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Four-dimensional (4D) printing is a unique application of additive manufacturing (AM) which enables additional shape transformations over time. Although 4D printing is an interesting and attractive phenomenon, it still faces several challenges before it can be used for practical applications: (i) the manufacturing cost should be competitive, and (ii) the shape transformations must have high dimensional accuracy and repeatability. In this study, an irreversible and repeatable thermoresponsive shape transformation method was developed using a material extrusion type AM process and a plain thermoplastic polymer (ABS) without a shape-memory function. Various types of annular discs were additively manufactured using printing paths programmed along a circular direction, and additional heat treatment was conducted as a thermal stimulus. The programmed circumferential anisotropy led to a unique 2D-to-3D shape transformation in response to the thermal stimulus. To obtain more predictable and repeatable shape transformation, the thermal stimulus was applied while using a geometric constraint. The relevant dimensional accuracy and repeatability of the constrained and unconstrained thermal deformations were compared. The proposed shape transformation method was further applied to AM and to the in situ assembly of a composite frame–membrane structure, where a functional membrane was integrated into a curved 3D frame without any additional assembly procedure.

Four-dimensional (4D) printing is an advanced application of additive manufacturing which enables additional shape transformations over time in response to external stimuli. For appropriate shape transformation, dedicated materials such as shape memory polymers or 3D printers supporting multi-material printing have been used. Recently, a facile 4D printing method was developed which used a fused filament fabrication type 3D printer and a plain thermoplastic filament. This method used the anisotropic thermal deformation of the FFF-printed part to intentionally impose anisotropy by programming orthogonal printing paths, which resulted in thermoresponsive shape transformation upon a thermal stimulation. While the previous studies used convective heating as the thermal stimulus and thus required a long heating time of more than 10 min, this study uses an infrared (IR) heating to enable rapid thermoresponsive shape transformation. An infrared heating system was developed which included an optical focusing unit, a masking unit and a movable heating stage. To investigate the speed of shape transformation, IR heating was performed on a rectangular strip (60 × 6 × 1.6 mm) and the relevant shape transformation time was compared with the previous convective heating result. The shape transformation proceeded rapidly, and after 70 s formed a fully-closed circular shape, corresponding to the 1/10 reduction compared with the convection type heating (more than 13 min). The IR heating was further applied to 2D-to-3D shape transformations of 2D star-shape and flower-shape specimens. For each specimen, a profiled mask was used to selectively irradiate IR on predefined regions and thus to localize the relevant thermoresponsive shape transformation. The global and local IR irradiations were then compared in terms of heating capability and the variability in shape transformations.