Mar 17, 2015

Making induction heated extruder

Standard extruders are heated by simple resistive heaters and you basically need to push enough 12 or 24 V DC electric current trough a resistor and simple MOSFET.

Induction heated extruders would have many advantages over them: faster heating up, no high temperature insulation is needed and less thermal mass. All of this could make induction heaters light and fast.
Main disadvantage is the more complex electric circuits needed to power it and more complex control unit since it is using much higher voltage and hundreds of kHz AC.

Based on a paper on induction nozzles for 3d printing standard FDM nozzles have several problems:

  • Slow convergence to desired steady state temperature at extruder tip, (many seconds, up to several minutes) and 
  • slow feedback loop for temperature control, (from 100's of ms to s) 
  • Lack of fine-grain temperature control at extruder tip, in steady state, the entire metal nozzle is essentially soaked to, or near, the melting temperature. 
  • Inconsistent feeder response due to varying liquid plastic volume near tip and 
  • limits on filament and extruded plastic drop size 

The extruder tip with inductive heating coil would be physically similar in appearance, but would have several distinct differences:

  • Rather than a metal nozzle, it would be made of a thermally insulating, nonconductive material such as glass or boron nitride. 
  • The actual heated element would be buried inside the tip to make direct contact with the plastic 
  • The power for heating is transferred through electromagnetic coupling of a driving coil to the heated element. The heated element, (and the molten plastic around it), are thermally isolated from the rest of the extruder. 
  • By using inductive heating and passive, digital temperature sensing of the heating target at the nozzle tip, significant improvements can be made to the issues above, resulting in faster production of more isotropic/mechanically stronger plastic prototypes. Also, the above problems typically put a limit on useable filament size, something this system should be able to surpass. 

Here is the comparison of resistive heated extruder vs. induction heated extruder:

Resistive compared to inductive heated extruder head, schematics made by aka47



RepRap builder SB made a post about his induction heated extruder, here is his work and schematics:

Induction heated extruder, you can clearly see the induction coils


The induction coil heats the sleeve made from mild steel (ferromagnetic) while the stainless steel is not heated directly because it is not ferromagnetic.



The electronics schematics are not yet available.

You can get more details here:

http://builders.reprap.org/2009/05/induction-heating.html

To get more information on induction heating you can also check related project of induction heated solder iron:

http://www.eevblog.com/forum/projects/diy-metcal-13-56-mhz-rf-supply/

First post about induction heated extruder on RepRap forum:

http://forums.reprap.org/read.php?2,481721

more detailed forum thread: http://forums.reprap.org/read.php?1,55188,55262

GitHub repository with preliminary design, many useful materials and thesis work on induction heated extruders:

https://github.com/UBCRapid/Extruders/tree/master/InductiveHeating

There are other people actively experimenting with this concept like Bulent, who made the extruder and posted a YT video of it working (his videos are not in English, but you will get some insight):




Here is a video showing more details, but again language is not English:



Here is a Reddit thread on attempt to make one:

http://www.reddit.com/r/3Dprinting/comments/1uoqyw/induction_hotend_first_steps/

As someone noticed in the comments, it would be interesting to see the induction extuder based on filament with metal particles where induction heats the filament itself. Then you could reduce the mass even further.

Another thing to mention is a possibility that the induction coil will interfere with nearby electronics and maybe emit noisy radio waves. It could also interact with build platform or other parts causing heating or melting damage.

If you want to build a serious desktop induction heater for metal melting of larger pieces here is a link:

http://www.rmcybernetics.com/projects/DIY_Devices/diy-induction-heater.htm

Inductive heated extruders are also being adapted on large scale for plastics industry with many benefits inefficiency and power saving: