Investigation of the influence of resin coating and heat treatment on the mechanical properties of topology-optimized parts made of polylactic acid (PLA) by the fused filament fabrication (FFF)

Fused filament fabrication (FFF) allows the manufacturing of complex and lightweight polymer components; yet, the mechanical performance of topology-optimized parts is constrained by interlayer weaknesses, residual stresses, and diminished crystallinity. This study systematically investigates the combined effects of heat treatment and resin coating on the compressive behavior of topology-optimized polylactic acid (PLA+) structures produced by FFF. Topology optimization was conducted utilizing the Solid Isotropic Material with Penalization (SIMP) approach to attain a specified mass reduction of 60% while maintaining structural stiffness. The optimized geometry was manufactured and later subjected to post-processing at various heat-treatment temperatures and durations, both with and without resin coating. A central composite design (CCD) inside a response surface methodology (RSM) framework was utilized to assess the individual and interaction effects of post-processing parameters on the maximum compressive load (MCL). Statistical investigation indicated that heat-treatment duration is the most significant variable, succeeded by temperature and coating condition. An ideal post-processing conditions around 82 °C for 90 minutes with resin coating provided a ~34% increase in MCL relative to the as-printed topology-optimized specimen. X-ray diffraction analysis verified a significant increase in crystallinity (≈232%), explaining the noted mechanical enhancement, whereas FESEM analysis indicated a consistent, defect-free coating layer with robust interfacial adhesion. The suggested combined optimization and post-processing strategy provides an efficient method for manufacturing lightweight PLA components with significantly enhanced load-bearing capacity for engineering applications.