Process-induced shrinking and warping in additively manufactured polycarbonate plates

Abstract

Most thermoplastic manufacturing processes, that do not include cutting, involves the melting and re-solidification of the raw material, which results in delamination, warpage, and shrinkage. These undesirable artifacts are introduced due to the build-up of residual stress during fabrication of the part. They not only affect the process reliability and repeatability, but also the service life and aesthetics of the final product. This is of particular concern in extrusion-based additive manufacturing of thermoplastics with relatively high melting temperatures, such as polycarbonate (PC). By controlling the process parameters, a certain degree of influence can be maintained on the multiple heating/cooling cycles and the corresponding phase transformations that induce differential shrinkage in the part. In the current study, the influence of the orientation of the fabricated part (flat and horizontal¹) on the process history, and as a result on the residual stress distribution in rectangular plates printed using fused filament fabrication (FFF) is studied. This work used a thermodynamically-consistent model previously derived for extrusion-based additive manufacturing to run simulations within ABAQUS. Corresponding experiments were conducted to validate the model, along with the error and repeatability analysis. The final dimensions of the plates measured from the experiments matched exceptionally well with the values measured from the simulations. The simulations predicted that the residual stress distribution in each orientation is extremely different. It mainly depended on the distribution of the weight fraction of the glass phase and temperature, which have significantly distinct patterns in both orientations. The simulation also predicted very different possible failure regions for the plates printed in the flat and horizontal orientations.