SU820650A3 - Method of electroerosion treatment - Google Patents

Abstract

1388301 Automatic control of electro-discharge machining ATELIERS DES CHARMILLES SA 21 March 1972 [25 March 1971] 13038/72 Heading G3R In an electro-erosion process, voltage pulses are supplied to a machining gap filled with fluid. The voltage and/or current across the gap are measured, together with the rate of decrease of the voltage, and at least one of the following parameters is automatically controlled: (a) a pulse characteristic, (b) the composition of the machining fluid, (c) the size of the gap. In the arrangement shown, a pulse generator 5 supplies controlled pulses to an electrode 3 spaced from a workpiece 2. The electrode is movable by a servomechanism 4, and the machining gap is filled with fluid, in the form of a dielectric liquid, supplied through a valve 12 from a reservoir 10. The mechanism 4 and valve 12 are both controlled by a circuit 13 which receives signals representing the machining voltage and current on lines 17, 17a and 18, 18a respectively. The circuit 13 also controls the operation of the pulse generator 5 over lines 14a-14f and may energize fault indicator lamps 31-34. The generator 5 includes monostable multivibrators 5a, 5b connected to a switching device 36 which controls a series transistor T 1 in a relay circuit 7. The current may be increased by turning on a parallel transistor T 2 through an AND gate ET1 controlled by the circuit 13. A third transistor T 3 ensures the establishment of discharge current by applying high voltage from a source 6b, under the control of an AND gate ET2. The beginning of the discharge can be detected by a device 5c connected to the multivibrators, and a line 19a receives a pulse when transistor T 1 turns on. The control circuit 13 includes a number of monitoring and comparator circuits, logic circuitry, and output control signal circuits. The monitoring circuits, Figs. 4-9 (not shown) receive current, voltage and timing signals, and use comparator circuits, transistors, field effect transistors and Zener diodes to produce signals indicative of various operating conditions of the machining process. These signals are then combined and distributed to appropriate control circuits connected to the pulse generator, electrode position servo, machining fluid valve, and warning lamps. The functions of the six monitoring circuits are as follows: Circuit IV, Fig. 4 (not shown) detects the presence of abrupt voltage variations during the current pulses. An insufficient rate of such variations causes illumination of lamp 31. Circuit V, Fig. 5 (not shown) responds to voltage variations from one discharge pulse to another, indicating that sparking is occurring at different points on the workpiece. Circuit VI, Fig. 6 (not shown) monitors the pollution level of the machining fluid. High pollution allows conduction through the fluid and prevents sparking. Warning lamp 32 may be energized and a control signal is fed on line 16 to the fluid supply valve 12, Fig. 12 (not shown). Circuit VII, Fig. 7 (not shown) detects the occurrence of a short circuit, illuminating lamp 33, and circuit VIII, Fig. 8 (not shown) monitors the electrode potential between the start of a voltage pulse and the beginning of current flow. Circuit IX, Fig. 9 (not shown) responds to non-operation of the transistor relay circuit 7 by illuminating lamp 34 and producing a signal on line 14f to energize a relay 35 which switches off the power supply. The outputs from monitoring circuits V, VII and VIII are combined in a control circuit, Fig. 10 (not shown) which produces the signal on line 15 to operate the electrode position servo 4. The characteristics of the pulses produced by generator 5 are controlled by signals on lines 14c, 14d, 14e. The pulse duration is determined by the signal on line 14c, connected to the multivibrator 5a and derived from monitoring circuits IV and V through an output circuit, Fig. 15 (not shown). The duration of the discharges is reduced if the rate of arcing is too high. The intervals between successive pulses are determined by the multi-vibrator 5b under the control of the signal on line 14d in such a way that the intervals are increased if a high rate of unsatisfactory pulses occurs. The signal is produced by an output circuit, Fig. 11 (not shown) of the control circuit 13. Finally, logic circuitry, Fig. 3 (not shown) is used to produce a line 14e a signal to cause switching device 36 to interrupt the discharges momentarily.

Description

one

The invention relates to electrophysical processing methods and, in particular, relates to an electroerosive processing method.

Processing methods are known in which the process parameters are controlled by the signal of the rate of change in the average voltage of the pulses applied between the electrodes 1.

The disadvantage of these methods is the low quality of the treated surface.

The purpose of the invention is to improve the quality of the surface.

This goal is achieved by the fact that the signal to change the parameters is produced at the time of decreasing the rate of voltage drop below a predetermined value.

The advantage of the proposed method consists in the possibility of detecting a special type of abnormal discharge so that the mechanical processing parameter, which most of all contributes to the occurrence of this anomaly, can be changed to eliminate this latter by maximizing the change in the processing conditions. In addition, this method allows combining a new criterion for detecting abnormal bits with other known criteria with

so that the resulting anomaly can be distinguished, for example, from a shorting arc or contamination used for the treatment of the liquid, and to change the corresponding processing parameter. Another advantage of the invention is the ability to detect abnormal bits and correct the processing parameters in both the workpiece processing mode and the final finishing mode.

