JPS5926414B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an electrical discharge machining apparatus that performs machining by repeatedly applying pulsed discharge to the machining gap between an electrode and a workpiece.

Recently, it has been found that by controlling the polarity, pulse width, peak value, etc. of pulsed discharge that is repeated in the machining gap, it is possible to perform machining with low electrode consumption of 1% or less. The degree of use and scope of use are rapidly expanding to 1, and its importance is increasing in the field of mechanical work.In normal electrode non-consumable (low consumable) machining, the electrode side is the positive electrode,
Machining is performed by using the workpiece side as the negative electrode and controlling the pulse width to be long and the pulse height to be low.On the other hand, in electrode consumable machining, the electrode side is the negative electrode and the workpiece side is the positive electrode, which is the opposite polarity. Performs high-speed machining by shortening the pulse width and increasing the repetition frequency.

In this way, arbitrary machining conditions can be set depending on the purpose of machining, but it may not always be possible to perform fully satisfactory machining depending on the material combination of the electrode and the workpiece.

That is, due to the electrical discharge between the electrode and the workpiece, during machining, a portion of the molten and vaporized metal vapor adheres to the other electrode, and this is caused by the combination of the electrode and workpiece materials. Depending on the conditions, there is a difference in the amount of adhesion from the positive electrode side to the negative electrode side and from the negative electrode side to the positive electrode side, and due to this difference, the amount of adhesion will gradually accumulate on one electrode. . For this reason, if the pulse discharge polarity is kept constant regardless of whether the electrode is used for non-consumable machining or consumable machining, depending on the conditions, the molten and vaporized metal vapor of the electrode material may adhere to the workpiece.
On the other hand, on the other hand, the metal material of the workpiece adheres to the electrode side and gradually accumulates, making machining unstable, which has the disadvantage of lowering machining speed and machining efficiency. The present invention has been proposed in view of this point, and includes a switch that supplies a predetermined polarity pulse to the machining power source and a switch that supplies a reverse polarity pulse by switching the voltage source on and off. A discrimination control device is provided for discriminating the detection signal of and switching the operation of both the switches.

The present invention will be described below with reference to an embodiment of the drawings. Reference numeral 1 represents an electrode, and 2 represents a workpiece, which face each other to form a machining gap.

31, 32 and 41, 42 are a pair of electronic switches, which are connected by a bridge as shown in the figure, with the power supply 5 of the machining energy source being connected between one of the opposing bridges, and the machining gap being between the other opposing bridges. Connected.

Reference numeral 6 denotes a gate pulse generating circuit that controls on/off the switches 31 and 32 on the opposite side of the bridge, which oscillates in response to detection of the state of the machining gap and generates a gate pulse.

It is also assumed that the pulse width, repetition frequency, etc. of the generated gate pulse can be controlled arbitrarily. And the ON of Nuittsuchi 31 and 32 by this gate parnu. By off-switching, a Parnu discharge that flows from the power source 5 into the machining gap from the electrode 1 to the workpiece 2 is repeatedly performed. The amplitude of the PALNU discharge current, that is, the peak value, is determined by the resistor 8 inserted in series with the switch.
1,82 change control. 7 turns on the opposite side nuts 41 and 42. This is a gate pulse generation circuit for off-control, which oscillates to generate a gate pulse when the operation of the gate pulse generation circuit 6 is stopped.

It is assumed that the pulse width of the generated pulse can be controlled arbitrarily.
This generated gate pulse causes the switches 41 and 42 to
is on. The power source 5 is turned off, and a Parnu discharge flows from the workpiece 2 to the electrode 1 in the machining gap.
The peak value of the PALNU discharge current is controlled by changing the resistors 91 and 92 inserted in series with the transistor. Reference numeral 10 denotes a discrimination device that discriminates the machining gap detection signal and controls the operation of the pulse generation circuit 6 or 7.

In machining using the above-mentioned apparatus, while the machining gap is normal, a gate pulse is applied from the pulse generation circuit 6 to the switches 31 and 32, and the switch is turned on. Repeated discharge is performed by off control.

