The causes of defects during MIM solvent debinding process and methods of improvement.

粉末射出成形對於複雜形狀零件具有極佳的成形能力，但若其溶劑脫脂過程中，參數控制不當會造成試片產生裂縫、裂痕、魚鱗紋等缺陷，於試片燒結後會影響成品外觀，需多加上研磨拋光等製程，增加成本，甚至於降低成品機械性質。為了有效改善溶劑脫脂產生之缺陷，本研究首先以一般的溶劑脫脂條件製造出試片缺陷，觀察試片缺陷的型態，再來針對溶劑脫脂參數，例如溶劑脫脂溫度、試片厚度、溶劑種類作比較，歸納缺陷形成起因及改善方法。 由雷射膨脹儀(in-situ dimension change)結果顯示，溶劑脫脂時膨脹量越大，試片越容易產生裂縫，且溶劑脫脂溫度一旦超過試片中石蠟之熔點，膨脹量將大幅提高，導致魚鱗紋產生；此魚鱗紋之成因是試片膨脹而造成鐵粉與黏結劑間附著能力變差，而316L不銹鋼粉表面與黏結劑附著能力不良，更容易產生魚鱗紋。此外，不同厚度之試片，其膨脹量隨著厚度增加而上升，因此工件尺寸複雜之零件，需注意其不同厚度相接處造成的缺陷。添加異丙醇於正庚烷溶劑中可有效降低試片膨脹量，而生胚經過烘烤後再施以溶劑脫脂的話，試片產生缺陷的機率亦大幅降低。Powder injection molding (PIM) has become a popular process in producing complex-shaped parts. However, defects are still frequently found , particular during solvent debinding. These defects will decrease the mechanical properties of the products. In order to improve that, the effect of solvent debinding temperature, specimen thickness, and different solvents were examined. The laser dilatometer analyses indicate that large amount of length changes usually occur when the solvent debinding temperature is higher than the melting point of the paraffin wax and fish scales are found on the surfaces. The fish scale is caused by the poor bonding between powder surfaces and binders, especially for 316L stainless steels. The length change also increases as specimen thickness increases. Thus, defects are found easily in complex-shaped parts. Moreover, it was found that adding IPA to heptane can decrease the specimen length changes. The specimens with baking process will also have higher yield after solvent debiding.第一章、文獻回顧………………………………………………………….1 1-1 前言………………………………………………………………..1 1-2 脫脂………………………………………………………………..2 1-2-1 溶劑脫脂………………………………………………………4 1-2-2 溶劑脫脂機制…………………………………………………6 1-2-3 脫脂造成之試片缺陷…………………………………………6 1-3 製程參數影響………………………………………………………8 1-3-1 溫度影響………………………………………………………9 1-3-2 黏結劑配比影響……………………………………………..12 1-3-3 黏結劑種類的影響…………………………………………..15 1-4 粉末特性對溶劑脫脂的影響……………………………………..18 1-4-1 粉末粒徑……………………………………………………..18 1-4-2 粉末形狀………………………………………………..……20 1-5 溶劑種類………………………………………………………….21 1-6 研究目的………………………………………………………….23 第二章、實驗步驟…….………………………………………………….24 2-1 實驗設計………………………………………………………...24 2-2 原料……………………………………………………………...24 2-2-1 金屬粉末……………………………………………………24 2-2-2 黏結劑………………………………………………………..27 2-3 混煉………………………………….…………………………..29 2-4 射出成形…………………………….…………………………..30 2-5 烘烤製程………………………………………………………...32 2-6 溶劑脫脂………………………………………………………...32 2-7 雷射膨脹儀……………………………………………………...34 2-8 連通孔測試……………………………………………………...35 2-9 測試儀器………………………………………………………...36 第三章、實驗結果與討論………………………………………………..37 3-1 雷射膨脹儀之校正………………………………………………37 3-2 溶劑脫脂後產生的缺陷…………………………………………39 3-2-1 標準製程之下溶劑脫脂試片缺陷之種類及比率…………39 3-2-2 高射壓製程之下溶劑脫脂試片統計………………………44 3-2-3 裂縫類型……………………………………………………49 3-2-4 魚鱗紋………………………………………………………57 3-2-5 射料乾燥與否對射出成形之影響…………………………62 3-3 溶劑脫脂溫度的影響……………………………………………65 3-4 烘烤(Baking)製程………….……...…………………………….72 3-4-1 烘烤溫度……………………………………………………72 3-4-2 烘烤後表面出現的液滴狀物體……………………………73 3-4-3 烘烤過後顯微組織的觀察…………………………………75 3-4-4 對良率的改善………………………………………………79 3-4-5 烘烤對溶劑脫脂速率的影響………………………………81 3-5 厚度對溶劑脫脂的影響…………………………………………84 3-6 溶劑種類的影響…………………………………………………89 3-6-1 異丙醇的添加………………………………………………90 3-6-2 正溴丙烷……………………………………………………92 第四章、結論……………………………………………………………..94 第五章、未來工作………………………………………………………...96 第六章、參考文獻………………………………………………………..9