以流變基礎研究射出成型品質

A Study for Injection Molding Quality Based on Rheology

許耿睿(Geng-Ruei Syu)

指導教授 ： 林忠志

國立虎尾科技大學/工程學院/機械與電腦輔助工程系碩士班/碩士(2013年)

摘要

在各種生產製程上塑膠成型技術運用非常廣泛，在射出成型中，塑膠黏度受到溫度、壓力與剪切率影響，但是射出成型過程中無法線上直接量測，因此常只利用模穴壓力感測器來探討壓力對黏度的影響，卻忽略了融膠流動時所產生的剪切率與剪切應力的影響，像是剪切應力過高會對塑膠材料產生負面作用，塑膠分子鏈易產生斷裂，使產品的機械強度大幅下降，但在肉眼上卻無法判斷。
本實驗是找兩種不同黏度的塑膠材料，運用兩組模穴壓力感測器安裝在模具內可同時得到時間與壓力數據，並以簡單的程式設計找出時間差與壓力差，代入黏度的公式，算出熔融塑料在模穴流動過程中剪切率、相對黏度和相對剪切應力等數據，可以計算剪切率、剪切應力、黏度等數據做為產品在射出過程中是否穩定的依據，並由調整射出速度與熔膠溫度兩參數，找出符合產品規格的成形視窗(Process Window)，並由成型視窗中加以探討射出成型時黏度、剪切率與剪切應力所譜出3D流變性質圖，再透過MoldFlow軟體分析，找出模擬的產品成型視窗，並由成型視窗中抓取點參數進行射出分析，譜出3D流變性質圖與實際實驗加以比對，且利用衝擊與拉伸試驗驗證流變性質圖對產品強度較佳的範圍。

關鍵字

剪切率 ； 黏度 ； 剪應力 ； 成型視窗 ； 流變性質圖

並列摘要

Injection process is popular due to a complicated part can be made efficiently. The raw material is melt and forced into a mold, then the part is ejected after a few seconds of cooling time. The melt behavior can be described by shear stress, shear rate, and viscosity. Different molding parameters can result in different melt state. Some injection molding quality can be detected through the melt state calculation. In this study, we propose a methodology to determine melt state based on Rheology, A mold installed with two pressure sensors in which different locations. As the time interval and pressure difference are gotten, shear stress, shear rate, and viscosity can be calculated immediately. Those information related to melt state can be regarded as the indication of injection molding quality.
In experimental, a specimen mold is prepared to validate the influence of melt state on molding quality. The specimens include tensile test specimen and impact test specimen according to ASTM D8638 and D256, respectively. In addition, how to construct a process window for injection molding is also proposed, which is useful for deterring molding quality.

並列關鍵字

shear rate ； viscosity ； shear stress ； process window ； rheological property.

參考文獻

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[2] John P.Beaumont., 2004, “Runner and Gating Design Handbook : Tools for Successful Injection Molding”, Hanser Gardner, 359-366

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[7] Kamber, et al., 2009, ”Experimental investigation of plastic injection molding: Assessment of the effects of cavity pressure and mold temperature on the quality of the final products”， Materials and Design , 30(8), pp. 3217–3224.

[18]張怡哲，2012，”射出成型模穴壓力的安裝設計與研究”，國立虎尾科技大學，碩士論文。