JPH06143041A - Wire electric discharge machining device - Google Patents

Abstract

PURPOSE:To prevent a deterioration of the processing surface resulting from a floating electrostatic capacity of a wire running mechanism. CONSTITUTION:Ferrite beads 7 and 10 are inserted and installed to a wire electrode 4. When a discharge is generated between the poles of a work 3 and the wire electrode 4 by a processing power source 13, a discharge current by an electrostatic energy accumulated to a floating electrostatic capacity between a wire running mechanism and a box body 1 is prevented from superposing to a discharge current by the processing power source 13, by the inductances of the ferrite beads 7 and 10. Since a radical startup of the discharge current can be blocked as well as the discharge energy flowing between the poles can be reduced, the surface coarseness and the form accuracy in a finishing process can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire electric discharge machine.

[0002]

2. Description of the Related Art In electrical discharge machining, a voltage is applied between a tool electrode and a workpiece to intermittently generate an electrical discharge, and a part of the workpiece is removed by a thermal action and a mechanical action associated with the electrical discharge. Is processed. Therefore, the shape accuracy and surface roughness in electric discharge machining are determined by the integration of individual single-shot electric discharge energies. Therefore, it is necessary to finely control the energy of single-shot electric discharge in finishing. The power source used in wire electric discharge machining is mainly of a capacitor discharge type, and the discharge energy E in this case is expressed by the following formula 1.

[0003] In ^{E = C · V 2/2} ... (1) above Equation 1, C is the capacitance of the capacitor, V is a capacitor charging voltage (voltage applied between the wire electrode and the workpiece). A certain amount of voltage is required to maintain stable discharge, and it is essential to keep the capacitance C of the capacitor small in order to miniaturize the discharge energy.

The capacitance C of the capacitor actually used for finishing is a very small capacitance of several tens of pF to several hundred pF, which means that the floating electrostatic capacitance of each part of the discharge circuit greatly affects the machining performance. ing. For this reason,
Conventionally, various countermeasures for stray capacitance have been implemented. In particular, as a measure against the floating electrostatic capacitance on the wire electrode side, it has been proposed to insulate the workpiece together with the wire electrode from the apparatus housing. In this case, since the stray capacitance formed by the wire electrode and the casing and the stray capacitance formed by the workpiece and the casing are connected in series, the capacitance can be reduced equivalently. Can be made.

[0005]

In the case of insulating the above-mentioned work piece from the housing, in order to secure the mechanical accuracy and rigidity required for the precision work, a piece such as a stone surface plate is required, which is very difficult. It will be expensive. Further, there is a drawback that the effect of reducing the electrostatic capacitance becomes weaker as the area increases. Therefore,
It is an object of the present invention to provide an electric discharge machining apparatus that does not insulate a workpiece and reliably and inexpensively prevents deterioration of a machined surface due to a floating electrostatic capacitance of a wire traveling mechanism section.

[0006]

According to the present invention, the influence of the stray capacitance is reduced by inserting an inductance in the charge / discharge path of the stray capacitance formed between the wire running mechanism and the device casing. Exclude. In particular, the above-mentioned inductance affects the machining current by inserting it into the wire traveling mechanism portion in the area other than the machining area from the feeding point that supplies machining power to the wire electrode, that is, in the section other than the machining area between the electrodes Eliminate the effects of stray capacitance without giving. Further, the inductance may be constituted by a high magnetic permeability magnetic circuit attached so as to surround the wire electrode, or may be constituted by a circuit element in which a resistance is connected in parallel with the inductance. Further, ferrite beads may be used instead of the inductance.

[0007]

When a discharge is generated between the wire electrode and the workpiece by the voltage application from the machining power source, the discharge current of the electrostatic energy accumulated in the floating capacitance is superimposed on the discharge current and flows. However, since it is blocked by the inductance inserted in the discharge path of the stray capacitance, the discharge current comes from the machining power source, the discharge energy is kept small, and the steep rise of the discharge current is prevented.
Improves the surface roughness of the machined surface. In particular, since the frequency of discharge is high frequency, the current blocked by the inductance is weak and high frequency. Therefore, the inductance may be a small high magnetic permeability element such as a ferrite bead. Since the ferrite beads have a large internal loss in the high frequency region, the electrostatic energy of the stray capacitance can be absorbed, the resonance between the inductance and the stray capacitance can be prevented, and the generation of resonance current can be prevented. Can also be prevented.

