MXPA00007014A - Apparatus for electrodischarge machining - Google Patents

Abstract

An apparatus for electrodischarge machining includes a quill (8) capable of moving in vertical directions;at least one set of linear motor rotors attached to the quill symmetrically with the axis of the quill;and a set of linear motor stators opposed to the set of rotors. An electrode mount (9) for holding a tool electrode (6) is attached to the lower end of the quill in such a manner that it is coaxial with the quill axis. Preferably, the set of rotors include magnet plates (12, 14) attached to the quill, and permanent magnets (11, 13, 15, 16) arranged in stripes on the magnet plates, while the set of stators include yokes (31, 41) and coils (32, 42) wound on the yokes. The quill has a vertical hole (8a) extending in its center, and air cylinder (61) is placed in the hole to balance the load of the quill. The quill has a density less than 4g/cm3, for example, composed of silicon nitride ceramic (Si3N4) or a compound of light metal and more than 40 percent ceramic by volume.

Description

MACHINING DEVICE FOR ELECTRICAL SHOCK FIELD OF THE INVENTION The present invention relates to an apparatus for electrical discharge machining to form holes of various shapes in a work piece by provoking an electric discharge between a tool electrode and the work piece and moving the electrode of tool towards the work piece.

BACKGROUND OF THE INVENTION An apparatus for electric discharge machining is widely used to precisely machine a solid workpiece in a mold or matrix. The workpiece is fixed to a table arranged in a work tank, and an electrode of a copper or graphite tool is attached to a vertically movable sleeve or poppet using a tool holder. The work tank is filled with dielectric fluid such as petroleum (kerosene), and the tool electrode is placed extremely close to the workpiece. A space between the work piece and the tool electrode is called a clear, and the size of this clear is from a few μm to a few tenths of a μm. If a pulse of energy is applied through the work piece and the tool electrode during the ignition time, the insulating characteristics of the dielectric fluid in the clearing are broken and electrical discharge occurs. Microscopic quantities of material from the work piece evaporate or melt due to heat from this electrical discharge, and flow into the dielectric fluid. At the end of the ignition time, the insulating characteristics of the dielectric fluid in the clearing are restored and thus the application of a pulse of energy during the shutdown time is stopped. As a result of the electric discharge, microscopic crater-shaped holes remain in the surface of the workpiece. An electric discharge machining device normally controls the ON time and the OFF time between 1 μsec and a few tenths of msec, to repeatedly apply a pulse of energy to the clear. The electric discharge machining apparatus causes the tool electrode to move towards the workpiece and down along the X axis and maintain the gap at a constant size. Since it is possible to remove microscopic quantities of material from the workpiece without the tool electrode coming into contact with the workpiece, a cavity having good surface roughness is precisely formed in the workpiece and that is complementary in shape to the tool electrode. This type of electrical discharge machining apparatus is different from a wire EDM using a mobile wire electrode and is referred to as a lead EDM. A flooded operation is important to produce a flow of dielectric fluid through the clear in order to wash the fragments removed from the workpiece away from the clear in an electrical discharge machining apparatus. The flooded operation serves to prevent undesirable secondary discharge from occurring between the tool electrode and the fragments removed from the work piece, and to restore reliable isolation during the OFF time. An expert operator will drill holes to suck contaminated dielectric fluid out of the clear and supply fresh dielectric fluid to the clear at appropriate positions on the tool electrode and workpiece. When the formation of the holes is restricted, such as due to the size or shape of the tool electrode, the operator will arrange an injection device in an appropriate position to inject dielectric fluid into the clear. Flooding is crucial in order to carry out a good machining faster and more precise, but creating a uniform flow through the entire clearing requires dexterity. An operation called a jump operation is known, where the tool electrode is caused to rise rapidly and fall rapidly periodically along the Z axis to almost completely expel the contaminated dielectric fluid within the clearing from the cavity inside. of the work piece. During the jump operation, the tool electrode moves conventionally at a rate of a few hundred mm / min. If the round-trip distance of the tool electrode is large, more fresh fluid flows into the clearing and more contaminated fluid is expelled from the clearing. The tool electrode is preferably made to raise at least one depth of a hole that is machined in the workpiece. However, since the material is not removed from the work piece during the skip operation, performing the skip operation very frequently will cause the rate of material removal to decrease.

BRIEF DESCRIPTION OF THE INVENTION An object of the present invention is to provide an electrical discharge machining apparatus that can effectively wash fragments removed from a workpiece away from a clearing without causing a decrease in the rate of material removal. Another object of the present invention is to provide an electrical discharge machining apparatus that can effectively wash fragments removed from a workpiece away from a clearing without the need for a high level of skill. Additional objects, advantages and novel aspects of the invention will be set forth in the description that follows, and those skilled in the art will be made apparent to read this description or practice of the invention. The objects and advantages of the invention can be realized and obtained by practicing the invention as mentioned in the appended claims. In order to achieve the above-described objects, an electrical discharge machining apparatus of the present invention for machining a workpiece causing a tool electrode to move towards the workpiece in a vertical direction while simultaneously causes an electrical discharge between the workpiece and the tool electrode, comprises, a sleeve movable in the vertical direction, an electrode mounting device, attached to a lower end of the sleeve coaxially with the sleeve, for mounting the tool electrode , at least one set of linear motor movers attached to the sleeve and arranged symmetrically about the central axis of the sleeve, and a set of linear motor stators, respectively facing the set of movers. Preferably, the set of movers includes magnetic plates attached to the sleeve and a row of permanent magnets disposed on the magnetic plates, and the set of stators includes a stock and a coil wound around the stock. More preferably, the sleeve has a hole at its center extending in the vertical direction, and an air cylinder for obtaining load balance of the sleeve is disposed in this hole. In another aspect of the present invention, an electrical discharge machining apparatus for machining a workpiece causing a tool electrode to move towards the workpiece in a vertical direction while causing an electrical discharge between the workpiece. workpiece and the tool electrode comprises, a sleeve movable in the vertical direction having a density of less than 4 g / cm 3, a device for mounting the electrode for fixing the tool electrode, attached to a lower end of the sleeve, a linear motor mover attached to the sleeve, and a linear motor stator facing the mover.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view showing one embodiment of an electric discharge machining apparatus of the present invention; Figure 2 is a horizontal cross-section of the sleeve driving device taken along line A-A of Figure 1; Figure 3 is a vertical cross section of the sleeve driving device taken along line B-B of Figure 1; Figure 4 is a vertical cross section of the sleeve drive device taken along line C-C of Figure 1; Figure 5 is a horizontal cross-section of another example of a sleeve guiding device taken along line A-A of Figure 1; Figure 6 is a vertical cross-section of another example of a sleeve driving device taken along line A-A of Figure 1; Figure 7 is a vertical cross section of another example of a sleeve driver device taken along line C-C of Figure 1; Figure 8 is a perspective view showing another embodiment of an electric discharge machining apparatus of the present invention; Figure 9 is a horizontal cross-section of the sleeve drive device taken along line A-A of Figure 8; Figure 10 is a vertical cross section of the sleeve drive device taken along line B-B of Figure 8; Figure 11 is a perspective view showing the sleeve driver device of Figure 8; Figure 12 is a perspective view showing thrust acting on the sleeve of Figure 8; Figure 13 is a horizontal cross section showing another example of a sleeve of the electric discharge machining apparatus.

PREFERRED MODE OF THE INVENTION Now one embodiment of the present invention will be described with reference to Figure 1, Figure 2, Figure 3 and Figure 4. As shown in Figure 1, a column 2 is disposed at the rear of a bed 1, and a movable body 3 is provided in bed 1 to be movable in the direction of the Y axis. A chair 4 is provided in the movable body 3 to be slidable in the direction of the X axis orthogonal to the Y axis. a working tank 5 filled with dielectric fluid in the chair 4. A work piece (not shown in the drawing) is fixed to a table (not shown in the drawing) disposed in the work tank 5. A tool electrode 6 placed near the workpiece is fixed to a device 9 for electrode assembly. The device 9 for electrode assembly is fixed to a lower end of a hollow sleeve 8 movable in the direction of the axis Z. In order to carry out a jump operation having a large amount of movement without lowering the removal rate of material, the electric discharge machining apparatus is capable of acceleration and deceleration in excess of 1G, and of accurately moving the tool electrode 6 at a speed of 10 m / min or faster. As shown in Figure 2, the sleeve 8 has a square cross section. As shown in Figure 3 and Figure 4, the device 9 for electrode assembly and the tool electrode 6 are arranged coaxially with the central axis QC of the sleeve 8, which means that the tool electrode 6 can be moved with good accuracy . A row of permanent magnets are arranged on both sidewalls of the symmetrical square columnar sleeve 8 around the central axis QC. In order to obtain high speed, care must be taken to ensure that high rigidity is maintained and that the sleeve is made of light weight. The sleeve 8 has a cylindrical hole 8a at its center extending in the vertical direction, and has a density of g / cm3 or less. The sleeve is preferably made of ceramic having a small coefficient of thermal expansion and a large young modulus. Specifically, silicon nitride (Si3N) ceramics having a density of 3.2 g / cm3, a youth modulus of 3.0-3.1x106 kgf / cm2, and a fracture hardness of 4.5-5.0 MPa m1 / 2 are selected. A method for manufacturing the ceramics will be described simply. First of all, a sintering agent of aluminum oxide (AI2O3), silicon dioxide (SiO2) or aluminum nitride (AIN) is added to particles of silicon nitride (Si3N). This mixture is formed in a hollow square column using, for example, an isostatic press method. This compacted body is then sintered using an atmospheric pressure sintering method or a pressurized sintering method. The sleeve 8 is preferably formed of a composite material of a light metal and at least 40% by volume of ceramic. The light metal contains aluminum and magnesium or alloys of these. The ceramic contains silicon carbide ceramic (SiC), aluminum oxide ceramic (AI2O3) and silicon nitride ceramic (SÍ3N4). A material composed of an aluminum alloy and 55% by volume of aluminum oxide ceramic has a density of 2.95 g / cm3, a modulus of young of 2.0 x 106 kgf / cm2 and a fracture hardness of 10.5 MPa m1 ' 2. A material composed of an aluminum alloy and 55% by volume of aluminum oxide ceramic has a density of 3.00 g / cm3, a modulus of young of 2.65 x 106 kgf / cm2 and a fracture hardness of 10.00 MPa m1 ' 2. These types of composite materials are formed, for example, by having a molten light metal penetrate a sintered ceramic body in nitrogen at 700-800s C. The permanent magnets are placed on a magnetic plate that is formed as thin as possible. a soft magnetic material such as iron, in order to form a good magnetic circuit between the permanent magnets. Some type of member is also provided between the sleeve 8 and the magnetic plate. In the illustrated embodiment, a magnetic plate 12 on which two rows of permanent magnets 11 are arranged is anchored to a wall surface of the sleeve 8, and a magnetic plate 14 on which two rows of permanent magnets 13 are disposed is adhered to. the other side wall of the sleeve 8. In order to guide the vertical movement of the sleeve 8, two linear-motion ball bearing rails 21 are attached to the front surface 2a of the column 2 in parallel therebetween. Upper and lower bearing holders 22 and 23 that engage with the rails 21 are attached to the rear surface of the sleeve 8. A frame 7 that supports fixed terminals facing the permanent magnets 11 and 13 is attached to the front surface 2a of the column 2 As shown in Figure 2 and Figure 4, fixed terminals comprising an excitation coil and a head are attached to respective vertical surfaces of the plates 7d and 7e so as to be symmetrical about the central axis of the sleeve 8. The plates 7d and 7e are fixed to windows 7a and 7b formed in both side walls of the frame 7. The heads 31 and 41 formed of laminated silicon steel sheets are respectively attached to the plates 7d and 7e, and the armature coils 32 and 42 are rolled around with respect to the cylinder heads 31 and 42. A space between the cylinder head 31 and the permanent magnet 11 and a space between the cylinder head 41 and the permanent magnet 13 are adjusted to be of the same size. do not. For example, these two spaces are adjusted to the same size using a plurality of screws provided in the plates 7d and 7e. As a result, a magnetic attraction force generated between the mobile terminals and fixed terminals of a linear motor is deviated. A number of tubes 33 and 43 through which coolant passes are accommodated in holes formed within the heads 31 and 41. A linear scale 51 is provided which is attached to a side wall of the sleeve 8 and a sensor 52 for reading the position of the sleeve on an inner side of the front wall 7c of the