DE2410666A1 - FEEDING CIRCUIT FOR ELECTRO-EROSION DEVICES - Google Patents

Description

SANTOS ANDINI ELOSEGUY BUTRQN BARACALDO / VIZCAYA / SPAIN

Feed circuit for electrical erosion devices

The present invention relates accordingly to a feed circuit for electrical discharge machines the preamble of claim 1.

In known supply circuits for electrical erosion devices, a direct current is supplied to the electrodes, which pulses of opposite polarity, which are generated with an external control circuit, are superimposed. Included the direct current component must be below the arc maintenance value, i.e. less than 30 volts, so that higher with the help of the pulses generated by the control circuit. Voltage and low power of the arc in desired Way can be kept under control.

409837/0880

It turns out, however, that such a feed circuit does not work in a satisfactory manner, which in particular is due to the fact that the voltage value of the direct current component in terms of a satisfactory Control must be made very low. It is therefore very difficult to use invariable impulses maintain a stable arc because of the changing physical conditions of the medium, i.e. dirt, impurities within the dialectic, the distance between the electrodes and the workpiece briefly occurring short circuits, temperature fluctuations, Changes in the electrode structure, differences in the material to be eroded, etc. Changes in the materials used Impulses appear necessary. This leads to uncontrollable inaccuracies in those produced by electrical discharge machining Erosions. Furthermore, graphite electrodes cannot be used as a rule, especially when cast iron is to be eroded with relatively high amounts of contamination «

Accordingly, it is an object of the present invention to provide a feed circuit for electrical discharge machines create which does not have these disadvantages mentioned above and which uses a very simple construction a small number of control elements ensures reliable erosion operation.

According to the invention, this is done in a feed circuit for electrical erosion devices of the type mentioned at the beginning achieved in that the features listed in the characterizing part of claim 1 are provided.

Within the scope of the present invention, there is the possibility that any Voltage used v / earth, so that it is guaranteed that regardless of the prevailing working conditions and the the medium used is to maintain an arc.

409837/0860

At the same time, there are extremely short pulse pauses within which by impulses of opposite polarity, which with the help of a powerful relaxation generator are generated, discharges of the electrode below a value of 0.1% occur, resulting in complete cancellation which leads the power causing the arc. At the time when the generator has no negative power supplies more, causes the voltage output by the main voltage source in the order of magnitude of 100 to 500 volts a restoration of the briefly interrupted erosion arc. In the context of the present invention can Furthermore, generators which can be produced very cheaply can be used with any power and voltage values.

In the context of the present invention, there is no reduced voltage in the area of the DC voltage power source used. On the other hand, voltage values in the order of magnitude of 1oo, 2oo, 3oo or even more volts are used, whereby the stability of the essentially unaffected or modified erosion arc is reliably maintained even if changes in the physical conditions of the medium occur. Because of attempts it was also possible to establish that at pulse frequencies in the order of magnitude of 20 kHz there are pauses between pulses greater than microseconds and longer than 1/10 at pulse frequencies on the order of 1oo to 25o kHz Microseconds are not necessary or recommended if the discharge at the electrode is desired to drop to 0.2% and small and economically manufacturable control generators are to be used. The minimum discharge at the Electrode depends on the form factors of the erosion pulses, the shortest pulse pauses, admittedly, in of the order of magnitude of the deionization time.

The very short duration of the excitation pulses can only be achieved with very powerful generators, in which a relaxation discharge of small

409837/0860

Capacitors occurs, but voltage values on the order of kilovolts are supplied. Have to Coupling or isolating transformers are used, which are provided with a closed magnetic circuit are. These transformers must have cores with very low losses and have high impulse induction.

