Origami fabrication, where planar sheets are permanently folded into complex three-dimensional forms, offers various advantages such as minimal material use and potential to create freeform shapes. At the large length scales, the folding processes in origami fabrication are performed using external forces applied by mechanical manipulators, as in the manufacturing of cardboard containers and folded metallic panels. However, at the sub-millimeter length scales, external mechanical manipulation is often not feasible and self-folding techniques are needed to fold the planar sheets towards their target form. In self-folding, inelastic strains within the sheets triggered by non-mechanical fields (e.g., thermal, chemical, electromagnetic) are used to perform the folding processes. This work presents a novel origami fabrication method that uses photolithography and self-folding to create polymer polyhedral structures of millimeter and submillimeter scales. First, patterned polymer sheets with less crosslinked folds and more crosslinked faces are produced using multi-step photolithography. Solvent is diffused into the fold regions during the development step of the photolithography process due to their low crosslinking density. The inhomogeneous solvent concentration throughout the thickness of the folds causes inhomogeneous strains at these regions once the solvent is removed by increasing the temperature, enabling self-folding. An analytical fold model that allows for the determination of the dimensions of the fold regions required to achieve a target fold angle is developed. The fold model is obtained by deriving analytical equations for the solvent concentration field and the fold bending response. Experiments are performed to calibrate and validate the fold model. Subsequently, the fold model is incorporated into existing origami design methods that consider smooth (bent) folds to enable the design of planar sheets which can be self-folded into target three-dimensional shapes. A parametric study quantifying the accuracy of the designed origami forms with smooth folds as compared with those having idealized creased folds is performed. The study quantifies the loss in shape accuracy as the size of the target shapes decreases. Finally, different polyhedral shapes are fabricated to demonstrate the capabilities of the developed method for origami fabrication.


Characterization and Design of Programmable Self-Folding Polymer Films

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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