JP6032726B2 - Electric discharge machining apparatus and electric discharge machining method - Google Patents

Description

  The present invention relates to a technique for performing electric discharge machining on a workpiece.

In electric discharge machining using electrostatic induction power feeding (see Non-Patent Document 1 and Patent Document 1 below), non-contact power feeding to an electrode is possible, and therefore power feeding to an electrode that rotates at high speed is easy. In micro EDM,
・ By rotating the electrode at a high speed, the discharge of machining waste by the machining fluid and cooling of the machining gap are promoted. ・ By the relative movement between the electrodes, the discharge points are dispersed on the electrode surface, so that the machining waste is removed. It is considered that the short circuit through the electrode and the local temperature rise on the electrode surface can be suppressed.

  In the previous research (Non-patent Document 2 below), it has been found that the machining speed can be improved by rotating the electrode at a high speed. In addition, when the electrode rotates at a low speed, machining waste is present in the gap between the workpiece and the side surface of the electrode, electric discharge is generated through the machining waste, and the cross-sectional shape of the hole becomes tapered, There is a problem that the hole diameter becomes large. On the other hand, in the following Non-Patent Document 2, since the scraps between the gaps can be eliminated by rotating the electrode at a high speed, the roundness and straightness of the formed hole can be improved, Small holes can be accurately formed. However, this method has a problem that it is structurally difficult to freely change the discharge energy because power is supplied to the electrodes in a non-contact manner. In particular, it has been difficult to obtain relatively large discharge energy.

M. Kunieda, A. Hayasaka, X. D. Yang, S. Sano and I. Araie: Study on Nano EDM Using Capacity Coupled Pulse Generator, Annals of the CIRP, 56, 1, (2007), pp.213-216 Yuuna Yazaki, Tomohiro Otano, Masanori Kunieda, Fuyufutsu: Micro-EDM using high-speed rotating electrodes with electrostatic induction, Journal of Japan Society for Precision Engineering, 77, 4, (2011), pp.394-399

JP 2006-263907 A

  The present invention has been made in response to the above-described problems. A main object of the present invention is to provide a technique capable of providing relatively large discharge energy to one discharge point in an electric discharge machining apparatus using electrostatic induction power feeding.

  Means for solving the above-described problems can be described as follows.

(Item 1)
It has a power supply, a feeding electrode, and a work electrode,
The power supply is configured to apply a power supply voltage having a predetermined frequency between the feeding electrode and a workpiece to be subjected to electric discharge machining by the work electrode,
The power supply electrode and the work electrode are electrically insulated and have a structure in which a power supply capacity is formed between them.
The work electrode is arranged facing the work piece, and has a configuration capable of machining the work piece by electric discharge between the two,
The frequency of the power supply voltage fed from the power supply is high enough to maintain a plasma state generated by discharge between the work electrode and the workpiece.

(Item 2)
It has a power supply, a feeding electrode, a work electrode, and a frequency control unit,
The power supply is configured to apply a power supply voltage having a frequency controlled by the frequency control unit between the power supply electrode and a workpiece to be subjected to electric discharge machining by the work electrode,
The power supply electrode and the work electrode are electrically insulated and have a structure in which a power supply capacity is formed between them.
The work electrode is arranged facing the work piece, and has a configuration capable of machining the work piece by electric discharge between the two,
The frequency control unit
A process for measuring an alternating voltage generated between the work electrode and the workpiece;
An electric discharge machining apparatus that performs a process of increasing a frequency of a power supply voltage supplied from the power supply so that an amplitude waveform of the AC voltage becomes a voltage amplitude when the discharge occurs.