Since such generators only have to give off energy for a very short period of time, i.e. during the actual Pulse pauses can be produced very easily and inexpensively. This also enables a controlled semiconductor element in the form of a thyristor or transistor is arranged parallel to the arc, which can be made very small because the total current flowing through this semiconductor element is in comparison is very small compared to the mean value of the erosion arc current. This controlled semiconductor element closes those in the arc occurring energy briefly during very short periods of time. This seems very beneficial to a repeal of the passive or to achieve undesired energies, which can otherwise occur by themselves within the arc. That However, the semiconductor element is not affected by the briefly occurring high energies of short circuits between the Electrode and the workpiece, because these energies in the event of a short circuit only between the electrode and the workpiece occur, wherein the outer circle formed by the semiconductor element is not bridged. In addition, this must controlled semiconductor element does not cancel the entire voltage between the electrode and the workpiece, but only Lower the voltage to a value in the order of magnitude of 12 to 15 volts, so that the arc is reliably extinguished takes place.

To ensure safe arc extinguishing for short periods of time to be able to carry out, counterpotentials, i.e. potentials of opposite polarity with an amplitude

4Q9837 / Q88Q

tude, which is slightly larger than the magnitude of the glass current voltage of the main current source. First this ensures that polarization inversion occurs between the electrode and the workpiece while at the same time, the damping pulses, which have a very high frequency, are taken into account. This can result in a lifting of the Energies of the moving ions are guaranteed by an ionic immobilization with the help of very rapid movements is caused.

The electric arc quenching

is still further improved if water is used instead of conventionally used oil or petroleum, because the same thing has a very high chemical inertness. The use of water also enables the use of higher energies than with oil and kerosene, the risk of flame formation does not occur in this case.

If water is used, it is assumed that the metal to be eroded or the one to be eroded Alloy resists the corrosive action of such an electrolyte, practically no wear at all the electrode. The best to treat within water Metals are copper, aluminum, brass, bronze, chrome-plated stainless steel, molybdenum, metallic carbides, Chrome vanadium, nickel, chrome alloy steels, etc.

As a dielectric, it is expedient to use slightly alkaline demineralized water, which is kept at a temperature of about 95 C.

With regard to the influence of the work surface

on the penetration depth it should be mentioned that with given current values and current frequencies an increase in surface area a proportional decrease in single speed for Consequence. It is therefore very useful to have one off

409837/0860

to use a large number of individual sections of the existing electrode set, resulting in very high electrical discharge machining speeds can be achieved without affecting the quality of the surface treatment. on In this way, processing can be achieved which can be achieved using known methods such as brushing, finishing, aligning, Milling and drilling are comparable because, within the scope of the present invention, very high processing speeds possible are. In the context of the present invention, the electrical erosion process can thus be very advantageous use compared to known methods.

In the context of the present invention, pulses of opposite polarity are the direct current of the Main power source superimposed. These pulses have current values which are greater than the maximum current for the erosion process, thus canceling out the supplied direct current energy takes place during each pulse pause. The peak voltage of these pulses is also greater than the DC voltage the main power source so that the polarity of the current between the electrode and the workpiece is inverted which makes it easier to extinguish the arc during breaks. This can only be done with very powerful pulse generators can be achieved, which block oscillators with, for example, vacuum valves or fast-switching semiconductor elements contain. Furthermore, capacitor discharge relaxation circuits can be used in this context those with hydrogen trodes are used. Air interrupters etc. are provided.

With regard to the frequency of the pulses and the pulse shapes used, it should be mentioned that a perfect pulse supply cannot be achieved with a single excitation circuit, and that the multiple advantages cannot be achieved with one single type and form of current pulses can be achieved.

409837/0880

The clutch transformer and the other switching elements only give optimal values within a not to wide frequency range, which does not need to be too wide. With the previously known electrodes of one-piece construction it is not possible to supply high currents and high frequencies without corresponding electrode wear at the same time and to obtain rough machining surfaces. It is therefore appropriate within the scope of the present invention, To provide feed devices which contain various pulse generators. It is therefore advantageous to if a high-frequency generator is provided, which can be set manually or automatically. In addition, should a low-frequency generator may be provided, which is designed accordingly.

The simultaneous use of two or more frequencies proves to be advantageous because it allows the machining speed is increased and the surface roughness is decreased. With the help of these two Generators, which are connected to the single direct current source, can both rough machining and Finishing can be influenced in a desired manner. With the help of the low frequencies, the rough machining can be done can be adjusted, while the finishing is influenced with the high-frequency generator.

Advantageous further developments of the invention result from the subclaims.

