, according to the waveform observation of the discharge voltage and the discharge current by the synchroscope, the delay time from the application of the voltage pulse to the start of the discharge is longer than that without high voltage superposition. It was confirmed that the machining gap was expanded by increasing the voltage and it was effective in reducing short circuits.

As described above, the air electric discharge machining of the present invention can be applied to drilling and hole drilling, but it is important to be able to perform three-dimensional shape forming machining in order to put such air electric discharge machining into practical use. Is. In the case of air processing, it is essential to flow air almost uniformly between the workpiece and the processing electrode. For example, when processing is performed using a cylindrical electrode, it is usually performed as shown in A of FIG. In the shape generation processing method, it is considered that there is no air flow on the side surface of the electrode where the electric discharge is generated and it is impossible to discharge the processing waste, so that the processing cannot be performed. Further, as shown in FIG. 9B, when rough cutting has already been completed and the finishing process is performed in the air,
The gap between the machining electrode and the work piece cannot be made uniform, and the supplied air escapes from the wide area between the gaps where discharge does not occur.
It is expected that machining cannot be performed because there is no air flow in the essential machining gap. Then, as shown in FIG. 6C, when a three-dimensional shape generating process was attempted by devising a machining electrode path that always machined at the end face of the electrode and with uniform electrodes, the supply air pressure was 0.3 MPa, The stroke depth is 10μ
25, the cross-section curve obtained as a result of processing as a concave truncated pyramid having a bottom of about 15 × 20 mm with other processing conditions as described in paragraph 0029 without superimposing a high voltage is shown in FIG.
It was shown to. The time required for processing was 84 minutes and 20 seconds, and the obtained processed surface roughness was Rmax of 10 μm. The wear rate of the processed electrode calculated from the cross-sectional curve in FIG. 25 was 0.62%, which was a very small result. Further, as shown in FIG. 25, the obtained angle is about 45 °, which is almost the same as that of the created program, which confirms the low consumption rate. From the above, it has been clarified that even in the three-dimensional shape creating process, the in-air process can be performed by devising the electrode path and can be the non-consumable process.

According to the present invention, in the aerial electric discharge machining method, according to the mechanism of electrode non-consumption that has been clarified up to now, the material combination of the machining electrode and the object to be machined is that the electrode is made of heat such as copper. It is premised that it has a high conductivity, and that the object to be processed usually has a chemical reactivity with a gas such as oxygen easily or at a high speed in a high temperature state of a molten state, or an electrode material. It is considered that a combination with an iron material such as steel having a higher melting point is more preferable, and from this viewpoint, it is preferable to use, for example, aluminum (Al) or an aluminum alloy as a processing electrode material for an iron-based workpiece. According to the report of the above-mentioned Document 1, the electrodes and the work piece are both made of steel by the electric discharge machining in the air flow.
Considering that it has already been reported that the electrode has low wear characteristics when it has a positive polarity, it is clear that the air-electric discharge machining of the present invention is promising.

In the processing method of the present invention, it is relatively easy to select and maintain the content ratio of the gas contained in the pressurized compressed gas that chemically reacts with the material to be processed, Further, the pressure of the compressed gas at the outlet of the pressure reducing valve and the flow rate at the outlet of the flow rate adjusting device, or as a result, the pressure and the flow rate of the supplied processing medium at the processing medium inlet of the cylindrical processing electrode, can be maintained at the set values relatively easily. Although easy, Z-axis servo control feed of rotating or oscillating electrode is used in drilling, and in so-called creation machining, even if the Z-axis is fixed after setting the depth of cut during electrical discharge machining, the machining feed direction is in the Y-axis 1-axis direction. On the other hand, since the servo feed control in the XY axis plane is performed, the diameter or outlet cross-sectional area of the outlet of a kind of disk-shaped nozzle of compressed gas from the machining gap is extremely small, but the change rate is considerably large. Constantly changing in The flow of compressed gas that passes through is large, and the range of changes in the state of contact with the processing waste and the molten portion of the surface to be processed is large, and the pressure, flow rate, and flow velocity of the pressurized gas flowing through the processing gap are fairly wide. It changes and the processing state changes,
The servo feed control needs to be precisely controlled with high speed response.

As the machining electrode, although the cylindrical body has a wall thickness of about 3 mm at the maximum as described above,
Therefore, the amount of processing gas used is about 2 to 15 N as described above.
l / min, and usually about 3 to 10 Nl / m
Since it is about in, the injection speed of the pressurized gas from the working gap is about 20 to 250 m / s, normally about 50 to 200 m.
It is considered to be within the range of about / s.

