The idea goes like this...

Normal FDM printer + an inkjet printhead (CMYK)

The system would be setup for dual extruders, but one of the extruders would be the inkjet. You would have CMYK inks (dyes) heated to just below boiling. The system would put down a layer of nylon plastic (due to its ability to be dyed easily), then put down a perimeter of ink in various colors. The colors would have to be specially sliced by a slicer software designed to do so.

The inkjet head would also have to be heated to keep the dyes up to temperature. You could also add an automatic agitator to keep the dyes suspended in the solution.

It's just a thought, and would need careful engineering to get the inkjet printhead functioning properly in the system

What do you guys think?

I've been thinking about this for a while. This topic discusses ways to make a diy print head: [forums.reprap.org]. Also I did a little expetiment printing ink onto PLA: [forums.reprap.org]. It would be great to see some progress made on this idea

Edit: this topic would be a lot better suited to the Developers sub-forum. It will quickly get lost under General.

Edited 1 time(s). Last edit at 03/17/2014 06:11PM by samp20.

I've seen this done on large commercial machines (can't remember which). I really like the idea but the fact that it has been done means their is likely a patent on the whole idea.

Maybe you could print in white ABS and make an ink based on acetone?

I know I've seen this idea in powder based printers, where the ink is a binder. However, I've never seen this idea in a traditional FDM style printer. It seems like the most difficult part would be to figure out how to get an inkjet to work putting out a single jet of ink. Most in modern printers put out a few lines of ink at a time to speed up printing. In addition, you'd have to wire up some crazy control circuitry and code to actually control the dang thing. Would be a pretty tough undertaking indeed...

Quote
drumguy560
It seems like the most difficult part would be to figure out how to get an inkjet to work putting out a single jet of ink. Most in modern printers put out a few lines of ink at a time to speed up printing.

You could give the ink magnetic properties and make it flow through a electro magnetic field?

I have made a little progress with this idea. I've 3D printed an inkjet which uses a piezo element to compress a chamber. I'm currently unable to test the electronics (visiting parents for the week), but I found a light tap of my finger on the piezo element was enough to eject a little water (Ink testing will be later). I've attached an image of the assembly.


The nozzle was made by inserting a pin into some hot glue then shaving off layers with a scalpel until a hole appears.

@samp20:

Looks like a cool project.
Got a link to the piezo that you're using, and how is it powered?

I don't know where the piezo was from. I salvaged it from a plastic enclosure. It is 32mm diameter if I remember correctly. I'm powering it from between 24-36V from my bench power supply,and switching it through a suitably rated mosfet. I have a 10kohm resistor in parallel with the piezo to relax it after firing. I haven't tested the electronics with the completed assembly yet.

Since this thread is about color printing on FDM, you may find this interesting...



Now what I'd really like to do is use an inkjet to color the objects... anyone willing to share experiences?

Paucus

Just throwing a future idea out there, by no means is this currently practical; an inkjet/hotend two-in-one. Around the main nozzle hole are more holes for the flow of ink, directly deposited onto extruded plastic.
An idea I've had, but know of no way to make and test something requiring precision as I don't see it being makeable with home tools.

Do you have a clear idea of how this would work. If you draw a picture or CAD drawing, I'll give it a shot at machining it.

Last I knew machining isn't that precise.
Imagine the bottom of an inkjet cartrige, the holes that the ink comes out of, spread around the inner, bottom of the FDM hole.
I'll draw something up and let you see.

Would you have separate holes for each color (so 4 holes)? or shoot the ink all out the same hole (with traces of previous color)? how do you push the ink out?
My idea was to mount a regular inkjet head next to the hotend, print the plastic first and then the ink, as in the current magic marker method... not simultaneously or in the same pass.

Paucus

Not just plain holes. I'm talking keeping the technology of the inkjet [but with higher temp materials], but making a nozzle/inkjet 2-in-1.

You would need to be careful not to heat the ink up too much otherwise you could end up drying the ink out and clogging the nozzle.

I think Pacaus' idea of mounting the inkjet next to the nozzle but separate is the way to go. Apart from getting a working inkjet in the first place, there is also the challenge of fitting it all onto the X-carriage. If we get really stuck for space then this (or another) tool changer is an option: [forums.reprap.org]

You can simply use dual X carriages, one for hotend, one for print cartridge. This way you can park one carriage when it's not in use.

I've been experimenting with various designs, and unfortunately haven't managed to get anything to work. I even tried replicating Adrian Bower's design [reprap.org]. I think my problem is my voltages are too low. Adrian was using around 100 volts to get his to work. At most I was using about 30V.

I've had another idea though. Would it be possible to use a low value surface mount resistor to rapidly boil the ink to eject a droplet? I've done some quick calculations to see if it's plausible.

Start with a volume of water/ink to boil of 1mm cubed. That will require 0.36 Joules to boil from 15C (Using [en.wikipedia.org]). Let's choose a heating time of 5ms (I'm assuming the thermal conductivity of water is insignificant for this duration), that'll require 71W. At 12V that's a 2ohm resistor and 6A. Those numbers don't seem too bad, and an 0402 resistor should be a good size to heat 1mm cubed of water/ink.

It should be fairly easy to experiment by submerging the resistor in a bowl of water, switch a MOSFET for 5ms, and see if a bubble of steam is generated.

EDIT: It just occurred to me that the heat isn't going to conduct from the resistor to the water immediately. Also the wires going to the resistor will probably conduct a some heat away.

Edited 1 time(s). Last edit at 05/20/2014 07:10PM by samp20.

I tried the above idea and ended up popping the resistor. Funnily enough, when the resistor did pop I got a tiny bubble of steam on the top surface. I think I need to try a lower power, but longer duration next time. When the resistor blew I was using approx 6W pulses of 1ms, with an interval of 1 second between pulses. The resistor did not blow straight away though. It took 10 or so pulses before it happened.

P.S. It's a bit embarrassing that I initially calculated 70W. I'm not sure what went wrong there.

Edited 1 time(s). Last edit at 05/23/2014 01:51PM by samp20.