frame 7. A linear motor propeller (not shown) receives sensing signals from the sensor 52 and supplies control signals to the armature coils 32 and 42. A cylinder 61 is provided to balance the load applied to the movable sleeve 8 which moves at gravitational acceleration in excess of 1G. In order to make the machine compact, the cylinder 61 is positioned within a hole 8a coaxial with the central axis QC, and an upper end of the cylinder 61 is fixed to the sleeve 8 using a flange. Because the cylinder 61 is provided right next to the sleeve 8, high responsiveness is ensured. A piston rod 63 is connected at one end to a piston 62, and at the other end to a joint plate 65. The hinge plate 65 is fixed to the column 2. Air pressure is maintained from an upper chamber 66 formed inside a cylinder 61 higher than the piston 62 at a value set by precise air regulators. Due to the cylinder 61, electrical power supplied to the coils 32 and 42 is retained while the sleeve is stationary. In order to prevent the invasion of dust, a number of bellows is provided in the spaces between the sleeve 8 and the frame 7. The device for guiding the sleeve 8, and the location of the linear scale 51, etc., are not limited to the embodiment shown in Figure 2, Figure 3 and Figure 4. For example, as shown in Figure 5, it is also possible to additionally provide a transverse roller bearing to vertically guide the movement of the sleeve 8 between the front wall of the sleeve 8 and the front wall 7c of the frame 7. It is also possible to provide the linear scale 51 of the rear wall of the sleeve 8, and providing the sensor 52 for detecting the position of the sleeve on the front surface 2a of the column 2. As shown in Figure 6 and Figure 7, the heads 31 and 41 can be attached to both walls of the sleeve 8 using plates 8b and 8c. In this case, the magnetic plate 12 to which the permanent magnet 11 opposite the cylinder head 31 is attached is supported on the frame 7 using the plate 7d. The magnetic plate 14 to which the permanent magnet 13 opposite the head 41 is attached is supported on the frame 7 using the plate 7e. A flexible hose extending from the refrigerant tubes 33 and 43, and a power supply line extending from the coils 32 and 42, are connected to the terminals 71 and 72. Now another embodiment of an apparatus will be described. electrical discharge machining of the present invention with reference to Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12. Elements that are the same as those in Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6 and Figure 7 have the same reference numerals attached to them, and the explanation will be omitted. The magnetic plates 12 and 14 to which rows of permanent magnets 15 and 16 are adhered respectively are respectively attached to the front wall and rear wall of a columnar square sleeve 8. As shown in Figure 11, individual permanent magnets are adhered to the magnetic plate inclined slightly from the horizontal direction, to reduce the fluctuations of the torque. The sleeve 8 has a square hole 8a coaxial with the central axis QC, to reduce its weight. The linear transverse roller guides 24 and 25 for guiding the sleeve 8 are provided between the two side surfaces of the sleeve and the frame 7. As shown clearly in Figure 10 a cylinder 61 is provided to obtain load balance of the sleeve 8 between a plate 7e attached to the head 41 and the column 2. A piston rod 63 is connected to the sleeve using a hinge plate 65. The force to drive the sleeve 8 will be described in detail with reference to Figure 12. The reference numeral GCL in the drawing represents a central line around which the rows of permanent magnets 15 and 16 are arranged symmetrically. A resultant FA force of thrust FA developed between the row of permanent magnets 15 and the stock 31 and the thrust FB developed between the row of permanent magnets 16 and the stock 41 occurs in the center line GCL of sleeve. The linear transverse roller guides 24 and 25 are arranged so that the respective guide surfaces cause the guiding force to act on the center line GCL. Accordingly, a force other than the vertical direction does not act on the linear transverse roller guides 24 and 25 to guide the sleeve 8. A lightweight sleeve can then be moved in the vertical direction at high speed and with good accuracy. Holes having a depth of 70 mm were machined into a workpiece using a rib-shaped graphite tool electrode having a width of 1.0 mm on the bottom surface and a length of 38 mm, and a 1 ° of each side surface. At this time, the time was set to 100 μs, shutdown time was set to 140 μs, the peak current value was set to 93A, the average air gap voltage was set to 55V, no-load voltage was set to 120V , jump rate was set at 30 m / min., and jump time for one cycle was set at 0.24 seconds. The material properties of the workpiece are defined in Japanese Industrial Standard SKD11. Even without flooding the machining apparatus by electric discharge, the machining regime remained almost constant and the machining was completed in 135 minutes. The foregoing description of preferred embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or limited to the precise form described., and obviously several modifications and variations are possible in light of the previous teaching. It is intended that the scope of the invention be defined by the appended claims. For example, the horizontal cross-section of the sleeve is not limited to being square. The cross section can be, for example, rectangular as shown in Figure 13, it is possible to be formed having two vertical surfaces that are parallel to each other.

