Investigation of the Effect of 3D Printing Parameters on the Bending Shape Recovery in 4D Printing Process

4D printing is an emerging phenomenon of additive manufacturing which is achieved by the 3D printing of shape memory materials. The printed parts can change their shapes when exposed to an external stimulus by controlling the 4D printing process. In this study, a relationship between applied pre-stress in the printing process and the amount of bending shape recovery was obtained using numerical simulations. Then, the effect of printing parameters of fused deposition modeling including layer thickness, printing speed, and nozzle diameter on the applied pre-stress in the printed polylactic acid parts was investigated. To reduce the cost and time as well as to increase the validity and accuracy, the central composite design method was used. Seventeen experimental tests were performed and a model was obtained between the mentioned parameters and applied pre-stress. In the following, R2 and Adj R2 of the model were obtained above 0.99 and 0.98, respectively, which indicates the high accuracy of the model. The model showed that the layer height, nozzle diameter, and printing speed have a significant effect on the applied pre-stress. Also, the applied pre-stress is inversely related to the layer height, nozzle diameter and is directly related to the printing speed. Simulations were performed under the conditions of maximum bending shape recovery and compared with the experimental model. The results showed that the error of the relationship between applied pre-stress and amount of shape recovery is 1.5% and the experimental model of printing parameters effect on the shape recovery is completely matched.