JPS6026647B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electric discharge machining apparatus, particularly an electric discharge machining apparatus using a discharge capacitor, in which a switching element is inserted into the charging circuit of the discharge capacitor, detects the start of discharge, and turns off the switching element. The present invention relates to an electric discharge machining apparatus that prevents transition to arc discharge while selecting a small charging time constant for the discharge capacitor, and uniformizes machining pulses and energy.

Conventionally, a so-called capacitor discharge system in which a discharge capacitor is provided as shown in FIG. 1A has been known in electric discharge machining apparatuses.

In this capacitor discharge method, a discharge capacitor 3 is charged from a DC power source 1 through a resistor 2, and when the terminal voltage yc of the capacitor 3 has increased to a predetermined level, a discharge electrode 4 and a workpiece 5 are connected. During this time, a spark discharge is generated and the workpiece 5 is machined. In the case of this capacitor discharge method, it is an extremely effective method because the machining current (discharge current) IP can be kept sufficiently large. If an attempt is made to increase the number of discharges, there is a risk of shifting to arc discharge. That is, FIG. 1B shows the time course of the terminal voltage Vc of the capacitor 3 in the capacitor discharge method, but the charging time constant is set to 4.
If an attempt is made to increase the angle 8 shown in the figure so that the terminal voltage Vc of the capacitor 3 rises rapidly as shown by the dotted line in the figure, the terminal voltage Vc of the capacitor 3 will rise rapidly immediately after discharge, resulting in undesirable arc discharge. will be moved to. Therefore, it is difficult to increase the machining speed by increasing the number of discharges per unit time. In order to prevent transition to arc discharge in the capacitor discharge method shown in FIG. 1A, a method is known in which a switching transistor 6 is inserted into the charging circuit of the capacitor 3 as shown in FIG. 2A.

In the method shown in FIG. 2A, the switching
The transistor 6 interrupts the voltage applied between the discharge electrode 4 and the workpiece 5 for a predetermined period of time to prevent transition to arc discharge, while the resistance value of the resistor 2 is selected to be small to meet the requirements. This is intended to increase the rising speed of the terminal voltage yc of the capacitor 3 during the period when the transistor 6 is on. However, in the case of the method shown in FIG. 2A, a signal 7 having a predetermined repetition period is applied to the base of the transistor 6.
During the ON period of the transistor 6, the discharge electrode 4
and the workpiece 5 so that the desired spark discharge is generated. FIG. 2B shows the time course of the capacitor terminal voltage Vc and the discharge electrode IP in the known method. As is clear from FIG. 2B, at what point during the ON period of the transistor 6 the discharge electrode 4 and the workpiece 5
It is uncertain whether a discharge will occur between the two. For this reason,
During the ON period, discharge occurs once and a sufficiently large discharge current 8 flows, but after that, a follow-on current 9 flows in the gap between the discharge electrode 4 and the workpiece 5 until the transistor 6 is switched to the OFF state. Flowing away. Current level 1 of the follow-on current 9
Now, let E be the voltage of the DC power source 1, R be the resistance value of the resistor 2, and let Eo be the discharge electrode in the above gap.
...---Given as '1'.

Therefore, if the resistance value R of the resistor 2 is selected to be small in order to improve the rising speed of the terminal voltage Vc of the capacitor 3 as described above, a relatively large competitive current 9 will flow. As is clear from FIG. 2B, the traverse current 9 flows for a longer period of time as the discharge occurs earlier during the ON period of the transistor 6, so that the machining energy per discharge becomes non-uniform. Put it away. In other words, the machining accuracy will be degraded. For this reason, in the system shown in FIG. 2A, the resistance value of the resistor 2 is selected to be small, and the number of discharges per unit time cannot be made as large as expected. FIG. 3A shows a method in which the method using the capacitor 3 is abandoned and the machining energy per discharge is made uniform.

