Shell Design Considerations for 3D Printing with Drones

Many researchers (e.g. Baarsen et. al. [2], Bos et. al. [3] , Galiaard et. al. [5], Perkins & Skitmore [11]) have reported on the potential innovations available when additive manufacturing (3D printing) is applied to the building design process, be it at the scale of an individual building component (Galiaard et. al. [5]) or the building itself (Baarsen et. al. [2]). However, by the very fact that the printing takes place inside the volume of the 3D printer, the finished product, even if printed at ‘architectural scale’ (Yasui et. al. [13]), must be smaller than the machine used to create it. To overcome this limitation, the authors are involved in a project to develop autonomous flying drones capable of 3D printing in the classic sense, by extruding liquid through a nozzle which then sets solid (www.aerial-abm.com). The initial focus is on using a foaming two-part polycarbonate composite, which possesses excellent properties in terms of minimizing raw-material weight for a given print volume, but whose tensile strength is limited and very variable. However, the general principle of compression only shell design assumes that self-weight will be the dominant load-case, and therefore much of the shell will be in compression, even under asymmetric wind load. If a shell is printed in a lightweight composite, this assumption is no longer valid, and there are repercussions for design in terms of the shapes of shells that can printed. This paper assesses the challenges for shell design introduced by the use of a lightweight material with low tensile strength, and discusses potential approaches to overcome such limitations in the context of 3D printing with flying drones.