JPS603932B2 - Electrical discharge machining method and equipment - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electric discharge machining method and apparatus, and more specifically, to an electric discharge machining method and apparatus that can obtain a glossy electric discharge machined surface with low surface roughness. Conventionally, various attempts have been made to obtain electrical discharge machined surfaces with smaller surface roughness by electrical discharge machining. For example, when performing electrical discharge machining using a non-storage type machining pulse power source, the surface roughness of the electrical discharge machined surface is improved by using the machining pulses and the presetting pulses.
The peak current of this type of pulse is quite high, and therefore the depth of the hole machined and removed by electric discharge is quite deep, and the obtained surface roughness is usually about 3 [muRmax]. Another method is to improve the rise characteristics of the pulse applied to the machining gap by inserting a capacitor between the output terminals of the machining pulse, thereby reducing the diameter of the hole cut by electric discharge, which results in surface roughness. There are ways to improve your performance. However, regardless of whether a non-accumulative type or an accumulative type pulse power source for machining is used, in order to maintain the effective discharge rate above a predetermined value, the pulse must have a fairly high peak value. As a result, the depth of scraping due to electrical discharge became deep, and a shiny electrical discharge machined surface could not be obtained. Therefore, in the past, if you wanted to make the machined surface shiny, it was necessary to perform electric discharge machining first and then perform polishing in a separate process, which increased the number of processes and increased processing costs. There was a problem with this. Therefore, an object of the present invention is to provide an electric discharge machining method and apparatus that can obtain a finished surface with extremely low surface roughness. A feature of the method of the present invention is that the main electrical discharge machining current is continuous with the main electrical discharge machining current. An auxiliary electrical discharge machining current having an obliquely lower peak value than that of the current is caused to flow through the electrical discharge machining gap for a longer time than the main electrical discharge machining current. The electric discharge machining apparatus according to the present invention includes a first means for generating a main machining pulse that is intermittently applied to the electric discharge machining gap, and a main electric discharge machining current that is continuous with the main electric discharge machining current generated by the main machining pulse. Pi-
and second means for applying to the electrical discharge machining gap a current having a peak below the peak value and having a duration of at least twice the duration of the main electrical discharge machining current. 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 present 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 reducing the machining gap 9 between the workpiece 6 and the machining electrode 8.
adjust the length of and generate electric discharge in the machining gap 9;
A workpiece 6 is subjected to electrical 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 unit 3 includes switching transistors 11 and 1 that are controlled to be turned on and off by control pulses P, P2 from the control pulse generator 10.
The emitters of the transistors 11 and 12 are commonly connected to the output terminal 13, and each collector is connected to the DC power supply 14 through current limiting resistors R, R2, respectively.
is connected to the positive terminal of the The negative terminal of the DC power supply 14 is connected to one output terminal 16, and each output terminal 13, 15 is connected to the workpiece 6 and the processing electrode 8 by conducting wires 16, 17, respectively. The control pulses P, , P2 are as shown in Fig. 2a and b,
It is a pulse train signal with matching rise timing,
The pulse T2 of the control pulse P2 is selected to be more than twice the pulse T of the control pulse P. The transistor 11 becomes conductive when the control pulse P is at the "1" level, and an electric discharge machining voltage is applied to the machining gap 9. On the other hand, the transistor 12 detects that the control pulse P2 is
1'' level, the electrical discharge machining voltage is applied to the machining gap 9 in a conductive state. As can be seen from the waveforms shown in FIG. Only 2 is turned on. Therefore, during the period M, the electric discharge machining current is limited to a value determined by the parallel resistance value R, R2 of the resistors R, , R2, and during the period S, the electric discharge machining current is limited according to the resistance value R2 of the resistor R2. . In the apparatus of this embodiment, R2=4R, 〆R2 are selected, and the peak value b of the auxiliary discharge machining current occurring in period S is approximately It has become poisonous. Then, the control pulse P2 becomes the "0" level at time t3, which is a little before the next control pulse P rises at time t4, and therefore both transistors 11 and 12 are off between time t3 and t4. Become. The above-described switching operations in transistors 1 and 12 are performed in the same manner for each cycle. According to such a configuration, the transistors 11 and 12 are provided in the discharge machining gap 9.
