筒狀薄壁射出成型品壁厚均勻性改善之分析

Abstract

醫療用自動注射器為一種攜帶方便的醫療裝置，常使用於急救與居家照護的情況。裝置的零件多數為塑膠射出成型品，其重要考量之一是外形尺寸，因此製品的變形必須控制在一定限度內。 本研究的目的為探討筒狀薄壁塑膠成型品壁厚不均的問題，並改善新製模具成型品的壁厚差異。 本研究使用有限元素分析軟體MOLDFLOW為研究工具，規劃不同模型設計、進澆位置與澆口大小等研究程序進行模芯偏移模擬分析。依據分析結果所得最佳數據的模型進行模具設計與製造，最終量測製品以確認壁厚均勻改善幅度。 研究結論顯示，從成品數據的量測、模具損傷，可以得知成品壁厚不均的原因是由高射壓注入的熔融塑膠料推擠模芯(Core Shift)所造成。比較改善前與改善後的成品量測數值發現，實際芯子最大位移量在厚度差異減少了0.13mm，也滿足設計規格。 設計射出成型品時，使用模流分析軟體可預測產品變形的趨勢，設計者再依據其結果改善製品，以減少產品開發與設計變更的時間與成本。

Pharmaceutical auto injector is a convenient type of medical device often used in emergency and home care. Because most of its components are manufactured through injection molding, in which the size of the components’ external dimensions is a critical concern, deformation must be controlled within acceptable limits. This study examined and eased the uneven wall thickness problem of the injection molding part of the cylindrical thin-wall product. Moldflow was used as a finite element analysis software instrument to plan different mold designs, and gate locations and sizes for analyzing core shift simulations. The model design that returned the optimal results was used to fabricate a physical copy to verify the improvement in thickness uniformity. Results show that injecting molten plastic materials under high pressure resulted in core shifts that attributed to thickness uniformity, as indicated by the physical specimen measurements and mold damage data. Comparing the measurement data obtained from specimens fabricated before and after using the improved mold design showed that maximal difference in displacement thickness was reduced by 0.13 mm, satisfying design specifications. Moldflow simulation software is useful for predicting trends in product deformation when designing injection molding products. Accordingly, designers can improve on the design, reducing time and saving costs during product development and design modification.