Showing papers on "Electrical discharge machining published in 1973"

Procedures and Precautions in Machining Titanium Alloys

Abstract: Titanium alloys have unique machining properties. While the cutting forces are only slightly higher than in machining steels, there are other characteristics that make these alloys more difficult to machine than steels of equivalent hardnesses. For example, the chip-tool contact area in turning a titanium alloy is only about one-third to one-half as great as that for turning a steel. Also, the thermal conductivity of titanium alloys is about one-sixth of that of steels. This combination of a small contact area and the low thermal conductivity results in very high cutting temperatures. At a cutting speed of 100 ft. /min., the temperature developed at the cutting edge of a carbide tool is 1000oF when cutting a steel, while on the titanium alloy, the temperature reaches 1300oF. Hence, the cutting speeds on titanium alloys must be lower in order to maintain a tool-chip temperature below that which results in short tool life.

Control system and method for electric discharge machining (EDM) using a predetermined portion of each discharge pulse for monitoring

Abstract: A method of and a system for the control of an electrical discharge machining (EDM) apparatus in which a parameter representing the condition of the machining gap is detected over a predetermined checking period, the discharge is evaluated and a good or effective discharge is discriminated from a poor or unsatisfactory discharge, and the system is controlled in response to the relative rates of occurrence of the satisfactory or unsatisfactory discharges.

Process and apparatus for electro-erosion machining by electrical discharges employing variable cut-off time intervals between pulse trains and/or pulse trains of variable durations

Abstract: An electro-erosion process and apparatus for improving the rate of material removal from a workpiece and for decreasing the rate of wear of the electrode tool in an electrical discharge machining apparatus, by controlling the average value of the machining current across the machining gap between the electrode tool and the workpiece by providing cut-off time intervals between consecutive pulse trains at a frequency of at least 200 Hz, and by controllably varying at least one of the parameters of operation consisting of the number of the pulses included within a single pulse train, the duration of application of said pulses within a single pulse train, and at least the longest of the intervals of time comprised between two consecutive voltage pulses.

System for the controlling of an apparatus for the electric discharge machining etc.

Abstract: Discrete electric-discharge pulses are applied across a dielectric-swept gap between an electrode and a workpiece by triggering an ON-OFF switch between its conductive and nonconductive states in accordance with parameters of the gap so that per pulse adaptive control of the individual machining discharges is effected. An integrator responsive to the gap current, may be used to operate the switch means which may be turned on upon the detection of a pilot discharge. The number of unsatisfactory discharges is detected and, if this number exceeds a predetermined level, is used to control a gap parameter. The integrator signal may be digitalized for accumulation in a counter controlling pulse duration and other parameters.

Method for finishing rolls

Abstract: Rolling mill rolls, such as the final rolls for a sheet cold rolling operation, are machined by electrical discharges in a lathe-type machine with a roll length electrode tool. High areas of the roll shape the adjacent surface of the electrode tool, either by a mechanical or electrical wear-in operation, so that such surface substantially complements the desired final roll contour. The shaped electrode tool is subsequently used for electrical discharge machining (EDM) the roll to the level of the lowest roll portions so as to impart a very uniform matte texture to the roll surface and provide a roll with substantially perfect cross-sectional circularily. If the machining is carried out with a segmented electrode tool, the tool is preferably moved slightly from time-to-time axially of the roll during at least the final stages of the machining process. Following the machining, the roll may be used without further processing as an improved substitute for rolls textured by the conventional shot blasting technique or it may be ground to a bright polish.

Residual Stresses and Surface Effects in Electro-Discharge Machining

Abstract: Electro-discharge machined specimens were obtained from two different relaxation-circuit machines and one pulse-generator machine. Determination of residual stresses was by a bending-deflection method, involving a very sensitive technique for continuously recording the deflections due to stresses released by an electro-chemical cell. Such a method is necessary for measuring stresses in the often very thin sub-surface layers due to electro-discharge machining.

Electrical discharge machining process employing brass electrode, silicone oil dielectric, and controlled voltage pulses

Abstract: Electrical discharge machining process in which the parameters are controlled to provide higher metal removal rates than heretofore considered possible, together with maintenance of good surface integrity. Specifically, the new process makes use of a brass electrode, a silicone oil dielectric, and a pulsating voltage between the electrode and the workpiece, the pulses of the voltage having a pulse duration ranging from 4 to 200 microseconds and an on time of from 20 to 80 percent of the period of such pulses.

Gap condition detector circuit

Abstract: A device for detecting the gap condition of electric discharge machining operations and effecting retraction of the work electrode, flushing of the workpiece, and interruption of the current pulses to the electrode when a preselected current is exceeded. The device includes means for adjusting the sensitivity, as well as the time of electrode retraction. In addition, the operating current range may be selected through a group of current limiting resistors each providing an input signal and isolated from the other resistors by way of a diode matrix.