In the case of this method, a microresistance 10, for example, is inserted in series in the discharge gap, the start of discharge is detected by the voltage drop across the resistor 10, and the transistor 6 is turned off when a predetermined time has elapsed from the start of the discharge. Switch to . After a predetermined off period is maintained to prevent transition to arc discharge, the transistor 6 is switched on again. In the case of this discharge method, as shown in FIG. 3B, the time L until the transistor 6 is turned off after the discharge gap is discharged is constant for each discharge, and the machining energy per time is made uniform. . However, in the case of the method shown in FIG. 3A, it is difficult to increase the machining current (discharge electrode) IP compared to the method using the capacitor 3 shown in FIG. 1A or FIG. 2A. Become. Therefore, the desired machining energy is obtained by selecting the above-mentioned time To to be relatively large. Generally, in an electric discharge machining apparatus, the machining amount ΔW per discharge and the surface roughness ARmax of the machined surface are expressed as follows. That is, △W=kl・d is 1・1P1-
4...[21ARmax=k2・70no.
5. 1P.

・４． ．． ．． ．． ．． ．． '3' However, k,,k2 are coefficients, 7on is the time width in which the discharge current IP flows, and IP is the discharge current.

The above formula ■ and {3! From the formula, in order to increase the machining amount △W, it is necessary to increase the discharge current IP with a time width of 7 on.
This is more effective than increasing the discharge current I.
It can be seen that even if P is increased, the surface roughness Rmax does not deteriorate that much.

From this, it can be seen that the so-called capacitor discharge method shown in FIG. 1A is preferable to the method shown in FIG. 3A, as long as it is possible to increase the number of discharges per unit time. Of course, it is not preferable that an undesired follow-on flow occurs as in the system shown in FIG. 2A. The present invention takes the above points into consideration and aims to provide an electrical discharge machining apparatus that employs a capacitor discharge method and overcomes the above-mentioned difficulties. This will be explained below with reference to FIG. 4 and subsequent figures. Fig. 4 is an explanatory diagram conceptually explaining the machining state by the electric discharge machining apparatus of the present invention, Fig. 5 is a circuit diagram of an embodiment of the electric discharge machining apparatus of the present invention, and Fig. 6 is a time diagram explaining the operation. The charts, FIGS. 7 and 8 each show a circuit diagram of another embodiment of the electrical discharge machining apparatus of the present invention.

In FIG. 4, Vc is the terminal voltage (or discharge gap voltage) of the discharge capacitor 3 shown in FIG. 5, which will be described later, ic,
id, IP are the currents ic, id, IP, shown in FIG. 5, respectively.
t represents time.

Further, ON and OFF represent the on period and off period of the transistor 6 shown in FIG. 5. In the case of the present invention, the charging time constant for the discharging capacitor 3 is made sufficiently small in order to increase the number of discharges per unit time.

That is, the resistance value R of the resistor 2 shown in FIG. 5 is selected to be sufficiently small. Therefore, as shown at the top of FIG. 4, the terminal voltage Vc (or discharge gap voltage VG) of the capacitor 3 rises rapidly immediately after the transistor 6 is turned on. Along with this, the current IC momentarily flows to charge the capacitor 3. When a discharge starts in the discharge gap, the start of the discharge is detected and the transistor 6 (FIG. 5) is controlled to be switched off. At this time, the capacitor 3 is discharged due to the start of the discharge, and a discharge current id flows toward the discharge gap. On the other hand, until the transistor 6 is completely switched off, a current IC flows from the DC power source 1 (FIG. 5) toward the discharge gap. Therefore, the machining current IP flowing through the discharge gap corresponds to the sum of the above-mentioned currents ic and id, as shown at the bottom of FIG. The transistor 6 (FIG. 5) has a predetermined off-period m.
, and then switched back on. In the case of the present invention, since the transistor 6 (FIG. 5) is switched off at the same time as the discharge starts, the longitudinal current 9 shown in FIG. 2B does not flow. Therefore, the machining energy per discharge is made uniform. The condition indicated by reference numeral 11 in FIG. 4 represents a condition in which the discharge gap is undesirably short-circuited.

In the case of the present invention, when the transistor 6 (FIG. 5) is turned on after time T, a current IC corresponding to the short circuit current is supplied from the DC power supply 1;
is immediately switched off again. Therefore, the above-mentioned self-current IC flows toward the discharge gap as the current IP
It flows like this. However, if the short-circuit condition occurs due to a machining chip intervening in the discharge gap,
It has the function of melting the processed chips, which is rather preferable. When the short circuit occurs, the off period of the transistor 6 is increased to L as shown in FIG. FIG. 5 shows a circuit configuration of an embodiment of the present invention, with reference numerals 1, 2, 3,
4, 5, and 6 correspond to FIG. 1A to FIG. 3A, 12 and 13 are fine resistances for detection, 14 are high resistances, and 1
5 represents a diode. Also 16 no, then 18
19 are rise detection circuits which generate a logic "1" signal when the voltage at the input terminal rises above a predetermined threshold; 19 is a time delay circuit provided as needed; 20 21 is a monostable circuit (timer) which, when a logic 0 is input, outputs a logic 0 only for a predetermined time T, from that point in time, and 21 is a time delay circuit that 22 is a monostable circuit (second timer) that creates a predetermined time delay L, and when a logic "0" is input, it outputs a logic "0" only from that point in time until a predetermined time T2. 26 represents a NAND circuit, and 27, 28, and 29 represent a NOT circuit. This will be explained below with reference to the time chart shown in FIG.

'1} When the power switch SW is in the off state, both the rise detection circuits 16 and 17 output logic "0", and as a result, the NAND circuit 26 outputs the logic "0" in FIG. A logic "0" is emitted as shown by o.

In this state, the transistor 6 is turned on via an amplifier circuit (not shown) or the like. [2} When turning on the power switch SW, as shown in Figure 6, the DC power supply 1
A charging current flows from the resistor 2 to the transistor 3 via the resistor 2 and the transistor 6.

Then, the terminal voltage Vc of the capacitor 3 rises rapidly. '
3' At this time, a current IC flows through the resistor 12 due to the charging current, and the rise detection circuit 17 generates a logic "1".

Furthermore, the rising edge detection circuit 18 issues a logic "1" with a momentary delay, and the signal V6 becomes a logic "0". However, since the charging current is in the opposite direction to the current id, the rising edge detection circuit 16 continues to generate the logic "OJ.'4" Therefore, the signal V4 is at the logic "1" and the NAND The circuit 24 becomes logic "0".

Further, the NAND circuit 23 continues to output logic "1". The logic "0" is delayed by the time delay circuit 21, and the signal V5 becomes logic "1". (5' At the timing when the above signal V5 becomes logic "1", signal V6 becomes logic "1".
0'' indicates a short circuit in the discharge gap, as will be described later.

However, when the power switch SW shown in FIG. 6 is turned on, there is no short circuit, so the NAND circuit 25 continues to output the logic "1". That is, the signal V7 remains at logic "1", the monostable circuit 22 is not activated, and the signal V8 remains at logic "1". '61 Next, when the discharge gap is discharged as shown in FIG. 6, currents ic and id flow simultaneously in this case.

Therefore, the rising edge detection circuits 16 and 17 both have logic "
1” is emitted. Therefore, the NAND circuit 23 becomes a logic "0", and the NAND circuit 24 continues to generate a logic "1". '
7) Assuming that the delay circuit 19 does not exist at this moment, the signal V3 becomes logic "0" by the NAND circuit 23, and as a result, the monostable circuit 20 changes from that point in time to a predetermined time T.
, the logic becomes "0" only during the period up to .

That is, the signal V9 becomes logic "0" only during that period. '81
As a result, the NAND circuit 26 has logic "1" only during the relevant period.
”, and the signals V and o become logic “1”.

Along with this, the transistor 6 is turned off for a period of time T, and then turned on again after the time T.The reason why the transistor 6 is turned off by the start of the discharge is as follows. Needless to say, this is to eliminate the competing current 9 as shown in FIG. 2B.

The switch to the on state after passing through the station is to provide a predetermined pause period to prevent transition to the arc state. ■ When a short circuit occurs in the discharge gap, as shown by reference numeral 11 in Figure 6, the current i from the DC power source 1
c does not go toward the capacitor 3, but toward the discharge gap where the short circuit occurs.

Therefore, the terminal voltage Vc of the capacitor 3 or the discharge gap voltage never rises. (11) In this case, the rising edge detection circuit 17 shown in FIG. 5 emits a logic "1", the rising edge detection circuit 16 emits a logic "0", and the rising edge detection circuit 18 continues to emit a logic "0".

As a result, the signal V5 becomes logic "1" with a delay of time, but even at this point, the signal V6 remains logic "1".
NAND circuit 25 issues a logic "0". That is, the signal V7 temporarily becomes logic "0". (12) As a result, monostable circuit 2
2 becomes logic "0" only for a period from the relevant point in time to a predetermined time.

