International Journal of Computer and Applications

Machining with electrochemical discharges is an unconventional technology able to machine several electrically non-conductive materials like glass or some ceramics. After almost 40 years of its first mention in literature, this technology remains an academic application and was never applied in industrial context. The knowledge about machining of non-conducting materials using electrochemical discharge phenomenon is reviewed up to this date with some particular attention to the electrochemical point of view. Some main limiting factors are highlighted and possible solutions are discussed.

Machining of non-conducting materials using electrochemical discharge phenomenon – An overview

Experimental investigations into electrochemical discharge machining (ECDM) of non-conductive ceramic materials

Micro-electrochemical discharge machining (ECDM) was studied in order to improve the machining of 3D micro-structures of glass. To minimize structures and obtain good surface microstructures, the effects of the electrolyte, the pulse on/off-time ratio, the voltage, the feedrate, the rotational speed, and the electrolyte concentration in the drilling and milling processes were studied.In ECDM, voltage is applied to generate a gas film and sparks on a tool electrode; however, high voltage produces poor machining resolution. To obtain a stable gas film over the whole surface of the tool at a low voltage, a new mechanical contact detector, based on a loadcell, was used; the immersion depth of the tool electrode in the electrolyte was reduced as much as possible. In this study, various micro-structures less than 100 μm in size, such as O 60 μm micro-holes, a 10 μm-thin wall, and a 3D micro-structure were fabricated to demonstrate the potential for micro-machining of glass by ECDM.

Micro-structuring of glass with features less than 100 μm by electrochemical discharge machining

The basic mechanism of the electrochemical discharge machining process is not yet completely understood and is still a subject of investigations. In the present work an attempt has been made to identify the underlying mechanism through experimental observations of time-varying current in the circuit. Based on these observations the basic mechanism of temperature rise and material removal is proposed.

An experimental study of discharge mechanism in electrochemical discharge machining

Mechanism of spark generation during electrochemical discharge machining: a theoretical model and experimental verification

Mechanism of material removal in electrochemical discharge machining: a theoretical model and experimental verification

Three-dimensional finite element analyses has been carried out using DEFORM 3D software on multi-stage hot forming of railway wheels involving the processes of upsetting, forging, and punching of wheels. Thermal analysis related to heating the blank in furnace and all intermediate heat transfer stages between deforming operations have been conducted. Rigid viscoplastic finite element method has been utilized for coupled thermo-mechanical analysis of the processes. Modeling of punching the wheel bore has been carried out using Cockcroft and Latham fracture criterion. Evolution of thermo-mechanical parameters at selected points within the workpiece has been studied in detail. The method of simulating the effects of various process parameters has been explained using relevant mathematical relations. This study shows that design, optimization, and analysis of process perturbations for multi-stage railway wheel manufacturing process can be done efficiently in three-dimensional finite element simulations instead of conventional time and cost intensive trials. It might be necessary to use the results of finite element analysis in shop-floor to enhance productivity and reduce wheel rejection.

Three-dimensional finite element analysis of multi-stage hot forming of railway wheels

Finite element (FE) analysis of forging process generally takes a long time to carry out Sometimes, it might be required to predict the results of FE analysis as accurately as possible in a less processing time A pre-analysis prediction of the results could also be helpful in some cases Soft computing-based expert system has been developed in the present work, to predict forging load and axial stress developed Forging load and axial stress have been calculated for an axi-symmetric part by varying the values of maximum contact friction stress and normal contact stiffness factor in ANSYS FE package Data generated in the process have been utilized for developing a fuzzy logic-based expert system, on the basis of the authors' knowledge, which has been optimized subsequently using a genetic algorithm (GA) Two other expert systems (ESs) have been developed automatically using the GA, without taking any aid from the manually-designed fuzzy logic system It has been found that the expert systems are able to make predictions of forging load and axial stress as accurately as the FE package can do Results of the ESs have also been seen to be comparable with the experimental results reported in the available literature Instantaneous prediction capability of the developed expert systems proves their suitability for on-line implementations

Expert system to predict forging load and axial stress

Electric discharge is a common tool nowadays for machining of materials. It may be through a liquid medium or through air. Any metals, hard alloys, and non-metals can be machined using the energy of electric discharge. In electric discharge machining (EDM), the discharge occurs between two electrodes through a liquid medium and it is applicable only for electrically conducting materials and alloys. In electrochemical discharge machining (ECDM), the medium is an aqueous electrolyte and it is of two types. In the first type, the discharge occurs between two electrodes. One of the electrodes is the workpiece, and the other is the tool. In the second type, the discharge occurs between one electrode and an electrolyte. It is used for electrically nonconducting materials and the discharge energy is utilized maintaining the nonconducting workpiece in proximity of the discharge. All these electrical discharges are transient phenomena and do not result in a stable discharge in the form of arc. The output parameters depend on the discharge energy that requires precise control to maintain the accuracy of the machining. For micromachining, the control of the discharge is paramount both in terms of energy and pattern. Using various shaped tools, machining media with additives, different types of applied potentials, and supporting mechanical motions are some of the attempts made to improve the machining output. Optimization of these parameters for machining particular materials (or alloys) is a popular field of research. The present work is directed toward the investigation of discharge initiation and development by analyzing the cell current and discharge voltage relationship for both EDM and ECDM. The rectangular direct current (DC) pulse with different frequencies and the duty factor (on–off time ratio) are used for investigation. Observations on the voltage–current relationship are made for the external potential prior to discharge at discharge and above the discharge potential. Though the external potential above the discharge voltage is useful for machining, these observations elucidate the mechanism regarding the initiation of the electric discharge under different conditions. The manner of discharge development in dielectrics and electrolytes is observed to be different. This understanding will aid in deciding the design of the discharge circuit including the external potential and its pattern for certain desired outputs in machining.

Indrajit Basak

Papers

Mechanism of spark generation during electrochemical discharge machining: a theoretical model and experimental verification

Mechanism of material removal in electrochemical discharge machining: a theoretical model and experimental verification

Three-dimensional finite element analysis of multi-stage hot forming of railway wheels

Expert system to predict forging load and axial stress

Electric discharge phenomenon in dielectric and electrolyte medium