Experiments, Modelling And Numerical Simulation Of The Sintering Process For Metallic Or Ceramic Powders

Sintering process is the important stage in powder injection moulding (PIM). Predicting the shrinkages and mechanical properties of the final sintered components is important for the design of injection mould and process parameters. The thesis focuses on the modeling, identification and numerical simulations of the sintering process. The experiment investigations are conducted for the sintering of PIM component in 316L stainless steel and alumina.The macroscopic sintering model based on the continuum mechanics is adopted in the study. In the employed thermal elasto-viscoplastic constitutive law, the expressions of shear and bulk viscosity modulus are derived from the viscous-elastic analogy and the creep models for diffusions. The empirical equations for evaluating the sintering stress and grain growth are introduced in the sintering model. In order to obtain the accurate simulation results, the identification for the model's parameters are conducted. For the sintering parts in 316L stainless steel powders, the densification is very fast and mainly accomplished in the narrow temperature range. The identifications are carried out for the three sintering stages respectively. The gravitational beam-bending tests are used to. identify the parameters in the viscosity modulus. Afterwards, the sintering experiments in dilatometer are carried out to obtain the in-situ shrinkage curves. It results in the next identification for the parameters in the expression of sintering stress. For the sintering parts in alumina, the densification occurs in the wider temperature range with relatively low rates. The identification for the parameters in the sintering model is conducted for the entire sintering process with in-situ shrinkage rate and shrinkage curves obtained from dilatometer tests. The determined viscosity and sintering stress for both materials are reasonable by comparing with the data in literatures.The numerical simulations based on the presented sintering model and identified parameters are realized by finite element method. Both the in-house software built on Matlab~? and the commercial software Abaqus~? are used for the simulations of sintering. The inhomogeneous green density distributions are imported into the sintering simulations. It represents the effect of segregation between the powders and binders in injection moulding process. The initial density fields are obtained by the bi-phasic injection simulations. The simulations have been carried out for the sintering of several components. The obtained results show that the gravity, friction and inhomogeneous green density have the apparent effects on the uneven shrinkages and distortions of the sintered parts. The strengths of the sintered components are predicted based on the evaluated density issued of the numerical simulations and a series of empirical expressions. The simulation results of shrinkages, distortions and strength are compared with the experimental ones.