Claims (17)

1. CLAIMS 1. An electric discharge machining device, for machining a workpiece causing a tool electrode to move towards the workpiece in a vertical direction while causing an electrical discharge between the workpiece and the work electrode. tool, comprising: a sleeve movable in the vertical direction; a device for mounting electrode, attached to a lower end of the sleeve coaxially with the sleeve, for mounting the tool electrode; at least one set of linear motor movers attached to the sleeve and arranged symmetrically about the central axis of the sleeve; and a set of linear motor stators, respectively facing the set of movers.
2. 2. The electric discharge machining apparatus of claim 1, wherein the set of movers includes a magnetic plate accommodated in the sleeve and a row of permanent magnets arranged in the magnetic plate, and the set of stators includes a stock and a coil wound around the stock.
3. 3. The electric discharge machining apparatus of claim 1, wherein the sleeve has a square columnar shape.
4. 4. The electric discharge machining apparatus of claim 1, wherein a hole extending in a vertical direction is formed in the center of the sleeve.
5. The electric discharge machining apparatus of claim 3, further comprising a first guide device, for guiding the sleeve, and a first side surface of the sleeve, and wherein the set of movers are respectively fixed to the two surfaces sides of the sleeve adjacent to the first side surface.
6. 6. The electric discharge apparatus of claim 1, further comprising an air cylinder for obtaining load balancing of the sleeve.
7. The electric discharge apparatus of claim 4, further comprising an air cylinder for obtaining load balancing of the sleeve.
8. The electrical discharge machining apparatus of claim 5, further comprising a second guiding device for guiding the sleeve to a side surface of the sleeve facing the first side surface.
9. The electric discharge machining apparatus of claim 1, wherein the set of movers includes a stock and a coil wound around the stock, and the set of stators includes a magnetic plate accommodated in the sleeve and a row of magnets permanent arranged in the magnetic plate.
10. 10. The electric discharge machining apparatus of claim 1, wherein the sleeve has a density of 4 g / cm3 or less.
11. 11. The electric discharge machining apparatus of claim 10, wherein the sleeve is made of ceramic.
12. 12. The electric discharge machining apparatus of claim 11, wherein the sleeve is made of silicon nitride ceramic (SÍ3N4).
13. 13, The electric discharge machining apparatus of claim 10, wherein the sleeve is made of a material composed of a light metal and at least 40% by volume of ceramic.
14. 14. An electric discharge machining apparatus for machining a workpiece causing a tool electrode to move toward the workpiece in a vertical direction while causing an electrical discharge between the workpiece and the electrode, which comprising: a sleeve movable in the vertical direction and having a density of less than 4 g / cm3; a device for mounting electrode to fix the tool electrode, attached to a lower end of the sleeve; a linear motor mover attached to the sleeve; and a linear motor stator facing the mover.
15. 15. The electric discharge machining apparatus of claim 14, wherein the sleeve is made of ceramic.
16. 16. The electric discharge machining apparatus of claim 15, wherein the sleeve is made of silicon nitride ceramic (SÍ3N4).
17. 17. The electric discharge machining apparatus of claim 14, wherein the sleeve is made of a material composed of a light metal and at least 40% by volume of ceramic. (54) Title: MACHINING EQUIPMENT FOR ELECTRIC SHOCK (57) Summary: An electric discharge machining apparatus comprises a sleeve movable in the vertical direction, at least one set of linear motor movers attached to the sleeve symmetrically about a central axis of the sleeve, and a simple set of stators of linear motor in front of the game of movers. A device for mounting an electrode to hold a tool electrode is attached to a lower end of the sleeve, and coaxially with the sleeve. Preferably, the fire of movers includes magnetic plates attached to the sleeve and a row of permanent magnets disposed on the magnetic plates, and the set of stators includes a stock and a coil wound around the stock. The sleeve has a hole in its center that extends in the vertical direction, and an air cylinder that provides counter-balance for the charge of the sleeve is disposed in this hole. The sleeve has a density of 4 g / cm 3 or less, and is made of, for example, silicon nitride (Si 3 N 4) ceramic or a material composed of a light metal and at least 40% by volume of ceramic.