First of all, a living hinge is not a biological entity nor does it move on its own. Think of the top of a Tic Tac container where the lid and the cover are a single piece, and the thin plastic holding them together flexes to allow you to reach the candies disguised as mints. [Xiaoyu “Rayne” Zheng] at Virginia Tech designed a method of multimaterial programmable additive manufacturing which is fancy-ese for printing with more than one type of material.
The process works under the premise of printing a 3D latticework, similar to the “FILL” function of a consumer printer. Each segment of material is determined by the software and mixed on the spot by the printer and cured before moving onto the next segment. Like building a bridge one beam at a time, if that bridge were meant for tardigrades and many beams were fabricated each minute. Mixing up each segment as needed means that a different recipe results in a different rigidity, so it is possible to make a robotic leg with stiff “bones” and flexible “joints.”
We love printing in different materials, even if it is only one medium at a time. Printing in metal is useful and could be consumer level soon, but you can print in chocolate right now.
Here’s some interesting work shared by [Ben Kromhout] and [Lukas Lambrichts] on making flexible 3D prints, but not by using flexible filament. After seeing a project where a sheet of plywood was rendered pliable by cutting a pattern out of it – essentially turning the material into a giant kerf bend – they got interested in whether one could 3D print such a thing directly.
The original project used plywood and a laser cutter and went through many iterations before settling on a rectangular spiral pattern. The results were striking, but the details regarding why the chosen pattern was best were unclear. [Ben] and [Lukas] were interested not just in whether a 3D printer could be used to get a similar result, but also wanted to find out what factors separated success from failure when doing so.
After converting the original project’s rectangular spiral pattern into a 3D model, a quick proof-of-concept showed that three things influenced the flexibility of the end result: the scale of the pattern, the size of the open spaces, and the thickness of the print itself. Early results indicated that the size of the open spaces between the solid elements of the pattern was one of the most important factors; the larger the spacing the better the flexibility. A smaller and denser pattern also helps flexibility, but when 3D printing there is a limit to how small features can be made. If the scale of the pattern is reduced too much, open spaces tend to bridge which is counter-productive.
Kerf bending with laser-cut materials gets some clever results, and it’s interesting to see evidence that the method could cross over to 3D printing, at least in concept.
It sounds like a challenge from a [Martin Gardner] math puzzle from the Scientific American of days gone by: is it possible to build a three-dimensional wooden box with only two surfaces? It turns out it is, if you bend the rules and bend the wood to make living hinge boxes with a laser cutter.
[Martin Raynsford] clearly wasn’t setting out to probe the limits of topology with these boxes, but they’re a pretty neat trick nonetheless. The key to these boxes is the narrow to non-existent kerf left by a laser cutter that makes interference fits with wood a reality. [Martin]’s design leverages the slot and tab connection we’re used to seeing in laser-cut boxes, but adds a living flex-hinge to curve each piece of plywood into a U-shape. The two pieces are then nested together like those old aluminum hobby enclosures from Radio Shack. His GitHub has OpenSCAD scripts to parametrically create two different styles of two-piece boxes so you can scale it up or (somewhat) down according to your needs. There’s also a more traditional three-piece box, and any of them might be a great choice for a control panel or small Arduino enclosure. And as a bonus, the flex-hinge provides ventilation.