HK1034220B - Apparatus for electrodischarge machining - Google Patents

Description

Electric discharge machining apparatus

Technical Field

The present invention relates to an electric discharge machining apparatus for forming holes of various shapes in a workpiece by feeding a tool electrode toward the workpiece while generating electric discharge between the tool electrode and a conductive workpiece.

Background

Electric discharge machining apparatuses are widely used for precision machining of hard conductive workpieces into dies or dies. The workpiece is fixed to a table disposed in the machining tank, and a tool holder for a copper or graphite tool electrode is attached to a spindle or a slide table that is movable in the vertical direction. The processing tank is filled with a dielectric liquid such as kerosene, and the tool electrode is positioned in close proximity to the workpiece. The gap between the tool electrode and the workpiece is called a gap, and its size is several μm to several tens μm. As soon as a power pulse is applied between the tool electrode and the workpiece during the on-time, the insulation of the dielectric liquid in the gap is destroyed and a discharge occurs. Due to the heat generated by this electric discharge, a small amount of the workpiece material evaporates or melts and flows into the dielectric liquid. When the on-time is over, the dielectric liquid in the gap recovers its insulating property, and thus the application of the power pulse is stopped during the off-time. Fine pores in the form of craters are left on the surface of the workpiece by the discharge. In an electric discharge machine, generally, an on time and an off time are controlled to be 1 μ sec to several tens msec, and a power pulse is repeatedly applied to a gap. The electric discharge machine lowers the tool electrode along the Z axis toward the workpiece to maintain the gap at a constant size. Since the tool electrode can remove a small amount of material from the workpiece without contacting the workpiece, a recess having a good rough surface and complementary in shape to the tool electrode is formed in the workpiece with high accuracy. Such an electric discharge machining apparatus is called a drill electric discharge machining apparatus (drill EDM) as distinguished from a wire electric discharge machining apparatus (wire EDM) using a traveling wire electrode.

The "flushing" action, in which a flow of dielectric liquid is generated through the gap in order to flush debris removed from the workpiece out of the gap, is important for electric discharge machining. The flushing action prevents undesirable secondary discharges from occurring between the debris removed from the workpiece and the tool electrode to help restore reliable insulation during the cut-off time. Prior to machining, a skilled worker forms a hole in an appropriate position of the tool electrode or the workpiece for introducing fresh dielectric liquid into the gap and for extracting contaminated dielectric liquid from the gap. When the formation of such a hole is limited by the size or shape of the tool electrode, an operator sets an ejection device for ejecting a dielectric liquid into the gap at an appropriate position. Although rinsing is critical for faster and more accurate electrical discharge machining, skill is necessary to produce uniform flow throughout the entire gap. The so-called "jump" operation is known in which the tool electrode is periodically and rapidly raised and lowered along the Z axis to flush almost all of the contaminated dielectric liquid out of the recess of the workpiece. In the jumping operation, conventionally, the tool electrode is moved at a speed of several hundred mm/min. As long as the reciprocating distance of the tool electrode is large, more fresh liquid flows into the gap and more contaminated liquid is drained from the gap. It is desirable to at least raise the tool electrode beyond the depth of the hole being machined in the workpiece. However, since the removal of the material from the workpiece cannot be performed in the jumping motion, the excessively frequent jumping motion lowers the material removal speed.

Disclosure of the invention

The invention aims to provide an electric discharge machining device which can efficiently wash away fragments removed from a workpiece from a gap without reducing the material removal speed.

Another object of the present invention is to provide an electric discharge machining apparatus which does not require high skill and can efficiently wash chips removed from a workpiece from a gap.

Additional objects of the invention, in part, will be set forth in the description which follows, and in part will be obvious to those skilled in the art upon examination of the following, or may be learned by practice of the invention.

In order to achieve the above object, an electric discharge machining apparatus according to the present invention for machining a workpiece by moving a tool electrode in a vertical direction toward the workpiece while generating electric discharge between the workpiece and the tool electrode includes:

a main shaft capable of moving in a vertical direction,

an electrode mounting device which is mounted on the lower end of the main shaft coaxially with the main shaft and mounts a tool electrode,

at least one set of linear motor movers symmetrically mounted on the main shaft about the center line of the main shaft, and

a set of linear motor stators respectively opposing the set of moving stators.

Preferably, the first stator includes a yoke and a coil wound around the yoke.

Further preferably, the main shaft has a hole extending in the vertical direction at the center thereof, and a cylinder for balancing the load of the main shaft is disposed in the hole.

