Modeling, Analysis and Simulation of Paste Freezing in Freeze-form Extrusion Fabrication

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. The paste freezes very quickly when deposited on a substrate in a freezing environment. However, as the part’s height increases, the freezing time increases as the heat conduction rate to the substrate decreases. The freezing time can exceed the time required to extrude one layer of paste due to water’s high latent heat, thus leaving the extruded paste in its semi-liquid state and causing the part to deform or even collapse. Therefore, dwell time is needed between layers, which may substantially increase the build time of the part. In this paper, the effects of the paste material, paste solids loading, convection coefficient, initial paste temperature, ambient temperature, total time between layers, and layer thickness on the freezing time of paste are investigated. The paste temperature and paste freezing time are computed for various process parameters via numerical simulation using the commercial code Fluent.