Showing papers on "Electrical discharge machining published in 1970"

Apparatus for machining through varying-frequency constant-duration pulse-controlled electric discharges

Abstract: Apparatus used for electric discharge machining, which senses the commencement of each discharge across the gap between the electrode and workpiece and cuts off each discharge after a predetermined time interval.

Electrical discharge machining device using logical control

Abstract: An automatic electrical discharge machining device, including a logic circuit and detecting units monitoring voltages and currents at different parts of the machining device circuit. The detecting units deliver their outputs to the logic circuit, for determining the short -circuit, large gap conductance, sustained arcing, and other detrimental conditions at the discharge gap, by suitably combining the outputs from the detecting units. Automatic control is made in response to the output from the logic circuit for regulating an electrode or various voltage pulses.

Electrical discharge machining short circuit protection system of the keyed type

Abstract: A circuit for providing machining pulse off-time control responsive to gap short circuit condition and responsive to gap open circuit condition. During the aforesaid short circuit condition, machining current is reduced by increasing machining pulse off-time. However, the pulse on-time is maintained constant and is substantially the same as before the occurrence of either gap short circuit or open circuit condition.

Electrical discharge machining pulse-polarity-reversing control

Abstract: A control for an EDM machine selectively reverses polarity of the electrical energy supply to the machining electrode. The control consists of double-pole double-throw switching means connected with a polarity reversing transformer and connected such that the energy source is either connected to the electrode directly or through a polarity reversing transformer. In the normal switch position, the polarity is such that the electrode is eroded slowly. In the reverse switch position, the electrode is eroded rapidly. A diode is provided in the servocontrols to allow normal machine operation.

Electrical discharge machining process and dielectric fluid useful therein

Abstract: An electrical discharge machining process using as a dielectric fluid a composition comprising a base oil and a minor amount of a conductivity additive containing a chromium salt of an alkyl salicylic acid and an alkaline earth metal salt of a dialkyl sulfosuccinate.

Method and apparatus for cooling the workpiece and/or the cutting tools of a machining apparatus

Abstract: A method and apparatus for dissipating heat generated during the machining and processing of metals or other materials which includes directing toward the workpiece and/or cutting tool a needle-like or sharp tooth-shaped probe that is connected to a high voltage direct current potential, and electrically insulating the workpiece and cutting tool from the machine

Protective system for electrical discharge machining power supply circuit

Abstract: A circuit is provided to sense an electrical parameter of the gap to determine whether electrical discharge machining is progressing properly. A gap parameter such as gap voltage or a voltage directly related to such parameter is compared to a variable reference voltage to provide reduction or interruption of machining power pulses. A control is included which conjointly controls frequency of machining pulses and the magnitude of the variable reference voltage.

Method of electrical discharge machining

Abstract: In electrical discharge machining, material is eroded away from a workpiece by electrical discharges occurring between an electrode and the workpiece. Coolant, that will change from a liquid to a gaseous state at a temperature and pressure below the temperature and pressure around the workpiece, is introduced in its liquid state into the gap between the electrode and the workpiece at the same time electrical discharges are passed across said gap. The liquid coolant experiences a temperature increase and a pressure decrease in the gap and flashes into its gaseous state thereby increasing in volume. Such volumetric increase results in a rapid gas flow away from the gap into the area around the workpiece that removes eroded particles. The change of state from a liquid to a gas is also accompanied by a decrease in temperature of the surrounding area including the electrode and the workpiece.

Structure for and method of electro erosion machining

Abstract: A high voltage, low current electric signal is placed across the electrode and workpiece in an electro erosion machining circuit in accordance with the disclosure to provide improved machining. The high voltage, low current signal may be continuous or pulsed and if pulsed, it may be initiated by intermittent low voltage, high current electro erosion machining pulses or independent therefrom. The high voltage, low current signals, if pulsed, may also be initiated prior to, at the same time as or subsequent to the low voltage, high current electro machining pulses and may be of the same or opposite polarity. If the high voltage, low current signal is pulsed, the frequency and pulse width may be varied. A capacitor may be selectively placed across the electrode and workpiece during electro erosion machining in conjunction with the high voltage, low current signal to further improve the machining characteristics of the low voltage, high current electro erosion machining signal.

Electric discharge machining method and apparatus

Abstract: Upon electric-discharge machining a workpiece by intermittently applying pulse voltages across a gap between it and the opposed electrode, a pause time following each pulse voltage is adjusted by predetermined small incremental amounts in accordance with the voltage conditions developed across the gap.

A method of erosively shaping a master die

Abstract: A method of shaping electrodes for use in electrical discharge machining processes comprising the steps of preparing an oversize cavity in a master die member on an apparatus that provides oscillatory rotary motion to either a die member or a model electrode member used to form the cavity of the die member, providing an abrasive surface on the cavity of master die member and utilizing in conjunction with the master die an apparatus, similar to that used to form the cavity in the master die member, to abrade and form an electrode workpiece member to an electrical discharge machining electrode of the size of the model electrode member.

Spark erosion head with means for rotating and gyrating the electrode

Abstract: The electrode-carrying head of an electrodischarge machining (EDM) apparatus includes a planetary-gear arrangement for rotating the electrode about its own axis as the electrode axis is, in turn, displaced relatively to the workpiece. This system enables the use of an electrode for various machining modes and eliminates the need for tool electrodes precisely complementary to the configuration to be produced.

