Unfortunately warp and or curl is the nature of the beast when dealing with
heat sintered materials. The trick is to keep the vectors as short as
possible. This may mean you have to build in some rather unusual
orientations. It sounds like you build in rather thick sections to start
with which is unfortunate. The short vectors prevent excess heat build up
in the sintered material and result in less internal stress along very long
vectors. A 7 inch vector will shrink more in aggregate than a 1/4 inch
vector. thus pulling on the previous layers which are already warmed close
to the materials glass transition. Your idea of using the "web and flange
philosophy will definately help as it will break up the vectors. As for
stiffness, you should see a comperable result if the webs and gussets are
designed properly. With regard to non-linear scaling factors, they do
exist, but they tend to be developed through trial and error based on
operating parameters, type of material run and wall thickness. So break out
your calipers and start measuring.
Hope this helps a little.
Liquid Plastic Solutions
----- Original Message -----
From: Miller, Michael W <Mike.Miller3@PSS.Boeing.com>
To: 'RPML www Mail List' <email@example.com>
Sent: Friday, March 30, 2001 4:29 PM
Subject: scale and warpage of sls
> Dear rpml,
> I'm looking at using my sls2000's to make some simple tooling out of
Duraform GF. My experience so far has been that the process is not quite
accurate enough. I'm looking for suggestions that might improve the parts.
> 1) Curl- The parts I'm making our relatively bulky.... 1 inch section
thickness. Even though the build looks dead flat, the finished parts are
warped or curled. I feel that this is an endemic, direct result of the
process, adding heat on top of the part and then subsequently having it cool
and shrink. Any thoughts on how to reduce this persistent phenomena? I
know orientation on a corner helps a little. What about designing the parts
for reduced mass without sacrificing stiffness by using a web and flange
philosophy... like I-beams? Alternatively, has anybody had much luck with
the outline feature? My experience has been that it's unreliable, at least
on the 2000's. Perhaps shelling the part with outline but filling the core
with lightly sintered material would alleviate the 'curl'. Unfortunately,
on the 2000's, this is quite slow because of the delay while the scanner
loads with new parameters. Are the 2500's fraught with curl?
> 2) Scaling- Has anybody developed non-linear scaling parameters? I
utilize a one dimensional Z-scale as a function of Z. For the GF I vary Z
scale 1.012 @ Z=0, 1.010 @ Z=3, and 1.008 @ Z=5. For X and Y I use a
constant scale, 1.023. Has anybody tried varying Z scale 3 dimensionally...
as a function of X,Y and Z?
> 3) Z adjust- I believe the z-adjust parameter in the 2000 software is
lousy. Horizontal holes do not come out round. Solid View has a z-shift
function that is fully adjustable as a function of downfacing angle that
results in much rounder rounds. Concur?
> 4) DTM- Does DTM have anything in the works to improve accuracy?
> Thanks for your insight,
> Disclaimer: Engineer and out the other!
> Experience is something you get right after you need it.
> Michael W Miller (firstname.lastname@example.org)
> The Boeing Company M/C 17-PE B-2T65
> Propulsion Experimental Hardware 206-655-3289
> Rapid Prototyping 655-4366 Lab 655-4365
> For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/
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