FR2473362A1 - METHOD AND APPARATUS FOR ELECTRICAL MACHINING WITH MACHINING LIQUID INTERACTING BETWEEN THE TOOL AND WORKPIECE - Google Patents

Abstract

The invention relates to a machining method and apparatus in which a workpiece is immersed in a machining liquid and a tool is juxtaposed with the workpiece to define between it and the workpiece a machining interface filled with the liquid. A multiplicity of ultrasonic assemblies 3 are arranged in the tank so as to be spaced apart from one another and to surround the interface between the tool 1 and the part 2 by transmitting waves to it via the liquid d machining, and are individually excited to emit ultrasonic vibrations at a frequency between 0.05 and 10 MHz. The invention applies in particular to machining by electrical means. (CF DRAWING IN BOPI)

Description

The present invention generally relates to the

  and more particularly a method and a machining apparatus. As used herein, the term "machining" refers both to a material removal process, such as crushing, profiling, cutting, drilling or grinding, in which

  the material is removed from a room, a process of addi-

  material, such as plating, deposition or formation, in which material is removed from a machining liquid and

added to the room.

  Specifically, although not exclusively, the invention relates to a method and apparatus for electrical machining, including stages and means suitable for stabilizing

  conditions in an electrical machining interval.

  As used herein, the term "electrical machining

  that "mainly refers to electric discharge machining

  However, it is understood that the invention also applies to any other form of electrical machining, such as electrochemical machining, electrochemical machining by discharges, and electro-deposition, as well as non-electrical or traditional machining, which use a process

  removal of mechanical material or abrasion.

  In one or other of the electrical removal and addition methods, as used herein, a tool electrode is juxtaposed to a workpiece to define a minute machining gap therebetween in the presence of a

  liquid or machining medium and an electric current is passed through

  between the electrode and the workpiece through the small

  machining center filled with liquid to remove

  material from the surface of the part or add electrically to this surface. A machining current source is provided to preferably provide a high current current electrical current in the region.

  the machining interval so that the removal or addition of

  material on the surface of the part can be

  in strict accordance with the shape of the electrode-tool.

  Means are usually provided for advancing either the tool electrode or the workpiece to the other element so as to keep the machining interval substantially constant as the removal or removal is made. addition

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  of material on the surface of the piece.

  It has long been found that the electrical machining of a conductive part, that is to say machining by electric discharges, electrochemical machining or electro-deposition, portions of parts juxtaposed with an electrode, is often characterized by a non-uniform current distribution across the gap separating the surface of the electrode from the surface of the workpiece. This inhomogeneous current distribution is most often due to contamination of the machining fluid in the form of accumulation or concentration of ions, machining chips and other products of interval, along the one or the other surface of the electrodes. In addition, the non-uniform current distribution between surfaces may also be a function of magnetic effects resulting from the current flow between

the electrode and the piece.

  U.S. Patent No. 3,252,881 attracts

  attention to the fact that it is possible to displace mechani-

  ionic contaminants in an electrochemical machining gap by mechanically oscillating the electrode toward and away from the workpiece at a relatively low sonic frequency (e.g. 10 Hz or 10 kHz). A similar result is also obtained when, at the same time as the electrode is mechanically vibrated, a gaseous fluid is injected into the electrolyte or, alternatively, a supersonic vibration is applied to the electrolyte inside the electrolyte. the electrode. It has been discovered that the supersonic vibration can have a frequency between 10 kHz and 10 MHz and that it must be produced by an electronic transducer mounted within

the tubular electrode.

  It has been found that ultrasonic vibration can be used in an electrical discharge machining process and in an electroplating process to remove gap-contaminating products in these processes. For example, in an electric discharge machining, it has been found that the ultrasonic vibration serves to stabilize the machining conditions and protects the workpiece and the electrode

  damage produced by a short circuit. In the electro

  deposition, the application of an ultrasonic vibration to

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  the electrolyte tends to remove the accumulation of electrolyte bubbles so that a thin deposit layer can be obtained on the surface of the part. In these

  processes, it is conventional to impart an ultrasonic vibration

  sonic to the machining liquid by means of a trans-

ultrasonic transducer.

