目前汽車鋁合金輪圈多半採用低壓鑄造方式生產，由於輪圈具有模型不透明性與幾何外型複雜的特徵，在產品開發前要掌握適當的製程參數並不容易，通常於生產完成後，觀察不適當的製程參數所產生的缺陷，憑著經驗與試誤方式，再予以調整製程參數，浪費大量時間與成本。 本文的目的是利用電腦輔助分析的優點，在產品開發時完成適當製程參數的設定，降低試誤所浪費的時間與成本。其方式為採用真實模型案例，探討加壓速率與環境自然冷卻對低壓鑄造鋁合金輪圈的充型與凝固過程的影響，分析捲氣與凝固的情形，提出改善的加壓條件與空氣強制對流冷卻位置與持續時間、離型劑厚度與模型幾何的修正，減少氣孔與縮孔缺陷。 結果顯示，充型過程中，若加壓速率過大，會在澆注口處形成液柱且強烈撞擊模型內壁產生大量的捲氣，並於輪轂區域產生渦流場，使得空氣滯留於輪轂區域，因此，降低加壓速率可明顯減少捲氣的發生。同時對降低的加壓速率作氧化膜分析，結果顯示此加壓速率可避免鋁液流經升液管、輪轂與肋區域的氧化膜捲入，但受到輪圈幾何外型的影響，氧化膜會殘留於胎環之中。凝固過程中，在自然環境冷卻條件下，縮孔發生於厚度變化大的區域，如胎環上緣、肋與胎環交界處以及胎環裝飾洞區域，必須在這些區域加入空氣強制對流冷卻、修正離形劑厚度與模型，增加或減少局部區域散熱量，方能達成方向性凝固，消除縮孔缺陷。 Low pressure die casting is currently the major process used to produce automobile aluminum alloy wheels. Due to the opacity of mold and the geometric complexity of wheel, it is laborious to set up the process parameters for manufacturing the wheels. Usually it depends on working experiences and try-and-error approaches to avoid the wheel defects, which therefore wastes a lot of time and costs. The purpose of this study is to reduce the waste of time and costs for manufacturing aluminum wheels by the low pressure die cast process by introducing the computer-aid-engineering (CAE) to help set up appropriate process parameters. We use a real mold to discuss the influence of pressure slopes and cooling schemes on the mold filling and solidification. The defects resulting from the entrained air and shrinkage pore are reduced by adjusting the pressure rising speed, the cooling time and locations, the thickness of the mold release agent and geometry of the mold. Simulation results reveal that fountains forming at the sprue intensely hit the mold cavity, which produce a lot of entrained air. The resulting vortices in the hub using trap the air if the pressure rising speed is too fast. Such entrained air and trapping phenomena can be eliminated largely by reducing the pressure speed, which also can prevent oxide films residing in the riser tube, hub and spokes. When only applied is natural convection to the solidification process it is found that shrinkage occur in the top of the rim, interface of spoke and rim and the decorated pores, which are all varying a lot in thickness. For the sake of defect elimination, we add force convection at certain locations of the mold, as well as modify the thickness of mold release agent and mold, so as to achieve the directional solidification by adjusting the local heat flux.
