DD204059A1 - CIRCUIT ARRANGEMENT FOR GENERATING THE EXTERNAL VOLTAGE FOR ELECTROEROSION - Google Patents

Abstract

The invention relates to a circuit arrangement for generating the Zuendspannung for electrical discharge, in which the charging process electrode workpiece capacity and Zuendvorgang the spark gap electrode workpiece is made with different impedances. The Zuendgenerator consists of a dynamic sub-generator for charging the electrode workpiece capacity and a static sub-generator for the maintenance of Zuendvorganges until the onset of the power pulse. Both subgenerators can be scanned by a common signal.

Description

Title of the invention

Circuit arrangement for generating the ignition voltage for electric discharge

Application of the invention

The invention relates to a circuit arrangement for generating the ignition voltage within a pulse generator for electrical discharge machining.

Characteristic of the known technical solutions

In static erosion generators, there has been a marked trend in recent years to use higher starting voltages to increase the machining speed while reducing the voltage pulse voltage to reduce the power dissipation of the generator.

In this case, an ignition voltage pulse in the range of 100 7 to 300 7 for generating the Sntladungskanal3 between the machining electrode and the workpiece to be machined upstream of the electrical power pulse for the actual electrical discharge machining. The emergence of the discharge channel is dependent on the height and the duration of the applied voltage and the voltage increase of the ignition voltage from the impedance of the voltage and the electrode Vferkstück capacity depends on, on the one hand to obtain the shortest possible voltage increase, the impedance the voltage source be small,

On the other hand, the ignition current must not be so large that this falsifies the technological results of the power pulse or the stability of the regulation of the spark gap is reduced. For this reason, the impedance of the Z and voltage source, the electrode workpiece surface and the gap conditions, such as geometry, purging, must be adjusted, which may necessitate constant correction of the impedance values.

Object of the invention

The aim of the invention is to avoid the disadvantages of the known embodiments and to find a technical solution that reduces the voltage rise time of the ignition voltage at the spark gap with the result of achieving an increase in the machining frequency and the AbtragsIeistung.

Explanation of the essence of the invention

The arrangement according to the invention provides a solution to realize the charging process of the capacitance electrode-workpiece and the ignition process of the dot gap electrode-workpiece with different impedances. The invention is characterized by an ignition generator consisting of a dynamic sub-generator for the rapid charging of the electrode-workpiece capacity and a static partial generator for holding the charge amount until the onset of ignition and maintaining the ignition discharge until the incipient power pulse, and both partial generators be scanned by a common start signal. The starting signal is derived via an impedance measuring from the positive exceeding a Meßspannungswertes by a voltage applied to the spark gap high-resistance auxiliary voltage, the measuring voltage is substantially below the ignition voltage and the pulse end of the dynamic ignition pulse is determined by immediate negative ignition by falling below the MeSspannungswertes.

embodiment

The circuit arrangement according to the invention will be explained in more detail below using an exemplary embodiment. The accompanying drawings show:

Fig. 1 block diagram of a Zündpulsgenerators with Impedanzmeß device and dynamic and static sub-generator

Pig. 2 Pulse diagram of the possible voltage waveforms at the spark gap

FIG. 3 partial section (FIG. 1)

a dynamic subgenerator 3 b, a static subgenerator 3 a

In Fig. 1 the following functional units are shown.

- the spark gap 1

- The impedance measuring device with the auxiliary voltage sources Ug (2) and U ₂ (3), the constant current circuit 4, for the adjustable measuring current and the decoupling diode. 7

Dynamic Part Generator 5

static partial generator 6

- Power pulse generator 8, with decoupling diode. 9

The mode of action is the following. First, the operation of the impedance device will be explained.

At the end of a power pulse, the spark gap electrode-workpiece has impedance values resulting from the spark gap voltage (15 ... 30 V) and the previous pulse working current (I ... 3OO A) with the corresponding slope of plasma charge carriers of different polarities.

Depending on the external parameters such as temperature, dielectric flow rate and type, electrode and workpiece material, a recombination of the charge carriers takes place, which increases the impedance value of the spark gap. This impedance increase is determined as an increase in voltage across the working gap, whereby the remaining spark gap results in a constant measuring current I ₀ flows. If the voltage reaches a value that guarantees the ability of the spark gap electrode-workpiece to rebound, the dynamic and static sub-generators are started.

