  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. Thermoshrinkage actuated 4D printing is an effective method
through flat structures 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 thermoshrinkage to create precise 3D
shells. This method prints triangular tiles connected by shrinkable connectors
from 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 algorithm for flattening 3D meshes ensures
precision in printing. FreeShell demonstrates its effectiveness through various
examples and experiments, showcasing accuracy, robustness, and strength,
representing advancement in fabricating complex freeform surfaces.
