底模設計對DC鑄造鋁錠的應力與翹曲缺陷之影響數值分析

Effect of Bottom Mold design on the Stress and Butt Curl of DC Casting Aluminum Ingot by Numerical Simulation

吳承翰(Cheng-Han Wu)；林惠娟(Huey-Jiuan Lin)

數值分析 ； 鋁合金 ； DC鑄造 ； 熱應力 ； Numerical analysis ； AA6063 ； DC casting ； stress

鑄造工程學刊

48卷2期（2022 / 12 / 01）

31 - 38

繁體中文;英文

DC（Direct-chill）鑄造是目前生產大尺寸鋁錠的主要技術，但至今依然有許多值得探討的議題。由文獻資料發現，鋁錠不均勻的冷卻，易產生較大的熱應力／應變，並導致熱／冷裂紋和翹曲（butt curl）缺陷，嚴重影響鋁錠最終品質。而藉由底模設計配合澆鑄條件，可改善鋁錠內部較大的熱應力／應變，並減緩底部翹曲程度，提升鋁錠整體的品質。為了瞭解底模設計在6063鋁合金對製程中鋁錠的應力場和翹曲的結果，本研究採用FLOW-3D CAST^(TM)套裝軟體，分析四種底模的設計和二次冷卻的熱傳係數對鋁錠的應力分布及翹曲的影響。該軟體利用FAVOR和有限差分法描述複雜的形體，以TruVOF精準分析液體的流動，並採用有限元素法進行熱應力分析，模擬流體凝固後的應力發展與形變。數值模擬分析結果得知，主拉伸應力分布於水冷模具下方、鋁錠角落、底模的長邊和鋁錠內部，而此拉伸應力的方向可能導致中心裂紋、J型裂紋和四分之一點裂紋的產生。雙曲底模再配合較低的熱傳係數，能降低鋁錠整體的應力值，可得到最小的變形量和翹曲量。

DC(Direct-chill) continuous casting is the main process for producing large size aluminum alloy ingot. From literatures, it is found that uneven cooling of aluminum ingots generates large thermal stress, which can easily lead to cracks and butt curl, seriously affecting the final quality of the ingot. The bottom mold design and casting conditions can improve the overall quality of the ingot by improving the thermal stress inside the ingot and reducing the butt curl. In order to understand the effect of mold design on the stress field and butt curl of 6063 aluminum ingots, this study used the FLOW-3D CAST^(TM) software package is used to analyze the effect of four mold designs on the stress distribution and butt curl of aluminum ingots. The software use FAVOR and finite difference method to describe the complex shape, TruVOF to accurately analyze the liquid flow, and finite element method to perform thermal stress analysis to simulate the stress development and deformation of the fluid after solidification. The results of the numerical simulation showed that the main tensile stresses were distributed under the water-cooled mold, at the corners of the aluminum ingot, on the long side of the bottom mold and inside the aluminum ingot, and the direction of the main tensile stresses may lead to the formation of central cracks, J-shaped cracks and quarter-point cracks. Among the four bottom mold designs, the bicurl bottom mold design reduces the overall stress value of the ingot and results in the least amount of deformation and butt curl of the ingot as a whole.

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