That is, the signal V8 becomes logic "0" only during that period.

(13) As a result, the NAND circuit 26 emits a logic "0" only during this period, and the signals V and o become logic "1".

Along with this, the transistor 6 is turned off for the time T, and turned on again after the time T2. (
14) Needless to say, the reason why the transistor 6 is switched off due to the short circuit detection is to prevent the short circuit current from continuing to flow into the short circuit discharge gap more than necessary.

The relatively long OFF period T2 can be considered to be due to the expectation that the discharge gap will be increased by means not shown in the drawings during this period. (15) When the above-mentioned time T2 has elapsed, the transistor 6 is turned on again, but if the short circuit has been eliminated at this time, the normal discharge state is resumed as shown in FIG.

(16) In the case of the present invention, as shown in FIG.
5 and a high resistance 14 with a relatively high resistance value.
A DC voltage from a DC power source 1 is applied to the discharge gap via the DC power source 1.

The purpose of applying the DC voltage is to generate an electrolytic machining action between the discharge electrode 4 and the workpiece 5 through the machining fluid (applied to the discharge gap during machining), and to machining the workpiece 5. This is because it is expected that the surface will be smoothed. (1
7) The DC voltage application expected for electrolytic processing has a high resistance of 14
It is done through.

Therefore, when a discharge occurs in the discharge gap, the high resistance 1
4, a very large voltage drop occurs, and the longitudinal current 9 as shown in FIG. 2B does not flow through the high resistance 14. Furthermore, even if the discharge gap is short-circuited, no short-circuit current will flow through the high resistance 14. (18) By applying a DC voltage through the high resistance 14, the voltage in the discharge gap becomes as shown by the dotted line in the diagram regarding voltage Vc shown in FIG.

That is, the discharge gap voltage becomes almost zero only when a discharge occurs and when a short circuit occurs. However, during other periods, the electrolytic machining action works to smooth the machined surface. FIG. 7 shows an embodiment of the present invention in which the configuration shown in FIG. 5 is further simplified.
9 and 20' correspond to FIG. 5, and 30 and 31 represent knot circuits.

In the case of this embodiment, a voltage drop is generated in the resistor 12 due to both the discharge current during normal discharge and the short circuit current during short circuit.

The rising edge detection circuit 16 detects this, creates a predetermined time delay as necessary by the circuit 19, and outputs the monostable circuit 20.
Input one logic "0". As a result, the transistor 6 is switched to the off state at that point in time, and a predetermined time T
o and is turned on again. Although this embodiment does not have a function of extending the OFF period in the event of a short circuit, the 5th embodiment switches the transistor 6 to the OFF state at the start of discharge or when a short circuit occurs to cut race current and short circuit current.
It is exactly the same as the case shown in the figure. However, when the time delay circuit 19 is inserted, the off period begins immediately after the start of discharge, etc., with a slight delay. FIG. 8 shows another embodiment of the invention.

Codes 1, 2, 3, 4, 5, 6, 12, 2021 in the diagram,
22, 23, 24, 26, 27 correspond to FIG.
33 is a rising detection circuit that detects a relatively large voltage generated between terminals a and b during normal discharge (approximately 100 A), and 33 is a short circuit current (20 to 3
0A) represents a rise detection circuit that detects a relatively small voltage generated between terminals a and b. It goes without saying that at the start of a normal discharge, the rise detection circuit 32 emits a logic "1", and at this time the rise detection circuit 33 also emits a logic "1".

This causes the NAND circuit 23 to output a logic "0", and the monostable circuit 20 turns off the transistor 6 for a period T. On the other hand, when a short circuit occurs, only the rising edge detection circuit 33 emits a logic "1". Therefore, the NAND circuit 24 is at logic "0"
, and the monostable circuit 22 turns off the transistor 6 only during the period L. As explained above, according to the present invention, it is possible to discharge a large current using a discharging capacitor, and while preventing the traversing current as shown in FIG. 2, the charging speed is increased and the number of discharges per unit time is greatly increased. It becomes possible to increase.

