JPS603930B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical discharge machining apparatus, and more specifically, to an electrical discharge machining apparatus that can provide a glossy electrical discharge machining surface.

In general, it is known that in order to reduce the surface roughness of a machined surface in an electric discharge machining apparatus using a non-storage pulse power supply for machining, the length of the machining pulse can be narrowed.

For this reason, in electric discharge machining equipment using conventional non-storage type pulse power supply circuits, a high-performance high-frequency switching element is used to generate narrower machining pulses,
The aim was to improve the surface roughness of the electrical discharge machined surface. However, the peak voltage of this type of pulse is a large value of several tens of volts, and the switching characteristics of switching elements used at such high voltages make the minimum value of the pulse for electrical discharge machining very low. Considering the effective discharge rate, the minimum value during the pulse was about 2 [rsec] from a practical standpoint. When machining is performed using such extremely narrow machining pulses, the obtained surface roughness value is usually about 3 [peak Rmax]. Therefore, if a machined surface roughness of less than this value is required, such as when the machined surface is desired to be a glossy surface, it becomes necessary to perform polishing in a separate process, which increases the number of processes. However, this method also had the problem of increasing processing costs. The object of the present invention is therefore to avoid narrowing the pulse length of conventional processing pulses below the above-mentioned limits.
It is an object of the present invention to provide an electrical discharge machining device which has a machining surface assembly degree of 4 and which can make the electrical discharge machined surface a glossy surface.

The present invention has been achieved through various experiments and research by the inventors, and has been developed by narrowing the pulse width of the electric discharge machining pulse and at the same time making the pulse rise characteristics gentle, thereby achieving a different cutting process than in the conventional electric discharge machining state. This is based on the knowledge that a shallow electrical discharge machining state can be obtained and that the state of the electrical discharge machined surface changes depending on the polarity of the machining pulse applied to the electrical discharge machining gap.

Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 shows an embodiment of an electrical discharge machining apparatus according to the invention.

The electric discharge machining device 1 includes a machining machine main body 2 which is schematically shown.
The processing pulse from the processing pulse power supply section 3 is supplied to the workpiece 6 immersed in the processing liquid 5 in the processing tank 4 and to the processing head 7. The applied voltage is applied between the processing electrode 8 and the processed electrode 8. An electrode feeding mechanism is provided in the processing head 7, and the processing electrode 8
can be moved toward and away from the workpiece 6.
Thereby, the length of the machining gap 9 between the workpiece 6 and the machining electrode 8 is adjusted, electric discharge is generated in the machining gap 9, and the workpiece 6 is subjected to electric discharge machining. Since this machining machine main body 2 has the same configuration as that of a conventional Z-axis controlled electrical discharge machining device, further detailed explanation of the machining machine main body 2 will be omitted. The processing pulse power supply section 3 has a switching transistor 1 that is controlled on and off by a pulse controller 10.
In the collector circuit of 1, the positive terminal of the DC power supply 12 is connected to the resistor 13.
The negative electrode of the DC power supply 12 is directly connected to the output terminal 14.

The other output terminal 15 and switching transistor 1
An air core coil 16 is provided between the first output circuit and the first output circuit. The air core coil 16 is connected to the switching transistor 1
The selection switch 17 selects the emitter of the switching transistor 1 from one of the taps a to d provided on the air-core coil 16. By connecting to the emitter circuit, the value of the inductance inserted into the emitter circuit can be adjusted.
A resistor 18 is inserted between the movable contact of the selection switch 17 and the output terminal 15, so that the selection switch 1
Regardless of the switching position of 9, the resistor 18 is connected to the air core coil 1.
6 in parallel. This resistor 18 is
In order to improve the reduction in the effective discharge rate and when the switching transistor 11 is turned off, the air core coil 16
This is provided to prevent unnecessary electrical discharge from occurring in the machining gap 9 due to the energy stored in the machining gap 9. The output terminals 14 and 15 are connected to the processing electrode 8 and the workpiece 6 through conducting wires 19 and 20', respectively, and the processing pulses are applied so that the workpiece 6 is on the positive side and the processing electrode 8 is on the - side. applied. As will be described in detail later, the selection of the polarity of this applied pulse has a significant effect on the finished state of the machined surface. The pulse controller 1 is used to control the duration of the pulse taken out from the emitter circuit of the switching transistor 11, and when it is desired to obtain an electrical discharge machined surface with a small surface roughness as in the case of finishing, conventional finishing is used. It is appropriately set to output a machining pulse of 10 [rsec] or less, which is the same pulse as the machining conditions.