(Item 3)
It has a power supply, a feeding electrode, a work electrode, and a frequency control unit,
The power supply is configured to apply a power supply voltage having a frequency controlled by the frequency control unit between the power supply electrode and a workpiece to be subjected to electric discharge machining by the work electrode,
The power supply electrode and the work electrode are electrically insulated and have a structure in which a power supply capacity is formed between them.
The work electrode is arranged facing the work piece, and has a configuration capable of machining the work piece by electric discharge between the two,
The frequency control unit
A process for measuring an alternating voltage generated between the work electrode and the workpiece;
An electric discharge machining apparatus that performs a process of increasing the frequency of the power supply voltage supplied from the power supply so as to eliminate a discharge delay time every half cycle of the AC voltage based on the amplitude waveform of the AC voltage.

(Item 4)
The frequency control unit further includes
In the item 2 or 3, the process of increasing the frequency of the power supply voltage is performed, and after the predetermined number of cycles or time has elapsed, the application of the power supply voltage is stopped and then the power supply voltage is applied again. The electrical discharge machining apparatus described.

(Item 5)
The frequency control unit further includes
Since the amplitude of the AC voltage generated between the work electrode and the workpiece becomes the voltage amplitude when the discharge occurs, the number of cycles thereafter reaches a predetermined number, and the The electric discharge machining apparatus according to Item 4 (when dependent on Item 2) for determining a predetermined number of cycles.

(Item 6)
The frequency control unit further includes
In the AC voltage generated between the work electrode and the workpiece, the discharge delay time for each half cycle disappears, and the number of cycles thereafter reaches a predetermined number. The electric discharge machining apparatus according to item 4 (when dependent on item 3).

(Item 7)
The electric discharge machining apparatus according to any one of items 1 to 6, wherein the work electrode is a wire used in wire electric discharge machining.

(Item 8)
The electric discharge machining apparatus according to any one of items 1 to 7, wherein the work electrode is rotatable about its own axis.

(Item 9)
A power source, a power supply electrode, and a work electrode;
The power supply electrode and the work electrode are electrically insulated, a power supply capacity is formed between them, an electric discharge machining apparatus is used, and an electric discharge machining method including the following steps:
(1) A step of applying a power supply voltage from a power source between the power feeding electrode and a workpiece to be subjected to electric discharge machining by the work electrode;
(2) By increasing the frequency of the power supply voltage supplied from the power supply, a continuous discharge is generated using the plasma state maintained between the work electrode and the work, and the work is Step to process.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the technique which can provide comparatively big discharge energy with respect to one discharge point in the electrical discharge machining apparatus using electrostatic induction electric power feeding.

It is explanatory drawing which shows schematic structure of the electric discharge machining apparatus in one Embodiment of this invention. The figure (a) shows the waveform of the power supply voltage, the figure (b) shows the waveform of the voltage between the workpiece and the work electrode, and the figure (c) shows the waveform of the discharge current. It is a figure which shows the relationship between a power supply voltage waveform and discharge current in case the frequency of a power supply voltage is low. It is a table | surface which shows the experimental condition in the Example of this embodiment. It is a graph which shows the experimental result in an Example. It is explanatory drawing which shows the experimental result in an Example. It is explanatory drawing which shows schematic structure of the electric discharge machining apparatus in the modification of this invention.

  Hereinafter, an electrical discharge machining apparatus according to an embodiment of the present invention (hereinafter, may be abbreviated as “machining apparatus”) will be described with reference to the accompanying drawings.

(Configuration of EDM)
The processing apparatus according to the present embodiment includes a power source 1, a feeding electrode 2, a work electrode 3, and a frequency control unit 4 (see FIG. 1). Moreover, in FIG. 1, the code | symbol 10 is attached | subjected to the workpiece processed by this processing apparatus.

  The power supply 1 is configured to apply a power supply voltage having a frequency controlled by the frequency control unit 4 between the feeding electrode 2 and the workpiece 10 to be subjected to electric discharge machining by the work electrode 3.

