Tuesday, March 30, 2010
selective laser sintering printer: part 4 (putting it all together)
a couple rainy days and the dorky need i have to make this thing work mean, another SLS post! :)
(click on the thumbnails for larger pictures)
i designed a new enclosure for the SLS printer that would let the build chamber, z-axis table (inside the chamber), pivotable mirror, laser, powder feed system, and electronics all fit together. i've been designing the system with the hopes that it would be both easily created by others and inexpensive, and so currently the whole system is essentially just a whole bunch of laser cut acrylic parts, a bunch of inexpensive steppers, and a trip to the hardware store for some bolts and ABS pipe. (i have some thoughts to design a laser-cuttable gimble system for the pivotable mirror, but that's a bit in the future).
the pivotable mirror just rests on top of the sides, which are set at 45° and directly above the build chamber.
one of the things i've been really trying to be creative with is the powder feed mechanism. traditionally, a commercial SLS printer will have two chambers with indexing z-axis tables, and a roller. one chamber will start with a thin layer of powder (the build chamber), and the other will start with a large amount of powder (the material supply chamber). after each layer, the build chamber will index down a little, the supply chamber will index up a little, and a roller will roll new material from the supply chamber to the build chamber.
the key elements here are supplying the build chamber with a thin, repeatable layer of powder, and having a lot of supply powder. i wanted to try and avoid having *two* chambers with indexing tables, as well as a roller (it seems like a lot of extra space and mechanism, if you can design something functionally equivalent). the system i came up with is as follows: a thin piece of acrylic rests on the platform above the build chamber, and it can slide back and forth overtop of the build chamber using a rack and pinion system. the sliding sheet is sandwiched in so that it can only ever move back and forth over the build chamber (not side to side, or up or down), such that if a layer of powder were put ontop of the build chamber, it would wipe off any that exceeded the height of the chamber itself. (this whole sliding thing is essentially the roller, but more of a squeegee)
in that sliding piece is also a long, thin slot. ontop of this slot one would put a little hopper full of powder. when the table indexes down, the slide will slowly slide over the chamber, the powder will fall down into the chamber, and ideally the slide will wipe away any that exceeds the height of the chamber. that's the idea, anyway. :)
the electronics are mounted under everything, with easy access. i had a few spare boards left over from a batch sent to goldphoenix that used a dsPIC33FJ256MC710 on them, so I repurposed them (since they have a breakout header for about 30 pins!), and plugged it into the little 4-axis stepper controller board from the previous post.
the sides were designed with lots of slots and holes, so that little extra bits could easily be added or removed or modified later without drilling anything. it's really handy! :)
here is the (almost) whole system, with a red laser pointer being used as a test.
(the stuff in the build chamber is actually the foam top of the table -- there isn't any powder yet. i hope the foam table will act as a bit of a seal, too, and prevent much powder from escaping below).
the powder hopper -- it's not very big, but the total chamber build volume isn't too big, either. i just glued this together tonight, but it's not glued onto the slide just yet.
after over-voltaging a bunch of DVD laser diodes, and taking apart a bunch of laser pointers for their collimating lenses, i've decided that it would just be a lot easier and more precise to find a pre-made laser module (and, so, i've been looking around ebay for one for the last week or so). i'm thinking 250mw minimum (like the DVD laser burner), but there are bunches of inexpensive 808nm 1000mw diodes on ebay. since these are near infrared, there's a much better chance that they'd be able to work on materials other than pure black plastic, and the additional power means a bunch of good things, including that each layer could be sintered quicker. (unfortunately it also means that one's eye could be damaged even that much quicker -- and the infrared lasers border on what is visible to the eye, so it's a bit more dangerous than a visible diode).
any thoughts for a complete (inexpensive) laser module with a collimating (or focusing, or both) lens would be fantastic, and as always i'm happy to hear comments/questions, or thoughts on where to find very fine ABS, nylon, or other thermoplastic powder.
thanks for reading!
[part 1] [part 2] [part 3] [cogsci.mcmaster.ca/~peter]
The manufacturers use a number of different plastics including some thermoplastics (I know acrylic is used, not sure what else might be available). You can get it in some really fine mesh sizes and in multiple colors (possibly black but, if not, you might be able to pair your laser choice to the color of the media). I looked up prices one time for potential use by the Candyfab project (I'm not affiliated with them but followed their work closely when they were active) and I remember it being pretty cheap in 50 pound bag quantities. If you want less, one of the manufacturers might be willing to send you some samples if you ask nicely.
