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joergen

New hot end design

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I thought about how the UM could be different and easier than all the other 3D printers out there, and the current design is plagued with clogging issues (for most beginners), temperature measurement issues (mine, and probably others), wasted energy (uninsulated alu block that is 15mm "away from the action") due to radiant heat, heat sink issues (upper part of the brass tube gets hot and causes backflow) etc etc.

So here is my idea for a new hot end that is a drastic deviation from all previous designs, with less parts, and probably lower production cost, and far superior energy efficiency:

_MG_2279.jpg

The idea is to find a steel nozzle (stainless won't work well, it needs to be magnetic), and use HF induction coils around it to heat it to temperature. The advantage is that it needs only 20% (or less) the electrical energy compared to the resistance heater cartridge, and it heats up in seconds, since only the iron the nozzle needs to be heated up. the disadvantage is that the nozzle and the coil are somewhat custom made, probably, and a different TC is necessary.

The nozzle is mounted to a M10 alu screw/rod that has an internal M7 thread. The M10 is simply screwed into the existing UM alu base plate (heat sink) and secured with 2 alu lock nuts.

The PTFT/PFA tube gets a M7 thread, and is screwed in all the way down to the nozzle... if it's short 1-3mm, no problem, too long is probably also no issue. This gives the bowden a ridiculous solid connection to the hot end, and would enable to print at insane pressure levels (down to 170C???). Heat affecting the PTFT/PFA is manageable, since the max operating temp of the tube is 260C (same as the PEEK), and this design would keep the heat far more contained in the nozzle than the current design. it should also fit into the existing head without much/any modification.

To do:

 


  • - Find an iron/steel nozzle that fits the specs (i don't think rust is an issue), M10 thread would be nice, if it's M12 would also work... anybody with a machine shop willing to weigh in how doable this is?
    - Come up with a design for an induction coil around the nozzle, and something that holds it in place (clay/putty?) (any electrical engineers here willing to help)?
    - Find/design an induction heating controller (daughter board, maybe later included on the UM PCB) that works with 19V DC from the traditional heater terminal)
    - Find a TC that attaches to the outside of the nozzle, or into a custom bore hole from the top.

 

all other parts are trivial

comments?

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Just an additional thought to the nozzle design:

it would be great if the nozzle would have a 4mm to 0.2-1.0mm funnel, to create a good shoulder for the alu/tube combo to sit on. (the sketch above shows a 10mm to 0.2-1.0mm funnel, which creates a far too large chamber with too much turbulence and not enough contact to the nozzle walls and bad heat transfer).

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There are some schematics from this online:

http://builders.reprap.org/2009/05/indu ... ating.html

http://builders.reprap.org/2009/05/circ ... ating.html

I see a big drawback: EMI. What you are looking at is actually a huge magnet that can cause interference with heartpacers and other electronic devices close to the machine.

Thanks so much for the links, very very helpful!

I don't think that EMI is such a problem: first of all, the magnetic field is relatively contained and small, not much different than a transformer in a wallwart... secondly induction cooktops are around for some time, and they work on the same principle, only much higher energy, and they haven't killed people with pacemakers yet (as far as I know)

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i'd support this....! How much would an actual proof of concept cost? Im sure we gather lets say 50 people together who each contribute say $XX for the prototype, we'd raise enough funds to get a prototype made?

I think the nozzle is the trickiest part, since i can't find any supplier... bronze is the most favorite material, mild steel is what we would need... the other issue might be if there is enough time/room/distance for the filament to melt before it has to squeeze through the nozzle.

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Interesting design concept, I'm also working on a new hot end, since clogging, energy waste and assembly/disassembly issues are bugging me. However I'll stick to the cartridge heater.

I think one of the larger drawbacks of your proposal is the steel part which functions as heater and nozzle at the same time. I thought about an induction heated steel part that sits between your alu/PEEK pipe and a standard Ultimaker/Makergear brass nozzle. So you would just have to replace the brass nozzle when changing extrusion diameters, instead of the whole steel nozzle, which is probably more complex and expensive than the standard brass ones.

Anyway, once you need someone to do a CAD drawing for prototype production, I could do this.

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