RE: SLS question

From: David K. Leigh (
Date: Tue Nov 05 2002 - 17:11:25 EET

This is an old one. . . I think we've talked about this several times on
the rp-ml and it probably has been a yearly topic of a technical
presentation at the SLS User's group.

Ok. . . Summary for Duraform PA. (GF is a little different)

The powder degrades as it is processed due to the heat of the processing.
So, the more temperature the powder was exposed to, the faster it degrades.
The part cake degrades more than the powder in the overflow.

The degradation primarily effects the laser power, beam offset, scale
values, processing temperatures, and surface finish of the part. I have not
noticed any significant material property changes. A "bad" part will look
bad, but usually has the same strength.

Typically, you can use the material anywhere from 3 full runs to 6 full runs
before you start noticing the degradation.

If you continue to use the same material over and over, you will not be able
to accurately predict your processing paramters or your shrink values.
Also, your surface finish may vary from build to build.

Bottom line, the best way to get consistent results in quality and
parameters is to establish a steady state powder strategy. The problem is,
out of any pound of powder in your inventory, can you tell me how many times
it has been processed? There has been a lot of work on powder handling and
testing. Tim Gornet has developed a good system for measuring the quality
of the powder. But, the measurement only works if you use systematic
approach to powder handling. You have to have a regimented sifting and
blending strategy. You will have to segregate used powder, new powder, and
blended powder. You will also have to blend in larger batches and maintain
a X:Y ratio of virgin to used powder. We have seen that a good blend for
duraform includes 30% to 50% virgin in the mixture.
David K. Leigh (254) 933-1000
Harvest Technologies, Inc. fax (254) 298-0125
Rapid Prototyping Services

  -----Original Message-----
  From: []On Behalf
Of Brian Caulfield
  Sent: Tuesday, November 05, 2002 7:28 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.
That is the difference between virgin powder and lets say powder that has
been ran through the SLS proces 10-20 times. Does the mechanical proerties
change etc..


This archive was generated by hypermail 2.1.4 : Tue Jan 21 2003 - 20:14:33 EET