Study On Process Control And Liquid Phase Migration Of Frezee-form Extrusion Fabrication For Ceramic Paste

Ceramic materials are widely used in aerospace,mechanical and biological engineering fields due to their wear resistance,high temperature resistance,high hardness and good corrosion resistance.However,the traditional manufacturing process of ceramic parts are complicated,difficult,and costly,which hinders the large-scale industrial application of ceramic parts.Therefore,it is of great theoretical significance and practical value for the further large-scale application of ceramic materials to study the forming process with low manufacturing cost,low environmental pollution and good forming quality.Freeze-form Extrusion Fabrication(FEF)technology is a novel rapid prototyping technology which uses an aqueous ceramic pastes as forming materials,formed parts directly from the three-dimensional model based on the principle of discrete stacking,decreased manufacturing costs,shorten the product development cycle.The extrusion process and the liquid phase migration phenomenon have an important influencing on the properties of the formed parts.In this paper,the process control and liquid phase migration of ceramic pastes were studied,and the variation of extrusion force during the forming process was analyzed.The model of the extrusion force was established and controlled,and the liquid phase migration occurred during the extrusion process was studied.The analysis and research results can provide theoretical basis and technical support for the rapid prototyping technology of ceramic materials,and has important theoretical significance and practical value.The main research contents of the thesis are as follows:Aiming at the problems existing in the overall cooling method of the forming equipment,a freeze-form extrusion fabrication experimental platform with independent intellectual property rights for ceramic parts was developed.The extrusion process was analyzed,the extrusion process model was established,and the model was verified by experiments.A dynamic model of the extrusion force was established for the interference factors in the forming process.An adaptive control system of the freeze-forming extrusion force for ceramic paste was established.The minimum variance self-correction principle was used to design the required control law.The adaptive algorithm was simulated,and the control effect was verified by experiments.The adaptive control of different extrusion forces was realized and the reliability of the controller was verifiedThe produced process and influencing factors of liquid phase migration during the extrusion process were analyzed.The extrusion process was divided into compaction and stable extrusion stages.The liquid phase migration model during the forming process was constructed with layered method based on Darcy's law.The influence of extrusion velocity and extrusion nozzle length on the liquid phase content in the extruded paste was studied,and the model was verified by experimentsThe simulation model of the paste extrusion process was established based on the characteristics of the extrusion process of aqueous ceramic pastes.The liquid phase migration process of aqueous ceramic pastes during the freeze-forming extrusion fabrication was simulated by Fluent software.The contours of velocity magnitude for the liquid phase and solid phase particles in the paste was obtained which indicates that the flow velocity of the liquid phase is higher than that of the solid phase particles during the extrusion process,and the liquid phase migration occurs during the extrusion process,and the simulation results were verified by experiments.The orthogonal test method was applied to the optimization of parameters influencing the liquid phase migration during the freeze-forming process.The optimal combination of process parameters and the importance rank of the factors affecting the liquid phase migration were obtained.The prediction model of liquid phase content in the extrudate was established based on the orthogonal experimental data.The calculation formula of liquid phase content in the extrudate was derived by the regression formula.The correctness of the prediction model was verified by comparing the prediction model results and the experimental results.The research results can provide a theoretical reference for the studying of the liquid phase content in the extrusion paste.