| 摘要 |
摘要
718plus超鎳基合金，在2005年由ATI Allvac 公司開發以來，其因為擁有比Inconel
718更好的高溫強度，在近年來常作為飛機引擎中燃燒室(Combustor)的主要材料而被使用著。燃燒室由於長期處在高溫高壓之環境底下運轉，幾何的高度複雜度及一體成形的需求使得其必須使用成形放電製程進行加工作業。過去在探討718合金於放電加工的應用方面已經有相當多的研究，但卻缺乏對於718plus
的文獻探討。
一套完整的成形放電製程，首先會利用小徑深孔放電加工在工件上欲成形部位通製一小孔，隨後進行線放電加工將其孔穴擴大，才會開始以掏料為主的雕模粗放電加工使加工部位預成形，最後才會進行雕模精放電來精修加工部位之表面特性。但由於放電加工乃屬於熱加工製成，故在加工後會再加工區域留下變質層，因此在放電加工製程結束後，會再加入流體研磨製成將之去除。
本研究之目的在於建立該新式航太材料於雕模放電加工中加工參數與特性間之關係。首先，探討以加工效率為主的粗放電加工，利用實驗設計手法減少實驗次數，將實驗結果施以變異數分析從數個參數中找出較顯著者(放電深度、電流、放電幅及休止幅)來建立迴歸模型以供反應曲面分析其相關性，並將該數學模型結合最佳化方法找出加工效率較優良之參數。接著，探討以表面特性為考量的精放電加工，分析顯著參數(電流、放電幅及休止幅)與表面特性間的關聯性。最後，擷取放電波形以建立放電型態及其他波形特性，探討與電極壽命有關的電極尺寸與放電訊號(放電型態、零秒延遲放電及平均延遲時間)間的關聯性。
關鍵字：雕模放電加工、航太材料、實驗設計、加工特性、表面特性、訊號偵測
Abstract
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.
Key words: die-sink EDM, aerospace material, DOE, processing
characteristics, surface characteristics, signal detection.
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