JP2010076036A - Electrode assembly, method and device for electric discharge machining - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform electric discharge machining efficiently by using a simple and inexpensive electrode structure. <P>SOLUTION: A grinding wheel processing device processes a grinding wheel S by generating corona discharge between the electrode assembly 22 and the grinding wheel S supported on a table 10 by applying voltage from a high-frequency power source 30. The electrode assembly 22 is constituted such that a plurality of so-called cables 23 are disposed parallel in a row and the apical ends are integrally fixed as one unit. One out of the plurality of electrical conductors is extruded to a predefined length toward the apical end side from each of the cables 23 so that a plurality of the electrodes 22a that is the apical end portion of the electrical conductors are disposed in a row in the array direction of the cables 23, and the corona discharge is generated between the grinding wheel S and each of the electrodes 22a by connecting each of the cable 23 in parallel to the high-frequency power source 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode assembly, an electric discharge machining method, and an electric discharge machining apparatus suitable for an electric discharge machining apparatus for machining a workpiece using an electric discharge phenomenon.

Conventionally, for example, a dressing device for a grindstone as disclosed in Patent Document 1 is known. This apparatus generates a corona discharge between an electrode disposed in proximity to a grindstone surface of a metal bond grindstone and the grindstone surface, thereby melting and removing a metal bond portion of the grindstone surface. It is to make a sharpening.
JP 2000-246634 A

  When plasma discharge machining is performed under atmospheric pressure, it is preferable to generate corona discharge using a discharge electrode having a narrow tip in order to stably generate plasma.

  However, when the discharge electrode becomes thinner, the processing range (area) per unit time becomes narrower and processing time is required. Therefore, in order to earn a processing area per unit time, for example, a discharge electrode having a regular number of conical or quadrangular pyramidal protrusions formed at the tip is used. Since the electrodes are difficult to manufacture and are expensive, it has been one of the factors that increase the cost of the apparatus.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to perform electric discharge machining more efficiently with a simple and inexpensive electrode structure.

  The present invention is an electrode assembly that is disposed close to a workpiece to generate a corona discharge between the workpiece and a plurality of conductors integrated with an insulating material. A plurality of the covered electric wires are arranged in parallel and in a row, and the end portions of these covered electric wires are fixed integrally so that the insulating materials of adjacent ones are in contact with each other. One electrode is provided so as to protrude from the insulating material to the front end side of the electric wire by a predetermined length, whereby a plurality of electrodes composed of the front end portion of the single conductor are provided in a row in the arrangement direction of the covered electric wires. .

  According to this electrode assembly, a certain range in the arrangement direction of the electrodes can be simultaneously processed by a roller in which corona discharge is generated between each electrode arranged in parallel and the workpiece. In addition, since this electrode assembly is configured by processing these end portions using a so-called covered electric wire, it can be manufactured easily and inexpensively. For example, a step of preparing a plurality of covered electric wires in which a plurality of conductors are integrally covered with an insulating material, and an electrode is formed by projecting one of the plurality of conductors to the tip side of each covered electric wire. And forming the covered wires in parallel and in a row and fixing the tips of the covered wires together so that the insulating materials of adjacent ones are in contact with each other, whereby the electrodes are mutually connected to the covered wires. It can be easily manufactured by going through a process of arranging them at intervals substantially equal to the diameter.

  Therefore, by following the electric discharge machining method of the present invention described below, a workpiece can be efficiently processed with a simple and inexpensive electrode structure. That is, the electric discharge machining method of the present invention is an electric discharge machining method for machining an electrically conductive and grounded workpiece, and the electrode assembly according to claim 1 is provided on a surface of the workpiece. The electrodes in the direction perpendicular to the arrangement direction of the electrodes while applying corona discharge by applying a machining voltage between the electrodes and the workpiece via the covered electric wires. Moving the workpiece and the electrode assembly relative to each other.

  Such an electric discharge machining method is useful for grinding wheels. That is, each electrode of the electrode assembly is brought close to each other so that a grindstone that supports abrasive grains with a conductive binder is opposed to the grindstone as the workpiece, and corona discharge is performed between each electrode and the grindstone. The grinding wheel surface can be sharpened by removing a part of the binder on the grinding wheel surface.

  According to this method, the grinding wheel (grinding wheel surface) can be sharpened efficiently with a simple and inexpensive electrode configuration as described above.

  On the other hand, an electric discharge machining apparatus according to the present invention includes a discharge electrode, and the discharge electrode is disposed between the workpiece and the discharge electrode so as to face the workpiece having conductivity. In an electric discharge machining apparatus for machining a workpiece by generating a corona discharge by applying a machining voltage, a support means for supporting the workpiece and grounding the workpiece, and supported by the support means And applying the machining voltage between the discharge electrode disposed so as to face the workpiece and movably provided relative to the workpiece, and the workpiece and the discharge electrode. A power source, and the electrode assembly is provided as the discharge electrode, and the electrode assembly is arranged so that the electrodes are arranged in a direction orthogonal to the relative movement direction, and each electrode is the covered wire Before Are those connected to the power supply.

  According to this electric discharge machining apparatus, the workpiece can be efficiently machined based on the electric discharge machining method as described above.

  As described above, according to the present invention, it is possible to efficiently process a workpiece while stably generating corona discharge in the atmosphere with a simple and inexpensive electrode configuration.

  A preferred embodiment of the present invention will be described with reference to the drawings.

  1 and 2 show an example of a grindstone machining apparatus (an electric discharge machining apparatus in which the electric discharge machining method according to the present invention is implemented), which is one of the electric discharge machining apparatuses according to the present invention, and FIG. 1 is a front view. FIG. 2 is a side view schematically showing the grindstone processing apparatus.

  The grindstone processing apparatus (hereinafter abbreviated as a processing apparatus) shown in the figure is a metal bond grindstone that supports diamond abrasive grains at a predetermined ratio using a conductive grindstone, specifically, a conductive metal bond as a binder. The grindstone surface is dressed using the discharge phenomenon under atmospheric pressure.

  The processing apparatus is arranged above a base 12, a table 10 movably supported on the base 12 (corresponding to the support means of the present invention), a drive mechanism for driving the table 10, and the table 10. A head 20 for processing, etc., with the grindstone S being supported on the table 10, while moving the grindstone S together with the table 10 with respect to the head 20 (while processing and feeding), The grindstone S is processed by the head 20.

  The drive mechanism includes rails 14 and 14 fixed on the base 12, a screw shaft 18 extending in parallel with the rails 14 and 14 and screwed into a nut portion 10a provided on the table 10, and A motor 16 connected to one end of the screw shaft 18 is provided, and the screw shaft 18 is rotationally driven by the motor 16 to move the table 10 along the rails 14 and 14 (machining feed). It is configured.

  The table 10 has a rectangular shape in plan view whose one side is parallel to the machining feed direction (X direction), and is arranged on the upper surface in a direction (Y direction) perpendicular to the machining feed direction. Two grindstone support portions 11a and 11b (referred to as first support portion and second support portion as appropriate) are provided. Although not shown, each of the support portions 11a and 11b includes a chuck mechanism (not shown), and is configured so that the grindstone can be positioned and fixed individually.

  In addition, although mentioned later, the 1st support part 11a of the one side (FIG. 2 left side) among these support parts 11a and 11b supports the grindstone S as a workpiece | work, and the 2nd support part 11b of the other side is The dummy grindstone Sd is supported.

  The head 20 is disposed in the movable region of the table 10 and above the table 10. The head 20 is provided so as to cross the table 10 in the width direction (Y direction), and is supported by a column 21 so as to be movable up and down and driven by a drive mechanism (not shown) including a screw feed mechanism and the like. It is like that.

  An electrode assembly 22 is disposed downward as a discharge electrode for grinding stone processing at a position facing the first support portion 11a in the head 20, and the electrode assembly 22 is disposed at a position facing the second support portion 11b. Apart from the assembly 22, a spare electrode 24 is disposed downward.