Device for removing material from a workpiece by means of spark erosion

Abstract: A spark erosion device including a storage capacitor which is periodically discharged across the gap between the electrode and workpiece. The improvement concerns means for limiting the duration of the arc discharge phase of the operation comprising, a source of constant current for charging the capacitor, means for disconnecting the current source from the capacitor when the gap breakdown voltage is reached, and the addition of an inductor in the capacitor discharge circuit to provide a resonant effect to limit the arc time across the gap.

The Multi-Circuit System Electric Discharge Machining Process

Abstract: Recently, the most important task in electric discharge machining is to increase of the working speed.The multi-circuit system electric discharge machining is a method of using a number of discharge circuits and corresponding number of electrodes to the circuit in order to get the working speed.But it is very difficult to control an autmatic feeding device and work of the single through hole.In this case. these electrodes are insulated electrically from each other and they are mechanically combined into one body so as to be fed by an automatic feeding device.Then it was revealed that the circuit number effciency is η=0.8 by experimental result.From this study, expect that the most effectual application of the multi-circuit system is discharge grinding machine

Method for making an electron-tube grid assembly

Abstract: A method for making an electron tube grid assembly comprises mounting in a concentric, radially spaced relationship at least one set of a plurality of thin-walled hollow cylIndrical electrode grid blanks, the blanks defining internal chambers therebetween and a central internal chamber. Then, radially aligned apertures are cut in the blanks by electrical discharge machining, whereby small particles of material are produced. The particles are flushed away from the cutting region by a continuous directed stream of fluid through each of the internal chambers and over the external surfaces at least in the cutting region.

Observations of Spark‐Erosion Damage in Copper Crystals

Abstract: The damage introduced by electrical discharge machining was investigated in low‐dislocation copper single crystals with a view toward determining the acceptability of the technique for the preparation of nearly perfect crystals. The damage was observed by anomalous x‐ray transmission, etch‐pitting, and x‐ray rocking curve halfwidths. It was concluded that with due care this technique could be used successfully, even for relatively soft crystals.

Increase of the Erosion Rate in Electric Discharge Machining by High-Speed Flow of Working Fluid

Abstract: The erosion rate in electric discharge machining is remarkably increased by letting the working fluid flow at high speed between an electrode and a work surface Flat work pieces of carbon steel are machined with a cylindrical electrode of graphite. The water-base working fluid mixed with electric-conductive powder is flashed through holes on the surface of the electrode. Use of this kind of the fluid permits not only of very high discharge current without any fear of firing but also of widening the discharge gap. The discharge current and the velocity of the working fluid are varied to 100-400A and 13-18m/s respectively. The experimental results indicate that with increasing the velocity of the working fluid at a constant discharge current the erosion rate increases finally approaching to a constant value over a critical velocity. The maximum erosion rate is shown to be proportional to the discharge current. The erosion rate with the positive polarity is about double as high as that with the negative polarity. Observation of the section of the work surface shows that increase of the erosion rate is due to perfect removal of the molton volume at the discharge point by the action of flow of Working fluid. The maximum erosion effeiciency obtained in the expericlent is 8g/kw min.

Experimental Evaluation Of The Material PropertiesFor Finite Element Analysis OfCold-Formed Steel Sections

Abstract: Experimental investigations to evaluate the mechanical properties, and the built in residual stresses of channel-shaped cold-roll-formed steel sections are reported in this paper. Tensile coupon tests were used to evaluate the mechanical properties at the flat zones and at the corner zones of the sections. Electrical resistance strain gauges with an "Electrical Discharge Machining" cutting technique was used to establish the magnitudes, and the distributions of residual stresses. Based on the experimental results, analysis models for the stress-strain relationship, the variation of the yield strength, and the residual stresses across the section have been established. The proposed material models have been incorporated within a large deformation elasto-plastic shell finite element to form a model for cold-formed steel sections. The efficiency and the accuracy of the proposed material properties models, as applied to a finite element model has been evaluated against corresponding experimental results of cold-formed steel sections subjected to axial compressive loads.

Electrical discharge machining power supply circuit with phase control for gap short circuit protection

Abstract: An EDM circuit includes a pulsed power supply periodically connected to the machining gap. The supply includes a multiphase AC power supply which includes a plurality of semiconductor controlled rectifiers, each coupled between a different phase and the gap for successive firing to provide controllable current to the gap. A control system interrupts firing of all semicontrolled rectifiers responsive to the sensing of gap short condition.

A Method of Adaptive Control of EDM

Abstract: Recently electrical discharge machining (EDM) has been used in vary wide fields, since its machining characteristics have markedly improved owing to the adoption of semiconductor switching elements. On the other hand machining techniques have become to be conplicated and to require considerable skills. For this kind of reason the tendency to start to apply adaptive control to EDM increased rapidly and Ford Motor's Company tried it first in 1967 to 1968. Mr. Fred, L, King (1) reported about this matter in detail. We also started to study on the adaptive control system of ELM several years ago, and have established the new control method by which satisfactory results have been obtained.In this paper we first report about the EDM phenomena which were investigated experimentally for the study of the adaptive control, and next introduce the new control method.

Contact resistance methods of hot machining

Abstract: Electrical contact resistance methods of workpiece heating for hot machining are described. The relative merits of three different techniques, namely cutting tool electrode, bar electrode and roller electrode are discussed. Increases in tool life when hot machining using electrical contact heating are reported and the possible industrial applications discussed.