Furthermore, machining energy per discharge can be made uniform. Furthermore, since the transistor is held in an off state for a predetermined period of time when discharge starts or a short circuit occurs, it is possible to prevent transition to arc discharge and undesired continuation of short circuit current. Therefore, it becomes possible to use a machining fluid such as ordinary water as the machining fluid used in this type of machining apparatus, and it becomes possible to significantly reduce machining costs. Further, by applying a DC voltage to the discharge gap through a high resistance, it is possible to improve the accuracy of the machined surface.

[Brief explanation of the drawing]

1A and 1B are explanatory diagrams for explaining a known electrical discharge machining device using a so-called capacitor discharge method, and FIGS. 2A and 2B are explanatory diagrams for explaining a known electrical discharge machining device that is an improved circuit of FIG. 1A. 3A and 3B are explanatory diagrams for explaining a known electrical discharge machining device that uniformizes machining energy, FIG. 4 is an explanatory diagram conceptually explaining the machining state by the electrical discharge machining device of the present invention, and FIG. A circuit diagram of one embodiment of the electrical discharge machining apparatus of the present invention, FIG. 6 shows a time chart explaining its operation, and FIGS. 7 and 8 each show a circuit diagram of another embodiment of the electrical discharge machining apparatus of the present invention. . In the figure, 1 is a DC power supply, 2 is a charging resistor, 3 is a discharge capacitor, 4 is a discharge electrode, 5 is a workpiece, 6 is a switching element, 12 and 13 are detection resistors, 14 is a high resistance, 15
1 is a diode, 16, 17, and 18 are rise detection circuits, 20 is a timer, and 22 is a second timer. Key bad (A) Bu' Tsutomu (b) Shio 2ne0 (^) Chi Z bad (b) Na3 bad (A) 73 Haji (b) Bu4 leg Sa S bad Yawa QO Juku' Tozu 8 bad

Claims (1)

[Claims] 1. A discharging capacitor is provided in parallel with a discharge electrode and a workpiece, and electrical energy charged in the discharge capacitor is discharged between the discharge electrode and the workpiece for machining. In the electric discharge machining apparatus, a switching element is provided in the charging circuit for the discharge capacitor, and
Discharge start detection means for detecting the start of discharge between the discharge electrode and the workpiece is provided, and the switching element is switched to an OFF state by a start detection output from the discharge start detection means. An electric discharge machining device characterized by the following. 2. A timer is provided that is activated by the discharge start detection output from the discharge start detection means, and the switching element is switched to an OFF state by the start detection output and by the time up output from the timer. The electric discharge machining apparatus according to claim 1, wherein the electric discharge machining apparatus is switched to an on state. 3. A short-circuit detection means is provided for detecting a short-circuit state occurring between the discharge electrode and the workpiece, and the switching element is switched to an OFF state by the short-circuit detection means. An electric discharge machining apparatus according to claim 1 or 2 above. 4. An electrical discharge machining device that includes a discharge capacitor in parallel with a discharge electrode and a workpiece, and performs machining by discharging electrical energy charged in the discharge capacitor between the discharge electrode and the workpiece, In addition to providing a switching element in the charging circuit for the above-mentioned discharging capacitor,
Discharge start detection means for detecting the start of discharge between the discharge electrode and the workpiece is provided, and the switching element is switched to an OFF state by a discharge start detection output from the discharge start detection means. In addition, a second timer is provided which is activated by a short circuit detection means for detecting a short circuit state occurring between the discharge electrode and the workpiece, and the switching element is turned off by the short circuit detection output. An electric discharge machining apparatus characterized in that the electrical discharge machining apparatus is switched to the ON state by a time-up output from the second timer. 5. In an electric discharge machining apparatus that includes a discharge capacitor in parallel with a discharge electrode and a workpiece, and discharges electrical energy charged in the discharge capacitor between the discharge electrode and the workpiece for machining, In addition to providing a switching element in the charging circuit for the above-mentioned discharging capacitor,
A discharge start detection means is provided for detecting the start of discharge between the discharge electrode and the workpiece, and the switching element is switched to an OFF state by a discharge start detection output from the discharge start detection means, and A diode is inserted into the discharge circuit of a discharge capacitor connected in parallel to the discharge electrode and the workpiece, and a DC power source is connected to the cathode side of the diode through a resistor having a high resistance value. An electric discharge machining apparatus characterized in that a DC voltage is applied by a power source to the discharge electrode and the workpiece through the resistor having the high resistance value.