JP5453640B2 - Electric discharge machine - Google Patents

Description

In the present invention, when micro machining is performed using a general electric discharge machine, a feed electrode is arranged, and the influence of inductance and stray capacitance generated in the circuit is eliminated by electrostatic induction by non-contact power feeding, thereby making the finer The present invention relates to an electric discharge machining apparatus capable of performing fine surface machining with electric discharge energy.

In micro electric discharge machining applied to fine machining, the capacity of the capacitor must be reduced as the machining becomes micro. However, in an actual machining machine, as shown in FIG. 1, between the plus and minus wires There are stray capacitances between the electrode holder and the processing table, between the tool electrode and the workpiece, and the charge charged there is discharged between the electrodes together with the original capacitor charge connected to the circuit. Accordingly, since the stray capacitance becomes dominant in the micro area, it is necessary to devise such as shortening the wiring as much as possible and making the holder and the table with an insulator.

Therefore, as a method to reduce the effect of stray capacitance and improve surface roughness by electrical discharge machining, a main power supply and an auxiliary power supply are installed. During finishing, the current supplied from the auxiliary power supply is the current to the main power supply. A method of providing a diode for preventing inflow, including a reverse bias power source for supplying a predetermined reverse bias voltage to the diode, and greatly reducing the influence of stray capacitance of the main power supply line (Patent Document 1), or an electric discharge machining apparatus A method of providing resistance (Patent Document 2) that suppresses the discharge between the electrode and the work piece caused by electrical energy accumulated in the stray capacitance in the power supply device and the pulse control unit, or first, Reduces the stray capacitance between the electrode and workpiece by adjusting the opening and closing means provided on the power supply line with low discharge energy, which has two power sources that generate the second discharge energy The method (Patent Document 3) it is known to. However, even with such a technique for reducing stray capacitance, the minimum surface roughness is about 0.4 μm.

Also, there is known an electric discharge machine (Patent Document 4) in which a cylindrical guide is mechanically fixed to a tool electrode and a large gap is provided so as not to affect the discharge process in order to shorten the power feeding path and eliminate the influence of inductance. However, a method for setting the gap large is known, but in this case, it is considered that the discharge energy between the tool electrode and the workpiece cannot be controlled small.

JP 7-276142 A JP 2000-42835 A JP 2002-66843 A JP 2004-122316 A

Provided is an electric discharge machining apparatus capable of performing finer machining using a general electric discharge machine.

The present inventors have no movement of electrons between the power supply electrode and the tool electrode, and determine the discharge energy only by the capacity formed between the power supply electrode and the tool electrode and the capacity between the tool electrode and the workpiece. Therefore, we thought that it was possible to perform fine processing compared to the conventional micro electric discharge machine in which the minimum critical discharge energy is determined by the stray capacitance generated in the circuit.

That is, the present invention is (1) a discharge for machining a workpiece by applying a pulse voltage to a tool electrode and a workpiece, which are arranged with a small inter-electrode distance, to generate discharge energy between the electrodes. In processing equipment,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A power supply electrode disposed opposite to the tool electrode power supply section with a constant gap;
A pulse power source in which the feeding electrode and the workpiece are connected;
Have
A voltage is applied from the pulse power supply, and electrostatic power is fed from the power supply electrode to the tool electrode power supply unit, thereby adjusting at least one of a distance between the power supply electrodes facing the tool electrode power supply unit and an opposing area. The discharge energy is determined on the basis of the capacitance C _1A formed by the capacitor C _2A formed by the gap between the tool electrode and the workpiece ,
A voltage between the tool electrode and the workpiece, comprising a voltage detection circuit in which a detection line of a voltage measurement probe arranged to hold the opposed surface of the tool electrode with a fixed gap and the workpiece are connected. An electrical discharge machining apparatus equipped with a measuring device for measuring the temperature .

(2) In an electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, to generate discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A capacitor with one terminal in contact with the tool electrode power supply unit;
A pulse power source wired to the other terminal of the capacitor and the workpiece;
Have
A voltage is applied from the pulse power source, and power is supplied by capacitive coupling of the capacitor and the tool electrode power supply unit. The capacitor C _3A and the capacitance C _4A formed by the gap between the tool electrode and the workpiece are provided. And the electric discharge machining apparatus, wherein the electric discharge energy is determined.

(3) In an electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, to generate discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A feeding electrode disposed opposite the workpiece with a constant gap;
A pulse power source connected to the tool electrode power supply unit and the power supply electrode;
Have
A voltage is applied from the pulse power source, and electrostatic work is fed to the workpiece from the feeding electrode, thereby adjusting at least one of the distance and the facing area of the feeding electrode facing the workpiece, and a capacitor C _1B is formed in the gap, and a capacitor C _2B is formed at the gap between the workpiece and the tool electrode, on the basis, and determines the discharge energy, the electric discharge machining apparatus.

( 4 ) The tool electrode and the workpiece comprising a voltage detection circuit in which a detection line of the voltage measurement probe arranged to hold the opposing surface of the tool electrode and a fixed gap and the workpiece are connected. The electrical discharge machining apparatus according to (2) or (3) , wherein the electrical discharge machining apparatus is equipped with a measurement device that measures an inter-electrode voltage.

