Thanks for responding to Ian's questionnaire. This type of information is
very insightful for those of us who do no have specific technologies, but
are trying to evaluate them, or trying to tracking the progress a company is
making with regard to its process.
Your response, while very appropriate to a user's group in this case, is
also valuable to those outside of the SLS user community. The somewhat
esoteric content of your response is typical of what must be learned and
characterized to be proficient in providing a particular service, and is
information which is not usually available in such an unbiased form. I
believe this to be true for any of the available Freeform technologies.
Thanks for taking the time.
E. Derek Smith
Motorola Radio Products Group
Engineering Prototype Center
8000 West Sunrise Blvd.
Ft. Lauderdale, Florida 33322
Ph: (954) 723-4790 Fax: (954) 723-4934
David K. Leigh wrote: [edited]
> Date: Wed, 14 Feb 1996 16:57:21 +0800
> From: email@example.com (Ian Gibson)
> Subject: SLS Nylon Composite
> 1. Do you encounter problems with curling, caking, bonus-z, etc. when
Every one of those problems will be experienced unless you get your
powder consistent and the settings right. (also assuming you don't
have problems with your IR Sensor)
> 2. Which problems do you encounter the most?
For me, caking and bonus-z. I tend to overcompensate at first
because I hate curling. You cannot easily fix that.
Density of part can be verified by looking at the "clarity" or
lack of it during the melt.
Curling can be detected because the part will either raise out of the bed or
the edges don't appear to have as much powder.
Caking is more difficult. In fine nylon, the material will actually melt
between parts, causing a bridge due to heat concentration.
Examine the cake. Solid Rock - Lower Temp. Drastically. Tough break
-out - Lower the part bed a couple of degrees. Delamination of part,
increase laser. Very rough texture (mottled), the powder is in BAD
shape. Too much growth - decrease laser, may be bad powder.
Build on angles, minimize large area cross sections, center the part.
Overhangs can be a problem.
Small features need to be oriented in X-Y plane for strength.
Heat the feeds until they are streaking. Then, keep them there.
Shrink can be a problem - fix is to run the scale parts and calculate shink
every build. Part bed temp. can also be a culprit.
You need to keep a consistent mixture of virgin to used. For example: 50%
virgin. Always run with 50% virgin. If you don't, the physical properties
and settings will vary from build to build, making your life miserable. It
is also suggested that you use a very fine mesh screen to sift with,
eliminating alot of the bad powder.
> 10. What percentage mix new/old powder do you use for NC?
DTM suggests 50%. But you will start to build up a stockpile of used
material. I wouldn't suggest going much less than that if you do not
have a good sifter. If you are able to sift with a 70 micron or
similar screen, you can go to as low as 10-20% virgin.
David K. Leigh
Rapid Prototyping Center
Phone (817) 742-1822
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