摘 要
鋁合金重力鑄造過程中，進模口流道大小影響進入模穴的整體入水流量，以及影響金屬液體是否能在最短時間內完成模穴的充滿。為了避免因過小的流量，導致在完成澆鑄前，金屬液體失溫而提早凝固所形成冷接(cold-shut)的澆鑄缺陷，本研究旨在透過CFD(計算流體力學/Computational Fluid Dynamics)軟體，模擬鋁合金重力鑄造澆鑄過程，目的要找出所謂臨界流量與鑄件型體係數在不同澆鑄溫度下之關係。根據Chivorinov規則，對任意一複雜鑄件所謂的冷接型體係數Spcold及冷接模具常數Bcold，進行此規則的修改，以得到兩者間避免冷接缺陷的線性關係公式。由澆鑄模擬結果，建立澆鑄溫度、鑄件型體、以及臨界流量三者間之關係。採用汽車鋁合金轉向節為本研究鑄件型體，分別在四個不同澆鑄溫度下、四個不同進模口方向、以及四個型體縮放倍率等變因，進行澆鑄模擬分析。模擬結果觀察到同樣的鑄件，較高的所謂冷接型體係數Spcold允許更久的澆鑄時間，亦即可以使用較低的入水流量而不產生澆鑄缺陷，利用求得之冷接臨界模具常數Bcold與冷接型體係數Spcold之關係，得以透過欲鑄造鑄件之冷接型體係數Spcold推算所需要的臨界入水流量(Qc)，藉此計算出不產生冷接缺陷之最小進模口大小，並得到模擬驗證。關鍵詞：鋁合金砂模重力鑄造、冷接、型體係數、模具常數、臨界進模口流量
ABSTRACT
In aluminum gravity casting, the size of the ingate affects the overall flow rate of molten aluminum entering the mold cavity. This also impacts whether the molten metal can completely fill a mold cavity in a very short time without the formation of the cold-shut defect , resulting from insufficient flow rate caused by a small ingate size. In this study, Computational Fluid
Dynamics (CFD) package was used to model the filling process of the aluminum knuckle casting. The purpose is to find the relationship between the critical flow rate and the casting shape factor at various initial filling temperatures.
Based on the Chvorinov rule, the so-called linear relationship between cold-shut shape factor Spcold and mold constant Bcold cold-shut prevention was constructed for arbitrary casting shape. The linear relations among the filling temperature, shape factor, and critical flow rate was established in this study. The automobile aluminum component, the knuckle, was used in the experiments. The experimental variables for modeling include the knuckle sizes with four magnification ratios, four initial filling temperatures, and four orientations of the bottom ingates.
The results show that the higher the cold-shut shape factor, the longer the filling time, and the lower the ingate flow rate required, without the formation of cold-shut defects. Using the obtained relationship between the cold-shut critical mold constant Bcold and the cold-shut shape factor Spcold relationship, the critical ingate flow rate (Qc) based on the designated casting component's cold-shut shape factor Spcold was inversely calculated. This calculation could be used to determine the minimum ingate size required to prevent the occurrence of cold-shut defects.
Keyword: aluminum alloy sand gravity casting, cold-shut defect, shape factor, mold constant, critical flow rate