  When the shape of the workpiece has irregular bends or involves deep boring or notching

  and thus constitutes a two- or three-dimensional shaping-

  1a, it has been found that the interval can not be uniformly decontaminated by a transducer element if it is arranged in a manner as proposed above. Satisfactory, effective and uniform decontamination of the gap over the entire working area treated by electrical machining

  therefore a problem in conventional vibration systems

ultrasonic

  It is therefore an object of the invention to provide an improved machining method and apparatus by which the region of the machining gap can be decontaminated satisfactorily, efficiently and uniformly. Another goal of

  the invention is to provide a method and apparatus for

  improved by which the decontamination of the region of the machining surfaces having a complex shape can be

  obtained in an extremely uniform manner.

  In a first aspect, the invention provides a method in which a workpiece is immersed in a machining liquid contained in a machining vessel and a tool is juxtaposed to the workpiece in the vessel to define between it and the part a machining interface filled with the machining liquid, the method being characterized in that there is a plurality of ultrasonic assemblies in the tank in such a way that they are spaced from each other and arranged to surround the interface by being able to transmit waves to it, in that these assemblies are excited individually to obtain ultrasonic vibrations of a frequency greater than 0.05 MHz and preferably not

  less than 0.1 bEz, and less than 10 WEz and preferably not more than

  than 2 MHz, and transmits vibrations to the region of

  Interfaoe via the internal liquid machining.

  In a second aspect, the invention provides a device

  having a tank for containing a machining liquid

  swimming in which is immersed the workpiece, and a tool that can be positioned to be juxtaposed to the workpiece in the tank to define between it and the workpiece a machining interface filled with the machining liquid,

  this device comprising a multiplicity of ultrasonic assemblies

  sonic elements arranged in the tank and spaced apart from each other so as to surround the region of the machining interface by being able to transmit waves to it, each of these sets

  comprising an electromechanical transducer, and means -

  power supply to individually excite the transducers and obtain at each location of these sets of ultrasonic vibrations of a frequency between 0.05 and 10 MHz, and preferably between 0.1 and 2 MHz, and to transmit these vibrations to the region of the machining interface through the machining liquid. Despite the earlier belief that it is difficult for ultrasonic waves of greater than 0.05 MHz to produce high power vibrations in a liquid medium and not to provide significantly better machining performance, now found that when these waves are created at several places spaced apart from each other in the tank and surrounding the machining interface, these ultrasonic waves of a vibratory frequency

  greater than 0.05 MHz and preferably 0.1 MHz, but less than

  less than 10 MHz, and preferably 2 MHz, can increase the removal rate or machining rate by 20 to 50% compared to conventional ultrasonic waves of inferior frequency and also allow to increase the effective distance from the site of generation of these waves to the site of the machining interface. It has been surprisingly found that such an increase in the removal rate is achieved with power sets.

very inferior.

  According to another advantageous characteristic of the in-

  vention, each ultrasonic assembly comprises a fluid injection nozzle and can be positioned to orient this nozzle in the direction of the machining interface, the method being further characterized in that

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  forced flow of machining fluid from a source

  of liquid through each of the nozzles

  tion of the machining interface, and that the vibra-

  High frequency ultrasonic waveforms provided by each set to this forced flow of machining liquid directed to the machining interface in the vessel. The liquid source preferably comprises a distribution chamber disposed inside or outside the tank and having an inlet for receiving the machining liquid and outlets connected to the nozzles by fluid conduits, each duct being preferably in the form of a self-supporting flexible tube, for example a multi-jointed tube. AT

  the interior of the distribution chamber is preferably

  a low-frequency vibrator that can vibrate the

  machining fluid at a low frequency of 100 Hz to 50 KHz.

  As a result, the machining liquid forcing

  in the region of the machining interval vibrates at frequencies

  low frequency sonic or ultrasonic frequencies, high frequency ultrasonic vibrations being superimposed

  to these first vibrations to each ultrasonic set.

