應用田口方法探討大平面薄壁鎂合金AZ91D 鑄件壓鑄製程條件之研究

Abstract

鎂合金壓鑄產品經常容易發生充填不足、熱裂、表面流紋與變形等缺陷，這些缺陷和射出壓力、射出速度、射出溫度與模具溫度等製程條件有密切關係。鎂合金製品之開發試作，一般係利用試誤法來求得較適當的製程條件之組合，但是，試誤過程既費時又無法保證穫得最佳的製程條件。近幾年，田口實驗設計法成了改善産品品質的有利工具，本研究結合Flow-3D模流分析軟體與田口實驗設計法規劃實驗分析條件，進行大平面薄壁鎂合金AZ91D(筆記型電腦底蓋產品)的模流分析，應用直交表和信號雜訊比來求出最佳的製程條件。模流分析之條件組合是以L9 直交表進行規劃設計，選擇射出壓力、射出速度、射出溫度、模具溫度爲控制因子，每一因子皆選擇三個實驗水準，品質目標設定為在模穴內必須具有最少固溶率、最小壓力差與最小溫度差。 由變異數分析求得最佳製程條件組合為射出壓力17Mpa、射出速度100m/s、射出溫度625℃、模具溫度250℃，再經由Flow-3D 模擬結果，三目標值均有明顯改進，可有效改善壓鑄件缺陷，提昇產品的穩健性。

Die casting products of magnesium alloys very often show non-filling, hot cracking, apparent flow mark and deformation etc. These defects are closely related with process conditions of filling time, fusion temperature, cooling temperature of die and maintaining pressure etc. Generally, in the development of magnesium die casting products, trial and error method was used to find the suitable combination of process conditions. It is time consuming and not necessarily assure the best results. Recently TAGUCHI experiment design methods are adopted for improving product quality. In this study, we combine TAGUCHI experiment design method with Flow-3D flow analysis package for simulation of making large plane thin wall workpiece of magnesium alloys. L9 orthogonal table was used, and filling time, fusion temperature, cooling temperature of die, maintaining pressure, viscosity was chose as control parameters. Three levels of each parameter were selected for the experiment. Minimum solid fraction and most homogeneous temperature and pressure distribution in the die cavity, were set as the best casting conditions. From variance analysis, we found out the combination of optimum process condition are, fusion pressure-17Mpa, fusion speed-100m/s, fusion temperature-625℃, cooling temperature of die-250℃. An independent analytical process parameters combination was selected based on the result found for die-casting simulation, and the result shows the improvement of the product.