[0008]

1 is a schematic view of an embodiment of the present invention. The work piece 3 is fixed to the table 2, and is mechanically attached to the apparatus housing 1 via the table 2 and is also electrically connected. The wire electrode 4 includes a wire supply reel 5, an upper tension roller 6, an upper ferrite bead 7, an upper wire guide 8, an electric discharge machining area with the workpiece 3, a lower wire guide 9, and a lower ferrite bead 10.
Wire recovery reel 1 via lower tension roller 11
It is configured to be sent to 2. The processing power source 13 and the table 2 are connected by a cable 15, and the wire guides 8 and 9 are connected by the cable 14 to the processing power source 13.

The upper and lower tension rollers 6 and 11 always apply a constant tension to the wire electrode 4 to prevent the wire electrode 4 from loosening or vibrating. The wire guides 8 and 9 control the positions of the wire electrode 4 and the workpiece 3, and the machining power source 1
It functions to feed the machining pulse current supplied from 3 through the cables 14 and 15 to the wire electrode 4. The wire electrode traveling mechanism including the wire supply reel 5, the upper and lower tension rollers 6 and 11, the upper and lower wire guides 8 and 9, and the wire collecting reel 12 is electrically insulated from the housing 1.

The structure of the wire electric discharge machine is almost the same as that of the conventional wire electric discharge machine, but the present embodiment is different from the conventional wire electric discharge machine in that the ferrite beads 7 and 10 are attached. Only to do.
The ferrite beads 7 and 10 are arranged so that the wire electrode 4 penetrates through the center thereof, and act as an inductance that suppresses discharge of the stray capacitance. In the wire electric discharge machine, the used wire is wound by the collecting reel 12, but a method of stacking and collecting the used wire on a spiral in a box of an insulator is also known,
The present invention can also be applied to this method.

FIG. 2 is an explanatory diagram of an electric circuit in this embodiment for explaining the influence of the stray capacitance. The machining power source 13 is connected to the wire electrode 4 by the cable 14 via the wire guides 8 and 9, and is also connected to the workpiece 2 by the cable 15 via the table 2.
In FIG. 2, the resistance of these cables 14 and 15 is R1,
The inductance is represented as L1. On the other hand, the case 1
Are electrically connected to the workpiece 3 via the table 2. The housing 1 and the wire running mechanism are insulated from each other, and there is a floating capacitance C between them. A discharge path due to the floating capacitance C is formed by the wire electrode 4, the workpiece 3, and the housing 1. In FIG. 2, the resistance of this discharge path is shown as R2, and the inductance is shown as L2. Further, the resistance of the ferrite beads 7 and 10 is Rr and the inductance is Lr.
Is represented.

When a voltage is applied between the wire electrode 4 and the workpiece 3 by the machining power source 13 to generate a discharge, a discharge current flows, for example, as indicated by "a" in FIG. On the other hand, there is a slight time delay from the application of a voltage to the gap between the wire electrode 4 and the workpiece 3 to the occurrence of discharge. During this time delay, the floating capacitance C is charged to the voltage applied to the wire electrode 4 and the workpiece 3, that is, the voltage between the electrodes. Then, the energy of the charged floating capacitance C is about to be discharged when the discharge is generated between the wire electrode 4 and the workpiece 3.

In the case where the ferrite beads 7 and 10 are not provided as in the conventional wire electric discharge machining apparatus and the resistance Rr and the inductance Lr in FIG. 2 are not provided, the energy stored in the floating electrostatic capacitance C is When a discharge occurs between the electrodes, a discharge current from the floating capacitance C flows between the wire electrode 4 and the workpiece 3 as indicated by "b" in FIG. Wire electrode 4 and work piece 3
A combined discharge current as indicated by "c" in FIG. 3 will flow between the gaps. This combined discharge current c has large energy and has a steep rising edge, which causes deterioration of processing accuracy and surface roughness.

However, as in the present invention, the floating capacitance C
In order to increase the impedance of the discharge path of the resistor Rr,
Ferrite beads 7 and 10 having inductance Lr
By providing, the impedance of the discharge path rises, the discharge current due to the floating capacitance C is suppressed, and deterioration of the machined surface can be prevented. In particular, as shown in the above example,
By arranging the ferrite beads 7 and 10 other than the section from the feeding point (the wire guides 8 and 9) to the wire electrode 4 to the discharge area between the wire electrode 4 and the workpiece 3, the ferrite beads 7 and 10 are arranged in the discharge path of the machining power source 13. By not affecting the influence, only the electric current from the machining power source 13 flows between the wire electrode 4 and the workpiece 3 as shown by "a" in FIG.
A good finished surface can be obtained.

