[JanTec Engineering] was fascinated by the idea of using a 3D printer’s hot end to inject voids and channels in the infill with molten plastic, leading to stronger prints without the need to insert hardware or anything else. Inspiration came from two similar ideas: z-pinning which creates hollow vertical channels that act as reinforcements when filled with molten plastic by the hot end, and VoxelFill (patented by AIM3D) which does the same, but with cavities that are not uniform for better strength in different directions. Craving details? You can read the paper on z-pinning, and watch VoxelFill in (simulated) action or browse the VoxelFill patent.
With a prominent disclaimer that his independent experiments are not a copy of VoxelFill nor are they performing or implying patent infringement, [JanTec] goes on to use a lot of custom G-code (and suffers many messy failures) to perform some experiments and share what he learned.
One big finding is that one can’t simply have an empty cylinder inside the print and expect to fill it all up in one go. Molten plastic begins to cool immediately after leaving a 3D printer’s nozzle, and won’t make it very far down a deep hole before it cools and hardens. One needs to fill a cavity periodically rather than all in one go. And it’s better to fill it from the bottom-up rather than from the top-down.
He got better performance by modifying his 3D printer’s hot end with an airbrush nozzle, which gave about 4 mm of extra length to work with. This extra long nozzle could reach down further into cavities, and fill them from the bottom-up for better results. Performing the infill injection at higher temperatures helped fill the cavities more fully, as well.
Another thing learned is that dumping a lot of molten plastic into a 3D print risks deforming the print because the injected infill brings a lot of heat with it. This can be mitigated by printing the object with more perimeters and a denser infill so that there’s more mass to deal with the added heat, but it’s still a bit of a trouble point.
[JanTec] put his testing hardware to use and found that parts with infill injection were noticeably more impact resistant than without. But when it came to stiffness, an infill injected part resisted bending only a little better than a part without, probably because the test part is very short and the filled cavities can’t really shine in that configuration.
These are just preliminary results, but got him thinking there are maybe there are possibilities with injecting materials other than the one being used to print the object itself. Would a part resist bending more if it were infill injected with carbon-fibre filament? We hope he does some follow-up experiments; we’d love to see the results.
What about concrete infill?
This, or some sort of resin etc.
Simply a liquid that’s poured in from a separate nozzle. Should be pretty simple to implement, just a tube and valve strapped to the side of existing extruder. Pay attention to setting times and maybe make a waste catchpot to keep the tube unblocked during longer prints.
Would mean there’s theoretically no limit to the depth of hole, or even the shape if air pockets are taken care of.
You could add a vibration motor to the bed to eliminate voids.
You could also just vibrate the bed with the stepper motors
There’s an open source mini lathe that is 3d printed and filled with concrete
I am having trouble finding info about that lathe. Any chance you have a link you cpild share?
https://www.youtube.com/watch?v=6Js8erWbsDQ
i’m amazed this works at all. the material isn’t really flow-y enough to fill a volume. when i actually want to strengthen a void, i fill it with a bolt or a dowel rod instead. these hacks to get X% more strength out of printed plastic seem to be of limited utility. there’s a very narrow range of requirements where the load is enough that plain reasonable-thickness reasonable-infill plastic won’t do it but hacked plastic will.
There are signmaking 3d printers that have a separate nozzle for UV curable resin and a heated glass bed lined with UV lamps – similar to https://www.youtube.com/watch?v=gGCD03feE9E .
That seems like the best use case for that process (if you are into eye-watering multicolored signs).
I do this with a replacement part I need to periodically reprint for a cigarette rolling machine. The reinforced section is actually a shear pin, simply 3d printed, even solid, sheared too easily. I use a 3D pen to fill it, and I have the tube shell backed up with aluminum so the shape is maintained. The pin is driven by a geneva gear, so when sheared off it just travels around and the machine gets no more stress.
The original has a bearing here and when it fails it pulls out parts from below it, so it can damage the machine pretty bad, especially if somebody keeps trying the button. They do not sell this part either, you need to send your machine back for repair. I’m probably on the tenth replacement, and it’s become a consumable, like it should have been.
Suddenly I’m thinking “why didn’t I think of that?”
Also I’m thinking “ok, leave some very small openings at the top of the voids and inject them with a syringe full of JB Weld (60% super fine powdered stainless steel in epoxy)”. It makes me wonder if I would be reinforcing with JB Weld or if I would just be 3D printing molds to make parts from JB Weld. Maybe when the stuff cures I could wash away the PLA with acetone and have an arbitrarily-shaped JB Weld part. Maybe that would work with any “cold cast” metal powder – brass, gold, uranium… probably not the latter.
I’m sure the goal here was to do it all in one automated pass, so clearly it’s a different objective and I salute the accomplishment. I’m just thinking about what I can do with a box of needles in my toolbox and no West Virginia Party Powder.