Reprap printing in multicolor...

Hi,

I know how much you guys love it when someone posts ideas on here without having experimented themselves, but I figured I'd throw this one out there as I haven't gotten around to starting a reprap myself (due to a mixture of budget, workload, and lazyness during what down time I do have). So, I'm posting this here in case it tickles anyone else's fancy while I'm getting around to starting.

I was trying to come up with a way to design a RepRap with multicolor printing capabilities. I figured that it would be a pain in the rear to add multiple extuders/nozzles for multiple colors of plastic and wouldn't provide an easy way to create complex colors without a unique nozzle/extruder per shade. I also figured that, even if it were possible, it would be a pain to design a nozzle that allowed you to mix multiple colors of molten plastics, at extrusion time, in highly accurate quantities.

Then, I thought about how some people modify standard inkjet printers to print, directly, onto non-standard surfaces (such as copper cladding so that they can etch PCBs more accurately). What I figured was that you could follow most of the steps of those projects but then added the printer to the RepRap as a second X/Y axis (or, I guess it would be more common to refer to it as U/V) connected to the main Z axis. After the normal RepRap printing process for each layer, the inkjet printer would go over the printed layer of plastic as if it were a normal piece of paper. Of course, the printer and the standard RepRap X/Y would have to be lined up correctly but you should be able to get away with just using the default printer drivers.

Now, at first glance it seems that only the top of the layer would get inked but that should be all that bad. As far as I can see from all the pictures, each layer of plastic seems to have a natural round that means half of it will be accessible to the print head. One problem that might come up is the ink running on the un-coated plastic but the head of the deposition process might help to dry the ink quickly, seal some of it in between the layers, and whatever does end up running might actually be beneficial if it runs under the "lip" of each layer onto the part of the plastic that isn't visible to the print head. Once the print was done, I'd imagine you'd probably want to spray the entire model with a couple of coats of clear coat in order to protect the ink from coming off.

Well, that's it. Please feel free to chime in if you think will, or wont, work.

-Shawn

I don't mind ideas! It's just the implied expectation that somehow someone else is going to magically find time to do all the difficult research and development for you.
Edison claimed "Genius is 1% inspiration, and 99% perspiration.". It's developing a concept into a working prototype that's the difficult bit.
:-)

I think what you're suggesting is adding another x-y axis to a reprap with a print head.

I *think* you'd be better off fixing a print head to the existing reprap extruder carriage. It could print one layer, come back and colour it, then print the next..

It occurs to me that a spray-nozzle might be more effective than a simple inkjet?

I'm not sure what kinds of paint stick to plastics like ABS - I vaguely remember seeing a printed model, but I've got no idea where.

Following on, I wonder if a dry powder applied to the hot melted plastic would stick enough to colour it? It might be messy, but might allow some colouring. Mixing might be an issue.

Interesting idea!

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Reprapping blog and other rants: [renoirsrants.blogspot.com]
My Reprap: [sites.google.com]

I know that this is not exactly what you are talking about, but you can color the ABS plastic quite nicely by coloring the 3mm filament with a permanent marker before it goes into the extruder. It takes a while for the color to start up, and longer for it to fade away. I suppose that this is the colored ABS in the extruder chamber being slowly diluted with new, uncolored plastic.

My 11 year old daughter suggested this technique, and it proved quite effective.

I have attached a picture. I started coloring the filament part way through the process of printing the bottom of the box.

Frank Davies

Well, the problem with using just the print head is that, as far as I know, inkjet technology is very proprietary. I know of no way to control the print-head separate from the whole printer. Apparently, Parallax used to sell a kit in collaboration with HP that did just this, but they seem to have discontinued it. What I was suggesting was removing the casing on an existing printer and modifying it so that, instead of moving a sheet of paper under the print head, the printer moves itself over the stationary 3d printed object. As far as the printer/software is concerned, it shouldn't be any different from normal operation. Of course, there may be a need to beef up the drive motor a little but that should be do-able. Like I said, come people online have done similar work so that they could use their existing inkjet printers to print PCB etching masks directly onto their boards.

As for the ink, I figured that, if allowed to dry, inkjet ink would probably dry onto ABS (at least well enough to last until you can seal it with a spray on clear coat or eurathane). After that, you'd just want to follow up with a few more coats, depending on how durable you need the object to be, and maybe sand with ultra-fine grade sand paper to create a smooth finish. Also, the more clear/translucent the plastic is the better this may work.

-Shawn

@fdavies: Very nice! I like how the color is so consistent. It seems to me that this, actually, lends some credence to the inkjet idea too. If the molton plastic absorbs the pigment in the ink, then what you would want to do is print the coloring for the layer, immediately, above. That way, when you put down the next layers plastic, it would soak up the ink. By the time you run the printer over the printed layer again, the plastic should have been allowed to cool to a point where it won't absorb it.

