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/
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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/
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.
http://hyrel3d.net/images/hinge/ninjaflex_hinge.png
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.
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.
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
Would it not do a better job of aligning the molecules if you used a bigger nozzle and moved fast to stretch the extrusion?Quote:
Originally Posted by Ama-fessional Molder
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.
Yup. The hinge in my image is about 4mm thick, and is very stiff. The load will determine how thick the seam should be.Quote:
Originally Posted by 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.
To be fair, that isn't a living hinge... well, it is. But only in a technical sense.Quote:
Originally Posted by Davo
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.
Nope.Quote:
Originally Posted by Mjolinor
You need to force the polymer through a constriction for that to happen. That's why the ideal thickness for a living hinge is no more than about .020" in molding. The very act of injecting it through the thin section of the mold is what straightens the polymers.
I just wondered if it is the same as those beer can plastic rings. They align when you stretch them that's why they get incredibly strong.
Ama, Are you saying something can be technically correct but not _really_ correct? I don't seem to follow your reasoning.
There have been videos of drill press drive belts printed in ninjaflex. It is very durable material. Tens of millions? No idea. What are the requirements of the item being designed? If I want a flexible hinge for a watertight container for my phone, so I don't lose the lid, I don't need it to last tens of millions of cycles. I might never open it 1000 times.
A living hinge, by definition, is made from the same material as the two pieces it connects. I actually made that statement backwards. It technically isn't, but basically is... if that makes sense. Since it isn't the same material it's just a *regular* hinge.
As I have said, if it only needs to survive a hundred or so cycles then it's perfectly fine. If you need more than that AND a rigid material for the rest of the case, then a living hinge isn't the answer for a 3d printed part.
Nope you are completely wrong on this point. Like I said use the RIGHT filament and there is absolutely no reason this can't be done.
The colorfab xt would easily give you thousands of flexes. I haven't got any left or I'd prove it.
Also polypropylene comes in a3d printable filament, that too would just keep on working.
And if you want a brilliant example of a lifetime living hinge (well dozens of them actually) look no further than the one piece grabbing hand:
https://www.youtube.com/watch?v=-n3yM-Suhuk
You need to wait till you've got your 3d printer and have used some of these filaments before making such sweeping statements :-)
I never said it can't be done. I said you aren't going to get the lifespan of a molded hinge out of it, by several orders of magnitude.
A molded hinge lasts millions of cycles.
I also said that you are not going to get that lifespan out of anything that requires a specific material other than flexible ones.
If you need to make something out of nylon, then you are stuck using nylon for the living hinge. If you print with a secondary material, then it is no longer a living hinge. By definition a living hinge is made with the same material as the rest of the part.
So it's all well and good to make toys with it, but if you need a working component that requires specific properties that the above mentioned polymer doesn't offer, then you need to print it with two materials, or live with the greatly reduced lifespan.
Which brings me to a question. Shower screen seals and other stuff like that has a hard part for clipping on the door and a soft part for sealing against whatever.
How do they do that. They look like all the same material and thicknesses don't vary enough but they are quite soft on the seal and hard on the clip.
2 shot molding, or overmolding. 2 shot usually involves molding both materials at once, in two steps, while overmolding uses a part from an external process and inserts it into the tool.
They mold one part of it first, then move it into a second cavity and shoot a secondary material over the top of the first.
For something like a long seal, it's a 2 part extrusion process. The first is extruded through a die, then it is ran almost immediately into a second die. Sometimes they punch out holes along the length of the first step in order to give the second material something to bind to.
Careful color matching takes care of the rest.
This is a 3 color/3-shot mold.
https://www.youtube.com/watch?v=GIghCNh1soM
Here's a better example, toothbrushes. These have the hard and soft materials.
https://www.youtube.com/watch?v=7PWJGW6v7s0
There is another type of this process that I recently got to see in action on 650 ton machines at Aptar in Mukwanago WI. The die has three parts, with a central "cube" that has cavities on 2 sides. The front half is injected, then the mold opens, turns 180 degrees, flips the caps closed, then ejects the finished parts that were previously in the back side, then it closes again. The process overmolds another color on top of the first.
The extruder for the second color is mounted on top of the machine, vertically.
96 cavities, two colors, and closed caps - 14 seconds per cycle.
I am trying to find a video of a similar process...
EDIT:
Here you go. This is a more advanced one, and obviously significantly more expensive, but the same idea as what Aptar was using.
These appear to have an HDPE or LDPE first shot, with the red second shot over the top. Of course I could be wrong about the material entirely.
https://www.youtube.com/watch?v=WCX0bS8syxo
Edit again... holy...
https://www.youtube.com/watch?v=dIls6EX9FrM
But those are two materials. I am talking about the ones that seem to use only one material.
nope - use the right material and the lifespan will be easily as good as injection moulded :-)
Given the way you can use very thin layers to form an actual flexible matrix that resists tearing in all directions, I suspect you could probably improve on injection moulded hinges.
There are some seriously amazing materials out there in 3d printer land.
Like I said, get your printer, try some of the more exotic filaments and then come back to me.
3d printed stuff can be way better than you seem to think it is :-)
People see the world through the filter of their own experience.Quote:
Originally Posted by curious aardvark
Can't wait till he gets his printer :-)
That first lightbulb moment is brilliant.
You keep saying "use the right material".
That doesn't work if the material you need is not conducive to a living hinge. We use 3d printed prototypes in my industry often. There's one sitting on my desk right now. Of course this one is just a large handle though.
If I need something that very specifically does NOT flex under load, then printing a living hinge with it would not work very well, would it?
Nylon is a great example of this, yet we can mold nylon living hinges without significant issue.
In my experience, workable living hinges can be made through FFF/FDM 3D printing. However, they will not nearly be half as strong and durable as IM'ed hinges due to the filament structure, material and heterogeneities. The best idea to me seems to use a dual extruder and print the hinge in a flexible material, with an uneven number of layers - 3 or higher - the outer layers being aligned with the bending direction.
Sorry CA but I'm with AFM on this. A living hinge requires specific conditions that can only be achieved when specific melt and flow criteria are being met. 3D printing cannot do this. You might get several flexions off a printed item but not the ridiculously high number as you would off an injection moulded item. 3D printed living hinges are for functional testing only.Quote:
Originally Posted by curious aardvark
I guess I'm just going to have to prove this :-)
And I presume you're totally disallowing flexible filaments ?
Given that polyflex will print stiff parts as well as totally flexible parts and is damn near indestructible. Printed some 0.4mm sheet a while back - could not tear it.
That's proved the point right there.
But there are other materials that will also do the job.
I have made some living hinges with Biome3D filament which is more flexible, and they work fine for hundreds of bends.
So not the amount you get with injection molding, but still nice enough to be useful for many things and if it breaks you simply reprint it. It opens up a lot of possibilities.
The standard swatches I print to show my clients the range of filaments I offer all include a living hinge. Flexible materials are best for this, woodfill is worst..
I am very interested to see the polyflex hinge.