The main electrical discharge machining current with the peak value a flows during the period when both of the An auxiliary electric discharge machining current having a value b of a/4 flows through the transistor 2 into the machining gap 9. Therefore, compared to flowing only the main electric discharge machining current, electric discharge is more likely to occur at each rising time of each control pulse P and P2, and the next electric discharge is encouraged. This is considered to be because the auxiliary electrical discharge machining current plays the role of a stepwise current. When this auxiliary electrical discharge machining current brings about a state in which electrical discharge is likely to occur as described above, the state of the electrical discharge current at the rising time of each control pulse P and P2 has a gradual rising characteristic without sudden electrical discharge pulses. The shape of the clay hole is shallow and the entrance is wide. In other words, it becomes a clay ball with a roundness that is almost flat. Therefore, the surface roughness of the machined surface can be significantly improved. FIGS. 7 and 8 show the time T of the main electrical discharge machining current. N and T during the time of auxiliary electrical discharge machining current. An example of a characteristic curve showing the surface roughness when the ratio between the peak value lp of the main electric discharge machining current and the peak value lp' of the auxiliary electric discharge machining current is changed is shown to show the surface roughness. An example of a characteristic curve is shown. This data is an example when steel is processed using a copper electrode, but the current direction does not change significantly depending on the materials of the electrode and workpiece. Based on the analysis results of the data obtained in this way, it is found that by applying the auxiliary electrical discharge machining current, the shape of the hole to be cut is made into the shape described above, and in order to reduce the surface roughness of the machined surface, the auxiliary electrical discharge machining current is It has been confirmed that it is essential to set the maximum value of Ta. A more preferable condition is that the length of period M is 1 [French s]
~10 [As], the length of period S is two folds from twice the length of period M, a is 0.2 [A] to 20 [A], and b is the value of a at that time. Decorate with Kayashita. By reducing the values of M and a, the surface roughness can be extremely reduced to 4.0 and the electrical discharge machined surface can be made glossy. In this embodiment, in order to ensure that the auxiliary electrical discharge machining current flows continuously with the main electrical discharge machining current, both transistors 1 and 1 are switched off during the period M.
However, transistors 12 and 12 are turned on at the same time.
It is also possible to set the period in which the auxiliary electrical discharge machining current is on to be only the period S, and to flow the auxiliary electrical discharge machining current continuously to the main electrical discharge machining current. However, in this case, the current caused by the transistor 12 is during the period M
Therefore, it is necessary to determine the values of the resistance values R. and R2 so that the condition of b≦quantity a is satisfied. FIG. 3 shows a modification of the machining pulse power supply section 3 shown in FIG. Therefore, when the transistor 12 is turned on, the DC power supply 2
The first point is that the electric discharge machining current is reduced from 0.
This is different from the embodiment shown in the figure. The control pulses P, P2 for switching the transistors 11, 12 may be the same as those explained in FIG. In this case as well, the transistor 12 is turned on at the same time as the transistor 11 is turned off, and as shown in FIG.
Of course, the control may be such that an electrical discharge machining current having a waveform as shown in the figure is passed through the machining gap. This is because the feature of the present invention is that the auxiliary electrical discharge machining current is caused to flow continuously with the main electrical discharge machining current. Reference numeral 21 in FIG. 3 indicates a diode for preventing backflow. FIG. 4 shows yet another modification of the machining pulse power supply section 3. This machining pulse power supply section 3'' uses a single power supply 14 and has two transistors in the collector circuit of the transistor 2. resistor R3
, R4 are inserted in series, and a collector emitter circuit of a transistor 11 is connected in parallel to the resistor R3, and each transistor 11, 12 receives a control pulse as shown in FIG. The on/off control is performed by P, , P2, respectively. According to such a configuration, during the period M, the resistor R3 is short-circuited, so the main electrical discharge machining current is limited by the resistor R4.On the other hand, during the period S, only the transistor 12 is turned on, so the auxiliary electrical discharge machining current is It will be limited by resistors R3 and R4.