  The electrode assembly 22 is integrally provided with a plurality of electrodes 22a, and is composed of a plurality of so-called covered electric wires 23 (electric wires obtained by integrally covering a plurality of conductors with an insulating material; hereinafter simply referred to as electric wires 23). Has been. Specifically, the tip portions of the electric wires 23 are integrally fixed so that the plural electric wires 23 are arranged in parallel and in a row and the insulating materials are in contact with each other, and one of the plural conductors is each covered electric wire. A plurality of electrodes 22 a made of the single conductor are provided in a line in the arrangement direction of the covered electric wires 23 by being provided so as to protrude by a predetermined length on the distal end side of 23.

  Similarly, the spare electrode 24 includes a covered electric wire 25 (simply referred to as an electric wire 25). That is, the spare electrode 24 is formed with an exposed portion of the conductor at the tip portion of the electric wire 25, and the other portion is removed while leaving one of the plurality of conductors in the exposed portion. A spare electrode 24 is configured. In the present embodiment, the electrodes 22a and 24 are configured using 3.5 sq wires having an outer diameter of 4 mm and an inner diameter of 3 mm (conductor diameter of 0.31 mm) as the electric wires 23 and 25, respectively.

  As shown in FIG. 2, each electrode 22a and the spare electrode 24 of the electrode assembly 22 are connected in parallel to each other via the electric wires 23 and 25, a connector outside the figure, and the like, and correspond to the high frequency power source 30 (corresponding to the power source of the present invention). )It is connected to the. The table 10 is grounded (grounded) via an electric wire 31 so that the grindstones S and Sd supported by the support portions 11a and 11b are grounded. With this configuration, a machining voltage can be applied between the grindstones S and Sd supported by the support portions 11a and 11b and the electrodes 22a and 24.

  Note that a switch 36 is provided between the spare electrode 24 and the high-frequency power source 30 to switch the spare electrode 24 and the high-frequency power source 30 between a conductive state and a non-conductive state. The switching is controlled by. The control device 34 is composed of, for example, an NC device that comprehensively controls the grindstone processing device, and includes an ammeter 38 that detects the value of the current supplied to the electrode 22a (any one) of the electrode assembly 22. The switch 36 is switched based on the detected current value.

  Next, the processing (sharpening) operation of the grindstone S of the grindstone processing apparatus will be described.

  Prior to disclosing work, first, the grindstone S, which is a workpiece, is positioned and fixed to the first support portion 11a, and the dummy grindstone Sd (hereinafter referred to as dummy Sd) is fixed to the second support portion 11b. Here, the grindstone S is a metal bond grindstone that supports diamond abrasive grains at a predetermined ratio using a metal bond as a binder as described above, and has a rectangular shape in plan view with a certain thickness dimension. The dummy Sd is made of a diamond grindstone made of the same material as the grindstone S. The thickness and length dimension (dimension in the X direction) are the same as those of the grindstone S except that the width (dimension in the Y direction) is narrower than the grindstone S. Is formed.

  As shown in FIGS. 1 and 2, the grindstone S and the dummy Sd are in a state in which the surface to be processed (grindstone surface) faces upward, and the upper surface of the dummy Sd is the surface to be processed of the grindstone S. It fixes to support part 11a, 11b so that it may become equal.

  When this operation is completed, processing of the grindstone S is started based on the operation of a start switch (not shown).

  When the start switch is operated, the table 10 is first driven, and the feed start position, that is, the grindstone S is disposed at a position where one end of the grindstone S (one end in the machining feed direction) faces the head 20 (electrode assembly 22). Then, the head 20 is driven, and the gap h (see FIG. 3) between the electrode assembly 22 (electrode 22a) and the grindstone S (grindstone surface) is adjusted to a predetermined dimension. In the present embodiment, the gap h is adjusted to approximately 4.2 mm. By driving the table 10 and the head 20 in this manner, the dummy Sd is similarly disposed at a position where one end of the dummy Sd faces the spare electrode 24, and the gap h between the dummy Sd and the spare electrode 24 is as described above. It is adjusted to a predetermined dimension.

