JP3664879B2 - Electric discharge machining method and electric discharge machining apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric discharge machining method and an electric discharge machining apparatus in which a workpiece is subjected to electric discharge machining by alternately switching the polarity of a machining voltage applied to an electric discharge machining gap.
[0002]
[Prior art]
For example, as disclosed in Japanese Patent Laid-Open No. 3-49824, in machining with an AC high frequency voltage, the discharge point is changed by changing the polarity of the machining voltage applied to the discharge machining gap for each discharge. It is known that a good quality processed surface can be obtained by dispersion. The same applies when electric discharge machining is performed using bipolar pulses. As described above, when the workpiece is subjected to electric discharge machining by alternately switching the polarity of the machining voltage applied to the electric discharge machining gap formed between the workpiece and the machining electrode, the polarity switching frequency of the machining voltage is set. It is well known that the surface roughness of the EDM surface tends to become finer as the value of E is higher, but particularly in the high frequency region of 7 MHz or higher, the capacitance between the EDM gap and the distributed inductance component on the circuit. It has been confirmed that a series resonance state (hereinafter referred to as a gap resonance state) occurs, and electric discharge occurs only in this gap resonance state, and as a result, an electric discharge machined surface having a surface roughness of about 0.2 μmRmax is obtained.
[0003]
However, when the machining area or machining state changes during machining, the impedance of the electrical discharge machining gap may change, and the gap resonance state may not be maintained. Therefore, conventionally, according to the change in impedance between the poles, the AC power source frequency and the matching device provided between the poles and the AC power source are automatically adjusted to maintain the gap resonance state and perform electric discharge machining. Is going.
[0004]
[Problems to be solved by the invention]
Thus, in order to perform electric discharge machining stably under the gap resonance state, it is necessary to change the AC power supply frequency in accordance with the change in the interelectrode impedance. Therefore, the problem is that the resonance frequency F0 is expressed by the following equation (1).
F0 = 1/2 · π · (LmCg) ^1/2 ... (1)
Lm: Wiring distribution inductance
Cg: Capacitance of EDM gap
Therefore, the resonance frequency F0 is greatly changed by the change of the opposing area of the gap (change of the plate thickness or wire diameter).
[0005]
For example, as an extreme example, when a workpiece whose thickness changes from 1 mm to 50 mm is processed, the area of the opposing gap increases by a maximum of 50 times (capacitance is proportionally 50 times). Similarly, it increases by 50 times, and the resonance frequency F0 changes about 1/7 times.
[0006]
By the way, since there is a close relationship between the frequency of the high-frequency AC power supply and the machined surface roughness, if the frequency changes by this amount, the machined surface roughness will not be constant. This means that the best surface roughness is determined by the plate thickness, and that the processed surface roughness deteriorates as the plate thickness increases. Furthermore, since the XY-axis stroke is different for each model, the length of the transmission line between the poles is different, and the distribution inductance Lm is also changed for each model due to the influence. Therefore, there is a possibility that a difference in surface roughness occurs depending on the model.
[0007]
As described above, according to the conventional method of performing electrical discharge machining with low surface roughness by generating gap resonance using a high-frequency AC voltage, in order to obtain a stable and high-quality processed surface, the thickness of the workpiece is There is a problem that the range of processing is narrowed because it requires limitation and limitation of models.
[0008]
In order to deal with this problem, for example, a bipolar output voltage whose polarity is periodically reversed is applied to the electric discharge machining gap formed between the workpiece and the machining electrode via a resistor, and the reverse polarity machining is performed. When the workpiece is EDM while periodically switching between the positive polarity machining and the positive polarity machining, the resistor is a resistor having a small resistance value during reverse polarity machining, and the resistor is a resistor having a large resistance value during positive polarity machining. It is conceivable to adopt an electric discharge machining method that is switched so that
[0009]
When the resistors are switched in this way, the value of the current supplied to the EDM gap is large during reverse polarity machining, small during positive polarity machining, and greater discharge energy than during positive polarity machining during reverse polarity machining. Electric discharge machining is performed. However, in reverse polarity machining, since the distribution of discharge energy to the workpiece side is small, electric discharge machining with small surface roughness is stably performed even when a large machining current is applied to the electric discharge machining gap. In addition, the machining current level is reduced at the time of positive polarity machining, and it is possible to prevent the discharge from being cut off at the end of the reverse polarity machining while suppressing the increase in surface roughness of the electric discharge machining surface. And since this electric discharge machining method does not use the resonance phenomenon, a high-quality electric discharge machining surface can be obtained without the need to limit the plate thickness or model of the workpiece.