Method and apparatus for electrical discharge machining

Abstract: A method and apparatus for shaping a workpiece by electrical discharge, the workpiece being shaped by a shaping electrode by intermittently impressing a voltage pulse across a working gap formed between the workpiece and the shaping electrode. The apparatus comprises a means for efficiently controlling the duration of a discharge across the working gap according to a condition dependent upon a no-load voltage impressing period, i.e., the period of operation beginning with the impression of the voltage pulse and ending with the occurrence of a discharge, and further according to the state of the working gap detected in terms of a processing voltage mean value. When a no-load voltage impressing period is inside a given interval, the duration of a discharge is increased according to the length of the period. Alternatively, when the no-load voltage impressing period is outside the given interval, the duration of a discharge corresponding to the state of the working gap is not increased. Accordingly, operating stability is improved and electrode consumption is minimized.

Method and apparatus for positioning an electrode-tool relative to a workpiece in electrical discharge machining

Abstract: A method and apparatus for maintaining the gap spacing between the electrode-tool and the workpiece, in electrical discharge machining, at an optimum value providing maximum material removal efficiency and minimum electrode-tool wear. The machining gap is automatically and adaptively maintained at its optimum value by comparing two electrical reference magnitudes, one which varies as a function of the average value of the time delays occurring between the moment at which the machining voltage is applied across the gap and the moment at which the electrical discharge takes place, and the other which is proportional to the rate of gap short circuits, and by deriving from such comparison a reference command signal for the servo system effecting the advance of the electrode-tool relative to the workpiece.

Method of controlling electrical discharge machining

Abstract: A method of controlling electrical discharge machining in which a machining discharge is initiated and the particular geometric characteristic of the site of the discharge is ascertained by detecting at least one of the gap variables over a predetermined checking period of the discharge and evaluated with respect to a reference value. A parameter of the discharge, e.g. duration and/or current magnitude is established at a particular value preset to correspond to a particular geometric characteristic and the discharge is terminated in accordance with the regulated parameter.

Method and apparatus for controlling the feed of an electrode-tool relative to a workpiece in electrical discharge machining

Abstract: A method and apparatus for controlling the advance, or feed, of an electrode-tool relative to a workpiece in electrical discharge machining, such as to provide maximum material removal efficiency and minimum electrode-tool wear. The control of the advance, or feed, of the electrode-tool is achieved by comparing a reference magnitude of predetermined value with an achieved magnitude depending upon the machining conditions, the achieved magnitude being obtained by measuring the random time delay between the moment at which a machining voltage pulse is applied across the machining gap between the electrode-tool and the workpiece and the moment at which an electrical discharge occurs across the gap.

Study of the Electro-Erosion Phenomenon of Fe and Zn

Abstract: Single electrical discharges were produced on Fe and Zn electrodes under conditions similar to Electro-Discharge Machining (EDM). Crater morphology and surface texture were studied by means of Scanning Electron Microscopy (SEM) and a method was developed to measure the volume of metal removed per unit of applied energy. In all cases the volume of metal removed from the cathode was found to be larger than that from the anode. The efficiency of metal removal was also obtained and shown to decrease as the applied electrical energy of the discharge is increased. In addition, Energy Dispersive Spectroscopy (EDS) studies indicate that the existence of cross metal deposition from dissimilar electrodes is independent of the energy of the discharge, of the polarity, and of the electrode material (Fe or Zn). The combination of observations from SEM and EDS provided information on the mechanism of electro-erosion.

Electronic spark treating and eroding metals

Abstract: A machine used differently for various machining functions utilizing either the electronic spark erosion of metals, or electronic spark emission surface treatment of metallic material. The machine includes a novel means for monitoring and controlling the electrode position, with relation to the work piece. The machine is constructed to readily allow: various electrical component use changes; mechanical changes in axis and angularity of work head for optimum electrode positioning; electrical polarity changes together with vibratory mechanical electrode activation resulting in significant spark working activity. An electrical circuit provides resistance-capacitance for spark power generation incorporating reserve capacitance power pulsing for extra sparking capability. A machine: composed of easily maintainable modular segments allowing interchangeability by incorporation or deletion of sections. A machine providing portable adaptability for various types of work to be used completely or in sections.

A Theory and Evaluation of Tool-Electrode Shape Degeneration in Electro-Discharge Machining

Abstract: An analytical approach is presented which provides the basis of the numerical analysis method for computation of tool-electrode shape degeneration in electro-discharge machining (e.d.m.). Following earlier work, the concept of ‘relative duty’ of the electrodes is utilized, and is found to predict the type, and to a less satisfactory degree the extent, of degeneration.Further experimental work confirms that the effect of local profile curvature on the local tool/work erosion ratio is greater than that suggested by the geometrical ‘relative duty’ concept. Subsequent incorporation of the empirical results of these tests into the numerical analysis brings the predicted shape degeneration behaviour into quite close agreement with experiment.Computed electrode profiles showing degeneration at different periods of elapsed sparking time are presented, together with the experimentally observed cases for comparison.