Further, an electric discharge machining apparatus according to the present invention for machining a workpiece by moving a tool electrode in a vertical direction toward the workpiece while generating electric discharge between the workpiece and the tool electrode includes:

having a density of 4g/cm³A vertically movable main shaft of the following density,

an electrode mounting device which is arranged at the lower end of the main shaft and is used for fixing the tool electrode,

a mover of a linear motor mounted on the main shaft, and

a stator of the linear motor opposite to the moving stator.

Brief description of the drawings

Fig. 1 is a perspective view showing one embodiment of an electric discharge machining apparatus of the present invention.

Fig. 2 is a cross-sectional view of the apparatus for driving the spindle, viewed along line a-a of fig. 1.

Fig. 3 is a longitudinal sectional view of the apparatus for driving the main shaft, viewed along the line B-B of fig. 1.

Fig. 4 is a longitudinal sectional view of the apparatus for driving the main shaft, viewed along the line C-C of fig. 1.

Fig. 5 is a cross-sectional view of another example of the device for guiding the spindle, as viewed along the line a-a of fig. 1.

Fig. 6 is a cross-sectional view of another example of the apparatus for driving the main shaft, viewed along the line a-a of fig. 1.

Fig. 7 is a longitudinal sectional view of another example of the apparatus for driving the main shaft, viewed along the line C-C of fig. 1.

Fig. 8 is a perspective view showing another embodiment of the electric discharge machining apparatus of the present invention.

Fig. 9 is a cross-sectional view of the apparatus for driving the spindle, viewed along the line a-a of fig. 8.

Fig. 10 is a longitudinal sectional view of the apparatus for driving the main shaft, viewed along the line B-B of fig. 8.

Fig. 11 is a perspective view showing the apparatus of fig. 8 driving a spindle.

Fig. 12 is a perspective view showing a thrust force acting on the main shaft of fig. 8.

Fig. 13 is a cross-sectional view showing another example of the spindle of the electric discharge machine.

Best mode for carrying out the invention

Referring to fig. 1, 2, 3, and 4, one embodiment of an electric discharge machining apparatus according to the present invention is described.