( 5 ) The measurement apparatus includes a piezoelectric element that displaces a support position of the workpiece with respect to the tool electrode,
Based on the voltage waveform between the tool electrode and the workpiece measured by the measuring device, it is determined whether the distance between the electrodes is too short and short-circuited, or too wide and close to an open state. A function of controlling the gap between the electrodes to an appropriate value at which discharge can occur by transmitting a control signal and adjusting the support position of the workpiece by displacing the workpiece by the piezoelectric element, The electric discharge machining apparatus according to (1) or (4) .

( 6 ) The measurement apparatus includes a servo motor that displaces a support position of the tool electrode with respect to the workpiece,
Based on the interelectrode voltage waveform of the tool electrode and the workpiece measured by the measuring device, determine whether the interelectrode distance is too short and short-circuited, or too wide and close to the open state, It has a function of controlling the gap between the electrodes to an appropriate value that can cause discharge by transmitting a control signal, controlling the servo motor, and adjusting the support position of the tool electrode. The electric discharge machining apparatus described in any one of (1), ( 4 ) and ( 5 ).

In conventional micro electrical discharge machining, the influence of stray capacitance generated in the circuit was dominant, but in the present invention, the influence of circuit inductance and stray capacitance can be reduced by adopting the electrostatic induction power feeding method. By controlling the two capacity ratios, the amount of discharge energy changes and the surface roughness of the workpiece can be controlled. In addition, since power can be supplied to the tool electrode power supply section that rotates at high speed, machining waste can be easily discharged, and high-precision micromachining can be performed without causing axial deflection of the tool electrode. Furthermore, the contact voltage is measured from a non-contact voltage measuring device that measures the contact voltage between the tool electrode and the workpiece without contact with the tool electrode. By combining a servo control circuit that adjusts the position of the spindle, the electrical discharge machine can be automated.

It is the figure which showed a mode that the electric charge which accumulated in the stray capacitance was discharged together with the capacitor | condenser discharge circuit by which charging and discharge are repeated alternately and pulsed discharge. It is a figure which shows the principle of the micro electrical discharge machining method using electrostatic induction electric power feeding of this invention. It is a figure which shows the equivalent circuit at the time of charge (a) and the time of discharge (b) of the equivalent circuit of the micro electrical discharge machining method using electrostatic induction power supply of this invention. It is the figure which simulated the voltage waveform between electrodes between a tool electrode and a workpiece obtained by analyzing the equivalent circuit of FIG. It is the figure which simulated the electric current waveform between electrodes between a tool electrode and a workpiece obtained by analyzing the equivalent circuit of FIG. It is a conceptual diagram of the apparatus of the example arrange | positioned on the outer side of the tool electrode electric power feeding part with which the power feeding electrode of this invention had a clearance gap and the tool electrode was fixed to the front-end | tip. Sectional drawing which shows the electrode outline which installed the electric power feeding electrode of Example 1 of this invention around the tool electrode, The figure which shows the outline of arrangement | positioning of the non-contact voltage measurement probe which detects a voltage between electrodes, and the oscilloscope which monitors a voltage It is. It is a figure which shows the voltage waveform between electrodes measured with the oscilloscope obtained from the experimental result of Example 1 of this invention. In Example 2 of the present invention, using the electric discharge machining apparatus of the present invention, machining was performed on a block gauge having a mirror surface, and the size of the resulting discharge trace was determined when the tool electrode was rotated and the tool It is a figure which shows the relationship between the discharge trace diameter in the case of electrode non-rotation, and a feeding electrode capacity | capacitance. It is a figure which shows the principle of the non-contact voltage measuring method of this invention. In Example 3 of this invention, it is the graph which compared the case where the non-contact voltage measurement of this invention was performed, and the case where it was not performed, and obtained discharge scar diameter. The conceptual diagram of the average electrode voltage detection circuit of this invention is shown. In the present invention, the influence on the interelectrode voltage V ₂ due to the difference in capacitance of the electrostatic dielectric capacitors C ₁ / C ₂ was examined. The capacitance ratio of the capacitor C _{1 /} C ₂ in FIG. 3 is a graph showing a machining gap voltage in the case of the 10. The influence on the interelectrode voltage V ₂ due to the difference in capacitance between the capacitors C _{1 and} C _{2 in} FIG. 3 was examined. Is a graph showing a machining gap voltage when the C 1 _/ C ₂ in volume ratio to 1. In the present invention, a workpiece is mounted on a piezoelectric table, and the height of the workpiece is detected and the distance between the poles is controlled by servo control in order to control the discharge energy generated between the tool electrode and the workpiece. The conceptual diagram of is shown. It is a conceptual diagram of the piezoelectric table servo feed control circuit of the present invention. In Example 4 of this invention, it is the figure which processed various servo control methods and manual gap control, and measured the surface roughness of the processing surface on the same conditions, and made it into the graph. It is the figure which compared the processing speed in Example 4 of this invention. When power is supplied from the tool electrode power supply unit side according to the present invention, when the power supply electrode is used, (a), and the capacitive coupling method using a capacitor is shown in FIG. It is the figure which showed the case where it couple | bonds with the capacitor | condenser by a capacitor | condenser with (a), and the apparatus when connecting the workpiece | work side by a feed electrode of this invention to (b). In Example 5 of this invention, it is a figure of the voltage between poles by the work side electric power feeding and tool side electric power feeding of this invention. In Example 5 of this invention, it is a figure which shows the relationship between the discharge trace diameter which arose in the process for several seconds by the work side electric power feeding and tool side electric power feeding of this invention, and electric power feeding capacity. In Example 5 of this invention, it is a photograph of the workpiece processed by arrange | positioning and supplying a feeding electrode on the work side. It is the figure showing the outline | summary of the method of the electric power feeding to a wire, the inductance which generate | occur | produces in a circuit, and a stray capacitance in the conventional wire electric discharge machining. It is a figure explaining the reason for the eccentricity of the wire, which occurs when the wire comes into contact with the supply electron, in the conventional wire discharge. It is the figure which showed the outline of the electric power feeding method at the time of applying the electrostatic induction electric power feeding method of this invention to wire electric discharge machining, and a circuit.