  The feed electrode 2 and the work electrode 3 are electrically insulated, and a feed capacitance C1 is formed between them. Specifically, in the present embodiment, a dielectric material such as air, oil, or deionized water is interposed between the feeding electrode 2 and the work electrode 3, and the dielectric material causes a gap between the two. Insulated. In the present embodiment, air is used as the dielectric material between the feeding electrode 2 and the work electrode 3. In this embodiment, the work electrode 3 can be moved relative to the feeding electrode 2 and the workpiece 10.

  In the present embodiment, the work electrode 3 faces the work piece 10 and is disposed slightly apart. Thereby, in this embodiment, the workpiece 10 can be machined by the electric discharge between the workpiece electrode 3 and the workpiece 10. In addition, the space between the work electrode 3 and the work piece 10 is usually filled with a dielectric material (for example, oil or deionized water). It is like that.

  Furthermore, the work electrode 3 of the present embodiment is rotatable about its own axis.

The frequency control unit 4 includes a voltage detection unit 41, a frequency adjustment unit 42, and a discharge count unit 43 (see FIG. 1). The frequency control unit 4 is configured to perform the following processing.
A process of measuring an AC voltage generated between the work electrode 3 and the workpiece 10 by the voltage detection unit 41;
A process in which the frequency adjustment unit 42 increases the frequency of the power supply voltage supplied from the power supply until “the measured amplitude of the alternating voltage reaches the voltage amplitude when the work electrode and the work are discharged”;
A process in which the frequency adjustment unit 42 stops applying the power supply voltage after performing the process of increasing the frequency of the AC power and the predetermined number of cycles is repeated, and then applies the power supply voltage again.

  Here, in the present embodiment, the discharge counting unit 43 determines that “the amplitude of the AC voltage generated between the work electrode 3 and the workpiece 10 has reached the voltage amplitude at the time of discharge, and the number of cycles thereafter. When the predetermined number is reached, the above-described predetermined cycle is determined ”. In addition, the discharge count unit 43 can detect the presence or absence of discharge, but a configuration in which a discharge detection unit for detecting discharge is separately provided is also possible.

  Detailed operation of the frequency control unit 4 will be described later.

(Operation of EDM)
Next, the operation of the electric discharge machine described above will be described with further reference to FIG.

(Application of power supply voltage)
First, a power supply voltage is applied between the power supply electrode 2 and the workpiece 10 by the power supply 1 (see FIG. 2A). Here, since the feed electrode 2 and the work electrode 3 are opposed to each other via a dielectric (for example, air), electric charges are induced on the facing surfaces of the two according to the capacitance formed therebetween. The Since the power supply voltage is an alternating current, an alternating voltage can be generated at the work electrode 3 according to the fluctuation of the power supply voltage. As a result, in the present embodiment, an alternating voltage can be generated between the work electrode 3 and the workpiece 10. As will be described later, this AC voltage can cause a discharge.

(AC voltage measurement)
Next, an AC voltage generated between the work electrode 3 and the workpiece 10 (hereinafter referred to as “machining gap voltage”) is measured by the voltage detection unit 41 of the frequency control unit 4. An example of the measured AC voltage waveform is shown in FIG. When this machining gap voltage exceeds the dielectric strength between the work electrode 3 and the workpiece 10 and a discharge delay time that varies statistically has elapsed, a discharge occurs between the two. This discharge delay time varies depending on the gap length (distance between the work electrode and the workpiece) and the machining waste concentration in the gap. An example of a pulse waveform of a current flowing by discharge is shown in FIG. The example of FIG. 2 shows a case where the first discharge occurs after the discharge delay time corresponding to one cycle of the AC voltage. The discharge delay time shown in FIG. 2 is a delay time outside the half cycle in which discharge occurs. Therefore, this is different from the “discharge delay time for each half cycle of the AC voltage” described later.

(Adjustment of power supply voltage frequency)
Next, the frequency of the power supply voltage is adjusted according to the AC voltage measured between the work electrode 3 and the work piece 10. This process will be described in detail below.

