US3893013A - Electric discharge machining circuit incorporating means for pre-ignition of the discharge channel - Google Patents

Electric discharge machining circuit incorporating means for pre-ignition of the discharge channel Download PDF

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Publication number
US3893013A
US3893013A US364640A US36464073A US3893013A US 3893013 A US3893013 A US 3893013A US 364640 A US364640 A US 364640A US 36464073 A US36464073 A US 36464073A US 3893013 A US3893013 A US 3893013A
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Prior art keywords
voltage
capacitor
pulse
ignition
circuit
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US364640A
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English (en)
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Nicolas Mironoff
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BOVARD AND CIE
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BOVARD AND CIE
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Priority claimed from CH809072A external-priority patent/CH562654A5/fr
Priority claimed from CH1542972A external-priority patent/CH582556A5/fr
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H1/00—Electrical discharge machining, i.e. removing metal with a series of rapidly recurring electrical discharges between an electrode and a workpiece in the presence of a fluid dielectric
    • B23H1/02—Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges
    • B23H1/022—Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges for shaping the discharge pulse train
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23H—WORKING OF METAL BY THE ACTION OF A HIGH CONCENTRATION OF ELECTRIC CURRENT ON A WORKPIECE USING AN ELECTRODE WHICH TAKES THE PLACE OF A TOOL; SUCH WORKING COMBINED WITH OTHER FORMS OF WORKING OF METAL
    • B23H2300/00—Power source circuits or energization
    • B23H2300/20—Relaxation circuit power supplies for supplying the machining current, e.g. capacitor or inductance energy storage circuits

Definitions

  • the present invention relates to electric discharge machining circuits (EDM) and, more particularly, to circuits based on the relaxation principle.
  • the current pulses causing material removal-hereafter called erosive or erosion pulses are generated with periodic discharge of an electric energy accumulator, such as a capacitor.
  • an electric energy accumulator such as a capacitor.
  • FIG. I is a schematic circuit diagram of a well known relaxation circuit, in which reference character C, is a capacitor, R a resistor limiting the charging current of the capacitor, L the self-inductance of the charging circuit, R and L,, the resistor and the self-inductance respectively, of the discharge circuit, U the (no load) voltage of a DC-source, E1 the electrode-tool, and p the workpiece.
  • FIGS. and 2b show voltage and current diagrams of the discharge produced by this circuit, wherein U is the charging voltage, U the breakdown voltage, and I and I the discharge and charge times respectively of the capacitor.
  • the process of ionization and deionization of the discharge channel can be schematically depicted by a curve representing the equivalent resistance of the channel.
  • a curve representing the equivalent resistance of the channel At the end of the discharge, if the latter is not followed by a new charge of the capacitor, the channel is quickly deionized and its equivalent resistance increases according to the curve R,. If, as is the case in a continuous working process, the capacitor is again recharged, the increasing voltage of this charge u, will brake the deionization of the channel, the equivalent resistance of which acquires the aspect of the curve R',
  • FIG. 3 illustrates this phenomenon.
  • the charging voltage curve u becomes u and that of the equivalent resistance of the channel R, becomes R",.. Both curves approach one another and may overlap.
  • the channel deionization then only partially occurs, the discharges follow each other irregularly, their recurrent frequency increases, and finally, the charging current of the capacitor easily transforms into a short-circuit throughout the interelectrode gap.
  • the working process is then interrupted, and the short-circuit arc damages the machined surface. Extinction of the short-circuit are by raising or retraction of the electrode-tool becomes that more difficult as the intensity of the charging current is greater.
  • the operation of a relaxation circuit is limited, on the one hand, by the ratio r /r constituting an important limitation of the working power at a relatively low level, and, on the other hand, is also limited by a high breakdown voltage U and, finally, by the discharge energy itself, because if the capacitance of the capacitor exceeds a certain limit, the intensity of the charging current, in case of a short-circuit, leads to an are, causing significant damage to the surface of the workpiece.