The invention is now to be explained and described in greater detail on the basis of exemplary embodiments, with FIG the accompanying drawing is referred to. Show it:

Fig. 1

a schematic circuit diagram. of the feed circuit, according to the invention,

409837/0 5 30

Fig. 2

a schematic circuit diagram of that shown in FIG Low frequency pulse generator,

Fig. 3

a graphic representation of the energy pulses used in the context of the present invention,

Fig. 4

a detailed representation of the feed circuit according to the invention,

Fig. 5

a schematic circuit diagram of a multiplex generator which can be used in the context of the present invention,

Fig. 6

a schematic circuit diagram of a thyristor circuit which can be used in the context of the present invention.

In the following, reference should now first be made to FIG. In which the within the scope of the present Invention occurring pulses are shown graphically. The figure shows the high-frequency pulses that occur 1, between which pulse pauses 2 occur. These pulse pauses 2 are generated with a pulse generator generated, which works if desired in the megahertz range. The pulse pauses 2 have a duration of between 1o and 1/100 microseconds. Furthermore, Jn this context low-frequency pulses 3 on which are formed by the timing circuit 1o to be described below. The in this context Occurring frequencies are in the range zv / ischen o, 2 and

409837/0860

50 kHz. In the area of the low-frequency pulses 3 relatively wide pulse pauses 4 occur, which with the help of a electronic switch - for example the thyristor 24 are generated, whereby the service factor of the feeder is changed. Fig. 3 also shows negative pulses 1 'which are caused by the difference in amplitude of the pulses compared to the DC value, which ensures faster arc extinction.

Fig. 1 shows a schematic circuit diagram of the feed circuit according to the invention. This feed circuit is provided with saturable reactances 5, with which the size of the input signal can be influenced. The magnetic These reactances 5 can be saturated with the aid of a manually or automatically adjustable input regulator 6 can be set. The output signal of the reactances 5 is fed to a rectifier unit 7, which acts as the main supply source serves. This rectifier unit 7 consists essentially of silicon rectifiers.

In the context of the present invention, a high-frequency pulse generator 8 is also provided, which is shown in Fig. 2 in detail. The duration of this High frequency pulse generator can be set with the help of a timing circuit 1o. The high frequency pulse generator 8 is connected on the output side to an isolating or coupling transformer 9, with which the pulses from the high-frequency pulse generator 8 superimposed on the direct current value of the rectifier unit 7 with opposite polarity will. Furthermore, a low-frequency pulse generator 11 is provided, which is also shown in detail in FIG is. How this low frequency pulse generator works is usually not interrupted. The output signal of the low frequency pulse generator 11 is a further Trenrf- and coupling transformer 12 supplied with which the

409837/0880

- 1ο -

Low frequency pulses from the low frequency pulse generator 11 are superimposed on the direct current value of the rectifier unit 7 with opposite polarity.

On the output side of the two transformers 9 and 12 a multiple electrode set 13 is provided, wherein the individual electrode sections are insulated from one another. The individual electrode sections are connected to separate resistors fed, whereby the short-circuit current is limited. In this way it is possible even at very high frequencies to use high currents, which is very important especially during finishing.

In parallel to the electrode set 13, a semiconductor element 14 is provided which corresponds to the pulses of the low frequency pulse generator 11 is controlled. With The help of this semiconductor element 14 is a complete cancellation of the existing energies both in electrostatic as well as achieved from an electromagnetic point of view, so that a satisfactory arc extinction comes about. the The semiconductor element 14 is controlled with the aid of a control circuit 15, which acts as a rapidly switching control element is trained. This control circuit 15 is from the low frequency pulse generator 11 controlled here.

FIG. 2 shows a schematic circuit diagram of the high-frequency pulse generator 8 shown in FIG. 1 bzv /. of the low frequency generator 11, which in corresponding Way are constructed. These generators have a rectifier circuit 16 which is used to supply energy. Output side of which the primary winding is an insulating and

STl

Coupling transformer 17 arranged, the secondary winding of which the pulses to be generated with a predetermined amplitude appear. The primary winding of the transformer 17 leads to a valve 18 which, as a high vacuum element, is the element

409837/0860

low density or air explosion. This valve 18 is controlled with the help of a control circuit 19, which turns the valve 18 on and off. In this connection, a lock oscillator can be used which Generates pulses of opposite polarity.