[0010]
However, when looking at the discharge machining gap side from the output end of the power supply device, there is a stray capacitance on the circuit, especially on the output line, so the value of the limiting resistor is different between positive polarity machining and reverse polarity machining. According to the configuration, the charge / discharge time constant of the circuit constituted by the resistor and the floating capacitance is different between positive polarity processing and reverse polarity processing.
[0011]
As a result, the voltage waveform applied to the electric discharge machining gap at no load is biased to the opposite polarity side, thereby causing a phenomenon that brass is coated as a thin film on the workpiece. This brass thin film coating state degrades the finish quality of the workpiece. For example, in parts processing of medical equipment, if a small amount of copper enters the processed surface, it may become a defective product that cannot be used.
[0012]
Accordingly, the object of the present invention is to obtain a stable electric discharge surface having a good surface roughness by switching the polarity of the electric discharge machining voltage between positive and negative without using resonance, and a thin film coating phenomenon of brass. An electrical discharge machining method and an electrical discharge machining apparatus are provided.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, according to the invention of claim 1, the workpiece is applied by alternately switching the polarity of the machining voltage to the electric discharge machining gap formed by the workpiece and the machining electrode. The Finish When performing electrical discharge machining, The processing electrode is the positive electrode and the workpiece is the negative electrode During reverse polarity machining Oke Than the level of machining current The processing electrode is the negative electrode and the workpiece is the positive electrode During positive polarity processing Oke The level of machining current to be reduced is reduced, and the parallel capacitance and LC parallel resonance on the circuit are made in parallel with the electric discharge machining gap. Equalize the positive and negative machining voltages in the no-load state To insert an inductance element for EDM characterized by A method is proposed.
[0014]
Reverse polarity machining that can reduce the EDM surface roughness can be performed with a large level of machining current, so that an electric discharge can be reliably generated in the EDM gap, and the EDM surface has a low surface roughness while ensuring stable machining. Can be obtained. On the other hand, during positive polarity machining where surface roughness tends to be large, the level of machining current is kept low, which makes it possible to machine the workpiece without increasing the surface roughness of the electric discharge machined surface, and reverse polarity It is possible to reliably cut off the discharge at the end of processing. Here, the capacitance component on the circuit floating on the output cable connected between the electric discharge machining gap and the power supply device is obtained by forming an inductance element and an LC parallel resonant circuit connected in parallel to the electric discharge machining gap. The effect of stray capacitance can be eliminated at the frequency of the output voltage. As a result, there is no charge / discharge to the floating capacitance, and the no-load voltage in the discharge machining gap is positive or negative polarity output from the machining power supply regardless of the resistance value of the resistor. It becomes the same level as the output voltage.
[0015]
According to the second aspect of the present invention, the bipolar output voltage whose polarity is periodically reversed is applied to the electric discharge machining gap formed between the workpiece and the machining electrode via the resistor. As processing voltage Applied, The processing electrode is the positive electrode and the workpiece is the negative electrode With reverse polarity machining The processing electrode is the negative electrode and the workpiece is the positive electrode While periodically switching between positive polarity machining, Finish In the electric discharge machining method, the resistor is a resistor having a small resistance value during the reverse polarity machining, and the resistor is switched to a resistor having a large resistance value during the positive polarity machining, and the electric discharge machining gap In parallel with the stray capacitance on the circuit and LC parallel resonance Equalize the bipolar machining voltage in the no-load state To insert an inductance element for EDM characterized by A method is proposed.
