Showing papers on "Electrical discharge machining published in 1992"

Electric discharge machining device

Abstract: PURPOSE:To make the whole capacity of a power source in a small size and reduce useless power loss, by providing inverters divided into one for high voltages and one for low voltage high currents, controlling the divided inverters synchronously, and applying the outputs to a machining gap in series. CONSTITUTION:AC-DC-HF-P inverters, one 51 for high voltages and one 52 for low voltage high currents, are provided and controlled synchronously, and the outputs are connected in series and applied to a machining gap 6 to start the discharge in the gap 6. After the start of discharge, sufficient machining currents are supplied from the inverter 52 for low voltage high currents. By dividing inverters into one 51 for high voltages and one 52 for low voltage high currents, the whole capacity of a power source can be made in a small size, and useless power loss can be reduced.

Electrical discharge texturing

Abstract: The paper outlines a low cost electrical discharge machining arrangement for the texturing of steel rolls used in the cold rolling of sheet steel and aluminium. The particular electrical discharge texturing (EDT) technique used affords a high degree of process control compared with more conventional methods and, therefore, optimisation of roll texture is possible through the selection of the appropriate operating variables. Sample EDT operating data are presented covering the effects of peak current and on-time relative to roll surface roughness (Ra) and peak count (Pc). Scanning electron micrographs are included of textured roll and sheet steel surfaces together with three dimensional topographical representations and a simulation of the effects of roll wear and topography transfer. Roll surface integrity data are also given which detail the structure and hardness of the white layer produced as a consequence of the EDT process.

Investigation of silicon wafering by wire EDM

Abstract: The new technology of silicon wafering by wire electrodischarge machining (EDM) was investigated to determine its mechanism of current-conducting and material removal. Target materials were n-type single-crystal silicon ingots with the resistivity of 7–15 cmΩ. It was found that the surface potential barrier of the semiconductors had a dominating effect on EDM cutting speed. Technological experiments were performed to determine the correlation between cutting speed and machining parameters. The machined surfaces were examined by scanning electron microscopy and X-ray energy dispersive spectrometer to test the surface finish and surface impurity. The results obtained show that the technique is effective for silicon wafering.

Bonding Tool and Its Fabrication

Abstract: The disclosure is directed to a bonding tool for use primarily in thermo-compression bonding of electronic circuit components and to a method of making the bonding tool. In one form of the disclosure, a holder is provided and has a substrate mounted at an end thereof. The holder is adapted to receive a heating element. A polycrystalline diamond film is disposed on the substrate, the film preferably being deposited by chemical vapor deposition. In a disclosed embodiment the substrate is a material selected from the group consisting of polycrystalline diamond, cemented tungsten carbide, silicon carbide, cubic boron nitride, and tungsten. In a further form of the disclosure, a ceramic substrate is provided which has a favorable thermal conductivity property as well as substantial electrical conductivity sufficient to permit shaping by electrical discharge machining ("EDM").

Preparation and properties of electroconductive Al2O3-based composites

Abstract: Al 2 O 3 -based composites with the addition of 20 and 30 vol.% of TiN, TiC, TiB 2 have been produced by hot pressing and by gas-pressure sintering. These electroconductive, toughened and reinforced composites proved to be suitable for the manufacture of complex shapes by electrical discharge machining. Mechanical, electrical and thermal properties have been correlated to the microstructure and to the composition. The mechanical properties of the hot-pressed samples reveal an increase in fracture toughness of 30–70% and in flexural strength of some 70% in comparison with the Al 2 O 3 matrix at room temperature. The oxidation, which takes place at the secondary phases, strongly affects the flexural strength at relatively high temperatures (≈700°C), limiting the potential operating temperature range for this type of composites.

Electrical discharge machining in dentistry.

Abstract: A brief history of electrical discharge machining (EDM) is given and the process is discussed. A description of the application of EDM for fabricating precision attachment removable partial dentures, fixed-removable implant prostheses, and titanium-ceramic crowns is presented. The advantages and disadvantages of the EDM process for the dental profession are evaluated. Although expensive, the procedure has merit.

