Design of FDM fabricated poly-lactic acid parts with forced-air cooling speed as the new control parameter to tune its shape memory effect

Poly lactic acid (PLA) as one of the shape memory polymers has extensively been used as the material in the 3D printing by fused deposition modeling process. In this study, we introduced the forced-air cooling speed as new control parameter in the fabrication process. A commercial material extrusion printer was retrofitted with a control module of forced-air cooling system. The shape memory effects of the PLA printed in different cooling speeds from 0–5 m s⁻¹ were first measured by submerging the printed coupon specimens into water bath at recovery temperature. It is found that the changes in dimensions were mainly anisotropic and dependent of the raster angle in printing, in addition to the controlled cooling speed. The shape memory strains were roughly in linear trend with the magnitude of cooling air speed. In other words, the shape memory effect of the PLA can be easily controlled by the cooling air speed in fabrication. X-ray diffraction measurement on the specimens before and after recovery treatment confirmed the shape memory effect was related to the partial crystallization of molecular structure. Moreover, the different cooling air speeds also induced different thermal stresses in the printed specimens which manifest its important role in the total shape memory strain. Finally, the proposed theoretical beam formulation for the recovery bending deflection was shown to have good prediction accuracy comparing with experimental measurements.