[0016]
When the resistors are switched in this way, the value of the current supplied to the EDM gap is large during reverse polarity machining, small during positive polarity machining, and greater discharge energy than during positive polarity machining during reverse polarity machining. Electric discharge machining is performed. However, in reverse polarity machining, since the distribution of discharge energy to the workpiece side is small, electric discharge machining with small surface roughness is stably performed even when a large machining current is applied to the electric discharge machining gap. In addition, the machining current level is reduced at the time of positive polarity machining, and it is possible to prevent the discharge from being cut off at the end of the reverse polarity machining while suppressing the increase in surface roughness of the electric discharge machining surface. Here, the capacitance component on the circuit floating on the output cable connected between the electric discharge machining gap and the power supply device is obtained by forming an inductance element and an LC parallel resonant circuit connected in parallel to the electric discharge machining gap. The effect of stray capacitance can be eliminated at the frequency of the output voltage. As a result, there is no charge / discharge to the floating capacitance, and the no-load voltage in the discharge machining gap is positive or negative polarity output from the machining power supply regardless of the resistance value of the resistor. It becomes the same level as the output voltage.
[0017]
According to the invention of claim 3, a bipolar pulse voltage whose polarity is periodically reversed is supplied to the electric discharge machining gap to Finish In an electric discharge machining apparatus for electric discharge machining, a DC power source that outputs a DC voltage, a bridge circuit in which a semiconductor switching element is provided on each side, and the DC voltage is input, and the bipolar circuit is output from the output of the bridge circuit. A control circuit for synchronously turning on and off semiconductor switching elements on opposite sides of the bridge circuit to obtain a neutral pulse voltage, and a circuit for applying the bipolar pulse to the electric discharge machining gap. Eliminate the effects of stray capacitance Even in the no-load state, the bipolar pulse voltage is equalized Therefore, an inductance element connected in parallel to the electric discharge machining gap is provided, and a first limiting resistance element is provided in series with the semiconductor switching element that is closed to take out a positive pulse from the bridge circuit, and from the bridge circuit A second limiting resistance element is provided in series with the semiconductor switching element that is closed to extract a negative polarity pulse, and the value of the first limiting resistance element is set higher than the value of the second limiting resistance element. Electrical discharge machining apparatus Is proposed.
[0018]
When the bipolar pulse voltage obtained from the output of the bridge circuit is applied to the electrical discharge machining gap in this way, the machining current when applying the positive polarity pulse voltage is higher than the machining current when applying the reverse polarity pulse voltage. And no charge and discharge to the floating capacitance component when no load is applied, and the no-load voltage of the discharge machining gap is used for machining regardless of the resistance value of the resistor, whether it is positive or reverse polarity. It becomes the same level as the bipolar output voltage output from the power supply device, and electric discharge machining can be performed by the method according to the first or second aspect of the invention.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a circuit diagram showing an example of an embodiment of an electric discharge machining apparatus according to the present invention. A wire cut electric discharge machining apparatus 1 shown in FIG. 1 is configured as an apparatus for applying a machining voltage V to an electric discharge machining gap G formed between a workpiece 3 and a wire electrode 4 of a machine body 2. And a power supply device for electric discharge machining comprising a first power supply section 5 for rough machining and a second power supply section 6 for finishing machining.
[0021]
The first power supply unit 5 has a known circuit configuration, and therefore details of the configuration are not shown. The rough machining voltage V1 from the first power supply unit 5 is applied as a machining voltage V to the electric discharge machining gap G via the low inductance output line 7 and the pair of relay contacts L1 and L2.
[0022]
On the other hand, the second power supply unit 6 is configured to be able to output a bipolar output voltage because the workpiece 3 is subjected to electrical discharge machining with a small surface roughness for finishing the workpiece 3. In the present embodiment, a bipolar pulse voltage V2 is output from the second power supply unit 6 as a bipolar output voltage, and the bipolar pulse voltage V2 is output via a pair of relay contacts L3 and L4 and a low capacitance output line 8. A machining voltage V is applied to the electric discharge machining gap G.
[0023]
Processing of the workpiece 3 using the first power supply unit 5 and the second power supply unit 6 is performed as follows. That is, by operating a switching relay (not shown), first, the relay contacts L1 and L2 are closed and the relay contacts L3 and L4 are opened, and the rough machining voltage V1 from the first power supply unit 5 is applied to the electric discharge machining gap G. A machining voltage V is applied to rough the workpiece 3. Thereafter, with the relay contacts L1 and L2 opened and the relay contacts L3 and L4 closed, the bipolar pulse voltage V2 from the second power source is applied to the electric discharge machining gap G as the machining voltage V, and the workpiece 3 is finished. Note that a series circuit of a relay contact L5 and a coil 30 is connected in parallel to the electric discharge machining gap G. The relay contact L5 is turned on and off simultaneously with the relay contacts L3 and L4 and discharged by the second power supply unit 6. The coil 30 is connected in parallel with the electric discharge machining gap G only during the machining operation, which will be described later.
