Laser joining of FDM-printed PLA components: feasibility and thermo-mechanical analysis

This study investigates the feasibility and performance of laser joining for polylactic acid (PLA) components produced via fused deposition modelling (FDM), aiming to overcome the inherent limitations of additive manufacturing in terms of interfacial adhesion and mechanical strength. A diode laser system was employed to join overlapping PLA samples under varying power and exposure time conditions, with energy density ranging from 3.48 to 12.93 J/mm2. Mechanical behaviour was assessed through single-lap shear tests, while morphological and thermal characterisation of the bonding interface was conducted via cross-sectional imaging and temperature analysis. Results show that optimal energy input promotes effective bonding, yielding shear strength values exceeding 10 MPa, significantly outperforming a monolithic control specimen. However, beyond a critical energy threshold, a decrease in apparent shear strength was observed. Detailed fracture analysis revealed that this drop was not due to interfacial weakening, but to cohesive failure within the PLA bulk material, indicating that the joint strength surpassed the substrate’s mechanical limits. Morphological analysis further highlighted the formation of a consolidated bulk region within the printed PLA under high-energy conditions, eliminating inter-filament voids typical of FDM and improving load-bearing capacity. Nonetheless, excessive energy input also induced visible surface deformation, posing potential aesthetic and dimensional limitations. These findings demonstrate that laser joining is a viable strategy for assembling FDM-printed PLA parts, enabling both functional bonding and microstructural enhancement.