Carbon 3D

[Hugues]

Ted talk here:
http://www.ted.com/talks/joe_desimone_w ... r#t-285853
with one of the inventor Jo DeSimone, and live demo.

[crusoe]

The biggest problem with floating resin on saturated salt water is miniscus effects and diffraction of light at the interface. You see all kinds of surface roughness on most top-down submersion style builds.

Also, you can't empty the vat back into the bottle, and exposure to air/moisture shortens the life of uncured resin.

[hegykc]

[hegykc]

All of our answers are here:

http://www.sciencemag.org/content/347/6228/1349.full

you will have to register to read the lengthy article, but it's free, and answers a lot!

"oxygen diffuses through the window and into the resin but decays with distance from the window, so that free radicals will overpower inhibiting oxygen at some distance from the window"
- that's a big answer right there

Another major one:
"dead zone thickness when pure oxygen is used below the window is about twice the thickness when air is used, with the dead zone becoming thinner as the incident photon flux increases"
-so pure oxygen delivery is possible, but why go through the trouble if air also works? Why? Well because oxygen delivery requires an apparatus, and that my friends you can both patent and sell. Placing an off the shelf micro film on the other hand, is neither patentable nor cash-able.
-----------------------------------------

This is the most amazing article I have ever read, ever. If I get struck by lighting tomorrow, I want you to know I died a happy man
It's all there. Explanations, equations, pictures and graphs. These guys really did the work. I approve their patent

Most important of all, it works!! Works with plain air, and plain permeable micro film with at least a couple hundred Barers. Which is ,by the way, my new favorite unit of measurement.

[Zenon]

So the oxygen decays into free radicals, but those still hang around (basically oxygen molecules with an extra electron, if I remember my chemistry correctly). I wonder what effect those have on the resin, since free radicals are usually highly reactive, or what effect the loss of an electron has on resin molecules. Unless they use some additive to interact with the oxygen and protect the resin?

Thanks for the update. Any chance you could post the whole article somewhere so we don't have to sign up?

[hegykc]

Go ahead and register, you won't regret it believe me. It's quick.

"Increasing either 'incident photon flux' or 'photoinitiator absorption coefficient' increases the concentration of free radicals in the resin and decreases the initial oxygen concentration by reaction. Additional oxygen diffuses through the window and into the resin but decays with distance from the window, so that free radicals will overpower inhibiting oxygen at some distance from the window. At the threshold distance where all oxygen is consumed and free radicals still exist, polymerization will begin"

I'm a terrible chemist but, from this text it would appear to me that "free radicals" exist in the resin by default, or are created by uv light coming into the resin, and they are responsible for neutralizing the oxygen that comes in through the membrane? Then at the distance where there is no more oxygen polymerization will occur.

EDIT: here is the answer, from a pdf on the website
"Free radicals either inhibit oxygen or initiate polymerization. A photoexcited photoinitiator (PI) can either be quenched with oxygen or cleave to
form a radical (R*). The radical can then either react with oxygen to form peroxide or initiate and propagate polymerization (i.e., curing)."

[Zenon]

That makes sense, I completely forgot about UV light creating free radicals as well.

[hegykc]

Read the EDIT of my last post

[adambx]

a few posts ago someone mentioned something about the video which seemed to have variable build speed. My guess is that as the exposed surface area gets larger, the vacuum force gets bigger(yes there is a force, it's just really small compared to building directly on the vat.) and as the force increases, the build speed is lowered to still allow for constant curing. Along with that the projector brightness needs to decrease, so the software portion is kind of a big deal if you want the print speed to be as fast as possible.

Thoughts?

[hegykc]

Yes there is a vacuum force, albeit much lower compared to a regular setup. The article talks about slower Z speed while the build platform is close to the vat floor, and when printing large flat parts. Resin viscosity also plays a part here.