RE: Using reused powder in SLS -reg

From: David K. Leigh (dkleigh@harvest-tech.com)
Date: Wed Dec 18 2002 - 20:25:25 EET


With Tim's melt flow index, you can mix to the desired quality and get
little to no variation attributed to the powder. If you are extremely
disciplined in your powder handling, you can greatly minimize the variation
due to powder and approximate the same results Tim can get with the melt
flow index. There have been several very good presentations on these topics
at the SLS Users group.

********************************************************************
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 Scott Tilton
  Sent: Wednesday, December 18, 2002 10:45 AM
  To: rp-ml@rapid.lpt.fi
  Subject: RE: Using reused powder in SLS -reg

  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.

  Doesnít 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 donít require as much tinkering with the scale and offset values to
keep the accuracy up.

  Still, Timís 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.

  Iíd be curious to know how well things can be kept constant using Timís
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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