Re: Absorb UV Light?

From: William G. Noack (
Date: Wed Feb 11 1998 - 21:14:07 EET


Interestingly, we just went through a similar exercise with our SLA500
(SL5180) where we were observing "scatter" in the vat near the laser
spot. We did not have any surface skinning and we were not experiencing
any build problems but we were concerned that we might be prematurely
aging the resin due to this apparent UV glow around the laser spot. We
tried 3 different lasers and all of them had the same scatter
characteristic. The intensity of the scatter is directly related to the
laser power level. We were unsure if this was a new problem or if it
was something that we just hadn't noticed in the past.

All of our optics were checked and we discussed this problem also with
Coherent at length. We then observed another SLA500 installation
(Thanks Steve!) and determined that the scatter was occuring there as
well. It was, however less apparent because the machine had been kept
perfectly clean near the spot rest position. We could see the scatter
though, by using a white business card and moving it around the vat near
the spot. The scatter generally extends 8" from the center of the spot
just as it had in our machine.

Back at our SLA500, we then took a laser power meter and moved the
sensor in and around the scatter area. We were unable to get any
measureable UV (<.002 W). So, my conclusion is that in our case, this
is not an unusual situation because it existed under so many different
cases. Second of all, I don't think it's a problem from a resin aging
stand point because we couldn't measure any UV energy.

I wouldn't focus too much attention on the "scatter" problem.
Unfortunately, I don't have any suggestions for you on the skinning.
I'd go through the basic checks though and make sure your AOM is
functioning correctly and that your contrast ratio is around 50:1 or
better. How old is your resin? How much quickcast do you use? You may
need to replace your resin. Hope this helps you resolve your problem.
Please post to the list your findings after this is resolved.

Morris Technologies

Bill Noack

Miller, Michael W wrote:
> We are getting surface skinning (cured resin) in the right front corner
> of our SLA500 near where the laser parks between layers. Our 3d
> maintenance person believes it is caused by laser reflection off all the
> resin spills on the cover plate. It has been suggested we dip the cover
> into hot water to soften and then remove the spilled resin. An
> alternate solution might be to paint? or apply some material in the area
> that would absorb rather than reflect the UV. Any suggestions as to
> what cheap and readily available material effectively absorbs UV?
> Thanks,
> Michael W Miller (
> The Boeing Company MS 17-PE B-XT62
> Propulsion Experimental Hardware 206-655-3289
> Rapid Prototyping 655-4366 Lab 655-4365
> For more information about the rp-ml, see

For more information about the rp-ml, see

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