Monday, May 31, 2010
selective laser sintering part 5: the laser
Just a quick post, since it's been a little bit since I made one. My thesis has been keeping me busy these days, which is good since there's been a lot of waiting for things to come in the mail. I ended up settling on a 1000mw 808nm laser diode for the first tests, and ordered some wide-spectrum glasses (600-1100nm, OD4) just incase I need to try a few different diodes.
I built a current-limited variable voltage supply using a reference design in the LM317 datasheet this past weekend, and added some large capacitors to try and filter out any large bumps. The laser diode didn't come with a datasheet, but the ebay seller listed it as running at approximately 2.2V at 1.2 amps. The supply is limited to 1.2 amps, but so far very slowly adjusting the voltage up (with a 10-turn pot), I'm only at ~1 amp at 2.5 volts, and that is about as far as I dare turn it up just yet.
There hasn't been much tinker time with the laser yet, but I did take it to some failed prints made with black ABS. The laser has no trouble melting the black ABS plastic from makerbot, or even cutting it and boring holes in it, depending on the distance. Using a print that's only a single layer thick, the laser seemed to be able to cut through fairly quickly, but also if the focus was such that a small area about 0.5 - 1mm wide was illuminated (instead of a point), it melted the layer rather quickly -- I think this is going to work just fine.
Now, to find some ABS plastic in powder form. The laser didn't heat or cut white polystyrene, so I think colour is still definitely going to be an issue here -- particularly in finding a black thermoplastic powder. I'll have to try some tests with the powder coatings that I have from earlier as well, although our tests with a 20W CO2 laser weren't encouraging, and the end result was partially fused but very, very brittle. This kind of makes sense, since powder coatings are meant to be very thin coatings, and are also meant to cure over 6-12 minutes at relatively high temperatures. I'm eager to try Vik's suggestion of a dark coloured sugar, just out of curiosity, to see what that might be like.
I have also decided to replace the SLS powder test rig that I described in previous posts with a much more full sized model, and I've been working on building this in my spare time over the past few weeks. More on this soon, hopefully. :)
thanks for reading,
This looks pretty cool so far.
Have you thought about using toner for printers for the powder?
I'm not sure exactly what it is mode of, but IIRC its mainly plastic, and is melted to the paper. So, might be worth a look into.
Thanks for the comment. A lot of folks have suggested this before :) , and we tried it with the powder coatings. Unfortunately it seems to be as brittle as the powder coatings. I think the mixture is about half polymer, half carbon black (for toner), and depending on the powder coating its about half polymer and half other things like pigments and curing agents (if I remember correctly).
My thoughts are that if we go the toner/powder coating way we might either (1) need a special mixture (that's almost entirely the polymer), (2) need to try different heat settings -- maybe if you just go a little slower and for longer you can get something less brittle, or (3) potentially 'cure' the part for 5-10 minutes in a toaster oven afterwards. (But if there's nothing for the part to cling to but itself, it might just melt).
There are lots of experiments to do and potential avenues of research on the materials side. I'd also just really like to come up with an easy to create rig that will grind up old prints and make me ABS thermoplastic powder the consistency of flour, it seems to melt so beautifully with the laser...
Alternatively, it might be time to research plastic manufactuerers and send out another batch of e-mails asking about thermoplastic in powder form.
... i'm testing with SLS and 5Watt-diodes and found a supplyer of different powdered plastics which hints me to mix white powder with dark pigments - i have carbon black, ceramic red and blue, some dark green and some thermoplastic pigments too.
Another area is melting coloured glass-powder or black stone-microspheres, what's working with 2-4Watts really good, but not with 1 Watt ...
That's really encouraging, would you like to collaborate? I had thought of mixing some fine carbon black with a lighter-coloured thermoplastic powder to see if warming the black powder might conduct sufficient heat to melt the surrounding plastic -- but I wasn't able to easily come across any thermoplastic powder to test this with. I would really love to hear where you've found a supplier.
I'm also currently working on putting together a test rig for everything, mostly in the form of an in expensive, mostly laser-cuttable rig that takes the form of a small SLS machine with separate build and feed tables/chambers. I have an engineering model made out of laser cut hardboard that I put together the other day so I can iron out the bugs.
you can e-mail me at jansenpa at mcmaster dot ca , if you would like.
the plastic supplyer (Color-Plastic) is in my town and distributes plastic-granules for other manufacturers, so dont have a normal shop ... but i have a good contact with the application laboratory ;)
My first test were with icing shugar and carbon black - when heating to much, the carbon black evaporates and you'll receive transparent shugar-trays with some grey inclusions, so better try with lower powers.
I'll ping you ...
Great SLS rig you have. Working on the same thing as you. by the way have u thought of using a laser collimator with your laser
Finally, have you tried a kitchen blender for powdering ABS? Will it blend? ;-)
Could you please tell me what was the Ebay seller and product? How much did it cost?
Would this laser work?
Do you think your laser could burn black paint for "PCB laser etching"?
I used a very similar laser to the one you found, although I think the one I found was a tiny bit cheaper -- around US$20 -- from someone in the US. It's a 1000mw 808nm 9mm dia (I think) diode, and I also purchased a $10 case/heatsink/glass focusing lens combination from an ebay seller somewhere in China.
Intuitively, if it can cut through ~0.3-0.5mm ABS thermoplastic, it might be able to vaporize a thin layer of paint with the proper setup. Give it a try, and let us know! :)
This would give you particle control on the high end grinders
This would give you particle control on the high end grinders
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