A detailed circuit diagram of a modified, improved embodiment of the feed circuit according to the invention is shown in FIG. This feed circuit has saturable reactances 2o with which those supplied to the arc medium energies can be measured. These saturable reactances 2o are set either manually or automatically with the aid of an input regulator 21, whereby the magnetic saturation of the reactances 2o is changed. The reactances 2o are on the output side with a Rectifier circuit 22 connected, which one made of silicon rectifiers existing bridging circle. This bridge circuit is fed, for example, via the Secondary winding of an isolating transformer, not shown.

Furthermore, a control circuit 23 is provided with which counter potentials are generated. With the help of this Control circuit 23, the conduction time of a blocking transistor 24 is influenced. The blocking transistor, which is connected to a Low frequency quenching circuit is connected, is able to the Interrupt short-circuit current if there is a metallic connection between the electrode and the workpiece. It can also be used to set the service factor will. A resistor 25 designed for low current values is provided in parallel with the thyristor 24, as a result of which a reliable operation of the blocking thyristor is maintained. In parallel with the blocking thyristor 24 and the resistor 25 is also provided with a quenching circuit 26, with which an automatic shutdown of the blocking thyristor 24 can be achieved.

A09837 / 0860

The blocking thyristor 24 is connected to a drain thyristor 27, which in response to a low frequency pulse generator 28 is controlled. The low frequency pulse generator 28 is used to increase the production speed, by increasing the surface roughness. This surface roughness is eventually caused by the influence a high-frequency generator 31 to be explained below is reduced. The low frequency pulse generator 28 is connected on the output side to an isolating and coupling transformer 29, in which a superimposition of the direct current component of the rectifier circuit 22 is made with low frequency pulses of opposite polarity.

In series with the transformer 29, a further isolating and coupling transformer 32 is provided, which with the aforementioned high frequency pulse generator 31 is connected. The interrupted functioning of this high frequency pulse generator 31 is controlled with the help of a control circuit 3o.

The transformer 32 comes with a set of electrodes 33 connected, which consists of a plurality of independent metallic sections. The individual sections of the electrode set 33 are fed via individual non-inductive separate resistors 34, whereby the short-circuit current is limited. In addition, further corresponding resistors 35 are provided, whereby the current of each electrode section of the electrode set 33 is brought to derive.

5 shows a schematic circuit diagram of an embodiment of a multiplex generator in which two different voltage values with different frequencies and different pulse durations are brought to superimposition. In this case, a three-phase power transformer is provided, its input or output voltage using an input regulator 37 can be measured or regulated. The secondary winding of the transformer 36 is with a Rectifier unit 38 connected, which is made of silicon rectifier

409837/0860

judges is built. With the help of this rectifier unit 38, voltages between 45 and 150 volts and current values up to 25o amperes can be delivered. On the output side of the rectifier unit 38, an isolating or coupling transformer 39 is provided which has a closed one Has a magnetic core made of Hipersil filaments with a thickness of 0.08 mm. This transformer 39 are of a low frequency pulse generator 4o pulses with a Frequency between 0.2 and 18 kHz and a pulse duration between 1 and 10 microseconds. This low frequency pulse generator is a relaxation oscillator in which capacitor discharges Kilovolts occur.

On the output side of the rectifier unit 38 is also a thyristor circuit 41 including the associated ones Control elements are provided with which the service factor of the low-frequency pulse generator is blocked very quickly 4ο can be controlled. At the same time, the destructive influence of short circuits can be avoided in this way on the electrodes and the workpiece can be avoided. Output side of the. Transformer 39 and the thyristor circuit 41 are a pair of terminals 42 to which the electrical discharge energies appear. In addition, a high-frequency pulse generator 43 is also provided, which in the Fre-, frequency range from 0.05 to 1 megahertz and above works, where the pulse duration is between o, o1 and 1 microsecond. A further direct current source 44 is also included A relatively low power is provided with which the influence on the erosion medium or the terminals 42 is bridged will. The generated by the high frequency pulse generator 43 High frequency pulses are transmitted to a special transformer 45 fed, which has an almost closed magnetic circuit with a narrow air gap, this Core made of a special ferrite material for high frequency Twists is made. The direct current source 44 is fed by a three-phase transformer 47, v / elcher

409837/0880

for example in the form of a variostat. The measurement of the DC power source 44 from the transformer

47 supplied voltage or its setting is carried out with the aid of a regulator 46.

