Effects of printing parameters on 4D-printed PLA actuators

Controlling the printing parameters of four-dimensional (4D) printed actuators can be used to set the internal strain of the actuators. This approach can be utilised when using the fused deposition modelling method to develop 4D-printed actuators, allowing non-manual shape programming. However, there is a lack of comprehensive studies that investigate the effects of printing parameters on the actuation performance of 4D-printed actuators. In this study, the effects of four printing parameters on the bending angle of 4D-printed polylactic acid (PLA) actuators are reported. These printing parameters include the printing speed, printing temperature, ratio of passive-to-active layers, and layer height. In addition, these printing parameters are investigated while changing the height of the actuators. The results show that increasing the printing speed increases the internal strain while increasing the printing temperature, layer height, or actuator height has the opposite effect. Moreover, it is found that a ratio of passive-to-active layers of 50% maximises the strain while selecting a higher or lower ratio causes the opposite effect. Based on the results, four mathematical predictive models are developed to determine the bending angle induced in the actuators when printed based on each printing parameter. Then, a predictive model that relates all the printing parameters and actuator height to the bending angle is developed. The predictive model is based on the characterization results of 534 PLA actuators, providing an R-squared value of 0.98. Then, a finite element analysis model is developed to replicate the shape memory effect in actuators. To prove the accuracy of the proposed concept, two grippers with four and eight fingers are developed. The results show that the printing parameters can be used to control the bending angle of each finger based on the design specifications.