From: Timothy J Gornet (tim.gornet@louisville.edu)
Date: Thu Dec 19 2002 - 16:54:50 EET
Scott,
The scale and offset change with each run of the powder (assuming no
addition of virgin powder). Therefore, if the powder quality is not
consistent with each build, neither will the scale and offsets be
exactly the same. We run scale and offset sample parts in each build.
Since instituting the melt index testing and blending to a specific
melt flow rate, our scale and offset has been rock solid and we have
been able to dial it in very well on our 2500 plus. In fact since we run
the scale and offset parts in each build, if our scanner calibration
starts to drift it shows up right away. Since we know the powder quality
we can determine if it is a hardware change or powder issue with the
melt index test.
Tim
Tim Gornet Computer Aided Engineering Consultant
INTERNET: tim.gornet@louisville.edu
SLUGNET: Vogt Bldg. Rm 101, University of Louisville, Louisville, KY
40292
PHONENET: (502)852-0714 FAXNET: (502)852-8890
Rapid Prototyping Center
http://www.louisville.edu/speed/rpc/
>>> Scott Tilton <stilton@protoprod.com> 12/18/02 11:45AM >>>
Yeah, it definitely needed to be explained a little better.
I thought about it for a little while and the best I could figure was
that
perhaps you could say it is more easy to get good accuracy with
slightly
used powder.
Doesn't the powder degrade quickly in the first build or two?
(depending on
conditions of course)
Which of course requires more attention to customize the scale /
offsets for
the state of the powder.
Then if you keep on building with the same powder . .the next several
builds
don't require as much tinkering with the scale and offset values to
keep the
accuracy up.
Still, Tim's idea sounds theoretically the best:
Maintain the powder at a constant state by blending in new powder with
the
old.
Then you remove one variable from the equation.
I'd be curious to know how well things can be kept constant using Tim's
Melt
Flow Index.
For instance . . . taking several different batches of powder and
then
blending in new powder until the test equipment indicates that the
batches
are now equivalent.
Run identical builds for each of those batches of powder: how much
variation is there going to be among the parts produced?
Scott Tilton
-----Original Message-----
From: David K. Leigh [mailto:dkleigh@harvest-tech.com]
Sent: Wednesday, December 18, 2002 10:04 AM
To: ramanathan baranitharan; rp-ml@rapid.lpt.fi
Subject: RE: Using reused powder in SLS -reg
Hmm
Virgin Powder: Less Accurate
Used Powder: More Accurate
How do you define "less" accurate?
How many builds did you run with virgin powder?
Did you change any parameters from build to build?
How do you define virgin powder?
What was the makeup of your used powder?
Did you run this on more than one machine to verify results?
Were the powder lots the same?
Many questions to be answered before anyone can conjecture on the
nature of
your results.
If you use the shrinkage values from used powder and run virgin powder
- you
will not get accurate results.
********************************************************************
David K. Leigh (254) 933-1000
Harvest Technologies, Inc. fax (254) 298-0125
Rapid Prototyping Services www.harvest-tech.com
-----Original Message-----
From: owner-rp-ml@rapid.lpt.fi [mailto:owner-rp-ml@rapid.lpt.fi]On
Behalf Of
ramanathan baranitharan
Sent: Tuesday, December 17, 2002 10:25 PM
To: rp-ml@rapid.lpt.fi
Subject: Using reused powder in SLS -reg
dear friends
I am a post graduate student doing research in Selective Laser
sintering
Polymer powders at PSG College of Technology
Machine : Sinterstation 2500 plus
material : Duraform PA (polyamide)
In my experiments I infer that accuracy of exposed powder is better
that
that of fresh powder with 11W laser power
what may be the reason behind it?
Before this experimentation we assumed that fresh powder may give
better
dimensional accuracy and using only fresh powder for industrial
projects.
-barani
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