Optimization of 3D printable cellular array structures for cushioning

Abstract

Cushions are energy absorbing structures or materials used in various applications including packaging, footwear and protective gears. They often come in the form of polymeric cellular structures such as foams. The cushion selection process conventionally involves testing of available foams and selecting the foam which is best suited for the target application. Optimized cushions would greatly improve the selection process and its effectiveness for a targeted task. Instead of selecting a cellular solid best suited for a particular application, the foam or the cellular structure itself is designed and optimized based on the requirements of the application. This requires understanding and control of the cellular structure’s design parameters and additive manufacturing (AM) or three-dimensional (3D) printing offers great design freedom for the fabrication of complex porous parts. Polyjet printing is a 3D printing process that is capable of producing complex polymer parts for various purposes (prototypes to functional parts). Polyjet printing is also capable of producing digital polymers which are polymers composing of up to three different polymer resins hence offering a range of physical and mechanical properties. This research aims to develop an optimized 3D printed cellular structure for cushioning purposes. The effect of cellular microstructure and density on the cushioning properties of the final structure will first be investigated. This is followed by the formulation of an optimization problem to optimize the design parameters of a cellular structure for cushioning purposes. To achieve the above, methods of evaluating cushioning properties were reviewed and a new cellular structure model was designed with the unit cells arranged in a regular array. The design allows the tuning of the structure’s stiffness and strength without affecting its weight i.e. maintaining its relative density. Theoretically, this new method of designing cellular structures allows for an exponential increase in stiffness by decreasing the cellular size. A mathematical model was then developed to accurately predict (R2 > 0.6) the mechanical response of the honeycomb during compressive deformation. A method which predicts the dynamic response of cellular structures using its static compressive data and the mathematical model were used to optimize the structure to meet various cushioning requirement. The optimized cushions were compared to conventional cushions for various applications. The optimized cushions are always lighter (50% ~ 90%) when compared to conventional cushions with similar thickness.