金屬粉末射出成形製程中胚體毛細吸附脫脂之數值模擬與實驗分析

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题名:	金屬粉末射出成形製程中胚體毛細吸附脫脂之數值模擬與實驗分析
作者:	陳志誠;Chih-Cherng Chen
贡献者:	機械工程研究所
关键词:	田口式實驗設計法;體適合有限元素法;達西定律;毛細吸附脫脂;變異數分析;wick-debinding;Darcy’s law;body-fitted FEM
日期:	2001-01-11
上传时间:	2009-09-21 11:32:46 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	毛細吸附脫脂在金屬粉末射出成形中，是一種影響成品品質甚鉅，且極為複雜之製程。胚體/吸附材組合體內部熔融狀黏結劑之脫脂流動，類似於多孔性介質流之現象。應用達西定律，本文除了建立一套模擬二維毛細吸附脫脂之理論模式外，並利用體適合有限元素法來模擬胚體之毛細脫脂過程，預測整個流動區域之壓力場和速度場分佈，以及脫脂時間和相關物理特性。為了簡化問題，假設黏結劑為單一成份，且初始以熔融狀態完全飽和充填於胚體中。此外，以視流法觀測模擬脫脂，並藉田口式實驗分析法，和L9直交表矩陣實驗方式及變異數分析，決定影響脫脂效果可控因子水準的最適化條件。最後，透過可同時量測滲透度與毛細壓力之簡易實驗裝置，將所得的實驗數據，經擬合後可獲取空孔度、滲透度與毛細壓力彼此間之關係。結果顯示，數值模擬預測脫脂時間，隨胚體厚度的平方成正比，且與實驗量測所得及早期文獻之結果，有極大的吻合程度，這證明了本文理論模式與體適合有限元素法，在模擬毛細吸附脫脂製程應用上的適用性和可靠性。當脫脂接近完成階段時，脫脂速率因黏結劑流動阻力之減少而急速增加。另外，低值的雷諾數和毛細數，說明了毛細效應遠勝於慣性力和黏滯力。實驗結果亦說明了在兼顧脫脂品質的要求下，影響脫脂參數最適化水準組合為3：1的胚體/吸附材鋼珠粒徑比、黏結劑種類為R-32潤滑油、鋼珠外型為光滑表面且吸附材內部為充填均勻情形，(亦即A1B2C1D1)，如此則可改善黏結劑的指狀缺陷約為15 dB和殘留量約為10 dB左右。值得一提的是，當脫脂過程完成時，黏結劑移動的外波前形狀和胚體的外邊界幾何形狀是幾乎一致的，此現象可做為決定吸附材使用量的參考依據。 Wick-debinding in metal injection molding (MIM) is an intricate phenomenon. The motion of molten binder is similar to the fluid flowing through a porous medium in the compact-wick material combination. In the present study, a mathematical model, based on Darcy’s law, is established. To simplify the problem, the assumptions of a single component binder and a fully saturated compact with molten binder are adopted. Body-fitted finite element method (BFEM) is used to calculate the distribution of pressure and other related properties during the wick-debinding of the 2D combination. Additionally, the flow visualization experiment, designed by the Taguchi’s method and a L9 orthogonal array, is qualitatively conducted to describe the process of binder removal. According to the analysis of ANOVA, the optimal control factors can be determined during the wicking process. However, a simple equipment is designed to measure the permeability and the capillary pressure simultaneously. Then the relationships of porosity versus permeability for the simulated porous samples, and the porosity versus capillary pressure for glycerin and R-68 oil are easily obtained. Results show that the prediction of debinding time versus compact thickness squared agrees well to the experimental data. The reliability and accuracy of the present numerical analysis is thus verified. When wicking process is nearly to be finished, the debinding rate increase quickly. Low Reynolds number and low capillary number indicate that capillarity is dominate over other effects, such as inertia force, viscous force, etc. Under the optimal settings, an improvement in the fingering defect and the residual of binder is about 15 dB and 10 dB, respectively. The shape of the flow front of the molten binder and the outer geometry of the compact are found to be closely matched in the final step of wick debinding.
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