  • the characteristics of the erosive pulses produced by relaxation circuits are determined by the above-mentioned conditions. These pulses are characterized by a great current intensity and a very short duration of the pulse.
  • the temperature of these spots reaches a value considerably beyond the fusion point of the workpiece and electrode-tool materials. Under these conditions the removal of material practically results in vaporization thereof. There thus results significant wear of the electrode-tool and unjustified loss of energy.
  • a primary object of the present invention is to utilize current pulses generated by simple energy accumulators of the electrostatic or electromagnetic type, imparting to these pulses parameters corresponding to the best working conditions, said pulses not being associated with the limitations discussed above.
  • an electric discharge machining circuit which utilizes, for the production of erosive current pulses, discharges delivered by electrical energy accumulation means, of which at least a part consists of an element based upon the voltage/current ratio of a capacitive type, and which element is intended to store and return or discharge the energy, wherein the voltage provided with the inception of each discharge is higher than the voltage used to charge said element.
  • the discharges of an energy accumulator are not initiated by its charging voltage, but by a higher voltage. Since the breakdown voltage of a dielectric is a function of the inter-electrode gap, the charging voltage of the accumulator will not provoke its discharge; this discharge will be solely conditioned by the momentary application of a higher voltage. Thus, the charging and discharging process of the energy accumulator be comes two independent phenomena; this will be that much more pronounced as the difference between the charging voltage of the accumulator and the breakdown voltage of the gap will be greater.
  • pre-ignition voltage is obtained by an independent pulse of very low energy, not affecting the surface of lower the workpiece, nor that of the electrode-tool, but sufficient to provoke incipient ionization of the discharge channel.
  • the equivalent resistance of this channel then drops to a value allowing for the passage of the discharge current of the accumulator charged at a low voltage.
  • the high conductivity of the channel is maintained by the intensity of the pulse current.
  • the di electric liquid rigidity in the inter-electrode gap again quickly re-establishes or sets up, the low charging voltage of accumulator having less influence upon the pro cess of channel deionization.
  • the unstable discharge frequency is another cause of poor efficiency of the machining: discharges separated by too short a frequency spacing gasify the liquid in the inter-electrode gap. This prevents the hydro-dynamic effect of the discharge from occurring normally. This effect, consisting of an explosion followed by an implosion of the gaseous cavity produced by the high temperature of the channel, is indeed responsible for the ejection of melted metal out of the impact zone.
  • the discharge pre-ignition embodiment in accordance with the invention allows this setting on a large scale and insures the evenness of the ratio t /t with good precision.
  • FIG. 1 is a schematic diagram of an eIectro-erosion machining circuit of the classical relaxation type
  • FIGS. 2a, 2b and 3 are explanatory diagrams of operation of the circuit depicted in FIG. 1;
  • FIG. 4 is a schematic diagram of an electro-erosion machining circuit according to the invention.
  • FIG. 5 is an explanatory diagram of operation of the circuit of FIG. 4;
  • FIG. 6 is a schematic diagram of another embodiment of the circuit according to the invention.
  • FIG. 7 is an explanatory diagram of operation of the circuit according to FIG. 6;
  • FIG. 8 is a schematic diagram of a third embodiment of electro-erosion machining circuit according to the invention.
  • FIG. 9 is an explanatory diagram of the operation of circuit of FIG. 8.
  • a capacitor C serves as energy accumulator.
  • This capacitor is charged to a voltage U, through the ballast resistor R which regulates the charge current intensity I
  • a selfinductance L which renders the charging voltage curve of the capacitor practically linear.
  • the discharge circuit of capacitor C comprises an adjustable selfinductance L the value of which determines the duration of the pulse.
  • a diode D suppresses the negative discharge arch or portion, rendering it unipolar.
  • the pre-ignition is obtained by means of a separate DC source which charges the capacitor C,,, to a voltage U which is greater than the voltage U,,.
