Showing papers on "Electrical discharge machining published in 2002"

The use of the orthogonal array with grey relational analysis to optimize the electrical discharge machining process with multiple performance characteristics

Abstract: In this paper a new approach for the optimization of the electrical discharge machining (EDM) process with multiple performance characteristics based on the orthogonal array with the grey relational analysis has been studied. A grey relational grade obtained from the grey relational analysis is used to solve the EDM process with the multiple performance characteristics. Optimal machining parameters can then be determined by the grey relational grade as the performance index. In this study, the machining parameters, namely workpiece polarity, pulse on time, duty factor, open discharge voltage, discharge current, and dielectric fluid are optimized with considerations of multiple performance characteristics including material removal rate, surface roughness, and electrode wear ratio. Experimental results have shown that machining performance in the EDM process can be improved effectively through this approach.

Optimisation of the EDM process based on the orthogonal array with fuzzy logic and grey relational analysis method

Abstract: In this paper, the use of the grey relational analysis based on an orthogonal array and fuzzy-based Taguchi method for optimising the multi-response process is reported. Both the grey relational analysis method without using the S/N ratio and fuzzy logic analysis are used in an orthogonal array table in carrying out experiments for solving the multiple responses in the electrical discharge machining (EDM) process. Experimental results have shown that both approaches can optimise the machining parameters (pulse on time, duty factor, and discharge current) with considerations of the multiple responses (electrode wear ratio, material removal rate, and surface roughness) effectively. It seems that the grey relational analysis is more straightforward than the fuzzy-based Taguchi method for optimising the EDM process with multiple process responses.

Thermal stresses due to electrical discharge machining

Abstract: The high temperature gradients generated at the gap during electrical discharge machining (EDM) result in large localized thermal stresses in a small heat-affected zone. These thermal stresses can lead to micro-cracks, decrease in strength and fatigue life and possibly catastrophic failure. A finite element model has been developed to estimate the temperature field and thermal stresses due to Gaussian distributed heat flux of a spark during EDM. First, the developed code calculates the temperature in the workpiece and then the thermal stress field is estimated using this temperature field. The effects of various process variables (current and duty cycle) on temperature distribution and thermal stress distribution have been reported. The results of the analysis show high temperature gradient zones and the regions of large stresses where, sometimes, they exceed the material yield strength.

Batch mode micro-electro-discharge machining

Abstract: This paper describes a micro-electro-discharge machining (micro-EDM) technique that uses electrode arrays to achieve high parallelism and throughput in the machining. It explores constraints in the fabrication and usage of high aspect ratio LIGA-fabricated electrode arrays, as well as the limits imposed by the pulse discharge circuits on machining rates. An array of 400 Cu electrodes with 20 /spl mu/m diameter was used to machine perforations in 50-/spl mu/m-thick stainless steel. To increase the spatial and temporal multiplicity of discharge pulses, arrays of electrodes with lithographically fabricated interconnect and block-wise independent pulse control resistance-capacitance (RC) circuits are used, resulting in >100/spl times/ improvement in throughput compared to single electrodes. However, it was found to compromise surface smoothness. A modified pulse generation scheme that exploits the parasitic capacitance of the interconnect offers similarly high machining rates and is more amenable to integration. Stainless steel workpieces of 100 /spl mu/m thickness were machined by 100 /spl mu/m/spl times/100 /spl mu/m square cross-section electrodes using in 85 s using an 80-V power supply. Surface smoothness was unaffected by electrode multiplicity. Using electrode arrays with four circuits, batch production of 36 WC-Co gears with 300 /spl mu/m outside diameter and 70 /spl mu/m thickness in 15 min is demonstrated.

Study of precision micro-holes in borosilicate glass using micro EDM combined with micro ultrasonic vibration machining

Abstract: Because of its excellent anodic bonding property and surface integrity, borosilicate glass is usually used as the substrate for micro-electro mechanical systems (MEMS) For building the communication interface, micro-holes need to be drilled on this substrate However, a micro-hole with diameter below 200 μm is difficult to manufacture using traditional machining processes To solve this problem, a machining method that combines micro electrical-discharge machining (MEDM) and micro ultrasonic vibration machining (MUSM) is proposed herein for producing precise micro-holes with high aspect ratios in borosilicate glass In the investigations described in this paper, a circular micro-tool was produced using the MEDM process This tool was then used to drill a hole in glass using the MUSM process The experiments showed that using appropriate machining parameters; the diameter variations between the entrances and exits (DVEE) could reach a value of about 2 μm in micro-holes with diameters of about 150 μm and depths of 500 μm DVEE could be improved if an appropriate slurry concentration; ultrasonic amplitude or rotational speed was utilized In the roundness investigations, the machining tool rotation speed had a close relationship to the degree of micro-hole roundness Micro-holes with a roundness value of about 2 μm (the max radius minus the min radius) could be obtained if the appropriate rotational speed was employed

