本論文在探討以工程塑料Noryl GFN3 進行射出加工時，在材料內部出現的空孔問題。Noryl材料最初由美國GE公司所開發的高分子材料，由於其加工性優良、尺寸穩定性好、吸水率低、絕緣性佳、耐熱性能、耐酸鹼、密度低及阻燃性高等特性，因而受到工業界廣泛應用。本實驗所使用的Nory材料為Sabic公司所生產的塑料產品，並添加有30%的玻璃纖維成份，故在品名上加註有GFN3字樣做區分。
本實驗是以射出成型方法加工出一塊厚度為40mm的工件，觀察其冷卻後空孔型態的差異。實驗開始首先刻意將材料的射出劑量做適當的減量，以確保材料冷卻收縮後可有適當的空孔數量供觀察。研究以射出參數中的”料溫”與”射出壓力”做為控制因子，進行2因子3水準的全因子實驗。射注後的工件透過 X-ray 進行非破壞式的缺陷檢測，再將所得到的底片經由灰階影像處理，以利於計算實驗後的空孔尺寸及數量。最終歸納出空孔的型態與各控制因子的相關性。由實驗結果中發現，高料溫及低射注壓力的參數條件可將材料內部的孔缺陷細化，以及材料內部的空孔尺寸越小，冷卻收縮的變形量越小 。

關鍵字 : Noryl、射出成型、空孔、料溫、射出壓力

Extended Abstract

Analysis of Voids Defect in Injection Molding Process

　Author: Yao-Tse Tsai
　　Advisor: Jung-Hua Chou

Department of Engineering Science College of Science

SUMMARY
This thesis explored the voids defect during injection which occurred in the core of engineering plastic Noryl GFN3. The experiments were based on injection molding technology to make the components with the thickness of 40mm and to observe the void characteristics after cooling. In the experiment, a shorter injection time was purposefully used to generate an enough number of holes for analysis. The injection control parameters were injection temperature and pressure with three levels each; i.e., a full factorial experiment of two factors with three levels each.

After the injection process, the work piece was inspected by the X- ray to observe the internal defects; the X-ray images were processed graphically using grayscales to obtain the size and quantity of the voids defect. Finally, summed voids patterns and each control factor correlation. The results showed that under conditions of high temperature and low pressure, the void size could be reduced; the void size could also be reduced.

Keywords: Noryl, injection molding, voids, injection temperature,
injection pressure

INTRODUCTION

Injection molding technology is a combination of multi-knowledge in order to have good quality. The technology is used extensively in plastic products, because not only the production is fast but also the profile can be controlled quite meticulously to suit a wide range of applications markets. On the other hand, despite the facts that the injection molding technology is good for mass production, short production cycle, stable quality, high precision and less waste, etc., defects could occur when the product thickness is large. This thesis explored mainly the relationship between the void defects and the injection molding process parameters.

MATERIALS AND METHODS

The material used in this experiment was Noryl GFN3, and the experiment deliberately used inadequate filling conditions in the injection molding process to generate void defects inside the mold components. Two parameters of injection pressure and injection temperature were used to design a 2-factors and 3-levels full factorial experiment. Then we used the X-ray non-destructive detection method to measure the characteristics of voids to determine the size and number of the defects. We also observed its deformation and surface defects after cooling to draw some conclusions. In this 2-factors 3-levels experiment, the nine experimental group, labeled from A to I as follows:

A: Injection temperature, 275℃; Injection pressure, 110 Mpa
B: Injection temperature, 275℃; Injection pressure, 160 Mpa
C: Injection temperature, 275℃; Injection pressure, 220 Mpa
D: Injection temperature, 285℃; Injection pressure, 110 Mpa
E: Injection temperature, 285℃; Injection pressure, 160 Mpa
F: Injection temperature, 285℃; Injection pressure, 220 Mpa
G: Injection temperature, 300℃; Injection pressure, 110 Mpa
H: Injection temperature, 300℃; Injection pressure, 160 Mpa
I: Injection temperature, 300℃; Injection pressure, 220 Mpa

RESULTS AND DISCUSSION

The average size of voids for each case is as below: A: diameter 2.21 mm; B: diameter 2.44 mm; C: diameter 2.67 mm D: diameter 2.49 mm; E: diameter 2.58 mm; F: diameter 2.42 mm; G: diameter 2.34 mm; H: diameter 1.51 mm; I: diameter 1.29 mm
For the surface quality checking results, in addition to the obvious bonding line on some parts, the rest had no obvious abnormalities. After comparing the deformation with voids of each experimental group, we are able to see that small voids had better ability of resisting deformation.

CONCLUSION

Under the conditions of injection temperature approaching 300℃ and lower injection pressure, the voids size was smaller.
2. For the injection pressure as lower as 110MPa alone, the voids could not be smaller.
3. The bonding line appeared easily in the condition of a low injection temperature.
4. A smaller void resisted deformation better.

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