Showing papers on "Electrical discharge machining published in 2004"

State of the art in wire electrical discharge machining (wedm)

Abstract: Wire electrical discharge machining (WEDM) is a specialised thermal machining process capable of accurately machining parts with varying hardness or complex shapes, which have sharp edges that are very difficult to be machined by the main stream machining processes. This practical technology of the WEDM process is based on the conventional EDM sparking phenomenon utilising the widely accepted non-contact technique of material removal. Since the introduction of the process, WEDM has evolved from a simple means of making tools and dies to the best alternative of producing micro-scale parts with the highest degree of dimensional accuracy and surface finish quality. Over the years, the WEDM process has remained as a competitive and economical machining option fulfilling the demanding machining requirements imposed by the short product development cycles and the growing cost pressures. However, the risk of wire breakage and bending has undermined the full potential of the process drastically reducing the efficiency and accuracy of the WEDM operation. A significant amount of research has explored the different methodologies of achieving the ultimate WEDM goals of optimising the numerous process parameters analytically with the total elimination of the wire breakages thereby also improving the overall machining reliability. This paper reviews the vast array of research work carried out from the spin-off from the EDM process to the development of the WEDM. It reports on the WEDM research involving the optimisation of the process parameters surveying the influence of the various factors affecting the machining performance and productivity. The paper also highlights the adaptive monitoring and control of the process investigating the feasibility of the different control strategies of obtaining the optimal machining conditions. A wide range of WEDM industrial applications are reported together with the development of the hybrid machining processes. The final part of the paper discusses these developments and outlines the possible trends for future WEDM research.

Improvement of machining characteristics of micro-EDM using transistor type isopulse generator and servo feed control

Abstract: This paper describes the improvement of machining characteristics of micro electrical discharge machining (micro-EDM) using a newly developed transistor type isopulse generator and servo feed control. The RC generator is mainly applied in conventional micro-EDM even though the transistor type isopulse generator is generally more effective for obtaining higher removal rate, because the transistor type generator is unable to generate iso-duration discharge current pulses with small pulse duration (several dozen nano-seconds), which is the normal level for micro-EDM. A new transistor type isopulse generator was therefore developed using a current sensor with high frequency response. With the new transistor type isopulse generator developed, the pulse duration can be reduced to about 30 ns, which is equivalent to the pulse duration used in finishing by the conventional RC pulse generator for micro-EDM. In order to achieve stable machining and improve machining characteristics, a new servo feed control system for micro-EDM using average ignition delay time to monitor the gap distance was also developed. By integrating the transistor type isopulse generator with this new servo feed control system, we were able to obtain a removal rate of about 24 times higher than that of the conventional RC pulse generator with a constant feed rate in both semifinishing and finishing. The effectiveness of the servo feed control proved higher in finishing than in semifinishing, whereas the transistor type isopulse generator was more effective in semifinishing than in finishing.

Micro machining glass with polycrystalline diamond tools shaped by micro electro discharge machining

Abstract: Brittle materials are difficult to mechanically micro machine due to damage resulting from material removal by brittle fracture, cutting force-induced tool deflection or breakage and tool wear. This paper demonstrates the feasibility of micro machining glass materials with polycrystalline diamond (PCD) micro tools that are prepared in a variety of shapes using non-contact micro electro discharge machining. The PCD tools contain randomly distributed sharp protrusions of diamond with dimensions around 1 µm that serve as cutting edges for micro machining grooves in soda-lime glass and pockets in ultra-low expansion glass. Results indicate that smooth surfaces are obtained with process conditions allowing material removal by ductile regime cutting instead of brittle fractures, and the PCD tools show very little wear. With further improvements in material removal rate, micro machining with PCD tools is a promising approach for producing micro molds and micro fluidic devices in glass materials.

Electro discharge machining of nickel–titanium shape memory alloys

Abstract: Electro discharge machining (EDM) is a common fabrication process for miniaturized components in medical technology and micro engineering today. As EDM induces material changes in the near surface zone, the surface integrity becomes ever more important, the smaller the components are. In order to characterize the influence of EDM on the near surface zone, basic metallurgical investigations on pseudo-elastic NiTi shape memory alloys (SMAs) were carried out. Material removal in EDM depends on the electric discharge processes between the tool and the workpiece electrode in a dielectric fluid. Material is removed by melting and vaporization in single sparks. This results in craters with varying size and depth depending on the discharge energy. The microstructure of this melting zone is characterized by hollows, cracks and precipitation. Cracks open at the surface in consequence of randomly and locally overlapping thermal shocks. The cracks grow vertically into the material, starting at the surface. In the melting zone, significant precipitations were detected and subsequently identified by EDX as titanium carbides. The material removal rate, which is an important process factor in manufacturing, approximately increases in linear proportion with the discharge energy, and achieves commercially interesting values by using an electrode made of copper and tungsten. The results of the microstructure analysis require the removal of the near surface zone to ensure the properties of the components. This is possible via a smooth EDM-process, followed by electrolytic polishing.

Microelectrode array fabrication by electrical discharge machining and chemical etching

Abstract: Wire electrical discharge machining (EDM), with a complementary chemical etching process, is explored and assessed as a method for developing microelectrode array assemblies for intracortically recording brain activity. Assembly processes based on these methods are highlighted, and results showing neural activity successfully recorded from the brain of a mouse using an EDM-based device are presented. Several structures relevant to the fabrication of microelectrode arrays are also offered in order to demonstrate the capabilities of EDM.