In the following, reference should be made to FIG

v / earth, in which the circuit diagram of a pulse generator working on the relaxation principle is shown.

This pulse generator has a high voltage rectifier unit 48, which emits a voltage of several kilovolts. Output side of this rectifier unit 48 a variable resistor 49 is provided with which the charging time of a through the rectifier unit

48 charged capacitor 5o and thus the repetition frequency of pulses 54 can be set. The capacitor 50 has a capacitance of approximately 0.05 to 0.05 microfarads and is designed for high charging voltages and short discharge times. In series with the capacitor 5o is an insulating and coupling transformer 51 is provided, the iron core of which is provided with a thin air gap, whereby through the Direct current component of the erosion current avoided saturation will. Parallel to dem.Kondensator 5o and the primary winding of the transformer 51 in series with it a series connection of thyristors 52 arranged in cascade is provided, whereby pulse times on the order of Tenths of nanoseconds and repetition rates of more than 7o kHz can be reached. Paiä-lel to the individual Thyristors 52, balancing resistors 53 are provided, many of which occur at the individual thyristors 52 Discharge counter voltages. Very short-term high-energy occurs on the secondary winding of the transformer 51 Output pulses 54 which are opposed to the direct current part of the arc.

409837/0860

Claims (7)

25 123 claims 1.1 Supply circuit for electrical discharge machines, in which to control the arc using a direct current pulse signals can be superimposed, characterized in that at least one powerful pulse generator (8, 11) of the relaxation type is provided, from which short-duration pulses can be fed to a transformer (9, 12), whose magnetic core has a thin air gap to avoid magnetic saturation and that with the help of the transformer the direct current value and the short-term pulses with opposite polarity can be superimposed. 2. Feed circuit according to Claim 1, characterized in that that at least two pulse generators are provided with different adjustable frequencies, accordingly With the help of a low-frequency pulse generator (11) high energy and short duration of use, rough pre-machining is feasible, while with the help of a high-frequency pulse generator (8) lower energy and long processing time finishing is feasible. 3. feed circuit according to claim 1 or 2, characterized in that the caused by the superposition The pauses between the pulses are extremely short, i.e. between 1 and 2%, with the pauses at pulse frequencies up to 3o kHz no longer than a microsecond and at pulse frequencies between 5o and 3oo kHz not are longer than 1/10, but greater than 1/100 microseconds. 409837/0860 4. Feed circuit according to one of claims 1 to 3, characterized characterized in that the pulse generators (8, 11) hydrogen gas switches or thyristors (52) have, with which a discharge from to high voltage values charged small capacitors (5o) is feasible. 5. Feed circuit according to one of the preceding claims, characterized in that a semiconductor discharge element in the form of a switching transistor parallel to the erosion arc or thyristor (14) is provided, whereby the longest and shortest durations of the pauses are determined. 6. Feed circuit according to one of the preceding claims, characterized in that one with a special Ignition and extinguishing circuit (26) provided blocking thyristor (24) is provided, with which during a few microseconds a short-circuit current when a metallic connection occurs between the electrode and the workpiece can be blocked, while at the same time thereby reducing the service factor can be set by inserting very long time periods. 7. Feed circuit according to one of the preceding claims, characterized in that the electrode set (33) from a plurality of mutually insulated held electrode sections in the order of magnitude of 5o to 2oo and above and that the individual electrode sections have individual resistances of a common feed point, whereby the yield is increased by a corresponding factor, without that the finish quality of the product is affected. 409837 / 086Q Feed circuit according to one of the preceding claims, characterized in that with regard to for maximum mobility and minimal chemical and thermal inertia as the processing medium alkaline water at a temperature above 90 ° C is used. 409837 / 08SQ