  First, as a premise, a case where the frequency of the power supply voltage is low will be described (see FIG. 3). In this case, even if the absolute value of the power supply voltage rises, discharge often does not occur immediately, and a high voltage state is maintained for a very short time corresponding to the power supply voltage value. When electric discharge occurs (see FIG. 3B), dielectric breakdown occurs, so that the machining gap voltage between the work electrode 3 and the workpiece 10 decreases (see FIG. 3A). When polarity inversion occurs, the machining gap voltage fluctuates by the amplitude W1 of the power supply voltage shown in FIG. Therefore, the value of the machining gap voltage when the frequency of the power supply voltage is low and the discharge is intermittently generated is as shown in FIG. 3A during the discharge delay time. For an object, a waveform with an amplitude of ± (W1−W2 / 2) and ± W2 / 2 after discharging is sequentially repeated. In electrostatic induction discharge machining, if the amplitude of the power supply voltage is W1, it may be considered that the voltage is applied to the machining gap without loss. Further, once the discharge occurs, the machining gap voltage decreases from, for example, 100 V to 20 V (this voltage is only an example, and the same is true for the reverse polarity). Thus, when the polarity of the power supply voltage is reversed with the amplitude of W1, the width varies with the width of W1 (that is, there is an offset) with reference to the lowered processing gap voltage (for example, 20V). For this reason, the above phenomenon occurs in amplitude. In the example of FIG. 3A, a discharge delay time exists every half cycle of the machining gap voltage, and then discharge occurs.

  However, according to the knowledge of the present inventor, when the frequency of the power supply voltage is sufficiently high, the value of the machining gap voltage repeats the amplitude W2 corresponding to the discharge, and the amplitude 2 (W1-W2 / 2) is almost the same. Dont return. This is considered to be due to the following reasons. That is, when the frequency of the power supply voltage is sufficiently high, the value (absolute value) of the machining gap voltage can be increased before the plasma state during discharge is eliminated. When the plasma state at the time of discharge is maintained, since the withstand voltage between the work electrode 3 and the workpiece 10 is low, the amplitude W2 before the machining gap voltage reaches W1-W2 / 2. It is considered that discharge occurs when the value reaches / 2. For this reason, the value of the machining gap voltage is considered to repeat a small amplitude W2.

  Therefore, in this embodiment, the frequency of the applied voltage from the power source 1 is increased by the frequency adjustment unit 42 while the value of the machining gap voltage is measured by the voltage detection unit 41. When the frequency of the applied voltage from the power supply 1 is increased, the machining gap voltage does not reach the amplitude 2 (W1-W2 / 2) and maintains the amplitude W2, so this is detected by the voltage detector 41, and at that time The frequency adjustment unit 42 maintains the frequency of the voltage (or higher frequency).

  Thus, in this embodiment, by increasing the frequency of the power supply voltage supplied from the power supply 1 until the amplitude of the machining gap voltage becomes the voltage amplitude at the time of discharge, the work electrode 3 and the workpiece 10 are It is possible to process the workpiece 10 by generating a continuous discharge between them.

(Counting the number of discharges)
Further, in the present embodiment, the discharge count unit 43 counts the number of discharges caused by the application of high frequency voltage. This can be performed by counting the repeated cycles with the voltage amplitude detected by the voltage detection unit 41 (in this example, the amplitude W2 during discharge).

  When the number of discharges reaches a predetermined number (usually determined in advance by the user, but can be configured to be dynamically set according to some condition), the frequency adjustment unit 42 causes the power supply 1 to Stop voltage application. The rest period may be a time enough to eliminate the plasma state caused by the discharge, and is usually a very short time. Although it depends on the implementation conditions, for example, it is considered that the discharge period and the rest period can be repeated with a period of about several μs to several tens of μs.