If the uncharged conductor (B) is brought close to the charged conductor (A), the conductor (B) is dissimilar to the side closer to the conductor (A) (if A is +), the far side It is known that the same kind (A +) of charge appears in this, and this phenomenon is called electrostatic induction.

As an example of the equivalent circuit of the present invention, when a feeding electrode, a tool electrode, and a workpiece as shown in FIG. 2 are arranged. Since there is no movement of electrons between the power supply electrode and the tool electrode, stray capacitance and inductance generated in the circuit can be ignored. When a pulse voltage V is applied to the power supply electrode and the workpiece at a constant period, the applied voltage V In FIG. 2A, an electrostatic dielectric phenomenon occurs, and electrons in the electrode move to cause a bias in charge.

At this time, in the machining gap between the tool electrode and the workpiece, the surface of the tool electrode is positively charged and the workpiece is negatively charged, thereby generating a potential difference between the electrodes and generating electric discharge. Electrons move from the workpiece to the tool electrode due to the discharge, FIG.

Next, the applied voltage is set to zero. The tool electrode is negatively charged by accepting electrons from the workpiece by discharge, and conversely, the workpiece and the feed electrode are both positively charged by discharging electrons by discharge, FIG. 2 (c).

Accordingly, since the tool electrode is negative and the workpiece is positively charged, a potential difference is generated between the electrodes, and a discharge is generated to move electrons from the tool electrode to the workpiece, FIG. 2D. In this way, processing is performed by repeating the cycle. Moreover, it turns out that this processing method is bipolar discharge from FIG.2 (b) and FIG.2 (d).

An equivalent circuit of the micro electric discharge machining method using the electrostatic dielectric power supply can be expressed as when the circuit shown in FIG. 3A is opened and when the electric discharge is shown in FIG. 3B. The internal resistance of the electrode is R ₀ , the capacitance formed between the feed electrode and the tool electrode feed section, and the tool electrode and the workpiece is C ₁ and C _2, and the voltage drop between the electrodes caused by the discharge is applied to the zener diode The replacement R and _Vd are used to represent the circuit during discharge when the tool electrode is positive and the workpiece is negatively discharged, whereas the tool electrode is negative and the workpiece is positively discharged. , V _d is inverted. Also, the voltage V (t) at the point a in the figure is assumed, the current flowing out from the point a to each circuit line is I ₁ (t), I ₂ (t), I ₃ (t), and the power supply voltage is given by Is the period of the applied voltage, and t _on is the pulse width. The time when the equivalent circuit shown in FIG. 3 is opened is expressed by Equation 2, and the time of discharge is expressed by Equation 3, which is as follows.

When opened, the following formula is used.

When discharging, the following equation is obtained.

FIG. 4 shows a voltage waveform between the machining gaps obtained by calculating these equations, and FIG. 5 shows a discharge current flowing through the machining gap. The applied voltage V was a unipolar rectangular wave with a period T = 110 μs, an amplitude of 150 V, and a duty of 45%. In addition, the circuit constants used for the calculation were C ₁ = 10 pF, C ₂ = ₁ pF, and R = 100Ω, respectively. The value of C ₁ is estimated as the capacity of the cylinder capacitor. The discharge voltage V _d was set to 20V, also the order using the actual value the internal resistance R ₀ of the power supply, the resistance R of the machining gap is the peak value of the discharge current is observed in the general microfabrication Set to match. The discharge voltage _{V d} was set to 20V. The simulation was started from the initial state in which the tool electrode was not charged, and it was assumed that no discharge occurred in the first period. It was assumed that discharge occurred at t = 5 / 4T, 7 / 4T, 9 / 4T, and 11 / 4T. After the discharge, the voltage between the electrodes became V _d = 20 V, the charge was discharged, and the insulation was restored at the moment when the current in the machining gap became 0 A, and the equivalent circuit was switched to the open state. 4A is a region in an open state, and FIG. 4B is a region where discharge is generated with the tool electrode being positive and the workpiece being negative, and at that moment, a discharge current flows as shown in FIG. . (C) is an area that is opened again after the end of discharge, and (d) is an area where the tool electrode is negative and the workpiece is positive and discharged. (A), (b), (c), and (d) in FIG. 5 correspond to the states (a), (b), (c), and (d) in FIG.

