Experiment And Simulation Of Micro Injection Molding And Microwave Sintering

Powder Injection molding process consists of four main stages:feedstock preparation, injection molding, debinding and sintering. The thesis presents the research on two main aspects:micro-injection molding and microwave sintering. The main contributions can be concluded in the following four aspects:Modification and supplement of previous algorithm for the simulation of injection molding process; Evaluation and implementation of surface tension effect for micro injection; Microwave sintering experiments of compacts based on 17-4PH stainless steel; Realization of the microwave sintering simulation with the coupling of multi-physics, including the classic microwave heating, heat transfer, and the supplement of model for sintering densification of powder impacts.For the improvement of filling simulation, the present study modifies the explicit vectorial algorithm for simulation of injection filling process. The wrongly directed filling patterns in actual commercial software have been improved, by the implementation of a suggested scheme, which is similar to upwind method. A reasonable numerical method relative to the outlet boundary condition is suggested to overcome the untrue delay of fully filling in the last filling stage. The results from these two modified algorithms are proved to be optimized and more reliable.For extending the in-house FEM software into the scope of micro injection, surface tension effect is taken into account in the injection molding simulation. Due to the lack of appropriate FEM method for curvature calculation, the present work proposed a systematic algorithm for implementation of the surface tension effect in finite element method. By the example of filling in micro channels, it indicates that the effect of surface tension shows the importance for the projects in sub-millimeter sizes, but does not represent the significant effect in ordinary injection molding.For microwave sintering of 17-4PH stainless steel powder, compared to the previous reports, some new discoveries have been found in the experiments. The author conform that the microwave sintering process for 17-4PH stainless steel can not only shorten greatly the sintering time, lower the peak sintering temperature, but also it provides higher sintered density and fewer defects in micro structure. Higher Vickers-hardness of microwave sintered compacts is also detected in the present work. Moreover, because of its rapid heating in the internal volumetric way, microwave sintering results in the obvious gradient in mechanic properties of the sintered material.Microwave sintering represents the coupling of multi-physics in electro-magnetic fields, heat generation, thermal conduction, and densification process of the powder compacts in sintering. The existing researches focuses on the studies of microwave heating and heat transfer, which couples with the evaluation of electromagnetic field, but none of them includes the densification behaviors of powder material. Bases on the sintering constitution of powder impacts, the mathematical model and simulation method for whole of the microwave sintering phenomena, from distribution of the electromagnetic field to the densification of sintered compacts, are determined in the present thesis. The simulation of microwave sintering process can be realized on the FEM platform of COMSOL Multi-physics. This work provides a reliable way for the further investigations on microwave sintering.