  Thereafter, a machining voltage is applied between each electrode 22a of the electrode assembly 22 and the grindstone S by the high-frequency power source 30, and the table 10 is driven at a constant feed rate. Thereby, processing of the grindstone S is started and detection of the value of the current supplied to the electrode 22a by the ammeter 38 is started. At this time, the switch 36 is off, that is, the spare electrode 24 and the high-frequency power supply 30 are in a non-conductive state, and therefore no voltage is applied between the spare electrode 24 and the dummy Sd.

  As described above, when a machining voltage is applied between each electrode 22a of the electrode assembly 22 and the grindstone S (grinding wheel surface), a corona discharge is generated between each electrode 22a and the grindstone S, thereby generating plasma. And the metal bond portion is mainly removed from the grindstone surface. That is, the grinding stone S is sharpened. At this time, if a corona discharge occurs in each electrode 22a, a certain range centered on each electrode 22a is conspicuous (see the broken line in FIG. 3), and thereby within a certain range over the arrangement direction of the electrodes 22a. Will be continuously conspicuous.

  And while a voltage is applied between each electrode 22a and the grindstone S in this way, the grindstone S is processed and fed to the electrode assembly 22 by driving the table 10, whereby one end side of the grindstone S. The grinding wheel surface is sharpened with a constant width in order.

  When processing of the grindstone S is started, the detection value of the ammeter 38 is monitored by the control device 34, and when the detection value reaches a predetermined threshold value, the switch 36 is switched from OFF to ON. The spare electrode 24 and the high-frequency power source 30 are switched to a conductive state, thereby suppressing an increase in current supplied to each electrode 22a. That is, the threshold value is set to a value slightly lower than the current value at the level at which arc discharge occurs between the electrode assembly 22 (electrode 22a) and the grindstone S (the level at which corona discharge transitions to arc discharge). When the detected value reaches this threshold value, the auxiliary electrode 24 and the high-frequency power source 30 are switched to a conductive state, whereby a voltage is applied between the auxiliary electrode 24 and the dummy grindstone Sd to generate a corona discharge. The current flowing through the spare electrode 24 causes a voltage drop due to the internal resistance 30a (output impedance) in the high-frequency power supply 30. As a result, the machining voltage applied between each electrode 22a and the grindstone S. Decreases instantaneously, and an increase in the value of the current flowing through each electrode 22a is suppressed. That is, by suppressing an increase in the current value supplied to each electrode 22a, the corona discharge generated between each electrode 22a and the grindstone S is prevented from unintentionally transitioning to arc discharge. It becomes.

  Thus, when the grindstone S is processed and fed to the end of the head 20, the high-frequency power supply 30 is stopped and the driving of the table 10 is stopped, whereby the processing of the series of grindstones S is completed.

  As described above, in this grindstone processing apparatus, the electrode assembly 22 having a constant processing (sharpness) width is obtained by arranging a plurality of electrodes 22a in a line, and the direction orthogonal to the arrangement direction (Y direction) of the electrodes 22a. Since the grinding wheel S is sharpened while relatively moving the grinding wheel S and the electrode assembly 22 in the (X direction), the grinding stone S can be sharpened efficiently.

  Moreover, since the electrode assembly 22 has a very simple configuration in which the electrodes 22a are provided by processing the ends of the plurality of covered electric wires 23, the electrode assembly 22 can be easily and inexpensively manufactured. For example, by preparing a plurality of covered electric wires 23 in which a plurality of conductors are integrally covered with an insulating material, and projecting one of the plurality of conductors toward the tip side of each covered electric wire 23 The step of forming the electrodes 22a, and the covered wires 23 are arranged in parallel and in a row, and the tip portions of the covered wires 23 are fixed together so that the insulating materials of adjacent ones are in contact with each other, thereby fixing each of the electrodes 22a. The electrode assembly 22 can be easily manufactured simply by going through a process of arranging them at a distance approximately equal to the diameter of the covered wire 23.

  Therefore, the grindstone S can be processed (sharpened) efficiently while stably generating corona discharge with a simple and inexpensive electrode configuration.