On the machining of alumina and glass

Abstract: Machining of electrically non-conducting materials like alumina and glass is still a major problem. Electrochemical spark machining (ECSM) process is a potential process for machining these materials. However, ECSM has its own inherent limitations. So far, only ordinary cutting tools have been used during ECSM by previous researchers, but the results obtained are not as good as anticipated. In the present work, electrochemical spark abrasive drilling (ECSAD) experiments have been conducted using abrasive cutting tools, with a view to enhance the capabilities of the process. Use of an abrasive cutting tool, when compared to a conventional cutting tool, has been found to improve the process performance, viz. enhanced material removal and increased machined depth. The workpiece materials used are alumina and borosilicate glass.

Development of the Cylindrical Wire Electrical Discharge Machining Process, Part 1: Concept, Design, and Material Removal Rate

Abstract: Results of applying the wire Electrical Discharge Machining (EDM) process to generate precise cylindrical forms on hard, difficult-to-machine materials are presented. The design of a precise, flexible, and corrosion-resistant underwater rotary spindle is first introduced. A detailed spindle error analysis identifies the major sources of error at different frequency spectrum. The spindle has been added to a conventional two-axis wire EDM machine to enable the generation of free-form cylindrical geometries. The mathematical model for material removal rate of the free-form cylindrical wire EDM process is derived. Experiments were conducted to explore the maximum material removal rate for cylindrical and 2D wire EDM of carbide and brass work-materials. Compared to the conventional 2D wire EDM of the same work-material, higher maximum material removal rates may be achieved in the cylindrical wire EDM, possibly due to better debris flushing condition.

Development of the Cylindrical Wire Electrical Discharge Machining Process, Part 2: Surface Integrity and Roundness

Abstract: This study investigates the surface integrity and roundness of parts created by the cylindrical wire EDM process. A mathematical model for the arithmetic average surface roughness on the ideal surface of a cylindrical wire EDM workpiece is first derived. Effects of wire feed rate and part rotational speed on the surface finish and roundness for brass and carbide work-materials at high material removal rates are investigated. The pulse on-time and wire feed rate are varied to explore the best possible surface finish and roundness achievable by the cylindrical wire EDM process. This study has demonstrated that, for carbide parts, an arithmetic average surface roughness and roundness as low as 0.68 and 1.7 mm, respectively, can be achieved. Surfaces of the cylindrical EDM parts were examined using Scanning Electron Microscopy (SEM) to identify the macro-ridges and craters on the surface. Cross-sections of the EDM parts are examined using the SEM to quantify the sub-surface recast layers and heat-affected zones under various process parameters. This study has demonstrated that the cylindrical wire EDM process parameters can be adjusted to achieve either high material removal rate or good surface integrity and roundness. [DOI: 10.1115/1.1475989]

High aspect ratio meso-scale parts enabled by wire micro-EDM

Abstract: Micro-electro discharge machining (EDM) is a subtractive meso-scale machining process. The Agie Excellence 2F wire micro EDM is capable of machining with a 25 micron diameter wire electrode and positioning the work piece to within ±1.5 microns. The over-burn gap can be controlled to within 3 microns to obtain a minimum feature radius of about 16 microns while achieving submicron surface finish and an imperceptible recast layer. For example, meso-scale gears that require vertical sidewalls and contour tolerances to within 3 microns can be wire EDMed into a variety of conductive materials. Material instabilities can affect the dimensional precision of machined meso-scale parts by material relaxation during the machining process. A study is done to investigate the machining performance of the wire micro EDM process by machining a high aspect ratio meso-scale part into a variety of metals (e.g. 304L stainless steel, Nitronic 60 Austentic Stainless, Beryllium Copper, and Titanium). Machining performance parameters such as, profile tolerance, perpendicularity, and repeatability are compared for the different materials. Pertinent inspection methods desirable for meso-scale quality assurance tasks are also evaluated. Sandia National Laboratories is developing meso-scale electro-mechanical components and has an interest in the assembly implications of piece parts fabricated by various meso-scale manufacturing processes. Although the wire EDM process is typically used to fabricate 2½ dimensional features, these features can be machined into a 3 dimensional part having other features such as hubs and chamfers to facilitate assembly.

