射出成形的冷卻策略對成形品的收縮特性的影響及其在成形精度控制上的應用

Abstract

高分子材料在各種加熱製程多少都會造成材料收縮，對於製品的精度有很大的影響，尤其射出成形製程更為明顯，隨著現代工業發展的進步，各種精密產品推陳出新，控制成形精度也成了一大課題。 本研究目的為探討冷卻速度差異對於成形品內部結構狀態以及收縮特性的影響。研究方法為透過低溫固定模溫冷卻、高溫固定模溫冷卻、區域差別速率冷卻等三種的冷卻方法，以射出成形製程取得圓筒狀成形品，再來探討其收縮性與結晶度之間的關係，使用的材料為玻璃轉移溫度T_g大於室溫的PA66及T_g小於室溫的PP。 研究結果顯示，PP材料之圓筒與PA66材料之圓筒，其結晶度均呈現高溫冷卻(80℃)高於低溫冷卻(10℃)之現象，並且愈靠近圓筒肉厚中心，結晶度愈高。而差別冷卻(內部10℃外部80℃)之結晶度則是介於高溫與低溫之間。另外收縮性比較，低溫冷卻之PP圓筒收縮率為8.78%低於高溫冷卻的10.17%；低溫冷卻之PA66圓筒收縮率5.39%高於高溫冷卻的4.96%，整體內徑均勻性均是低溫冷卻優於高溫冷卻。

Polymer materials would have shrinkage problem in heating processes, particularly in injection molding process. With the development of modern industry, the needs of high-precision product are increasing. As the result, the accuracy control has become an important issue. This study has investigated the effects of cooling rate on the internal structure and shrinkage characteristics of polymer products. Three kinds of cooling strategy, low temperature cooling, high temperature cooling and reginal different rate of cooling, are used during the injection molding of cylinder product. Products with different cooling strategy are investigated for finding the relationship between shrinkage characteristics and the crystalline structure of the products. The experimental materials are PA66 (T_g>T_r) and PP (T_g<T_r). Experimental results show that the crystallinities of both PP and PA66 cylinder products with high temperature cooling(80℃) are higher than that with low temperature cooling(10℃). As closer to the middle zone of cylinder wall, the crystallinity becomes higher. And the crystallinity of product with reginal different rate cooling(inside 10℃ outside 80℃) is between product with high temperature cooling and low temperature cooling. For the comparison of shrinkage, the shrinkage of PP cylinder with low temperature cooling is 8.78%, which is lower than the10.17% of high temperature cooling. The shrinkage of PA66 cylinder with low temperature cooling is 5.39%, which is higher than the high temperature cooling’s 4.96%. About uniformity of whole inside radius, low temperature cooling is better than high temperature cooling.