| dc.description.abstract | Electrical discharge machining (EDM) possesses excellent machining performances for difficult-to-machining materials and micro precision parts. The EDM surface reveals the defects of micro cracks and pores due to violent temperature gradient during machining, and the surface topography exhibits discharge craters owing to the material is removed from machined surface. Generally, the surface quality of EDM is poor. Therefore, the investigation of surface fine-finish and modification to improve the surface quality and strength is necessary for extending the EDM applications.
This study proposes surface fine-finish and modification methods to ameliorate the surface defects on EDM. In this investigation, a series of experiments were carried out to explore the effects on surface fine-finish and modification including added conductive powder into dielectric, integrated the mechanisms of EDM with ultrasonic machining (USM), and combined EDM with ball burnish machining (BBM). Since the material removal rate (MRR) of EDM is lower than conventional machining, the objective of surface fine-finish and modification methods for EDM not only concern the effects of surface improvement to obtain high quality surface but also the machining efficiency and precision. Thus, the machined surface quality, machining efficiency, and precision need to be considered simultaneously for EDM applications and they are also the interesting topics in this investigation.
Experimental results show that added conductive particle of mixture powder into dielectric could expand the discharge gap to facilitate the expelling of debris and divide the discharge energy to reduce the surface roughness. Moreover, the added powder could be transferred and penetrated to the machined surface by ionization of the discharge column. Therefore, the machined surface achieves the modification and reinforcement. In addition, the combined process of EDM with USM possesses not only the electrical discharge to vapor and melt the material but also the abrasive that driven by ultrasonic vibration to harm and impact the workpiece. Thus, the MRR of the combined process of EDM with USM is higher than conventional EDM. Furthermore, the abrasive that is added into dielectric becomes the agent of surface modification, experiment results show that the machined surface could obtain the effects of particle reinforcement and solid-solution strengthening. The machined surface received the discharge alloying via combined EDM with USM. In addition, experimental results show that the combined process of EDM with BBM deformed materials via the action of smooth ZrO2 balls on EDM surface to eliminate the cracks, pores and discharge craters. The combined process can achieve surface fine-finish and modification effects to gain flat and finish surface integrity. Moreover, the ZrO2 balls will not disturb the EDM proceeding to reduce the machining efficiency. From the series of empirical investigations, we can obtain the surface fine-finish and modification via our processes to reach the high quality surface with high machining efficiency and precision for modern industrial applications.
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