DIY Self-Assembling 4D Printing

A 4D printed object is like a 3D printed object, but it changes shape or self-assembles when its environment changes. [Teaching Tech] has been reading about this technology and decided to try to replicate it using his conventional 3D printer.

His attempts to make a joint that changes when submerged in the water looked at several options: material that can absorb water, material that expands with temperature, and — the selected option — a dissolvable locking mechanism. Essentially, a hinge is held open by a water-soluble lock. When water dissolves the lock, the hinge can spring to its natural position.

Like most experiments, this one had a few false starts. But you always learn something each time. The final design had a TPU hinge and spring with PLA structural beams. The TPU required flat printing, so various pieces have to be rotatable so they can be placed in their final orientation after printing.

Usually, multi-material setups are for printing different colors of the same kind of plastic, it’s possible to use different plastics, but it can be tricky. As a compromise, [Teaching Tech] did one print using PLA and TPU, but printed the PVA locks in a separate pass and installed them on the print at the end. The first finished 4D print wasn’t entirely successful. The hot water slowly dissolved the PVA, but it also deformed the PLA. A redesign of the lock made a big difference.

We aren’t sure this is practical yet, but we are sure someone has a need for this technique and it could be made very practical with a little work. The last time we saw 4D printing, there were magnets involved. We think this is an exciting time where people aren’t just trying to get conventional printing to work well, but are pushing the envelope with new techniques like conical slicing, for example.

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Shape Shifting Structures Work With Magnets

In The Dark Knight, Lucius Fox shows Bruce Wayne a neat bit of memory weave fabric. In its resting state, it is a light, flexible material, but when an electrical current is applied, it pops into a pre-programmed shape. That shape could be a tent or a bat-themed paraglider. Science has not caught up to Hollywood in this regard, but the concept has been demonstrated in a material which increases its rigidity up to 318% within one second when placed in a magnetic field. Those numbers do not mean a lot by themselves, but increasing rigidity in a reversible, non-chemical way is noteworthy.

The high-level explanation is that hollow tubes are 3D printed and filled with magnetorheological fluid which becomes more viscous in the presence of a magnet because the ferrous suspended particles bunch up to form chains instead of sliding over one another. Imagine a bike tire filled with gel, and when you need a little extra traction the tire becomes softer, but when you are cruising on a paved trail, the tire becomes as hard as a train wheel to reduce friction. That could be darn handy in more places than building a fast bike.