- 期刊
鋁合金重力金屬模具常數和型體形狀係數影響冷接缺陷的研究
The Study of Cold Shut Defect Influenced by the Shape Factor and the Mold Constant in Aluminum Die Casting
摘要
鋁合金金屬模重力鑄造之澆鑄過程中，金屬液體因為澆鑄流量太小，造成尚未澆鑄完成而液體過早凝固，即產生所謂冷接（cold shut）或滯流（misrun）等鑄造缺陷。為了避免這些缺陷，本研究針對型體係數（shape factor, Sp）和模具常數（mold constant, B）分別與臨界流量關係的電腦計算流體力學（Computational Fluid Dynamics, CFD）的數值模擬研究，以分析其理論意義，及最終能建立入水口（ingate）的尺寸大小之設計公式及準則。進行四種型體鋁合金鑄件，搭配三種金屬模具初始溫度（673K、723K、及753K）進行所謂最小所需入水口流量（critical minimum flow-rate, Qc）的鑄造模擬。從同一種鑄件型體以不同放大倍率的放大或縮小，進行鑄造的模擬後，找出分別鑄件最大允許澆鑄時間（maximum critical filling time, tc）；依據Chvorinov's Rule可以分析得出鑄件型體的凝固模數（solidification modulus of casting, Mc）與允許澆鑄時間的平方根（√tc）的線性關聯。此線性關係式的斜率，即所謂澆鑄型體的臨界模具常數（critical cold-shut mold constant, Bcold）。再由Bcold與其所謂的無因次型體的形體係數（cold-shut Shape factor, Spcold）建立關聯，則可以應用此關係式來預測任一鋁合金鑄件型體之最大允許澆鑄時間，即可以訂定避免冷接缺陷的入水口尺寸設計準則。
並列摘要
In the process of the aluminum gravity die casting, the filling process is not completed and the liquid metal is solidified prematurely, resulting in so-called cold shut or misrun defects within the casting, due to the flow rate of the filling being minimized. To avoid these defects, the purpose of this study is to analyze the theoretical meaning and the relationship among the shape factor (Sp), mold constant, and critical flow rate using Computational Fluid Dynamic (CFD) modeling, and to build up the rule for ingate design. The four types of casting were cast in three initial mold temperatures with 673K, 723K, and 753K to find out the critical filling flow rate (Qc) in the ingates. From modeling the various magnifications of the same geometric shape of the castings, the maximum critical filling time (tc) can be found. Based on Chvorinov's Rule, the relationship between the solidification modulus of the casting (Mc) and the square root of the critical filling time (√tc) could be developed. The slope of that linear relationship is the so-called critical mold constant (B_(cold)). From the relation between the B_(cold) and Sp_(cold), the rule of ingate size design with maximizing critical filling time could be created to avoid cold shut defects.