EFFECT OF PASTE PROPERTIES ON EXTRUDATE FREEZING TIME IN FREEZE-FORM EXTRUSION FABRICATION PROCESSES

摘要

During the freeze-form extrusion fabrication process for aqueous-based pastes, the sub-zero temperature environment aids the part in maintaining its shape by freezing the water present in the paste. However, while some pastes can be frozen properly, other pastes using the same extrusion strategy may be kept in semi-liquid state and cause the part to deform or even collapse. Therefore, different dwell times are needed between layers for different pastes, which may substantially increase part build time. In this paper, a simplified one-dimensional model was developed and validated by the commercial code Fluent. The paste temperature and paste freezing time were computed for various process parameters via numerical simulation using this model. As the layer number increases, the paste freezing time reaches a steady state. The relationship between the steady state freezing time and the paste material and solids loading was studied. The simulations show the paste freezing time decreases due to the increase in paste thermal conductivity, solids loading and total time between layers.