Simulation of PTFE sintering: Thermal stresses and deformation behavior

A finite element model has been used to study the sintering process of polytetrafluoroethylene (PTFE) cylinders in order to predict residual thermal stresses; both solid (rods) and hollow (billets) blocks were studied. The simulation of the process was performed considering three separate stages: thermal, deformation, and stress analysis. For each stage, relevant material properties were determined experimentally. In particular, the deformation behavior of PTFE was thoroughly investigated by means of thermo-mechanical analysis (TMA). It is shown that experimental results can be explained considering deformation recovery and orientation effects. Predictions of the model are compared with experimental measurements performed on real PTFE-sintered cylinders. Temperature and deformation distributions determined with the model agree well with experimental data. Fair agreement between predicted and experimentally measured residual stresses is obtained, and the influence of cylinder size and applied cooling rate on residual stresses is correctly predicted. (C) 2004 Society of Plastics Engineers.