Printing force analysis in FDM-based 4D printing of singular lines: A numerical and experimental study

Fused deposition modeling (FDM)-based 4D printing (4DP) provides a low-cost pathway to fabricate programmable structures, but its broader adoption is limited by an incomplete understanding of how process conditions affect internal stress development and resulting shape change. Building on prior work linking 4DP to the shape-memory cycle, this study investigates how process parameters influence the flow and temperature fields during the deposition of a singular line. Printing force is measured in situ and compared with wall shear force from a high-fidelity thermofluid simulation. The numerical framework is calibrated using infrared thermography and a Cross–Williams–Landel–Ferry (Cross-WLF) viscosity model for polylactic acid (PLA). Sensitivity analysis identifies gap height, nozzle temperature, and volumetric flow rate as the dominant parameters governing the printing force, while printing speed serves as an effective design variable for manipulating the printing force continuously. The simulations further show that shear rates are concentrated at the nozzle exit and the deposition front, explaining heterogeneous pre-strain across the filament cross-section. Experimental and numerical trends are consistent: increasing nozzle temperature reduces the printing force, while increasing printing speed increases it. This combined experimental–numerical approach provides a methodology to improve process control by analyzing flow conditions during smart structure manufacturing.