Tuesday, March 30, 2010

 

selective laser sintering printer: part 4 (putting it all together)

hi folks,

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!
peter

[part 1] [part 2] [part 3] [cogsci.mcmaster.ca/~peter]

Comments:
Looks like you have made a lot of progress! Can't wait to start seeing some parts from this thing in the future. I for one would be interested in seeing some strength numbers from the parts as well if you have any way to test that. Plastic parts can only work for so many application with their limited material strength. Also, I love the plexiglass look of the machine. Keep up the good work!
 
@Peter: Not sure if you saw my comment on your last SLS posting (I was a little late to the party), but I might have a source for powdered thermoplastic you can use. Have you ever explored plastic blasting media (as in "sand blasting")? It's used for cleaning surfaces that are a little more fragile than those sand is used on.

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.
 
Oh, also, impressive progress on the project. Keep up the awesome work.
 
cpwebste: thanks! the strength will depend on the material. i don't think anything made with the powder coatings will be very strong (infact, if our initial tests were correct, the parts will infact be quite brittle), but it'd be an interesting demonstration until some better material is found.

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?
 
Amazing work/progress!!

Thanks for sharing ;-)
 
here's a bunch of polymer powders, take a look
http://www.tradekey.com/ks-polymer-powder/
and here:
http://www.industrial-chemical-manufacturer.com/redispersible-polymer-powder.htm

I'll keep looking & let you know if I find more but these are a good start.
 
What about laser printer toner for the powder?
 
@guy: thanks! i found similar sites using google, too. unfortunately the companies listed on those sites tend to only be interested in extremely large quantities, on the order of metric tonnes (in my experience). also, most of those powderes appeared white, which i think would require a much more powerful laser to sinter.

@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 mixed up a 3 part powder for a lab experiment a vinyl copolymer of sorts, it a toner resin that when exposed to light in the range of 800nm to 906nm would harden very quick, using styrene monomer, a methacrylic as well as a toner designed for high def color printing, the powder is 2nm to 2.4nm in size. theres 3 other compnants that are easy to obtain. The problem is economics, most of the supply come in large quantity, ie.. the methacrylic comes in 4.55 kilo packages, its cheap about 3 bux, the problem I found was proper storage, after more then around 18 days the mix would start to catalyze on its own making a block that was near impossible to do anything with. Particle separation was another longterm issue as static would cause a few of the components to clump. Still, it works its cheap and its under 3nm in size pp. what was kool is you can take an off the shelf color toner and mix a portion into it to give it the color you wanted. I got the laser pump and lenses from Jameco just fyi, if you want the final mix let me know and I can e-mail you the compound list and a cpl suppliers I have dealt with.
 
Guy posted the link to one of the suppliers, you can get most of the other stuff from a chemical supply company. http://www.industrial-chemical-manufacturer.com/redispersible-polymer-powder.htm
 
Hi Austin,

I'd be really interested to learn more, would you be able to post the details on the SLS printer workthread?

http://forums.reprap.org/read.php?153,41456,41456#msg-41456

thanks!
peter
 
Here's a (nearly) random thought. Dentists use materials that cure under UV light. I don't know that UV lasers are available, but the idea is to use materials that are "cured" rather than melted. Curing agents could be heat, light, liquids, etc.
 
have you measured or done the math on the temperature you'll have at the focal point? If it is high enough you might try powdered aluminum instead of plastic which I have bought before from several sources and is quiet inexpensive and a dark gray color which should pickup IR well. Might want a CO2 atmosphere for that though.

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.
 
now that I think of it Woods metal 50% bismuth, 25% lead, 12.5% tin, and 12.5% cadmium. could be modified slightly to melt at a higher level, increase the tin and lead, this would produce a rather hard substance, not strong enough to be a mechanical part but enough for tooling around with designs and it would be very inexpensive to make. just toxic as all h$*
 
metals /really/ are very unlikely to work -- you would need extremely powerful lasers at wavelengths (that i don't think are commonly available), and in cases there's a real danger of the metals combusting (like with aluminum).

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!
 
A search on ebay for "PVC Powder" looks very promising. Because the particles are so fine it should melt easily and allow fine details. It also seems to be very affordable and available in small quantities.

Alternatively, going very low tech here, some glitter is made out of plastic.

Good luck. Watching this project eagerly.
 
Now that you point it out, powdered plastic also has the potential to be dangerously combustible. You're definitely going to want to keep electronics away from the main build area and all air currents to a minimum.
 
Have you tested maltodextrin (the same material that guy used from the link in your first post)?
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.
 
Maybe nylon

https://www.blogger.com/comment.g?blogID=31599891&postID=5163422127490483452&page=0&token
 
Sorry if I missed it, but what sort of program are you looking to use to actually maneuver the laser to trace out each layer of the object to be sintered?
 
Hi Aaron,

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! :)
 
For the sake of being geeky...
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!
 
Hey, I've read this project here for a time now and been looking for meltable powders, and like, five minutes ago, i ran into what i think is the best suited thing i found up to now: tonner.

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!
 
Greetings from Argentina.
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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