光硬化樹脂SL模具於射出成形的脫模特性與流動行為研究

Abstract

本論文是以光硬化樹脂SL(Stereo-lithography)材料製作之快速模具，應用於塑膠射出成形為探討對象，內容包括SL模具的脫模特性與模穴內的材料流動行為研究。利用光硬化方法所製作的射出成形用SL模具的缺點是，模具之強度、熱傳導性與耐磨耗性不及金屬模具；根據過去的研究發現，模具壽命約在百模以下，而且模具之破壞多在成形脫模時發生。因此，本研究設計製作一套模擬保壓與冷卻狀況的壓縮實驗裝置，而以射出成形時的溫度、壓力與冷卻時間為實驗參數，進行脫模特性實驗，調查脫模力與模具表面粗度的變化，用以分析SL模具的破壞機制，以作為延長使用壽命及模具壽命評估的參考。實驗結果發現脫模力之大小與模溫、保壓與冷卻時間有關。而且SL模仁的表面粗糙度不至於因脫模次數的增加而有太大的變化。 對於SL模具中的高分子材料流動及缺陷生成特性研究，設計了基本的長直平板狀流路，以實際射出充填來實驗模擬各種條件下平板流路內的材料流動狀況。此SL模仁流路射出成形研究，係針對高分子材料流變特性且著重於充填、保壓與冷卻參數的探討，且藉由壓力分布量測，據以分析材料內部的剪切應力特性。另一方面，對充填後成品試片，觀察是否有融合線或流痕等缺陷生成，進行分析，以作為將來SL模仁薄流路射出成形模具設計及成形條件的參考。實驗與分析結果證實，射速低、模溫低時易生成流痕現象；對射出後成品試片之表面粗度量測值分析發現提高模具溫度與射出速度，將會改善射出成品的表面粗度。而對於SL模具的熱傳導性不佳與溫度分布不均，造成的殘餘熱應力，可以從射出成品試片的光彈相片得到驗證。對模穴壓力影響方面，改變射出壓力、塑料溫度與模具溫度有明顯的影響。

This dissertation is concerned with the demolding characteristics and flow behavior of Stereolithography(SL) mold in polymer injection molding. The drawbacks of SL mold are that the tool strength, thermal conductivity and erosion resistance are lower than those of the conventional metal mold. Previous study has shown that the SL tool life was limited under 100 shots and tool damage often occurs during part ejection. In this study, a compression test fixture was designed to simulate hold pressure and cooling conditions in the injection process. The experiments were performed using various cooling time, hold pressure and temperatures. The demolding force and surface roughness were measured to evaluate tool life and failure mechanism. The experimental results showed that the demolding force has close relation with cooling time and mold temperature. The surface roughness of the SL mold plate does not change dramatically with the increase of the demolding times. As to the defects of injection molded parts, there exists weld line, flow mark and solid skin. Flow behavior of polymer in thin wall cavity is investigated by the injection molding on flow channel of SL mold. The experiments were performed with various process parameters to investigate the defects occurrence in the injection molded parts. Moreover, the injection molded parts were examined whether the defects occurred and analyzed as the reference for the future SL mold design. The experimental results showed that defects occurrence has close relation with injection speeds and mold temperatures. Flow marks of SL mold occur more easily when the mold temperature and the injection speed are low. There was no significant change on surface roughness of SL mold insert after injection molding. By increasing the mold temperature and the injection speed, the surface roughness of the molded part can be improved. The CAE mold flow analysis and results of pressure distribution measurement results indicate that the injection pressure, melt and mold temperature have substantially effect on cavity pressure and shear stress.