Therefore, by selecting R3 and R4, electrical discharge machining can be performed by the method of the present invention. In Figure 5,
Other embodiments of the invention are shown. In FIG. 5, the main body of the processing machine is omitted and only the processing pulse power supply section 30 is shown. This processing pulse power supply 30 has a switching transistor 32 that is controlled on and off by a control pulse P3 from a control pulse generator 31, and the collector of the transistor 32 has a negative terminal connected to the - output terminal 15. The emitter of the transistor 32 is connected to the positive terminal of a DC power supply 33 via a resistor R5, and the emitter of the transistor 32 is connected to the output terminal 13 via a parallel circuit 34 of a resistor R6 and an inductor L. These output terminals 1
3 and 15 are connected to a workpiece and a processing electrode of a processing machine main body (not shown). The control pulse P3 from the control pulse generator 31 is a pulse train signal having a predetermined constant period and a constant pulse, as shown in FIG. 6a,
Conventional ones can be used. When the control pulse P3 is applied, the transistor 32
is in the ON state only during the period when R is at the "1" level, and as a result, the main electric discharge machining current flows through the resistor R5 and the parallel circuit 34. Since the parallel circuit 34 includes an inductor L, the rise of the main electrical discharge machining current when the control pulse P3 rises is rather gradual (the sixth
(see figure). Next, when the control pulse P3 falls at t6, the current supply from the DC power source 33 is cut off, but the energy from the main electrical discharge machining current is transferred to the inductor L' of the parallel circuit 34 provided in the main electrical discharge machining current path. Because of the accumulated energy, even after the transistor 32 is turned off, the auxiliary electrical discharge machining current flows through the electrical discharge machining gap in succession to the main electrical discharge machining current. This auxiliary electrical discharge machining current is transmitted in the same direction as the main electrical discharge machining current through a series circuit consisting of a diode 3 and a resistor R7, which is inserted and connected between the output terminal 15 and the emitter of the transistor 32. Flows into the machining gap. The peak value of this auxiliary electrical discharge machining current is also a subcutaneous value of the main electrical discharge dish current similar value, and the period during which the current flows (t7 - t6) is the period during which the main electrical discharge machining current flows (t6 - t5). The value of each element is determined to be twice or more. The function of the auxiliary electrical discharge machining current in this embodiment is the same as that in the previous embodiment, and because of this auxiliary electrical discharge machining current, the subsequent main electrical discharge machining current flows more easily, and the rise at the beginning of the current flow is smoothed out. In addition, as mentioned above, the rise is made gentle by the action of the inductor L, so the shape of the discharge clay becomes nearly flat and rounded, which greatly contributes to reducing the surface roughness of the machined surface. It turns out. In the embodiment shown in FIG. 5, the value of the DC power supply 33 is set to 150 to 35.
0 [V], the value of resistor R5 is 10

[0] ~ 1 [lk○]
, the value of resistor R6 is 10 [Q] to 100 [Q], the value of resistor 7 is 0 to 10 [Q], the value of inductor L is at least 3 [H], and during the on-time of control pulse P3, By setting the value of each element to satisfy the above-mentioned essential conditions as 1 [ARmax
) was able to obtain a glossy surface. In this embodiment, since the energy source of the auxiliary electric discharge machining current is an inductor, the current waveform is in a form that decreases exponentially. FIG. 9 shows yet another embodiment of the invention. In FIG. 9, as in the case of FIG. 5, only the machining pulse power source section 40 is shown without the main body of the processing machine, and parts corresponding to those in FIG. 5 are given the same reference numerals. The explanation will be omitted. This processing pulse power supply section 401 is equipped with a capacitor 41 connected between the emitter of the transistor 32 and the negative electrode of the DC power supply 33, and a diode 42 is connected in parallel to the capacitor 41 with the polarity shown. ing. The first output terminal 13 is connected to the emitter of the transistor 32, and the first output terminal 15 is connected to the inductance 4.
3 and a resistor 44 through a parallel circuit 45.
