[en] Highlights: • A 3D thermal model was developed to simulate the XPP melt packing process. • Simulations of 3D viscoelastic melt packing process were performed. • The heat transfer and flow-induced stresses in 3D cavities were analyzed. • Effects of processing conditions on the stress and density were studied. - Abstract: In this study, a 3D weakly compressible viscoelastic flow model with the thermal effect is developed for simulations of the non-isothermal XPP melt packing process. The 3D multi-field coupled model is solved by the collocated finite volume CLEAR algorithm with the AVLSMART scheme. The numerical model is validated against the benchmark problem. The XPP melt packing process in a rectangular cavity is simulated, and the predicted flow-induced birefringence is in agreement with the experimental and numerical results reported in the literature. For a case with a rather complex cavity, the XPP melt packing process in a 3D hemispherical shell cavity is further simulated. The distributions of melt temperatures, flow-induced stresses as well as the corresponding rheological characteristics of XPP melt in 3D cavity are vividly presented, which are difficult to be captured by previous simulations and experiments. Especially, the present model allows the effects of melt temperature and holding pressure on the first normal stress difference and density to be studied. It is shown that with an increase in melt temperature, the absolute values of the first normal stress difference increases slightly and the density decreases gradually, while the high holding pressure improves significantly the first normal stress difference and density. Numerical results demonstrate that the present 3D thermal model is an effective tool for simulating real-world viscoelastic polymer melt packing processes.