In order to prove that the simulation shown above is correct, a processing experiment was conducted. FIG. 6 shows a conceptual diagram of an apparatus arranged outside the tool electrode power supply unit in which the power supply electrode of the present invention has a gap and the tool electrode is fixed to the tip on the same axis. The tool electrode feeding portion rotates while being pressed against the V-shaped bearing and the upper bearing via a steel ball by a pulley and belt. By using a V-shaped bearing, the runout is extremely small, high rotational accuracy is obtained, and high-precision machining is possible. With the tool electrode power supply portion inserted into the hollow pipe as the power supply electrode, the power supply electrode was fixed while being pressed against the V-shaped bearing for power supply electrode. The tool electrode power supply unit and the power supply electrode were set to be concentric when attached. In order to perform fine electrical discharge machining in which the tool rotates using electrostatic induction power feeding, it is necessary to insulate the tool electrode power feeding unit from the apparatus main body. Therefore, the V-shaped bearing uses ceramic which is an insulator at a portion in contact with the tool electrode power supply portion, and further, the tool electrode power supply portion is insulated from the apparatus main body by making the fixing portion of the upper bearing made of resin. The DC motor is driven to rotate the tool electrode power feeding unit via the pulley and belt.

The tool electrode of tungsten (φ0.31) is soldered to the center of the tip of the tool electrode feed portion (φ3.8) inserted into the feed electrode having a length of 125 mm. The feeding electrode is a copper pipe (outer diameter φ66.35, inner diameter φ4.5), and the tool electrode feeding portion is inserted into the hollow portion. FIG. 7 shows a cross-sectional view of the feeding electrode and the tool electrode. The power supply electrode and the tool electrode power supply unit were supported in parallel with a certain gap, and the tool electrode was fixed at the tip of the tool electrode power supply unit and arranged with a gap between the workpiece and the electrode. A non-contact voltage measuring probe measures the charge of the tool electrode and measures an inter-electrode voltage waveform between the tool electrode and the workpiece with an oscilloscope.

The electrode part of FIG. 7 is fixed to the main shaft of a die-sinking electric discharge machine (Sodic AQ-35L, processing range X2660 mm Y250 mm Z250 mm) used for general mold processing, and the workpiece is fixed in an acrylic processing tank, The processing tank is installed on a precision displacement table placed on the processing table of the processing machine.

Although the discharge pulse circuit of the processing machine was used, a transistor discharge circuit that applied a voltage with a constant pulse width at a constant period was selected instead of an isopulse with a constant discharge duration. Further, since the voltage waveform between the electrodes appearing between the electrodes is different from the conventional one, the servo feed control of the processing machine cannot be used. Therefore, the machining of the distance between the poles and the machining feed were carried out by manually moving the workpiece up and down using a precision displacement table without using the feed of the electric discharge machine. At that time, the voltage waveform between the electrodes was visually observed with an oscilloscope, and the scale was adjusted so that the discharge continued. Table 1 shows the processing conditions.

As shown in FIG. 7, the non-contact voltage measuring probe has an annular shape that is concentric with the tool electrode, and is arranged with a certain distance from the feeding electrode. When the voltage of the tool electrode changes, an electric field is generated between the tool electrode and the non-contact voltage measuring probe, and charges are accumulated in the non-contact voltage measuring probe due to an electrostatic induction phenomenon. Therefore, the voltage between the electrodes divided by the ratio of the capacitance between the tool electrode and the probe and the stray capacitance of the detection line can be measured, and the voltage waveform between the electrodes can be monitored with an oscilloscope.

FIG. 8 shows the voltage waveform between the electrodes monitored with an oscilloscope. Regions (a), (b), (c), and (d) shown in the figure correspond to regions of the same symbol in FIG. Although it is not the waveform when the first discharge occurs as in the simulation, it can be seen from FIG. 8 that the processing method of the present invention is a bipolar discharge. The actual measured inter-electrode voltage waveform and the inter-electrode voltage waveform obtained by analyzing the equivalent circuit (FIG. 4) are shown in FIGS. 4 and 8 at (a), (b), (c), and (d). Qualitatively agree with each other, that is, the processing method of the present invention can be correctly expressed by an equivalent circuit, and the principle can be proved.

The capacitance C ₁ between the feeding electrode and the tool electrode facing the tool electrode feed section, the dielectric constant of the machining gap epsilon, the tool electrode feeding outer diameter a, a feeding electrode inner diameter b, and the feeding electrode length L Then, it can obtain | require by Formula 4.

In the machining method of the present invention, the discharge energy is determined by two capacities, a capacity (C ₁ ) formed between the feeding electrode and the tool electrode and a capacity (C ₂ ) formed between the tool electrode and the workpiece. The Further, in the processing method of the present invention, the applied voltage V is divided as shown in Equation 5.

