78 Nonconventional Technologies Review 2012 Romanian Association of Nonconventional Technologies Romania, June, 2012 STUDIES ABOUT THE ROUGHNESS OF THE SURFACES MACHINED BY EDM Carmen Purcar 1 and Carmen Simion 2 1 Universitatea “Lucian Blaga” din Sibiu, Facultatea de Inginerie, carmen.purcar@gmail.com 2 Universitatea “Lucian Blaga” din Sibiu, Facultatea de Inginerie, carmen.simion@ulbsibiu.ro ABSTRACT: Where force suction flushing is not feasible, alternative methods to clear the debris effectively from the gap between the electrodes in EDM have been attempted, e.g. the application of a magnetic field, low frequency vibration of the electrode or special motion of the electrode. The rotating electrode permits one to improve the machining rate, form and dimensional accuracy in the machining process, performs roughing and finishing operations with the same tool and helps to stabilize the erosion process. The paper presents the experimental investigation of EDM of steel with a copper electrode in respect of surface roughness by using a rotative electrode. KEY WORDS: electro-discharge machining (EDM), electro-discharge grinding (EDG), rotating electrode, roughness. 1. INTRODUCTION Today’s manufacturing industry is facing challenges from advanced difficult-to-machine materials (tought super alloys, ceramics and composites), stringent design requirements (high precision, complex shapes and high surface quality) and machining costs. Advanced materials play an increasingly important role in modern manufacturing industries, especially in aircraft, automobile, tool, die and mould making industries. The greatly-improved thermal, chemical and mechanical properties of material (such as improved strength, heat resistance, wear resistance and corrosion resistance), while having yielded enormous economic benefits to manufacturing industries through improved product performance and product design, are making traditional machining processes unable to machine them or unable to machine them economically. The high costs associated with machining ceramics or composites, for example, and damage generated during machining are major impediments to the implementation of these materials. For example [1], the costs of machining structural ceramics (such as silicon nitride) often exceed 50% of the total production costs in the engine industry. In these cases, current machining methods cannot be used and innovative techniques or modifications of existing methods are needed. In addition to the advanced materials, stringent design requirements also pose major problems in the manufacturing industry. More and more complex shapes (such as an aerofoil section of a turbine blade, complex cavities in dies and moulds, non-circular, small and curved holes), low rigidity structure and micromechanical components with tight tolerances and fine surface quality are often needed. Traditional machining is often ineffective in machining these parts. To meet these challenges, new processes need to be developed. Electro-discharge machining (EDM) is one of the non-traditional machining methods widely used today. In fact, EDM is no longer “non-conventional” or “non-standard” machining. EDM is now [2] the fourth most popular machining process, selling more than all other processes except milling, turning and grinding , with EDM sales increasing from about 0,5 percent of the 1960 machine tool market to about 6 percent of the 1998 market. The increasing strength of EDM is based on the rapid improvements in its price/performance rations, on the new applications made feasible by the improved performance economics and on a growing awareness of the advantages of EDM by metalworking industry in general. The ongoing theoretical and experimental research efforts to study the EDM process can be classified into the following four main groups [2], [3]: 1. studies conducted to understand the physical aspects of spark mechanism through specially constructed instruments and equipment, high speed photography, spectroscopy, X-ray and radioactive tracers etc. Three different kinds of theories (electromechanical, thermo mechanical and thermoelectric) for material removal have been proposed based on the experimental results. 2. the second group of investigation consists of attempts to obtain qualitative and quantitative relationships between the technological parameters (such as corrosion rate, surface integrity) and input variables (work and tool material properties and machining parameters such as current and pulse duration). Empirical relationships in the form of regression equations and plots based on experimental results of actual electrical discharge machining operations related to a machine and combinations of work and tool material are usually provided by the manufacturer as approximate guidelines for selecting machining parameters. Theoretical heat transfer models for a single discharge situation. Different types of heat sources ranging from a point source to a time-varying circular source have been considered in the development of deterministic as well as stochastic thermal models. In the absence of a clear-cut quantitative evaluation of metal removal efficiency, the thermal models have a limited validity. Many off-line optimization schemes needed for adaptive control of EDM are built around these empirical and/or theoretical expressions. 3. recent research attempts which form the group have been aimed at developing adaptive control systems by identifying, monitoring and controlling the gap condition. 4. the fourth group of investigation consists of attempts to improve the technological parameters by application of a magnetic field, special planetary motion of the tool