SLS Printer

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Photo 1

Sls laser powder 1.jpg


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Selective Laser Sintering (SLS) Printer

Release status: unknown

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Description documenting the development of a simple selective laser sintering 3D printer
License GPL
Author Peter
Contributors
Based-on Sui Generis
Categories SLS, Laser, Powder, Files Missing
CAD Models none
External Link none

Contents


This page describes attempts to build a Selective Laser Sintering (SLS) based 3D printer, using as many inexpensive and off-the-shelf components as possible.


FILE ID# TYPE DESCRIPTION AVAILABLE FORMATS CREATED/RESERVED BY
Your-File-Name SOLID MODEL ASSEMBLY These are CAD files for the Solid Model Assembly .xml.zip, .stl.zip --Example User 12:00, Today's Date 20xx (UTC)
Your-File-Name CAD FILES FOR PARTS These are CAD files for each part. .xml.zip, .stl.zip --Example User 12:00, Today's Date 20xx (UTC)
Your-File-Name EVEN MORE FILES These are are even more files. .xml.zip, .stl.zip --Example User 12:00, Today's Date 20xx (UTC)|-
Your-File-Name SOLID MODEL ASSEMBLY This is the final finished machine N/A --Example User 12:00, Tomorrow's Date, 20xx (UTC)
Please edit this and click the links to put in your own files! --Sebastien Bailard 08:34, 10 September 2010 (UTC) 


Background

Methodology
Benefits compared to extrusion
Issues compared to extrusion

Laser Source

Inexpensive
Laser power affects ultimate choices of materials
Focusable, or very small collimated beam

Pivotable Mirror

Gimble
Two rotating mirrors out of phase

Build Chamber

Heated
Indexing table
Seal

Powder Feeder and Roller

Heated
Chamber/indexing table based
Feeder/"print head" hopper based
Roller purpose (compaction, even layer)
Importance of very small layer thicknesses

Build Materials

ABS Thermoplastic Powder
PA12 Powder

Source http://www.alibaba.com/product-free/125562893/polyamide_12_powder.html

"powder coating" powder
laser printer toner
alternative materials (glass, etc.)

Working Notes

Everything below this point is working notes.

first tests building a powder-based stereolithography printer: part 1

hi folks,

i'm a bit sleepy, but i thought i'd post this while it's fresh:

after seeing really interesting powder-based printer designs like this one, that place down a layer of powder then "print" a binding material onto it, i began to wonder (as others have) if we could build a similar setup using ABS powder and a laser diode to fuse the material together. designs like this have a bunch of benefits, including the potential to use the powder as it's own support material. (and, after a few weeks of tinkering with building an extruder for a second printer that *constantly* clogs, i think i needed a break to think about better days when we won't need to rebuild extruders, or hope we build working ones in the first place... ). my goals for this tinkering are to build things with common off-the-shelf materials wherever possible, and so I went searching for some form of ABS powder, as well as a laser diode.

After some searching, it looks like ABS powder really isn't easy to come by, and it's most often found in pellet form. Zach had a similar idea a while back ( link ), and so I asked him if he'd had any luck. He said he never got past the materials research stage, but that polyester-based powders used as powder coatings sounded promising since ABS powder was so hard to come by.

I figured that if I was going to use a DVD burner laser, I'd need some black powder to absorb the radiation (since a 250mw red laser is relatively low power to melt plastic that isn't black). I sent an email to our local hackerspace in hamilton, thinkhaus, and folks were really encouraged by the idea. One of the folks there, jason, ended up finding a local place that manufactures powder coatings. I called up a fellow there and told him about the idea, and he was extremely kind and prepared up some samples of black powder coatings, one a polyester, and the other a polyester-epoxy hybrid. jason and i did some tinkering with both these as well as some laser printer toner (since it's carbon mixed with a polymer). jason tried both with the hackerspace's laser cutter, as well as just heating a bunch of the stuff up in a popcan. in both cases each powder (polyester-based, polyester-epoxy hybrid, as well as laser toner) fused, but the product was VERY brittle. the pop-can tests that melted material to be a few millimeters thick showed that the problem seems to be with the material itself -- unfornately, even relatively thick pieces would snap pretty easily. (though powder coatings do contain quite a few different materials in them for curing, flow, and pigment, so it's quite possible that some particular combination might work).

so, not much luck on that front. i would really like to get my hands on a good couple of cups of black ABS powder, or make some. (random thought: i think the size of the powder will be fairly critical -- ideally one would want to maximize the ratio of surface area to volume of each little ABS grain, such that the laser diode could more easily heat up relatively little volume).

---

so, i decided to work some on a little test rig to try out different powder materials (and, conceivably, with some better seals, you might even be able to use it for liquid stereolithography). i figure that you don't need a great deal of print volume to test if the material is viable or not, so i decided to make a "mini stereolithography" system -- infact, it's almost pocket sized, save some of the larger mounting bits.

here's my progress so far (in picture form): (click on the thumbnails for much larger versions)


first i went out and picked up this DVD burner. it's a 24x (the fastest i could find), so the diode in it should be around the 200-250mw range if memory serves. (clearly here i should add in the usual warnings -- LASERS CAN BLIND YOU AND THE FOLKS AROUND YOU INSTANTLY, unless you know exactly what you're doing and take appropriate saftey precautions, you shouldn't attempt this!).



off came the cover



and here's the diode -- it's even labeled (the pins are DVD, GND, and CD). The CD one is likely infrared, and even with lightscribe likely only within the ~40mw range -- so not too useful. But still plenty powerful enough to blind me instantly, and invisible so I'd never know. So I left that pin alone! :)



i soldered some leads on the diode, and tested it out to make sure the pins were correct, and to get an idea of the voltage.



even though the diode was still in the focusing housing, i thought i'd give it a try to see what sort of heat it could produce on some black plastic. the focus of these lenses is on the order of about 1mm from their surface, so the material has to be up pretty close.



having the diode on for a couple seconds heated it up pretty well, and i tried moving the head back and forth a bit and it produced a really faint line. so, it works, but i decided to take the diode out and not deal with all the optics in the DVD burner that weren't really required for this.



there are lots of interesting beamsplitters and lenses and such in modern CD/DVD combination readers/writers, and i often save these bits for tinkering. the diode was epoxied in, so it took a little bit to get it out.



i put some wire wrap leads on the diode



and tested it out. for some reason i remember reading the current should be around 200-250ma, but i'm not sure where. this turned out to be about 2.5V for this diode.



a quick test with the diode right against the surface --



this worked *much* better than when the diode was within the DVD burner optics, and even quickly turning the power on and off yielded distinct melting.



being a laser, the beam should be coherent and come out in a straight line with some width -- so i decided to see if i could get the same results from a bit of a distance -- a few centimeters above the plastic. unfortunately the laser beam divered quite a bit, and this didn't yield any melting, even for quite a few seconds of exposure.



(as can be seen here -- no melting under the raised laser diode configuration)


---



i had wandered around home depot for half an hour or so for ideas to make the indexing build chamber for the powder. i figured that a simple idea would be to just make it round, and find two pieces of pipe that fit snugly within each other -- the outer one would be the chamber, and the inner one would have a little piece put over the top to act as a "table", and index down within the larger outer pipe by a small lead screw or some other mechanism. here are the various pieces of pipe that i found. i think the outer pipe (the black one) is around 1.25 inches in diameter.



here are the critical bits. there's the black outer pipe for the "chamber" (left), a smaller white pipe that fits right into it that's threaded on the inside to be the "indexing table" (right), and a third pipe that screws into the "indexing table", that acts as the lead screw (center). you could attach a stepper to this, or just index it down manually.



here's the "indexing table" piece (top) fitting right into the "lead screw" (bottom).



and here's the whole idea, where the "table" and "lead screw" fit with the "chamber".



they fit together something like this, where the "table" ends up mostly inside the "chamber", starting mostly near the top but being able to be pulled down quite a bit. the "lead screw" piece is always outside of the chamber, and doesn't move up or down. (the "table" would index up or down, while the "chamber" and "lead screw" parts would be vertically stationary).



i foraged around looking for something to build the actual "table" out of, and was thinking plastic or even cardboard, so that you'd get a bit of a very rudimentary seal around the edges (although it's probably not critical if a little bit of the material leaks out). one of the folks at the hackerspace offered me some dense foam, and it seems like an even better idea than the cardboard -- it's pretty stiff but also a bit flexible, and expands to form a seal while still making it easy to move the table up and down! i cut out a circular piece to fit the "chamber", about 5 to 10mm thick.



checking the fit, it was nice and snug, but easy to slide the table up and down. i epoxied it to the "indexing table", making sure not to get any onto the "chamber".






it was around this time i had a crazy idea, and noticed that the "chamber" happened to be around the same size as the hole for the spindle cap in the DVD drive! i was thinking about how to mount the table, and decided to give it a try, so i cut out the spindle cap cover.



and removed it, revealing a nice perfectly sized hole!



AND it looks like everything fits! the chamber fits right ontop of the hole without falling in, while the table slides right through it with a bit of space to spare.



look at that!



the indexing table needs some guide rails to make sure it only goes up and down, rather than spinning in place, when the lead screw is rotated. i found the rails used in the DVD burner, and made up some slides and holders out of acrylic.



from top to bottom, here's the foam table proper, epoxied to the "indexing table" piece. the indexing table has a plastic guide (two holes, drilled in a piece of scrap acrylic) superglued to it. the "lead screw" screws into the indexing table, and beside the lead screw at the base is a keeper for the rails, also made out of some scrap acrylic. everything is resting on a piece of scrap acrylic that's being used as a base.



and here it is with the chamber on top, too.



the bottom of the "lead screw" should be resting flat against the base, and after measuring everything when the table was indexed all the way up, i determined that the setup would need a bit more height than just the DVD drive cover would have, so I brought it up a bit with some L-brackets. (it actually needs to come up a bit more, but I didn't have any larger brackets, so I made up some little acrylic spacers for screws, too).



and, here it is all together. too cool! :) i drilled some holes in the metal DVD case beside the spindle holder aperture to act as upper keepers for the guide rails.


---


so, that's my progress so far, and now i'll have to forage for some tiny steppers to both index the table, as well as move the laser on the x and y axis. the travel is extremely small -- the build area will be about an inch in diameter, with a height of about 1cm. that's pretty tiny, but should be more than enough to test different powder materials to see if they can successfully build very small parts with sufficient structural integrity. the neat thing is that the whole thing can come apart pretty easily, so it can be washed out to prepare for a new material. hopefully once the steppers and axis are on there, it'll still be just as easy.

hope you've enjoyed my little story! (and i hope my supervisors don't read it -- i'm supposed to be working on my dissertation). ~peter


Notes

Intial announcement: http://builders.reprap.org/2010/02/first-tests-building-powder-based.html

Related

Useful Links

Discussion of Advantages and Disadvantages of different Tool head processes. has some discussion of SLS vs EBM.

Naive questions: Why not use selective laser melting (SLM)?

NASA uses selective laser melting to make rocket engine oxygen/hydrogen fuel injectors ( "NASA: 3D printed rocket engine component generated a record thrust" ).