As for sources of lasers, I hear the blue-ray laser modules are supposed to be pretty strong. I'm not sure how they compare to DVD burners though.
sblaszek: hmm! that's an interesting idea. do you know how fine the size of the blasting media is? i really think the material has to be about the consistency of flour, in order to maximize the surface area to volume ratio and really give a low-powered laser the chance to work.
would you happen to know of any sources?
I'll keep looking & let you know if I find more but these are a good start.
@bogdan: thanks, but in [part 1] we examined both laser printer toner and powder coatings for plastic, and found them to be very brittle when sintered with a laser in thin films, as well as brittle when larger amounts were heated over a flame and allowed to cool.
I'd be really interested to learn more, would you be able to post the details on the SLS printer workthread?
I buy it here: http://www.elementalscientific.net/
8 mesh is $2.50 an ounce US. Copper powder is $3/ounce. They have lead, iron and others in powder form too.
There are other ceramic materials which might sinter at a low enough temperature too.
the whole goal of this project is to make something simple, inexpensive, and above all else as safe as possible. CO2 chambers, exploding materials, and 100W lasers definitely don't fit those design requirements :). Black ABS or nylon powder, whereever we eventually find it, and 250-1000mw laser diodes, potentially harvested from DVD burners, are much closer to the goal.
but thanks for the thoughts!
Alternatively, going very low tech here, some glitter is made out of plastic.
Good luck. Watching this project eagerly.
It is very cheap, very very thin, powder-like food additive (a Polysaccharide, so should be easy to melt). There were already a project once that used lasers on sugar to do rapid prototyping, but ordinary sugar isn`t so thin, so results sucked (http://hackaday.com/2009/05/29/rapid-prototyping-with-sugar-and-lasers/), but I think that maltodextrin should work, it melts easily.
Not sure if final result might be rigid enough, but should be worth testing.
I'll code something up to parse (for instance) gcode files and move the laser to the appropriate position, since the electronics and firmware are of my own design.
To actually generate those gcode files, I'll likely use either skienforge or slice and dice -- both of those should get one at least most of the way there for testing purposes.
The solution might be even simpler than using either of those programs, and perhaps even just involve raster tracing a bitmap of a given layer onto the material (in this case, things would be completely solid too, which is nice -- but there might be issues with warping or other such things that we won't really have a good idea of until we try).
school has been keeping me very busy lately, and i'm working to finish up my thesis in the next few months. that being said, a one watt IR laser diode arrived just yesterday, some appropriate saftey glasses for the diode a week earlier, and hopefully the diode enclosure will arrive soon too! :)
My first reaction to seeing the laser bed's diameter was 'that looks about right to build warhammer minis'
I do certainly hope your 1W laser is enough to work on whatever material you end up with!
I was cracking open a tonner cartridge from HP which, for my surprise, looks like was full all this time - being tonner so thin and light, i couldn't tell.
I'll do some experiments on how to manage it, since i'm having some problem with the powder (thinking of wetting and forming the powder into a block, that could be scratched to harvest the powder back). Although being so thin, a preliminar test on how it behaves when melted on a metal plate shows that it has good stability, not shrinking or turning into a blob.
Keep up the great work!
Your work is awesome!! Laser cut acrylic home-made-machines are the best. And 3D printing is the 3rd Industrial Revolution.
Sometime ago I started building a powder 3d printer; not laser, just catalyst printer (instead of ink). But I found some troubles with the printing part, and the project got stuck.
I will adapt your laser idea to my project and finish it.
The material I found to use as powder is an acrylic dentist use to make dental implants. Also used by FX masters to make vampire's fables.
It's called Poly(Methyl Methacrylate) a.k.a PMMA. And it's sold in dentist's tools stores.
It comes in little plastic bottles. It is so thin, that is almost untouchable. And it's very cheap. It comes with a catalyst, but also melts easily. It is very hard once dried. And you can harden it more by spraying the printed object with the catalyst.
Hope this idea helps you.
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