[0024]
Next, the configuration of the second power supply unit 6 will be described. Reference numeral 9 denotes a DC power source that outputs a DC voltage E. Reference numeral 10 denotes a bridge circuit in which switching transistors 11 to 14 and resistors 15 to 18 are provided on each side and connected as shown in the figure. In the bridge circuit 10, the connection point 10 </ b> A of the switching transistors 11 and 12 and the connection point 10 </ b> B of the switching transistors 13 and 14 are input parts, and the connection point 10 </ b> C of the resistors 15 and 17 and the connection of the resistors 16 and 18 are connected. The point 10D is an output unit. A DC voltage E from a DC power supply 9 is applied to the input section, and a bipolar pulse voltage V2 is obtained from the output section as described below.
[0025]
Reference numeral 20 denotes a control circuit for controlling on / off of the switching transistors 11 to 14 provided on each side of the bridge circuit 10, and includes a pulse generator 21 and an inverter 22. The pulse signal from the pulse generator 21 is output as it is as the control pulse signal PA, and the inverter 22 outputs the inverted control pulse signal PB obtained by inverting the level of the control pulse signal PA ((A in FIG. 2). ) And (B)).
[0026]
The control pulse signal PA is applied to the gates of the switching transistors 11 and 14 of the bridge circuit 10 as gate control signals for on / off control, and the inversion control pulse signal PB is applied to the switching transistors 12 and 13 of the bridge circuit 10. A gate control signal for on / off control is applied to the gate. Therefore, the switching transistor 11 is turned on / off simultaneously with the switching transistor 14, while the switching transistor 12 is turned on / off simultaneously with the switching transistor 13. As can be seen from FIGS. 2A and 2B, the ON operation of the switching transistors 11 and 14 and the ON operation of the switching transistors 12 and 13 are alternately performed. As a result, the output portion of the bridge circuit 10 The bipolar pulse voltage V2 whose polarity is inverted at the same cycle as the control pulse signal PA is output.
[0027]
When the polarity of the bipolar pulse voltage V2 obtained at the output portion of the bridge circuit 10 is positive, that is, when the workpiece 3 is in an output state in which the potential is higher than that of the wire electrode 4, the electric discharge machining gap G When the value of the machining current flowing is IH and the polarity of the bipolar pulse voltage V2 obtained at the output section of the bridge circuit 10 is negative, that is, the output state in which the workpiece 3 is at a lower potential than the wire electrode 4 In this case, when the value of the machining current flowing in the electric discharge machining gap G is IL, the total resistance value of the resistors 15 and 18 is greater than the total resistance value of the resistors 16 and 17 in order to satisfy IL> IH. Is also set larger. In the present embodiment, the resistor 15 has the same value as the resistor 18, and the resistor 16 has the same value as the resistor 17.
[0028]
Next, the operation of the second power supply unit 6 will be described with reference to FIG. The switching transistors 11 to 14 of the bridge circuit 10 are controlled to be turned on and off by the control pulse signal PA and the inverted control pulse signal PB (see FIGS. 2A and 2B) from the control circuit 20 as described below. The bipolar circuit 10 outputs a bipolar pulse voltage V2. FIG. 2C shows an example of the waveform of the machining voltage V at this time.
[0029]
That is, in the periods T1, T3, T5, T7,..., The switching transistors 11 and 14 are turned off and the switching transistors 12 and 13 are turned on, and the DC voltage E from the DC power source 9 is a low resistance resistor 16, 17 is output. Accordingly, the discharge energy at a level where the machining voltage V is relatively high and the machining current is large is supplied to the electric discharge machining gap G so that the wire electrode 4 is positive and the workpiece 3 is negative, and the workpiece 3 is reversed. Electric discharge machining with polarity. In the electric discharge machining with the reverse polarity, since the electric discharge energy distribution to the workpiece is small, an electric discharge machining surface having a small surface roughness can be obtained while performing a stable electric discharge. In the example shown in FIG. 2, electric discharge is generated in the electric discharge machining gap G only in the periods T3 and T5.
