Abstract
Thermoplastic polyurethanes (TPU) are increasingly being used in additive manufacturing design due to their abilities to exhibit extreme elastic properties under an applied stress. In this work, processing parameters in material extrusion (ME) of TPU filaments were investigated to provide a model for component stiffness as a function of the printing conditions. This model allows designers to target processing parameters and conditions to meet constraints of stiffness within flexible components. In this study, a full factorial design of experiments methodology was employed to provide a systematic method for experimentally analyzing the influence and effect of number of outer shells, infill percentage, and infill pattern on compressive strength. Based on the data collected from these experiments, a statistical regression model is presented that can be used to predict rigidity in TPU parts manufactured through material extrusion. Based on the results of the initial model, additional investigations were carried out into impact of number of infill line intersections, exterior corners, and TPU hardness (shore 85A and 95A). It was found that shore hardness and infill percentage had the largest impact with respect to stiffness but that all factors were significant and the only interaction not significant at α = 0.05 was the two-factor interaction of infill pattern and number of external shells. The effect of exterior corners were highlighted due to their additional stiffness as they essentially act as thicker columns in the perimeter of the parts.
