JPS5926413B2 - Electric discharge machining equipment - Google Patents

Description

[Detailed description of the invention] In electrical discharge machining, which involves machining while maintaining a minute gap, control of removing machining debris is extremely important, as is the tracking control of the machining gap, and the quality of this control greatly affects the performance of electrical discharge machining. .

Conventionally, this is controlled by jetting, suctioning, etc. of the machining fluid using a pump device, but since changes in the flow rate, jet pressure, suction pressure, etc. of the fluid by this pumping device are usually controlled by a manual screwdriver, etc. Optimum control cannot be achieved in which the concentration of machining debris present in the machining gap is always controlled to a constant level, and this constant concentration of machining debris is stirred and distributed uniformly in the machining fluid. In electrical discharge machining, in order to increase machining speed and perform stable machining, the machining area, which changes as machining progresses, is detected by the electrode shape, and this is used as a signal to constantly set the current density. It has been considered to control and change the on-pulse width, off-pulse width, peak value, etc. of the pulse power source for machining so as to approach the best value determined by the process, but this change control of the pulse power source changes the rate of generation of machining waste. That is, for example, if the on-pulse width and peak value are kept constant and the off-pulse width is varied to control the repetition frequency of discharge, the amount of machining waste generated in proportion to the repetition frequency can be approximately predicted. The flow rate, jet pressure, and suction pressure levels of the pump device are automatically changed and controlled by the machining area proportional signal so that the concentration of machining debris present in the machining gap is always constant during removal of generated debris. . The present invention will be explained below with reference to an embodiment of the drawings. Reference numeral 1 denotes an input terminal for a detection pulse signal proportional to the pulse discharge generated in the machining gap between the electrode and the workpiece, and the signal pulse is counted by a counter 2. .

Reference numeral 3 denotes a presetting device for presetting the number of pulses to be counted, and the counter 2 outputs a signal when it counts this preset number.

4 is an input terminal for a signal detected as a digital pulse signal by an encoder, Magnescale, etc., of the electrode feeding distance for follow-up control of the machining gap, and the input signal is sent to the counter 5.
It is counted by

This counter 5 outputs a count number based on the output signal of the counter 2. Reference numeral 6 denotes a clock pulse oscillator, which replaces the output of the counter 5 with this clock pulse and inputs it to the next counter 7.

8 is a divider 1, which outputs a machining area proportional signal by dividing the signal preset by the device 3, that is, the preset number of discharge repetitions N and the signal L proportional to the electrode feeding distance from the counter 7; It is an output display device.

The area proportional signal of the divider 18 is transferred to the next comparator 10.
and is compared with the reference value here. 11 is the determined on-pulse width τ.

This is a presetting device for presetting a reference value according to machining conditions such as n and peak value σθ, and the reference value can be changed by changing machining conditions such as τ00 and Ip. 1
2 is a counter that counts the difference or ratio output signal obtained by comparing the detection signal with the reference value by the comparator 10 while converting it with a clock pulse from the oscillator 6; 13 is a decoder; 14 is a memory that temporarily stores the output of the decoder 13; 15 is the decoder, and this output gives the off-pulse width τ.

The relay group 16 that switches and controls Ff is operated.
17 is a group of relays that switches the machining liquid jet pressure of the pump device, that is, the jet pressure control valve, etc.; this is also connected to the decoder 1;
It is activated by the output of 5.

In the above, if the number N of sampling pulses by the preset device 3 is preset to 10,000, for example, when the counter 2 counts the discharge pulses detected from the terminal 1, the signal will be output when the count reaches 10,000. In addition to counter 5, the count number of counter 5 is output. At this time, counter 5 is connected to terminal 4.
The signal pulses of the electrode feeding distance from the
This count number L is replaced by a clock pulse and counted by the force N counter 7, and the number is 1 by the divider 18).
L division is performed.

Generally, in electric discharge machining, the volume of a crater produced by one discharge energy is the amount of machining by a single pulse, and theoretically the amount of machining W by the discharge energy and pulse. is proportional and is expressed as follows. Therefore, the machining amount W of N discharge pulses is as follows.

