FR2458348A2 - METHOD AND DEVICE FOR SUPPLYING ELECTRIC PULSES OF AN ELECTRIC DISCHARGE MACHINING MACHINE - Google Patents

Abstract

METHOD AND DEVICE FOR PROVIDING A MACHINING INTERVAL G BY ELECTRICAL DISCHARGES OF SUCCESSIVE TRAINS FAR IN THE TIME OF DISCREET ELEMENTARY PULSES OF A PREDETERMINED POLARITY IN RELATION TO AN ELECTRODE-TOOL 1 AND TO A PIECE 2. WE PRODUCE A END HIGH FREQUENCY ALTERNATIVE ELECTRIC SENSITIVE TO THE PULSE FREQUENCY BY MEANS OF A GENERATOR 3, THE ENERGY IS TRANSMITTED IN THE FORM OF AN UNREGENTED ALTERNATIVE ELECTRIC CURRENT UP TO THE IMMEDIATE PROXIMITY OF THE MACHINING INTERVAL, AND ON CYCLICALLY INTERRUPTS THE TRANSMITTED CURRENT WHILE STRAIGHTENING IT TO PROVIDE SUCCESSIVE TRAINS AT THE MACHINING INTERVAL.

Description

The present invention relates to a feeding method and a circuit

  high frequency energy supply of a machine for machining electric discharges, as described in the French patent application NI 79 05 790 filed March 6, 1979 in the name of the Applicant. More particularly, the invention relates to a method and a device

  to provide electro-discharge machining pulses

  high-frequency terminals between a tool electrode and a workpiece, through a machining interval swept by a machining (dielectric) fluid, in a machine

  machining by electric discharges.

  An electric discharge machining machine is

  commonly equipped with a power supply for

  generate high frequency machining pulses at intervals

  machined with dielectric, formed between the electrode-

  tool and the workpiece, in a working tank containing

  collecting or collecting the dielectric. In circuits and

  in conventional methods of supplying energy for the

  electrical discharge, the machining pulses are produced in one unit (energy supply unit) installed separately from the actual machine carrying the mechanical components and the working tank in which is defined the machining interval between

  the tool electrode and the workpiece. The food unit

  separate compartment contains in its cabinet all the main electrical components necessary to produce a succession of unidirectional energy pulses at its output.

  predetermined polarity with respect to the electrode

  tool and to the workpiece, the output of the unit being connected to the machining interval by means of a cable or elongated electrical conductor; consequently, the energy pulses leaving the unit are transmitted to the machining interval by this cable. As a result

  the resistance and the leakage inductance of the cable or

  driver impede the transmission of energy pulses

  unidirectional and cause a loss of power.

  considerable distortion and distortion of the waveform of

  pulses transmitted to the machining interval. As a result

  therefore, the removal of material has hitherto been

  undesirably limited, the machining efficiency

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  is too weak and the entire feeding unit becomes

  extremely large and eassive in conventional machines

  electrical discharge machining.

  The French Patent Application mentioned at the beginning describes a method and a device for supplying high frequency electric discharge machining pulses between a

  electrode-tool and a workpiece, through a

  machining time swept by a machining fluid, in an electric discharge machining machine. The described method includes the steps of: producing high frequency alternating electrical energy by means of a unit

  of generator. high frequency arranged at a distance from the

  machining time, transmitting electri-

  native high frequency to an area at immediate proximity to

  the machining interval by a transmission medium presented

  both input terminals coming directly from the unit

  of high frequency generator, and straighten the electrical energy

  rectifier high frequency near the gap

  machining to form a succession of impulses of a

  given in relation to the tool electrode and the

  to machine, thus constituting the machining pulses by de-

  electrical charges, the frequency of which is generally

between 1 kHz and 5 MHz.

  An apparatus or circuit device for carrying out the method has also been described. It comprises: unidirectional current conducting means placed at

  proximity to the machining gap and connected to the electrode-

  tool and piece by respective drivers of long-

  and a generator of alternative electrical energy

  tive high frequency away from the machining interval and

  providing high frequency alternative electric energy

  quence on its way out; transmission means for connecting the generator to the unidirectional conductive means of

  current to enable transmission of electrical energy

  produced at this output in the form of a high-frequency alternating current, close to

  the machining interval, the unidirectional conductive means

  current are adapted to rectify the high frequency alternating electric energy near

  the machining interval to form a succession of impulse

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  of a given polarity with respect to the tool electrode and the workpiece, constituting the machining pulses by

electric shocks.