  In this embodiment, as described above, the electrode 22a is configured using the 3.5 sq line having an outer diameter of 4 mm and an inner diameter (conductor total diameter) of 3 mm. This is based on the test results shown in FIG. It is. In this test, as shown in FIG. 4, for the electrode assembly 22 having two electrodes 22a, the interval h between the electrode 22a and the grindstone S is set to 4.2 mm, and a constant machining voltage (4 kV) is set by the high frequency power source 40. 5 kHz) is evaluated by changing the type of the electric wire 23 in a sharp state when a certain time (20 s) is applied. In addition, the width | variety (dimension of the left-right direction of FIG. 4) of the grindstone S is 7 mm. The distance h (4.2 mm) between the electrode 22a and the grindstone S is a value that is considered to cause the best occurrence of corona discharge, and is a value obtained experimentally.

  As shown in FIG. 5, when an 8 sq electric wire (electric wire diameter 6.0 mm, conductor diameter 0.45 mm) is used as the electric wire 23, an unprocessed portion is generated in the central portion, which is because the pitch between the electrodes is wide. it is conceivable that. The gap h between the electrode 22a and the grindstone S is slightly improved, but in this case, the generation of corona discharge becomes unstable.

  When a 5.5 sq electric wire (electric wire diameter 5.0 mm, conductor diameter 0.31 mm) or a 3.5 sq electric wire (electric wire diameter 4.0 mm, conductor diameter 0.31 mm) is used as the electric wire 23, it extends over the entire width direction of the grindstone S. Processing was possible. However, in the case of a 5.5 sq electric wire, machining unevenness occurred in the central portion, and uniform machining was difficult. When the distance h between the electrode 22a and the grindstone S is changed, the tendency is the same although it is slightly improved.

  When a 2 sq electric wire (electric wire diameter: 3.5 mm, conductor diameter: 0.26 mm) was used as the electric wire 23, an unprocessed portion remained at the end of the grindstone S, but the other processing conditions were generally good. Therefore, it can be considered that the entire grinding wheel S can be satisfactorily processed by increasing the number of electrodes 22a.

  From this result, if the electrode assembly 22 is configured by applying a wire 23 having a nominal cross-sectional area (sq) of 3.5 sq or less, a constant width in the arrangement direction of the electrodes 22a is processed continuously and uniformly. It can be considered that it is possible. However, when the electric wire 23 is 2 sq or less, it is necessary to increase the number of electrodes 22a (electric wires 23) as the processing width becomes narrower. Therefore, from the viewpoint of securing a wide machining width with a small number of electrodes 22a, it is considered preferable to configure the electrode assembly 22 with the 3.5 sq electric wires 23.

  By the way, the grindstone processing apparatus described above is an example of the grindstone processing apparatus according to the present invention (the grindstone processing apparatus capable of performing the grindstone processing method according to the present invention). As long as it does not deviate from the above, it can be appropriately changed.

  For example, in the above-described embodiment, the grindstone processing apparatus for processing the plate-shaped grindstone S has been described. A main shaft is provided, the grindstone S is fixed to the main shaft, and the electrode assembly 22 in which the electrodes 22a are arranged in the direction of the grindstone axis is disposed so as to face the grindstone surface, and the main shaft and the grindstone S are rotationally driven integrally. The electrode assembly 22 may be configured to perform electric discharge machining. For example, when the grindstone processing apparatus according to the present invention is incorporated into an internal grinder or a cylindrical grinder, this configuration can be employed.

  In the embodiment, in order to prevent arc discharge from occurring when an overcurrent flows to the electrode assembly 22 (electrode 22a) side, the spare electrode 24 is connected to the high-frequency power source 30 and the spare electrode 24 is connected. The dummy grindstone Sd is discharged with a current to lower (decrease) the machining voltage. For example, by arranging the electrode assembly 22 (electrode 22a) and the spare electrode 24 close to each other, You may make it discharge with respect to the grindstone S which is a workpiece. According to this configuration, since the auxiliary electrode 24 discharges the grindstone S shared with the electrode assembly 22, the energization conditions on the electrode assembly 22 (electrode 22a) side and the auxiliary electrode 24 side are made more equal. Accordingly, inconveniences such as an unstable discharge state on the electrode assembly 22 (electrode 22a) side at the time of discharging from the preliminary electrode 24 can be favorably avoided.