Effect of near-surface residual stress and microstructure modification from machining on the fatigue endurance of a tool steel

Abstract: This study concerns the effect of machining on the fatigue life of an EN X155CrMoV12 tool steel (SAE J438b), with regard to the generation of near-surface residual stress and microstructural modification of the machined surface. Two possible methods for machining tool steels were compared: electro-discharge machining (EDM), a high energy density process, and milling, a more conventional cutting process. Particular attention was given to characterization of the surface roughness, microstructure, and residual stress, using a combination of microstructural analysis, crack observation, scanning electron microscopy (SEM), x-ray diffraction (XRD), and chemical composition changes by energy-dispersive x-ray. A decrease of around 35% in the fatigue limit was observed for the EDM samples, compared with the milled samples. This was attributed to a tensile residual stress state after EDM, combined with significant phase transformation and hydrogen embrittlement. The milled surfaces showed no microstructural transformation or surface cracking and contained compressive residual stresses, all of which contributed to an improved fatigue resistance.

Micro electro discharge machine with an inchworm type of micro feed mechanism

Abstract: A micro electro discharge machine with an inchworm type of micro feed mechanism has been developed. The prototype of micro electro discharge machine is comprised of a wire electro discharge grinding unit, a rotating unit of electrode, RC circuitry for micro electro discharge generation and a subsystem detecting and controlling machining process, in addition to the inchworm mechanism. In the design of the inchworm mechanism, a novel clamp mechanism with force magnifying structure is devised to increase its thrust capability and a pair of guide sleeves together with the clamps are used to decrease yawing error. The inchworm mechanism prototype has 60 mm stroke only limited by the length of the shaft, less than 2 μm yawing error and reaches to 30N output thrust force. The machining experiments carried out on the micro EDM prototype are also described. The techniques to machine micro electrode, micro holes with high aspect ratio, micro structures on stainless steel and silicon materials are discussed. Micro electrode diameter as small as 25 μm and micro holes with minimum size of less than 50 μm are obtained. And the maximum aspect ratios of micro electrodes and micro holes exceed 20 and 10 respectively.

Sensors in manufacturing

Abstract: Unit Processes in Manufacturing Needs and Roles of Monitoring Systems Principles of Sensors in Manufacturing Sensors for Machine Tools and Robots Sensors for Macro-- and Micro--geometric Features of Workpieces Sensors for Process Monitoring (Casting, Forming, Laser Processing, Electrical Discharge Machining, Coating, ...) Developments in Manufacturing and their Influence on Sensors

Study of the Batch Production of Micro Parts Using the EDM Process

Abstract: The micro machining of copper plates by the electrical discharge machining (EDM) process is described. Tungsten carbide was selected as the material for the electrode. Experiments were carried out on a conventional CNC-EDM machine to investigate machining of micro holes, and micro slots. The results show that micro holes, and micro slots can be successfully processed on a conventional CNC-EDM machine. To improve the productivity of micro parts using the EDM process, a batch production method of micro EDM using multi-electrodes has been studied. A new technique for preparing multi-electrodes has been developed. Results also show that the batch production of micro parts using EDM is feasible and that the batch production of micro parts using EDM process with multi-electrodes is very effective.

Wire electrical discharge machining of metal bond diamond wheels for ceramic grinding

Abstract: The application of cylindrical wire Electrical Discharge Machining (EDM) for profile truing of metal bond diamond wheels is presented. Instead of using the mechanical force to break the diamond and matrix in the grinding wheel, the wire EDM process uses the thermal energy or electrical sparks between the wire and rotating grinding wheel to remove the metal bond and form the wheel. The design and manufacture of a corrosion-resistant, precise spindle with the high-electrical current capability for wire EDM truing of grinding wheel is first introduced. Three truing configurations were designed to study effects of wire EDM process parameters and to investigate the level of form accuracy and corner radii achievable by the wire EDM truing of diamond wheels. Results show that the wire EDM process can efficiently generate the μm-scale precision form on the diamond wheels. The wheel, after truing, was used to grind the silicon nitride workpiece. Grinding forces and wheel wear rate were measured. In the beginning of the grinding, high wheel wear rate was identified. The subsequent wheel wear rate was considerably lower and stabilized.

Use of micro ultrasonic vibration lapping to enhance the precision of microholes drilled by micro electro-discharge machining

Abstract: In microhole machining of metal, micro electro-discharge machining (MEDM) is an effective method that can easily create a hole with a diameter under 100 μm. Due to the poor surface quality and shape of MEDM, a machining method that compounds MEDM and micro ultrasonic vibration lapping (MUVL) is proposed here to allow the production of high precision microholes with high aspect ratios. In our investigations, first, a circular or stepped circular microtool was made by the MEDM process, and the tool was used to create a microhole on a small piece of titanium plate in the same machining process. Finally, the abrasive particles driven by the same tool were utilized to grind this hole in the MUVL procedure, and a hole with a diameter about 100 μm can be obtained. Owing to the microtool and workpiece not taking apart from the clamping apparatus during different machining steps, the microhole was processed in the co-axial situation, so the precise shape and perfect surface can be obtained easily. For example, the diameter variation between the entrances and exits of the microholes could reach a value of about 5 μm when the workpiece had a thickness of 500 μm, if the circular microtools was used. Meanwhile, the roundness of the microholes clearly improved, regardless of whether circular or stepped tools were used. However, owing to the perfect grinding effect between the microholes and microtools, the stepped circular tools produced high quality surfaces more easily than the circular tools.

3D surface topography assessment of the effect of different electrolytes during electrochemical polishing of EDM surfaces

Abstract: In many countries the most common polishing practice in die making is to hand polish the part as a finishing operation after the electro discharge machining process (EDM). The usual polishing abrasives are silicon carbide paper and diamond paste of different grit sizes. However, during the last decade researchers especially in Japan and the USA have tried to combine EDM and electrochemical machining (ECM) in one machine so as to use the positive aspects of each individual process. The ECM process uses high density, typically 50 A/cm 2 , and also a pulse current with a servo-controlled electrode. These investigators have mostly used sodium nitrate solutions (of different concentrations) as the electrolyte. This paper deals with an experiment that was undertaken in order to assess the effect of four different electrolytes in an electrochemical polishing process (ECP) on the surface topography of EDM surfaces. The primary set of 3D surface parameters was used as a basis to characterise the surface produced by the combined processes in different electrolytic media.

Surface modification of Al-Zn-Mg alloy by combined electrical discharge machining with ball burnish machining

Abstract: The study investigated the feasibility of modifying the surface of Al–Zn–Mg alloy by a combined process of electric discharge machining (EDM) with ball burnish machining (BBM). A novel process that integrates EDM and BBM is also developed to conduct experiments on an electric discharge machine. Machining parameters of the combined process, including machining polarity, peak current, power supply voltage, and the protruding of ZrO2, are chosen to determine their effects on material removal rate, surface roughness and the improvement ratio of surface roughness. In addition, the extent to which the combined process affects surface modification is also evaluated by microhardness and corrosion resistance tests. Experimental results indicate that the combined process of EDM with BBM can effectively improve the surface roughness to obtain a fine-finishing and flat surface. The micropores and cracks caused from EDM are eliminated during the process as well. Furthermore, such a process can reinforce and increase the corrosion resistance of the machined surface after machining.

3D surface characterisation of electropolished EDMed surface and quantitative assessment of process variables using Taguchi Methodology

Abstract: The electro discharge machining (EDM) process produces surfaces that require some form of finishing operation This is done in order to improve the surface texture and appearance of the component’s surface However, it is also desirable to remove the white uppermost recast layer (produced by the EDM process) so as to improve the functional performance of the surface Electropolishing or electrochemical polishing (ECP) is one technique that is used mainly to improve the appearance of steels as well as for passivation of stainless steels However, this process is very complex in nature, and it is not well understood how the different process parameters influence the surface integrity of the component in salt solutions The aim of this paper is to present the results of a preliminary design of experiment of an EDM+ECP process sequence using Taguchi methodology 3D characterisation of the surfaces has been done and ANOVA technique has been used to assess the quantitative influence of the different process factors of ECP The results have shown that the direct current is the most dominant factor in modifying the surface texture, especially the Sq and Sm 3D parameters The interaction effect between current and distance between electrodes is relatively important as compared to the individual effect of the latter variable