On the other hand, as shown in FIG. 2, the inductance value of the air-core coil 16 is determined so that the rising portion of the waveform of the electrical discharge machining pulse rises gradually as shown by the dotted line. It was confirmed that the larger the value of this inductance, the more gradual the rise characteristics of the pulse waveform, and the more gradual the rise of this pulse waveform, the smaller the surface roughness of the electrical discharge machined surface. The reason why the surface roughness of the electrical discharge machined surface is reduced by making the rise characteristics of the thin machining pulse less than 10 [sec] more gradual is as follows.

By narrowing the machining pulse, the size of the hole cut by the electric discharge becomes smaller, which can reduce the surface roughness, but in addition to this, by making the rise of the pulse gentle, the condition of the electric discharge becomes smaller. This is because the depth of the hole carved out by the electric discharge becomes shallower and the size of the hole becomes wider at the same time. According to experiments, it has been confirmed that by making the rise characteristic of the machining pulse gentle in this manner, the surface roughness of the electrical discharge machined surface can be reduced to about 1 [Rmax]. In addition, the inductance of the air-core coil necessary to obtain such good surface roughness is such that it cancels out the stray capacitance that exists on the switching element side when viewed from the air-core coil, and still maintains a gentle pulse rise characteristic. Therefore, an inductance of at least 3 [French H] or more is usually required. Moreover, if the rising characteristic of the machining pulse is made gentle in this way, the effective discharge rate in the discharge machining gap will be reduced.

In order to improve the reduction in effective discharge rate, a resistor 18 is connected in parallel to the air-core coil 16, so that a DC bias is applied to the machining gap. Therefore, as shown in FIG. 2, the shape of the green leading edge of the processing pulse once rises vertically due to the resistor 18;
It will rise gradually depending on the value of the inductance of the air-core coil 16. Therefore, compared to the case where the resistor 18 is not provided, the so-called discharge becomes more rapid and the effective discharge rate can be improved. As a result, the surface roughness of the machined surface can be made extremely small and a glossy surface can be obtained without significantly reducing the electrical discharge machining speed. Of course, in order to improve the effective discharge rate, it is also effective to increase the DC power supply voltage, and in conventional devices, the DC main power supply voltage is about 60 to 100 volts, but according to experiments, it is effective to increase the DC power supply voltage. When the rise characteristics were made gentler, an effective discharge rate almost equivalent to that of the conventional method could be obtained by using a DC power supply voltage of 150 volts or more. In addition, the value of the DC power supply voltage is 1
The voltage is not limited to 50 volts or more, and a glossy machined surface with small surface roughness can be obtained even with a voltage of about 60 to 100 volts, as in the case of conventional devices.