  • the variable resistor R' regulates the charging current intensity I'
  • the capacitor C is preceded and followed by selfinductances L, and L',,,. This cell or unit forming a delay line, of course can be followed by other identical cells: C' L",,, etc.
  • the diode D directs the high voltage pulsc U',, in the discharge circuit.
  • the equivalent resistance of the channel is very low, the current 1' is added to the discharge current of capacitor C,, and does not charge the capacitor (s) C,,,-.
  • the channel extinguishes and the equivalent resistance of the inter-electrode gap quickly increases.
  • the capacitances of the capacitor (s) C,,. and the value of the self-inductances L, determine the pause preceding the next pre-ignition discharge.
  • FIG. 5 shows the rate of voltage and current curves across the discharge gap.
  • U and U are respectively the charging voltage of the capacitor C, and the capacitor (s) C U,, and U',, represent the breakdown voltage of capacitors C,, and C, respectively; 14,, the voltage of the discharge arc;
  • the waiting time of the pre-ignition which is determined by the values of C,,, and L can be regulated. but remains invariable during the machining process.
  • the essential parameters of the erosive discharge pulse i.e. the ratio of the maximum intensity of the pulse current i and its duration r,,which determine the density of the calorific energy on the spots of the discharge-is regulated by the adjustable selfinductance L,,, the value of which determines the duration of the erosive pulse I
  • the maximum current intensity of this pulse i depends upon the capacitance of the capacitor C,, and its charging voltage U,,.
  • the various machining rates which are a function of the energy of each discharge, are either obtained by changing the capacitance of the capacitor C,, or by varying its charging voltage U.,.
  • FIG. 6 Another embodiment of the invention is schematically shown in FIG. 6.
  • the moment of pre-ignition is fixed not in terms of the waiting time, as in the previous embodiment, but in terms of the charging voltage of the capacitor C,,.
  • the charging and discharging circuits of the capacitor C are identical to those of the circuitry of FIG. 4.
  • the pre ignition is obtained as follows:
  • a low capacitance capacitor C is charged by the charging current of capacitor C,, through a potentiometer P.
  • the charging voltage of capacitor C reaches a certain value (v)
  • the unijunction transistor Tr starts to conduct and renders conductive the transistor Tr supplied with a low voltage current by means of an auxiliary source S
  • This current then flows through the primary of a. pulse transformer T,.
  • the secondary of this transformer delivers a high voltage pulse which is superimposed upon the charging voltage of capacitor C,, and pre-ignites the discharge channel.
  • the moment of pre-ignition is regulated by the potentiometer P, which allows attaining the voltage (v) of the emitter of the unijunction transistor Tr at a moment corresponding to a chosen value of the charging voltage of capacitor C,,.
  • FIG. 7 shows voltage and current diagrams across the discharge gap, according to the second embodiment of the invention.
  • the main desirability of this last embodiment is that, if the pre-ignition moment is regulated in terms of the charging voltage of the capacitor C,, then the discharge of this capacitor C,, always corresponds to a well defined value of its charging voltage, and this, regardless of the capacitance of the capacitor C,, and regardless of the intensity of the charge current I,.,,.
  • the machining power ie the discharge frequency
  • the maximum machining power at a given working rate-which is dependent upon the minimum time separating consecutive discharges can be obtained by means of a simple regulation of the intensity of the charging current. This simplifies the application of an automatic regulation device in electro-erosion machining.
  • pre-ignition pulses of a given energy the value of which can be adjustable, but is not subordinate to the variations of machining conditions such as, for instance, the changes of the machining rate.
  • the pre-ignition voltage in order to ionize a channel through which will pass the discharge current of a capacitor charged to a voltage lower than the breakdown voltage of the inter-electrode gap, the pre-ignition voltage not only must be high enough, but the pre-ignition pulses also must be of sufficient energy to open wide enough the channel of electric conductivity, and thus insure a regular sequence of the capacitor discharges at the precise moment corresponding to a determined value of its charging voltage.