  In addition to the provision of the spare electrode 24 as described above, a specific configuration for reducing the machining voltage when an overcurrent is generated in the electrode assembly 22 (electrode 22a) is, for example, from the electrode 22a to the grindstone S and There may be provided an earth circuit or the like having a resistance value equivalent to the energization path on the electrode 22a side leading to the earth (ground) through the table 10 and connected in parallel to the electrode 22a with respect to the high frequency power source 30. . This configuration can also theoretically enjoy the same effects as the above embodiment.

1 is a schematic front view showing a grindstone machining apparatus which is one of electric discharge machining apparatuses according to the present invention. 1 is a schematic side view of a grindstone processing apparatus including a diagram of an electric system for controlling discharge. It is the principal part expansion schematic of the head which shows the structure of an electrode. It is a schematic diagram which shows the test conditions of an electric discharge machining test. It is a table | surface which shows the result of an electric discharge machining test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Table 20 Head 22 Electrode assembly 22a Electrode 23,25 Covered electric wire 24 Spare electrode 30 High frequency power supply 34 Control apparatus 36 Ammeter 38 Switch S Grindstone Sd Dummy grindstone

Claims (5)

An electrode assembly that is disposed close to the workpiece to generate a corona discharge between the workpiece and the workpiece,
A plurality of covered electric wires in which a plurality of conductors are integrally covered with an insulating material are arranged in parallel and in a row, and the tip portions of these covered electric wires are fixed integrally so that adjacent insulating materials are in contact with each other, One of the plurality of conductors of each covered electric wire is provided so as to protrude from the insulating material to the electric wire tip side by a predetermined length, whereby a plurality of electrodes composed of tip portions of the one conductor are arranged in the arrangement direction of the covered electric wires The electrode assembly is provided in a line. A method of manufacturing an electrode assembly that is disposed close to a workpiece and generates a corona discharge between the workpiece and the workpiece,
A step of preparing a plurality of covered electric wires in which a plurality of conductors are integrally covered with an insulating material, and an electrode is formed by projecting one of the plurality of conductors to the tip side of each covered electric wire And arranging the covered wires in parallel and in a row and fixing the tip portions of these covered wires together so that the insulating materials of adjacent ones are in contact with each other, whereby the respective electrodes and the diameter of the covered wires are mutually fixed. And a step of arranging the electrodes in a state of being arranged at substantially equal intervals. An electrical discharge machining method for machining an electrically conductive and grounded workpiece,
The electrodes of the electrode assembly according to claim 1 are brought close to the surface of the workpiece, and a corona is applied by applying a machining voltage between each electrode and the workpiece via the covered electric wire. Moving the workpiece and the electrode assembly relative to each other in a direction perpendicular to the arrangement direction of the electrodes while generating an electric discharge. The electric discharge machining method according to claim 3,
The electrodes of the electrode assembly are brought close to each other so that the grindstone that supports the abrasive grains by the conductive binder is opposed to the grindstone as the workpiece, and corona discharge is generated between the electrodes and the grindstone. Then, the grinding wheel surface is sharpened by removing a part of the binder on the grinding wheel surface. Corona discharge is generated by applying a machining voltage between the work piece and the discharge electrode in a state where the discharge electrode has a discharge electrode and the discharge electrode is arranged close to the work piece having conductivity. In an electric discharge machining apparatus for machining the workpiece,
Supporting means for supporting the workpiece and grounding the workpiece;
The discharge electrode disposed to face the workpiece supported by the support means and provided to be movable relative to the workpiece;
A power source for applying the machining voltage between the workpiece and the discharge electrode;
The electrode assembly according to claim 1 is provided as the discharge electrode, the electrode assembly is arranged so that the electrodes are arranged in a direction orthogonal to the relative movement direction, and each electrode includes the covered electric wire. Each of which is connected to the power source via the electric discharge machining apparatus.