As shown in fig. 1, a column 2 is disposed behind a bed 1, and a moving body 3 is provided on the bed 1 so as to be slidable in the Y-axis direction. The slide plate 4 is slidably provided on the movable body 3 in an X-axis direction perpendicular to the Y-axis. A processing tank 5 filled with dielectric liquid is arranged on the sliding plate 4. A workpiece (not shown) is fixed to a table (not shown) disposed in the processing tank 5. A tool electrode 6, which is positioned close to the workpiece, is mounted on an electrode mounting device 9. The electrode mounting device 9 is fixed to the lower end of a hollow main shaft 8 that is movable in the Z-axis direction. In order to perform a jumping operation with a large movement amount without reducing the material removal speed, the electric discharge machining apparatus can move the tool electrode 6 with high accuracy at a speed of 10m/min or more by acceleration and deceleration exceeding the gravitational acceleration (1G). As shown in fig. 2, the main shaft 8 has a square cross section. Since the electrode mounting device 9 and the tool electrode 6 are arranged coaxially with the center line QC of the spindle 8 as shown in fig. 3 and 4, the tool electrode 6 can be moved with high accuracy. The permanent magnet pieces in a row are disposed symmetrically about the center line QC on both side walls of the square-cylindrical main shaft 8. Care is taken to both maintain high stiffness and reduce the weight of the main shaft 8 in order to obtain high acceleration. A main shaft 8 having a cylindrical hole 8a extending in a vertical direction at the center thereof and having a height of 4g/cm³The following densities. These are, preferably, made of ceramics having a small coefficient of thermal expansion and a large elastic modulus. In particular, the selection has a density of 3.2g/cm³Density of 3.0 to 3.1X 10⁶kgf/cm²An elastic modulus of 4.5 to 5.0MPa m^1/2Silicon nitride (Si) of fracture toughness of₃N₄) A ceramic. A method of manufacturing the ceramic spindle will be described briefly. First, alumina (Al)₂O₃) Silicon dioxide (SiO)₂) Or aluminum nitride (AlN) is added to silicon nitride (Si)₃N₄) Of the particles of (a). The mixture is molded into a hollow square column by, for example, an isostatic pressing method. The molded body is sintered by, for example, an atmospheric pressure sintering method or an atmosphere heating sintering method. The main shaft 8 may also be made of a composite material of light metal and more than 40 vol% of ceramic. Light metals, including aluminum or magnesium and their alloys. Ceramics, including silicon carbide (SiC) ceramics, aluminum oxide (Al)₂O₃) Ceramics and silicon nitride (Si)₃N₄) A ceramic. Composite of aluminium alloy and 55 volume% alumina ceramic having 2.95g/cm³Density of 2.0X 10⁶kgf/cm²Elastic modulus of (2) and 10.5MPa · m^1/2Fracture toughness of (2). Composite of an aluminium alloy and 55 volume% alumina ceramic having 3.00g/cm³Density of 2.65X 10⁶kgf/cm²Elastic modulus of (2) and 10.0MPa · m^1/2Fracture toughness of (2). Such a composite material is produced, for example, by impregnating a ceramic sintered body with a molten light metal in nitrogen at 700 to 800 ℃. The permanent magnet pieces are arranged on a magnet plate made of an iron-based soft magnetic material as thin as possible in order to form a good magnetic path therebetween. No member is provided between the spindle 8 and the magnet plate. In the illustrated embodiment, the magnet plate 12 on which two rows of permanent magnets 11 are arranged is attached to one side wall of the spindle 8, and the magnet plate 14 on which two rows of permanent magnets 13 are arranged is attached to the other side wall of the spindle 8. To guide the vertical movement of the main shaft 8, two linear motion ball bearing guide rails 21 are mounted parallel to each other on the front surface 2a of the upright 2. Upper and lower bearing blocks 22 and 23 fitted to the guide rail 21 are mounted on the main shaft 8On the rear wall of the housing. Frame 7 supporting a stator facing permanent magnets 11 and 13 is attached to front surface 2a of column 2. As shown in fig. 2 and 4, a stator composed of a field coil and a yoke is mounted on respective vertical surfaces of the plates 7d and 7e symmetrically with respect to the center line of the main shaft 8. The plates 7d and 7e are fixed to windows 7a and 7b formed on both side walls of the frame body 7. Yokes 31 and 41 composed of laminated silicon steel sheets are mounted on the plates 7d and 7e, respectively, and armature coils 32 and 42 are wound on the respective magnetic pole teeth of the yokes 31 and 41. The gap between yoke 31 and permanent magnet 11 and the gap between yoke 41 and permanent magnet 13 are adjusted to the same size. For example, these two gaps are adjusted to the same size by a plurality of thrust springs and tension springs provided on the plates 7d and 7 e. As a result, the magnetic attraction force occurring between the mover and the stator of the linear motor is cancelled out. A plurality of pipes 33 and 43 through which the cooling fluid passes are inserted into holes formed in the respective yokes 31 and 41. The linear motor 51 is attached to the front wall of the spindle 8, and a sensor 52 for reading the position of the spindle 8 is provided inside the front wall 7c of the housing 7. A driving device (not shown) of the linear motor receives the detection signal of the sensor 52 and supplies a control signal to the armature coils 32 and 42. An air cylinder 61 for balancing the load of the main shaft 8 which can move at an acceleration of 1G or more is provided. In order to miniaturize the machine, the cylinder 61 is disposed coaxially with the center line QC in the hole 8a, and its upper end is fixed to the main shaft 8 by a flange 64. Since the cylinder 61 is disposed next to the main shaft 8, high responsiveness thereof is ensured. The piston rod 63 is connected at one end to the piston 62 and at its other end to the connecting plate 65. A horizontally extending web 65 is secured to the upright 2. The air pressure of the upper chamber 66 formed in the cylinder 61 above the piston 62 is maintained at a constant value by means of a precision air regulator. By means of the cylinder 61, the power supplied to the coils 32 and 42 is saved when the main shaft 8 is stationary. Several snakeskin covers are provided in the gap between the main shaft 8 and the housing 7 to prevent dust from entering.

The means for guiding the spindle 8 and the position of the linear scale 51 are not limited to the embodiments shown in figures 2, 3 and 4. For example, as shown in fig. 5, it is preferable to add a close-contact roller bearing 23 for guiding the vertical movement of the main shaft 8 between the front wall of the main shaft 8 and the rear wall 7c of the housing 7. A sensor 52 for detecting the position of the spindle 8 by providing the linear scale 51 on the rear wall of the spindle 8 may be provided on the front surface 2a of the column 2.

As shown in fig. 6 and 7, the yokes 31 and 41, may be mounted on both side walls of the main shaft 8 with plates 8b and 8 c. In this case, the magnet plate 12 to which the permanent magnet 11 facing the yoke 31 is bonded is supported by the frame 7 through the plate 7 d. The magnet plate 14 to which the permanent magnet 13 facing the yoke 41 is bonded is supported by the frame 7 with a plate 7 e. Flexible hoses extending from the cooling pipes 33 and 43, or power lines extending from the coils 32 and 42, are connected to the terminals 71 and 72.

Referring to fig. 8, 9, 10, 11, and 12, another embodiment of the electric discharge machining apparatus according to the present invention is described. The same elements as those in fig. 1, 2, 3, 4, 5, 6 and 7 are given the same reference numerals, and the description thereof will be omitted.