  The unidirectional conductive means of current can

  can be constituted by a rectifier alternating or

  by a two-wave rectifier, and the means of trans-

  mission can be a cable or power line, for example a coaxial cable of conventional design, adapted

  to carry high frequency alternating energy.

  In addition, a transformer (reducer) may be provided upstream of the unidirectional current conducting means along the transmission means to obtain electrical machining pulses applied to the machining interval.

of desired amplitude.

  According to the described technique, since the machining energy from the generator is transmitted in the form of a high frequency alternating current until it reaches the vicinity of the machining gap, there is a low energy loss and low distortion of the voltage or waveform of the current in the transmission means 7, which allows machining at an increased removal rate with maximum power consumption that can easily be transmitted according to a frequency of the order of the megacycle. In addition, the low energy loss by the transmission means makes it possible to use a

  compact generator with reduced capacity and size.

  The transformer and the rectifier can be mounted on a part of the walls of the working tank or even directly on the head, column or frame of the machine bearing

  the tool electrode or the workpiece. The transformer is advantageous

  small size because the energy it transmits is high frequency. The recovery of the high

  frequency transformed by the rectifier close to the in-

  Machining time provides current pulses from

  polarized or unidirectional swimming that are applied to the interval without substantial loss of power and without

distortion of the waveform.

  The machining current pulses obtained by redres-

  high-frequency alternating current may have an extremely narrow pulse duration T

  between 1 and 100 microseconds and a pulse interval

  T off between 0.1 and 50 microseconds, each

  these durations can be established at the generator and applied

  at the machining interval without loss of power. A succession of machining pulses presenting such

  short T on and T off times can produce

  finely divided electrical gauges that protect from coarse material removal on the surface of the workpiece for precision machining. In addition,

  by applying a repetitive induced discharge pulse

  with a short interval, the machining interval

  allows a subsequent discharge to take place before the

  the interval resulting from the previous discharge. This effectively avoids the misses for each elemental impulse so that is obtained a speed

  increased repetition of charges; each discharge

  the removal of material with maximum efficiency, a machining process is achieved at

  high speed and high efficiency.

  The French Patent Application mentioned at the beginning also pointed out that, in order to achieve an efficiency and a

  machining stability better, it is desirable to interrup-

  periodically or intermittently, high-frequency electrical impulses such that discharges

  Interval machining takes place in the form of succes-

  intermittent discharges of high frequency elementary discharges.

  For this purpose, the high frequency generator comprises, besides

  a high frequency AC oscillator

  an output frequency between 1 kHz and 5 MHz,

  a pulse generator capable of providing series of im-

  pulses with relatively long Tn-action times, and with relatively long Toff-off times, and thus capable of repetitively interrupting the high-frequency alternating current output. As a result, the output of the generator provides successive trains of high frequency alternating pulses. The successive trains are transmitted by

  the transmission means to the rectifier close to the inter-

  machining area and converted by the latter into successive trains of unidirectional pulses applied in

  through the machining interval. The impulses

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  which form each train can here have a pulse duration T 1 of between 100 and 100 microseconds and an interval T'off between pulses between 0.5 and 50 microseconds and, in connection with its frequency, they are defined by the high frequency AC oscillator. When the rectifier is alternating, T on = Toff

  for the pulse duration and the interval, and when the

  The oscillator can also be adapted to produce an asymmetric alternating current obtained by, for example, superimposing a symmetrical alternating current of adjustable frequency with a direct current of polarization, in which case any desired combination of pulse duration and pulse interval can be obtained, satisfying either the relation T on> T off or the relation T on <T off according to what is required for a combination

  particular electrode material and machining conditions.