The above explanation has been about the relationship between the rise characteristics of the machining pulse and the electrical discharge machining surface.
The relationship between the polarity of the machining pulse applied to the machining gap 9 and the electrical discharge machining surface that occurs between 1 and 15 will be described. Generally, which of the workpiece or the processing electrode is connected to the positive output terminal of the processing power source is determined by the material of the workpiece and the like. However, as a result of various experiments conducted by the present inventor, an inductance was inserted into the output circuit of the switching circuit to make the rise of the narrow pulse more gradual, as shown in Figure 2. It has been confirmed that the machining state of the electrical discharge machined surface is significantly influenced by the polarity of the machining pulse applied to the electrical discharge machining gap. According to experiments, when copper is used as a processing electrode and iron is processed, the inductance of the coil is set to 6 [mountain H], the value of resistor 18 is set to 20 [0], and the applied voltage is set to 270 [V]. ] Under the conditions, the workpiece 6 is machined by connecting the output terminal 15 of the processing pulse power source 3 to the workpiece 6 and connecting the first power terminal 14 to the processing electrode 8. When a machining pulse is applied to the working electrode 8 so as to have a positive potential, it is possible to obtain not only a lower surface roughness but also a glossier electric discharge machined surface compared to conventional electric discharge machining diamond layer machining. It was done. Furthermore, experiments were conducted with various combinations using copper tungsten and silver tungsten as machining electrodes and stainless steel and super steel as workpieces, but in all combinations, the same shiny electrical discharge machining was achieved. I was able to get a face.
Therefore, according to this electric discharge machining, finishing machining and/or mirror polishing, which were conventionally performed in a separate process from electric discharge machining, are no longer necessary, so that the number of processes can be reduced. On the other hand, under the same conditions as described above, the application sacrifice of the machining pulse is reversed, that is, the machining electrode 8 is connected to the workpiece 6.
As a result of machining experiments by applying machining pulses to create a positive potential for No electrical discharge machined surface was obtained. Incidentally, the inductance value of the coil 6 [AH], the value 20 [Q] of the resistor 18, and the applied voltage 270 [V] are merely examples, and the present invention is not limited to these values. In this way, by narrowing the pulse width of the machining pulse and at the same time making the rise of the machining pulse gradual, and by selecting the applied polarity of the machining pulse so that the workpiece is positive with respect to the machining electrode, it is possible to A glossy electrical discharge machined surface can be obtained regardless of the material of the object and the machining electrode.

Furthermore, the surface roughness of the electrical discharge machined surface can be set to a desired value by adjusting the switching position of the selection switch 9. According to this device, as mentioned above, it is possible to obtain an electrical discharge machined surface with lower surface roughness without extremely narrowing the width of the machining pulse, making it possible to use inexpensive elements as switching elements. In addition to being able to reduce the cost of the device, it is also possible to significantly improve the performance. In the above embodiment, a case has been shown in which a processing pulse power supply circuit is provided with only one switching circuit for generating processing pulses. The present invention can be similarly applied to a machining pulse power supply circuit in which a switching circuit is further provided corresponding to the power supply and machining pulses are applied to the machining gap using a DC main power supply and a high-voltage superimposed power supply. In this case as well, the above-mentioned effects can be obtained. According to the present invention, as described above, an extremely excellent effect is achieved in that a shiny electrical discharge machined surface with a smaller surface roughness can be obtained without narrowing the width of the pulse for machining beyond the conventional limit. play.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an embodiment of the present invention, and FIG.
FIG. 3 is a waveform diagram showing the waveform of processing pulses used in the apparatus shown in the figure. 1... Electric discharge machining device, 2... Processing machine main body,
3... Power source for processing pulses, 6... Workpiece, 8... Machining electrode, 9... Machining gap, 10... Pulse controller, 11...
Switching transistor, 12...DC power supply, 1
4,15...Output terminal, 16...Air core coil, 18...Resistor, 19,20...
Conductor. Figure/Figure 2

Claims (1)

[Scope of Claims] 1. A processing machine main body that performs the required relative movement between the processing electrode and the workpiece, and a processing pulse that is supplied to the processing gap between the processing electrode and the workpiece. In the electrical discharge machining apparatus, the electrical discharge machining apparatus includes a non-accumulated machining pulse power source for generating a pulse width of 10 μsec.
c] A switching circuit that generates the following pulses, an inductance element of 3 [μH] or more provided on the output side of the switching circuit to give gentle rising characteristics to the pulses generated in the switching circuit, and a machining gap. and a resistance element connected in parallel to the inductance element in order to facilitate the initiation of discharge by the pulse, and the machining pulse causes the workpiece to have a positive potential with respect to the machining electrode. An electric discharge machining apparatus characterized in that electric discharge machining is applied to the machining gap with such polarity. 2. The electric discharge machining apparatus according to claim 1, wherein the inductance element is an air-core coil. 3 The power supply voltage applied to the switching circuit is 15
The electric discharge machining apparatus according to claim 1, characterized in that the voltage is 0 [V] or more.