射出成型用之石膏模具導熱特性研究

在一般常見的射出成型中，模溫是藉由冷卻的方式來控制模具溫度，為利用恆定溫度的冷卻液在冷卻水路中循環以冷卻模具與熔膠。在充填階段，由於熔膠接觸到模具會得使靠近模具表面的熔膠部份會先產生凝固，造成熔膠可流動的部位減少，並且由於熔膠黏度的提高，導致熔膠充填模穴的能力降低。一些用於小批量生產的暫代型模具，如環氧樹脂模、石膏模等，當應用於射出成型時，常用來生產測試用之原型，由於模具的材質在熱機械性質的表現皆不如傳統鋼模，因此在射出成型時容易積聚熱量於模具表面，使得模具表面溫度升高，除非針對產品的製程進行最佳化，否則會造成模具壽命降低，以及射出產品的缺陷。為了改善這些問題，本研究將透過添加碳黑粉體於石膏中，以及利用銅製的導熱機構，在模仁製作過程中埋入，增加石膏模仁的熱傳導與吸熱效果，使用ANSYS 軟體進行理論分析與實驗結果證實添加碳黑可提高石膏模的熱傳導性，而導熱機構可更快速的將熱分散至模仁其它部位與模座，達到降低模具表面溫度的效用。

關鍵字

射出成型；石膏；快速模具；熱傳導；模溫

並列摘要

In conventional injection molding, the mold temperature control is obtained by a continuous cooling method, in which a coolant with constant temperature is circulated in the cooling channels to cool the mold and the polymer melt. During the filling stage, this causes an abrupt polymer solidification close to the mold surface, which reduces the section open to flow and, due to the viscosity increase, causes a decrease of the ability of the polymer melt to fill the cavity. Some temporary molds for a small batch of production, such as epoxy mold and gypsum mold, are used in injection molding very often for short runs of functional prototypes. The thermo-mechanical properties of this mold material is far from those of conventional steel molds, therefore the heat is easily accumulated on the mold surface during the injection molding. It causes the mold lifetime decreased and defects in the molded parts unless the process is optimized for the specific part. A methodology that adds carbon black powder into hemihydrates during gypsum mold as well as a heat sink made of copper is installed into gypsum mold to enhance heat dissipation is proposed. A CAE software, ANSYS is implemented to verify the effect of the proposed method and experiment is prepared for validation. Results show that the carbon black powder and the heat sink can improve the heat transfer from the cavity toward the gypsum mold. To achieve the effect of reducing the mold temperature.

並列關鍵字

Injection molding ； Gypsum ； Rapid tooling ； Heat conduction ； Mold temperature

參考文獻

[2]S. Rahmati and P.M. Dickens, 1997, "Stereolithography for Injection Mould Tooling", Rapid Prototyping Journal, Vol.3, No.2, pp. 53-60.

[3]S. Rahmati, P.M. Dickens, 2007, "Rapid tooling analysis of Stereolithography injection mould tooling", International Journal of Machine Tools and Manufacture, Vol.47, pp.740-747

[10]李國豪，2016，“石膏模仁應用在射出成型可行性之研究”，國立虎尾科技大學，機械與電腦輔助工程系碩士論文

[11]L‐E. Rännar, A. Glad, C‐G. Gustafson, 2007, "Efficient cooling with tool inserts manufactured by electron beam melting", Rapid Prototyping Journal, Vol. 13, Issue: 3, pp. 128-135,

[13]N.B. Singh, B. Middendorf, 2007, "Calcium Sulfate Hemihydrate Hydration Leading to Gypsum Crystallization", Progress in Crystal Growth and Characterization of Materials, Vol. 53, pp. 57~77

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射出成型用之石膏模具導熱特性研究

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