_{Here, V c1,} V _c2 are each _C 1, _{C 2} of the charging _{voltage, Q 1,} Q ₂ are each _C 1, charge that is charged to _{C 2.} Accordingly, when the feed electrode length L is shortened, the capacitance C ₁ formed between the feed electrode and the tool electrode is reduced, and V _c1 is increased, so that the interelectrode voltage V _c2 of the machining gap is reduced and the discharge energy is reduced. Can be reduced. When the applied voltage from the pulse power source is determined and the specifications of the power supply electrode are determined, the capacitances C ₁ and C ₂ are determined by Equation 3, and the discharge voltage is determined.

Therefore, compared to a conventional electric discharge machine in which the minimum critical discharge energy is determined by the stray capacitance generated in the circuit, the present invention has an effect of inductance and stray capacitance generated in the circuit by a method of electrostatically feeding the tool electrode. Since it is processed only by the discharge of a minute charge charged between the electrodes, fine processing becomes possible, and furthermore, non-contact power supply is possible, so the rotating tool electrode power supply part, gas bearing, Electric discharge machining using a magnetic bearing or the like becomes possible.

If the voltage between the tool electrode and the workpiece is lowered in order to reduce the discharge energy, the gap between the tool electrode and the workpiece becomes narrower. Therefore, processing becomes unstable. Therefore, in the apparatus of the present invention, the power supply electrode and the tool electrode power supply unit are separately supported, the tool electrode is designed to be rotatable by a pulley, and even when the distance between the electrodes is small, the structure can be easily discharged. It was.

The amount of change in the capacitance C ₁ due to the difference in the inner diameter and length of the feeding electrode was determined by calculation, and the results are summarized in Table 2.

Using the electrical discharge machining apparatus of the present invention, machining was performed on the mirror gauge block gauge for several seconds in the machining condition table 3, and the size of the resulting electrical discharge mark was rotated at 3000 rpm. The effect of tool rotation was compared between the case and the case where the tool electrode was not rotated.

The diameter of the discharge mark was measured using a confocal laser microscope (LETY OLS3000 manufactured by OLYMPUS). A graph summarizing the observation results of the discharge marks is shown in FIG. With the conventional non-rotating tool, discharge could only be confirmed up to a power supply capacity of 6.6 pF, but with the rotary tool used this time, discharge traces could be obtained even when the power supply capacity was reduced to 1.9 pF. In addition, the non-rotary tool could only perform stable machining up to a power supply capacity of 13 pF, but the rotary tool could perform stable machining up to 7.5 pF. The smaller the power supply capacity, the smaller the charging voltage V _C2 , the smaller the discharge energy, the narrower the gap between the electrodes where discharge occurs, and it will be difficult to discharge the scraps. Therefore, it is considered that the discharge trace was obtained with a smaller power supply capacity of 1.9 pF than when the non-rotating tool electrode was used.

If the machining is performed with a smaller power supply capacity, the discharge energy can be reduced, so that the roughness of the machined surface may be further improved. However, when using a power supply capacity of 1.9 pF with which the minimum discharge trace was obtained, discharge concentration occurred on the machined surface and machining did not proceed. This is considered to be because the gap between the electrodes where the discharge starts is 2 μm or less, and the minute distance between the electrodes where the discharge flies can not be maintained properly manually. In order to prevent discharge concentration, it is necessary to automatically control the gap between the electrodes in units of μm.

In order to grasp the state between the electrodes, it is necessary to detect the time average value of the voltage between the electrodes (hereinafter referred to as the average voltage between the electrodes). However, in order to measure the voltage between the electrodes in the electric discharge machining apparatus of the present invention, it is impossible to connect the detection line directly to the tool electrode power feeding portion that rotates at high speed. Therefore, in the present invention, the interelectrode voltage is measured using a non-contact voltage measurement method.

The principle of the non-contact voltage measurement method is shown in FIG. A non-contact voltage measurement probe (metal with a detection line) is placed in the vicinity of the tool electrode in a non-contact manner. In the case of FIG. 10, it is a ring concentric with the tool electrode. When the voltage of the tool electrode changes, an electric field is generated between the tool electrode and the non-contact voltage measuring probe, and charges are accumulated in the non-contact voltage measuring probe due to an electrostatic induction phenomenon.
The voltage between the electrodes is the sum of the voltage V _CP applied to the capacitance C _P between the tool electrode and the probe (hereinafter referred to as a non-contact probe capacitance C _P ) and the voltage V _CS applied to the floating capacitance C _S between the detection lines. It can be considered that both V _CP and V _CS change according to the change of the interelectrode voltage. Therefore, it is possible to capture the change in the interelectrode voltage by measuring the voltage V _CS between the detection lines. If the voltage captured here changes between open and short circuits, servo control of the gap between the electrodes can be performed based on the voltage.

When processing while non-contact voltage measurement, since the non-contact probe capacitance C _P is applied to the electrostatic capacitance C ₂ between the conventional tool electrode-workpiece, there is a possibility that the discharge energy changes. As a result, the processing characteristics may change. Therefore, the effect was investigated.

When the non-contact voltage measurement was performed and when it was not performed, processing was performed for several seconds on the mirror gauge block gauge under the processing conditions shown in Table 4, and the obtained discharge traces were compared. Feeding capacity _{C 1} using this time is 7.5 pF.

