A-Line Is a Magical 4D Printing System

As a reader of the Hackster blog, it’s probably safe to assume you’re familiar with the basics of 3D printing. In standard FFF (Fused-Filament Fabrication) 3D printing, thermoplastic filament is pushed through a hot nozzle and deposited on the build plate. By depositing many layers, a three-dimensional object can be fabricated. That is incredibly useful for rapid prototyping, and has revolutionized engineering research and development. Now, a team from Carnegie Mellon University’s Morphing Matter Lab has created a 4D printing system called A-line.

In this case, the fourth dimension is time. It refers to the fact that the 3D-printed objects are designed to morph into a completely new shape after they have been printed. In most of the examples they present, the designs start as a narrow stick-like object. Then, at a later time, those objects can be exposed to heat in order to form completely new shapes. They could, for instance, turn into a spiral. Or the end of the stick could form a hook for. The shape that the stick becomes can be controlled with a combination of the pre-print design process, and how heat is applied during the transformation.

A-line relies on the same thermodynamic physical principles behind common mechanical devices like bimetallic thermostats. Different materials contract and expand at different rates when exposed to a temperature change. In the case of a thermostat, that’s two metals stacked on top of each other. Temperature changes cause the bimetallic strip to bend as one metal expands more than the other. The same concept is used here, except it’s the density and filament deposition pattern of the 3D-printed structure that causes the expansion differential. By controlling which parts of the structure are more dense — or in-line — during the design process, the resulting deformation can be controlled. The 3D-printed stick just needs to be exposed to heat to morph. The plastic will then harden, so the object will retain its new shape.