Lasers!

Everyone loves lasers it seems. How realistic is the idea of ripping a laser unit out of an old DVD-burner, and using it to heat, melt or etch? Is such a unit capable of enough power to melt the ABS/PE/PLA types of materials we're talking about here?

If it can melt, we might have the possibility of a variant RepRap with a build tank, acting on layers or powder, SLS style. That method has its advantages to a lot of things we want to build. It does not require support structures, and improves resolution (to the grain size of the power). admittedly, it does require tanks, and sounds messy.


Ian.


[en.wikipedia.org]

Edited 1 time(s). Last edit at 03/15/2009 04:54AM by ian918m.

lol! We were discussing just that idea a few days ago in the Reprap core team. It's certainly an interesting idea and can be made to give excellent resolution. It also conveniently solves the support material problem.

One problem, though, is how to get the positioning system to move fast enough to take advantage of the higher resolution and get get stuff printed in reasonable amunts of time without resorting to an optical positioning system which is kind of expensive.

The other problem is getting polymer resins in fine powder form. Most resins come in 3 mm pellets. Powdered product is out there but buying it in something smaller than 20 kg bags could prove a little tricky.

Edited 1 time(s). Last edit at 03/15/2009 07:45AM by Forrest Higgs.

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

This is a similar concept to what was attempted with the candyfab project ( candyfab.org ). Unfortunately, it seems to have stalled. Basically, they used a bin full of sugar and focused hot air instead of lasers. There were a number of suggestions to replace the sugar with plastic and using lasers or high intesity focused light. The advantage of focused light being that it isn't coherent and is only dangerously concentrated at a single point.

One possible source for powdered plastic is in the form of blasting media (as in "sand" blasting). A number of companies make blasting media from thermoplastics such as PVC and can provide it in very fine grit form. You would have to buy in bags of at least 50lbs, but I don't remember it being too expensive. You might even be able to find it in dark colors that might improve the absorption of the light energy.

We have a laser cutter at work and are told not to cut PVC, are there in other media that you know of?

The problem with PVC, is it released chlorine when it melts or burns. This is bad for most laser systems because it erodes the optics, not to mention what would happen if didn't ventilate your setup well enough.

One possible media is powdercoat plastics. These are very fine powders, generally polyesters with a melting point around 180 C. They are available in a variety of colors. The main drawback is cost which runs around $5 US for a 1 cup (236 cc) (about 1.5 oz). The powder is fine enough to spray like a liquid. The material that results is tough, slightly flexible and chemically inert. Just a thought.

Brian D

5 dollars for 236 cc (14.4 cubic inches) is actually pretty cheap. We pay ~$5 a cubic inch for our stratus (FDM) and We recently speced an Objet model whose model material is about 4.20, I think the Zcorp is a little cheaper 2.50 a cc but then you need resin... Were can you buy this stuff?

Now the objet printer is interesting it uses an inkjet process to deposit a photopolymer and then UV cures it. I wonder if you could do the same on an inkjet using a photopolymer "ink refill?"

It turns out I mixed up my plastics when I posted. I meant to say Acrylic rather than PVC. Acrylic seems to be a more popular media on the market. One possible source can be found here:

[www.greenhillsupply.com]

They seem to want $2.25 per pound for a 50 pound bag of 60 mesh and finer acrylic media. Not sure how fine these guys can go, but I've seen it listed at much finer grades. Using Wikipedia, I tracked down the density of acryilic as 1.19g per cubic centimeter. Assuming my math is right, that comes to $2.25 per ~381 cc or ~$0.10 per cubic inch. This seems to be a little less than 1/3 of the cost of the, above mentioned, plastic powder coat material.

Here's a manufacturer that goes as low as 60/80 grit (0.18-0.25 mm):

[www.blastingaccessories.com]

...and here is a retailer that claims to be able to go as fine as 100/270 mesh (0.152mm - 0.053mm):

[www.corrosionspec.com]

>This is a similar concept to what was attempted with the candyfab project ( candyfab.org ). Unfortunately, it seems to have stalled.

