« Posts under general UV curing chemistry

Experience of a 3D Stereo Lithography System Operator

On a comment on “A little bit about UV Curable resins…” post, Traumflug shared some really amazing information that I thought deserved to be blogged on its own, for future easy reference when people start trying some UV curing of they own:

“Here I can talk a bit about my experience as an operator of a 3D Systems stereolithography system. Early SLA resins were all clear, and they produced quite even layer thicknesses. So, coloring the resin isn’t essential at all.
When you expose UV-curable resin to light, it starts hardening at the top (where “top” = “closer to the light source”) and the more light you bring in, the thicker this layer gets. However, the exposure has to be above some threshold to work at all. Not enough light and no hardening takes place.
To find out the relation between exposure and layer thickness, simply expose just one layer, then take this single layer out, postprocess (wash) it as normal, and you can measure the thickness. The minimum layer thickness is very low, like 0.01 mm. Much lower than you can reasonably handle.
Minimum layer thickness also isn’t essential to build accuracy or layer thickness. It’s no problem to advance in 0.1 mm steps, but to expose for 0.2 or 0.3 mm. This way, parts of the resin get exposed twice or three times, wich doesn’t hurt at all.
After all, the SLA slicing algorithm makes the bottom layer (here the top layer) intentionally extra thick, to achieve better build accuracy. More accuracy, because the first layer is more mechanically stable (think of overhangs). The drawback is, this introduces some complications in the slicing algorithm to compensate for this extra thickness. In other words, you have more fun creating a good slicing software.”

Thanks again for sharing this, Traumflug!!!

A little bit about UV Curable resins…

I was looking for ways to mix UV blockers into epoxy resin (to mix an UV blocker into the solarez zerovoc – the cheapest UV resin I found so far), and I found this: http://www.dymax.com/pdf/pds/3069.pdf

Nothing new here… an adhesive from Dymax that cures fast on UV and blue light… but what catch my eye was the second page… the 2 graphs showing the depth of cure relation with time of exposition and light intensity… And then I realize:

If this product has a depth/exposion time relation, it means that it already partially blocks the light from penetrating deep into the material, which means that we MAY be able to control the cure by just adjusting the exposure time per layer… If we do the math right, we may be able to cure JUST the amount we want from the bottom, by doing really quick expositions, specially if the material is NOT SO FAST to cure… actually, the slower it is, the more difficult it would be to cure a ticker layer… which is EXACTLY what we want! :)

We could also experiment with adding SOLVENT to the mix instead of a blocker, just to make it HARDER to form the reaction that cures the material, increasing the chances of curing just a tiny layer… just some more to think about it and experiment once we get a prototype working!

Last, but not least, in case someone runs into figuring what viscosity “cP” is, this is a nice useful table to figure how viscous a material is:

Some typical viscosities (cP at 20°C)
air 0.02 motor oil SAE 20 125
acetone 0.3 motor oil SAE 50 540
methanol 0.6 castor oil 986
water 1.0 glycerin 1490
ethanol 1.2 pancake syrup 2500
mercury 1.5 maple syrup 3200
linseed oil (raw) 28 treacle 20,000
corn oil 72 peanut butter 250,000
olive oil 84 window putty 100,000,000

 

A Really Nice Resource about UV cure

http://www.uvabcs.com/uvlight.php

Lots of information there to learn a bit more about UV curing materials, techniques and more…Also, find this really nice supplier of UV adhesives in Canada (yeah… I’m in Canada), which is really hard to find: http://www.ellsworthadhesives.ca/

They have a really nice search system, were you can refine the list by selecting  different aspects of the material, like viscosity, cure time, etc. Unfortunately, theres no prices whatsoever… everything has to be quoted! =(