A high-permeability magnetic circuit that surrounds the wire electrode may be used as an inductance for preventing the discharge of the stray capacitance C, but the current to be blocked is weak and high frequency (from the machining power source 13 to the wire electrode 4 and the workpiece). The repetition frequency of the voltage applied between the poles between the objects 3 is a high frequency, and thus the frequency of the discharge current of the floating electrostatic capacitance C is also a high frequency.) Therefore, the ferrite beads 7 and 10 are small in size. It suffices to pass the high-permeability element (1) through the wire electrode. Especially, since the ferrite beads have a large internal loss in the high frequency region,
Since the electrostatic energy accumulated in the floating electrostatic capacitance C can be absorbed, even if the resonance occurs with the floating electrostatic capacitance and the oscillating current flows only with the inductance, this The discharge current from the floating capacitance C can be suppressed.

FIG. 4 is a diagram showing a main part of an embodiment when the present invention is applied to a wire electric discharge grinding machine. The wire electrode 4 passes from the wire supply reel 5 through the ferrite beads 7 and 10, the wire guide 8 and the wire recovery reel 12
Sent to. A workpiece (shaft) 3 is arranged at a position facing the wire guide 8, and electric discharge is generated at this position to perform electric discharge grinding. In this electric discharge grinding method, since the wire electrode 4 is supported by the wire guide 8 at the electric discharge point, there is no eccentricity or wobbling of the wire and it is used for machining a fine shaft or the like.

Also in this wire electric discharge grinding process, by disposing the ferrite beads 7 and 10, the electric discharge from the electrostatic capacitance between the wire traveling mechanism and the housing can be suppressed by the ferrite beads. Since the energy can be kept minute and the sudden rise of the discharge current can be prevented, fine processing becomes possible.

[0018]

According to the present invention, since the inductance is inserted in the charging / discharging path of the floating electrostatic capacitance formed between the wire traveling mechanism and the apparatus housing, discharge is generated between the wire electrode and the workpiece. At this time, although the discharge from the floating capacitance also tries to occur together, the inserted inductance suppresses the discharge from the floating capacitance. Therefore, the discharge current that flows between the wire electrode and the workpiece is only the current from the machining power source, so that the machining energy can be kept small and the sharp rise of the discharge current is prevented. In addition to being able to improve, the surface roughness of the processed surface of the workpiece can be improved.

In particular, the use of ferrite beads having an inductance instead of the inductance and passing the ferrite beads through the wire electrode can suppress the discharge of the electrostatic capacitance, so that the object can be achieved inexpensively and easily. be able to. Furthermore, since the ferrite beads have a large internal loss in the high frequency region, they can absorb the electrostatic energy accumulated in the stray capacitance, so resonance occurs with the capacitance only with the inductance, and resonance occurs. It is effective even when a current flows.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an electric circuit in the present embodiment for explaining the influence of floating capacitance.

FIG. 3 is an explanatory diagram of a discharge current.

FIG. 4 is an explanatory view of a main part of an embodiment when the present invention is applied to a wire electric discharge grinding machine.

[Explanation of symbols]

 1 Device Case 2 Table 3 Workpiece 4 Wire Electrode 5 Wire Supply Reel 6,11 Tension Roller 7,10 Ferrite Bead 8,9 Wire Guide (Electronic Supply) 12 Wire Recovery Reel 13 Processing Power Supply 14,15 Cable C Floating Static Capacitance Rr Ferrite bead resistance Lr Ferrite bead inductance

Claims (5)

[Claims] 1. A wire is used as a tool electrode, an intermittent electric discharge is generated between the wire electrode and a workpiece, the workpiece is removed, and the wire traveling mechanism is electrically connected to the apparatus casing. In a wire electric discharge machine which is insulated from a wire, a wire electric discharge machine in which an inductance is inserted in a charging / discharging path of a floating capacitance formed between a wire traveling mechanism and a device housing. 2. The wire electric discharge machining apparatus according to claim 1, wherein the inductance is inserted in a wire traveling mechanism portion on a side opposite to a machining area from a power supply for supplying machining power to a wire electrode. 3. The wire electric discharge machining apparatus according to claim 1, wherein the wire electric discharge machining apparatus is constituted by a high-permeability magnetic circuit attached so as to surround the wire electrode as the inductance. 4. The wire electric discharge machine according to claim 1 or 2, which is configured by a circuit element having a characteristic that a resistor is connected in parallel with the inductance instead of the inductance. 5. The wire electric discharge machine according to claim 1 or 2, wherein ferrite beads are used instead of the inductance.