FACTORS AFFECTING THE REPRODUCTION ACCURACY IN ELECTRICAL DISCHARGE MACHINING

Abstract

Ele ctro discharge machining (EDM) is primarily a copying process in which the tool electrode shape is reproduced on the work. This process is at present successfully employed in die making industry, aerospace, nuci ear, automotive and electronic industries etc. In addition the process can be used for sinking, cutting of complicated profiles, machining of sieves and grids, thread cutting, curved hole drilling, hardening of cutting tool tips etc. Recent addition to the process of EDM is the development of EDM wire cutting, planetary wire cutt-ing, erosion grinding, electro chemical discharge machining (ECDM). The phenomenon of metal removal in EDM is highly complex in nature with many interacting factors. When a pulsed DC source is applied between tool and work for a short interval of time with a dielectric flow between the work tool interface, the power intensity of the order of 107 to 108 KW/m2 results in the EDM spark. This high energy input on the electrode surface causes- rate of temperature rise of the order of 1'09 to 1010 °C/sec., re suiting into melting and evaporation of electrode surfaces leaving behind tiny craters, which is the characteristics of the EDM surface texture. Most of the past work on EDM has been carried out on the mechanism of metal removal taking into account the thermal modelling technique and on the dielectrics performance. A few reports do appear on the tool shape de"eneration., determination of working length of tool electrode. Very little information is available on the reproduction accuracy aspects of EDM. Some report on the rounding of sharp corners in EDM is also available: