超臨界流體應用於提升金屬粉末射出成型件流動性之探討

粉末射出成型(Powder Injection Molding, PIM)是一種將傳統製程的粉末冶金技術(Powder Metallurgy, P/M)與射出成型技術(Conventional Injection Molding, CIM)結合的製造方法。在傳統製程中，金屬件產品的製造手法包含鑄造、鍛造、機加工成型等常見的製造方式，其中各項製程皆具有其獨一的長處及短處，因而不同的金屬產品都具有適合自己的製程方法。相對於傳產統金屬製造，粉末射出成型對於複雜形狀的產品的製造以及量產上更具優勢。在金屬材料上常見的材料為各類不鏽鋼、高速鋼與鎢銅，而陶瓷材料則以氧化鋁與氧化鋯為主，然而此類材料及製程由於粉末熔體本來黏度高而流動性不佳，再加上如要在薄而長且間距小的產品應用如散熱鰭片，對於射出成型過是一大挑戰。本研究首次提出藉由超臨界流體輔助來提升粉末熔膠流動性的概念，對於不鏽鋼粉末材料射出成型進行流動性指標改善的探討。，研究成果顯示區段射出壓力差優化後降低約76.2%、流動長度優化後增加約149%，且生胚及脫脂燒結產品皆具有工業標準不鏽鋼密度之95.4%以上。然而超臨界流體的使用稀釋了塑膠的黏度，雖然流動性增加但粉膠分離的現象也更明顯伴隨產生，宜再加入氣體反壓技術使流動性增加的同時也兼顧均勻性的需求。

關鍵字

金屬粉末射出成型；超臨界流體；流動性；流動長度；區段射出壓力差；生胚密度；熱脫燒結密度

並列摘要

Powder injection molding is an integrated manufacturing method that combines conventional powder metallurgy (P/M) and injection molding (CIM). In the conventional manufacturing process, the common manufacturing methods of metal products involve casting, forging, and machining. Each of these processes exhibits its unique strengths and weaknesses; therefore, different metal products correspond with different suitable manufacturing methods. Compared with conventional metal manufacturing, powder injection molding is more advantageous for the manufacture and mass productions with complex shapes. In terms of metal materials, common materials are stainless steel, high-speed steel, and tungsten copper, while aluminum oxide and zirconium oxide are common for ceramic materials. The melted form of these materials exhibits high viscosity and low mobility. Thus, it would be considerably challenging for the injection molding to apply such materials to thin, long, and small spacing products, such as heatsinks. This study proposed the unprecedented concept of using a supercritical fluid to improve the mobility of melting powders. This concept was applied to optimize the mobility index of the injection molding of stainless steel powder materials. The results indicated that the optimized interval injection pressure difference was reduced by 76.2%, and the optimized flow length was increased by 149%. Moreover, both the green compact and debinded and sintered products exhibited an industrial standard stainless steel density of 95.4% and above. However, the use of supercritical fluid decreased the viscosity of plastic. As the mobility increases, the segregation of powder and plastic also becomes apparent. Therefore, this study suggested that the gas counter pressure technology could be applied to increase the mobility while meeting the requirement of material homogeneity.

並列關鍵字

Metal injection molding ； Supercritical fluid ； Fluidity ； Flow length ； Section injection pressure difference ； Green part density ； Brown part density

參考文獻

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