Electrical discharge machining apparatus

Abstract: An apparatus for electrical discharge machining (EDM) is disclosed having a housing and a workpiece support assembly secured to the housing for holding a workpiece in a predetermined location. An EDM electrode is attached to the housing for performing the EDM machining. A tank assembly is also attached to the housing and movable between a machining position and a retracted position. In the machining position, the tank assembly encompasses a workpiece secured to the workpiece support area and filled with a dielectric fluid necessary for the EDM machining process. In its retracted position, the tank assembly is spaced away from the workpiece to facilitate access to the workpiece for removal of the finished workpiece and reattachment of a new workpiece in preparation for the next EDM machining operation.

Electrical discharge machine and machining method therefor

Abstract: A method and apparatus for detecting and controlling the operation of an electric discharge machine for machining a workpiece. The machining is conducted by generating pulse discharges at a machining gap formed by a machining electrode and the workpiece opposed to each other. The alternating-current components or high frequency components of at least one of the current, voltage and impedance of the machining gap, the rectified components thereof, or amplitude, frequency or other signal characteristics thereof are detected and processed for control of the machining. The processing may include frequency analysis, pulse counting, threshold detection and the like using analog and digital processing.

Prosthesis fabrication using electrical discharge machining

Abstract: Fixed-removable implant prostheses provide solutions for some of the problems associated with implant dentistry, especially in the maxilla. The technique for using electrical discharge machining to create a precise passive fit between the substructure bar and the removable suprastructure is presented. The advantages, disadvantages, and complications associated with this type of prosthesis are discussed.

Pulse train studies in EDM with controlled pulse relaxation

Abstract: Pulse train studies reveal the typical characteristics of the spark discharges associated with EDM. It has been observed that the use of reverse polarity and a powder-compact tool electrode influences the discharge phenomenon and results in an appreciable amount of deposition on the work surface. In the present investigation, electro-discharge machining has been carried out using combined pulse generation and a relaxation circuit which also enhances the tool electrode transfer and the pulse trains have been recorded using a dual-trace storage oscilloscope and an X-Y plotter.

Expanding heat source model for thermal spalling of TiB2 in electrical discharge machining

Abstract: A model is presented to explain the recently reported mechanism of thermal spalling for shaping high melting point ceramics by electrical discharge machining. Since previous models fail to explain the experimental observations completely, an expanding circular heat source created by growth of plasma is assumed to act on the surface. Erosion of materials by spalling is caused by thermally induced compressive stresses during heating-up periods and tensile stresses during cooling-down periods. This model explains material removal for anodic erosion in general (wire-cutting machines) and for cathodic erosion (die-sinking machines) whenever long pulse duration is used. Simulation of the model for TiB2 provides a local melt front that penetrates to a depth of submicrometer, then recedes as pulse duration increases. Spalling develops flakes with thickness correlated to pulse duration. The results were verified by the experimental observations which showed that large flakes having the predicted maximum thickness as well as few quenched spherical droplets containing titanium were obtained.

Wire cut electric discharge machining method

Abstract: In a wire cut electric discharge machining method, feeding units having wire electrode feeding mechanisms are provided for wire electrodes different in diameter, respectively. The feeding units are moved, one at a time, to a wire electrode feeding path by cylinders coupled detachably to thereto, respectively, whereby the wire electrodes different in diameter are automatically replaced with each other, and machining conditions are automatically selected according to the diameter of a wire electrode and a machining process which are to be used. Therefore, the workpiece can be machined with the wire electrode most suitable for the given machining configuration. Thus, the method is high in machining accuracy and in machining efficiency.

Fabrication and testing of carbon-carbon grids for ion optics

Abstract: Ion optics measuring 16.5 cm in diameter and 1.0 mm in thickness were fabricated from carbon-carbon composites that were woven from a high-tensile-modulus carbon fiber. Plate flatness varied by less than 0.05 mm. Several methods were investigated for forming ion-extraction apertures in the carbon-carbon plates, including laser machining, mechanical drilling, and conventional electric discharge machining. Tests conducted using a quartz dilatometer indicated that the coefficient of thermal expansion of the carbon-carbon plates varied between -0.51 to -1.8 x 10 exp -6/degree C at plate temperatures between 173-773 K. Sputter-erosion experiments indicate that carbon-carbon erodes at a rate approximately 25 percent below molybdenum under the same conditions. These material properties indicate that carbon-carbon may be superior to molybdenum for use as ion optics electrodes for ion engines.

Controlled apparatus for electrical discharge machining

Abstract: A controlled EDM apparatus comprises at least one electrode mounted in a base, a driver for positioning the base, a system for providing electrical energy to the electrode, a monitor for measuring the electrical discharge frequency of the electrode, and a controller responsive to the monitor for controlling either the driver or the energy providing system. The apparatus operates by measuring the electrical discharge frequency of the electrode and controlling at least the duration of machining in accordance with the frequency measured.