  • a further object of the invention is to provide he pre-ignition of the discharge channel in terms of the :harging voltage of the capacitor, attaining this by simile means which, on the one hand, allow for easy reguating of all the pre-ignition pulse parameters, without esorting to a separate power supply, and which, on the ither hand, insure for an automatic adaptation of the nergy of these pulses to the various machining rates.
  • FIG. 8 An embodiment of the invention suitable for these lurposes is shown in FIG. 8.
  • the charging and disharging circuits of the capacitor C consist of a resistor R limiting the intenity of the charge current, if desired a self-inductance as a charging voltage smoothing means, and an adistable self-inductance L, regulating the duration of he discharge pulses.
  • the diode D eliminates the nega- .ve portion or arch of the pulses. rendering them uniolar.
  • the pre-ignition circuit consists of a transformer T, 1e primary of which is connected across the positive nd negative terminals of the capacitor C by means of n adjustable resistor R and a Zener diode DZ.
  • the :condary of the transformer T is connected to the disharge circuit by means of an adjustable resistor R and diode D
  • FIG. 9 shows the voltage and current curves across 1e discharge gap.
  • the Zener diode DZ starts to conduct.
  • the ilient feature of the Zener diode consists in a sharp se of the current I as soon as the typical Zener volt- ;e is reached.
  • the intensity of this current is regulated y the resistor R
  • the sharp rise of this current in the rimary induces in the secondary a current pulse I at voltage U,, higher than the charging voltage of capaci- Pl C
  • the intensity of this current is adjustable by means of the resistor R
  • the diode D allows to direct the additional voltage of the pre-ignition pulse which is equal to U,, U in the inter-electrode gap d.
  • the diode D separates the pre-ignition circuit from the discharge circuit during the charging time of the capacitor C.
  • the release of the current I by the Zener diode D2 occurs in an extremely short time, and the charging voltage of the capacitor C as well as the moment of its discharge are fixed, resulting in an automatic stabilization of the energy of each discharge pulse and of their frequency.
  • the bias (or slope) of the pre-ignition voltage u and accordingly, the time t,, between the moment of release of the current I by the Zener diode DZ and the start of the discharge are determined by the self-inductance of the windings of the transformer T.
  • the time 1, can be reduced to a minimum and the preignition of the discharge channel can become practically instantaneous.
  • the ratio of the charging voltage of the capacitor and the pre-ignition voltage is determined by the transformation ratio of the transformer T. Since the preignition voltage determines the breakdown gap, the variation of the number of turns of the secondary (which can be made by various taps or studs on the secondary) allows to vary the inter-electrode lateral gap in each rate of machining-this being an important technological factor in EDM.
  • the pre-ignition pulse energy is regulated by the resistors R, and R When one machining rates is switched to another, for instance from a low power rate to a higher one, the capacitance of the capacitor C and the charging current intensity I are increased. The current intensity l released by the Zener diode D2, increases then in the same proportion, which automatically increases the energy of the pre-ignition pulse.
  • the circuit thus allows to select the best parameters of the pre-ignition pulses and the energy of these pulses then automatically vary in terms of the machining rate.
  • This pre-ignition circuit works without any additional adaptation means, whatever the polarity of the discharge.
  • the setting of this polarity is obtained by means of the inverter l,,.
