石膏模仁應用在射出成型可行性之研究

Design and Fabrication of Injection Mold Using Gypsum

李國豪(Guo-Hao Li)

指導教授 ： 林忠志

國立虎尾科技大學/工程學院/機械與電腦輔助工程系碩士班/碩士(2016年)

摘要

本研究探討使用石膏(Gypsum)做為快速模具(Rapid Tooling)的可行性，石膏是結晶型硫酸鈣(CaSO4)，屬於多孔性材料，強度較低，容易產生崩角、斷裂等情形，無法用於高壓成形上，僅能運用在低壓成形中，例如:澆鑄成形，本研究主要是透過不同配方與機械加壓的方式使其硬度提高到可以射出的壓力而不崩裂，實驗方法是將石膏直接進行翻模的製作，為了增加石膏的強度，硬化過程中使用荷重加壓在石膏上，使粉體之間的強度能夠更加密實，另外添加黏著劑，提高石膏的結構強度。
首先製作各種配方石膏進行硬度測試與壓縮強度測試，將製作好的石膏塊進行後處理的加工，製作成模仁外輪廓型狀，方便嵌入模具中，以射出實驗檢測不同配方參數的石膏表面其沖刷性與沾黏性，判定石膏的強度是否能夠用於射出成形中，並製作簡單形狀進行轉寫性的量測。
實驗結果得到石膏增加壓縮負荷，進行射出發現負荷施加越重，其石膏表面的沾黏性越少，反之沒有增加負荷的石膏在射出一定次數後就有嚴重的沾黏情形發生，並探討添加黏著劑是否有效的提升石膏整體的強度，射出時黏著劑無法承受高溫而熔化，造成石膏表面強度降低，使沾黏情況提前發生，最後將得到最佳的石膏製作參數，並與金屬模具進行射出比較結合線強度，以及探討石膏的轉寫性能力。

關鍵字

射出成型 ； 石膏 ； 快速模具

並列摘要

This study addresses the potential of gypsum as a candidate for the mold insert for injection mold. The design and fabrication process of the mold insert is implemented, starting with the gypsum powder, mixing the powder with binder, forming and machining the powder block into the mold insert, assembly and validation by injection test. This work provides an alternative mold-making process that can create tools quickly and with minimum labor cost for pilot run during product development. Traditionally the mold made of gypsum only can be applied in low pressure molding process such as casting, vacuum forming, etc. as result of its porosity. However the weak strength of gypsum makes it too brittle to be used in injection mold directly. In an attempt to develop a rapid and feasible method for making the mold insert with better Compressive strength, some processing parameters for gypsum preparation were investigated in this study. The mold insert made of gypsum were mechanically characterized and the influences of binder with different ratios, mechanical compression for the mold insert preparation, and thickness of the mold insert were assessed. The results showed the potential of the mold insert made of gypsum to compete with conventional techniques for improving venting, especially for the injection molding of small quantity of parts; also, it was showed that this technique allows the injection molded parts with adequate mechanical performance in welding line and, therefore, does not need to be restricted to the production of mockups and prototypes.

並列關鍵字

rapid tooling ； gypsum ； injection molding

參考文獻

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