  It was found that this resulted in an increase

  noticeable speed and machining efficiency, a cooling

  increased tool life, resulting in longer tool life, the ability to machine sharper corners, and greater machining stability due to

  example, the suppression of arc discharges or short-term

  circuits. Low-frequency sonic or ultrasonic vibrations of the distribution chamber and high-frequency ultrasonic vibrations in the nozzle region can

  applied to the forced current of machining fluid, simul-

temporarily or alternatively.

  The high frequency ultrasonic vibrations applied to the forced current of machining fluid by the nozzles at each of the assemblies have their amplitude preferably modified according to the state of the machining interface. Thus, the current supply means may have a control circuit associated with the electromechanical transducers of the assemblies or control circuits each associated with each transducer for controlling the amplitude of the high frequency ultrasonic vibrations applied to the machining liquid.

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  in response to the condition of the machining interface. The interface condition can be measured in terms of voltage, current, resistance or impedance between the tool and

the room.

  Advantageously, ultrasonic assemblies are provided to surround the machining interface by fixing them to different wall portions of the vessel and orienting them in the direction of the machining interface. The electromechanical transducers of these sets can be excited by the current source, either in synchronism,

offset.

  It has also been found that it is sometimes desirable for at least one of the ultrasonic assemblies arranged to surround the interface of the machine to emit ultrasonic vibrations of a frequency different from the frequency

  ultrasonic vibrations provided by the other

  ble. Alternatively, there may be at least one auxiliary ultrasonic assembly surrounding, with the set of primary ultrasonic assemblies, the machining interface; this auxiliary assembly can emit ultrasonic vibrations of a

  frequency between 20 and 50 kHz. In this case, the

  primary varieties are adapted to emit vibrations

  ultrasonics with a frequency between 0.1 and 1.6 MHz.

  In this case, an increase in speed has been noted.

  removal of chips or machining products from

  machining face, which significantly increases the frequency of discharges in a machining operation by

electric shocks.

  The invention will be better understood on reading the

  detailed description, given below as an example

  only certain embodiments, in connection with the attached drawing in which: - Figures 1 and 2 are respectively views in

  elevation and plan, schematically illustrating a

  according to the invention in which three ultrasonic assemblies are arranged to surround the machining interface by transmitting waves through the machining liquid; FIG. 3 is a graph on which the frequency of the ultrasonic waves and on the ordinate are plotted on the abscissa.

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  the power of these waves, the graph representing how power varies with frequency; FIG. 4 is a graph on which the frequency of the ultrasonic waves is plotted on the abscissa and the average rate of material removal by machining is given on the ordinate, the graph showing an optimum range of ultrasonic frequencies with the sets of FIGS. 1 and 2; ; FIG. 5 is a graph on which the frequency of the ultrasonic waves is plotted on the abscissa and the distance between the assemblies and the machining interface which improves the machining efficiency; FIG. 6 is an elevation view in partial section schematically representing an embodiment of the invention in which several ultrasonic assemblies are arranged around the machining interface and each comprise a fluid spray nozzle, the nozzles being connected. by respective flexible tubes to a chamber

  fluid distribution arranged internally or externally

  laughter of the tank; FIG. 7 is an elevation view in partial section of an apparatus essentially of the type of FIG. 6, comprising an electric machining current supply source and circuit means for detecting the state of a interface or electrical machining interval

  and consequently control the excitation of ultra-high

  son-ic; FIG. 8 is a perspective view schematically showing a multiplicity of ultrasonic assemblies arranged to surround the machining gap by being mounted on different wall portions of the vessel; FIG. 9 is a circuit diagram showing a form of connection of the high frequency current source to the multiplicity of ultrasonic assemblies; FIG. 10 is a circuit diagram showing another form of connection of the high frequency current source to the plurality of ultrasonic assemblies; FIG. 11 is a graph on which the rate of removal by machining by electric discharges as a function of the machining depth can be compared, in the case of one embodiment of the invention, and in the case of conventional systems. ; FIG. 12 is a perspective view schematically showing a multiplicity of ultrasonic assemblies arranged in a manner similar to that of FIG. 8, but divided into a first group and a second group.

  which operate respectively at ultrasonic frequencies

  higher and lower levels; and FIG. 13 is a circuit diagram showing a power supply system for exciting assemblies

ultrasound of Figure 12.

  The principles, embodiments, and advantages of the present invention will become apparent by first examining the results of a series of experiments performed by electroerosion machining a SKD-11 cold-work-die steel piece with an electrode. cylindrical copper of

  mm diameter. Figures 1 and 2 show the electrode-

  tool 1 and workpiece 2, and several sets -

  ultrasonic, here three, respectively marked 3, 4 and 5

  and arranged to surround the interface region or inter-

  machining zone defined between the tool electrode 1 and the part 2 in the presence of a machining liquid, for example a liquid hydrocarbon or distilled water, contained in a tank not shown. The assemblies 3, 4 and 5 are arranged at equal distance D from the periphery of the zone of the machining gap and are individually oriented to direct the ultrasonic waves produced by each assembly to the region of the machining zone through the machining liquid. Each set 3, 4 and 5 includes an electromechanical transducer and these transducers are

  excited in synchronism by a current source.

  In the experiments, kerosene or paraffin was used as the machining liquid and the machining parameters were chosen to obtain a surface roughness R max of 6 microns. By varying the frequency F of the transducer vibrations and the distance D, the average removal rate (machining speed) and the maximum effective distance D max were measured until a given machining depth was obtained. , the results being shown respectively in FIGS. 4 and 5. In this case, transducers operating at frequencies below 200 kHz have

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  an output power of 20 Watts and transducers operating at frequencies between 500 and 800 kHz

  have an output power of 15 W. In addition, trans-

  The drivers operating respectively at 1.6 MHz and 2 MHz have respective output powers of 10 and 8 W. The rela-

  between the frequency and the output power of the trans-

  ductors is shown in Figure 3.

  Figures 4 and 5 show that the removal rate

  medium and the maximum effective distance D are each

  when the frequencies of vibrations or ultrasonic waves

  Sonic values are lower than given values. When these values are exceeded, the removal rate and the distance

  maximum effective D max both increase significantly.

  It should be noted particularly that the average removal rate and the maximum effective distance are both constant

  and independent of the frequency when it is inferred

  than 100 kHZ. When the frequency is between kHz and 2 MHz, especially between 300 kHz and 1 MHz, these two parameters, average removal rate and maximum effective distance D, increase significantly despite a reduction in the ultrasonic output power. The average removal rate can be multiplied by 1.5 while the distance

  maximum efficiency can be multiplied by 2.

  In general, when the vibratory frequency of the ultrasonic waves emitted by the ultrasonic assemblies surrounding the region of the machining interval is within the specified range, the machining is performed more rapidly to obtain a given surface roughness or allows to obtain a smoother surface finish with a given removal rate. In addition, the machining becomes more stable and the control

  the machining operation is easier.

  FIG. 6 shows a liquid projection system for electrical machining, in particular for machining by electric discharges according to the principles of the invention. The system comprises a housing 11 in which is elastically mounted a liquid distribution chamber 12 with a liquid inlet 12a. The outlets of the chamber 12 consist of a multiplicity of flexible but self-supporting tubes 13, 14 and 15, for example in the form of multi-jointed stainless steel tubes or of chloride tubes.

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  vinyl, connected together to dispense process fluid

  swimming arriving from the arrival 12a in these tubes. Ultrasonic assemblies 3, 4 and 5 are attached to the individual free ends of the tubes 13, 14 and 15 and are arranged in the manner described in connection with Figures 1 and 2 or in a manner to be described. each ultrasonic assembly 3, 4 and 5 comprises an electromechanical transducer 3a, 4a, 5a and a spout 3b, 4b, 5b having central openings in correspondence of each other to form a liquid spray nozzle so that each stream. distributed through the tubes 13, 14 and 15 can be projected and directed to the region of the machining gap. The transducer 3a, 4a, 5a is excited by a current source 10 to emit ultrasonic vibrations at a frequency of between 0.05 and 10 MHz, preferably between 0.1 and 2 MHz, and to apply via nozzles 3b, 4b and 5b the vibrations on each projected stream of the machining liquid

  directed to the area of the machining interval.

