| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 105 === 718plus, developed by ATI Allvac company in 2005, is a nickel-based super alloy having higher temperature strength than Inconel 718 and is found cost-effective, and now the material has been utilized for producing combustors. Combustors, a major part of aerospace engine, having complex bore shape and long-term working in high pressure and temperature environment, require seamless process so that EDM is applied. In the past, the studies of EDM with Inconel 718 have been found, but those with alloy 718plus can be hardly traced. The full process of shaping combustors with EDM is: drilling a deep hole on workspace by discharge, reaming by WEDM, preforming (rough-EDM stage) and surface finishing (finish-EDM stage) by die-sink EDM. After EDM process, it usually utilizes abrasive flow machining to remove recast layer remained by EDM (one kind of thermal energy processes) because it is detrimental to mechanical properties. The goal of this thesis is to investigate the relation between operation parameters and processing characteristics in die-sink EDM process. In first stage, efficiency issue of rough-EDM is considered, and DOE (Design of Experiment) is utilized to identify the significant parameters by ANOVA (Analysis of Variance) with minimum experiment times. Then, the regression model is established with those parameters so as to construct reaction plane and optimized results are obtained. In the following finish-EDM, we investigate the relation between the significant parameters and surface characteristics. Finally, the discharge signals in relation to different electrode sizes is analyzed with a view to possibly monitoring the status of electrode.
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