JPS6263014A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To remove arc marks and swarf existing in a machining gap by dint of an electrodischarge machining impact, by aiming at safety for a switching element or the like in a way of cutting off a discharge current at the time of a short, while letting a pulse current flow at the specified interval even if a small quantity. CONSTITUTION:The resistance value of a safety resistor 4 inserted into a circuit is set to the smallest possible extent so as to be the low resistance value of such an extent as making a current of more than the rated current value flow into a switching element 5, for example, so as to be less than one half of the resistance value letting a rated current flow, in selection. With this constitution, power to be consumed at this discharge circuit comes yet smaller than ever before. Next, output timing of a controller 6 or a short discriminator 8 should be set in advance so as to turn off the switching element 5 in case of being short-circuited at a machining gap G. And, a pulse current is made to flow into this machining gap at the specified interval, giving an electric discharge machining impact to arc marks and swarf, and they are removed whereby pulse electric discharge machining is automatically resumable.

Description

[Detailed Description of the Invention] 1□----■■■■■■訃□--1 The present invention relates to an electric discharge machining device, which minimizes the resistance value of the machining power supply circuit and reduces the limiting capacity of the switching element in the event of a short circuit. The present invention relates to an electric discharge machining apparatus equipped with a discharge circuit that cuts off a discharge current or a resting current midway through the process.

2. Description of the Related Art In general, electrical discharge machining equipment is composed of a capacitor charging circuit and a discharging circuit. In its basic circuit, the charging circuit includes a DC power supply, a series circuit of a resistor, and a capacitor, and the capacitor discharging circuit includes a series circuit of a DC power supply, a resistor, and a capacitor. One includes a series circuit of a capacitor, a switching element, a safety resistor, and the machining gap between an electrode and a workpiece, and the other includes a series circuit of a capacitor, a switching element, a safety resistor, and a machining gap between an electrode and a workpiece. There is a power supply circuit that applies machining pulses to the machining gap formed between the workpiece and the workpiece.

−〜−Gee ＾danmi poor sweet potatoes! In either case, if a large safety resistor is included in the event of a short circuit in the machining gap, only a slightly large current will flow, but if such a safety resistor is not present, the current value will rise dramatically and the switching element transistor or FF , T, etc., a current exceeding the rated current value will flow, causing trouble. But what about the resistance value of the safety resistor? If it is made too large, much of the machining energy will be consumed here, which is not very desirable as a source circuit for an electric discharge machining device. In addition, short circuits may be caused by machining debris accumulated in the machining gap, and may be resolved by removing the machining debris.

Taking these points into consideration, the present invention generates voltage pulses by intermittently applying voltage pulses to the machining gap between the electrode and the workpiece while leaving a pause period. In electric discharge machining in which electric discharge is performed by electric discharge, the voltage (pulse) application circuit is composed of a DC power source for machining, an on/off switching element, its safety resistor, and a series circuit of the machining gap, and the safety resistor. The value of f is set small so that a large current greater than the rated current flows through the switching element when the machining gap is short-circuited. Whenever the machining gap short circuit signal is detected, it is detected that the discharge current flowing through the switching element rises to the rated current value of the hind limb switching element that starts the discharge, and the voltage pulse (discharge flowing) is stopped. It is intended to be cut off from.

Effect Therefore, in this proposal, is the resistance value of the safety resistor equal to the rated current of the switching element? By minimizing the electrical discharge resistance below the predetermined resistance value, the loss of machining energy consumption during normal electrical discharge machining will be much lower.Besides, prior to shorting the machining gap, switching elements such as transistors, PET, etc. The switching element is connected to a voltage current (
Since the cut-off is made in the middle of the discharge current (discharge current), safety can be maintained by cutting off the circuit in the event of a short circuit accident in the machining gap. Moreover, at a predetermined interval in the machining gap,
A cut-off voltage pulse is applied from the middle and a small discharge current flows. In other words, the discharge current with a narrow pulse width and current peak flows after a sufficient pause time, so the gap is isolated from the arc discharge environment. The discharge current is quickly released, arc marks and machining debris present in the machining gap are machined using the discharge current, and the discharge current is further removed to maintain a normal environment and restart the discharge machining.

Basics! To explain the present invention with reference to an embodiment, FIG. 1 shows a basic circuit according to the present invention, where 1 is a power source and 2 is an electrode.

5 is a workpiece; 4 is a safety resistor installed in a circuit connected in series with the power source 1, electrode 2, and workpiece 5; 5 is a switching element; and 6 is a control device.

7 is a detection resistor for detecting a short-circuit state between the electrode 2 and the workpiece 5; 8 is a short-circuit discriminator; and 9 is an AND circuit.

10 is a switching element such as a transistor.

