球墨鑄鐵排氣歧管之澆鑄模擬研究

近年來，汽車產業已是一個高度發展且成熟的工業，汽車零組件的品質更是要求完美。特別是在安全的考量，使這些零件必須重量輕、強度高與零缺陷，其中排氣歧管更是要求高品質的汽車零件之一，係由球墨鑄鐵材料製作而成。在澆鑄過程中，由於球化劑中的鎂、鈰容易與空氣形成強烈的氧化反應，這些氧化物缺陷對球墨鑄鐵造成許多危害，因此了解氧化層的形成是非常重要的。本研究利用模擬計算觀察球墨鑄鐵排氣歧管的澆鑄過程，討論流動與凝固對澆鑄的影響，以了解缺陷的形成。模擬結果發現，鑄件中氧化物的分佈，不僅受液態金屬的溫度影響，也受流動模式影響。在同一個位置有多個方向的流動匯集，若有不適當的流動，造成捲入更多氧化膜，降低鑄件品質；相反的，流動型態若充分的填滿流道系統，則是較為合適的流動型態。高品質的鑄件應當盡力減少氧化物的產生，因此本研究利用澆注系統設計的改善，可以調整流動的型態進而提升排氣歧管之鑄件品質。

關鍵字

模擬；表面缺陷；鑄造；球墨鑄鐵；排氣歧管

並列摘要

In recent years, high quality automobile parts are demanded in the highly developed and sophisticated car industry. Especially for safety concerns, these parts not only require light weight and high strength but also have to be defect free. Exhaust manifold is one of quality demanding parts which are made of ductile iron. The ductile irons are known to bear detrimental oxide defects formed by oxidation of Mg and Ce containing nodulizing agents when contacting with air. It is important to understand the formation of oxide defect in casting of complex castings such as exhaust manifold. In this study, the casting of a ductile iron exhaust manifold is computationally simulated. Influence of flow pattern is discussed to understand the formation of possible defects. Simulation results show that the distribution of oxides in the mold cavity is not only affected by temperature of liquid metal but is also affected by the flow pattern. The flow pattern in one location of the mold cavity sometimes is affected by flow streams from multiple directions. Inappropriate flow pattern design can result in the entrapment of oxide films which cause the degradation of casting quality. In contrast, a suitable flow pattern results in steady flow filling of the runner system sequentially and during the casting process. A high quality part without oxide defects could be produced. Therefore, flow pattern design during casting should be taken into consideration for improvement in complex casting quality.

並列關鍵字

Simulation ； Surface Defect ； Casting ； Ductile Iron ； Exhaust Manifold

國際替代計量

球墨鑄鐵排氣歧管之澆鑄模擬研究

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