嵌入式射出成型製品殘留應力之研究與改善

Abstract

嵌入式射出成型能省去組裝程序並提升組件強度而逐漸被廣泛應用於產品設計上，但由於金屬嵌入件與塑膠的線膨脹系數差距甚大，導致成品在經過熱循環等環境應力影響之後會從嵌入件附近產生開裂破壞。 本研究設計一含有圓柱嵌入件之平板試片，以四種不同模溫與嵌入件溫度的射出參數製作試片，之後對試片施以退火處理，以觀察未接近圓柱區域、塑料流經圓柱前後的殘留應力，以獲得嵌入件對塑件熱殘留應力與流動殘留應力的影響，然後再以熱循環試驗與液態氮焠火探討殘留應力與開裂破壞之間的關聯性。 實驗結果得知，嵌入件附近退火對殘留應力減低的效果會降低，並且成型時嵌入件溫度越高退火所需時間越久，而開裂會出現在嵌入件附近殘留應力的峰值處。

Insert molding is gradually adopted in the product design because it reduces the process of assembly and raises the strength of products. However, the coefficient of thermal expansion (CTE) difference between metal and plastic is significant. It induces crack around the insert parts when these plastic parts encounter temperature variation. A flat specimen with cylindrical insert was designed. We made 4 types of specimens, each type with different mold temperature and insert parts temperature.We compared the residual stress around the insert part and areas away from insert part before and after annealing. Differences that the insert made on thermal residual stress and flow residual stress were discussed. We used temperature cycling and liquid nitrogen quenching to find the relation between cracks and residual stress. Experiment results showed that the effect of annealing for decreasing the residual stress reduced in areas around the insert parts. Higher insert parts temperature in injection increased the annealing time for elimination of residual stress. The cracks appeared at peaks of residual stress.