Shrinkage properties of ceramic injection moulding part with a step-contracted cross-section in the filling direction

The need for ceramic materials in microelectromechanical systems (MEMS) is increasing quickly. A typical form of designed ceramic micro parts involves the structuring of several micro columns and/or thin walls on a substrate. This work considers the use of a model mould with a straight mould cavity and a step-contracted cross-section in the filling direction. The injection moulding of such of ceramic micro part is experimentally simulated. The effect of the mould cavity contraction ratio, moulding conditions, and the solid loading of the ceramic/binder mixture on the distribution of the transverse shrinkage of the moulding parts at moulded, debinded, and sintered stages, respectively, are examined. Experimental results reveal that transverse shrinkage of the region downstream from the step-contracted cross-section clearly exceeds that of the region upstream in all three stages. Furthermore, transverse shrinkage varies greatly in the plane of the step-contracted cross-section. The magnitude of the variation in transverse shrinkage in the step-contracted cross-section increases with the contraction ratio of the mould cavity. Appropriately increasing either the holding pressure or the filling pressure of the mould cavity reduces the variation in the transverse shrinkage of the step-contracted cross-section. Moreover, using the ceramic/binder mixture with a composition similar to that of critical solid loading can lower the internal stress caused by sintering in the vicinity of the step-contracted cross-section.