塑膠射出成型之結合線與殘留應力之改善研究

Abstract

塑膠射出成型是塑膠產品的量產方法之一。在產品的生產過程中，結合線與殘留應力兩大缺陷是最常見的問題。在結合線部分，本研究提出了四種模具機構（模內快速加熱/冷卻機構、模內旋轉機構、模內沖模機構，模具局部加熱機構），分別應用於傳統塑膠射出成型、添加金屬粉末塑料的射出成型，以及嵌入成型三種製程之結合線消除；在殘留應力部分，本研究以不同的熱處理參數對塑膠射出成型試片進行測試，再以光彈法量測不同的熱處理條件後的殘留應力大小。□

實驗結果顯示，在傳統射出成型製程中，模內快速加熱冷卻機構可以大幅改善傳統射出成型製程之結合線缺陷，結合線部分的材料強度可提昇約6.8%，結合線深度則可由12μm降低至0.5μm。在添加金屬粉末之塑料射出成型中，模內旋轉機構在低轉速下（25 rad/sec）可讓結合線模糊，但是無法完全消除，反之模內沖模機構則可製作出完全無結合線之產品。在嵌入成型部分，以實際產品（潛水用呼吸調節器與螺柱試片）進行測試，實驗結果顯示在局部加熱下，呼吸調節器的生產良率由原本的30%提昇至100%，螺柱試片的螺柱強度也可提昇約5%~20%。殘留應力實驗則顯示熱處理的確可降低射出成型件之殘留應力，對於肉厚在 2.5mm 以下之PC實驗試片，30分鐘的熱處理時間已可減少50%以上之殘留應力。

Plastic injection molding is one of the mass production methods of plastic products. In the production process, weld lines and residual stress are the most common defects of plastic products. In weld lines research, four mold mechanisms, (namely, rapid heating and cooling system, in-mold rotating system, in-mold punching system, and local heating system) were designed to eliminate the weld lines for traditional injection molding, plastics with metal powders injection molding and insert molding. In residual stress research, different heat treatment parameters were tested in plastic injection molding parts. In this respects, photoelastic method was to use measure the extent of the residual stress relief of the parts.

Experimental results showed that in traditional injection molding, rapid heating and cooling system can improve the weld lines defects, weld lines strength was raised for about 6.8%, the depth of the weld lines were reduced to 0.5μm from 12μm; in the injection molding of the plastic with metal powders, in-mold rotating system can blur the weld lines in low rotate speed (25 rad/sec) but can’t completely eliminate the defects. However, in-mold punch system can produce the plastic parts with no weld lines in the same production process; in insert molding, two plastic parts (regulator for SCUBA diving and boss test parts) was tested, the experimental results showed that with the local heating system, the yield of the regulator was raised from 30% to 100%; the strength of the boss test parts raises from 5%~20%. In residual stress research, the experimental results showed that the heat treatment of the injected plastic parts reduce the residual stress. Polycarbonate test parts with thickness less than 2.5mm, heat treated for 30 minutes showed that a decrease of 50% of the residual stress can be achieved.