[[alternative]]A Study on the Remelted Layer and Mechanical Properties of Wire-

[[abstract]]本研究為建立ADI ( austempered ductile iron )的加工資料庫，以 非傳統線切割放電加工( Wire-EDM )來取代傳統的械械加工法。實驗材料 有三批，皆經最佳韌性與最佳強度、硬度組合的溫度條件下(以機械性質 測試得知)進行沃斯回火恆溫熱處理。實驗結果顯示，縮孔、鑄疵等缺陷 對ADI機械性質具嚴重與不利的影響外，對線切割放電加工亦會造成放電 集中而斷線，最後無法加工。在線切割放電加工特性方面：(一)ADI加工 後的表面粗糙度隨放電加工參數的放電時間(on time)值增加而變大，放 電表面與一般加工後之模具鋼不同且較差，有著相當多的空洞與石墨汽化 後凹坑；(二)以迴歸模擬預測ADI的線切割放電加工速度，其影響因素的 重要性依序是：工作物厚度、放電時間、床台進給率、母材的球墨數及 ADI的殘留沃斯田鐵量；(三)線切割放電加工時，需調整銅線在不斷線前 提下為最大張力、加工液噴嘴壓力及適當加工液的電阻係數等放電加工參 數，並使成最佳的組合，方能使鼓形引起的中央切割部尺寸凹陷問題減至 最低，以達精密加工的目的。ADI經線切割放電加工後，其表面的軟化變 質層與雕模放電加工所產生的硬化層不同外，在OM、Hv和SEM觀察其厚度 尺寸也有所不同，且切割ADI時產生大量氣泡的攪拌使變質層厚度比切割 SKD者較小外，變質層及鄰接區域的微結構也改變，使材料的衝擊韌性降 低。材料原為最佳韌性沃斯回火溫度(356~363。C)熱處理時的衝擊破斷面 扭曲變形，衝擊值愈高斷面扭曲變形愈嚴重，斷裂方向為四十五度最大剪 應力方向；而沃斯回火溫度(300。C)熱處理時，有理想的硬度、強度組合 ，其衝擊後的斷面為垂直九十度的劈裂破壞。 The purpose of this study is to build machining data base of ADI, in order to replace traditional machining with non- traditional machining of Wire-EDM. Three types of ductile irons were used to develope ADIs of the optimum toughness, strength and hardness via different austempering treatments. Results showed that not only defects of materials casting plausibly was disadvantages to mechanical properties of ADIs but also led to wire-breakage as machining of Wire-EDM.The effects of ADI on the characteristics of machinability of Wire-EDM as below: (1) With increasing on time of cutting conditions, the surface roughness of ADIs increases. The Wire-EDMd surface of ADIs was rougher than that of SKD due to microvoids forming of decarburization and vaporization of graphite nodules at remelted layer of ADIs; (2) The factor's order of cutting feedrate for ADIs measured by simulated regression as followed: thickness of the workpiece, on time, feedrate override of the table, nodule counts of materials, retained austenite content; (3) In order to acquire the precision of workpieces by setting higher water flow rate, resistivity of dielectric fluid and wire tension prior to wire- breakage. The thickness and hardness distributions of remelted layer in cross-sectional area of Wire-EDMd surface differed from that of EDM. The dimension of remelted layer of ADIs in cross-sectional area of Wire-EDMd surface was not as the same as in terms of measuring instruments such as OM, Hv and SEM. Although there was the thinner distributions of ADI than that of SKD due to strong stirring of more bubbles forming, the changed microstructure of remelted layer and adjacency deteriorated impact energy of mechanical properties. The more impact energy, the more severe distorted cross-section cracked from 45。angles of maximum shear stress as ADIs austempered at 356~363。C; the flat fracture front of cleavage acquired as austempered at 300。C the same as brittle type. The purpose of this study is to build machining data base of