  The distribution chamber 12 preferably comprises other means for vibrating the machining fluid at a lower sonic or ultrasonic frequency, for example between 100 Hz and 50 KHz. These means may comprise a vibrating plate 21 supported by a rod 22 disposed inside the chamber 12 and arranged to be moved in both directions at a desired frequency by an electromagnetic system 23 excited by a current source 24. The rod is mounted resiliently on the bottom of the housing 11 by a spring 25. Two limiting pins 26 are provided in the chamber 12 to determine the position

  bottom of the vibrating plate 21.

  Because of these auxiliary vibration means, each

  liquid flow projected by each set of ultrasonic nozzle

  Sonic 3, 4 and 5, vibrates at low frequency and high frequency ultrasonic vibrations from operation

  transducers 3a, 3b, 3c are superimposed on these vibrators.

  low frequency. As a result, the chips and resulting tar in the machining interval of the EDM process are removed more easily from this gap or interface. In addition, the electrode-tool is better cooled, which ensures a longer life

  large, the machined angles are more acute and the removal rate

is increased.

  Figure 7 shows a distribution chamber 12, a housing 11 and flexible tubes 13, 14 and 15 in a form similar to Figure 6; ultrasonic assemblies 3, 4 and 5 are arranged at the individual free ends of the tubes and arranged to surround the region of the machining gap G defined by a machining electrode 1 and a workpiece 2 immersed in a liquid. machining 27 contained in a tank 28. The tool electrode 1 and the workpiece 2 are connected to a machining current source 29 which provides a series of electrical machining pulses at the same time.

  through the machining gap G filled with dielectric liquid

  to remove material from the workpiece 2. During a machining operation, the tool electrode 1 can be moved in three dimensions to form a cavity

2a in room 2.

  The high-frequency ultrasonic current source 10 is connected to the respective transducers of the ultrasonic assemblies by a parallel connection of a resistor 31 and an on-off switch 32, which in this case is actuated by an electromagnetic coil 33. A measurement resistor 34 is mounted between the tool electrode 1 and the workpiece 2 in parallel with the machining current source to detect the state of the interval in terms of the voltage measured at the resistor 34. A control circuit 35 is sensitive at the measured voltage and is designed to excite the winding

  33 when the voltage falls below a preselected threshold

  tioned. Therefore, if the machining condition is normal or satisfactory, the resistor 31 is in a circuit

  between the current source 10 and each of the ultrasonic assemblies

  Sonic 3, 4 and 5, to produce ultrasonic waves at a limited level. When the gap voltage falls below the threshold value, indicating a short-circuit condition due to clogging of the gap region by the products of the machining, the winding 33 is excited and

  closes the switch 32, thereby shunting the limit resistor

  current 31 or directly connecting the source of

  current 10 to each of the transducers of the sets 3, 4 and 5.

  The latter are then excited to produce ultra-violet waves.

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  at a maximum level and speed up interval cleaning. Although the casing 11 is shown at

  outside the tank 28, it can be arranged inside.

  In one embodiment of the invention shown in FIG. 8, six similar ultrasonic assemblies 3, 4, 5, 6, 7 and 8 are arranged to surround the region with a gap or machining interface between an electrode surface. activates it with a tool electrode 1 in the form of a

  cone, and a workpiece 2 in the form of a retentive block.

  the gullet supported by two rails in the tank 28 containing a machining liquid at a level such that the sets 3 to 8 and the region G of the machining gap are completely

  immersed. In this embodiment, one of the ultra-high

  Sonic 3 is mounted to tilt on a support arm 37 ending in a yoke, on the branches 37a and 37b of which it is fixed by a screw or a bolt 38. The upper end of the arm 37 carries a sleeve 37c supported on a base 39 in the form of a yoke and is adjustably fixed by a screw or a bolt 40. The position of the sleeve 37c on the arm 37 and, therefore, the length of the latter from its base 39 or the vertical position of the ultrasonic set

  3 can be adjusted by a pin 41. The base 39 is mounted--

  sliding on a guide rail 42 formed on an inner wall 28a of the tank 28. The position of the base 39 on the guide rail 42 and therefore, the horizontal position of the assembly 3 is adjustable via a blocking flange 43. The angular position of the assembly 3 on the branches of the end cap of the support arm 37, and thus the angular orientation of the assembly 3 in the

  The system can be adjusted by locking the bolt 38. The other ultrasonic assemblies 4, 5, 6, 7 and 8 are supported

similar on the wall portions

  side of the tank 28, although they have not been

  for the sake of clarity.

