Showing papers on "Electrical discharge machining published in 2000"

Non-conventional machining of particle reinforced metal matrix composite

Abstract: Particle Reinforced Metal Matrix Composites (PRMMC's) have proved to be extremely difficult to machine using conventional manufacturing processes due to heavy tool wear caused by the presence of the hard reinforcement. This paper presents details and results of an investigation into the machinability of SiC particle reinforced aluminium matrix composites using non-conventional machining processes such as Electro Discharge Machining (EDM), laser cutting and Abrasive Water Jet (AWJ). The surface integrity of the composite material for these different machining processes are examined and compared. The influence of the ceramic particle reinforcement on the machining process was analysed by tests performed on samples of the non-reinforced matrix material.

A new method of optimising material removal rate using EDM with copper–tungsten electrodes

Abstract: Electrical discharge machining (EDM) is widely used in the production of dies. This paper describes an investigation into the optimisation of the process which uses the effect of carbon which has migrated from the dielectric to tungsten–copper electrodes. This work has led to the development of a two-stage EDM machining process where different EDM settings are used for the two stages of the process giving a significantly improved material removal rate for a given tool wear ratio.

Experimental investigation of effects of cutting parameters on surface roughness in the WEDM process

Abstract: The experimental study presented in this paper aims to select the most suitable cutting and offset parameter combination for the wire electrical discharge machining process in order to get the desired surface roughness value for the machined workpieces. A series of experiments have been performed on 1040 steel material of thicknesses 30, 60 and 80 mm, and on 2379 and 2738 steel materials of thicknesses 30 and 60 mm. The test specimens have been cut by using different cutting and offset parameter combinations of the “Sodick Mark XI A500 EDW” wire electrical discharge machine in the Middle East Technical University CAD/CAM/Robotics Center. The surface roughness of the testpieces has been measured by using a surface roughness measuring device. The related tables and charts have been prepared for 1040, 2379, 2738 steel materials. The tables and charts can be practically used for WEDM parameter selection for the desired workpiece surface roughness.

High-aspect-ratio WC-Co microstructure produced by the combination of LIGA and micro-EDM

Abstract: A high-aspect-ratio WC-Co (tungsten carbide super hard alloy) microstructure has been produced by a new microfabrication process which combines LIGA and micro-EDM (electro-discharge machining). The 1 mm long microstructure with gear pattern has a variation of 4 μm in the outside diameter along its length. In the process, LIGA fabricated electrodes of negative geometry are electroplated in a metal plate for use in the micro-EDM. Since the arrangement is extremely precise the serial micro-EDM processes for one workpiece can be implemented by exchanging worn electrodes for new ones via X–Y positioning between the workpiece and each electrode. In this type of machining any bulk conductor can be chosen as the material, which is to be shaped into a microstructure. WC-Co chosen in this experiment has a much larger Young's modulus and hardness than ordinary electroplated materials. The fabricated high-aspect-ratio WC-Co microstructures can have high resistance to buckling and wear when used as mechanical components or tools.

Feasibility study of rotary electrical discharge machining with ball burnishing for Al2O3/6061Al composite

Abstract: This study investigates the feasibility and optimization of a rotary EDM with ball burnishing for inspecting the machinability of Al2O3/6061Al composite using the Taguchi method. Three ZrO2 balls attached as additional components behind the electrode tool offer immediate burnishing following EDM. Three observed values (machining rate, surface roughness and improvement of surface roughness) are adopted to verify the optimization of the machining technique. In addition, six independent parameters are chosen as variables for evaluating the Taguchi method; these variables are categorized into two groups: (1) electrical parameters, i.e. peak current, pulse duration and non-load voltage; and (2) non-electrical parameters, i.e. flushing pressure of dielectric, rotational speed of electrode and residual height of hump. Experimental results indicated a feasible technique for applying rotary EDM with ball burnishing in machining the Al2O3/6061 composite. Optimization of this technique is also discussed.

Material removal by spalling during EDM of ceramics

Abstract: This paper introduces the concept of a rapid rough-machining regime for die-sink electrical discharge machining (EDM) of advanced ceramics, offering potentially high rates of material removal and improved process efficiency. Whereas the conventional material removal mechanisms of spark erosion involve melting, dissociation and evaporation, the authors have established that prolonged high-energy discharges (in this paper as arc-related discharges) promote areas of spalling in which surface layers of ceramic material are released as large flakes by thermal-shock induced fracture. This paper describes tests on sialon–TiN and SiC–TiB2 composites. No catastrophic fracture of these materials was observed under arcing conditions, clearly demonstrating their robustness. Flakes of material typically up to several hundred microns across and one hundred microns thickness were isolated from captured debris, often segmented by vertical cracking. Sectioning of the eroded work-piece revealed shallow sub-surface cracking which ran parallel to the machined surface, typically following its profile at near-constant depth and which usually limited the extent of vertical cracking to the layer of material above. Subject to optimising electrode pulsation and delivering controlled, randomly distributed high energy discharges, this regime offers the potential for a reliable and fast “fissile planing” technique in which material is removed in shallow layers.

Electrochemical spark trepanning of alumina and quartz

Abstract: Alumina and quartz (brittle, electrically non-conducting, and inert in nature) are popular materials in advanced engineering industries, but their shaping by die conventional machining processes is not possible; even ECM and EDM can't be employed to shape them because of their electrically nonconducting nature. However, an attempt has been made to find out the capabilities of a new process called electro-chemical spark machining (ECSM), in machining these electrically non-conducting, hard, brittle, and high temperature resistant materials. In this work, eccentrically rotating tools have been used. This tool configuration has made it possible to relax the limited depth constraint, and it has been possible to drill 2.35 mm deep through holes in quartz samples and 1.35 mm deep holes in alumina. Through an experimental parametric study, it was found that beyond a certain value of electrolyte temperature, the ECSM process performance starts deteriorating. SEM photographs reveal that the combined actio...

Improvement of EDM efficiency of silicon single crystal through ohmic contact

Abstract: This paper describes the improvement of the machining rate of electrical discharge machining (EDM) for silicon single crystals by reducing the contact resistance between the silicon single crystal and metal electric feeder. To decrease the resistance of the rectifying contact between a p-type silicon wafer and the metal feeder, attempts to achieve ohmic contact were made by plating the contact surface of the silicon wafer with aluminum by vacuum evaporation, followed by the diffusion process. To accomplish an ohmic contact between n-type silicon and metal, gold–antimony alloy was used in place of aluminum. The influence of polarity on the machining rate is also discussed from the viewpoint of the rectifying nature of the interface between the arc plasma and silicon single crystal.

Methods for shaping and finishing prosthetic joint components including polycrystalline diamond compacts

Abstract: A method of rough shaping a prosthetic joint component that includes a generally spherical polycrystalline diamond compact by electric discharge machining is disclosed. The discharge machining electrode roughens a polycrystalline diamond compact sphere while the electrode and the sphere are rotating about different axes. By controlling the amount of discharge current, the depth and amount of the heat affected zone can be minimized. In the case of a polycrystalline diamond compact, the heat affected zone can be kept to about 3 to 5 microns in depth and is easily removable by grinding and polishing.

Design of a fuzzy controller for the adaptive control of WEDM process

Abstract: This paper addresses the design of a fuzzy controller for the control of the wire electrical discharge machining (WEDM) process. The power consumption and short circuit ratio are chosen as control parameters. Incorporated with pulse trains analysis and experience, fuzzy rules for the control of the WEDM process are formulated. A DSP-based on-line pulse monitoring system is developed, and the fuzzy control system is implemented on a PC-486. In the developed control system, a reference power level is specified beforehand, and feed is adjusted according to the computed actual machining power. Off time is regulated automatically so that short circuit ratio will not exceed a specific value. Fine tuning of feed and pulse off-time is conducted if the variation in the average ignition delay time is too large. Experiments show that the developed control strategy results in very satisfactory transient and steady state responses as compared with a conventional control scheme.

Method and apparatus for electrical discharge machining

Abstract: An electrical discharge machining (EDM) apparatus includes a single workpiece fixture for holding a workpiece and a plurality of machining heads for machining different features into the workpiece. For example, a first machining head is arranged to machine a first feature into the workpiece, and a second machining head is arranged to machine a second feature into the workpiece. Each machining head is connected to a separate control system so as to operate independently.

An Investigation into Improving Worn Electrode Reliability in the Electrical Discharge Machining Process

Abstract: In this paper, the use of a strength-stress interference model to study electrode reliability during wear in electrical discharge machining has been reported. In order to improve the electrode reliability, the Taguchi method, which is a powerful tool for parameter design of performance characteristics is used to determine machining parameters for minimum electrode wear ratio in electrical discharge machining operations. Through this study, not only is the electrode reliability improved, but also the machining parameters that significantly affect the electrode wear ratio in electrical discharge machining oper- ations are obtained. Experimental results are provided to verify this approach. To estimate the electrode reliability, it is necessary to develop a mathematical model to analyse the mechanism of electrode wear during the electrical discharge machining pro- cess (2-4). In this paper, the use of a strength-stress inter- ference model (5) to study electrode reliability in electrical discharge machining is reported. The effect of machining time on electrode reliability can be evaluated based on this model. For reliability analysis purposes, how the machining parameters affect the electrode reliability is a very important research task (6). In order to improve electrode reliability, the Taguchi method (7-9), which is a powerful tool for parametric design of performance characteristics, is used to determine the optimal machining parameters with the minimum electrode wear ratio in electrical discharge machining operations. It is shown that the Taguchi parameter design can optimise the electrode wear ratio through the settings of machining parameters and reduce the sensitivity of the system performance to sources of variation in electrical discharge machining. In what follows, the use of a strength-stress interference model to study electrode reliability is introduced first. Then, parametric design using the Taguchi method for improving the electrode wear ratio is discussed. The experimental details when using the Taguchi method of parameter design and the strength-stress interference model are described for determining the optimal machining parameters for improving electrode reliability. The paper concludes with a summary of this study.

Formation of carbides by electro-discharge machining of alpha iron

Abstract: Fil: Cabanillas, Edgardo Domingo. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes. Departamento de Materiales; Argentina

Electric discharge machining device

Abstract: In machining, a short-circuit determination reference time stored in a parameter memory is changed by a short-circuit determination reference time changing device in response to rpm or a rotational speed of a rotating electrode, duration of a short-circuit detected between the electrodes is measured by a short-circuit duration time determining device, and a short-circuit evading operation is executed by a short-circuit back control device in a case where the duration of a short-circuit has surpassed the short-circuit determination reference time.

Fabrication of implant overdentures that are passive and biocompatible.

Abstract: Passive-fitting mesostructures and superstructures are required to be superimposed on osseointegrated endosseous implants. The tightening of an inaccurate framework to the abutments will transmit stresses to the bone-implant interface. Precision, until now, has been inconsistent and unpredictable with conventional methods of casting, soldering, and welding techniques. By machining the framework with the Spark Erosion method using electrodischarge machining, a substantial improvement in the passive seat of the prosthetic elements is achieved. Chemical reactions caused by galvanic corrosion are also important factors in the precise approach to the treatment planning of implant-supported prostheses. The application of a pure 11.8% grade 1 titanium casting system allows the restorative team to fabricate porcelain-fused-to-metal crowns and bridges, conventional fixed-removable restorations and implant prostheses in pure titanium within completely biocompatible parameters that are absolutely mercury free. This article explains why the spark erosion machining and the unique titanium casting system have a significant impact on today's implant dentistry.

Electro-discharge machining of mesoscopic parts with electroplated copper and hot-pressed silver tungsten electrodes

Abstract: Recent advances in the development of plasma etchers for silicon has brought machines to the market which are able to etch silicon with high etch rates (>5m min 1 )a t high anisotropy (taper of sidewalls 1m m and microelectromechanical systems with feature sizes <100m. In this work micromachined silicon is used as a mold for electroplating copper and for hot-pressing silver tungsten. After removing the silicon, the copper or silver-tungsten is used as an electrode for electro-discharge machining. Using these process steps nearly any conductive material can be shaped, in particular magnetic materials like amorphous metal which are difficult or impossible to machine otherwise. The fabrication of the electrodes is described as well as the influence of the electrode material on the achieved quality of the final part.

Electrode wire for wire electric discharge machining

Abstract: PROBLEM TO BE SOLVED: To provide an electrode wire for wire electric discharge machining capable of realizing a higher speed than a conventional electrode wire to reduce machining cost. SOLUTION: In this electrode wire for wire electric discharge machining in which a core member is made of copper zinc alloy containing zinc of 15 to 30 wt.%, an outer layer 3 is formed with a thickness of 6% or more of a finish outside diameter of high zinc brass having zinc concentration of 48 to 68 wt.% on a surface of the core member, and a zinc covered layer is provided with a thickness of 0.5 to 2% of a total finish outside diameter as an outermost layer 4 at its outer periphery furthermore, it is possible to realize a higher machining speed at which a workpiece is cut by 20% or more than the conventional wire when, in particular, a dielectric constant of the electrode wire calculated according to an calculation expression of electrode wire dielectric constant becomes 23% or more, preferably, it becomes 29% or more in the case of copper alloy when the core member contains zinc of 15 wt.%, and it becomes 27% or more in the case of copper alloy when the core member contains zinc of 20 wt.%, and it becomes 24% or more in the case of copper alloy when the core member contains zinc of 30 wt.%.

Current mode controlled LCC resonant converter for electrical discharge machining applications

Abstract: In this paper, a contribution to the electrical discharge machining (EDM) technology is presented. The final aim of this research is to develop small size EDM systems and determine the influence of the voltage and current of the output electrical arc on the quality and efficiency of the workpiece machining. The proposed system is a DC to DC LCC resonant converter intended to generate current controlled arc pulses at a constant frequency that erode the workpiece. The benefits of this proposal are: (1) the system has inherent protection under short circuit; (2) a simple linear controller results in a highly robust feedback control under load changes; and (3) the transistors turn-on at zero voltage is guaranteed at any load value. The output voltage is intended to be adjusted by an external system that controls the arc distance.

Electrical discharge machining of ZrO2 /TiN particulate composite

Abstract: An experimental study was conducted into the electrical discharge machining (EDM) characteristics of a zirconia based composite with 30 vol.-%of a titanium nitride dispersoid added to provide a conductive network. The material removal rates and tool wear were assessed under normal sparking and induced arcing conditions and the influences of the main machining parameters are discussed for both conditions. The apparent cost effectiveness of material removal by arcing discharges was highlighted by assessment of the specific volumetric power consumption (SVPC). Subsequent microscopic analysis of the arced surface and the debris collected during machining under induced arcing indicated the major mechanism of material removal to be a combination of three distinct fracture events: subsurface lateral cracking caused by rapid heating, vertical cracking caused by the tetragonal/monoclinic phase transformation in the zirconia matrix, and thermal shock induced fracture on rapid cooling.