Multi-physics Modeling and Analysis in 3D Printing of Multi-scale, Multi-functional and Multi-material Porous Structures
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Porous structures have broad applications in different fields, and the fabrication methods have evolved for decades. With the combination of inkjet printing and ice-template technique, the selective freezing three-dimensional (3D) printing is developed to fabricate multi-scale and multi-functional porous structures with excellent geometrical and functional properties. A controllable process enables manipulations on operating conditions and material properties to attain desired product quality and process efficiency. To achieve a manageable process, the impacts from environments, operational settings, and material properties need to be quantified. This research aims to investigate parameter-process-structure relation of this novel process with a combined experimental and modeling methodology.To predict the behavior of jetted ink droplets with different input signals and material properties, a transient Volume of Fluid (VOF) model of the inkjet process is created. The simulation results show that jetted ink droplets exhibit disparate morphologies with different inputs and material feeds, which furtherly form distinct microstructures inside the printed parts. To verify the proposed simulation model, images of real droplets are captured by the high-speed camera and compared with the simulation outcomes. The impacts of factors are revealed with the assist of the proposed simulation model, which can serve as guidance for process manipulations to achieve desired results.The dynamic thermal condition affects both ink solidification and ice crystal growth, which determine the macroscopic-scale structure and microscopic-scale structure, respectively. To stabilize thermal condition during the printing process, a novel cold source design based on Phase Change Materials (PCM) is proposed in this research, with reasonable verification by the hardware-in-loop experimental studies. The result proves PCM is more reliable than other cold sources both temporally and spatially, and it can significantly improve the quality and efficiency of fabrication. A heat-transfer simulation model is constructed for prediction of dynamic temperature distribution within the part body and verified by experiments, in order to facilitate the thermal management. Factors such as part geometry, driving temperature, tool path and inter-layer waiting time are all proved to have influences on the fabrication quality. Lastly, an interfacial diffusion simulation is proposed to explore the impacts of thermal conditions and material properties on interfacial diffusion while fabricating multi-material structures. Based on the prediction out of the simulation, material properties in different phases and thermal conditions can both profoundly affect the forming of interfaces between materials. Fabrication strategies are presented according to the prediction out of the simulation for specific requests of the interface between different materials.