An inexpensive 3D printer was recently used by researchers at Carnegie Mellon University to create flat plastic items that, when heated, fold themselves into predetermined shapes. Others have explored self-folding materials, but they have typically relied on exotic compositions or depended on sophisticated processing techniques that were more expensive or not widely available.
This team worked with a common FDM printer using a continuous filament of melted thermoplastic. These materials contain residual stress that is relieved as the thermoplastic contracts. Thisstress relief creates warped edges and surfaces that are normally seen as a defect.
However, controlling the warpage by varying the speed at which thermoplastic material is deposited and combining rubber-like materials with warp-prone materials, the objects emerge from the printer as hard, flat plastic. When the part is placed in water hot enough to turn it soft and rubbery, but without melting it, the folding process is triggered.
Researchers feel these self-folding plastic objects represent the first step toward products such as emergency shelters that could be shipped flat and folded into shape when introduced to heat. Self-folding materials are quicker and cheaper to produce than solid 3-D objects, making it possible to replace noncritical parts or produce prototypes at a lower price. Additional cost-cutting applications could include molds for boat hulls and other fiberglass products.