As shown in FIG. 2, when a pulse signal having a predetermined pause interval is sent from the control device 6 to the switching element 5, the DC voltage of the power source 1 is transferred to the electrode 2 and the unsheathed sword via the safety resistor 4 due to the operation of the switching element 5. A machining pulse voltage having a pause interval as shown in Fig. 2 is applied to the machining gap G between the pole 2 and the workpiece S, and when the machining gap G between the pole 2 and the workpiece S is normal, the machining pulse voltage shown in Fig. 5 is applied. Electric discharge machining is performed while showing voltage changes as shown in FIG. 4 and current changes as shown in FIG.

Further, a pulse signal having a predetermined pause interval Z shown in FIG. 2 is sent from the control device 6 to the AND circuit 9. The resistance value of the second resistor 4 inserted into the discharge circuit is a resistance that is extremely low enough to cause a current exceeding the rated current to flow through the switching element 5, and is, for example, 172 or less, which is the resistance value that allows the rated current to flow. The value is chosen as small as possible.

A detection signal from the safety resistor 4 which also serves as current detection is sent to an AND circuit 9.

The detection signal of the detection resistor 7 is sent to the short circuit discriminator 8, and the processing r
When vJ gap G is short-circuited, the short-circuit discriminator 8 outputs,
The output signal is sent to an AND4 circuit 9. Therefore, when pulse discharge is being performed with a normal machining gap G, no signal is output from the short circuit discriminator 8, so the AND circuit 9 receives a signal from the safety resistor 4 and the control device 6. However, it does not output any output.

Therefore, electric discharge machining pulses are continuously applied to the machining gap G, and electric discharge machining is continued. At this time, the power consumed by this discharge circuit is less than that of the conventional system because the resistance value of the safety resistor 4 is selected to be as small as possible. Ten thousand swords ■
If a short circuit accident occurs in the work space RG, switching element 5
The current increases according to the current 1-hour characteristic shown in FIG. 5, and when it reaches point T below the rated current value P, the switching element 5 is turned off.The output timing of the control device 6 or the short circuit discriminator 8 is set in advance Accordingly, the output signal t of the AND circuit 9 is sent to the switching element 10 to turn it on, and by bypassing the flow from the control device 6 to the switching element 5, the switching element 5t is turned on. By repeating this action and short-circuiting a small pulse current from the switching element 5 at predetermined intervals as shown in FIG. Non-arc pulse discharge can occur from areas where the current amplitude is large and the pause time is large compared to the pulse width, and is one of the causes of short circuits. Shock it to remove it.

According to the present invention, the safety resistor 4 can be selected to have a value as small as possible than the predetermined resistance value that causes the rated current to flow through the switching element, and the loss of machining energy consumed by the safety resistor 4 can be minimized. It can be done.

When a short circuit accident occurs in the machining gap G, the discharge current rises to a certain value T below the rated current value P of the switching element 5, and by turning off the switching element 5, the discharge circuit is closed immediately before the short circuit accident occurs. It can be turned off to ensure the safety of circuit elements such as switching elements. Moreover, this action t (by repeating the above-mentioned slight discharge t
Ry! - Because the pulse current is passed through the machining gap G at a predetermined pulse interval, it has the effect of automatically restarting pulsed electrical discharge machining by removing machining debris, which is one of the causes of short circuits, from the sum of the pulse currents. It is something.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of the present invention, FIG. 2 is a diagram showing machining voltages having predetermined pause intervals, and FIG. 3 is a diagram showing voltage changes during machining using the machining voltages shown in FIG. 2. FIG. 4 is a diagram showing changes in current corresponding to voltage changes in FIG. 5, and FIG. 5 is a current versus time characteristic diagram of a switching element. 1 is a power supply, 2 is an electrode, 5 is a workpiece, 4 is a safety resistor, 5
&niswitching element, 6 is a control device, 7 is a detection resistor,
8 is a short circuit discriminator, and 9 is an AND circuit.

Claims (1)

[Claims] (1) In electrical discharge machining, in which machining is performed by electrical discharge generated by applying voltage pulses intermittently with pauses in the machining gap between the electrode and the workpiece, the voltage pulse application circuit is used as a machining DC power supply. It consists of a series circuit of an on/off switching element, its safety resistance, and the machining gap, and the value of the safety resistor is set to be small so that a large current greater than the rated current flows through the switching element when the machining gap is short-circuited. In the electrical discharge machining circuit, whenever a voltage pulse is applied to the machining gap and a discharge occurs, when the machining gap short circuit signal is detected, the discharge current flowing through the switching element changes after the discharge starts. An electric discharge machining apparatus characterized in that the voltage pulse (discharge current) is cut off midway by detecting that the current rises to the rated current value of the element.