  While the discharge generated at the amplitude W2 is continued, it is considered that the discharge using the same plasma state (that is, the discharge to the same location) is performed, so that the accumulated discharge energy to the same discharge location is increased. Can do. The conventional electrostatic induction power supply has a problem that the processing energy to the same discharge location is small. On the other hand, in the present embodiment, by controlling the frequency of the applied voltage as described above, it is possible to perform a plurality of discharges on the same discharge point, thereby substantially the same discharge. There is an advantage that the processing energy to the part can be increased. Thereby, the processing amount to the same discharge location can be increased. Therefore, maintaining a high frequency so as to have a small amplitude W2 as described above corresponds to “a frequency that is high enough to maintain a plasma state generated by the discharge between the work electrode and the workpiece”.

  Moreover, in this embodiment, there also exists an advantage that a discharge point (namely, process location) can be moved by providing the discharge | restoration period of discharge intentionally.

(Example)
Electric discharge machining was performed using the electric discharge machining apparatus having the configuration of the above-described embodiment and under the experimental conditions shown in FIG. In FIG. 4, “Modulation frequency” means the timing at which the above-described pause period is inserted. For example, if the frequency is 20 kHz, a high frequency voltage is applied for 25 μs, and the voltage application is paused for the subsequent 25 μs. The results are shown in FIGS. Note that a tungsten shaft of φ125 μm was used as the work electrode, and carbon steel was used as the work piece.

  As shown in FIG. 5A, when the power supply frequency is 1 MHz, no continuous discharge occurs, and a large amplitude W1 is applied except for the moment when intermittent discharge occurs.

  On the other hand, as shown in FIG. 5 (b), when the power supply frequency is increased to 10 MHz, no electric discharge occurs in the initial stage, so that the machining gap voltage amplitude is large (that is, W1), but continuous electric discharge will eventually occur. As a result, the amplitude of the machining gap voltage decreases (that is, W2). Therefore, by measuring the machining gap voltage, the number of continuous discharges (that is, to the same machining point) can be measured.

  FIG. 6 shows a machining shape obtained by electric discharge machining. At 1 MHz (FIG. 6 (a)), since the discharge points are dispersed, only shallow machining holes are obtained, but at 10 MHz ((FIG. 6 (c)), the discharge points are limited for a certain number of periods. Due to the concentration, it was possible to obtain a deep machining hole in the machining time of the same length due to the accumulation of such continuous discharge, as shown in FIG. Thus, it can be seen that a large machining energy can be obtained in the apparatus of this embodiment, because the hole diameter in Fig. 6 (c) is large because welding has occurred on the electrode due to abnormal discharge, This is considered to be prevented by appropriately controlling the modulation frequency (that is, the timing when the discharge pause occurs).

  In this embodiment, the discharge state is determined using the amplitude of the machining gap voltage. Since the machining gap voltage may have a DC component (that is, offset), there is an advantage that accurate determination can be made by using the amplitude.

(Modification 1)
In the above-described embodiment, an electrode that rotates around the axis is used as the work electrode 3. However, a wire used in wire electric discharge machining can be used as the work electrode. This example is shown in FIG. Here, reference numeral 203 is attached to the work electrode. The wire constituting the work electrode 203 moves in one direction (in the example shown, the direction from top to bottom).

  In this example, the wire can be fed via a dielectric (for example, appropriate oil, deionized water, or air) by feeding electrodes 2a and 2b.

  Further, in FIG. 7, reference numerals 21 and 22 denote guides for guiding the wire.

  In the conventional wire electric discharge machining, since the wire is moved and brought into contact with the supply electron, the supply electron is worn, and there is a possibility that the travel route of the wire is slightly changed. If there is such a path change, there is a problem that the accuracy of electric discharge machining is deteriorated.

  On the other hand, according to the apparatus of the first modification, since the wire and the feeding electrode are not in contact with each other, there is an advantage that a change in the travel route of the wire can be avoided. Since other advantages are the same as those of the above-described embodiment, detailed description is omitted. The configuration other than the above can be the same as that of a conventional wire electric discharge machine.

