具有銷孔的扁平狀陶瓷射出成形元件的收縮特性研究

Abstract

製品的幾何精度與強度是陶瓷射出成形元件之兩個首要的基本要求。在幾何形狀複雜的陶瓷元件射出成形製程中，收縮率是左右製品的尺寸與形狀精度的主要因素，甚至由於不良的收縮率分佈而會導致產生斷裂等缺陷，而陶瓷製品的收縮量亦與脫脂、燒結過程後的機械強度有密切的關係。造成收縮率的差異，其原因與陶瓷粉末的性質、混合物材料的流變特性等因素有關。 本研究利用具有銷孔及90o彎角幾何形狀的模具來進行陶瓷粉末射出成形實驗，探討氧化鋯粉末與不同的黏結劑混合後，在不同的射速及射壓的成形條件下的結果，並觀測各個階段的外觀缺陷、收縮率與機械強度上的影響。方法上，藉由CCD顯微鏡及數位游標尺分別來量測生胚及燒結體各方向的尺寸並計算出收縮率，且觀察成形至燒結過程中產生的缺陷，最後亦測量燒結完成品的硬度、密度及三點彎曲強度以得知收縮率與機械強度的關係。 研究結果顯示，在射出成形中，具有銷孔及90o彎角幾何形狀的模具所產生的擾流及剪切作用，改變了陶瓷混合物內的粉粒配向，導致燒結後的銷孔及90o彎角處之收縮量改變，以及後續測試的抗彎強度變小。此外，收縮率與緻密度的關係直接反應於製品的抗彎強度。

Geometric precision and strength are two primary requirements for ceramic injection molded components. In the process of geometrically complex ceramic injection molding, shrinkage is one of the most important factors which affects dimensional precision and loss of shape. Non-uniform shrinkage will lead to defects such as fracture. In addition, shrinkage also has a closely relationship with mechanical strength of ceramics after debinding and sintering processes. The variation of shrinkage was related to the character of ceramic powder and the rheological properties of ceramic mixtures. In this study, we used the geometrically L-type mold with a pin hole to conduct the ceramic injection molding experiment, investigating the phenomenon of the zirconic powder mixed with different binder systems under different injection speed and injection pressure. At the same time, we observed the defects of shape and shrinkage on the various molding stages, which impacts on mechanical strength. We measured dimensions of the green body and sintered specimens in three orthogonal directions by CCD microscope and digital vernier caliper respectively and then calculated the shrinkage rate. Furthermore, we observed defects during injection molding, debinding, and sintering processes, and finally measured the hardness, the density, and the flexural strength of sintered specimens. Through this, we obtained the relationship between shrinkage and mechanical strength. Experimental results indicated that there were turbulent flow and shear effect resulted from the L-type mold with a pin hole during ceramic injection molding. They not only changed particle orientation of the ceramic mixtures, but also brought about changes of sintered shrinkage in a pin hole and L-type position. As the following test, we found flexural strength become smaller. Besides, the relationship of shrinkage and densification directly affected flexural strength of ceramic products.