The discharge polarity at this time is as shown in the figure, with the electrode 1 being the positive pole and the workpiece 2 being the negative pole.During stable machining, high frequency waves are generated in the machining gap due to the discharge, and the average of the flowing current is The gap state can be easily detected by detecting various signals such as an increase in value, and since this detection signal is always above a certain level during stable machining, the discrimination result by the discrimination device 10 is the output signal is added to the PALNU generation circuit 6, which continues to operate and turns on the switches 31 and 32.
By off-switching, a discharge with constant polarity is generated and machining is performed. However, during such machining, the amount of metal material deposited from the negative electrode to the positive electrode and from the positive electrode to the negative electrode depends on the machining conditions such as the material combination of the electrode 1 and the workpiece 2, the pulse width of the pulse discharge, and the wave height value. As a result, the amount of one-force electrode material adhering and depositing on the other-force electrode material gradually increases. For example, when machining a Fe workpiece with a Cu electrode, a polar Pärnu discharge is performed with the Cu electrode as the positive electrode and the Fe workpiece as the negative electrode, and the machining is performed under electrode non-consumable machining conditions with a Pärnu width of 140μSec and a wave height of 40A. The amount of metal vapor deposited in the case is Cu
The amount of material attached to Fe material is about 13% of the total, and Fe material is attached to C.
The amount of Cu material that adheres to the U material is approximately 8 (: fl), so the Cu material gradually adheres and accumulates on the Fe material. When dissimilar metals are deposited in this manner, the discharge becomes unstable, and arcs, short circuits, etc. occur frequently. Therefore, the average current flowing through the machining gap is reduced, the high frequency energy is also reduced, and the servo device that controls the gap is not stable, so that the state during normal machining cannot be maintained. This gap state is easily detected by detecting one or a combination of various change signals, and the detection signal is discriminated by the discriminator 10, but if the detection signal is below or above a certain level, The pulse generating circuit 6, which has been operating up to this point, is stopped, and the pulse generating circuit 7 is then activated. The level setting of the discrimination device is set to obtain the best machining effect based on the given test results, and thus, when the detection signal reaches the set level, it is reversed and the parnu generation circuit 7 is activated, and the detection signal 4 is activated.
Turn on 1,42. Turn it off and add PARNU of the opposite polarity to the gap, causing a PARNU discharge of the opposite polarity. The pulse width and peak value at this time can be changed arbitrarily by adjusting the pulse circuit 7 and the resistors 91 and 92. In the case of the desired machining, for example, electrode non-consumable machining, the electrode 1 is
control so as not to cause excessive wear and damage to the intended processing. Further, this reverse polarity pulse discharge is not limited to one pulse, but may be repeated a plurality of times. However, when a reverse polarity pulse discharge is performed in this way, the state of adhesion of metal vapor between the electrode 1 and the workpiece 2 changes completely from the previous discharge, and usually the adhesion state is reversed, If the electrode material adheres to the workpiece 2 side, much of the material will adhere from the workpiece 2 to the electrode 1 side due to the reverse polarity pulse discharge, and the adhering metal on the workpiece side will be reduced or removed. will be done. If the deposited metal is removed in this way, the machining becomes stable again, the gap returns to normal, and the detection signal is determined by the discriminator 10, which confirms that the normal machining state has returned to normal. If so, the operation of the pulse generation circuit 7 is stopped and the pulse generation circuit 6 is activated, and the switches 31 and 32 are turned on by this output gate pulse. The electrode is turned off and the polarity pulse discharge flowing from the electrode 1 to the workpiece 2 is repeated to perform machining under the desired conditions.

If machining becomes unstable again due to adhesion and accumulation of dissimilar metals, the PURNU generation circuit 7 is driven to generate a reverse polarity pulse discharge, and this is repeated to continue stable electric discharge machining. and combination of workpieces,
In addition, target machining can be easily performed under arbitrary machining conditions. For example, a Fe workpiece with a parnu width of 140 μm can be
When performing non-consumable electrode machining under machining conditions where the S1 peak value is 40 A and the discharge polarity is positive on the electrode side and negative on the workpiece side, reverse polarity pulse and pulse width 25 μS1 are applied during unstable machining.
When Pärnu discharge with a peak value of 15 A was performed, stable machining was always performed and the machining speed could be increased approximately 1.42 times. The pulse width, peak value, etc. of the reverse polarity Parnu discharge depend on the material combination of the electrode and workpiece, whether the electrode is expendable or non-consumable, or the state of adhesion and deposition of dissimilar metals depending on processing conditions such as roughing and finishing. Since the reverse polarity pulse discharge varies in various ways, the parnu width, peak value, etc. of the reverse polarity pulse should be changed within a range that does not damage the target machining due to the reverse polarity pulse discharge.

In addition, the timing for performing this reverse polarity pulse discharge may be determined by detecting and determining the change in the state of the machining gap that becomes unstable, and then determining the optimum time to perform the reverse polarity pulse discharge. It has been experimentally confirmed that when machining is performed by repeating a certain number of pulse discharges, the state of A polar parnu discharge may be performed. In any of the above cases, the present invention performs machining while performing reverse polarity Parnu discharge to remove deposits of dissimilar metals from the workpiece or electrode material on the electrode or workpiece, so that the process is always stable. It is possible to continue machining, and the pulse width, peak value, and discharge timing of the reverse polarity pulse discharge can be arbitrarily set and controlled. The optimum effect can be exerted, and the intended original processing can be performed stably without damage.

By eliminating such unstable machining caused by adhesion of dissimilar metals, the desired machining can be performed with any combination of electrodes and workpieces, as well as consumable machining with electrodes, machining without consumable electrodes, rough machining, and finishing machining. It has the remarkable effect of making it possible to perform machining under arbitrary machining conditions such as, and moreover, machining with maximum performance.

[Brief explanation of drawings]

The drawing is a configuration diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1. In an electric discharge machining device that processes a machining gap between an electrode and a workpiece by repeatedly applying pulse discharge, a switch supplies a pulse of a predetermined polarity to the machining gap and a pulse of opposite polarity is supplied by switching a voltage source on and off. An electric discharge machining apparatus comprising: a switch; and a discrimination control device which discriminates a detection signal voltage from the machining gap between a reference level and above and a reference level and switches the operation of both the switches in accordance with the detected signal voltage.