RE: SLS question

From: Timothy J Gornet (
Date: Wed Nov 06 2002 - 16:17:45 EET

We have done extensive testing of the changes in the DuraForm powder
during the SLS process and have presented our work at the last two SLS
User's Groups and this years SFF. Mechanical properties, surface finish,
scale and offset, and melt point change with each heat history. We have
developed a method to quantify powder quality and fitness so that one
can blend to a specific powder quality and minimize part and process
variations due to powder degradation. "Hot" (Long single layer times,
large scan area) builds and "cold" (Short layer times, smaller scan
area) builds degrade differently. PA and GF also degrade at different

With direct manufacturing increasing utilizing SLS our goal was to have
a way to blend the exact amount of virgin to a used powder batch to
obtain a target powder. Our process use the melt index as the control
parameter and we have developed complete blending curves for the PA and
GF. This allows us to keep our machine parameters constant and know when
powder is not worth putting back into the process stream.

The degradation is dependent upon heat history just as in injection
molding. We have assisted other SLS users with implementing this process
control with great success.

Email me if you would like a copy of one of the presentations. Also, a
plug for the SLS User's group - make sure to go to it each year- there
is a lot of great information exchanged.


Tim Gornet Computer Aided Engineering Consultant
SLUGNET: Vogt Bldg. Rm 101, University of Louisville, Louisville, KY
PHONENET: (502)852-0714 FAXNET: (502)852-8890
Rapid Prototyping Center

>>> Scott Tilton <> 11/05/02 09:21AM >>>
I'd love to know of any studies or experiments either formally
published, or
informal observations and notes.
I would say that there are a BUNCH of variables involved that make a
quantification like "how many times it runs through the machine"
Some guy who runs his machine at high temperatures to avoid curling
get anywhere near the powder life as someone who runs theirs at a
Someone who keeps only the loose fluffy part cake powder is going to
more powder life than someone who recycles every last crumb.
I run many of the same parts over and over and over year round.
While I can see how the degradation of the powder affects the products
surface finish, accuracy and ability to build small detailed features,
I do
not know to what extent the mechanical properties of the parts produced
Nor do I have the ability / resources to do a bunch of experimentation
research on this topic.
It'd be nice if 3D systems would do that for us.
Or maybe someone else would step up to the plate with an SLS
material and be more forthcoming with such information on their
Just my opinion.
Scott Tilton
-----Original Message-----
From: Brian Caulfield []
Sent: Tuesday, November 05, 2002 8:28 AM
To: Rapid Mailing List
Subject: SLS question
Does anybody know of any study that was carried outon the degradation
of PA
powder with regards to the number of times it was used on the machine.
is the difference between virgin powder and lets say powder that has
ran through the SLS proces 10-20 times. Does the mechanical proerties
change etc..

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