酸化物超伝導セラミックスの放電加工

概要

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Oxide-superconductor Ceramics can be machined by the electric discharge machining (EDM), since these seramics have an electrical conductivity at room temperature. However, the change in physical properties of the machined surface due to the heating effect of electric discharge is supposed to occur, because oxide- superconductors are known to be unstable at temperatures above 450℃. In this study, EDM is performed on YBa2Cu3O7-δ superconductor ceramics, and machining characteristic and some physical proterties of machined surfaces are investigated. In addition, the author constructed a mathematical model of the heat conduction of the workpiece in the single shot EDM and computer calculations are performed by using this model. Results obtained are as follows : (1) To maintain stable discharge during machining, a small duty factor, less than 2% depending on the pulse width and peak current value, was required. (2) A degenerated layer is formed on the machined surface probably due to resolidification of the melted surface layer. This layer has a high resistivity compared with that of the bulk material. (3) Differences of the machining characteristics between the oxide-superconductor ceramics and the metalic workpieces were clearly shown by their thermal properties.
1999-01-29