(Modification 2)
The frequency control unit of the above-described embodiment performs a process of increasing the frequency of the power supply voltage supplied from the power supply so that the amplitude of the AC voltage (processing gap voltage) becomes the voltage amplitude when the discharge occurs. . However, the frequency of the power supply voltage fed from the power supply may be high enough to maintain the plasma state generated by the discharge between the work electrode and the work piece. This is because if this condition is satisfied, continuous discharge to substantially the same discharge point can be realized.

  Therefore, instead of the above-described configuration, the frequency control unit is configured to increase the frequency of the power supply voltage until the discharge delay time for each half cycle of the AC voltage is eliminated based on the amplitude waveform of the AC voltage. Can do. In this case, since it is necessary to confirm the “discharge delay time”, it is also necessary to confirm the timing at which the discharge has occurred. This confirmation can be performed by, for example, a discharge count unit, but a functional element for confirming discharge can be separately provided. Based on the delay time from the rise of the power supply voltage to the discharge timing, the “discharge delay time for each half cycle” can be confirmed.

  There are other methods for determining whether the frequency is high enough to maintain the plasma state, such as comparing the average value of the squared value after passing the machining gap voltage through a high-pass filter and removing the offset. The method can be adopted.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Power supply 2 * 2a * 2b Feed electrode 3.203 Work electrode 4 Frequency control part 41 Voltage detection part 42 Frequency adjustment part 43 Discharge count part 10 Workpiece

Claims (6)

It has a power supply, a feeding electrode, a work electrode, and a frequency control unit ,
The power supply is configured to apply a power supply voltage having a predetermined frequency between the feeding electrode and a workpiece to be subjected to electric discharge machining by the work electrode,
The power supply electrode and the work electrode are electrically insulated and have a structure in which a power supply capacity is formed between them.
The work electrode is arranged facing the work piece, and has a configuration capable of machining the work piece by electric discharge between the two,
Wherein the frequency of the power supply voltage fed from the power source is a high frequency to the extent that the plasma state can be maintained caused by the discharge between the work electrode and the workpiece
The frequency control unit
A process for measuring the amplitude of the alternating voltage generated between the work electrode and the work piece;
An electric discharge machining apparatus configured to perform a process of setting a frequency of the power supply voltage supplied from the power supply so that an amplitude of the AC voltage becomes a voltage amplitude when the electric discharge occurs . The frequency control unit further includes
It performs a process of setting the frequency of the power supply voltage, and, after a predetermined number of cycles or time has elapsed, to suspend application of the power supply voltage, then again, to claim 1 for performing processing for applying the power supply voltage The electrical discharge machining apparatus described. The frequency control unit further includes
Since the amplitude of the AC voltage generated between the work electrode and the workpiece becomes the voltage amplitude when the discharge occurs, the number of cycles thereafter reaches a predetermined number, and the The electric discharge machining apparatus according to claim 2 , wherein a predetermined number of cycles is determined. The tool electrode is electric discharge machining apparatus according to any one of claims 1 to 3, which is a wire used in wire electric discharge machining. The tool electrode is electric discharge machining apparatus according to any one of claims 1 to 4 which is rotatable about the axis of its own. A power source, a power supply electrode, and a work electrode;
An electric discharge machining method using the electric discharge machining apparatus in which the power supply electrode and the work electrode are electrically insulated and a power supply capacity is formed therebetween, and includes the following steps:
(1) A step of applying a power supply voltage from a power source between the power feeding electrode and a workpiece to be subjected to electric discharge machining by the work electrode;
(2) you to configure the frequency of the power supply voltage supplied from the power source to bring about continuous discharge using plasma state maintained between said tool electrode and said workpiece, said The step of machining the workpiece ,
Here, the process of setting the frequency of the power supply voltage supplied from the power supply is as follows:
A process for measuring an alternating voltage generated between the work electrode and the workpiece;
And a process of setting the frequency of the power supply voltage supplied from the power supply so that the amplitude of the AC voltage becomes the voltage amplitude when the discharge occurs .