A review on the use of environmentally-friendly dielectric fluids in electrical discharge machining

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Abstract

Electrical discharge machining became a commercial process after the discovery of the importance of the dielectric fluid, which affects factors such as productivity and quality. Health, safety and environment are also important factors, particularly when oil-based fluids are used. This paper presents a literature survey on the use of dielectric fluids that provide an alternative to hydrocarbon oil. It has been reported that water-based dielectrics may replace oil-based fluids in die sink applications. Gaseous dielectrics such as oxygen may also be the alternative. Nonetheless, these need further research in order to be commercially viable.

Introduction

Electrical discharge machining (EDM) is a highly developed technology which accounts for about 7% of all machine tool sales in the world [1]. EDM can be applied in a very wide range of operations including the manufacture of moulds and dies, surface texturing of steel rolls, surface alloying, production of aero engine components, production of components for electronic industries and manufacture of metallic prosthesis.

The bases of EDM were probably established already in 1694, when Sir Robert Boyle described the phenomena of electric discharges in a gap [2]. However, it was only in early 1940 that electrical discharge machining started to become a well-know manufacturing process when Boris and Natalie I. Lazarenko discovered the decisive role of the dielectric fluid [3]. Since then, EDM has experienced a dramatic evolution.

There are different variations of EDM processes; these can be classified according to the type of dielectric fluid used. Die sink EDM generally operates with hydrocarbon oil, while wire, micro-EDM and fast hole drilling usually work with deionised water.

The dielectric fluid fulfils an extremely important function regarding productivity, costs and quality of the machined parts. Health, safety and environment are also important aspects, particularly when hydrocarbon oil is used. This work will cover a review on the performance of water-based dielectrics and gaseous dielectrics for die sink EDM, aiming to have a view on the potential of dielectrics alternatives to hydrocarbon oil.

Section snippets

Water-based dielectrics for die sink EDM

Research over the last 20 years has involved the use of plain water, water mixed with organic compounds and commercial water-based dielectrics.

EDM with gaseous dielectrics

The use of a dielectric liquid as the working medium for EDM has never been questioned since Lazarenko discovered its decisive role in the performance of the process. One of the main functions of the dielectric is the restriction of the spark in order to have a higher density of energy and as consequence a higher performance. This has been reported to occur only when a dielectric liquid is used. If the sparks happened in the air, for example, the erosion effect would be very small because the

Environmental aspects

The manufacturing industry has been considered as one of the main sources of environmental pollution [22] and machining processes play an important role since it is the most widely used manufacturing process [23]. The minimisation of environmental impact has been an important topic for manufacturers all around the world, especially after the introduction of ISO 14000 environmental management system standards. In addition to maximising quality and cost, it is imperative for manufacturing

Costs

Few publications are available on operating costs of die sink EDM using fluids alternative to hydrocarbon oil. Dünnebacke [11] found that the total operating cost when machining with commercial water-based Elbolub was ∼36% higher than with BP180 hydrocarbon. One of the most important costs was the water deionisation process. Costs that were found to be higher when water is used include equipment depreciation (21%), electrical energy (15%), dielectric losses (78%) and filtering aids (57%).

Conclusions

There is extensive evidence that hydrocarbon oils are more efficient than deionised/distilled water in die sink applications. However, water may result in higher levels of material removal rate in some situations.

Some authors have studied the feasibility of adding organic compounds to deionised water and obtained a performance higher than that of hydrocarbon oils for roughing and finishing operations. Increase in material removal rates of up to 100% in roughing operations has been reported.

Some

Acknowledgments

The authors would like to thank CAPES Foundation (Brazil) for supporting this work.

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