Fused deposition modeling (FDM) is one of layer-manufacturing technologies that have been widely used for rapid prototyping applications in product design and development. Due to the intensive energy, rapid cooling and phase changes, parts made by FDM and other layer-manufacturing processes are deviated from the designed geometry, and some require laborious post-processing. Most severe form inaccuracies such as curl, warping, and delamination are attributed to the residual stress accumulations during prototype fabrications. This study investigates the FDM process, which comprises complicated heat and mass transfer phenomena coupled with mechanical loading and phase changes. A finite element analysis model using element activations has been developed to simulate the mechanical and thermal phenomena in FDM, and further used for residual stress and part distortion simulations. The model has also been used to study the toolpath effects on the FDM process. Toolpath patterns affect the residual stresses not only in the magnitude, but also in the distribution which shows stress concentrations aligned with the primary direction of the toolpath. Experimentally fabricated and measured prototypes show that the part distortion-center shifts distinctly due to different toolpath patterns, which is consistent with the residual stress characteristics in the simulations. From the simulations, it is also shown that the short-raster toolpath results in higher residual stresses, and thus possibly larger distortions, than the long-raster and alternate-raster patterns, both having similar stress distributions and distortion features.

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