Electric discharge machine power supply circuit

Abstract: An electrical discharge machine equipped with a machining gap voltage application circuit having switching circuits capable of switching between a first voltage application state wherein one terminal of a first direct-current power supply is connected to an electrode and the other terminal thereof is connected to a workpiece and a first voltage is applied to the gap, a second voltage application state wherein the one terminal is connected to the workpiece and the other terminal is connected to the electrode and a second voltage is applied to the gap, and a second voltage application reset state where the second voltage is not applied to the gap. The switching circuits are operative during a first period of time when the second voltage application state and a second voltage application reset state alternate with each other, and a second period of time when the first voltage application state exists, the first and second periods are repeated in a predetermined sequence.

Dual-purpose fluid for cutting and electrical discharge machining

Abstract: A cutting and machining fluid applicable to both cutting and electrical discharge machining. This cutting and machining fluid comprises a water-soluble organic compound that shows an electrical resistivity of not less than 10,000 Ω.cm when it is contained in deionized water having an electrical resistivity of not less than 1,000,000 Ω.cm, in a concentration of from 1 to 10 % by weight, a nonionic surface active agent, or a mixture of these. The organic compound is selected from the group of ethylene glycols, propylene glycols, glycol monoethers, and polyoxyethylene fatty acid esters.

High performance electrode wire for electric discharge machining and process for preparing same

Abstract: According to this method, a layer of Zn is formed on a copper or copper-alloy wire and this wire is heat treated at a temperature less than the beta prime-beta transition temperature of the binary alloy Cu-Zn until an outer layer (31) consisting of a homogeneous beta prime phase is formed. Then, after having selectively removed the oxides present on the surface of the wire, the wire is drawn at a drawing ratio greater than 100 % in order to obtain an electrode (1) according to the invention. Electrodes for electroerosion having an outer metal layer (3) made of Cu-Zn alloy in the homogeneous beta prime ( beta ') phase and free of oxide inclusions with a junction (32) of low thickness.

Wire-cut electrical discharge machine having wire electrode cutting device

Abstract: A wire cutting mechanism for smoothly cutting a broken cutting wire of a wire electrode cutting device that positively guides the scrape position of the wire electrode to a disposal passage. The cutting mechanism has a feed mechanism positioned above a wire cutter to control the feed of the wire electrode during the cutting operation. Both the cutter and the feed mechanism are mounted on a plate that is displaceable in order to align the wire electrode feed with the disposal passage when the wire electrode has been broken and must be cut to ensure accurate feeds the cutting zone. The cutting mechanism, when positioned for cutting, feeds the broken end of the electrode wire for a predetermined time so that the wire electrode enters the disposal passage prior to cutting.

Electrical discharge machining apparatus and method

Abstract: In an electrical discharge machining apparatus, by adjusting a machining condition changing switch, machining condition changing programs are called from a memory, the machining conditions called from a machining condition group and temporarily memorized in the memory are changed according to the programs, and machining is carried out by machining means according to the machining conditions changed.

Method and apparatus for sink-type electrical discharge machining with control of pyrographite buildup

Abstract: A touch-type sensor is employed to detect the precise location of a corner of a machining electrode that may be susceptible to pyrographite buildup prior to actual machining of a workpiece. By detecting the precise location in this manner, a base or origin value can be maintained for subsequent comparison when the electrode is periodically checked for icicle formation or electrode erosion. When a deviation from the base or origin value is determined, one or more of a plurality of machining parameters, such as machining on time, wear ratio, fluid flow rate, or jumping height is modified in accordance with the amount of deviation detected. In order to further optimize the machining rate of the workpiece, the surface area of the electrode is periodically determined. The aforementioned machining parameters are varied accordingly, so that the optimum average current across the inter-electrode gap, as it relates to surface area, may be maintained. Furthermore the temperature at the surface of the machining electrode can be periodically determined. As the temperature at the surface approaches the critical temperature for pyrographite buildup and the like, the machining parameters can be modified to achieve the optimum machining rate.

Wire electrode for electro-discharge machining

Abstract: A wire electrode for electro-discharge machining made of a Cu alloy containing 38 to 50 percent by weight of Zn. The Cu alloy may also contain 0.01 to 1.0 percent by weight of Zr, 0.001 to 0.05 percent by weight in total of at least one element selected from a group of Ce, Ti, Mg, Bi and Mn, and/or 0.01 to 2.0 percent by weight of at least one element selected from a group of Al, Si, Fe, Ca and La. A method of manufacturing a wire electrode for electro-discharge machining, comprising the steps of preparing a Cu alloy material containing 38 to 50 percent by weight of Zn and thinning the Cu alloy material employing roll working and/or warm working at least in a part of working process.

Electric discharge machining gap control circuit

Abstract: PURPOSE:To prevent the disconnection of a wire electrode due to the uncertain elements such as the dispersion of the electric discharge of a working liquid and the vibration of a wire and increase the speed of electric discharge machining, by controlling the pulse width and repose time of the applied voltage pulse in correspondence to the generated electric discharge state. CONSTITUTION:An electric power source circuit consisting of dc power sources 8 and 9, transistors 10 and 11, and resistors 12 and 13 is connected between a wire electrode 15 and a workpiece 14, and the electric discharge for electric discharge machining is generated by switching the transistors 10 and 11 by two gate signals outputted by a pulse generating circuit 1 and preamplifiers 2 and 3. The first pulse between two outputted pulses of the pulse generating circuit 1 is utilized for confirming the normalcy of the electric discharge. The normal electric discharge state is detected by a comparator 5 and a differential circuit 6, and the short circuit state is detected by a comparator 4 and an AND gate 7, and the pseude between-electrode short circuit state similar to the short circuit state is detected by a counter 8 and a data comparison circuit 19. The width and repose time of the pulse voltage for electric discharge are controlled in correspondence with each state.

Method and apparatus for treating the dielectric used in electrical discharge machining

Abstract: An electrical discharge machining (EDM) apparatus having one or more dielectric tanks, each having one or more compartments, connected to an EDMing tank by pipes, defining input and output dielectric paths and having selectively placed therein pumps and control valves. The tanks are used for containing dielectric during roughing and finishing operations. Filters are used in the paths for removal of particles suspended in the dielectric. A filter loop with input and output paths containing a bidirectional filter can be used to filter and store finishing powders from a finishing dielectric and to regenerate the finishing dielectric by backwashing the filter with clean dielectric to replace the powder in the dielectric. Various combinations of inputs, discharge and filter paths may be used with various designs of dielectric tanks, having one or more compartments, in order to meet particular operational requirements. The operation of valves and filters in the disclosed invention can occur automatically, in response to the output from various detectors, positioned to identify respective system parameters.

Wire-cut electrical discharge machine having wire electrode cutting device

Abstract: A cutting mechanism for use in an electrical discharge cutting machine that has a frame mounting a wire electrode cutter, a pair of rollers to feeder the wire electrode and a sensor for detecting the presence of the wire electrode. The frame can be moved from side-to-side so that it may be positioned to feed the wire electrode to a machining zone or to a disposal box when a portion of the wire electrode is to be cut off following a breakage of the wire electrode.

Surface layer forming apparatus using electric discharge machining

Abstract: An apparatus for forming surface layers on electrodes by electric discharge machining. A machining gap, between an electrode and a workpiece is filled with a dielectric mixture containing metallic or submetallic powder. The apparatus uses a swinging mechanism to move the electrode during processing. The apparatus uses a high-voltage superposition circuit to superpose a voltage of 100-400 V across the gap. The apparatus uses a current limiting resistor of 100-300Ω to ensure that the main circuit supplies a low voltage of approximately 100 V to the machining gap. In a second embodiment, the apparatus prevents electrode cracking by dispersing the discharges throughout, and widening, the machining gap.

Spark erosion machine using electrical discharge between electrode and workpiece - has memory for storing basic machining conditions and machining condition call-up selector for selecting appts. machining conditions from memory

Abstract: The machine includes a memory (21) which stores programs to control the machining process and a selection unit (22) to acitvate the desired program. A switching unit (25) controls a machining condition-alteration function. An operating unit (26) alters the machining condition-alteration programme corresp. to the machining conditions, which are carried out in reaction to a signal from the switching unit (25). The machining is carried out by the machining control unit (27) corresp. to the machining conditions, which were altered by the operating unit (26). A further memory (24) is provided for storing the machining condition-alteration programmes. ADVANTAGE - Machining conditions simply altered for quick and stable machining without breaking wire.