反壓對氣體輔助製程中熔膠阻力影響之研究

Study on the Gas Counter Pressure in Gas-Assisted Injection Molding by Melt drag

黃宣淵(Hsuan-Yuan Huang)

指導教授 ： 鍾文仁

中原大學/工學院/機械工程研究所/碩士(2015年)

https://doi.org/10.6840/cycu201500735

摘要

氣體輔助射出成型(Gas Assisted Injection Molding, GAIM)技術在塑膠射出成型中，是屬於綠色節能射出技術的一種，其原理是將熔融塑料充填入模穴中，在熔膠尚未充填完成，短射情況下則開始充填氣體，直到熔膠填滿整個模穴，藉由氣體在內部掏空處均勻的進行保壓及冷卻，接著將氣體排出即完成製程，以減少塑料達到節能減碳的目的。
氣體輔助射出成型對於成型品質的改善有許多幫助，礙於氣體具可壓縮性，不容易作精密控制，在成品應用上仍有穿透長度不足與皮層厚度不均等缺點，容易產生成品收縮不均以致影響其外觀；熔膠流動阻力對輔助氣體的穿透力為影響製程的主要因素，而影響氣體穿透力的參數為輔助氣體充填壓力，壓力控制需在流動管路加裝壓力感測器，並透過氣體輔機的可調參數來做變化；而氣體反壓技術(Gas Counter Pressure, GCP)以往多被應用在發泡成型(Foaming Injection Molding)中來控制氣泡大小方向，藉以改善發泡成型品的成品品質。
本研究設計迴紋針件模仁，進行具反壓對氣體輔助製程中熔膠阻力影響的實驗，主要透過控制氣體反壓壓力與輔助氣體充填壓力於固定壓差，觀察由固定壓差60bar、70bar、80bar、90bar成型過程中熔膠阻力流動變化，分析成品穿透長度、熔膠阻力與成型參數的關係，歸納其製程的特性；探討反壓對氣體輔助製程中熔膠阻力及成型品穿透率的影響，建立反壓對氣體輔助製程中熔膠阻力的資料庫。
實驗結果顯示，反壓對氣體輔助製程中熔膠阻力影響，主因熔膠呈現黏彈性行為，其特性為熔膠黏度與壓力相關，壓力愈大、熔膠愈黏，熔膠黏度上升、流動阻力隨之變大，固定壓差壓力過低時產品不易成形；適當的固定壓差有助於抑制熔膠產生噴泉流效應且幫助中空成形；固定壓差在高壓時，需較高的射出壓力、穿透長度則無明顯差異，無法發揮效益；在輔助氣體壓力相同，反壓壓力增加，熔膠充填流速慢、此時黏度高，凝固層厚度增加，穿透截面積縮小，一次穿透與總穿透長度變化呈現隨反壓壓力上升而增加的趨勢；在反壓壓力相同，輔助氣體壓力增加，輔助氣體推動較多的熔膠體積前進，凝固層厚度減少，穿透截面積增大，一次穿透與總穿透長度變化呈現隨輔助氣體壓力上升而減少的趨勢。

關鍵字

氣體輔助射出成型 ； 氣體反壓 ； 熔膠阻力 ； 固定壓差

並列摘要

Gas-assisted injection molding technology(GAIM) a kind of green energy in plastic injection molding, which is injecting gas into the short shot melt in the packing stage. Compressed gas is used as the medium to push melt and maintain pressure. Thus, plastic can be saved effectively to reduce carbon.
Though gas-assisted injection molding has some great improvements in injection quality, compressed gas is still not easy to control preciously, therefore, the final applied products have some defects such as insufficient penetration length, uneven thickness and uneven shrinkage which affects its appearance. Melt flow resistance of gas penetration is the main factor affecting the manufacturing process, and the gas pressure in packing stage would affect the gas penetration. The pressure sensor is installed in the flow pipe, and control the pressure by the adjustable parameters. Gas Counter Pressure (GCP) technology is applied on Forming Injection Molding to control the direction of the bubble size, so as to improve the molding quality.
The study uses the mold core with the shape of paperclip to discuss how the gas counter pressure works in gas-assisted injection molding by melt drag test. Observing how the flow changes by controlling the gas counter pressure and auxiliary gas injection pressure at a constant pressure difference (60bar, 70bar, 80bar and 90bar). And analyzing the relationship between penetration lengths, melt drag flow and molding parameters. This study discussed the effects of counter pressure mechanism on gas-assisted injection molding process and established the database about the mold flow resistance of counter pressure.
Experimental results show that the main factor of counter pressure affecting melt resistance is the viscoelastic behavior of the melt in gas-assisted injection molding. The greater the pressure is, the more melt viscosity became. The proper constant pressure difference helps to inhibit melt flow effect Fountain Flow Effect and helps to produce a hollow. Low constant pressure difference forming product is not easy. Constant pressure difference at high pressures was no significant difference about penetration length, unable to play a benefit.

並列關鍵字

Gas-Assisted Injection Molding(GAIM) ； Gas Counter Pressure(GCP) ； Melt drag ； Constant Pressure Difference

參考文獻

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