FIG. Figure 1 shows a schematic general view of an EDM machine; in fig. 2 shows various possible voltage curves used for processing as a function of time during the period of the processing pulse; in fig. 3 is an electrical circuit capable of determining the rapidity of the processing voltage drop during discharge.

The machine has a table 1, a tank designed to install the workpiece 2. The electrode 3 can be moved in the direction of the part 2 by the servo-mechanism 4.

The processing current is supplied by a pulse generator 5, which mainly consists of one or more sources of constant voltage 6 and electronic switches 7 and which is connected to part 2 and electrode 3, respectively, by conductors 8 and 9.

The machine has a reservoir 10 in which the working fluid is contained. This fluid is pumped and pumped through pipe 11 with a valve 12 to electrode 3.

The machine also has a trace w, its device 13 acting on a pulse generator 5 through the control system shown conditionally as connection 14. The device 13 also has an output 15 for controlling the servo-mechanism 4 providing movement of the electrodes, and an output 16 controlling valve 12 which regulates the flow of working fluid. The next device 13 also contains two inputs 17 connected to the workpiece and an electrode, and inputs 18 connected to the shunt S for current measurement.

According to the invention, it is provided to change at least one of the processing parameters as soon as during the establishment of current pulses the voltage drop rate falls below a predetermined value.

Thus, it is possible to detect in advance the deterioration of the treatment conditions and to change at least one processing parameter in order to restore good processing conditions.

The high rate of voltage drop during the establishment of the discharge indicates a very large contamination of the liquid used for the treatment. To eliminate this drawback, you can change: either the characteristic values of the indicated voltage and / or current pulses; either a physical or chemical state of the working fluid filling the gap, or the gap between said electrodes.

FIG. Figure 2 shows the voltage curve arising between the electrode and the workpiece during the processing pulse. At ta, the voltage is applied to the treatment period, and it is usually stated that the waiting time from U to ti, which can vary considerably, before the voltage drops to the level Ui. This level is reached after setting the treatment current. The decrease in voltage from its initial value t / 2 TO the level Ui occurs more or less quickly, curves a and b illustrate the decrease in voltage during normal discharges. Curve c illustrates the SLOW slow reduction of the voltage caused by the contamination of the fluid, which thus becomes a conductor.

According to the invention, it is established whether the voltage drop curve is higher or lower than the limiting curve b during each discharge. This can be, for example, installed using the electrical circuit shown in FIG. 3

This circuit is a contamination detector that is sensitive to the rate of voltage reduction that is observed by the electrode and the workpiece at the time of the establishment of current pulses after applying a voltage pulse. This detector is connected to inputs 17.

With abrupt changes in voltage between these terminals, alternating components pass through capacitor Ci and through the diode when their front is negative and charge capacitor Cz when their front is positive, i.e. when the voltage between the electrode and the part is falling.

The voltage of the capacitor Cz will be compared with the reference voltage with the help of comparator 19. The output of this comparator 19 is superimposed on a memory device with a delay of 20, which is triggered when a discharge current of any pulses occurs. Thus, the multivibrator (storage device) 20 stores the output signal of the comparator 19 at the beginning of each bit. The constant RC capacitor Cz, which is discharged at resistance J, is small enough to almost completely discharge the capacitor between the end of the pulse and the start of the next. The multivibrator has two outputs 21 and 22. When the system detects the presence of contamination, line 21 does not receive a signal, while line 22 receives one signal. In the absence of contamination, it is the line 21 that is under voltage, and the line 22 does not have a signal.

It is obvious that to provide for numerous variants of the described method, namely, instead of forming two signals of a given magnitude on lines 21 and 22, depending on whether the rate of voltage drop is lower or higher than a predetermined value, one could use a signal whose magnitude depended on the rate of decrease of the indicated tension. Such a signal could be

would be formed, for example, by the voltage appearing at the terminals of the capacitor Cz, and this voltage could be measured some time after the start of the setting of the discharge current.

Claims (1)

Invention Formula The method of electroerosive processing, including the regulation of processing parameters depending on the magnitude of the rate of fall of the average voltage of the pulses applied between the electrodes, characterized in that, in order to improve the quality of the surface to be treated, the signal for changing the parameters is produced at the time of decreasing the rate of voltage drop below a predetermined value. Sources of information taken into account in the examination 1. A. Livshits and others. Fundamentals of extreme control of electric pulse machines, ENIMS, 1962, p. 75-78. g and t, WITH, / 7 - WITH i.i: