SLS Nylon Composite

From: Ian Gibson (
Date: Wed Feb 14 1996 - 10:57:21 EET

I have a number of questions that I would like to put to anyone using nylon
composite on the DTM SLS machine.

I have a student who is currently building an expert system program to help
in compiling the build profile for SLS parts. She is initially concentrating
on NC for convenience. It is also the material that we build most parts from.

Part of the program involves setting the all-important left/right feed
temperatures, part PID set-point, downdraft, and fill laser power values. As
you will know from experience and the material data sheets, there are a
number of problems associated with these values. What I would like to know is:-

1. Do you encounter problems with curling, caking, bonus-z, etc. when using NC?
2. Which problems do you encounter the most?

3. Are you able to diagnose problems
        before build?
        during build?
        prior to the next build?

4. If you are able to diagnose problems before build, is this because you
use the same settings for each build or because you can identify possible
changes in the default settings from the part geometry?

5. Do you adjust the part orientation to minimise the possible problems? If
so, what features do you try and avoid?

6. If you are able to diagnose problems during build, are there visual clues
that lead you to make changes?

7. Do you find that you have to reduce part feed temperatures at periodical
intervals during the build? If so, what scheme do you use (e.g. 1 degree per

8. Do you find you have had to rebuild a part because of incorrect settings?
Can you give an example? What do you commonly have to change for the next build?

9. Have you experienced any problems resulting from recycling material too
many times or from powder contamination?

10. What percentage mix new/old powder do you use for NC?

11. Are there any other problems that you have encountered that may be
relevant to this questionnaire?

12. Is there any other information you feel may be useful (e.g. normal part
type, application, etc.)

Sorry for the level of detail in some of these questions. Many of the
reasons for asking have resulted from our own experiences. What I am looking
for is confirmation as to whether others have had similar, or indeed other
problems that we have yet to encounter.

Dr Ian Gibson
Dept. Mechanical Engg.
University of Hong Kong
Hong Kong

tel: +852 2859 7901
fax: +852 2858 5415

Remember, as my Grandmother used to say, "Sit still and behave yourself!".
She was full of wisdom, my Grandmother.

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