The obtained discharge scar diameter was measured using a confocal laser microscope (LETY OLS3000 manufactured by OLYMPUS). The measurement results are shown in FIG. It can be seen that the size of the discharge traces obtained is almost the same when the non-contact voltage measurement is performed and when the non-contact voltage measurement is performed. Therefore, the influence on the discharge energy by performing the non-contact voltage measurement is considered to be small. Moreover, since the non-contact probe capacity | capacitance used this time is as small as 0.75 pF, it is thought that the influence became small.

As described above, it was found that the change in the interelectrode voltage can be detected by using the non-contact voltage measurement method. However, in the electric discharge machining using electrostatic induction power supply, as shown in the voltage waveform diagram in FIG. If they are taken, they will cancel each other out on the plus side and minus side and become close to zero. Therefore, it is necessary to make the absolute value before taking the time average of the interelectrode voltage.

Therefore, an attempt was made to produce a circuit for detecting the average interelectrode voltage. FIG. 12 is a conceptual diagram of the average interelectrode voltage detection circuit manufactured this time. First, the voltage between the electrodes is detected in a non-contact manner and input to a high-impedance differential amplifier circuit using an operational amplifier. The input impedance of the operational amplifier used here is 10 ¹² Ω. The voltage between the electrodes transformed to an appropriate magnitude by the differential amplifier circuit is converted to an absolute value, smoothed using an RC circuit, and output through a buffer amplifier.

The present inventors examined the influence on the interelectrode voltage V _c2 due to the difference in capacitance between C ₁ and C _{2 in} FIG. Figure 13 is a machining gap voltage in the case where the capacity of the C ₁ to 10 times the C _2, FIG. 14 is a graph obtained by calculating the inter-electrode voltage when the capacity of C ₁ was set equal to the capacitance of C _2.

From this graph, the machining gap voltage V _c2 is different from the ratio of the capacitance _{C 1} and _{C 2,} in the case of _C 1 / _{C 2} is 10 in FIG. 13, from the case _C 1 / _{C 2} in FIG. 14 is 1, It can be seen that the value of V _C2 is more than twice as large. This increases the voltage of the machining gap of the tool electrode and the workpiece, would like to increase the discharge energy, in the case of roughing, the capacitance of C ₁ is set larger than C _2, the surface of the workpiece with small discharge energy processing the but in the case of micromachining in need, by reducing the capacity of the C _1, it is possible to reduce the discharge energy to an appropriate level. However, excessively lowering the C _1, the discharge be less likely to occur is understood voltage of the machining gap becomes too small.

Until now, the gap between the poles was controlled by manually moving the precision displacement table with the workpiece up and down manually, but the appropriate gap between the poles could not be maintained manually, and there was a variation in roughness due to the occurrence of discharge concentration. Further microfabrication has been difficult. Therefore, the workpiece was mounted on a piezoelectric table and servo control of the gap between the poles was performed to improve the machining characteristics. FIG. 15 shows a conceptual diagram of the control system.

First, the voltage between the electrodes is detected by a ring-shaped non-contact voltage measuring probe installed in parallel with the feeding electrode, and input to a differential amplifier circuit having a high input impedance using an operational amplifier. Then, the difference between the voltage between the electrodes obtained by averaging the differential amplification outputs as an absolute value and the servo reference voltage that can be arbitrarily set is calculated and input to the piezoelectric element driver. The piezoelectric element driver amplifies the input voltage and outputs it to the piezoelectric element. The piezoelectric element is displaced according to the input voltage. Thus, the displacement amount of the piezoelectric table is determined from the difference between the average inter-electrode voltage and the servo reference voltage, and the control of the inter-electrode gap can be servoed.

In the servo feed method, the average inter-electrode voltage is compared with a reference servo voltage that can be arbitrarily set by the operator, and the inter-electrode distance is controlled so that they match. A piezoelectric table / servo feed control circuit shown below was fabricated using the output of the average interelectrode voltage detection circuit, and an experiment was conducted.

FIG. 16 shows an outline of the experimental apparatus. The piezoelectric table is supported by an elastic hinge and can be driven in only one direction. The gap between the electrodes was adjusted by fixing the machining tank and the workpiece on the piezoelectric table and driving the piezoelectric table in the vertical direction. In the piezoelectric table / servo control conceptual diagram shown in FIG. 15, the difference between the average inter-electrode voltage and the servo reference voltage that can be arbitrarily set is input to the piezoelectric element driver. The piezoelectric element driver amplifies the input voltage and outputs it to the piezoelectric element. The piezoelectric element is displaced according to the input voltage. Thus, the displacement amount of the piezoelectric table is determined from the difference between the average inter-electrode voltage and the servo reference voltage, and the inter-electrode gap control can be servoed. The maximum displacement within the range of 0 to 150 V that can be input to the piezoelectric table was 18 μm. Since the gap between the electrodes in micro electric discharge machining is several μm or less, the displacement of 18 μm is large enough for controlling the gap between the electrodes.

Similarly, the spindle / servo control may be performed by comparing the average inter-electrode voltage with an arbitrarily set servo reference voltage on the discharge detection board inside the processing machine, and performing servo control so that the two coincide. Therefore, in order to perform servo control, it is only necessary to be able to input the output of the average interelectrode voltage detection circuit to the discharge detection substrate in the processing machine.

