Abstract
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.
Highlights
Recent advances in three-dimensional (3D) printing, known as additive manufacturing (AM), allow the process to be used for conventional prototyping and for the direct fabrication of functional parts [1,2,3]
The constrained heat treatment showed uniform deformation with significantly reduced deviations in the inner radius (37.73–38.03 mm) and outer radius (47.85–48.50 mm). These results indicate that the constrained heat treatment ensures uniform and repeatable shape transformation in frame–membrane composite structures
In this study, a cost-effective and reliable shape transformation method was developed for producing annular frame structures
Summary
Recent advances in three-dimensional (3D) printing, known as additive manufacturing (AM), allow the process to be used for conventional prototyping and for the direct fabrication of functional parts [1,2,3]. Four-dimensional (4D) printing is a unique application of AM that enables the shape of additively manufactured parts to be transformed over time [4]. It has various functional applications, especially for the fabrication of components where self-assembly, self-repair, or self-adaptability is required [5,6]. The most widely used stimulus-responsive materials in 4D printing are so-called smart materials such as shape memory polymers (SMPs) [11].
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