  As a result, pulse trains, each train comprising a series of unit pulses having a pulse duration T on and a pulse interval T off, occurring at a frequency f, are obtained with a duration Ton and Toff interval relatively long, at a frequency F, through the machining gap between the tool electrode and the workpiece to allow machining at increased efficiency. The duration of action Ton and the duration of cut-off Toff can be each between 10 microseconds and 100 milliseconds, while the frequency F of the trains can spread out between 100 Hz and 100 KHz, these parameters of trains being chosen according to conditions and settings

particular machining.

  An interval detector may be provided for monitoring the state or condition of machining at the interval, in response to one or more of the interval variables such as range voltage and impedance, or on an average basis, either on an instant basis, inside

  of each pulse train or between pulse trains

  adjacent areas, with a control device for the

  pulse meters sensitive to the interval detector to control one or more of the controllable parameters of trains such as Ton, Toff and F. Of course, the parameters

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  On, Toff and / or elementary pulses within each train can be simultaneously set optionally, with an additional control device associated with

  the high frequency AC oscillator.

  The command of the pulse train parameters is

  to reduce the duration of action Ton and / or to increase

  Maintain the Toff cut-off time, and, in other words, to decrease the number of elementary impulsinns within each train and / or to increase the period during which bs elementary pulses are interrupted in each recurrent cycle of train elementary pulses, when the interval detector indicates deterioration

  machining condition, requiring correction or reinstatement

  in response to the interval variables. Thus, the machining chips, the tar and the accumulated gases produced by the

  discharges and remaining in the machining interval are effi-

  evacuated when increasing cut-off times and

  decreasing the time required to maintain the inter-

  machining range-in an optimal state, which makes it possible to cause stable machining discharges with unit trains

  successive impulses. It is also advantageous to control

  derive the average machining current by changing the action times and cut-off times of the trains to allow various high or low speed machining operations or in response to variations in the machining area in which

  the tool electrode and the workpiece are juxtaposed.

  The high frequency oscillator may oscillate whenever the action signal arrives at its input from the

pulse generator.

  The present invention generally relates to a method and an electric discharge machining machine as described in the foregoing and in the Application for

Patent mentioned at the beginning.

  The method according to the invention consists in providing

  successive trains spaced in the time of elemen-

  discrete areas at an electric discharge machining interval, the elementary pulses being derived

  a high frequency generator placed at a distance from the

  machining area and transmitted in the form of a non-rectified high frequency alternating electric current to unidirectional current conducting means arranged near the machining gap for rectifying the high frequency alternating electric current so as to

  to form the discrete elementary impulses of a p8la-

  given, the unidirectional current conducting means being connected to the tool electrode and the workpiece by

  respective conductors of minimum lengths for

  elementary pulses at the machining interval, the method comprising the step of controlling the

  operation of the unidirectional current conducting means

  to cyclically interrupt the impulses

  unidirectional and train with these pulses

  successive trains of impulses distant in time.

  The device according to the invention comprises a gen-

  high frequency generator away from the machining interval

  and providing a high frequency alternating current

  at its exit, means conducting electricity

  unidirectional placed close to the usable interval

  to rectify the high-frequency alternating electric current and form discrete elementary pulses of a given size, connecting transmission means

  the output of the high frequency generator to the conductive means

  unidirectional electricity transmitters for transmitting high frequency alternating electric current to the unidirectional electricity conducting means, and means

  control means associated with the electrically conductive means

  to unidirectionally interrupt the operation of the

  tion of these and allow for basic impulses

  to be transmitted in the form of successive pulse trains spaced in time at intervals

  machining, the unidirectional electricity

  are connected to the tool electrode and to the

  piece through respective conductors of minimal lengths

  males. The unidirectional current conducting means are advantageously constituted by a thyristor exhibiting

  a pair of main electrodes connected to the electrode

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  tool and the workpiece and oriented to establish the desired polarity and to control the excited electrodes by means of pulses forming the control means for cyclically interrupting the passage of the rectified discrete elementary pulses from the high frequency alternating current . An interval detector is

  preferably also in the vicinity of the usable interval

  to detect the conditions of discharge in the

  valle of machining and to act on the pulse means to control the pulse interruption mode and the production of successive trains spaced in time

  of discrete elementary pulses.