  Ultrasonic assemblies 3 to 8 comprise electromechanical transducers each comprising a piezoelectric or electrostrictive or magnetostrictive element; these elements are connected in phase with each other to the generator

  high frequency 10, as shown in FIG. 9.

  We can change the layout of the circuit, as we see

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  in FIG. 10, to mount an amplifier i0a, lob, 10c,

  d, 10e, 10f between the generator 10 and each of the transducers

in sets 3 to 8.

Example.

  A SKD-11 steel workpiece with a copper electrode as a tool and kerosene as a machining liquid are milled by EDM, while using varying numbers of ultrasonic assemblies each operating at a frequency of 0.8 MHz. The machining pulses have a pulse duration of 10 microseconds, a pulse interval of 5 microseconds, and a peak intensity of 25 A. The results are shown in the graph of Fig. 11 in which the removal rate machining (g / mm) is plotted on the ordinate and the machining depth (mm) is

  abscissa. On the graph, curve A corresponds to the

  of a single ultrasonic unit, curve B at two

  sets, and curve C to four ultrasonic sets.

  The embodiment of FIG. 12 shows the use of a first group of ultrasonic assemblies 3, 4 and 5 operating at a high ultrasonic frequency in the range of 0.1 to 1.6 MHZ and a second group of sets

  ultrasound systems 6, 7 and 8 operating at an ultrasonic frequency

  weak sonic between 20 and 50 kHz; the assemblies 3 to 5 and 6 to 8 in each group are arranged symmetrically so as to surround the machining gap defined between the tool

  1 and the piece in the tank as previously described.

  In FIG. 13, the sets 3, 4 and 5 of the first group are excited in phase with one another by a current source 100 constituted by a DC source 101, a high frequency oscillator 102 and an amplifier 103. while the sets 6, 7 and 8 of the second group are excited in phase with each other by a current source 104 comprising a DC source 105,

  a low frequency oscillator 106 and an amplifier 107.

  The present invention therefore provides an improved method and apparatus for machining, in particular by electro-erosion, parts with better machining efficiency, better

  stability and better performance.

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Claims (25)