However, in the non-contact voltage measurement, the voltage detected at the time of a short circuit does not become 0V due to the influence of stray capacitance. The output of the average inter-electrode voltage detection circuit is, for example, + 6V when open and + 2V when short-circuited, whereas the input voltage to the discharge detection board is from -5V when open to 0V when short-circuited Must be in the range. Therefore, the output of the average inter-electrode voltage detection circuit is inverted and amplified so that -5V is output when open and 0V is output when short-circuited, and an offset voltage is further applied.

It is also possible to perform cooperative servo control using the above-described piezoelectric table in combination with servo feed control and machining axis servo feed control. Because the frequency response of the piezoelectric table is higher than that of the machine tool spindle, control between the poles is mainly performed by the piezoelectric table, and the gap between the poles is controlled by the machine tool spindle so that the displacement of the piezoelectric table does not exceed the upper or lower limit. Just do it.

FIG. 17 shows the measured machined surface roughness measured by the servo control method described above under the same conditions as the manual gap control. The average value measured 20 times on the same processed surface was 0.55 μmRz by the piezoelectric table servo control, 0.73 μmRz by the spindle servo control, and 0.85 μmRz by the cooperative control, with respect to 0.62 μmRz manually. However, since the roughness is observed in the same processed surface, the roughness is considered to be almost the same regardless of the gap control method.

Moreover, the processing speed at this time is shown in FIG. Whereas the processing speed is 376μm ³ / min manually interpolar gap control, 549μm ³ / min in the piezoelectric table servo control, in the spindle servo control 1185μm ³ / min, in a cooperative control be 1329μm ³ / min The machining speed was the fastest with the coordinated control that was considered to be the most responsive. In addition, the machining speed was slower with the piezoelectric table servo control, which is considered to be more responsive than the spindle servo control. If the gain is too high, short-circuiting is likely and machining becomes unstable, resulting in a slow machining speed. From the above, the servo control of the inter-electrode gap control has made the machining shape and surface roughness almost the same as the case of manual inter-electrode gap control, but the machining speed can be increased 1.5 to 3.5 times. It was.

As for the position where the power supply electrode is arranged in the tool electrode power supply part with a gap, in addition to the cylindrical shape surrounding the tool electrode power supply part, the power supply electrode is supplied to a position facing the upper facing surface of the tool electrode power supply part with a small distance between the electrodes. It is also possible to control the discharge energy by arranging the electrodes and controlling the gap between the power supply electrode and the tool electrode power supply unit or the facing area.

According to the principle of the present invention, it is possible to provide a gap between the power supply electrode and the tool electrode power supply unit to control the capacitance and control the discharge energy. it is close to the workpiece, by remembering small gap to the workpiece and the feed electrode, adjusting same result even when the electrostatic capacitance C _1A to workpiece from the feed electrode should be obtained. Alternatively, the capacitance can be adjusted in the same way by connecting a capacitor terminal to the tool electrode power supply unit and capacitively coupling it, and selecting the electrode area of the capacitor, the distance between the electrodes, the dielectric constant of the substance interposed between the electrodes, etc. Similarly, it is also possible to connect the capacitor terminal and the work piece by capacitive coupling, control the electrostatic capacity, and adjust the discharge energy. The conceptual diagram of the apparatus is as shown in FIG. 19, when power is supplied from the tool electrode power supply side, and when the power supply electrode is used, FIG. 19A shows the capacitive coupling method using a capacitor. FIG. 20 (a) shows an apparatus when the workpiece side is connected by a feeding electrode, and FIG. 20 (b) shows a case of capacitive coupling with a capacitor. When capacitive coupling is performed on the workpiece side, FIG. 20A can also be represented by the same equivalent circuit as when power is supplied from the tool side. In order to confirm that both showed the same performance, it processed actually.

Therefore, instead of the electrostatic capacitance C _1A generated between the power feeding electrode and the tool electrode, a commercially available capacitor C _3A for power feeding was connected to the workpiece through a table, and processing was performed under the conditions shown in Table 5. The tool electrode used a tungsten shaft, and the gap between the electrodes was controlled by manually moving the precision displacement table on which the workpiece was placed up and down. And _{C 1B} capacitor 27pF in FIG. 21 (a) when in close proximity to the feeding electrode to the workpiece side, in the case of setting the _{C 1A} capacitance 28pF when close to (b) tool side, comparing the machining gap voltage waveform FIG.

From FIG. 21, when the position of the feeding electrode is different, the value of the voltage between the electrodes is different, but the waveform of the same pattern is seen at the time of opening and discharging, and FIG. 22 shows the C _1A capacity and the capacitor capacity. changing the C _1B, performs several seconds machining, measuring the discharge traces diameter obtained as a feeding capacity, can see that the more feed capacity larger discharge crater diameter is large, the micro-machining, by adjusting the feeding capacity It can be seen that the surface roughness can be controlled. 23 shows an example of a workpiece that is microfabricated with _{C 1B} feeding capacity 27pF to work side.

