氣體反壓對於射出成型流場特性/分子排向以及成型品品質影響之初步評估

Preliminary Evaluation on the Influence of Gas Counter Pressure on the Process Flow Characteristics, Molecular Orientation and Qualities of Injection Molded Parts.

黃松煒(Sung-Wei Huang)

指導教授 ： 陳夏宗

中原大學/工學院/機械工程研究所/博士(2012年)

https://doi.org/10.6840/cycu201201074

摘要

無論傳統射出成型或是革新射出成型如氣體輔助射出成型、超臨界流體微細發泡射出成型、共同射出或多成分射出成型等都受到一些共同性的製程特性限制。特別是熱塑性高分子在模穴間隙的流動產生高度的排向，再加上波前的噴泉效應，這些高度排向的高分子被凍結在溫度較低的模穴表面形成流動殘留應力。分子的高度排向會產生不等向性的性質，特別是不等向性收縮，使得產品的精度難以控制。本研究採取創新氣體反壓技術控制使高分子流動過程中的排向差異降低，消除流動產生的應力，將是有
效提升產品品質與良率的重要關鍵。
本研究以不同塑膠材料(PP、PS)、產品厚度(0.6mm、1.2mm)和射出率(5、10、15、20、30 cm3/s)，在有、無氣體反壓狀態下，以拉伸試片作為基礎實驗的比較，探討機械性質含拉伸強度與彈性係數的變化以及試片收縮率的差異；利用排向所造成的結晶度改變以及產品厚度橫截面波前的比較作討論，最後透過可視化模具與高速攝影配合內部氣體輔助成型案例，說明模內氣體反壓的建立同樣在進階製程具影響性，對氣體穿透狀態有可控制的效果。
研究結果顯示，氣體反壓對於傳統射出成型具有兩種效果，一是降低分子排向、二是反向持壓。收縮率在實驗與分析結果都呈現在有氣體反壓的參數而降低；實驗之收縮率降低在帄行流動方向平均0.0293%~0.1188%，垂直流動方向平均0.0173%~0.0668%。在彈性係數結果方面，有氣體反壓的實驗組數都呈現提升的趨勢，平均增加程度為0.4588%~2.8850%。在拉伸強度部分因材料黏度因素，在PP材料會因氣體反壓的持壓效果而增強，於厚度0.6mm、1.2mm試片強度分別增加0.1937%、4.6014%，在PS材料則受氣體反壓的排向抑制下降低了1.8994%。在結晶度的結果，在具氣體反壓抑制因排向產生之流動引發結晶，於厚度0.6mm、1.2mm 試片結晶度分別下降1.987%、2.560%。從SEM測量波前剖面圖可得到氣體反壓明顯將波前抑制而平緩，而低黏度材料PP具有更明顯的效果。在可視化與內部氣體射出成型得到反壓的阻力會直接影響其穿透性，在傳統氣體輔助成型於無反壓阻力下，穿透長度高於具氣體反壓壓力(30bar)成型2.44 倍，在穿透面積則達2.28 倍。

關鍵字

氣體輔助射出成型 ； 可視化 ； 分子排向 ； 結晶度 ； 機械性質 ； 氣體反壓 ； 收縮率

並列摘要

Although injection molding is the most cost-effective way for the production of plastic components for industrial needs, it is subjected to restriction in process characteristics. So as the other innovation process including gas-assisted injection, microcellular foam injection, co-injection, etc..
When hot melt flows within the narrow gap of mold cavity, it induces highly orientated polymer molecular chain. Moreover, due to the fountain flow effect,hot melt is brought to the mold surface and become frozen resulting in the flow-induced residual stress. Both factors contribute to the warpage formation significantly and make the high accurate dimension not easily achieved.
In this study, the various polymer material (PP, PS), and product thickness(0.6mm, 1.2mm), and flow rate (5, 10, 15, 20, 30 cm3/s) were discovered with the developed technology of gas counter pressure (GCP). The conventional and GCP molding were be performed to investigate the associated influence on part shrinkage, mechanical property, crystallinity and the shape of melt front cross-section. Finally, the gas-assisted molding of filling characteristics was conducted through the visualization method, transparent mold and high speed camera.
As from the results, the GCP had two effects in conventional injection molding (CIM). One is the restriction of molecular orientation, and the other is counter holding effect. In the results of shrinkage, the experimental and simulated both showed the shrinkage would be reduced under GCP of condition.
In the experimental results, the average reducing ratio were from 0.0293% to 0.1188% in paralleled flow direction, 0.0173% to 0.0668% in perpendicular flow direction. In the results of elastic module, the degree would be enhanced
with GCP of condition, and the average increasing ratios were from 0.1529% to 0.9617%. In the results of tensile strength, due to the holding effect of GCP, the average increasing ratios of PP resin were 0.1937% (0.6mm) and 4.6014%(1.2mm) respectively. The average decreasing ratios of PS resin was 1.8994%,because of the restricted molecular orientation. In the results of crystallinity, the
average decreasing ratios were 1.987% (0.6mm) and 2.560% (1.2mm)respectively. From the results of SEM diagram, the profile of melt-front would be obviously flatted with GCP. In the visualized molding case, the penetration of gas-assisted injection molding (GAIM) would directly affect by GCP. The conventional GAIM results of penetrated length and area were respective 2.44 and 2.28 times, than GAIM combined with GCP.

並列關鍵字

Shrinkage ； Gas counter pressure ； Molecular orientation ； Crystallinity ； Mechanical property ； Gas-Assisted Injection Molding ； Visualization

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