Magnet plates 12 and 14 to which a row of permanent magnets 15 and 16 are respectively attached are respectively mounted on the front wall and the rear wall of the square-cylindrical spindle 8. As shown in fig. 11, each permanent magnet is attached to the magnet plate with a slight inclination from the horizontal direction in order to reduce torque ripple. The main shaft 8 has a square cylindrical hole 8a coaxial with the center line QC for weight reduction. Linear closely-arranged roller guides 24 and 25 for guiding the main shaft 8 are provided between both side surfaces of the main shaft 8 and the frame body 7. As clearly shown in fig. 10, a cylinder 61 for balancing the load of the main shaft 8 is provided between the plate 7e to which the yoke 41 is attached and the column 2. The piston rod 63 is connected to the main shaft 8 with a connecting plate 65. Referring to fig. 12, the force for driving the main shaft 8 will be described in detail. Reference numeral GCL in the figure denotes a center line where the permanent magnet rows 15 and 16 are symmetrically arranged. A resultant force TF of a thrust force FA generated between the permanent magnet array 15 and the yoke 31 and a thrust force FB generated between the permanent magnet array 16 and the yoke 41 coincides with the center line GCL of the main shaft. The linear roller guides 24 and 25 are arranged in the guide surfaces so that the guide force thereof coincides with the center line GCL. Thus, a force other than the vertical direction does not act on the linear closely-placed roller guides 24 and 25 that guide the main shaft 8. Thus, the main shaft 8, which is reduced in weight, can be moved in the vertical direction with high accuracy at high acceleration.

Holes of 70mm depth were machined in the workpiece using a ribbed graphite tool electrode with a bottom 1.0mm wide and 38mm long, each side having a 1 ° inclination. At this time, the ON time 100 μ sec, the OFF time 140 μ sec, the current peak value 93A, the average gap voltage 55V, the no-load voltage 120V, the "jump" speed 30m/min, and the "jump" time 0.24sec of 1 cycle were set. The material of the work was SKD11 of Japanese Industrial Standard. Although the "rinsing" was not performed, the processing speed was almost constant, and the processing was terminated at 135 minutes.

It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obviously, many modifications and variations are possible in light of the above teaching. For example, the cross section of the main shaft 8 is not limited to a square. These may be, for example, rectangular, or may be in the shape of two vertical faces parallel to each other as shown in fig. 13.

The embodiments shown are chosen in order to explain the nature of the invention and its practical application. The scope of the invention is defined by the appended claims.

Claims (13)

1. An electric discharge machining apparatus for machining a workpiece by moving a tool electrode in a vertical direction toward the workpiece while generating electric discharge between the workpiece and the tool electrode, comprising:

a main shaft capable of moving in a vertical direction,

an electrode mounting device which is mounted on the lower end of the main shaft coaxially with the main shaft and mounts a tool electrode,

at least one set of linear motor movers symmetrically mounted on the main shaft about the center line of the main shaft, and

a set of stators of the linear motor, which are respectively opposite to the set of moving stators.

2. The electric discharge machine of claim 1, wherein the group of the moving elements includes a magnet plate attached to the spindle and a row-like permanent magnet disposed on the magnet plate, and the group of the stators includes a yoke and a coil wound around the yoke.

3. The electric discharge machining apparatus according to claim 1, wherein the main shaft has a square column shape.

4. The electric discharge machining apparatus of claim 1, wherein the main shaft has a hole extending in a vertical direction at a center thereof.

5. The electric discharge machining apparatus of claim 3, wherein the 1 st side of the main spindle includes a 1 st guide for guiding the main spindle, and a plurality of movers are respectively installed on both sides of the main spindle adjacent to the 1 st side.

6. The electric discharge machine of claim 1, wherein a cylinder for balancing a load of the spindle is included.

7. The electric discharge machine of claim 4, comprising a cylinder disposed in the bore of the spindle for balancing the load of the spindle.

8. The electric discharge machining apparatus according to claim 5, wherein the side of the main shaft opposite to the 1 st side includes a 2 nd guide for guiding the main shaft.

9. The electric discharge machine of claim 1, wherein the stator includes a yoke and a coil wound around the yoke, and the stator includes a magnet plate attached to the spindle and permanent magnets arranged in a row on the magnet plate.

10. The discharge of claim 1Machining apparatus in which the spindle has a height of 4g/cm³The following densities.

11. The electric discharge machining apparatus of claim 10, wherein the main shaft is made of ceramic.

12. The electric discharge machining apparatus of claim 11, wherein the main shaft is made of silicon nitride (Si)₃N₄) Is made of ceramics.

13. The electric discharge machining apparatus of claim 10, wherein the main shaft is made of a composite material of a light metal and 40% by volume or more of a ceramic.