Study on vertical printing of thermally driven PLA actuators: residual stress modulation in FDM-based 4D printing

The study addresses a gap in 4D printing research: while many works focus on planar deformation, the mechanisms behind how printing parameters affect vertically printed structures are not well understood. The authors propose a thermally driven vertical 4D printing method for PLA and systematically study how nozzle temperature, line width, layer height, and printing speed affect bending angle and flattening load. They report that nozzle temperature and printing speed have the strongest influence on residual stress regulation, and provide a parameter set that yields a bending angle of 44.960° and a flattening load of 7.64 N. They also compare residual stress development between vertical and planar printing modes, concluding that vertical printing accumulates less heat and dissipates thermal energy more efficiently, leading to smaller deformations. Finally, they fabricate a programmable thermally responsive fan-blade structure that combines planar and vertical printing strategies with gradient settings of line width and speed, which they state validates the feasibility of vertical printing for multi-level deformation control in complex structures.