Determination of the flow stress and thermal properties of ceramic powder feedstock in ceramic injection molding

摘要

To simulate numerically the material behavior of a ceramic powder feedstock that consist of a two-phase mixture of zirconia powder and polymer binder, a material model is needed that incorporates the change in volume fraction and temperature dependency of viscosity. Heat transfer occurs between the feedstock and the mold during ceramic injection molding (CIM). The feedstock is heavily influenced by thermal properties such as thermal conductivity and specific heat. In this study, three models are proposed to explain the material and thermal properties: a rigid-plastic flow stress model that is dependent on volume fraction and viscosity, a thermal conductivity model, and a specific heat model as a function of temperature. The material parameters in each model are obtained by using the optimization method. Error functions are defined as the differences between the experimental measurements and numerical simulation results. The parameters are determined by minimizing the error functions. The confirmation simulation for each model is conducted by applying cases that are not directly used in the optimization. The results of the confirmation simulation tend to follow the experimental results well, with correlation coefficients exceeding 0.92. The numerical simulation of the CIM process with the determined parameters is compared with the flow behavior of an actual CIM process. Simulation results, such as flow pattern and direction, are in good agreement with the measured feedstock behavior. Therefore, the method for determining the material parameters of the proposed models is feasible.