Advanced Curvilinear Finite Element Modeling of Thermally Induced Expansion in Large Format Extrusion‐Based Polymer Additive Manufacturing

Additive manufacturing of polymer‐based molds offers a cost‐effective alternative for composite tooling used in autoclave processes. However, accurately modeling their thermomechanical behavior remains challenging due to geometric complexity, process‐induced anisotropy inherent to fused deposition–based Large Format Additive Manufacturing (LFAM), and anisotropic heat transport characteristics. This study presents a coupled convection–conduction thermomechanical analysis of an LFAM polymer mold subjected to autoclave heating. A surface‐aligned curvilinear coordinate system is used to decouple surface‐normal and tangential thermal expansion components, enabling a more physically consistent interpretation of deformation in curved mold regions. Results show that analyses in a global Cartesian framework, while capturing overall thermal trends, can introduce curvature‐driven projection artifacts that exaggerate local temperature gradients and obscure deformation interpretation. In contrast, the curvilinear formulation produces a smoother surface temperature field, improves hotspot identification, and distinguishes surface‐normal and tangential expansion mechanisms critical for dimensional accuracy. Transient simulations also reveal a time lag between autoclave air and mold temperature response due to the low thermal conductivity and anisotropic heat transfer behavior of extrusion‐based polymer structures. These results demonstrate that surface‐aligned curvilinear coordinate formulations provide a robust framework for thermomechanical analysis of anisotropic LFAM polymer molds under autoclave conditions.