摘 要
球墨鑄鐵控制臂鑄件凝固過程中鑄件中較薄處先期凝固，形成所謂一鑄件兩熱點型體鑄件。本研究提出以最佳熱襯設計，貼附額外的熱襯型體於此鑄件中兩熱點間較薄處，以增加此薄處的凝固時間，消除凝固時形成兩熱點現象。
使用商業計算流體力學數值凝固模擬軟體，進行虛擬兩熱點鑄件型體之凝固模擬實驗，以找尋最佳冒口及熱襯型體。提出無單位所謂兩熱點型體係數(Sp*)，並建立最佳冒口和熱襯、分別與虛擬鑄件之凝固模數比值，再與Sp*的關係式。
當控制臂之無單位兩熱點型體係數內插帶入關係式，所需要的最佳Mf、Mp、及Mc，再進行凝固模擬，得到縮孔距離Ds為正值縮孔位於冒口內，因此此關係式，成功得到驗證。
關鍵詞：控制臂、兩熱點型體鑄件、冒口設計、熱襯設計、方向性凝固、凝固模數、兩熱點型體係數
ABSTRACT
Spheroidal graphite iron control-arm castings are considered as the two-hotspot geometry castings. In this study, an optimized padding design is proposed. By attaching an additional padding geometry next to the thinner section between the two hotspots, the local solidification time of the thinner section is extended, preventing premature solidification and eliminating the formation of two hotspots.
A commercial computational fluid dynamics (CFD) solidification simulation package was employed to analyze the solidification behavior of a two-hotspot cast and to optimize the padding geometry to be attached in the thinner region. In this study, a dimensionless Hotspot Shape Factor (Sp*) is proposed. This factor is used in a regression conversion formula to convert dummy castings to actual castings. Subsequently, the inverse linear relationships for the optimized solidification modulus ratios of the feeder/cast (Mfc) and padding/cast (Mpc) against Sp* were respectively proposed.
To verify this proposed relation, a commercially complex, structured ductile iron control-arm cast was applied. From interpolating the Sp* value of this control arm into the relation equation, the optimized solidification modulus ratios of Mf:Mp:Mc are derived. Finally, in the solidification modeling result, the shrinkage distance DS is a positive value, implied that the shrinkage occurs within the feeder. The proposed relation was successfully validated.
Keywords: Control-arm, Two-hotspot geometry cast, Feeder design, Padding design, Directional solidification, Solidification modulus, Two-hotspot shape factor.