Based on the above results, even when the electrostatic electrode for power supply is attached at a position in contact with either the tool electrode side or the workpiece side, the same level of discharge trace is obtained, and the contact voltage is non-contact. It was found that the gap between the electrode between the tool electrode and the workpiece can be servo controlled by using the piezoelectric table.
In addition, as shown in FIG. 24, wire electric discharge machining is used for cutting a workpiece using a metal wire as a tool electrode. However, there is a deterioration in processing characteristics due to wear of the power supply, a minimum discharge energy limit value, and a delay in the rise of the discharge current waveform due to the effects of stray capacitance and inductance.

Further, by bringing the wire into contact with the power supply, as shown in FIG. 25, the center of the wire is eccentric from the center of the wire guide hole, and when the machining direction is changed or the wire is tilted, the position of the wire center is changed. There has been a problem that the machining accuracy is deteriorated due to deviation from the center of the wire guide hole.

However, as shown in FIG. 26, since the non-contact power feeding method of the present invention is used for wire electric discharge machining, the machining characteristics are not changed due to the wear of the power supply, so that it is not necessary to replace expensive power supply, Economical.

Further, since the wires of the power supply electrode and the tool electrode are not in contact with each other, the influence of stray capacitance due to the very long power supply line can be ignored. Furthermore, since the power feeding section is axisymmetric, errors in the wire position and wire tilt angle caused by non-axisymmetric when feeding by pressing the power supply can be reduced, and even if the error cannot be reduced to zero, it is corrected with NC data. It is also easy to do.

100 Tool electrode feeder 150 Tool electrode 200 Feed electrode 250 Feed capacitor 300 Workpiece L Feed electrode length P Non-contact voltage measurement probe PW Pulse power supply O Oscilloscope T Precision displacement table Z Insulation tape

Claims (6)

In the electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, generating discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A power supply electrode disposed opposite to the tool electrode power supply section with a constant gap;
A pulse power source in which the feeding electrode and the workpiece are connected;
Have
A voltage is applied from the pulse power supply, and electrostatic power is fed from the power supply electrode to the tool electrode power supply unit, thereby adjusting at least one of a distance between the power supply electrodes facing the tool electrode power supply unit and an opposing area. The discharge energy is determined on the basis of the capacitance C _1A formed by the capacitor C _2A formed by the gap between the tool electrode and the workpiece ,
A voltage between the tool electrode and the workpiece, comprising a voltage detection circuit in which a detection line of a voltage measurement probe arranged to hold the opposed surface of the tool electrode with a fixed gap and the workpiece are connected. An electrical discharge machining apparatus equipped with a measuring device for measuring the temperature . In the electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, generating discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A capacitor with one terminal in contact with the tool electrode power supply unit;
A pulse power source wired to the other terminal of the capacitor and the workpiece;
Have
A voltage is applied from the pulse power source, and power is supplied by capacitive coupling of the capacitor and the tool electrode power supply unit. The capacitor C _3A and the capacitance C _4A formed by the gap between the tool electrode and the workpiece are provided. And the electric discharge machining apparatus, wherein the electric discharge energy is determined. In the electric discharge machining apparatus for machining the workpiece by applying a pulse voltage to the tool electrode and the workpiece, which are arranged with a small distance between the poles, generating discharge energy between the poles,
The tool electrode is coupled on the same axis, and a tool electrode power supply unit that is insulated and supported so as to be rotatable with the tool electrode.
A feeding electrode disposed opposite the workpiece with a constant gap;
A pulse power source connected to the tool electrode power supply unit and the power supply electrode;
Have
A voltage is applied from the pulse power source, and electrostatic work is fed to the workpiece from the feeding electrode, thereby adjusting at least one of the distance and the facing area of the feeding electrode facing the workpiece, and a capacitor C _1B is formed in the gap, and a capacitor C _2B is formed at the gap between the workpiece and the tool electrode, on the basis, and determines the discharge energy, the electric discharge machining apparatus. A voltage between the tool electrode and the workpiece, comprising a voltage detection circuit in which a detection line of a voltage measurement probe arranged to hold the opposed surface of the tool electrode with a fixed gap and the workpiece are connected. The electrical discharge machining apparatus according to claim 2 , wherein the electrical discharge machining apparatus is equipped with a measurement device that measures the above. The measuring device includes a piezoelectric element that displaces a support position of the workpiece with respect to the tool electrode,
Based on the voltage waveform between the tool electrode and the workpiece measured by the measuring device, it is determined whether the distance between the electrodes is too short and short-circuited, or too wide and close to an open state. A function of controlling the gap between the electrodes to an appropriate value at which discharge can occur by transmitting a control signal and adjusting the support position of the workpiece by displacing the workpiece by the piezoelectric element, The electric discharge machining apparatus according to claim 1 or 4 . The measuring device has a servo motor for displacing a support position of the tool electrode with respect to the workpiece;
Based on the interelectrode voltage waveform of the tool electrode and the workpiece measured by the measuring device, determine whether the interelectrode distance is too short and short-circuited, or too wide and close to the open state, It has a function of controlling the gap between the electrodes to an appropriate value that can cause discharge by transmitting a control signal, controlling the servo motor, and adjusting the support position of the tool electrode. The electric discharge machining apparatus according to any one of claims 1, 4, and 5 .