Electrode supporting cartridge assembly for electrical discharge machining apparatus

Abstract: A cartridge assembly for supporting a plurality of substantially parallel electrodes in electrical discharge machining apparatus. The EDM apparatus includes a frame and a carriage mounted on the frame for guided movement in a vertical direction, the cartridge assembly being removably mounted on the carriage so that the electrodes extend vertically. Manually operable gripper means is provided for feeding the electrodes downwardly after each machining operation into engagement with the workpiece so as to compensate for electrode wear experienced during one or more preceding machining operations. Positive stop anti-short power means is combined with the carriage to enable retraction of the electrodes out of engagement with the workpiece into a predetermined spaced relation with the workpiece at least as great as the desired spark gap spacing between the electrodes and the workpiece during machining. The cartridge assembly includes a cartridge member provided with contact blocks connected to a supply of current and engaged with the electrodes during machining.

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

Abstract: An electric discharge machining circuit utilizing for the production of erosive current pulses, discharges delivered by electric energy accumulation means, at least a part of which consists of a capacitive type element based upon the voltage/current ratio and intended to store and return the energy, wherein the voltage provided with the inception of each discharge is higher than the voltage used to charge said element.

Electrode-feeding device for an electrical discharge machining apparatus

Abstract: A reversible servo-motor having a rotatable shaft is mounted on a base plate and an arm is fixed to the shaft to guide an electrical discharge machining electrode along a circular path to form the convex and concave surfaces of two adjacent air foils that make up the nozzles of a nozzle block of a steam turbine.

Electrical discharge machining power supply with protective system for output switch failure

Abstract: A digitally controlled multivibrator for the power supply is used to supply machining power pulses of predetermined ON and OFF time duration The pulse output from the digital multivibrator is passed through at least one intermediate drive stage to trigger an electronic output switch, which is operatively connected both to a main DC power source and the gap, to actually provide the machining power pulses thereto Responsive to a predetermined drop in drive signal being furnished to the output switch, the cut-off of the main machining power source is provided through operation of a field effector transistor switch In addition, the protective system which would cut off the output switch in its fail-short condition is inhibited for the duration of any gap short circuit condition

Servo feed control for electrical discharge machining

Abstract: A servo system for electrical discharge machining processes adapted to regulate a spark-discharge gap in electro-discharge machining The system includes a gap voltage sensing means, a reference voltage source, and an electrically operated motive means connected therebetween The gap voltage sensing means senses a scaled down voltage which is proportional to the peak gap voltage resulting from each machining pulse Sensing of the peak voltage on a per pulse basis provides more responsive control of the servo feed mechanism, thereby maintaining optimum gap spacing between an electrical discharge machining electrode and workpiece

Method for electrical discharge machining employing periodic extended pulse off time

Abstract: Electrical discharge machining is provided by generating a series of rectangular machining power pulses at a controllable on-off time duration. Provision is made for introducing extended off time duration between groups of pulses to contribute to the improvement of cutting stability. In an alternate embodiment of the invention, a single on time pulse is provided intermediate a pair of spaced pulse groups.

Electrical discharge machining power switch short circuit detection

Abstract: To detect short circuit failures of power switches in electrical discharge machining power supplies, the voltages developed across the power switches are sampled and, if any one of the sampled voltages is below a predetermined level, the delivery of power to the gap is interrupted.

Short circuit protection system for electrical discharge machining power supply apparatus

Abstract: A protection circuit which responds to gap short circuit condition to provide appropriate interruption of machining power pulses to the gap. Responsive to gap voltage drop below a predetermined level an electronic switch is used to shunt current from a drive transistor which provides an output from the pulse generator to interrupt the drive signal output during the continuation of the gap short circuit condition. The circuit includes a field effect transistor and a controlled fast charging network for a capacitor controlling triggering of the transistor.

Some further research on the breakdown mechanism in electro-discharge machining

Abstract: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.

Pulse generator and method for electrical discharge machining

Abstract: The pulse generator is operable both in the regular machining mode and in the gap capacitor mode. Included in the generator is a first multivibrator for providing a train of machining power pulses of widely variable and controllable ON-OFF time ratio or duty factor. Also included is a second pulse generator operated in phase with the first but providing pulses of a substantially limited duty factor. During finishing operation in the gap capacitor mode, the pulses from the second multivibrator only are gated to provide operation of the electronic output switch and thus the generation of the machining power pulses. Accordingly, the ON-time is operated with an upper limit during the gap capacitor operating mode.

Method of repairing spinnerettes

Abstract: A method of repairing damaged spinnerettes having a damaged area on the face thereof, comprising machining said damaged area by electrical discharge machining.