[0030]
Next, in the periods T2, T4, T6, T8,..., The switching transistors 11 and 14 are turned on, the switching transistors 12 and 13 are turned off, and the DC voltage E from the DC power supply 9 is a high-resistance resistor 15. , 18 are output. Accordingly, the discharge voltage is supplied to the electric discharge machining gap G at a level where the machining voltage V is relatively low and the machining current is small so that the wire electrode 4 is negative and the workpiece 3 is positive, and the workpiece 3 is positive. Is electrical discharge machining. EDM with positive polarity has a large amount of discharge energy distribution to the workpiece, but since the level of discharge energy is low, the surface roughness of the EDM surface of the workpiece 3 is reduced and the required finish machining is possible. It becomes. The polarity of the machining voltage V applied to the electric discharge machining gap G is reversed at each transition from the periods T1, T3, T5, T7,... To the periods T2, T4, T6, T8,. Therefore, in particular, the discharge for reverse polarity machining by the machining voltage V can be once interrupted quickly, and thus the finishing can be performed stably and satisfactorily as a whole.
[0031]
In this way, reverse polarity machining and positive polarity machining are alternately and stably performed at a predetermined cycle determined by the control pulse signal PA, and the workpiece 3 can be finished with a small surface roughness. 2D is a waveform diagram of the electric discharge machining current I flowing through the electric discharge machining gap G. FIG. From FIG. 2D, the workpiece 3 is stably processed with a large machining current by reverse polarity machining to obtain a small surface roughness electric discharge machining surface, and the workpiece 3 is processed at a low machining current by positive polarity machining. It can be seen that it has been processed to help reduce surface roughness.
[0032]
By the way, when the electric discharge machining gap G side is viewed from the output end of the second power supply unit 6, there is a stray capacitance mainly due to the capacitance component of the output line 8. Therefore, when the bipolar pulse voltage V2 from the second power supply unit 6 is applied as the machining voltage V to the electric discharge machining gap G, considering the case of no load in which no discharge occurs in the electric discharge machining gap G, the bipolar polarity When the output polarity of the pulse voltage V2 alternately changes in a predetermined cycle, resistors having different values are alternately connected in series to the stray capacitance depending on whether the bipolar pulse voltage V2 has a positive polarity or a reverse polarity. The Rukoto. As a result, a phenomenon occurs in which the value of the processing voltage V in the no-load state differs between the case of positive polarity and the case of negative polarity. When this phenomenon occurs, a so-called brass coating phenomenon occurs in which the surface of the workpiece 3 is coated with brass, and the quality of the processed surface of the workpiece 3 is impaired.
[0033]
In order to eliminate this problem, when the relay contacts L3 and L4 are closed for finishing by the second power supply unit 6, the relay contact L5 is also closed at the same time, and the coil 30 is connected in parallel to the electric discharge machining gap G. A parallel resonance circuit is configured by the coil 30 and the stray capacitance, and the resonance frequency of the parallel resonance circuit is configured to substantially match the frequency of the control pulse signal PA. For this reason, the inductance value of the coil 30 is determined based on the value of the stray capacitance and the frequency of the control pulse signal PA.
[0034]
Thus, when the second power supply unit 6 is used, the coil 30 is connected in parallel with the electric discharge machining gap G, so that the impedance when the electric discharge machining gap G is viewed from the output of the second power supply unit 6 is substantially pure resistance. Thus, even if the value of the resistor inserted between the DC power supply 9 and the electric discharge machining gap G changes when the polarity of the bipolar pulse voltage V2 is switched, the voltage of the bipolar pulse voltage V2 remains at no load. Since the machining voltage V is applied to the electric discharge machining gap G almost as it is, no brass coating is generated in the electric discharge machining gap 3.
[0035]
FIG. 3 is a diagram showing an electrical equivalent circuit during the finishing process of the electric discharge wire cut electric discharge machining apparatus 1 of FIG. In FIG. 3, reference numeral 40 denotes a power supply unit for generating the bipolar pulse voltage V <b> 2 composed of the DC power supply 9 and the bridge circuit 10, and R is an internal resistance value of the power supply unit 40. C1 is a capacitance value of the floating capacitance, L1 is an inductance value of distributed inductance due to wiring to the electric discharge machining gap G, and L2 is an inductance value of the coil 30.