The product of the machining area S and the electrode feed amount L in the machining depth direction is considered to be proportional to the machining amount W, and is expressed by:

Therefore, the other output of the divider 18 is a signal proportional to the machining area S, and the machining area that changes every moment with respect to the electrode feeding direction according to the progress of the force is output from the divider 18 and displayed on the display 19. Is displayed. This detection signal is also applied to a comparator 10 and compared with a preset reference value. Let the signal just detected be slope = B, let the preset value be A, and compare it with the comparator 10 and output the difference A-B. If the machining area increases, the output of the comparator 10 will become smaller, and the opposite will occur. When the machining area decreases, the output increases, and this is the counter 12.
is counted, divided by a decoder 13, and outputted as a switching signal through a memory 14 and a decoder 15.
τ of the relay circuit 16. Switching control of Ff is such that when the machining area increases and A-B becomes smaller, an off pulse τ is controlled by the output signal of the counter 15 proportional to A-B. Ff
is small, therefore, the number of discharge repetitions per unit time is increased to increase the machining speed, and when the machining area decreases and A-B becomes large, the off-pulse τ is set in proportion to this A-B. F
Multi-stage switching of the relay circuit 16 is performed to increase the power level. Therefore, for example, when machining is performed on a small machining area with the sharp part of the electrode tip facing the workpiece at the beginning of machining, the current density increases and arc discharge is likely to occur. Sometimes the off-pulse τ is detected by area proportional signal. By greatly controlling Ff, arc generation can be prevented, and if the machining volume gradually increases as the electrode penetrates into the workpiece as machining progresses, this increase rate will Off pulse τ accordingly. Efficient machining can be performed by controlling Ff to a small value and controlling the machining speed so that it always approaches the set current density and increases the machining speed so that the electrode feeding speed does not decrease due to a decrease in current density. Also, just before the end of machining, the machining area decreases again, and at this time, the off-pulse τ is again adjusted according to the decrease in area. By greatly controlling Ff, it is possible to prevent the occurrence of abnormal electrical discharges such as arcs, and to complete extremely stable high-speed machining until the end of machining. 10,000 thus off-pulse τ.

When Ff is controlled to control the discharge repetition circular wave number, the amount of machining debris generated naturally changes, and when the repetition frequency is increased due to an increase in the machining area, the rate of machining debris generation increases proportionally.
On the other hand, if the area is reduced and the repetition frequency is lowered, the rate of generation of machining debris will be reduced. So decoder 1
The output of No. 5 is also applied to the switching relay circuit 17 of the machining fluid pump device to control changes in the machining fluid jet pressure. In other words, when the comparison output A-B decreases as the machining area increases, the discharge repetition frequency is controlled to increase, and at the same time the jet pressure is controlled to increase, increasing the effect of removing generated machining debris, and conversely decreasing the machining area. When A-B increases as a result of this, the relay circuit 17 controls to reduce the discharge repetition frequency and the jet pressure. Therefore, since the discharge repetition frequency and the machining fluid jet pressure are always controlled at a constant relationship ratio, machining debris may accumulate in the gap, or more machining debris may be removed than necessary, causing electrical discharge. It is possible to perform stable electric discharge machining by always having a constant concentration of machining debris in the machining gap and stirring it to evenly mix and distribute it in the machining fluid. It is.

In addition, the processing pulse control is described above with τ. 0,,1p constant (
Of course, even though it is said to be constant, the individual pulses are controlled depending on the state of the machining gap, and an adaptive control pulse power source that is adaptively controlled within a certain range above and below the set value is sometimes used), and τ0ff We have explained the case of using a machining area proportional signal to calculate τ.

Not only one but two or three of Ff, τ0n, and Ip may be changed and controlled using a machining area proportional signal (in this case, the repetition frequency of discharge may be constant).
. In addition, the control of the pump device that supplies machining fluid is not limited to the jet pressure, but the flow velocity or suction pressure may also be controlled by changing the machining area proportional signal, and in that case, the purpose of controlling the machining waste concentration at a constant level can also be achieved. . In addition, in detecting the machining area proportional signal, a timer (not shown) is provided and the count N of the number of discharge repetitions of the counter 2 shown in the figure and the feed amount count number L of the counter 5 are proportionally adjusted at predetermined time intervals C.
Area detection may also be performed.

[Brief explanation of the drawing]

The figure is a circuit diagram of one embodiment of the present invention.

Claims (1)

[Claims] 1. A pump device is provided to supply machining liquid to the machining gap between the machining electrode and the workpiece, and a pulse power source is provided to supply machining pulses, and a servo that provides servo feed of follow-up control to the electrode or the workpiece. In the electric discharge machining apparatus equipped with the device, a device for detecting the number of repetitions of electrical discharge repeated in the machining gap, a device for detecting a follow-up feed distance for keeping the machining gap small by the servo device, and both of these devices. A calculation device is provided to detect a machining area proportional signal by dividing a signal proportional to the number of discharge repetitions detected by the detection device and a signal proportional to the follow-up feed distance, and processing is performed using the detection output signal of the calculation device as a signal. a control device that automatically changes and controls the level of one of the on-pulse width, off-pulse width, and peak value of the pulse power source so that the current always approaches a set current density; and processing the detection output signal of the arithmetic device as a signal. Automatically changing the level of one of the flow rate, jet pressure, and suction pressure of the machining fluid supplied by the pump device so that the machining debris present in the machining gap is always maintained at a preset constant concentration even if the area changes. An electrical discharge machining device equipped with a control device.