  1. Machining method in which a workpiece is immersed in a machining liquid contained in a tank and a tool is juxtaposed to the piece in the tank to define between it and the workpiece a machining interface filled with the liquid machining, characterized in that there is a plurality of ultrasonic assemblies in the vessel such that they are spaced from each other and arranged to surround the region of the interface by transmitting waves thereto. via the machining liquid, in that these assemblies are excited individually to emit ultrasonic vibrations at a frequency of between 0.05 and 10 MHz,   and in that we transmit these vibrations to the region of the in-   terface through the machining liquid.   2. Method according to claim 1, characterized in that   that the frequency is between 0.1 and 2 MHz. -   3. The method of claim 1, wherein each of the ultrasonic assemblies comprises a nozzle and can be positioned to orient this nozzle in the direction of the machining interface, characterized in that a forced liquid flow is established. machining from the source-of   fluid through each of the nozzles in the direction of   machining face and applying ultrasonic vibration to each of the assemblies to establish a forced flow of liquid   Machining directed to the machining interface in the tank.   4. Method according to claim 3, characterized in that excites in vibration at a frequency of 0.1 to 50 kHz this forced current of machining liquid before doing so pass in the nozzle.   5. Process according to any one of the claims   1 to 4, characterized in that the state of the machining interface is measured to emit an electrical signal representing it and in that at least one parameter of the vibrations is controlled   in response to this electrical signal.   6. Method according to claim 1, characterized in that the ultrasonic assemblies are excited in phase one.   with each other by a high frequency power source.   7. Method according to claim 1, characterized in that there is at least one additional ultrasonic unit operating at a frequency between 20 kHz and 50 kHz 2473362   to transmit waves in the region of the inter-   machining face via the machining liquid.   8. Process according to claim 7, characterized in that   that several additional ultrasonic assemblies are   placed to surround the region of the machining interface. 9. Method according to claim 8, characterized in that these additional ultrasonic assemblies are excited in   phase with each other by a low frequency power source   quence independent of the high frequency power source.   Method according to claim 1, characterized in that the tool is a discharge machining tool electrode   and that the machining liquid is a dielectric liquid   cudgel. A machining apparatus having a vessel for containing a machining liquid in which the workpiece is immersed, and a tool positionable to be juxtaposed to the workpiece to define between it and the workpiece a workpiece.   machining interface filled with this machining liquid,   characterized in that it comprises a multiplicity of ultrasonic assemblies arranged in the tank and spaced one of   the other so as to surround the area of the user interface.   able to transmit waves, each of the   electromagnetic transducer, and current supply means for individually energizing said transducers and emitting at each location thereof   sets of ultrasonic vibrations at a common frequency   between 0.05 and 10 MHz, and to transmit these vibrations to the region of the machining interface via the machining fluid.   12. Apparatus according to claim 11, characterized in that the transducers and the power supply means are adapted to emit ultrasonic vibrations   at a frequency between 0.1 and 2 MHz.   13. Apparatus according to claim 11, characterized in that each ultrasonic assembly comprises a liquid injection nozzle and can be positioned to orient the latter towards the region of the machining interface and thereby form a forced liquid flow of machining from the liquid source through each of the nozzles in the direction   of the machining interface, and that each ultrasonic unit 16 2473362   sonic is adapted to apply these ultrasonic vibrations to each of the forced currents of the directed machining liquid   to the machining interface in the tank.   14. Apparatus according to claim 13, characterized in that the liquid source comprises a distribution chamber with a liquid inlet for receiving the liquid.   machining center and a multiplicity of connected outputs   to said nozzles by individual liquid conduits   duels. 15. Apparatus according to claim 14, characterized in that each individual liquid conduit comprises a flexible tube, but self-supporting, to allow to position the ultrasonic assembly associated with it to a location   predetermined with a predetermined orientation.   16. Apparatus according to claim 15, characterized in that the self-supporting flexible tube is a metal tube with multiple joints.   Apparatus according to claim 14, characterized in that the distribution chamber is adapted to be   arranged inside the tank.   18. Apparatus according to claim 14, characterized in that low frequency vibrator means are   arranged in the distribution chamber to excite   machining fluid that is there at a frequency between 0.1 and 50 kHz.   Apparatus according to claim 11 or claim   cation 13, characterized in that sensor means   know the electrical conditions at the machining interface to emit an electrical signal and that control means are responsive to this electrical signal to act on the power supply means and control at least one parameter of the ultrasonic vibrations emitted by each of the sets.   20. Apparatus according to claim 11, characterized in that each ultrasonic assembly is removably mounted on a side wall portion of the vessel by means for adjusting its vertical position, means for adjusting its horizontal position and means to allow adjustment of its angular position, each of these means being independent of others. 17 2473362   Apparatus according to claim 11, characterized   in that each set includes an electronic transducer   mechanical, each transducer being connected in phase with the others to a common high frequency generator constituting the current supply means. Apparatus according to claim 21, characterized in that the electromechanical transducer is selected from the class consisting of a piezoelectric element, a   electrostrictive element and a magnetostrictive element.   23. Apparatus according to claim 11, characterized   in that it comprises at least one additional ultrasound assembly   disposed in the vessel for transmitting waves to the region of the machining gap and that it can be energized by current supply means independent of the first current supply means for emitting ultrasonic vibrations to a frequency between and 50 kHz.   24. Apparatus according to claim 21, characterized in that several additional ultrasonic assemblies   are arranged to surround the region of the machining interface.   Apparatus according to claim 24, characterized in that the additional ultrasonic assemblies are   connected in phase with each other at the second power supply current.