FreeShell: A Context-Free 4D Printing Technique for Fabricating Complex 3D Triangle Mesh Shells

Freeform thin-shell surfaces are critical in various fields, but their fabrication is complex and costly. Traditional methods are wasteful and require custom molds, while 3D printing needs extensive support structures and post-processing. Thermal shrinkage actuated 4D printing is an effective method for fabricating 3D shell. However, existing research faces issues related to precise deformation and limited robustness. Addressing these issues is challenging due to three key factors: (1) Difficulty in finding a universal method to control deformation across different materials; (2) Variability in deformation influenced by factors such as printing speed, layer thickness, and heating temperature; (3) Environmental factors affecting the deformation process. To overcome these challenges, we introduce FreeShell, a robust 4D printing technique that uses thermal shrinkage to create precise 3D shells. This method prints triangular tiles connected by shrinkable connectors using a single material. Upon heating, the connectors shrink, moving the tiles to form the desired 3D shape, simplifying fabrication and reducing material and environment dependency. An optimized mesh layout algorithm computes suitable printing structures that satisfy the defined structural objectives. FreeShell demonstrates its effectiveness through various examples and experiments, showcasing precision, robustness, and strength, representing advancement in fabricating complex freeform surfaces.