[0036]
Assuming that the frequency of the control pulse signal PA, that is, the frequency of the bipolar pulse voltage V2 is 5 MHz, when the value of C1 is about 500 PF, the value of L2 may be about 2 μH. If the coil 30 is set to such a value, the impedance when the electric discharge machining gap G is viewed from the power supply unit 40 is almost only the resistance value of the electric discharge machining gap G. Therefore, in the no-load state, V2≈V.
[0037]
4A shows an example of a no-load voltage waveform of the machining voltage V when the bipolar power supply voltage 6 is applied from the second power source 6 to the electric discharge machining gap G using the coil 30. FIG. . On the other hand, FIG. 4B shows an example of a no-load voltage waveform of the machining voltage V when the bipolar pulse voltage V2 is applied from the second power supply unit 6 to the electric discharge machining gap G without using the coil 30. It is shown. Comparing the voltage waveforms of (A) and (B) of FIG. 4, it can be seen that the bias of the voltage is remarkably improved by inserting the coil 30.
[0038]
FIG. 5 shows an example of the surface roughness state of the electric discharge machining surface of the workpiece 3 machined using the electric discharge machining power supply device 1 shown in FIG. The conditions for this processing are:
DC power supply voltage 45V
Frequency 5MHz
Electrode voltage (electrode positive electrode) 40V (no load)
(Electrode negative electrode) 40V (no load)
Resistance 16, 17 (electrode positive electrode) 5Ω + 5Ω = 10Ω
Resistance 15, 18 (electrode negative electrode) 25Ω + 25Ω = 50Ω
It is.
As can be seen from FIG. 5, even if the plate thickness of the workpiece 3 changes, the surface roughness state of the electric discharge machining surface hardly changes. It was also confirmed that no brass coating was generated.
[0039]
According to the configuration shown in FIG. 1, in the bipolar pulsed power supply having a relatively low high frequency region transistor bridge circuit configuration with a frequency of 5 MHz or less, the positive side limiting resistance value is higher than the reverse side limiting resistance value. By using it, it is possible to improve the roughness of the machined surface by making the discharge current at the time of voltage application on the positive electrode side lower than that on the reverse electrode side (in this case, the no-load voltage waveform shown in FIG. Become). Furthermore, in order to generate LC parallel resonance with the stray capacitance on the circuit, a predetermined inductance is inserted in parallel between the poles, thereby making the impedance composed of the stray capacitance and the parallel inductance infinite. As a result, the influence of the stray capacitance is eliminated, and the bias toward the reverse polarity side of the no-load voltage caused by the difference in limiting resistance value between the positive electrode and the reverse electrode can be eliminated. In this circuit configuration, a no-load voltage waveform is applied across the electrodes with equal polarity. However, when discharge occurs, the discharge current is different between the positive side and the reverse side. The surface roughness can be improved by suppressing the above.
[0040]
In this way, a high-quality processed surface can be obtained in a relatively low frequency range of 5 MHz, and further stable processing can be performed without becoming a gap resonance state. In addition, it is possible to obtain a stable and high-quality machined surface without much influence from the distributed inductance on the mechanical structure of the electric discharge machine, and because there is no bias in the no-load voltage waveform, brass adheres to the workpiece. The phenomenon does not occur.
[0041]
In the above-described embodiment, the case where the present invention is applied to a wire-cut electric discharge machine has been described. However, the present invention is not limited to the configuration of the embodiment, and can be widely applied to a die-cut electric discharge machine or the like. The same effect can be obtained.
[0042]
【The invention's effect】
According to the present invention, as described above, when the machining voltage is applied to the electric discharge machining gap formed by the workpiece and the machining electrode while alternately switching the polarity between positive and negative, the workpiece is subjected to electric discharge machining. By making the discharge current at the time of voltage application on the positive electrode side lower than that on the reverse electrode side, the roughness of the machined surface can be improved. Normally, when machining with an AC power supply or bipolar pulse power supply that is equal in both polarities, it is considered that the surface roughness is determined by the positive electrode side discharge with a large energy distribution to the workpiece. By suppressing the discharge current at the time, it becomes possible to improve the surface roughness.