It is connected to the negative pole of No.3. According to such a configuration,
When the transistor 32 is turned on at t8 in response to the pulse P3 (Figure IQ a), the charging current from the DC power supply 33 flows into the capacitor 41 via the resistor R5, thereby The capacitor 41 is charged. As a result, the voltage Vc across the capacitor 41 is 10th
The voltage rises as shown in FIG. is applied to the electrical discharge machining gap. In this case, since the diode 42 is reverse biased by the voltage Vc,
No current flows through diode 42. Therefore, at t=t9, the main electric discharge machining current flows into the electric discharge machining gap due to the voltage Vc. When the transistor 32 is turned off at t=rao, the main electrical discharge machining current rapidly decreases, and the supply of the main electrical discharge machining current from the DC power supply 33 is thereby stopped.
The energy stored in the inductance 43 by flowing through t=etc. Thereafter, the electric discharge machining current will flow through the diode 42 into the electric discharge machining gap as an auxiliary electric discharge machining current. The direction of this auxiliary electrical discharge machining current is the same as the direction of the main electrical discharge machining current. Even in the case of the circuit shown in FIG. 9, the peak value ls of the auxiliary electrical discharge machining current is 1 of the peak value IM of the main electrical discharge machining current.
/ male end, and the time when the auxiliary electrical discharge machining current flows (t, o) is the time when the main electrical discharge machining current flows, t,
The value of each element is determined to be more than twice o-t9). Although FIG. 9 shows a so-called non-storage type transistor using a switching transistor 32,
It is also possible to use a so-called energy storage type circuit in which the emitter-collector of the transistor 32 is short-circuited. In the above embodiments, a non-accumulative type was described, but the present invention can be similarly applied to an accumulating type. According to the present invention, as described above, by continuously flowing the auxiliary electric discharge machining current following the main electric discharge machining current, electric discharge is more likely to occur, and the electric discharge clay has a flatter and rounded shape. It has extremely excellent effects such as significantly improving the surface roughness of the electrical discharge machined surface and making it possible to obtain a glossy surface by electrical discharge machining alone.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram shown together with a schematic mechanism diagram of an embodiment of the present invention, FIGS. 2a to 2c are waveform diagrams for explaining the operation of the device shown in FIG. 1, and FIG. FIG. 4 is a circuit diagram showing a modification of the processing pulse power supply section shown in FIG. 1, and FIG. 5 is a circuit diagram of a processing pulse power supply section according to another embodiment of the present invention.
6a and 6b are waveform diagrams for explaining the operation of the circuit in FIG. 5, FIGS. 7 and 8 are characteristic curve diagrams showing experimental results, and FIG. 9 is a diagram showing a further example of the present invention. FIGS. 10a to 10c are waveform diagrams for explaining the operation of the embodiment shown in FIG. 9. 1... Electric discharge machining device, 2... Processing machine main body, 3, 3', 3'', 30... Power supply section for machining pulses, 6... Workpiece, 8... Machining electrode, 9... Machining gap, 10, 31... Control pulse generator, 11, 12, 32... Transistor,
14, 20, 33...DC power supply, L...Inductor, R
．． ~R7...Resistor, P,~P3...
control pulse. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6. Figure 7 Figure 8 Figure 9 Figure 10

Claims (1)

[Claims] 1. An electrical discharge machining method in which electrical discharge machining is performed by intermittently applying main processing pulses to flow a main electrical discharge machining current to an electrical discharge machining gap between a workpiece and a processing electrode, Continuously following the main electrical discharge machining current, an auxiliary electrical discharge machining current having a peak value of 1/2 or less of the peak value of the main electrical discharge machining current is applied to the machining gap for a time of at least twice the time width of the main electrical discharge machining current. An electric discharge machining method characterized by flowing. 2. The electric discharge machining method according to claim 1, wherein the auxiliary electric discharge machining current is supplied so that its value decreases exponentially with the passage of time. 3. In an electric discharge machining device that performs electric discharge machining by applying a machining pulse to the electric discharge machining gap between a workpiece and a machining electrode, a main machining pulse that is intermittently applied to the electric discharge machining gap is generated. the main electrical discharge machining current generated by the main electrical discharge machining pulse has a peak that is equal to or less than 1/2 of the peak value of the main electrical discharge machining current, and has a time width of the main electrical discharge machining current; and a second means for applying an auxiliary electrical discharge machining current having a duration twice or more to the machining gap.