Minor change of subject, but CandyFab is relaunching soon.

> Minor change of subject, but CandyFab is relaunching soon. smiling smiley

Aswome, good to hear. You were making some great progress for a while and then it kinda died before you had managed to release any of the plans. Looking forward to see what you come out with.

Typically, they use nylon powder in SLS systems. At my university, I believe they make the nylon powder for the SLS machine by ball milling larger nylon shavings. I don't think a DVD laser would have enough power to fuse plastic powder, at least not very fast, as a CO2 laser is typically used.

Could the laser be replaced with a lens focusing sunlight? Not usable at night or on overcast days, but probably powerful enough (vaporizes ants quite effectively). The software would have to have astronomical tracking ability, and the compass orientation of the device would have to be precisely set whenever it was moved.

... only effective in equatorial regions without any cloud in the sky - best working in deserts ;-)

You need a really sophisticated piece of software which handles online energy-measurement respective melting/sintering line-speed (energy dissipation over daytime and occasionally dimming through clouds)

If you want to use a focusing lens instead of a laser, just use a large Wattage light.

... you wouldn't receive focus-diameters smaller 5mm with enough energy - typical lamp-heads for soldering with light are very expensive (typically >2000 USD) and only for spotsizes down to 3mm (sometimes even 2mm).

Typical sintering/soldering CO2-lasers with 5 to 20 Watts power will have focus diameters of 0.5 to 0.2mm and the price in OEM is maybe the same, so they're much more effective ...

On an interesting note, I'm pretty sure that this kind of thing (focusing of high-wattage/high-heat bulb) is how the "Desktop Factory" works, based on what they've said about their "imaging subsystem" being one of their major issues.

Has anyone though about using a TIG welder to fuse powdered aluminium?
There would probably need to be some work done to get fine resolution, but TIG equipment should be much cheaper and safer than lasers.

And by using TIG kit... I esentially mean fitting a TIG tip in the same way as an extruder, and pumping enough current into a bed of powdered AL to get it to melt/sinter. Hopefully the AL itself, whether melted or still in the powder form would conduct enough for this to work.
It would still probably need protective gases and stuff like that.. and I doubt the resolution would be too great to begin with...

But is it an interesting thought? or just a silly idea?

... unfortunatelly the TIG-plasmabeam will blow away the powder, so you can't build homogene trays or surfaces

Another common method is blowing metallic powder through a plasmabeam so molten droplets will land and fuze to the surface ...

Viktor

Ha, figured there was a reason nobody was already devloping such a system..

Would it work any better if you dropped the conducting tip down to touch the AL, so instead of an arc forming it instead acts like a resistance welder?

i think it's possible to melt the tip of a metal wire with a high current and 'dip' the tip, so a droplet will add to the fabbed object - but the handling and uniformity of the placed volumes isn't so trivial.

So try first with simpler/common methods and when this works, evolve further

Viktor

VDX Wrote:
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> ... unfortunatelly the TIG-plasmabeam will blow
> away the powder, so you can't build homogene trays
> or surfaces
>
> Another common method is blowing metallic powder
> through a plasmabeam so molten droplets will land
> and fuze to the surface ...
>
> Viktor

What about focussed induction heating?

> What about focussed induction heating?

Surely if you are inducing currents to heat the media, the resulting EMF will blow the media away from inductor, and probably all the other particles of media...?

... there are many possibilities - we had some talk in the past about placing molten metallic beads like building with lego-blocks ...

One essential point is the adhesion between the already fabbed body and the new placed tray/bit, then you adress the accuracy (step-resolution, tray-diameter or bit-size), material selection/changing, surface-finish and some other aspects defining the usability/seriousness of the fabbed output.

The area of interesting possibilities and methods is virtually unlimited - try it and/or make it!

Viktor