In this case, a high-quality electric discharge machined surface can be obtained even in a high frequency region where the frequency of the bipolar output voltage such as bipolar pulse is relatively low, and further stable machining is possible even if the gap resonance state is not achieved. A stable and high-quality machined surface can be obtained without being greatly affected by changes in the thickness of the workpiece, the wire diameter, and the distributed inductance on the mechanical structure of the electric discharge machine.
[0043]
In addition, the inductance connected in parallel with the electric discharge machining gap can eliminate the bias of the machining gap voltage to the opposite polarity when there is no load. Even when a configuration that is larger than the machining energy at the time is adopted, a high-quality electric discharge machining surface can be obtained without causing a phenomenon that brass adheres to the machining surface.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an example of an embodiment of a wire cut electric discharge machining apparatus according to the present invention.
2 is a signal waveform diagram of each portion for explaining the operation of the electric discharge machining power supply device of FIG. 1; FIG.
FIG. 3 is an electrical equivalent circuit diagram of an electric discharge machining apparatus for explaining the action of a coil connected in parallel to the electric discharge machining gap.
4A is a waveform diagram showing a no-load voltage waveform when a coil is connected in parallel to the electric discharge machining gap, and FIG. 4B is a waveform showing a no-load voltage waveform when no coil is connected in parallel to the electric discharge machining gap. Figure.
FIG. 5 is a graph for illustrating an example of surface roughness of an electric discharge machining surface when electric discharge machining is actually performed using the electric discharge machining apparatus of FIG. 1;
[Explanation of symbols]
1 Wire-cut EDM
2 Processing machine body
3 Workpiece
4 Wire electrode
6, 60 Second power supply unit
9, 62 DC power supply
10 Bridge circuit
10A-10D connection point
11-14 switching transistors
15-18 resistors
20 Control circuit
30 coils
61 AC power supply
E DC voltage
G EDM gap
I Electric discharge machining current
PA control pulse signal
PB inversion control pulse signal
V Machining voltage
V2 Bipolar pulse voltage

Claims (3)

When the electric discharge machining gap formed by the workpiece and the machining electrode is applied by alternately switching the polarity of the machining voltage between positive and negative, and the workpiece is subjected to finish electric discharge machining, the workpiece is used as the positive electrode. The machining current level in the positive polarity machining with the machining electrode as the negative electrode and the workpiece as the positive electrode is smaller than the machining current level in the reverse polarity machining with the negative electrode as the negative electrode, and the circuit is in parallel with the electric discharge machining gap. discharge machining method being characterized in that the working voltage of the positive and negative in unloaded state is the stray capacitance and the LC parallel resonance of the upper so as to evenly insert the to order of the inductance element. A bipolar output voltage whose polarity is periodically reversed is applied as a machining voltage to the electric discharge machining gap formed between the workpiece and the machining electrode via a resistor, and the machining electrode is used as a positive electrode. In the method of finishing electric discharge machining of the workpiece while periodically switching between the reverse polarity machining using the workpiece as a negative electrode and the positive polarity machining using the machining electrode as the negative electrode and the workpiece as the positive electrode, The resistor is a resistor having a small resistance value, and at the time of the positive polarity machining, the resistor is switched to become a resistor having a large resistance value, and the floating capacitance on the circuit and the LC parallel resonance are in parallel with the electric discharge machining gap. discharge machining method being characterized in that so as to insert an inductance element evenly to order the machining voltage of the bipolar in unloaded state is a. In an electric discharge machining apparatus for finishing electric discharge machining of a workpiece by supplying a bipolar pulse voltage whose polarity is periodically reversed to an electric discharge machining gap, a DC power source that outputs DC voltage, and a semiconductor switching element on each side ON / OFF control by synchronizing the semiconductor switching elements on opposite sides of the bridge circuit to obtain the bipolar pulse voltage from the bridge circuit to which the DC voltage is input and the output of the bridge circuit. a control circuit for, in the electric discharge machining gap to equalize the bipolar pulse voltage in the unloaded state to eliminate the influence of stray capacitances on the circuit for applying the bipolar pulse to said discharge machining gap Said semiconductor device comprising an inductance element connected in parallel and closed to extract a positive pulse from said bridge circuit A first limiting resistance element is provided in series with the switching element and a second limiting resistance element is provided in series with the semiconductor switching element that is closed to extract a negative pulse from the bridge circuit. Is set to be higher than the value of the second limiting resistance element.

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