US RE28,734 E · EDM power supply for generating self-adaptive discharge pulses

Abstract

An EDM (electric-discharge machining) power supply system for generating self-adaptive discharge pulses wherein an electrode is spacedly juxtaposed with a workpiece across a discharge gap while a dielectric liquid coolant is passed therethrough. The electrode and the workpiece are relatively displaced during the machining of the latter to maintain the gap spacing generally constant via a servomechanism. According to the invention, there is applied across the electrode and the workpiece a direct-current arc-striking voltage sufficient to initiate discharge across the gap while permitting the voltage to build up thereacross to a level constituting a function of conductivity characteristic of the gap and to decay with a discharge across the gap. An analog signal is derived across the gap and represents the voltage buildup and decay thereacross. Machining current flow through the gap across the electrode and the workpiece is triggered by a digital signal derived when the analog signal exceeds a threshold value and initiation of the discharge is induced by the arc-striking voltage. A second digital condition terminates the machining current flow which is controlled by a semiconductive power switch turned on and off instantaneously in dependence upon the digital conditions. A limited current high-voltage source is connected in a closed loop circuit with the electrode, the workpiece and the gap to provide the voltage buildup across the latter, while the voltage across the gap is detected by a voltage divider or the like and the output of this voltage divider is supplied via an integrating circuit in a squaring or gating-type logic device, e.g., a Schmitt trigger capable of producing the digital output for triggering the semiconductive power switch of the machining-current power supply.

Claims50

Dependent claims

A method of machining a conductive workpiece comprising the steps of:

a. spacedly juxtaposing an electrode with said workpiece across a discharge gap while passing a dielectric liquid therethrough.
b. relatively displacing said electrode and said workpiece during the machining thereof to maintain the gap spacing generally constant;
c. applying across said electrode and said workpiece a direct current arc-striking voltage sufficient to initiate discharge across said gap while permitting said voltage to build up thereacross to a level constituting a function of conductivity characteristics of said gap and to decay with discharge across said gap;
d. deriving an analog signal representing the voltage build up and decay across said gap;
and
e. triggering a machining current flow through said gap across said electrode and said workpiece upon said signal exceeding a first threshold value and upon initiation of a discharge by said voltage, and terminating said machining current flow through said gap upon detection of a value of the analog signal declining to a second threshold value less than said first threshold value.

3 more elements

A power supply for electrical discharge machining wherein a tool electrode is spacedly juxtaposed with a workpiece constituting a counterelectrode across a machining gap flooded with a dielectric liquid coolant, said power supply comprising:

a main source of machining current including an electronically triggerable power switch connected in series with said electrodes and said gap;
an auxiliary source of arc-striking voltage connected in a closed-loop arrangement with said gap for building up a voltage thereacross;
sensing means including a voltage-dividing resistor having a pair of output terminals connected across said gap for producing an output indicative of the breakdown conditions of said gap;
means including an integrating network having a capacitor bridged across said output terminals for forming an analog signal from said output related to the gap conditions;
and
threshold gating means including a Schmitt trigger responsive to said analog signal for establishing a first digital state and a second digital state, said threshold gating circuit being connected to said power switch for substantially instantaneously rendering same conductive and terminating conductivity of said power switch upon the occurrence of said digital states respectively, said Schmitt trigger having an input transistor with a base connected to said capacitor, and means establishing two threshold values for said Schmitt trigger effective to produce an output signal upon the voltage across said capacitor exceeding one of said threshold values and terminating said output signal upon the voltage across said capacitor attaining a second threshold value less than the first threshold value, the output signal of said Schmitt trigger being applied to said power switch for rendering same conductive.

3 more elements

a main source of machining current including an electronically triggerable power switch connected in series with said electrodes and said gap;
an auxiliary source of arc-striking voltage connected in a closed-loop arrangement with said gap for building up a voltage thereacross;
sensing means connected across said gap for producing an output indicative of the breakdown conditions of said gap;
means forming an analog signal from said output related to the gap conditions;
threshold gating means responsive to said analog signal for establishing a first digital state and a second digital state, said threshold gating circuit being connected to said power switch for substantially instantaneously rendering same conductive and terminating conductivity of said power switch upon the occurrence of said digital states respectively, said means forming said analog signal from said output including an integrating network connected between said sensing means and said threshold gating means, said sensing means including a voltage divider connected between said electrodes across said gap and having output terminals connected to said integrating network, said integrating network including at least one capacitor in circuit with said output terminals and chargeable at a rate controlled by a potential appearing across said output terminals, said threshold gating means including a Schmitt trigger circuit having an input connected to said capacitor and means establishing two threshold values for said Schmitt trigger circuit effective to produce an output signal upon the voltage across said capacitor exceeding one of said threshold values and terminating said output signal upon the voltage across said capacitor attaining the second threshold value, the output signal of said Schmitt trigger circuit being applied to said power switch for rendering the same conductive;
and
a timer for connecting sequentially successive portions of said voltage divider in circuit with said capacitor for adjusting the charging and discharging rate of said capacitor during the electrical discharge machining process.

4 more elements

A power supply for electrical discharge machinining wherein a tool electrode is spacedly juxtaposed with a workpiece constituting a counterelectrode across a machining gap flooded with a dielectric liquid coolant, said power supply comprising:

a main source of machining current including an electronically triggerable power switch connected in series with said electrodes and said gap;
an auxiliary source of arc-striking voltage connected in a closed-loop arrangement with said gap for building up a voltage thereacross;
sensing means connected across said gap for producing an output indicative of the breakdown conditions of said gap;
means forming an analog signal from said output related to the gap conditions;
and
threshold gating means responsive to said analog signal for establishing a first digital state and a second digital state, said threshold gating circuit being connected to said power switch for substantially instantaneously rendering same conductive and terminating conductivity of said power switch upon the occurrence of said digital states respectively, said means forming said analog signal from said output including an integrating network connected between said sensing means and said threshold gating means, said sensing means including a voltage divider connected between said electrodes across said gap and having output terminals connected to said integrating network, said integrating network including at least one capacitor in circuit with said output terminals and chargeable at a rate controlled by a potential appearing across said output terminals, said threshold gating means including a Schmitt trigger circuit having an input connected to said capacitor and means establishing two threshold values for said Schmitt trigger circuit effective to produce an output signal upon the voltage across said capacitor exceeding one of said threshold values and terminating said output signal upon the voltage across said capacitor attaining the second threshold values, the output signal of said Schmitt trigger circuit being applied to said power switch for rendering same conductive, said Schmitt trigger circuit including a first transistor connected to said capacitor and a second transistor connected to said first transistor and producing said output signal of the Schmitt trigger circuit, said means establishing said threshold values including at least one variable resistor connected in circuit with at least one of said transistors, said capacitor being a variable condenser.

3 more elements

Dependencies are inferred from the claim text.

EDM power supply for generating self-adaptive discharge pulses

Life of this patent

EDM power supply for generating self-adaptive discharge pulses

Life of this patent

Abstract

Claims50