| dc.description.abstract | In electrical discharge machining (EDM), materials are removed by thermal energy transformed from electrical energy. This technique can be applied to remove materials with high hardness and strength, which are difficult to machine by traditional methods. During the process, the workpiece is subject to rapid heating and cooling under a violent temperature gradient. As a result, defects such as microcracks and pores are formed, to deteriorate the surface quality and shorten the life cycle. In view of such drawbacks, this study aims to enhance the high precision quality of electrical discharge machined surface.
Three approaches to improve the surface roughness and to achieve a mirror-like surface quality are proposed. Three techniques including the addition of surfactant to dielectric, the spraying of dielectric material and the combination of EDM with electrophoretic deposition polishing (EDP) are further studied. For the first approach, the experimental results reveal that adding surfactant Span20 to kerosene can disperse carbon and debris through the molecular reaction of the surfactant. As a result, carbon accumulation and concentrated discharge are reduced and material removal rate can be improved by 40-85%. Similarly, the addition of Al powder and surfactant Tween 80 to kerosene helps reduce the agglomeration of Al powder, thus ensuring even distribution of Al powder in the dielectric, which in turn improves surface roughness by 60%. The second approach influences the impedance of the electrical discharge profile by spraying thin films with different thickness, which consumes part of the discharge energy. The bulges on the surface are removed by the second electrical discharge, leaving craters of even depth and thus improve the surface roughness by 33%. In addition, the surface roughness stability is together with an increase in surface roughness improved by 18%. Finally, combining EDM with EDP using 0.3µm of Al2O3 particles can improve the initial surface roughness from 0.52 µmRa to a mirror-like surface of 0.068 µmRa. In addition, the total working time required for the polishing process can also be reduced significantly to around 5 to 10 minutes. | en_US |