9finite Element Analysis on the Sintering of Stainless Steeel 316l Powder Compacts

Implementation of an accurate sintering model into a finite element simulation program can significantly improve Powder Metallurgy (P/M) part properties and processing efficiency. The densification and creep behavior of stainless steel powders during free sintering has been simulated and the material model has been implemented by linking user subroutines to the ABAQUS finite element code. This approach is based upon the continuum theories of elastic and nonlinear-viscous deformation of porous bodies. The nonuniform density distribution of the green compact is considered as an initial condition for the FEM model. The porosity is updated during the simulation. Grain growth, gravity, thermal expansion, thermal conductivity, and other heterogeneous factors are also considered during the simulation. Several applications with different powder size range have been performed and the simulation results of axial shrinkage and density distribution changes have been compared before and after sintering. Dilatometry tests have been performed to validate the simulation results. INTRODUCTION Die pressing of the powder and sintering of the powder compact are the economically most important methods for P/M products. Due to the variation of cross-section of a compact and the friction effect, die pressing usually results in an inhomogeneous density distribution which causes shape distortions of the part during sintering. Since hard machining of the sintered parts is expensive, one of the main goals in the industrial production process is the optimization of the processing route with respect to the geometry of the as-sintered part. Compared with the empirical optimization, numerical simulation is much less expensive and saves a lot of time, especially for a newly designed product. In order to simulate the sintering process using finite element method, a basic material continuity assumption has to be set. Several constitutive laws based upon the continuum theories have been developed for modeling of sintering, e.g. Riedel (1990), Olevsky (1998). Many groups have modeled the sintering process, e.g. Sun & Riedel (1995), Zipse (1997), Kim and Jeon (1998), Gillia and Bouvard (1998), Gasik and Zhang (2000).