降低鋁合金壓鑄加工品氣孔發生率之研究

本研究以鋁合金A356為原料，應用壓鑄法來探討液晶顯示器金屬外殼的成型過程;因為壓鑄件所需要投資的模具金額相當耗資，而研發者為了能將壓鑄模具的投資成本攤提到最小化的狀況，會在設計壓鑄模具時，同時為將來可能會衍生出來的版本預留一些肉厚，以便於後製程的加工需求，這也造成了在壓鑄製程上因為肉厚過厚的問題而常無法避免氣孔品質問題的產生，特別是當氣孔的位置出現在CNC加工的位置時，其最終成品常無法通過IP67防水測試，所以本研究的重點在利用模流分析軟體來事先推演出氣孔的位置及大小。為了確認問題的所在與可能的不良情況，首先使用模流分析軟體C3P.Cast模擬鋁合金A356在模穴中流體與氣體充填和排出的情形，以預測壓鑄充填時可能會發生的缺陷，再以實際生產出來的產品做驗證分析與比對，來得到最佳化之澆口尺寸、流道、溢料區和排氣井，最後再針對壓鑄中常見的氣孔問題在模流分析軟體上進行模擬和分析。本研究針對一片現有的液晶顯示器金屬外殼執行模具修改前後的模流分析，並以其結果和實際的壓鑄品進行驗證分析和比對，該模具在未修改前因有1-2毫米的氣孔問題導致產品良率低下，經過模流分析出來的結果，將進料澆口的寬度加大及取消掉一個小溢料區與加長排氣井後，可以很明顯看到流體的波向趨近穩態，實際壓鑄品所得到的氣孔尺寸改善到約0.1-0.3毫米，氣孔的位置也控制在可容許的位置，使得液晶顯示器金屬外殼在IP67的良品率上大幅提升。

關鍵字

IP67 ；氣孔；鋁合金 A356 ；壓鑄；模流分析

並列摘要

This research aims to investigate the case for Aluminum alloy A356 with die casting technology of LCD shell’s molding process; because die casting part need to make big investment on mold so RD will make the mold to be used in several versions and the investment can be amortized to a minimum value. Therefore, RD need to keep a thick wall in casting part for prevent different need in CNC machining process in future. Due to the design of thick wall, it would be hard to avoid porosity issues occur in casting part. Especially when porosity is located on CNC machining area, it would be hard to pass IP67 test in the final LCD display. So this research focus in how to use mold flow simulation software to simulate porosity size and porosity location. In order to identify defective symptoms and root causes, we use software C3P.casting to simulate the filling process and analysis potential failures inside the cavity. Then taking advantage of the realistic experiment from the factory we did experiment to prove and validate the efficiency of simulation results. The simulation results would be able to acquire the best filling procedures including gate, runner and material over flow area. This case is mainly focus on LCD display metal cover to do mold flow simulation analysis and reducing the defect rate of porosity. Based on the investigation results of difference between before and after mold modification; before mold modification the porosity size is about 1-2mm and the production yield is low. After mold modification on enlarge the gate size、remove some area of runner and extend over flow length, the mold flow analysis results shows a stable filling procedure within cavity. And we have smaller porosity between 0.1-0.3mm and big improvement on production yield which prove the simulation results.