Re: Beefy SLA part warpage question.

Date: Sat Jan 08 2000 - 05:07:15 EET

In a message dated 1/6/00 5:52:12 PM Eastern Standard Time, writes:

<< I have had this problem building "beefy" ACES parts as well, with all three
 machines and resins we've had over the years >>
This is the sort of competitive information that if I told you all, I might
have to kill you, but here goes.
I noticed something back in the good old days with the Allied Signal Resins
while trying to dial in the cure parameters, if you put too much energy into
the hatching you could get a serious mounding effect, very noticeable on a
large flat part. What is an appropriate amount of energy for a thin wall
(.060 ~ .080) type part, is waaaay too much for a heavy wall (say .125 on up)
part. I'm not too sure about the theory, perhaps there is a scattering effect
on a dense part and the energy is spread out, or perhaps there is more
catalyst embedded in the part. Theoretically there is a point at which the
swelling/mounding would exactly counteract the "shrink". The solution I have
found to this sort of distortions, is to decrease the energy being put into
the hatching. You could change the cure depths for hatching, but there is a
more elegant approach. We have two sets of build styles for Aces parts. One
for small delicate parts, and another that we call wide hatch for massive
parts. I make some parts in the 3 plus pound range many times on the SLA250,
so we have a lot of experience with them. The "wide hatch"(trademark not
pending) style is just double the hatch spacing of the standard Aces style.
It's sort of a poor mans variable spot size, without having to spend
$700,000. There are some side benefits as well, the .SLI file size will be
smaller and the throughput will be faster. You will need to experiment with
your resin laser combination to find the optimum. Build some large, flat,
thick parts, I would think anything over 0.5 thick will show if you are on
the right track.
Good luck Mr. Phelps,
Andy Scott
Lockheed Martin Aero Sys

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