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Centrifugal laser sintering

Posted by timthelion 
Centrifugal laser sintering
January 08, 2015 05:29PM

I'm new to laser sintering. So new, infact, that I'm still stupid and naive enough to be having semi-utopian fantasies about it. I'd like to do some basic experiments with an idea that I've got in my head to put the powder in a centrifuge while sintering. As I said, I don't know anything about laser sintering, and I'm just mulling over the idea to see if it's worth while. I'd love to hear your opinions on it.

Re: Centrifugal laser sintering
January 08, 2015 09:38PM
Ok, interesting idea. Here's how I would rough & ready prototype it for liquid SLA:

* Materials:
** Vertcal centrifuge (1m diameter so we don't have to go so fast) with water-tight sides
*** The sides should be high enough to contain all the SLA fluid for a full build when the centrifuge is stopped (to prevent spills on a power outage)
** Hall sensor + magent on centrifuge or optical encoder as timing/sync pulses for laser control.
** UV Laser on a lead screw on a stepper
*** This could be near the bed or near the rotation axis of the centrifuge
** Peristaltic pump to dispense SLA fluid into centrifuge/remove fluid after build
** Big tub of SLA fluid.
** Arduino

The build process would go as follows:

* Spinup to 9.8m/s^2 centripetal acceleration (dry)
* Per layer:
** Rotate peristalic pump N times to dispense one layers worth of SLA fluid
** Per line of layer:
*** Step laser one spot-width
*** Wait for sync pulse from centrifuge sensor
*** Blit laser pattern for the line
** After all lines are printed, retract laser to home step position.
* After all layers are printed, spin down
* Drain SLA fluid
* Remove parts form the centrifuge

For people with the know-how, a '1-D mirror galvo on a stick' would do nicely too.

The slicer software will need to know how to compensate for the curved SLA fluid layer, but that's a Simple Matter of Mathematics.

If this was run horizonally, it would have the nice property of automatically draining, you'd just need to accommodate the density of the SLA fluid and gravity for the slight slope...

Hmmm... Convert a washing machine to a bulk SLA printer? Hook up water intake to a 55 gallon drum of SLA, rewire it to be on a constant spin cycle, make a 'galvo on a stick' to do the laser sweeps....
Re: Centrifugal laser sintering
January 09, 2015 08:36AM
Interesting experiment:

Put a round pan on a motor so that it is spinning with it's axis perfectly vertical, turn it on and slowly pour in water, the surface of the water, once it calms down will form a perfect parabola. Even if the force at the edge of the pan is 1G, the angle of the water at that point won't be vertical, but 45o from horizontal (makes it easy to find the focal point, by the way).

For a twist on this, fill the pan with salt water instead, then float enough SLA resin on top to completely cover the surface. After waiting for the whole fluid to calm down and seperate out, turn on a UV light and it will cure the SLA into a perfect parabolic dish. Unless you wait a very long time for the layers to separate (and cure it long enough to cure all of the resin), the bottom surface might be too imperfect to make a lens, I haven't tried it with clear resin.

EDIT, almost forgot, line the sides of the pan with wax, so that you can actually remove the bowl once you've made it.

Edited 1 time(s). Last edit at 01/09/2015 08:38AM by Feign.
Re: Centrifugal laser sintering
January 09, 2015 02:14PM
I'm not really interetsed in SLA. Expensive resin with poor mechanical properties. Sure, it's got high precision and requires a cheeper laser, but it's not really practical for building "things" that you'll actually use. Furthermore, I don't really see the point in centrifugal SLA. The whole purpose of my idea is to eventually use multiple materials, and pick and place into models during build time. You don't get anything like that with SLA.
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