Study On Simulation Optimization And Material Forming Of Direct Write 3D Printing Device Based On Silicon Nitride Ceramics

Silicon nitride（Si₃N₄）ceramic materials have been widely designed and applied in many industrial fields due to their excellent physical and mechanical properties.However,the high elastic modulus and hard and brittle characteristics of materials itself make it particularly difficult to process and manufacture,especially for the molding and processing of products with complex geometrical structures.Therefore,the emergence of ceramic material 3D printing technology might provide potential solutions to offset this problem to a certain extent.At present,among many 3D printing methods for ceramic materials,direct-write 3D molding technology has received widespread attentions due to its potential advantages such as low equipment cost,simple raw material preparation,high molding efficiency,and simple post-processing technology.However,the problems associated with low printing precision and poor interface quality between printing layers in this direct-write 3D molding method have also seriously affected its development and application.In this study,the research subject focused at the high-efficiency 3D molding and advanced manufacturing of non-oxide Si₃N₄ceramics.Through custom-designed and built high-precision direct-write printing equipment,the simulation technology is firstly employed to optimize the key paraments and structures of the equipment extrusion system,and design and optimize the Si₃N₄ ceramic printing paste formula.The design optimization formula and processing parameters were then applied to realize the multi-precision 3D molding of Si₃N₄ceramics.The electromagnetic field assisted sintering was finally performed on the printed samples,and its basic indicators and material performance were subsequently characterized after sintering.The research,based on the existing 3D printing technology from an open source,aimed at the molding characteristics of ceramic materials,carried out the overall design and optimization of the direct-write 3D printing system platform,and focused on the upgrade of the paste extrusion and the motion control system,and also manufacturing.After completing the design and improvement of the entire direct-write 3D printing machine,the research applied ANSYS FLUENT simulation software,using Si₃N₄ceramics as the model material,to conduct fluid simulation analysis and comparison between the"air pressure extrusion"and"screw extrusion"processes of the paste.The"screw extrusion"method was down selected to complete the parameter optimization for this extrusion structure,and to realize the trial production of the equipment.Based on this experimental platform,tasks were conducted to simulate the extrusion process of Si₃N₄ ceramics under different molding accuracy,to match the simulation results with the compatibility of process analysis,and ultimately to provide guidance of processing parameters for the actual printing process.Finally,from the point of view of practical application,the formula of Si₃N₄-based ceramic printing paste under the conditions of low organic additive content and high molding stability was developed based on results of experimental testing and comparative analysis.After achieving high-quality 3D Si₃N₄ceramic molds with different printing precisions,the electromagnetic field assisted sintering technology was employed for rapid pressure-less sintering of the printed samples.Results showed that the density could reach more than 90%.Observations also showed that the overall microstructure was uniform,but the samples exhibited obvious pore phase distribution.With the improvement of printing accuracy,the distribution of microstructure defects such as pores gradually decreased,but,on the contrary,the macroscopic compressive strength and modulus of the samples gradually decreased.The objective of this thesis,from the perspective of mechanical design and manufacturing and ceramic material preparation,is to systematically and comprehensively study the direct-write 3D molding and sintering process for non-oxide ceramics such as Si₃N₄.This research would help to fill the technical gap in the field of direct-write 3D printing for Si₃N₄ceramic,and provide the important corner stone for the integrated design and manufacturing of non-oxide ceramic components with the assistance of pressure-less sintering through the externally applied electromagnetic fields.