以熱處理方式消除射出成型製品殘留應力之研究

Abstract

塑膠製品由於較金屬產品輕，且有良好的強度，成型又容易，因此廣泛用於各項產業中，如電子產業、汽車產業等等。而隨著材料品質的改良，近年來亦大量應用在光學產業以及精密機械產業。塑膠射出成型是塑膠製品最常用的製造方法，射出成型製程的最大優點在於一次製程中可直接做出各種複雜外型的製品，但由於成型過程中溫度的劇烈變化，外觀問題（如結合線）與殘留應力產生變成不可避免的缺陷。殘留應力除了影響尺寸精度，也會在二次加工上發生問題。 本研究主要之目的即為研究塑膠製品於射出成型冷卻後，使用熱處理之方式，達到鬆弛塑膠製品之殘留應力，改善塑膠製品射出成型時產生之殘留應力現象。實驗時改變不同熱處理時間，並以光彈法觀測計算熱處理前後試片之等效應力值。實驗結果顯示塑膠試片於不同熱處理時間後，其等效應力降低效果隨著時間增加而遞減，並且以熱處理方式消除塑膠試片之殘留應力有其極限。再觀察PC材料實驗數據可以得知，熱處理效果隨厚度增加而增加，但是PS材料則沒有明顯此關係，並且比較非結晶與半結晶性塑膠，可以發現半結晶性塑膠之熱處理效果較差，原因推斷為不平均之結晶作用導致抵銷熱處理之好處，並且使熱處理效果較不穩定。

關鍵字：塑膠、射出成型、殘留應力、熱處理

Because the desity of plastics is lighter than metals ,besides, plastics possesses good strength and easy to form complicated shapes . It is generally used in almost every industry , including electronics , automobile and motorcycle industries ,etc. The improvement of plastic materials , It is also extensively used in optics and precise machinery. Injection molding process is a general process to fabricate plastic products. The advantages of injection molding process includes fabricating complex shapes in one process. However, since in the injection process, the material experience drastic changes in temperature , the problems of appearance and residual stress is hard to prevent. The residual stress influence not only the dimensions ,but also the second finish process. The major purpose of this research is to heat treat the plastic specimen after injection molding process to reduce the residual stress caused during injection molding process. The specimens were put under different heat treatment process and the equivalent stress of each plastic specimen were calculated by Photoelastic stress analysis. After Analyze the plastic specimens after different heat treatment time , we found the effect of heat treatment decreasing with the increasing time. There is a limitation of decreasing the residual stress of plastic specimens by heat treatment in certain temperature. After analyze the data of PC material, we found the thicker the plastic specimens is, the better the effect of reducing residual stress by heat treatment is. But the PS material did not exhibit such an apparent relation. After comparing the crystalline and amorphous plastic material, we found the effect of reducing residual stress of crystalline plastic material is worse than amorphous plastic material. The reason about this may come from the unequally crystallization of the amorphous plastics reducing the effect of heat treatment. And the unequally crystallization effect cause the unstable effect of reducing residual stress by heat treatment.

Keyword：Plastic, Injection Molding, Residual stress, Heat treatment