  The invention will be well understood on reading the

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a circuit diagram illustrating a current source for electric discharge machining according to the present invention; and FIG. 2 is a chronological graph and a waveform diagram illustrating the operating mode of the

circuit of Figure 1.

  In Figure 1, a tool electrode 1 is shown juxtaposed to a workpiece 2 so as to form a machining gap G in a working tank T. The tool electrode 1 may have any shape, for example compact tubular or three-dimensional shapes, depending on the particular mode of electric discharge machining to be performed. In wire or wire cutting electric discharge machining, a continuous elongate wire electrode, or the like, is generally used. The tray T is generally mounted on a work table or frame (not shown) and is a part of an electric discharge machining machine having the function of serving as a reservoir or dielectric collector in which is defines the machining interval G. Any known source (not shown) of dielectric liquid is provided to supply the machining liquid to the machining gap G so that the latter is filled and swept by this liquid to drive out machining chips, tars and gases out of the gap while serving

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  of machining agent by electric discharges. During the machining operation, the tool electrode 1 is advanced relative to the workpiece 2 by a servomechanism (not shown) to maintain constant the gap G extending between the electrode and the workpiece. According to an important feature of the invention, a high frequency alternating current generator 3 is disposed remote from the machining gap G and has a

  output 3a connected via a high frequency transmission means

  4, for example a coaxial cable, in the vicinity of the machining gap G. In this latter zone are arranged unidirectional current conducting means 5

  constituted by a thyristor having terminals of electro-

  negative and positive 5a and 5b connected to the electrode-

  tool 1 and in part 2 by conductors 1a and 2a,

  poles, of minimum length. Driver 2a is represented

  comprising a secondary winding 6b of a transformer

  6 high frequency generator whose primary winding is excited by the transmitted high frequency alternating current

  by the transmission means 4 from the generator 3.

  The driver 2a also comprises a resistor 7 of

  detection, and a circuit comprising in series another thyris-

  tor 8, a high voltage auxiliary source 9 and a resistor

  Current limiting current 10 is connected in parallel with the series circuit of the thyristor 5 and the resistor 7 of detection. The detector Il of discharge at the interval includes

  circuits 12, 13, 14 and 15 Schmitt rocker. Others

  Schmitt 16 and 17 are designed to detect a short-

  circuit at the interval and a stall of the interval, res-

  tively. A pair of flip-flop elements 18, 19 have respective outputs connected to the respective control electrodes 5c and 8c of the thyristors 5 and 8. The output of the bistable element 18 is also supplied to a

  clock 20 which, in turn, leads to a circuit 21 of re-

  the return of which is returned to the terminal

  engagement of the bistable element 18. The terminal

  cleaving of the latter is connected to the output of the

Schmitt rocker 17.

  AND gates 22, 23, 24 and 25 are associated as discriminators by their input side with the gap discharge detector circuit 11 and have their respective outputs connected to clocks 26, 27, 28 and 29 having

  different time constants or operating times.

  An OR gate 30 is connected to the outputs of the clocks 26, 27, 28 and 29 and its output is connected to the interlock terminal of

  the bistable element 19. The reclosing terminal of this

  deny is connected to the trigger terminal of the element

  bistable 18. Another terminal of engagement of the bis-element

  table 19 is excited by the voltage terminal + e via a

  controller 31 with a start push button. Another community

  32 is connected between the output of the OR gate 30 and the

  interlocking terminal of the bistable element 19; it is normal

  maliciously closed and is only open at the end of an operation

  machining. An emergency unit 33 responsive to the setting in

  circuit or any other disturbance of the machine, and an electrode advance unit 34 associated with the servomechanism, are

  also shown arranged, with the high frequency generator

  quence 3, away from the machining interval G. The generator 3 provides a high frequency alternating current preferably between 1 kHz and 5 MHz

  which generally corresponds to a frequency f or repetition speed

  forming the elementary machining pulses applied across the machining gap G. The high frequency alternating current produced by the generator 3 at a location remote from the machining gap G on the working low T is transmitted by the transmission means 4 which leads to the primary winding 6a of the transformer 6. The latter serves to lower the level of the voltage of the high frequency output of the generator 3 and to establish the peak pulse current at a desired value in immediate proximity

  of the machining interval G. The width of the pulses applied

  across the machining interval is given by

  the orientation of the rectifier 5 and, as shown, is

  pre to make the anode electrode 1 and the cathode part 2

  This can be reversed depending on the particular material of the electrode and the conditions or settings

machining to be chosen.