When performing the drilling or drilling by the air electric discharge machining method of the present invention, it is considered that the electrode is given a translational (swing) motion when the drilled hole becomes deeper, for example, about the electrode diameter or more. However, there is a possibility that it will be difficult to discharge the processing waste and it will be difficult to process, but in such a case, it is conceivable to turn the Z axis upside down as explained in the drawings and the like. As a method of supplying gas, for example, a compressor for supplying compressed air and an oxygen cylinder for supplying compressed oxygen may be combined to contain a desired proportion of oxygen or supply compressed gas. . The above 2
It is meaningless to say that the duty factor of the pulse width in each of the experimental examples (1) to (3) is about 70%, and the relationship between the duty factor and the machining performance is significantly different from the conventional empirical rule. There are few things, but in the case of processing using a pressurized gas containing a gas (oxygen) that chemically reacts with the workpiece material at a higher ratio, the increase of the duty factor is small and the pulse width is small. It was recognized that the rate of impact was large for speeding up and decreasing wear rate.

[0037]

As described above, although the air-electric discharge machining method of the present invention is still in the research and development stage, it has already been clarified that the conventional machining method has a slow machining speed and a large electrode consumption rate. In the machining of the finishing machining area, which has been regarded as a weak point of the electric discharge machining in liquid, there are restrictions on the machining method and mode, but the electrode is not consumed and machining can be performed at a high machining speed. In addition, a flammable machining liquid for conventional submerged electric discharge machining, which requires a gas that chemically reacts with the workpiece material, a pressure gas supply device containing the gas, a device for collecting and processing the machining waste, etc. In addition, it has many advantages by not requiring a circulating treatment supply device of machining fluid, and is convinced that it is a useful invention for opening a new page for electric discharge machining.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an overall configuration of an apparatus for carrying out an air-electric discharge machining method according to the present invention.

FIG. 2 is an enlarged side view of an electric discharge machine unit shown in FIG.

3A to 3F are cross-sectional views of different cylindrical electrodes.

FIG. 4 is a characteristic diagram of a machining speed with respect to a machining voltage pulse width in air electric discharge machining using different gases as machining media.

FIG. 5 is a characteristic diagram of a machining electrode wear rate with respect to a machining voltage pulse width, similar to FIG.

FIG. 6 is a characteristic curve diagram of each machining amount per discharge with respect to a machining voltage pulse width when electric discharge machining is performed in a liquid and in air with cylindrical electrodes having different wall thicknesses.

FIG. 7 is a characteristic curve diagram of a machining amount per discharge for machining in a liquid and in air for different wall thicknesses of a cylindrical electrode.

FIG. 8 is a characteristic curve diagram of an electrode wear rate with respect to a machining voltage pulse width of machining in liquid and in air by using a cylindrical electrode having a specific wall thickness.

FIG. 9 is a characteristic curve diagram regarding the short-circuit rate, similar to FIG.

FIG. 10 is a characteristic curve diagram relating to the influence of application of electrode rotation and translational (swing) motion on the characteristic of the short circuit rate with respect to the machining voltage pulse width.

11A, 11B, and 11C are explanatory diagrams regarding an experiment and a measuring method for measuring the consumption mechanism of the working electrode.

FIG. 12 is a characteristic curve diagram of an electrode removal depth and a work material adhesion layer thickness with respect to a discharge duration of a discharge pulse.

FIG. 13 is an explanatory diagram of an analysis model in heat conduction analysis of electrodes.

FIG. 14 is a characteristic curve diagram of melting depth with respect to discharge duration width of the analysis result.

FIG. 15 is a characteristic curve diagram of the electrode removal depth and the workpiece material attachment layer thickness with respect to the discharge duration width of the simulation result.

FIG. 16 is a wiring diagram illustrating a schematic configuration of an improved machining pulse power supply circuit used for carrying out the air discharge machining of the present invention.

FIG. 17 is a characteristic curve diagram of machining speed with respect to machining depth when different supply air pressures are set.

FIG. 18 is a characteristic curve diagram of the machining amount per discharge pulse.

FIG. 19 is a characteristic curve diagram of the same effective discharge frequency.

FIG. 20 is a characteristic curve diagram of the same short circuit rate.

FIG. 21 is a characteristic curve diagram of each processing speed when FIG. 17 and a high voltage pulse are superimposed on the processing voltage pulse power supply.

FIG. 22 is a characteristic curve diagram of the machining amount per discharge pulse when FIG. 18 and a high voltage pulse are superimposed on FIG.

23 is a characteristic curve diagram of FIG. 19 and the effective discharge frequency when a high voltage pulse is superposed on FIG.

24A, 24B and 24C are explanatory views of a processing method, and A and B
FIG. 3 is an explanatory view of a machining mode to which the air-electric discharge machining of the present invention is unsuitable, and C is a machining mode that is applicable.

FIG. 25 is a vertical cross-sectional explanatory view of a machining model machined by applying the air discharge machining method of the present invention.

[Explanation of symbols]

 1, processing electrode 2, electrode chuck 3, rotating device 4, processing head 5, feed screw 6, 12, 13, servo motor 7, encoder 8, rotational speed detection device 9, workpiece 10, processing table 11, xy cross Table 14, drive device 15, CNC control device 15A, computer 15B, input device 15C, storage device 15D, numerical control device 16, electric discharge machining pulse power source 17, DC voltage source 18, electronic switch element 19, current limiting resistor 20, Voltage pulse condition setting device 21, reverse voltage prevention diode 22, discharge state detection device 23, compressed gas supply device 24, air dryer 25, decompression adjustment valve 26, flow meter and flow rate adjustment device 27, base 28, processing chip processing nozzle

Claims (10)

[Claims] 1. A machining electrode and a work piece are made to face each other with a minute machining gap therebetween, and the machining feed and the feed positioning can be controlled so that the machining gap is relatively close in the opposing direction, and the machining medium is provided in the machining gap. Discharge generated by repeatedly applying intermittent voltage pulses with a dwell time generated by controlling the electronic switch element to turn on and off the direct current voltage source between the electrode and the work piece in a state where the In the electrical discharge machining method for machining a workpiece by means of the method described above, the machining surface of the machining electrode facing the workpiece is approximately 0.
It has a thin wall width of 05 to 3 mm and extends over a length greater than the width in a direction intersecting with the width direction, and may face a surface to be processed in a processing region of a workpiece or a part of the surface to be processed. The machining target is formed in the machining gap with a substantially uniform fine machining gap formed between the machining electrode and the machining surface of the machining electrode over substantially the entire machining surface of the machining electrode. A pressurized gas containing a gas that chemically reacts with the material is sprayed as a processing medium so that it is forcedly circulated in the width direction so as to be interposed, and the electrode and the workpiece are almost opposed to each other. Discharge by the applied voltage pulse, in a state where relative rotation about an axis in the direction of rotation and / or relative translational movement of a fine stroke in a direction substantially perpendicular to the axis in the opposite direction are applied. Of the opposite direction Drilling by Engineering feed, or given aerial discharge machining method characterized by machining the opposite portions of the electrode working surface is sequentially moved to with respect to the processing region of the workpiece at the infeed amount position of the counter. 2. The air-electric discharge machining method according to claim 1, wherein the gas that chemically reacts with the workpiece is oxygen. 3. The pressurized gas containing a gas that chemically reacts with the material to be processed is compressed air, preferably compressed gas richer in oxygen than air, or compressed oxygen. The air-electric discharge machining method described. 4. The method according to claim 1, wherein the pressurized gas is supplied to the processing gap at a pressure of at least 0.05 MPa and not more than 1.0 MPa. The air electric discharge machining method described in. 5. The pressurized gas is introduced into the processing gap by 20 m.
/ S to 250 m / s, preferably 50 m / s to 20
The air-electric discharge machining method according to any one of claims 1, 2 or 3, wherein the flow is interposed at a flow rate of 0 m / s. 6. A supply amount of a gas that chemically reacts with the workpiece material, which is heated and melted by the average discharge power under the set processing conditions, and further, is melted and scattered according to the amount of the workpiece material. Is controlled, the air electric discharge machining method according to claim 1, 2, 3, 4, or 5. 7. The object to be processed is an iron-based alloy containing iron as a main component, and the processed electrode is copper or a copper-based alloy containing copper as a main component. , 4, 5, or 6, any one of the electrical discharge machining method in the air. 8. The processing electrode is formed of a thin tubular body or a cylindrical body having a thin width.
3. The air electric discharge machining method according to any one of 3, 4, 5, 6, or 7. 9. The intermittent machining voltage pulse applied with a dwell time between the machining electrode and the object to be processed is applied and discharged as a positive polarity with the machining electrode as a negative electrode. Claims 1, 2, 3, 4, 5, 6,
7. The air electric discharge machining method according to any one of 7 and 8. 10. The discharge power supplied with a pause between the machining electrode and the workpiece has a no-load voltage of 100V.
It is to be supplied by a parallel arrangement of a main machining pulse power source having a low front and rear voltage and a large discharge current, and at least one auxiliary pulse power source having a high no-load voltage of 200 V or more and a small current capacity. Claims 1, 2, characterized in that
3. The air electric discharge machining method according to any one of 3, 4, 5, 6, 7, 8, or 9.