Electrochemical Spark Machining Research Articles

ELECTROCHEMICAL SPARK TREPANNING OF ALUMINA AND QUARTZ

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 action of melting and chemical etching seems to be the probable mechanism of material removal.

On the analysis of the electrochemical spark machining process

The electrochemical spark machining (ECSM) process has been proved as a potential process for machining of low machinability high-strength electrically non-conducting materials, but the mechanism of material removal during the process, by and large, is not yet understood. In the present work, the electrochemical discharge is modelled as a phenomenon similar to that which occurs in arc discharge valves. This phenomenon is used to explain various experimental results, on the basis of circuit and arc discharge valve characteristics. The spark energy and the approximate order of hydrogen gas bubble diameter are computed by the proposed valve theory. Material removal rate is evaluated by modelling the problem as a 3-D unsteady state heat conduction problem. The problem is solved by the finite element method to compute the temperature distribution which is post-processed for estimating material removal per spark, overcut obtained in the machined cavity, and attainable maximum penetration depth. The conclusion drawn is that the application of valve theory to the ECSM process seems to be realistic. Estimated material removal rate, overcut and maximum penetration depth show a good agreement with experimental findings.

Experimental investigations into ECSD process using various tool kinematics

Machining of electrically non-conducting materials, i.e. ceramics, composites, etc., is still a major problem. Electrochemical spark machining (ECSM) is found to be a potential process for machining these materials. However, ECSM has its own inherent problems too. So far, only non-rotational tools with gravity feed have been used 'by previous researchers, but the performance of such tools has been reported to be poor. In the present work, electrochemical spark drilling (ECSD) experiments have been conducted using various tool kinematics with a view to enhancing the process capabilities. Use of a rotational tool with controlled feed has been found to improve the process performance. Significant improvement in the “limiting value” of the machined depth during ECSD has been observed while using a tool with orbital motion. Geometrical parameters and surface integrity of the machined specimens have also been studied and presented.

MACHINING OF FIBER-REINFORCED COMPOSITES

Since the introduction of glass fiber-reinforced polymer composites in the early 1940s, composite materials development was driven by the needs of space, defense, and aircraft industries where performance rather than cost was the prime consideration. At the beginning, conventional machining techniques were adopted to machine glass fiber-reinforced composites for convenience as well as to keep the capital costs down. This was followed by significant advancements in tool materials and tooling design. With the development of new and more challenging metal-matrix and ceramic-matrix composites, conventional manufacturing processes proved to be inadequate or even inappropriate to process them. Need and opportunity, therefore, exists for alternate nontraditional machining operations, such as laser machining, water jet (WJ) and abrasive water jet (AWJ) cutting, electrical discharge machining, ultrasonic-assisted machining, and electrochemical spark machining. When composites become more popular and are used in large volume in the civilian sector, such as auto and other consumer industries, material and processing costs will be the driving factors. A high degree of automation for the mass manufacturing of composite parts will be required to bring the costs down and compete with other materials. Advancements in the nontraditional machining processes offer an opportunity to process these materials economically, thus realizing the full potential of the composite materials. This paper gives a broad overview on the various issues involved in machining (conventional and nonconventional) of fiber-reinforced composites. The field of composites, in general, and machining of composites, in particular, are so broad that it would not be possible to do justice by discussing each aspect of composite material machining without ending up with a voluminous document. This review, therefore has to be limited to a few aspects of composite materials and their machining techniques. It may also be pointed out that in this review certain areas are dealt more in-depth than others. Personal preferences and availability of material in the open literature are some of the reasons for this nonuniformity in coverage. Also, some areas are more actively pursued than others. An attempt is made to highlight some of the issues and opportunities in the area of machining of composites.

Machining piezoelectric (PZT) ceramics using an electrochemical spark machining (ECSM) process

Machining of advanced engineering materials such as composites and ceramics is important but it is very difficult and uneconomical to do so by conventional methods of machining. A need for new techniques for machining these advanced engineering materials cannot be over-emphasized. In this study, the authors have attempted to explore the feasibility of using an electrochemical spark machining (ECSM) process for machining of electrically partially conductive materials like piezoelectric ceramics (namely lead zirconate titanate PZT) and carbon fibre epoxy composites. A travelling wire electrochemical spark machining (TW-ECSM) set-up is designed and fabricated. This paper briefly describes some of the design features of the set-up. Experiments are conducted to investigate the effects of supply voltage and concentration of electrolyte on average diametral overcut and material removal rate. Material removal rate is found to increase with increase in supply voltage and electrolyte concentration (up to 22.5%). It has also been observed that machining of partially electrically conductive materials using the present ECSM set-up results in physical contact between cathode (wire) and work (partially conductive), or travelling wire and debris. This leads to undesirable arcing/sparking which causes deterioration of the machined surface characteristics.