  Since the machining current from the generator 6 is transmitted in the form of a high current

  frequency until it reaches the proximity of the inter-

  machining valle G, there is a small power loss and low distortion of the voltage or waveform of the current in the transmission means 4, which allows high speed machining of removal with a maximum electric current that can be easily transmitted even

  with a frequency in the megacycle domain.

  In addition, the low power loss in the transmission means 4 makes it possible to apply a compact generator 3

  and smaller in size and capacity.

  The transformer 6 and the thistor 5 can be mounted on part of the walls of the work tank T or directly on the head, column or frame of the machine carrying the tool electrode 1 and the part 2. The transformer 6 is advantageously of a small size since the power transmitted by him is at high frequency. The rectification of the high frequency transformed by the thyristor 5 near the machining gap G provides polarized or unidirectional machining current pulses which are applied to the machining zone G without substantial power loss.

or waveform distortion.

  The machining current pulses obtained by rectifying

  High-frequency alternating current may have an extremely narrow pulse duration, between 1 and 100 microseconds and an off interval between pulses between 0.5 and 50 microseconds, each of these data

  can be established at Generator 3e applied to the inter-

  G machining valleys without loss of power. A series of im-

  Machining pulses with such short T on and T off times can produce finely divided electrical discharges, which prevents coarse material removal on the surface of the workpiece, thus allowing for precision machining. In addition, with a discharge pulse created repetitively with a short interval, a subsequent discharge can take place in the machining interval G before complete deionization of the gap G following the previous discharge. This effectively prevents misfires of each elemental pulse so that an increased discharge repetition rate is achieved, each individual discharge contributing to

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  material removal with maximum efficiency; a high speed and high efficiency machining process

is thus provided.

  For the operation of the circuit shown in FIG. 1, the switch 32 is initially open, so that the bistable elements 18 and 19 are maintained in the reset state and the thyristors 5 and 5 are 8

  are kept in a non-conductive state.

  To perform a given machining operation by de-

  electrical charges, the tool electrode 1 and the part 2 are placed at their machining start position and various elements of the machine (not shown) are turned on, after which the switch 32 is closed. supply

  machining liquid at the G interval begins and the general

  4 is excited to supply the high frequency alternating current by the transmission means 4 to the winding

primary 6a of the transformer 6.

  Then, pressing the start push button associated with switch 31 causes the element to pass through.

  bistable 19 to its latching state so that the thy-

  ristor 8 is made conductive. This allows the transformer 6 to develop an induction current VA in a circuit

* series connecting the source 9 auxiliary current to the electrode-

  tool 1 and part 2, and causes the addition of the voltage to

  xiliary VD of the source 9 and the inductive voltage VAsu-

  placed on each other, which develops across the machining interval G. This additive or peak voltage (VD + VA) is set at a value well above the voltage

  interval and acts in such a way as to provoke

  the electrical discharge across the machining interval G. The cut-off discharge in this state is not

  not self-sufficient because of a high resistance value

  strength of the current limiting resistor

posed in this series circuit.

  Interval cutoff or establishment of the discharge

  electrical power is detected by the Schmitt trigger 17 and

  the setting of the bistable element 18 in the engaged state

  mation. This causes the conductive state of the thyristor, which in turn causes the return of the bistable element 19

  in its reclosing state and at the same time

  The thyristor 5 in the conductive state now establishes a discharge path comprising the secondary winding 6b of the transformer 6 and the resistor 7 in series with the tool electrode 1 and the part 2. The electromotive force in this discharge circuit is provided by only a half-wave of the voltage-induction VA of the transformer 6 and, because of a low resistance value of the resistor 10, allows the development of a level of

  sufficient current for machining. At the same time, thyroid

  ristor 8 is cut off and the auxiliary power source 9 is disconnected from the discharge circuit as soon as the voltage

additive VD + VA becomes zero.

