產品幾何效應對長纖維微觀結構與巨觀翹曲變形影響之研究

近年來因節能與環保的需求，輕量化已成為各國主要政策發展之一，尤其是利用纖維強化塑膠(Fiber Reinforce Thermoplastics, FRT)來取代部份金屬零組件，其具有高強度、重量輕之材料特性，使汽車重量能大大減輕。然而應用射出成型製備纖維強化塑膠時，由於新世代產品之幾何越變越複雜，加上材料本身特性與操作條件複合後，造就了熔膠在模穴中的流動行為變得難以掌握及預測，因而纖維如何透過其微結構之變化，進而達成巨觀之強化效果，至今仍未完全地明瞭。因此，本研究之目的為利用三種不同澆口型態的標準拉伸試片模型(定義為Model I, II, III)的射出成型系統，探索因為設計、材料差異及操作條件變化下，纖維微結構如何受到影響，並進而造成巨觀形狀之變異，其中Model I, II, III分別是側邊單點進澆、直接單點進澆、雙點進澆。具體執行方法是先採用Moldex3D進行之模擬分析，之後再進行實際之試模驗證與研究。CAE模擬分析結果顯示，由於系統幾何設計之效應，三個標準拉伸試片模型呈現非常不同之翹曲變形之行為，此時我們雖然預期纖維強化了塑料強度，但卻導致Model I 往下方翹曲並且往內彎；在此同時Model II 卻往上方翹曲，而Model III 變形相對不明顯。為探索此項差異之成因，我們深入觀察纖維排向分佈(Fiber Orientation Distribution, FOD)發現，由於熔膠進入不同產品幾何時之入口效應(Entrance Effect) 引發不對稱的流場，造成不對稱之纖維排向分佈所導致特殊之翹曲變形。另外針對纖維長度對產品翹曲品質之模擬分析，可以發現纖維長度越長，對翹曲變形的改善效果更佳的明顯。此等翹曲變形改善行為也利用實驗驗證，趨勢及量值皆吻合。再則，針對纖維長度對樣品拉伸強度的變化之研究，隨著添加的纖維長度增加，拉伸強度有顯著的提升，以Model I為例，從純PP拉伸強度約為20 N/mm2，至纖維長度為25 mm約為140 N/mm2，增強了7倍。但有經過幾何入口效應之影響，不同區域所呈現之拉伸強度有明顯之差異。

關鍵字

射出成型；纖維強化塑膠；纖維微結構；澆口型態；收縮翹曲

並列摘要

Due to its great potential and capability, the fiber reinforced thermoplastics (FRT) material and technology have been applied into industry recently. However, due to the microstructures of fiber inside plastic matrix are very complex, they are not easy to be visualized. The connection from microstructures to the final shrinkage/warpage is far from our understanding. In this study, we have performed a benchmark with three standard specimens based on ASTM D638 where those specimens have different gate designs. Due to the geometrical effect, the warpage behaviors are quite different for those three specimens. Although we expect long fiber reinforced to enhance strength, it causes one specimen warped downward and bended inward, another warped upward, and the other slightly upward at the same time. The difference might be due to the interaction of the entrance effect of molten plastic with fiber content to cause high asymmetrical fiber orientation distribution (FOD). We further studied that the asymmetrical FOD is introduced by the entrance effect from the sprue entrance of the part to the gate of each standard specimen. This entrance effect will cause the variation of FOD and further influence the fiber distribution and the bundle phenomena. Moreover, the experimental study is also performed to validate the simulation results. From short shot testing to the warpage and bending measurement for each individual model, overall, the tendency for both numerical simulation and experimental results is in a reasonable agreement. However, some deviation still existed which needs for further study. Furthermore, in the fiber length effect study experimentally, the longer fiber reinforced the less warpage. Also, the elongation and strength of injected parts can be enhanced significantly as fiber length increased. For example, from pure PP to FRP with 25 mm fiber inside, the strength can be increased from 20 N/mm2 to 140 N/mm2 .

並列關鍵字

Injection molding ； Fiber reinforce thermoplastics ； Fiber microstructure ； Gate type ； Shrinkage and warpage

參考文獻

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產品幾何效應對長纖維微觀結構與巨觀翹曲變形影響之研究

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