Living Hinge Design GUide

[MattDavis]

I own a 3D printer and was trying to find a way to make a hinge for one of my projects.

I came across a informative guide regarding living hinges that I found to be very helpful: https://revpart.com/living-hinge-design-guide/

[Davo]

I think it's better to build your hinge from flexible material, like Ninjaflex. You can use the appropriate number of layers to give you the flexibility/rigidity you need.

[Ama-fessional Molder]

A living hinge is highly dependent on the injection molding process, and one cannot create a "proper" living hinge with a 3D printer. The whole point of a living hinge is to force the material through a very thin area of the die, which lines up the polymer structure to a consistent orientation perpendicular to the hinge joint.

Without this structure, the polymer chains will not extend across the joint and will eventually separate, breaking the hinge. With proper polymer chain orientation a living hinge can last tens of millions of cycles. Without, it might last just ten.

All that being said, if you can print the hinge correctly (orientation of the strands perpendicular to the hinge axis), and you use the correct material, AND you keep the thickness to a proper level (I would say no more than .20 at most), you can get a functional part. It won't last as long as an injection molded hinge, but should get you by for prototypes.

http://www.caddedge.com/stratasys/3d...nge-protoytpes

This seems to be a good read on the subject, but even that link basically states that around a hundred cycles is a good upper limit to expect.

A bulky, thick joint with a secondary flexible material is not something that we recommend for most applications in the injection molding industry, though it does have it's place.

[Ama-fessional Molder]

I have a sneaking suspicion that you could obtain better results with an extruding head that has a .020" or smaller nozzle diameter and a long channel. This would force the polymer chains to orient parallel to the melt stream, and would cause a much stronger extrusion in that axis... But I doubt a 3d printer would be very fast or effective with such a nozzle - that is a very, very small hole.

[CSMonkey]

Reminds me of some discussions about redesigning for the process during an EOS user meeting quite a few years ago. EOS gave a presentation based on user feedback from a previous meeting, regarding living hinge design.

http://webbuilder5.asiannet.com/ftp/...0sintering.pdf

An interesting read about process specific designs.

Rich

[Mjolinor]

I have a sneaking suspicion that you could obtain better results with an extruding head that has a .020" or smaller nozzle diameter and a long channel. This would force the polymer chains to orient parallel to the melt stream, and would cause a much stronger extrusion in that axis... But I doubt a 3d printer would be very fast or effective with such a nozzle - that is a very, very small hole.

Would it not do a better job of aligning the molecules if you used a bigger nozzle and moved fast to stretch the extrusion?

[curious aardvark]

actually you can make a perfectly useable living hinge with an fdm machine.
BUT you need to use the right material and make it around the 0.2-0.4mm thickness.
Some of these materials are amazingly strong and tough.


I'd stack a living hinge made from colorfabs xt co-polyester filament against anything you can make with injection moulding.

And obviously the stiffer flexible filaments like polyflex can do it with inpunity.
I'd always use two layers as the slicer lays the second layer down across the first so you get a very tough final material.

But I must have spent 5 minutes bending the xt 1.75mm filament backwards and forwards and it just couldn't care less.
While it is very expensive stuff - it's my current favourite material.

[Davo]

actually you can make a perfectly useable living hinge with an fdm machine.

Yup. The hinge in my image is about 4mm thick, and is very stiff. The load will determine how thick the seam should be.

[curious aardvark]

I've printed polyflex at 0.2mm thick and even at that thinness it's almost impossible to tear with your hands.

The colorfab xt was stronger, and at that thickness really flexible.

[Ama-fessional Molder]

Yup. The hinge in my image is about 4mm thick, and is very stiff. The load will determine how thick the seam should be.

To be fair, that isn't a living hinge... well, it is. But only in a technical sense.

As for durability, yeah it is totally possible. But I have never heard of a 3d printed living hinge lasting tens of millions of flex cycles. A few hundred is pretty reasonable to expect from a good one, but I would like to see some mechanical testing on this subject to really get an idea.

That's far beyond our scope though I think.