  The clock 20 is set to establish a duration T1, at the expiration of which it makes the delay circuit or clock 21 operative. The delay clock has a period T2 at the expiry of which it triggers the bistable element 18 to its reclosing state. Consequently, the alternating positive component of the output voltage VA of the transformer 6 remains supplied under

  the form of a succession of pulses rectified internally

  machining valle G during the duration period T1 and T2. Here, as shown in FIG. 2, the period T1 is chosen to correspond to a greater number of cycles of the high frequency alternating current, whereas the period T2 is set to correspond to a small number of cycles of the current. The Schmitt latches 12 to 15 constituting the discharge state or characteristic detector 11, and the Schmitt flip-flop 16 have trigger levels E12 to E15 and a trigger level E16, respectively, the following relationship being satisfied: E12Z4El3 4E144E15 E16. The peak voltage Ep detected at resistor 7 is set to indicate the occurrence of a discharge characteristic

  optimal at the machining interval G when E13, Ep 4E14.

  When Ep is smaller than E13, the discharge current is too small or unsatisfactory whereas when Ep is more

  larger than E14, the discharge current is excessive.

  Thus, when optimal interval discharges

  continue to be born, the Schmitt latches 12 and 13 provide outputs while the Schmitt latches 14 and 15 remain de-energized. As a result, when the clock 20 provides a

  output pulse, the AND gate 23 is selected to trans-

  setting the output of the Schmitt trigger 13 to selectively cause the action of the clock 27. When the discharge current is abnormally low, the AND gate 22 is set to transmit the output of the Schmitt trigger.

  12 for selectively causing the clock to move 26.

  When the discharge current is excessive but is suitable for satisfying the relation E14 Ep 4 El5, the clock 28 is

  chosen in the same way. When E15 EpZ..El6, the clock

  ge 29 works. This results in the selective excitation of one of the various clocks 26-to 29 to establish the cut-off time Toff in connection with the particular level of the

  Discharge current at the interval.

  When the bistable element 18 is reset, the elec-

  5c control trode thyristor 5 is de-energized so that the development of the first negative alternation of the high frequency alternating voltage of the transformer 6, according to its main electrodes 5a and 5b, causes its setting non-conduction condition, thus ceasing the duration

  Tone of a succession of discrete elementary impulses.

  The operating times T26 to T29 of the clocks 26 to 29 are determined so as to satisfy the relation T26 t T274T28ZT29 and to establish in a variable manner the interval

  Toff between successive trains of elemen-

  In the end of its selected operating time T26, T27, T28 or T29, the clock 26, 27, 28 or 29 provides a short pulse of output. which is fed via the OR gate 30 to the bistable element 19 so as to bring the latter into the engagement condition. this allows the thyristor 8 to come into the conduction state. The cycle repeats itself for

  the continuation of the electrical discharge machining operation

c.

  In the illustrated installation, the electrode feed unit 34 is also shown excitable in connection with the discharge state detector 11, especially when an excessively low impedance condition prevails at the machining interval. G. When the gap current is high enough to trigger the Schmitt circuit 15, the second output of the AND gate is used to activate the unit 34, thereby causing the reciprocating or cyclic movement of the tool electrode. 1 from the machining position as long as

  the condition persists or for a predetermined duration.

  In addition, when the machining current is high enough to trigger the Schmitt circuit 16, the emergency unit 33 is also energized to cut off the source.

current.

  In this embodiment, the transformer 3, the thyristors 5 and 8, the discharge state detection unit 11 and the components associated therewith, are

  preferably all ready for immediate proximity to

  machining zone G in which the machining discharges are produced. This effectively eliminates unwanted distortions

  of the impulse waveform and allows the characteris-

  pulses not to be significantly influenced by external "noises". Operations of observation of the state of the interval and control of the pulses of high

  accuracy can be achieved accordingly.

  The invention thus provides a high-frequency current supply circuit and a power supply method for providing machining pulses in the form of successive trains of pulses to an electric discharge machining interval. discrete elementary elements, said circuit and said method ensuring better machining results while allowing the entire supply unit to

  current to be compact and simplified.