-Shawn

The most important thing now is to have a multi head system that can change heads on the fly.
Well 3 heads really, plastic/support/plot-pen.

I've got ideas on how to do this, but I don't have a 3D printer yet to try those ideas out.

For colouring, I had ideas of 4 interchangeable heads, sort of how a plotter may work, 1 for each colour as you have in your printer now, Black, Blue, Yellow, Red.
Downside is that it is possible for the feed stocks to get tangled

Another idea was having a single head with 4 colours of feed stock that are forced into a single nozzle.
This idea is very difficult to do.

I had also seen the other 3D print technology of using powder and depositing coloured binder to get the colours, but again, how to do this for plastics on the fly? All ideas i've come to rely heavily on proprietary print heads from printers.
I'm sure this method can be done, and it would be the easiest to implement!

Edited 1 time(s). Last edit at 06/26/2009 05:35PM by Grogyan.

Adding a pigment or paint layer separately would probably reduce strength of the finished object.

However, as has been pointed out above, a marker pen works to an extent.

So, it might be possible to introduce pigments to the main injection flow from separately controlled reservoirs, or from smaller pigment filiaments.

Monofiliment sewing thread migh be a good candidate for the latter, else you could use powder pigments, with controlled release apertures. Machine vibration should help with steady release.

(rubbing my hands in glee, that I have 5 x servo motor control channels already designed on my machine... still got to get the gcode working though !)

Graham.

My idea was to only print pigment to a thin depth on the, overall, printed object. The internal parts of the object would be normal plastic-on-plastic layers. That should ensure that the printed object doesn't lose much, if any, strength.

-Shawn

Attached is what I was thinking about for at least two color capability.
This is an extension of a single head design I am currently working on.
With an appropriate clutching mechanism, when the stepper is turned
one direction one filament is extruded and the other direction causes the
other filament to be extruded.

The extruder assemblies could be made pretty flat, so you could stack several together
all be driven by one motor and extend to more than two colors.

This is not something I am actually building yet. I just did a quick and dirty extension
of the single head design I am currently working on.

Not a bad idea, though I wouldn't consider it multiple color but possibly a good way to lay down a support materal when we find it.

Need some kind of way to reverse it, maybe manual cranks for when you have to change the material?

fdavies Wrote:
-------------------------------------------------------
> I know that this is not exactly what you are
> talking about, but you can color the ABS plastic
> quite nicely by coloring the 3mm filament with a
> permanent marker before it goes into the extruder.
> It takes a while for the color to start up, and
> longer for it to fade away. I suppose that this
> is the colored ABS in the extruder chamber being
> slowly diluted with new, uncolored plastic.
>
> My 11 year old daughter suggested this technique,
> and it proved quite effective.

LOL, that was my approach too. I thought I was being really smart. I was being smart alright, but 'only' about as smart as a 11 year old girl.

> I have attached a picture. I started coloring the
> filament part way through the process of printing
> the bottom of the box.

I've been doing this too. But I didn't use as much colorant as you did: [picasaweb.google.com]
That box looks very good. I don't need to buy light colored plastics.

I was planning on adding CMYK-based color pigments with an injection needle near then orifice (at the inside). But I want to have a second extruder first (don't want to ruin a production version).

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Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]

I have an idea that may offer a solution, however I cannot test it. If you had pigment in FEEDS into the final stage of the plastic deposition head while the plastic was still hot & liquid (maybe heated liquid pigment to prevent premature cooling & clogging of the deposition head?) in about 6 nozzles you could theoretically custom mix somewhat accurately the color of the plastic at the time of deposition, however, you would need to come up with software to control this. Let me know if you try it! I'm very interested to see if it works.

A roatatable disk with a hole in it, oher than the hole for the assembly, so as you turn the disk the hole moves to the next colour.
Only downside is the wastage of plastic to get a string colour of your choice

You could mount airbrushes around the extruder nozzle to spray coloring on the extruded plastic while it's still hot; the right kind of paint or pigment might bond quite nicely to the molten surface. And you could fire the paint sprayers at will for color blends and quick color changes.

[rapmanv3.blogspot.com]

There are pigments that are made of finely-ground ABS plastic, used in most of the vivid modern tattoo inks.

These should dissolve in acetone nicely and would chemically bond with ABS models.

Hi Sam! Sounds like the perfect stuff to work with, except that it might be expensive. For tattoo's you'd need only a little. Now to find a supplier. I could go to the tattoo shop around the corner

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Regards,

Erik de Bruijn
[Ultimaker.com] - [blog.erikdebruijn.nl]