In Pig. 2, the resulting savings and electricity flows are shown. Raise the Soannung over the spark gap U _x , and the

ever

associated current waveform I ^ are the resulting in an evaluation control signals Up for correcting the spark gap and the Zündpulsstromes 1 " illustrated. The end of the preceding power pulse is marked with the time O. At this time, the recombination of the charge carriers in the previous spark gap, which is completed at time t "begins, that makes the change in the number of carriers as a resistance and thus voltage increase noticeable, which has reached the value IL at time t ^ . By changing the measuring current Iq, the time interval ("--t _{2) can be} set This time interval approximately corresponds to the hitherto usual pause between two operating pulses and is dependent on the measuring electrode current I _{Q and} the thickness of the flexible electrode workpiece O 2 U- by the supply voltage (positive plank) the start of both the dynamic and the static generator takes place If the voltage connected to the spark gap by both partial generators reaches the value U <<, the dynamic partial generator is switched off rollover switched off in the spark gap before reaching the voltage U, "because it is passed in this case, the voltage value U. negative edge, which is dispensed a corresponding stop signal in said impedance. with the start of the firing pulses (voltage U ₁ positive edge) takes place at the same time Start of a monostable multivibrator as ma Maximum time limit for the dynamic ignition pulse, after which the dynamic ignition pulse is switched off. This case occurs when the current electrode workpiece capacity of the previous spark gap is so large that for the set measuring current Iq the charging time from the voltage value U. to the voltage value U _{2 is} greater than the predetermined time of the monostable multivibrator. Under certain circumstances, this case also occurs in such a way that the contamination of the dielectric is large, or too large a discharge current flows, which connects the complete charging of the electrode-workpiece capacitance to the voltage Up in the predetermined time interval

> R h

In all three cases - positive increase at Up, negative plank at U ₁ , expiry of the maximum time limit - no start is made for the monostable multivibrator of the power pulse. This is only started when the full ignition voltage value Un. Up a rollover occurs, that is, a negative plank is present at the voltage value Up. At the same time the static partial generator is switched off with the end of the power pulse.

Claims (7)

Erfindungsaneprüohe 1 · Circuit arrangement for generating the ignition voltage for electric discharge, characterized by an ignition generator consisting of a dynamic partial generator (5) for the rapid charging of the electrode-workpiece capacity and a static partial generator (6) for holding the charge quantity until the inserter) , the ignition and Au for real attitude of the ignition discharge until the onset of power pulse, consists and both partial generators are switched by a common start signal via an impedance measuring (2; 3; 4; 7) from the positive exceeding a Meßspannungswertes by one at the spark gap applied high-impedance Hilfsspaunung is derived, the measuring voltage is substantially below the ignition voltage and the pulse end of the dynamic ignition pulse is determined at immediate ignition by negative undershooting dee Meßspannungswertes. 2. Circuit arrangement according to item 1, characterized in that the current value of the dynamic ignition pulse is determined by the voltage increase required for the maximum processing frequency from the electrode-workpiece capacitance. 3. Circuit arrangement according to item 1, characterized in that the pulse end of the dynamic ignition pulse is determined by reaching the maximum ignition open circuit voltage » 4 »circuit arrangement according to item 1 and 3, characterized in that the maximum pulse duration of the dynamic ignition pulses is predetermined by a timer · 5. Circuit arrangement according to item 1, characterized in that the current value of the static partial generator (6) is in the range of the minimum current necessary for the time-limited maintenance of an ignited discharge process. 6. Circuit arrangement according to item 1 and 5 »characterized in that the pulse end of the static ignition pulse is given at the ignition with subsequent power pulse by the end of the power pulse · 7 · Circuit arrangement according to item 1.5 and 6, characterized in that the pulse end of the static ignition pulse is infinite in the event of ignition and control signals for the feed system of the electric discharge machining system can be derived when exceeding predetermined Zündverzugsbereichen. For this 3 sheets of drawings