  • An electrical discharge machining circuit for generating and automatically applying recurrent erosive pulses across a machining gap defined by an electrode tool and a workpiece, comprising an electrical circuit incorporating:
  • electric energy accumulator means for recurrently storing electrical energy and discharging such electrical energy across said machining gap in the form of erosive current pulses via a conductive circuit
  • said electrical energy accumulator means including a capacitor coupled in parallel with the machining gap for recurrently storing electrical energy and returning said stored electrical energy to the machining gap, which capacitor has a voltage which increases and decreases correlutively with said stored electrical energy,
  • pre-ignition voltage delivering circuit means connected in circuit with said electric energy accumulator means and including voltage threshold means coupled to said capacitor and responsive to the voltage thereon, and inductive transformer means having a primary winding and a secondary winding, said primary winding being coupled to said voltage threshold means and to said capacitor for causing a current to pass through said primary winding only when said voltage of said capacitor reaches a predetermined value in relation to said voltage threshold means and said current in said primary winding causing a voltage to appear across said secondary winding.
  • diode means coupled between said machining gap and said capacitor for applying across said machining gap the higher of two voltages, the one of which is a voltage delivered only from said capacitor via said conductive circuit and fed to said gap without passing through said secondary winding as a main erosive pulse voltage. and the other of which is a voltage delivered at least from said secondary winding as a pre-ignition voltage.
  • pre-ignition voltage delivering means applies to said gap a pre-ignition, high voltage, low-current pulse of low energy defining a pre-ignition pulse, said pre-ignition voltage possessing a magnitude sufficient to pre-ignite a channel of erosive pulse, said main erosive pulse voltage being the voltage across said capacitor applied to said gap as an erosive pulse of lower voltage capable of producing a high-intensity discharge in said gap when the latter has just been preignited by said pre-ignition pulse.
  • pre-ignition voltage delivering means are arranged for causing said secondary winding to deliver a voltage in the form of a pre-ignition pulse voltage having a constant peak value, said pulse of constant peak value being added to said voltage across said capacitor for forming said pre-ignition voltage applied by said diode means as said pre-ignition pulse alternately with said main erosive pulse voltage applied in other instants as a lower-voltage high-intensity pulse.
  • the electric discharge machining circuit as defined in claim 2 including means for recharging said capacitor as a predetermined rate each time a main erosive pulse discharge ends in correlation with a deionisation in said gap occurring upon each discharge of said capacitor, when said voltage across said capacitor approaches zero, and
  • pre-ignition voltage delivering means are arranged for causing said secondary winding to deliver a voltage in the form of a short-duration pulse sufficient to pre-ignite a discharge channel in said gap, said pre-ignition pulse being obtained by causing said current to pass through said primary winding at an instant when, during a recharging of said capacitor, said voltage across said capacitor reaches a predetermined desired value, said inductive transformer means transforming a rapid increase of said current flowing through its primary into a voltage pulse on its said secondary winding, of a greater voltage than said predetermined desired value for the charging voltage of said ca pacitor.
  • transformer means comprises a step-up transformer.
  • transformer means has a transformation ratio selected to control the ratio of predetermined desired charging voltage of the capacitor and the voltage of said pre-ignition pulse.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
US364640A 1972-06-01 1973-05-29 Electric discharge machining circuit incorporating means for pre-ignition of the discharge channel Expired - Lifetime US3893013A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH809072A CH562654A5 (en) 1972-06-01 1972-06-01 Electric discharge machining cct. based on relaxation - capacitively provides higher voltage for pre-ignition of discharge channel