Claims (15)

  1. Method for providing a machining interval by de-t electrical charges of successive trains distant in the   time of discrete elementary pulses of a pre-existing polarity   determined with respect to a tool electrode and a workpiece, characterized in that it comprises the steps of: producing a high frequency alternating electrical energy substantially at the frequency of said elementary pulses by means of an alternating current generator unit high frequency disposed away from the machining gap; transmit high frequency energy in the form of a non-rectified alternating electric current through a   means of transmission to the immediate vicinity of the   machining time; and interrupt cyclically at the said   close to the transmitted high frequency alternating electric current while straightening the latter to provide the said   successive trains spaced in the time of elemen-   of said predetermined polarity for the application of   direct application across the machining interval by de- electric charges.   2. Method according to claim 1, characterized in that   that said frequency is between 1 kHz and 5 MHz.   3. Method according to claim 2, characterized in that   that the time of action and the cut-off time of the trains suc-   cessives spaced in time each have a duration   between ten microseconds and one hundred milliseconds.   A method according to claim 1, characterized in that it further comprises the steps of detecting the characteristic of the discharges at the interval which results from the application of the elementary pulses to the electric discharge machining interval in the aim of providing a control signal, and modifying with said control signal the cyclic production of successive trains spaced in time. 5. Method according to claim 4, characterized in that the cyclic production of successive trains spaced in time is.modified by controlling the cut-off time of said trains. 6. Method according to claim 4, characterized in that the cyclic production of successive trains spaced in 17 2458348   the time is changed by controlling the action time of the trains. 7. The method according to claim 4, characterized in that the measurement of detecting the characteristic of the discharges at the interval is carried out for a finite period of time.   of each elementary pulse train.   8. The method of claim 1, characterized in that it further comprises the measurement of superimposing a   high voltage and low intensity pulse with a   elemental drive in an initial period of each train.   9. Method according to claim 1, characterized in that it further comprises the measurement of transforming, in said vicinity of the machining interval G and before   its recovery, the high frequency alternating current   quence transmitted at a desired voltage level of impulses elementary discrete.   A circuit device for providing at an electric discharge machining interval successive trains spaced in time from discrete elementary pulses of predetermined polarity with respect to a tool electrode   and a coin, characterized in that it comprises: a general   a high frequency alternating current transformer disposed away from the electric discharge machining gap, for providing a high frequency alternating electric current substantially at the frequency of the discrete elementary pulses; of the   means of transmission for transmitting, in the form of   non-rectified alternating current, the high frequency current   lablement produced in the immediate vicinity of the interval of   electric discharge; conducting means of the   unidirectional electrical power and switch means placed in said proximity and connected to the tool electrode and the workpiece by means of respective conductors of minimum lengths to cyclically interrupt the electric current   alternating high frequency transmitted while straightening this   deny so as to provide successive trains spaced in time from discrete elementary pulses to said polarity   predetermined, for the direct application across the   Machining time by electric discharges.   11. Circuit device according to claim 10, characterized in that it further comprises a transformer placed in said proximity of the machining interval and   connected upstream of the unidirectional current conducting means   and switching means to transform the   high frequency alternating current voltage level   quence transmitted to a desired level before recovery. Circuit device according to claim 10,   characterized in that said transmission means comprises a coaxial cable.   Circuit arrangement according to claim 10,   characterized in that it further comprises means for detecting   the state of discharge placed in the proximity of the   machining time to detect the characteristic of   charges in the range resulting from the application of the elementary pulses to the electric discharge machining interval, for the purpose of providing a control signal, and   control means placed in said proximity for modulating   with the control signal the cyclical production of   successive trains spaced in time.   Circuit device according to claim 13,   characterized in that the detection means of the state of de-   charge include clock means for setting in time the detection of the characteristic of discharges in   the interval during the final period of each train of discrete elementary drives.   Circuit device according to claim 10,   characterized in that it further comprises circuit means   bake placed in the vicinity of the machining gap to superimpose a high voltage and low intensity pulse to an elementary pulse for an initial period of time. each train.