Microstructure analysis of the martensitic stainless steel surface fine-cut by the wire electrode discharge machining (WEDM)

Abstract: In this research, quenched and tempered martensitic stainless steels, AISI 440A, were subjected to multi-cutting passes by wire electrical discharge machining (WEDM). The WEDM is widely applied to final surface shaping of harden steel. The steel was roughly machined at first cutting pass, semi-finished by two cutting passes, and then finished by one cutting passes, all machined by WEDM. The negatively polarized wire electrode (NPWE) was used for all of these four cutting passes. Some finished specimens were further extra-finished by using the positively polarized wire electrode (PPWE). Microstructures of the finished surfaces using NPWE as well as PPWE were studied with scanning and transmission electron microscopes (SEM and TEM). Chemical composition was analyzed by an energy-dispersive X-ray spectrometer (EDX) integrated in SEM or TEM. The study of the finished surfaces with NPWE shows that a heat-affected zone (HAZ) of about 1.5 μm thick was developed. The HAZ is composed of very fine equiaxed martensitic grains of about 200 nm with concentrated dislocations, but the temper-induced carbides were not found. A few spherical deposits of wire electrode material were also registered. Oxides with ca. 10 nm in diameter were detected around the deposits. The spherical deposits were characterized as “bull eye” in TEM according to their appearance. For the surface finished with PPWE, no obvious HAZ was detected, but a very thin (

A Study of Optimization of Machining Parameters for Electrical Discharge Machining of Boron Carbide

Abstract: The correct selection of manufacturing conditions is one of the most important aspects to take into consideration in the majority of manufacturing processes and, particularly, in processes related to electrical discharge machining (EDM) of conductive ceramic materials. It is these conditions that determine such important characteristics as surface roughness, electrode wear, and material removal rate. In this article, a review of the state of art of the die-sinking EDM processes for conductive ceramic materials, as well as a description of the equipment used for carrying out the experiments, are presented. Also, a series of mathematical models will be devised using design of experiments techniques combined with multiple linear regression, which will allow us, while only performing a small number of experiments, to select the optimal machining conditions for the finishing stage of the EDM process. To that end, in this piece of work, a study will be made of the influence of the most important factor...

Investigation of the spark cycle on material removal rate in wire electrical discharge machining of advanced materials

Abstract: The development of new, advanced engineering materials and the need for precise and flexible prototypes and low-volume production have made the wire electrical discharge machining (EDM) an important manufacturing process to meet such demands. This research investigates the effect of spark on-time duration and spark on-time ratio, two important EDM process parameters, on the material removal rate (MRR) and surface integrity of four types of advanced material: porous metal foams, metal bond diamond grinding wheels, sintered Nd-Fe-B magnets, and carbon–carbon bipolar plates. An experimental procedure was developed. During the wire EDM, five types of constraints on the MRR due to short circuit, wire breakage, machine slide speed limit, and spark on-time upper and lower limits are identified. An envelope of feasible EDM process parameters is generated for each work-material. Applications of such a process envelope to select process parameters for maximum MRR and for machining of micro features are discussed. Results of Scanning Electron Microscopy (SEM) analysis of surface integrity are presented.

Accuracy improvement of wire-EDM by real-time wire tension control

Abstract: In this paper, a closed-loop wire tension control system for a wire-EDM machine is presented to improve the machining accuracy. Dynamic models of the wire feed control apparatus and wire tension control apparatus are derived to analyze and design the control system. PI controller and one-step-ahead adaptive controller are employed to investigate the dynamic performance of the closed-loop wire tension control system. In order to reduce the vibration of wire tension during wire feeding, dynamic absorbers are added to the idle rollers of wire transportation mechanism. Experimental results not only demonstrate that the developed control system with dynamic absorbers can obtain fast transient response and small steady-state error than an open-loop control system, they also indicate that the geometrical contour error of corner cutting is reduced with approximately 50% and the vertical straightness of a workpiece can be improved significantly.

Optical emission spectroscopy of electrical discharge machining plasma

Abstract: Plasma created during electrical discharge machining is systematically investigated using optical emission spectroscopy. Typical spectra show a strong H-alpha and continuum radiation, with many lines emitted by impurities coming from electrode and workpiece materials. The dielectric molecules are cracked by the discharge. Changing polarity affects the electrode wear and workpiece erosion rates, which can be qualitatively seen on the spectra. Time-resolved spectroscopy shows that the plasma density reaches 2 x 10(18) cm(-3) at the beginning of the discharge. This extreme density causes the merging of lines, strong Stark broadening and shift of the H-alpha line. Afterwards, the density decreases rapidly with time. The electron temperature remains roughly constant around 0.7 eV. The low temperature and the high density measured prove that the EDM plasma is non-ideal (Gamma similar or equal to 0.45). Absence of the H-beta line, asymmetric shape of the H-alpha line and complex structures around H-alpha are other spectroscopic evidences of the plasma non-ideality.

Spark-eroded particles: Influence of processing parameters

Abstract: Ni particles were prepared by spark erosion in a fixed-gap apparatus, and in the usual “shaker-pot” assembly, in an investigation of the influence of various processing parameters on the particles’ properties. The sizes of the particles were studied as functions of spark energies ranging from 10 μJ to 1 J, and a scaling relation derived from a simple model was verified. Several different static and rotating electrode configurations were compared with respect to their suitability for producing significant yields of small particles. The advantages of stirring the dielectric with the fixed-gap apparatus and of rotating the electrodes were demonstrated. Water, kerosene, and liquid argon and nitrogen were used as dielectric liquids. When compounds were formed, the reaction with the dielectric proceeded inversely with particle size. Spark erosion in kerosene at low spark energies, followed by annealing, proved to be an effective method to produce fine nickel particles.