CH1542972A CH582556A5 (en) 1972-10-25 1972-10-25 Electric discharge machining cct. based on relaxation - capacitively provides higher voltage for pre-ignition of discharge channel

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US (1) US3893013A (enExample)
DE (1) DE2302040A1 (enExample)
ES (1) ES415470A1 (enExample)
FR (1) FR2186324B1 (enExample)
GB (1) GB1423856A (enExample)
IT (1) IT986933B (enExample)
NL (1) NL7307545A (enExample)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4114080A (en) * 1977-04-05 1978-09-12 Greenwood Quentin E Explosion simulating device
US4713516A (en) * 1984-05-11 1987-12-15 Ag Fur Industrielle Elektronik Agie Losone B. Locarno Pulse generator for spark erosive metal working
US4788399A (en) * 1984-06-29 1988-11-29 Nicolas Mironoff Electrical circuit for electro-discharge machines
US5149931A (en) * 1989-04-11 1992-09-22 Mitsubishi Denki K.K. Power source for electric discharge machining
EP0980735A3 (en) * 1998-08-19 2004-01-21 Riken Micro-discharge truing device and fine machining method using the device
US20070023399A1 (en) * 2005-08-01 2007-02-01 Ernst Buhler Method and generator for electrical discharge machining
US20100176105A1 (en) * 2007-02-28 2010-07-15 Matsushita Electric Industrial Co., Ltd. Welding output control method and arc welding equipment
US20150298231A1 (en) * 2012-11-08 2015-10-22 Smaltec International, Llc Portable micro-deburring component using micro-electrical discharge machining process

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2722629A (en) * 1946-06-28 1955-11-01 Kenneth J Germeshausen Electric system
US3247439A (en) * 1961-12-22 1966-04-19 Fastener Corp Energy supply circuit
US3289064A (en) * 1961-12-22 1966-11-29 Fastener Corp Energy supply circuit
US3417306A (en) * 1965-02-09 1968-12-17 Bendix Corp Regulated voltage capacitor discharge circuit
US3437902A (en) * 1965-12-09 1969-04-08 Fuel Res & Instr Co Firing control circuit
US3757697A (en) * 1972-02-02 1973-09-11 Bendix Corp Remotely controlled blasting machine

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2722629A (en) * 1946-06-28 1955-11-01 Kenneth J Germeshausen Electric system
US3247439A (en) * 1961-12-22 1966-04-19 Fastener Corp Energy supply circuit
US3289064A (en) * 1961-12-22 1966-11-29 Fastener Corp Energy supply circuit
US3417306A (en) * 1965-02-09 1968-12-17 Bendix Corp Regulated voltage capacitor discharge circuit
US3437902A (en) * 1965-12-09 1969-04-08 Fuel Res & Instr Co Firing control circuit
US3757697A (en) * 1972-02-02 1973-09-11 Bendix Corp Remotely controlled blasting machine

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4114080A (en) * 1977-04-05 1978-09-12 Greenwood Quentin E Explosion simulating device
US4713516A (en) * 1984-05-11 1987-12-15 Ag Fur Industrielle Elektronik Agie Losone B. Locarno Pulse generator for spark erosive metal working
US4788399A (en) * 1984-06-29 1988-11-29 Nicolas Mironoff Electrical circuit for electro-discharge machines
US5149931A (en) * 1989-04-11 1992-09-22 Mitsubishi Denki K.K. Power source for electric discharge machining
EP0980735A3 (en) * 1998-08-19 2004-01-21 Riken Micro-discharge truing device and fine machining method using the device
US20070023399A1 (en) * 2005-08-01 2007-02-01 Ernst Buhler Method and generator for electrical discharge machining
US7812277B2 (en) * 2005-08-01 2010-10-12 Agie Charmilles Sa Method and generator for electrical discharge machining
US20100176105A1 (en) * 2007-02-28 2010-07-15 Matsushita Electric Industrial Co., Ltd. Welding output control method and arc welding equipment
US8723081B2 (en) * 2007-02-28 2014-05-13 Panasonic Corporation Welding output control method and arc welding equipment
US20150298231A1 (en) * 2012-11-08 2015-10-22 Smaltec International, Llc Portable micro-deburring component using micro-electrical discharge machining process
US10556282B2 (en) * 2012-11-08 2020-02-11 Smaltec International, Llc Portable micro-deburring component using micro-electrical discharge machining process

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Publication number Publication date
FR2186324B1 (enExample) 1980-02-08
ES415470A1 (es) 1976-05-16
FR2186324A1 (enExample) 1974-01-11
IT986933B (it) 1975-01-30
NL7307545A (enExample) 1973-12-04
GB1423856A (en) 1976-02-04
DE2302040A1 (de) 1973-12-13

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