Machining of composite materials. Part II: Non-traditional methods

Machining of composite materials is difficult due to the heterogeneity and heat sensitivity of the material and the high abrasiveness of the reinforcing fibres. This results in damage being introduced into the workpiece and very high tool wear. The use of traditional machining methods was reviewed in Part I of this paper. Here new methods are considered: laser, waterjet, electro-discharge, electro-chemical spark, and ultrasonic machining. These various techniques have been applied to organic matrix composites with aramid, glass, graphite fibre reinforcement but also to metal matrix and ceramic matrix composites.

Experimental Investigations into Traveling Wire Electrochemical Spark Machining (TW-ECSM) of Composites

Fiber reinforced composites, though relatively new, have already become important engineering materials. So far the main emphasis of research has been on the development of materials, but nowadays more attention is being paid to the industrial manufacture of products made of composites. Conventional machining methods and some unconventional machining methods like laser beam machining (LBM) and water jet machining (WJM) cannot be effectively applied for machining of composites due to the resulting problems of air borne dust, tool wear, and thermal damage. Recently electrochemical spark machining (ECSM) has been applied for the cutting and drilling of holes in composites. The success achieved in the application of ECSM for cutting of composites has stimulated interest in exploring the prospects of use of traveling wire electrochemical spark machining (TW-ECSM) process for cutting of composites. An apparatus for TW-ECSM is designed and fabricated in the laboratory. The results about the feasibility of the process and its performance during machining of composites are presented in this paper. Experiments are carried out on glass-epoxy and kevlar-epoxy composites, using sodium hydroxide (NaOH) as electrolyte. The wire and the workpiece were kept in physical contact with each other by the use of a gravity feed mechanism. The effects of voltage and concentration of the electrolyte on material removal rate, average diametral overcut, tool wear rate, and wire erosion ratio are reported. The theoretical analysis of the mechanism of the process identifies the thermo-mechanical phenomena as the main source of material removal in ECSM.

Investigations into machining of composites

Fibre reinforced plastics (FRP) have an important place in the field of engineering materials. Initially, the main emphasis in research was on the development of materials. Currently, however, more attention is being paid to the industrial production of FRP products. Normally, conventional methods for machining of these materials are used, but reports have indicated poor performance of these conventional types of cutting tools during machining of FRP. In this paper, a new approach using electrochemical spark machining (ECSM) for cutting and drilling holes in composites is proposed. The feasibility of using ECSM for machining FRP was first ascertained. Then a parametric study of the process was performed by planning the experiments using a ‘design of experiments’ concept as well as a ‘one variable at a time’ approach. Kevlar-fibre-epoxy and glass-fibre-epoxy composites as work materials, copper as the tool material and an aqueous solution of NaCl as electrolyte were used. It is concluded that ECSM is a viable solution for cutting FRP. However, for achieving the desired accuracy, surface finish and economics of the process, the machining parameters need to be optimized.

Experimental Investigations into Electrochemical Spark Machining of Composites

Reports have indicated the poor performance of the conventional type of cutting tools during machining of composites. In this paper electrochemical spark machining (ECSM) for the cutting and drilling of holes in the composites is being proposed. The feasibility of using ECSM for composites was first ascertained. Then, kevlar-fiber-epoxy and glass-fiber-epoxy composites as work material, copper as tool material, and an aqueous solution of NaCl as electrolyte were used. It has been concluded that the ECSM is a viable solution for cutting of Fiber Reinforced Plastics (FRP). For achieving desired accuracy, surface finish, and economics of the process, the machining parameters should be optimized.

Spark-machining of photoconductive indium antimonide

The spark machining of indium antimonide is assessed as a means of making photoconductive infra-red detectors. Surfaces produced by electrochemical etching, mechanical polishing and spark machining are compared. Conclusions drawn are that spark-erosion cutting of detector shapes off a substrate is feasible; but that shaping and surface machining of a mounted detector do not give satisfactory results.